Dc Diode Papvd to Durability

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CVD. See

chemical vapour deposition.

CVI.

See

chemical vapour infiltration.

cyaniding

Carbonitriding using a cyanide-based salt bath

-

IFHT DEFINITION.

See

carbonitriding.

D

DC diode PAPVD.

A

plasma assisted

PVD

process

in

which

the

object

to be

coated

is

made

one of the

cathodes

of a DC

glow discharge,

the

chamber walls acting

as the

earthed

anode.

DC triode PAPVD.

See

triode on plating

and

triode sputter deposition.

deboriding treatment.

A

thermochemical method

for the

removal

of

boron from

a

prior

borided steel surface. The process is conducted in an atmosphere con taining H

2

and CH

4

at

temperatures of 900-1020

0

C. Boron is usually rem oved in the form OfB

2

O

3

.

decarburisation.

Loss of carbon from a steel surface to a level well below that of the core,

often as the result of prolonged high temperature exposure in an oxidising atmosphere.

decarburisation depth.

Distance from the surface of a decarburised object to a specified

limit which depends on the character of the decarburisation. The

limit can be set in terms of a specified structure, hardness, or carbon

content - IFHT DEFINITION.

decorative chrom ium plating. See

chromium plating

decorative coating.

Any

coating primarily produced

to

enhance

the

appearance

of an ob-

ject. For example see

gilding.

degreasing.

Any

methods that achieve

the

removal

of

organic compounds, such

as

grease

or oil, from the surface of an object, e.g., see vapour degreasing.


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denitriding.

Th erm oc he m ica l t rea tment for the remov a l of excess n i t rogen f rom

the surface of a ni t r ided objec t ' - IFH T D EF IN IT IO N .

deposit.

A synonym for coating (noun), but also referring to any adherent surface solid

formed, for exam ple, as a result of wear or corrosion.

deposition.

The act of laying dow n a metallic or non-metallic layer onto a substrate. There

are numerous deposition techniques; these include electroplating, plasma spraying, PVD

and CV D.

deposition rate.

Used in connection with coating technologies, like plasma spraying, p lasma

assisted PVD or CVD. Expressed in mm/min, jiim/min or |nm/hr.

derusting.

See

descaling.

descaling. Any process used for the purpose of removing the scale from heavily oxidised

metal. This can be achieved by mechanical (abrasive blasting, tumbling, brushing) or chem ical

me ans (alkaline descaling, acid descaling (pickling) or salt bath descaling).

designer surface. An engineered surface with optimal constitution, treatment depth and

properties, designed with intent for specific application(s).

detonation gun D-gun) spraying. A combustion spraying techn ique whereby particles of

coating material, typically WC-Co, are passed through a combustion tube, fuelled by a

mixture of oxygen and acetylene gases. Ignition is provided by a spark plug 4.3 or 8.6 times

per second. The com position of the combusting gas can be adjusted to be oxidising, neutral

or reducing. The flame temperature is -3000 K and coating powder particles can attain

velocities ~ 800 m/s. It is an extremely noisy torch (150 dB) requiring intensive screening

and operator protection. Union Carbide C orporation is the principal owner and operator of

this technology. Also see high velocity air fuel (HVA F) spraying and high velocity oxygen

fuel (HVOF) spraying.

D-gun spraying.

See

detonation gun (D-gun) spraying.

diamond coatings. Diamond coatings can be deposited by many methods. Presently, the

most favoured technique is microw ave plasma CV D. Diamond co atings are crystalline and

are usually characterised by a combination of methods which include, Ram an spectroscopy,

X-ray diffraction and surface morphology . Also see

hot ilament CVD

and

microwave plasma

CVD.

diamond-like coatings DL C). Very hard (-3000-4000 kg/mm

2

) carbon coatings with

little or no crystallinity (amorphous). Initially such coatings proved unsatisfactory for tribological

protection because of poor substrate adhesion and unfavourable residual stress. Some recent progress


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has been m ad e wh ereby appropriate sub-layers of transition metal carbides and nitrides are deposited

prior to deposition of a DLC. This is particularly important when depositing DLC onto metallic

substrates. D L C s can be deposited by sputter deposition or plasma assisted C V D .

diffuse cycle. The second part of the boost-diffuse method. See vacuum carburising and plasma

carburising.

diffusion coating.

Any process that produces a surface enriched in another element through solid

state diffusion and (usually) resulting in the formation of intermetallic or interstitial compounds.

Processes include

aluminising, bonding, chromising, sherardising, siliconising

and

vanadising.

By

conven tion, it specifically

excludes

carburising, carbonitriding, nitriding, and nitrocarburising.

diffusion metallising.

'Therm oche mical treatment involving the enrichmen t of the surface layer of

an object with one or mo re metallic element' - IFH T D EFIN ITION .

Diffusion coating with metals alone. Processes include aluminising, chromising, sherardising and

vanadising but should exclud e the technology of siliconising, since silicon is a non-m etal. Ho wever,

som e authors still regard siliconising as a diffusion metallising proc ess.

diffusion period .

That time of a thermoch emical treatment w hen the active specie(s) diffuse into the

substrate. To provide distinction from, for exam ple, the heating and cooling cycles.

diffusion profile.

T he concentration of elements in the diffusion zone following a therm ochem ical

diffusion treatmen t. A lso see

concentration profile.

diffusion w ea r. A term first invok ed by Trent and Lo ladze in the 1950s, to account for the rake face

cratering of cem ented ca rbide cutting tools, observed after cutting plain carbon and lo w alloy steels at

relatively high speed (>1 00m /min). Other workers have termed this effect 'dissolution/diffusion w ear '

or 'solution w ear'. For cemented carbide tools, comprising W C -C o or W C-(W

5

TIJaJ^Jb)C-Co (termed

'straight gra de ' and 'steel cutting gra de' carbides respectively), the W C g rains bec om e sm oothly

wo rn. In the case of 'steel cutting grade ' cemen ted carbides, microsections, m ade no rmal to the rake

face surface, reveal that the W C pha se is preferentially wo rn; the (W,Ti,Ta,Nb)C phase being less

severely wo rn, stands prou d of the adjacent W C grains. Th e preferential w ear of the W C p hase is

attributed to its higher solid solubility limit in y-Fe (present in the hot steel chip shear zone during

cutting) co m pa red to that of the (W,Ti,TaJSfb)C ph ase.

Othe r tool materials, like high speed steel and ceramics can be w orn by this type of mec hanism , e.g.,

whe n sialon tools are used to cut low alloy and plain carbon steels at cutting speed s abov e 20 0 m /min ;

similarly Al

2

O

3

-ZrO

2

ceramics exhibit a similar effect when used to cut titanium alloys at cutting

speeds above 50 m /min. TiN and TiC coatings, deposited by PV D o r CV D, are also worn in this w ay

wh en used to cut steels above 100 m/m in although other mec hanism s like

discrete plastic deforma-

tion

make a s ignif icant contr ibut ion. For fur ther de ta i ls see

Metal Cutting

by E.M . Trent ,

But te rwor ths , 3 rd Edi t ion , 1991.


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diffusion zone.

'That part of the case where elements introduced by

thermochem ical treatment are held in solid solution or partially

precipitated in the matrix. The concentration of these elements

decreases continuously towards the core ' - IFHT DE FINITION

A term used especially in connection with nitrided steels. In this example it refers to the

zone of coherent nitride precipitation, residing beneath the compound layer, which

constitutes 95 to 99 of the depth of the nitrided 'c as e', see

nitriding.

The nitrogen content

of the diffusion zone range s from nearly 20at- adjacent the com pound layer to below

lat- adjacent the core structure.

dimensionless wear coefficient. See Archard s w ear equation.

diode sputter dep osition. A sputter deposition process in which the substrate serves as a

positive or positive-ground electrode, relative to the cathodic sputter sources; a less com-

monly used configuration. Also

see bias sputter deposition.

dip coating. Any technique whereby a coating is formed by immersing a solid in a liquid

which subsequently bonds to the solid surface. The most common types include

hot dip

aluminising or hot dip galvanising. The term also refers to coating by immersion in ce-

ramic slip or even polymeric solutions (organic paints).

dip coating with ceramics.See ceramic dip coating.

dip coating w ith plastics.

See

plastic dip coating.

dip painting. See plastic dip coating.

direct current plasma CVD.

Plasma assisted CVD in which the plasma is generated by a

direct current (DC ) power supply.Often more problematic than

r dio

frequency (RF) plasma

CVD.

discrete plastic deformation. A common wear mechanism of PVD and CVD ceramic

coatings (TiC, TiN and Al

2

O

3

) when used to cut steel at speeds above 100 m/min. The

mechanism increases with increasing cutting speed (temperature) and is the principal rake

face w ear mechanism OfAl

2

O

3

coated cem ented carbide tools. The mechanism culminates

in the rem oval of wear fragments through ductle fracture (see diagram , seque nce 1 to 4 and

micrograp h). It should be appreciated that coating temperatures often exceed 1100

0

C when

cutting steel; at these temperatures TiC, TiN and Al

2

O

3

behave p lastically. Also see P. A.

Dearnley, R. F. Fow le, N. M. Co rbett and D. Doy le,

Surface Engineering,

1993, 9, 312-

318.


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discrete plastic deforma tion A CV D TiC coating undergoing

r ke

face wear throu gh discrete p lastic

deformation caused by the high temperatures and shear stresses developed while cutting an AISI

1046 normalised steel at 300 m/min 0.25 mm/rev. CFD = chip flow direction. Field em ission SEM.

CFD

i

4

DISCRETE

PLASTIC

DEFORMATION

CER MIC

CO TING

SPERITIES

CHIP FLOW

DIRECTION

P. A. Deamley 1994

WE R P RTICLE


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displacement CVD reaction. Also known as an exchange reaction. A CVD reaction be-

tween a volatile compound (MX

2

) and a substrate (Z):

This reaction is usually self-limiting i.e., it stops after a solid layer, M

(s)

, has been deposited

which serves as a diffusion barrier to further reaction. For exam ple see

gaseous chromising.

DLC. See diamond-like coatings

double-stage nitriding.

See comm ents on Floe Process under

gaseous nitriding.

drip-feed carburising. See

gaseous carburising.

dry blast cleaning. A general term encom passing shot blasting, grit blasting and sand blast-

ing.

dry galvanising.

H ot dip galvanising in w hich the object, after degreasing and pickling, is

immersed in an aqueous flux solution, then dried and immersed in a molten zinc bath. A

rather inappropriate term.

drying. The process of removing residues from washing operations by means of hot or cold

air, freon, infra-red radiation or centrifugal action.

dull finish. A surface of poor specular reflectivity. M att surface is also an acceptable term .

duplex nickel plating. A nickel electroplating process involving the deposition of two lay-

ers of nickel: (i) semibright and; (ii) bright. These serve as an undercoat for subsequent

chrome plating.

duplex surface engineering. A com bination of two sequential (and mu tually com pat-

ible, from the treatment temperature perspective) surface engineering methods to

achieve a synergistic surface property design. At the time of writing, much interest is

being shown in extending the application range of thin (~5jLim) ceramic coatings (like

TiN and TiC) to low yield strength (~500-100 0M .Pa) substrates by prior strengthen ing

via a thermo chem ical diffusion treatment. Feasible duplex treatments include: (i) CV D

after carburising, followed by quenching (to permit the y-Fe — > a' -F e transfom ation);

(ii) PVD after nitriding. Note: carburising temperatures ~ CVD temperatures; PVD

temperatures ~ nitriding temperatures. Initial trials have been carried out in two dis-

tinct operations. M ore recent efforts have focused on enabling each process to be car-

ried out sequentially in the same vessel.

durability. The ability of a surface engineered material to endure in-service wear, corro-

sion or fatigue.

Dc Diode Papvd to Durability

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