Effect of Al Addition on the Microstructure and Mechanical Properties of Al_xCrCoNi Medium Entropy Alloys Prepared via the Magnetron Co-Sputtering

The effect of Al addition on the microstructural evolution, hardness, and deformation behavior of a nanostructured CrCoNi medium entropy alloy prepared by co-sputtering is studied in detail. With an increase in the Al content, the hardness of the alloy first increased (reaching 13.8 GPa) and then decreased (10.7 GPa), while the microstructure changed from nanocrystalline to a nanocrystalline/amorphous dual-phase structure. During plastic deformation, the appropriate amounts of the amorphous region and nanocrystalline mixed structure prevent shearing and grain rotation. Moreover, the amorphous shell also acts as a dislocation source that emitted and absorbed dislocations constantly and prevented grain boundary sliding to some extent. This work provides a novel approach to improve the mechanical properties of nanostructured medium entropy alloy films by controlling their composition and microstructure.