Microstructural statistics for low-cycle fatigue crack initiation in & alpha; plus & beta; 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 & alpha; and & beta; 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.

Automated summary

Twist grain boundaries (BTGB) are critical microstructures for fatigue crack initiation in titanium alloys. Different microstructures of Ti-Al-V based alloys were tested in low-cycle fatigue. Early cracking occurred at BTGB in all alloys and microstructures. The weak sensitivity to moderate differences in α and β stabilizers content and microstructural features was observed. Criteria for identifying crack initiation sites were defined. An automatic processing routine was applied to analyze the spatial distribution of BTGB susceptible to cracking. The low associated density implies that large microstructural regions must be considered to include microstructural configurations prone to crack nucleation, which may play a critical role in the high lifetime variability of Ti alloys.