Coated componentsGreater performance andreliability

Coated componentsGreater performance and reliability

04

Published byOC Oerlikon Balzers AGOerlikon Balzers HeadquartersIramali 18P.O.box 1000LI-9496 BalzersLiechtenstein

Tel +41 81 784 7500E-Mail: info.balzers@oerlikon.comwww.oerlikon.com/balzers

© 20103rd edition/November 2010

Copying, translation into otherlanguages, microfilming, electronicprocessing and all other forms ofreproduction and transmission areforbidden without written permissionfrom the publisher.

05

Contents

It all comes down to the surface 07

Tribology under the magnifying glass 09

The tribological system 09Friction 10Typical wear mechanisms 11Failings of simple material solutions 12Advantages of surface treatment 12

Comprehensive surface technology 13

Surface treatment processes 13PVD and PACVD processes 16Hard coatings: classification and nomenclature 19Properties of BALINIT® coatings 20BALINIT® coatings at a glance 21Advantages of BALINIT® coatings 28Limitations of BALINIT® coatings 29

Coating as a design element 31

Choosing the right materials 31Materials and their coatability 32Hardness and strength of materials 34Component surface quality 34Component design for coating 35Conservation and packaging 36

Application tailored solutions 37

Engine technology 37Engines 37Motor sport 41Fuel injection 43

Mechanical drives 45Vehicle gears 45Industrial drives 49Ball- and roller-bearings 51

Fluid technology 55Compressors 55Hydraulic pumps and hydraulic motors 57Valves and fittings 60

Other applications 61

06

Partners in your success 65

Research and development 65Test methods for quality assurance 66Test methods for specification and analysis 68Applications support 71Custom services 71Production process and process engineering 73Quality management 74

Glossary 75Tribology, PVD technology and coatings

07

It all comes down to the surface

Friction is a key factor in the performance and service life of precision compo-nents. Frictional behaviour is chiefly governed by the properties of the componentsurface, therefore great importance is attached to methods of treating surfacesto improve their wear and corrosion resistance and thus reduce friction.

Oerlikon Balzers (hereinafter: Balzers)plasma-assisted coating processeshave proved themselves excellent forcreating economical, reliable tribosys-tems. Collaboration with our custom-ers has taken us far beyond just coat-ing: Today’s customer also looks forcompetent help and support in theearly development and design phasesas well as professional project man-agement, quality management, logis-tics and processes to meet the needsof mass production.

BALINIT® coatings offer reproduciblequality in every run by virtue of thePVD and PACVD processes that Bal-zers has developed, together withtechnical quality systems that enablethe manufacturer to meet and maintainspecifications in the production pro-cess.

Experience has shown that many tribo-systems can be optimised through thechoice of the right coating. BALINIT®

standard coatings cover a range ofproperties and make it possible to pickthe coating that will yield the desiredresults. What is more, Balzers workswith the customer to devise customsolutions for getting specific outcomes,thus allowing scope for creativity indesign.

Coating enhances component perfor-mance, reliability and service life andpermits lighter, more compact designs.Reduced energy consumption and theuse of environmentally benign productsin smaller quantities are further advan-tages that come into play in the build-ing of machines and equipment just asthey can in engine and vehicle making.

Components of machine tools, textilemachines, injection moulding equip-ment for plastics, and equipment forfood processing now come with BALI-NIT® coatings as a standard feature.Coating is also a proven technique influid technology, used to upgradecritical components in hydraulic drives,pumps and valves.

BALINIT® coating lends itself to massproduction of engine components andenhances the performance of thewhole system. Examples include BALI-NIT®-coated components in state-of-the-art diesel injection systems as wellas wrist pins, tappets and piston rings.As a partner to renowned automakersand suppliers, Balzers is totally com-mitted to developing innovative tech-nologies.

This booklet will provide designers andtheir customers, as well as operatingand maintenance engineers, with anoverview of the processes used tomake wear-resistant, low-friction sur-faces with improved corrosion resist-ance. It will show off, in particular, thecapabilities and advantages of BALI-NIT® PVD and PACVD coatings.

08

09

Tribology under the magnifying glass

Solving any wear problem begins with a careful analysis of the tribological systemand all the factors that affect it. Such an analysis reveals what frictional statesand wear mechanisms occur and when. Engineered processes for treating com-ponent surfaces, coating in particular, often result in more efficient solutions thanpure material or design alternatives.

The tribological system

A tribological system consists of com-ponent surfaces that are in movingcontact and thus become tribologicallyactive. Friction and the resulting weardepend heavily on the compositionand structure of the materials in thesystem. A further effect is often due tolubricants such as oil, grease or water.Particles on the surfaces also affectwear. Other factors at work include theprevailing service temperatures, theloads applied, and loading modessuch as sliding, rolling, oscillating andpulsating. All these effects govern the

Tribosystem

1 Base object2 Opposed body3 Surrounding influences:TemperatureRelative humidityPressure

4 Intermediate material:OilGreaseWaterParticlesContaminants

5 Load6 Motion

tribological system and its behaviour,and thus the extent, nature and pro-gress of wear. The fundamental con-nection is thus between friction andwear.

1

34

5

6 6

2

10

Friction

Friction in a tribosystem can be clas-sified by the state of the contact be-tween interacting surfaces:

Dry friction occurs when the inter-acting surfaces are in direct contact.

Boundary friction is an intermediatestate between dry and mixed lubrica-tion, in which adsorbed lubricantmolecules cover the interacting sur-faces.

Mixed friction is a superposition offrictional states such as dry, boundaryand fluid. Here the load is taken uppartly by solid-to-solid contact andpartly by a load-bearing lubricant film.

Fluid friction is friction in a liquidlubricant film that completely separatesone contact partner from the other(hydrodynamic and hydrostatic friction).

All these frictional states obey the rulethat friction (and thus the danger ofwear) increases with increasing directcontact between the two relativelymoving partners. The degree of frictionin a tribosystem is described by the

Coefficient of friction µ

Viscosity x sliding speed vnormal force FN

Dry friction (d < R) Mixed friction (d ≈ R)

Fluid friction(d >> R)

FN FN FN

v v v Opposed bodyIntermediate materialBase object

Distancebetweenbodies

Surface roughness R

d

Stribeck curve: schematic graph of friction

coefficient of friction µ, which dependson the frictional state and the tribologi-cal factors that are at work in an appli-cation process.

The Stribeck curve shows that thecoefficient of friction is especially lowfor fluid friction in oil-lubricated tribo-systems. This state, however, depends

on constant service conditions andappropriate system design. Mixedand boundary friction often cannot becompletely avoided, despite lubrica-tion, and this is especially true whena triboprocess is being started up orallowed to run down. A wide varietyof wear mechanisms can occur as aresult.

Stribeck curve: oil lubricationand friction coefficientThe Stribeck curve describes how thecoefficient of friction varies in oil-lubri-cated tribosystems. Low values areseen above all in fluid friction, that is,when the sum of the roughness (asper-ity) heights of the frictional partners isless than the thickness of the lubricantfilm. This condition can come aboutonly if the parameters viscosity/slidingspeed/load (normal force) are in the

proper proportion. What is more, thedesign of the tribosystem must permitthe formation of a gap that narrows inthe direction of flow, because thelubricant film must be able to exert apressure against an externally appliedforce. Mixed, boundary or dry frictioncan occur if the thickness of the lubri-cant film becomes smaller as thesliding speed decreases or the loadincreases.

11

Typical wear mechanisms

It seldom happens in practice that a wear mechanism occurs alone in a tribosys-tem. As a rule, several of these mechanisms act together or in succession duringthe wear process. Failure due to wear, however, commonly results from onemechanism playing a dominant role.

Tribo-oxidation involves a chemicalreaction induced by the tribological(frictional) contact and yielding prod-ucts that have a detrimental effect onthe tribological processes at the sur-faces. For example, a closely toler-anced pair of components or the seatof a rolling bearing may seize up.

Tribo-oxidation can be controlled bylowering the temperature and the co-efficient of friction, providing inert (un-reactive) contact surfaces or designingsurfaces with better form stability.

Consequences include fretting corro-sion.

Surface fatigue results from repeti-tive (pulsating or alternating) mechani-cal or hydraulic loads that lead to crackformation and propagation below theloaded surface, culminating in damageto the surface. If the surface is loadedby friction, wear can be reduced bydiminishing the friction coefficient. In

terms of hydraulic loads, the hardnessand elasticity of the material are crucial.

Consequences of surface fatigue in-clude cracking, pitting and micropit-ting, especially where elements are inrolling contact. On hydraulic compo-nents cavitation-erosion occurs.

Abrasive wear comes about whenmaterial is torn away by hard or sharp-edged particles in between the inter-acting surfaces, but can also resultfrom hard or sharp-edged (abrasive)surfaces and asperity peaks of one orthe other partner. Abrasion is promot-ed when the surfaces have very differ-

ent hardnesses or when the hardersurface is sufficiently rough or sharp-edged.

Consequences include scratches,grooves, chips and material removalat the surfaces.

Adhesive wear occurs when twotribologically active surfaces in a stateof mixed or dry friction form an inti-mate, adhesive bond. This can be thecase if the surfaces have the samecomposition or show a strong tenden-cy to combine and there is no protec-tive passive film.

Consequences include cold weldingwith material transfer, pits, smearing orsimilar damage to the surface struc-tures (scuffing, scoring, galling).

12

Failings of simple material solutions

Advantages of surface treatment

The identification of wear mechanismsin tribosystems gives the first pointer tohow wear might be combatted:

- Reducing the friction coefficient- Increasing the surface hardness- Applying inert surface coatings

If the sole approach tried in order toreduce wear is selection of the ma-terials of construction, it turns out that

some materials offer tribological advan-tages such as high strength but havedrawbacks such as susceptibility tocorrosion at the same time. Otherconstraints on material selection arisefrom requirements on design, weight,function, cost, availability, and environ-mental considerations.

The treatment of component surfaces,on the other hand, offers a better out-look for success. For one thing, it maybe possible to produce the desiredtribological behaviour in the systemwithout a costly change of design ormaterials. For another, surface treat-ments open up room for design im-provements while the component isstill under development. Surface prop-erties can be manipulated in order torealise certain advantages in the tech-nological competition:

- Longer service life- Ability to tolerate greater loads- Ease and low cost of maintenance- Environmental gains and conserva-tion of resources

- Improved response in kinetic systems- Lower energy consumption- Resistance to corrosion- Possibility of designing to closetolerances

- Use of lower-cost base materials

Greater scope for design is openedup especially with surface coatingsapplied by PVD (physical vapour de-position) or PACVD (plasma-assistedchemical vapour deposition). The basematerial provides strength and tough-ness, while the coating guards againstwear and corrosion and reduces fric-tion. The main coating materials usedare carbon-based, but nitride coatingshave also proved useful for manyapplications.

13

Surface treatment processes

DIN (German Institution for Standards)guideline 8580 identifies two classes ofmanufacturing processes by which thetribological processes that take placeat material surfaces can be influenced:

- Application of coatings by suchprocesses as electrodeposition, ther-mal sputtering or deposition from thegas or vapour state (PVD/PACVD)

- Modification of material pro-perties by means of nitriding orboronising, for example.

All these processes have special appli-cations associated with their distinctiveproperties. In many cases, however, avariety of processes can be employed,particularly when stresses are not toogreat.

Electroplating processesThe most important electrochemicaland chemical processes for protectionagainst wear and corrosion are hardchrome-plating and chemical nickel-plating.

Hard chrome (approx. 1,200 HV) isapplied in coating thicknesses of up to200 µm. It is suitable for componentssubject to abrasive wear, but micro-cracking inherent in the process limitsits use against corrosion. While micro-cracks can be avoided by applicationof a thin coating (a few µm thick with ahardness of 1,200 HV), such a coatingoffers only limited wear resistance.

Chemical nickel can be applied overa range of hardnesses, depending onthe process conditions; the maximumis approx. 600 HV. The advantage ofchemical nickel coatings lies chiefly incorrosion protection. The tribologicalproperties can be enhanced by inclu-sions (dispersion) of hard (diamond,silicon carbide) or soft (PTFE) phases.

The nitriding process involves dif-fusing nitrogen into the steel surfaceto harden the metal in the boundaryzones down to a typical depth of 0.5mm. A hardness of approx. 900 HV isattained in the outer diffusion zone. Acompound layer (iron nitride such asFe4N) up to 20 µm thick can be formed,depending on the process conditionsand the substrate material. These ni-tride zones are resistant to moderatewear and corrosion.

Many electroplating and nitriding pro-cesses involve environmentally prob-lematic media. In addition, classicalhard chrome-plating baths containhexa-valent chromium compounds,which are carcinogenic. The construc-tion of some kinds of electrochemicalplants is no longer feasible in manyindustrial regions; the same is true ofsalt-bath nitriding plants.

Comprehensive surface technology

A comparison of engineered surface treatment methods for precision compo-nents reveals that PVD and PACVD coating processes enjoy many advantages:Not only do they make it possible to apply wear-resistant, low-friction hard coat-ings in a precise, environmentally safe way that is tailored to the application inquestion, but they can also be modified to reach target figures such as hardness,friction coefficient and thickness. Balzers groups these hard coatings under theBALINIT® brand.

14

Key properties of PVD and PACVDprocesses include:

- A wide range of coatings can bemade. The high vacuum employedmakes it possible to achieve coatingproperties that are not available withgases and baths at atmosphericpressure (thermal spraying, nitriding,electro- or chemical deposition). Theresulting coatings offer good adhe-sion, high hardness and wear resist-ance, and these properties are oftenspecially tailored for the service inquestion.

- PVD/PACVD processes as used forcomponent coating operate at rela-tively low coating temperaturesof 200-500 °C. These temperaturesare chosen to lie at or below the tem-pering temperature of steels in orderto avoid altering the fundamentalmaterial properties.

1 Plasma spraying2 Electrolytic and chemical deposition3 Phosphating4 Nitriding (white layer)5 Boronising6 CVD7 PVD, PACVD

Coating thickness [µm]

10

1

100

1,000

0 400 1,000200 600 800 1,200

Coating temperature [°C]

1

2

34

5

6

7

Coating thicknesses and process temperatures

- Coatings are thin, typically 0.5-4µm. This feature in conjunction withclose tolerancing means that thecomponent retains its form, fit anddimensions after coating without theneed for costly refinishing.

- PVD/PACVD processes are environ-mentally benign and do not entailthe use or emission of pollutants. Thegases used are noble gases such asargon together with ordinary workinggases such as hydrogen and acetyle-ne. No toxic reaction products aregenerated.

15

Sliding-wear test

Experimental method:1 Ball, nonrotating, diam. 3 mmAISI 52100 (DIN 1.3505), 60 HRC

2 Test ring: AISI 52100 (DIN 1.3505), 60 HRCAbrasive-blasted or polished, N4Coated

Test conditions:F = 30 Nv = 0.3 m/sDry contact

Coefficient of friction

AISI 52100 (DIN 1.3505) uncoated

AISI 4142 (DIN 1.7225) nitridedCr electroplated

BALINIT® C (WC/C-PVD)

X

XX

Ni-P chemicalX

X = Test stopped on account of severe abrasive wear

0

0.2

0

0.4

0.6

200 800100 300

Sliding distance [m]

Dry-running/Sliding-wear test

v

1

2

F

Tribological advantages:PVD and PACVD coatingsCoatings applied by PVD and PACVDoffer far superior tribological perfor-mance:

- PVD and PACVD coatings, particular-ly carbon coatings, feature a uniquecombination of protection againstscuffing and abrasion.

- The dry-running qualities of treatedand untreated components illustrate,above all, what protection againstscuffing and surface fatigue resultsfrom surface coatings. Data from

sliding-wear tests show that, after arunning-in phase, BALINIT® carbon-based coatings have low coefficientsof friction, which have a positiveeffect especially under conditions ofdeficient (starved) lubrication andmixed friction.

- PVD hard coatings have only a slightchemical-physical interaction withmetals. For this reason, they are alsowell-suited to preventing tribo-oxida-tion. The properties of PVD coatingsalso improve corrosion protectionand thus guard components fromexternal factors.

Protection against Protection against Protection against Application areasScuffing Abrasion Corrosion

Electroplated hard chrome + ++ + Chemical apparatus,food industry, hydraulics

Electroless nickel plating + + +++ Chemical apparatus,food industry, hydraulics

Diffusion processes + ++ + Engine components, tools(nitriding, nitrocarburisation, boronising)

Plasma spraying + ++ ++ Turbine vanes

CVD (thermal) ++ ++ + Tools

PVD hard coatings ++ ++ + Tools, machinery, engine(TiN, TiCN, TiAIN, CrN) components, motor sport

PVD/PACVD carbon coatings +++ ++ ++ Machinery, engine components,(WC/C, DLC) motor sports

Applications of surface treatment processes

16

PVD and PACVD processes

The advantages set forth on the previous pages explain why Balzers has fo-cussed on PVD (physical vapour deposition) and PACVD (plasma-assisted chemi-cal vapour deposition) for the coating of precision components. The technologiesused are ones that work with plasma assisted processes and can be both flexiblyand precisely controlled: sputtering, ion plating, arc evaporation andPACVD.

1 Argon2 Reactive gas3 Planar magnetron

evaporation source(coating material)

4 Components5 Vacuum pump

1 2

3 344

5

< 250 °C

12 3

55

8

7

6

4 4

1 Electron beam source2 Argon3 Reactive gas4 Planar magnetron

evaporation source(coating material)

567 Auxiliary anode8 Vacuum pump

< 250 °C ComponentsLow-voltage arc discharge

SputteringIn reactive sputtering (cathodic sputter-ing), cleaned and pretreated compo-nents for coating are placed on a turn-table and loaded into the vacuumchamber of a PVD sputtering machine.After the components have been heat-ed, they are bombarded with argonions (ion etching) to produce a cleanmetal surface free of atomic contami-nants – a key requirement for coatingadhesion. Next, a high negative electricpotential is applied to the sputteringsources, which contain the coating ma-terial. A gas discharge is struck, lead-ing to the formation of positive argonions, which are accelerated toward thecoating material and evaporate it. Areactive gas containing the nonmetallic

elements of the coating is admitted tothe chamber, and the sputtered par-ticles react with it. A thin, compacthard coating with the desired structureand composition is thus formed on thecomponents. In order to maintain aconsistent coating thickness, thecomponents are rotated about one orseveral axes at constant speed duringthe coating process.

Balzers uses sputtering only to applythe WC/C coating. The coatingmaterial contains tungsten, while thereactive gas contains carbon. Thecoating system that results is made upof a carbon and hydrogen matrix withinclusions containing tungsten. ThisWC/C coating (a-C:H:W) is marketedas BALINIT® C.

Enhanced sputteringThe BALINIT® CNI chromium nitridecoating is applied by an enhancedsputtering process, which works on asimilar principle. The coating materialcontains chromium, nitrogen gas ispresent, and there is an additionalionisation step. A low-voltage arc dis-charge in the middle of the machineenhances the plasma intensity several-fold and thus produces a much higherdegree of ionisation.

17

12 3

44

8

6

7

5

1 Electron beam source2 Argon3 Reactive gas4 Components5 Coating material6 Crucible (anode)7 Low-voltage arc discharge8 Vacuum pump

7

< 500 °C

1 Argon2 Reactive gas3 Arc sources

(coating materialand backing plate)

4 Components5 Vacuum pump

1 2

44

5

< 500 °C3 3

Ion platingIon plating is a PVD process involvingreactive electron-beam evaporation.In ordinary sputtering, a metal plate isbombarded with argon atoms to gen-erate the coating material. The metalliccomponent for ion plating (e.g., tita-nium or chromium) is evaporated by alow-voltage arc. Balzers employs ionplating to apply, among others, theBALINIT® A titanium nitride coat-ing.

Arc EvaporationIn arc evaporation, an arc is struckbetween the backing plate (anode) andthe coating material (cathode). The arcmoves over the coating material andevaporates it. Because of the high cur-rents and power densities employed,the evaporated material is ionised to ahigh degree. Reactive gas and metalions hit the component surface andare deposited there as the coatingmaterial. Balzers uses this process tomake, among others, the BALINIT®

FUTURA NANO titanium-alumin-ium nitride coating.

1 2

6

3 3

4

5

12 Reactive gas34 Plasma sheath5 High-frequency connection

Vacuum pump6

< 250 °C

Argon

Components

PACVD processThe high-frequency PACVD processcomes into play when Balzers appliesthe BALINIT® DLC metal-free car-bon coating. The setup is similar tothat used for sputtering, but a high-frequency AC voltage is imposed aftera metallic adhesion film has beensputtered. A gas discharge, initiated inthe vacuum chamber after the reactiongas is injected, generates carbon andhydrogen atoms (ions and radicals),which form a compact coating on thecomponents. The coating propertiescan be controlled by changing theapplied voltage.

18

1

5

2 3

6 6

10

8

7

4 4

1 Electron beam source2 Argon3 Reactive gas4 Planar magnetron

evaporation source(coating material)

65

9

7 Low-voltage arc discharge8 Auxiliary anode

10

9

Plasma sheathComponents

High-frequency connectionVacuum pump

< 250 °C

7

6

2 Oxygen environment forcathodic arc soucesReactive gas O2

43

6

Vacuum pump

1

10

9 Pulsed high-power substrate voltage

7 Auxiliary anode8 Pulsed cathodic

arc evaporation

Electron beam source

Arc sources (coating material and backing plate)

Low-voltage arc discharge5 Components

2 3

4 455

10

< 600 °C

+

9

1

+ –

8

Combined PVD/PACVD processThe enhanced sputtering process iscombined with PACVD in order to ap-ply carbon-containing multifunc-tional coatings such as BALINIT®

DLC STAR. A hard, tough metal layeris deposited by sputtering, and PACVDis used to build up the tribologicallyeffective carbon coating on top of it. Incontrast to conventional combinationcoatings, Balzers multifunctional coat-ings are made in a single process thatyields homogeneous, defect-free coat-ings of uniquely high quality and adhe-sion strength.

P3eTM Pulse Enhanced ElectronEmissionWith the P3e™ coating technology,Balzers became the world’s first com-pany to deposit hard corundumtyped aluminium-oxide basedcoatings in a PVD process at tem-peratures significantly below 600 °C.Such coatings formerly could be pro-duced only by CVD at much highertemperatures. For certain qualities ofcemented carbides, however, the CVDprocess poses the danger of embrittle-ment, and it was nearly impossible tocoat steels at all. PVD oxide coatingswere developed primarily for tools, butthey are also suitable for mechanicalelements where insulating propertiesare desired along with resistance tohigh temperatures and corrosion.

19

Quite a large number of coatings canbe made by the PVD and PACVDprocesses that have been described.Their classification and nomenclaturebegins with a separation of the mostimportant hard coatings into threegroups. The first includes coatings inwhich metals and nitrogen combine toform metal nitrides (TiN, CrN, TiAlN,etc.). The second group comprisescarbide coatings generated from met-als and carbon (TiC, WC, NbC, etc.).There are also blends of materialsfrom these two groups (such as TiCN).Carbon coatings containing metals(a-C:H:Me) and those free of metals(a-C:H) make up the third group.

In nitride hard coatings, metal atomsfrom groups IV-VI of the periodic sys-tem (Ti, Cr) form compounds with non-metal atoms (C, N, O). Stoichiometriccompounds (i.e., 50% metal atomsand 50% nonmetal) are commonlychosen because such compoundsfrequently offer the most favourableproperties.

Carbon coatings are most oftenformed through the use of hydrocar-bons. The kind of amorphous hydro-carbon network (a-C:H) produced willvary with the process conditions. Thecarbon atoms can have graphitic (sp2)or diamond-like (sp3) bonds; the coeffi-cient of friction as well as the hardnessof the coating depend on the ratio ofthe bonding type. As a consequence,an inconsistent blend of material, pro-

cess and group nomenclature is en-countered in the market. The Englishabbreviation “DLC” (diamond-like car-bon), for example, refers to the wholegroup of amorphous carbon coatings,but DLC is inadequate as a term forany individual carbon coating belong-ing to this group.

The Balzers product family of carboncoatings has its own brand names,with BALINIT® C denoting the a-C:H:Wsystem (WC/C) and BALINIT® DLC thea-C:H coating.

Hydrogen-free carbon coatings makeup a further class. These are identifiedas tetragonal carbon or amorphousdiamond (ta-C).

Hard coatings: classification and nomenclature

Scientific name Balzers brands Other names foundin the market

Metal-free carbon coatings a-C:H BALINIT® DLC DLC (diamond-like carbon)iC (ionic carbon)a-DLC

Metal-containing carbon coatings a-C:H:Me BALINIT® C DLC (diamond-like carbon)Me-DLCMeC (metal-carbon)

Me = metal iC/Me(e.g. tungsten, titanium, Me-C:Htantalum) MeC/C

MCH

Hydrogen-free carbon coatings ta-C Amorphous carbonAmorphous diamond

Nomenclature of carbon coatings

Metal:Ti, Cr, Al

Nonmetal:C, N, B

Nitride coatings Carbon coatings

Coating materials and material structure

Graphite (sp2) DLC (sp2 and sp3) Diamond (sp3)

20

BALINIT® PVD and PACVD coatingshave qualities that make them superblywell-suited to use on precision compo-nents:

- High hardness- Good wear resistance- Low coefficient of friction- Good corrosion resistance- Thin coatings- High precision, excellentreplication of contours

- Good adhesion

The coating thicknesses generallyrange from 0.5 to 5 µm, whereby thecoatings exactly match the surfacetopography of the component and soremain faithful to its shape. Edge sharp-ness and surface roughness remainvirtually unchanged. This means thatremachining is no longer needed; thecoating can become the last step incomponent manufacturing.

Coating adhesion: Ion etching be-fore the start of material depositionresults in excellent metallurgical bond-ing of the coating to the substratematerial. In spite of their great hard-ness, BALINIT® coatings adhere sowell that flaking does not occur evenwhen the surface undergoes plasticdeformation.

Properties of BALINIT® coatings

Excellent replication of contours with BALINIT® coatings Excellent adhesion of BALINIT® coatings

BALINIT ® C BALINIT ® CSTAR

Coating material a-C:H:W (WC/C) CrN + a-C:H:W

Typical microhardness (HK 0.01)*/*** 1,000 I 1,500 1,000 I 1,500

Typical coating thickness (µm) 1 - 4 3 - 5

Increase in surface roughness Ra (µm)* approx. 0.02 approx. 0.02

Coefficient of friction against steel (dry)* 0.1 - 0.2 0.1 -0.2

Coating temperature (°C) < 250 < 250

Maximum service temperature (°C)* 300 300

Coating colour anthracite anthracite

Protection against abrasive wear + I ++ + I ++Protection against adhesive wear +++ +++Protection against tribo-oxidation ++ ++Protection against surface fatigue +++ ++Protection against corrosion* + + +

Properties and tribological effectiveness of BALINIT® coatings

* Depends on application and test conditions** Ion plating*** HK (Knoop hardness) corresponds approximately to HV (Vickers hardness)

21

BALINIT® coatings at a glance

BALINIT® CBALINIT® C Star

PropertiesBALINIT® C is a metal-containingamorphous carbon coating (a-C:H:Wor WC/C) with a multilamellar structure.Phases rich in tungsten carbide andcarbon alternate every few atomiclayers, giving a very low coefficient offriction at dry running: 0.1 to 0.2. InBALINIT® C STAR, the combination ofa metallic support layer (CrN) with thetribologically effective carbon coatingenhances the load-bearing capacity.

BenefitsBALINIT® C is highly resistant to adhe-sive wear (scuffing) in particular. It hasa high load-bearing capacity even un-der conditions of deficient lubricationor dry contact. Thanks to its low fric-tion coefficient, it also acts to reducesurface fatigue (pitting) and tribo-oxi-dation (fretting corrosion). The 1,000

Overall coating structure Section from WC/C coating

WC/Ccoating

WC coating

Cr intermediatelayer

Substratematerial

0.1 µm

Whitelamellae:WC-rich

Blacklamellae:C-rich

Coating structure of BALINIT® CThe multilamellar structure of the BALINIT® C coating results in good running-inand burnishing behaviour and reduces dry friction.

BALINIT ® DLC BALINIT ® DLC BALINIT ® CNI BALINIT ® D BALINIT ® A BALINIT ®

STAR FUTURA NANO

a-C:H CrN + a-C:H CrN CrN TiN TiAlN

> 2,000 > 2,000 1,750 1,750 2,300 3,300

0.5 -3 2 - 4 1 - 4 1-4 1-4 1 - 4

approx. 0.02 approx. 0.02 approx. 0.02 approx. 0.2 approx. 0.03** / approx. 0.2 approx. 0.2

0.1 -0.2 0.1 -0.2 0.5 0.5 0.4 0.4

< 250 < 250 < 250 < 500 / < 250 < 500 / < 250 < 500 / < 250

350 350 700 700 600 900

black black silver-grey silver-grey gold-yellow violet-grey

+++ +++ ++ ++ ++ ++++++ +++ ++ ++ ++ ++++ ++ ++ ++ ++ ++++ ++ ++ ++ ++ ++++ ++ ++ ++ ++ ++

22

Component coated with BALINIT® C

uncoated frictional partner

BALINIT® C

MoS2 = Molybdenum disulfide PTFE = Polytetrafluoroethylene (Teflon®)

Coefficient of friction

BALINIT® DLC (a-C:H)

BALINIT® C (a-C:H:W)

X = Test stopped on account of severe adhesive wear

0

0.2

0

0.4

0.6

1,000 5,000500 1,500250 750 1,250 1,750

AISI 52100 (DIN 1.3505) uncoated

Coated with MoS2

Coated with PTFE

PVD-coated with MoS2

Sliding distance [m]

X

X X X

BALINIT® C: comparison of frictional performance

HK grade of BALINIT® C is used whereabrasive conditions are milder and sur-face pressures are high but slidingspeeds are relatively low. This BALI-NIT® C grade shows excellent running-in and burnishing behaviour underconstant sliding load by virtue of itsmoder-ate hardness. The harder (1,500HK) grade of BALINIT® C can be usedwhere sliding speeds are higher; it of-fers better protection against abrasivewear. BALINIT® C STAR has beenfound to perform well under very highsurface pressures on soft substrates.

Special frictional properties

Dry runningDry running is the case most frequentlystudied – not because it is the mostcommon application but because it iswell-defined and easy to measure. Thiscondition brings out the special qual-ities of the BALINIT® C (WC/C) coating:its very good burnishing behaviourduring run-in and its slight coatingtransfer, with burnishing of the matingpart as a side effect. In comparisonwith other friction-reducing materialssuch as MoS2, graphite-based paintsand Ni-PTFE coatings, WC/C com-bines low friction with high wear resist-ance.

Number of load cycles

uncoateddry

uncoatedlubricated

BALINIT® Cdry

BALINIT® Clubricated

1,400

29,000

150,000

Terminated after 2,000,000106

105

104

103

102

10

1

107

FZG testSpeed: 1,000 rpmSurface pressure: 1,000 N/mm2

Lubricant: Esso CL46B (plant-based)Lubricant feed rate: 1 drop per minuteSource: IMM (TU Dresden)

BALINIT® C in dry running and starved lubrication (gear test)

Burnishing and material transfer with BALINIT® C coating

Before running-in After running-in

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Wear [µm]

5

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

BALINIT® C1000WC/C

BALINIT® C1500WC/C

BALINIT® DLC BALINIT® CNI

290 N 1,200 N

No measurablewear at 290 N

Mixed frictionCarbon coatings are employed in lu-bricated systems far more often thanin dry-running ones. The behaviour ofcoatings with, and in comparison to,lubricants has been demonstrated ina gear scuffing test (see page 22).Experiments performed by the IMM(Institute of Machine Elements andMachine Design) at the Technical Uni-versity of Dresden show that both lightlubrication and WC/C coating can leadto marked gains in service life, but thebest results are obtained with a combi-nation of the two. This means on theone hand that coating cannot supplantregular lubrication, but on the otherhand that lubrication and WC/C coat-ing act in a positive synergy.

Not only carbon but also nitride coat-ings come out well in mixed-frictiontests. Chromium nitride in particularmay actually surpass carbon coatings.

Coatings and additivesAdditives are frequently employed toreduce wear in lubricated systems. Ef-forts to identify the action of additiveswhen used with coated parts havebeen under way for some years. Theeffects have been found to be slight onthe whole. The coating (WC/C is theone most studied) and the additivework together positively in many casesbut negatively in many others. For ex-ample, sulphur-based high-pressureadditives together with the tungstenin the WC/C coating form WS2 com-pounds that reduce friction similarlyto MoS2. This effect was measured atshort running times, high pressuresand low sliding speeds.

In most instances the coating has themore robust and permanent action.This is no surprise, for the coating isapplied as a uniform, hard and wear-resistant film while additives take theform of small soft particles that comeinto play only under load.

Block-ring testBlock coatedSpeed: 0.3 m/sLoad: 290 N/1,200 NOil: 5W-30

Performance of BALINIT® coatings in mixed friction

Two trends lie in store for the future.Firstly, additive use will decline on en-vironmental grounds, with coatingsused instead. Secondly, additives arebeing developed and tested that cancooperate with PVD coatings to delivergreater performance than either prac-tice alone.

ApplicationsBALINIT® C finds use in all domains ofmechanical engineering, in motors andtransmissions, and also in fluid technol-ogy. This coating also aids functionalreliability in systems where lubricantsmust not be employed (cryogenic andvacuum systems, clean rooms, foodequipment). BALINIT® C is particularlysuitable for case-hardening as well asball- and roller-bearing steels becauseit can be applied at temperaturesunder 200 °C.

24

Typical structure of a multifunctionBALINIT® coating of the STAR series:1 Base material (component)2 CrN supporting layer3 Tribologically effective carbon layer

3

2

1

1 µm

0.1 0.2 0.3 0.4 0.500123456789

10111213

Coefficient of wear [10-15 m3/Nm]

Coefficient of friction against steel [dry]

BALINIT® C1500 (a-C:H:W)

BALINIT® C1000 (a-C:H:W)

BALINIT® DLC (a-C:H)

CrN

TiNTiAlN

Carbon coatings

Nitride coatings

Coefficient of friction and wear

BALINIT® DLCBALINIT® DLC STAR

PropertiesBALINIT® DLC is a pure, metal-free,amorphous carbon coating that con-tains only carbon and hydrogen. Itsdiamond (sp3) bonding content ishigher than in BALINIT® C coatings.The coating is therefore very hard andcompact (>2,000 HK). It also featuresextreme chemical stability and a dryfriction coefficient of 0.1 to 0.2.A special coating technology resultsin very good adhesion despite highinternal stresses. For extreme loadsituations, the carbon coating can becombined with a metallic (CrN) sup-port layer (BALINIT® DLC STAR).

BenefitsBALINIT® DLC is suitable for the mostdrastic wear conditions and high rela-tive sliding speeds. The strengths ofthis coating lie in protection againstabrasion, tribo-oxidation and adhesion(scuffing). The coating can accommo-date surface pressures that wouldquickly lead to scuffing and cold weld-ing under normal service conditions.Frictional losses are minimised andcorrosion resistance is enhanced.BALINIT® DLC STAR improves theload-bearing capacity of hard DLCcoatings.

Wear coefficient and frictionWhere parts experience sliding wear,a combination of low friction and highabrasion resistance is crucial. Frictionis measured in the pin-disc dry sliding-wear test. Abrasion resistance is deter-mined in the calowear test, where asteel ball rotates on the surface anddiamond paste is added so that theball grinds a spherical pit in the coat-ing. The lowest friction and wear rates,and thus the best conditions for slid-ing-wear applications, are achievedwith BALINIT® DLC coatings.

25

BALINIT® DLC STAR coatingfor valve seatsSliding wear and abrasion are not theonly loads on components such as theinjector needles of diesel injection sys-tems. High cyclical tensile-compressiveloads combined with extremely fastmicro-motions also act on the conicalseal surfaces that work at high fre-quency to regulate fuel feed. Thesesurfaces not only experience frictionand abrasion but are also subject tosevere surface fatigue. Both the hard

multifunctional carbon coating BALI-NIT® DLC STAR and nitride coatingshave proven to perform well undersuch conditions. In the case of BALI-NIT® DLC STAR, the DLC coatingensures good running-in behaviourwhile wear is generally blocked at theCrN-DLC interface. Scanning electronmicrographs show this clearly: Thewhite spots indicate the tips of col-umnar CrN crystals and the surround-ing dark areas represent the run-inDLC coating.

BALINIT® DLC STAR coating for valve seats

Needle seat (schematic) Top view on worn surfaceBright dots: tips of CrN grainsDark background: run-in DLC coating

Fracture surface of BALINIT® DLC STAR coating

CrN

DLC

ApplicationsBALINIT® DLC coatings are used inmotor sports, in the automotive andtextile industries, instrumentation,pumps, seals, valves and other preci-sion components where good wearresistance and high surface qualityare needed. The virtues of this coatingalso come into play in severely stressedcomponents of modern diesel fuel-injection systems. BALINIT® DLC STARdecisively improves the performanceand durability of valve-train compo-nents, wrist pins and high-pressurepump components.

26

Coating structure of BALINIT® CNI

This chromium nitride coating offers not just greathardness but also a high degree of tightness andsmoothness. Coated components show improvedwear and corrosion resistance as well.

Comparison of CrN applied by PVD withelectroplated hard chrome in the 48 hr salt-spraytest of DIN 50021 SS.Specimen: Untreated ball-bearing steelAISI 52100 (DIN 1.3505)Surface quality: N2 / Ra = 0.04 / Rz = 0.4

Area not corroded [%]

0

10

20

30

40

50

60

4 µmPVD - CrN

34 µmElectroplatedhard chrome

54 %

27 %

Corrosion test

BALINIT® CNI

PropertiesBALINIT® CNI is a chromium nitride(CrN) coating applied by a specialprocess that yields a particularly dense,smooth coating. The increase in rough-ness Ra is less than 0.02 µm, insidenormal manufacturing tolerances, andthe coating hardness of 1,750 HK issubstantially greater than that of elec-troplated hard chrome (approx. 1,000HK).

BenefitsComponents coated with BALINIT®

CNI display good wear resistance andgood frictional qualities under condi-tions of deficient lubrication whenthey are subject to severe mechanicalloads. At the same time, they showimproved corrosion resistance. Be-cause the coating temperature is lessthan 250 °C, a broad range of ma-terials can be coated. The coatingsare faithful to the component shapeand can thus be applied as the finalstep in the manufacturing process; nofurther machining is needed. What ismore, the production process doesnot generate pollutants or residues.

ApplicationsThe application spectrum of BALINIT®

CNI extends from wear protection inmachinery and hydraulics (pistons) tothe automotive (valve train compo-nents, piston rings) and the aircraft in-dustry. As BALINIT® coatings are FDA(Food and Drug Administration) ap-proved, BALINIT® CNI can be appliedto parts that come into direct contactwith foods. Other applications arisewherever thin electroplated chromeand nickel have been used in the past.By virtue of its special process, BALI-NIT® CNI has also proved a highly con-ductive material and exhibits excellentchemical stability at electrical junctions.Chemical electrodes, hot contacts andfuel-cell applications are applicationsin which BALINIT® CNI provides goodelectrical conductivity even in the mostdrastic environments.

A key property of PVD coatings istheir thinness, which sets them apartfrom conventional electroplated andthermal spray coatings. The gaps be-tween these processes, however, areincreasingly being closed with thinnerelectroplated as well as thicker PVDcoatings. CrN coatings up to 50 µmthick are now being applied to relative-ly precise parts subject to heightenedabrasive or corrosive wear. Typicalexamples are coatings for piston rings,pumps for abrasive media and com-ponents of textile machinery (threadguides and components in contactwith fibres).

27

BALINIT® D

PropertiesBALINIT® D is a chromium nitride (CrN)coating applied by reactive ion platingor arc evaporation. This process iscarried out at temperatures of up to500 °C.

BenefitsBALINIT® D displays a good combina-tion of abrasion, corrosion and oxida-tion resistance. The coating is marked-ly harder (about 1,750 HK) than hardchrome and adheres better.

ApplicationsLarge components such as housingsand shafts that are not temperature-sensitive are coated with BALINIT® Dfor the mechanical, automotive andaircraft industries. Coatable materialsinclude titanium and nodular iron butalso high tempering temperaturesteels.

BALINIT® A

PropertiesBALINIT® A, a titanium nitride (TiN)coating, is applied by ion plating orarc evaporation, as is BALINIT® D.In contrast to that coating, it employstitanium in place of chromium.

BenefitsBALINIT® A can be used everywhere,offering high hardness (around 2,300HK), good frictional qualities (frictioncoefficient 0.4) and stability at hightemperatures.

ApplicationsHigh tempering temperature steels andsome lower tempering temperaturesteels can be coated with BALINIT® A.The coating is employed where highabrasion resistance is desired, oftencombined with a decorative function.

Impact erosive wearIn fluid technology, impact erosive wearis crucial where the flow of abrasivemedia is controlled. Metal-on-metalsliding is secondary under these con-ditions. Surfaces and coatings mustcombine hardness and toughness inorder to stand up to this kind of load.Nitride coatings such as TiN or CrNas well as DLC coatings with a nitridesupport layer (BALINIT® DLC STAR)are best suited to these requirements.

Wear [µm]

0

0.3

0.2

0.1

0.4

0.5

0.6

0.7

0.8

0.9

WC/Csputtered

DLCPACVD

CrN-DLCSputter-CVD

TiNIonplating

CrNsputtered

Crelectroplated

Steel HSS

Test: centrifugal impeller200 µm particles of SiO2, 80 m/s, impact angle 90°

Nitride and carbon coatings in impact erosive wear

BALINIT® FUTURA NANO

PropertiesBALINIT® FUTURA NANO is a titaniumaluminium nitride (TiAlN) coating, ap-plied by arc evaporation at tempera-tures up to 500 °C. As against chro-mium nitride and titanium nitride coat-ings, it is optimised in terms of hard-ness (3,300 HK), coefficient of friction,residual stress and maximum servicetemperature.

BenefitsThis coating displays extraordinarilygreat wear resistance, impact strengthand high-temperature stability (up to900 °C).

ApplicationsBALINIT® FUTURA NANO is usedchiefly for engine components undergreat temperature stress (valves) andfor automotive structural parts subjectto severe abrasive wear. Good resultsare also achieved on components forhydraulic machinery.

28

The characteristic properties of BALI-NIT® offer many advantages in prac-tical application and thus afford muchscope to the designer.

BALINIT®

- enhances reliability and length-ens service life. Many mechanicalelements perform critical functions,and just a few micrometers of wearcan result in failure. BALINIT® wearprotection guarantees higher reliabilityand increased service life.

- protects dry-running systems.The low friction coefficients of BALI-NIT® permit operation with deficientlubrication as well as emergencyoperation in case of an undesiredloss of lubricant. Coatings also allowsystems to function where lubricantsare not permissible, as in cryogenicand vacuum equipment, the foodindustry, clean rooms and spacetechnology.

- replaces costly materials.While the base material provides theneeded strength, BALINIT® impartshardness and good frictional behav-iour. This makes it possible to cutcosts by replacing expensive ma-terials such as cemented carbides,ceramics and bronze with steel.Examples include cemented carbidesin pump shafts, bronze bushings inhydraulic systems or wrist pin bear-ings in internal combustion enginesand the metals used for plain bear-ings.

Advantages of BALINIT® coatings

Environmentally benign coatingWhen you use BALINIT® coatings,you are adopting an advanced technol-ogy. In contrast to many conventionalcoating processes such as phosphat-ing, nitriding, electro- and chemicalplating (hard chrome, chemical nickel,etc.), the BALINIT® vacuum processgenerates no polluting compounds,emissions or residues. If you mustmeet environmental limits or manufac-turing standards, or if you are seekingISO 14001 certification, BALINIT®

coatings can offer new avenues to you.

Bronze bushing replaced by coatingof wrist pin.

- boosts power and reducesweight. BALINIT® coatings comeinto their own where higher tribo-logical loads and higher mechanicalloads occur at the same time. BALI-NIT® C, for example, enhances theload-bearing capacity of gear wheels,so that they can be made smaller andthus lighter but still handle increasedburdens.

- lessens the need for lubricationand maintenance. Oil lubricationdrives up operating costs because ofthe continual need for inspection andmaintenance. Lifetime lubrication withgrease, however, often fails to meetstringent tribological requirements.A supplemental BALINIT® coatingimproves tribological performanceand greatly lengthens maintenanceintervals.

- reduces the threat of corrosion.Thanks to this quality of BALINIT®

coatings, severely loaded compo-nents can function reliably even inunfavorable environments.

- eliminates the need for rema-chining. The thinness of BALINIT®

coatings and the appropriate tem-peratures at which they are appliedmean no increases in roughness andno uncontrolled dimensional changesof components. Homogeneity andgeometrical integrity mean thatmanufacturing tolerances can beheld below 1 µm and make it possi-ble to place coating as the last stepin the process when manufacturingprecision components.

- helps protect the environment.Lubricants and additives pollute, soareas such as fluid technology areincreasingly using water-based hy-draulic fluids (HFA fluids) or additive-free lubricating oils. There is also arising demand for ozone-neutral re-frigerants in climate-control applica-tions. When wear problems resultfrom these shifts, BALINIT® coatingsoffer new solution approaches.

29

Limitations of BALINIT® coatings

Advantages aside, there are limits onthe use of a BALINIT® coating in somesituations:

Replacement forcorrosion-resistant steelThe corrosion resistance of a coatedcomponent depends on the coatingmaterial, the base material, the corro-sive medium and the surface rough-ness of the component. While BALI-NIT® coatings do enhance corrosionresistance, PVD-coated unalloyedsteels cannot replace corrosion-resist-ant steel, as corrosive media can getthrough tiny local defects in the thinhard coatings and cause pitting cor-rosion in the base material.

Continuous dry runningBALINIT® coatings extend the servicelives of precision components in allfrictional states: hydrodynamic lubri-cation, mixed friction and dry friction.While the coating permits dry runningin emergencies, it does not match thefriction coefficient of an oil film and socannot serve as a long-term substitutefor lubrication in severely loaded tribo-systems (no cooling action).

Heavy abrasive wearIn spite of their greater hardness, thinhard coatings offer only a marginalimprovement where even cementedcarbides are subject to tenths of amillimetre of wear.

Unfavourable componentgeometryFor physical and engineering reasons,coatability is limited when deep holesand deep, narrow slots and grooves(cavities) are present.

D

L

Coatability of internal contours

Rule of thumb for acceptable coating adhesion and thickness:Opening (diameter D) should be greater than depth (length L) tobe coated.

From problem solverto design elementThe performance potential and appli-cation range of BALINIT® coatings arefar from exhausted. The outcome ofcoating can be optimised only by anearly, comprehensive analysis of theentire tribosystem with all its elementsand their properties, as well as theinteractions between the frictionalpartners. The answer lies in the highlydeveloped field of surface engineer-ing, which Balzers offers you in theearly phases of design.

30

31

Any user who means to exhaust the full potential of wear-protection coatingsmust include them in the design phase. This is when the component form, themanufacturing method, and the selection of material and heat treatment can beoptimally brought into accord with a highly effective coating. A coating thusaffords scope for designing a more powerful system.

Coating as a design element

Hardness [HRC]

50

55

60

65

70

Tempering temperature [°C]

Range of coating temperature for BALINIT® C

0 100 200 300 400

Tempering diagram for AISI 52100 / DIN 1.3505

Coordination of tempering andcoating temperatures

Choosing the right materialsThere are essentially no limitationson the coating of steels by PVD andPACVD processes. For each materialused, the temperature of the final heattreatment - usually the tempering tem-perature in the case of steels - mustbe higher than the coating tempera-ture, since coating is the last step inmanufacturing.

Mechanical engineers commonly selecthardened unalloyed steel (such as ball-bearing steel AISI 52100/DIN 1.3505)for severely loaded parts. This repre-sents a good compromise betweeneconomics and strength. Processdefinitions for the most important PVDand PACVD coating processes takethis factor into account. These coat-ings are applied in the range of thetempering temperature between 150and 250 °C. Good coating adhesionrequires that the temperature be aminimum (approx. 100 to 150 °C) atthe start of the process. The tempera-ture can rise in the course of coating,depending on the part dimensions andbatch loading. But the coating tem-perature should not exceed the tem-pering temperature by much, if at all,so that the hardness will not be undulyreduced. In practice, a somewhat

higher temperature and a slight lossof hardness (2-5 HRC) may well beaccepted for the sake of a robust pro-cess and good coating adhesion. It isrecommended that these values beset down and documented in qualityagreements.

The following pages offer suggestionson the selection of a suitable materialand on how to design, pretreat andconserve components in the right wayfor coating.

32

SteelBall- and roller-bearing steel,case-hardening steel and special-purpose tool steels are typicalmaterials for precision components.These and other low tempering tem-perature steels can be coated at tem-peratures up to 200 °C. Typical repre-sentatives include AISI 52100 (DIN1.3505) and AISI 5115 (DIN 1.7131).

Heat-treatable steels and highertempering temperature toolsteels such as AISI M2 (DIN 1.3343)and HSS pose no problems for coat-ing. The lower hardness of heat treat-able steels, however, means that theyare not often employed for precisioncomponents.

Nitrided steels can be coated, butthe porous parts of the compoundlayer (white layer) have to be removedfirst. Components must be lightly re-ground or microblasted before coating.The most common nitriding processesare gas-phase, salt-bath and plasmanitriding. The plasma process providesthe best basis for subsequent PVD orPACVD coating because the formationof the white layer can be suppressedin this process.

Austenitic steels can be hard-coated by all PVD/PACVD processes.With these soft steels it must be con-sidered that while thin coatings reducefriction and wear, they do not increasethe resistance to deformation.

General-purpose engineeringsteels can be coated with all PVDand PACVD hard coatings, but thesetypical structural steels, with lowerstrength and supporting action, areseldom used for precision components.

Cast ironFrom the standpoint of temperature,cast iron is well-suited to coating.The tribological qualities of the com-ponent can be improved by coating,but graphite inclusions in the basematerial affect the coating structure.

Nonferrous metalsNickel and titanium alloys arereadily coatable and are used primarilyfor special applications such as cor-rosion protection and lightweight con-struction.

Copper, magnesium and alumin-ium alloys are coatable in specialcases. The age-hardening conditionsare an important factor in alloy selec-tion. Hot age hardening at the highestpossible temperature is recommended.Nonferrous alloys have low hardnessand supporting action under high sur-face pressures, so their use is restrict-ed to loads that the materials canhandle.

Brass can only be coated after chemi-cal nickel-plating.

Aluminium alloys display natural or arti-ficial (hard anodised) oxide films. Thereare two options for coating aluminiumalloys without hard anodising: prelimi-nary chemical nickel-plating (a thick-ness of 5 µm is sufficient) followed bystandard coating processes, or theuse of special processes if no chemicalnickel is applied.

Chrome-plated and nickel-platedmetals can in principle be coated.Such electroplate/PVD compositecoatings, in which the electroplatedlayer has limited adhesion to the sub-strate, are best employed under com-bined corrosion and wear conditionswhere mechanical loads are not toosevere.

Sintered materialsAs a rule, cemented carbides canbe coated without any restriction butmechanical operations such as grind-ing must be modified as appropriate.Cemented carbides should be ma-chined with coolant-lubricants contain-ing cobalt inhibitors. Sintered metalswith open pores cannot be coatedbecause residues from the sinteringprocess outgas in vacuum, interferingwith the plasma processes.

Other materialsSuitable ceramics, that is, conduc-tive or metallised ones, can be coated.Oxide ceramics such as aluminiumoxide need special processes that per-mit coating application even thoughan insulating surface is present.

Because of their lack of conductivityand their sensitivity to high tempera-tures, plastics are not coatable withBALINIT®.

Materials and their coatability

33

Materials BALINIT® C BALINIT® DLC BALINIT® CNI BALINIT® D BALINIT® Aa-C:H:W a-C:H CrN CrN TiN

BALINIT®

FUTURA NANOTiAlN

Steels withheat-treatment temperatures > 500 °C

Heat-treatable steels + + + + +Cold-working steels + + + + +Hot-working steels + + + + +High-speed steels + + + + +Austenitic steels + + + + +Age-hardened steels + + + + +

Steels withheat-treatment temperatures around 200 °C

Ball- and roller-bearing steels + + +Case-hardening steels + + +Hardenable chrome steels + + +Low tempering temperature tool steels + + +

Other materials

General engineering steels + + + + +Nitrided steels (after pretreatment) + + + + +Cast iron

Chrome-plated metals

Nickel-plated metals

Nickel alloys + + + + +Titanium alloys + + + + +Copper alloys

Aluminium alloys

Cemented carbides + + + + +Sintered metals (after pretreatment)

Ceramics

Plastics – – – – –

Coatable materials

+ coatable– not coatable

conditionally coatable (inquire)

34

Hardness and strength of materials

Coating

badly ground well ground

The hardness and load-bearing capac-ity of materials play a special role incoating because typical PVD/PACVDcoatings are not self-supporting. Ahard substrate offers adequate sup-porting action for the coating and pre-vents it from breaking up (“eggshelleffect”).

Therefore as a rule of thumb, toapply a coating, the greater the loadon the component, the harder the sub-strate material must be (> 45 HRC).Plasma nitriding or case-hardening ofsoft steels can produce a boundaryzone that will support the coating. Ifsubsequent loss of hardness is to beavoided, the tempering temperaturemust be higher than the temperatureat which the component is coated.Do not reduce the substrate hardnessof the component to be coated.Furthermore, it is advisable to coatthe harder surface in the tribosystem.

Component surface quality

Along with strength, the surface condi-tion of the component affects coatingperformance. A necessary conditionfor good coating in a vacuum processis therefore:

A readily coatable componentis one that has been groundor polished, well cleaned, andconserved for shipping.

- Coolants employed in grinding mustnot contain calcium sulfonates, com-pounds of boron or iodine, or silicone-based antifoaming agents.

- Ground, honed, polished or lappedsurfaces must be cleaned of abrasivecompounds and their residues.

- Brazed and soldered joints must befree of pipes, fluxes and cadmium.

- Blind holes and internal threads mustbe free of hardness salts and othercontaminants.

- Chips, wax, adhesive tape, paint andother nonmetallic contaminants mustbe removed from the components,also grinding dust, cleanser residues,fingerprints and the like.

- The components must be demagnet-ised.

Roughness plays a central role in fric-tion and wear processes. The smallerthe roughness, the better the tribologi-cal properties. Improving the surfacequality, however, comes with costs aswell. This is true for both uncoatedsurfaces and those that will receivecoatings. For severely loaded precisioncomponents, designers specify thewell-ground surfaces (Rz = 0.5-5 µm).PVD coatings follow the surface topo-graphy exactly, and there is just a verysmall increase in roughness.

A roughness in the high range (i.e., 3to 5 µm) can be chosen when applying“softer” coatings such as BALINIT® C(WC/C, approx. 1,000 HK), thanks tothe very good running-in and burnish-ing qualities and the good behaviourtowards the mating part. With hardnitride and DLC coatings, the rough-ness Rz should be between 0.5 and1 µm to avoid unduly great wear tothe mating part.

The increase in roughness with PVDcoatings is generally negligible. Thereis an increase of approx. 0.2 µm inRz with sputtering, evaporation andPACVD processes, and approx. 2 µmwith arc coating. Methods such asblasting or brushing have becomestandard in order to remove rough-ness peaks (droplets) after arc coating.

The following details should be kept inview:

- Surfaces must be metallically bright.Corroded, brown-finished, steam-blued or similarly treated surfacescannot be coated.

- Ground surfaces must not displayburrs, grinding cracks, oxide skinsor rehardening burns.

35

Component design for coating

The best coating results will be achieved if component condition and geometryare in harmony with the physical and engineering conditions of cleaning, prepa-ration and coating.

Component condition- Components are fixtured for coating.Allowance should be made for thesurface covered by the fixture, whichwill remain uncoated.

- Surfaces that must be left uncoatedare covered by a mechanical mask.Optimal component design mustpermit this, since the use of pastes(as in nitriding) is not possible.

- Preassembled (glued, screwed orpressed together) components can-not be coated. The joint surfaces willoutgas in vacuum and may not lendthemselves to adequate cleaning.Welded structures must be putthrough a stress-relief anneal beforecoating.

Coated surface =functional surfaceThe designer can exert a good dealof control over unit coating costs bytaking into account the coating fromthe very beginning of the componentdesign process. The configuration isbest if only the component with thefunctional surface has to be coated -that is, other surfaces of the compo-nent are not coated needlessly and noexpense is incurred in masking themoff. The illustration shows an example.If the functional surface of the wormis rigidly attached to the shaft stubs,the entire component must be coated.A better solution is to make the wormand stubs separately. This approachsaves space in the coating machineand thus optimizes the number ofcomponents per batch. The two partscan be joined or press-fitted togetherafter coating.

coatedfunctional surface

uncoateduncoated coatedfunctional surface

A component designed for coating: More units per coating batch.

A component not designed for coating: Fewer units per coating batch, need for masking.

- Blind holes can be coated, but theyshould not have a depth greater thantheir diameter.

Geometry, dimensions andweightsIn addition to the condition, the ge-ometry and weight of the componentmust be considered. The maximumsize and weight of a component forcoating depend on the coating select-ed. The maximum weight is about3,000 kg, or a diameter of 1,300 mmand a length of 1,500 mm.

36

Conservation and packaging

Optimal coating results do not dependsolely on component design. Thechoice of the right coating for the ap-plication is also crucial to boostingcomponent and system performance,as the next chapter will demonstrate.Balzers offers both proven, standardsolutions and customised coatings forspecific needs.

The parts must be guarded againstrusting in the course of transport. Thiscan be done by treating them with aslight water-displacing oil, which canbe removed without residue by alkalinecleaning after delivery. An alternative isVCI (volatile corrosion inhibitor) paperin a vacuum package. Undiluted oil,grease or wax should not be used.These conserving agents are difficultto remove and would interfere with thesensitive baths used in cleaning sys-tems.

When emulsion coolants are used inmanufacturing, it is essential to cleancomponents thoroughly before con-servation. This must be effected inan aqueous process using deionisedwater. Otherwise, water hardness canresult in lime deposits on the parts;such deposits can combine with theconserving agent to form durable sur-face residues that cannot be removedby chemical means.

The use of oils in fabrication processeshas proved not to be a problem, be-cause there is less danger of residueson the parts.

Proper packaging guards componentsfrom harm due to external factors andkeeps them from damaging one an-other. A packaging that is also suitablefor repeated use and for return ship-ment is advisable.

For mass-production parts we recom-mend consulting with us on fabricationmedia and packaging. We shall beglad to assist you.

37

Application tailored solutions

The chief objectives of today’s designers and design engineers as they work outnew and innovative concepts include lighter weight, higher output from more-compact mechanisms, lower emissions, and minimal lubrication and maintenance.As requirements on systems grow more stringent, so do requirements on theircomponents, and classical materials soon reach their limits. Potential for perfor-mance can be greatly enhanced with application-tailored BALINIT® hard coatings;indeed, only BALINIT® makes new design solutions feasible in many cases.

Engine technology

Boosted fuel economy, reduced emis-sions, greater power and passengercomfort are among the challenges thathave led vehicle and engine developerstoward innovative engine designs:

- Gasoline engines with direct fuel in-jection, variable valve timing, smallerdisplacement and turbo charging, aswell as fuel-cell hybrid technology

- Diesel engines with high-pressureinjection, soot filters and exhaust gasrecirculation and capable of runningon low-sulphur fuels

Drastic testing in motor sports is oftena first step toward the adoption ofcoated components in the automotiveindustry. Mechanical components forracing service are designed for maxi-mum strength and must be as light aspossible at the same time. BALINIT®

coatings are crucial for the reliablefunctioning and long life of these com-ponents in hard racing service.

Free mean effective pressureFMEP [bar]

0.2

0

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

600 1,000 1,400 1,800 2,200

Engine speed [rpm]

Piston train

Generator

Fuel system

Steering pumpAir compressorValve train

Oil pump

Water pump

Crankshaft

This test programme result shows how much friction loss is due to individual engine components and thushow these components affect fuel consumption in a truck diesel engine.Source: IVECO Motorenforschung AG

Wear of diesel truck engine by parts

Engines

Design innovations aimed at boostingefficiency, such as lighter aluminiumengine blocks, are costly in terms ofdevelopment. Less effort has beenfocussed on cutting internal frictionand how this will affect power output.Frictional losses in engines occur atpiston/connecting rod joints, crank-shafts, valve trains and oil pumps,among other places. A reduction in

friction will bring about not just greateroutput but also a potential for lowerfuel consumption and emissions.Solutions based on BALINIT® carbonor metal coatings have proven them-selves both in automotive productionand in racing. The very good wear andfriction behaviour of these coatingsimproves the performance and servicelife of engine components such astappets, wrist pins and piston rings.

38

Valve trainBALINIT® C and BALINIT® CNI arerecommended for the coating of tap-pets in high volume production. TheWC/C coating displays its specialadvantages in low friction, while theCrN coating stands out chiefly in thegood wettability of the very fine sur-

Frictional torque [Nm]

1,0000 2,000 3,000 4,000 5,000 6,000 7,0000

0.5

1.0

1.5

2.0

2.5

3.0

Engine speed [rpm]

Phosphated

WC/C-coated

Test method: Cylinder-head test stand, non-firedSource: Ford/INA

Friction reduction in the valve train of a passenger carwith carbon coating of tappets

Coating of engine parts reduces friction andthereby increases the output and efficiency ofthe drive system.

Power consumption [kW]

Engine speed [rpm]

500

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

2.0

2,0001,000 1,500

uncoatedBALINIT® DLC-coated

Reduced valve-train power consumption withBALINIT® DLC-coated tappets (truck engine)

face. With regard to service life andwear, both coatings are far superior toconventional phosphating. BALINIT®

coatings have found acceptance inmotor sports for friction and wear re-duction. BALINIT® DLC STAR is usedon a large scale for the coating of camfollowers and tappets.

BALINIT® DLC-coated tappet

Measurable advantages are alsogained in truck engines. Tappets coat-ed with DLC were tested on an en-gine test stand. They proved to reducefrictional power consumption by asmuch as 400 W in comparison withuncoated cast-iron tappets at higherspeeds.

39

Piston ringsPiston rings cause significant frictionallosses in engines, while being subjectto added wear as a result of risingignition pressures and exhaust gasrecirculation. For this reason, a widevariety of anti-wear coatings offerpotential improvement. Electroplatedcoatings with fine dispersed carbides

Tribometer: Cameron-Plint TE77Load: 8 MPaTemperature: 80 °CTest duration: 6 hFrequency: 10 HzCylinder liners: Grey cast ironOil: Lubrizol TH 53303

Treatments applied to piston-ring surface only

Source: Scania AB

Cylinder-liner wear [mg]

0.1

0

0.1

0.2

0.2

0.3

Plasma-sprayed Nitrided Hard chrome Chromeceramic

BALINIT® C(WC/C)

x = no wear detectedPiston-ring wear [mg]

X

XX

Wear of cylinder liners with variously treated piston rings

and PVD coatings are finding greaterand greater acceptance along with theproven coatings for piston rings, suchas hard chrome and molybdenum,plus nitriding for steel rings. A bench-mark trial has shown that BALINIT® Cis among the best solutions. In a com-parison with the most important stand-ard coatings, BALINIT® C displays theleast ring and cylinder wear.

A simulation with passenger-car pistonrings showed that PVD-CrN and PVD-WC/C sustained greater loads in thescuffing test than hard-chrome-coatedor nitrided rings. What is more, CrNdisplayed the lowest wear while frictionwas least with WC/C. An engine testprovided impressive confirmation ofthese results, with WC/C and CrNcutting the frictional power consump-tion (at 2,000 rpm) by 9-20 % in com-parison with hard chrome coating andnitriding.

Friction coefficient Normalised wear

0.10

0.08

0.06

0.04

0.02

0

0.12

0.2

0.4

0.6

0.8

1.0

1.2

0

Normalised wear Friction coefficient

Hard chrome Nitrided CrN - PVD WC/C - PVD

Friction and wear tests on piston rings (passenger car)

Test conditions (model test):Wear test: 100 N, 600 cm/min, 60 minFriction test: 100 N, 100 cm/minLubricant: oilCylinder liner: cast iron

40

Wrist pinsThe high injection and combustionpressures typical of today’s dieseland racing engines mean very severepressures where the wrist pin is incontact with the small eye of the con-necting rod. Bronze bushings, whichare commonly used as wrist-pin bear-ings, can well reach their strain limit.BALINIT® DLC or BALINIT® DLC STARcoatings on the wrist pins take overthe friction-reducing function of thebushings and render them super-fluous. These coatings also permit alighter, stiffer connecting rod design.What is more, BALINIT® coatingseffectively prevent scuffing of materialin the wrist-pin hole of the aluminiumpiston.

Results on piston rings in two-strokeengines for recreational and sport ve-hicles were similarly convincing. Somechrome dispersion coatings (eventhose established in the field) were notup to the challenge of this application,failing by heat checking. A series oftests was dedicated to comparinga variety of PVD coatings: Here sput-tered CrN coatings (BALINIT® CNI)showed the lowest wear. They areapplied in a thickness of 10 µm inseries.

In addition to replacing conventionalcoatings for piston rings, DLC andWC/C coatings are also employed asrunning-in coatings on nitrided, chrome-plated or flame-sprayed piston-ringsurfaces.

Wear [µm]

BALINIT® ATiN

BALINIT® C1000WC/C

BALINIT® C1500WC/C

BALINIT® DLC BALINIT® CNl

6

5

4

3

2

1

0

7

Piston ring wear in two-stroke engines

Running time: 50 hours

When wrist pins are coated by PVDprocesses, not only the bronze bush-ing becomes unnecessary and thewear is reduced. There is also amarked reduction in friction and thusin engine power consumption. Fric-tional power consumption, measuredat high revolutions and high ignitionpressure, was cut by as much as600 W in a test rig.

Reduction of power consumption [W]

Ignition pressure: –– 45 bar –– 65 bar –– 90 bar –– 115 bar –– 135 bar –– 155 bar 600

500

400

300

200

100

700

800 1,000 1,200 1,400 1,600 1,800 2,000 2,200

Engine speed [rpm]

0

Reduced friction with BALINIT® DLC-coated wrist pins (truck engine)

41

95

85

75

65

55

45

35

67.8 Nm at 10,045 rpm

113.0 HP at 12,145 rpm110.6 HP at 12,145 rpm

BALINIT®-coateduncoated

Torque [Nm]

Speed [rpm]

Power output [HP]

120

110

100

90

80

70

60

50

40

308,000 10,000 12,000

70.0 Nmat 9,646 rpm

Wear and friction reductionin motorcyclesThe coating of tappets, finger fol-lowers, wrist pins and transmissionparts in sport motorcycles yields im-proved wear resistance as well asgains in power. A dynamometer testshowed a 2.2 % power increase fora Kawasaki Ninja. Today mass-pro-duced wrist pins and finger followersare coated with BALINIT® DLC.

Motor sport

Innovations in motor sport often foreshadow mass-production applications inautomaking. This holds for coatings as well. A variety of PVD-coated componentshave long been used in nearly every category of motor sport, above all in thevalve train, piston group, transmission and chassis and suspension parts.

Motorcycle: Kawasaki NinjaParts coated:Tappets: BALINIT® DLCWrist pins: BALINIT® C (WC/C)Transmission: BALINIT® C (WC/C)

Power gain: 2.4 HP = 2.2 %Increase in torque:2.2 Nm = 3.3 % at lower speed

Friction reduction

Tappets from a Kawasaki racing motorcycle.Left: uncoated, after approx. 250 km; severe wearnecessitates replacement.Right: BALINIT® DLC-coated, after approx. 1,000 km;almost no wear; still in service.

Shock absorbersThe coating of shock absorbers isnot just a matter of appearance. Theexcellent sliding properties of PVDcoatings also lead to better response(reduced stick-slip) and improvedanti-diving behaviour. The coatingsused are TiN, DLC and TiAlN. BALINIT® FUTURA NANO (TiAlN)-coated motorcycle shock absorber tube

42

Formula 1Formula 1 racecars could not competewithout thin hard coatings. DLC andnitride coatings are applied to engineparts under extreme loads, such ascamshafts, finger followers, valves andconnecting rods, in order that they canwithstand high speeds and high sur-face pressures and meet the need forlonger service life.

The small eyes of connecting rods arecoated in order to allow operationwithout bushings. In most cases thefrictional partner of the small eye is aDLC-coated wrist pin. The lateral sur-faces of the connecting rods are coat-ed so that frictional losses at the crankarms can be reduced to the greatestextent possible.

Valves experience severe loads at seat,tip and shank. Ductile CrN coatings(such as BALINIT® CNI) have provenserviceable for exhaust valves, WC/Cor DLC for intake valves. DLC coat-ings, commonly over a nitride baselayer (e.g., BALINIT® DLC STAR), areemployed in the valve train.

Furthermore, a long list of steering andsuspension parts, as well as threadedconnectors made of titanium, receiveWC/C or TiN coatings.

Titanium parts can be additionally oxi-dised in a special process (Ti-Plus).Along with a TiO2 layer, an oxygendiffusion coating typically 10-15 µmthick is applied; the latter affords goodsupport to the rather soft titaniumalloys. This process has found accept-

ance for valve spring retainers amongother parts, but it is ideally suited tointernal surfaces (holes) as well.

Where service conditions are critical,piston rings can no longer reliably holdthe aluminium pistons away from thecylinder walls. Carbon coatings on thealuminium pistons eliminate the dangerof seizing. Coating the piston-ringgrooves simultaneously provides effec-tual protection against cyclical frictionalwear due to the side flanks of thepiston rings.

BALINIT®-coated parts for motor sport

43

Innovative diesel injection systemssuch as unit injector and common railwere milestones in engine technology.Injection pressures in diesel engineshave risen to 2,000 bar and beyond,and these systems provide both opti-mal fuel utilisation and improved engi-ne emission values. The high pressureshowever, impose extreme stresses onconventional materials used for injec-tion system components and unac-ceptable wear can result. Increasedcontact forces and correspondinglynarrow lubrication clearances makelubrication more difficult, further pro-moting wear.

These processes have the followingconsequences:

- Plungers and injector needles mustbe manufactured to a tolerance ofless than 1 µm in order to preventleaks in operation. Acceptable life-time wear rates are in the order oftenths of a micrometre.

- The prevailing pressures exert suchstresses on hardened steel bearingcomponents that scuffing may occur.

- Classical materials such as bronzesin plain bearings can experienceplastic deformation.

BALINIT® carbon coatings offer qual-ities that enhance the performancelimits of the materials and protect se-verely stressed precision componentsagainst adhesive and abrasive wear.At the same time, these coatings haveideal emergency running properties,so that operating life is extended evenunder starved lubrication conditions.In practice, these coatings help boosteffective engine output, lengthen main-tenance intervals, and reduce fuel con-sumption and emissions of soot andother pollutants.

Mass-produced BALINIT® C, BALINIT®

DLC and BALINIT® DLC STAR coat-ings have become indispensable forthe functioning of injectors, plungersand plain bearings in common-rail andunit injector systems. Hard coatings,however, have been in service evenlonger, for example in in-line and dis-tributor pumps employed in commer-cial vehicles, marine diesel enginesand stationary power plants.

Fuel injection

Pump plunger

Plate

Polygon ring

Schematic drawing of a diesel injection pump BALINIT®-coated polygon ring for adiesel injection pump

44

Common-rail injectorsBALINIT® DLC sets a new standard incommon-rail systems. The hard car-bon coating provides great abrasionresistance for the tribologically stressedcomponents in modern common-railinjectors. These components musthandle high surface pressures and atthe same time stand up to severe abra-sive stress due to ultrafine particles inthe fuel. BALINIT® DLC gives thesecomponents the needed service life.

Pump plungers for marine,locomotive and utility vehicleapplicationsSince the 1980s, Balzers has appliedPVD coatings to plungers for in-line,distributor and single-cylinder pumpsused in marine diesel engines, enginesfor construction machinery and station-ary plants (emergency generator sys-tems). These applications feature theuse of heavy oil and contaminatedfuels, leading to premature wear andhigh maintenance costs. For this rea-son, original-equipment plungers in theinjection pumps of large engines arecoated with BALINIT® C or BALINIT®

DLC, which contributes to bettereconomy and lower emissions.

Service life [h]

0.1

0.01

1

10

100

1,000

10,000

WC/Cuncoated BALINIT® DLC

0.05

20

2,000

Test conditionsMaterial: AISI 52100 (DIN 1.3505) bearing steelCriterion for stopping test: Material wear of 1 µmDiesel injector under accelerated operating conditions

Service life ofcommon-rail injector plungers

Unit-injector system:plain bearingsThe BALINIT® C carbon coatingstrengthens many components in theunit-injector system, such as the plainbearings that transfer the motion fromcam to plunger. In a floating systemwith a pin, a bushing and a roller, thepin and bushing are coated with BALI-NIT® C to safeguard against wear.

45

Mechanical drives

The design of drive components forvehicles and machinery is marked bytrends such as the use of lightweightconstruction, higher efficiencies, moresevere loads, lower lubricant consump-tion and longer maintenance intervals.These requirements tend to increasethe wear of bearing and transmissioncomponents. Alternative material se-lection can only rarely meet thesechallenges.

Wear-protection coatings offer a dif-fer-ent approach. Their use guards com-ponents against scuffing and pit-ting and extends their service lives,thus making the whole system moredurable.

The BALINIT® C carbon coating, forexample, has proved its worth in theplanetary transmissions of constructionmachinery and commercial vehicles, inthe emergency operating reserve of

Vehicle gears

Wear modes and causes of failures ingear transmissions depend on the loadand the peripheral speed:

- Sliding wear occurs at low periph-eral speed when there is no continu-ous lubricant film between the toothfaces, so that the surfaces come intodirect contact (mixed friction).

- Scuffing can come about at lowperipheral speed when loads aremore severe. This process can alsoresult if the viscosity and thicknessof the lubricating film decrease withrising peripheral speed and tempera-ture, so that the lubricating film ulti-mately ruptures. Scuffing is common-ly preceded by wear to the toothfaces.

- Pitting is a further possibility if aload-bearing lubricant film is presentbut the loading capacity is limited bythe compressive strength of the gearsurface. Due to continuous cyclicloads at high contact pressures, finecracks are produced at grain bounda-ries or at inclusions beneath the sur-face. These cracks lead to detach-ment of particles from the surface,leaving small pits on the tooth faces.

- Micropitting is attributable tostarved lubrication. Microscopiccracking and chipping give thevisual impression of gray spots.

The use of case-hardened steels vir-tually exhausts the load-bearing capac-ity of gears. The danger of scuffing ismitigated by additives in the gear oil.Carbon coatings, however, are moreeffective against all wear mechanismsin transmissions.

The BALINIT® C (WC/C) coating in par-ticular separates metallic gear surfacesreliably under mixed friction conditions.

The danger of scuffing and micropittingis reduced, while the maximum loadcapacity (pitting resistance) is increasedcompared to case-hardened gears. Asource for this improvement lies in theexcellent running-in behaviour of BALI-NIT® C. The coating reduces local sur-face pressures (Hertzian pressure) andenhances the reliability of poorly lubri-cated gears.

Wear limit

Pittinglimit

Tooth fracture limit

Scuffinglimit

No damage

Peripheral speed

Torque

Service limits of gear drives

helicopter transmissions, and in racingtransmissions, where it reduces frictionand boosts power. Another applicationarea where coating protects againstsurface fatigue, tribo-oxidation, brinel-ling and also permits unlubricatedoperation is for rollers and races inindustrial roller bearings, which experi-ence very severe loading.

46

High-speed spur gearsBALINIT® C quadruples the servicelife of gears. The standard FZG C testshows that the fatigue strength isincreased by 10-15 % over case-hardened but uncoated gears. In thetest the failure criterion for gear servicelife was defined as single-tooth wearof 4 % due to pitting. The key factorsin these improved figures were thelower local surface pressure (Hertzianpressure), which resulted from reducedfriction in the rolling contact, and theoutstanding running-in behaviour ofBALINIT® C.

Tooth face pressure [N/mm2]

2

2,000

1,900

1,800

1,700

1,600

1,500

2,100

64 8 1082107864

Number of loading cycles

BALINIT® C (WC/C)

uncoated

Pitting wear with combinedsurface treatmentsPVD coating is not, however, the onlyoption for increasing the pitting resist-ance of gears. Other treatments in-clude combined case-hardening andnitriding (duplex treatment) and surfacepolishing by the Vibrofinish process.Gears show marked gains in pittingresistance and service life as a resultof both PVD coating with WC/C andduplex treatment, but the best resultscome about with a combination ofVibrofinish and WC/C coating.

Hertzian pressure [N/mm2]

1052,000

2,200

2,400

2,600

2,800

108106 107

Cycles

EH + WC/C

EHDH EH + Vibro + WC/C

Test conditions:Oil: Mobil Jet / 80 °CSliding/rolling ratio: 24 %Speed: 2,860 rpmMaterial: M50 Nil / > 700 HVSource: J. Kleff and D. Wiedmann,ZF Asset Brite Euram Project

EH: case-hardened, 0.7-0.9 mmDH: duplex-hardened, 1,050, HV10WC/C: BALINIT® C-coated, 1,000 HV / 2 µmVibro: Agusta superfinish, Rt 3.2 / 0.6 µm

High-speed gears in severe service

Test method: FZG C testMaterial: Case-hardened steelHardness: 62 HRCRoughness: Rz = 3 µmCriterion for stopping test:4 % material loss per tooth(weight) by wear

Uncoated transmission gear:surface fatigue (pitting) despitecontinuous lubricant film

Rolling-contact fatigue test

47

Gear wear by scuffingScuffing, a consequence of starvedlubrication, is an important mechanismof gear wear. Simulating the processon the test stand involves supplyingonly very small quantities of lubricantand comparing the results with coat-ings. Experiments at the IMM (Instituteof Machine Elements and MachineDesign) at the Technical University ofDresden have shown that service lifecan be significantly extended by eitherlight lubrication or a WC/C coating, butthe best results are obtained with acombination of the two. This means onthe one hand that coating cannot sup-plant regular lubrication, but on theother hand that lubrication and WC/Ccoating act in a positive synergy.

Spur gears for motorcyclesThe practical impact of protectinggears against scuffing was illustratedby an emergency that occurred duringa motorcycle race. The transmissionwas threatened with scuffing due toa loss of oil, but amazingly the riderwas able to finish the race thanks tocoating of the most severely stressedgears. An analysis showed that theuncoated gears had perceptible wearmarks but the coated ones displayedvirtually no abrasion.

Number of load cycles

uncoateddry

uncoatedlubricated

BALINIT® Cdry

BALINIT® Clubricated

1,400

29,000

150,000

Terminated after 2,000,000106

105

104

103

102

10

1

107

Total wear of sun and planetary gears [mg]

100

0

200

300

400

500

600

0 40 80 200120 160

uncoated

Sun and planetary gearsBALINIT® C-coated

Operating time [h]

Planetary gear set forconcrete mixersA quite different kind of load causeswear in the planetary gears of concretemixers. The very low speed and thesimultaneously high surface pressuremean that no lubricant film can form,and the sun wheel, the most greatlystressed component, is subject to se-vere abrasion. With BALINIT® C (WC/C)coating, wear is practically brought toa halt after a running-in phase.

Gear wheel wear in dry running and starved lubrication

FZG testSpeed: 1,000 rpmSurface pressure: 1,000 N/mm2

Lubricant: Esso CL46B (plant-based)Lubricant feed rate: 1 drop per minuteSource: IMM (TU Dresden)

Test conditions:Gear tooth profile: FZG-CLow-speed wearLoad: 2,180 MPa (316 KSI)Sliding speed: 0.04 m/s

Model test: planetary gears

Gears from a motorcycle spur geartransmission after loss of oil:BALINIT® C (WC/C)-coated (left),uncoated (right)

48

Transmissions for aircraftFor weight reasons titanium alloysare replacing steel more and more ingears. The low hardness and poor ad-hesive wear resistance of Ti-alloys canbe overcome by using BALINIT® C.

But also steel gears benefit from BALI-NIT® coatings. E.g., helicopters musthave the ability to run under emer-gency conditions (transmission fluidloss) long enough to land safely. Testsof carburised steel helicopter trans-missions revealed an increase from ascant hour to over six hours of emer-gency reserve with BALINIT® C coat-ing.

Reduction of power consumption [kW]

0.5

0

1.0

1.5

2.0

2.5

40 50 60 70 80 90 100

uncoated

BALINIT® C

Oil temperature [°C]

Temperature [°C]

-0.5

200

150

100

50

0

250

5.5 6.54.51.50.5 3.52.5

Time [h]

Standard transmissionuncoated

BALINIT® C-coatedtransmission

X X = Test ended because of wear

Torsen differentialsThe performance of differentials in pas-senger cars is impaired by friction andwear arising chiefly on cold starting.Engineers are successfully improvingreliability with WC/C coatings.

Rear-axle gearboxes in trucksVery great friction develops in truckrear-axle gearboxes with spiral bevelgears. Development engineers havetherefore studied whether PVD coat-ings could cut this friction. They foundthat frictional losses could be reducedby 1-1.5 kW (depending on the oiltemperature) with WC/C coating.

Helicopter transmission

BALINIT® C-coated gears permit emergency operation for a considerablylonger time after a loss of transmission fluid.Source: P. Maret and C. Varailhon / EUROCOPTER France

Reduction in truck rear-axle powerconsumption by BALINIT® coating

Gear ratio: 2.93Speed: 1,100 rpm

49

Wear rate of bronze gear [mg/h]

0

100

10

0

1,000

300100 200

Test time [h]

Worm BALINIT® C (WC/C)-coated

Worm uncoated

Industrial drives

Worm gears with coated wormLubrication is not always enough toprotect helical-gear transmissions,which are coming under more andmore severe stress, against frictionand wear. Worm systems, for example,work under very unfavourable tribo-logical conditions. The sliding motionand the force between the worm andgear faces make it difficult for a lubri-cant film to form. For this reason, thegear is most often made of bronze inorder to avoid scuffing. In service,how-ever, the teeth of the bronze gearwear away quickly and the gear mustbe realigned or replaced. Carbon coat-ings can improve the reliability andperformance of worm drives in severalways. In the worm transmission of alaser machining device, for example,coating the steel worm with BALINIT® Creduces wear of both the worm andthe bronze gear.

Worm gear sets: greater loads, longer service lives

Worm set data:Number of teeth (gear): 41Angle: 12.5°Shaft spacing: 100 mm

Test conditions:Worm speed: 400 rpm

Materials:Worm: AISI 5115 (DIN 1.7131)Gear: Bronze, DIN 2.1060.03 (GZ-CuSn12Ni)

Worm gears withcoated steel wheelAccurate workpiece positioning inmachine tools is effected with wormgears. When a classical bronze wheelis used, wear leads to errors that can-not be entirely compensated by fineadjustments; the result is dimensionalerrors in the work. Costly remachiningis necessary particularly for expensiveparts such as turbine blades. As acountermeasure, the bronze wheel isreplaced with a WC/C-coated steelwheel. The coating performs two func-tions: It emulates the frictional qualitiesof the bronze and at the same time itshardness works with the supportingaction of the steel to protect againstwear.

50

Cam and follower drive systemBALINIT® C wins the comparison testby a clear margin: The values and timevariation of load and velocity in camdrives imply poor lubrication conditionsand a danger of excessive wear. In thesearch for a better solution, couplesinvolving hardened steel, ceramic(Si3N4) and hardened steel with PVDcoating were compared. By far thebest results came about when oneor both rollers were coated wtih BALI-NIT® C. 0.01 0.1 1 10

Coefficient of wear [10-12 m3/Nm]

Test roller Mating roller100Cr6 - 100Cr6

Si3N4 - 100Cr6

Si3N4 - Si3N4

TiN - 100Cr6

TiN - TiN

WC/C - 100Cr6

WC/C - WC/C

100Cr6 = AISI 52100WC/C = BALINIT® C

ϕ

n1

FN(ϕ)

n2

Contact force: 0-2,000 NHertzian pressure: 0-1,106 MPaSlippage: 10 %Speeds: n2 = 200 rpm / n1 = 0.9 · n2Source: Surface Engineering Laboratory, University of Siegen

Ø 377

Ø 362

Cam

Roller

Cam drives incan-forming machinesVery great forces must be transmittedin can-forming machines, and so camdrives are used. The low speed ofmotion means that no adequate lubri-cant film can form, and the surfaceshave a tendency to scuff. WC/C coat-ing of the rollers produced a significantincrease in the service life of the camdrive.

Simulation of cam drive

51

Ball screw drive systemBALINIT® C makes it possible to boostthe speed of machine-tool operations.Lead screws are often used in the feedof these machines, but positioningspeeds are limited by wear and frictionbetween the balls and the returntubes. Practical tests have shown thatWC/C coating of the balls in particularcan reduce the frictional torque andstick-slip effects.

Frictional torque [Nm]

0

1.15

1.05

0.95

0.85

0.75

0.65

0.55

0.45

0.35

1.25

400300100 200

Speed [rpm]

uncoatedreturn tube coated, balls uncoatedballs coated, return tube uncoatedballs and return tube coated

Ball screw drive

BALINIT® C (WC/C) reduces friction and wear and cuts the frictional torque of the ball screw drive.Source: WBK, Institute of Machine Tools and Production Science, University of Karlsruhe

Ball- and roller-bearings

The typical rolling motion in ball- androller-bearings means that friction andwear conditions are generally good.When loads are severe and lubricationis poor, however, wear mechanismscan arise that will ultimately harm theentire tribosystem:

- Scuffing in case of starved lubrication- Abrasion due to contaminants- Surface fatigue (pitting) when over-loading occurs- Fretting and brinelling in the presenceof vibration

A variety of materials are currently usedin an attempt to combat these andother problems. One example is a verypure form of the standard bearing steelAISI 52100 (DIN 1.3505). Nitrided orchrome-plated steels offer protectionagainst corrosion, while tool steels aresuitable for high-temperature applica-tions and ceramic rollers can serve invery high-speed applications.

For some applications and some fric-tional requirements, however, conven-tional materials are not adequate andspecial materials are too costly. BALI-NIT® coatings offer an excellent solu-tion in these cases by virtue of theirgreat hardness and dimensional stabil-ity. By affording effective protectionagainst wear, these PVD coatings re-veal new tribological potential, especial-ly where extreme service conditions(high/low temperatures, aggressiveenvironments, vacuum, clean-roomsettings) limit reliability and make lubri-cation difficult or impossible.

52

Cylindrical-roller thrust bearingsSpecially designed test stands areused to study the frictional and wearbehaviour of roller bearings. Criticallubrication conditions and loads lead-ing to scuffing are preferably investi-gated on stands for cylindrical-rollerthrust bearings. Because this type ofbearing is inherently subject to hightribological stress.

Service life [h]

0

10

100

1,000

Rings and RollersBALINIT® C (WC/C)-

coated

uncoated

Temperature: 30 °CCoefficientof friction: 0.004Roller wear: 5 mg

> 250

1.5

FE-8 test standBearing type: 81206Load: 33 kNCage material: PA 66Speed: 15 rpmDry runningSource: IME, Aachen University (RWTH Aachen)

Material pairs for roller bearingsThe Institute for Machine Elementsand Machine Design at RWTH AachenUniversity studied the development ofwear in thrust bearings with variouscombinations of WC/C coatings. Inone series only the rollers were coated,in another only the rings, in anotherboth frictional partners. Interestingly,bearings with all coated componentsdisplayed only the second-best wearbehaviour, after those with coatedrings.

Wear [mg]

0

1

2

3

4

5

6

7

8

9

Rollers:Rings:

RollerShaft ringHousing ring

WC/CWC/C

100Cr6WC/C

WC/C100Cr6

The advantage of coating only therings over coating the rollers is under-standable because more contact areais coated and the coating itself issomewhat thicker. There is no directway to account for the poorer behav-iour with all coated components; onepossible interpretation is that steelsurfaces with the selected lubricantcooperate with the WC/C coating toproduce especially good running-inand wear conditions. But this findingcannot necessarily be extended to

Test conditions:Test stand: FE8 thrust bearingBearing: 81212Speed: 7.5 rpmAxial thrust: 80 kNContact pressure: 2,000 MPaBearing temperature: 70 °CRunning time: 80 hBase material: AISI 52100 / DIN 1.3505Source: J. Loos, RWTH Aachen

Effect of material pair with coating of thrust bearing components

other tribosystems: It applies in the firstinstance only to systems with a ten-dency towards adhesive wear. If abra-sion and surface fatigue are in ques-tion, it is better to coat both frictionalpartners.

53

Partial coating of rollersAnother interesting experiment involvedcoating various numbers of the rollersbut not all of them. The aim was toshow whether and how well coatingprotects against wear even when notall the rollers are coated. Surprisingly,even a few coated rollers bring aboutmarked improvements. Coating justtwo of a maximum of 15 rollers cuts

Total wear [%]

0

100

75

54

18

4 1 0.2

1 2 4 8 12 150

20

40

60

80

100

Number of WC/C-coated rollers

Surface fatigueEarly in the 1980s tests on spindlebearings showed that a reduction inrace wear can be expected with WC/Ccoating. More recent measurementshave been carried out to examine indetail the actions of the individual com-ponents. Test-stand trials on radialbearings have shown for example thatapplying a WC/C coating to the innerrings yields only a slight extension ofservice life because now the uncoatedrollers begin to wear. Only when therings and the rollers are coated does asignificant increase in life come about.

Bearing type: 7014 P4 spindle bearingTest duration: 50 hSpeed: 19,000 rpmSpeed coefficient: 1.7 · 106

Lubricant: Grease

20 µm

4 µm

WC/C coating

Ball bearing Race uncoated

RaceWC/C-coated

Test conditions:Test stand: FE8 thrust bearingBearing: 81212Speed: 7.5 rpmAxial thrust: 80 kNContact pressure: 2,000 MPaBearing temperature: 70 °CRunning time: 80 hBase material: AISI 52100 / DIN 1.3505Source: J. Loos, RWTH Aachen

Wear behaviour with various numbers of rollers coated

Race wear in high-speed spindlebearings

wear by some 50 %, and treating halfthe rollers results in more than a 90 %decrease in wear. This behaviouroccurs because the coated rollerspromote good running-in and burnish-ing even for the rings, which alsoreceive some of the coating material.The same phenomenon can also beobserved in respect of the uncoatedrollers.

54

Ball bearingsBALINIT® C effectively protects ballbearings against tribo-oxidation andbrinelling under severe static-vibratingloads. Electroplated chrome andTeflon® (PTFE) coatings had little effectagainst these forms of wear. The WC/Ccoating reduces wear and noise, andbearings in such settings as electrical-discharge machining (EDM) equipmentshowed a more than doubled servicelife.

Time to failure [h]

20

0

40

60

80

100

120

140

lubricated:electroplated Cr orPVD-CrN or PTFE

dry:BALINIT® C (WC/C)

64

> 128

Wear reduction with BALINIT® C (WC/C)-coatedroller bearings in EDM machines.Source: INA/Balzers

Bearing ballsBALINIT® C is applied not only to innerand outer races and cylinders but alsoto the balls in ball bearings. The typicalcoating thickness is 0.5-1 µm with auniformity in the order of ± 0.1 µmmeasured over the full circumference.The slight increase in roughness isoffset by the good burnishing qualitiesof the coating.

Linear guides for semiconductorcomponent assemblyLubrication is not acceptable in someindustries. In semiconductor manufac-turing, for example, machinery mustoperate without lubrication on groundsof cleanliness. Drive components mustnone the less operate reliably over longservice lives. This goal is achieved inlinear guides by applying a WC/C coat-ing to the rollers. WC/C-coated railswith uncoated steel rollers displaymarkedly longer life than uncoatedrails with ceramic rollers.

Service life [cycles]

10

1

102

103

104

105

106

107

108

Ceramic rollersuncoated WC/C- coated

rail

Ball bearings undervibrating load

Load: 20 % of dynamic load coefficient CDrySource: Schneeberger / Roggwil

55

Fluid technology

The Montreal Protocol requires that,after 2020 chlorofluorocarbons (CFCs)are no longer used in automotive andhome air conditioners, compressorsand refrigerators. New concepts basedon environmentally benign refrigerants,however, generally involve poorer lubri-cation and wear properties.

Makers of hydraulic drives are alsomore and more confronted with lubri-

Compressors

CFCs used as coolants in compres-sors mix well with lubricants and gen-erally permit the operation of compres-sors without wear and other causesof upsets. In contrast, environmentallybenign CFC-free refrigerants are poorlymiscible with lubricants, so that refrig-erant and oil phases separate. Lubri-cation is often inadequate as a result,and mechanical components cannotbe protected against wear over therequisite service life.

Air compressors operated withoutlubricant are subject to similar require-ments, with corrosion even more of aproblem because of humid serviceenvironments.

Manufacturers of air and refrigerantcompressors are increasingly takingadvantage of PVD coatings, whichpermit reliable compressor operation.

cation and corrosion issues. The trendtoward lighter weights and higherpressures and speeds means that hy-draulic system components must beable to handle more-severe tribologicalstresses. In fields where water is usedas the pressure medium instead of oil,or where hydraulic components areexposed to more-drastic corrosive andabrasive operating conditions, thereare even more requirements that mustbe met.

Hard coatings have been proposed asa way of addressing these problems.BALINIT®-coated components experi-ence much less wear and thus extendthe life of coolant and air compressors,hydraulic pumps, and hydraulic andpneumatic valves and fittings. Whatis more, coating makes it possible tophase out costly materials such asbronze, carbide and ceramic.

Wear [µm]

0.01

0.1

1

10

100

15

5

0.1 < 0.1

Ring Vaneuncoated

RingVane only BALINIT® C-coated

Vane

Ring

Vane

Vane compressorsOperation with CFC-free refrigerantsentails deficient lubrication resulting insevere wear. Coating the steel vaneswith BALINIT® CNI or BALINIT® Cmarkedly reduces wear of the com-pressor vanes and rings.

Even non-chlorinated hydrocarbonsmust be regarded as problematicalwith an eye to the future. While these

Test conditionsDuration: 1,000 hPressure: 3.5 N/mm2

Temperature: 100 °CRefrigerant: CFC-freeRing material: Cast ironVane material: Steel

Vane compressors with CFC-free refrigerants

substances do not harm the ozonelayer, they do contribute to the green-house effect. Carbon dioxide (CO2),on the other hand, is a very environ-mentally safe coolant. It is being testedfor use in vane and piston compres-sors for household appliances andvehicles. In both systems, CrN andWC/C coatings combined with glycoland ester-based lubricants yield verygood frictional and wear behaviour.

56

Surface wear [%]

0

80

60

20

40

5

100

1,000

Running time [h]

PVD-CrN

uncoated

BALINIT® C (WC/C)

Screw compressorsConventional screw-type air compres-sors are designed for synchronised dryrunning or unsynchronised operationwith oil injection. Where safety or en-vironmental considerations rule out oilinjection, complicated designs withsynchronising gears have had to beused. Tests with BALINIT®-coatedrotors have shown that unsynchro-nised equipment can function reliablyif water injection is used in place of oil.Scuffing occurs in a very short timewithout the coating. While chromiumnitride (CrN) improves the wear behav-iour, 1,000 hours’ operation wearsaway 60 % of the CrN-coated sur-faces. With BALINIT® C, no furthersurface wear can be detected after3 % running-in wear.

Screw compressors with water injection

Test conditions:Both rotors coatedSliding speed: 50 m/sTest duration: 1,000 hCooling and lubrication with waterUnsynchronisedSource: University of Dortmund

57

Wear [µm]

0

0

5

10

25205 1510

Total length of bearing rollers [mm]

Standard bearingWC/C-coated

Radial-piston hydraulic motor

Wear reduction with WC/C coating of roller bearings in the radial-piston motorLoad: 70 kNTemperature: 50 °CTest duration: 58,000 revolutionsSpeed: 6 rpmLubricant: Shell Tellus 68 S / 4 mg/l ISO MTDSource: U. Olofsson, H. Sjöström, U. Sjödin / ASME Journal of Tribology

Hydraulic pumps andhydraulic motors

High pressure, extreme flow velocitiesand the presence of fine particlesstress water-pump components, oftento the point that carbide is no longeran adequate material solution. Theexceptionally hard BALINIT® DLC andBALINIT® FUTURA NANO coatingsoffer good wear protection, therebyopening up further scope for designinnovations.

Other severely stressed hydraulic com-ponents are also protected againstsuch wear mechanisms as erosion,cavitation, deformation, adhesion andabrasion when BALINIT® coatings areapplied.

The qualities of hard coatings alsomake them suitable for special applica-tions. For example in mining (danger offire) or forestry (environmental pollution)mineral oils cannot be employed aspressure media. Low flammable water-based hydraulic media (HFA, HFC) areused in these fields. BALINIT® coatingscan meet the tribological challenges(e.g. insufficient lubrication) in all suchcases.

Radial-piston pumpsRadial-piston motorsHigh power density in very compacthydraulic motors makes lubricationdifficult, so that frictional losses andadhesive wear occur. BALINIT® C cutsstatic friction between the rollers andthe grey-iron pistons by 40 %; energylosses on motor starting are loweredby 18 %; and stick-slip processes donot occur. Furthermore, WC/C coatingprevents scuffing and improves theperformance of bearing rollers somuch that virtually no wear can bedetected after 58,000 revolutions. Incontrast, an uncoated steel roller dis-plays as much as 10 µm of wear.

58

Axial piston pumpsMaking the sliding-shoe componentsfrom BALINIT® C-coated steel insteadof bronze improves durability in axialpiston pumps. The system becomesmore resistant to abrasion, mechanicaloverload and deformations that typi-cally affect bronze shoes as a result ofrising pressures and speeds. The coat-ing safeguards the sliding function andincreases wear protection, while thesteel prevents deformations. BALINIT®

C also improves the frictional behav-iour of the axial pistons, thus prevent-ing scuffing damage that results fromstarved lubrication.

Sliding shoe

Increase in clearance Δh [µm]

0

1

2

3

4

5

6

7

8

9

soft plate

soft plate:

hard plate:

Bronze107 HV

GGG 40150 HV

Ck 45440 HV

Ck 45440 HV

Ck 45440 HV

Nitrided steel Nitrided steel Nitrided steel Nitrided steelBALINIT® C-

coated

Nitrided steelBALINIT® D-

coated

hard plate

Ck 45 = AISI 1045GGG 40 = AISI 60-40-18

Hard plate Particles

MediumSoft plate

h

Three-body wear:Particle concentration: 2.5 g/lParticle size: 0-50 µmOriginal clearance h: 32 µmMedium: HFA oil-water emulsionSource: PhD Thesis, St. Lehner,Institute for Fluid Power Drives and Controls,Aachen University (IFAS, RWTH Aachen)

Abrasive behaviour of materials for hydraulic components

Bronze: abrasive wear and deformation

Steel and BALINIT® C (WC/C): wear < 1 µm

Test conditions:Max. pressure: 350 barMax. speed: 2,200 rpmTest duration: 1,000 hours

Abrasion properties ofhydraulic system materialsA pairing of hard and soft materials ofconstruction is often used to minimisewear in axial piston pumps; an exam-ple is nitrided steel against bronze forthe cylinder drum and valve plate. The

optimal combination was determinedby model measurements of the wearbehaviour of various materials, includ-ing PVD-coated components. Solidparticles in the flowing medium causea measurable increase in the clearancebetween the discs under test. Marked

improvements come about if soft slid-ing materials are replaced by a heat-treatable steel (AISI 1045/DIN 1.1191)and the hard plate is given a PVDcoating at the same time. The entiresystem gains in abrasion resistance.

59

Abrasion-resistanthigh-pressure pump pistonsEven where carbide (Vickers hardness1,500) is used in high-pressure pumps,grooves can develop and give rise toleakage. The BALINIT® DLC carboncoating, with its high Knoop hardness(over 2,000), improves the abrasionresistance. Expensive materials suchas carbide or ceramic pistons can thusbe replaced by hardened steel providedsurface pressures are not too high.

Vane pumps withadditive-free oilUncoated vanes in a vane pumptested with additive-free hydraulic oilscuff after just a few minutes. In prac-tice, vanes coated with BALINIT® Cshow a markedly longer service lifethan uncoated vanes and those coatedwith titanium nitride (TiN).

Service life [h]

0.01

0.1

1

10

100

1,000

10,000

uncoated TiN BALINIT® C

Bearing steelAISI 52100(DIN 1.3505)

High-speed steelAISI M2

(DIN 1.3343)

Bearing steelAISI 52100(DIN 1.3505)

Delivery losses [l/min]

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Pressure [bar]

0 10 20 30 40 50 60 70

Gear shaft and gear ringcoated

Gear shaft and gear ringuncoated

Internal gear pumpsComponents (such as the gear shaftand gear ring) of internal gear pumpshandling abrasive media are subjectto such severe wear that unacceptabledelivery losses occur. A hard, extra-thick (approx. 7 µm) TiAlN coatinggreatly reduces wear and thus loss ofcapacity.

BALINIT® C (WC/C)-coated vanes extend pumpservice life, especially when hydraulic media with littlewear-protection power are employed.Hydraulic medium: Additive-free mineral oil

Screw pumps in water serviceBALINIT® C prevents seizure in smallscrew pumps operated in fresh wateror in maritime applications. The screwspindles are made of corrosion-resist-ant steels with a slight tendency to-ward abrasive wear. The WC/C coat-ing, which is inert to attack by water,prevents such wear and improvesservice life.

60

Increase in clearance Δh [µm]

Ck 45 = AISI 104514

12

16

10

8

6

4

2

0Cast ironCast iron

Ck 45 / 650 HVuncoated

Ck 45 / 650 HVWC/C-coated

14

2

Valve housing:

Valve plunger:

Valve housing

Valve plungerParticlesMedium

Δh

Leakage protection forhydraulic valvesPVD carbon coatings such as BALI-NIT® C guard valves against wear andthus allow them to operate preciselyand efficiently without leakage. By vir-tue of their great hardness, these coat-ings protect the precision geometries

Valves in air conditioningsystemsCorrosion and tribo-oxidation threatenthe stems of the valves that control theadmission of outside air in climate-con-trol systems. Applying BALINIT® C andBALINIT® DLC coatings cuts the coeffi-cient of friction and distinctly improvescorrosion protection, so that the valvescan perform their precise control func-tion far longer.

Valves and fittings

Valves and fittings often suffer corrosion coupled with abrasion and erosion bysuspended particles. Abrasion resistance and protection against scuffing andcorrosion are essential requirements in the fabrication of components for high-pressure systems in particular.

Solution concepts that unite all these properties, however, are virtually impossibleto implement with classical material pairings and without the use of coatings.

of housings, seats and plunger edgeseven when contaminated media arepresent. The net effect is to preventleakage. In a trial with proportionaldirectional control valves and a HFAhydraulic fluid, wear was cut to afraction of that measured on an un-coated valve of heat-treatable steel.

Wear behaviour of BALINIT® C (WC/C)-coatedhydraulic valves

Flow rate: 50 l/minValve type: 4/3 proportional control valveMedium: HFA oil-water emulsionSource: PhD Thesis, St. Lehner,Institute for Fluid Power Drives and Controls,Aachen University (IFAS, RWTH Aachen)

Dry operation ofpneumatic valvesBALINIT® C lowers outage costs bymaking it possible for pneumatic valvesto operate without lubricant. Thesevalves perform functions such as pre-cisely controlling the motion of paperwebs in papermaking machines. Theyare usually lubricated with grease, butthey seize up, causing an expensiveproduction stoppage, if the lubricationis lost. Coating with WC/C reducesfriction to the point that the pneumaticvalves can function without any greaseat all.

61

Machine tools

Machine tools have to produce evermore quickly and precisely. The conse-quences include greater stresses andhence more wear, which works againstmachining precision and product qual-ity. BALINIT® coatings contribute tomaintaining precision as well as provid-ing custom-tailored wear protectionfor machine-tool components such asgearboxes, clamping systems, leadscrews, guide rails and disc cams.

Clamping systemsBALINIT® C and BALINIT® DLC keepclamping systems working at a highlevel of precision. Collet chucks sufferundesired and precision-impairingwear, particularly where clamping oper-ations are fast, as in mass production,or clamping forces are high. Coatingwith BALINIT® C and BALINIT® DLCcuts down on tribo-oxidation and fret-ting and thus improves the efficiencyof clamping systems.

Other applications

Machinery and systems where longlife and/or reliability is needed imposeextreme requirements on precisioncomponents, with an increasing riskof failure. Coating with BALINIT® cansignificantly boost the performance,reliability and service life of mechanicalcomponents so that they can meet allsuch specifications.

Many areas of mechanical engineeringbenefit from the performance-enhanc-ing qualities of coatings. Functional re-liability is improved, maintenance inter-vals lengthened and operating costslowered.

Several BALINIT® coatings are ap-proved for food industry and medtechapplications by RCC (Registration andConsulting Company) and FDA (Foodand Drug Administration).

Injection moulding machines

Sliding elements such as ejectors,gates and cores in injection mouldingmachines are effectively protectedagainst wear and scuffing by BALI-NIT® C. The coating is a must whenthe end product is not permitted tocome into contact with lubricants andmouldrelease agents as they contami-nate it. By virtue of its anti-adhesionproperties, BALINIT® also reduces the

Ejectors for plastics mouldsBALINIT® C (WC/C) prevents seizingof ejectors, improving reliability in theinjection moulding.

adhesion of molten stock to screwtips, backflow valves, nozzles andshutoff needles.

Threaded coresLubricants and mould-release agentsmust not be employed in the injectionmoulding of caps for pharmaceuticalpackagings. With BALINIT®-coatedcores, the maintenance interval for a30-cavity mould can be extended fromone week to over eight months. Re-liable demoulding and a 10 % shortercycle time result in a 20 % gain inproductivity.

62

Textile machinery

Components of textile machines experi-ence severe abrasive wear from fibresand additives (e.g., titanium oxide) aswell as contaminants (dust). What ismore, increasingly fast motions in themachines imply high sliding speeds inmetallic frictional contacts.

Weaving machinery

Weft yarn holdersBorided steel has been used for weftyarn holders in gripper looms. How-ever, the surface treatment producesa relatively rough surface resulting inpoor performance. Coating with BALI-NIT® CNI combines high hardness(thus wear resistance) with surfacesmoothness, so that the yarns can bereliably held.

The most highly stressed reeds inweaving looms are coated with TiN,CrN and DLC. DLC coatings are em-ployed in texturing machines. TiN, CrNor DLC coatings are applied to nozzlesin air-jet looms.

Opening cylinder of an open-end spinning framewith BALINIT® CNI coating

Thread guides with BALINIT® DLC coating

Spinning ring with BALINIT® CNI coating

Food processing machinery

Corrosion in food processing machin-ery is often combatted with austeniticstainless steels. However, becausethese are relatively soft materials, wearand scuffing are major problems. Ad-ditional problems arise, for example,when filling plungers run in a closelytoleranced cavity, the product exertsonly a slight lubricating action, andmay contain powdered additives thatincrease wear. In many cases lubri-cants and conventional coatings can-not be considered because all ma-terials that come into contact withfoodstuffs have to be inert to them.BALINIT® coatings meet these require-ments and are FDA approved.

Metering plungersCoating with BALINIT® CNI greatlyimproves the functioning of meteringplungers used to fill marmalade jars.Corrosion results both from the escapeof fruit acid and from condensationwhen the equipment is not operating.Also abrasive wear occurs at gasketsdue to deposits of marmalade. WithBALINIT® CNI coating, filling stationscan run without maintenance for manymonths.

Spinning machinesCrN coatings have proven their worthon opening cylinders of open-endspinning machines as well as on ringsof ring spinning frames.

Carbon coatings in ring spinningframes fail prematurely because of thetoo high temperatures produced by theextremely high speed of the ring travel-lers.

CrN and DLC coatings are applied tosteel and ceramic thread guides.

63

The gold-yellow colour of BALINIT® A(TiN) serves to distinguish coated fromuncoated instruments for ophthalmicsurgery. What is more, the coating isvalued for its aesthetic effects.

Precision mechanics

Coatings are used in precision me-chanics to reduce friction and wearand also for decorative purposes. Forexample, sliding guides for micro-scopes and sliding case elements formobile telephones are coated withWC/C.

Components for mechanical watches(pinions, shafts, bearings, springs,spring housings) are coated with BALI-NIT® C and BALINIT® DLC in order tolengthen service intervals and permitoil-free operation. In addition, carbonand nitride coatings are applied to lendan attractive colour and appearanceto these articles. Elements made ofsteel, nickel-plated brass and siliconare coated.

Medical technology

Cleanliness and lubricant-free opera-tion are essential for the use of medi-cal apparatus, but these conditionsmake surgical instruments susceptibleto wear. The BALINIT® C and BALINIT®

DLC carbon coatings have proved ad-vantageous in many respects. Theyprevent scuffing and ensure properfunctioning even under dry conditions,as in pneumatic components of de-vices for the implantation and extrac-tion of bone-marrow needles or insurgical bone saws. At the same time,they safeguard components and de-vices against corrosion during sterili-sation.

64

65

This strategy meets the requirementsthat govern a successful componentcoating business today:

- Focus on custom coating solutions

- Efficient manufacturing structure andcustomer-oriented project manage-ment

- Integration of specific know-how ontypical tribosystems leading to a flairfor picking the right coating andprocess

In this way Balzers can achieve thegoal it has set itself: to be a partnerand advisor in development, withcompetence in not just coatings butalso components and systems.

Partners in your success

Balzers expertise and services: competence forcomponent and system

Analysis and quality assuranceAlong with standardised quality assur-ance methods, Balzers can providedetailed services such as tribologicalproblem work-ups and metallographicexaminations and assessments. Ad-vanced measurement techniques forcoatings in the order of 1 µm thick arealso offered.

Partnership for developmentBalzers works with independent labora-tories and research institutes for es-pecially difficult tasks calling for highlyspecialised test methods. What ismore, in an effort to continuously im-prove its coatings, Balzers cooperatesclosely with respected practitioners ofspecial measurement techniques inorder to develop metrological systemsfor quality assurance and testing ofcoated components.

BALINIT®

Applications supportProduct development

LogisticsPretreatment

Coating of precision components Quality assurance

Research and development

The solid know-how that Balzers hasacquired in coating processes is basedon our world-wide business experienceand our close contacts with industry aswell as many industrial engineering anddesign institutions.

Development of coatings,applications and equipmentIn the Balzers R&D centre at the Liech-tenstein headquarters, laboratory staffcarry out applications studies for cus-tomers and do basic research on PVDand PACVD processes that hold prom-ise for mass production. New coatingsare tested at loads far greater thanthose met with in component servicein order to push the envelope of coat-ing performance and systematicallyeliminate defects. The BALINIT® pro-duct family and the range of coatingsolutions are thus more and more opti-mised in terms of desired productspecifications. Plant and manufacturingtechniques are also in steady develop-ment, as are technical quality systemsfor production. The development ofnew coatings is carried on at manu-facturing plants in order to ensure arapid transfer to mass production.

Since the BALINIT® rollout in 1980, Balzers PVD technology has been used tocoat many hundreds of millions of components for renowned automotive manu-facturers and their suppliers as well as for the mechanical engineering industry.The processes have found use in both low and high volume production. Balzershas gained a position of world leadership in the field, pursuing a strategy thatbegins with research and development and culminates in a high standard ofquality implemented in a global network of coating and application centres.

66

Abrading ball

Coating

Substrate

BALINIT® coatingwith abradedspherical indentation(top view)

D

A

B

v rv

Spherical abrasion test:The coating thickness D is calculated from themeasurements A and B and the ball radius r.

Test methods for quality assurance

Reliable methods of measurement(standard test conditions, referencesubstrates, ambient conditions) areessential if the properties of PVD andPACVD coatings are to be determinedand assessed. Judging the quality ofa coated component that has beenmass produced requires making abinding statement regarding the speci-fications submitted by the customer.

To this end, Balzers employs methodsthat comply with VDI (German Engineer-ing Society) Guidelines 3824 (Sheet 4)and 3198.

Method Attribute Constraints Precision Destructive for Destructive forCoating Substrate

Spherical abrasion Coating thickness Geometry 0.3 - 0.5 µm yes yesRoughness

X-ray fluorescence (XRF) Coating thickness Geometry 0.3 - 0.5 µm no noComposition (element)

FTIR Infrared spectroscopy Coating thickness DLC-coating > 0.5 µm 0.1 µm no no

Rockwell hardness (HRC) Substrate hardness Substrate hardness ± 1 HRC yes yesGeometry

Rockwell test Coating adhesion Substrate hardness ± 0.5 HF-Class yes yesGeometry

Stylus profilometer Roughness Geometry * no no

Test methods for quality assurance

* Function of test conditions

Determination of coatingthickness by calo grindingIn this method, a spherical cup isground with a steel ball. The sphericalcalotte is measured and the coatingthickness is calculated.

67

Rockwell diamond indenter

Coating

SubstrateFA AFA A

BALINIT® coating with HRC indentation (top view)

Use of Rockwell indentation to measure adhesion:Coating adhesion is determined by comparing the damage in region Aof the Rockwell indentation to a series of standard images.

Coating thickness measurementby x-ray fluorescence (XRF)Coating thickness is measured byirradiating the surface under test withbroad-band x-rays. The intensities ofthose x-ray fluorescence lines, whichare characteristic of the coating, areused as a measure of coating thick-ness. Calibrated spectra for the coat-ing and substrate materials understudy are stored in the instrument. Thesubstrate and coating material of aspecimen must be known; the corre-sponding values are input as refer-

TiN coating

WC grains

Co binder

X-ray excitation Ti intensity W-intensity

Coating thickness measurementby infrared spectroscopyA special infrared (IR) procedure hasbeen devised for BALINIT® DLC. Infra-red light directed at the IR-transparentDLC coating is partly transmitted andpartly reflected; the coating thicknessis determined from the interferenceeffect.

ences before the measurement isperformed. The instrument then com-putes the coating thickness from theobserved intensities for the coatingand substrate material.

Adhesion testby Rockwell methodA conventional Rockwell hardness test(DIN 50103) is performed, and thenthe network of cracks and coatingflakings at the periphery of the inden-tation is examined under the opticalmicroscope. The adhesion is rated insix adhesion classes as set forth inVDI Guideline 3198.

Stylus profilometerMany critical precision parts today aremanufactured to micrometer toler-ances and must display the specifiedgeometry after coating as well. Char-acteristics such as diameter, planarityand concentricity therefore have to betested and documented after coating.

Visual inspection withthe optical microscopeSurface defects can have a detrimen-tal effect on the tribological properties.Visual inspection to assess surfacequality is performed with the opticalmicroscope or illuminated magnifier;in large-scale production, totally auto-mated camera systems are employed.Standardised defect catalogues usedas references describe the typicalfeatures of ground and coated parts.

389.05

µm

237.14 µm

68

Method Attribute Prerequisites Precision Destructive for Destructive forCoating Substrate

Cross section grinding/fracture Coating thickness none 0.1 - 0.5 µm yes yesSEM, microscope Coating structure

EDX / SEM Coating composition Detectable element: * no noEnergy-dispersive X-ray boron or higherspectroscopy

Nano-/microhardness Coating hardness Geometry, roughness, ± 20 % yes nocoating thickness > 1µm

Scratch test Coating adhesion Substrate hardness * yes yesGeometry

Calowear test Coefficient of wear Planar surface * yes noRoughness

Tribometer Coefficient of friction Geometry * yes yesRotation, Oscillation Lifetime test

Surface scanner Surface topography Geometry * no no

Coating structure Depth profile analysis Geometry ± 2 % yes yes

XRD structure analysis Crystal structure Geometry * yes yes

Methods used for specification and analysis

* Function of test conditions

While the methods used in the factorysupport economical, standardisedquality assurance in mass production,more profound analytical methods areavailable for development purposes.Some of these, however, are quiteexpensive and therefore do not oftenfind use in quality assurance.

Balzers employs the following instru-ments:

Scanning electron microscopes(SEM) with EDXThese microscopes yield high-resolu-tion images of the surface. They useEDX (energy-dispersive x-ray spectros-copy) systems to analyse the coatingcomposition and identify the elementspresent. The SEM is also used toanalyse the wear mechanism at workin a tribosystem. The photomicrographat right shows fatigue wear on a criti-cally stressed valve-train componentcoated with DLC.

1µm

Coating fatigue in a severely loaded DLC-coatedvalve-train component.Scanning electron micrograph, 8,000x

Scratch diamond

Coating

Substrate material

Scratch in BALINIT®-coatedsurface, top view

v

F

S

Scratch testA Rockwell C diamond is drawn overthe coated surface under an increas-ing load. The coating adhesion is as-sessed by examination under theoptical microscope to determine thenature and extent of coating damageversus load.

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Abrasive wear test (Calowear)The coating is abraded with a steelball and an abrasive paste, and itscoefficient of wear is determined fromthe results. In contrast to the case ofthickness measurement, the grindingproceeds only partway into the coat-

Polishing ball

Grinding slurry

Coating

Substrate material

B

v rv

TribometerThe tribometer is used to measure thecoefficient of friction µ or the wear be-haviour of surfaces. The specimens fortest can be set in rotation or oscillationduring the measurement, and lubricantmay be added depending on the pur-pose of the measurement.

Rigidly clamped steel ball, uncoated

Specimen, coated

Wear trace in WC/C coating

Normal force FN

v

Load Uncoated, clamped oscillating steel ball

Cylinder, coated

Frictional trace on cylinder

ing, not right through. The test involvesstandardised parameters such asconfiguration, sphere size, speed anddiamond slurry. The wear volume isthen compared with a reference ma-terial, most commonly a standardDLC coating.

Tribometer for sliding wear testTribometer with oscillating motion

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Surface scannerThis laser scanner operates withouttouching the specimen and producesa three-dimensional scan record usedto verify the quality and roughness ofcoated component surfaces.

Structure analysis byx-ray diffractionXRD analysis uses x-ray diffraction toidentify the crystalline phases of hardcoatings. The instrument holds allpossible phases of such coatings inmemory and compares them with thespecimen.

Nanohardness andmicrohardnessBecause of the relatively large testloads used in the classical Vickers andKnoop methods of hardness measure-ment, all that is determined is the plas-tic deformation of the indentations. Thediamond used to measure thin filmsmust not penetrate to more than 10 %of the coating thickness. Very light testloads (10-50 mN) are needed as aconsequence. Given the shallownessof penetration, the elastic deformationcontribution must also be taken intoaccount, and so dynamic methodsare employed. Loading and unloadingcurves are recorded for use in deter-mining the coating hardness; the re-sults are then converted to conven-tional Knoop and Vickers hardnesses.Simple Knoop measurements areperformed on the less-elastic nitridecoatings, but dynamic penetrationmeasurements are essential for highlyelastic DLC coatings.

Load [mN]

Loading curve

Unloading curve

0

10

20

30

40

50

0 0.5

Depth of penetration [µm]

Under load: elastic and plastic deformation

After unloading:plastic deformation only

F

A

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Applications support

Balzers places worldwide applicationssupport at your fingertips:

Tribology and materialsconsultingYears of research and experience withPVD coating processes point to tribo-logical solution concepts that can mini-mise wear and friction in a wide rangeof applications.

Early collaboration in productdevelopmentOne way of fully realising the technicaland economic potential of coatings ata reasonable cost in time and moneyis to involve a team of specialists - sur-face engineers, manufacturing engi-neers, tribologists and designers - atan early point in the development ofcomponents that will be coated. Bal-zers can serve as a design partner,casting an expert eye on the system,bringing its long experience to bear onhigh volume production, and offeringadvice on component design for coat-ing.

Convenient applicationssupport centresA global network of applications sup-port centres enables customers to getquick service on-site and gives themearly access to Balzers’ technologicalinnovations. Balzers has representa-tives in all major industrial regions ofEurope, the Americas and Asia. Everysite provides the same consistentlyhigh standard of quality in all areas ofcompetence, procedures and technicalcapabilities. The development of novel,one-off coating solutions is the mostintensive form of applications supportfor Balzers customers.

Custom services

Balzers has made it a goal to put totaltechnological competence behind theservices it offers throughout the value-creation chain of production tech-niques and processes. Coating equip-ment and processes are devised andimproved at Balzers and their use isoriented to minimising costs. Contrib-uting factors include:

- Flexible employment and optimalutilisation of plant capacity withmodular coating systems- Short turnaround times- Minimal use of consumables- Integration of PVD coating equip-ment into automated production- Upgrading of automated productioncycles in collaboration with cus-tomers with the aim of improvingquality and productivity

Depending on customer requirementsregarding technology, flexibility andreadiness to invest, Balzers along withits coating service offers access to anumber of PVD business models.

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Sales of equipment andproduction linesWhen a customer wants to integratecoating into the production processand take responsibility for this function,Balzers sells single systems or turn-keyproduction lines. Here the customeracquires a well-defined coating pro-cess with an assurance of equipmentfunctioning and coating quality. What ismore, Balzers offers support, whetherin the form of staff training and qualifi-cation, service agreements, or retrofitsto equipment and processes.

Job coatingFrom incoming inspection of compo-nents to coating and reshipping, Bal-zers offers the entire production pro-cess on a job basis. This means bigcost and quality advantages for thecustomer, as well as savings on know-how acquisition, staff training andpractical operations. The global net-work of Balzers coating centres iscontinually expanding. Because pro-duction cycles in the centres are close-ly tied to delivery deadlines, Balzersalso offers comprehensive logisticsthat can be integrated seamlessly intocustomer process chains and adaptedto the needs of the industry.

In-house coatingFor high volume production, Balzerscan locate where the customerchooses, thus providing short routesand long-term advantages. This meansthat Balzers performs componentcoating on site in a way that can beintegrated into the customer’s pro-duction cycles. Furthermore, Balzerstakes full responsibility for this service.

Customer-oriented products and services

World-wide coating serviceAll the centres employ the same equipment and the same know-how. The setup guarantees a high,reproducible standard of quality (ISO 9001, ISO/TS 16949).

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Production process and process engineering

Incoming inspectionThe components for coating arechecked to verify number of pieces,material and surface condition. Thesteps in carrying out the job are thendetermined on the basis of the cus-tomer’s specifications.

CleaningThis step involves several treatmentsin an ultrasonic cleaning line usingaqueous alkaline solvents with no pol-luting additives.

Clean surfaces are essential for coatingadhesion, so Balzers lays great stresson surface preparation for PVD coat-ing. The last steps in treatment andconservation preceding application ofthe coating are defined in consultationwith the customer and adapted asnecessary to the requirements of PVDcoating.

The cleaning of components for highvolume production is simplified byshipment in special baskets and byautomatic loading of the cleaning line.

The path that leads from incoming inspection of precision components for coat-ing to shipment back to the customer is a specialised production process. Itsmany steps can be tailored to the coating that is required and its special qualities.

PretreatmentIf further treatments are needed, Bal-zers employs appropriate technologies.Heating in vacuum furnaces, for ex-ample, serves to remove material resi-dues from tight holes, while micro-blasting takes off porous surface layers.

Loading a batchBefore coating, the components areloaded on an interchangeable turntableand placed in the coating system. Thisoperation is mostly automated in thecase of high volume production. Thecustomized configuration and fixturingof the components ensures repro-ducible precision.

CoatingThe coating step consists of a seriesof automatically controlled and docu-mented processes. The special Balzerscoating technology involves the follow-ing operations:- Pump-down of the coating system toa base pressure of around 10-6 mbar- Equipment and safety check- Heating of components to the propertemperature- Ion etching to get atomically cleancomponent surfaces- Coating by a PVD/PACVD process- Cooling down- Equipment check and process check

Balzers’ coating know-how becomesapparent at the transition from theetching to the coating phase. Optimaladhesion of the functional coating isensured by precisely controlled appli-cation of suitable intermediate filmsby monolayer or multilayer processes.Control of the plasma parameters de-termines the coating properties, whilethe tested hardware provides theneeded process reliability.

Final inspectionThe last stage of inspection involveschecking properties such as hardness,coating thickness and adhesion andperforming a visual examination. Inhigh volume production, an agreednumber of test pieces are removedand agreed test parameters are usedfor statistical process control. Inspec-tion of mass-produced components isautomated whenever economicallyfeasible.

Quality management

Certified quality managementAll Balzers coating centres throughout the world are certified under ISO 9001.Centres specialising in coating parts for the automotive industry are also certified to ISO/TS 16949.

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Post-processing and conservationIn many cases Balzers carries out post-processing, for example when thecoated components must be demag-netised or conserved.

Mechanical finishing of coatings isbecoming more and more important.Even though coating increases thesurface roughness only slightly, the re-moval of tiny metal droplets or growtherrors can further increase the tribo-logical performance of coated parts.

Packaging and shippingCoated components are usually re-shipped in the same containers inwhich they were received. Savings canbe realised if the components arrivealready packed in suitable cleaningbaskets.

10 µm

Surface of a PVD arc coating with droplets,without finishing

10 µm

Surface of a PVD arc coating after finishing

Quality management does not startwhen the goods are received. Anunderstanding of what quality meansand an active partnership with the cus-tomer impel Balzers to provide supportthroughout the course of a project.This effort includes customised solutionproposals that range from the choiceof coating to (for example) how a pro-duct can be optimally packaged andconserved for shipment in order tocreate the best conditions for the coat-ing process.

“Zero defects”The Balzers quality objective is “zero de-fects.” This level of quality is achievedwith certified, process-based qualitymanagement. All Balzers coatingcentres world-wide have ISO 9001certification. Furthermore, Balzers wasthe first coating company to receive aQS-9000 certificate for coating centresthat have specialised in the coating ofprecision components. All production

facilities supplying the automotiveindustry are additionally certified underISO/TS 16949. Currently the coatingcentres in Lagny-sur-Marne/FR, MiltonKeynes/UK and Luxembourg/LU areaccredited to NADCAP quality stand-ard for the aerospace industry.

To Balzers, quality means meeting thecustomer’s requirements; this is thekey to customer satisfaction. Controlof the coating process, modern testinglaboratory management, availability oftest instruments, and the use of statis-tical process control (SPC) are there-fore the day-to-day components ofBalzers technical quality control, whichis based on many years’ experiencein high volume production.

Quality management is not somethingstatic but a process that is a way oflife and an area of continuous improve-ment for Balzers.

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Glossary

AbrasionAbrasive wearRemoval of material from surfacesby hard or sharp-edged surfaces orparticles and by contaminants in themedium between surfaces.

AdhesionAdhesive wearFormation of adhered material at theinterface between two sliding solids,which when broken can result in trans-fer of material. The extent of this trans-fer is greater the more intimate thecontact and the smaller the amount offoreign substances present betweenthe surfaces.

Anti-wear coatingsSee Hard coatings.

Arc evaporationA vacuum coating process in whichthe coating material is evaporated byan electric arc.

BALINIT®

Trademark for hard coatings made andmarketed by Balzers.

BatchProducts placed in coating equipmentfor processing in a single operation.

BrinellingPermanent deformation of a materialdue to vibrating and oscillating loads(e.g., in ball bearings).

CarouselA rotating fixture that holds compo-nents on special mounts.

Cavitation erosionDamage to a solid surface in contactwith a flowing liquid due to pressurewaves generated by collapsing(imploding) vapour bubbles.

CavitiesTight or narrow depressions (holes,grooves) in a surface, making thematerial difficult to coat by PVD orPACVD.

Chemical plating(chemical nickel)Electro less deposition of metal coat-ings from salt solutions with a reducingagent, coatings contain phosphorousor boron.

Coefficient of frictionThe coefficient of friction µ is the ratioof frictional force to normal force be-tween two bodies in relative motion(µ = FR/FN). The coefficient of dry fric-tion is the value measured in a systemwith no lubrication.

Cold weldingSolid bonding between two sliding sur-faces due to metal-to-metal contactunder high pressure or with insufficientseparation by lubrication (see alsoAdhesion).

CorrosionDamage to a metal, beginning at thesurface, due to chemical or electro-chemical reactions with partners in theambient medium.

CrN coating(chromium nitride)A hard coating applied by PVD.

CVD(chemical vapour deposition)A thermally activated chemical processfor depositing a coating from the gasphase under vacuum.

DegassingThermal treatment in a vacuum systemto allow through and blind holes andsurfaces to outgas (see also outgas-sing).

DLC coating(diamond-like carbon)A hard coating applied by PACVD.

Eggshell effectA failure of hard coatings under heavyload due to inadequate support by thesubstrate. The initial damage has acracked eggshell-like appearance.

Electroplating(electroplated chrome, nickel)Electrochemical deposition of metalcoatings on electrically conductivesurfaces from salt solutions.

ErosionDamage to a solid surface in contactwith a flowing liquid, caused by me-chanical action of hard particles in theliquid.

FrettingA form of wear occurring when twofrictional partners move tangentially toeach other in small oscillating motions.See also Adhesion.

Fretting corrosionSee Tribo-oxidation.

FrictionThe mechanical resistance observedwhen bodies in contact move relativeto one another. Friction manifests itselfas a force or as energy.

Friction(type or mode)Friction is described as sliding, rollingor combined sliding and rolling, ac-cording to the way in which the fric-tional partners move.

Frictional stateFriction is described as dry, boundary,mixed, fluid or gas friction, accordingto the state of the contact betweenthe frictional partners.

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GallingA more severe form of adhesive wearassociated with gross surface damage,chipping and transfer or displacementof large material fragments.

Hard coatingsCoatings of very hard materials (com-monly metal carbides or nitrides,sometimes silicides, or diamond-likecarbon) applied to surfaces in order toimpart greater resistance to wear andlower the coefficient of friction.

Heat-treatmentThe temperature of the final heat treat-ment (tempering, precipitation harden-ing, annealing) must not be exceededduring coating because structuralchanges in the part may occur other-wise.

Hertzian pressureEffective pressure at the surface ofcontact between two arbitrarily curvedsolids.

Ion etchingRemoval of material from a surface byion bombardment.

Ion platingA vacuum coating process in whichthe coating material is evaporated byan electron beam.

IonisationDegree of ionisationProduction of electrically charged par-ticles (ions and electrons) in a gas byvarious kinds of excitation (e.g., tem-perature, electric arc, high-frequencywaves). The strength or extent ofionisation is measured by the degreeof ionisation.

MicroblastingBombardment of a surface with veryfine abrasive (e.g., corundum with agrain size of 10-20 µm) in order toremove contaminants or impart struc-ture or texture.

Micropitting(grey staining)A form of surface degradation found ingears, thought to be related to surfacefatigue.

Monolayer coatingA hard coating applied in the form ofa single homogeneous layer.

Multilayer coatingA “stack” of hard coating layers varyingin their properties.

Nitriding(including plasma nitriding)A thermochemical treatment for up-grading (hardening, passivating) sur-face regions of ferrous materials byallowing nitrogen from solutions orgases to diffuse into the material.Called “plasma nitriding” if performedwith the aid of a plasma.

OutgassingThermal evaporation of organic resi-dues and trapped gases.

PACVD(plasma-assisted chemical vapourdeposition)A vacuum process for depositing acoating from the gas phase by achemical reaction aided by a plasma.

Passivating layerA layer that renders a surface lesssusceptible to chemical attack.

PhosphatingA chemical treatment of ferrous ma-terials with a dilute phosphoric acid,by which the surface is converted toan integral, mildly protective layer ofinsoluble phosphate.

PittingSee Surface fatigue.

PlasmaA gas-like state often called the “fourthstate of matter”, comprising electricallycharged species (ions, electrons, ex-cited and neutral particles).

Plasma polymerA coating made up of a polymer de-posited from the gas phase by plasmaaction.

Plasma-assisted coatingprocessesSee Vacuum coating processes.

PVD(physical vapour deposition)A vacuum coating process in whichthe coating material is physically de-posited from the vapour phase. Pro-cesses include ion plating, thermal/arcevaporation and sputtering.

Residual stressElastic stresses in a coating, existingwhen no external forces and momentsare applied and mechanical equilibriumholds. Residual stresses affect suchproperties as coating adhesion.

ScuffingLocalised surface damage in betweensliding surfaces due to adhesive wear,associated with cold welding and thebreakdown of lubrication at high loadsand/or sliding speeds.

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SeizingThe most severe form of adhesivewear: cold welding due to high frictionbetween the mating parts.

SputteringEnhanced sputteringA vacuum coating process in whichthe coating material is atomised by ionbombardment.

Stick-slipThe discontinuous or jerky motionof two frictional partners. Static andsliding friction alternate.

SubstrateThe component or the parent materialto be coated.

Surface engineeringDesign and treatment of surfaces toachieve optimum wear properties.

Surface fatigueDamage to a surface due to dynamicloading. Surface fatigue results in theformation of cracks and the removal ofmaterial in particle form (pitting, micro-pitting).

TiN coating(titanium nitride)A hard coating applied by PVD.

TribologyThe science and technology of inter-acting surfaces in motion relative toone another. Tribology deals withprocesses such as wear, friction andlubrication.

Tribo-oxidationThe oxidation of surfaces caused byfrictional contacts in the tribosystem(e.g., fretting corrosion).

TribosystemTribological systemThe tribosystem consists of the struc-ture and the input and output condi-tions. The structure includes the ma-terial elements (frictional partners,lubricant, contaminants), their prop-erties and interactions. As the inputconditions (forces, motion, tempera-ture) act upon the structure, they aretransformed into useful quantities(work performed) and loss quantities(friction, wear).

Ultrasonic cleaningThe cleaning of solid surfaces inliquids (aqueous detergent solutionsor organic solvents) with the aid ofultrasound.

Vacuum coating processesProcesses for the application ofhomogeneous coatings to materialsurfaces using chemical and physicalprocesses carried out under highvacuum. Vacuum coating processesinclude PVD, CVD and PACVD.

WC/C coating(tungsten carbide/carbon)A hard coating applied by PVD.

WearProgressive loss of material fromthe surface of a solid body due totribological action.

Wear mechanismsThe physical and chemical processesthat cause the damage or wear.Wear mechanisms include adhesion,abrasion, surface fatigue and tribo-oxidation.

Wear resistanceCoefficient of wearThe ability of a solid body to preventprogressive loss of material from itssurface due to mechanical loading.The coefficient of wear is determinedby system-specific measurements.

Wear-protection coatingsSee Hard coatings.

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HQ040EN(1011)