Electrospark Deposition of Ti-Ta Coatings on Ti6Al4V Titanium Alloy: Oxidation Resistance and Wear Properties

Abstract

Ti-Ta coatings were deposited on titanium alloy by electrospark deposition in the anode mixture of titanium granules and tantalum powder in an argon atmosphere. The cathode weight gain kinetics, tantalum concentration, structure, oxidation resistance, microhardness, and tribotechnical properties of the coatings were studied. It was shown that, with increasing tantalum concentration in the anode mixture, the net cathode gain during 10 min of treatment increased monotonically. The average thickness of the deposited coatings varied in the range from 30.9 to 39.1 µm. The concentration of tantalum in the coating composition increased with increasing tantalum powder concentration in the anode mixture. The coating structure was dense without longitudinal and transverse cracks. With an excess of tantalum powder in the anode mixture, the discharge energy was not enough to completely melt it. The phase composition included α-Ti and a bcc tantalum solid solution in β-Ti. With increasing powder concentration in the anode mixture, the intensity of the bcc-phase peaks increased relative to the α-Ti peaks. The surface hydrophobicity of Ti-Ta coatings was higher than that of uncoated Ti6Al4V titanium alloy. The developed method can be used to produce Ti-Ta coatings with up to 5.9 times higher oxidation resistance compared to Ti6Al4V alloy. The high oxidation resistance of Ti-Ta coatings is explained by the formation of a dense and durable TiO₂ layer. The surface microhardness of Ti-Ta coatings ranged from 4.72 to 4.91 GPa. The friction coefficient was in the range of 0.87–0.97. The wear resistance was 23 to 36 times higher as compared to the titanium alloy.