Densification behavior and microstructure evolution of hot-pressed SiC-SiBCN ceramics

Densification behavior and microstructure evolution of hot-pressed SiC-SiBCN ceramics were studied between 1660 °C and 1830 °C. Polyborosilazane was chosen as the SiBCN precursor and pyrolyzed at 1000 °C in inert atmosphere before use. Samples with SiBCN contents of 10% and 20% in weight were prepared. During the sintering, at temperatures <1660 °C, the density of all the samples showed a minor increase because of solid state particles rearrangement. Above 1660 °C, the density increased rapidly because of the grain boundary sliding with a non-Newtonian viscous boundary phase. After grain boundary sliding, grain-boundary diffusion enhanced by B and C elements from the SiBCN material was responsible for the further densification. The microstructure of the samples hot pressed at 1660 °C appeared particle packing state. The two samples can achieve almost full density when they were hot pressed at 1830 °C/40 MPa for 90 min.