Mechanical and thermal properties of AlN–BN–SiC ceramics

Mechanical and thermal properties were characterized for two AlN:BN:SiC composite ceramics produced from BN with different particle sizes. The ceramics were hot pressed at temperatures from 1950 to 2100 °C to 97% relative density. For both materials, the matrix (90:10 vol% SiC:AlN) had a grain size of 0.4 μm, and the BN grains (10 vol%) were crystallographically aligned. Microhardness values were between 20 and 22 GPa, while fracture toughness values were between 2.5 and 3.1 MPa m^1/2. Other properties were found to be dependent on testing direction. Elastic moduli were between 260 and 300 GPa and strengths were 630 MPa for small particle BN additions. Thermal conductivity was calculated to be between 25 and 37 W/m K at room temperature and 17 and 25 W/m K at 900 °C. The low values compared to traditional SiC ceramics were attributed to AlN–SiC solid solution formation and sub-micron matrix grain sizes.