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Abstract
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Understanding how defect morphology strongly influences both microstructural evolution and corrosion behavior is essential for establishing a process–defect–property linkage in laser powder bed fusion (L-PBF) 17-4PH stainless steel. In this study, the influence of process parameters and volumetric energy density (VED) on defect morphology, δ-ferrite formation, hardness, and electrochemical behavior was systematically investigated. Quantitative image analysis revealed that lack-of-fusion defects dominate at low VED, while keyhole defects appear at high VED due to excessive energy input. X-ray diffraction and electron backscatter diffraction indicate a BCC-dominant microstructure, which is consistent with substantial retention of δ-ferrite as the primary solidification phase, attributed to the rapid cooling and high thermal gradient inherent to L-PBF. Electrochemical impedance spectroscopy and potentiodynamic polarization tests showed that defect morphology critically affects charge-transfer resistance (Rct) and corrosion current density (icorr), suggesting that interconnected lack-of-fusion pores may provide preferential corrosion initiation sites. The optimized process window (65–75 J mm−3) achieved a dense δ-ferrite microstructure with superior hardness (294 HV) and enhanced corrosion resistance. These findings elucidate the direct correlation between process parameters, defect morphology, and corrosion behavior, providing practical guidance for optimizing L-PBF 17-4PH stainless steel components for service in corrosive environments.
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