Self-reinforced silicon nitride ceramic with crystalline grain b

Details Self-reinforced silicon nitride ceramic with crystalline grain b Self-reinforced silicon nitride ceramic with crystalline grain b

1991-02-19

1992-03-24

Group, Karl

Abrasive tool making process, material, or composition

With inorganic material

501 95, 501 97, 501 98, 264 65, C04B 3558

Patent

active

050984497

ABSTRACT:
A fully densified, self-reinforced silicon nitride ceramic body of high fracture toughness and high fracture strength is disclosed comprising (a) .beta.-silicon nitride in the form of whiskers having an average aspect ratio of at least about 2.5, and (b) a crystalline grain boundary phase having an oxynitride apatite structure, as determined by X-ray crystallography.
A process for preparing the above identified silicon nitride body comprising hot-pressing a powder mixture containing silicon nitride; silica; a densification aid including strontium oxide; a conversion aid, such as, yttrium oxide; and a compound, such as, calcium oxide which enhances growth of .beta.-silicon nitride whiskers, under conditions such that densification and the in situ formation of .beta.-silicon nitride whiskers having a high aspect ratio occur, and thereafter annealing the densified composition for a time sufficient to produce a crystalline grain boundary phase having an oxynitride apatite structure.

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