Strength Degradation and Crack Propagation in Thermally Shocked Al ₂ O ₃

Abstract

Strength degradation and crack propagation in Al 2 O 3 are shown to depend on the initial strength and grain size of the material. The strengths of single‐crystal sapphire and polycrystalline Al 2 O 3 specimens with grain sizes of 10, 34, and 40 μ m decreased discontinuously at the critical quenching temperature. In contrast, the strength of polycrystalline Al 2 O 3 with a grain size of 85 μm decreased gradually as the quenching temperature increased. The strength retained after thermal shock and the extent of crack propagation decrease with increasing initial strength and grain size, respectively, in Al 2 O 3 .