Hardness and Young's modulus evolution of low-power plasma sprayed Inconel 625 coatings exposed to high temperatures

The use of renewable energy sources has been increasing in recent years as it aims to balance the production of fossil fuels by 2050. Among the various alternatives, concentrated solar power plants are considered the most feasible due to their capability of storing energy. Ongoing research is conducted to enhance the performance of third-generation plants by achieving higher temperatures. It makes necessary to explore new materials. This research is focused on concentrated solar power plants with central tower receivers, for which coatings used nowadays do not withstand the new requirements. For this reason, an alternative plasma sprayed Inconel 625 coating has been proposed. This study confidently presents an analysis of the high temperature exposure effects on the coating's mechanical properties at two temperatures, 520 and 800 °C. The study focuses on the Young's modulus and hardness, and the results demonstrate a significant improvement in these properties due to the formation of secondary phases. Coating hardness increased gradually from 4.12 GPa to 5.3 GPa during exposition at 520 °C. In contrast, the increment was attained quickly during the first 24 h exposure at 800 °C, reaching 4.5 GPa, and then maintained for all times studied. The microstructure was characterized using transmission electron microscopy, which identified the presence of carbides and intermetallic phases. The application of these coatings will significantly enhance the performance of solar receivers due to their superior properties compared to the currently available Pyromark coatings.