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A comparative study of fatigue properties of TiVN and TiNbN thin films deposited on different substrates
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A comparative study of fatigue properties of TiVN and TiNbN thin films deposited on different substrates Hikmet Ciceka,⁎, Ozlem Baranb, Aysenur Kelesc, Yasar Totikc, Ihsan Efeogluc a b c
Erzurum Technical University, Mechanical Engineering, Turkey Erzincan University, Mechanical Engineering, Turkey Ataturk University, Mechanical Engineering, Turkey
A R T I C L E I N F O
A B S T R A C T
Keywords: Multipass scratch TiVN TiNbN Fatigue
Transition metal nitrides, especially ternary phase films attract attention due to their high mechanical and tribological features. Besides these, fatigue properties play a very important role on the performance in service life of these types of films. TiVN and TiNbN films were deposited on M2 and H13 steel substrates by reactive magnetron sputtering system. Fatigue properties of the films were characterized via multipass scratch tests. 100, 250 and 500 cycles with bidirectional multipass scratch tests were conducted at room temperature by applying 20 N constant load. Structural properties were determined with X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Mechanical features of the films were observed with nano hardness tests. Fatigue behaviors, deformation types, coefficient of frictions of the films and effect of different substrates were discussed comparatively. According to the results, the TiVN films showed better fatigue resistance than the TiNbN films although critical adhesion load value of the TiNbN films was higher than the TiVN films. The TiVN films generally showed ductile type cracks at the edge of the tracks and the TiNbN films showed more brittle type cracks. Additionally, the films deposited on M2 substrates exhibited better strength than those of H13 substrates.
1. Introduction Metal nitride films are used to protect the surface of cutting tools and machine parts against wear, fatigue and corrosion for years. In particular binary TiN, CrN and AlN etc. are widely used in industry. Recently, ternary metal nitride films such as TiZrN [1], TiVN [2], TiNbN [3] and TiAlN [4] have been produced and have generally better properties than the binary ones. Using the closed field unbalanced magnetron sputtering (CFUBMS) system to synthesize for these types of films provides good advantages such as higher film purity, adhesion, homogeneity and density. TiVN films usually have better hardness and wear resistance than the traditional TiN films [5,6]. The ratio of V atoms in the TiVN films affects the film properties and also, about 50% nitrogen show good properties [2]. Protective films must have good mechanical and tribological features. In addition to all these, fatigue behavior is an issue of high importance. Up to now, many researches have studied structural properties [7], mechanical and adhesion properties [2], fracture and tribological behaviors [8] and optical properties [9] but there is no research reported about the fatigue behavior of the TiVN films. TiNbN ternary films also have good mechanical and tribological properties and
⁎
are commercially used for abraded machine part surfaces and especially for prosthesis due to its bio-compatibility [10]. Some studies have been done about the TiNbN films but fatigue properties have not been reviewed. The purpose of this study is to determine the fatigue properties of TiVN and TiNbN thin films with bidirectional multipass scratch tests at three different number cycles. In addition, two types of substrates (H13 — chromium hot work steel and M2 — molybdenum high speed tool steel) were used to examine the substrate effect. The films were deposited with reactive magnetron sputtering method. The obtained results were analyzed comparatively. 2. Experimental Traditional CFUBMS was used to grow TiVN and TiNbN ternary thin films. The films were deposited on M2 and H13 tool steels (chemical compositions were given in Table 2). Before the deposition process, the steel substrates were mechanically polished with SiC emery paper from 240 to 1200 mesh grit and then the substrates' surfaces were treated with α-alumina powder grain size of 0.05 μm as a final action. The surface roughness (Ra) reached a value of about 0.05 μm measured with
Corresponding author at: Erzurum Technical University, Turkey. E-mail address: [email protected] (H. Cicek).
http://dx.doi.org/10.1016/j.surfcoat.2017.06.078 Received 30 March 2017; Received in revised form 30 May 2017; Accepted 7 June 2017 0257-8972/ © 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Cicek, H., Surface & Coatings Technology (2017), http://dx.doi.org/10.1016/j.surfcoat.2017.06.078
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Table 1 Deposition parameters of the TiVN and TiNbN films. Films
Substrate pulsed-dc parameters
Working pressure (Pa)
Ti target current (A)
V target current (A)
Nb target current (A)
Time (min)
Ti interlayer
100 V, 150 Hz, 2 μs 100 V, 150 Hz, 2 μs 100 V, 150 Hz, 2 μs
0.33
1.5
–
–
5
0.33
1.5
1.5
–
80
0.33
1.5
–
1.5
80
TiVN TiNbN
Fig. 3. Cross-section SEM images of the TiNbN and the TiVN thin films.
Table 2 Elemental composition of the TiVN and the TiNbN films. Fig. 1. XRD patterns of the TiVN films deposited on M2 and H13 substrates.
EDS
Atomic percentage (at.%)
Films
Ti
V
Nb
N
TiVN TiNbN
29.86 26.16
27.12 –
– 26.55
43.02 47.29
Substrates
C
Mn
Si
Cr
V
Mo
Fe
m2 h13
0.83 0.38
0.27 0.4
0.33 1.1
4.2 5.3
2.0 0.9
5.1 1.5
87,27 90.42
Table 3 Mechanical properties of the TiVN and the TiNbN films. Films/properties
Nanohardness (GPa)
Thickness (nm)
Critical loads, Lc (N)
TiVN
29 20 35 26
360
60 42 63 47
TiNbN
M2 H13 M2 H13
400
Fig. 2. XRD patterns of the TiNbN films deposited on M2 and H13 substrates.
ion cleaning process for 20 min. To improve the adhesion of the films to the substrate, Ti interlayer was used. Improving the density and also adhesion of the films, pulsed-dc was applied to the substrates. 1.5 A current was applied to the Ti, V and Nb targets during the deposition process. Finally, TiVN and TiNbN films were deposited for 80 min separately. The substrates were spun around the center of the chamber with 1.5 rpm to obtain uniform films and the distance between the targets and substrates was set as 90 mm. The details of the deposition parameters are given in Table 1. The chemical compositions, the microstructure properties and the thickness of the TiVN and TiNbN films were analyzed with SEM and EDS. Crystal structures of the films were determined via XRD with a
a profilometer. In order to remove sticky particles from the surfaces ultrasonic cleaning process was carried out in ethanol bath. After all, the steel substrates etched with 5% nitric acid solution in 10 s. Deposition processes were conducted in argon and nitrogen gas atmosphere. Argon gas was used to sputter atoms from the targets and create plasma. Nitrogen gas was used as reactive gas to obtain nitride phases of the films and kept constant at 40%. One titanium, one vanadium and one niobium target were placed in the vacuum chamber for growing the films. Chamber vacuum pressure was reduced below the 133 × 10− 5 Pa then argon gas was released in the chamber. The negative voltage (800 V) was applied to the substrates in order to perform 2
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Fig. 4. The microscope images of the TiVN and the TiNbN thin films deposited on H13 and M2 substrates after 100 cycles of multipass scratch tests.
CuKα (λ: 1.5405 Å) radiation source. Measurement values were obtained at 2θ:20–110° scan range and 2°/min scan speed. Nanohardness values of the films were identified with NanoHardness with Berkovich inderter tip under 1 mN load. Fatigue behaviors of the deposited films were evaluated with multipass scratch tester Revetest®, produced by CSM Instruments. In the multipass scratch test, the tip moves a certain distance on the sample under constant load and create bidirectional force by moving back and forth on the same track hence films were forced to fatigue. The applied constant load was determined considering the critical load value of the films. In general, between 20% and 50% of the critical load value was determined as constant fatigue load. In this study, approximately 50% of the critical load value (20 N) was decided as constant load. The tip speed was 10 mm/min, the scratch length was 3 mm and the acoustic emission sensitivity was 2, and were set fixed for all of the tests. Rockwell-C diamond tip (200 μm tip radius) was used in all of the tests. The relative humidity was about 45%. Three different bidirectional cycles (100, 250 and 500) were applied to the films and the fatigue behaviors were evaluated.
orientation of the peaks were almost the same in both substrates except for a minor TiVN (200) peak only seen in M2 substrate. TiVN (111) peak was dominantly present. On the other hand it was seen that TiVN (220) peak and TiVN (311) peak were also seen in the structure. The peaks came from the substrates and were marked as Fe (ferrous). According to the XRD results, the TiVN films were successfully synthesized when compared to the literature [11]. The XRD patterns of deposited TiNbN films are given in Fig. 2. According to the graph, the TiNbN (111) peak has the highest intensity, and TiNbN (220) and TiNbN (311) peaks are present on M2 and H13 substrates. In addition to all these, the small TiNbN (200) peak can be observed only at M2 substrates. Also, Fe peaks address the reflections of the substrates. According to these peaks the TiNbN films were produced successfully and the obtained peaks correspond to the values in the literature [1]. The cross-section SEM images of the TiNbN and the TiVN films deposited on glass substrates are given in Fig. 3. The images showed that both TiNbN and TiVN films have a very dense and semi-columnar structure as we request for this type of films. The thickness of the films is 400 ± 10 nm for TiNbN and 360 ± 10 nm for TiVN. Although these thickness values seem a little low for protective coatings, there are lots of similar thinner films in the literature [7,12] and they seem to perform satisfactorily. When we look at the fracture surface, it is seen that both films showed very similar brittle cracks. The roughness of the films are very similar and value is about 0.02 μm.
3. Results and discussion 3.1. Structure of the films Crystallographic structure patterns of the TiVN film deposited on M2 and H13 substrates are given in Fig. 1. It was observed that the 3
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Fig. 5. The microscope images of the TiVN and the TiNbN thin films deposited on M2 and H13 substrates after 250 cycles of multipass scratch tests.
deposited on the harder substrate was higher and vice versa as expected. The hardness measurement was not affected by the substrate hardness because the depth of indenter penetration was less than one in ten of the film thickness.
3.2. Elemental composition The elemental compositions of synthesized TiVN and TiNbN films are given in Table 2. According to the EDS results, Ti and N atoms are commonly present in the films as expected. The atomic percentage of V is (27.12) a little bit high while the target currents of V and Nb are the same. It is likely that this difference emerged from different sputtering yield of V and Nb atoms. The vanadium sputtering yield is about 85 Å/s and the niobium is 80 Å/s hence atomic percentage of V atoms is slightly higher than Nb. Atomic percentages of nitrogen are slightly different, 43.02 for TiVN films and 47.29 for TiNbN films. At this point, it is seen that nitrogen ratio is related to Ti ratio in films. Nitrogen ratio in the films is low while the Ti ratio is high and vice versa.
3.4. Fatigue properties Fatigue is a very important critical feature for the hard protective films. In this study we investigated the fatigue properties of the TiVN and the TiNbN films deposited on M2 and H13 substrates with multipass scratch tests under three different numbers of cycles comparatively. The constant load values applied in such works are generally taken as 20 to 50% of the critical adhesion loads (Lc) of the films [13–16]. The critical load values of the films were given in Table 2. We have specified 20 N as the constant load value here and 100, 250 and 500 cycle tests were conducted. Scratch track images and coefficient of friction values of the films were categorized considering the number of the cycles. The track images of the TiVN and the TiNbN films after 100 cycles of multipass scratch test are given in Fig. 4. When looked at the scratch tracks of the films deposited on M2 substrates, both films showed brittle fractures at the edge of the tracks and there were no adhesive cracks seen between the films and substrates. In addition, a small amount of medium size debris can be seen in the TiNbN film and some pieces of small size debris are in place in the TiVN film. Both films deposited on M2 substrates showed great fatigue resistance at 100 cycles under 20 N subcritical load. On the H13 substrates, the same brittle fractures were also observed at the edge of the tracks and some little adhesive cracks
3.3. Mechanical properties Hardness values of the films were observed via nanohardness tests under 1 mN load in order to obtain lower than 0.1 value of indentation depth/film thickness ratio. The nanohardness results of the films are given in Table 3. The highest hardness value was obtained from the TiNbN film deposited on M2 substrate as 35 GPa and the lowest hardness value was obtained from the TiVN film deposited on H13 substrate as 20 GPa. It is clearly seen that the TiNbN films are harder than the TiVN films when the same substrate is taken into account. This result is consistent with the literature [3,10,11]. On the other hand, hardness of the films was seriously affected from the substrate hardness. The uncoated substrate hardness values were 5.6 GPa for M2 and 3 GPa for H13 respectively. These results reveal that the hardness of the films 4
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Fig. 6. The microscope images of the TiVN and the TiNbN thin films deposited on M2 and H13 substrates after 500 cycles of multipass scratch tests.
pieces of debris were embedded to the substrate firmly where they are formed and could not move with the indenter motion due to higher substrate hardness so they were regularly distributed in the tracks. As a result, the TiNbN and the TiVN films deposited on H13 substrates showed fatigue resistance but not as good as deposited on M2 substrates. The track images of the TiNbN and TiVN films after the highest cycle (500) are shown in Fig. 6. Looking at the M2 substrate, the films still maintain their continuity and there aren't any adhesive failures so they still showed very good fatigue resistance after 500 cycles of scratching. Brittle fractures occurred at the edge of the tracks. The debris distribution is similar with 100 and 250 cycles but the differences are size and numbers that increased. This situation was expected due to the increase in the number of cycles. On the other hand, when we look at the H13 substrates, the adhesive failures increased even more and films could not maintain their continuity hence fatigue failures occurred both the TiVN and the TiNbN films but a little more at the TiNbN. The debris distribution is similar with lower cycle tests and collected at the end regions. The friction coefficient graphs of the TiVN and the TiNbN thin films deposited on M2 and H13 substrates under 100, 250 and 500 cycles of multipass scratch tests are given in Fig. 7. The coefficient of friction (COF) values of the substrates after 500 cycles were 0.4 ± 0.02 for M2 and 0.56 ± 0.04 for H13. When we looked at the 100 cycle results, the
can be seen in the TiNbN film while seen nowhere in the TiVN. These adhesive cracks can be attributed to high hardness of the TiNbN film (26 GPa) and low (47 N) Lc value. Although the Lc value of TiVN film (42 N) is smaller than the TiNbN film, adhesive failure has not occurred in the TiVN. At this point, we can say that the difference between hardness values of the film and the substrate is another factor affecting the fatigue resistance. Fig. 5 shows the multipass scratch track images of the films after 250 cycle passes. Firstly, when we look at the films deposited on M2 substrates, there are no adhesive failures or chippings in the tracks. Brittle fractures are clearly seen at the edge of the tracks. The debris is embedded in the films and this is almost homogeneously dispersed. Both films deposited on M2 maintained their continuity. On the H13 substrates, TiNbN film continued to show adhesive failures. At the TiVN films, some little adhesive failures can be seen in the track in addition to the brittle fractures at the edges. On the other hand, it is seen that the debris distribution is different from the films deposited on M2 substrates. The debris is generally embedded at the end regions of the tracks and some pieces of debris were found in middle of the tracks. This situation probably emerged from the lower hardness value of the H13 substrate compared to M2. The hardening debris severed from the films was embedded to substrate and could be moving easily with the indenter tip motion due to lower hardness of H13 substrates hence they were collected at the end of the scratch regions. At the M2 substrate the 5
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Fig. 7. The coefficients of friction of the TiVN and the TiNbN thin films deposited on M2 and H13 substrates under 100, 250 and 500 cycles of multipass scratch tests.
films deposited on M2 substrates, the COF values showed quite stable behavior. The COF values started at 0.05 on the first contact and after 10 cycles dropped to 0.02 and stayed around this value. It is seen that the COF values of the TiNbN film are a bit lower than TiVN films at all cycles. This is because of the general behavior of the relationship between hardness and COF [17,18]. The TiNbN film (35 GPa) was harder than TiVN (29 GPa) hence it showed lower COF values. On the H13 side, the starting point of the COF values is closer to 0.05 but after 20 cycles, it occurred slightly later compared to M2 and COF values reached the stable values at 0.02. This slightly delayed stability emerged most probably from the lower hardness of H13 substrates compared to M2. At the end of the cycles, TiNbN films showed slightly low COF values similar to the deposited films on M2. On the other hand, COF values of the TiNbN film exhibited more unstable behavior compared to the films deposited on M2 substrate due to the formation of the adhesive failures.
When the COF results of 250 cycles are examined, at the M2 substrates, COF values started at 0.05 in the first contact then decreased to 0.02 after 25 cycles. These values also gradually diminished to the stable value of 0.017 until the number of cycles reached 125, and remained stable until the end of the 250 cycles. Similar to the 100 cycle results, the TiNbN film showed slightly low COF values. On the H13 side, both films showed more undulating course considering the 100 cycle result. This emerged from the increase in the adhesive failure at both films. Up to 250 cycles, COF values of TiNbN decreased and reached 0.015 and COF values of the TiVN decreased slightly and reached 0.018. Finally, looking at the 500 cycle results, at the M2 substrates, COF values of both films showed quite stable behavior. COF values of the TiNbN film are slightly lower than the TiVN and reached nearly 0.013 at least. The COF values of the TiVN film also showed very stable behavior and nearly reached 0.018 at the end of the 500 cycle. On the 6
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H13 side, both films showed good stable COF values at about 0.017. After the 250 cycle, COF values of TiVN film showed a rapid increase and reached up to a value of nearly 0.37. This unwanted situation emerged from the increasing of adhesive failures also seen in the track images (Fig. 6). When the indenter reached the substrate where the adhesive failure occurred, the COF value increased. From this point of view, we can say that evidence of the adhesive failures started at about 250 cycle for the TiVN film deposited on H13 substrate. At the TiNbN film, stable COF value continued up to 350 cycle with quite a slight reduction. After 350 cycle, COF value started to increase and reached up to 0.022 values. It is observed that the TiNbN film deposited on H13 substrate started to have the adhesive failures at about 350 cycles. Studies in the literature [13,14,19–22] and this study showed that multipass scratch test resistance (fatigue like behavior) of the films is affected from the hardness of the films and substrates and the critical adhesion load of the films (Lc) and thickness of the films. It is known that the critical adhesion load (Lc) and the thickness of the film positively affect the fatigue strength [13,20–22]. On the other hand, increasing the ratio in the hardness values of the film and the substrate negatively affect the fatigue resistance. From this point of view, an empirical formula can be developed between the fatigue strength and these properties are mentioned when the pass cycle numbers, applied constant load, scratch tip type and tip speed are the same. To shorten features into symbols: Hf Hs Lc T FS
• • •
• •
Hardness of the film (GPa) Hardness of the substrate (GPa) Critical adhesion force (Newton) Thickness of the film (μm) Fatigue strength
Empirical formula for fatigue strength: FS =
References [1] I. Grimberg, V. Zhitomirsky, R. Boxman, S. Goldsmith, B. Weiss, Multicomponent Ti–Zr–N and Ti–Nb–N coatings deposited by vacuum arc, Surf. Coat. Technol. 108–109 (1998) 154–159. [2] C. Montero-Ocampo, E.A. Ramírez-Ceja, J.A. Hidalgo-Badillo, Effect of codeposition parameters on the hardness and adhesion of TiVN coatings, Ceram. Int. 41 (2015) 11013–11023. [3] Ł. Łapaj, J. Markuszewski, J. Wendland, A. Mróz, M. Wierusz-Kozłowska, Massive failure of TiNbN coating in surface engineered metal-on-metal hip arthroplasty: retrieval analysis, J. Biomed. Mater. Res. B Appl. Biomater. 104 (2016) 1043–1049. [4] P. Li, L. Chen, S.Q. Wang, B. Yang, Y. Du, J. Li, M.J. Wu, Microstructure, mechanical and thermal properties of TiAlN/CrAlN multilayer coatings, in: Int, J. Refract. Met. Hard Mater. (2013) 51–57. [5] O. Knotek, W. Burgmer, C. Stoessel, Arc-evaporated Ti-V-N thin films, Surf. Coat. Technol. 54–55 (1992) 249–254. [6] J.H. Ouyang, T. Murakami, S. Sasaki, High-temperature tribological properties of a cathodic arc ion-plated (V,Ti)N coating, Wear 263 (2007) 1347–1353. [7] T. Deeleard, A. Buranawong, A. Choeysuppaket, N. Witit-Anun, S. Chaiyakun, P. Limsuwan, Structure and Composition of TiVN Thin Films Deposited by Reactive DC Magnetron Co-sputtering, Procedia Eng. (2012), pp. 1000–1005. [8] B. Deng, Y. Tao, D. Guo, Effects of vanadium ion implantation on microstructure, mechanical and tribological properties of TiN coatings, Appl. Surf. Sci. 258 (2012) 9080–9086. [9] C. Wiemer, F. Lévy, F. Bussy, Determination of chemical composition and its relationship with optical properties of Ti-N and Ti-V-N sputtered thin films, Surf. Coat. Technol. 68–69 (1994) 181–187. [10] A.P. Serro, C. Completo, R. Colaço, F. dos Santos, C.L. da Silva, J.M.S. Cabral, H. Araújo, E. Pires, B. Saramago, A comparative study of titanium nitrides, TiN, TiNbN and TiCN, as coatings for biomedical applications, Surf. Coat. Technol. 203 (2009) 3701–3707. [11] Y.-Y. Chang, W.-T. Chiu, J.-P. Hung, Mechanical properties and high temperature oxidation of CrAlSiN/TiVN hard coatings synthesized by cathodic arc evaporation, Surf. Coat. Technol. 303 (2016) 18–24. [12] M.E. Uslu, A.C. Onel, G. Ekinci, B. Toydemir, S. Durdu, M. Usta, L.C. Arslan, Investigation of (Ti,V)N and TiN/VN coatings on AZ91D Mg alloys, Surf. Coat. Technol. 284 (2015) 252–257. [13] I. Efeoglu, R.D. Arnell, Multi-pass sub-critical load testing of titanium nitride coatings, Thin Solid Films 377–378 (2000) 346–353. [14] S.J. Bull, D.S. Rickerby, Multi-pass scratch testing as a model for abrasive wear, Thin Solid Films 181 (1989) 545–553. [15] H. Cicek, I. Efeoglu, Fatigue and adhesion properties of martensite and austenite phases of TiNi shape memory thin films deposited by magnetron sputtering, Surf. Coat. Technol. 308 (2016) 174–181. [16] F. Bidev, Ö. Baran, E. Arslan, Y. Totik, I. Efeoǧlu, Adhesion and fatigue properties of Ti/TiB2/MoS2 graded-composite coatings deposited by closed-field unbalanced magnetron sputtering, Surf. Coat. Technol. 215 (2013) 266–271. [17] I. Efeoglu, R.D. Arnell, S.F. Tinston, D.G. Teer, The mechanical and tribological properties of titanium aluminium nitride coatings formed in a four magnetron closed-field sputtering system, Surf. Coat. Technol. 57 (1993) 117–121. [18] I. Efeoglu, Ö. Baran, F. Yetim, S. Altıntaş, Tribological characteristics of MoS2–Nb
Hs × Lc × T [N⋅μm] Hf (1)
It can be said that the film with high FS value shows better fatigue strength. Applying this formula (Eq. (1)) to the films in this work;
TiVN on M2: FS =
5.6 × 60 × 0.36 = 4.17 29
TiNbN on M2: FS =
5.6 × 63 × 0.4 = 4.03 35
TiVN on H13: FS =
3 × 42 × 0.36 = 2.27 20
TiNbN on H13: FS =
successfully synthesized and thickness of the films are 400 nm for TiNbN and 360 nm for TiVN. The highest hardness value obtained from TiNbN film deposited on M2 substrate was 35 GPa and the lowest was TiVN film deposited on H13 substrate as 20 GPa. The highest adhesion critical load (Lc) was 63 N obtained from the TiNbN film deposited on M2 substrate and the lowest was 42 N obtained from the TiVN film deposited on H13 substrate. It was observed that the film hardness was affected by the substrate hardness. After 100 cycle multipass scratch test all the films showed very good fatigue strength except some slight adhesive cracks in the TiNbN film deposited on H13 substrate. After 250 cycle multipass scratch test, the films deposited on H13 substrates showed some adhesive cracks but the film deposited on M2 substrate still showed very good fatigue strength. After 500 cycle multipass scratch test, the density of the adhesive cracks in the films deposited on H13 substrates increased but the films deposited on M2 substrates showed better resistance to the adhesive cracking. The coefficient of the friction values of the films started at about 0.055 and then decreased down to nearly 0.015. The TiNbN films showed slightly lower COF values than the TiVN films. An empirical formula was developed for fatigue strength (FS) of the films considering the film and substrate hardness, critical adhesion load (Lc) and the thickness of the films.
3 × 47 × 0.4 = 2.17 26
According to these results, the lowest FS value is 2.17 for TiNbN on H13 and also the film with the lowest fatigue strength. After this, FS values are ranked as 2.27 for TiVN on H13, 4.03 for TiNbN on M2 and 4.17 for TiVN on M2. When we looked at the multipass scratch test results, it is seen that these results overlap with each other. On the other hand, this formula should be analyzed with more films to reinforce its accuracy. But it is possible to obtain a preliminary idea of which film will exhibit better fatigue strength when these properties are known. 4. Conclusion The TiVN and the TiNbN thin films were deposited on M2 and H13 substrates via reactive magnetron sputtering method. Structural, mechanical and fatigue properties of the films were investigated and the results are listed below.
• XRD patterns showed that the TiVN and the TiNbN thin films were 7
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H. Cicek et al. solid lubricant film in different tribo-test conditions, Surf. Coat. Technol. 203 (2008) 766–770. [19] A.-T. Akono, F.-J. Ulm, Scratch test model for the determination of fracture toughness, Eng. Fract. Mech. 78 (2011) 334–342. [20] F. Yildiz, A. Alsaran, Multi-pass scratch test behavior of modified layer formed during plasma nitriding, Tribol. Int. 43 (2010) 1472–1478.
[21] E. Arslan, Ö. Baran, I. Efeoglu, Y. Totik, Evaluation of adhesion and fatigue of MoS2–Nb solid-lubricant films deposited by pulsed-dc magnetron sputtering, Surf. Coat. Technol. 202 (2008) 2344–2348. [22] S.J. Bull, Failure mode maps in the thin film scratch adhesion test, Tribol. Int. 30 (1997) 491–498.
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A comparative study of fatigue properties of TiVN and TiNbN thin films deposited on different substrates Hikmet Ciceka,⁎, Ozlem Baranb, Aysenur Kelesc, Yasar Totikc, Ihsan Efeogluc a b c
Erzurum Technical University, Mechanical Engineering, Turkey Erzincan University, Mechanical Engineering, Turkey Ataturk University, Mechanical Engineering, Turkey
A R T I C L E I N F O
A B S T R A C T
Keywords: Multipass scratch TiVN TiNbN Fatigue
Transition metal nitrides, especially ternary phase films attract attention due to their high mechanical and tribological features. Besides these, fatigue properties play a very important role on the performance in service life of these types of films. TiVN and TiNbN films were deposited on M2 and H13 steel substrates by reactive magnetron sputtering system. Fatigue properties of the films were characterized via multipass scratch tests. 100, 250 and 500 cycles with bidirectional multipass scratch tests were conducted at room temperature by applying 20 N constant load. Structural properties were determined with X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Mechanical features of the films were observed with nano hardness tests. Fatigue behaviors, deformation types, coefficient of frictions of the films and effect of different substrates were discussed comparatively. According to the results, the TiVN films showed better fatigue resistance than the TiNbN films although critical adhesion load value of the TiNbN films was higher than the TiVN films. The TiVN films generally showed ductile type cracks at the edge of the tracks and the TiNbN films showed more brittle type cracks. Additionally, the films deposited on M2 substrates exhibited better strength than those of H13 substrates.
1. Introduction Metal nitride films are used to protect the surface of cutting tools and machine parts against wear, fatigue and corrosion for years. In particular binary TiN, CrN and AlN etc. are widely used in industry. Recently, ternary metal nitride films such as TiZrN [1], TiVN [2], TiNbN [3] and TiAlN [4] have been produced and have generally better properties than the binary ones. Using the closed field unbalanced magnetron sputtering (CFUBMS) system to synthesize for these types of films provides good advantages such as higher film purity, adhesion, homogeneity and density. TiVN films usually have better hardness and wear resistance than the traditional TiN films [5,6]. The ratio of V atoms in the TiVN films affects the film properties and also, about 50% nitrogen show good properties [2]. Protective films must have good mechanical and tribological features. In addition to all these, fatigue behavior is an issue of high importance. Up to now, many researches have studied structural properties [7], mechanical and adhesion properties [2], fracture and tribological behaviors [8] and optical properties [9] but there is no research reported about the fatigue behavior of the TiVN films. TiNbN ternary films also have good mechanical and tribological properties and
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are commercially used for abraded machine part surfaces and especially for prosthesis due to its bio-compatibility [10]. Some studies have been done about the TiNbN films but fatigue properties have not been reviewed. The purpose of this study is to determine the fatigue properties of TiVN and TiNbN thin films with bidirectional multipass scratch tests at three different number cycles. In addition, two types of substrates (H13 — chromium hot work steel and M2 — molybdenum high speed tool steel) were used to examine the substrate effect. The films were deposited with reactive magnetron sputtering method. The obtained results were analyzed comparatively. 2. Experimental Traditional CFUBMS was used to grow TiVN and TiNbN ternary thin films. The films were deposited on M2 and H13 tool steels (chemical compositions were given in Table 2). Before the deposition process, the steel substrates were mechanically polished with SiC emery paper from 240 to 1200 mesh grit and then the substrates' surfaces were treated with α-alumina powder grain size of 0.05 μm as a final action. The surface roughness (Ra) reached a value of about 0.05 μm measured with
Corresponding author at: Erzurum Technical University, Turkey. E-mail address: [email protected] (H. Cicek).
http://dx.doi.org/10.1016/j.surfcoat.2017.06.078 Received 30 March 2017; Received in revised form 30 May 2017; Accepted 7 June 2017 0257-8972/ © 2017 Elsevier B.V. All rights reserved.
Please cite this article as: Cicek, H., Surface & Coatings Technology (2017), http://dx.doi.org/10.1016/j.surfcoat.2017.06.078
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Table 1 Deposition parameters of the TiVN and TiNbN films. Films
Substrate pulsed-dc parameters
Working pressure (Pa)
Ti target current (A)
V target current (A)
Nb target current (A)
Time (min)
Ti interlayer
100 V, 150 Hz, 2 μs 100 V, 150 Hz, 2 μs 100 V, 150 Hz, 2 μs
0.33
1.5
–
–
5
0.33
1.5
1.5
–
80
0.33
1.5
–
1.5
80
TiVN TiNbN
Fig. 3. Cross-section SEM images of the TiNbN and the TiVN thin films.
Table 2 Elemental composition of the TiVN and the TiNbN films. Fig. 1. XRD patterns of the TiVN films deposited on M2 and H13 substrates.
EDS
Atomic percentage (at.%)
Films
Ti
V
Nb
N
TiVN TiNbN
29.86 26.16
27.12 –
– 26.55
43.02 47.29
Substrates
C
Mn
Si
Cr
V
Mo
Fe
m2 h13
0.83 0.38
0.27 0.4
0.33 1.1
4.2 5.3
2.0 0.9
5.1 1.5
87,27 90.42
Table 3 Mechanical properties of the TiVN and the TiNbN films. Films/properties
Nanohardness (GPa)
Thickness (nm)
Critical loads, Lc (N)
TiVN
29 20 35 26
360
60 42 63 47
TiNbN
M2 H13 M2 H13
400
Fig. 2. XRD patterns of the TiNbN films deposited on M2 and H13 substrates.
ion cleaning process for 20 min. To improve the adhesion of the films to the substrate, Ti interlayer was used. Improving the density and also adhesion of the films, pulsed-dc was applied to the substrates. 1.5 A current was applied to the Ti, V and Nb targets during the deposition process. Finally, TiVN and TiNbN films were deposited for 80 min separately. The substrates were spun around the center of the chamber with 1.5 rpm to obtain uniform films and the distance between the targets and substrates was set as 90 mm. The details of the deposition parameters are given in Table 1. The chemical compositions, the microstructure properties and the thickness of the TiVN and TiNbN films were analyzed with SEM and EDS. Crystal structures of the films were determined via XRD with a
a profilometer. In order to remove sticky particles from the surfaces ultrasonic cleaning process was carried out in ethanol bath. After all, the steel substrates etched with 5% nitric acid solution in 10 s. Deposition processes were conducted in argon and nitrogen gas atmosphere. Argon gas was used to sputter atoms from the targets and create plasma. Nitrogen gas was used as reactive gas to obtain nitride phases of the films and kept constant at 40%. One titanium, one vanadium and one niobium target were placed in the vacuum chamber for growing the films. Chamber vacuum pressure was reduced below the 133 × 10− 5 Pa then argon gas was released in the chamber. The negative voltage (800 V) was applied to the substrates in order to perform 2
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Fig. 4. The microscope images of the TiVN and the TiNbN thin films deposited on H13 and M2 substrates after 100 cycles of multipass scratch tests.
CuKα (λ: 1.5405 Å) radiation source. Measurement values were obtained at 2θ:20–110° scan range and 2°/min scan speed. Nanohardness values of the films were identified with NanoHardness with Berkovich inderter tip under 1 mN load. Fatigue behaviors of the deposited films were evaluated with multipass scratch tester Revetest®, produced by CSM Instruments. In the multipass scratch test, the tip moves a certain distance on the sample under constant load and create bidirectional force by moving back and forth on the same track hence films were forced to fatigue. The applied constant load was determined considering the critical load value of the films. In general, between 20% and 50% of the critical load value was determined as constant fatigue load. In this study, approximately 50% of the critical load value (20 N) was decided as constant load. The tip speed was 10 mm/min, the scratch length was 3 mm and the acoustic emission sensitivity was 2, and were set fixed for all of the tests. Rockwell-C diamond tip (200 μm tip radius) was used in all of the tests. The relative humidity was about 45%. Three different bidirectional cycles (100, 250 and 500) were applied to the films and the fatigue behaviors were evaluated.
orientation of the peaks were almost the same in both substrates except for a minor TiVN (200) peak only seen in M2 substrate. TiVN (111) peak was dominantly present. On the other hand it was seen that TiVN (220) peak and TiVN (311) peak were also seen in the structure. The peaks came from the substrates and were marked as Fe (ferrous). According to the XRD results, the TiVN films were successfully synthesized when compared to the literature [11]. The XRD patterns of deposited TiNbN films are given in Fig. 2. According to the graph, the TiNbN (111) peak has the highest intensity, and TiNbN (220) and TiNbN (311) peaks are present on M2 and H13 substrates. In addition to all these, the small TiNbN (200) peak can be observed only at M2 substrates. Also, Fe peaks address the reflections of the substrates. According to these peaks the TiNbN films were produced successfully and the obtained peaks correspond to the values in the literature [1]. The cross-section SEM images of the TiNbN and the TiVN films deposited on glass substrates are given in Fig. 3. The images showed that both TiNbN and TiVN films have a very dense and semi-columnar structure as we request for this type of films. The thickness of the films is 400 ± 10 nm for TiNbN and 360 ± 10 nm for TiVN. Although these thickness values seem a little low for protective coatings, there are lots of similar thinner films in the literature [7,12] and they seem to perform satisfactorily. When we look at the fracture surface, it is seen that both films showed very similar brittle cracks. The roughness of the films are very similar and value is about 0.02 μm.
3. Results and discussion 3.1. Structure of the films Crystallographic structure patterns of the TiVN film deposited on M2 and H13 substrates are given in Fig. 1. It was observed that the 3
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Fig. 5. The microscope images of the TiVN and the TiNbN thin films deposited on M2 and H13 substrates after 250 cycles of multipass scratch tests.
deposited on the harder substrate was higher and vice versa as expected. The hardness measurement was not affected by the substrate hardness because the depth of indenter penetration was less than one in ten of the film thickness.
3.2. Elemental composition The elemental compositions of synthesized TiVN and TiNbN films are given in Table 2. According to the EDS results, Ti and N atoms are commonly present in the films as expected. The atomic percentage of V is (27.12) a little bit high while the target currents of V and Nb are the same. It is likely that this difference emerged from different sputtering yield of V and Nb atoms. The vanadium sputtering yield is about 85 Å/s and the niobium is 80 Å/s hence atomic percentage of V atoms is slightly higher than Nb. Atomic percentages of nitrogen are slightly different, 43.02 for TiVN films and 47.29 for TiNbN films. At this point, it is seen that nitrogen ratio is related to Ti ratio in films. Nitrogen ratio in the films is low while the Ti ratio is high and vice versa.
3.4. Fatigue properties Fatigue is a very important critical feature for the hard protective films. In this study we investigated the fatigue properties of the TiVN and the TiNbN films deposited on M2 and H13 substrates with multipass scratch tests under three different numbers of cycles comparatively. The constant load values applied in such works are generally taken as 20 to 50% of the critical adhesion loads (Lc) of the films [13–16]. The critical load values of the films were given in Table 2. We have specified 20 N as the constant load value here and 100, 250 and 500 cycle tests were conducted. Scratch track images and coefficient of friction values of the films were categorized considering the number of the cycles. The track images of the TiVN and the TiNbN films after 100 cycles of multipass scratch test are given in Fig. 4. When looked at the scratch tracks of the films deposited on M2 substrates, both films showed brittle fractures at the edge of the tracks and there were no adhesive cracks seen between the films and substrates. In addition, a small amount of medium size debris can be seen in the TiNbN film and some pieces of small size debris are in place in the TiVN film. Both films deposited on M2 substrates showed great fatigue resistance at 100 cycles under 20 N subcritical load. On the H13 substrates, the same brittle fractures were also observed at the edge of the tracks and some little adhesive cracks
3.3. Mechanical properties Hardness values of the films were observed via nanohardness tests under 1 mN load in order to obtain lower than 0.1 value of indentation depth/film thickness ratio. The nanohardness results of the films are given in Table 3. The highest hardness value was obtained from the TiNbN film deposited on M2 substrate as 35 GPa and the lowest hardness value was obtained from the TiVN film deposited on H13 substrate as 20 GPa. It is clearly seen that the TiNbN films are harder than the TiVN films when the same substrate is taken into account. This result is consistent with the literature [3,10,11]. On the other hand, hardness of the films was seriously affected from the substrate hardness. The uncoated substrate hardness values were 5.6 GPa for M2 and 3 GPa for H13 respectively. These results reveal that the hardness of the films 4
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Fig. 6. The microscope images of the TiVN and the TiNbN thin films deposited on M2 and H13 substrates after 500 cycles of multipass scratch tests.
pieces of debris were embedded to the substrate firmly where they are formed and could not move with the indenter motion due to higher substrate hardness so they were regularly distributed in the tracks. As a result, the TiNbN and the TiVN films deposited on H13 substrates showed fatigue resistance but not as good as deposited on M2 substrates. The track images of the TiNbN and TiVN films after the highest cycle (500) are shown in Fig. 6. Looking at the M2 substrate, the films still maintain their continuity and there aren't any adhesive failures so they still showed very good fatigue resistance after 500 cycles of scratching. Brittle fractures occurred at the edge of the tracks. The debris distribution is similar with 100 and 250 cycles but the differences are size and numbers that increased. This situation was expected due to the increase in the number of cycles. On the other hand, when we look at the H13 substrates, the adhesive failures increased even more and films could not maintain their continuity hence fatigue failures occurred both the TiVN and the TiNbN films but a little more at the TiNbN. The debris distribution is similar with lower cycle tests and collected at the end regions. The friction coefficient graphs of the TiVN and the TiNbN thin films deposited on M2 and H13 substrates under 100, 250 and 500 cycles of multipass scratch tests are given in Fig. 7. The coefficient of friction (COF) values of the substrates after 500 cycles were 0.4 ± 0.02 for M2 and 0.56 ± 0.04 for H13. When we looked at the 100 cycle results, the
can be seen in the TiNbN film while seen nowhere in the TiVN. These adhesive cracks can be attributed to high hardness of the TiNbN film (26 GPa) and low (47 N) Lc value. Although the Lc value of TiVN film (42 N) is smaller than the TiNbN film, adhesive failure has not occurred in the TiVN. At this point, we can say that the difference between hardness values of the film and the substrate is another factor affecting the fatigue resistance. Fig. 5 shows the multipass scratch track images of the films after 250 cycle passes. Firstly, when we look at the films deposited on M2 substrates, there are no adhesive failures or chippings in the tracks. Brittle fractures are clearly seen at the edge of the tracks. The debris is embedded in the films and this is almost homogeneously dispersed. Both films deposited on M2 maintained their continuity. On the H13 substrates, TiNbN film continued to show adhesive failures. At the TiVN films, some little adhesive failures can be seen in the track in addition to the brittle fractures at the edges. On the other hand, it is seen that the debris distribution is different from the films deposited on M2 substrates. The debris is generally embedded at the end regions of the tracks and some pieces of debris were found in middle of the tracks. This situation probably emerged from the lower hardness value of the H13 substrate compared to M2. The hardening debris severed from the films was embedded to substrate and could be moving easily with the indenter tip motion due to lower hardness of H13 substrates hence they were collected at the end of the scratch regions. At the M2 substrate the 5
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Fig. 7. The coefficients of friction of the TiVN and the TiNbN thin films deposited on M2 and H13 substrates under 100, 250 and 500 cycles of multipass scratch tests.
films deposited on M2 substrates, the COF values showed quite stable behavior. The COF values started at 0.05 on the first contact and after 10 cycles dropped to 0.02 and stayed around this value. It is seen that the COF values of the TiNbN film are a bit lower than TiVN films at all cycles. This is because of the general behavior of the relationship between hardness and COF [17,18]. The TiNbN film (35 GPa) was harder than TiVN (29 GPa) hence it showed lower COF values. On the H13 side, the starting point of the COF values is closer to 0.05 but after 20 cycles, it occurred slightly later compared to M2 and COF values reached the stable values at 0.02. This slightly delayed stability emerged most probably from the lower hardness of H13 substrates compared to M2. At the end of the cycles, TiNbN films showed slightly low COF values similar to the deposited films on M2. On the other hand, COF values of the TiNbN film exhibited more unstable behavior compared to the films deposited on M2 substrate due to the formation of the adhesive failures.
When the COF results of 250 cycles are examined, at the M2 substrates, COF values started at 0.05 in the first contact then decreased to 0.02 after 25 cycles. These values also gradually diminished to the stable value of 0.017 until the number of cycles reached 125, and remained stable until the end of the 250 cycles. Similar to the 100 cycle results, the TiNbN film showed slightly low COF values. On the H13 side, both films showed more undulating course considering the 100 cycle result. This emerged from the increase in the adhesive failure at both films. Up to 250 cycles, COF values of TiNbN decreased and reached 0.015 and COF values of the TiVN decreased slightly and reached 0.018. Finally, looking at the 500 cycle results, at the M2 substrates, COF values of both films showed quite stable behavior. COF values of the TiNbN film are slightly lower than the TiVN and reached nearly 0.013 at least. The COF values of the TiVN film also showed very stable behavior and nearly reached 0.018 at the end of the 500 cycle. On the 6
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H13 side, both films showed good stable COF values at about 0.017. After the 250 cycle, COF values of TiVN film showed a rapid increase and reached up to a value of nearly 0.37. This unwanted situation emerged from the increasing of adhesive failures also seen in the track images (Fig. 6). When the indenter reached the substrate where the adhesive failure occurred, the COF value increased. From this point of view, we can say that evidence of the adhesive failures started at about 250 cycle for the TiVN film deposited on H13 substrate. At the TiNbN film, stable COF value continued up to 350 cycle with quite a slight reduction. After 350 cycle, COF value started to increase and reached up to 0.022 values. It is observed that the TiNbN film deposited on H13 substrate started to have the adhesive failures at about 350 cycles. Studies in the literature [13,14,19–22] and this study showed that multipass scratch test resistance (fatigue like behavior) of the films is affected from the hardness of the films and substrates and the critical adhesion load of the films (Lc) and thickness of the films. It is known that the critical adhesion load (Lc) and the thickness of the film positively affect the fatigue strength [13,20–22]. On the other hand, increasing the ratio in the hardness values of the film and the substrate negatively affect the fatigue resistance. From this point of view, an empirical formula can be developed between the fatigue strength and these properties are mentioned when the pass cycle numbers, applied constant load, scratch tip type and tip speed are the same. To shorten features into symbols: Hf Hs Lc T FS
• • •
• •
Hardness of the film (GPa) Hardness of the substrate (GPa) Critical adhesion force (Newton) Thickness of the film (μm) Fatigue strength
Empirical formula for fatigue strength: FS =
References [1] I. Grimberg, V. Zhitomirsky, R. Boxman, S. Goldsmith, B. Weiss, Multicomponent Ti–Zr–N and Ti–Nb–N coatings deposited by vacuum arc, Surf. Coat. Technol. 108–109 (1998) 154–159. [2] C. Montero-Ocampo, E.A. Ramírez-Ceja, J.A. Hidalgo-Badillo, Effect of codeposition parameters on the hardness and adhesion of TiVN coatings, Ceram. Int. 41 (2015) 11013–11023. [3] Ł. Łapaj, J. Markuszewski, J. Wendland, A. Mróz, M. Wierusz-Kozłowska, Massive failure of TiNbN coating in surface engineered metal-on-metal hip arthroplasty: retrieval analysis, J. Biomed. Mater. Res. B Appl. Biomater. 104 (2016) 1043–1049. [4] P. Li, L. Chen, S.Q. Wang, B. Yang, Y. Du, J. Li, M.J. Wu, Microstructure, mechanical and thermal properties of TiAlN/CrAlN multilayer coatings, in: Int, J. Refract. Met. Hard Mater. (2013) 51–57. [5] O. Knotek, W. Burgmer, C. Stoessel, Arc-evaporated Ti-V-N thin films, Surf. Coat. Technol. 54–55 (1992) 249–254. [6] J.H. Ouyang, T. Murakami, S. Sasaki, High-temperature tribological properties of a cathodic arc ion-plated (V,Ti)N coating, Wear 263 (2007) 1347–1353. [7] T. Deeleard, A. Buranawong, A. Choeysuppaket, N. Witit-Anun, S. Chaiyakun, P. Limsuwan, Structure and Composition of TiVN Thin Films Deposited by Reactive DC Magnetron Co-sputtering, Procedia Eng. (2012), pp. 1000–1005. [8] B. Deng, Y. Tao, D. Guo, Effects of vanadium ion implantation on microstructure, mechanical and tribological properties of TiN coatings, Appl. Surf. Sci. 258 (2012) 9080–9086. [9] C. Wiemer, F. Lévy, F. Bussy, Determination of chemical composition and its relationship with optical properties of Ti-N and Ti-V-N sputtered thin films, Surf. Coat. Technol. 68–69 (1994) 181–187. [10] A.P. Serro, C. Completo, R. Colaço, F. dos Santos, C.L. da Silva, J.M.S. Cabral, H. Araújo, E. Pires, B. Saramago, A comparative study of titanium nitrides, TiN, TiNbN and TiCN, as coatings for biomedical applications, Surf. Coat. Technol. 203 (2009) 3701–3707. [11] Y.-Y. Chang, W.-T. Chiu, J.-P. Hung, Mechanical properties and high temperature oxidation of CrAlSiN/TiVN hard coatings synthesized by cathodic arc evaporation, Surf. Coat. Technol. 303 (2016) 18–24. [12] M.E. Uslu, A.C. Onel, G. Ekinci, B. Toydemir, S. Durdu, M. Usta, L.C. Arslan, Investigation of (Ti,V)N and TiN/VN coatings on AZ91D Mg alloys, Surf. Coat. Technol. 284 (2015) 252–257. [13] I. Efeoglu, R.D. Arnell, Multi-pass sub-critical load testing of titanium nitride coatings, Thin Solid Films 377–378 (2000) 346–353. [14] S.J. Bull, D.S. Rickerby, Multi-pass scratch testing as a model for abrasive wear, Thin Solid Films 181 (1989) 545–553. [15] H. Cicek, I. Efeoglu, Fatigue and adhesion properties of martensite and austenite phases of TiNi shape memory thin films deposited by magnetron sputtering, Surf. Coat. Technol. 308 (2016) 174–181. [16] F. Bidev, Ö. Baran, E. Arslan, Y. Totik, I. Efeoǧlu, Adhesion and fatigue properties of Ti/TiB2/MoS2 graded-composite coatings deposited by closed-field unbalanced magnetron sputtering, Surf. Coat. Technol. 215 (2013) 266–271. [17] I. Efeoglu, R.D. Arnell, S.F. Tinston, D.G. Teer, The mechanical and tribological properties of titanium aluminium nitride coatings formed in a four magnetron closed-field sputtering system, Surf. Coat. Technol. 57 (1993) 117–121. [18] I. Efeoglu, Ö. Baran, F. Yetim, S. Altıntaş, Tribological characteristics of MoS2–Nb
Hs × Lc × T [N⋅μm] Hf (1)
It can be said that the film with high FS value shows better fatigue strength. Applying this formula (Eq. (1)) to the films in this work;
TiVN on M2: FS =
5.6 × 60 × 0.36 = 4.17 29
TiNbN on M2: FS =
5.6 × 63 × 0.4 = 4.03 35
TiVN on H13: FS =
3 × 42 × 0.36 = 2.27 20
TiNbN on H13: FS =
successfully synthesized and thickness of the films are 400 nm for TiNbN and 360 nm for TiVN. The highest hardness value obtained from TiNbN film deposited on M2 substrate was 35 GPa and the lowest was TiVN film deposited on H13 substrate as 20 GPa. The highest adhesion critical load (Lc) was 63 N obtained from the TiNbN film deposited on M2 substrate and the lowest was 42 N obtained from the TiVN film deposited on H13 substrate. It was observed that the film hardness was affected by the substrate hardness. After 100 cycle multipass scratch test all the films showed very good fatigue strength except some slight adhesive cracks in the TiNbN film deposited on H13 substrate. After 250 cycle multipass scratch test, the films deposited on H13 substrates showed some adhesive cracks but the film deposited on M2 substrate still showed very good fatigue strength. After 500 cycle multipass scratch test, the density of the adhesive cracks in the films deposited on H13 substrates increased but the films deposited on M2 substrates showed better resistance to the adhesive cracking. The coefficient of the friction values of the films started at about 0.055 and then decreased down to nearly 0.015. The TiNbN films showed slightly lower COF values than the TiVN films. An empirical formula was developed for fatigue strength (FS) of the films considering the film and substrate hardness, critical adhesion load (Lc) and the thickness of the films.
3 × 47 × 0.4 = 2.17 26
According to these results, the lowest FS value is 2.17 for TiNbN on H13 and also the film with the lowest fatigue strength. After this, FS values are ranked as 2.27 for TiVN on H13, 4.03 for TiNbN on M2 and 4.17 for TiVN on M2. When we looked at the multipass scratch test results, it is seen that these results overlap with each other. On the other hand, this formula should be analyzed with more films to reinforce its accuracy. But it is possible to obtain a preliminary idea of which film will exhibit better fatigue strength when these properties are known. 4. Conclusion The TiVN and the TiNbN thin films were deposited on M2 and H13 substrates via reactive magnetron sputtering method. Structural, mechanical and fatigue properties of the films were investigated and the results are listed below.
• XRD patterns showed that the TiVN and the TiNbN thin films were 7
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H. Cicek et al. solid lubricant film in different tribo-test conditions, Surf. Coat. Technol. 203 (2008) 766–770. [19] A.-T. Akono, F.-J. Ulm, Scratch test model for the determination of fracture toughness, Eng. Fract. Mech. 78 (2011) 334–342. [20] F. Yildiz, A. Alsaran, Multi-pass scratch test behavior of modified layer formed during plasma nitriding, Tribol. Int. 43 (2010) 1472–1478.
[21] E. Arslan, Ö. Baran, I. Efeoglu, Y. Totik, Evaluation of adhesion and fatigue of MoS2–Nb solid-lubricant films deposited by pulsed-dc magnetron sputtering, Surf. Coat. Technol. 202 (2008) 2344–2348. [22] S.J. Bull, Failure mode maps in the thin film scratch adhesion test, Tribol. Int. 30 (1997) 491–498.
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