Abstract:An intermediate strength coarse grain γ-TiAl based alloy Ti-46Al-5Nb-1W(at.%) has been studied in this paper to assess the fatigue properties under different surface conditions both before and after thermal exposure. It has been found that although the majority of specimens were fatigued under condition of σmax <σ0.2 before thermal exposure, pre-yield crack initiation can still occur in coarse lamellar grains, especially in soft orientation. Improvement of the surface quality in the coarse grain alloy for better fatigue performance is found to be less effective in the coarse grain alloys than in the fine grain alloys. It has been also found that the embrittlement effects owing to oxygen release and ordered phase formation caused by thermal exposure were not particularly considerable. On the contrary, the fatigue performance was enhanced because of a long-term immersion of these specimens within warm air, within which residual stresses were releases and defects become less harmful. The degree to which the fatigue performance was enhanced is controlled by the surface quality. The coarse alloy exhibits a relatively low fatigue notch sensitivity factor, which is only 0.27 before exposure and 0.32 after exposure for a V-notch.