Enhancing the Fatigue Behavior of PBF-LB In718 Through Surface Quality Optimization

Abstract

This study investigates the fatigue behaviour of heat-treated Inconel 718, fabricated using laser powder-bed fusion (PBF-LB) and subjected to surface treatment by electropolishing. Samples were heat-treated and mechanically polished to reduce surface roughness from 5.2 µm to 0.3 µm. Fatigue testing revealed that electropolishing significantly improved fatigue resistance, increasing the fatigue limit by over 90%, from 220 to 420 MPa. Despite these improvements, the fatigue limit reached only 0.58 times the theoretical ideal value of 1.6*HV, indicating a remaining susceptibility to surface defect-driven fatigue failure. Microstructural analysis via EBSD showed epitaxial grain growth in the build direction, with a homogenous face-centered cubic (FCC) phase, though traces of brittle Laves phase are likely present. Hardness testing indicated minor cyclic softening after higher stress amplitude, with values decreasing from 450 HV to 436 HV. Fracture consistently initiated at the surface, with cracks propagating through cleavage before transitioning to transgranular propagation. Overall, the findings demonstrate that while electropolishing enhances fatigue performance, further optimization is needed to mitigate surface-initiated failures in PBF-LB Inconel 718 components.