Excellent mechanical, electrical and current-carrying tribological properties of nano/micro composite TiO2-x coating prepared by supersonic plasma spraying

Synthesis of TiO2-x conductive ceramics with good comprehensive properties is of great significance. In this work, nano (n-TiO2) and submicron (m-TiO2) agglomerated powders are used to prepare the nano/micro composite TiO2-x coating by plasma spraying. For comparison, the conventional TiO2-x coating is also fabricated with submicrometer structure powders. The phase constitution, microstructure, mechanical properties, electrical conductivity and tribological behaviors of the coatings are studied. The results show that the content of TiO2-x in the conventional coating is higher than that of the composite coating. While the composite TiO2-x coating exhibits the denser microstructure with improved microhardness, fracture toughness and bonding strength. Furthermore, the electrical conductivity of the composite TiO2-x coating is more than twice that of the conventional TiO2-x coating. The conventional TiO2-x coating shows the lower friction coefficient than the composite TiO2-x coating under dry friction condition, whereas the composite coating has the lower wear loss. When the tribology tests are conducted under current-carrying condition of 2A, the friction coefficients of the two coatings decline and their values show little difference. However, the wear rates of the coatings as well as the corresponding counterparts increase notably with the electric current. In general, the main wear mechanisms of the coatings under dry friction condition are adhesion wear accompanied by fatigue wear, which then changes into adhesion wear and abrasive wear under current-carrying condition.