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Al2O3 composites in high vacuum
Materials Chemistry and Physics 104 (2007) 109–112
Thermal stability of Ti3AlC2/Al2O3 composites in high vacuum J.X. Chen, Y.C. Zhou ∗ , H.B. Zhang, D.T. Wan, M.Y. Liu High-performance Ceramic Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China Received 30 March 2005; received in revised form 16 January 2007; accepted 27 February 2007
Abstract The thermal stability of Ti3 AlC2 /Al2 O3 composites in high vacuum was investigated. On the sample surface, Ti3 AlC2 can decompose with the formation of TiC0.67 and gaseous Al at first, then Ti evaporation results in the irregular morphology of non-stoichiometric TiCx . At the same time, the amount of Al2 O3 particles becomes less with increasing the soaking time. Finally, Al2 O3 particles disappear and a layer of non-stoichiometric TiCx forms on the sample surface. But the bulk Ti3 AlC2 /Al2 O3 composites always keep stable during the vacuum treatment. © 2007 Elsevier B.V. All rights reserved. Keywords: Thermal stability; Ti3 AlC2 /Al2 O3 composites; Vacuum
1. Introduction Ti3 AlC2 is a member of layered ternary carbides that possess an unusual combination of the properties of both ceramics and metals [1–4]. It is usually expected as a potential structural material, especially for high-temperature applications. But the low hardness and low strength limit its application. Many efforts have been made to improve its mechanical properties [5–9]. One of the most effective ways is to fabricate Ti3 AlC2 /Al2 O3 composites [5]. There have been a few papers on the thermal stability of Ti3 AlC2 [1,10–12]. The results disclosed that the thermal stability of Ti3 AlC2 depended strongly on the environment. Pietzka and Schuster [1] estimated that the decomposition temperature was 1360 ◦ C based on a series of experiments in a tungsten furnace. Wang and Zhou [11] demonstrated that continuous inner protective scales of Al2 O3 formed on bulk Ti3 AlC2 at high temperatures in air. When Ti3 AlC2 powders in an Al2 O3 crucible were heated up to 1460 ◦ C in Ar, the top powders translated into non-stoichiometric TiCx and Al2 O3 by the selective oxidation of Al, while the bottom powders were still stable [12].
∗
Corresponding author. Tel.: +86 24 23971765; fax: +86 24 23891320. E-mail address: [email protected] (Y.C. Zhou).
0254-0584/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2007.02.091
The aim of this paper is to study the thermal stability of Ti3 AlC2 /Al2 O3 composites in high vacuum. The evolution of Al2 O3 particles during vacuum treatment is helpful in understanding of the thermal stability of Ti3 AlC2 . 2. Experimental procedure Two materials, Ti3 AlC2 and Ti3 AlC2 /10 vol.%Al2 O3 composite (hence forth denoted as TAC-10), were used to investigate the thermal stability of Ti3 AlC2 /Al2 O3 composites in high vacuum. Both materials were fabricated by using in situ hot pressing/solid–liquid reaction process [13–15]. The details can be found elsewhere [5]. There are no impurities, such as TiC, in the materials examined by X-ray diffraction (XRD). The relative density of all samples is higher than 97% of theoretical density. The sample size is 3 mm × 10 mm × 10 mm. Table 1 lists the testing temperatures, soaking times and materials used in this study. All of the tests were performed at a pressure of ∼5 × 10−3 Pa in a furnace using molybdenum as the heating element. The phase compositions at the surface of the samples after vacuum treatment were characterized by using XRD. Surface and cross-section morphologies of the samples were observed via scanning electron microscope (SEM). Elemental composition analysis was performed via the energy dispersive spectroscopy (EDS) equipped with the SEM.
3. Results and discussion Fig. 1 shows the XRD spectra of as-prepared Ti3 AlC2 and a Ti3 AlC2 sample after soaking in high vacuum for 30 h at 1150 ◦ C. After vacuum treatment, TiCx (JCPDS card number
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J.X. Chen et al. / Materials Chemistry and Physics 104 (2007) 109–112
Table 1 Summary of the temperatures, soaking times and materials of the samples used in this study Sample number
Temperature (◦ C)
Soaking time (h)
Material
1 2 3 4 5
1150 1100 1100 1100 1150
30 5 15 60 30
Ti3 AlC2 TAC-10 TAC-10 TAC-10 TAC-10
32-1383) becomes the main phase on the sample surface and only small quantity of Ti3 AlC2 was detected in the area. The back-scattered electron image and the corresponding EDS spectrum of the sample 1 are shown in Fig. 2. Loose and fine particles with irregular shape appear on the sample surface (Fig. 2(a)). The corresponding EDS spectrum for whole visual field (Fig. 2(b)) shows that there is no Al element on the sample surface. So, a layer of TiCx forms on the top surface of sample 1 due to the decomposition of Ti3 AlC2 . The following equation can be used to depict the decomposition of Ti3 AlC2 : Ti3 AlC2 (s) → 3TiC0.67 (s) + Al(g)
(1)
This equation is similar to that for Ti3 SiC2 proposed by Racault et al. [16], and the only difference is the gaseous Si for the decomposition of Ti3 SiC2 . Zhou et al. [17] studied the electronic structure of all layered ternary carbides called “312” phase, including Ti3 AlC2 , Ti3 SiC2 , and Ti3 GeC2 . They disclosed that the bonding between Al (Si and Ge) and the Ti–C–Ti–C–Ti covalent bond chain was relatively weak. So, here the decomposition path is reasonable. It is worth noting that the morphology of TiCx changes significantly from the initial polished surface. On the one hand, the volume change for Eq. (1) is negative (V = −21%), which will result in a porous surface layer. On the other hand, due to the fact that the vapour pressure of Ti is larger than that of C [18], the non-stoichiometric TiC0.67 can lose weight further by Ti evaporation, which also causes the contraction
Fig. 1. X-ray diffraction patterns of as-prepared Ti3 AlC2 (a) and sample 1, Ti3 AlC2 soaked at a pressure of ∼5 × 10−3 Pa for 30 h at 1150 ◦ C (b).
Fig. 2. Back-scattered electron image of the surface of sample 1 (a) and its corresponding EDS spectrum (b). The sputtering of gold was previously performed on the sample surface.
of the surface layer [19]. Thus, the fine TiCx particles with irregular shape on the sample surface can be readily understood. The above results show that Al2 O3 cannot form on the sample surface of Ti3 AlC2 during vacuum treatment at 1150 ◦ C. What will happen to Ti3 AlC2 /Al2 O3 composites when they are treated in vacuum? As listed in Table 1, besides vacuum treatment at 1150 ◦ C for 30 h, the samples of TAC-10 were also treated at a lower temperature, 1100 ◦ C, with the soaking time of 5–60 h. Fig. 3 shows the morphology evolution of TAC-10 with soaking time. In the back-scattered electron images, the light gray phase is Ti3 AlC2 and the dark gray phase is Al2 O3 . It can be seen that the amount of Al2 O3 particles becomes less with increasing the soaking time (Fig. 3(a–c)). Finally, Al2 O3 particles disappear on the sample surface (Fig. 3(d)). Simultaneously, the sample surface becomes loose and porous. Burns et al. [20,21] found that high-temperature vacuum annealing could lead to the decomposition of Al2 O3 film. The desorption of Al+ , AlO+ , Al2 O+ and O+ ionic species took place on the film surface. In our cases, the element analysis by EDS (not shown) also confirms the decrease in the content of Al2 O3 on the TAC-10 surface with increasing the soaking time.
J.X. Chen et al. / Materials Chemistry and Physics 104 (2007) 109–112
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Fig. 3. Back-scattered electron images of the surfaces of polished as-prepared TAC-10 (a), and the samples treated at 1100 ◦ C with soaking time of 5 h (b), 15 h (c), and 60 h (d). The light gray phase is Ti3 AlC2 and the dark gray phase is Al2 O3 .
A large cavity indicated in Fig. 4 is an evidence of the Al2 O3 evaporation. Most of Al2 O3 particles in TAC-10 distribute uniformly, but the agglomeration is unavoidable, as shown in Fig. 3(a). Once the agglomerated Al2 O3 particles with large size entirely evaporate from the sample surface, the large cavities leave. Certainly, the evaporation of the dispersed Al2 O3
Fig. 4. Back-scattered electron image of the surface of sample 5, TAC-10 soaked for 30 h at 1150 ◦ C.
particles with small size and the decomposition of Ti3 AlC2 also take place during the vacuum treatment. It is also worth noting that there are some large TiCx particles on the sample surface, which reflects the ununiformity of the initial Ti3 AlC2 grains. To understand the decomposition process of TAC-10 further, the phase composition and morphology of sectioned sample 5 were examined by SEM. It can be seen that the dark gray Al2 O3 particles only exist in the inner part of the sample, as shown in Fig. 5(a). Fig. 5(b) shows the concentration profiles taken along the black line in Fig. 5(a). Obviously, the outer layer is rich in C and poor in Al, while the concentrations of O and Ti are almost constant except for Al2 O3 particles. So, the decomposition of TAC-10 only occurs near the surface and the inner Ti3 AlC2 and Al2 O3 are still stable in high vacuum at 1150 ◦ C. Recently, Low et al. [22,23] reported that the very low partial pressure of oxygen in vacuum treatment could facilitate the surface formation of TiCx through the thermal dissociation of Ti3 SiC2 . In that case TiCx was expected to improve the hardness, wear, fatigue and damage resistance of Ti3 SiC2 . It should be noted that the TiCx layer is very thin (<3 m) in our cases, so higher treatment temperatures are needed to obtain thick hardened layer.
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J.X. Chen et al. / Materials Chemistry and Physics 104 (2007) 109–112
4. Conclusions Ti3 AlC2 /Al2 O3 composites are not stable on the sample surface in high vacuum at 1100 and 1150 ◦ C. Ti3 AlC2 can firstly decompose with the formation of TiC0.67 and gaseous Al, then TiC0.67 can lose weight further by Ti evaporation. For Al2 O3 particles, they can also decompose and evaporate from the sample surface. Finally, a layer of TiCx forms on the sample surface of Ti3 AlC2 /Al2 O3 composites. But this decomposition process is very slow and the inner Ti3 AlC2 and Al2 O3 are still stable. Acknowledgments This work was supported by the National Outstanding Young Scientist Foundation for Y. C. Zhou under Grant No. 59925208, Natural Sciences Foundation of China under Grant No. 50232040, ‘863’ project. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] Fig. 5. Back-scattered electron image of the polished cross-section sample 5 (a) and the corresponding concentration profiles taken along the black line (b).
[23]
M.A. Pietzka, J.C. Schuster, J. Phase Equilib. 15 (1994) 392. N.V. Tzenov, M.W. Barsoum, J. Am. Ceram. Soc. 83 (2000) 825. X.H. Wang, Y.C. Zhou, Acta Mater. 50 (2002) 3141. I.M. Low, J. Eur. Ceram. Soc. 18 (1998) 709. J.X. Chen, Y.C. Zhou, Scr. Mater. 50 (2004) 897. J.X. Chen, M.Y. Liu, Y.W. Bao, Y.C. Zhou, Int. J. Mater. Res. 97 (2006) 1115. J.H. Han, S.W. Park, K.Y. Do, J. Rare Earth 22 (2004) 85. J.X. Chen, J.L. Li, Y.C. Zhou, J. Mater. Sci. Technol. 22 (2006) 455. Y.C. Zhou, J.X. Chen, J.Y. Wang, Acta Mater. 54 (2006) 1317. X.H. Wang, Y.C. Zhou, Mater. Res. Innovations 7 (2003) 381. X.H. Wang, Y.C. Zhou, Corros. Sci. 45 (2003) 891. X.H. Wang, Y.C. Zhou, Chem. Mater. 15 (2003) 3716. Y.C. Zhou, Z.M. Sun, S.Q. Chen, Y. Zhang, Mater. Res. Innovations 2 (1998) 142. X.H. Wang, Y.C. Zhou, J. Mater. Chem. 12 (2002) 455. X.H. Wang, Y.C. Zhou, Z. Metalkd. 93 (2002) 66. C. Racault, F. Langlais, R. Naslain, J. Mater. Sci. 29 (1994) 3384. Y.C. Zhou, Z.M. Sun, X.H. Wang, S.Q. Chen, J. Phys.: Condens. Matter 13 (2001) 10001. T.E. Louis, Transition Metal Carbides and Mitrides, Academic Press, New York, 1971, p. 76, 136. T. Shikama, H. Shinno, M. Fukutomi, M. Fujitsuka, M. Kitajima, M. Okada, Thin Solid Films 101 (1983) 233. R.P. Burns, A.J. Jason, M.G. Inghram, J. Chem. Phys. 40 (1964) 2739. R.P. Burns, J. Chem. Phys. 44 (1966) 3307. I.M. Low, P. Manurung, R.I. Smith, D. Lawrence, Key Eng. Mater. 224–226 (2002) 465. I.M. Low, Mater. Lett. 58 (2004) 927.
Thermal stability of Ti3AlC2/Al2O3 composites in high vacuum J.X. Chen, Y.C. Zhou ∗ , H.B. Zhang, D.T. Wan, M.Y. Liu High-performance Ceramic Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China Received 30 March 2005; received in revised form 16 January 2007; accepted 27 February 2007
Abstract The thermal stability of Ti3 AlC2 /Al2 O3 composites in high vacuum was investigated. On the sample surface, Ti3 AlC2 can decompose with the formation of TiC0.67 and gaseous Al at first, then Ti evaporation results in the irregular morphology of non-stoichiometric TiCx . At the same time, the amount of Al2 O3 particles becomes less with increasing the soaking time. Finally, Al2 O3 particles disappear and a layer of non-stoichiometric TiCx forms on the sample surface. But the bulk Ti3 AlC2 /Al2 O3 composites always keep stable during the vacuum treatment. © 2007 Elsevier B.V. All rights reserved. Keywords: Thermal stability; Ti3 AlC2 /Al2 O3 composites; Vacuum
1. Introduction Ti3 AlC2 is a member of layered ternary carbides that possess an unusual combination of the properties of both ceramics and metals [1–4]. It is usually expected as a potential structural material, especially for high-temperature applications. But the low hardness and low strength limit its application. Many efforts have been made to improve its mechanical properties [5–9]. One of the most effective ways is to fabricate Ti3 AlC2 /Al2 O3 composites [5]. There have been a few papers on the thermal stability of Ti3 AlC2 [1,10–12]. The results disclosed that the thermal stability of Ti3 AlC2 depended strongly on the environment. Pietzka and Schuster [1] estimated that the decomposition temperature was 1360 ◦ C based on a series of experiments in a tungsten furnace. Wang and Zhou [11] demonstrated that continuous inner protective scales of Al2 O3 formed on bulk Ti3 AlC2 at high temperatures in air. When Ti3 AlC2 powders in an Al2 O3 crucible were heated up to 1460 ◦ C in Ar, the top powders translated into non-stoichiometric TiCx and Al2 O3 by the selective oxidation of Al, while the bottom powders were still stable [12].
∗
Corresponding author. Tel.: +86 24 23971765; fax: +86 24 23891320. E-mail address: [email protected] (Y.C. Zhou).
0254-0584/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2007.02.091
The aim of this paper is to study the thermal stability of Ti3 AlC2 /Al2 O3 composites in high vacuum. The evolution of Al2 O3 particles during vacuum treatment is helpful in understanding of the thermal stability of Ti3 AlC2 . 2. Experimental procedure Two materials, Ti3 AlC2 and Ti3 AlC2 /10 vol.%Al2 O3 composite (hence forth denoted as TAC-10), were used to investigate the thermal stability of Ti3 AlC2 /Al2 O3 composites in high vacuum. Both materials were fabricated by using in situ hot pressing/solid–liquid reaction process [13–15]. The details can be found elsewhere [5]. There are no impurities, such as TiC, in the materials examined by X-ray diffraction (XRD). The relative density of all samples is higher than 97% of theoretical density. The sample size is 3 mm × 10 mm × 10 mm. Table 1 lists the testing temperatures, soaking times and materials used in this study. All of the tests were performed at a pressure of ∼5 × 10−3 Pa in a furnace using molybdenum as the heating element. The phase compositions at the surface of the samples after vacuum treatment were characterized by using XRD. Surface and cross-section morphologies of the samples were observed via scanning electron microscope (SEM). Elemental composition analysis was performed via the energy dispersive spectroscopy (EDS) equipped with the SEM.
3. Results and discussion Fig. 1 shows the XRD spectra of as-prepared Ti3 AlC2 and a Ti3 AlC2 sample after soaking in high vacuum for 30 h at 1150 ◦ C. After vacuum treatment, TiCx (JCPDS card number
110
J.X. Chen et al. / Materials Chemistry and Physics 104 (2007) 109–112
Table 1 Summary of the temperatures, soaking times and materials of the samples used in this study Sample number
Temperature (◦ C)
Soaking time (h)
Material
1 2 3 4 5
1150 1100 1100 1100 1150
30 5 15 60 30
Ti3 AlC2 TAC-10 TAC-10 TAC-10 TAC-10
32-1383) becomes the main phase on the sample surface and only small quantity of Ti3 AlC2 was detected in the area. The back-scattered electron image and the corresponding EDS spectrum of the sample 1 are shown in Fig. 2. Loose and fine particles with irregular shape appear on the sample surface (Fig. 2(a)). The corresponding EDS spectrum for whole visual field (Fig. 2(b)) shows that there is no Al element on the sample surface. So, a layer of TiCx forms on the top surface of sample 1 due to the decomposition of Ti3 AlC2 . The following equation can be used to depict the decomposition of Ti3 AlC2 : Ti3 AlC2 (s) → 3TiC0.67 (s) + Al(g)
(1)
This equation is similar to that for Ti3 SiC2 proposed by Racault et al. [16], and the only difference is the gaseous Si for the decomposition of Ti3 SiC2 . Zhou et al. [17] studied the electronic structure of all layered ternary carbides called “312” phase, including Ti3 AlC2 , Ti3 SiC2 , and Ti3 GeC2 . They disclosed that the bonding between Al (Si and Ge) and the Ti–C–Ti–C–Ti covalent bond chain was relatively weak. So, here the decomposition path is reasonable. It is worth noting that the morphology of TiCx changes significantly from the initial polished surface. On the one hand, the volume change for Eq. (1) is negative (V = −21%), which will result in a porous surface layer. On the other hand, due to the fact that the vapour pressure of Ti is larger than that of C [18], the non-stoichiometric TiC0.67 can lose weight further by Ti evaporation, which also causes the contraction
Fig. 1. X-ray diffraction patterns of as-prepared Ti3 AlC2 (a) and sample 1, Ti3 AlC2 soaked at a pressure of ∼5 × 10−3 Pa for 30 h at 1150 ◦ C (b).
Fig. 2. Back-scattered electron image of the surface of sample 1 (a) and its corresponding EDS spectrum (b). The sputtering of gold was previously performed on the sample surface.
of the surface layer [19]. Thus, the fine TiCx particles with irregular shape on the sample surface can be readily understood. The above results show that Al2 O3 cannot form on the sample surface of Ti3 AlC2 during vacuum treatment at 1150 ◦ C. What will happen to Ti3 AlC2 /Al2 O3 composites when they are treated in vacuum? As listed in Table 1, besides vacuum treatment at 1150 ◦ C for 30 h, the samples of TAC-10 were also treated at a lower temperature, 1100 ◦ C, with the soaking time of 5–60 h. Fig. 3 shows the morphology evolution of TAC-10 with soaking time. In the back-scattered electron images, the light gray phase is Ti3 AlC2 and the dark gray phase is Al2 O3 . It can be seen that the amount of Al2 O3 particles becomes less with increasing the soaking time (Fig. 3(a–c)). Finally, Al2 O3 particles disappear on the sample surface (Fig. 3(d)). Simultaneously, the sample surface becomes loose and porous. Burns et al. [20,21] found that high-temperature vacuum annealing could lead to the decomposition of Al2 O3 film. The desorption of Al+ , AlO+ , Al2 O+ and O+ ionic species took place on the film surface. In our cases, the element analysis by EDS (not shown) also confirms the decrease in the content of Al2 O3 on the TAC-10 surface with increasing the soaking time.
J.X. Chen et al. / Materials Chemistry and Physics 104 (2007) 109–112
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Fig. 3. Back-scattered electron images of the surfaces of polished as-prepared TAC-10 (a), and the samples treated at 1100 ◦ C with soaking time of 5 h (b), 15 h (c), and 60 h (d). The light gray phase is Ti3 AlC2 and the dark gray phase is Al2 O3 .
A large cavity indicated in Fig. 4 is an evidence of the Al2 O3 evaporation. Most of Al2 O3 particles in TAC-10 distribute uniformly, but the agglomeration is unavoidable, as shown in Fig. 3(a). Once the agglomerated Al2 O3 particles with large size entirely evaporate from the sample surface, the large cavities leave. Certainly, the evaporation of the dispersed Al2 O3
Fig. 4. Back-scattered electron image of the surface of sample 5, TAC-10 soaked for 30 h at 1150 ◦ C.
particles with small size and the decomposition of Ti3 AlC2 also take place during the vacuum treatment. It is also worth noting that there are some large TiCx particles on the sample surface, which reflects the ununiformity of the initial Ti3 AlC2 grains. To understand the decomposition process of TAC-10 further, the phase composition and morphology of sectioned sample 5 were examined by SEM. It can be seen that the dark gray Al2 O3 particles only exist in the inner part of the sample, as shown in Fig. 5(a). Fig. 5(b) shows the concentration profiles taken along the black line in Fig. 5(a). Obviously, the outer layer is rich in C and poor in Al, while the concentrations of O and Ti are almost constant except for Al2 O3 particles. So, the decomposition of TAC-10 only occurs near the surface and the inner Ti3 AlC2 and Al2 O3 are still stable in high vacuum at 1150 ◦ C. Recently, Low et al. [22,23] reported that the very low partial pressure of oxygen in vacuum treatment could facilitate the surface formation of TiCx through the thermal dissociation of Ti3 SiC2 . In that case TiCx was expected to improve the hardness, wear, fatigue and damage resistance of Ti3 SiC2 . It should be noted that the TiCx layer is very thin (<3 m) in our cases, so higher treatment temperatures are needed to obtain thick hardened layer.
112
J.X. Chen et al. / Materials Chemistry and Physics 104 (2007) 109–112
4. Conclusions Ti3 AlC2 /Al2 O3 composites are not stable on the sample surface in high vacuum at 1100 and 1150 ◦ C. Ti3 AlC2 can firstly decompose with the formation of TiC0.67 and gaseous Al, then TiC0.67 can lose weight further by Ti evaporation. For Al2 O3 particles, they can also decompose and evaporate from the sample surface. Finally, a layer of TiCx forms on the sample surface of Ti3 AlC2 /Al2 O3 composites. But this decomposition process is very slow and the inner Ti3 AlC2 and Al2 O3 are still stable. Acknowledgments This work was supported by the National Outstanding Young Scientist Foundation for Y. C. Zhou under Grant No. 59925208, Natural Sciences Foundation of China under Grant No. 50232040, ‘863’ project. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] Fig. 5. Back-scattered electron image of the polished cross-section sample 5 (a) and the corresponding concentration profiles taken along the black line (b).
[23]
M.A. Pietzka, J.C. Schuster, J. Phase Equilib. 15 (1994) 392. N.V. Tzenov, M.W. Barsoum, J. Am. Ceram. Soc. 83 (2000) 825. X.H. Wang, Y.C. Zhou, Acta Mater. 50 (2002) 3141. I.M. Low, J. Eur. Ceram. Soc. 18 (1998) 709. J.X. Chen, Y.C. Zhou, Scr. Mater. 50 (2004) 897. J.X. Chen, M.Y. Liu, Y.W. Bao, Y.C. Zhou, Int. J. Mater. Res. 97 (2006) 1115. J.H. Han, S.W. Park, K.Y. Do, J. Rare Earth 22 (2004) 85. J.X. Chen, J.L. Li, Y.C. Zhou, J. Mater. Sci. Technol. 22 (2006) 455. Y.C. Zhou, J.X. Chen, J.Y. Wang, Acta Mater. 54 (2006) 1317. X.H. Wang, Y.C. Zhou, Mater. Res. Innovations 7 (2003) 381. X.H. Wang, Y.C. Zhou, Corros. Sci. 45 (2003) 891. X.H. Wang, Y.C. Zhou, Chem. Mater. 15 (2003) 3716. Y.C. Zhou, Z.M. Sun, S.Q. Chen, Y. Zhang, Mater. Res. Innovations 2 (1998) 142. X.H. Wang, Y.C. Zhou, J. Mater. Chem. 12 (2002) 455. X.H. Wang, Y.C. Zhou, Z. Metalkd. 93 (2002) 66. C. Racault, F. Langlais, R. Naslain, J. Mater. Sci. 29 (1994) 3384. Y.C. Zhou, Z.M. Sun, X.H. Wang, S.Q. Chen, J. Phys.: Condens. Matter 13 (2001) 10001. T.E. Louis, Transition Metal Carbides and Mitrides, Academic Press, New York, 1971, p. 76, 136. T. Shikama, H. Shinno, M. Fukutomi, M. Fujitsuka, M. Kitajima, M. Okada, Thin Solid Films 101 (1983) 233. R.P. Burns, A.J. Jason, M.G. Inghram, J. Chem. Phys. 40 (1964) 2739. R.P. Burns, J. Chem. Phys. 44 (1966) 3307. I.M. Low, P. Manurung, R.I. Smith, D. Lawrence, Key Eng. Mater. 224–226 (2002) 465. I.M. Low, Mater. Lett. 58 (2004) 927.