Fatigue failure by creep cavity growth at high temperatures

Abstract

The relative importance is assessed of fatigue failure by grain boundary cavity growth and coalescence. Cavity growth is calculated by considering the instantaneous values of stress and strain rate during a fatigue cycle. The fatigue life due to cavity growth is then compared with that due to crack propagation. It is predicted that cavity growth becomes important when long tensile holds at constant strain are incorporated in the fatigue cycle. Decreasing the strain rate decreases the relative importance of cavity growth. A mechanism map is presented which shows the operative regions for the fracture mechanisms. This enables fatigue data obtained at fast strain rates with short hold times to be extrapolated to slower strain rates and longer hold times provided there is no change in fracture mechanism.