Influence of microstructure on fatigue fracture characteristics of Al2O3
Kido Mitsuo; Okabe Takuji; Hasegawa Hitoshi
Abstract:In order to improve the fatigue fracture characteristics of Al2O3, the fracture behavior of two kinds of Al2O3, whose microstructure was controlled by sintering additives, was investigated under static and cyclic loading. It was observed that there was a significant difference in fracture behavior between the fine equiaxial grained Al2O3 (Material M) and the coarse columnar grained one (Material SC). The examination of fatigue lifetime showed that the fatigue strength of Material SC was higher than that of Material M, but simultaneously a significant decrease by cyclic loading. The crack propagation rate da/dt of Material M made no difference between in air and in water, but that of Material SC accelerated in water. According to the results of an energy dispersive X-ray spectroscopy (EDX) analysis on the fracture surface of Material SC, it was found that the sintering additive components of Si and Ca decreased markedly in SCG region under cyclic loading in water, and it was expected that hydration reaction on the glass phase of grain boundary occurred actively by water. Consequently, the reason why the fatigue strength of Material SC decreased under cyclic loading in water was considered to the significant promotion of stress corrosion cracking at the crack tip which is caused by marked decrease of particle bridging effect (i.e., increase in KItip). Key Words:Al2O3 ceramics, grain shape, grain boundary phase, particle bridging effect, stress corrosion cracking