Effect of bias voltage on the growth of super-hard (AlCrTiVZr)N high-entropy alloy nitride films synthesized by high power impulse magnetron sputtering

The purpose of this paper is to explore the effect of bias voltage on plasma discharge characteristics, element concentration, microstructure, morphology, and mechanical properties of super-hard (AlCrTiVZr)N high-entropy alloy nitride (HEAN) films synthesized by high power impulse magnetron sputtering (HiPIMS). Results show that all HiPIMS-deposited (AlCrTiVZr)N films and the DCMS reference sample present a single NaCl-type FCC structure. Compared with DCMS, HiPIMS can produce a higher ionization fraction of the HEA target elements, thereby improving the structure and mechanical properties, while reducing the deposition rate. With increasing bias voltage in HiPIMS, the ion bombardment is continuously enhanced due to the increasing flux and energy of ionized particles reaching the films. The altered plasma environment splits the growth of (AlCrTiVZr)N films into two regions: The bias voltages of 0 V to −150 V offer a moderate ion bombardment effect, while further increasing bias voltage up to −200 V makes the ion bombardment effect excessive. It is observed that the (AlCrTiVZr)N films deposited at −150 V have a compact and featureless structure with preferred orientation of (1 1 1), the smallest grain size of 11.3 nm, a high residual compressive stress of −1.67GPa, thereby exhibiting the highest hardness of 48.3 GPa which attains the super-hard grade.