Holmberg2007-FrictionWearCoatedSurfaces

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Friction and wear of coated surfaces — scales, modelling and

simulation of tribomechanisms

Kenneth Holmberg a ,⁎, Helena Ronkainen a , Anssi Laukkanen a , Kim Wallin b

a VTT Technical Research Centre of Finland, Finland b Academy of Finland, Finland

Available online 21 August 2007

Abstract

Coating a surface with a thin layer changes the surface material properties and is an important tool for controlling friction and wear. The

tribological mechanisms, scale effects and parameters influencing the friction and wear of coated surfaces are discussed. The basic friction and

wear mechanisms can be reduced to: friction by adhesion, ploughing and hysteresis and wear by adhesion, abrasion and fatigue combined with

material fracture. The tribochemical and surface physical effects and surface fatigue taking place before material fracture are treated here as pure

surface material modification mechanisms. Scale effects in a tribological contact are illustrated by explaining typical surface roughness related

tribological mechanisms for diamond and DLC coated surfaces. For diamond coatings asperity interlocking effects are important for rough

surfaces, graphitisation is a dominating mechanism for smooth engineering surfaces and hydrogenising of dangling bonds may be crucial for

physically smooth surfaces. For DLC coated surfaces, surface graphitisation is important with rougher surfaces; building up transfer layers and

graphitisation is crucial for smooth engineering surfaces and hydrogenising of dangling bonds can explain superlubricity for physically smooth

surfaces. An analysis of dominating surface parameters such as elastic, plastic and fracture behaviour of the top surface, the coating, the coating/

substrate interface and the substrate in addition to the coating thickness forms the basis for surface modelling. A stress intensity factor analysis of

crack growth shows the importance of considering both modes I, II and III loading, crack spacing and location of crack, while crack orientation,

location in crack field as well as load biaxiality have minor influences. It is shown how surface 3D FEM modelling generates stress and strainvalues at the nano level, within bond layers at coating/substrate interfaces and around cracks and forms the basis for better understanding the

origin of wear.

© 2007 Elsevier B.V. All rights reserved.

Keywords: Tribology; Coatings; Modelling; Scale effects; Diamond; Diamond-like carbon (DLC)

1. Introduction

Energy saving, environmental, economic and safety aspects in

our society all emphasise the importance of controlling frictionand wear in machinery and devices. Lubrication with oil is the

most common way to control friction and wear. However, the use

of liquid lubricants is often not so desirable for environmental

reasons, problems with keeping it in the contact zone, ageing,

circulating, storing, contamination etc. Surface engineering,

where the surface properties of the moving contacts are changed

in a favourable way by deposition or surface treatment now offers

another efficient way of controlling friction and wear.

The development of the vacuum deposition techniques,

chemical vapour deposition (CVD) and physical vapour deposition (PVD), has been of major impact, since they make

it possible to deposit a thin layer of only a few micrometers (or

down to nanometer thickness) on the surfaces of most

engineering materials. The geometrical change is minimal and

the surface layer may have properties covering an extremely

wide range, from hard diamond and ceramic coatings to very

soft polymeric or lamella-structured films [1].

In the 1980s hard ceramic TiN, TiC and Al203 coatings were

commercially introduced as surface layers on tools in the

production industry, and wear rates were decreased by one to

two orders of magnitude or more. In the 1990s very low friction

Available online at www.sciencedirect.com

Surface & Coatings Technology 202 (2007) 1034–1049www.elsevier.com/locate/surfcoat

⁎ Corresponding author. VTT Technical Research Centre of Finland, P.O. Box

1000, 02044 VTT, Finland. Tel.: +358 20 7225370; fax: +358 20 7227077.

E-mail address: [email protected] (K. Holmberg).

0257-8972/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.surfcoat.2007.07.105

mailto:[email protected]://dx.doi.org/10.1016/j.surfcoat.2007.07.105http://dx.doi.org/10.1016/j.surfcoat.2007.07.105mailto:[email protected]


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diamond, diamond-like carbon (DLC) and MoS2 surface layers

were investigated and some of them were introduced commer-

cially. Their friction and wear properties were again one to two

orders of magnitude lower than for earlier solutions and they

were suitable for components in engines and devices requiring

both low friction and low wear. In the 2000s much development

work has been focussed on modifying the structures of the thincoatings in a controlled way. This includes the development of

different multi-component and nanostructured coatings such as

layered coatings, gradient coatings, doped coatings, nanocom-

posite coatings etc. This development has been reviewed

recently by several authors [2–8].

These advanced surface engineering technologies make it

possible to tailor the surfaces and their properties with great

precision even to molecular and atomic levels (Fig. 1). How-

ever, there is one problem. It is easy to specify for some

application that a certain level of low friction and low wear is

needed but we have still no good generic tools to specify the

surface properties that may result in the required tribological behaviour. The problem is to specify the optimal surface

parameters like coating thickness, surface roughness, coating

material and its structure resulting in a certain hardness,

elasticity, residual stress and fracture toughness of the coating,

bond layers and substrate. There is much empirically-based

experience on how to choose a suitable coating for a specific

purpose but still no systematic tool for this. Much of the surface

engineering development work is still based on a trial and error

approach. Only a few parameter interactions have been

theoretically modelled, to a limited extent [1,9–17].

In this article we present our systematic approach to

modelling and simulation of surface properties for tribological

purposes. We first discuss the basic tribological mechanismsinvolved, indicate the importance of scale effects and illustrate it

by a discussion on scale effects for diamond and DLC coated

surfaces, discuss the parameters influencing friction and wear of

coated surfaces in micro level contacts and finally show how

deformations, stresses and strains can be modelled by advanced

three dimensional finite element method (3D FEM) and form a

basis for surface fracture analysis. The aim is to proceed in the

direction of systematic surface design for tribological

applications.

2. Basic friction and wear mechanisms

There are a number of classifications of friction and wear mechanisms published [18–21]. Two basic friction mechan-

isms, adhesive friction and ploughing, are normally mentioned.

The variety of classification suggestions is much larger for wear.

In the early days wear was typically classified based on its

appearance on the surface after the contact event. Examples of

such appearance based classes are scoring, scuffing, pitting,

gouging, spalling, fretting and galling. Some of these classes are

more or less related to certain applications, such as gear

contacts. The classifications used have recently been based

more on the fundamental mechanisms of material removal due

to the increased knowledge of the fundamental wear processes.

The most widely used classifications are: adhesive wear,abrasive wear, fatigue wear and tribochemical wear [1,21].

We believe that the classification of basic friction and wear

mechanisms can be developed even one step further and suggest

the classification shown in Fig. 2. Friction is the motion

resisting force at a certain moment in the process of motion

between the two surfaces in contact. This may be due to:

1) adhesion, that is breaking the adhesive bonds between the

two surfaces,

2) ploughing , that is resistance originating from elastic and

possibly plastic deformation when a harder countersurface

moves through a softer or more elastic surface and

3) hysteresis, that is resistance originating form continuouselastic deformation within one of the surfaces in motion.

In the basic friction mechanisms no material removal is

involved. Some debris in the contact zone would make the

contact mechanisms much more complicated but still the basic

mechanisms for motion resistance are those mentioned above.

Fig. 1. The advanced surface coating deposition techniques offer large possibilities to modify and tailor the top surface mechanical and chemical properties that governthe friction and wear behaviour in industrial applications.

1035 K. Holmberg et al. / Surface & Coatings Technology 202 (2007) 1034 – 1049


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Wear is the process of detachment of material from one

surface. It is different from friction in the sense that it is not

taking place at a certain moment but during a time period when

the surfaces are in moving contact. The detachment of material

may be due to:

1) adhesion + fracture, that is the adhesive lifting or shearing

force is causing such high tension and shear stresses in the

surface that they exceed the material strength and a crack is

formed, resulting in crack growth and material detach-

ment — a wear debris has been formed,

2) abrasion + fracture, that is a hard countersurface moves

through a softer surface and deforms it to the extent that suchhigh mainly shear stresses are formed that they exceed the

material strength and a crack is formed, resulting in crack

growth, fracture and material detachment — a wear debris

has been formed,

3) fatigue + fracture, that is compressive loading of the surface

deforms it to the extent that such high, mainly shear, stresses

are formed that they exceed the material strength and a crack

is formed, resulting in crack growth and material detach-

ment — a wear debris has been formed. The crack growth

process may take place during a number of loading cycles.

By definition wear always includes material removal. Normally fracture is a term describing bulk failure of brittle

materials. Here the term is understood more widely as a process

starting from loss of cohesion between bond structures in the

material, continuing as crack propagation and resulting in debris

being liberated from the surface.

The above classification of the basic wear mechanisms is

focussing on how the material removal takes place. For this

reason tribochemical wear is not included. The chemical

processes that take place on a surface are certainly important

but they are not mechanisms that cause material removal. They

are chemical reactions that cause surface material modification,

either improvement or degradation, and changes in, e.g., the

plastic and elastic properties and fracture resistance of the top

surface. The changed surface properties will either increase or

decrease the strength of the material and its resistance to

cracking and material removal. However, the basic mechanisms

of material removal in so-called tribochemical wear are still one

of the three mentioned above.

Actually the fatigue wear as it is normally considered can be

divided into two phases. In the first phase is only material

modification taking place without any material removal. During

continuous loading of the surface the close to surface material

properties are slowly changed. The second phase, that is the

wear or material removal phase, starts when the changed

material cannot any more withstand the loading and a crack is

created, it grows, material is liberated and debris is formed.It is interesting to note that the friction hysteresis mechanism

is based on elastic material deformation and thus it is in a sense

similar to the ploughing mechanisms, only the geometry is

different. The same goes for the fatigue and fracture wear

mechanism that is based on material deformation by compres-

sion and shear and is in that sense similar to the abrasion

mechanism. So the next step would perhaps be to consider only

two basic friction and wear mechanisms. For friction it would

be adhesive friction and elastic and plastic deformation

controlled friction. For wear it would be adhesive wear and

plastic deformation and fracture controlled wear. The surface

material modification processes, surface chemistry and fatigue,would be considered separately as non wear processes.

3. Scales in tribology

It is important to understand the basic mechanisms especially

when trying to model and predict friction and wear in different

contact situations. At the same time it is also important to

remember that very seldom do they appear in a contact situation

purely as such. Normally the basic mechanisms are combined in a

very complex way due to a more complicated contact geometry,

involving roughness and debris, due to inhomogeneous surface

materials with changing properties and due to variations in

loading and sliding conditions. The main parameters influencing

Fig. 2. The basic friction and wear mechanisms are related to adhesion, ploughing and hysteresis. In the case of wear these contact mechanisms result in material

fracture, detachment and removal.



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the tribological process are illustrated in Fig. 3. During the sliding

contact some of the parameters will change, surface layers are

formed, strain hardening takes place, local temperature rises

causing softening, etc. and after one sliding event we may have a

new set of parameters controlling the friction and wear.

It is often useful to study the tribological phenomena on

different size levels. Fig. 4 shows typical contact conditions that

occur on a macro level when a hard sphere is sliding on a flat

surface deposited with a thin coating [22]. Even if the number of

influencing parameters is large the situation is still not hopeless

to control. In each contact situation there is typically a limited

number of some five to ten parameters that dominate the friction

and wear behaviour. If we can identify them and understand

their interactions then we are well on the road to predicting and

controlling both friction and wear. Dominating parameters in

the contact situations shown in Fig. 4 are the coating/substrate

hardness relationship (hard on soft or soft on hard), coating

thickness, surface roughness and debris in the contact. These are

very important parameters since in a typical PVD or CVD

coated contact coating thickness, surface roughness and wear

debris are all in the size range of some few micrometers and thus

their interrelationship is crucial.

Thewhole picture is becomingeven more complicated since we

have friction and wear related phenomena appearing on different

Fig. 4. Main parameters influencing the friction in a macro-contact with thin coated surfaces are the hardness of the coating and the substrate, the coating thickness, the

surface roughness and debris in the contact zone. These parameters result in several different contact conditions, each of which can be modelled by a set of dominating parameters and interaction mechanisms.

Fig. 3. The tribological contact process is determined by a number of geometry, material and energy related parameters, including changes that can be described on e.g.

macro- micro- and nano-level and results in friction, wear and changed contact conditions.



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size levels. In some cases we have shearing taking place on a nanolevel due to molecular or atomic interactions. In other cases we talk

about cracks appearing at asperity collisions on a microlevel. Or

when observing the prevention of contacts by elasto-hydrody-

namic lubrication we calculate the pressure and lubricant film

thickness on a macrolevel. Forces and vibrations are observed on

component level while the efficiency and lifetime is estimated on

machinery level. These length scales of tribology that represent

different approaches to identify and understand characteristic

tribology related phenomena are illustrated in Fig. 5 [23].

Here we can talk about tribology on five different length

scale levels:

Nanotribology or molecular tribology includes phenomenarelated to the interaction between molecules and atoms, such as

the effects of van der Waals forces and related interatomic

phenomena, determined by the crystal and bonding structures of

materials.

Microtribology or asperity tribology relates to aspects

typically taking place at the peaks of the surface topography.

Phenomena such as adhesion between asperities, fracture, elastic

and plastic deformation, debris formation, surface layer

formation and topography changes are all important at this scale.

Macrotribology or contact tribology relates to aspects often

covering the whole contact zone, such as the longer-range

stresses present within contacting bodies. Combined loadingresponse is important particularly in highly-loaded applications

like gears, bearing elements and rollers. Macro-level stresses

influence observable wear mechanisms such as scuffing,

scoring and pitting.

Component tribology or decitribology is related to defining

and measuring typical parameters originating from the interac-

tion of components, and which define their performance, such

as torque, forces, vibrations, clearance and alignment.

Machinery tribology or unitribology describes the perfor-

mance-related phenomena for a system of components

assembled in a machine or a piece of equipment. The parameters

of interest are performance, efficiency, reliability and lifetime

estimation.

4. Friction and wear mechanisms of diamond and DLCcoated surfaces

Detailed investigations in the 1990s and 2000s carried out in

many laboratories world wide have shown that extremely low

friction and wear can be measured for sliding contacts with one

or both surfaces covered by a thin diamond or DLC coating

(Table 1). In the most favourable cases the wear has been

undetectable and the friction coefficient has been even below

0.001, which is called super lubricity [24–28]. The mechanisms

Fig. 5. The tribological process has been studied on machinery level, component level, contact level, asperity level and molecular level.

Table 1

Friction coefficients values and wear rates from the literature for diamond,

diamond-like carbon and doped DLC coatings [29]

Property Diamond

coatings

Hydrogen free

DLC

Hydrogenated

DLC

Modified/

doped DLC

Structure CVD

diamond

a-C a-C:H a-C:Me

ta-C ta-C:H a-C:H:Me

a-C:H: x

Me=W,Ti….

x =Si,O,N,F,

B…

Atomic

structure

sp3 sp2 and sp3 sp2 and sp3 sp2 and sp3

Hydrogen

content

– N1% 10–50%

μ in vacuum 0.02–1 0.3–0.8 0.007–0.05 0.03

μ in dry N2 0.03 0.6–0.7 0.001–0.15 0.007μ in dry air

5–15%

0.08–0.1 0.6 0.025–0.22 0.03

μ in humid air

15–95% RH

0.03–0.15 0.05–0.23 0.02–0.5 0.03–0.4

μ in water 0.002–0.08 0.07–0.1 0.01–0.7 0.06

μ in oil 0.03

k in vacuum 1–1000 60–400 0.0001

k in dry N2 0.1–0.2 0.00001–0.1

k in dry air

5–15%

1–5 0.01–0.4

k in humid air

15–95%

0.01–0.06 0.0001–400 0.01–1 0.1–1

k in water 0.0001–1 – 0.002–0.2 0.15

k in oil – (0.1)

The wear rate k is given in 10−6 mm3/N·m units.



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resulting in these conditions were first not very clear toresearchers. Some mechanisms have been proposed, such as the

dangling bond mechanism, surface graphitisation and transfer

layer formation. All three of these have been convincingly

shown to work both experimentally and theoretically. However,

in the literature these mechanisms are often mixed and it is not

clearly understood which mechanism is dominating in which

conditions.

We believe that it is easier to understand the governing

friction and wear mechanisms by analysing the tribological

contact condition at different length scales. We call the levels

macro, micro and nano scale and they are closely linked to the

roughness of the surfaces in contact. On a macro scale we look at what we would call typical engineering surfaces with a

surface roughness in the range of Ra =0.1–1 μm. On a micro

scale the surfaces are what we would call smooth engineering

surfaces with a roughness in the range of Ra =0.01–0.1 μm.

And on nano scale the surfaces are physically smooth with a

roughness in the range of Ra = 1–30 nm. In addition to the

surface roughness the surrounding environment is another

important parameter that we consider.

- Diamond coatings sliding in air or vacuum (Fig. 6a) at a

macro scale may have a very rough, sometimes pyramid

shaped, topography, Ra =0.1–1 μm; the friction coefficient is

μ=0.1–0.7 and the wear rate k =0.1–100 · 10−6 mm3/N m.

The contact mechanism is dominated by asperity interlock-

ing, asperity breaking and asperity ploughing.

- Diamond coatings sliding in air, water or oil (Fig. 6 b) with

micro scale smooth topography, Ra =0.01–0.1 μm, have a

friction coefficient of μ=0.001–0.1 and a wear rate k =0.0001–

0.1· 10−6 mm3/N m with the lowest μ and k values measured in

water. A graphite film of the thickness h =100–200 nm isformed on the contacting surfaces. The contact mechanism is

shear within sp2 hybridised graphitic basal planes, formed by

transformation from sp3 by sliding asperities at high local

temperature and pressure.

- Diamond coatings sliding in air at T b600 °C and non-

vacuum (Fig. 6c) nano scale molecularly smooth topogra-

phy, Ra = 1–30 nm, have a friction coefficient that is

μ=0.03–0.15 and a wear rate of k =0.01–5 · 10−6 mm3/N

m. The contact mechanism is shear between two flat layers

of single hydrogen atoms at dangling bonds. Only weak van

der Waals bonds between the atoms are present and no

strong chemical bonding is involved.

Corresponding contact conditions at the macro, micro and

nano scales are shown in Fig. 7 for diamond-like carbon coatings.

Fig. 6. Different tribological contact mechanisms determining friction and wear

for diamond coated surfaces described on (a) macro scale with engineering

surfaces, (b) on micro scale with smooth engineering surfaces and (c) on

nanoscale with physically smooth surfaces.

Fig. 7. Different tribological contact mechanisms determining friction and wear

for diamond-like carbon coated surfaces described on (a) macro scale, (b) microscale and (c) nano scale.



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- DLC coatings sliding in air, water or oil (Fig. 7a) at a macro

scale with a rough topography, Ra =0.1–1 μm, have a

friction coefficient μ =0.01–0.6 and a wear rate k =0.0001–

1 · 10−6 mm3/N m. The contact mechanism is graphitisation

of the top surfaces with shear within sp2 graphitic basal

planes resulting in low shear resistance. In some cases the

surface roughness may inhibit graphitisation resulting inhigh friction and wear.

- DLC coatings sliding in air against a steel or ceramic

countersurface (Fig. 7 b) with micro scale smooth topography,

Ra =0.01–0.1 μm, have a friction coefficient μ=0.05–0.3

and a wear rate k =0.0001–10 · 10−6 mm3/N m. The contact

mechanism is first smoothening of the countersurface by

building up a transfer layer containing typically Al, C, Cr,

and Fe. The transfer layer thickness is h =100 – 200 nm.

Graphitisation occurs on both the DLC top surface and the

countersurface transfer layer. Shear takes place within the

sp2 graphitic basal planes.

- DLC coatings sliding in dry nitrogen (Fig. 7c) with nano scale molecularly smooth topography, Ra = 1–30 nm, have a

friction coefficient that is μ =0.001–0.15 and a wear rate of

k =0.00001–0.1 · 10−6 mm3/N m. The contact mechanism is

shear between two flat, highly hydrogenated layers of single

hydrogen atoms at dangling bonds. A positive atomic dipole

charge of the hydrogen atoms out from the surface at both

surfaces gives rise to repulsive forces.

The data given above originate from a number of

experimental studies listed in Table I. The mechanisms referred

to are summarised from the most recent literature [1–3,6,27–

29]. The parameter representing the hydrogen content

in DLC coatings has not been included in the presentationabove in order to more clearly illustrate the scale effect. The

hydrogen effect has been analysed and discussed in detail

elsewhere [29].

5. Dominating surface parameters in a coating contact

Complete modelling of a tribological contact is a most

complex task. This is on one hand due to the large number of

influencing parameters, related to contact geometry, material

properties and energy input, and on the other hand, due to the

number of interactions taking place simultaneously on dif-

ferent scales with a variation of up to ten orders of magnitude both in terms of size and time, as illustrated in Fig. 5. The

picture gets even more complex when we introduce coatings on

the surfaces. Still it is possible to get very useful results from

tribological modelling by not trying to be too generic and

instead focussing on a specific contact case and specific

contact phenomena related to limited contact conditions.

Advanced finite element method (FEM) techniques offer

today a very good tool for tribological modelling of the mecha-

nical behaviour, including deformations, stresses and strains, of

a tribological contact both on macro and micro scales [9–17].

Molecular dynamic simulation (MDS) has developed rapidly

over the last decade boosted by the increased computer power

and software development. It has turned out to be a very useful

tool for tribological modelling at the nano scale [30–33]. In the

following we will focus on showing how FEM modelling helps

us understand the interactions in a tribological contact with thin

coatings on the micro scale level.

Based on the analysis of the basic friction and wear

mechanisms discussed above in Section 2 we will first analyse

different contact situations and indicate the tribologicallydominating parameters that should be the focus in a modelling

study.

The friction and wear is governed by the shear taking place

at the top surface and in the deformed surface layer, and by

the elastic, plastic and fracture behaviour both at the top surface

and in the deformed surface layer. A thin coating is typically

a part of this deformed surface layer. In addition surface

degradation may take place due to tribochemical and fatigue

processes that influence on the surface strength to withstand

loaded conditions. Thus the crucial material parameters are the

elastic modulus, the hardness or shear strength and the fracture

toughness on the top surface, in the coating, at the coating/ substrate interface and in the substrate under the coating, as

shown in Fig. 8. In this presentation hardness, H , is used as a

symbol representing the resistance to plastic deformation due

to its common use (even if referring to the elastic– plastic

constitutive response of the material would be the correct

expression).

In this presentation we limit ourselves to the conditions of a

sphere sliding over a flat coated surface, ideally smooth

surfaces, homogenous materials and no contamination or wear

debris involved. The influence of these parameters in a coated

contact has been discussed elsewhere [1,6].

Adhesive friction is dominated by the shear taking place in

the surface top layer or the shear in between the two interactingsurfaces (see Fig. 2). Surface chemistry, reaction and transfer

layers and structural parameters, like hydrogen content for DLC

coatings, are important. The coefficient of friction

la ¼ f suð Þ ð1Þ

Ploughing friction is dominated by the elastic and plastic

behaviour of the coating and the substrate. Structural properties,

multilayer, gradient, modified and doped structures and structural

parameters, like sp2/sp3-ratio for DLC coatings, are important. The

Fig. 8. Symbols used for material parameters in a coated surface.



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capacity of the coating/substrate system to withstand deformation is

frequently called load carrying capacity. The coefficient of friction

l p ¼ f E c; H c; E s; H s; hð Þ ð2Þ

Hysteresis friction is mainly dominated by the elastic

properties of the substrate but also to some extent by the elastic

properties of the coating. The coefficient of friction

lh ¼ f E s; E c; hð Þ ð3Þ

Adhesive wear is dominated by the fracture behaviour in thesurface top layer, in the coating, at the coating/substrate interface

and in the substrate. With fracturewe understand here the property

of the material to resist cracking, intrinsic detachment and

breaking to parts. The adhesive force, F a , from the counterface

tries to tear off part of the surface material over the contact area A

(Fig. 9a). When surface roughness is included A will decrease and

the adhesive wear typically decrease. The wear rate

k ¼ V adh=wd s ¼ f K u; K c; K i; K sð Þ ð4Þ

where V adh is the volume of adhesive wear, w is the load and s is

the sliding distance.

The breaking of the material may take place at different

locations in the surface depending on the material strength at

each location as shown in Fig. 9 b–e. Due to the depth of the

debris detachment the result is

- top layer fragments dominated by K u (Fig. 9 b),

- coating fragments dominated by K c (Fig. 9c),

- coating delamination dominated by K i (Fig. 9d) or

- substrate and coating debris dominated by K s (Fig. 9c).

Abrasive wear is dominated by geometrical collision of the

two moving surfaces resulting in high stresses, material shear

and fracture, and debris formation. The collisions may be due to

hard asperity or debris ploughing or asperity collisions, as

shown in Fig. 10. The wear rate

k ¼ V abr =wd s ¼ f K c; K i; K s; H c; H i; H s; hð Þ ð5Þ

Due to the depth of the debris detachment the result is

- coating fragments dominated by K c,

- coating delamination dominated by K i or

- substrate and coating debris dominated by K s.

Fatigue wear is a result of material degradation where the

strength of the material decreases to a level so that it cannot anymore withstand the repeated loading. The result is fracture,

cracking, and debris formation (Fig. 11). It is dominated by the

Fig. 9. Two surfaces attach to each other by adhesion (a) and the movement of

the top surface results in an adhesive force, F a , that tries to detach material over

an area, A, from one of the surfaces. The detachment may take place (b) at thetop surface, (c) within the coating, (d) at the coating/substrate interface and (e) in

the substrate.

Fig. 10. Abrasive wear is characterised by a hard asperity (a) or debris (b) that

deforms the countersurface in a ductile or brittle way resulting in fracture,

cracking and debris generation.

Fig. 11. Fatigue wear is characterised by repeated loading of the coated surface

resulting in cracking at the surface in the coating, at the interface or in thesubstrate, followed by fracture, material detachment and debris generation.



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elastic and fracture properties of the coating, the coating/substrate

interface and the substrate. The loading may be rolling or sliding.

The wear rate

k ¼ V fat =wd s ¼ f K u; K c; K i; K s; E c; E i; E s; hð Þ ð6Þ

Due to the depth of the debris detachment the result is

- top layer fragments dominated by K u,

- coating fragments dominated by K c,

- coating delamination dominated by K i or

- substrate and coating debris dominated by K s.

Surface modification is here considered separately from the

pure wear mechanisms since it alone will not result in material

liberation. Still it is very important to consider in a wear process

since it often precedes the wear event and may be the reason for

wear to start. Typical surface modification mechanisms are

chemical reactions taking place at the surface and material

fatigue from repeated loading.Chemical reactions and sometimes even physical structural

modifications, such as oxidation of metallic coatings, graphi-

tisation of DLC and crystallographic re-orientation of MoS2coatings, take place mainly at the top surface and influence the

shear, τ u, and fracture, K u, properties and thus the adhesive

friction and adhesive wear. Sometimes also the whole coating

structure and the coating/substrate interface may be affected.

Fatigue is a result of repeated compressional loading on the

material that weakens the molecular structure by including

cumulative damage to a level that it cannot take the loading any

more. The maximum compressional stress peaks are normally

under the coating in the substrate because the coating layer is

very thin. Thus the substrate elastic properties, E s, and fracture

toughness, K s, are crucial. If the stress peaks are high also closer

to the surface, the elastic and fracture properties of both the

coating and the coating/substrate interface, E c, K c, E i and K i,

may also be important.

6. Modelling the surface loading conditions, stresses and

strains

6.1. The contact geometry

In our work the tribosystem of a sphere sliding on a coatedflat surface with increasing normal load was chosen for the

study. This corresponds to the contact of the diamond tip sliding

against the coating in a scratch tester and thus there is much

empirical information available to compare with. The method is

widely used today by the coating industry and coating

development laboratories, as well as in research for evaluating

the tribological properties of coatings. The scratch test is

generally accepted as a good and efficient method for the

quality assessment of a coated surface [34]. In the scratch test

procedure the diamond stylus has a Rockwell C geometry with a

120° cone and a 200 μm radius spherical tip. The scratch test

procedure is described in the European Standard prEN 1071-3

[35].

6.2. Contact mechanisms, deformations and stress generation

The material loading and response conditions in a scratch

tester have been divided into three phases by Holmberg [36] to

illustrate the contact and deformation mechanisms involved.

Phase one represents the ploughing of a stylus in the substrate

material. The substrate material is deformed by elastic and plastic deformation and a groove is formed. Phase two re-

presents the bending and drawing of the coating like a sheet

on top of the substrate surface. The upper surface of the

coating rubs against the stylus front surface and the force

required for pulling the coating is equal to the frictional force

on the coating against the stylus front surface. The bending

movements cause stresses and stress release in the coating.

Phase three represents pulling the coating from one point on

the surface when fixed over the substrate. The increasing

pulling force results in cracks at the place of maximum tensile

stress.

The sliding spherical diamond tip deforms the surface both plastically and elastically as schematically shown in Fig. 12. At

the initial stage a small spherical indent is formed and the plastic

material flow pushes up the material around the indent in a torus

formed shape. As the tip moves forward a groove with increasing

depth is formed. Under the tip there is both plastic and elastic

deformation while in the surface behind the tip only the plastic

part prevails. Another torus shape is formed in front of the tip.

The stress field in the coated surface is formed as a result of

the following four effects:

1) Friction force. The friction force between the sliding tip and

the surface results in compressional stresses from the

pushing force in front of the tip and tensional stresses fromthe pulling force behind the tip.

2) Geometry changes. The elastic and plastic deformations are

spherical indent, groove and torus shaped. They result in

bending of the coating as shown in Fig. 12. The stresses are

both compressional and tensional.

3) Bulk plasticity concentration. The spherical indentation

pattern causes the substrate to deform plastically, reaching

its peak value at an angle of about 45° from the plane of

symmetry in the plane of the coating. This can be identified

with local tensile stress minima and maxima of deformation

between the tensile stress peaks around the indenter (at

locations of 0 and 90°, respectively).4) Residual stresses. It is very common especially for thin

ceramic coatings that they, due to the deposition process,

contain even very considerable compressional residual

stresses. These are typically of the order of 0.5–3 GPa but

values even as high as 10 GPa may appear [1,37,38].

When the diamond stylus is drawn over the surface with an

increasing normal load, a very complex and dynamic stress field

is formed with stress concentrations at changing locations. For

e.g. a TiN or DLC coated steel surface it typically results in a

coating fracture and spalling pattern. The formation of cracks in

the groove of a scratch tester has been shown by several authors

[35,39–43]. They can typically be described as a) angular



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cracks, b) parallel cracks, c) transverse semi-circular cracks, d)

coating chipping, e) coating spalling, and f) coating break-

through. Methods for the determination of mechanical properties

of coatings and contact stresses have been reported [44,45].

6.3. Modelling the contact by three dimensional finite element

method

A three dimensional finite element model has earlier been

reported and was now further developed for calculating the

stresses and strains in the coated surface and for identifying

the stress concentrations where the first cracks of the coated

surface are expected to occur [9–11,17]. The scratch test

experiment was discretised using the inherent symmetry of

the geometry and introducing a finite element mesh where

mesh sizing is of the order of the coating thickness (Fig. 13).

After analysing the convergence behaviour of the boundary

value problem and assessing whether suitable accuracy of contact-related field variables can be attained, a suitable

mesh density around the contact area was found to be

25 nm–8 μm. Bilinear hybrid elements were used in Abaqus

6.6-3, 6.2-1 and Warp3D 15.3 finite element software. The

volume of the finite element slit taken to describe the scratch

t est confi gurati on w as 12× 4 × 2 m m3 (length, width,

thickness). The substrate deformation behaviour was char-

acterised as elastic– plastic with isotropic hardening, while

the coating was modelled to behave in a linear –elastic

manner. The sliding spherical diamond tip was modelled as

completely rigid.

The kinetic formulation was presented applying a finite

strain deformation description. The contact event was

modelled by describing two contact zones, commonly

referred to as the master and slave surfaces, where the

master surface is the one having greater rigidity. During the

progress of the experiment the relative positions of the master

and slave surfaces define the contact event. The contact

formulation was of the finite sliding type due to large localdeformations and the distance the tip travels during the

experiment. The contact was presented as a ‘hard contact ’

between smooth surfaces, i.e. tractions are transferred at the

instant of contact but not before. Computational initial

oscillations were treated with viscous damping. A velocity-

independent Coulombian friction model was used to

characterise related surface interactions, and the surface-

hardening effect due to plastic deformation of the substrate

Fig. 13. Schematic illustration of the three dimensional finite element mesh. The

mesh sizing is in the range of 0.025–

100μ

m and the number of mesh degrees of freedom is about 500.000.

Fig. 12. The stress field in a coated surface resulting from a sliding sphere is a result of four loading effects: friction force, geometrical deformations, bulk plasticity

concentration and residual stresses. Illustration (a) shows the loading effects with exaggerated dimensions and deformations and (b) with correct dimension

interrelationships.



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included in the model. The basic model is in detail described

in [10].

The results are inferred and analysed primarily with

respect to the first principal stress. Generally, studies in the

current field apply the von Mises equivalent stress to

characterise deformation and failure events. However, the

von Mises stress has its greatest potential in understandingand modelling deformation-related events, such as the

plasticity of metals, and is not usually associated with the

brittle type of failure. It can be argued, and has often been

presented [46] that local unstable cracking is more dependent

on the prevailing tensile stress state than the practically non-

existent state of deformation, and that deformation-related

parameters and invariants do not comply with the physical

appearance of fracture. Most local approach models for such

failure micromechanisms rely on the first principal stress.

Since the current work is related to cracking of a brittle layer

incapable of exhibiting much more than elastic deformation

all the way to final rupture, it can be expected that the use of the first principal stress as a fundamental stress component to

explain the physical fracture patterns will bring about the

most success.

Compared to real scratch tester contact conditions, the

following limitations have been set for the sake of simplicity:

- Compressive residual stresses normally occurring in ceramic

thin coatings are not included in the simulation cases

reported here. They have been introduced into the model and

results with residual stresses have been reported separately

[17,47].

- The stress relaxation effect of previously generated cracks on

the stress distribution is not included in the present simulations.

- The surfaces in the model are ideally smooth, which means

that surface roughness effects are not considered.

- The materials are considered to be fully homogenous and

free from contaminants, pinholes and such defects often

occurring in thin ceramic coatings.

7. Simulation of surface stresses and strains

7.1. Simulated contact conditions

The above described contact conditions and sliding processhave been simulated by the computer model. The following

parameters were used in the calculations of the stress and strain

distributions:

Scratch test parameters: sliding distance 10 mm, load

increases linearly from 5 N pre-load and 0.5 μm indentation

depth before sliding starts to 50 N and 3 μm indentation depth at

10 mm sliding distance, and the sliding velocity is not included

in the model, i.e. the model is time independent.

Sliding stylus (Rockwell C): radius of the spherical tip

200 μm, the material is diamond, Young's modulus 1140 GPa,

hardness 80 GPa, Poisson's ratio 0.07, and the roughness is

ideally smooth.

Coating: thickness 2 μm, the material is titanium nitride

(TiN) deposited by PVD, Young's modulus 300 GPa, hardness

25 GPa, Poisson's ratio 0.22, and the roughness is ideally

smooth.

Bond layer: thickness 500 nm, hard ceramic layer with a

Young's modulus of 500 GPa and Poisson's ratio 0.22.

Substrate: the geometry is an ideally smooth plate, thematerial is High Speed Steel, Young's modulus 200 GPa,

hardness 7.5 GPa, Poisson's ratio 0.29, the yield strength is

estimated from ultimate bending strength to 4100 MPa, and the

strain hardening coefficient is 20.

Friction: The values for the coefficient of friction were

measured from samples corresponding to the above material

combination. In the simulations a constant value 0.08 was used

for the coefficient of friction due to friction from interfacial

shear which excludes the ploughing component of friction.

7.2. First principal stresses of a TiN coated steel surface with

hard bond layer

One typical simulated stress distribution is shown in Fig. 14.

The figure is a topographical stress-field map where each colour

corresponds to a certain stress level range at the surface and at

the intersection shown in the figure. The observation direction is

similar to that in Fig. 12 but the spherical tip is invisible in order

to display the stresses. The border of the corresponding contact

area of the coated plate and the sphere is close to the green to

yellow colour transition half circle where the stresses are close

to zero.

The smoothly changing stress field shows a considerable

compressional stress under the diamond tip, indicated by green

and blue colours, and the variations in the tensile stressesaround the contact zone, indicated by the orange and red

colours. The maximum compressional stresses under the tip are

about 5200 MPa and the compressional stresses ranges about

40 μm down below the surface. It can also well be seen that

there is a thin range of high tensile stresses within the bond layer

right under the loaded tip. These tensile stresses are about

3000 MPa just under the tip. A circular region of high tensile

stresses is seen as a red belt around the contact zone. It has its

maximum value at some distance behind the back of the contact

zone at the location of the formed groove edge. Here it reaches a

level of about 3300 MPa. This is the place where the first cracks

normally occur in scratch test experiments with similar coatedsurfaces. Behind the contact zone there is a tail of high residual

tensile stresses on the surface in the groove area having values

of about 2500 MPa.

Fig. 15 shows a close up of the part of Fig. 14 just at the back

end of the contact zone by the symmetry plane. It shows both

the distribution of the rapid stress change in this region and the

very high tensile stresses in the bond layer just behind the

contact zone, being as high as 5150 MPa.

7.3. Strain in a TiN coated steel surface with hard bond layer

The strain distribution for the same contact conditions as in

Fig. 14 is shown in Fig. 16. The dark red region directly under



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the loading tip shows large strain due to both elastic and plastic

deformation and it reaches about 40 μm down under the surface.

The red tail behind the contact region shows the residual plasticstrain just under the groove and it reaches about 20 μm down

under the groove surface.

7.4. First principal stresses of a TiN coated steel surface with

interface crack

Cracks at the surface will have a considerable influence on the

formed stress fields. The lateral cracks generated at the interface

Fig. 15. Close up of the region just behind the back of the contact zone at the interface plane in Fig. 14.

Fig. 14. Topographical stress-field maps showing first principal stresses on the coating and at the symmetry plane intersection of the steel sample coated with a 2 μm

thick TiN coating ( E =300 GPa), a 500 nm hard interface layer ( E =500 GPa) and loaded by a sliding spherical diamond tip. Sliding direction is from left to right. The

values on the colour scale are given as MPa. The stress field at 15 N load and 2.1 mm of sliding is shown.



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between the coating and the substrate are of special interest since

they indicate the break down of the coating/substrate adhesion.

The growth of these lateral cracks result in the formation of larger

detached coating flakes and coating delamination from the

surface. Fig. 17 shows the stress pattern and the high stresses

formed by the ends of one short lateral crack at the interface.

Fig. 17. Topographical stress-field maps showing first principal stresses at the symmetry plane intersection of the steel sample coated with a 2 μm thick TiN coating

( E =300 GPa), having a 1 μ

m long lateral crack at the coating/substrate interface and loaded by a sliding spherical diamond tip. Sliding direction is from left to right.The values on the colour scale represent relative stress at 10 N load and 1.2 mm sliding.

Fig. 16. Topographical strain-field maps showing equivalent strain on the coating and at the symmetry plane intersection of the steel sample coated with a 2 μm thick

TiN coating ( E =300 GPa), a 500 nm hard interface layer ( E =500 GPa) and loaded by a sliding spherical diamond tip. Sliding direction is from left to right. The values

on the colour scale represent the equivalent strain at 15 N load and 2.1 mm of sliding.



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7.5. Crack propagation in a TiN coated steel surface

The crack propagation has been studied by Boundary Element

Method (BEM) by [17] based on analysisof the simulated stresses

in the coated surface. The parameters influencing on crack

propagation studied can be summarised as (Fig. 18):

1) loading modes, (I, II, III).

2) orientation of the crack, (θ= 0, 20°, 45°)

3) density of the crack field, crack spacing (ρ=5, 10, 30 μm and∞)

4) location of the crack in the crack field, (centrecrack,

centrecrack+1 etc., edgecrack)

5) location of the crack on the scratch groove (middle cracks,

side cracks)6) tensile load biaxiality in loading mode I, (β =0, 0.5, 1)

Observe that the crack spacing ρ=∞=infinite corresponds to

one single crack and ρ= 0 to an infinite number of cracks

approaching each other.

The results of the BEM analysis are summarised in Fig. 19.

BEM analysis results for single crack cases with different crack

angles are presented for uniaxial tension and for loading modes

II and III (in-plane and out-of-plane shear). The results are presented using the equivalent SIF concept, i.e.

K E ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi K 2I þ K

2II þ 1 þ mð Þ K

2III

q ð7Þ

The crack angle is defined such that cracks oriented at an

angle of 0 degrees are perpendicular to the applied uniaxial

tension. All results were presented over a normalized crack front

parameter, s, and given normalized with the value of stress

intensity factor (SIF) at the deepest point of the single crack case

under uniaxial tension. It was shown that crack oriented from the

perpendicular plane towards tension exhibit a somewhat smaller

equivalent crack driving force, the differences being of the order of 15% for crack tilted 20° and 30% for crack tilted 45°.

Different loading mode effects to crack driving force are

indicated, mode II component is being somewhat pronounced

over the mode III. The effects of biaxial loading are of the order

of 5–10% with biaxiality ratios (β ) of 1 and 0.5, β =σ22∞ / σ11

∞ ,

where the stress components are applied at model boundary.

The effects of crack field density on straight cracks with

uniaxial tension are depicted. A single uniaxial tension crack

Fig. 18. Crack growth parameters studied and used terminology.

Fig. 19. The effect of different crack growth parameters on normalized stress intensity factor (SIF).



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case is provided for reference. Two effects are noted, first how

crack density introduces a differing driving force to variable

density crack fields and second, how center and edge cracks

exhibit a somewhat different driving force dependant on crack

density. For crack fields with a lower density the crack driving

force is higher in comparison to dense crack cases and separate

cracks are relatively independent of each other, i.e. different cracks have nearly identical crack driving forces. It was noted,

that the crack density is an extremely important parameter in

evaluating the SIF values, the effects being morethanmeaningful.

Crack location, i.e. whether edge or center cracks are

concerned, has similar effects as with straight cracks under

unidirectional tension. Loading biaxiality had no remarkable

effect on straight scratch bottom cracks, but the differences

become noticeable when angular cracks are concerned. The

differences for the ρ= 5 μm crack field are at their maximum of

the order of 35%, the biaxiality effects affect edge and center

crack field cracks much in the same fashion and of the same order

of magnitude. Biaxial loading is seen to have a similar effect aswith the middle crack fields, the overall difference between the

single transversal middle crack being of the order of 40–60%.

Different density crack fields are seen to produce relatively field

density insensitive results, whilst differing quite a bit from the

single crack solution, the difference being of the order of 80%.

8. Conclusions

The article discusses the basic friction and wear mechanisms,

scale effects and parameters influencing the friction and wear of

surfaces coated with thin films. This forms the basis for surface

optimisation by modelling, stress simulation and surface fracture

calculations.It is shown that the basic friction and wear mechanisms can

be reduced to friction by adhesion, ploughing and hysteresis and

wear by adhesion, abrasion and fatigue combined with material

fracture. The tribochemical and surface physical effects and

surface fatigue taking place before material fracture are treated

as pure surface material modification mechanisms.

The scale effects in a tribological contact are illustrated by

explaining typical surface roughness related tribological

mechanisms for diamond and DLC coated surfaces. For

diamond coatings asperity interlocking effects are important

for rough surfaces, graphitisation dominates for smooth

engineering surfaces and hydrogenisation of dangling bondsmay be crucial for physically smooth surfaces. For DLC coated

surfaces surface graphitisation is important with rougher

surfaces, building up transfer layers and graphitisation is crucial

for smooth engineering surfaces and hydrogenising of dangling

bonds can explain superlubricity for physically smooth

surfaces.

An analysis of dominating surface parameters such as elastic,

plastic and fracture behaviour of the top surface, the coating, the

coating/substrate interface and the substrate in addition to the

coating thickness forms the basis for surface modelling. The

dominating parameters depending on the governing basic wear

mechanisms have been identified. Stress simulations locate high

tensile stresses on the top surface behind a sliding spherical tip

and high residual tensile stresses in the coating covering the

deformed groove. Hard interlayers between the coating and

substrate generate extremely high tensile stresses and the

formation of stress concentrations at crack ends for cracks at the

coating/substrate interface are shown.

A stress intensity factor analysis of crack growth shows the

importance of considering all modes I, II and III stresses, crack spacing and location of crack in the scratch groove, while crack

orientation, location in crack field as well as load biaxiality have

minor influences.

The study shows how surface 3D FEM modelling generates

stress and strain values at nano level, at coating/substrate

interfaces and around cracks and forms a basis for understanding

the origin of wear. Micro and nano scale modelling, simulation

and fracture calculations are very useful tools for a systematic

approach to finding optimal surface and coating parameters and

for successful surface design for a specific application.

Acknowledgements

The authors want to acknowledge the following colleagues

for the interesting and valuable discussions in relation to the

work: Allan Matthews, Sheffield University, UK; Philippe

Kapsa, Ecole Central de Lyon, France; Henry Haefke and Imad

Ahmed, CSEM, Switzerland; Ali Erdemir, Argonne National

Laboratory, USA; Koij Kato, Tohoku University, Japan; and

Kaj Pischow and Rosa Aimo, Savcor Coatings.

The financial support of TEKES the Finnish Technology

Agency; Taiho Kogyo Tribology Research Foundation, Japan;

Savcor Coatings, Finland; and the VTT Technical Research

Centre of Finland is gratefully acknowledged.

References

[1] K. Holmberg, A. Matthews, Coatings Tribology — Properties, Techniques

and Applications in Surface Engineering, Tribology Series, vol. 28,

Elsevier, Amsterdam, 1994, p. 442.

[2] A. Erdemir, C. Donnet, in: B. Bhushan (Ed.), Modern Tribology

Handbook, CRC Press, New York, 2001, p. 871.

[3] A. Erdemir, C. Donnet, in: G.W. Stachowiak (Ed.), Wear — Materials,

Mechanisms and Practice, Tribology in Practice Series, John Wiley &

Sons, Chichester, UK, 2005, p. 191.

[4] S. Hogmark, S. Jacobson, M. Larsson, U. Wiklund, in: B. Bhushan (Ed.),

Modern Tribology Handbook, CRC Press, New York, 2001, p. 931.

[5] K. Holmberg, A. Matthews, in: B. Bhushan (Ed.), Modern Tribology


[6] K. Holmberg, A. Matthews, in: G.W. Stachowiak (Ed.), Wear — Materials,

Mechanisms and Practice, Tribology in Practice Series, John Wiley &

Sons, Chichester, UK, 2005, p. 123.

[7] M. Cartier(Ed.), Handbook of Surface Treatmentsand Coatings, Tribologyin

Practice Series, Professional Engineering Publishing, London, 2003, p. 412.

[8] B.G. Mellor, Surface Coatings for Protection against Wear, CRC Press,

Woodhead Publishing Ltd, Cambridge, UK, 2006, p. 429.

[9] K. Holmberg, A. Laukkanen, H. Ronkianen, K. Wallin, S. Varjus, Wear

254 (2003) 278.

[10] K. Holmberg, A. Laukkanen, H. Ronkianen, K. Wallin, S. Varjus, J.

Koskinen, Surf. Coat. Technol. 200 (2006) 3793.

[11] K. Holmberg, A. Laukkanen, H. Ronkianen, K. Wallin, S. Varjus, J.

Koskinen, Surf. Coat. Technol. 200 (2006) 3810.

[12] N. Ye, K. Komvopoulos, Trans. ASME, J. Tribol. 125 (2003) 692.

[13] N. Ye, K. Komvopoulos, Trans. ASME, J. Tribol. 125 (2003) 52.[14] Z.Q. Gong, K. Komvopoulos, Trans. ASME, J. Tribol. 125 (2003) 16.



16/16

[15] Z.Q. Gong, K. Komvopoulos, Trans. ASME, J. Tribol. 126 (2004) 9.

[16] Z.Q. Gong, K. Komvopoulos, Trans. ASME, J. Tribol. 126 (2004) 655.

[17] A. Laukkanen, K. Holmberg, J. Koskinen, H. Ronkianen, K. Wallin, S.

Varjus, Surf. Coat. Technol. 200 (2006) 3824.

[18] P.J. Blau, Friction and Wear Transitions of Materials — Break-in, Run-in,

Wear-in, Noyes Publications, Park Ridge, New Jersey, USA, 1989, p. 476.

[19] B. Bhushan, Principles and Applications in Tribology, John Wiley & Sons,

New York, 1999, p. 1020.[20] K.C. Ludema, in: B. Bhushan (Ed.), Modern Tribology Handbook, CRC

Press, New York, 2001, p. 205.

[21] K. Kato, K. Adashi, in: B. Bhushan (Ed.), Modern Tribology Handbook,

CRC Press, New York, 2001, p. 273.

[22] K. Holmberg, Surf. Coat. Technol. 56 (1992) 1.

[23] K. Holmberg, Tribol. Int. 34 (2001) 801.

[24] A. Erdemir, O. Erilmaz, G. Fenske, J. Vac.Sci. Technol., A 18(2000) 1987.

[25] A. Erdemir, G.R. Fenske, M.K. Kazmanil, O.L. Eryilmaz, Proc. of 2nd

World Tribology Congress, 3–7.9, Austrian Tribology Society, Vienna,

Austria, 2001, p. 265.

[26] P.L. Dickrell, W.R. Sawyer, A. Erdemir, Trans. ASME, J. Tribol. 126

(2004) 615.

[27] A. Erdemir, Tribol. Int. 37 (2004) 577.

[28] A. Erdemir, Tribol. Int. 37 (2004) 1005.

[29] H. Ronkainen, K. Holmberg, in: C. Donnet, A. Erdemir, Springer, NewYork, in press.

[30] U. Landtman, W.D. Luedtke, E.M. Ringer, Wear 153 (1992) 3.

[31] M.O. Robbins, M.H. Müser, in: B. Bhushan (Ed.), Modern Tribology


[32] G.T. Gao, P.T. Mikulski, G.M. Chatneuf, J.A. Harrison, J. Phys. Chem., B

107 (2003) 11082.

[33] J. Gao, W.D. Luedtke, D. Gourdon, M. Ruths, J.N. Israelachvivli, U.

Landman, J. Phys. Chem., B 108 (2004) 3410.

[34] N. Jennet, R. Jacobs, J. Meneve, Proc. MST Conf.: Adhesion Aspects of

Thin Films, 15–16.12, 2003, p. 20.

[35] European Standard, Advanced Technical Ceramics — Methods of Tests

for Ceramic Coatings — Part 3: Determination of Adhesion and other Mechanical Failure Modes by Scratch Test, prEN1071-3, 1999, p. 42.

[36] K. Holmberg, Tribol. Finn. — J. Tribol. 19 (2000) 24.

[37] S. Bull, Tribol. Int. 30 (1997) 491.

[38] E. Zoestbergen, J. De Hosson, Surf. Eng. 18 (2002) 283.

[39] S. Bull, Surf. Coat. Technol. 50 (1991) 25.

[40] J. von Stebut, R. Rezakhanlou, K. Anoun, H. Michel, G. Gantois, Thin

Solid Films 181 (1989) 555.

[41] P. Hedenquist, M. Olsson, S. Jacobson, S. Hogmark, Surf. Coat. Technol.

41 (1990) 31.

[42] M. Larsson, M. Olsson, P. Hedenquist, S. Hogmark, in: Uppsala

University, Sweden, Dr Thesis by M. Larsson, No. 191/1996.

[43] Y. Wang, S. Hsu, P. Jones, Wear 218 (1998) 96.

[44] S. Liu, Q.J. Wang, Surf. Coat. Technol. 201 (2007) 6470.

[45] S. Liu, Q. Wang, G. Liu, Wear 243 (2000) 101.

[46] F. Beremin, Metall. Trans. 14a (1983) 2277.[47] K. Holmberg, H. Ronkainen, A. Laukkanen, K. Wallin, A. Erdemir, O.

Eryilmaz, Wear, in press.


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