Fabrication and properties of AlN/BN composite ceramics by hot-pressing sintering

AlN/BN composite ceramics were prepared by hot-pressing sintering, using AlN powder and h-BN powder as raw material, without adding sintering aids. The effects of sintering temperature (1750-1900℃) on the relative density, phase composition, microstructure, mechanical properties, thermal conductivity and dielectric properties of the composite ceramics were investigated. The results show that the dense AlN/BN composite ceramics, a relative density more than 98.6%, can be prepared when the sintering temperature reaching 1850℃. The as-prepared samples have homogeneous microstructure, fine grain size and clean grain boundary. The accumulation resulting from h-BN plate-like grains and significant impurity phase were not observed. As the sintering temperature increasing, the relative density, mechanical properties, thermal conductivity and dielectric properties (1 MHz) of the as-prepared samples were significantly improved. When the sintering temperature is 1900℃, the as-prepared samples have a relative density 99.3%, bending strength 482± 42 MPa, fracture toughness 4.4± 0.4 MPa·m^1/2, Vickers hardness 8.56±0.33 GPa, thermal conductivity 47.2 W·m^-1·K^-1, dielectric constant 7.64, and dielectric loss 4.62×10^-4.