Microstructural Evolution in Liquid‐Phase‐Sintered SiC: Part I, Effect of Starting Powder

The effect of starting SiC powder (β‐SiC or α‐SiC), with simultaneous additions of Al 2 O 3 and Y 2 O 3 , on the microstructural evolution of liquid‐phase‐sintered (LPS) SiC has been studied. When using α‐SiC starting powder, the resulting microstructures contain hexagonal platelike α‐SiC grains with an average aspect ratio of 1.4. This anisotropic coarsening is consistent with interface energy anisotropy in α‐SiC. When using β‐SiC starting powder, the β→α phase transformation induces additional anisotropy in the coarsening of platelike SiC grains. A strong correlation between the extent of β→α phase transformation, as determined using quantitative XRD analysis, and the average grain aspect ratio is observed, with the maximum average aspect ratio reaching 3.8. Based on these observations and additional SEM and TEM characterizations of the microstructures, a model for the growth of these high‐aspect‐ratio SiC grains is proposed.