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• Failure mechanism of titanium alloy is identified under multiaxial loading in the VHCF. • A pragmatic equivalent method for multiaxial to uniaxial load is proposed. • A multiaxial fatigue life prediction method based on uniaxial S-N curve is proposed. Fatigue failure mechanism of Ti60 titanium alloy under tension–torsion multiaxial loading in the very high cycle regime was studied first, and the results showed that the shear/axial stress ratio directly affects the failure mechanism. When the shear/axial stress ratio is relatively small, cracks tend to originate from the subsurface in single-point initiation mode, and the larger the shear/axial stress ratio, the more cracks tend to originate from the surface in multi-point initiation mode. Then, a pragmatic equivalent method for multiaxial to uniaxial load based on the law of shear/axial stress ratio on fatigue strength was proposed. Based on this method and uniaxial S - N curve, the fatigue lives of Ti60 specimens under shear/axial stress ratios of 1.37, 1.95, and 3.53 was predicted, and the experimental results showed that the prediction error is basically within a factor of 3. [ABSTRACT FROM AUTHOR]

• Crack initiation on the oversized facet formed by α p phase cluster cleavage is found. • The size of oversized facet can be predicted by the value of stress intensity factor range. • A simplified model is proposed to describe the microstructure short crack propagation. • A full-life prediction model based on crack propagation is proposed in VHCF regime. • A deterministic life prediction model considering the effect of temperature is proposed. The very high cycle fatigue crack initiation mechanism of Ti60 titanium alloy at different temperatures was studied. The results showed that the initiation of cracks occurred on oversized facets in the subsurface. Based on this crack initiation mechanism, a full-life prediction model based on crack propagation at room temperature was first proposed, and then a very high cycle fatigue life prediction model considering temperature was proposed based on the degradation law of tensile strength at different temperatures. The experimental and predicted life results of Ti60 specimen at room temperature with 300 °C and 500 °C showed that the proposed method can effectively predict the very high cycle fatigue life, and the error is within a factor of 3. [ABSTRACT FROM AUTHOR]