Ongoing developments in machining and tooling towards higher speeds and temperatures call for new coatings suitable for these extreme conditions to protect tools from severe tribological damages and prolong their lifetime. By transferring basic concepts of high entropy alloys towards nitride coatings, HEA-based ceramics could enable better mechanical properties, wear resistance and thermal stabilities.

In this contribution results on selected purely refractory HEA nitride coatings as well as coatings containing non-refractory elements such as Al or Si will be presented. The coatings were deposited via DC vacuum arc deposition from compound targets. The coating microstructures in dependence of the substrate bias and chamber pressure were analyzed via SEM, TEM and XRD. Additionally, coating toughness was estimated via nanoindentation and scratch testing. High hardness up to 37 GPa was observed especially in the case of coatings containing non-refractory elements. The high hardness can be attributed to a strong grain refinement effect in those coatings deposited at elevated substrate bias.

To further improve the mechanical properties two design strategies will be discussed. Doping of the coatings with additional weak and strong nitride forming elements as well as multilayer approaches will be explored on selected examples and changes in microstructure and mechanical properties will be presented. For alternating (AlCrNbSiTiV)N/TiN multilayers an improvement in hardness from 33 towards up to 40 GPa was observed.

From the current point of view nanostructured HEA nitride coatings are a promising group of materials for wear applications under severe conditions.