A Continuum Mechanics Model for Crack Initiation at Grain-boundary Triple Points in High-temperature Deformation

Abstract

Typical intergranular cracks often initiate at the grain-boundary triple junction due to blocking of grain-boundary sliding in polycrystalline metallic materials. The theoretical discussion has not fully been made on the nucleation of grain-corner cracks at high temperature where the diffusional recovery occurs. In this study, a continuum mechanics model which incorporates the recovery effect by diffusion of atoms has been developed to explain the initiation of a wedge-type crack during high-temperature deformation. A good correlation is found between the result of calculation based on this model and the experimental result of creep rupture tests on austenite steels. It is found that there is a critical creep rate for wedge-type cracking. The model is also applied to the prediction of rupture life in creep. The direction of deformation periodically changes in fatigue. A discussion is then made on the initiation of a grain-boundary wedge-type crack in high-temperature fatigue where the deformation is path-dependent. The result of calculation based on the present model satisfactorily explains the experimental observations.