Effect of sintering aids boron and carbon on high temperature deformation behaviour of β-silicon carbide

In order to clarify the effects of sintering aids (B+C) on high temperature deformation behaviour of β-SiC, HIPed Η-SiC without sintering aids and pressureless sintered Η-SiC with B and C addition were subjected to compression tests at temperatures from 2170 to 2270 K and at strain rates from 6 × 10^-6 to 2 × 10^-5 s^-1. In addition, dislocation structure developed during deformation was analyzed by transmission electron microscopy (TEM). It was found that the flow stress of β-SiC without sintering aids was ca. twice as much as that of the B+C added one. The appearance of the stress-strain curves was noticeably different between them: while the steady state was observed on the stress-strain curves for β-SiC without additives, the flow stress oscillation was observed, followed by yield drop for B+C added ones. TEM observations revealed that dislocations in B+C added β-SiC were dissociated into the Shockley partial dislocations with much larger width than dislocations in β-SiC without additives. This observation suggested that the addition of B+C would probably reduce the stacking fault energy. The observed differences in deformation behaviour will be discussed from the viewpoints of differences in the magnitude of the stacking fault energy and in the mobility of two partial dislocations.