抄録
Temperature dependency of bending strength and fracture toughness are investigated for silicon nitride ceramic at high temperature. Furthermore, stable crack growth mechanism and crack propagation properties are studied. The bending strength is fairly constant from room temperature to 1173K. However, it decreases monotonously with further increasing temperature. Load-deflection curves show non-linear behavior in fracture toughness test at temperature above 1573K. Both fracture toughness and crack initiation toughness evaluated from R-curve are almost constant over the tested temperature range, but the crack growth resistance increases with temperature rise. This stable crack growth decreases with increasing cross head speed. Viscous flow area reflecting the process zone is revealed along the crack path at high temperature by thermal etching. The viscous flow area tends to extend with temperature rise and becomes smaller with increasing cross head speed.
