High-temperature mechanical and thermal properties of h-BN/30 vol%Y2SiO5 composite

High-temperature mechanical and thermal properties of h-BN/30 vol%Y2SiO5 composite were systematically investigated in this study. The composite exhibits an improved elastic modulus and strength at high temperatures. The elastic modulus reaches a maximum of 98 GPa at 1478 K, and the flexural strength increases from 119±3 to 188±12 MPa in the range from room temperature to 1473 K. These improvements in the mechanical properties of the material are primarily attributed to the closing of microcracks in both the h-BN matrix and the h-BN/Y2SiO5 interphase. Particularly, the strengthening effect at 1473 K results from the healing of surface defects by borosilicate glass formed during testing in air. The linear coefficients of thermal expansion in the temperature range of 373 to 1573 K in the perpendicular and parallel directions are determined to be 4.4–5.0×10−6 and 7.9–9.2×10−6 K−1, respectively. The room-temperature thermal conductivities in the perpendicular and parallel directions are determined to be 42 and 28 W ·m−1 ·K−1; these values subsequently decrease to 18 and 12 W ·m−1 ·K−1 at 1473 K, respectively.