? › ß reverse phase transformation in silicon carbide in silicon nitride-particulate-reinforced-silicon carbide composites

Abstract

The ? › ß reverse transformation in SiC is observed in Si3N4-particulate-reinforced-SiC composites made from as-received ?-SiC and ?-Si3N4 powders. However, the transformation does not occur to any great extent in composites made from deoxidized Si3N4-SiC powder compacts. Detailed transmission electron microscopy shows that most interfaces are covered with an ~ 10 Å thick amorphous intergranular film in the composites made from as-received powders, whereas most interfaces are free of such films in the composites made from deoxidized powder compacts. These observations indicate that the ? › ß reverse transformation in SiC is encouraged by a nitrogen-containing liquid phase that occurs at high temperature in the composites made from the as-received powders. A mechanism is proposed to account for the experimental observations.