Microstructural Evolution and Mechanical Properties in Dissimilar Laser Welding of Inconel 718 and PH 17-7

Abstract

This study investigates the microstructural evolution and mechanical performance of autogenous pulsed Nd: YAG laser-welded dissimilar joints between Inconel 718 and PH 17-7 precipitation-hardening stainless steel. Characterization via scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) revealed that rapid solidification kinetics promote a morphological transition from columnar and cellular to equiaxed dendritic structures in the fusion zone. Although interdendritic microsegregation of Nb and Mo drove the precipitation of brittle Laves phases, the extreme cooling rates of the pulsed laser restricted these phases to a discrete, discontinuous morphology rather than a continuous network. This microstructural suppression preserved a strong strength-ductility synergy, yielding an ultimate tensile strength of similar to 800 MPa and > 20% elongation. Fractography confirmed mixed-mode failure localized within the weld metal, characterized by microvoid coalescence at the discrete Laves interfaces. Microhardness mapping demonstrated a uniform profile, interrupted by a localized hardness surge at the PH 17-7 fusion boundary attributed to untempered lath martensite and delta-ferrite formation. This work establishes autogenous pulsed laser welding as an effective methodology for synthesizing robust Inconel 718/PH 17-7 dissimilar joints by tailoring interfacial phase morphologies and microsegregation.