Tribo-oxidation of cathodic arc ion-plated (V,Ti)N coatings sliding against a steel ball under both unlubricated and boundary-lubricated conditions

The friction and wear characteristics of (V,Ti)N coatings deposited by cathodic arc ion plating (CAIP) have been studied by using a Schwingungs Reibung und Verschleiss (SRV) tester with reciprocating motion against a SAE 52100 steel ball from room temperature to 300 °C. The (V,Ti)N coatings exhibit a friction coefficient of 0.57-1.28 under unlubricated condition and of 0.18-0.19 under boundary-lubricated condition, depending on wear parameters used. The effects of load, frequency and temperature on the friction and wear of the (V,Ti)N coatings have been discussed. The worn surfaces and wear debris generated under different wear conditions are examined by means of scanning electron microscopy and Raman spectroscopy to identify the tribochemical reaction and phase structures generated during the wear process. Metastable FeO-type and stable Fe₂O₃-type iron-based oxides are formed on worn surfaces under both boundary-lubricated and unlubricated conditions as well as some (V,Ti,Fe)₂O₅ and rutile TiO₂ oxides. The dissolved oxygen in the lubricant plays a very important role in oxidational wear of (V,Ti)N coatings under boundary-lubricated conditions.