Extreme-temperature oxidation behavior of nickel-based superalloys up to 1345 °C and the magnetic properties of their oxide layers

• Extreme-temperature oxidation and magnetism of Ni-based superalloys are studied. • At 1345 °C, the inner oxide is a thickened zone with dispersed oxides. • Ta/W oxides form near (Ni,Co) spinels, promoting micropores and interfacial cracks. • Oxidation at 1345 °C induces room-temperature ferromagnetism from Ni 0 -rich regions. The high-temperature oxidation behavior of DD6 and DD9 alloys at 1050, 1200, and 1345 °C for 5 h, together with the magnetic properties of the resulting oxide layers, was thoroughly investigated. At 1050 and 1200 °C, both alloys exhibit a distinct trilayer structure consisting of an outer (Ni,Co)O layer, a complex-oxide intermediate layer and a continuous inner Al 2 O 3 layer. At 1345 °C, catastrophic oxidation occurs, but the oxide layer still shows a nominal trilayer configuration, in which the inner Al 2 O 3 layer is replaced by a thickened region of dispersed complex oxides with cracks and voids. Unlike the paramagnetic behavior at 1050 and 1200 °C, oxidation at 1345 °C leads to room-temperature ferromagnetic behavior, arising primarily from regions with a very high Ni concentration in the oxide layer where metallic Ni 0 is detected, with possible minor contributions from Ni/Co-containing magnetic oxides, porous (Ni,Co)O, and oxygen-vacancy-related defects. Overall, these findings indicate that oxide-layer magnetism could potentially be exploited for nondestructive evaluation and may provide useful insights for the design of magnetic materials.