Thermomechanical Fatigue and Creep–Fatigue Interaction of Inconel 718 Additively Manufactured by Laser Beam Powder Bed Fusion

This study investigates the Ni-based superalloy Inconel 718 produced by laser beam powder bed fusion (PBF-LB) under thermomechanical fatigue (TMF) loading. Strain-controlled TMF tests under in-phase and out-of-phase conditions were conducted in the temperature range from 300°C to 650°C. To increase creep–fatigue interaction, tensile dwell times of 10 min at 650°C were introduced in some in-phase TMF tests. After hot isostatic pressing, solution annealing and age-hardening, the PBF-LB material recrystallized and exhibited finely dispersed γ″ precipitates, typical of Inconel 718. In this state, the material showed a cyclic
deformation behavior comparable to that of conventionally-rolled Inconel 718. In tests without dwell times, the TMF lifetimes of PBF-LB Inconel 718 reached almost those of conventionally-rolled Inconel 718. Introducing dwell times significantly reduced the TMF life of PBF-LB Inconel 718. The results suggest that this effect can be attributed to a lack of grain boundary precipitates, which may facilitate grain boundary sliding and promote intergranular crack propagation.