STUDY OF THE EARLY STAGE OF SINTERING AND PHASE TRANSFORMATIONS IN BETA SILICON CARBIDE USING TRANSMISSION ELECTRON MICROSCOPY
Abstract
The initial stage of (beta)-SiC sintering and concurrent (beta) (--->) (alpha) phase transformation have been investigated by TEM. A new SiC sintering mechanism which is operative at low temperatures is proposed. Unlike sintering of metallic particles, sintering at low temperatures in SiC takes place only when the mutual orientations of the neighboring particles are the same. Sintering at low temperatures is first observed at around 1800(DEGREES)C. Particles in contact with similar (111) plane orientations reorient themselves into exact (111) plane and then sinter to form one-dimensionally elongated particles. These sintered particles are associated with the formation of bands of twins parallel to one of the {111} planes of (beta)-SiC. As the sintering temperature increases the tendency to form elongated particles increases and the bands transform into mixtures of microsyntactic (alpha) and (beta). The transformation is first observed at around 1950(DEGREES)C. Sintering among randomly oriented particles is first observed at around 2100(DEGREES)C. The characteristic sintering mechanism at low temperatures is ascribed to the high energy of formation of grain boundaries in SiC.
Degree
Ph.D.
Subject Area
Materials science
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