- Email: [email protected]
ZrCN multilayer coatings
Journal of Alloys and Compounds 803 (2019) 1005e1015
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Microstructure and mechanical properties evaluation of cathodic arc deposited CrCN/ZrCN multilayer coatings Sung-Hsiu Huang a, b, Cheng-Yi Tong c, Tsung-Eong Hsieh a, Jyh-Wei Lee c, d, e, f, * a
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan Gigastorage Corporation, Hsinchu, Taiwan c Department of Materials Engineering, Ming Chi University of Technology, Taiwan d Center for Plasma and Thin Films Technologies, Ming Chi University of Technology, Taiwan e Department of Mechanical Engineering, Chang Gung University, Taoyuan, Taiwan f Plastic and Reconstructive Surgery, Craniofacial Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2019 Received in revised form 20 June 2019 Accepted 28 June 2019 Available online 29 June 2019
For the development of advanced nanoscale multilayer protective coatings, proper design of microstructure and chemical composition of carbon containing sequential transition metal nitride nanolayers is an important issue. In this work, five different nanostructured CrCN/ZrCN multilayer coatings were deposited periodically by cathodic arc evaporation. The bilayer period of the CrCN/ZrCN multilayer coatings was kept at 20 nm. The C2H2 gas flow ratio was adjusted from 6.3 to 20.0% for achieving CrCN/ ZrCN multilayer coatings with 2.3e4.2 at.% carbon content. Nanolaminated CrCN and ZrCN nitride layers and thin amorphous carbon nitride mixed nanolayers ~5 nm thick were obtained as the carbon content reached 4.2 at.%. It was found that the hardness and adhesion quality were strongly improved by the carbon addition to the CrCN/ZrCN multilayer coatings. An increase of 2.6e4.6 GPa in hardness was found for the CrCN/ZrCN multilayer coatings due to the balance of solution hardening effect of carbon atoms and the softening by the amorphous mixed nanolayer. An optimal combination of high hardness, 28.9 GPa, and good adhesion, 41 N of upper critical load were achieved when the carbon content was 4.2 at.% for the CrCN/ZrCN multilayer coatings. © 2019 Elsevier B.V. All rights reserved.
Keywords: Cathodic arc evaporation CrCN/ZrCN Multilayer Nanoindenter Tribological properties Scratch test
1. Introduction In recent years, cathodic arc evaporation (CAE) technology has been widely applied in the traditional decorative and tool industries [1,2], and also to fabricate advanced nanocomposite [3] and nanolaminated thin films [4,5]. Among the transition metal nitride thin films, CrN is widely used in industries due to its higher thermal stability, good tribological properties [6] and better corrosion resistance [7], which is considered as a candidate to replace TiN coatings in several applications [8]. By addition of carbon into the CrN thin film, the hardness and tribological performance can be effectively improved [3,9e12]. A better toughness, wear resistance and longer service life were obtained for the CrN/ CrCN multilayered thin films deposited on wood cutting tools when
* Corresponding author. Department of Materials Engineering, Ming Chi University of Technology, Taiwan. E-mail address: jeffl[email protected] (J.-W. Lee). https://doi.org/10.1016/j.jallcom.2019.06.370 0925-8388/© 2019 Elsevier B.V. All rights reserved.
a proper C2H2 flow rate of 10 sccm was used [13]. On the other hand, ZrN thin film is characterized for its good mechanical properties [14] and good corrosion resistance [15], which make ZrN a popular material applied widely in industries. Research work on ZrN-based TiN/ZrN [16] and CrN/ZrN [4,5,17e19] multilayered coatings has revealed that excellent mechanical properties were achieved due to the combination of suitable nanoscale multilayered features. Recently, carbon containing ZrCN thin films were applied due to their high hardness [20], anti-corrosion [21] and tribological behaviors [22]. Better mechanical properties were achieved for ZrCN coatings containing higher carbon content [23,24]. For the development of advanced nanoscale multilayer protective coatings, simultaneous growth of a nanocrystalline hard phase and amorphous carbon is an interesting concept [25,26]. For example, transition metal nitride coatings containing higher C content, such as TieAleNeC [25] and VeAleCeN [26], were grown with special nano-architectures (nanocomposite and nanolaminated coatings consisting of metastable hard phase and amorphous carbon) and exhibited promising tribological
1006
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
deposited as an adhesion layer. Multilayered coatings were deposited by alternately rotating the substrates between the plasma of Cr and Zr targets. The specimens were hanged in the fixture in the center of the coater with a self-rotating speed of 10 rpm and a revolutionary speed of 2 rpm. The schematic top-view of the coater and the configuration of targets and substrates are shown in Fig. 1. The bilayer period was kept at the same value ~20 nm for each multilayered coating. Various carbon contents were obtained by different flow rates of N2, f(N2), and acetylene (C2H2), f(C2H2), gas mixtures during the deposition process. The DC power current values for the Cr and Zr targets were all 90 A. The designed thickness ratio of ZrCN to CrCN layers was around 1:1, which was calculated based on the thickness values of ZrCN and CrCN monolayer coatings under the same deposition conditions. The detailed deposition parameters are listed in Table 1. It appears that the C2H2 gas flow ratio, f(N2)/(f(N2) þ f(C2H2), increased from 6.3 to 20.0% as the C2H2 flow rate increased from 7.5 to 30 sccm. The C2H2 gas flow ratio and carbon contents were further used to discuss their effects on the characteristics of CrCN/ZrCN multilayered thin films. The chemical composition of the CrCN/ZrCN thin films deposited on Si wafers was analyzed by field emission electron probe microscopy (FE-EPMA, JXA-8500F, JEOL, Japan) with the aid of the ZAF-corrected program [29]. The average chemical composition of each coating was obtained from three different measurement areas. The depth profile of the chemical composition of selected coatings deposited on Si wafer substrates was explored with Auger electron spectroscopy (AES, Auger NanoProbe, 670 PHI Xi, PerkinElmer, USA). The phase compositions of coatings deposited on Si wafer substrates were evaluated by grazing angle X-ray diffraction (XRD6000, Shimadzu, Japan) with an incident angle of 2 . Cu Ka radiation generated at 30 kV and 20 mA from a Cu target was used. Fourier transform infrared spectroscopy (FTIR, Spectrum One, PerkinElmer, USA) measurements were performed to explore the type of chemical bonds of the CN structure of each thin film deposited on Si wafer substrate. The surface roughness of each coating deposited on Si wafer substrate was measured by a 3D laser scanning microscope (VKe9700K, KEYENCE, Japan). The scan area was 700 mm 500 mm. Three different regions were selected for the surface roughness measurement for each coating. The surface and cross-section morphology of each coating deposited on Si wafer substrate was obtained by field emission scanning electron microscopy (FE-SEM, JSM-6701F, JEOL, Japan) and transmission electron microscopy (TEM, JSM-2100, JEOL, Japan). The residual stress of films deposited on Si wafer substrates was calculated using Stoney's equation [30]. The dimension of thin film deposited Si wafer for residual stress
performance. The research work on ZrCN-based carbonitride multilayer coatings is limited. For example, Zr/ZrCN multilayers were fabricated for medical implant applications [27] and TiCN/ ZrCN multilayers were studied due to their high hardness [28]. The effect of the bilayer periods (L) on the hardness and tribological properties was reported on CrN/ZrN multilayered coatings in previous work [4]. Adequate hardness and excellent tribological properties were achieved for multilayered coatings with the same thickness ratio of CrN and ZrN layers and a bilayer period of 20 nm [4]. However, no effort was ever made on the microstructure and mechanical properties evaluation for nanolaminated CrCN/ZrCN coatings. In this study, five CrCN/ZrCN multilayered coatings containing different carbon contents with the same L value (20 nm) and the same CrCN to ZrCN layer thickness ratio were fabricated by CAE process. The influence of carbon concentration on the microstructure, mechanical properties and tribological performance of CrCN/ZrCN multilayered coatings was investigated. 2. Experimental procedure In this study, five CrCN/ZrCN multilayered thin films with different carbon contents were deposited on P-type (100) silicon wafers and hardened and polished AISI420 stainless steel discs by a cathodic arc evaporation system (KMARC, Kuen Min Tech. Co., Taiwan). Chromium and zirconium targets with a purity of 99.99 wt % and diameters of 101.6 mm were used. Microparticle filters were used to reduce the amount of macroparticles and pin hole defects on the surface. A pure CrZr interlayer around 60 nm thick was
Fig. 1. The schematic top-view of the coater and the configuration of targets and substrates.
Table 1 Deposition parameters and chemical compositions of CrCN/ZrCN multilayer thin films. Sample designation
A
B
C
D
E
C2H2 flow rate, f(C2H2) (sccm) N2 flow rate, f(N2) (sccm) C2H2 flow ratio, f(N2)/(f(N2)þf(C2H2)) (%) Chemical composition (at.%)
7.5 112 6.3 28.6 ± 0.1 21.8 ± 0.5 46.5 ± 0.6 2.3 ± 0.0 0.8 ± 0.3 90 1.2 102 Ar plasma for 15 min at 0.81 150 100 26
12.5 111 10.1 28.9 ± 0.5 21.0 ± 0.2 46.6 ± 0.7 2.6 ± 0.2 0.8 ± 0.2
17.5 115 13.2 29.8 ± 1.4 20.9 ± 1.0 45.2 ± 2.7 3.0 ± 0.1 1.1 ± 0.1
25.0 122 17.0 24.3 ± 0.3 25.8 ± 0.3 44.7 ± 0.1 4.1 ± 0.1 1.1 ± 0.3
30.0 120 20.0 26.2 ± 0.4 24.2 ± 0.4 44.7 ± 0.2 4.2 ± 0.0 0.7 ± 0.3
Target current (A) Base pressure (Pa) Plasma etching Working pressure (Pa) Substrate temperature (oC) Substrate bias (V) Deposition time (min)
Cr Zr N C O
1.33 Pa under substrate bias 800 V
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
measurement was around 15.0 15.0 0.525 mm3. It is important to point out that some requirements, such as the coating thickness is much smaller than that of the Si substrate, and the Si substrate thickness is also much smaller than the width of the Si substrate, must be satisfied for correctly calculating the residual stress of each thin film using Stoney's equation [30]. The hardness and elastic modulus of the thin films deposited on AISI420 substrates were measured by a nanoindenter (TI-900, TriboIndenter, Hysitron, USA) using a Berkovich 142.3 diamond probe at a maximum applied load of 5 mN. Eight indentations were made on the surface without macroparticle and pin hole defects for each coating. The maximum indentation depth was limited to around 100 nm, which was around the one-tenth of the film thickness. The loading and unloading rates of the nanoindentation were all 1000 mN/s. The holding time was 5 s. A scratch test (Scratch Tester, J & L Tech. Co., Korea), with a maximum load of 100 N was adopted to explore the adhesion properties of thin films deposited on AISI420 substrates. Three scratch tracks were tested for each specimen. The adhesion strength quality of thin films deposited on AISI420 substrates was evaluated by a Daimler Benz Rockwell-C (HRC-DB) tester [31]. Three HRC-DB tests were made for each coating. A ball-on-disk wear tester (Wear Tester, J & L Tech. Co., Korea) was used to investigate the performance of coatings deposited on AISI420 substrates. A cemented tungsten carbide (WC-6 wt.% Co) ball, 6 mm in diameter was adopted as the stationary ball. A normal load of 5 N was applied. The rotation speed was 200 rpm with a wear track diameter of 8 mm. The test temperature was 20 C, and the relative humidity was kept at 60%. The wear length was 500 m for each test. The wear rate of each coating was determined based on the following equation [32]:
WR ¼
tð3t 2 þ 4b2 Þ2pr 6bFn S
(1)
where t is the average depth of the wear track, b is the average width of the wear track, r is the radius of the wear track, Fn is the normal load and S is the sliding distance. The average t and b values were determined using a surface profilometer to measure eight cross-sections of each wear track. Only one wear test was conducted for each coating. 3. Results and discussion 3.1. Composition and phase characterization of CrCN/ZrCN multilayer thin films According to the chemical composition analysis data of CrCN/ ZrCN multilayer thin films by FE-EPMA as listed in Table 1, the carbon content increases from 2.3 to 4.2 at.% when C2H2 flow ratio increases from 6.3 to 20.0%, respectively. However, higher carbon containing thin films were not prepared due to the instability of plasma during deposition when the C2H2 flow ratio was higher than 20.0%. According to Table 1, with the increase of C2H2 flow ratio, the N and Cr contents first increase followed by a decrease, and the Zr content has a highest value, 25.8 at.%, at 17.0% of C2H2 flow ratio. In comparison, the nitrogen content of coatings decreases gradually from 46.5 to 44.7 at.% when the carbon content increases from 2.3 to 4.2 at.% and the C2H2 flow ratio increases from 6.3 to 20.0%. A similar result was also reported in a previous study on CrCN coatings [3]. We suggest that the substitutional effect of carbon elements for replacing the nitrogen elements in the ZrN and CrN lattice sites is responsible for this chemical composition evolution. The Cr content decreases with increasing acetylene flow ratio and changes from 28.6 to 26.2 at.%. Meanwhile, the Zr content increases from 21.8 to 24.2 at.% as the C2H2 flow ratio and carbon content
1007
Fig. 2. The Auger electron depth profiling of the E coating.
increase. We suggest that the lower formation free energy for ZrC phase than that of CrxC phases [33] will attract more Zr atoms into the coating when the carbon content increases. It is also noticed that an oxygen contamination around 0.7e1.1 at.% is found for each coating. In order to investigate the detailed chemical compositions of individual layers, Auger electron depth profiling of the E coating is shown in Fig. 2. The sputtering rate in the first 5 min was 2.6 nm/ min and then decreased to 1 nm/min. According to the depth profiling data shown in Fig. 2, the CrCN, ZrCN and a mixed layer can be identified. Although the rather complex chemical composition variations can be seen for each element in Fig. 2, the obvious change of Cr and Zr contents are found for each individual layer. The significantly higher carbon content as shown in the AES data on the coating surface are attributed to the outermost surface contamination. In Fig. 2, the carbon and nitrogen concentrations deviate from 7.8 to 16.7 at.% and from 44.7 to 60.7 at.%, respectively, within different layers. The maximum Cr content of 34.9 at.% can be seen in the CrCN layer, whereas the highest Zr concentration of 23.6 at.% is discovered in the ZrCN region. The average chemical compositions for the individual ZrCN and CrCN layers are 22.6% Zr, 6.4% Cr, 57.3% N, 13.7% C and 10.4% Zr, 32.4% Cr, 47.0% N, 10.2% C (in at.%), respectively. The nitrogen and carbon contents are lower in the CrCN layer as compared with the ZrCN layer. For the mixed layer, the average chemical composition is 20.1% Zr, 11.5% Cr, 56.0% N and 12.4% C (in at.%). It appears that the nitrogen and carbon contents in this mixed layer are higher than these in CrCN layer. The chemical compositions of Zr and Cr, 20.1 and 11.5%, in the mixed layer are less than 22.6% Zr in the ZrCN and 32.4% Cr in the CrCN layers, respectively. We believe that this mixed layer is a mixture of ZrCN, CrCN and amorphous carbon nitride phases. It should be noticed that during AES analysis the oxygen concentration was not detected as shown in Fig. 2. The glancing angle XRD patterns of CrCN/ZrCN multilayer thin films deposited with different C2H2 flow ratios are shown in Fig. 3. The CrN (111), (200), (220) and the ZrN (111), (200), (220) and (311) reflections are labeled in Fig. 3. However, the CrN (111) reflection of D coating is not obvious. The CrN (200) reflection can only be observed for E coating. The CrN (220) diffraction peaks are hard to be found in all samples. Positions of the ZrN (111) diffraction peaks shift very slightly to a higher diffraction angle, whereas the CrN (111) diffraction peaks shift very slightly toward a lower diffraction angle with increasing C2H2 flow ratios. It appears that the substitution of carbon atoms into the nitrogen and anion sites of CrN and
1008
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
Fig. 3. X-ray diffraction patterns of the CrCN/ZrCN multilayer thin films.
ZrN lattice and the generated residual stress should have an influence on these peak shifts in Fig. 3. The average grain size of each multilayer coating is hard to calculate due to the overlapping of ZrN and CrN diffraction peaks. In addition, very weak b-Cr2N (002) and (111) reflections are also found indicating its rather low phase content in the coating. The existence of Cr2N and CrN mixed two phases structure was also discovered in the CrCN coatings [10,11]. No Zr or Cr related carbide and oxide phases are found in Fig. 3. In this work, no satellite peaks are found for each multilayer coating. It is suggested that the Bragg peak intensity is typically much smaller for non-epitaxially grown multilayers, and the satellite peaks may be hidden in the background even if a perfect composition modulation is present [34]. In order to understand the effect of carbon and nitrogen contents on the phase structure and to investigate the existence of the amorphous CN phase in the coatings, FTIR measurements were further conducted. The FTIR reflection spectrum of coatings prepared with different carbon contents is shown in Fig. 4. There are three characteristic peaks for the CN phase at 1200-1300 cm1(CeN), 16001700 cm1 (C]N) [35] and 2200 cm1 (C^N) [36]. The absorption peaks corresponding to CeN and C]N bonds at ~1290 cm1 and ~1600 cm1 can be found for each coating. Meanwhile, no obvious C^N characteristic peak can be recognized for all coatings. In addition, the absorption peak at ~1045 cm1 can be attributed to the NeN bond [37]. This amorphous carbon nitride phase was also revealed in the CrCN [9,12] and ZrCN [24] coatings. Effects of the amorphous carbon nitride phase contained mixed layers on the mechanical properties of the CrCN/ZrCN multilayer coatings will be discussed later. Furthermore, the FTIR spectra of C and E coatings differ from the other three. The detailed reason still needs further investigation. According to the FTIR analysis results, carbon and nitrogen bonded atoms under different chemical bonding configurations are observed for the CrCN/ZrCN multilayer thin films. However, it should be noticed that, as compared with the broad adsorptions in the 1150-1800 cm1 region for carbon nitride powders [37], the adsorption intensities of multilayer coatings are relatively weaker due to a small amount of the amorphous carbon nitride phase in
Fig. 4. Fourier transform infrared spectra of the CrCN/ZrCN multilayer thin films.
this work. On the other hand, no G and D bands characteristic of a carbon phase are found for each CrCN/ZrCN multilayer thin film by the Raman spectroscopy analysis, which is possibly due to the rather low amount of carbon contents in this work. 3.2. Microstructure characterization of CrCN/ZrCN thin films A typical surface morphology consisting of macroparticles and pinholes was observed on the surface for each coating as illustrated in Fig. 5. The average surface roughness, Ra, and average size of macroparticles of each thin film analyzed from three different regions are listed in Table 2. The scattered roughness values indicate that the randomly distributed surface defects have strong influence on the measurement result. The average size values of macroparticles ranging from 1.7 to 2.2 mm can be observed. Meanwhile, the chemical nature of the macroparticles is pure metallic Cr or Zr, implying the droplets were from the metallic targets during deposition. The cross-sectional morphologies for all coatings are depicted in Fig. 6(a)e(e). The thickness of each coating is around 1 mm. The laminated microstructure and pure CrZr interlayer can be observed for each coating. It is also found that columnar structure can be recognized for D and E coatings when the C2H2 flow ratio and carbon content are higher than 17.0% and 4.0 at.%, respectively. The detailed cross-sectional morphologies of A and E coatings are further investigated by TEM. Fig. 7(a) shows the cross-sectional TEM micrograph and selected area electron diffraction (SAED) patterns for the A coating containing 2.3 at.% C. The laminated microstructure can be observed clearly. The CrN and ZrN phases can be identified according to the SAED patterns. The cross-sectional TEM dark-field image of the ZrN (200) lattice plane and corresponding SAED patterns of the A coating are shown in Fig. 7(b). Obviously, the sequential ZrCN and CrCN multilayers as indicated by markers in Fig. 7(b) can be clearly observed through the dark field image technique. The average thickness value for the bright
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
1009
Fig. 5. The surface SEM morphologies of (a) A, (b) B, (c) C, (d) D and (e) E CrCN/ZrCN multilayer thin films.
Table 2 Characteristics of CrCN/ZrCN multilayer coatings: surface roughness, macroparticle size, residual stress, critical loads, HF values, coefficient of friction (COF), average wear depth and wear rate. Sample designation
A
B
C
D
E
C2H2 flow rate, f(C2H2) (sccm) C2H2 flow ratio, f(N2)/(f(N2)þf(C2H2) (%) Surface roughness, Ra (nm) Macroparticle size (mm) Residual stress (GPa) Lc1 (N) Lc2 (N) HF COF Wear depth (mm) Wear rate (mm3m1N1)
7.5 6.3 112 ± 9 2.2 ± 1.0 2.36 12.5 ± 0.4 22.7 ± 1.8 6 0.45 ± 0.02 0.31 ± 0.11 8.1 107
12.5 10.1 80 ± 28 1.7 ± 0.4 2.08 24.4 ± 1.2 35.7 ± 0.6 5 0.44 ± 0.04 0.50 ± 0.07 1.2 106
17.5 13.2 69 ± 21 1.9 ± 1.1 2.60 25.0 ± 2.7 36 ± 1.0 3 0.42 ± 0.03 0.36 ± 0.11 9.2 107
25.0 17.0 130 ± 38 2.1 ± 1.0 3.06 e 41.3 ± 3.8 1 0.41 ± 0.05 0.95 ± 0.08 2.1 106
30.0 20.0 69 ± 19 1.8 ± 0.8 2.93 e 41.0 ± 1.4 1 0.46 ± 0.04 0.72 ± 0.18 1.4 106
ZrN and dark CrN layer is around 10 nm, respectively, which is close to the designed value. The cross-sectional TEM bright field image, dark-field image of the ZrN (200) lattice plane and corresponding SAED patterns of the E coating with 4.2 at.% C are depicted in Fig. 8(a)-(b), respectively. Similarly, the nanolaminated structure is
also revealed. Again, the average thickness for the bright ZrN layer and dark CrN layer is around 10 nm. Fig. 8(c) illustrates the multilayered structure at higher magnification. The average CrCN/ZrCN bilayer period is calculated to be 20 nm. It is also noticed that a thin layer around 5 nm thick can be observed between each bilayer. In
1010
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
Fig. 6. The cross-sectional SEM morphologies of (a) A, (b) B, (c) C, (d) D and (e) E CrCN/ZrCN multilayer thin films.
addition, the fine columnar structure around several tens nm wide can be observed in the TEM images in Figs. 7 and 8 for A and E coatings. According to the depth profiling data shown in Fig. 2, the CrCN, ZrCN and mixed layer can be identified. As we discussed before, the average chemical composition of the mixed layer is 20.1 at.% Zr, 11.5 at.% Cr, 56.0 at.% N and 12.4 at.% C. It appears that a rather complicated mixed structure consisting of ZrCN, CrCN and amorphous carbon nitride phases were possibly formed in this mixed layer. In this work, a big discrepancy between the FE-EPMA data and AES results is observed. In general, the quantitative FE-
EPMA data is more accurate than that of the AES results. However, the chemical analysis results brought by the FE-EPMA are the integration of each ZrCN and CrCN layers due to its spatial resolution limit (around 500 nm). Meanwhile, the AES data can provide the chemical composition variation of individual layer on nanoscale, although the accuracy is not that good as compared with FEEPMA. An apparent multilayer structure with a periodic thickness of 2 nm was obtained for the CrCN coatings with high carbon content (46.43 at.%) due to a larger amount of carbon doping [10]. The
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
1011
Fig. 7. The cross-sectional TEM micrographs for the A coating (a) bright field image and selected area electron diffraction patterns and (b) dark field image and selected area electron diffraction patterns of ZrN(200). The position of the CrCN/ZrCN multilayer is labeled in (b).
carbon contained amorphous nanolayer was also reported for the CrCN coating containing 4.9 at.% carbon in previous study [3]. Selfassembled metal/amorphous carbon multilayer thin films were also studied [38,39]. It was reported that the weak carbide former metals with limited carbon solubility would result in a phase separation process during sputtering process [39]. However, a different formation mechanism is proposed in this work. It is suggested that although the carbon solubility of ZrN and CrN is high, the mixed layer between the CrCN and ZrCN bilayers was produced due to the decomposition of C2H2 gas into carbon atoms/ions and then codeposited with the Cr and Zr atoms/ions in the plasma onto the surface of CrCN/ZrCN multilayer to form a C, N, Cr and Zr containing amorphous mixed nanolayer when the specimen was rotated to the opposite side of the Cr and Zr targets plasma region as shown in Fig. 1. A similar mechanism for the formation of carbon containing nanolayers was also reported in the deposition of CrCN coatings in previous work [3]. It is noticeable that no mixed monolayer was found between the CrCN and ZrCN layers due to the short distance between the Cr and Zr targets. It is supposed that the mixed layer will be seen again in deeper region according to the TEM image in Fig. 8 (c) for the periodically nanostructure at higher magnification. 3.3. Mechanical properties of CrCN/ZrCN multilayer thin films The residual stress of each coating is listed in Table 2. Compressive stress values around 2e3 GPa are found for multilayer
Fig. 8. The cross-sectional TEM micrographs for the E coating (a) bright field image and selected area electron diffraction patterns, (b) dark field image and selected area electron diffraction patterns of ZrN(200) and (c) bright field image at higher magnifications. The thickness of the mixed layer and CrCN/ZrCN multilayer are also labeled in (c).
coatings due to the 100 V substrate bias applied during deposition. The hardness, elastic modulus and H/E ratio, the resistance of materials against elastic strain to failure, of the CrCN/ZrCN multilayer thin films as a function of carbon content are shown in Fig. 9. The related data of a CrN/ZrN multilayer thin film with a bilayer period of 20 nm [4] was also inserted as a reference. The hardness values of all coatings are in the range of 26e28 GPa. The lowest hardness, 26.1 GPa is obtained for the A coating consisting of
1012
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
Fig. 9. The relationships between the hardness, elastic modulus, H/E ratios versus the carbon content for the CrCN/ZrCN multilayer thin films. The related data for a CrN/ZrN multilayer coating is also inserted.
2.3 at.% C, whereas the highest H/E ratio is achieved due to its lowest modulus, 239 GPa. The hardness increases to around 28.1 GPa and keeps at around 27.2e27.9 GPa when the carbon content is higher than 2.6 at.% and the C2H2 flow ratio is higher than 10.1%. As compared with the hardness data, 23.5 GPa, of the CrN/ ZrN multilayer thin film [4] inserted in Fig. 9, an increase of around 2.6e4.6 GPa in hardness is found for the CrCN/ZrCN coating. The hardening mechanism of carbon doping into transition metal nitride coatings was discussed by Hong et al. [40]. They discovered that the residual stress induced by the lattice distortion of carbon doping was the main hardening mechanism. Hu and Jiang [10] suggested that the hardness of CrCN coatings can be improved by the higher carbon content up to 46.43 at.% due to the dispersion hardening by the microcrystals and clusters consisting of hybridized carbon and CreC compounds. Meanwhile, the hardness enhancement of CrCN coatings was reported by the point defect, i.e., the incorporation of substitutional carbon on anion site with increasing carbon content [41]. In Fig. 9, with the increase of the carbon content, the hardness and elastic modulus both first increase followed by a decrease. We suggest that a hardness saturation phenomena at 27.5e27.9 GPa for D and E coatings is caused by the balance of two factors, the solution hardening by lattice
Fig. 10. The optical micrographs of the whole scratch tracks for (a) A, (b) E and surface morphologies of (c) A and (d) E coatings at higher magnifications revealing the spalling of thin films.
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
Fig. 11. The morphologies of indentation craters for (a) A, (b) C and (c) E coatings after HRC-DB test.
distortion of substitutional carbon atoms/ions into the CrN and ZrN lattice sites, and the softening effect brought by the increasing amount of soft amorphous carbon nitride contained mixed layers. In this study, the adhesion of multilayered coatings was evaluated by scratch and the HRC-DB tests. The critical loads obtained from the scratch test can be used to estimate the adhesion of the coatings, which are listed in Table 2. The adhesion strength is usually determined by the following terms: LC1 and LC2 [42]. LC1, the lower critical load, was defined as the load where first cracks occurred. LC2, the upper critical load, was defined as the load when
1013
the first exposure of the substrate on the scratch track occurred. The optical micrographs of whole scratch tracks of A and E coatings are shown in Fig. 10 (a) and (b), respectively. Fig. 10 (c) and (d) further reveal the morphologies of the scratch tracks and spalled coatings at higher magnifications where the critical loads were determined for A and E coatings, respectively. Severe chipping failures are found for the A coating, whereas conformal cracking is observed for E coating containing higher carbon content. No chipping failure is found for the higher carbon contained D and E coatings indicating that good adhesion is achieved. According to the scratch test results, values of the lower and upper critical load increase with increasing carbon content. For the HRC-DB test, the adhesion level from HF1 to HF4 exhibits sufficient adhesion quality, whereas HF5 and HF6 represent insufficient adhesion [31]. The adhesion quality of each multilayer coating is listed in Table 2. It is found that the HF value decreases with increasing carbon content indicating that the better adhesion is achieved. The surface morphologies of indentation craters for A, C and E coatings are shown in Fig. 11 (a) to (c). Severe spallation of coatings is found for A (Fig. 11 (a)) and B coatings, implying insufficient adhesion. On the other hand, only circular cracks and very tiny chipping are found for C (Fig. 11(b)), D and E (Fig. 11(c)) coatings, containing higher than 3.0 at.% C. The circular cracks occurred due to the highest hardness of C coating. In this work, good adhesion properties for the CrCN/ ZrCN multilayer thin films containing more than 3.0 at.% carbon can be discovered. The coefficient of friction (COF) value per second was collected for each coating when the ball-on-disk wear test was in the steady state. The average COF and the scattering of the acquired data, the standard deviation, for each coating were thus calculated and listed in Table 2. The average COF values remain on the same level ranging from 0.41 to 0.46. The wear depth and wear rate are also listed in Table 2. According to the detailed microstructure analysis of the wear track by SEM and energy dispersive X-ray spectroscopy (EDS), a very smooth wear track is observed and no wear debris from the WC-Co counterpart is found on the wear track for each coating. Therefore, the width of wear track and the wear rate determined by optical method were both smaller than these determined by the surface profiling method. The minimum wear rate, 8.1 107 mm3/ N/m, is observed for the A coating containing 2.3 at.% C. Nevertheless, the wear rate values are in the range of 8.1 107 to 2.1 106 mm3/N/m for all coatings. Apparently, no direct relationships between the COF, wear rate and carbon content for the CrCN/ZrCN multilayer coatings can be found in this work. Similar findings were reported in our previous work on CrCN coatings [3]. The amorphous carbon nitride coatings have been studied [43e45] due to their good mechanical property, lower COF and good wear resistance, which show very promising tribological applications. The amorphous carbon nitride phase was also revealed in the CrCN [9,12] and ZrCN [24] coatings. Silva and coworkers [24] found that the amorphous carbon nitride phase formed in the ZrCN coatings, which provided a lower COF of 0.1e0.2 as the nitrogen and carbon contents reaching higher than 44 and 10 at.%, respectively. Although the amorphous carbon nitride contained mixed nanolayers are confirmed by the FTIR, AES and TEM for the E coating, the COF of E coating is still high, 0.46 ± 0.04. It appears that the effect of amorphous carbon nitride contained mixed nanolayers on the tribological performance of all CrCN/ZrCN coatings in this work is negligible. We suggest that the lower carbon content of 4.2 at.% and limited thickness around several nm of each amorphous carbon nitride contained mixed nanolayer is not adequate to act as a lubricant in the CrCN/ZrCN coating. It is also noticed that the mechanical and tribological properties are almost the same for D and E coatings due to limited difference in carbon contents. In addition, the effect of surface macroparticles
1014
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
as shown in Fig. 5 on the tribological performance of coating should be noticed. In general, the metallic macroparticles can provide plastic stress relief effect and stop the crack propagation within the coating [46]. The macroparticles also act as abrasive particles to increase the wear rate and COF values of the coatings [47]. However, the plastic stress relief effect or the abrasive wear effect by the macroparticles were not evident in this study. It is suggested that the wear rate and COF values of each coating were not strongly influenced by the appearance of macroparticles, which were likely to be rubbed on the surface in this work. Finally, We can conclude that the CrCN/ZrCN multilayer coating with 4.2 at.% carbon concentration have the optimal hardness of 27.9 GPa and high adhesion upper critical load of 41 N due to the compensation of the solution hardening by carbon addition and the softening effect by amorphous carbon nitride contained mixed layers.
[5]
[6]
[7]
[8]
[9]
4. Conclusions [10]
In this study, five CrCN/ZrCN multilayer thin films with increasing carbon contents ranging from 2.3 to 4.2 at.% were prepared by cathodic arc evaporation (CAE) using 6.3e20.0% of C2H2 gas flow ratios. Nanolaminated carbon containing nitride layers and thin amorphous carbon nitride mixed nanolayers were explored by FTIR and TEM. Typical macroparticles were found on the coating surface. For each CrCN/ZrCN multilayer thin film, CrN and ZrN were the main phases, whereas a small amount of Cr2N phase was also detected. The nanolaminated structures with bilayer period of 20 nm and equal CrCN to ZrCN thickness ratio were achieved. The carbon content in the ZrCN layer was higher than that in CrCN layer. A thin amorphous nanolayer ~5 nm thick containing mixed chemical concentrations of Cr, Zr, C and N was observed between the CrCN/ZrCN bilayers as the carbon content reached 4.2 at.%. The positive dependence of hardness and adhesion properties of coatings on the addition of carbon was clearly shown. An increase of 2.6e4.6 GPa in hardness was obtained for the nanolaminated coatings as the carbon contents were in the range of 2.3e4.2 at.%. It can be concluded that, for the present study, the optimal hardness and adhesion properties were achieved when the carbon content was 4.2 at.% for the CrCN/ZrCN multilayer coatings.
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
Acknowledgement The authors would like to thank the financial support by Ministry of Science and Technology (MOST) in Taiwan under the Project numbers of MOST100-2622-E-131-001-CC2, MOST 106-2218-E131-003, MOST 107-2218-E-131-001, and MOST 107-2221-E-131002-MY3.
[19]
[20]
[21]
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.06.370.
[22]
References
[23]
[1] B. Navinsek, P. Panjan, I. Milosev, PVD coatings as an environmentally clean alternative to electroplating and electroless processes, Surf. Coating. Technol. 116e119 (1999) 476e487. https://doi.org/10.1016/S0257-8972(99)00145-0. [2] D.M. Sanders, A. Anders, Review of cathodic arc deposition technology at the start of the new millennium, Surf. Coating. Technol. 133e134 (2000) 78e90. https://doi.org/10.1016/S0257-8972(00)00879-3. [3] C.Y. Tong, J.W. Lee, C.C. Kuo, S.H. Huang, Y.C. Chan, H.W. Chen, J.G. Duh, Effects of carbon content on the microstructure and mechanical property of cathodic arc evaporation deposited CrCN thin films, Surf. Coating. Technol. (2013) 482e486. https://doi.org/10.1016/j.surfcoat.2012.01.009. [4] S.H. Huang, S.F. Chen, Y.C. Kuo, C.J. Wang, J.W. Lee, Y.C. Chan, H.W. Chen,
[24]
[25]
J.G. Duh, T.E. Hsieh, Mechanical and tribological properties evaluation of cathodic arc deposited CrN/ZrN multilayer coatings, Surf. Coating. Technol. 206 (2011) 1744e1752. https://doi.org/10.1016/j.surfcoat.2011.10.029. S.-F. Chen, Y.-C. Kuo, C.-J. Wang, S.-H. Huang, J.-W. Lee, Y.-C. Chan, H.-W. Chen, J.-G. Duh, T.-E. Hsieh, The effect of Cr/Zr chemical composition ratios on the mechanical properties of CrN/ZrN multilayered coatings deposited by cathodic arc deposition system, Surf. Coating. Technol. 231 (2013) 247e252. https://doi.org/10.1016/j.surfcoat.2012.03.002. S. Wan, J. Pu, D. Li, G. Zhang, B. Zhang, A.K. Tieu, Tribological performance of CrN and CrN/GLC coated components for automotive engine applications, J. Alloy. Comp. 695 (2017) 433e442. http://doi.org/10.1016/j.jallcom.2016.11. 118. J. Jagielski, A.S. Khanna, J. Kucinski, D.S. Mishra, P. Racolta, P. Sioshansi, E. Tobin, J. Thereska, V. Uglov, T. Vilaithong, J. Viviente, S.-Z. Yang, A. Zalar, Effect of chromium nitride coating on the corrosion and wear resistance of stainless steel, Appl. Surf. Sci. 156 (2000) 47e64. https://doi.org/10.1016/ S0169-4332(99)00350-5. G. Berg, C. Friedrich, E. Broszeit, C. Berger, Development of chromium nitride coatings substituting titanium nitride, Surf. Coating. Technol. 86e87 (1996) 184e191. https://doi.org/10.1016/S0257-8972(96)03042-3. Q. Wang, F. Zhou, X. Ding, Z. Zhou, C. Wang, W. Zhang, L.K.-Y. Li, S.-T. Lee, Microstructure and water-lubricated friction and wear properties of CrN(C) coatings with different carbon contents, Appl. Surf. Sci. 268 (2013) 579e587. http://doi.org/10.1016/j.apsusc.2013.01.027. P. Hu, B. Jiang, Study on tribological property of CrCN coating based on magnetron sputtering plating technique, Vacuum 85 (2011) 994e998. https:// doi.org/10.1016/j.vacuum.2011.02.007. J. Zhang, X. Su, L. Shan, Y. Liu, P. Zhang, Y. Jia, Preparation and tribocorrosion performance of CrCN coatings in artificial seawater on different substrates with different bias voltages, Ceram. Int. 45 (2019) 9901e9911. https://doi.org/ 10.1016/j.ceramint.2019.02.031. Y. Ye, Y. Wang, C. Wang, J. Li, Y. Yao, An analysis on tribological performance of CrCN coatings with different carbon contents in seawater, Tribol. Int. 91 (2015) 131e139. http://doi.org/10.1016/j.triboint.2015.07.002. Y. Kong, X. Tian, C. Gong, P.K. Chu, Enhancement of toughness and wear resistance by CrN/CrCN multilayered coatings for wood processing, Surf. Coating. Technol. 344 (2018) 204e213. https://doi.org/10.1016/j.surfcoat. 2018.03.027. J.-L. Ruan, D.-F. Lii, H.-H. Lu, J.S. Chen, J.-L. Huang, Microstructural and electrical characteristics of reactively sputtered ZrNx thin films, J. Alloy. Comp. 478 (2009) 671e675. https://doi.org/10.1016/j.jallcom.2008.11.103. J.-H. Huang, K.-L. Kuo, G.-P. Yu, Oxidation behavior and corrosion resistance of vacuum annealed ZrN-coated stainless steel, Surf. Coating. Technol. 358 (2019) 308e319. https://doi.org/10.1016/j.surfcoat.2018.11.054. X.M. Xu, J. Wang, J. An, Y. Zhao, Q.Y. Zhang, Effect of modulation structure on the growth behavior and mechanical properties of TiN/ZrN multilayers, Surf. Coating. Technol. 201 (2007) 5582e5586. https://doi.org/10.1016/j.surfcoat. 2006.07.132. O.V. Maksakova, S. Simoẽs, A.D. Pogrebnjak, O.V. Bondar, Ya. O. Kravchenko, T.N. Koltunowicz, Zh. K. Shaimardanov, Multilayered ZrN/CrN coatings with enhanced thermal and mechanical properties, J. Alloy. Comp. 776 (2019) 679e690. https://doi.org/10.1016/j.jallcom.2018.10.342. Z.G. Zhang, O. Rapaud, N. Allain, D. Mercs, M. Baraket, C. Dong, C. Coddet, Microstructures and tribological properties of CrN/ZrN nanoscale multilayer coatings, Appl. Surf. Sci. 255 (2009) 4020e4026. https://doi.org/10.1016/j. apsusc.2008.10.075. O. Maksakova, S. Simoẽs, A. Pogrebnjak, O. Bondar, Y. Kravchenko, V. Beresnev, N. Erdybaeva, The influence of deposition conditions and bilayer thickness on physicalmechanical properties of CA-PVD multilayer ZrN/CrN coating, Mater. Char. 140 (2018) 189e196. https://doi.org/10.1016/j.matchar. 2018.03.048. M.M. Larijani, M.B. Zanjanbar, A. Majdabadi, The effect of carbon fraction in Zr(C, N) films on the nano-structural properties and hardness, J. Alloy. Comp. 492 (2010) 735e738. https://doi.org/10.1016/j.jallcom.2009.12.035. J. Xu, H.J. Huang, Z.Y. Li, S. Xu, H. Tao, P. Munroe, Z.-H. Xie, Corrosion behavior of a ZrCN coated Ti alloy with potential application as a bipolar plate for proton exchange membrane fuel cell, J. Alloy. Comp. 663 (2016) 718e730. https://doi.org/10.1016/j.jallcom.2015.12.197. F. Zhou, K. Fu, B. Liao, J. Yu, C. Yang, X. Zhang, Effect of carbon content on nanostructural, mechanical and electrochemical characteristics of selforganized nc-ZrCN/a-CNx nanocomposite films, Appl. Surf. Sci. 327 (2015) 350e357. https://doi.org/10.1016/j.apsusc.2014.11.181. M. Braic, V. Braic, M. Balaceanu, C.N. Zoita, A. Kiss, A. Vladescu, A. Popescu, R. Ripeanu, Structure and properties of Zr/ZrCN coatings deposited by cathodic arc method, Mater. Chem. Phys. 126 (2011) 818e825. https://doi.org/ 10.1016/j.matchemphys.2010.12.036. E. Silva, M. Rebelo de Figueiredo, R. Franz, R. Escobar Galindo, C. Palacio, A. Espinosa, S.V. Calderon, C. Mitterer, S. Carvalho, Structureeproperty relations in ZrCN coatings for tribological applications, Surf. Coating. Technol. 205 (2010) 2134e2141. https://doi.org/10.1016/j.surfcoat.2010.08.126. M. Stueber, U. Albers, H. Leiste, S. Ulrich, H. Holleck, P.B. Barna, A. Kovacs, P. Hovsepian, I. Gee, Multifunctional nanolaminated PVD coatings in the system TieAleNeC by combination of metastable fcc phases and nanocomposite microstructures, Surf. Coating. Technol. 200 (2006) 6162e6171. https://doi.org/10.1016/j.surfcoat.2005.11.012.
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015 [26] M. Stueber, H. Holleck, H. Leiste, K. Seemann, S. Ulrich, C. Ziebert, Concepts for the design of advanced nanoscale PVD multilayer protective thin films, J. Alloy. Comp. 483 (2009) 321e333. https://doi.org/10.1016/j.jallcom.2008. 08.133. [27] M. Balaceanu, T. Petreus, V. Braic, C.N. Zoita, A. Vladescu, C.E. Cotrutz, M. Braic, Characterization of Zr-based hard coatings for medical implant applications, Surf. Coating. Technol. 204 (2010) 2046e2050. https://doi.org/10.1016/j. surfcoat.2009.11.022. [28] M. Balaceanu, M. Braic, V. Braic, G. Pavelescu, Properties of arc plasma deposited TiCN/ZrCN superlattice coatings, Surf. Coating. Technol. 200 (2005) 1084e1087. https://doi.org/10.1016/j.surfcoat.2005.01.077. [29] J. Goldstein, D.E. Newbury, D.C. Joy, C.E. Lyman, P. Echlin, E. Lifshin, L. Sawyer, J.R. Michael, Scanning Electron Microscopy and X-Ray Microanalysis, Plenum Press, 2003, p. 404. [30] G.G. Stoney, The tension of metallic films deposited by electrolysis, Proc. R. Soc. London, Ser. A 82 (1909) 172e175. https://doi.org/10.1098/rspa.1909. 0021. [31] H. Jehn, G. Reiners, N. Siegel (Eds.), Beuth Verlag, Berlin, 1993, p. 213. nkov [32] S. Ma, J. Proch azka, P. Karva a, Q. Ma, X. Niu, X. Wang, D. Ma, K. Xu, S. Veprek, Comparative study of the tribological behaviour of superhard nanocomposite coatings nc-TiN/a-Si3N4 with TiN, Surf. Coating. Technol. 194 (2005) 143e148. https://doi.org/10.1016/j.surfcoat.2004.05.007. [33] S.R. Shatynski, The thermochemistry of transition metal carbides, Oxid. Metals 13 (1979) 105e118. https://doi.org/10.1007/BF00611975. [34] P.C. Yashar, W.D. Sproul, Nanometer scale multilayered hard coatings, Vacuum 55 (1999) 179e190. https://doi.org/10.1016/S0042-207X(99)00148-7. [35] M. Neuhaeuser, H. Hilgers, P. Joeris, R. White, Windeln, Raman spectroscopy measurements of DC-magnetron sputtered carbon nitride (a-C:N) thin films for magnetic hard disk coatings, J. Diam. Relat. Mater. 9 (2000) 1500e1505. https://doi.org/10.1016/S0925-9635(00)00276-4. [36] X.A. Zhao, C.W. Ong, Y.C. Tsang, Y.W. Wong, P.W. Chan, C.L. Choy, Reactive pulsed laser deposition of CNx films, Appl. Phys. Lett. 6 (1995) 2652. https:// doi.org/10.1063/1.113114. [37] J. Sui, J.J. Lu, Synthesis of carbon nitride powder by selective etching of TiC0.3N0.7 in chlorine-containing atmosphere at moderate temperature, Mater. Chem. Phys. 123 (2010) 264e268. https://doi.org/10.1016/j. matchemphys.2010.04.008.
1015
[38] W.Y. Wu, J.M. Ting, Self-assembled alternating nano-scaled layers of carbon and metal, Chem. Phys. Lett. 388 (2004) 312e315. https://doi.org/10.1016/j. cplett.2004.03.004. €ss, [39] W.Y. Wu, J.M. Ting, H. Zutz, D. Lyzwa, I. Gerhards, C. Ronning, H. Hofsa Comparative study of self-assembling of multilayers using reactive sputter deposition and mass selective ion beam deposition, Diam. Relat. Mater. 17 (2008) 1494e1497. https://doi.org/10.1016/j.diamond.2008.01.048. [40] E. Hong, T. Kim, S.-H. Lee, J.W. Lee, H. Lee, Atomic structure and residual stress of carbon-doped TiMeN (Me ¼ Zr, Al, and Cr) coatings on mechanical properties, Ceram. Int. 45 (2019) 9192e9196. https://doi.org/10.1016/j.ceramint. 2019.01.263. [41] J. Almer, M. Oden, G. Håkansson, Microstructure, stress and mechanical properties of arc-evaporated Cr-C-N coatings, Thin Solid Films 385 (2001) 190e197. https://doi.org/10.1016/S0040-6090(01)00759-3. n, C. Ericsson, G. Håkansson, H. Ljungcrantz, Microstructure and me[42] M. Ode chanical behavior of arc-evaporated CreN coatings, Surf. Coating. Technol. 114 (1999) 39e51. https://doi.org/10.1016/S0257-8972(99)00019-5. [43] P. Wang, M. Sugo, K. Adachi, Stable and super-low friction of amorphous carbon nitride coatings in nitrogen gas by using two-step ball-on-disk friction test, Lubr. Sci. 27 (2015) 137e149. https://doi.org/10.1002/ls.1258. [44] P. Wang, W. Zhang, D. Diao, Low friction of graphene nanocrystallite embedded carbon nitride coatings prepared with MCECR plasma sputtering, Surf. Coating. Technol. 332 (2017) 153e160. https://doi.org/10.1016/j. surfcoat.2017.06.084. [45] F.J. Flores-Ruiz, M.D. Tucker, K.D. Bakoglidis, X. Yu, A.J. Gellman, A. HerreraGomez, L. Hultman, J. Rosen, E. Broitman, Micro-tribological performance of fullerene-like carbon and carbon-nitride surfaces, Tribol. Int. 128 (2018) 104e112. https://doi.org/10.1016/j.triboint.2018.07.009. [46] R.L. Boxman, S. Goldsmith, Macroparticle contamination in cathodic arc coatings: generation, transport and control, Surf. Coating. Technol. 52 (1992) 39e50. https://doi.org/10.1016/0257-8972(92)90369-L. [47] P. Harlin, U. Bexell, M. Olsson, Influence of surface topography of arcdeposited TiN and sputter-deposited WC/C coatings on the initial material transfer tendency and friction characteristics under dry sliding contact conditions, Surf. Coating. Technol. 203 (2009) 1748e1755. https://doi.org/10. 1016/j.surfcoat.2008.12.011.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Microstructure and mechanical properties evaluation of cathodic arc deposited CrCN/ZrCN multilayer coatings Sung-Hsiu Huang a, b, Cheng-Yi Tong c, Tsung-Eong Hsieh a, Jyh-Wei Lee c, d, e, f, * a
Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan Gigastorage Corporation, Hsinchu, Taiwan c Department of Materials Engineering, Ming Chi University of Technology, Taiwan d Center for Plasma and Thin Films Technologies, Ming Chi University of Technology, Taiwan e Department of Mechanical Engineering, Chang Gung University, Taoyuan, Taiwan f Plastic and Reconstructive Surgery, Craniofacial Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 April 2019 Received in revised form 20 June 2019 Accepted 28 June 2019 Available online 29 June 2019
For the development of advanced nanoscale multilayer protective coatings, proper design of microstructure and chemical composition of carbon containing sequential transition metal nitride nanolayers is an important issue. In this work, five different nanostructured CrCN/ZrCN multilayer coatings were deposited periodically by cathodic arc evaporation. The bilayer period of the CrCN/ZrCN multilayer coatings was kept at 20 nm. The C2H2 gas flow ratio was adjusted from 6.3 to 20.0% for achieving CrCN/ ZrCN multilayer coatings with 2.3e4.2 at.% carbon content. Nanolaminated CrCN and ZrCN nitride layers and thin amorphous carbon nitride mixed nanolayers ~5 nm thick were obtained as the carbon content reached 4.2 at.%. It was found that the hardness and adhesion quality were strongly improved by the carbon addition to the CrCN/ZrCN multilayer coatings. An increase of 2.6e4.6 GPa in hardness was found for the CrCN/ZrCN multilayer coatings due to the balance of solution hardening effect of carbon atoms and the softening by the amorphous mixed nanolayer. An optimal combination of high hardness, 28.9 GPa, and good adhesion, 41 N of upper critical load were achieved when the carbon content was 4.2 at.% for the CrCN/ZrCN multilayer coatings. © 2019 Elsevier B.V. All rights reserved.
Keywords: Cathodic arc evaporation CrCN/ZrCN Multilayer Nanoindenter Tribological properties Scratch test
1. Introduction In recent years, cathodic arc evaporation (CAE) technology has been widely applied in the traditional decorative and tool industries [1,2], and also to fabricate advanced nanocomposite [3] and nanolaminated thin films [4,5]. Among the transition metal nitride thin films, CrN is widely used in industries due to its higher thermal stability, good tribological properties [6] and better corrosion resistance [7], which is considered as a candidate to replace TiN coatings in several applications [8]. By addition of carbon into the CrN thin film, the hardness and tribological performance can be effectively improved [3,9e12]. A better toughness, wear resistance and longer service life were obtained for the CrN/ CrCN multilayered thin films deposited on wood cutting tools when
* Corresponding author. Department of Materials Engineering, Ming Chi University of Technology, Taiwan. E-mail address: jeffl[email protected] (J.-W. Lee). https://doi.org/10.1016/j.jallcom.2019.06.370 0925-8388/© 2019 Elsevier B.V. All rights reserved.
a proper C2H2 flow rate of 10 sccm was used [13]. On the other hand, ZrN thin film is characterized for its good mechanical properties [14] and good corrosion resistance [15], which make ZrN a popular material applied widely in industries. Research work on ZrN-based TiN/ZrN [16] and CrN/ZrN [4,5,17e19] multilayered coatings has revealed that excellent mechanical properties were achieved due to the combination of suitable nanoscale multilayered features. Recently, carbon containing ZrCN thin films were applied due to their high hardness [20], anti-corrosion [21] and tribological behaviors [22]. Better mechanical properties were achieved for ZrCN coatings containing higher carbon content [23,24]. For the development of advanced nanoscale multilayer protective coatings, simultaneous growth of a nanocrystalline hard phase and amorphous carbon is an interesting concept [25,26]. For example, transition metal nitride coatings containing higher C content, such as TieAleNeC [25] and VeAleCeN [26], were grown with special nano-architectures (nanocomposite and nanolaminated coatings consisting of metastable hard phase and amorphous carbon) and exhibited promising tribological
1006
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
deposited as an adhesion layer. Multilayered coatings were deposited by alternately rotating the substrates between the plasma of Cr and Zr targets. The specimens were hanged in the fixture in the center of the coater with a self-rotating speed of 10 rpm and a revolutionary speed of 2 rpm. The schematic top-view of the coater and the configuration of targets and substrates are shown in Fig. 1. The bilayer period was kept at the same value ~20 nm for each multilayered coating. Various carbon contents were obtained by different flow rates of N2, f(N2), and acetylene (C2H2), f(C2H2), gas mixtures during the deposition process. The DC power current values for the Cr and Zr targets were all 90 A. The designed thickness ratio of ZrCN to CrCN layers was around 1:1, which was calculated based on the thickness values of ZrCN and CrCN monolayer coatings under the same deposition conditions. The detailed deposition parameters are listed in Table 1. It appears that the C2H2 gas flow ratio, f(N2)/(f(N2) þ f(C2H2), increased from 6.3 to 20.0% as the C2H2 flow rate increased from 7.5 to 30 sccm. The C2H2 gas flow ratio and carbon contents were further used to discuss their effects on the characteristics of CrCN/ZrCN multilayered thin films. The chemical composition of the CrCN/ZrCN thin films deposited on Si wafers was analyzed by field emission electron probe microscopy (FE-EPMA, JXA-8500F, JEOL, Japan) with the aid of the ZAF-corrected program [29]. The average chemical composition of each coating was obtained from three different measurement areas. The depth profile of the chemical composition of selected coatings deposited on Si wafer substrates was explored with Auger electron spectroscopy (AES, Auger NanoProbe, 670 PHI Xi, PerkinElmer, USA). The phase compositions of coatings deposited on Si wafer substrates were evaluated by grazing angle X-ray diffraction (XRD6000, Shimadzu, Japan) with an incident angle of 2 . Cu Ka radiation generated at 30 kV and 20 mA from a Cu target was used. Fourier transform infrared spectroscopy (FTIR, Spectrum One, PerkinElmer, USA) measurements were performed to explore the type of chemical bonds of the CN structure of each thin film deposited on Si wafer substrate. The surface roughness of each coating deposited on Si wafer substrate was measured by a 3D laser scanning microscope (VKe9700K, KEYENCE, Japan). The scan area was 700 mm 500 mm. Three different regions were selected for the surface roughness measurement for each coating. The surface and cross-section morphology of each coating deposited on Si wafer substrate was obtained by field emission scanning electron microscopy (FE-SEM, JSM-6701F, JEOL, Japan) and transmission electron microscopy (TEM, JSM-2100, JEOL, Japan). The residual stress of films deposited on Si wafer substrates was calculated using Stoney's equation [30]. The dimension of thin film deposited Si wafer for residual stress
performance. The research work on ZrCN-based carbonitride multilayer coatings is limited. For example, Zr/ZrCN multilayers were fabricated for medical implant applications [27] and TiCN/ ZrCN multilayers were studied due to their high hardness [28]. The effect of the bilayer periods (L) on the hardness and tribological properties was reported on CrN/ZrN multilayered coatings in previous work [4]. Adequate hardness and excellent tribological properties were achieved for multilayered coatings with the same thickness ratio of CrN and ZrN layers and a bilayer period of 20 nm [4]. However, no effort was ever made on the microstructure and mechanical properties evaluation for nanolaminated CrCN/ZrCN coatings. In this study, five CrCN/ZrCN multilayered coatings containing different carbon contents with the same L value (20 nm) and the same CrCN to ZrCN layer thickness ratio were fabricated by CAE process. The influence of carbon concentration on the microstructure, mechanical properties and tribological performance of CrCN/ZrCN multilayered coatings was investigated. 2. Experimental procedure In this study, five CrCN/ZrCN multilayered thin films with different carbon contents were deposited on P-type (100) silicon wafers and hardened and polished AISI420 stainless steel discs by a cathodic arc evaporation system (KMARC, Kuen Min Tech. Co., Taiwan). Chromium and zirconium targets with a purity of 99.99 wt % and diameters of 101.6 mm were used. Microparticle filters were used to reduce the amount of macroparticles and pin hole defects on the surface. A pure CrZr interlayer around 60 nm thick was
Fig. 1. The schematic top-view of the coater and the configuration of targets and substrates.
Table 1 Deposition parameters and chemical compositions of CrCN/ZrCN multilayer thin films. Sample designation
A
B
C
D
E
C2H2 flow rate, f(C2H2) (sccm) N2 flow rate, f(N2) (sccm) C2H2 flow ratio, f(N2)/(f(N2)þf(C2H2)) (%) Chemical composition (at.%)
7.5 112 6.3 28.6 ± 0.1 21.8 ± 0.5 46.5 ± 0.6 2.3 ± 0.0 0.8 ± 0.3 90 1.2 102 Ar plasma for 15 min at 0.81 150 100 26
12.5 111 10.1 28.9 ± 0.5 21.0 ± 0.2 46.6 ± 0.7 2.6 ± 0.2 0.8 ± 0.2
17.5 115 13.2 29.8 ± 1.4 20.9 ± 1.0 45.2 ± 2.7 3.0 ± 0.1 1.1 ± 0.1
25.0 122 17.0 24.3 ± 0.3 25.8 ± 0.3 44.7 ± 0.1 4.1 ± 0.1 1.1 ± 0.3
30.0 120 20.0 26.2 ± 0.4 24.2 ± 0.4 44.7 ± 0.2 4.2 ± 0.0 0.7 ± 0.3
Target current (A) Base pressure (Pa) Plasma etching Working pressure (Pa) Substrate temperature (oC) Substrate bias (V) Deposition time (min)
Cr Zr N C O
1.33 Pa under substrate bias 800 V
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
measurement was around 15.0 15.0 0.525 mm3. It is important to point out that some requirements, such as the coating thickness is much smaller than that of the Si substrate, and the Si substrate thickness is also much smaller than the width of the Si substrate, must be satisfied for correctly calculating the residual stress of each thin film using Stoney's equation [30]. The hardness and elastic modulus of the thin films deposited on AISI420 substrates were measured by a nanoindenter (TI-900, TriboIndenter, Hysitron, USA) using a Berkovich 142.3 diamond probe at a maximum applied load of 5 mN. Eight indentations were made on the surface without macroparticle and pin hole defects for each coating. The maximum indentation depth was limited to around 100 nm, which was around the one-tenth of the film thickness. The loading and unloading rates of the nanoindentation were all 1000 mN/s. The holding time was 5 s. A scratch test (Scratch Tester, J & L Tech. Co., Korea), with a maximum load of 100 N was adopted to explore the adhesion properties of thin films deposited on AISI420 substrates. Three scratch tracks were tested for each specimen. The adhesion strength quality of thin films deposited on AISI420 substrates was evaluated by a Daimler Benz Rockwell-C (HRC-DB) tester [31]. Three HRC-DB tests were made for each coating. A ball-on-disk wear tester (Wear Tester, J & L Tech. Co., Korea) was used to investigate the performance of coatings deposited on AISI420 substrates. A cemented tungsten carbide (WC-6 wt.% Co) ball, 6 mm in diameter was adopted as the stationary ball. A normal load of 5 N was applied. The rotation speed was 200 rpm with a wear track diameter of 8 mm. The test temperature was 20 C, and the relative humidity was kept at 60%. The wear length was 500 m for each test. The wear rate of each coating was determined based on the following equation [32]:
WR ¼
tð3t 2 þ 4b2 Þ2pr 6bFn S
(1)
where t is the average depth of the wear track, b is the average width of the wear track, r is the radius of the wear track, Fn is the normal load and S is the sliding distance. The average t and b values were determined using a surface profilometer to measure eight cross-sections of each wear track. Only one wear test was conducted for each coating. 3. Results and discussion 3.1. Composition and phase characterization of CrCN/ZrCN multilayer thin films According to the chemical composition analysis data of CrCN/ ZrCN multilayer thin films by FE-EPMA as listed in Table 1, the carbon content increases from 2.3 to 4.2 at.% when C2H2 flow ratio increases from 6.3 to 20.0%, respectively. However, higher carbon containing thin films were not prepared due to the instability of plasma during deposition when the C2H2 flow ratio was higher than 20.0%. According to Table 1, with the increase of C2H2 flow ratio, the N and Cr contents first increase followed by a decrease, and the Zr content has a highest value, 25.8 at.%, at 17.0% of C2H2 flow ratio. In comparison, the nitrogen content of coatings decreases gradually from 46.5 to 44.7 at.% when the carbon content increases from 2.3 to 4.2 at.% and the C2H2 flow ratio increases from 6.3 to 20.0%. A similar result was also reported in a previous study on CrCN coatings [3]. We suggest that the substitutional effect of carbon elements for replacing the nitrogen elements in the ZrN and CrN lattice sites is responsible for this chemical composition evolution. The Cr content decreases with increasing acetylene flow ratio and changes from 28.6 to 26.2 at.%. Meanwhile, the Zr content increases from 21.8 to 24.2 at.% as the C2H2 flow ratio and carbon content
1007
Fig. 2. The Auger electron depth profiling of the E coating.
increase. We suggest that the lower formation free energy for ZrC phase than that of CrxC phases [33] will attract more Zr atoms into the coating when the carbon content increases. It is also noticed that an oxygen contamination around 0.7e1.1 at.% is found for each coating. In order to investigate the detailed chemical compositions of individual layers, Auger electron depth profiling of the E coating is shown in Fig. 2. The sputtering rate in the first 5 min was 2.6 nm/ min and then decreased to 1 nm/min. According to the depth profiling data shown in Fig. 2, the CrCN, ZrCN and a mixed layer can be identified. Although the rather complex chemical composition variations can be seen for each element in Fig. 2, the obvious change of Cr and Zr contents are found for each individual layer. The significantly higher carbon content as shown in the AES data on the coating surface are attributed to the outermost surface contamination. In Fig. 2, the carbon and nitrogen concentrations deviate from 7.8 to 16.7 at.% and from 44.7 to 60.7 at.%, respectively, within different layers. The maximum Cr content of 34.9 at.% can be seen in the CrCN layer, whereas the highest Zr concentration of 23.6 at.% is discovered in the ZrCN region. The average chemical compositions for the individual ZrCN and CrCN layers are 22.6% Zr, 6.4% Cr, 57.3% N, 13.7% C and 10.4% Zr, 32.4% Cr, 47.0% N, 10.2% C (in at.%), respectively. The nitrogen and carbon contents are lower in the CrCN layer as compared with the ZrCN layer. For the mixed layer, the average chemical composition is 20.1% Zr, 11.5% Cr, 56.0% N and 12.4% C (in at.%). It appears that the nitrogen and carbon contents in this mixed layer are higher than these in CrCN layer. The chemical compositions of Zr and Cr, 20.1 and 11.5%, in the mixed layer are less than 22.6% Zr in the ZrCN and 32.4% Cr in the CrCN layers, respectively. We believe that this mixed layer is a mixture of ZrCN, CrCN and amorphous carbon nitride phases. It should be noticed that during AES analysis the oxygen concentration was not detected as shown in Fig. 2. The glancing angle XRD patterns of CrCN/ZrCN multilayer thin films deposited with different C2H2 flow ratios are shown in Fig. 3. The CrN (111), (200), (220) and the ZrN (111), (200), (220) and (311) reflections are labeled in Fig. 3. However, the CrN (111) reflection of D coating is not obvious. The CrN (200) reflection can only be observed for E coating. The CrN (220) diffraction peaks are hard to be found in all samples. Positions of the ZrN (111) diffraction peaks shift very slightly to a higher diffraction angle, whereas the CrN (111) diffraction peaks shift very slightly toward a lower diffraction angle with increasing C2H2 flow ratios. It appears that the substitution of carbon atoms into the nitrogen and anion sites of CrN and
1008
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
Fig. 3. X-ray diffraction patterns of the CrCN/ZrCN multilayer thin films.
ZrN lattice and the generated residual stress should have an influence on these peak shifts in Fig. 3. The average grain size of each multilayer coating is hard to calculate due to the overlapping of ZrN and CrN diffraction peaks. In addition, very weak b-Cr2N (002) and (111) reflections are also found indicating its rather low phase content in the coating. The existence of Cr2N and CrN mixed two phases structure was also discovered in the CrCN coatings [10,11]. No Zr or Cr related carbide and oxide phases are found in Fig. 3. In this work, no satellite peaks are found for each multilayer coating. It is suggested that the Bragg peak intensity is typically much smaller for non-epitaxially grown multilayers, and the satellite peaks may be hidden in the background even if a perfect composition modulation is present [34]. In order to understand the effect of carbon and nitrogen contents on the phase structure and to investigate the existence of the amorphous CN phase in the coatings, FTIR measurements were further conducted. The FTIR reflection spectrum of coatings prepared with different carbon contents is shown in Fig. 4. There are three characteristic peaks for the CN phase at 1200-1300 cm1(CeN), 16001700 cm1 (C]N) [35] and 2200 cm1 (C^N) [36]. The absorption peaks corresponding to CeN and C]N bonds at ~1290 cm1 and ~1600 cm1 can be found for each coating. Meanwhile, no obvious C^N characteristic peak can be recognized for all coatings. In addition, the absorption peak at ~1045 cm1 can be attributed to the NeN bond [37]. This amorphous carbon nitride phase was also revealed in the CrCN [9,12] and ZrCN [24] coatings. Effects of the amorphous carbon nitride phase contained mixed layers on the mechanical properties of the CrCN/ZrCN multilayer coatings will be discussed later. Furthermore, the FTIR spectra of C and E coatings differ from the other three. The detailed reason still needs further investigation. According to the FTIR analysis results, carbon and nitrogen bonded atoms under different chemical bonding configurations are observed for the CrCN/ZrCN multilayer thin films. However, it should be noticed that, as compared with the broad adsorptions in the 1150-1800 cm1 region for carbon nitride powders [37], the adsorption intensities of multilayer coatings are relatively weaker due to a small amount of the amorphous carbon nitride phase in
Fig. 4. Fourier transform infrared spectra of the CrCN/ZrCN multilayer thin films.
this work. On the other hand, no G and D bands characteristic of a carbon phase are found for each CrCN/ZrCN multilayer thin film by the Raman spectroscopy analysis, which is possibly due to the rather low amount of carbon contents in this work. 3.2. Microstructure characterization of CrCN/ZrCN thin films A typical surface morphology consisting of macroparticles and pinholes was observed on the surface for each coating as illustrated in Fig. 5. The average surface roughness, Ra, and average size of macroparticles of each thin film analyzed from three different regions are listed in Table 2. The scattered roughness values indicate that the randomly distributed surface defects have strong influence on the measurement result. The average size values of macroparticles ranging from 1.7 to 2.2 mm can be observed. Meanwhile, the chemical nature of the macroparticles is pure metallic Cr or Zr, implying the droplets were from the metallic targets during deposition. The cross-sectional morphologies for all coatings are depicted in Fig. 6(a)e(e). The thickness of each coating is around 1 mm. The laminated microstructure and pure CrZr interlayer can be observed for each coating. It is also found that columnar structure can be recognized for D and E coatings when the C2H2 flow ratio and carbon content are higher than 17.0% and 4.0 at.%, respectively. The detailed cross-sectional morphologies of A and E coatings are further investigated by TEM. Fig. 7(a) shows the cross-sectional TEM micrograph and selected area electron diffraction (SAED) patterns for the A coating containing 2.3 at.% C. The laminated microstructure can be observed clearly. The CrN and ZrN phases can be identified according to the SAED patterns. The cross-sectional TEM dark-field image of the ZrN (200) lattice plane and corresponding SAED patterns of the A coating are shown in Fig. 7(b). Obviously, the sequential ZrCN and CrCN multilayers as indicated by markers in Fig. 7(b) can be clearly observed through the dark field image technique. The average thickness value for the bright
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
1009
Fig. 5. The surface SEM morphologies of (a) A, (b) B, (c) C, (d) D and (e) E CrCN/ZrCN multilayer thin films.
Table 2 Characteristics of CrCN/ZrCN multilayer coatings: surface roughness, macroparticle size, residual stress, critical loads, HF values, coefficient of friction (COF), average wear depth and wear rate. Sample designation
A
B
C
D
E
C2H2 flow rate, f(C2H2) (sccm) C2H2 flow ratio, f(N2)/(f(N2)þf(C2H2) (%) Surface roughness, Ra (nm) Macroparticle size (mm) Residual stress (GPa) Lc1 (N) Lc2 (N) HF COF Wear depth (mm) Wear rate (mm3m1N1)
7.5 6.3 112 ± 9 2.2 ± 1.0 2.36 12.5 ± 0.4 22.7 ± 1.8 6 0.45 ± 0.02 0.31 ± 0.11 8.1 107
12.5 10.1 80 ± 28 1.7 ± 0.4 2.08 24.4 ± 1.2 35.7 ± 0.6 5 0.44 ± 0.04 0.50 ± 0.07 1.2 106
17.5 13.2 69 ± 21 1.9 ± 1.1 2.60 25.0 ± 2.7 36 ± 1.0 3 0.42 ± 0.03 0.36 ± 0.11 9.2 107
25.0 17.0 130 ± 38 2.1 ± 1.0 3.06 e 41.3 ± 3.8 1 0.41 ± 0.05 0.95 ± 0.08 2.1 106
30.0 20.0 69 ± 19 1.8 ± 0.8 2.93 e 41.0 ± 1.4 1 0.46 ± 0.04 0.72 ± 0.18 1.4 106
ZrN and dark CrN layer is around 10 nm, respectively, which is close to the designed value. The cross-sectional TEM bright field image, dark-field image of the ZrN (200) lattice plane and corresponding SAED patterns of the E coating with 4.2 at.% C are depicted in Fig. 8(a)-(b), respectively. Similarly, the nanolaminated structure is
also revealed. Again, the average thickness for the bright ZrN layer and dark CrN layer is around 10 nm. Fig. 8(c) illustrates the multilayered structure at higher magnification. The average CrCN/ZrCN bilayer period is calculated to be 20 nm. It is also noticed that a thin layer around 5 nm thick can be observed between each bilayer. In
1010
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
Fig. 6. The cross-sectional SEM morphologies of (a) A, (b) B, (c) C, (d) D and (e) E CrCN/ZrCN multilayer thin films.
addition, the fine columnar structure around several tens nm wide can be observed in the TEM images in Figs. 7 and 8 for A and E coatings. According to the depth profiling data shown in Fig. 2, the CrCN, ZrCN and mixed layer can be identified. As we discussed before, the average chemical composition of the mixed layer is 20.1 at.% Zr, 11.5 at.% Cr, 56.0 at.% N and 12.4 at.% C. It appears that a rather complicated mixed structure consisting of ZrCN, CrCN and amorphous carbon nitride phases were possibly formed in this mixed layer. In this work, a big discrepancy between the FE-EPMA data and AES results is observed. In general, the quantitative FE-
EPMA data is more accurate than that of the AES results. However, the chemical analysis results brought by the FE-EPMA are the integration of each ZrCN and CrCN layers due to its spatial resolution limit (around 500 nm). Meanwhile, the AES data can provide the chemical composition variation of individual layer on nanoscale, although the accuracy is not that good as compared with FEEPMA. An apparent multilayer structure with a periodic thickness of 2 nm was obtained for the CrCN coatings with high carbon content (46.43 at.%) due to a larger amount of carbon doping [10]. The
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
1011
Fig. 7. The cross-sectional TEM micrographs for the A coating (a) bright field image and selected area electron diffraction patterns and (b) dark field image and selected area electron diffraction patterns of ZrN(200). The position of the CrCN/ZrCN multilayer is labeled in (b).
carbon contained amorphous nanolayer was also reported for the CrCN coating containing 4.9 at.% carbon in previous study [3]. Selfassembled metal/amorphous carbon multilayer thin films were also studied [38,39]. It was reported that the weak carbide former metals with limited carbon solubility would result in a phase separation process during sputtering process [39]. However, a different formation mechanism is proposed in this work. It is suggested that although the carbon solubility of ZrN and CrN is high, the mixed layer between the CrCN and ZrCN bilayers was produced due to the decomposition of C2H2 gas into carbon atoms/ions and then codeposited with the Cr and Zr atoms/ions in the plasma onto the surface of CrCN/ZrCN multilayer to form a C, N, Cr and Zr containing amorphous mixed nanolayer when the specimen was rotated to the opposite side of the Cr and Zr targets plasma region as shown in Fig. 1. A similar mechanism for the formation of carbon containing nanolayers was also reported in the deposition of CrCN coatings in previous work [3]. It is noticeable that no mixed monolayer was found between the CrCN and ZrCN layers due to the short distance between the Cr and Zr targets. It is supposed that the mixed layer will be seen again in deeper region according to the TEM image in Fig. 8 (c) for the periodically nanostructure at higher magnification. 3.3. Mechanical properties of CrCN/ZrCN multilayer thin films The residual stress of each coating is listed in Table 2. Compressive stress values around 2e3 GPa are found for multilayer
Fig. 8. The cross-sectional TEM micrographs for the E coating (a) bright field image and selected area electron diffraction patterns, (b) dark field image and selected area electron diffraction patterns of ZrN(200) and (c) bright field image at higher magnifications. The thickness of the mixed layer and CrCN/ZrCN multilayer are also labeled in (c).
coatings due to the 100 V substrate bias applied during deposition. The hardness, elastic modulus and H/E ratio, the resistance of materials against elastic strain to failure, of the CrCN/ZrCN multilayer thin films as a function of carbon content are shown in Fig. 9. The related data of a CrN/ZrN multilayer thin film with a bilayer period of 20 nm [4] was also inserted as a reference. The hardness values of all coatings are in the range of 26e28 GPa. The lowest hardness, 26.1 GPa is obtained for the A coating consisting of
1012
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
Fig. 9. The relationships between the hardness, elastic modulus, H/E ratios versus the carbon content for the CrCN/ZrCN multilayer thin films. The related data for a CrN/ZrN multilayer coating is also inserted.
2.3 at.% C, whereas the highest H/E ratio is achieved due to its lowest modulus, 239 GPa. The hardness increases to around 28.1 GPa and keeps at around 27.2e27.9 GPa when the carbon content is higher than 2.6 at.% and the C2H2 flow ratio is higher than 10.1%. As compared with the hardness data, 23.5 GPa, of the CrN/ ZrN multilayer thin film [4] inserted in Fig. 9, an increase of around 2.6e4.6 GPa in hardness is found for the CrCN/ZrCN coating. The hardening mechanism of carbon doping into transition metal nitride coatings was discussed by Hong et al. [40]. They discovered that the residual stress induced by the lattice distortion of carbon doping was the main hardening mechanism. Hu and Jiang [10] suggested that the hardness of CrCN coatings can be improved by the higher carbon content up to 46.43 at.% due to the dispersion hardening by the microcrystals and clusters consisting of hybridized carbon and CreC compounds. Meanwhile, the hardness enhancement of CrCN coatings was reported by the point defect, i.e., the incorporation of substitutional carbon on anion site with increasing carbon content [41]. In Fig. 9, with the increase of the carbon content, the hardness and elastic modulus both first increase followed by a decrease. We suggest that a hardness saturation phenomena at 27.5e27.9 GPa for D and E coatings is caused by the balance of two factors, the solution hardening by lattice
Fig. 10. The optical micrographs of the whole scratch tracks for (a) A, (b) E and surface morphologies of (c) A and (d) E coatings at higher magnifications revealing the spalling of thin films.
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
Fig. 11. The morphologies of indentation craters for (a) A, (b) C and (c) E coatings after HRC-DB test.
distortion of substitutional carbon atoms/ions into the CrN and ZrN lattice sites, and the softening effect brought by the increasing amount of soft amorphous carbon nitride contained mixed layers. In this study, the adhesion of multilayered coatings was evaluated by scratch and the HRC-DB tests. The critical loads obtained from the scratch test can be used to estimate the adhesion of the coatings, which are listed in Table 2. The adhesion strength is usually determined by the following terms: LC1 and LC2 [42]. LC1, the lower critical load, was defined as the load where first cracks occurred. LC2, the upper critical load, was defined as the load when
1013
the first exposure of the substrate on the scratch track occurred. The optical micrographs of whole scratch tracks of A and E coatings are shown in Fig. 10 (a) and (b), respectively. Fig. 10 (c) and (d) further reveal the morphologies of the scratch tracks and spalled coatings at higher magnifications where the critical loads were determined for A and E coatings, respectively. Severe chipping failures are found for the A coating, whereas conformal cracking is observed for E coating containing higher carbon content. No chipping failure is found for the higher carbon contained D and E coatings indicating that good adhesion is achieved. According to the scratch test results, values of the lower and upper critical load increase with increasing carbon content. For the HRC-DB test, the adhesion level from HF1 to HF4 exhibits sufficient adhesion quality, whereas HF5 and HF6 represent insufficient adhesion [31]. The adhesion quality of each multilayer coating is listed in Table 2. It is found that the HF value decreases with increasing carbon content indicating that the better adhesion is achieved. The surface morphologies of indentation craters for A, C and E coatings are shown in Fig. 11 (a) to (c). Severe spallation of coatings is found for A (Fig. 11 (a)) and B coatings, implying insufficient adhesion. On the other hand, only circular cracks and very tiny chipping are found for C (Fig. 11(b)), D and E (Fig. 11(c)) coatings, containing higher than 3.0 at.% C. The circular cracks occurred due to the highest hardness of C coating. In this work, good adhesion properties for the CrCN/ ZrCN multilayer thin films containing more than 3.0 at.% carbon can be discovered. The coefficient of friction (COF) value per second was collected for each coating when the ball-on-disk wear test was in the steady state. The average COF and the scattering of the acquired data, the standard deviation, for each coating were thus calculated and listed in Table 2. The average COF values remain on the same level ranging from 0.41 to 0.46. The wear depth and wear rate are also listed in Table 2. According to the detailed microstructure analysis of the wear track by SEM and energy dispersive X-ray spectroscopy (EDS), a very smooth wear track is observed and no wear debris from the WC-Co counterpart is found on the wear track for each coating. Therefore, the width of wear track and the wear rate determined by optical method were both smaller than these determined by the surface profiling method. The minimum wear rate, 8.1 107 mm3/ N/m, is observed for the A coating containing 2.3 at.% C. Nevertheless, the wear rate values are in the range of 8.1 107 to 2.1 106 mm3/N/m for all coatings. Apparently, no direct relationships between the COF, wear rate and carbon content for the CrCN/ZrCN multilayer coatings can be found in this work. Similar findings were reported in our previous work on CrCN coatings [3]. The amorphous carbon nitride coatings have been studied [43e45] due to their good mechanical property, lower COF and good wear resistance, which show very promising tribological applications. The amorphous carbon nitride phase was also revealed in the CrCN [9,12] and ZrCN [24] coatings. Silva and coworkers [24] found that the amorphous carbon nitride phase formed in the ZrCN coatings, which provided a lower COF of 0.1e0.2 as the nitrogen and carbon contents reaching higher than 44 and 10 at.%, respectively. Although the amorphous carbon nitride contained mixed nanolayers are confirmed by the FTIR, AES and TEM for the E coating, the COF of E coating is still high, 0.46 ± 0.04. It appears that the effect of amorphous carbon nitride contained mixed nanolayers on the tribological performance of all CrCN/ZrCN coatings in this work is negligible. We suggest that the lower carbon content of 4.2 at.% and limited thickness around several nm of each amorphous carbon nitride contained mixed nanolayer is not adequate to act as a lubricant in the CrCN/ZrCN coating. It is also noticed that the mechanical and tribological properties are almost the same for D and E coatings due to limited difference in carbon contents. In addition, the effect of surface macroparticles
1014
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015
as shown in Fig. 5 on the tribological performance of coating should be noticed. In general, the metallic macroparticles can provide plastic stress relief effect and stop the crack propagation within the coating [46]. The macroparticles also act as abrasive particles to increase the wear rate and COF values of the coatings [47]. However, the plastic stress relief effect or the abrasive wear effect by the macroparticles were not evident in this study. It is suggested that the wear rate and COF values of each coating were not strongly influenced by the appearance of macroparticles, which were likely to be rubbed on the surface in this work. Finally, We can conclude that the CrCN/ZrCN multilayer coating with 4.2 at.% carbon concentration have the optimal hardness of 27.9 GPa and high adhesion upper critical load of 41 N due to the compensation of the solution hardening by carbon addition and the softening effect by amorphous carbon nitride contained mixed layers.
[5]
[6]
[7]
[8]
[9]
4. Conclusions [10]
In this study, five CrCN/ZrCN multilayer thin films with increasing carbon contents ranging from 2.3 to 4.2 at.% were prepared by cathodic arc evaporation (CAE) using 6.3e20.0% of C2H2 gas flow ratios. Nanolaminated carbon containing nitride layers and thin amorphous carbon nitride mixed nanolayers were explored by FTIR and TEM. Typical macroparticles were found on the coating surface. For each CrCN/ZrCN multilayer thin film, CrN and ZrN were the main phases, whereas a small amount of Cr2N phase was also detected. The nanolaminated structures with bilayer period of 20 nm and equal CrCN to ZrCN thickness ratio were achieved. The carbon content in the ZrCN layer was higher than that in CrCN layer. A thin amorphous nanolayer ~5 nm thick containing mixed chemical concentrations of Cr, Zr, C and N was observed between the CrCN/ZrCN bilayers as the carbon content reached 4.2 at.%. The positive dependence of hardness and adhesion properties of coatings on the addition of carbon was clearly shown. An increase of 2.6e4.6 GPa in hardness was obtained for the nanolaminated coatings as the carbon contents were in the range of 2.3e4.2 at.%. It can be concluded that, for the present study, the optimal hardness and adhesion properties were achieved when the carbon content was 4.2 at.% for the CrCN/ZrCN multilayer coatings.
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
Acknowledgement The authors would like to thank the financial support by Ministry of Science and Technology (MOST) in Taiwan under the Project numbers of MOST100-2622-E-131-001-CC2, MOST 106-2218-E131-003, MOST 107-2218-E-131-001, and MOST 107-2221-E-131002-MY3.
[19]
[20]
[21]
Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jallcom.2019.06.370.
[22]
References
[23]
[1] B. Navinsek, P. Panjan, I. Milosev, PVD coatings as an environmentally clean alternative to electroplating and electroless processes, Surf. Coating. Technol. 116e119 (1999) 476e487. https://doi.org/10.1016/S0257-8972(99)00145-0. [2] D.M. Sanders, A. Anders, Review of cathodic arc deposition technology at the start of the new millennium, Surf. Coating. Technol. 133e134 (2000) 78e90. https://doi.org/10.1016/S0257-8972(00)00879-3. [3] C.Y. Tong, J.W. Lee, C.C. Kuo, S.H. Huang, Y.C. Chan, H.W. Chen, J.G. Duh, Effects of carbon content on the microstructure and mechanical property of cathodic arc evaporation deposited CrCN thin films, Surf. Coating. Technol. (2013) 482e486. https://doi.org/10.1016/j.surfcoat.2012.01.009. [4] S.H. Huang, S.F. Chen, Y.C. Kuo, C.J. Wang, J.W. Lee, Y.C. Chan, H.W. Chen,
[24]
[25]
J.G. Duh, T.E. Hsieh, Mechanical and tribological properties evaluation of cathodic arc deposited CrN/ZrN multilayer coatings, Surf. Coating. Technol. 206 (2011) 1744e1752. https://doi.org/10.1016/j.surfcoat.2011.10.029. S.-F. Chen, Y.-C. Kuo, C.-J. Wang, S.-H. Huang, J.-W. Lee, Y.-C. Chan, H.-W. Chen, J.-G. Duh, T.-E. Hsieh, The effect of Cr/Zr chemical composition ratios on the mechanical properties of CrN/ZrN multilayered coatings deposited by cathodic arc deposition system, Surf. Coating. Technol. 231 (2013) 247e252. https://doi.org/10.1016/j.surfcoat.2012.03.002. S. Wan, J. Pu, D. Li, G. Zhang, B. Zhang, A.K. Tieu, Tribological performance of CrN and CrN/GLC coated components for automotive engine applications, J. Alloy. Comp. 695 (2017) 433e442. http://doi.org/10.1016/j.jallcom.2016.11. 118. J. Jagielski, A.S. Khanna, J. Kucinski, D.S. Mishra, P. Racolta, P. Sioshansi, E. Tobin, J. Thereska, V. Uglov, T. Vilaithong, J. Viviente, S.-Z. Yang, A. Zalar, Effect of chromium nitride coating on the corrosion and wear resistance of stainless steel, Appl. Surf. Sci. 156 (2000) 47e64. https://doi.org/10.1016/ S0169-4332(99)00350-5. G. Berg, C. Friedrich, E. Broszeit, C. Berger, Development of chromium nitride coatings substituting titanium nitride, Surf. Coating. Technol. 86e87 (1996) 184e191. https://doi.org/10.1016/S0257-8972(96)03042-3. Q. Wang, F. Zhou, X. Ding, Z. Zhou, C. Wang, W. Zhang, L.K.-Y. Li, S.-T. Lee, Microstructure and water-lubricated friction and wear properties of CrN(C) coatings with different carbon contents, Appl. Surf. Sci. 268 (2013) 579e587. http://doi.org/10.1016/j.apsusc.2013.01.027. P. Hu, B. Jiang, Study on tribological property of CrCN coating based on magnetron sputtering plating technique, Vacuum 85 (2011) 994e998. https:// doi.org/10.1016/j.vacuum.2011.02.007. J. Zhang, X. Su, L. Shan, Y. Liu, P. Zhang, Y. Jia, Preparation and tribocorrosion performance of CrCN coatings in artificial seawater on different substrates with different bias voltages, Ceram. Int. 45 (2019) 9901e9911. https://doi.org/ 10.1016/j.ceramint.2019.02.031. Y. Ye, Y. Wang, C. Wang, J. Li, Y. Yao, An analysis on tribological performance of CrCN coatings with different carbon contents in seawater, Tribol. Int. 91 (2015) 131e139. http://doi.org/10.1016/j.triboint.2015.07.002. Y. Kong, X. Tian, C. Gong, P.K. Chu, Enhancement of toughness and wear resistance by CrN/CrCN multilayered coatings for wood processing, Surf. Coating. Technol. 344 (2018) 204e213. https://doi.org/10.1016/j.surfcoat. 2018.03.027. J.-L. Ruan, D.-F. Lii, H.-H. Lu, J.S. Chen, J.-L. Huang, Microstructural and electrical characteristics of reactively sputtered ZrNx thin films, J. Alloy. Comp. 478 (2009) 671e675. https://doi.org/10.1016/j.jallcom.2008.11.103. J.-H. Huang, K.-L. Kuo, G.-P. Yu, Oxidation behavior and corrosion resistance of vacuum annealed ZrN-coated stainless steel, Surf. Coating. Technol. 358 (2019) 308e319. https://doi.org/10.1016/j.surfcoat.2018.11.054. X.M. Xu, J. Wang, J. An, Y. Zhao, Q.Y. Zhang, Effect of modulation structure on the growth behavior and mechanical properties of TiN/ZrN multilayers, Surf. Coating. Technol. 201 (2007) 5582e5586. https://doi.org/10.1016/j.surfcoat. 2006.07.132. O.V. Maksakova, S. Simoẽs, A.D. Pogrebnjak, O.V. Bondar, Ya. O. Kravchenko, T.N. Koltunowicz, Zh. K. Shaimardanov, Multilayered ZrN/CrN coatings with enhanced thermal and mechanical properties, J. Alloy. Comp. 776 (2019) 679e690. https://doi.org/10.1016/j.jallcom.2018.10.342. Z.G. Zhang, O. Rapaud, N. Allain, D. Mercs, M. Baraket, C. Dong, C. Coddet, Microstructures and tribological properties of CrN/ZrN nanoscale multilayer coatings, Appl. Surf. Sci. 255 (2009) 4020e4026. https://doi.org/10.1016/j. apsusc.2008.10.075. O. Maksakova, S. Simoẽs, A. Pogrebnjak, O. Bondar, Y. Kravchenko, V. Beresnev, N. Erdybaeva, The influence of deposition conditions and bilayer thickness on physicalmechanical properties of CA-PVD multilayer ZrN/CrN coating, Mater. Char. 140 (2018) 189e196. https://doi.org/10.1016/j.matchar. 2018.03.048. M.M. Larijani, M.B. Zanjanbar, A. Majdabadi, The effect of carbon fraction in Zr(C, N) films on the nano-structural properties and hardness, J. Alloy. Comp. 492 (2010) 735e738. https://doi.org/10.1016/j.jallcom.2009.12.035. J. Xu, H.J. Huang, Z.Y. Li, S. Xu, H. Tao, P. Munroe, Z.-H. Xie, Corrosion behavior of a ZrCN coated Ti alloy with potential application as a bipolar plate for proton exchange membrane fuel cell, J. Alloy. Comp. 663 (2016) 718e730. https://doi.org/10.1016/j.jallcom.2015.12.197. F. Zhou, K. Fu, B. Liao, J. Yu, C. Yang, X. Zhang, Effect of carbon content on nanostructural, mechanical and electrochemical characteristics of selforganized nc-ZrCN/a-CNx nanocomposite films, Appl. Surf. Sci. 327 (2015) 350e357. https://doi.org/10.1016/j.apsusc.2014.11.181. M. Braic, V. Braic, M. Balaceanu, C.N. Zoita, A. Kiss, A. Vladescu, A. Popescu, R. Ripeanu, Structure and properties of Zr/ZrCN coatings deposited by cathodic arc method, Mater. Chem. Phys. 126 (2011) 818e825. https://doi.org/ 10.1016/j.matchemphys.2010.12.036. E. Silva, M. Rebelo de Figueiredo, R. Franz, R. Escobar Galindo, C. Palacio, A. Espinosa, S.V. Calderon, C. Mitterer, S. Carvalho, Structureeproperty relations in ZrCN coatings for tribological applications, Surf. Coating. Technol. 205 (2010) 2134e2141. https://doi.org/10.1016/j.surfcoat.2010.08.126. M. Stueber, U. Albers, H. Leiste, S. Ulrich, H. Holleck, P.B. Barna, A. Kovacs, P. Hovsepian, I. Gee, Multifunctional nanolaminated PVD coatings in the system TieAleNeC by combination of metastable fcc phases and nanocomposite microstructures, Surf. Coating. Technol. 200 (2006) 6162e6171. https://doi.org/10.1016/j.surfcoat.2005.11.012.
S.-H. Huang et al. / Journal of Alloys and Compounds 803 (2019) 1005e1015 [26] M. Stueber, H. Holleck, H. Leiste, K. Seemann, S. Ulrich, C. Ziebert, Concepts for the design of advanced nanoscale PVD multilayer protective thin films, J. Alloy. Comp. 483 (2009) 321e333. https://doi.org/10.1016/j.jallcom.2008. 08.133. [27] M. Balaceanu, T. Petreus, V. Braic, C.N. Zoita, A. Vladescu, C.E. Cotrutz, M. Braic, Characterization of Zr-based hard coatings for medical implant applications, Surf. Coating. Technol. 204 (2010) 2046e2050. https://doi.org/10.1016/j. surfcoat.2009.11.022. [28] M. Balaceanu, M. Braic, V. Braic, G. Pavelescu, Properties of arc plasma deposited TiCN/ZrCN superlattice coatings, Surf. Coating. Technol. 200 (2005) 1084e1087. https://doi.org/10.1016/j.surfcoat.2005.01.077. [29] J. Goldstein, D.E. Newbury, D.C. Joy, C.E. Lyman, P. Echlin, E. Lifshin, L. Sawyer, J.R. Michael, Scanning Electron Microscopy and X-Ray Microanalysis, Plenum Press, 2003, p. 404. [30] G.G. Stoney, The tension of metallic films deposited by electrolysis, Proc. R. Soc. London, Ser. A 82 (1909) 172e175. https://doi.org/10.1098/rspa.1909. 0021. [31] H. Jehn, G. Reiners, N. Siegel (Eds.), Beuth Verlag, Berlin, 1993, p. 213. nkov [32] S. Ma, J. Proch azka, P. Karva a, Q. Ma, X. Niu, X. Wang, D. Ma, K. Xu, S. Veprek, Comparative study of the tribological behaviour of superhard nanocomposite coatings nc-TiN/a-Si3N4 with TiN, Surf. Coating. Technol. 194 (2005) 143e148. https://doi.org/10.1016/j.surfcoat.2004.05.007. [33] S.R. Shatynski, The thermochemistry of transition metal carbides, Oxid. Metals 13 (1979) 105e118. https://doi.org/10.1007/BF00611975. [34] P.C. Yashar, W.D. Sproul, Nanometer scale multilayered hard coatings, Vacuum 55 (1999) 179e190. https://doi.org/10.1016/S0042-207X(99)00148-7. [35] M. Neuhaeuser, H. Hilgers, P. Joeris, R. White, Windeln, Raman spectroscopy measurements of DC-magnetron sputtered carbon nitride (a-C:N) thin films for magnetic hard disk coatings, J. Diam. Relat. Mater. 9 (2000) 1500e1505. https://doi.org/10.1016/S0925-9635(00)00276-4. [36] X.A. Zhao, C.W. Ong, Y.C. Tsang, Y.W. Wong, P.W. Chan, C.L. Choy, Reactive pulsed laser deposition of CNx films, Appl. Phys. Lett. 6 (1995) 2652. https:// doi.org/10.1063/1.113114. [37] J. Sui, J.J. Lu, Synthesis of carbon nitride powder by selective etching of TiC0.3N0.7 in chlorine-containing atmosphere at moderate temperature, Mater. Chem. Phys. 123 (2010) 264e268. https://doi.org/10.1016/j. matchemphys.2010.04.008.
1015
[38] W.Y. Wu, J.M. Ting, Self-assembled alternating nano-scaled layers of carbon and metal, Chem. Phys. Lett. 388 (2004) 312e315. https://doi.org/10.1016/j. cplett.2004.03.004. €ss, [39] W.Y. Wu, J.M. Ting, H. Zutz, D. Lyzwa, I. Gerhards, C. Ronning, H. Hofsa Comparative study of self-assembling of multilayers using reactive sputter deposition and mass selective ion beam deposition, Diam. Relat. Mater. 17 (2008) 1494e1497. https://doi.org/10.1016/j.diamond.2008.01.048. [40] E. Hong, T. Kim, S.-H. Lee, J.W. Lee, H. Lee, Atomic structure and residual stress of carbon-doped TiMeN (Me ¼ Zr, Al, and Cr) coatings on mechanical properties, Ceram. Int. 45 (2019) 9192e9196. https://doi.org/10.1016/j.ceramint. 2019.01.263. [41] J. Almer, M. Oden, G. Håkansson, Microstructure, stress and mechanical properties of arc-evaporated Cr-C-N coatings, Thin Solid Films 385 (2001) 190e197. https://doi.org/10.1016/S0040-6090(01)00759-3. n, C. Ericsson, G. Håkansson, H. Ljungcrantz, Microstructure and me[42] M. Ode chanical behavior of arc-evaporated CreN coatings, Surf. Coating. Technol. 114 (1999) 39e51. https://doi.org/10.1016/S0257-8972(99)00019-5. [43] P. Wang, M. Sugo, K. Adachi, Stable and super-low friction of amorphous carbon nitride coatings in nitrogen gas by using two-step ball-on-disk friction test, Lubr. Sci. 27 (2015) 137e149. https://doi.org/10.1002/ls.1258. [44] P. Wang, W. Zhang, D. Diao, Low friction of graphene nanocrystallite embedded carbon nitride coatings prepared with MCECR plasma sputtering, Surf. Coating. Technol. 332 (2017) 153e160. https://doi.org/10.1016/j. surfcoat.2017.06.084. [45] F.J. Flores-Ruiz, M.D. Tucker, K.D. Bakoglidis, X. Yu, A.J. Gellman, A. HerreraGomez, L. Hultman, J. Rosen, E. Broitman, Micro-tribological performance of fullerene-like carbon and carbon-nitride surfaces, Tribol. Int. 128 (2018) 104e112. https://doi.org/10.1016/j.triboint.2018.07.009. [46] R.L. Boxman, S. Goldsmith, Macroparticle contamination in cathodic arc coatings: generation, transport and control, Surf. Coating. Technol. 52 (1992) 39e50. https://doi.org/10.1016/0257-8972(92)90369-L. [47] P. Harlin, U. Bexell, M. Olsson, Influence of surface topography of arcdeposited TiN and sputter-deposited WC/C coatings on the initial material transfer tendency and friction characteristics under dry sliding contact conditions, Surf. Coating. Technol. 203 (2009) 1748e1755. https://doi.org/10. 1016/j.surfcoat.2008.12.011.