Influence of molybdenum silicide additions on high-temperature oxidation resistance of silicon nitride materials
- Fraunhofer-Inst. Ceramic Technologies and Sintered Materials, Dresden (Germany)
The influence of additions of molybdenum disilicide (MoSi{sub 2}) on the microstructure and the mechanical properties of a silicon nitride (Si{sub 3}N{sub 4}) material, with neodymium oxide (Nd{sub 2}O{sub 3}) and aluminum nitride (AlN) as sintering aids, was studied. The composites, containing 5, 10, and 17.6 wt% MoSi{sub 2}, were fabricated by hot pressing. All materials exhibited a similar phase composition, detected by X-ray diffractometry. Up to MoSi{sub 2} additions of 10 wt%, mechanical properties such as strength, fracture toughness, or creep at 1,400 C were not affected significantly, in comparison to that of monolithic Si{sub 3}N{sub 4}. The oxidation resistance of the composites, in terms of weight gain, degraded. After 1,000 h of oxidation at 1,400 and 1,450 C in air, a greater weight gain (by a factor of approximately three) was obtained, in comparison to that of the material without MoSi{sub 2}. Nevertheless, after 1,000 h of oxidation, the degradation in strength of the composites was considerably less severe than that of the material without MoSi{sub 2}. An additional layer was formed, caused by processes at the surface of the Si{sub 3}N{sub 4} material, preventing the formation of pores, cracks, or glassy-phase-rich areas, which are common features of oxidation damage in Si{sub 3}N{sub 4} materials. This surface layer, containing Mo{sub 5}Si{sub 3} and silicon oxynitride (Si{sub 2}ON{sub 2}), was the result of reactions between MoSi{sub 2}, Si{sub 3}N{sub 4}, and the oxygen penetrating by diffusion into the material during the high-temperature treatment.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 417751
- Journal Information:
- Journal of the American Ceramic Society, Vol. 79, Issue 9; Other Information: PBD: Sep 1996
- Country of Publication:
- United States
- Language:
- English
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