Ultra-strong nanostructured Co-Ni-V medium entropy alloy thin film designed by interface strengthening

Abstract In this work, amorphous and nanocrystalline Co-Ni-V medium entropy alloy (MEA) thin films were prepared by magnetron sputtering via tuning substrate temperature. The nanocrystalline Co-Ni-V thin film deposited at 673 K containing ultrahigh-density stacking faults was found to be more superior to amorphous Co-Ni-V thin film deposited at 473 K and some other face-centered cubic (fcc)-structured materials by exhibiting higher hardness of ∼9.5 GPa and yield strength of ∼4.0 GPa. The strengthening mainly stems from various defects including nanograin boundaries and high-density stacking faults, which were found to possibly serve as strong impediments to dislocation motion. Moreover, the weak boundaries between adjacent nanocolumns with relatively weak bonding is eliminated with increasing substrate temperature, which also contributes to the enhanced strength/hardness for the nanocrystalline Co-Ni-V film as compared with amorphous Co-Ni-V film. The prepared ultra-strong nanostructured Co-Ni-V MEA thin film exhibits high yield strength and micro-compressive plasticity (over 50%), suggestive of the relatively strong material among some reported fcc-structured metals and alloys. These results on nanostructured Co-Ni-V MEA thin film demonstrate that besides refining grain, interface strengthening, i.e., improving nanocolumn interface bonding via substrate temperature and introducing high-density stacking faults via rapid cooling of vapor deposition, could be considered when designing high strength alloy thin films for potential micro-electron-mechanical system applications.