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Effect of microstructure on oxidation resistance of MoSi2 fabricated by spark plasma sintering
ARTICLE IN PRESS
Vacuum 73 (2004) 623–628
Effect of microstructure on oxidation resistance of MoSi2 fabricated by spark plasma sintering Jyunichi Kuchinoa,*, Kazuya Kurokawab, Tamaki Shibayamab, Heishichiro Takahashib b
a Graduate School of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan Center for Advanced Research of Energy Technology, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan
Abstract In order to clarify the effect of microstructure on oxidation resistance of MoSi2, structure and oxidation resistance of sintered MoSi2 were studied. Sintered MoSi2 was fabricated by a spark plasma sintering method from the two kinds of starting material, MoSi2 powder and mixed powders of elemental Mo and Si. Dense MoSi2 containing few SiO2 inclusions was fabricated by applying in situ synthesis using mixed powders of Mo and Si. Oxidation behavior in the accelerated oxidation temperature region of MoSi2 showed that accelerated oxidation was remarkably suppressed. r 2004 Elsevier Ltd. All rights reserved. Keywords: MoSi2; Structure; In situ synthesis; Spark plasma sintering; Sintering behavior; Oxidation resistance
1. Introduction Molybdenum disilicide (MoSi2) has a high melting point, a relatively low density and a brittle-to-ductile transition temperature at around 1173 K [1], and it shows excellent resistance to oxidation at temperatures above 1073 K. MoSi2 is therefore a promising material for ultra-high temperature applications in oxidizing atmospheres. It is well known that the excellent resistance of MoSi2 to oxidation is due to the formation of a protective SiO2 scale due to selective oxidation of Si. On the other hand, at low temperatures, especially at temperatures around 773 K, MoSi2 shows accelerated oxidation *Corresponding author. Fax: +81-117-067-119. E-mail address: [email protected] (J. Kuchino).
behavior due to simultaneous oxidation of Mo and Si. The accelerated oxidation of MoSi2 finally causes disintegration of compact into powder, a phenomenon known as ‘‘pesting’’. Suppression and mechanism for accelerated oxidation behavior have been reported by many researchers, including us [2–6]. Accelerated oxidation of MoSi2 is influenced by material factors (composition [7,8] and density [9–12]) and by environmental factors (oxidation temperature [7,8] and atmosphere [6]). Temperatures of around 773 K and defects such as pores and cracks cause greatly accelerated oxidation, resulting in pesting in a short oxidation time. Therefore, defects such as cracks, pores, and SiO2 inclusions have been thought to be major factors affecting accelerated oxidation [5,11–13]. Much interest has recently been shown in spark plasma sintering (SPS) due to significant improvements in the synthesis and processing of new
0042-207X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2003.12.081
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advanced materials. There have been several reports on MoSi2 and MoSi2-based composites by the SPS method, for example, FGMs of MoSi2/ SiC composites [14], improvement of mechanical property of MoSi2 [15], and simulation of sintering conditions [16], densification of MoSi2 including nano-phases [17]. Our previous study [6] demonstrated that in situ synthesized MoSi2-SiC composites have outstanding resistance to accelerated oxidation. In the present study, the relationship between structure and oxidation behavior at 773 K of dense MoSi2 fabricated from MoSi2 powder and from mixed powders of elemental Mo and Si was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetry (TG).
2. Experimental Dense MoSi2 was fabricated by an SPS method. The SPS system is shown schematically in Fig. 1. The starting materials were MoSi2 powder (average grain size: B3 mm) and mixed powders of Mo (2.5 mm) and Si (200 mesh). The latter powders were in a stoichiometric ratio corresponding to MoSi2 and mixed in an agate mortar for 1.8 ks. The powder was packed into a graphite die under a compressive stress of about 40 MPa, and then a pulsating current (12 ms on and 2 ms off) was passed through the powder and the graphite die in an evacuated chamber (6 Pa). Sintering temperature was measured by a digital radiation thermometer, and sintering behavior was monitored by measuring change in the thickness of the compact body. The sintering was carried out at a heating rate of 0.17 K/s, maximum sintering temperature of 1673 K, and holding time of 600 s at 1673 K. Specimens for oxidation tests and observation of structures were cut from the sintered body. The surfaces of specimens were polished to a 1-mm diamond finish and then cleaned ultrasonically in an acetone bath for 600 s. The polished surfaces and fractured surfaces of MoSi2 were observed using SEM. The microstructures of sintered MoSi2 were investigated using TEM. The specimens for TEM were cut into 2.5 mm 1.0 mm 0.3 mm
Fig. 1. Schematic of SPS apparatus.
pieces. Each piece was bonded on a stainless-steel ring for thinning by a focused ion beam (FIB) method. Finally, a selected area of each piece was thinned to a thickness of less than 100 nm by Gaion sputtering. Isothermal oxidation tests of MoSi2 were carried out in air at 773 K. The oxidation kinetics was obtained by measuring weight gain of specimens by oxidation. Oxidation products on MoSi2 were analyzed using X-ray diffraction (XRD).
3. Results and discussion 3.1. Sintering behavior of MoSi2 Sintering behavior of MoSi2 was examined by measuring continuously change in thickness of the compact body. Fig. 2 shows sintering behavior of
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cles, occurs at a temperature of about 1200 K. Densification of MoSi2 proceeds with increase in temperature and is completed at a temperature of about 1500 K. In sintering of the mixed powders of Mo and Si, the following reaction occurs: Mo þ 2Si-MoSi2 :
ð1Þ
As can be seen in Fig. 2(b), transition from expansion to shrinkage occurs at a temperature of about 1100 K, and then abrupt shrinkage is observed in the temperature range from 1300 to 1500 K, especially at temperatures above 1450 K. This shrinkage is thought to be related to the above reaction, in addition to an intermediate product of Mo5Si3. Differential thermal analysis (DTA) showed that an exothermic reaction due to the formation of MoSi2 occurred at 1703 K. The results indicate that there is disagreement (temperature difference: about 250 K) between sintering temperature and actual temperature of mixed powders of Mo and Si, because the former is the temperature measured at the surfaces of graphite die. The relative density of MoSi2 sintered from MoSi2 powder measured by Archimedes method was about 99%, and that of MoSi2 from the mixed powders of Mo and Si was also about 99%. Therefore, in either starting powders, fully dense MoSi2 can be fabricated by applying the SPS method. 3.2. Microstructure of MoSi2
Fig. 2. Sintering behavior of (a) MoSi2 powder and of (b) mixed powders of Mo and Si.
the MoSi2 powder and the mixed powders of Mo and Si. Increase in stroke means shrinkage of specimens, and decrease means expansion in specimens. It is notable that displacements of specimens are an indication of occurrence of reaction and densification of MoSi2 compact during sintering, as reported by Orru et al. [17]. Slight expansion in the initial stage of sintering is caused by thermal expansion of gas and particles by heating. As can be seen in Fig. 2(a), transition from expansion to shrinkage in the MoSi2 powder, indicating the formation of necks between parti-
Polished surfaces of sintered MoSi2 were observed by SEM. Fig. 3(a) and (b) show the polished surfaces of the compacts fabricated from MoSi2 powder and from elemental Mo and Si. SiO2 inclusions, the formation of which may be caused by adsorbed oxygen, are observed in both sintered bodies. However, the formation of SiO2 inclusions in the sintered body fabricated by in situ synthesis is remarkably suppressed compared with that in the sintered body from MoSi2 powder. Fig. 4(a) and (b) show the fractured surfaces of the sintered bodies fabricated from MoSi2 powder and from elemental Mo and Si. As can be seen in Fig. 4(a), the fracture occurs at grain boundaries and SiO2 inclusions are distributed widely in grain boundaries of MoSi2. On the other hand, the SEM
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Fig. 3. Polished surfaces of sintered MoSi2 fabricated from MoSi2 powder (a) and from mixed powders of Mo and Si (b).
image of in situ synthesized MoSi2 shows intragranular fracture, and few SiO2 inclusions are observed. The above results indicate that use of in situ synthesis for sintering of MoSi2 is an effective means for suppressing the formation of SiO2 inclusions. This is thought to be due to the evaporation of volatile MoO3 with a high vapor pressure at lower temperatures before the formation of MoSi2. The formation of MoO3 results from the reaction of Mo particles and oxygen adsorbed to them, resulting in the suppression of the formation of SiO2 inclusions. Fig. 5 shows a TEM bright-field image of MoSi2 sintered at 1673 K from MoSi2 powder, in which the dark phase is MoSi2 and the bright phase is SiO2 inclusion. SiO2 is formed at the triple point and grain boundaries.
Fig. 4. Fractured surfaces of sintered MoSi2 fabricated from MoSi2 powder (a) and by in situ synthesis (b).
As shown in Fig. 6, a TEM bright-field image of MoSi2 fabricated by in situ synthesis showed that no SiO2 is formed at the triple point and in grain boundaries. SiO2 in grain boundaries probably become a preferential path for O2 inward diffusion. Therefore, it is thought that MoSi2 matrix adjacent to SiO2 inclusions in grain boundaries act as sites for simultaneous oxidation of Mo and Si. 3.3. Oxidation behavior It is well known that accelerated oxidation of MoSi2 is severe at temperatures around 773 K. Such severe oxidation is caused by the simultaneous oxidation of Mo and Si, and this
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Fig. 7. Oxidation behavior of MoSi2 oxidized in air at 773 K. Fig. 5. TEM bright-field image of MoSi2 fabricated from MoSi2 powder.
and H2O vapor pressure in the atmosphere. Mass gain in oxidation of defect-less MoSi2 fabricated by in situ synthesis is negligibly small even for 540 ks. The above-described results indicate that MoSi2 fabricated by in situ synthesis has higher resistance to oxidation at 773 K than MoSi2 fabricated from MoSi2 powder and that SiO2 inclusions formed during the sintering process strongly affect accelerated oxidation behavior of MoSi2 at low temperatures.
4. Conclusion Fig. 6. TEM bright-field image of MoSi2 fabricated from mixed powders of Mo and Si.
simultaneous oxidation is liable to occur at defects such as SiO2 inclusions, cracks and pores [12]. Fig. 7 shows the mass gain of MoSi2 during oxidation at 773 K. There is an induction period in the initial stage (for 180 ks) of oxidation of MoSi2 fabricated from MoSi2 powder, during which mass gain is very small. After the induction period, the mass gain increases at a higher rate, i.e., accelerated oxidation behavior occurs. According to the result of our previous study [12], the duration of the induction period depends on defects in MoSi2
MoSi2 powder and mixed powders of Mo and Si were sintered by using an SPS method, and the microstructures and the oxidation behavior at 773 K of the sintered bodies were compared. The following results were obtained. (1) SiO2 inclusions, which assist accelerated oxidation of MoSi2, are liable to be formed in grain boundaries. (2) Dense MoSi2 which containing few SiO2 inclusions can be fabricated by using mixed powders of Mo and Si. (3) In situ synthesized MoSi2 shows excellent resistance to oxidation even in the accelerated oxidation temperature region.
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Acknowledgements We would like to express our sincere thanks for the financial support from the Hosokawa powder technology foundation.
References [1] Umakoshi Y, Hirano T, Sakagami T, Yamane T. Scr Metal 1989;23:87–90. [2] Kurokawa K, Kuchino J, Hara H, Takahashi H, Shibayama T, Takahashi H. Mater High Temp 2001;18:357–62. [3] Cockerman BV, Wang G, Rapp RA. Oxid Metals 1996; 45:77–108. [4] Maruyama T, Yanagihara K. Mater Sci Eng 1997; A239–240:828–41. [5] Yanagihara K, Przybylski K, Maruyama T. Oxid Metals 1997;47:277–93.
[6] Kurokawa K, Ube M, Takahashi Hi, Takahashi He. J Phys IV 2000;10:6-3–6-8. [7] Berztiss DA, Cerchiara RR, Gulbransen EA, Pettit FS, Meier GH. Mater Sci Eng 1992;A155:165–81. [8] Mescher PJ. Met Trans 1992;23A:1763. [9] Fitzer E, Remmele W. Fifth International Conference on Composite Materials, AIME, 1985. p. 515. [10] Mckamey CG, Tortorelli PF, De Van JH, Carmichael CA. J Mater Res 1992;7:2747. [11] Becker S, Rahmel A, Schutze M. Solid State Ionics 1992;53/56:280–9. [12] Kurokawa K, Houzumi H, Saeki I, Takahashi H. Mater Sci Eng 1999;A261:292–9. [13] Grabke HJ, Meier GH. Oxid Metals 1995;44:147–76. [14] Carrillo-Heian EM, Carpenter RD, Paulino GH, Gibeling JC, Munir ZA. J Am Ceram Soc 2001;84(5):962–8. [15] Shimizu H, Yoshinaka M, Hirota K. Mater Res Bull 2002; 37:1557–63. [16] Heian EM, Feng A, Munir ZA. Acta Mater 2002;50: 3331–46. [17] Orru R, Woolman J, Cao G, Munnir ZA. Mater Res 2001; 16:1439–48.
Vacuum 73 (2004) 623–628
Effect of microstructure on oxidation resistance of MoSi2 fabricated by spark plasma sintering Jyunichi Kuchinoa,*, Kazuya Kurokawab, Tamaki Shibayamab, Heishichiro Takahashib b
a Graduate School of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan Center for Advanced Research of Energy Technology, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo 060-8628, Japan
Abstract In order to clarify the effect of microstructure on oxidation resistance of MoSi2, structure and oxidation resistance of sintered MoSi2 were studied. Sintered MoSi2 was fabricated by a spark plasma sintering method from the two kinds of starting material, MoSi2 powder and mixed powders of elemental Mo and Si. Dense MoSi2 containing few SiO2 inclusions was fabricated by applying in situ synthesis using mixed powders of Mo and Si. Oxidation behavior in the accelerated oxidation temperature region of MoSi2 showed that accelerated oxidation was remarkably suppressed. r 2004 Elsevier Ltd. All rights reserved. Keywords: MoSi2; Structure; In situ synthesis; Spark plasma sintering; Sintering behavior; Oxidation resistance
1. Introduction Molybdenum disilicide (MoSi2) has a high melting point, a relatively low density and a brittle-to-ductile transition temperature at around 1173 K [1], and it shows excellent resistance to oxidation at temperatures above 1073 K. MoSi2 is therefore a promising material for ultra-high temperature applications in oxidizing atmospheres. It is well known that the excellent resistance of MoSi2 to oxidation is due to the formation of a protective SiO2 scale due to selective oxidation of Si. On the other hand, at low temperatures, especially at temperatures around 773 K, MoSi2 shows accelerated oxidation *Corresponding author. Fax: +81-117-067-119. E-mail address: [email protected] (J. Kuchino).
behavior due to simultaneous oxidation of Mo and Si. The accelerated oxidation of MoSi2 finally causes disintegration of compact into powder, a phenomenon known as ‘‘pesting’’. Suppression and mechanism for accelerated oxidation behavior have been reported by many researchers, including us [2–6]. Accelerated oxidation of MoSi2 is influenced by material factors (composition [7,8] and density [9–12]) and by environmental factors (oxidation temperature [7,8] and atmosphere [6]). Temperatures of around 773 K and defects such as pores and cracks cause greatly accelerated oxidation, resulting in pesting in a short oxidation time. Therefore, defects such as cracks, pores, and SiO2 inclusions have been thought to be major factors affecting accelerated oxidation [5,11–13]. Much interest has recently been shown in spark plasma sintering (SPS) due to significant improvements in the synthesis and processing of new
0042-207X/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2003.12.081
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advanced materials. There have been several reports on MoSi2 and MoSi2-based composites by the SPS method, for example, FGMs of MoSi2/ SiC composites [14], improvement of mechanical property of MoSi2 [15], and simulation of sintering conditions [16], densification of MoSi2 including nano-phases [17]. Our previous study [6] demonstrated that in situ synthesized MoSi2-SiC composites have outstanding resistance to accelerated oxidation. In the present study, the relationship between structure and oxidation behavior at 773 K of dense MoSi2 fabricated from MoSi2 powder and from mixed powders of elemental Mo and Si was studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetry (TG).
2. Experimental Dense MoSi2 was fabricated by an SPS method. The SPS system is shown schematically in Fig. 1. The starting materials were MoSi2 powder (average grain size: B3 mm) and mixed powders of Mo (2.5 mm) and Si (200 mesh). The latter powders were in a stoichiometric ratio corresponding to MoSi2 and mixed in an agate mortar for 1.8 ks. The powder was packed into a graphite die under a compressive stress of about 40 MPa, and then a pulsating current (12 ms on and 2 ms off) was passed through the powder and the graphite die in an evacuated chamber (6 Pa). Sintering temperature was measured by a digital radiation thermometer, and sintering behavior was monitored by measuring change in the thickness of the compact body. The sintering was carried out at a heating rate of 0.17 K/s, maximum sintering temperature of 1673 K, and holding time of 600 s at 1673 K. Specimens for oxidation tests and observation of structures were cut from the sintered body. The surfaces of specimens were polished to a 1-mm diamond finish and then cleaned ultrasonically in an acetone bath for 600 s. The polished surfaces and fractured surfaces of MoSi2 were observed using SEM. The microstructures of sintered MoSi2 were investigated using TEM. The specimens for TEM were cut into 2.5 mm 1.0 mm 0.3 mm
Fig. 1. Schematic of SPS apparatus.
pieces. Each piece was bonded on a stainless-steel ring for thinning by a focused ion beam (FIB) method. Finally, a selected area of each piece was thinned to a thickness of less than 100 nm by Gaion sputtering. Isothermal oxidation tests of MoSi2 were carried out in air at 773 K. The oxidation kinetics was obtained by measuring weight gain of specimens by oxidation. Oxidation products on MoSi2 were analyzed using X-ray diffraction (XRD).
3. Results and discussion 3.1. Sintering behavior of MoSi2 Sintering behavior of MoSi2 was examined by measuring continuously change in thickness of the compact body. Fig. 2 shows sintering behavior of
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cles, occurs at a temperature of about 1200 K. Densification of MoSi2 proceeds with increase in temperature and is completed at a temperature of about 1500 K. In sintering of the mixed powders of Mo and Si, the following reaction occurs: Mo þ 2Si-MoSi2 :
ð1Þ
As can be seen in Fig. 2(b), transition from expansion to shrinkage occurs at a temperature of about 1100 K, and then abrupt shrinkage is observed in the temperature range from 1300 to 1500 K, especially at temperatures above 1450 K. This shrinkage is thought to be related to the above reaction, in addition to an intermediate product of Mo5Si3. Differential thermal analysis (DTA) showed that an exothermic reaction due to the formation of MoSi2 occurred at 1703 K. The results indicate that there is disagreement (temperature difference: about 250 K) between sintering temperature and actual temperature of mixed powders of Mo and Si, because the former is the temperature measured at the surfaces of graphite die. The relative density of MoSi2 sintered from MoSi2 powder measured by Archimedes method was about 99%, and that of MoSi2 from the mixed powders of Mo and Si was also about 99%. Therefore, in either starting powders, fully dense MoSi2 can be fabricated by applying the SPS method. 3.2. Microstructure of MoSi2
Fig. 2. Sintering behavior of (a) MoSi2 powder and of (b) mixed powders of Mo and Si.
the MoSi2 powder and the mixed powders of Mo and Si. Increase in stroke means shrinkage of specimens, and decrease means expansion in specimens. It is notable that displacements of specimens are an indication of occurrence of reaction and densification of MoSi2 compact during sintering, as reported by Orru et al. [17]. Slight expansion in the initial stage of sintering is caused by thermal expansion of gas and particles by heating. As can be seen in Fig. 2(a), transition from expansion to shrinkage in the MoSi2 powder, indicating the formation of necks between parti-
Polished surfaces of sintered MoSi2 were observed by SEM. Fig. 3(a) and (b) show the polished surfaces of the compacts fabricated from MoSi2 powder and from elemental Mo and Si. SiO2 inclusions, the formation of which may be caused by adsorbed oxygen, are observed in both sintered bodies. However, the formation of SiO2 inclusions in the sintered body fabricated by in situ synthesis is remarkably suppressed compared with that in the sintered body from MoSi2 powder. Fig. 4(a) and (b) show the fractured surfaces of the sintered bodies fabricated from MoSi2 powder and from elemental Mo and Si. As can be seen in Fig. 4(a), the fracture occurs at grain boundaries and SiO2 inclusions are distributed widely in grain boundaries of MoSi2. On the other hand, the SEM
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Fig. 3. Polished surfaces of sintered MoSi2 fabricated from MoSi2 powder (a) and from mixed powders of Mo and Si (b).
image of in situ synthesized MoSi2 shows intragranular fracture, and few SiO2 inclusions are observed. The above results indicate that use of in situ synthesis for sintering of MoSi2 is an effective means for suppressing the formation of SiO2 inclusions. This is thought to be due to the evaporation of volatile MoO3 with a high vapor pressure at lower temperatures before the formation of MoSi2. The formation of MoO3 results from the reaction of Mo particles and oxygen adsorbed to them, resulting in the suppression of the formation of SiO2 inclusions. Fig. 5 shows a TEM bright-field image of MoSi2 sintered at 1673 K from MoSi2 powder, in which the dark phase is MoSi2 and the bright phase is SiO2 inclusion. SiO2 is formed at the triple point and grain boundaries.
Fig. 4. Fractured surfaces of sintered MoSi2 fabricated from MoSi2 powder (a) and by in situ synthesis (b).
As shown in Fig. 6, a TEM bright-field image of MoSi2 fabricated by in situ synthesis showed that no SiO2 is formed at the triple point and in grain boundaries. SiO2 in grain boundaries probably become a preferential path for O2 inward diffusion. Therefore, it is thought that MoSi2 matrix adjacent to SiO2 inclusions in grain boundaries act as sites for simultaneous oxidation of Mo and Si. 3.3. Oxidation behavior It is well known that accelerated oxidation of MoSi2 is severe at temperatures around 773 K. Such severe oxidation is caused by the simultaneous oxidation of Mo and Si, and this
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Fig. 7. Oxidation behavior of MoSi2 oxidized in air at 773 K. Fig. 5. TEM bright-field image of MoSi2 fabricated from MoSi2 powder.
and H2O vapor pressure in the atmosphere. Mass gain in oxidation of defect-less MoSi2 fabricated by in situ synthesis is negligibly small even for 540 ks. The above-described results indicate that MoSi2 fabricated by in situ synthesis has higher resistance to oxidation at 773 K than MoSi2 fabricated from MoSi2 powder and that SiO2 inclusions formed during the sintering process strongly affect accelerated oxidation behavior of MoSi2 at low temperatures.
4. Conclusion Fig. 6. TEM bright-field image of MoSi2 fabricated from mixed powders of Mo and Si.
simultaneous oxidation is liable to occur at defects such as SiO2 inclusions, cracks and pores [12]. Fig. 7 shows the mass gain of MoSi2 during oxidation at 773 K. There is an induction period in the initial stage (for 180 ks) of oxidation of MoSi2 fabricated from MoSi2 powder, during which mass gain is very small. After the induction period, the mass gain increases at a higher rate, i.e., accelerated oxidation behavior occurs. According to the result of our previous study [12], the duration of the induction period depends on defects in MoSi2
MoSi2 powder and mixed powders of Mo and Si were sintered by using an SPS method, and the microstructures and the oxidation behavior at 773 K of the sintered bodies were compared. The following results were obtained. (1) SiO2 inclusions, which assist accelerated oxidation of MoSi2, are liable to be formed in grain boundaries. (2) Dense MoSi2 which containing few SiO2 inclusions can be fabricated by using mixed powders of Mo and Si. (3) In situ synthesized MoSi2 shows excellent resistance to oxidation even in the accelerated oxidation temperature region.
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Acknowledgements We would like to express our sincere thanks for the financial support from the Hosokawa powder technology foundation.
References [1] Umakoshi Y, Hirano T, Sakagami T, Yamane T. Scr Metal 1989;23:87–90. [2] Kurokawa K, Kuchino J, Hara H, Takahashi H, Shibayama T, Takahashi H. Mater High Temp 2001;18:357–62. [3] Cockerman BV, Wang G, Rapp RA. Oxid Metals 1996; 45:77–108. [4] Maruyama T, Yanagihara K. Mater Sci Eng 1997; A239–240:828–41. [5] Yanagihara K, Przybylski K, Maruyama T. Oxid Metals 1997;47:277–93.
[6] Kurokawa K, Ube M, Takahashi Hi, Takahashi He. J Phys IV 2000;10:6-3–6-8. [7] Berztiss DA, Cerchiara RR, Gulbransen EA, Pettit FS, Meier GH. Mater Sci Eng 1992;A155:165–81. [8] Mescher PJ. Met Trans 1992;23A:1763. [9] Fitzer E, Remmele W. Fifth International Conference on Composite Materials, AIME, 1985. p. 515. [10] Mckamey CG, Tortorelli PF, De Van JH, Carmichael CA. J Mater Res 1992;7:2747. [11] Becker S, Rahmel A, Schutze M. Solid State Ionics 1992;53/56:280–9. [12] Kurokawa K, Houzumi H, Saeki I, Takahashi H. Mater Sci Eng 1999;A261:292–9. [13] Grabke HJ, Meier GH. Oxid Metals 1995;44:147–76. [14] Carrillo-Heian EM, Carpenter RD, Paulino GH, Gibeling JC, Munir ZA. J Am Ceram Soc 2001;84(5):962–8. [15] Shimizu H, Yoshinaka M, Hirota K. Mater Res Bull 2002; 37:1557–63. [16] Heian EM, Feng A, Munir ZA. Acta Mater 2002;50: 3331–46. [17] Orru R, Woolman J, Cao G, Munnir ZA. Mater Res 2001; 16:1439–48.