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

Abstract

High-temperature mechanical and thermal properties of h-BN/30vol%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 98GPa at 1478K, and the flexural strength increases from 119±3 to 188±12MPa in the range from room temperature to 1473K. 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 1473K 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 1573K in the perpendicular and parallel directions are determined to be 4.4–5.0×10−6 and 7.9–9.2×10−6K−1, respectively. The room-temperature thermal conductivities in the perpendicular and parallel directions are determined to be 42 and 28W·m−1·K−1; these values subsequently decrease to 18 and 12W·m−1·K−1 at 1473K, respectively.