Microstructure, Phase Composition and Physical and Mechanical Properties of a Monolayer High–Entropy Coating (TiZrVCrAl)N Deposited by the Vacuum–Arc Method on Coarse–Grained and Ultrafine–Grained Titanium Alloy Ti–6Al–4V

This article presents the results of experimental work on the vacuum–arc deposition of high–entropy monolayer nitride coatings of the (TiZrVCrAl)N system on the surface of substrates made of Ti–6Al–4V structural titanium alloy with an initial coarse–grained and ultrafine–grained structure formed by equal–channel angular pressing. A structural and phase analysis of the formed coatings was performed, and their physical and mechanical properties were assessed. It was found that the formation of an ultrafine–grained structure by methods of severe plastic deformation in the substrate leads to a significant improvement in the characteristics of the monolayer coating compared to the coarse–grained structure: the microhardness of the resulting coating increases from 702.1 to 1283.4 HV, the critical loads of the appearance of the first cracks (Lc1) and local delamination of the coating (Lc2) during the scratch test increase by ~33% and ~36%, respectively. X–ray diffraction analysis and precision microstructural studies revealed the formation of a coating on an ultrafine–grained substrate with a finer structure with a coherent scattering regions size of 6.57 nm compared to 9.20 nm for a coarse–grained substrate. The obtained results convincingly demonstrate the positive influence of the ultrafine–grained structure of the substrate on the formation of high–entropy coatings with improved physical and mechanical properties, including microhardness, adhesive strength and structural–phase stability.