Hierarchical nanostructure of CrCoNi film underlying its remarkable mechanical strength

A CrCoNi medium entropy alloy thin film is fabricated using magnetron sputtering. It exhibits a unique hierarchical nanostructure, featuring (1) a high density of planar defects (mostly stacking faults plus a small number of twin boundaries), (2) a dual-phase configuration (a mix of face-centred- cubic and hexagonal-close-packed), and (3) vertically aligned, textured nanocolumns, each with a width of similar to 100 nm. The hierarchical nanostructure in this study is original, especially for its dual phase combination, since the bulk CrCoNi medium entropy alloy generally presents a single phase face-centred-cubic structure. The CrCoNi film shows a hardness quadruple that of its facecentred- cubic structured counterpart. The formation and its role of the hierarchical nanostructure in producing such mechanical strength are discussed. Published by AIP Publishing.