Passivity and breakdown mechanisms in laser powder bed fusion processed Ni-based Alloy 625: Influence of scan strategy

This study investigates the influence of scan strategy on the microstructure, electrochemical behaviour, and passive film stability of Ni-Cr-based Alloy 625 fabricated via Laser Powder Bed Fusion (L-PBF). Four distinct scan strategies of No Pattern 180, No Pattern, Stripes, and Chess were evaluated under identical processing parameters. While hardness and subgrain size remained largely unaffected, significant differences were observed in dislocation density, which strongly correlated with passive layer integrity. Electrochemical analyses revealed that higher dislocation densities, particularly in the No Pattern 180 strategy, led to lower current densities in both passive and breakdown regions, despite similar corrosion potentials and Volta-potential values across all strategies. Mott-Schottky analysis confirmed reduced defect densities in the passive oxide layer of high-dislocation samples, and potentiostatic testing under tensile loading showed fewer breakdown events compared to low-dislocation samples. The results emphasize the importance of scan strategy choice not only for mechanical properties, but also for optimising corrosion resistance in additively manufactured components.