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Oxidation resistance of SiAlCN: H-coatings
Surface & Coatings Technology 201 (2007) 5172 – 5175 www.elsevier.com/locate/surfcoat
Oxidation resistance of SiAlCN: H-coatings D. Allebrandt (Probst) ⁎, H. Hoche, H. Scheerer, E. Broszeit, C. Berger Institute of Materials Technology, Darmstadt University of Technology, Grafenstr. 2, 64283 Darmstadt, Germany Available online 7 September 2006
Abstract Silicon–aluminum–carbon-nitride films were deposited by means of reactive RF magnetron sputtering onto various metal substrates. The films were prepared by sputtering a partially aluminum covered silicon target in a reactive gas mixture of nitrogen and acetylene. The composition throughout the depth of the films was investigated by glow discharge optical emission spectrometry (GDOES). Additionally mechanical properties (hardness, elastic modulus, and film thickness) were measured. The mechanical properties of the SiAlCN coatings were comparable to the properties of SiCN coatings. The coated samples were subjected to oxidation tests in air, at temperatures of 700–1000 °C. GDOES concentration– depth profiles of the samples were recorded before and after the oxidation test to study changes in the composition and the film–substrate interface. To determine the influence of the aluminum addition, the results are compared to SiCN coatings. © 2006 Elsevier B.V. All rights reserved. PACS: 62.20.Qp; 66.30.Ny; 81.15.Cd; 81.65.Mq Keywords: PVD; Mechanical properties; Oxidation resistance; Silico-aluminum carbonitride; Thin film
1. Introduction Due to environmental concerns as well as for economical reasons, dry or minimal quantity lubrication machining is demanded from today's cutting tools. The extreme conditions the tool experiences during dry operation, especially with respect to temperature, requires the development of new coatings which are able to retain their functionality at temperatures above of 800 °C. Conventional hard coatings, such as CrN or TiN, are failing in this application at temperatures above ∼ 600 °C, due to oxidation [1,2]. SiCN glasses are known to have a good high-temperature stability [3,4], high oxidation resistance [5,6] and high creep resistance [7]. Amorphous SiCN films are obtained through various deposition techniques but mainly through CVD and PVD techniques. SiCN coatings were shown to posses interesting properties such as high hardness [8,9] and low friction coefficient [10,11] — making them suitable for wear protection applications. Moreover, earlier studies involving SiCN films, tested in dry reciprocating sliding at temperatures up to 600 °C against ceramic counter bodies, showed that the coatings exhibit temperature independent wear
behavior [12]. The addition of aluminum is expected to increase the oxidation resistance further [13]. L. An et al. [13] produced bulk silico-aluminum carbonitride ceramics through pyrolysis and subjected them to annealing treatments at temperatures up to 1200 °C. The SiAlCN material exhibited an anomalously high resistance to oxidation and hot corrosion. It is believed that the reason for this behavior is due to the formation of a dense aluminum oxide layer which is inhibiting the diffusion of oxygen. In this study however, thin SiAlCN films were deposited onto various metal substrates (S652 HSS, nickel base super alloy PM1000 and the alloy TiAl6V4). Due to the differences of the coefficient of thermal expansion between the coating and the substrate material the annealing temperature had to be limited to 800 °C. Temperatures above 700 °C often led to cracking and/or flaking off of the film. Especially with the steel substrates, temperatures above 700 °C posed a problem presumably due to the volume change of the bcc → fcc transformation. While the brittleness of the films remains a problem, the oxidation behavior and the mechanical properties were promising. 2. Experimental details
⁎ Corresponding author. Tel.: +49 6151 163051; fax: +49 6151 164170. E-mail address: [email protected] (D. Allebrandt (Probst)). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.07.204
The SiAlCN films were deposited onto the aforementioned substrates using a commercial Alcatel SCM 601 RF magnetron
D. Allebrandt (Probst) et al. / Surface & Coatings Technology 201 (2007) 5172–5175
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3. Results and discussion
Fig. 1. GDOES concentration–depth profile of the film SiCN1.5 on PM1000 before (A) and after (B) annealing at 700 °C. Note the oxidation layer in (B) at the surface of the film and the broadening of the interface due to diffusion.
sputter PVD system. Prior to deposition, the chamber was evacuated to at least 3 × 10− 6 mbar. The substrates were cleaned ultrasonically in acetone and treated in argon plasma. For film deposition a silicon target which had aluminum pieces placed in the sputter racetrack was utilized. The reactive gases nitrogen and acetylene were used to produce the SiAlCN films. The compositions of the films could be varied by adjusting the gas flows and the number of aluminum pieces on the target. The film thickness was determined by the ball cratering method. The hardness of the coatings was determined with the instrumented indentation testing method using a Shimadzu DUH 202 ultra micro-hardness tester, equipped with a Vickers diamond, at a testing load of 100 mN. Additionally the elastic moduli were calculated from the indentation curves. During these tests, ten indentations were analyzed according to the method of Oliver and Pharr following the procedure of DIN EN ISO 145771 using the “indent analyzer” software by ASMEC GmbH. The adhesion and cohesion of the films were investigated by using a CSEM Revetest scratch tester according to DIN 1071-3. Acoustic emission and tangential force are recorded online while increasing the load at a rate of 10 N/mm to a maximum load of 100 N. Concerning the adhesion and cohesion, failure morphologies of the scratches were investigated using an optical microscope. Concentration–depth profiles of the films were recorded using glow discharge optical emission spectroscopy (GDOES, Spektruma GDA 750). The depth profiles were obtained before and after subjecting the samples to an annealing treatment at various temperatures in air to study the evolution of the changes at the film surface and the film–substrate interface.
Using the setup described above, SiAlCN films were produced. The films were X-ray amorphous and grey to black in appearance. Because of the amorphous nature of the films they do not tend to develop a specific stoichiometry. Therefore, their chemical composition is highly dependent on the deposition conditions — specifically, on the reactive gas flows, the sputter power and the total pressure. Keeping the aforementioned deposition parameters constant while varying the total pressure (argon partial pressure), led to increasing carbon content with increasing total pressure. The increasing pressure also led to a slight increase in sputter rates, resulting in slightly higher silicon and aluminum contents in the films. Consequently, the nitrogen content was greatly reduced. For the corresponding SiCN films the behavior was quite different. With increasing total pressure the incorporation of carbon increased as with the SiAlCN films. However, the concentration of nitrogen remained approximately the same. Contrary to the SiAlCN films the increase in total pressure led to a sharp decrease of silicon in the films. To asses the oxidation resistance, both the SiCN and the SiAlCN films were annealed at 700 °C for 3 h. The coated samples were placed in an oven and subjected to a heating cycle with a 3-h heating-up period (RT to 700 °C), a 3-h hold period (700 °C) and a 15-h cooling-down period (700 °C–150 °C). The slow heating-up and cooling-down was done to avoid the cracking of the films due to the mismatch of the coefficient for thermal expansion. Fig. 1 shows the GDOES composition– depth profile of the SiCN1.5 film, produced at 1.5 Pa total pressure, before (Fig. 1-A) and after (Fig. 1-B) annealing. Comparing the graphs, it is revealed that the SiCN film is
Fig. 2. GDOES composition–depth profile of SiAlCN1.5 on PM1000 before (A) and after (B) annealing at 700 °C. The grey bar at the interface represents its broadening due to diffusion.
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Fig. 3. GDOES concentration–depth profiles of SiAlCN1.0 and SiAlCN2.0 on PM1000 after annealing at 700 °C. Due to the presumably less dense structure of the coating at higher deposition pressure, the oxidation depth increases slightly, while a marked increase in thickness of the interface region occurs with increasing pressure.
strongly affected by the annealing in air. The composition of the film changes — the carbon content increases slightly, while the silicon content is slightly decreased. The surface of the film is clearly affected by oxidation. A silicon oxide layer is formed on the surface of the SiCN film with a thickness of about 0.1 μm. Another notable change in the film substrate compound is the strong interdiffusion of the coating and the base material, resulting in a pronounced broadening of the interface region. The composition of the SiAlCN films is unaffected by the annealing treatment. The most important result is however, that the oxidation layer that was present in the annealed SiCN samples was not observed in the SiAlCN samples. While there seems to be a slight increase of the intensity of the oxygen signal compared to the pre-annealed GDOES measurement, there is no distinctive oxidized layer like in the SiCN films. Presumably the aluminum in the films leads to the formation of a very thin and dense surface layer of aluminum oxide inhibiting further oxidation. Focusing the attention towards the film–substrate interface reveals another important difference to the SiCN films. The interdiffusion causing a pronounced broadening of the interface in the SiCN films is greatly reduced by the addition of aluminum (compare Figs. 1-B and 2-B). However, at this point it is not entirely clear how the addition of aluminum in the films limits the interdiffusion. Silica glasses containing aluminum have a lower free volume and a lower interstitial size, increasing the packing density [13]. Figs. 3-A, 2-B and 3-B) show a sequence GDOES composition–depth profiles after the annealing of films deposited at different total pressures. The darkened areas in the
Fig. 4. GDOES concentration–depth profiles of SiAlCN0.8 on TiAl6V4 before (A) and after (B) annealing at 800 °C. The annealing at 800 °C resulted in the formation of a very thin oxidation layer at the surface. Almost no broadening of the interface due to the denser structure which developed at 0.8 Pa deposition pressure.
graphs visualize the interface region affected by diffusion. Clearly, with increasing total pressure during the deposition, the thickness of the interface region increases after the annealing treatment due diffusion processes. Apparently amorphous film deposition takes place in a similar way as suggested for crystalline films by Thornton in his zone model [14]. Increasing deposition pressure leads to structures of lower density. However, micro-specimen of the films did not reveal this (the pressure influence can be clearly observed in crystalline columnar films). A further decrease of the deposition pressure accompanied with tweaking the deposition parameters resulted in a film (SiAlCN0.8; Fig. 4) which withstood the annealing treatment at 800 °C with nearly no changes. Again, no distinct oxidation layer was measured. The film deposited on the titanium substrate did not show the typical interface broadening seen before with the nickel substrates. Table 1 Samples, deposition pressure, mechanical properties before and after annealing Sample
Deposition HIT Young's HIT (after pressure (before modulus (before annealing) [Pa] annealing) annealing) GPa GPa GPa
Young's modulus (after annealing) GPa
SiCN1.5 SiAlCN1.0 SiAlCN1.5 SiAlCN2.0 SiAlCN0.8
1.5 1.0 1.5 2 0.8
201 ± 11 165 ± 4 183 ± 8 187 ± 6 184 ± 19
20.1 ± 0.8 16.6 ± 1.6 14.0 ± 0.9 16.1 ± 0.5 18.8 ± 1.1
212 ± 9 172 ± 17 185 ± 13 186 ± 6 193 ± 11
17.9 ± 0.9 17.5 ± 0.5 20.3 ± 1.0 20.5 ± 0.6 25.1 ± 2.8
D. Allebrandt (Probst) et al. / Surface & Coatings Technology 201 (2007) 5172–5175
The hardness and the elastic moduli of the SiAlCN films were slightly lower than in the corresponding SiCN films (Table 1). The hardness values ranged from 14–17 GPa before annealing and the moduli of elasticity were in the range of 170–190 GPa. The annealing treatment led to a decrease in hardness for the SiCN films. This behavior is thought to be the result of the formation of a silicon oxide layer, which is soft in comparison to the coating. For the SiAlCN films on the other hand, the annealing led to a slight increase in hardness. This hardness increase is presumed to be the result of the formation of a very thin and hard aluminum oxide layer. A summary of the mechanical properties before and after annealing for the different films is given in Table 1.
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layer. SiAlCN films on the other hand, experience an increase of hardness due to the presumed formation of a thin, dense and hard aluminum oxide layer. However these findings have to be confirmed in further studies. Further investigations on SiAlCN coatings will need to evaluate the oxidation behavior quantitatively as well as focusing on the cohesion of the film and the adhesion to the substrate to avoid cracking and flaking due to the expansion coefficient mismatch. Acknowledgements The authors acknowledge the financial support of the German Research Foundation (DFG).
4. Summary References Sputtered SiAlCN thin films were produced using a silicon/ aluminum target and nitrogen and acetylene as reactive gases. Both SiAlCN and SiCN films were subjected to annealing treatments for several hours at temperatures of up to 800 °C. While the SiCN films formed an oxidized surface layer of about 0.1 μm thickness, the SiAlCN films were virtually unaffected. However, it is believed that a very thin and dense oxide layer of predominantly aluminum oxide is formed on the SiAlCN films as well. Interdiffusion of the substrate material and the amorphous film resulted in a broadening of the interface region. The magnitude of the diffusion during the annealing treatment was significantly reduced by the addition of aluminum and highly dependent on the deposition pressure. The SiAlCN films had similar mechanical properties as the corresponding SiCN films before annealing. The annealing treatment however, led to a slight decrease in hardness for the SiCN films — possibly due to the formation of a silicon oxide
[1] T. Kacsich, K.-P. Lieb, Thin Solid Films 235 (1994) 4. [2] C. Ernsberger, J. Nickerson, T. Smith, A.E. Miller, D. Banks, J. Vac. Sci. Technol., A 4 (1986) 2784. [3] D. Mocaer, et al., J. Mater. Sci. 28 (1993) 2615. [4] C. Haluschka, et al., J. Eur. Ceram. Soc. 20 (2000) 1355. [5] R. Riedel, et al., Nature 374 (1995) 526. [6] R. Raj, L. An, S. Shah, R. Riedel, C. Fasel, H.J. Kleebe, J. Am. Ceram. Soc. 84 (2001) 1803. [7] R. Riedel, et al., J. Am. Ceram. Soc. 81 (1998) 3341. [8] A.L. Baia Neto, et al., Thin Solid Films 293 (1997) 206. [9] K.B. Sundaram, et al., Mater. Sci. Eng., A Struct. Mater.: Prop. Microstruct. Process. 368 (2004) 103. [10] D. Bielinsky, et al., Tribol. Lett. 13 (2) (2002). [11] C. Fernández-Ramos, et al., Diamond Relat. Mater. 11 (2002) 169. [12] D. Probst, et al., Surf. Coat. Technol. 200/1-4 (2005) 355. [13] L. An, et al., Adv. Eng. Mater. 6 (5) (2004) 337. [14] J.A. Thornton, J. Vac. Sci. Technol. 11 (1974) 666.
Oxidation resistance of SiAlCN: H-coatings D. Allebrandt (Probst) ⁎, H. Hoche, H. Scheerer, E. Broszeit, C. Berger Institute of Materials Technology, Darmstadt University of Technology, Grafenstr. 2, 64283 Darmstadt, Germany Available online 7 September 2006
Abstract Silicon–aluminum–carbon-nitride films were deposited by means of reactive RF magnetron sputtering onto various metal substrates. The films were prepared by sputtering a partially aluminum covered silicon target in a reactive gas mixture of nitrogen and acetylene. The composition throughout the depth of the films was investigated by glow discharge optical emission spectrometry (GDOES). Additionally mechanical properties (hardness, elastic modulus, and film thickness) were measured. The mechanical properties of the SiAlCN coatings were comparable to the properties of SiCN coatings. The coated samples were subjected to oxidation tests in air, at temperatures of 700–1000 °C. GDOES concentration– depth profiles of the samples were recorded before and after the oxidation test to study changes in the composition and the film–substrate interface. To determine the influence of the aluminum addition, the results are compared to SiCN coatings. © 2006 Elsevier B.V. All rights reserved. PACS: 62.20.Qp; 66.30.Ny; 81.15.Cd; 81.65.Mq Keywords: PVD; Mechanical properties; Oxidation resistance; Silico-aluminum carbonitride; Thin film
1. Introduction Due to environmental concerns as well as for economical reasons, dry or minimal quantity lubrication machining is demanded from today's cutting tools. The extreme conditions the tool experiences during dry operation, especially with respect to temperature, requires the development of new coatings which are able to retain their functionality at temperatures above of 800 °C. Conventional hard coatings, such as CrN or TiN, are failing in this application at temperatures above ∼ 600 °C, due to oxidation [1,2]. SiCN glasses are known to have a good high-temperature stability [3,4], high oxidation resistance [5,6] and high creep resistance [7]. Amorphous SiCN films are obtained through various deposition techniques but mainly through CVD and PVD techniques. SiCN coatings were shown to posses interesting properties such as high hardness [8,9] and low friction coefficient [10,11] — making them suitable for wear protection applications. Moreover, earlier studies involving SiCN films, tested in dry reciprocating sliding at temperatures up to 600 °C against ceramic counter bodies, showed that the coatings exhibit temperature independent wear
behavior [12]. The addition of aluminum is expected to increase the oxidation resistance further [13]. L. An et al. [13] produced bulk silico-aluminum carbonitride ceramics through pyrolysis and subjected them to annealing treatments at temperatures up to 1200 °C. The SiAlCN material exhibited an anomalously high resistance to oxidation and hot corrosion. It is believed that the reason for this behavior is due to the formation of a dense aluminum oxide layer which is inhibiting the diffusion of oxygen. In this study however, thin SiAlCN films were deposited onto various metal substrates (S652 HSS, nickel base super alloy PM1000 and the alloy TiAl6V4). Due to the differences of the coefficient of thermal expansion between the coating and the substrate material the annealing temperature had to be limited to 800 °C. Temperatures above 700 °C often led to cracking and/or flaking off of the film. Especially with the steel substrates, temperatures above 700 °C posed a problem presumably due to the volume change of the bcc → fcc transformation. While the brittleness of the films remains a problem, the oxidation behavior and the mechanical properties were promising. 2. Experimental details
⁎ Corresponding author. Tel.: +49 6151 163051; fax: +49 6151 164170. E-mail address: [email protected] (D. Allebrandt (Probst)). 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.07.204
The SiAlCN films were deposited onto the aforementioned substrates using a commercial Alcatel SCM 601 RF magnetron
D. Allebrandt (Probst) et al. / Surface & Coatings Technology 201 (2007) 5172–5175
5173
3. Results and discussion
Fig. 1. GDOES concentration–depth profile of the film SiCN1.5 on PM1000 before (A) and after (B) annealing at 700 °C. Note the oxidation layer in (B) at the surface of the film and the broadening of the interface due to diffusion.
sputter PVD system. Prior to deposition, the chamber was evacuated to at least 3 × 10− 6 mbar. The substrates were cleaned ultrasonically in acetone and treated in argon plasma. For film deposition a silicon target which had aluminum pieces placed in the sputter racetrack was utilized. The reactive gases nitrogen and acetylene were used to produce the SiAlCN films. The compositions of the films could be varied by adjusting the gas flows and the number of aluminum pieces on the target. The film thickness was determined by the ball cratering method. The hardness of the coatings was determined with the instrumented indentation testing method using a Shimadzu DUH 202 ultra micro-hardness tester, equipped with a Vickers diamond, at a testing load of 100 mN. Additionally the elastic moduli were calculated from the indentation curves. During these tests, ten indentations were analyzed according to the method of Oliver and Pharr following the procedure of DIN EN ISO 145771 using the “indent analyzer” software by ASMEC GmbH. The adhesion and cohesion of the films were investigated by using a CSEM Revetest scratch tester according to DIN 1071-3. Acoustic emission and tangential force are recorded online while increasing the load at a rate of 10 N/mm to a maximum load of 100 N. Concerning the adhesion and cohesion, failure morphologies of the scratches were investigated using an optical microscope. Concentration–depth profiles of the films were recorded using glow discharge optical emission spectroscopy (GDOES, Spektruma GDA 750). The depth profiles were obtained before and after subjecting the samples to an annealing treatment at various temperatures in air to study the evolution of the changes at the film surface and the film–substrate interface.
Using the setup described above, SiAlCN films were produced. The films were X-ray amorphous and grey to black in appearance. Because of the amorphous nature of the films they do not tend to develop a specific stoichiometry. Therefore, their chemical composition is highly dependent on the deposition conditions — specifically, on the reactive gas flows, the sputter power and the total pressure. Keeping the aforementioned deposition parameters constant while varying the total pressure (argon partial pressure), led to increasing carbon content with increasing total pressure. The increasing pressure also led to a slight increase in sputter rates, resulting in slightly higher silicon and aluminum contents in the films. Consequently, the nitrogen content was greatly reduced. For the corresponding SiCN films the behavior was quite different. With increasing total pressure the incorporation of carbon increased as with the SiAlCN films. However, the concentration of nitrogen remained approximately the same. Contrary to the SiAlCN films the increase in total pressure led to a sharp decrease of silicon in the films. To asses the oxidation resistance, both the SiCN and the SiAlCN films were annealed at 700 °C for 3 h. The coated samples were placed in an oven and subjected to a heating cycle with a 3-h heating-up period (RT to 700 °C), a 3-h hold period (700 °C) and a 15-h cooling-down period (700 °C–150 °C). The slow heating-up and cooling-down was done to avoid the cracking of the films due to the mismatch of the coefficient for thermal expansion. Fig. 1 shows the GDOES composition– depth profile of the SiCN1.5 film, produced at 1.5 Pa total pressure, before (Fig. 1-A) and after (Fig. 1-B) annealing. Comparing the graphs, it is revealed that the SiCN film is
Fig. 2. GDOES composition–depth profile of SiAlCN1.5 on PM1000 before (A) and after (B) annealing at 700 °C. The grey bar at the interface represents its broadening due to diffusion.
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D. Allebrandt (Probst) et al. / Surface & Coatings Technology 201 (2007) 5172–5175
Fig. 3. GDOES concentration–depth profiles of SiAlCN1.0 and SiAlCN2.0 on PM1000 after annealing at 700 °C. Due to the presumably less dense structure of the coating at higher deposition pressure, the oxidation depth increases slightly, while a marked increase in thickness of the interface region occurs with increasing pressure.
strongly affected by the annealing in air. The composition of the film changes — the carbon content increases slightly, while the silicon content is slightly decreased. The surface of the film is clearly affected by oxidation. A silicon oxide layer is formed on the surface of the SiCN film with a thickness of about 0.1 μm. Another notable change in the film substrate compound is the strong interdiffusion of the coating and the base material, resulting in a pronounced broadening of the interface region. The composition of the SiAlCN films is unaffected by the annealing treatment. The most important result is however, that the oxidation layer that was present in the annealed SiCN samples was not observed in the SiAlCN samples. While there seems to be a slight increase of the intensity of the oxygen signal compared to the pre-annealed GDOES measurement, there is no distinctive oxidized layer like in the SiCN films. Presumably the aluminum in the films leads to the formation of a very thin and dense surface layer of aluminum oxide inhibiting further oxidation. Focusing the attention towards the film–substrate interface reveals another important difference to the SiCN films. The interdiffusion causing a pronounced broadening of the interface in the SiCN films is greatly reduced by the addition of aluminum (compare Figs. 1-B and 2-B). However, at this point it is not entirely clear how the addition of aluminum in the films limits the interdiffusion. Silica glasses containing aluminum have a lower free volume and a lower interstitial size, increasing the packing density [13]. Figs. 3-A, 2-B and 3-B) show a sequence GDOES composition–depth profiles after the annealing of films deposited at different total pressures. The darkened areas in the
Fig. 4. GDOES concentration–depth profiles of SiAlCN0.8 on TiAl6V4 before (A) and after (B) annealing at 800 °C. The annealing at 800 °C resulted in the formation of a very thin oxidation layer at the surface. Almost no broadening of the interface due to the denser structure which developed at 0.8 Pa deposition pressure.
graphs visualize the interface region affected by diffusion. Clearly, with increasing total pressure during the deposition, the thickness of the interface region increases after the annealing treatment due diffusion processes. Apparently amorphous film deposition takes place in a similar way as suggested for crystalline films by Thornton in his zone model [14]. Increasing deposition pressure leads to structures of lower density. However, micro-specimen of the films did not reveal this (the pressure influence can be clearly observed in crystalline columnar films). A further decrease of the deposition pressure accompanied with tweaking the deposition parameters resulted in a film (SiAlCN0.8; Fig. 4) which withstood the annealing treatment at 800 °C with nearly no changes. Again, no distinct oxidation layer was measured. The film deposited on the titanium substrate did not show the typical interface broadening seen before with the nickel substrates. Table 1 Samples, deposition pressure, mechanical properties before and after annealing Sample
Deposition HIT Young's HIT (after pressure (before modulus (before annealing) [Pa] annealing) annealing) GPa GPa GPa
Young's modulus (after annealing) GPa
SiCN1.5 SiAlCN1.0 SiAlCN1.5 SiAlCN2.0 SiAlCN0.8
1.5 1.0 1.5 2 0.8
201 ± 11 165 ± 4 183 ± 8 187 ± 6 184 ± 19
20.1 ± 0.8 16.6 ± 1.6 14.0 ± 0.9 16.1 ± 0.5 18.8 ± 1.1
212 ± 9 172 ± 17 185 ± 13 186 ± 6 193 ± 11
17.9 ± 0.9 17.5 ± 0.5 20.3 ± 1.0 20.5 ± 0.6 25.1 ± 2.8
D. Allebrandt (Probst) et al. / Surface & Coatings Technology 201 (2007) 5172–5175
The hardness and the elastic moduli of the SiAlCN films were slightly lower than in the corresponding SiCN films (Table 1). The hardness values ranged from 14–17 GPa before annealing and the moduli of elasticity were in the range of 170–190 GPa. The annealing treatment led to a decrease in hardness for the SiCN films. This behavior is thought to be the result of the formation of a silicon oxide layer, which is soft in comparison to the coating. For the SiAlCN films on the other hand, the annealing led to a slight increase in hardness. This hardness increase is presumed to be the result of the formation of a very thin and hard aluminum oxide layer. A summary of the mechanical properties before and after annealing for the different films is given in Table 1.
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layer. SiAlCN films on the other hand, experience an increase of hardness due to the presumed formation of a thin, dense and hard aluminum oxide layer. However these findings have to be confirmed in further studies. Further investigations on SiAlCN coatings will need to evaluate the oxidation behavior quantitatively as well as focusing on the cohesion of the film and the adhesion to the substrate to avoid cracking and flaking due to the expansion coefficient mismatch. Acknowledgements The authors acknowledge the financial support of the German Research Foundation (DFG).
4. Summary References Sputtered SiAlCN thin films were produced using a silicon/ aluminum target and nitrogen and acetylene as reactive gases. Both SiAlCN and SiCN films were subjected to annealing treatments for several hours at temperatures of up to 800 °C. While the SiCN films formed an oxidized surface layer of about 0.1 μm thickness, the SiAlCN films were virtually unaffected. However, it is believed that a very thin and dense oxide layer of predominantly aluminum oxide is formed on the SiAlCN films as well. Interdiffusion of the substrate material and the amorphous film resulted in a broadening of the interface region. The magnitude of the diffusion during the annealing treatment was significantly reduced by the addition of aluminum and highly dependent on the deposition pressure. The SiAlCN films had similar mechanical properties as the corresponding SiCN films before annealing. The annealing treatment however, led to a slight decrease in hardness for the SiCN films — possibly due to the formation of a silicon oxide
[1] T. Kacsich, K.-P. Lieb, Thin Solid Films 235 (1994) 4. [2] C. Ernsberger, J. Nickerson, T. Smith, A.E. Miller, D. Banks, J. Vac. Sci. Technol., A 4 (1986) 2784. [3] D. Mocaer, et al., J. Mater. Sci. 28 (1993) 2615. [4] C. Haluschka, et al., J. Eur. Ceram. Soc. 20 (2000) 1355. [5] R. Riedel, et al., Nature 374 (1995) 526. [6] R. Raj, L. An, S. Shah, R. Riedel, C. Fasel, H.J. Kleebe, J. Am. Ceram. Soc. 84 (2001) 1803. [7] R. Riedel, et al., J. Am. Ceram. Soc. 81 (1998) 3341. [8] A.L. Baia Neto, et al., Thin Solid Films 293 (1997) 206. [9] K.B. Sundaram, et al., Mater. Sci. Eng., A Struct. Mater.: Prop. Microstruct. Process. 368 (2004) 103. [10] D. Bielinsky, et al., Tribol. Lett. 13 (2) (2002). [11] C. Fernández-Ramos, et al., Diamond Relat. Mater. 11 (2002) 169. [12] D. Probst, et al., Surf. Coat. Technol. 200/1-4 (2005) 355. [13] L. An, et al., Adv. Eng. Mater. 6 (5) (2004) 337. [14] J.A. Thornton, J. Vac. Sci. Technol. 11 (1974) 666.