Cryogenic Mechanical Properties of Ti-6Al-4V Alloys with Three Levels of Oxygen Content

Abstract

Tensile, fracture toughness, and high cycle fatigue tests were done at 293, 77, and 4 K for Ti-6Al-4V alloys with three levels of oxygen content. The alloys were investigated both in as-forged condition and in the rolled condition. Rolling did not necessarily make α grains finer, but changed the shape from plate-like to globular. Strengths depended mainly on the oxygen content; the lower content produced lower strengths. The alloy with lowest oxygen content showed the best ductility at 4 K. The fracture toughness at cryogenic temperature was also enhanced by the reduction of oxygen. In the lowest oxygen alloy, no drop in the fracture toughness was observed between 293 and 4 K. Fatigue properties were influenced by the forming process. The rolled materials had higher fatigue strength than the forged materials. The difference was accentuated at 4 K. This is believed to be due to the difference in the morphology of α grains. The lowest oxygen alloy showed the highest fatigue strength at 4 K.