Microstructure based cracking behavior and life assessment of titanium alloy under very-high-cycle fatigue with elevated temperatures

•Grain-related facetted cracking along 45° is a typical interior failure mode.•Threshold value and transition size decrease with increasing of temperature.•Interior facet-IMZ-fisheye failure mechanism is proposed.•A temperature-based FIP life prediction approach is developed. High and very high cycle fatigue tests for TC11 titanium alloy were performed to clarify the interior cracking behavior under fully reversed and pulsating tension at three service temperatures. According to the estimation of threshold values for small and long crack growth, the fatigue design curves are established. Combined with electron backscatter diffraction and fracture mechanics analysis, the interior cracking is closely related to grain strength and size, and microtexture. The interior failure is attributed to the facet formation caused by larger αp phase fracture. Based on FIP model, a temperature-based method is proposed to predict the crack nucleation life.