Microstructures and properties of SiB_0.5C_1.5N_0.5 ceramics consolidated by mechanical alloying and hot pressing

Nanostructured SiB_0.5C_1.5N_0.5 ceramics were formed by two routes of mechanical alloying and consolidated by hot pressing. Nano-sized 6H-SiC, 3C-SiC and BCN were the main phases for two SiB_0.5C_1.5N_0.5 ceramics. For the SiBCN ceramics fabricated from the powders milled by one-step milling, the content of 6H-SiC is higher than that of ceramic fabricated from the powders milled by two-step milling. The flexural strengths for the former and latter were 312.8 MPa and 423.4 MPa at room temperature, respectively. At high temperature, the strengths of the former reduced 8.2% and 28.0% at 1000 °C and 1400 °C, respectively. The reduction rates of strengths for the latter were 11.3% and 38.5%, respectively. The average thermal expansion coefficients of two SiBCN ceramics consolidated at 1900 °C were about 4.5 × 10^-6/°C.