High-temperature tribological properties of a cathodic arc ion-plated (V,Ti)N coating

The high-temperature tribological properties of a cathodic arc ion-plated (V,Ti)N coating have been investigated with a SRV high-temperature friction and wear tester. After heating in air at temperatures above 500 °C, V₂O₅ and TiO₂ phases were identified on surfaces of (V,Ti)N coating with V₂O₅-type platelets as the major oxidized product. (V,Ti)N coatings exhibit a friction coefficient in the range of 0.53-1.08 and a wear rate in the range of 1.69 × 10^-7-1.31 × 10^-5 mm³/Nm, depending on test temperature used. At low temperatures, the presence of oxide debris induced by tribological stressing on the load-bearing regions reduces direct contact between (V,Ti)N coating and Al₂O₃, and generates a mild wear, however, adherent and compacted wear-protective oxide layers are not developed. At temperature of 500 °C or above, the wear-protective oxide layers containing thermally-oxidized V₂O₅ platelets deform plastically to produce a lubricious and smooth appearance to reduce friction. Raman spectroscopy was used to identify the structures of wear debris and coating surfaces after wear tests. Tribochemical reactions are the dominating wear phenomena at low temperatures. The wear debris generated during the wear process consists mainly of the V₂O₅-type tribo-oxides.