Compositions: ceramic – Ceramic compositions – Refractory
Patent
1993-06-16
1994-05-17
Group, Karl
Compositions: ceramic
Ceramic compositions
Refractory
501 92, 501 98, C04B 3558
Patent
active
053127889
ABSTRACT:
A silicon nitride sintered body has a composition consisting essentially of 85 to 94% by weight .beta. silicon nitride, 6 to 15% by weight grain boundary phase consisting essentially of (i) at least two rare earth elements, wherein yttrium is considered a rare earth, and, optionally, strontium which, calculated as SrO, is 0-2 percent by weight of the total body, and (ii) at least two of Si, N, O and C, and an additive consisting essentially of a metal-carbon compound present in the amount of about 0.2 to 3.5% by volume. The additive is substantially homogeneously dispersed within the sintered body. The sintered body has a density at least 95% of theoretical and the ceramic has high strength and high toughness and is especially suited for industrial applications such as components for gas turbine and automotive engines. The sintered body has a microstructure wherein (i) the .beta. silicon nitride grains are acicular and have an average grain width ranging from 0.5 to 1.5 .mu.m, (ii) at least 25% of the grains have width greater than 0.7 .mu.m, and at least 10% of the grains have width greater than 1 .mu.m, and (iii) no more than 5% of grains have width greater than 3.5 .mu.m and apparent aspect ratio greater than 5, with the proviso that the average aspect ratio is at least 1.8.
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Li Chien-Wei
Yamanis Jean
Allied-Signal Inc.
Buff Ernest D.
Criss Roger H.
Group Karl
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