Effect of relative density on cyclic oxidation resistance properties of MoSi₂

Abstract

MoSi₂ powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi₂ materials at 1 473 K was investigated by TGA, SEM and XRD. The results show that the “pesting” is not found in all materials after being oxidized for 480 h. The density has no essential relation to the “pesting”. The oxidation curve of specimens with lower density shows two-step oxidation kinetics. Both the first stage (0–1 h) and the second stage (1–480 h) nearly obey linear kinetics, but the oxidation rates are obviously different. The oxidation kinetics of MoSi₂ with higher relative density nearly follows parabolic law. The mass gains of MoSi₂ with the lowest relative density (78.6%) and the highest relative density (94.8%) are increased by 10.390 and 0.135 mg/cm², respectively. The oxide scale of materials with lower densities is non-protective and makes the oxygen diffusion easy. A dense scale in the material with higher density is formed, which acts as a diffusion barrier to the oxygen atoms to penetrate into the matrix, showing much better high temperature oxidation resistance. The phases distribution of oxidation scale from the outside to the inside is SiO₂→Mo₅Si₃→MoSi₂.

Keywords

MoSi₂ / relative density / diffusion / oxidation resistance

References

[1] VasudevanA. K., PetrovicJ. J.. A comparative overview of molybdenum disilicide composites [J]. Materials Science and Engineering A, 1992, A155: 1-17

[2] KuchinoJ., KurokawaK., ShibayamaT.. Effect of microstructure on oxidation resistance of MoSi₂ fabricated by spark plasma sintering [J]. Vacuum, 2004, 73: 623-628

[3] MitraR., RamaR. V. V.. Effect of minor alloying with Al on oxidation behaviour of MoSi₂ at 1 200 °C [J]. Materials Science and Engineering A, 1999, A260: 146-160

[4] MaruyamaT., YanagiharaK.. High temperature oxidation and pesting of Mo(Si,A1)₂ [J]. Materials Science and Engineering A, 1997, A239/240: 828-841

[5] LohfeldS., SchtzeM.. Oxidation behavior of particle reinforced MoSi₂ composites at temperature up to 1 700 °C(part I): Literature review [J]. Materials and Corrosion, 2005, 56(2): 93-97

[6] YanJ.-h., LiY.-m., ZhangH.-a., TangS.-wen.. Mechanical properties and high temperature oxidation behavior of La₂O₃-Mo₅Si₃/MoSi₂ [J]. The Chinese Journal of Nonferrous Metals, 2006, 16(10): 1730-1735

[7] KurokawaK., HouzumiH., SaekiI.. Low temperature oxidation of full dense and porous MoSi₂ [J]. Materials Science and Engineering A, 1999, A261: 292-299

[8] NatesanK., DedviS. C.. Oxidation behavior of molybdenum silicides and their composites [J]. Intermetallics, 2000, 8: 1147-1158

[9] BerztissD. A., CerchiaraR. R., GulbransenE. A., PettitF. S.. Oxidation of MoSi₂ and comparison with other silicide materials [J]. Materials Science and Engineering A, 1992, A155: 165-181

[10] YanJ.-h., ZhangH.-a., LiY.-min.. Oxidation behaviors of MoSi₂ with different density at high temperature of 700–1 200 °C [J]. Chinese Journal of Rare Metals, 2007, 31(1): 18-21

[11] ZhangF., ZhangL.-t., ShanA.-d., WuJ.-sheng.. Oxidation of stoichiometric poly-and single-crystalline MoSi₂ at 773 K [J]. Intermetallics, 2006, 14: 406-411

[12] ChouT. C., NeihT. G.. Mechanism of MoSi₂ pest during low temperature oxidation [J]. Journal of Materials Research, 1993, 8(1): 214-226

[13] LiuY. Q., ShaoG., TsakiropolosP.. On the oxidation behaviour of MoSi₂ [J]. Intermetallics, 2001, 9: 125-136

[14] BartlettR. W., Marsuoka, TakahashiH.. High temperature oxidation of molybdenum disilicide [J]. Journal of the American Ceramic Society, 1965, 48(11): 551-552

[15] ChangC., LiM.-s., ChenC.-z., TianL.-yan.. Microstructure of high-temperature oxidation layer of molybdenum disilicide [J]. Acta Metallurgica Sinica, 2003, 39(2): 126-130