Электроискровое нанесение порошка карбида вольфрама на титановый сплав Ti6Al4V

Abstract

Titanium alloys are attracting the attention of researchers and engineers because of their unique combination of high specific strength, corrosion resistance and biocompatibility, but they are characterized by high wear. Therefore, the study of new methods for making protective coatings on titanium alloys is relevant. A mixture of titanium granules with tungsten carbide powder was used to prepare coatings on the titanium alloy Ti6Al4V by the method of electrospark granules deposition. Three mixtures of granules with a tungsten carbide content of 2.1, 4.1 and 6.0 vol.% were prepared. According to the data of X-ray analysis, it was found that the following phases were observed in the composition of the coatings: WC, W2C, W, αTi and β-(W, Ti)C1−x. Carbides W2C, (W, Ti)C1−x and metallic tungsten were formed as a result of the decarburization of WC upon its interaction with molten titanium under the conditions of an electric discharge. Large inclusions of tungsten carbide surrounded by a metallic Ti-W-C binder were observed in the microstructure of the coatings. According to the data of energy dispersive analysis, the concentrations of tungsten and carbon decreased when scanning from the surface layers of the coating to the substrate. The average values of the microhardness of the coatings increased from 7.9 to 9.2 GPa with an increase in the concentration of WC powder in the mixture of granules. The average values of the friction coefficients of the coatings were in the range of 0.33 – 0.48, which is 35 ± 3 % lower than that of the Ti6Al4V alloy. Tests for wear in the dry friction mode at loads of 25 and 70 N showed that the wear rate of the coatings ranged from 0.38 ×10−5 to 1.68 ×10−5 mm3 / Nm. The best wear resistance under both loads was demonstrated by the coatings deposited with the addition of 4.1 vol.% WC, which make it possible to increase the wear resistance of the Ti6Al4V alloy up to 18 times. Thus, the prospect of electrospark deposition of cermet coatings with enhanced mechanical properties on a titanium alloy using tungsten carbide powder mixed with titanium granules is shown.