Influence of the position and size of various deterministic defects on the high cycle fatigue resistance of a 316L steel manufactured by laser powder bed fusion

Optimized 316L steel samples were manufactured using laser powder bed fusion and tested in high cycle fatigue at R = 0.1. They showed microstructural crack initiation and outstanding fatigue properties. Additional fatigue testings were then carried out on samples containing deterministic defects of various sizes and positions. All results summarized in a Kitagawa-Takahashi diagram show that the critical defect size is around 20 mu m for surface defects and reach 380 mu m for internal pores. Fracture surface analysis revealed that the large size gap between surface and internal fatigue crack initiation could be linked to the local gaseous environment in the pores.