Thermal Fatigue Behavior of Alumina Ceramics by Water Quenching Method.

Abstract

Thermal fatigue behavior of four kinds of alumina ceramics, having different fracture toughness/ bending strength ratio, was investigated. After the testpieces pre-cracked by Knoop indentation were heated in a constant temperature, they were quenched in water, and their propagated crack lengths were measured. Since the heat transmission condition varied from natural convection to nucleant boiling in the range of this experimental temperature, the heat transfer coefficient was corrected before illustrating the (KImax/KIC)-V curve. The thermal fatigue behavior of each alumina ceramics was discussed quantitatively based on the fatigue parameters n and A, which were derived from the crack propagation rate equation V=A(KI/KIC)n. For the alumina ceramics in which transgranular fracture was mainly observed, the n values were hardly different but logA values decreased with increasing particle size. This indicated that the crack propagation rate became low. For those in which more larger particles or pores were observed, the logA values and the crack propagation rate were quite different. Those different behaviors on thermal fatigue may be explained by different propagation mechanisms at crack tips. The control of microstructure is important for thermally used ceramics, because the microstructure determines the crack propagation pass.