Effects of Al content on the mechanical properties and corrosion behavior of Ni-Al coatings on 310S heat-resistant steel for CSP plants

Abstract: Material selection is crucial in concentrated solar power technology due to the significant impact of high-temperature corrosion. The Ni-Al coating on the steel is an effective approach to corrosion resistance. The alterations in microstructure, hardness, toughness, adhesion and corrosion inhibition properties of Ni-Al coatings were examined across varying Al concentrations after oxidation processes. Cracks appeared on the surface of coatings with pre-oxidation Al content ranging from 9.9 at.% to 23.3 at.%, and no continuous Al2O3 oxide film was formed. Notably, as the Al content rose to 41.0 at.%, and a continuous α-Al2O3 oxide film was successfully formed. It showed the best toughness and elastic modulus (181.6 GPa), and relatively high coating hardness (8.0 GPa). The corrosion results show that when the Al content is 41.0 at.%, the corrosion resistance of high-temperature molten chloride salt is the best. The oxidation layer formed by the pre-oxidation has a blocking effect on the migration of elements from the molten salt into the coatings. The results provide a route to fabricate Ni-Al coatings that possess integrated strength, toughness and corrosion resistance suitable for protective coating applications in concentrated solar power system.