Crack initiation mechanism of titanium alloy in very high cycle fatigue regime at 400℃ considering stress ratio effect

Abstract

Fatigue behavior of titanium alloy with various stress ratios was investigated at 400℃ in VHCF regime. Cracks initiation depends on the formation of facets and is related to the maximum shear stress. The formation of facets is induced by basal or prismatic slips with the high Schmid factor inside αp grains. The morphology of αp grains will affect the crack initiation. The high-density GNDs are found to be accumulated along with the basal or prismatic slips, then form subgrain boundaries (sub-GBs) inside αp grains. With the cyclic loading, the created sub-GBs will further form facets, thus initiating the microcracks.