Damage mechanism study of TC17 titanium alloy during high-cycle fatigue crack initiation and propagation

This paper investigated the fatigue damage mechanisms during crack initiation and propagation by analyzing the macroscopic and microscopic characteristics of the fracture and microstructural changes in TC17 titanium alloy after high-cycle fatigue testing. The results showed that the surface fracture of the netted basket-weave structure was rougher, with more significant fluctuations. Cleavage planes formed by basal slip and prismatic slip in the crack source zone existed. The fatigue crack initiating was related to the formation of these cleavage planes. The variation in the spacing of fatigue striations, within the crack propagation zone, reflected the crack propagation rate. Based on the Paris formula, it was found that the crack initiation life of high-cycle fatigue accounts for more than 85 % of the total fatigue life. It was observed that microvoids and cracks were easily formed in the coarse lamellar α phase with a large area of dislocations pile-up at the α/β phase boundaries, which indicated that fatigue crack propagation was related to the formation of microvoids and cracks in the coarse α phase. These findings reveal the formation mechanism of fatigue damage in TC17 titanium alloy and provide a new theoretical basis for fatigue life prediction and material design of titanium alloy.