Combinatorial mapping of high-temperature oxidation in SS316L–IN718 dissimilar alloys printed by laser-directed energy deposition

Functionally graded materials (FGMs) enable the investigation of oxidation behavior across variable compositions, allowing efficient evaluation of how gradual changes in alloy content influence high-temperature performance. In this study, stainless steel 316 L (SS316L) and Inconel 718 (IN718) were combined to produce both a nine-layer gradient FGM and a bimetallic sample via laser-directed energy deposition (LDED). After prolonged high-temperature exposure to 500 h at 850 °C in air, the effects of composition and interface design on oxidation resistance were systematically examined using localized analysis of oxide scale formation and microstructural evolution. A clear improvement in oxidation resistance and oxide adhesion was observed above a threshold of 30 wt.% IN718 in the FGM with gradient composition. At the same time, the abrupt transition in bimetallic print did not result in severe spallation due to interdiffusion at the interface. The results further reveal that an intermediate IN718 region (10–20 wt.%) is prone to solidification cracks that promote internal oxidation, and that, in the IN718-rich areas (70–100 wt.%), microhardness decreases after oxidation due to the dissolution of strengthening phases (γ'/γ'') and grain coarsening. This combinatorial and composition-sensitive approach, utilizing FGMs, offers valuable new insights for designing oxidation-resistant materials for high-temperature applications.