Creep and oxidn. resistant sintered SiAlON ceramic - produced without expensive encapsulated hot isostatic pressing operation.

: Frassek, L.; Woetting, G.; Schubert, C.; Klemm, H.

Abstract
A sintered polycrystalline material, consisting of alpha-prime and beta-prime SiAlON and amorphous and/or crystalline grain boundary phases and opt. contg. inclusion and/or reinforcing components, has a creep strain of less than 0.5% at 1400 deg. C./100 MPa after 30 hrs. in a bending creep test in air and pref. has a stationary creep rate of less than 5 x 10-5/hr. during a bending creep test at 1400 deg. C. and 100 MPa stress in air. Also claimed is the prodn. of the above material by (a) grinding together either Si3N4, Al2O3, Y2O3 and/or one or more rare earth oxides or Si3N4 and a pre-synthesised alpha-prime SiAlON raw material; (b) moulding the resulting powder to a green body; (c) hot pressing; (d) gas or normal pressure sintering; and (e) post-treating at 1500-2000 (pref. 1750-2000) deg. C. and 5-2000 (pref. 50-1000) bars pressure, pref. using nitrogen and/or noble gas as pressure medium. ADVANTAGE - The material has excellent long term high temp. properties (esp. high creep and o xidn. resistance) and can be produced using a relatively high sintering aid content and without the use of expensive encapsulated hot isostatic pressing.