Microstructural evolution in reaction-bonded silicon carbide

TLDR: In this paper, a detailed microstructural investigation of reaction-bonded silicon carbide has been performed using both fully bonded and quenched samples and other specially prepared specimens containing large original single crystals of known crystallographic habit.

Abstract: A detailed microstructural investigation of reaction-bonded silicon carbide has been performed using both fully-bonded and quenched samples and other specially prepared specimens containing large original single crystals of known crystallographic habit. The development of the epitaxial SiC overgrowth on the original SiC particles has been followed and found to proceed by the progressive growth and coalescence of identically-oriented nuclei. This epitaxial layer grows with a habit characteristic ofβ (cubic) SiC and then transforms toα-SiC in the high temperature region behind the reaction front. The formation of faceted grain boundaries is explained by this growth morphology. Furthermore, SiC:SiC grain boundaries, SiC:SiC epitaxial boundaries and SiC:Si interfaces have all been characterized by TEM techniques. The grain boundaries are of particular interest since they usually comprise a thin (∼1 nm) layer of amorphous SiC with occasional suicide and graphite inclusions. The general cleanliness of the vast majority of interfacial area is a result of the removal of the impurities insoluble in SiC by liquid silicon moving through the sample. The overall distribution of impurities is discussed. Other microstructural features have been characterized and texturing due to original particle alignment during fabrication of the green compact investigated. The control of the mechanical properties of reaction-bonded silicon carbide by these various microstructural features is discussed. A basis for an explanation of the interesting trace-impurity-controlled contrast seen in secondary electron images of these materials is also established.