The role of δ phase for fatigue crack propagation behavior in a Ni base superalloy at room temperature

The fatigue crack propagation behavior of a Ni base superalloy at room temperature with various volume fractions of δ phase was investigated. The result shows that fatigue crack growth rate of the alloy increases as δ phase volume fraction increases, while both the fatigue crack propagation resistance and the strength of the alloy decrease. The characteristic of δ phase on crack propagation behavior is depended on the dislocations slipping blocked by granular δ phase with low length-diameter radio. On the other hand, dislocations easily piled up around long needle-like δ phase which leads to stress concentration. This stress concentration causes δ phase debonding from the matrix and helps the crack easy propagates along long needle-like δ phase surrounded by precipitates free zone (PFZ).