Modifications of microstructures and mechanical properties of CoCrFeMnNi high entropy alloy films by adding Ti element

Abstract

The phase evolution, microstructure and mechanical properties of CoCrFeMnNiTix (x = 0, 0.2, 0.4, 0.6, and 0.8 in molar ratio, denoted as Tix hereafter) high entropy alloy films (HEAFs) were studied in this work. The films were prepared by co-sputtering of CoCrFeMnNi alloy and Ti targets. Abundant nanotwins were observed in the Ti0 and Ti0.2 films and the crystalline structures of both films were identified to be a single FCC phase. In Ti0.4 and Ti0.6, the matrix exhibited an amorphous structure, and both the nanocrystalline grains and nanotwins were embedded in the amorphous matrix. With further addition of Ti, the Ti0.8 film transformed to an amorphous structure. As a result, there was a phase transition from a single FCC to an amorphous structure with the increasing Ti content. Furthermore, nanoindentation tests showed that the hardness of the films increased from 6.62 GPa in Ti0 to 8.99 GPa in Ti0.8. Micropillar compression tests showed that the fracture strain decreased from >19.42% (no fracture) to 7.78% with the increasing Ti content. The best mechanical properties in compression were observed in Ti0.4, and the compressive yield and fracture strengths were 2.82 and 4.44 GPa, respectively, with the fracture strain of 12.4%, which was achieved by a balanced amount of nanocrystalline grains in the amorphous matrix.