Formation of elongated particles in β-SiC compacts

The mechanism of bonding of β-SiC particles in a compact in a sintering process at relatively low temperatures has been investigated by TEM. The initial sign of bonding is observed at around 1800°C. At these temperatures, SiC particles are found to bond together only when their mutual orientations are the same. Similarly oriented grains at contact reorient themselves by rotation to the same orientation and then bond, thus forming elongated particles. As the temperature increases, the tendency to form elongated particles increases. The formation of boundaries between differently oriented particles is observed only at around 2100°C and above in similar compacts. The mechanism of bonding of particles in the same orientation at low temperatures is ascribed to high self-energy of dislocations common to covalent-bonded materials and, hence, the high energy of formation of grain boundaries.