Effect of stress ratio on high cycle fatigue behavior of TNM‐TiAl alloy

In order to investigate the effect of stress ratio on room temperature high‐cycle fatigue life of Ti‐43.5Al‐4Nb‐1Mo‐0.1B alloy, high‐cycle fatigue life test of TNM‐TiAl alloy at stress ratio of −1, −0.5, 0.1, 0.5, 0.8, and 1 was performed on the universal testing machine. The fracture mechanism of TNM‐TiAl alloy under different stress ratios was determined by observation and analysis of microstructure and fracture surface by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and optical microscope (OM). The results show that fatigue life of TNM‐TiAl alloy with different stress ratios is mainly affected by the mean stress and stress amplitude. The fatigue life decreases with the increase of the stress amplitude and with the decrease of the mean stress. When the stress amplitude is constant, the higher the stress ratio is, the higher the mean stress in the loading process is, the lower the fatigue life is. The sensitivity of the stress amplitude of TNM‐TiAl alloy gradually increases with the increase of the stress ratio. The different cracking mechanism and fracture mechanisms at various stress ratio are revealed. Highlights Different stress ratios affected various fatigue fracture processes of TNM‐TiAl alloy. An equal life curve was obtained to reveal the effects of different stress ratios on TNM‐TiAl alloy. Various stress ratio affects length‐width ratio of the lamellar colonies, leading to various deformation behaviors.