112̄0〉-orientation-dependent crack initiation in a titanium alloy under dwell fatigue

The crystal orientation of titanium alloys significantly influences the nucleation of dwell fatigue cracks, which deteriorate the service life of aero-engine components. Although soft/hard orientation combinations, depending on the orientation relationship between c -axes and loading directions, are widely recognized as favored crack nucleation sites, the effect of 〈112̄0〉 orientations of soft grains on the cracking of adjacent hard grains is also crucial, and experimental investigation is desired. Here, we report that soft grains with a “rotation angle”, corresponding to the 〈112̄0〉 orientation, between 15° and 30° are more prone to induce cracking in hard grains, for the reason that prismatic dislocation slips in these soft grains exert a higher stress normal to the basal plane of adjacent hard grains. In contrast, soft grains with a “rotation angle” between 0° and 15° rarely cause cracking in hard grains. A stress component parameter is proposed according to the “rotation angle”, which can accurately predict the nucleation of fatigue cracks in titanium alloys. The findings shed light on the quantitative analysis of crack nucleation and the prediction of fatigue performance.