Tribological Properties of Graphite-like and Diamond-like c

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Tribology International 37 (2004) 949–956

www.elsevier.com/locate/triboint

Tribological properties of graphite-like and diamond-likecarbon coatings

S.K. Field �, M. Jarratt, D.G. Teer

Teer Coatings Ltd., West Stone House, Berry Hill Industrial Estate, Droitwich, Worcestershire WR9 9AS, UK

Abstract

Two hard, carbon-based solid lubricant coatings, Graphit-iC2 and Dymon-iC2, have been developed which offer considerablebenefits over traditional diamond-like carbon (DLC) coatings. Both have extremely high wear resistance and load-bearing capa-bility, in contrast to many commercial DLCs which tend to be brittle, and very low friction characteristics. The development ofthe coatings is described, and details of their tribological properties in air and water are given. The structure of the coatings hasbeen studied and related to the tribological properties, and the mechanism for the low friction and wear rates is discussed. Thecoatings are proving successful in increasing the lifetime and efficiency of many mechanical parts, including automotive fuel injec-tion components, gears, bearings, tappets, gudgeon pins, etc. They offer benefits for tooling, used for forming or machining ofsoft materials, and are used on dies and moulds. Other application areas include surgical tools and implants.# 2004 Elsevier Ltd. All rights reserved.

Keywords: Friction; Wear; DLC

1. Introduction

As environmental restrictions on the use of lubri-cants grow tighter, and costs associated with disposalincrease, there is increasing demand for solid lubricantcoatings that allow contacting surfaces to rub againstone another with reduced friction and wear. One ofthe most promising candidate coatings is diamond-likecarbon (DLC).However, the term DLC covers a wide range of dif-

ferent carbon-based coatings, that includes amorphousmaterials that contain up to approximately 40 at.%hydrogen (a-C:H) and materials that contain less than1 at.% hydrogen (a-C) [1]. These can be produced bydifferent processes and differ considerably in physicalcharacteristics and tribological performance.Most DLC coatings are hard, and demonstrate low

friction characteristics in comparison to conventionalnitride coatings such as TiN, CrN, etc. Hence, a largeamount of research has been generated on their depo-sition and characterisation, and subsequently the develop-

ment of the material for industrial applications [2].Unfortunately, the current range of applications is lim-ited, as most commercially available DLC coatings sufferfrom poor levels of adhesion, high intrinsic stresses andlow load-bearing capability, i.e. the ability to supportnormal and tangential loads, particularly when depositedon alloy steels.In order to reduce the internal stresses, various

metals have been added. These Me:C coatings aretougher, but are also much softer [3]. The adhesion isbetter [4] but they can be used only at moderately highcontact pressures.Two carbon-based solid lubricant coatings (Graphit-

iC2 and Dymon-iC2) have recently been developedthat are capable of supporting high contact pressureswith excellent tribological properties, whilst protectingcontacting surfaces by providing a low friction transferfilm [5,6].Graphit-iC2 is a hydrogen-free, amorphous, carbon–

chromium coating (a-C) whilst Dymon-iC2 is a hydro-genated, amorphous, carbon coating (a-C:H). Bothcoatings possess very low specific wear rates (typically

� 1� 10�17 m3 N�1 m�1 dry against WC–Co) and lowfriction coefficients (<0.1) and can withstand high con-tact pressures (>3.4 GPa) [6,7].

950 S.K. Field et al. / Tribology International 37 (2004) 949–956

This paper details the tribological properties of both

carbon coatings and gives industrial application exam-

ples for each.

2. Coating development

Graphit-iC2 is deposited by closed field unbalanced

magnetron sputter ion plating [8] from carbon and chro-

mium targets using unbalanced magnetrons in a closed

field arrangement (Fig. 1). The resultant high plasma

density produces a dense, non-crystalline, electrically

conducting carbon coating with sp2 bonding. The hard-

ness is dependent on the deposition parameters, typi-

cally 15–25 GPa but can be over 40 GPa. Using a

chromium interlayer excellent adhesion is achieved. The

coefficient of friction is dependent on the load and coun-

terface material but is generally below 0.1.In the early stages of coating development, pure car-

bon coatings (on top of the Cr adhesion layer) were

deposited. These demonstrated low wear rates (10�17

m3 N�1 m�1) in pin on disc tests with a 5-mm WC–Co

pin, under dry conditions at low and moderate loads

(up to 45 N). However, at higher loads, the wear rate

increased significantly resulting in premature failure.

The tribological properties were improved by co-depos-

iting a small mount of chromium (~5 at.%) during the

coating process. The resultant carbon–chromium com-

posite coating (Graphit-iC2) showed the same low

wear rates at loads up to 140 N, and the low friction

characteristics of the pure carbon. These exceptional

wear properties have enabled the application of this

coating for a wide range of tools and components.Dymon-iC2 is also deposited using a closed field

unbalanced magnetron sputter ion plating system

(Fig. 1) but the process is one of plasma enhanced

chemical vapour deposition using a hydrocarbon gas

precursor. The bias voltage applied to the substrates is

pulsed direct current (DC) but the plasma is further

enhanced by additional radio frequency (RF) electro-

des. This type of system means that upscaling to large

production systems is easy, and also the bias voltage

and ion current to the samples can be independently

controlled so that the deposition parameters can be

optimised to control the coating properties. The hard-

ness is dependent on the deposition parameters and is

typically 12–18 GPa. Again, a chromium layer is used

to give good adhesion to the substrate. The coating is

an amorphous, metal free, hydrogenated carbon coat-

ing with a significant proportion of sp3 bonds. It is

electrically insulating. The coefficient of friction is

slightly less than that of Graphit-iC2 and the wear rate

in dry pin on disc tests using a 5-mm ball with loads as

high as 100 N is 10�17 m3 N�1 m�1 similar to that of

the Graphit-iC2.

3. Structure and physical properties

3.1. Graphit-iC2

The Graphit-iC2 coating structure is generally dense

and amorphous, although high resolution TEM has

detected fine regions of nano-crystalline graphite within

the amorphous carbon matrix. Fig. 2a and b, respect-

ively, represent a transmission electron microscopy sec-

tion and a selected area diffraction pattern from a

standard Graphit-iC2 coating and show that the film is

dense without short range order (broad diffraction

rings).Results from Raman spectroscopy have been difficult

to interpret, but it can be stated that no significant

amount of sp3 bonding has been detected in the coat-

ings and all the evidence indicates that the bonding is

almost entirely sp2. The friction characteristics mea-

sured in the pin on disc test are similar to those of

graphite but the Graphit-iC2 coating is much harder

than graphite and the wear resistance is much higher.Adhesion tests were performed on the Graphit-iC2

coating. The results of a Rockwell C indentation and a

scratch test are presented in Figs. 3a and b, respecti-

vely. There is no evidence of cracking or delamination

of the coating indicating excellent adhesion.

Fig. 1. The closed field unbalanced magnetron sputter ion plating

system (plan view). The arrangement of the magnetron’s polarity clo-

ses the magnetic field and enhances the ion bombardment of the sub-

strates.

S.K. Field et al. / Tribology International 37 (2004) 949–956 951

3.2. Dymon-iC2

The Dymon-iC2 coating has a dense, amorphousstructure. Fig. 4 shows a transmission electronmicroscopy selected area diffraction pattern from astandard Dymon-iC2 coating, and shows that the filmis dense without short range order (broad diffractionrings).Fig. 5a and b, respectively, represent a Rockwell C

indention and the end of a scratch channel performedon the Dymon-iC2 coating. They both indicate thatthe Dymon-iC2 coating was well adhered to the M42substrate with little cracking and no evidence ofadhesive failure.

4. Tribological properties

4.1. Graphit-iC2

4.1.1. Pin on disc tests in airPin on disc tests have been performed at the Univer-

sity of Salford comparing the pure carbon Graphit-iC2 coating, the Cr containing Graphit-iC2 and acommercial DLC (a typical hydrogenated Me:C) [9].Some of these test results are shown in Fig. 6, which

plots the specific wear rate against load for these three

coatings. The large difference in wear rate between the

Graphit-iC2 coatings and the Me:C coatings is appar-

ent as is the increase in the load-bearing capacity of the

multi layer Graphit-iC2 coatings.Further pin on disc tests were performed at Teer

Coatings (using a 5-mm diameter tungsten carbide ball

as the pin and Graphit-iC2 coated M42 plates as the

discs) to study the effect of load on the tribological per-

formance. Fig. 7 shows the typical evolution of the

ig. 2. TEM section (a) and a selected area diffraction pattern (b) from a standard Graphit-iC2 coating [5
F ].
Fig. 3. Rockwell C indentation (a) and scratch test (b) performed on a standard Graphit-iC2 coating.

selected area diffraction pattern fr
Fig. 4. TEM om a standard
Dymon-iC2 coating.


friction coefficient as a function of the sliding time dur-

ing two pin on disc tests performed on the Graphit-

iC2 coating with normal loads of 40 and 80 N.It can be seen that the friction coefficient changes

during the test as might be expected, the rate of change

being greater at the start of the test. At the beginning

of the pin on disc test, the friction coefficient is usually

around 0.15 and decreases (during a running in period)

to reach a steady-state value, typically below 0.07. The

specific wear rate is also much higher at the start of

testing and decreases during the running in period. The

reduction in both of these parameters is usually aided

by the formation of a lubricious transfer layer on the

counter surface (explained in more detail later). The

amount of wear that takes place in the early stages of

testing is related to the relative hardness of the two

rubbing surfaces, and, in dry tests, is thought to be

influenced by the time taken for the transfer layer to

form. The hardness of the Graphit-iC2 coating can be

varied, whilst retaining its low friction characteristics,

to suit different counterfaces and minimise counterface

wear.

Both the friction coefficient and the specific wear rateof the coating depend on the normal load applied dur-ing the pin on disc test. The higher the applied load,the lower the friction coefficient and the specific wearrate. Fig. 7 shows typical results obtained by testing atdifferent loads. The steady-state friction coefficient wasfound to decrease from 0.07 to 0.05 when the load wasincreased from 40 to 80 N, and the specific wear rate ofthe Graphit-iC2 coating was 4:3� 10�17 and 2:1�10�17 m3 N�1 m�1 for 40 and 80 N, respectively.Optical microscopy of the counterpart was performedat different times during the running in period of the 80N pin on disc test. The decrease in friction coefficientappeared to be connected to the formation of a trans-fer layer on the WC–6% Co ball. The size of the trans-fer layer and the amount of debris accumulated on thesliding ball increased with the sliding time and wasfound to be constant as soon as the friction coefficientreached a steady-state value. The decrease in frictioncoefficient during the running in period is a very com-plex phenomenon, as it usually involves a third bodybetween the coating and the sliding counterpart. How-

Fig. 5. Rockwell C indentation (a) and scratch test (b) performed on a Dymon-iC2 coating.

Fig. 6. Comparison of specific wear rates for Graphit-iC2 coatings

and DLC as a function of load.

Fig. 7. Evolution of the friction coefficient as a function of the slid-

ing time using applied normal loads of 40 and 80 N.


ever, possible explanations for the friction behaviourobserved are:

. The normal load applied during the pin on disc testinduces structure transformations at the surface ofthe amorphous Graphit-iC2 coating creating a thinlayer of crystalline graphite at the surface. Duringthe running in period, the re-crystallisation processtakes place at the top surface of the coating andallows the formation of a lubricious graphite-likefilm between the coating and the counterpart. Thehigher the normal load, applied during the pin ondisc test, the greater the level of re-crystallisation atthe top surface of the coating and the lower thesteady-state value of the friction coefficient.

. As the pin on disc test is a unidirectional rubbingtest, the applied normal load encourages there-orientation of the re-crystallised top layers of theGraphit-iC2 coating so that the basal planes areparallel to the sample surface. Higher normal loadsresult in more re-orientation and lower friction coef-ficients. An explanation of this re-orientationphenomenon has been suggested by Yang et al. [10]and more direct evidence will be published shortly.

. Both the phenomena presented previously occursimultaneously and lead to the formation of anorientated lubricious transfer layer on the slidingcounterpart.

The effect of sliding speed on the tribological per-formance has been investigated [10]. At high loads(80 N), the specific wear rate remains low (�3�10�17 m3 N�1 m�1) up to speeds of 400 mm s�1. Test-ing at lower loads increased the maximum sliding speedobtained without significant increase in specific wearrate. At 20 N, the specific wear rate was found to be

below 5� 10�17 m3 N�1 m�1 for speeds up to the limitof the test equipment (1 m s�1). It is thought that theseresults are related to the temperature generated at therubbing surface.

4.1.2. Reciprocating wear tests in de-ionised waterAs Graphit-iC2 is a graphite-like carbon-based coat-

ing, its tribological properties are highly dependent onthe relative percentage of humidity (%RH) of the testatmosphere, the higher the %RH, the lower the frictioncoefficient and the specific wear rate of the coating. Asreported by different authors [11,12], water vapouradsorbed on the top surface of graphite weakens thebonds between the basal planes of its hexagonal struc-ture and gives it good frictional behaviour.Reciprocating wear tests were carried out using a

5-mm tungsten carbide ball against a Graphit-iC2

coated M42 steel plate at loads up to 100 N, under de-ionised water. The cycle time was 2 s and the length of

each pass was 3 mm with constant sliding speed. Fig. 8compares the performance of the Graphit-iC2 coatingwith a standard DLC (Me:C) coating. The Me:C coat-

ing failed after 5400 cycles.The Graphit-iC2 coating showed no sign of failure

after 10,000 cycles when the test was stopped and it

was not possible to detect any measurable wear using aball crater within the wear track.

4.1.3. Pin on disc test in de-ionised waterPin on disc tests were performed at Teer Coatings

using a 5-mm diameter tungsten carbide ball as the pinand Graphit-iC2 coated M42 plates as the discs, in

de-ionised water [13]. The specific wear rate of theGraphit-iC2 coating was found to vary between

1:1� 10�17 and 5:1� 10-17 m3 N�1 m�1 for test loads

between 10 and 80 N. These rates are similar to orbetter than those obtained in dry conditions. Again,

the good tribological properties of Graphit-iC2 underwater can be attributed to water adsorbed on the topsurface of graphite weakening the bonds between the

basal planes of its hexagonal [11,12] as described pre-viously.

4.2. Dymon-iC2

4.2.1. Pin on disc tests in airFig. 9 shows the evolution of the friction coefficient

as a function of the sliding distance using applied nor-mal loads of 20, 40, 60, 80 and 100 N.The initial value of the friction coefficient for all the

‘static-start’ pin on disc tests was between 0.1 and 0.15.The rate of decrease, the steady-state friction coefficient

and the specific wear rate of the coating were foundto be dependent on the load. The greater the normalload the faster the decrease, the lower the steady-

state friction coefficient and the lower the specificwear rate. The steady-state friction coefficient and

the specific wear rate ranged from 0:07 and 2:5�10�17 m3 N�1 m�1, respectively for 20 N (contact

Fig. 8. Reciprocating wear test of 100 N of Graphit-iC2 and DLC

in de-ionised water.


pressure �1 GPa) to 0.02 and 9:8� 10�18 m3 N�1 m�1,respectively for 100 N (contact pressure �3:5 GPa).Dymon-iC2 is a metastable hydrogenated amorph-

ous carbon (a-C:H) coating which contains a mixtureof sp2 and sp3 bonds. It has been reported by differentauthors [14,15] that the low friction coefficient of a-C:H coatings can be attributed to the formation of alubricious graphite-like transfer layer formed duringsliding between the counterpart and the coating. Theformation of this tribo-layer is believed to come fromthe release of hydrogen from the coating surface duringsliding due to friction-induced localised annealing atcontact asperities, which destabilise the sp3 bonds [16].In our case, the increase of the normal load during

the pin on disc tests should increase the contact tem-perature between the ball and the coating and conse-quently increase the desorption rate of hydrogen fromthe surface. Thus, the higher the normal load, the fas-ter the formation of the graphite-like lubricious layerand the faster the decrease of the friction coefficient toits steady-state value. The faster formation of the pro-tective graphite-like layer between the ball and thecoating also explains the decrease of its specific wearrate as the normal load is increased.The effect of sliding speed on the friction and specific

wear rate of the Dymon-iC2 coating has also beeninvestigated [6]. Dymon-iC2 was tested using an 80-Nload and linear sliding speeds of 0.1, 0.2, 0.3, 0.4, 0.5and 0.6 m s�1 for a distance of 720 m with 5-mm diam-eter WC–6% Co pin.The rate of decrease of the coefficient of friction was

similar for all sliding speeds tested. The steady-statecoefficient of friction was reached within the first 100 mand showed a slight trend towards lower values withthe sliding speed, ranging from 0.04 for a sliding speedof 0.1 m s�1 and 0.03 for 0.6 m s�1. The specific wear

rate showed no obvious correlation with sliding speed

and was in the range �1:2 1:6� 10�17 m3 N�1 m�1.

Optical microscopic analysis of the countersurface pin

showed a similar amount of transfer material on the

pin, in and ahead of the contact area. The majority was

easily removed, but a small amount remained in the

contact area. Only slight smoothing of the outermost

peaks of the surface roughness was observed on the pin

for all sliding speeds, indicating that the transfer layer

had protected the contacting surface. In further tests,

counterface wear measurements taken after pin on disc

testing [13] showed lower wear of WC/Co surfaces tes-

ted against Dymon-iC2 than for those tested against

Graphit-iC2.The authors intend to investigate the surface of the

coating after rubbing to determine whether the applied

normal load encourages the graphitisation and re-

orientation of the top layers of the Dymon-iC2 coating

as suggested by Yang et al. [10] to explain the low fric-

tion of Graphit-iC2.The wear rate and friction coefficient of Dymon-iC2

when tested under water is greatly increased in com-

parison to testing in dry conditions. This is in contrast

to Graphit-iC2, which performs well under water. A

possible explanation for the poorer performance of

Dymon-iC2 could be that the presence of water

restricts the formation of the transfer layer. Although

Gardos [17] has attributed the increase of the friction

coefficient of hydrogenated DLC films in humid air to

the increase in the van der Waals bond strength of

hydrogen bonding to adsorbed water molecules (~5

kcal mol�1) compared to the bonding of hydrocarbons

(~2 kcal mol�1).

the friction coefficient as a function of the sliding distance using applied normal loads equal to 20,
Fig. 9. Evolution of 40, 60, 80 and 100 N.


5. Application examples

Both Graphit-iC2 and Dymon-iC2 have extremelylow specific wear rates, very low friction coefficientsand are capable of sustaining loads much higher thanpreviously reported DLCs. These properties make bothcoatings suitable for a wide range of applications. Inparticular, the coatings offer the potential to protectmechanical parts, increasing their life or efficiency, orboth. The coatings perform well under oil and offersimilar protection to parts when dry, negating the needfor the use of lubricants in many cases, or offering pro-tection during start-up, shut-down and periods of fluidstarvation.

5.1. Graphit-iC2

5.1.1. Engine components/machineryGraphit-iC2 coatings are now in full production to

provide wear protection and lubrication for compo-nents used in fuel injection systems. Further applica-tions include heavily loaded automobile parts such asgudgeon pins, cam followers, gears and bearings, whereearly tests have indicated that the coating has greatpotential. Graphit-iC2 is also being used in the textileindustry to prevent fretting wear of chuck bodies.

5.1.2. Medical applicationsGraphit-iC2 coatings are being developed and tested

for use in artificial hip joints. They have shown topresent no bio-compatibility problems. The very lowwear rate of ~10�18 m3 N�1 m�1 found in pin on disctests for coated CoCr compares to a rate of ~10�15 m3

N�1 m�1 found for uncoated CoCr [18]. The uncoatedhip joints are claimed to have a useful life of around12–15 years, whereas the wear rates obtained for theGraphit-iC2 coating suggest that this could beextended to over 50 years. Other medical applicationsinclude medical tools such as bone cutting saws andbroaches, and dental instruments.

5.1.3. Drilling test resultsThe best drilling results for Graphit-iC2 have been

obtained when drilling aluminium alloy without lubri-cant. Typical results are given in Table 1, which com-pares the number of holes drilled before drill failure,for coated and uncoated drills, for two different feedrates. The drill was deemed to have failed when thespindle load reached a set limit determined fromexperience. It can be seen that the Graphit-iC2 coateddrill has given an improvement of almost seven timesover an uncoated drill using a feed rate of 0.127 mm/rev and an improvement of almost three times for afeed rate of 0.191 mm/rev.Further drilling results for the Graphit-iC2 coating

have been published previously [19].

5.2. Dymon-iC2

The Dymon-iC2 coating is currently in productionfor use in the unlubricated cold forming of tin, wherecontact pressures of around 2 GPa are reached. Thecoating was selected after dry cold forming simulationsshowed little metal build-up on the coated surface dur-ing testing, and a low friction coefficient of 0.1–0.2 incomparison to 0.4–0.7 for uncoated WC–Co tools. Fulldetails of the test and the results are given elsewhere,including similar results for aluminium alloy and stain-less steel [20]. As the use of lightweight alloys becomespredominant in industry, the number of forming appli-cations is expected to increase.Other examples of current applications are CD/

DVD stamper blocks, pick and place nozzles for theelectronics industry, moulds for the medical industryand automotive/aerospace parts that require protec-tion against fretting wear.

6. Conclusions

The new solid lubricant coatings Graphit-iC2 andDymon-iC2 offer many advantages over previous solidlubricant coatings because of their good adhesion,hardness, wear resistance and load-bearing capability.They also have many advantages over conventionalhard coatings because of their low friction and lubri-cating properties.As a result of these tribological properties, the coat-

ings are currently in use in a wide range of applicationsincluding cutting and forming tools. They have alsobeen shown to have considerable potential in heavilyloaded applications, such as gears and engine partswhere coatings have previously found little or no suc-cess.

References

[1] Fontaine J, Donnet C, Grill A, Le Mogne T. Tribochemistry

between hydrogen and diamond-like carbon films. Surface and

Coatings Technology 2001;146–147:286.

[2] Matthews A, Eskildsen SS. Engineering applications for dia-

mond-like carbon. Diamond and Related Materials 1994;3(4–6):

902–11.

Table 1

Drilling test results, workpiece Al 6% Si 3.5% Cu alloy (319 series),

1/400 diameter drills, blind holes 3/4 mm deep

Drill type U
ncoated Graphit-iC2
3055 rpm, feed rate 0.127 mm/rev

Number of holes drilled before drill failure. 1
27 867
3055 rpm, feed rate 0.191 mm/rev

Number of holes drilled before drill failure.
40 110


[3] Aisenberg S, Chabot R. Ion-beam deposition of thin films of

diamondlike carbon. Journal of Applied Physics 1971;42:2953.

[4] Monaghan D, Teer DG, Logan PA, Efeoglu I, Arnell RD.

Deposition of wear resistant coatings based on diamond like

carbon by unbalanced magnetron sputtering. Surface and

Coatings Technology 1993;60:525.

[5] Yang S, Camino D, Jones AHS, Teer DG. Deposition and

tribological behaviour of sputtered carbon hard coatings.

Surface and Coatings Technology 2000;124:110.

[6] Jarratt M, Stallard J, Renevier NM, Teer DG. An improved

diamond-like carbon coating with exceptional wear properties.

Diamond and Related Materials 2003;12(3–7):1003–7.

[7] Yang S, Teer DG. Investigation of sputtered carbon and

carbon/chromium multi-layered coatings. Surface and Coatings

Technology 2000;131:412.

[8] Teer DG. Magnetron ion plating, UK Patent No. GB 2 258

343B.

[9] Jones AHS, Camino D, Jiang J, Teer DG. Novel high wear

resistant diamond-like carbon coatings deposited by magnetron

sputtering of carbon targets. Journal of Engineering Tribology

1998;212:301–6.

[10] Yang S, Li X, Renevier NM, Teer DG. Tribological properties

and wear mechanism of sputtered C/Cr coating. Surface and

Coatings Technology 2001;142–144:85–93.

[11] Savage RH. Graphite lubrication. Journal of Applied Physics

1948;19:1–10.

[12] Deacon RF, Goodman JF. Lubrication by lamellar solids. Wear

1958;243A:464–82.

[13] Stallard J, Mercs D, Jarratt M, Wilbur P, Teer DG, Shipway

PH. A Study of the tribological behaviour of three carbon-based

coatings, tested in air, water and oil environments at high loads.

Surface and Coatings Technology 2004;177–178:545–51.

[14] Liu Y, Erdemir A, Meletis EI. An investigation of the relation-

ship between graphitization and frictional behavior of DLC

coatings. Surface and Coatings Technology 1996;86–87:564.

[15] Erdemir A, Bindal C, Pagan J, Wilbur P. Characterization of

transfer layers on steel surfaces sliding against diamond-like

hydrocarbon films in dry nitrogen. Surface and Coatings Tech-

nology 1995;76–77:559.

[16] Liu Y, Erdemir A, Meletis EI. A study of the wear mechanism

of diamond-like carbon films. Surface and Coatings Technology

1996;82:48–56.

[17] Gardos MN. In: Spear KE, Dismukes JP, editors. Synthetic dia-

mond: emerging CVD science and technology. New York: John

Wiley & Sons, Inc; 1994, p. 419.

[18] Streicher RM, Semlitsch M, Schon R, Weber H, Rieker C.

In: Dowson D (ed.) Advances in Medical Tribology. London:

M. E. P. Ltd.; 1998, p. 83–92.

[19] Fox V, Jones A, Renevier NM, Teer DG. Hard lubricating coat-

ings for cutting and forming tools and mechanical components.

Surface and Coatings Technology 2000;125:347.

[20] Renevier NM, Poulat S, Jarratt M, Teer DG. New unidirec-

tional single pass procedure using wear tester equipment for

assessment of suitable coatings and other materials for forming

operations. ICMCTF 2002, San Diego, CA, USA, 22–26 April

2002.

Documents

Tribological Properties of Graphite-like and Diamond-like c