Silicon nitride with improved high temperature strength

Details Silicon nitride with improved high temperature strength Silicon nitride with improved high temperature strength

1988-01-15

1990-02-27

Dixon, Jr., William R.

Compositions: ceramic

Ceramic compositions

Refractory

501 98, 264 65, 264 66, C04B 3558

Patent

active

049046241

ABSTRACT:
The flexural strength and stress rupture life of isostatically hot pressed silicon nitride containing between 1 and 12 weight percent of rare earth oxide and not more than 0.5 weight percent alumina is substantially increased by treating green bodies in flowing nitrogen at a temperature between 1000.degree. and 1500.degree. C. before degassing for the isostatic hot pressing. The iron content of the bodies is also reduced by this heat treatment, and this is believed to eliminate sources of fracture failure. Silicon nitride bodies with a flexural strength in excess of 525 MPa at 1370.degree. C. and with stress rupture lives reliably in excess of 200 hours at 300 MPa stress at 1370.degree. C. can be prepared in this way. The strain rates of silicon nitride under high temperature stress can also be reduced.

REFERENCES:
patent: 4560669 (1985-12-01), Matsuhiro et al.
Pp. 120-127, Materials Evaluation Ceramic Materials for Advanced Heat Engines (1985), D. C. Larsen et al.

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