PHASE-TRANSFORMATION FROM ALPHA'-SIALON TO BETA'-SIALON BY LIQUID INFILTRATION IN Y-SI-AL-O-N SYSTEM

Abstract

The formation of beta'-sialon from alpha'-sialon during infiltration of a glass matrix has been investigated. Sintered alpha'-sialon containing large grains of about 5 mu m has been resintered within a glass matrix of which the composition is in equilibrium with beta'-sialon. During resintering the glass matrix has penetrated into sintered alpha'-sialon specimen and induced the transformation of alpha'-sialon into beta'-sialon. 3 trace of alpha' is found within beta' grains formed. The nucleation of beta' grains is thus believed to occur not on the preexisting alpha' grains but in the penetrated glass matrix. The concentration of Al in beta' grains increases from their centre towards their edge, implying that the glass matrix has continuously penetrated with resintering time. Continuous penetration of glass matrix and thus a concentration gradient in the penetrated glass is also confirmed by a directional growth of 12H polytype grains formed between transformed beta' and bulk glass matrix.