Unveiling oxidation mechanism and microstructural evolution of L-DED Ni₃Al-based intermetallic alloy at 800 ​°C via multi-scale characterization and thermodynamic calculations

This study investigates the oxidation behavior and microstructural evolution of a Ni₃Al-based IC-221 ​M alloy fabricated via laser-directed energy deposition (L-DED) during exposure at 800 ​°C in air. The alloy exhibits parabolic oxidation kinetics and significantly outperforms commercial 32Cr3Mo1V steel in oxidation resistance. Multiscale characterization reveals that a continuous Al₂O₃–Cr₂O₃ inner scale and a discontinuous outer NiO layer form rapidly, effectively inhibiting oxygen ingress. Initially, Zr-rich phases transform to ZrO₂, providing a temporary diffusion barrier, but later develop cracks that accelerate oxidation. Long-term exposure leads to refinement of the L1₂ cellular structures and the precipitation of coherent (Ni, Cr)₃(Cr, Al) phases in the face-centered cubic (FCC) matrix, which contribute to increased hardness. Thermodynamic modeling and diffusion simulations confirm the roles of phase composition and cation transport in scale formation. These insights advance the understanding of oxidation mechanisms in L-DED intermetallics and support the development of oxidation-resistant alloys for high-temperature applications.