Fatigue crack growth behavior of laser powder bed fusion additive manufactured Ti-6Al-4V: Roles of post heat treatment and build orientation

•Fatigue crack growth rates were measured for laser powder bed fusion Ti-6Al-4V.•α′/α lath thickness main factor controlling fatigue crack growth rates and thresholds.•Roughness induced crack closure also contributed to fatigue thresholds.•Microstructure sensitive growth when cyclic plastic zone less than packet/colony size.•Non-orthogonal build orientation had negligible effect on fatigue crack growth. Effects of build orientation (0°, 45°, 90°) and post heat treatments (hot isostatic pressing 820 °C, 950 °C or annealing 1020 °C) on the fatigue crack growth rates (FCGRs) of Ti-6Al-4V fabricated by laser powder bed fusion were examined. Coarser α′/α lath thicknesses resulted in slower FCGRs and higher fatigue thresholds while texture and build orientation had little influence. Fatigue thresholds were defined by the ability to transfer slip from one α′/α lath to another, with a minor role of roughness induced crack closure. The transition away from microstructure sensitive FCG occurred where the packet/colony size equaled the cyclic plastic zone size.