Crack-tip plasticity mediated grain refinement and its resisting effect on the fatigue short crack growth

Fatigue short crack growth governed by the crack-tip plasticity dominates the fatigue life and strength of metallic materials or structural components. Here, for the first time, we discover a new mechanism of resisting fatigue short crack growth by grain refinement near the crack-tip driven by dynamic recrystallization in a Ni-based superalloy during high-cycle fatigue. The local cumulative plastic strain plays a determining role in the crack-tip grain refinement and concurrent dissolution of nanoprecipitation. Comprehensive microstructural analysis provides the evidence that the refined grains reduce the plastic micro-strain gradient in the vicinity of the crack-tip, which causes the crack blunting and deflection towards the interface of coarse-fine grains, hence decelerating the short crack growth. Although the grain refinement reduces the local stress threshold in the fine-grained areas (FGA), the dominant effects of FGA are identified to provide additional microstructural resistance to the propagation of short cracks.