Impact of oxygen-doping on heterostructure evolution and mechanical properties of FeCrNi alloy fabricated via laser directed energy deposition

Abstract

Oxygen has garnered significant attention for its ability to regulate phase transformations in alloys, thereby markedly enhancing their mechanical properties. This study focuses on the structural evolution and mechanical property modulation of FeCrNi alloys. Through oxide doping, single-layer FeCrNi (MEA), Ti₃Fe₃₃Cr₃₂Ni₃₂ (MEA-T) and Ti₃Fe₃₁Cr₃₀Ni₃₀O₆ (MEA-O) alloys were successfully fabricated by laser directed energy deposition. A combination of experimental methods and molecular dynamics simulations was employed to evaluate alloy performance and analyze deformation mechanisms. The results demonstrate partial melting of TiO₂ in MEA-O, with in-situ synthesized oxide heterostructures significantly increasing geometrically necessary dislocation density, confirming their critical role in promoting dislocation nucleation and strengthening the coating. Furthermore, semi-coherent structures formed between distinct oxides coordinate cross-interface dislocation slip, reducing stress concentration and brittle fracture risk, thereby enhancing load transfer efficiency. Compared to oxygen-free alloys, MEA-O synergistically improves elastic modulus due to nanoscale precipitates and high-density semi-coherent interfaces at phase boundaries that restrict dislocation motion. Additionally, MEA-O coatings exhibit significantly enhanced wear resistance and friction reduction performance under both ambient and elevated temperatures. Conversely, Ti-doped MEA-T alloy shows performance degradation during high-temperature friction tests. Molecular dynamics simulations reveal titanium doping increases the γ_usf value of MEA-T, facilitating dislocation slip during deformation. However, precipitation strengthening causes non-uniform distribution of strengthening phases and grain refinement. These strengthening phases and grain boundaries collectively hinder dislocation propagation, increasing stacking fault roughness and stress concentration, consequently degrading the high-temperature wear resistance of the coating.