Compositions: ceramic – Ceramic compositions – Refractory
Patent
1993-07-23
1997-06-10
Group, Karl
Compositions: ceramic
Ceramic compositions
Refractory
501 87, 501 92, 501 973, C04B 3558
Patent
active
056375409
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 02 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 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 and a fracture origin, at least 90% of which is comprised of large acicular .beta.Si.sub.3 N.sub.4 grains, the average size of which ranges from about 15 to 50 .mu.m. Such a ceramic has high strength, high toughness and long term durability, and is especially suited for industrial applications such as components for gas turbine and automotive engines.
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Goldacker Jeffrey A.
Li Chien-Wei
Allied-Signal Inc.
Buff Ernest D.
Criss Roger H.
Group Karl
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