Microstructure and mechanical properties of high entropy alloy nitride coatings deposited via direct current cathodic vacuum arc deposition

Six different high entropy alloy nitride coating systems namely (AlCrTaTiZr)N, (AlCrMoTaTiZr)N, (AlCrNbSiTiV)N, (HfNbTiVZr)N, (CrHfTiVZr)N and (HfNbTaTiVZr)N were deposited via direct current (DC) cathodic vacuum arc deposition from powder metallurgically produced (PM) targets. The coating compositions, microstructures and mechanical properties were subsequently analyzed in dependence of the substrate bias voltage (0-300 V) and the working pressure (0.5-5 Pa). All deposited coatings displayed a single-phase fcc microstructure. Further, the coatings could be split into two groups regarding their mechanical properties as well as their microstructure. For the coatings containing Al, the indentation hardness reached up to 35.5 GPa. For those coatings a pronounced grain refinement effect at increasing substrate bias voltages was observed. The solely refractory coatings on the other hand displayed a lower indentation hardness up to 32.7 GPa. They remained columnar throughout the whole studied bias voltage range. The working pressure analyzed on the two exemplary coatings (AlCrTaTiZr)N and (HfNbTaTiVZr)N did not greatly influence the mechanical properties, yet a change in microstructure towards columnar grain growth was observed for (AlCrTaTiZr)N.