Stable nanocrystalline high-entropy alloy coatings deposited by cold-spraying: Indentation deformation behavior evaluated by nanoindentation and atomic force microscopy

The leading edges of structural components such as compressors and turbine blades operating in extreme environments undergo extensive erosive and abrasive wear from impinging solid erodents like abrasive sand particles. Although traditional coatings are extensively applied on the surfaces of such components for protection and to mitigate degradation, these coatings may not always withstand the impact of solid erodents. Here, newly developed lightweight, stable nanocrystalline high-entropy alloy (NC-HEA) coatings were deposited onto an A36 steel substrate using a cold-spray additive manufacturing method, while nanoindentation technique coupled with atomic force microscopy was used to assess their nanomechanical response. Despite being 25 % lighter, NC-HEA coatings exhibit nearly four times the hardness of the steel substrate. Furthermore, the deposited HEA coatings subjected to heat treatment show notable hardness and elastic moduli enhancement. This demonstrates the simultaneous stability of the NC-HEAs against grain growth even while hardness increases. Altogether, we investigate the stability of the NC-HEA coatings and elucidate the operational strengthening mechanisms that contribute to the increased hardness values.