Silicon nitride based article with improved fracture...

Details Silicon nitride based article with improved fracture... Silicon nitride based article with improved fracture...

C - Chemistry, Metallurgy

04

B

261/1

C04B 35/58 (2006.01) B23C 3/00 (2006.01) C04B 41/85 (2006.01)

Patent

CA 1336102

A densified silicon nitride-based ceramic body of improved fracture toughness and improved strength. The ceramic body comprises a first phase of beta-silicon nitride grains having an aspect ratio of about 1-10 and an equivalent diameter of about 0.25-10 microns, and an intergranular, silica-based second phase of silica and one or more suitable oxide densification aids. In the first phase, if the aspect ratio of the beta-silicon nitride grains is less than about 1.5, the equivalent diameter of the grains is at least about 0.4 microns. Similarly, if the equivalent diameter of the grains is less than about 0.4 microns, the aspect ratio is at least about 1.5. The starting formulation used to form the ceramic body comprises silicon nitride and about 0.5-12% by weight of the densification aids. The ceramic body has a fracture toughness of at least 5.0 MPa?m and a modulus of rupture of at least 700 MPa. A composite body is described in which 10-50% by volume of the silicon nitride and densification aids is substituted by refractory whiskers or fibers having an aspect ratio of 3-150 and an equivalent diameter greater than that of the beta-silicon nitride grains. The whiskers or fibers are uniformly distributed in the ceramic body. Processes for producing and using the ceramic body are also described.

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