Effect of Oxidation on Mechanical Properties of Fibrous Monolith Si3N4/BN at Elevated Temperatures in Air |
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| Authors: | Young-Hag Koh Hae-Won Kim Hyoun-Ee Kim John W. Halloran |
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| Affiliation: | School of Materials Science and Engineering, Seoul National University, Seoul, 151–742, Korea;Materials Science and Engineering Department, University of Michigan, Ann Arbor, Michigan 48109–2136 |
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| Abstract: | The oxidation behavior and its effect on the mechanical properties of fibrous monolith Si3N4/BN after exposure to air at temperatures ranging from 1000° to 1400°C for up to 20 h were investigated. After exposure at 1000°C, only the BN cell boundary was oxidized, forming a B2O3 liquid phase. With increasing exposure temperature, the Si3N4 cells began to oxidize, forming crystalline Y2Si2O7, SiO2, and silicate glass. However, in this case, a weight loss was observed due to extensive vaporization of the B2O3 liquid. After exposure at 1400°C, large Y2Si2O7 crystals with a glassy phase formed near the BN cell boundaries. The oxidation behavior significantly affected the mechanical properties of the fibrous monolith. The flexural strength and work-of-fracture decreased with increasing exposure temperature, while the noncatastrophic failure was maintained. |
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| Keywords: | oxidation mechanical properties silicon nitride |
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