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Adhesion improvement of cubic boron nitride film on high speed steel substrate by BNX implanted buffer interlayer
Surface & Coatings Technology 201 (2007) 6723 – 6725 www.elsevier.com/locate/surfcoat
Adhesion improvement of cubic boron nitride film on high speed steel substrate by BNX implanted buffer interlayer Zhihai Cai ⁎, Ping Zhang, Jun Tan National Key Laboratory for Remanufacturing, Academy of Armored Force Engineering, Beijing, 100072, China Available online 3 November 2006
Abstract One of the major problems for the deposition of cubic boron nitride(c-BN) films on W6Mo5Cr4V2 high speed steels(HHS) is the poor adhesion of the film to the substrate. For the purpose of improving adhesion, the BNX implanted buffer layer was introduced between the HSS and c-BN film deposited by the RF-magnetron sputtering. The influence of the BNX buffer layer on adhesion was investigated and the results showed that when the N/B ratio of the buffer layer is about 1:1, the adhesive strength of c-BN film to the HHS substrate reached the maximum, about 28.47 N, which is sixteen times higher than that of c-BN film deposited without the buffer layer. According to the XPS analysis, the surface of buffer interlayer was mainly in BN phase, which is the main reason to reduce the internal stress and improve the adhesion strength of c-BN films. © 2006 Published by Elsevier B.V. Keywords: Cubic boron nitride film; Adhesion; Ion implantation; Buffer interlayer
1. Introduction
2. Experimental procedures
Cubic boron nitride (c-BN) is one of the most perspective hard coating materials for its unique chemical and physical properties such as high hardness next to diamond, high chemical and thermal stability, and not reacting with ferrous metals. [1–3] Up to now, most examination works on the deposition of c-BN film are on the silicon substrates. There are only few reports on the deposition of c-BN on high speed steel. [4] The major problem in depositing c-BN on high speed steels is the poor adhesion. The c-BN film is often peeled off from the high speed steel shortly after deposition and occasionally even during deposition. Several techniques, such as reducing internal stress with soft buffer interlayer [5], lessening the mismatch difference between films/substrate, [6] and modifying chemical composition near the surface [7,8], for the adhesion improvement of c-BN film to silicon substrate have been presented. In this paper, we attempted to use the implanted BNX buffer interlayer to improve the adhesion of c-BN films on high speed steel substrate. The influence of the buffer layer on adhesion strength of c-BN films was investigated.
The c-BN film was prepared by RF-magnetron sputtering. Fig. 1 shows the schematic diagram of the apparatus used. A target of hot pressed h-BN was assembled as the cathode. Radiofrequency power was applied to HSS to generate a negative selfbias voltage. The magnetic coil was used to produce magnetic field to confine the movement of electric particles in the plasma so as to increase the density of plasma near target and substrate. The buffer interlayer was formed by first depositing a pure boron layer about 100 nm on the HSS substrate using a Kaufman ion source. The nitrogen ion implantations into HSS substrate were carried out at the energy of 50 keV. Nitrogen concentration of the buffer layer was controlled by varying the implantation dose of nitrogen ion from 1.6 × 1017 to 12.8 × 1017 ions/cm2 corresponding to implantation time from 0.5 h to 4 h. Finally the c-BN films were deposited under the conditions given in Table 1. The chemical composition ratio of N/B in the buffer interlayer was measured by an electron probe microanalyzer (EPMA). The c-BN film with the buffer interlayer was analyzed by infrared absorption spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The depth profiles of the c-BN films with the buffer interlayer were measured by XPS. The etching of film was carried out by argon ion at the energy of 3 keV. And the analytic area is 0.8 × 0.8 mm2. Adhesive
⁎ Corresponding author. Tel.: +86 10 66719249; fax: +86 10 6719249. E-mail address: [email protected] (Z. Cai). 0257-8972/$ - see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.surfcoat.2006.09.037
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Z. Cai et al. / Surface & Coatings Technology 201 (2007) 6723–6725
Fig. 2. Change in chemical composition ratio N/B of BNX buffer layer with implantation time.
Fig. 1. Schematic illustration of the RF sputtering system for the deposition of BN films.
measurements of c-BN films to HSS substrate were carried with a scratch tester apparatus. The surface of c-BN was analyzed by AFM with Si3N4 needle, working in a constant force model. 3. Results and discussion 3.1. Composition and structure of implanted buffer interlayer Fig. 2 shows the N/B ratio of the BNX layer with different implantation time. It can be seen that N/B increases approximately linearly with increasing implantation time. And the N/B ratio of 1:1 can be obtained at about 3 h implantation time. Fig. 3 shows XPS depth concentration profiles of the implanted buffer interlayer on the HSS substrate with the nitrogen implantation dose of 9.6 × 1017 ions/cm2. From it, the distribution of boron element appeared rather evenly, and nitrogen concentration distribution appeared to be gauss model. The depth profile of the implanted buffer interlayer shows an interfacial mixing of the buffer layer and the substrate. The chemical bond state of boron near the surface of buffer layer for this sample was investigated by XPS (Fig. 4). From Fig. 4, it can be seen that the B 1s binding energy of buffer interlayer exhibits a characteristic peak at binding energy 190.5 eV, which is close to the BN standard binding energy (190.1–190.8 eV). It means that the surface of buffer interlayer was mainly in BN phase structure.
3.2. IR analysis of c-BN films Fig. 5 shows infrared absorption spectra of the c-BN film about 200 nm in thickness with the buffer interlayer and without buffer interlayer. Two absorption peaks are observed in the spectrum of the c-BN films, one peak at 1062 cm− 1 (reststrahlen band) which originates from the c-BN structure, another peak at 780 cm− 1 corresponding to h-BN structure. From Fig. 5, it can be seen that the peak position of the c-BN films without buffer interlayer is 1062 cm− 1, and the peak position of the c-BN film with buffer interlayer is 1048 cm− 1. This shift is considered to be due to the reduction of internal stress in the c-BN film [9]. And the peak of h-BN phase disappeared in the c-BN film with buffer interlayer. It means that the c-BN content increased with the buffer interlayer. This can be explained that the formation of BN phase near the surface of buffer interlayer is helpful for the nucleus and growth of subsequent c-BN films. 3.3. Adhesion strength of c-BN films to HSS substrate A scratch tester was used for adhesion measurements. During the measurement, a diamond stylus (radius 10 μm) scratches the surface of the c-BN film at a constant speed of
Table 1 Experimental conditions for the deposition of c-BN films Parameter
Pre-sputtering
Deposition
RF power (W) Substrate bias voltage(V) Substrate temperature (°C) Ar/N2 gas flow ratio Duration time (min)
350 − 300 25 Pure Ar 10 min
300 − 200 400 5:2 120
Fig. 3. Depth profile analysis of the buffer interlayer on high speed steel substrate.
Z. Cai et al. / Surface & Coatings Technology 201 (2007) 6723–6725
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Fig. 4. B 1s spectra of the implanted buffer layer.
4 mm/min with gradual increase of load applied vertically to the stylus. The resistance of the stylus is linear with increasing load applied to the diamond stylus, but becomes abrupt as soon as the c-BN films begin to peel off from the substrate. The adhesion of the c-BN films on HSS substrate was evaluated from the peeling loads at which the resistance of the stylus showed an abrupt increase. These values of the peeling load are obtained from the average of five measurements. Fig. 6 shows the adhesion strength of the c-BN films changed with the N/B ratio in the buffer interlayer. From Fig. 6, the critical load of c-BN films without buffer interlayer was 1.75 N. And the adhesive strength of c-BN films increased significantly after the use of implanted buffer interlayer. When the N/B ratio is about 1:1, the adhesive strength of c-BN film reached the maximum, about 28.47 N, sixteen times higher than that of c-BN film without buffer interlayers. When the nitrogen implantation dose increased, the N/B ratio of the buffer interlayer increased further, however, the adhesive strength of c-BN film decreases greatly. It is assumed that the reason why the implanted buffer interlayer improved adhesion is that the implantation of nitrogen and boron ions created a favorable gradient of chemical composition near the surface of the substrate. When the N/B ratio is about 1:1 in the buffer interlayer, BN compound was the main phase formed near the surface of the buffer
Fig. 6. Adhesion strength of the c-BN films changed with N/B ratio in the buffer interlayer.
interlayer. The formation of BN phase reduced the mismatch extent between c-BN films and HSS substrate and therefore reduced the internal stress of c-BN film significantly and made it better for the nucleation and growth of c-BN films. 4. Conclusions The adhesion improvement of the c-BN film deposited by RF-magnetron sputtering on the HSS substrate has been investigated using BNX implanted buffer layer. XPS analysis shows that an interfacial mixing between the buffer layer and the substrate appeared and the surface of buffer interlayer was mainly in BN phase. It was found that the adhesive strength of c-BN film improved greatly when the N/B ratio for BNX buffer layer is about 1:1 and the formation of BN phase on HSS surface was the main reason to improve the adhesion strength greatly between c-BN films and HSS substrate. Acknowledgements This research is funded by NNSF, Project No.5997106s and supported by the national key laboratory for remanufacturing. The authors also express their great gratitude to Mrs. Liu fen for the help of XPS analysis, and to Mr Liu weimin for the help of scratch analysis. References
Fig. 5. Change in infrared absorption spectrum of c-BN films before and after use of buffer interlayer.
[1] A. Abdellaoui, A. Bath, Mater. Sci. Eng., B, Solid-State Mater. Adv. Technol. 47 (1997) 257. [2] Collazo-Davila, E. Bengu, L.D. Marks, M. Kirk, Diamond Relat. Mater. 8 (1999) 1091. [3] V. Khvostov, I.Yu Konyashin, Appl. Surf. Sci. 157 (2000) 178. [4] Y.K. Yap, T. Aoyama, Y. Wada, et al., Diamond Relat. Mater. 9 (2000) 592. [5] G. Schwarz, Friess, G.K. Wolf, Surf. Coat. Technol. 125 (2000) 106. [6] E. Guiot, S. Benayoun, G. Nouet, Diamond Relat. Mater. 10 (2001) 1357. [7] S. Kurooka, T. Ikeda, K. Kohama, Surf. Coat. Technol. 166 (2003) 111. [8] P.B. Mirkarimi, K.F. McCarty, G.F. Cardinale, et al., J. Vac. Sci. Technol. A 14 (1) (1996) 251. [9] S. Watanabe, S. Miyake, M. Murakawa, Surf. Coat. Technol. 49 (1991) 406.
Adhesion improvement of cubic boron nitride film on high speed steel substrate by BNX implanted buffer interlayer Zhihai Cai ⁎, Ping Zhang, Jun Tan National Key Laboratory for Remanufacturing, Academy of Armored Force Engineering, Beijing, 100072, China Available online 3 November 2006
Abstract One of the major problems for the deposition of cubic boron nitride(c-BN) films on W6Mo5Cr4V2 high speed steels(HHS) is the poor adhesion of the film to the substrate. For the purpose of improving adhesion, the BNX implanted buffer layer was introduced between the HSS and c-BN film deposited by the RF-magnetron sputtering. The influence of the BNX buffer layer on adhesion was investigated and the results showed that when the N/B ratio of the buffer layer is about 1:1, the adhesive strength of c-BN film to the HHS substrate reached the maximum, about 28.47 N, which is sixteen times higher than that of c-BN film deposited without the buffer layer. According to the XPS analysis, the surface of buffer interlayer was mainly in BN phase, which is the main reason to reduce the internal stress and improve the adhesion strength of c-BN films. © 2006 Published by Elsevier B.V. Keywords: Cubic boron nitride film; Adhesion; Ion implantation; Buffer interlayer
1. Introduction
2. Experimental procedures
Cubic boron nitride (c-BN) is one of the most perspective hard coating materials for its unique chemical and physical properties such as high hardness next to diamond, high chemical and thermal stability, and not reacting with ferrous metals. [1–3] Up to now, most examination works on the deposition of c-BN film are on the silicon substrates. There are only few reports on the deposition of c-BN on high speed steel. [4] The major problem in depositing c-BN on high speed steels is the poor adhesion. The c-BN film is often peeled off from the high speed steel shortly after deposition and occasionally even during deposition. Several techniques, such as reducing internal stress with soft buffer interlayer [5], lessening the mismatch difference between films/substrate, [6] and modifying chemical composition near the surface [7,8], for the adhesion improvement of c-BN film to silicon substrate have been presented. In this paper, we attempted to use the implanted BNX buffer interlayer to improve the adhesion of c-BN films on high speed steel substrate. The influence of the buffer layer on adhesion strength of c-BN films was investigated.
The c-BN film was prepared by RF-magnetron sputtering. Fig. 1 shows the schematic diagram of the apparatus used. A target of hot pressed h-BN was assembled as the cathode. Radiofrequency power was applied to HSS to generate a negative selfbias voltage. The magnetic coil was used to produce magnetic field to confine the movement of electric particles in the plasma so as to increase the density of plasma near target and substrate. The buffer interlayer was formed by first depositing a pure boron layer about 100 nm on the HSS substrate using a Kaufman ion source. The nitrogen ion implantations into HSS substrate were carried out at the energy of 50 keV. Nitrogen concentration of the buffer layer was controlled by varying the implantation dose of nitrogen ion from 1.6 × 1017 to 12.8 × 1017 ions/cm2 corresponding to implantation time from 0.5 h to 4 h. Finally the c-BN films were deposited under the conditions given in Table 1. The chemical composition ratio of N/B in the buffer interlayer was measured by an electron probe microanalyzer (EPMA). The c-BN film with the buffer interlayer was analyzed by infrared absorption spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS). The depth profiles of the c-BN films with the buffer interlayer were measured by XPS. The etching of film was carried out by argon ion at the energy of 3 keV. And the analytic area is 0.8 × 0.8 mm2. Adhesive
⁎ Corresponding author. Tel.: +86 10 66719249; fax: +86 10 6719249. E-mail address: [email protected] (Z. Cai). 0257-8972/$ - see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.surfcoat.2006.09.037
6724
Z. Cai et al. / Surface & Coatings Technology 201 (2007) 6723–6725
Fig. 2. Change in chemical composition ratio N/B of BNX buffer layer with implantation time.
Fig. 1. Schematic illustration of the RF sputtering system for the deposition of BN films.
measurements of c-BN films to HSS substrate were carried with a scratch tester apparatus. The surface of c-BN was analyzed by AFM with Si3N4 needle, working in a constant force model. 3. Results and discussion 3.1. Composition and structure of implanted buffer interlayer Fig. 2 shows the N/B ratio of the BNX layer with different implantation time. It can be seen that N/B increases approximately linearly with increasing implantation time. And the N/B ratio of 1:1 can be obtained at about 3 h implantation time. Fig. 3 shows XPS depth concentration profiles of the implanted buffer interlayer on the HSS substrate with the nitrogen implantation dose of 9.6 × 1017 ions/cm2. From it, the distribution of boron element appeared rather evenly, and nitrogen concentration distribution appeared to be gauss model. The depth profile of the implanted buffer interlayer shows an interfacial mixing of the buffer layer and the substrate. The chemical bond state of boron near the surface of buffer layer for this sample was investigated by XPS (Fig. 4). From Fig. 4, it can be seen that the B 1s binding energy of buffer interlayer exhibits a characteristic peak at binding energy 190.5 eV, which is close to the BN standard binding energy (190.1–190.8 eV). It means that the surface of buffer interlayer was mainly in BN phase structure.
3.2. IR analysis of c-BN films Fig. 5 shows infrared absorption spectra of the c-BN film about 200 nm in thickness with the buffer interlayer and without buffer interlayer. Two absorption peaks are observed in the spectrum of the c-BN films, one peak at 1062 cm− 1 (reststrahlen band) which originates from the c-BN structure, another peak at 780 cm− 1 corresponding to h-BN structure. From Fig. 5, it can be seen that the peak position of the c-BN films without buffer interlayer is 1062 cm− 1, and the peak position of the c-BN film with buffer interlayer is 1048 cm− 1. This shift is considered to be due to the reduction of internal stress in the c-BN film [9]. And the peak of h-BN phase disappeared in the c-BN film with buffer interlayer. It means that the c-BN content increased with the buffer interlayer. This can be explained that the formation of BN phase near the surface of buffer interlayer is helpful for the nucleus and growth of subsequent c-BN films. 3.3. Adhesion strength of c-BN films to HSS substrate A scratch tester was used for adhesion measurements. During the measurement, a diamond stylus (radius 10 μm) scratches the surface of the c-BN film at a constant speed of
Table 1 Experimental conditions for the deposition of c-BN films Parameter
Pre-sputtering
Deposition
RF power (W) Substrate bias voltage(V) Substrate temperature (°C) Ar/N2 gas flow ratio Duration time (min)
350 − 300 25 Pure Ar 10 min
300 − 200 400 5:2 120
Fig. 3. Depth profile analysis of the buffer interlayer on high speed steel substrate.
Z. Cai et al. / Surface & Coatings Technology 201 (2007) 6723–6725
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Fig. 4. B 1s spectra of the implanted buffer layer.
4 mm/min with gradual increase of load applied vertically to the stylus. The resistance of the stylus is linear with increasing load applied to the diamond stylus, but becomes abrupt as soon as the c-BN films begin to peel off from the substrate. The adhesion of the c-BN films on HSS substrate was evaluated from the peeling loads at which the resistance of the stylus showed an abrupt increase. These values of the peeling load are obtained from the average of five measurements. Fig. 6 shows the adhesion strength of the c-BN films changed with the N/B ratio in the buffer interlayer. From Fig. 6, the critical load of c-BN films without buffer interlayer was 1.75 N. And the adhesive strength of c-BN films increased significantly after the use of implanted buffer interlayer. When the N/B ratio is about 1:1, the adhesive strength of c-BN film reached the maximum, about 28.47 N, sixteen times higher than that of c-BN film without buffer interlayers. When the nitrogen implantation dose increased, the N/B ratio of the buffer interlayer increased further, however, the adhesive strength of c-BN film decreases greatly. It is assumed that the reason why the implanted buffer interlayer improved adhesion is that the implantation of nitrogen and boron ions created a favorable gradient of chemical composition near the surface of the substrate. When the N/B ratio is about 1:1 in the buffer interlayer, BN compound was the main phase formed near the surface of the buffer
Fig. 6. Adhesion strength of the c-BN films changed with N/B ratio in the buffer interlayer.
interlayer. The formation of BN phase reduced the mismatch extent between c-BN films and HSS substrate and therefore reduced the internal stress of c-BN film significantly and made it better for the nucleation and growth of c-BN films. 4. Conclusions The adhesion improvement of the c-BN film deposited by RF-magnetron sputtering on the HSS substrate has been investigated using BNX implanted buffer layer. XPS analysis shows that an interfacial mixing between the buffer layer and the substrate appeared and the surface of buffer interlayer was mainly in BN phase. It was found that the adhesive strength of c-BN film improved greatly when the N/B ratio for BNX buffer layer is about 1:1 and the formation of BN phase on HSS surface was the main reason to improve the adhesion strength greatly between c-BN films and HSS substrate. Acknowledgements This research is funded by NNSF, Project No.5997106s and supported by the national key laboratory for remanufacturing. The authors also express their great gratitude to Mrs. Liu fen for the help of XPS analysis, and to Mr Liu weimin for the help of scratch analysis. References
Fig. 5. Change in infrared absorption spectrum of c-BN films before and after use of buffer interlayer.
[1] A. Abdellaoui, A. Bath, Mater. Sci. Eng., B, Solid-State Mater. Adv. Technol. 47 (1997) 257. [2] Collazo-Davila, E. Bengu, L.D. Marks, M. Kirk, Diamond Relat. Mater. 8 (1999) 1091. [3] V. Khvostov, I.Yu Konyashin, Appl. Surf. Sci. 157 (2000) 178. [4] Y.K. Yap, T. Aoyama, Y. Wada, et al., Diamond Relat. Mater. 9 (2000) 592. [5] G. Schwarz, Friess, G.K. Wolf, Surf. Coat. Technol. 125 (2000) 106. [6] E. Guiot, S. Benayoun, G. Nouet, Diamond Relat. Mater. 10 (2001) 1357. [7] S. Kurooka, T. Ikeda, K. Kohama, Surf. Coat. Technol. 166 (2003) 111. [8] P.B. Mirkarimi, K.F. McCarty, G.F. Cardinale, et al., J. Vac. Sci. Technol. A 14 (1) (1996) 251. [9] S. Watanabe, S. Miyake, M. Murakawa, Surf. Coat. Technol. 49 (1991) 406.