Fatigue Properties of Ti-6Al-4V Alloy in Vacuum at Cryogenic Temperature

Abstract

In the present study, the fatigue properties of a 720 ° C/1h annealed Ti‐6Al‐4V alloy have been evaluated under the following conditions: in air at room temperature (RT), in vacuum at RT and in vacuum at cryogenic temperature, using a vacuum‐cryogenic electric fatigue machine. Fracture surfaces of the fatigued specimens and the microstructures in regions adjacent to fracture surface were examined by scanning election microscopy (SEM) and transmission election microscopy (TEM). The results showed that the fatigue strength of Ti‐6Al‐4V alloy decreased in the order of the following conditions: in vacuum at cryogenic temperature, in vacuum at RT and in air at RT. The longest fatigue life of the alloy could be obtained in vacuum at cryogenic temperature, while the shortest one in air at room temperature. Crack initiation site, crack prorogation path and rapid failure zone were distinguishable on the fractured surfaces of the specimens fatigued either in air or in vacuum at room and cryogenic temperatures. Generally, the fatigue cracks initiated at the surface of the specimens and many dimples could be found in the rapid failure zone. Dislocation slip was found to be the main deformation mode under the three testing conditions.