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

Effects of build orientation (0 degrees, 45 degrees, 90 degrees) and post heat treatments (hot isostatic pressing 820 degrees C, 950 degrees C or annealing 1020 degrees C) on the fatigue crack growth rates (FCGRs) of Ti-6Al-4V fabricated by laser powder bed fusion were examined. Coarser alpha '/alpha 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 alpha '/alpha 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.

Automated summary

The study found that the fatigue crack growth rates of Ti-6Al-4V material are influenced by build orientation and post heat treatments, while texture and build orientation have minimal impact on slow crack growth rates and fatigue thresholds. The definition of fatigue thresholds lies in the ability to transfer slip from one α' / α laths to another, with some effect of crack closure induced by roughness. The transition away from microstructure sensitive fatigue crack growth occurred when the packet/colony size equaled the cyclic plastic zone size.