Hydrothermal deposition of MoS2 on electrospark Ti – Al coatings on Ti6Al4V alloy and their characteristics

Abstract

Antifriction layers on titanium alloy Ti6Al4V can be obtained by creating a developed structure of lubricant pockets, followed by the application of dry self-lubricating substances. The structure and tribological behavior of Ti – Al intermetallic coatings after hydrothermal deposition of molybdenum disulfide (MoS2) have been studied. Titanium aluminide coatings with a regular network of cracks were obtained by electrospark treatment of the Ti6Al4V alloy in an equimolar mixture of titanium and aluminum granules. To fill the lubricant voidnesses in the MoS2 coatings, the hydrothermal synthesis method was used in a solution of thiourea and sodium molybdate at 220 oC. The structure of the coatings was studied by X-ray diffraction analysis, scanning electron microscopy, X-ray microanalysis, and Raman spectroscopy. The wear resistance of the coatings was studied according to the ASTM G99 standard with dry sliding friction using counterbodies in the form of discs made of high-speed steel P6M5 at a speed of 0.47 m/s under a load of 25 N. It was found that intermetallic compounds Ti3Al, TiAl, TiAl3 and TiAl2 were overwhelming. In the structure of Ti – Al coatings, a regular network of cracks with a thickness of 0.77 ± 0.3 μm and a specific area on the coating surface of 2.2 ± 0.35% was established. It was shown that as a result of hydrothermal synthesis, a MoS2 layer is formed on the surface of the samples, consisting of spherical particles with a diameter of 3.09 ± 0.63 μm. Based on the data of energy dispersive spectroscopy (EDS) mapping, it was concluded that cracks in Ti – Al coatings are also filled with MoS2. According to the results of tribological tests, it was found that the hydrothermal deposition of MoS2 on Ti – Al coatings enables to reduce their friction coefficient by 30%, and the reduced wear in dry sliding friction by 2 times. The conducted studies show the promise of hydrothermal deposition of MoS2 on Ti – Al coatings in order to study tribotechnical properties.The study was supported by the Russian Science Foundation (No. 19-73-00031).