The hot corrosion behaviors of the aluminide coatings with different treatments on the surface of Ni-based alloy at high temperature were investigated. The aluminide coating modified by three different methods (pretreatment, Pt-modification and both), and then all the specimens were oxidized in lab air with NaCl salt at 1050 °C. During cycle oxidation, oxide scales on the surface of the aluminide coatings presented different morphologies, composition and corrosion behaviors. The oxide scale on the surface of the as-received aluminide coating without any treatments showed a poor dense and a bad adherence. However, the oxide scale on the surface of the aluminide coating with both Pt-modification and pre-oxidation exhibited the best hot corrosion resistance. In the NaCl corrosion environment, different treatments resulted in different corrosion mechanisms. Without any treatments, the oxide scale with NaCl at high temperature occurred internal active oxidation, which could promote the corrosion process and form the pores in the oxide scale. The internal active oxidation also presented in the oxide scale on the surface of the aluminide coating with pre-oxidation.

As a potential accident-tolerant fuel cladding material, we studied the method of preparing FeCoNiCrMo coatings on zircaloy-4 substrates by atmospheric plasma spraying (APS) technology to explore the high-temperature oxidation behavior of the FeCoNiCrMo coatings at 1100 °C in high-temperature steam. Various surface analysis techniques such as X-ray diffraction, electron probe microanalysis, and scanning electron microscopy were used to analyze the phase composition and microstructure of the oxidized products. The oxidation behavior of the FeCoNiCrMo coatings and the diffusion of the FeCoNiCrMo coatings to the zircaloy-4 substrates were analyzed. After oxidation at 1100 °C, a dense Cr2O3 oxide layer was formed on the coating’s surface, which grew from 1.5 to 3 μm after 15 to 60 min of oxidation, and the FeCoNiCrMo coatings and the substrates diffused simultaneously. The oxidation tests showed that the FeCoNiCrMo coatings prepared by APS can effectively delay the oxidation of zircaloy-4 substrates.

Temperature and atmosphere have a significant effect on the oxidation of MCrAlY (M = Ni, Co) bond coating. The initial growth behavior of the NiCrAlHf bond coat alloy was investigated at 1100 °C under different atmospheric conditions and using heating methods. A thick Al2O3 oxide layer and large HfO2 particles were observed, perhaps due to metastable oxide growth at low temperatures when using stepped heating. However, in air and water vapor atmospheres, the oxide scale was thinner and the HfO2 precipitates were smaller in stepped heating than in constant heating. The size and distribution of the HfO2 particles might have induced different microstructures, particularly voids within the oxide scale.

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