Superplastic forging nitride ceramics
AssigneeJupiter Technologies, Inc.
InventorsPrakash C. Panda, Edgar R. Seydel, Rishi Raj
Life of this patent
Estimating the term…
Abstract
The invention relates to producing relatively flaw free silicon nitride ceramic shapes requiring little or no machining by superplastic forging This invention herein was made in part under Department of Energy Grant DE-AC01-84ER80167, creating certain rights in the United States Government. The invention was also made in part under New York State Science and Technology Grant SB1R 1985-10.
Claims12
A process for preparing silicon nitride ceramic parts which are relatively flaw free and which need little or no machining, said process comprising the steps of
- (a) preparing a starting powder by wet or dry mixing ingredients comprising by weight from about 70% to about 99% silicon nitride, from about 1% to about 30% of liquid phase forming additive and from 1% to about 7% free silicon;
- (b) cold pressing to obtain a preform of green density ranging from about 30% to about 75% of theoretical density;
- (c) sintering at atmospheric pressure in a nitrogen atmosphere at a temperature ranging from about 1400.degree. C. to about 2200.degree. C. to obtain a density which ranges from about 50% to about 100% of theoretical density and which is higher than said preform green density, and
- (d) press forging workpiece resulting from step (c) by isothermally uniaxially pressing said workpiece in an open die without initial contact between said workpiece and die wall perpendicular to the direction of pressing and so that pressed workpiece does not contact die wall perpendicular to the direction of pressing, to substantially final shape in a nitrogen atmosphere utilizing a temperature within the range of from about 1400.degree. C. to essentially 1750.degree. C. and strain rate within the range of about 10.sup.-7 to about 10.sup.-1 seconds.sup.-1, the temperature and strain rate being such that surface cracks do not occur, said pressing being carried out to obtain a shear deformation greater than 30% whereby superplastic forging is effected.
A process for preparing near net shape parts of nitride ceramics or composites thereof with titanium carbide particles, said process comprising the steps of
- (a) providing a starting powder comprising by weight from about 70% to about 99% nitride ingredient and from 30% to about 1% oxide additive, and when said nitride ingredient comprises silicon nitride, from 1% to about 7% free silicon,
- (b) cold pressing to obtain a preform of green density ranging from about 30% to about 75% of theoretical,
- (c) sintering at atmospheric pressure in a nitrogen atmosphere at a sintering effective temperature in the range of 800.degree. C. to about 2200.degree. C. to obtain a density which ranges from about 50% to about 100% of theoretical density and which is higher than said preform green density,
- (d) press forging workpiece from step (c) by isothermally uniaxially pressing said workpiece in an open die so that said workpiece does not contact die wall perpendicular to the direction of pressing, to substantially final shape in a nitrogen atmosphere utilizing a temperature within the range of from about 1300.degree. C. to essentially 1750.degree. C. when no titanium carbide is present and to about 2000.degree. C. when titanium carbide is present, and a strain rate within the range of about 10.sup.-7 to about 10.sup.-1 seconds.sup.-1, the temperature and strain rate being such that surface cracks do not occur, said pressing being carried out to obtain a shear deformation greater than 30% whereby superplastic forging is effected.
Dependencies are inferred from the claim text.