Oxidation behavior of porous NiAl prepared through reactive synthesis

Porous NiAl alloys were prepared by die-pressing Ni + Al powder mixtures and vacuum sintering. The porous NiAl has a porosity of 50% with permeability of 1.1 × 10³ m³ m^-2 kPa^-1 h^-1. Cyclic oxidation of porous NiAl alloys was tested in air at 400, 600, 800 and 1000 °C, respectively. The oxidation kinetic curves were determined by weight gains of samples under different cyclic conditions. Through characterizing the formation of the oxide layers formed on the external and internal surfaces, it was found that the porous NiAl alloys exhibit excellent isothermal and cyclical oxidation resistance. Only very small peak for oxide phase can be detected by XRD even when the sample was oxidized at 800 °C for 160 h. The pore structure remains stable due to the formation of very thin and incontinuous oxide films at 800 °C. The oxide scales consist primarily of α-Al₂O₃ at 1000 °C. The porous NiAl has provided a better oxidation resistance in the given environment compared to porous 316L stainless steel (316LSS), showing a promising alternative to the 316LSS in severe environment.