Y. Fang et al., Bimodal microstructure in silicon nitride-barium aluminum silicate ceramic-matrix composites by pressureless sintering, J AM CERAM, 83(7), 2000, pp. 1828-1830
A distinct bimodal microstructure has been obtained in a Si3N4-BAS (barium
aluminum silicate) ceramic-matrix composite by pressureless sintering, It i
s shown that the addition of coarse beta-Si3N4 seeds causes abnormal grain
growth in this composite, and hence encourages the formation of a bimodal m
icrostructure. This abnormal grain growth is due to the nature of the heter
ogeneous nucleation mechanism in Si3N4 alpha-to-beta phase transformation,
and is promoted by the transformation. After complete phase transformation,
further abnormal grain growth is comparably slow and governed by the Ostwa
ld ripening mechanism. Therefore, a stable bimodal microstructure can be ea
sily achieved by pressureless sintering.