Microstructures and mechanical properties of CoCrFeMnNiV_x high entropy alloy films

In the present work, CoCrFeMnNiV_x (x = 0, 0.07, 0.3, 0.7, 1.1) high entropy alloy films were fabricated by magnetron co-sputtering. For low contents of V, typical face-centered cubic (fcc) peaks were identified in X-ray diffraction patterns. With the increasing V content, the diffraction peaks became broadened and the formation of an amorphous phase was promoted. TEM observations showed abundant nanotwins in the films with low V contents and the transition from fcc to the amorphous structure with the increasing V content. Mechanical properties of the films were studied using nanoindentation and micro-pillar compression tests. The films exhibited a high hardness ranging from 6.8 to 8.7 GPa. The serrated flow associated with shear banding showed in the stress-strain curves for films with x ≥ 0.3. When x = 0.07, the excellent yield strength of 3.79 GPa and ultimate compressive strength of 4.93 GPa were achieved with little sacrifice in ductility. The presence of nanotwins contributed to the strain hardening effect.