Microstructural, electrochemical, and high-temperature tribological insights into uni- and bi-directionally deposited SS316L–Inconel 718 bi-metallic structures

This study examines SS316L-Inconel 718 bi-metallic structures (BMSs) fabricated by wire arc additive manufacturing using uni- and bi-directional deposition strategies. The bi-directional BMS had a refined microstructure of fine equiaxed grains with less elemental segregation, which translated into better corrosion resistance. Electrochemical tests supported this: the bi-directional BMS showed a lower corrosion current density (Icorr = 128.706 nA) and a higher polarization resistance (Rp = 4532 Ω) than the uni-directional BMS (Icorr = 173.197 nA; Rp = 2496 Ω). In hot corrosion tests, the bi-directional BMS formed a more adherent, stable oxide scale, with smaller mass variation and better resistance to scale spallation and fluxing. High-temperature wear testing, however, revealed a clear trade-off. The uni-directional BMS reached a total wear depth of about 95 µm, whereas the bi-directional BMS wore far more, at around 280 µm. Microstructural analysis attributed the wear of the uni-directional BMS mainly to abrasion and mild oxidation, and that of the bi-directional BMS to severe oxidative and adhesive wear, causing oxide delamination and faster material loss. Deposition strategy therefore strongly affects performance: the bi-directional BMS suits corrosion-dominated environments, while the uni-directional BMS is preferable where high-temperature wear resistance is critical.