High-Temperature Deformation Behavior of Cold-Sprayed High-Entropy Alloy Coatings Revealed by In-Situ Nanoindentation

Cold spray has emerged as a promising solid-state deposition technique for producing dense coatings while avoiding the oxidation and phase decomposition associated with high-temperature thermal spray processes. When combined with high-entropy alloys (HEAs), cold spray offers new opportunities for developing mechanically robust and thermally stable coatings for extreme environments. In this study, HEA coatings were fabricated using cold spray deposition and their thermo-mechanical response was investigated using in-situ high-temperature nanoindentation. Microstructural characterization reveals a heterogeneous coating structure consisting of severely deformed particles, inter-particle interfaces, and localized phase evolution during thermal exposure. Temperature-dependent nanoindentation measurements show distinct regimes of thermal softening and strengthening, associated with recovery processes, phase transformation, and the formation of intermetallic phases within the coating. These mechanisms lead to significant changes in hardness and elastic modulus during thermal exposure. The results demonstrate how the combined effects of severe plastic deformation during deposition and subsequent thermal evolution govern the mechanical stability of cold-sprayed HEA coatings. This work highlights the importance of coupling advanced in-situ mechanical testing with microstructural characterization to understand deformation mechanisms in emerging coating systems.