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ZrN coatings
Surface & Coatings Technology 201 (2007) 5186 – 5189 www.elsevier.com/locate/surfcoat
Enhancing mechanical and tribological performance of multilayered CrN/ZrN coatings J.J. Zhang, M.X. Wang, J. Yang, Q.X. Liu, D.J. Li ⁎ College of Physics and Electronic Information Science, Tianjin Normal University, Tianjin 300074, China Available online 9 August 2006
Abstract The CrN/ZrN multilayered coatings with nanoscale bilayer period were synthesized at different substrate rotary speeds (4–11 rpm) and reaction gas flows in an unbalances reactive dc magnetron sputter chamber. XRD, AES, XPS, Nano indenter and tribometer were employed to investigate the influence of substrate rotary speed, species of reaction gases and flows on microstructure, mechanical and tribological properties of the coatings. A layer structure with small modulation period synthesized by a proper percentage of NH3 in N2 reaction gas was proved to be of benefit to synthesize high hard (32 GPa) and low wear-resistant (wear rate: 0.3865 × 10− 5 mm3/Nm) CrN/ZrN coatings. These properties were related to strongly mixed Cr–N and Zr–N preferred orientations and nanolayer structure. © 2006 Elsevier B.V. All rights reserved. PACS: 68.65.Ac; 81.15.Jj; 81.65.Lp; 81.40.Np Keywords: Magnetron sputtering; CrN/ZrN; Multilayered coating
1. Introduction Magnetron sputtering has developed rapidly over the last decade to the offer the same functionality as much thicker films produced by other surface coating techniques. It now makes a significant impact in application areas including hard, wearresistant coatings, low friction coatings, corrosion-resistant coatings, decorative coatings [1–3]. Nanoscale multilayers are well-known for increasing hardness as the period is reduced, usually reaching values that surpass those of their individual components, resulting in the improvement of the mechanical and tribological properties [4,5]. Transition metal nitride coatings, mainly based on titanium, chromium and zirconium, are widely used as protective coatings against wear and corrosion due to their desirable high melting point, high hardness, lower friction coefficient, high chemical stability and corrosion resistance [5–9]. However, few reports on nanoscale CrN/ZrN multilayered coatings can be found in recent literatures. In this work, we focus on this model grown in a dc reactive magnetron sputtering chamber by varying deposition parameters. Our aim is to obtain insight into the ⁎ Corresponding author. Tel./fax: +86 22 23540278. E-mail address: [email protected] (D.J. Li). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.07.093
significance of these process parameters on the structure and mechanical properties of the multilayered CrN/ZrN coatings. 2. Experimental detail The CrN/ZrN multilayered coatings were synthesized in an unbalances reactive magnetron sputter chamber. Prior to deposition, silicon (100) substrates were heated to 250 °C and then etched for 10 min by Ar+ at − 600 V. The base pressure was down to 10− 4 Pa. Ar, N2, and NH3 gas flows were independently controlled using the mass-flow controllers. The deposition of the multilayered coatings started with the deposition of a couple 10 nm Zr buffer layer to increase coating adhesion. By alternately exposing the substrates to the Cr (99.9%) source and the Zr (99.9%) source set on opposing position using varying substrate rotation (4 to 11 rpm), the multilayered coatings with different layer modulation periods were grown. The total pressure was kept at 0.26 Pa no matter how change N2 or NH3 flows. DC power supplies were run in constant mode with 1 kW and 1.2 kW applied to Cr and Zr targets. A negative bias of 200 V was applied to the substrate during deposition. The thicknesses (1–1.2 μm) of the coatings were measured using a XP-2 profiler. This system was also used to perform residual stress test. A Nano Indenter XP system was employed
J.J. Zhang et al. / Surface & Coatings Technology 201 (2007) 5186–5189
to perform nanoindentation and elastic modulus tests. In this measurement, the hardness and elastic modulus were measured as a continuous function of depth from a single indentation experiment. Wear tests were performed in a humidity of 30% at 23 °C using a MS-T3000 tribometer (ball-and-disk) with a Si3N4 ceramic ball sliding on the specimen under an applied load of 2 N. The diameter of the wear track was 5 mm; the sliding velocity was held constant 1000 rpm. Wear track analysis was performed using the profiler. XRD was used for structural analysis of the coatings using a D/MAX 2500 (Japan) diffractometer. The element compositions and their depth profiles of the coatings were investigated by Auger electron spectroscopy (AES, PHI-610, USA). XPS studies were performed with a VG ESCALAB 5 multi-techniques electron spectrometer, in order to investigate element chemical bonding states. 3. Result and discussion Fig. 1 shows the XRD patterns of the CrN/ZrN and monolithic layers synthesized at gas flow of 0.63 sccm for N2 and 0.17 sccm for NH3 under identical other operation parameters. The structure investigation of CrN and ZrN monolithic layers reveal a typical face-centered-cubic structure. However, only a broad and weak ZrN(111) peak is found in the multilayer structure. The reason is that CrN layer periodic deposition suppresses crystal growth of ZrN. Another reason is due to thinner ZrN layer within a modulation period due to a lower deposition rata. The thicknesses of individual CrN and ZrN layers for all deposition parameters are calibrated using the film growth rate measured by the thickness of coatings grown using a profilometer. 70%/30% CrN/ZrN is controlled and achieved within each bilayer thickness for all multilayers. Therefore, individual ZrN thickness is estimated to be 0.7 nm for this case (see later analysis of low-angle XRD pattern). A new strong texture appears at 61.06° in the structure of this multilayer. This seems to reveal a phase transformation from cubic NaCl CrN to
Fig. 1. High-angle and low-angle XRD patterns of CrN/ZrN and monolithic layers.
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Fig. 2. Sputter depth profile of the CrN/ZrN coating.
hexagonal Cr2N due largely to stress change in the coating growth, but could not be identified conclusively. On the other hand, if the stress/strain relationship changes, the diffraction peak also shifts, according to Bragg's law. Therefore, the peak at 61.06° might also correspond to shift CrN (220) texture. So, it could not be concluded whether the peak at 61.06° corresponded to the Cr2N (211) preferred orientation or shifted CrN (220) phase. But, it is believed that the presence of a proper amount of NH3 in the process gas is able to produce a mixed polycrystalline
Fig. 3. XPS (a) Cr2P and (b) Zr3d spectra obtained from the CrN/ZrN coating.
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Fig. 4. Nanoindentation hardness and elastic modulus of the CrN/ZrN coatings vs. estimated period Λ.
Fig. 6. Residual stress and nanoindentation hardness of the CrN/ZrN coatings vs. NH3/N2 flow rate.
in the multilayered structure due to its activity, which may cause a positive effect on its mechanical properties. The low-angle XRD patterns give direct information on the modulation period Λ from CrN/ZrN multilayered coatings. Their values were calculated to be 2.2 and 3.6 nm at the substrate rotary speed of 11 and 4 rpm, respectively, from the orientation peaks using standard Bragg equation. It is clear that low rotary speed corresponds to thicker modulation period. Fig. 2 shows the AES depth profile of the identical multilayer. C and O contaminations on the surface decrease sharply after 1 min sputtered cleaning with Ar+ (3.0 keV). The concentrations of N, Cr, Zr as main elements in the coating keep a constant throughout the thickness. It implies that the chemical reaction of Cr and Zr with N are dominant processes in the synthesis of the coatings. The low-angle XRD pattern indicated its modulation period to be 2.2 nm. However, it is hard to detect this value in this measurement due to too thinner individual thickness. A clearer result of the possible chemical bonding states of Cr and Zr with N for this coating can be obtained from individual XPS signal. Cr2P peak with high resolution after sputtered cleaning is shown in Fig. 3(a). It is fitted using the Gaussian peak shape to two components: a peak at 575.8 eV which is
identified as originating from Cr–N bonds, and a weak peak at 577.9 eV which may be attributed to contaminant species Cr–O. Fitting result of Zr3d peak (Fig. 3(b)) after sputtered cleaning indicates the presence of Zr–N and Zr–(N,O) bonds in the coating. This XPS result is agreement with XRD and AES analysis. The hardness and elastic modulus of the multilayered coatings vs. estimated period are shown in Fig. 4. To compare with the multilayered CrN/ZrN coatings, the hardness and modulus values of the monolithic ZrAlN and ZrB2 coatings synthesized at gas flows of 0.63 sccm for N2 and 0.17 sccm for NH3 under identical other operation parameters are also shown in the figures. All multilayered coatings reveal higher hardness and elastic modulus than the rule-of-mixtures value of monolithic CrN and ZrN coatings. It appears that the hardness and the elastic modulus of the CrN/ZrN coatings decrease with increasing Λ, i.e. with decreasing rotary speed of substrates. The maximum hardness is up to 32 GPa when the rotary speed is at 11 rpm. The increase in hardness and modulus can be understood by examining the structures. The nanolayers and interfaces are the keys in developing its hardness, because the CrN/ZrN interfaces can be able to produce barriers to dislocation glide and
Fig. 5. Residual stress of the CrN/ZrN coatings vs. estimated period Λ.
Fig. 7. Wear rate and friction coefficient of the CrN/ZrN coatings vs. estimated period Λ.
J.J. Zhang et al. / Surface & Coatings Technology 201 (2007) 5186–5189
columnar grain growth across layers. Of course, dislocation blocking due to coherency strains for different nanocrystalline grains also makes a contribution to hardness enhancement. On the other hand, a strong mixture of Cr–N and Zr–N preferred orientations has a higher hardness and modulus which result in the increases observed in the nanolayered coatings. The residual stresses of the multilayered coatings vs. estimated period are shown in Fig. 5. The residual stresses of the coatings exhibit the compressive ones. Their values decrease approximately with increased period. The coating with Λ = 2.2 nm indicates the lowest stress (2.3 GPa), which promotes adhesion and is vital to extending the service life of the substrate tool material in application. Fig. 6 shows the effect of NH3/N2 flow rate on the mechanical properties of CrN/ZrN coatings deposited at a constant substrate rotary speed of 11 rpm. With NH3/N2 flow rate increase, the hardness and compressive stress of the coatings enhance obviously. When the NH3/N2 flow rate was 27%, the hardness gets to the highest (32 GPa). This result proves the supposition above that the presence of a proper amount of NH3 in the process gas is of benefit to mechanical properties. One can understand the mechanism for the formation of nitride during thin film synthesis under different process parameters in many books [10]. At lower gas flow, the nitrogen atoms, which result from the dissociation of reaction gas molecules, are being consumed by the reaction with Cr and Zr atoms resulting in the formation of a substoichiometric film. With flow increasing, the nitrogen content of the CrN and ZrN is steadily increasing, and the preferred orientation for multilayer CrN/ZrN coatings changes from fcc(111) to fcc(220). It is well-known that dissociation of N atoms from NH3 gas is much easier than that from N2 due to lower bond energy in NH3 molecules. Therefore, there are much more N atoms involved in the nitride formation process during the coating synthesis in N2–NH3 mixture gas, which is one of the main reasons for the production of strongly mixed crystalline phases. The wear rate and friction coefficient of the coatings were shown in Fig. 7. It appeared that the wear rate of monolithic CrN coating is lower than monolithic ZrN coating, multilayered coating's (Λ = 3.6 nm) was amid of two monolithic coatings. A 6–24 times decrease to 0.3865 × 10− 5 mm3/Nm is observed for the hardest multilayered coatings with 1.5 nm thick modulation period. This measurement also shows that when investigating
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wear resistance, it is critically important to look at its dependence on other mechanical properties except friction coefficient. 4. Conclusions The new generation of protective coatings of cutting tools must possess desirable mechanical and tribological properties during high-speed cutting process. For practical reasons, it would be most desirable to accomplish this with nanometer scale multilayered coatings. This work shows that magnetron sputtering can produce small modulation period CrN/ZrN multilayered coatings with high hardness and wear resistance. The presence of a proper amount of NH3 in the process gas is of benefit to the reaction process between Cr or Zr and nitrogen. A nanolayer structure with strongly mixed Cr–N and Zr–N preferred orientations are responsible for hardness and wear resistance enhancement. Acknowledgements This work is supported by the Applied Basic Key Project of Tianjin (043801011) and the National Natural Science Foundation of China under Grant No.50472026. References [1] J.J. Olaya, S.E. Rodil, S. Muhl, E. Sanchez, Thin Solid Films 474 (2005) 119. [2] D.B. Lewis, Q. Luo, P.Eh. Hovsepian, W.D. Munz, Surf. Coat. Technol. 84 (2004) 225. [3] K. Lukaszkowicz, L.A. Dobrzanski, A. Zarychta, J. Mater. Process. Technol. 157–158 (2004) 380. [4] Q. Yang, D.Y. Seo, L.R. Zhao, Surf. Coat. Technol. 177–178 (2004) 204. [5] J. Romero, E. Martınez, J. Esteve, A. Lousa, Surf. Coat. Technol. 180–181 (2004) 335. [6] R. Lamni, E. Martinez, S.G. Springer, R. Sanjines, P.E. Schmid, F. Levy, Thin Solid Films 447–448 (2004) 316. [7] Z.B. Zhao, Z.U. Rek, S.M. Yalisove, J.C. Bilello, Surf. Coat. Technol. 185 (2004) 329. [8] Z.B. Zhao, Z.U. Rek, S.M. Yalisove, J.C. Bilello, Thin Solid Films 472 (2005) 96. [9] C.P. Liu, H.G. Yang, Mater. Chem. Phys. 86 (2004) 370. [10] J.E. Mahan, Physical Vapor Deposition of Thin Films, John Wiley & Sons, Inc., New York, 2000.
Enhancing mechanical and tribological performance of multilayered CrN/ZrN coatings J.J. Zhang, M.X. Wang, J. Yang, Q.X. Liu, D.J. Li ⁎ College of Physics and Electronic Information Science, Tianjin Normal University, Tianjin 300074, China Available online 9 August 2006
Abstract The CrN/ZrN multilayered coatings with nanoscale bilayer period were synthesized at different substrate rotary speeds (4–11 rpm) and reaction gas flows in an unbalances reactive dc magnetron sputter chamber. XRD, AES, XPS, Nano indenter and tribometer were employed to investigate the influence of substrate rotary speed, species of reaction gases and flows on microstructure, mechanical and tribological properties of the coatings. A layer structure with small modulation period synthesized by a proper percentage of NH3 in N2 reaction gas was proved to be of benefit to synthesize high hard (32 GPa) and low wear-resistant (wear rate: 0.3865 × 10− 5 mm3/Nm) CrN/ZrN coatings. These properties were related to strongly mixed Cr–N and Zr–N preferred orientations and nanolayer structure. © 2006 Elsevier B.V. All rights reserved. PACS: 68.65.Ac; 81.15.Jj; 81.65.Lp; 81.40.Np Keywords: Magnetron sputtering; CrN/ZrN; Multilayered coating
1. Introduction Magnetron sputtering has developed rapidly over the last decade to the offer the same functionality as much thicker films produced by other surface coating techniques. It now makes a significant impact in application areas including hard, wearresistant coatings, low friction coatings, corrosion-resistant coatings, decorative coatings [1–3]. Nanoscale multilayers are well-known for increasing hardness as the period is reduced, usually reaching values that surpass those of their individual components, resulting in the improvement of the mechanical and tribological properties [4,5]. Transition metal nitride coatings, mainly based on titanium, chromium and zirconium, are widely used as protective coatings against wear and corrosion due to their desirable high melting point, high hardness, lower friction coefficient, high chemical stability and corrosion resistance [5–9]. However, few reports on nanoscale CrN/ZrN multilayered coatings can be found in recent literatures. In this work, we focus on this model grown in a dc reactive magnetron sputtering chamber by varying deposition parameters. Our aim is to obtain insight into the ⁎ Corresponding author. Tel./fax: +86 22 23540278. E-mail address: [email protected] (D.J. Li). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.07.093
significance of these process parameters on the structure and mechanical properties of the multilayered CrN/ZrN coatings. 2. Experimental detail The CrN/ZrN multilayered coatings were synthesized in an unbalances reactive magnetron sputter chamber. Prior to deposition, silicon (100) substrates were heated to 250 °C and then etched for 10 min by Ar+ at − 600 V. The base pressure was down to 10− 4 Pa. Ar, N2, and NH3 gas flows were independently controlled using the mass-flow controllers. The deposition of the multilayered coatings started with the deposition of a couple 10 nm Zr buffer layer to increase coating adhesion. By alternately exposing the substrates to the Cr (99.9%) source and the Zr (99.9%) source set on opposing position using varying substrate rotation (4 to 11 rpm), the multilayered coatings with different layer modulation periods were grown. The total pressure was kept at 0.26 Pa no matter how change N2 or NH3 flows. DC power supplies were run in constant mode with 1 kW and 1.2 kW applied to Cr and Zr targets. A negative bias of 200 V was applied to the substrate during deposition. The thicknesses (1–1.2 μm) of the coatings were measured using a XP-2 profiler. This system was also used to perform residual stress test. A Nano Indenter XP system was employed
J.J. Zhang et al. / Surface & Coatings Technology 201 (2007) 5186–5189
to perform nanoindentation and elastic modulus tests. In this measurement, the hardness and elastic modulus were measured as a continuous function of depth from a single indentation experiment. Wear tests were performed in a humidity of 30% at 23 °C using a MS-T3000 tribometer (ball-and-disk) with a Si3N4 ceramic ball sliding on the specimen under an applied load of 2 N. The diameter of the wear track was 5 mm; the sliding velocity was held constant 1000 rpm. Wear track analysis was performed using the profiler. XRD was used for structural analysis of the coatings using a D/MAX 2500 (Japan) diffractometer. The element compositions and their depth profiles of the coatings were investigated by Auger electron spectroscopy (AES, PHI-610, USA). XPS studies were performed with a VG ESCALAB 5 multi-techniques electron spectrometer, in order to investigate element chemical bonding states. 3. Result and discussion Fig. 1 shows the XRD patterns of the CrN/ZrN and monolithic layers synthesized at gas flow of 0.63 sccm for N2 and 0.17 sccm for NH3 under identical other operation parameters. The structure investigation of CrN and ZrN monolithic layers reveal a typical face-centered-cubic structure. However, only a broad and weak ZrN(111) peak is found in the multilayer structure. The reason is that CrN layer periodic deposition suppresses crystal growth of ZrN. Another reason is due to thinner ZrN layer within a modulation period due to a lower deposition rata. The thicknesses of individual CrN and ZrN layers for all deposition parameters are calibrated using the film growth rate measured by the thickness of coatings grown using a profilometer. 70%/30% CrN/ZrN is controlled and achieved within each bilayer thickness for all multilayers. Therefore, individual ZrN thickness is estimated to be 0.7 nm for this case (see later analysis of low-angle XRD pattern). A new strong texture appears at 61.06° in the structure of this multilayer. This seems to reveal a phase transformation from cubic NaCl CrN to
Fig. 1. High-angle and low-angle XRD patterns of CrN/ZrN and monolithic layers.
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Fig. 2. Sputter depth profile of the CrN/ZrN coating.
hexagonal Cr2N due largely to stress change in the coating growth, but could not be identified conclusively. On the other hand, if the stress/strain relationship changes, the diffraction peak also shifts, according to Bragg's law. Therefore, the peak at 61.06° might also correspond to shift CrN (220) texture. So, it could not be concluded whether the peak at 61.06° corresponded to the Cr2N (211) preferred orientation or shifted CrN (220) phase. But, it is believed that the presence of a proper amount of NH3 in the process gas is able to produce a mixed polycrystalline
Fig. 3. XPS (a) Cr2P and (b) Zr3d spectra obtained from the CrN/ZrN coating.
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Fig. 4. Nanoindentation hardness and elastic modulus of the CrN/ZrN coatings vs. estimated period Λ.
Fig. 6. Residual stress and nanoindentation hardness of the CrN/ZrN coatings vs. NH3/N2 flow rate.
in the multilayered structure due to its activity, which may cause a positive effect on its mechanical properties. The low-angle XRD patterns give direct information on the modulation period Λ from CrN/ZrN multilayered coatings. Their values were calculated to be 2.2 and 3.6 nm at the substrate rotary speed of 11 and 4 rpm, respectively, from the orientation peaks using standard Bragg equation. It is clear that low rotary speed corresponds to thicker modulation period. Fig. 2 shows the AES depth profile of the identical multilayer. C and O contaminations on the surface decrease sharply after 1 min sputtered cleaning with Ar+ (3.0 keV). The concentrations of N, Cr, Zr as main elements in the coating keep a constant throughout the thickness. It implies that the chemical reaction of Cr and Zr with N are dominant processes in the synthesis of the coatings. The low-angle XRD pattern indicated its modulation period to be 2.2 nm. However, it is hard to detect this value in this measurement due to too thinner individual thickness. A clearer result of the possible chemical bonding states of Cr and Zr with N for this coating can be obtained from individual XPS signal. Cr2P peak with high resolution after sputtered cleaning is shown in Fig. 3(a). It is fitted using the Gaussian peak shape to two components: a peak at 575.8 eV which is
identified as originating from Cr–N bonds, and a weak peak at 577.9 eV which may be attributed to contaminant species Cr–O. Fitting result of Zr3d peak (Fig. 3(b)) after sputtered cleaning indicates the presence of Zr–N and Zr–(N,O) bonds in the coating. This XPS result is agreement with XRD and AES analysis. The hardness and elastic modulus of the multilayered coatings vs. estimated period are shown in Fig. 4. To compare with the multilayered CrN/ZrN coatings, the hardness and modulus values of the monolithic ZrAlN and ZrB2 coatings synthesized at gas flows of 0.63 sccm for N2 and 0.17 sccm for NH3 under identical other operation parameters are also shown in the figures. All multilayered coatings reveal higher hardness and elastic modulus than the rule-of-mixtures value of monolithic CrN and ZrN coatings. It appears that the hardness and the elastic modulus of the CrN/ZrN coatings decrease with increasing Λ, i.e. with decreasing rotary speed of substrates. The maximum hardness is up to 32 GPa when the rotary speed is at 11 rpm. The increase in hardness and modulus can be understood by examining the structures. The nanolayers and interfaces are the keys in developing its hardness, because the CrN/ZrN interfaces can be able to produce barriers to dislocation glide and
Fig. 5. Residual stress of the CrN/ZrN coatings vs. estimated period Λ.
Fig. 7. Wear rate and friction coefficient of the CrN/ZrN coatings vs. estimated period Λ.
J.J. Zhang et al. / Surface & Coatings Technology 201 (2007) 5186–5189
columnar grain growth across layers. Of course, dislocation blocking due to coherency strains for different nanocrystalline grains also makes a contribution to hardness enhancement. On the other hand, a strong mixture of Cr–N and Zr–N preferred orientations has a higher hardness and modulus which result in the increases observed in the nanolayered coatings. The residual stresses of the multilayered coatings vs. estimated period are shown in Fig. 5. The residual stresses of the coatings exhibit the compressive ones. Their values decrease approximately with increased period. The coating with Λ = 2.2 nm indicates the lowest stress (2.3 GPa), which promotes adhesion and is vital to extending the service life of the substrate tool material in application. Fig. 6 shows the effect of NH3/N2 flow rate on the mechanical properties of CrN/ZrN coatings deposited at a constant substrate rotary speed of 11 rpm. With NH3/N2 flow rate increase, the hardness and compressive stress of the coatings enhance obviously. When the NH3/N2 flow rate was 27%, the hardness gets to the highest (32 GPa). This result proves the supposition above that the presence of a proper amount of NH3 in the process gas is of benefit to mechanical properties. One can understand the mechanism for the formation of nitride during thin film synthesis under different process parameters in many books [10]. At lower gas flow, the nitrogen atoms, which result from the dissociation of reaction gas molecules, are being consumed by the reaction with Cr and Zr atoms resulting in the formation of a substoichiometric film. With flow increasing, the nitrogen content of the CrN and ZrN is steadily increasing, and the preferred orientation for multilayer CrN/ZrN coatings changes from fcc(111) to fcc(220). It is well-known that dissociation of N atoms from NH3 gas is much easier than that from N2 due to lower bond energy in NH3 molecules. Therefore, there are much more N atoms involved in the nitride formation process during the coating synthesis in N2–NH3 mixture gas, which is one of the main reasons for the production of strongly mixed crystalline phases. The wear rate and friction coefficient of the coatings were shown in Fig. 7. It appeared that the wear rate of monolithic CrN coating is lower than monolithic ZrN coating, multilayered coating's (Λ = 3.6 nm) was amid of two monolithic coatings. A 6–24 times decrease to 0.3865 × 10− 5 mm3/Nm is observed for the hardest multilayered coatings with 1.5 nm thick modulation period. This measurement also shows that when investigating
5189
wear resistance, it is critically important to look at its dependence on other mechanical properties except friction coefficient. 4. Conclusions The new generation of protective coatings of cutting tools must possess desirable mechanical and tribological properties during high-speed cutting process. For practical reasons, it would be most desirable to accomplish this with nanometer scale multilayered coatings. This work shows that magnetron sputtering can produce small modulation period CrN/ZrN multilayered coatings with high hardness and wear resistance. The presence of a proper amount of NH3 in the process gas is of benefit to the reaction process between Cr or Zr and nitrogen. A nanolayer structure with strongly mixed Cr–N and Zr–N preferred orientations are responsible for hardness and wear resistance enhancement. Acknowledgements This work is supported by the Applied Basic Key Project of Tianjin (043801011) and the National Natural Science Foundation of China under Grant No.50472026. References [1] J.J. Olaya, S.E. Rodil, S. Muhl, E. Sanchez, Thin Solid Films 474 (2005) 119. [2] D.B. Lewis, Q. Luo, P.Eh. Hovsepian, W.D. Munz, Surf. Coat. Technol. 84 (2004) 225. [3] K. Lukaszkowicz, L.A. Dobrzanski, A. Zarychta, J. Mater. Process. Technol. 157–158 (2004) 380. [4] Q. Yang, D.Y. Seo, L.R. Zhao, Surf. Coat. Technol. 177–178 (2004) 204. [5] J. Romero, E. Martınez, J. Esteve, A. Lousa, Surf. Coat. Technol. 180–181 (2004) 335. [6] R. Lamni, E. Martinez, S.G. Springer, R. Sanjines, P.E. Schmid, F. Levy, Thin Solid Films 447–448 (2004) 316. [7] Z.B. Zhao, Z.U. Rek, S.M. Yalisove, J.C. Bilello, Surf. Coat. Technol. 185 (2004) 329. [8] Z.B. Zhao, Z.U. Rek, S.M. Yalisove, J.C. Bilello, Thin Solid Films 472 (2005) 96. [9] C.P. Liu, H.G. Yang, Mater. Chem. Phys. 86 (2004) 370. [10] J.E. Mahan, Physical Vapor Deposition of Thin Films, John Wiley & Sons, Inc., New York, 2000.