The initiation of surface cracks in single-crystal superalloy components exposed to an oxidizing environmental under thermomechanical loading condi-tions is known to be linked to the presence of internal 10-20 μm-diameter casting defects (i.e. porosities), and to the localization of inelastic strain. In this work, the effects of oxidation on both the local degradation of the superalloy microstructure and the initiation of surface cracks from such defects is investi-gated. The approach relies on a rate-dependent crystallographic theory to describe the viscoplastic behaviour of the single crystal, and on a coupled oxidation-deformation framework to incorporate explicitly the effects of micro-structural degradation due to oxidation. Predictions of the formation of surface cracks under constant far-field loading, linked to the nucleation and coalescence of microcracks from internal porosities, are obtained from a recently proposed mechanistic anisotropic void growth model. Coupled oxidation-deformation finite-element analyses in compact tension fracture specimens show that environmental effects reduce the time to crack initiation from blunt notches owing to an increase in the accumulated inelastic deformation in the vicinity of the porosities.
展开▼
