T&n Technology Limited

John Woodthrope

Nicholas Dominic Butler

Francisco C Fernandez

Inigo I Zubillaga

It is known to obtain from a sinterable powder (e.g., of silicon nitride+metallic oxide sintering aid) a shaped article with at least 95% theoretical density, by the hot isostatic pressing of a preshaped body of the powder while that body is encapsulated in a gas-impermeable capsule which is plastic at the temperature of the hot gas by which the isostatic pressure is applied. Until now, a pressure of the order of 100 MPa has been treated as the practical minimum necessary for hot isostatic pressing. By the invention, a pressure less than 20 MPa is used, in conjunction with a degassing of the preshaped body, carried out prior to encapsulation, as in a vacuum whose pressure is no more than a few mm of mercury, and preferably less than 1 mm (approximately equal to 0.15 kPa).

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Rugby, United Kingdom

John Woodthrope