α→β Reverse Phase Transformation in Silicon Carbide in Silicon Nitride‐Particulate‐Reinforced‐Silicon Carbide Composites

Abstract

The α→β reverse transformation in SiC is observed in Si 3 N 4 ‐particulate‐reinforced‐SiC composites made from as‐received α‐SiC and α‐Si 3 N 4 powders. However, the transformation does not occur to any great extent in composites made from deoxidized Si 3 N 4 ‐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 α→β 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.