Tuning the Microstructure and Mechanical Properties of Cold Sprayed Equiatomic CoCrFeMnNi High-Entropy Alloy Coating Layer

Abstract

An equiatomic CoCrFeMnNi high entropy alloy (HEA) coating layer was prepared via a cold spray (CS) process. In order to control the microstructure and nano-indentation properties of the CS HEA, heat treatments were employed. CS HEA coating layer showed a heterogeneous microstructure where ultra-fine grains were formed at the particle interfaces, while coarse grains were formed inside the particles. Furthermore, deformation twins (DTs) were also formed inside the particles due to severe plastic deformation (SPD) in each particle generated during the CS deposition. For the 550 °C heat treatment (HT), fine Cr-rich precipitates were additionally formed at the grain boundary and particle boundary. By contrast, recrystallization occurred during 850 °C HT, while the size of the Cr-rich precipitate increased. The nano-indentation hardness of the CS HEA coating layer was 10.9 GPa, which was ~ 3 times higher than that of the conventional cast HEA. The superior hardness of the CS HEA might has been enabled due to the combination of the high dislocation density, DTs, and ultra-fine grains. Based on the results above, the strategy to control the microstructure and mechanical properties through HT of the equiatomic CoCrFeMnNi HEA coating layer prepared via the CS process has been discussed.