Influence of molybdenum silicide additions on high-temperature oxidation resistance of silicon nitride materials

Journal Article · Sun Sep 01 04:00:00 EDT 1996 · Journal of the American Ceramic Society

DOI:https://doi.org/10.1111/j.1151-2916.1996.tb08993.x· OSTI ID:417751

Klemm, H; Tangermann, K; Schubert, C; Hermel, W ^[1]

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1. 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, Journal Name: Journal of the American Ceramic Society Journal Issue: 9 Vol. 79; ISSN 0002-7820; ISSN JACTAW
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
AIR
ALUMINIUM NITRIDES
CHEMICAL COMPOSITION
COMPOSITE MATERIALS
CREEP
DIFFUSION
FRACTURE PROPERTIES
HOT PRESSING
MECHANICAL PROPERTIES
MICROSTRUCTURE
MOLYBDENUM SILICIDES
NEODYMIUM OXIDES
OXIDATION
POWDERS
SILICON NITRIDES
ULTIMATE STRENGTH
WEIGHT MEASUREMENT
X-RAY DIFFRACTION