Microstructural statistics for low-cycle fatigue crack initiation in α+β titanium alloys: A microstructure based RVE assessment

(0001) twist grain boundaries (BTGB) have been identified as critical microstructure configurations regarding fatigue crack initiation in titanium alloys. In the presently reported study, Ti-Al-V based alloys with different microstructures were tested in the low-cycle fatigue regime. Early cracking occurred at BTGB for all investigated alloys and microstructures. Microstructural statistics collected at crack initiation sites revealed a weak sensitivity to moderate differences in α and β stabilizers content and microstructural features. Criteria for the identification of crack initiation sites were then defined using this dataset. An automatic processing routine was applied on large-scale electron back-scattered diffraction maps to analyze the spatial distribution of BTGB susceptible to cracking. The low associated density implies that large microstructural regions, i.e., typically > 1 mm2, must be considered to include microstructural configurations prone to crack nucleation. It is likely to play a critical role in the high lifetime variability of Ti alloys.