Compositions: ceramic – Ceramic compositions – Carbide or oxycarbide containing
Patent
1987-12-21
1989-03-21
Dixon, Jr., William R.
Compositions: ceramic
Ceramic compositions
Carbide or oxycarbide containing
501 97, 501 98, C04B 3558
Patent
active
048143014
ABSTRACT:
The invention relates to polycrystalline sintered articles comprising at least 50% by weight of crystalline silicon nitride phase of which at least 90% by weight is in the .beta.-form, and at least one secondary crystalline intergranular silicate phase, and having a density of at least 99% of the theoretically possible density, a modulus of elasticity at room temperature of less than 300 kN/mm.sup.2, a short-term bending strength at room temperatue, measured according to the 4-point method, of at least 600 N/mm.sup.2 which, up to 1200.degree. C., decreases by less than 50%, and a long-term bending strength, measured according to the 4-point method, which is characterized by a numerical value of more than 40 at 1200.degree. C. for the crack growth resistance parameter n.
These polycrystalline sintered articles are manufactured, by sintering with or without the use of pressure, a mixture of silicon nitride powder, crystalline silicates of natural or synthetic origin having melting points in the range of from 1350.degree. C. to 1950.degree. C. as sintering additives and metal carbides having melting points at least from 1500.degree. C. as nucleus formers.
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Lipp Alfred
Steinmann Detlef
Dixon Jr. William R.
Elektroschmelzwerk Kempten GmbH
Knab Ann M.
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