Influence of stress-relief annealing temperature on impact toughness and fracture behavior of ti80 alloy

Abstract

Stress-relief annealing is a critical step in the engineering application of Ti80 alloy, but the effect of its temperature on impact toughness remains unclear. In this work, the Ti80 alloy was first solution treated at 970 °C for 1 h and air cooled, then subjected to stress-relief annealing at 530 °C–620 °C. The microstructure, impact toughness, and crack initiation/propagation behaviors were systematically characterized. Results show that with increasing annealing temperature, the αt needles in βtrans coarsen from 19.95 nm at 530 °C to 62.71 nm at 620 °C, while the dislocation density and subgrains in αp decrease. Thus, the hardness of both phases drops, while βtrans remains the softer phase. Impact toughness drops sharply from 50 J at 530 °C to 24 J at 620 °C. Fracture analysis shows that higher annealing temperature reduces plastic deformation in the initiation zone, shrinks the shear lip, and straightens the crack path. Mechanistic analysis reveals that microvoids preferentially nucleate inside βtrans and at αp/βtrans interfaces. The decrease in impact toughness results from the combined effects of a lower crack initiation threshold due to softening of βtrans and a weaker crack propagation resistance due to coarsening of αt.