Elimination of grain boundaries and its effect on the properties of silicon nitride ceramics

Abstract To eliminate the excess grain boundary phase in silicon nitride ceramics prepared through hot pressing and a post-sintering heat treatment, carbon was introduced into the sintered ceramics. This was accomplished in two ways: first, a small amount of carbon was used as a sintering additive; however, this creates large pores in the ceramics, resulting in a decrease in the thermal conductivity and mechanical properties of the samples. Alternatively, the C/Si3N4 power bed could be used instead of the BN/Si3N4 power bed, which obviously eliminates the grain boundary phase. Further, the C/Si3N4 power bed possess excellent mechanical properties while increasing the thermal conductivity of the samples. Therefore, the silicon nitride ceramics with 123 W m−1 K−1 thermal conductivity and 986 MPa bending strength of can be obtained using the C/Si3N4 powder bed during the post-sintering heat treatment.