Synergistic effect of defects and microstructure on fatigue strength of additively manufactured precipitation hardening 17-4PH stainless steel

3D-printed components have potential applications in the fabrication of complex parts because of their advantages such as low wastage and cost-effectiveness. However, the durability of additively manufactured metallic components is not comparable to that of conventionally fabricated components, owing to the defects introduced during fabrication. The effect of inclusions on the fatigue strength of additively manufactured metallic components has been extensively investigated using the Murakami model. However, the interaction between the defects and the typical microstructure fabricated by additive manufacturing is yet to be revealed, although the unusual heating history during the fabrication process considerably affects the microstructure. This study aims to reveal the synergistic effect of defects and microstructure on the fatigue strength of additively manufactured precipitation-hardened 17-4PH stainless steel. Fatigue tests were conducted on additively manufactured precipitation-hardened 17-4PH stainless steel. The fatigue limit estimated using Murakami's model revealed that the summed area of the defects with the surrounding aggregation region could provide a better prediction. The carbide aggregates, produced via heating/cooling during Powder Bed Fusion (PBF), promoted microcrack propagation.