METHOD OF MAKING A DENSIFIED SILICON NITRIDE/OXYNITRIDE COMPOSITE

摘要

Powder mixt. comprising Si3N4 and sufficient yttrium silicon oxynitride to form a viscous soln. with at least part of Si3N4 during sintering, is shaped and then densified to required dimensions by firing with or without applied pressure. Oxynitride pref. contains at least 75% Y10Si6O24N2(H-phase) and can be added as 6-18 wt.% and over 98% purity to mixt., or can be formed in situ from stoichiometric addns. of Y2O3 and SiO2. Densification is pref. by hot pressing at 1600-1700 deg.C. and 2500-4000 psi for 30-80 min. or by sintering at 1704-1760 deg.C for 2-12 hr. without mechanical pressure. Specific compsn. includes 0.4-3% Al2O3 and 6-18% H-phase.