Effects of substrate bias on the structure and mechanical properties of (Al1.5CrNb0.5Si0.5Ti)Nx coatings

Abstract (Al1.5CrNb0.5Si0.5Ti)Nx high-entropy nitride coatings were designed and investigated in this study. Nitride coatings are deposited under a sufficient amount of nitrogen at 415 °C on Si by direct current magnetron reactive sputtering from a non-equimolar Al1.5CrNb0.5Si0.5Ti high-entropy alloy target. The effects of substrate bias (Vs) on film structure and mechanical properties are studied. All these coatings have a single NaCl-type face-centered cubic structure and nearly stoichiometric ratio of (Al1.5CrNb0.5Si0.5Ti)50 N50. A distinct refinement of microstructure of the films is observed when Vs varies from 0 V to − 100 V. Typical columnar structure transits into a dense and featureless structure and grain size decreases from 70 nm to 5 nm. Similar refinement remains at larger bias(− 150 or − 200 V). At the same time, the residual compressive stress increases from near zero to − 3.9 GPa at − 150 V and then decreases to − 3.2 GPa at − 200 V. The hardness increases from 12 GPa at 0 V, peaks at 36 GPa at − 100 V, and then decreases to 26 GPa at − 200 V. The structural evolution strengthening mechanism are discussed and compared with equimolar high-entropy nitrides.