Fatigue crack growth behavior of L-PBF IN718: The influence of processing and post-processing conditions

This study investigated the fatigue crack growth (FCG) behavior of laser powder bed fused Inconel 718, addressing the effect of processing condition and heat treatment (HT). Processing conditions were altered by using either Ar or N 2 shielding gas, respectively using plasma and N 2 gas atomized powders, and by changing the laser energy input. Two HT schedules, both comprising stress relief, solution anneal, and age, were applied at two solution temperatures of 1065 °C and 970 °C. The resulting effects were evaluated by conducting FCG tests on compact tension specimens at R = 0.1. Detailed microstructural and fractographic analyses were performed. The microstructural length scale was affected by the degree of recrystallization in grains and the presence of secondary phase particles. These length scale variations resulted in different fracture surface roughness and affected FCG in the threshold region. Coarser microstructures exhibited stronger FCG resistance in the threshold region due to greater roughness induced crack closure. By incorporating the low angle misorientation in grains, an effective grain size measure was proposed to represent the length scale which correlated well with threshold stress intensity factor (SIF) range, ΔK th . Finally, due to the differences in microstructural related deformation mechanisms, the SIF range at the onset of unstable FCG exhibited the same dependence on microstructure as ΔK th .