New classes of high-entropy alloys, which consist of at least 5 main elements with atomic concentrations 5-35 at.%, are under great interest in modern material science. It is also very important to explore the limits of resistance of high-entropy alloy nitrides to implantation by high-energy atoms. Structure and properties of nanostructured multicomponent (TiHfZrNbVTa)N coatings were investigated before and after ion implantation. We used the Rutherford backscattering, scanning electron microscopy with energy dispersive X-ray spectroscopy, high resolution transmission electron microscopy and scanning transmission electron microscopy with local microanalysis, X-ray diffraction and nanoindentation for investigations. Due to the high-fluence ion implantation (N + , the fluence was 10 18 cm −2 ) a multiphase structure was formed in the surface layer of the coating. This structure consisted of amorphous, nanocrystalline and initial nanostructured phases with small sizes of nanograins. Two phases were formed in the depth of the coating: fcc and hcp (with a small volume fraction). Nitrogen concentration reached 90 at.% near the surface and decreased with the depth. Nanohardness of the as-deposited coatings varied from 27 to 34 GPa depending on the deposition conditions. However, hardness decreased to a value of 12 GPa of the depth of the projected range after ion implantation and increased to 23 GPa for deeper layers.

a b s t r a c tMultielement high entropy alloy (HEA) nitride (TiHfZrNbVTa)N coatings were deposited by vacuum arc and their structural and mechanical stability after implantation of high doses of N + ions, 10 18 cm À2 , were investigated. The crystal structure and phase composition were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy, while depth-resolved nanoindentation tests were used to determine the evolution of hardness and elastic modulus along the implantation depth. XRD patterns show that coatings exhibit a main phase with fcc structure, which preferred orientation varies from (1 1 1) to (2 0 0), depending on the deposition conditions. First-principles calculations reveal that the presence of Nb atoms could favor the formation of solid solution with fcc structure in multielement HEA nitride. TEM results showed that amorphous and nanostructured phases were formed in the implanted coating sub-surface layer ($100 nm depth). Concentration of nitrogen reached 90 at% in the near-surface layer after implantation, and decreased at higher depth. Nanohardness of the as-deposited coatings varied from 27 to 38 GPa depending on the deposition conditions. Ion implantation led to a significant decrease of the nanohardness to 12 GPa in the implanted region, while it reaches 24 GPa at larger depths. However, the H/E ratio is P0.1 in the sub-surface layer due to N + implantation, which is expected to have beneficial effect on the wear properties.

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