Diamond-like Carbon (DLC) coatings represent an interesting research subject for various groups of
researchers having interests in surfaces tribology and corrosion. This paper discusses issues relating to the
friction and mechanical behaviour, for 4 types of DLC coating systems deposited on heat treatable steel
hardened and high-tempered (a multilayer of WC/C (a-C:H:W); CrC+a-C:H, a single layer of a-C:H, plasma
nitriding + Si doped DLC (PN+Si-a-C:H). These films were synthesized using a single or a combined
process consisting in either r. f. reactive magnetron sputtering or/followed by Plasma Assisted Chemical
Vapour Deposition (PACVD). The tribological properties (friction coefficient) were obtained and discussed
in correlation with the mechanical properties (the adherence, the nanoindentation hardness) and thickness
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3491

Cojocariu, C.

Costinescu, L.

Marin, A.

Munteanu, D.

SocioEconomic Challenges Journal (Sumy State University)

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES 
Vol. 1 No 2, 02NFC26(4pp) (2012) 
 
 
2304-1862/2012/1(2)02NFC26(4) 02NFC26-1  2012 Sumy State University 
Performant DLC Films with Enhanced Wear Resistance 
 
L. Costinescu, C. Cojocariu, A. Marin, D. Munteanu 
 
 Department of Materials Science and Engineering, “Transilvania” University, 500036 Brasov, Romania 
 
(Received 23 June 2012; revised manuscript received 21 July 2012; published online 10 August 2012) 
 
 Diamond-like Carbon (DLC)  coatings represent an interesting research subject for various groups of 
researchers having interests in surfaces tribology and corrosion. This paper discusses issues relating to the 
friction  and mechanical behaviour, for 4 types of  DLC coating systems deposited on heat treatable steel 
hardened and high-tempered (a multilayer of WC/C (a-C:H:W); CrC+a-C:H, a single layer of a-C:H,  plas-
ma nitriding + Si doped DLC (PN+Si-a-C:H). These films were synthesized using  a single or a combined 
process consisting in either r. f. reactive magnetron sputtering or/followed by Plasma Assisted Chemical 
Vapour Deposition (PACVD). The tribological properties (friction coefficient) were obtained and discussed 
in correlation with the mechanical properties (the adherence, the nanoindentation hardness) and thickness 
 
Keywords: Diamond-like carbon (DLC), Tribological properties, Hardness, Adherence. 
 
  PACS numbers: 81.05.Uw, 81.40.Pq 
 
 
1. INTRODUCTION 
 
The diamond-like carbon (DLC) coatings have been 
developed for a wide range of technological and indus-
trial applications.  It is a tribological coating used 
mainly in the field of mechanical engineering in order 
to reduce friction and wear, such as drilling and cutting 
tools [1-3]. 
In recent years,diamond-like carbon (DLC) films 
have  attracted widespread attention due to their ex-
treme characteristics of high hardness, chemical inert-
ness, low friction coefficient, good wear resistance, 
thermal conductivity,and high transparency across a 
large part of the electromagnetic wave spectrum [4-7]. 
In mechanical engineering, low friction signifies a 
lower loss of energy, higher reliability and a better 
wear resistance [8]. However, these films have a prob-
lem; they may easy peel off from the substrate in cer-
tain situations involving friction. The failure of the film 
is related to a bad adhesion to the substrates, and other 
characteristics of the film itself, for instance internal 
stresses, hardness, surface roughness, topography and 
elastic modulus. In order to overcome this problem and 
improve the mechanical and tribological behavior of the 
films according to various requirements, different inter-
layer systems have been proposed. The deposition of 
interlayers such as titanium, silicon, chromium, CrN or 
tungsten, have been developed to enhance the adhesion 
on metal substrates, compositionally graded coatings 
have been deposited to minimize the stress concentra-
tion and improve the coating adhesion , and also duplex 
process including diffusion treatments previous to the 
coating have been proposed. Plasma nitriding of a steel 
substrate is a good possibility because it improves the 
tribological behavior,increases the load capability of the 
coating and extends its lifetime. But the characteristics 
of the nitride interlayer are very important because 
they can influence not only the adhesion but also the 
mechanical behavior of the system, for example, the 
presence of a compound layer may deteriorate the load 
bearing capacity in low alloyed steels . Also in stainless 
steels, a top porous and brittle nitrided layer affects the 
adhesion and it is necessary to remove it prior to the 
DLC deposition [9]. 
DLC films may be produced by a great number of 
deposition techniques such as plasma-assisted chemical 
vapor deposition (PACVD) through a hydrocarbon  dis-
charge, sputtering of agraphite target, arc-discharge, 
pulsed laser deposition (PLD), and ion-beam 
assisted deposition (IBAD) [10,11]. 
Different types of DLC coatings have different me-
chanical and electrical properties, depending mainly on 
the type of deposition. The tribological properties of 
DLC coatings do not depend only on the type of coating, 
but also on the working conditions or contact parame-
ters. For this reason the coefficient of friction depends 
on the coating's thermal stability, which is subject to 
the structure, as well as on the atmosphere in which 
the coating is operating. A very important factor in 
DLC coating performance is also the humidity and the 
type of gas in which a coating is operating. DLC coat-
ings with hydrogen content show a very low friction in 
dry air of about 0.05. The increase of humidity results 
in the increase of the coefficient of friction and at hu-
midity over 90%, friction shows values from 0.15 to 0.3 . 
On the other hand, for the amorphous carbon (a-C), the 
coefficient of friction decreases with the increase in the 
relative humidity [8]  
However, the tribological properties of diamond-like 
carbon coatings change significantly with the change in 
environment as in vacuum, in room atmosphere [12], 
and in different relative humidity [13, 14, 15]. 
The doping of DLC coating with different metals 
(Ti, Nb, Ta,Cr, Mo, W, Ru, Fe, Co, Ni, Al, Cu in Ag) 
leads to the changes in their mechanical properties 
(lower internal stress and hardness, improved adhe-
sion) as well as in their tribological properties [8]. 
The W–DLC coating, which was a WC doped hydro-
genated diamond-like carbon coating with a multilayer 
structure of WC and a-C:H, was deposited in a reactive 
sputtering process at a deposition temperature of ~ 
230 °C. The undoped a-C:H coating was deposited by a 
commercial plasma-assisted chemical vapour deposi-
tion (PACVD) process with a deposition temperature of 
~200 °C. A thin (≈0.1 μm) intermediate Cr layer was 
used for all coatings in order to improve the adhesion. 
 L. COSTINESCU, C. COJOCARIU, A. MARIN, D. MUNTEANU PROC. NAP 1, 02NFC26 (2012) 
 
 
02NFC26-2 
The doped and undoped DLC coatings were about 2 μm 
thick and had a hardness of 1200 HV and 2000 HV re-
spectively [8]. 
Nanoindentation and nanoscratch tests were per-
formed for diamond-like carbon (DLC) coatings on the 
different steel substrates in order to investigate the 
deformation and failure behaviors of the coat-
ing/substrate systems and their tribological properties 
[1]. 
Staedler and Schiffmann have systematically inves-
tigated the correlation of nanomechanical and na-
notribological behaviors of thin DLC coatings on differ-
ent substrates (AlTiC, Si(100), fused silica, SU8 photo-
resist) using nanoindentation and nanoscratch tech-
niques. The substrates cover the range of very soft 
(SU8 photoresist) up to very hard (AlTiC ceramic) ma-
terials showing a clear influence on the tribological 
response of the DLC/substrates. Therefore, the primary 
focus of the research is to investigate the mechanical 
and tribological properties of DLC coatings on different 
steel substrates in order to gain a better understanding 
of the predominant deformation mechanisms that oc-
curred in response to nanoindentation and nanoscratch 
and further choosing the ideal steel substrate [1]. 
In this paper nanoindentation and nanoscratch 
tests were performed for diamond-like carbon (DLC) 
coatings on the single steel substrate in order to inves-
tigate their mechanical and tribological properties.  
 
2. EXPERIMENTAL PROCEDURE 
 
Physical vapour deposited (PVD) diamond-like car-
bon (DLC) coatings have been well known for their ex-
cellent tribological properties with low friction [16]. 
Recent reports showed that properties of DLC can be 
favourably influenced by doping with ceramic com-
pounds. The tungsten carbide/carbon (WC/C) coating is 
a WC-doped hydrogenated DLC coating (Me-C:H), 
which contains W in the diamond-like amorphous-
hydrogenated-carbon matrix (a-C:H). The WC/C coat-
ings usually show low friction, high wear resistance 
and good adhesion, and thus are particularly suitable 
for friction reduction, structural and engineering appli-
cations. Moreover, the low deposition temperature 
(lower than 200 ◦C) makes it possible for WC/C coatings 
to be deposited on lots of materials. Thus, the WC/C 
coatings are gaining considerable scientific and indus-
trial interest [17]. Most experimental studies and re-
ports so far about WC/C coatings have been on the dep-
osition techniques and mechanical characterizations 
[18], but the general tribological properties of such 
coatings are beginning to get more attention. 
The enhanced sputtering process is combined with 
PACVD in order to apply carbon-containing multi-
functional coatings such as DLC (CrC+a-C:H). A 
hard, tough metal layer is deposited by sputtering, and 
PACVD is used to build up the tribologically effective 
carbon coating on top of it. In contrast to conventional 
combination coatings, multifunctional coatings are 
made in a single process that yields homogeneous, de-
fect-free coatings of uniquely high quality and adhesion 
strength. 
In the present study, the CSM Nano Indentation 
Tester (Nano Hardness Tester: NHT) has been used to 
evaluate Hardness and elastic modulus of the DLC 
films. Indentations were made by using a Berkovich 
diamond tip.  
A typical indentation experiment consists of seven 
subsequent segments: approaching the surface; deter-
mining the contact point; loading to the peak load; 
holding the tip for 10 s at the peak load; unloading 90% 
of peak load; holding the tip for 100 s at 10% of the 
peak load for thermal drift correction; and finally un-
loading completely [1]. 
The hardness and elastic modulus were obtained 
from the curves using Oliver–Pharr method. The hard-
ness was measured continuously during the indenta-
tion, with the continuous stiffness measurement (CSM) 
technique employed. 
In the scratch testing, a diamond tip was pulled 
over the coated surface with continuously increasing 
normal load from 1 N to 30 N. The diamond tip was a 
Rockwell 100C6 diamond with a 1200 cone and a 100 
µm radius spherical tip. The loading rate was 43 N/min 
and the loading speed was 6 mm/min and the scratch 
length was 4 mm. The remaining groove depth and 
width was measured by surface profilometry and the 
information was used for modeling work [19]. 
The scratch test procedure is described in more de-
tail in the European Standard prEN 1071-3. An optical 
microscopy examination was carried out for the coat-
ings after scratch testing and the typical crack behavior 
was recorded [20].  
A ball-on-disk tribo-meter (CSEM Instrument) was 
used  to measure the coefficient of friction μ or the wear 
behaviour of surfaces.   
The tribological tests were performed in dry air. A 6 
mm diameter SiC ball was used as the mating materi-
al. The 10 N loads were used, respectively, on the ball 
for measurements. The sliding speed was kept in 7.85 
[cm/s] for a fixed sliding contact cycle of 1500.0 [lap]. 
Ambient temperature in the chamber was controlled 
between 23 and 24 0C. The friction coefficient of the 
films was continuously recorded during the test. 
 
3. RESULTS  AND DISCUSSION 
 
Ten indentations were made on each sample at the 
same condition and the results are presented in the fig. 
1. The hardness was measured continuously during the 
indentation. 
 The ratio of hardness to modulus is related to wear 
resistance, the higher the ratio is, the better the wear 
resistance is. It is found that element Cr improves the 
hardness, the modulus and the roughness, but reduces 
the wear resistance [21]. 
As shown in fig.1 CrC/DLC has good hardness end 
modulus  values. 
For the (PN / Si-a-C:H), the lower coefficients of 
the elastic modulus are found for the films that had 
highest Si (at.%) incorporation. An increase in Si con-
tent in DLC could reduce the coefficient of elastic mod-
ulus but grows the ratio of hardness. 
 
 PERFORMANT DLC FILMS WITH ENHANCED WEAR RESISTANCE PROC. NAP 1, 02NFC26 (2012) 
 
 
02NFC26-3 
 
 
Fig. 1 – The nanoindentation results with ten separate in-
dents for the four samples 
 
Although it has good properties of hardness and 
modulus of elasticity fig. 2 shows that CrC/DLC has a 
high coefficient of friction. 
When sliding against pure titanium, the WC/C coat-
ing exhibited mild wear and small tendency to pick up 
counter material in both the sliding conditions. The 
good anti-adhesion properties of the WC/C coating in 
sliding contact with pure titanium can be attributed to 
the low chemical affinity of the WC/C coating for tita-
nium material and the graphitization of the WC/C coat-
ing surface with formation of a protective graphite 
transfer film on the counterpart which had positive 
effect on the coefficient of friction and wear resistance 
of the friction pair. The WC/C coating with good anti-
adhesion properties is potential candidate in the fields 
of the tribological applications related to titanium ma-
terial which usually has poor tribological characteris-
tics because of the adhesion [16]. 
The DLC film with a Si interlayer shows a low fric-
tion coefficient. This result reveals that the adhesion 
between the DLC film and the substrate is improved by 
the Si interlayer. Furthermore, a segment-structured 
DLC film shows a low friction coefficient until 12.000 
revolutions, which is twice as many revolutions as the 
continuous film. This result led us to the conclusion that 
the fracture of the DLC film can be successfully avoided 
by applying segment structuring. Additionally, abrasive 
wear seems to be decreased because the debris were 
trapped in the spaces between segments, and the frac-
ture of the film was stopped by the gaps between seg-
ments [22]. 
In the case of (PN / Si-a-C:H), the lower coefficients 
of friction are found for the films that had highest Si 
(at.%) incorporation. An increase in Si content in DLC 
could reduce the coefficient of friction due to accelera-
tion of tribo-chemical reactions [23].  
Si incorporation has been widely studied and is re-
ported as being effective in reducing friction coefficients 
in ambient humid air with only limited deterioration of 
the wear resistance [24].  
The adhesion of the coatings was determined using 
the conventional scratch-test method [20], which 
showed that the LC2 (first crack) value was comparable 
for all coatings, as can be seen in Fig. 3. 
The scratching curve in Fig. 4 was used to study the 
behavior of DLC coatings during the loading process 
 
 
 
Fig. 2 – Different frictions behaviour of DLC films at the same 
load 
 
 
    
             CrC / a-C:H                                        WC / C 
   
              Si / DLC                                               DLC 
 
Fig. 3 – The first crack, the LC2 value, for coating types 
 
 
Fig. 4 – Scratch penetration depth as a function of progres-
sively applied normal load 
 
There are many papers reporting the friction and wear 
performance, certain DLC films are very soft  and easily 
scratch able, while others show pretty hard and resistant 
to wear. On another hand, if the coating only cracked in a 
roughly semicircular arc along the scratch without peeling 
off, the adherence was considered good [25]. 
 L. COSTINESCU, C. COJOCARIU, A. MARIN, D. MUNTEANU PROC. NAP 1, 02NFC26 (2012) 
 
 
02NFC26-4 
An optical microscopy examination was carried out 
for the coatings after scratch testing and the typical 
crack behaviour was recorded. The first cracks ap-
peared for the all coating types as angular cracks on 
the edges of the scratch grooves [19], similarly to what 
is shown in Fig. 3. 
According to data represented in fig. 4 WC / C have 
the best adherence of all samples analyzed. 
 
4. CONCLUSION 
 
The nanoindentation /scratch technique can provide 
us very useful information about the elastic modulus, 
hardness, friction and wear properties. 
It is found that element Cr improves the hardness, 
the modulus and the roughness, but reduces the wear 
resistance. 
An increase in Si content in DLC could reduce the 
coefficient of elastic modulus but grows the ratio of 
hardness. 
 
ACKNOWLEDGMENTS 
 
This paper is supported by the Sectoral Operational 
Programme Human Resources Development (SOP 
HRD), ID76945 financed from the European Social 
Fund and by the Romanian Government. 
 
 
 
REFERENCES 
 
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4. J. Robertson, Mater. Sci. Eng. R37 129 (2002). 
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Performant DLC Films with Enhanced Wear Resistance

Electronic Sumy State University Institutional Repository

PROCEEDINGS OF THE INTERNATIONAL CONFERENCE NANOMATERIALS: APPLICATIONS AND PROPERTIES Vol. 1 No 2, 02NFC26(4pp) (2012)   2304-1862/2012/1(2)02NFC26(4) 02NFC26-1  2012 Sumy State University Performant DLC Films with Enhanced Wear Resistance  L. Costinescu, C. Cojocariu, A. Marin, D. Munteanu   Department of Materials Science and Engineering, “Transilvania” University, 500036 Brasov, Romania  (Received 23 June 2012; revised manuscript received 21 July 2012; published online 10 August 2012)   Diamond-like Carbon (DLC)  coatings represent an interesting research subject for various groups of researchers having interests in surfaces tribology and corrosion. This paper discusses issues relating to the friction  and mechanical behaviour, for 4 types of  DLC coating systems deposited on heat treatable steel hardened and high-tempered (a multilayer of WC/C (a-C:H:W); CrC+a-C:H, a single layer of a-C:H,  plas-ma nitriding + Si doped DLC (PN+Si-a-C:H). These films were synthesized using  a single or a combined process consisting in either r. f. reactive magnetron sputtering or/followed by Plasma Assisted Chemical Vapour Deposition (PACVD). The tribological properties (friction coefficient) were obtained and discussed in correlation with the mechanical properties (the adherence, the nanoindentation hardness) and thickness  Keywords: Diamond-like carbon (DLC), Tribological properties, Hardness, Adherence.    PACS numbers: 81.05.Uw, 81.40.Pq   1. INTRODUCTION  The diamond-like carbon (DLC) coatings have been developed for a wide range of technological and indus-trial applications.  It is a tribological coating used mainly in the field of mechanical engineering in order to reduce friction and wear, such as drilling and cutting tools [1-3]. In recent years,diamond-like carbon (DLC) ﬁlms have  attracted widespread attention due to their ex-treme characteristics of high hardness, chemical inert-ness, low friction coefﬁcient, good wear resistance, thermal conductivity,and high transparency across a large part of the electromagnetic wave spectrum [4-7]. In mechanical engineering, low friction signifies a lower loss of energy, higher reliability and a better wear resistance [8]. However, these films have a prob-lem; they may easy peel off from the substrate in cer-tain situations involving friction. The failure of the film is related to a bad adhesion to the substrates, and other characteristics of the film itself, for instance internal stresses, hardness, surface roughness, topography and elastic modulus. In order to overcome this problem and improve the mechanical and tribological behavior of the films according to various requirements, different inter-layer systems have been proposed. The deposition of interlayers such as titanium, silicon, chromium, CrN or tungsten, have been developed to enhance the adhesion on metal substrates, compositionally graded coatings have been deposited to minimize the stress concentra-tion and improve the coating adhesion , and also duplex process including diffusion treatments previous to the coating have been proposed. Plasma nitriding of a steel substrate is a good possibility because it improves the tribological behavior,increases the load capability of the coating and extends its lifetime. But the characteristics of the nitride interlayer are very important because they can influence not only the adhesion but also the mechanical behavior of the system, for example, the presence of a compound layer may deteriorate the load bearing capacity in low alloyed steels . Also in stainless steels, a top porous and brittle nitrided layer affects the adhesion and it is necessary to remove it prior to the DLC deposition [9]. DLC ﬁlms may be produced by a great number of deposition techniques such as plasma-assisted chemical vapor deposition (PACVD) through a hydrocarbon  dis-charge, sputtering of agraphite target, arc-discharge, pulsed laser deposition (PLD), and ion-beam assisted deposition (IBAD) [10,11]. Different types of DLC coatings have different me-chanical and electrical properties, depending mainly on the type of deposition. The tribological properties of DLC coatings do not depend only on the type of coating, but also on the working conditions or contact parame-ters. For this reason the coefficient of friction depends on the coating's thermal stability, which is subject to the structure, as well as on the atmosphere in which the coating is operating. A very important factor in DLC coating performance is also the humidity and the type of gas in which a coating is operating. DLC coat-ings with hydrogen content show a very low friction in dry air of about 0.05. The increase of humidity results in the increase of the coefficient of friction and at hu-midity over 90%, friction shows values from 0.15 to 0.3 . On the other hand, for the amorphous carbon (a-C), the coefficient of friction decreases with the increase in the relative humidity [8]  However, the tribological properties of diamond-like carbon coatings change signiﬁcantly with the change in environment as in vacuum, in room atmosphere [12], and in different relative humidity [13, 14, 15]. The doping of DLC coating with different metals (Ti, Nb, Ta,Cr, Mo, W, Ru, Fe, Co, Ni, Al, Cu in Ag) leads to the changes in their mechanical properties (lower internal stress and hardness, improved adhe-sion) as well as in their tribological properties [8]. The W–DLC coating, which was a WC doped hydro-genated diamond-like carbon coating with a multilayer structure of WC and a-C:H, was deposited in a reactive sputtering process at a deposition temperature of ~ 230 °C. The undoped a-C:H coating was deposited by a commercial plasma-assisted chemical vapour deposi-tion (PACVD) process with a deposition temperature of ~200 °C. A thin (≈0.1 μm) intermediate Cr layer was used for all coatings in order to improve the adhesion.  L. COSTINESCU, C. COJOCARIU, A. MARIN, D. MUNTEANU PROC. NAP 1, 02NFC26 (2012)   02NFC26-2 The doped and undoped DLC coatings were about 2 μm thick and had a hardness of 1200 HV and 2000 HV re-spectively [8]. Nanoindentation and nanoscratch tests were per-formed for diamond-like carbon (DLC) coatings on the different steel substrates in order to investigate the deformation and failure behaviors of the coat-ing/substrate systems and their tribological properties [1]. Staedler and Schiffmann have systematically inves-tigated the correlation of nanomechanical and na-notribological behaviors of thin DLC coatings on differ-ent substrates (AlTiC, Si(100), fused silica, SU8 photo-resist) using nanoindentation and nanoscratch tech-niques. The substrates cover the range of very soft (SU8 photoresist) up to very hard (AlTiC ceramic) ma-terials showing a clear influence on the tribological response of the DLC/substrates. Therefore, the primary focus of the research is to investigate the mechanical and tribological properties of DLC coatings on different steel substrates in order to gain a better understanding of the predominant deformation mechanisms that oc-curred in response to nanoindentation and nanoscratch and further choosing the ideal steel substrate [1]. In this paper nanoindentation and nanoscratch tests were performed for diamond-like carbon (DLC) coatings on the single steel substrate in order to inves-tigate their mechanical and tribological properties.   2. EXPERIMENTAL PROCEDURE  Physical vapour deposited (PVD) diamond-like car-bon (DLC) coatings have been well known for their ex-cellent tribological properties with low friction [16]. Recent reports showed that properties of DLC can be favourably influenced by doping with ceramic com-pounds. The tungsten carbide/carbon (WC/C) coating is a WC-doped hydrogenated DLC coating (Me-C:H), which contains W in the diamond-like amorphous-hydrogenated-carbon matrix (a-C:H). The WC/C coat-ings usually show low friction, high wear resistance and good adhesion, and thus are particularly suitable for friction reduction, structural and engineering appli-cations. Moreover, the low deposition temperature (lower than 200 ◦C) makes it possible for WC/C coatings to be deposited on lots of materials. Thus, the WC/C coatings are gaining considerable scientific and indus-trial interest [17]. Most experimental studies and re-ports so far about WC/C coatings have been on the dep-osition techniques and mechanical characterizations [18], but the general tribological properties of such coatings are beginning to get more attention. The enhanced sputtering process is combined with PACVD in order to apply carbon-containing multi-functional coatings such as DLC (CrC+a-C:H). A hard, tough metal layer is deposited by sputtering, and PACVD is used to build up the tribologically effective carbon coating on top of it. In contrast to conventional combination coatings, multifunctional coatings are made in a single process that yields homogeneous, de-fect-free coatings of uniquely high quality and adhesion strength. In the present study, the CSM Nano Indentation Tester (Nano Hardness Tester: NHT) has been used to evaluate Hardness and elastic modulus of the DLC films. Indentations were made by using a Berkovich diamond tip.  A typical indentation experiment consists of seven subsequent segments: approaching the surface; deter-mining the contact point; loading to the peak load; holding the tip for 10 s at the peak load; unloading 90% of peak load; holding the tip for 100 s at 10% of the peak load for thermal drift correction; and finally un-loading completely [1]. The hardness and elastic modulus were obtained from the curves using Oliver–Pharr method. The hard-ness was measured continuously during the indenta-tion, with the continuous stiffness measurement (CSM) technique employed. In the scratch testing, a diamond tip was pulled over the coated surface with continuously increasing normal load from 1 N to 30 N. The diamond tip was a Rockwell 100C6 diamond with a 1200 cone and a 100 µm radius spherical tip. The loading rate was 43 N/min and the loading speed was 6 mm/min and the scratch length was 4 mm. The remaining groove depth and width was measured by surface profilometry and the information was used for modeling work [19]. The scratch test procedure is described in more de-tail in the European Standard prEN 1071-3. An optical microscopy examination was carried out for the coat-ings after scratch testing and the typical crack behavior was recorded [20].  A ball-on-disk tribo-meter (CSEM Instrument) was used  to measure the coefficient of friction μ or the wear behaviour of surfaces.   The tribological tests were performed in dry air. A 6 mm diameter SiC ball was used as the mating materi-al. The 10 N loads were used, respectively, on the ball for measurements. The sliding speed was kept in 7.85 [cm/s] for a fixed sliding contact cycle of 1500.0 [lap]. Ambient temperature in the chamber was controlled between 23 and 24 0C. The friction coefficient of the films was continuously recorded during the test.  3. RESULTS  AND DISCUSSION  Ten indentations were made on each sample at the same condition and the results are presented in the fig. 1. The hardness was measured continuously during the indentation.  The ratio of hardness to modulus is related to wear resistance, the higher the ratio is, the better the wear resistance is. It is found that element Cr improves the hardness, the modulus and the roughness, but reduces the wear resistance [21]. As shown in fig.1 CrC/DLC has good hardness end modulus  values. For the (PN / Si-a-C:H), the lower coefficients of the elastic modulus are found for the films that had highest Si (at.%) incorporation. An increase in Si con-tent in DLC could reduce the coefficient of elastic mod-ulus but grows the ratio of hardness.   PERFORMANT DLC FILMS WITH ENHANCED WEAR RESISTANCE PROC. NAP 1, 02NFC26 (2012)   02NFC26-3   Fig. 1 – The nanoindentation results with ten separate in-dents for the four samples  Although it has good properties of hardness and modulus of elasticity fig. 2 shows that CrC/DLC has a high coefficient of friction. When sliding against pure titanium, the WC/C coat-ing exhibited mild wear and small tendency to pick up counter material in both the sliding conditions. The good anti-adhesion properties of the WC/C coating in sliding contact with pure titanium can be attributed to the low chemical affinity of the WC/C coating for tita-nium material and the graphitization of the WC/C coat-ing surface with formation of a protective graphite transfer film on the counterpart which had positive effect on the coefficient of friction and wear resistance of the friction pair. The WC/C coating with good anti-adhesion properties is potential candidate in the fields of the tribological applications related to titanium ma-terial which usually has poor tribological characteris-tics because of the adhesion [16]. The DLC film with a Si interlayer shows a low fric-tion coefficient. This result reveals that the adhesion between the DLC film and the substrate is improved by the Si interlayer. Furthermore, a segment-structured DLC film shows a low friction coefficient until 12.000 revolutions, which is twice as many revolutions as the continuous film. This result led us to the conclusion that the fracture of the DLC film can be successfully avoided by applying segment structuring. Additionally, abrasive wear seems to be decreased because the debris were trapped in the spaces between segments, and the frac-ture of the film was stopped by the gaps between seg-ments [22]. In the case of (PN / Si-a-C:H), the lower coefficients of friction are found for the films that had highest Si (at.%) incorporation. An increase in Si content in DLC could reduce the coefficient of friction due to accelera-tion of tribo-chemical reactions [23].  Si incorporation has been widely studied and is re-ported as being effective in reducing friction coefficients in ambient humid air with only limited deterioration of the wear resistance [24].  The adhesion of the coatings was determined using the conventional scratch-test method [20], which showed that the LC2 (first crack) value was comparable for all coatings, as can be seen in Fig. 3. The scratching curve in Fig. 4 was used to study the behavior of DLC coatings during the loading process    Fig. 2 – Different frictions behaviour of DLC films at the same load                    CrC / a-C:H                                        WC / C                  Si / DLC                                               DLC  Fig. 3 – The first crack, the LC2 value, for coating types   Fig. 4 – Scratch penetration depth as a function of progres-sively applied normal load  There are many papers reporting the friction and wear performance, certain DLC films are very soft  and easily scratch able, while others show pretty hard and resistant to wear. On another hand, if the coating only cracked in a roughly semicircular arc along the scratch without peeling off, the adherence was considered good [25].  L. COSTINESCU, C. COJOCARIU, A. MARIN, D. MUNTEANU PROC. NAP 1, 02NFC26 (2012)   02NFC26-4 An optical microscopy examination was carried out for the coatings after scratch testing and the typical crack behaviour was recorded. The first cracks ap-peared for the all coating types as angular cracks on the edges of the scratch grooves [19], similarly to what is shown in Fig. 3. According to data represented in fig. 4 WC / C have the best adherence of all samples analyzed.  4. CONCLUSION  The nanoindentation /scratch technique can provide us very useful information about the elastic modulus, hardness, friction and wear properties. It is found that element Cr improves the hardness, the modulus and the roughness, but reduces the wear resistance. An increase in Si content in DLC could reduce the coefficient of elastic modulus but grows the ratio of hardness.  ACKNOWLEDGMENTS  This paper is supported by the Sectoral Operational Programme Human Resources Development (SOP HRD), ID76945 financed from the European Social Fund and by the Romanian Government.    REFERENCES  1. T.H. Zhang, Y. Huan, Comp. Sci. Tech. 65, 1409 (2005). 2. Y. Lifshitz, Diam. Relat. Mater. 8, 1659 (1998). 3. T. Staedler, K. Schiffmann, Surf. Sci. 482-485, 1125 (2001). 4. J. Robertson, Mater. Sci. Eng. R37 129 (2002). 5. M. Yatsuzuka, Y. Oka, M. Nishijima, K. Hiraga, Vacuum 83, 190 (2008). 6. G.X. Xie, B.R. Zheng, W. Li, W. Xue, Appl. Surf. Sci. 254, 7022 (2008). 7. M. Minn, S.K. Sinha, Thin Solid Films 518, 3830 (2010). 8. M. Sedlaček, B. Podgornik, J. Vižintin, Materials Charac-terization 59, 15 (2008). 9. E.L. Dalibon, S.P. Brühl, D. Heim, J. Phys.: Conf. Series 370, 012029 (2012). 10. S.R.P. Silva, Handbook of Thin Materials (Academic Press: Guildford: 2002), p. 403. 11. W. Ensinger, Review of Scientiﬁc Instruments 63, 5317 (1992). 12. H. Ronkainen, S. Varjus, K. 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Performant DLC Films with Enhanced Wear Resistance

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