Mechanical and thermal properties of h-BN based composite containing dual glass phases at elevated temperatures

High-temperature mechanical and thermal properties of h-BN based composite containing amorphous silica and Yb-riched silicate glass phases were systematically investigated in this work. Owing to anisotropic microstructure of h-BN matrix, the obtained composite demonstrates anisotropic mechanical and thermal properties. The composite possesses higher elastic modulus at 1673 K than that at room temperature and presents excellent high-temperature stiffness. Flexural strengths in parallel and perpendicular directions reach 496 ± 22 and 258 ± 21 MPa at 1073 K, respectively, and increases by 74 and 66% compared with the room-temperature strengths of 285 ± 4 and 155 ± 5 MPa. The composite containing dual glass phases shows lower coefficients of thermal expansion in the temperature range of 473-900 K, the values are −1.4 × 10−6 and 0.3 × 10−6  K−1 for the perpendicular and parallel directions, respectively. Thermal conductivities in the perpendicular and parallel directions at 373 K are 24.8 and 14.8 W m−1 K−1, respectively, and then decrease to 14.9 and 9.3 W m−1 K−1 at 1473 K.