Tribotechnical Characteristics of Vacuum-Arc Coatings Mo–S–Ti–C on Titanium Alloy VT5, Formed with Assistant Influence of Gas-Discharge Plasma

The aim of the work is to identify the most effective conditions and modes for the synthesis of Mo–S–Ti–C coatings on titanium alloy VT5, providing the best tribological characteristics.

The coatings were applied by vacuum arc evaporation of cathodes on a modernized NNV-6.6-I1 installation. The cathodes were produced using self-propagating high-temperature synthesis. Assistance to the gas discharge plasma during coating application was provided by an autonomous plasma source with a heated cathode. In this case, the bias potential on the substrate, the deposition time, and the composition of the working gas environment — argon and/or a mixture of argon and nitrogen in a ratio of 1:1 — were varied.

It has been established that the use of assisting action of gas discharge plasma on deposited coatings provides a 2—3 times increase in their hardness. Using energy-dispersive X-ray spectroscopy, the presence of both sulfide-forming elements (Mo, S) and elements capable of forming solid carbides (Ti, C) was revealed in the evaporated cathodes and in the applied coatings. X-ray structural analysis confirmed the synthesis of compounds of the Mo₂S₃ and TiC type in both cathodes and coatings. In the most effective version of a three-layer coating using, along with argon, additionally nitrogen in gas discharge plasma, the formation of a strengthening phase TiN was also recorded. Tribological tests were carried out under friction conditions without lubricant. It was established that the most effective version of a three-layer coating with the addition of nitrogen in a gas discharge plasma, compared to the initial VT5 alloy, showed a decrease in the friction coefficient under a load on the counterbody of 1 N — by 2 times, under a load of 5 N — by 3 times; the wear rate in both cases decreased by an order of magnitude or more. Thus, the presented technological method ensures the formation of a gradient-layered coating architecture and appears promising for industrial application.

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