The Influence of Process Parameters on the Low-Cycle Fatigue Properties of 316L Steel Parts Produced by Powder Bed Fusion

Abstract

In this paper, the influence of the additive manufacturing (AM), powder bed fusion (PBF) process parameters on the low-cycle fatigue (LCF) properties of 316L steel samples is shown. Based on the previous research, five parameter groups were selected. To make this analysis broader, research results of AM parts have been compared to the conventionally made counterparts. Such an approach allowed analyzing the manner different parameters affect the tensile and LCF behavior. The preliminary tests indicated that AM specimens are characterized by 65 pct of the total LCF strength in comparison to the conventionally made material. Further LCF tests indicated differences in the dissipated energy of some samples, which was visible in the hysteresis loops generated during testing in the total strain amplitude range from 0.30 to 0.45 pct. Based on the Morrow approach, it was possible to register an increased share of the plastic component during the fracture process in the Additive Manufacturing (AM) parts in the LCF tests with the total strain amplitude above 0.45 pct. The final microscopical investigation of parts’ fractures surfaces indicated the influence of the layered structure, and internal imperfections (such as unmelted powder particles and lack of fusion) of the as-built AM parts on the cracking process, which caused an increased number of multiplanar cracks and generation of the complex fracture morphology characterized by the layered structure of AM parts and share of imperfections—mostly porosity caused by unmelted powder particles which potentially was a base of secondary stage cracks.