Microstructure, mechanical and corrosion performance of magnetron sputtered (Al0.5CoCrFeNi)Nx high-entropy alloy nitride films

High-entropy alloy nitride (HEAN) films of (Al0.5CoCrFeNi)Nx were deposited on 304 steel and silicon plates using reactive DC magnetron sputtering. The effect of nitrogen flow fraction (RN =0%, 6%, 13%, 23%, 40%) on the microstructure and performance of HEAN films was studied. The deposition rate showed a negative relationship with the nitrogen flow ratio. The N concentration raised with the increasing RN ratio, reaching a maximum value of 33 at% (RN =40%). The as-deposited Al0.5CoCrFeNi film presented an FCC + BCC dual phase structure. With the addition of nitrogen, the HEAN film transformed FCC + BCC structure to a composite structure composed of FCC nanocrystals and amorphous. All the HEAN films grew the smooth surface with nano-clusters. With increasing RN ratio, the average size of clusters decreased from 203 nm to 83 nm, resulting in a denser film. The HEAN films exhibited enhanced hardness, retaining relatively good plasticity. The hardness and elastic modulus reached a maximum value of 14.42 GPa and 212 GPa at RN = 23%, respectively. The HEAN films showed good adhesion with substrate and had no obvious cracks during scratching. Under 3.5 wt% NaCl solution, the increasing RN ratio contributed to the higher Ecorr and lower icorr for HEAN films, with excellent corrosion resistance (Ecorr=0.054 V, icorr=0.72 μA/cm2) at RN = 23%. The incorporation of N showed promising potential in improving the performance of AlCoCrFeNi alloy.