Pressureless flash sintering of α-SiC: Electrical characteristics and densification

Abstract

The application of an electric field over a ceramic powder compact at elevated temperatures gives rise to “flash sintering”. The phenomenon occurs at a critical combination of field and temperature, which leads to a rapid increase in the electric power dissipated within the sample. This results in sample densification in far shorter timescales than those required with conventional sintering. This paper reports the first successful pressureless flash sintering of SiC with B and C sintering aids. Mean relative densities of up to 94.4% have been achieved in several minutes using an alumina tube furnace at 1500 °C. The sample temperature during flash sintering was similar to those used for conventional sintering of SiC (2100–2200 °C). The electrical response of SiC during the flash event was consistent with thermal runaway. However, the negative temperature coefficient of resistivity responsible for the runaway originated primarily from the effects of sintering, in contrast to the case with oxide ceramics. The rapid sintering was attributed to the rapid heating and the formation of a liquid phase. The densest specimen had a grain size of 5.9 µm ± 0.5 µm and a Vickers hardness (HV5) of 24.7 GPa ± 0.5 GPa. These values were similar to those of conventionally sintered specimens of the same powder but the production time of the flash sintered samples was reduced by more than 6 h and with a furnace temperature lower by 700 °C.