High temperature fatigue behavior of a near-alpha titanium alloy

High-cycle and very-high-cycle fatigue at 450 °C in near-α titanium with bi-modal microstructure are investigated. Stress-life duality appears with one data group spanning from 105 to 107 and the other from 107 to 109 cycles, characterized by surface and subsurface cracking, respectively. Misfit strain induced by the high misorientation of a particular primary α-grain relative to its surroundings, termed as local texture, promotes the subsurface fatigue-crack initiation. Fatigue strength increases up to 100 MPa owing to cyclic pre-strain at 450 °C, but the duality remains. Strain hardening by activation of prismatic slip is responsible for the improved fatigue strength.