- Email: [email protected]
Oxidation resistance of Cr1−XAlXN and Ti1−XAlXN films
Surface and Coatings Technology 165 (2003) 163–167
Oxidation resistance of Cr1yXAlXN and Ti1yXAlXN films Masahiro Kawatea, Ayako Kimura Hashimotob, Tetsuya Suzukia,* a
Department of Mechanical Engineering, Keio University 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan National Institute of Advanced Industrial Science and Technology (AIST) Advanced Carbon Research Center, 1-1-1 Higashi, Tsukuba 305-8565, Japan
b
Received 30 April 2002; accepted in revised form 9 July 2002
Abstract Cr1yXAlXN films were synthesized on mirror-polished stainless steel substrates by the arc ion plating method using Cr1yXAlX alloy targets with diffent Al contents. Oxidation resistance of films was estimated by heating substrates in air at 800, 900 and 1000 8C and subsequent analysis by the X-ray diffraction method (XRD). The XRD peaks from Ti0.7Al0.3N films, annealed at 800 8C for 14 h, disappeared and the peaks from iron oxides consequently appeared. The oxidation resistance of Ti1yXAlXN films improved with increasing Al content X. On the other hand, the peaks from Cr1yXAlXN films which were annealed at 800 8C did not change at all, but Cr1yXAlXN films were slightly oxidized over 900 8C. It is considered that the oxidation resistance of Cr1yXAlXN films was superior to that of Ti1yXAlXN films. 䊚 2002 Elsevier Science B.V. All rights reserved. Keywords: Arc evaporation; Nitrides; Aluminium alloy; Chromium alloy; Oxidation
1. Introduction Ti1yXAlXN and films show high hardness, good thermal stability and oxidation resistance, and are applied to dry machining and high speed cutting operations w1,2x. Oxidation behavior of Ti1yXAlXN films has been investigated for several years and it has been accepted that they are oxidized over 800 8C w3–5x. It is known that oxidation resistance of CrN films is superior to that of TiN films w5,6x. As the addition of Al improves the oxidation resistance of TiN films, we expect a similar effect of Al in CrN films. There are some reports on Cr1yXAlXN films, especially on the phase transition from the NaCl structure to wurtzite structure w7–9x. Ide et al. deposited Cr1yXAlXN films with Xs0.25, 0.5, 0.75 and 1 and investigated on the oxidation behavior between 700 and 1000 8C for 1 h. They found that Cr1yXAlXN films did not oxidize at 900 8C and aluminum oxide was formed on top of Cr1yXAlXN films at the initial stage of the oxidation w10x. However, the oxidation behavior of Cr1yXAlXN films has not been fully analyzed yet w11x. *Corresponding autho. Fax: q81-45-566-1495. E-mail address: [email protected] (T. Suzuki).
In this study, Cr1yXAlXN and Ti1yXAlXN films were synthesized by the arc ion plating (AIP) method using alloy targets with differing Al contents. Oxidation resistance of Cr1yXAlXN and Ti1yXAlXN films was investigated by changing X values and analyzed by the X-ray diffraction (XRD) method, energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). 2. Experimental procedure Cr1yXAlXN and Ti1yXAlXN films were deposited on mirror-polished stainless steel substrates (20=20=1 mm SUS 304) by the AIP method using binary alloy targets. Before the deposition, the substrates were etched for 5 min in argon plasma and bombarded for 3 min by ions ejected from targets at bias voltage of y1000 V. Then, the binary alloy targets were arc-discharged for 20 min with an arc current of 100 A under nitrogen atmosphere maintained at 3.3 Pa. The substrates were biased at y20 V with temperature of ;300 8C during film deposition. The average thickness of films was found by cross-sectional SEM observation to be 5–6 m. Oxidation behavior was investigated by heating films in air at 800, 900 and 1000 8C for 2–20 h, respectively.
0257-8972/03/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 2 . 0 0 4 7 3 - 5
164
M. Kawate et al. / Surface and Coatings Technology 165 (2003) 163–167
Fig. 1. XRD patterns from Ti1yX AlX N films annealed at 800 8C: (a) Ti0.3 Al0.7 N after oxidation for 14 h; (b) Ti0.3 Al0.7 N after oxidation for 12 h; (c) Ti0.4Al0.6N after oxidation for 14 h; (d) Ti0.4Al0.6N after oxidation for 12 h; (e) Ti0.7Al0.3N after oxidation for 14 h (f) Ti0.7Al0.3N after oxidation for 12 h.
The films were placed into an alumina plate and heated in a furnace and then were cooled in air. Crystal structures of oxide layers were identified by the XRD method using Cu Ka radiation. The XRD method was operated by the grazing angle mode at 20 kV and 20 mA. The incident X-ray beam angle was 28. The surface and cross-sectional morphology of as-deposited and annealed films was investigated by SEM. Atomic ratios of Al against other metals in Cr1yXAlXN and Ti1yXAlXN films were measured with EDX to compare with those of targets.
Al- rich Ti1yXAlXN films such as Ti0.4Al0.6N and Ti0.3Al0.7N films, Al2O3 and TiO2 peaks with the rutile type were identified and the peaks of Ti1yXAlXN films
3. Results and discussion 3.1. Oxidation behavior of Ti1yXAlXN films Fig. 1 shows XRD patterns from Ti0.7Al0.3N, Ti0.4Al0.6N and Ti0.3Al0.7N films heated at 800 8C for 12 and 14 h, respectively. The crystal structure of Ti0.7Al0.3N and Ti0.4Al0.6N films was the NaCl type and that of Ti0.3Al0.7N was the wurtzite type w2x. For the Ti0.7Al0.3N films annealed for 12 and 14 h, the peak intensities from TiAlN films decreased with annealing time and completely disappeared and those from iron and chromium oxides appeared since the diffusion of oxygen in the reached substrate. On the other hand, for
Fig. 2. Scanning electron micrograph of Ti0.7 Al0.3 N films annealed at 800 8C for 2 h.
M. Kawate et al. / Surface and Coatings Technology 165 (2003) 163–167
165
Fig. 3. XRD patterns from (a) Cr0.6Al0.4N and (b) Cr0.4Al0.6N films annealed at 900 8C between 0 and 20 h.
still exist. The peaks of iron oxide did not appear even when annealing time was over 20 h. Ti0.7Al0.3N films protected the substrate from oxidization for 12 h. It was
found that the oxidation resistance of Ti1yXAlXN films improved with the increase of Al content X. Fig. 2 shows scanning electron micrograph of Ti0.7Al0.3N film after annealing at 800 8C for 2 h. The whisker with 1;2 mm in Fig. 2 was observed around droplets at the early stage of oxidation. As annealing time increased, large particles with 5;20 mm were observed on the surface, and correspondingly the surface roughness became much larger. The surface of Ti0.7Al0.3N films was completely coated with clusters of oxide crystal in the specimen of 14 h. For the Ti0.4Al0.6N and Ti0.3Al0.7N films, the whisker and clusters of oxide crystal were observed around droplets but the surface roughness did not become larger compared with Ti0.7Al0.3N films. 3.2. Oxidation behavior of Cr1yXAlXN films
Fig. 4. Scanning electron micrograph of Cr0.3 Al0.7 N films annealed at 900 8C for 14 h.
The XRD intensities of Cr1yXAlXN films annealed at 800 8C did not change even when annealing time was over 20 h compared with Ti1yXAlXN films. For Cr0.6Al0.4N films, the small peaks from Cr2O3 appeared after 10 h annealing at 800 8C. Fig. 3 shows XRD patterns from (a) Cr0.6Al0.4N and (b) Cr0.4Al0.6N films heated at 900 8C for 0 to 20 h. The crystal structure of Cr0.6Al0.4N and Cr0.4Al0.6N films was the NaCl type and
166
M. Kawate et al. / Surface and Coatings Technology 165 (2003) 163–167
Fig. 5. Scanning electron micrographs of the fracture surface of (a) Cr0.6 Al0.4 N, (b) Cr0.4 Al0.6 N and (c) Cr0.3 Al0.7 N films annealed at 800 8C for 20 h.
that of Cr0.3Al0.7N was the wurtzite type w9x. When Cr0.6Al0.4N films were heated at 900 8C, the peaks drastically decreased in the specimen for 4 h and did not change after 4 h. On the other hand, the peaks Cr0.4Al0.6N and Cr0.3Al0.7N gradually decreased and still existed even when the annealing time was over 20 h. Similar to the case of 900 8C, the Cr0.6Al0.4N peaks drastically decreased and the C0.3Al0.7N and Cr0.3Al0.7N peaks decreased gradually after 1000 8C annealing. The peaks of Al2O3 gradually increased as shown Fig. 3a,b. Exfoliation was observed in the all specimens over 12 h. It is concluded that the oxidation resistance of Cr1yXAlXN films improves with the increase of Al content X as in the case of Ti1yXAlXN films and was superior to that of Ti1yXAlXN films. The surface morphology of Cr1yXAlXN films heated
at 800 8C did not change even after 20 h. Fig. 4 shows scanning electron micrographs of Cr0.3Al0.7N film after annealing at 900 8C for 14 h. Some oxide crystals with ;3 m as shown in Fig. 4 were observed for the specimen of Cr0.4Al0.6N and Cr0.3Al0.7N films. Fig. 5 shows scanning electron micrographs of the fracture surface of (a) Cr0.6Al0.4N, (b) Cr0.4Al0.6N and (c) Cr0.3Al0.7N films annealed at 800 8C for 20 h, respectively. For all Cr1yXAlXN films, oxide layers with thickness of 1;2 m were formed on top of films. Cr0.6Al0.4N, and Cr0.4Al0.6N films had a typical columnar structure w9x as shown in Fig. 5a,b. The interface between oxide and nitride layer was clearly observed. Since the peaks of oxides did not be identified by XRD method and the first layer consisted of Al by EDX analysis, first oxide layer is presumably amorphous
M. Kawate et al. / Surface and Coatings Technology 165 (2003) 163–167
aluminum oxide similar to TiAlN films w10x. The cracks of first layer seem to be formed when a sample was broken. Since the adhesion strength between oxide and nitride layer was weak, exfoliation and voids between oxide and nitride layer which were made by sample cutting was observed. Many voids were seen in the second layer of Cr0.3Al0.7N films as shown in Fig. 5c. 4. Summary Cr1yXAlXN and Ti1yXAlXN films were synthesized by the AIP method changing Al contents, X, and investigated with respect to oxidation behavior. The results obtained are as follows: 1. The oxidation resistance of Ti1yXAlXN films was improved with the increase of Al content X. 2. The oxidation resistance of Cr1yXAlXN films improved with the increase of Al content X and was superior to that of Ti1yXAlXN films. 3. As in the case of TiAlN films, Cr1yXAlXN films formed protective aluminum oxide layer at the film surface.
167
Acknowledgments The authors acknowledge Ultra Finish Technology Co. for its help in polishing substrates. References w1x O. Knotek, W.D. Munz, ¨ T. Leyendecker, J. Vac. Sci. Technol. A 5 (1987) 2173. w2x A. Kimura, H. Hasegawa, K. Yamada, T. Suzuki, Surf. Coat. Technol. 120–121 (1999) 438. w3x W.D. Munz, ¨ J. Vac. Sci. Technol. A 4 (1986) 2717. w4x T. Ikeda, H. Satoh, Thin Solid films 195 (1991) 99. w5x H. Ichimura, A. Kawana, J. Mater. Res. 8 (1993) 1093. w6x H. Ichimura, A. Kawana, J. Mater. Res. 9 (1994) 151. w7x A. Sugishima, H. Kajioka, Y. Makino, Surf. Coat. Technol. 97 (1997) 590. w8x Y. Makino, K. Nogi, Surf. Coat. Technol. 98 (1998) 1008. w9x M. Kawate, A. Kimura, T. Suzuki, J. Vac. Sci. Technol. A 20 (2002) 569. w10x Y. Ide, K. Inada, T. Nakamura, High Temperature Mater. Processes 19 (2000) 265. w11x J. Vetter, E. Lugscheider, S.S. Guerreiro, Surf. Coat. Technol. 98 (1998) 1233.
Oxidation resistance of Cr1yXAlXN and Ti1yXAlXN films Masahiro Kawatea, Ayako Kimura Hashimotob, Tetsuya Suzukia,* a
Department of Mechanical Engineering, Keio University 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan National Institute of Advanced Industrial Science and Technology (AIST) Advanced Carbon Research Center, 1-1-1 Higashi, Tsukuba 305-8565, Japan
b
Received 30 April 2002; accepted in revised form 9 July 2002
Abstract Cr1yXAlXN films were synthesized on mirror-polished stainless steel substrates by the arc ion plating method using Cr1yXAlX alloy targets with diffent Al contents. Oxidation resistance of films was estimated by heating substrates in air at 800, 900 and 1000 8C and subsequent analysis by the X-ray diffraction method (XRD). The XRD peaks from Ti0.7Al0.3N films, annealed at 800 8C for 14 h, disappeared and the peaks from iron oxides consequently appeared. The oxidation resistance of Ti1yXAlXN films improved with increasing Al content X. On the other hand, the peaks from Cr1yXAlXN films which were annealed at 800 8C did not change at all, but Cr1yXAlXN films were slightly oxidized over 900 8C. It is considered that the oxidation resistance of Cr1yXAlXN films was superior to that of Ti1yXAlXN films. 䊚 2002 Elsevier Science B.V. All rights reserved. Keywords: Arc evaporation; Nitrides; Aluminium alloy; Chromium alloy; Oxidation
1. Introduction Ti1yXAlXN and films show high hardness, good thermal stability and oxidation resistance, and are applied to dry machining and high speed cutting operations w1,2x. Oxidation behavior of Ti1yXAlXN films has been investigated for several years and it has been accepted that they are oxidized over 800 8C w3–5x. It is known that oxidation resistance of CrN films is superior to that of TiN films w5,6x. As the addition of Al improves the oxidation resistance of TiN films, we expect a similar effect of Al in CrN films. There are some reports on Cr1yXAlXN films, especially on the phase transition from the NaCl structure to wurtzite structure w7–9x. Ide et al. deposited Cr1yXAlXN films with Xs0.25, 0.5, 0.75 and 1 and investigated on the oxidation behavior between 700 and 1000 8C for 1 h. They found that Cr1yXAlXN films did not oxidize at 900 8C and aluminum oxide was formed on top of Cr1yXAlXN films at the initial stage of the oxidation w10x. However, the oxidation behavior of Cr1yXAlXN films has not been fully analyzed yet w11x. *Corresponding autho. Fax: q81-45-566-1495. E-mail address: [email protected] (T. Suzuki).
In this study, Cr1yXAlXN and Ti1yXAlXN films were synthesized by the arc ion plating (AIP) method using alloy targets with differing Al contents. Oxidation resistance of Cr1yXAlXN and Ti1yXAlXN films was investigated by changing X values and analyzed by the X-ray diffraction (XRD) method, energy dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM). 2. Experimental procedure Cr1yXAlXN and Ti1yXAlXN films were deposited on mirror-polished stainless steel substrates (20=20=1 mm SUS 304) by the AIP method using binary alloy targets. Before the deposition, the substrates were etched for 5 min in argon plasma and bombarded for 3 min by ions ejected from targets at bias voltage of y1000 V. Then, the binary alloy targets were arc-discharged for 20 min with an arc current of 100 A under nitrogen atmosphere maintained at 3.3 Pa. The substrates were biased at y20 V with temperature of ;300 8C during film deposition. The average thickness of films was found by cross-sectional SEM observation to be 5–6 m. Oxidation behavior was investigated by heating films in air at 800, 900 and 1000 8C for 2–20 h, respectively.
0257-8972/03/$ - see front matter 䊚 2002 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 2 . 0 0 4 7 3 - 5
164
M. Kawate et al. / Surface and Coatings Technology 165 (2003) 163–167
Fig. 1. XRD patterns from Ti1yX AlX N films annealed at 800 8C: (a) Ti0.3 Al0.7 N after oxidation for 14 h; (b) Ti0.3 Al0.7 N after oxidation for 12 h; (c) Ti0.4Al0.6N after oxidation for 14 h; (d) Ti0.4Al0.6N after oxidation for 12 h; (e) Ti0.7Al0.3N after oxidation for 14 h (f) Ti0.7Al0.3N after oxidation for 12 h.
The films were placed into an alumina plate and heated in a furnace and then were cooled in air. Crystal structures of oxide layers were identified by the XRD method using Cu Ka radiation. The XRD method was operated by the grazing angle mode at 20 kV and 20 mA. The incident X-ray beam angle was 28. The surface and cross-sectional morphology of as-deposited and annealed films was investigated by SEM. Atomic ratios of Al against other metals in Cr1yXAlXN and Ti1yXAlXN films were measured with EDX to compare with those of targets.
Al- rich Ti1yXAlXN films such as Ti0.4Al0.6N and Ti0.3Al0.7N films, Al2O3 and TiO2 peaks with the rutile type were identified and the peaks of Ti1yXAlXN films
3. Results and discussion 3.1. Oxidation behavior of Ti1yXAlXN films Fig. 1 shows XRD patterns from Ti0.7Al0.3N, Ti0.4Al0.6N and Ti0.3Al0.7N films heated at 800 8C for 12 and 14 h, respectively. The crystal structure of Ti0.7Al0.3N and Ti0.4Al0.6N films was the NaCl type and that of Ti0.3Al0.7N was the wurtzite type w2x. For the Ti0.7Al0.3N films annealed for 12 and 14 h, the peak intensities from TiAlN films decreased with annealing time and completely disappeared and those from iron and chromium oxides appeared since the diffusion of oxygen in the reached substrate. On the other hand, for
Fig. 2. Scanning electron micrograph of Ti0.7 Al0.3 N films annealed at 800 8C for 2 h.
M. Kawate et al. / Surface and Coatings Technology 165 (2003) 163–167
165
Fig. 3. XRD patterns from (a) Cr0.6Al0.4N and (b) Cr0.4Al0.6N films annealed at 900 8C between 0 and 20 h.
still exist. The peaks of iron oxide did not appear even when annealing time was over 20 h. Ti0.7Al0.3N films protected the substrate from oxidization for 12 h. It was
found that the oxidation resistance of Ti1yXAlXN films improved with the increase of Al content X. Fig. 2 shows scanning electron micrograph of Ti0.7Al0.3N film after annealing at 800 8C for 2 h. The whisker with 1;2 mm in Fig. 2 was observed around droplets at the early stage of oxidation. As annealing time increased, large particles with 5;20 mm were observed on the surface, and correspondingly the surface roughness became much larger. The surface of Ti0.7Al0.3N films was completely coated with clusters of oxide crystal in the specimen of 14 h. For the Ti0.4Al0.6N and Ti0.3Al0.7N films, the whisker and clusters of oxide crystal were observed around droplets but the surface roughness did not become larger compared with Ti0.7Al0.3N films. 3.2. Oxidation behavior of Cr1yXAlXN films
Fig. 4. Scanning electron micrograph of Cr0.3 Al0.7 N films annealed at 900 8C for 14 h.
The XRD intensities of Cr1yXAlXN films annealed at 800 8C did not change even when annealing time was over 20 h compared with Ti1yXAlXN films. For Cr0.6Al0.4N films, the small peaks from Cr2O3 appeared after 10 h annealing at 800 8C. Fig. 3 shows XRD patterns from (a) Cr0.6Al0.4N and (b) Cr0.4Al0.6N films heated at 900 8C for 0 to 20 h. The crystal structure of Cr0.6Al0.4N and Cr0.4Al0.6N films was the NaCl type and
166
M. Kawate et al. / Surface and Coatings Technology 165 (2003) 163–167
Fig. 5. Scanning electron micrographs of the fracture surface of (a) Cr0.6 Al0.4 N, (b) Cr0.4 Al0.6 N and (c) Cr0.3 Al0.7 N films annealed at 800 8C for 20 h.
that of Cr0.3Al0.7N was the wurtzite type w9x. When Cr0.6Al0.4N films were heated at 900 8C, the peaks drastically decreased in the specimen for 4 h and did not change after 4 h. On the other hand, the peaks Cr0.4Al0.6N and Cr0.3Al0.7N gradually decreased and still existed even when the annealing time was over 20 h. Similar to the case of 900 8C, the Cr0.6Al0.4N peaks drastically decreased and the C0.3Al0.7N and Cr0.3Al0.7N peaks decreased gradually after 1000 8C annealing. The peaks of Al2O3 gradually increased as shown Fig. 3a,b. Exfoliation was observed in the all specimens over 12 h. It is concluded that the oxidation resistance of Cr1yXAlXN films improves with the increase of Al content X as in the case of Ti1yXAlXN films and was superior to that of Ti1yXAlXN films. The surface morphology of Cr1yXAlXN films heated
at 800 8C did not change even after 20 h. Fig. 4 shows scanning electron micrographs of Cr0.3Al0.7N film after annealing at 900 8C for 14 h. Some oxide crystals with ;3 m as shown in Fig. 4 were observed for the specimen of Cr0.4Al0.6N and Cr0.3Al0.7N films. Fig. 5 shows scanning electron micrographs of the fracture surface of (a) Cr0.6Al0.4N, (b) Cr0.4Al0.6N and (c) Cr0.3Al0.7N films annealed at 800 8C for 20 h, respectively. For all Cr1yXAlXN films, oxide layers with thickness of 1;2 m were formed on top of films. Cr0.6Al0.4N, and Cr0.4Al0.6N films had a typical columnar structure w9x as shown in Fig. 5a,b. The interface between oxide and nitride layer was clearly observed. Since the peaks of oxides did not be identified by XRD method and the first layer consisted of Al by EDX analysis, first oxide layer is presumably amorphous
M. Kawate et al. / Surface and Coatings Technology 165 (2003) 163–167
aluminum oxide similar to TiAlN films w10x. The cracks of first layer seem to be formed when a sample was broken. Since the adhesion strength between oxide and nitride layer was weak, exfoliation and voids between oxide and nitride layer which were made by sample cutting was observed. Many voids were seen in the second layer of Cr0.3Al0.7N films as shown in Fig. 5c. 4. Summary Cr1yXAlXN and Ti1yXAlXN films were synthesized by the AIP method changing Al contents, X, and investigated with respect to oxidation behavior. The results obtained are as follows: 1. The oxidation resistance of Ti1yXAlXN films was improved with the increase of Al content X. 2. The oxidation resistance of Cr1yXAlXN films improved with the increase of Al content X and was superior to that of Ti1yXAlXN films. 3. As in the case of TiAlN films, Cr1yXAlXN films formed protective aluminum oxide layer at the film surface.
167
Acknowledgments The authors acknowledge Ultra Finish Technology Co. for its help in polishing substrates. References w1x O. Knotek, W.D. Munz, ¨ T. Leyendecker, J. Vac. Sci. Technol. A 5 (1987) 2173. w2x A. Kimura, H. Hasegawa, K. Yamada, T. Suzuki, Surf. Coat. Technol. 120–121 (1999) 438. w3x W.D. Munz, ¨ J. Vac. Sci. Technol. A 4 (1986) 2717. w4x T. Ikeda, H. Satoh, Thin Solid films 195 (1991) 99. w5x H. Ichimura, A. Kawana, J. Mater. Res. 8 (1993) 1093. w6x H. Ichimura, A. Kawana, J. Mater. Res. 9 (1994) 151. w7x A. Sugishima, H. Kajioka, Y. Makino, Surf. Coat. Technol. 97 (1997) 590. w8x Y. Makino, K. Nogi, Surf. Coat. Technol. 98 (1998) 1008. w9x M. Kawate, A. Kimura, T. Suzuki, J. Vac. Sci. Technol. A 20 (2002) 569. w10x Y. Ide, K. Inada, T. Nakamura, High Temperature Mater. Processes 19 (2000) 265. w11x J. Vetter, E. Lugscheider, S.S. Guerreiro, Surf. Coat. Technol. 98 (1998) 1233.