Microstructural characterization of “REFEL” (reaction-bonded) silicon carbides

Abstract

Quantitative characterization of the microstructure of a number of samples of reactionbonded (REFEL) silicon carbide has been undertaken employing transmission and scanning electron microscopy, optical microscopy, and electron and X-ray diffraction techniques. Impurity-controlled secondary electron SEM image contrast has proved particularly useful in differentiating between the SiC present in the initial compact and that formed during the reaction-bonding process, and, in contrast to previous descriptions of the microstructure, it has been found that the newly-formed SiC is deposited from the supersaturated solution of carbon in molten silicon both epitaxially on the original SiC grains, maintaining the sameα-polytypic stacking sequences, and by nucleation of fine cubicβ-SiC elsewhere. The relative quantities of material occurring by these two mechanisms have been found to vary from sample to sample, although the epitaxial growth on the original grains always occurs to some extent and is responsible for the bulk cohesion of the material. Some conclusions have been drawn concerning the reaction model and the process parameters controlling the microstructure of this type of material.