Fatigue Behavior of Laser Powder Bed Fused GRX-810 Alloy: Effect of Post-Processing

This study examines the influence of post-processing operations, i.e., surface machining and hot isostatic pressing (HIP), on the fatigue behavior of newly developed, oxide dispersion strengthened GRX-810 alloy at room temperature. The GRX-810 specimens are manufactured via laser powder bed fusion additive manufacturing technology. The effects of individual and combined post-processing operations are investigated by comparing the micro-mechanisms affecting the fatigue behavior of un-machined specimens with machined ones in non-HIP and HIP conditions. Crystallographic facets are found at the crack initiation sites of both machined and unmachined specimens, which are due to operation of persistent slip bands. Surface defects (i.e., surface micro-notches) and volumetric defects promote the formation of persistent slip bands (PSBs), accelerate fatigue crack initiation, and reduce fatigue life. By removing and minimizing these defects, both machining and HIP improve fatigue resistance. In addition to its reducing effect on volumetric defects, HIP also improves fatigue lives by forming large populations of intragranular carbide particles which could impede PSBs and delay crack initiation. Finally, the combined operation of both machining and HIP results in in the best fatigue resistance.