Abstract. This work reports on the tribological performance of three different commercial hard PVD coatings (TiN, TiCN and nACo) with lubricating extra films of Al 2 O 3 , Ni-WS 2 and diamondlike carbon (DLC). WC-Co hardmetal has been used as substrate material. Wear tests, employing two counter bodies of Al 2 O 3 and hardmetal WC-Co, were performed for the PVD coatings with and without the extra films. The results showed that the presence of DLC extra film reduces the coefficient of friction of the PVD hard coatings TiN and nACo. Furthermore, the wear of TiN coatings was reduced in the presence of an extra Ni-WS 2 lubricant film

Alsayed Abdel Aal

Eron Adoberg

Lauri Aarik

Liina Lind

Priit Kulu

Renno Veinthal

CiteSeerX

 193
Estonian Journal of Engineering, 2012, 18, 3, 193–201            doi: 10.3176/eng.2012.3.04 
 
 
 
 
 
 
 
 
Tribological  properties  of  PVD  coatings  with   
lubricating  films 
 
Liina Linda, Eron Adoberga, Lauri Aarikb, Priit Kulua, Renno Veinthala 
and Alsayed Abdel Aalc 
 
a  Department of Materials Engineering, Tallinn University of Technology, Ehitajate tee 5, 19086 
Tallinn, Estonia; liina.lind@ttu.ee 
b  Institute of Physics, University of Tartu, Riia 142, 51014 Tartu, Estonia 
c  Institute of Particle Technology, Clausthal University of Technology, Arnold Sommerfeld St. 6, 
38678 Clausthal-Zellerfeld, Germany 
 
Received 8 June 2012, in revised form 30 July 2012 
 
Abstract. This work reports on the tribological performance of three different commercial hard 
PVD coatings (TiN, TiCN and nACo) with lubricating extra films of Al2O3, Ni-WS2 and diamond-
like carbon (DLC). WC-Co hardmetal has been used as substrate material. Wear tests, employing 
two counter bodies of Al2O3 and hardmetal WC-Co, were performed for the PVD coatings with and 
without the extra films. The results showed that the presence of DLC extra film reduces the 
coefficient of friction of the PVD hard coatings TiN and nACo. Furthermore, the wear of TiN 
coatings was reduced in the presence of an extra Ni-WS2 lubricant film. 
 
Key words: PVD coating, thin film, tribology, self-lubrication, coefficient of friction. 
 
 
1. INTRODUCTION 
 
Physical vapour deposited (PVD) coatings have established a strong position 
in the tooling industry. Thin hard coatings are widely used to protect the tools 
from wear, to use substrate steels with higher toughness in cutting elements and 
altogether to extend tool life time. However, there are some limits related to the 
application of PVD coatings. For example, it has been demonstrated that 
multilayer and gradient coatings on hardmetal and cold work tool steel substrates 
under the conditions of dry sliding wear tests have a tendency to increase the 
coefficient of friction (CoF) and to decrease the elasticity modulus (E) and 
hardness (H) ratio [1].  
 194
Different types of hard coatings like TiN [2], Al2O3 (Alumina) [3], diamond-
like carbon [4–6] and sulphide-containing films [6,7] can be applied for wear pro-
tection to lower the CoF or suppress the adhesive wear in poorly lubricated and 
high stress contacts. Previous studies have reported that hybrid PVD + atomic 
layer deposited (ALD) hard coatings have a positive effect on corrosion 
protection [8]. However, the effect of the ALD film on the wear resistance has not 
been studied to our knowledge.  
The present study is part of an assignment to create thin hard coating systems 
for tooling industry in order to improve the commercial coatings known today. In 
this work, thin lubricating extra films were deposited on top of PVD coated 
surfaces. The influence of the extra films on the CoF and wear was studied. 
 
 
2. EXPERIMENTAL 
 
WC-Co hardmetal (10 wt% of Co) specimens with hardness of 1640 HV were 
used as substrate materials for the base coatings. Three base coatings, all 
containing elements of Ti and N, were used in the study – monolayer of TiN, 
gradient coating TiCN and gradient nanocomposite nACo (nc-Ti1-xAlxN)/ 
(a-Si3N4). Substrate specimens were polished to Ra 0.003 µm and cleaned in an 
ultrasonic bath with isopropanol. Immediately after the cleaning procedure, 
samples were placed into the vacuum chamber and sputter-cleaned in argon 
plasma. Thin metallic Ti layer was deposited onto substrates prior to the main 
coating. Deposition of TiN, TiCN and nACo coatings were carried out in the arc 
plating PVD unit PLATIT-π80 using Lateral Rotating ARC-Cathodes (LARC) 
technology. The deposition temperature was 450 ºC for each coating. Thickness 
of the coatings was measured using the kalotest method with the kaloMAX 
tester. Surface roughness was measured with Perthometer Concept M by Mahr 
and nanohardness was received from Platit [9]. Properties of base coatings are 
given in Table 1. Adhesion of the coatings was evaluated by Rockwell indenta-
tion test (A scale), according to technical specification CEN/TS 1071-8.  
Extra films used in the experiment were atomic film of Al2O3, sub-micron 
diamond-like carbon film and a micrometer thick nickel and tungsten disulphide 
composite film (Ni-WS2). 
Al2O3 film was deposited in a flow-type low-pressure ALD reactor [10] in a 
flow of nitrogen (99.999%, AS AGA). Prior to deposition, the samples were 
pretreated with acetone (99.5%, Carl Roth GmbH&CO) and isopropyl alcohol  
 
 
Table 1. Properties of PVD base coatings 
 
 Nanohardness, up 
to, GPa [9] 
Average roughness 
Ra, µm 
Average max height of 
the profile Rz, µm 
Coating 
thickness, µm 
TiN 24  0.04 0.91 2.5  
TiCN 32  0.04 0.95 3.1  
nACo 40  0.08 1.26 2.3 
 195
(99.7%, Carl Roth GmbH&CO). For preparation of reference samples, Al2O3 
films were deposited also on Si substrates. The Si(100) substrates were cleaned 
by etching in HF to remove the native oxide, and then rinsed in de-ionized water. 
The Al2O3 film was deposited using 400 cycles Al(CH3)3 (98%, Strem 
Chemicals) and H2O at 300 °C with the ALD cycle times 3/2/2/5 s. Mass thick-
ness of Al2O3 films, grown by the ALD method on Si(100) substrates, was 
determined using EPMA data and STRATA and FLA programs [11]. 
Deposition of diamond-like carbon films was carried out in the PVD unit 
PLATIT-π80 using LARC technology at the temperature of 400 ºC. Recipe para-
meters were set according to recommendations from Platit in order to achieve 
film thickness of approximately 300 nm. 
For the deposition of Ni-WS2 composite coatings, an eutectic mixture of 
choline chloride and ethylene glycol, containing NiCl2 and WS2 powder, was 
employed. Electrodeposition experiments were carried out in open air conditions, 
using a three-electrode cell setup. During deposition process, the bath was stirred 
by a magnetic stirrer (10 rpm) in order to keep the particles dispersed and prevent 
sedimentation. Composite coatings were deposited at potential –0.9 V and tem-
perature 70 ºC. After deposition, samples were rinsed with iso-propanol to ensure 
removal of the ionic liquid, and subsequently dried under vacuum at room tem-
perature for 2 hours. The gravimetric method (weight gain) was used to calculate 
the coating thickness.   
Reciprocating wear experiments were conducted using CETR-UMT-2 tribo-
meter. Tests were carried out with two different counter bodies (supplied by 
Redhill): corundum (Al2O3) and tungsten carbide-cobalt (WC-Co) with 6 wt% of 
cobalt. Hardness and modulus of elasticity of Al2O3 was 1700 HV and 350 MPa, 
respectively; and for WC-Co 1500 HV and 640 MPa, respectively. Diameter of 
the ball was 3 mm, reciprocating distance 1 mm, contact force 2 N, frequency 
5 Hz and time 10 min. All of the experiments were repeated at least twice and 
additional experiments were conducted for those samples where differences in 
the first two results were observed. Average CoF was determined over the period 
of 1500–3000 cycles, i.e. after stabilization depths of wear scars were determined 
using Bruker ContourGT-K0X White Light Interferometric Optical Profiler.  
 
 
3. RESULTS  AND  DISCUSSION 
 
3.1.  Adhesion  of  PVD  coatings  and  thickness  of  additional  films 
 
Adhesion between base coatings and the substrates was determined with 
Rockwell indentation test. Adhesion was very good – Class 0 (no cracks or 
adhesive delamination within the indent region) for nACo, or good – Class 1 
(cracking without adhesive delamination of the coating) for TiN and TiCN 
coatings. Table 1 shows the thickness of PVD coatings of TiN, TiCN and nACo. 
The thickness of extra films was the following: Al2O3 – 0.04 µm, DLC – 0.3 µm 
and Ni-WS2 – 1.0 µm.  
 196
3.2.  Reciprocating  sliding  wear  of  different  coating  systems 
 
Among the base coatings, TiCN demonstrated the best wear resistance in the 
specific conditions. TiN and nACo coatings were most susceptible to wear. 
Repeating the experiments with both counter bodies revealed some differences 
derived from the material of the counter body.  
 
3.2.1. Effect of the counter body material on the CoF of base coatings 
Wear behaviour of base coatings was studied using Al2O3 and WC-Co counter 
bodies. CoF dependence on the sliding ball material is shown in Fig. 1. Both of the 
nACo and TiN coatings showed more stable behaviour and lower CoF with  
WC-Co counter body. With nACo base coating Al2O3 counter body demonstrated 
remarkably higher CoF and wear depth, probably due to higher hardness of Al2O3. 
SEM secondary electron images of worn surfaces of nACo coating are presented in 
Fig. 2 and those with nACo + DLC coating in Fig. 3. With Al2O3 counter body 
(Fig. 2a), the wear is greater but the wear track is smoother. Larger contact 
pressure takes place with WC-Co (Fig. 2b) and the counter body is transferring and 
tearing the coating leaving a smaller wear track.  
 
 
 
 
Fig. 1. Effect of the counter body material on the CoF of the base coatings.  
 
 
  
 
Fig. 2. SEM images of the nACo base coating, sliding against Al2O3 (a) and WC-Co (b) ball 
counterface. 
 197
 
 
Fig. 3. SEM image of reciprocating wear experiment with nACo+DLC coating. 
 
 
3.2.2. Effect of different extra films on CoF 
It was observed that the presence of Al2O3 extra films on PVD coatings  
did not add tribological advantage to the PVD coatings (Fig. 4a). Some  
changes in the CoF during the “run-in” period are visible though for robust 
applications such influence will probably not be detectable. The effect of an 
ultra-thin extra film of Al2O3 disappears after the first 100 cycles and the CoF for 
the samples with the extra film levels off to the coefficient of PVD base coatings. 
Probably the extra film thickness is insufficient in order to provide protection to 
the base coating. 
The presence of thin sub-micron DLC extra films on PVD coatings decreases 
the CoF and improves wear performance of the base coatings (Fig. 4b). On the 
basis of our experiment, it was noticed that the DLC film was able to provide 
remarkable protection to the substrate regardless of the base coating. Wearing out 
of the DLC coating was not noticed for any of the coating systems. SEM-
secondary electron image of nACo+DLC is presented in Fig. 3. Wear track is 
remarkably smaller than for nACo coating without the extra film (Fig. 2). 
Figure 4c represents the results for PVD coatings with Ni-WS2 extra film 
(corundum counter body). For nACo+Ni-WS2, CoF was lower up to 1000 cycles, 
however, afterwards the extra film failed and CoF reached the level of nACo 
base coating. The Ni-WS2 extra film on TiN and TiCN was able to keep a 
reasonably stable low CoF up to 3000 cycles.  
Sulphide-containing film of Ni+WS2 was reliant on the base coating as it 
behaved differently for all three PVD coatings. The effect of Ni-WS2 film on top 
of base coatings is presented in Fig. 5 where the wear behaviours of base 
coatings with and without the extra lubricant films are compared. The effect of 
the Ni-WS2 film is remarkable for the TiN coating, while in case of the nACo 
coating, the effect depends on the counter body. 
Table 2 shows an overview of the reciprocating wear experiment results and 
grouping of the wear behaviours. From the data, a relation between CoF and  
 
 198
 
Fig. 4. Effect of extra films: (a) Al2O3 atomic film (sliding against WC-Co ball counterface);  
(b) DLC film (sliding against WC-Co ball counterface); (c) Ni-WS2 film (sliding against Al2O3 ball 
counterface). 
 
 
depth of the wear scar was noticed. Larger wear scars indicate a greater frictional 
coefficient. However, there were some exceptions. For the nACo coating systems 
(Table 2, group 4), depth of the wear scar was relatively deep, while the CoF 
remained low (0.4) with the hardmetal counter body. Ni-WS2 in “group 2” 
coatings was able to suppress wear until the failure of the extra layer.  
 
 
 199
Table 2. Results of reciprocating wear tests with different PVD base coatings and extra films 
 
Classification based on wear 
behaviour 
Coating Counterbody1) Depth of 
wear 
scar, µm 
CoF 
TiN+DLC WC-Co/Al2O3 0.10 0.16 
TiCN+DLC WC-Co/Al2O3 0.13 0.16 
TiCN / TiCN+Al2O3 WC-Co/Al2O3 0.15 0.16 
Group 1: TiCN coating and 
DLC extra film on PVD base 
coatings. Low CoF and depth 
of wear scar. nACo+DLC WC-Co/Al2O3 0.14 0.18 
 
TiCN+Ni-WS2 WC-Co/Al2O3 0.05 0.35 
TiN+Ni-WS2 WC-Co/Al2O3 0.11 0.35 
Group 2: Ni-WS2 extra film 
on base coatings. Increased 
CoF for TiCN and TiN but 
low wear. For nACo lower 
CoF for a short period is 
achieved, however, extra film 
wears out during the 
experiment.2) 
 
nACo+Ni-WS2 Al2O3   0.952) 0.45/0.782) 
Group 3: TiN coating. CoF is 
lower than for nACo, wear is 
high. 
 
TiN / TiN+Al2O3 WC-Co/Al2O3 0.77 0.54 
nACo+Ni-WS2 WC-Co 0.45 0.64 
Group 4: nACo, nACo+ 
Ni-WS2 and nACo+Al2O3 
coatings with hardmetal 
counter body. Although nACo 
has higher CoF compared to 
TiN coating, wear is lower. 
 
nACo / nACo+Al2O3 WC-Co 0.40 0.66 
Group 5: nACo / nACo+ 
Al2O3 with Al2O3. Highest 
CoF and wear.  
nACo / nACo+Al2O3 Al2O3 1.65 0.84 
 
1) WC-Co/Al2O3 – no difference in results with different counter bodies.  
2)  The Ni-WS2 coating wears out after about1200 cycles and therefore two values of CoF are given: 
CoF over a period of 100–1100 cycles / CoF over a period of 1500–3000 cycles. Wear scar depth 
is given only after the end of experimental 3000 cycles. 
 
 
4. CONCLUSIONS 
 
The paper considers tribological properties (wear and coefficient of friction) 
of commercial PVD coatings with lubricating extra films of Al2O3, DLC and  
Ni-WS2. From the study the following conclusions can be made. 
1. TiCN coatings showed the lowest coefficient of friction (0.15–0.20) and 
wear independence of the counter body material or of the extra lubricant 
films.  
2. Atomic layer deposited Al2O3 extra films on PVD coatings did not add 
tribological advantage to the base coatings, probably due to insufficient 
thickness of the film. Wear and CoF remained on the same level as for PVD 
 200
commercial coatings, only minor changes in the “run-in” period were 
noticed. 
3. Addition of DLC extra film on top of the base coatings resulted in a reduced 
CoF (to the level of 0.16–0.18) and wear of commercial PVD coatings TiN 
and nACo.  
4. Extra film of Ni-WS2 was able to provide good protection against wear of 
TiN and TiCN coatings in our experimental conditions; behaviour on nACo 
base coating was dependent on the counter body material. Extra film Ni-WS2 
needs further studies before it is possible to make more profound con-
clusions. For example, it remains unclear whether the protective effect of  
Ni-WS2 will be preserved under higher loads or different setups and what is 
the reason for different behaviour with varied counter bodies. 
 
 
ACKNOWLEDGEMENT 
 
The work was supported by the Ministry of Education and Research (target 
financed project SF 01400091S08) and Graduate School „Functional materials 
and technologies”, financed by Archimedes in Estonia. The authors are thankful 
to F. Endres from Clausthal University of Technology for support and to  
V. Mikli from Materials Research Centre of Tallinn Universtity of Technology 
for SEM studies of worn surfaces. 
 
 
REFERENCES 
 
  1. Sivitski, A. Sliding Wear of PVD Hard Coatings: Fatigue and Measurement Aspects. PhD 
Thesis, TUT Press, 2010. 
  2. Stachowick, G.W. and Batchelor, A.W. Engineering Tribology. Butterworth-Heinemann, 
Boston, 2001. 
  3. Gao, Y., Wang, C., Yao, M. and Liu, H. The resistance to wear and corrosion of laser-cladding 
Al2O3 ceramic coating on Mg alloy. Appl. Surf. Sci., 2007, 253, 5306–5311. 
  4. Voevodin, A. A. and Donley, M. S. Preparation of amorphous diamond-like carbon by pulsed 
laser deposition: a critical review. Surf. Coat. Tech., 1996, 82, 199–213. 
  5. Kennedy, F. E., Lidhagen, D., Erdemir, A., Woodford, J. B. and Kato, T. Tribological 
behaviour of hard carbon coatings on steel substrates. Wear, 2003, 255, 854–858. 
  6. Taube, K. and Bewilogua K. Encyclopedia of Materials: Science and Technology. Elsevier, 
2001, 9286–9293. 
  7. Spalvins, T. Deposition of MoS2 films by physical sputtering and their lubrication properties in 
vacuum. ASLE Trans., 1969, 12, 36–43.  
  8. Marin, E., Guzman, L., Lanzutti, A., Fedrizzi, L. and Saikkonen, M. Chemical and electro-
chemical characterization of hybrid PVD + ALD hard coatings on tool steel. Electrochem. 
Commun., 2009, 11, 2060–2063. 
  9. Coatings Specifications – Coating Guide. http://www.platit.com/coatings/coating-specifications 
(accessed 05/06/2012). 
10. Aarik, J., Aidla, A., Kiisler, A.-A., Uustare, T. and Sammelselg, V. Influence of substrate tem-
perature on atomic layer growth and properties of HfO2 thin films. Thin Solid Films, 1999, 
340, 110–116. 
 201
11. Sammelselg, V., Aarik, J., Aidla, A., Kasikov, A., Heikinheimo, E., Peussa, M. and Niinisto, L. 
Composition and thickness determination of thin oxide films: comparison of different 
programs and methods. J. Anal. Atom. Spectrom., 1999, 14, 523–527. 
 
 
Määrivate  katetega  füüsikaliste  aurustussadestuspinnete 
triboloogilised  omadused  
 
Liina Lind, Eron Adoberg, Lauri Aarik, Priit Kulu, Renno Veinthal ja 
Alsayed Abdel Aal 
 
Artikkel käsitleb isemäärivate katetega (Al2O3, DLC ja Ni-WS2) kaetud 
tuntud õhukeste kõvapinnete (TiN, TiCN ning nACo) triboloogilisi omadusi. 
Alusmaterjalina on kasutatud WC-Co kõvasulamit. Kulumiskatsete alusel võr-
reldi isemäärivate katetega kaetud katsekehasid puhaste kõvapinnetega. Katse-
tused viidi läbi erinevast materjalist kuulidega (kõvasulam WC-Co ja alumii-
niumoksiid Al2O3). Teemandilaadne (DLC) kate vähendas hõõrdetegurit TiN-i ja 
nACo kõvapinnete puhul ning Ni-WS2 lisakate vähendas TiN-pinde kulumist. 
 
 


Tribological properties of PVD coatings with lubricating films

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Tribological properties of PVD coatings with lubricating films

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