Tailoring degradation resistance in SS316L-inconel 718 BMSS by deposition strategy: Microstructural, electrochemical, and high-temperature wear insights

To address the critical knowledge gap concerning the influence of thermal history on multi-material degradation, this novel investigation systematically correlates uni- and bi-directional wire arc additive manufacturing (WAAM) deposition strategies with the microstructural evolution, corrosion resistance, and high-temperature wear mechanisms of SS316L-Inconel 718 Bi-Metallic Structures (BMSs). The bi-directional BMS showed a refined microstructure with fine equiaxed grains and reduced elemental segregation, resulting in excellent corrosion resistance. Electrochemical testing confirmed these observations, showing a lower corrosion current density (Icorr = 128.706 nA) and higher polarization resistance (Rp = 4532 Ω) for the bi-directional BMS, compared to the uni-directional BMS, which displayed a higher corrosion current density (Icorr = 173.197 nA) and lower polarization resistance (Rp = 2496 Ω). In the hot corrosion experiments, the bi-directional BMS developed a more adherent and stable oxide scale, and mass variation and resistance to scale spallation and fluxing were reduced. However, wear testing at elevated temperatures revealed the existence of a strong wear trade-off, wherein in the case of the uni-directional BMS, the resulting total wear depth was about 95 µm, while in the case of the bi-directional BMS, substantially increased wear (around 280 µm) was observed. Microstructural analysis showed that the uni- and bi-directional BMS experienced mostly abrasive and mild oxidative wear and severe oxidative and adhesive wear, respectively, which induced oxide delamination and accelerated material loss. Ultimately, this study establishes actionable design guidelines for tailoring WAAM-fabricated BMSs to specific industrial applications.