Properties of Metal, Nitride, Oxide, and Carbide Coatings Produced from High-Entropy Alloys

Abstract

The introduction of high-entropy alloys, notable for their increased hardness and thermal stability, gave impetus to the study of their properties in coatings. High-entropy metal coatings are characterized by high hardness, ranging from 7 to 19 GPa. The general laws governing the influence of various parameters on the mechanical properties of high-entropy metal coatings were analyzed. Single-layer metal, nitride, oxide, and carbide coatings and multilayer nitride coatings from high-entropy alloys produced by different deposition techniques were examined. The phase composition, structure, hardness, elastic modulus, and friction coefficient of the coatings were determined. The mechanical properties of high-entropy coatings, along with those of cast alloys, depend on the lattice parameter. With increase in the lattice parameter in bcc metal coatings, the elastic modulus and hardness decrease. The increased hardness of vacuum high-entropy coatings contributes to decrease in their friction coefficient compared to the cast state. The influence of pressure in the sputtering chamber and the voltage applied to the substrate on properties of the nitride coatings was established. The capabilities of producing thick (up to 80 μm) coatings combining metal and nitride interlayers from high-entropy alloys and determining their properties were shown. For the high-entropy carbide in the TiZrNbVTaHf system, the influence of the lattice parameter on hardness was revealed. The lowest friction coefficient (0.05) was observed in high-entropy oxide coatings. The high-entropy coatings showed high hardness. A hardness level of 19 GPa was reached for a metal coating based on the TiZrNbTaHfCr alloy, 63 GPa for a nitride coating based on the TiZrNbVHf alloy, and 48 GPa for a carbide coating based on the TiZrNbVHfTa alloy. The analysis showed that nitride coatings were the hardest, while the lowest friction coefficient was possessed by oxide coatings.