Effect of Pt modification on oxidation properties and microstructure of NiAl coatings

NiAl coatings was fabricated on Hastelloy X substrate by atmospheric plasma spraying technique, and Pt was electroplated on NiAl coatings and vacuum diffusion was performed to prepare high performance Ni-Al-Pt coatings. High temperature oxidation tests were carried out on NiAl coatings and Pt modified coatings to observe and analyze the oxidation behavior, phase composition and microstructure of the two coatings. The oxidation kinetic curve results show that, compared with the NiAl coatings, the oxidation kinetics curve of the modified coating is closer to the parabola, and the weight gain in the late oxidation period is slower. XRD results show that the Pt modified coating can quickly form a continuous and dense Al₂O₃ film on the surface at the initial stage of oxidation. When it is oxidized to 90 h, the coating surface is still mainly α-Al₂O₃. The SEM results showed that after Pt modified coating oxidation for 30 min, a mixed structure of θ-Al₂O₃ and α-Al₂O₃ appeared on the surface of the coating. After the coating was oxidized for 35 h, the θ-Al₂O₃ basically transformed into continuous and dense α-Al₂O₃. When the coating is oxidized for 90 h, the coating surface is mainly composed of sheet-like α-Al₂O₃ and agglomerated NiO, the coating still has higher oxidation resistance.