Oxidation Behavior of Ni-Based Oxide Dispersion-Strengthened Alloy Fabricated by Direct Energy Deposition at 1100 °C

Additive manufacturing (AM) produced Ni-based oxide dispersion-strengthened (ODS) alloy is promising for fabricating intrinsic structural parts under high-temperature operating condition, while little effort has been focused on the oxidation behavior of such alloys by AM. In this study, cyclic oxidation behavior and microstructure of additively manufactured Ni-based ODS alloy were evaluated up to 1100 °C for 2040 thermal cycles. The oxide layer and microstructure were characterized at various thermal cycles using scanning electron microscope (SEM), transmission electron microscope (TEM), and x-ray diffractometer (XRD), respectively. The results showed ultrafine Y-rich particles (<20 nm) in both as-printed and oxidized ODS coupons. In the early oxidation stages, continuous Al₂O₃ formed underneath oxide mixture of Cr₂O₃ and NiO with oxide spallation of Cr₂O₃ and NiO due to the thermal expansion mismatch at later oxidation stages. Uniform oxide dispersion of yttria contributed the stability of Al₂O₃ layer and thus preserved γ′ phase in the alloy substrate as well as fine grain structure by reducing elemental diffusion and blocking dislocation movement.