Study on the Wear Resistance and Failure Mechanisms of Thermal Sprayed Nanostructured TiO2 Coating by Regulating the Proportion of Partially Melted Regions

Abstract

Thermal-sprayed nanostructured ceramic coatings typically exhibit a bimodal structure composed of partially melted (PM) and fully melted (FM) regions, and the proportion of the PM regions significantly affects the overall performance of the coatings. In this study, nanostructured TiO₂ coating with varying proportion of the PM regions was fabricated using plasma spray by adjusting the spraying powers. The microstructure, mechanical properties and tribological behaviors, as well as failure mechanisms under extreme working condition of the coatings, were systematically investigated. The results showed that an increase in spraying powers led to a decrease in the proportion of the PM regions, which resulted in higher microhardness but lower fracture toughness of the coatings. The differences in the mechanical properties of the coatings with varying structures were primarily reflected in the PM regions. Although the weak bonding among the droplets in the PM regions made them more prone to generating wear debris, it also provided a certain degree of protection to the coatings against further wear. The wear failure mechanisms of the coatings with higher PM regions were mainly abrasive wear and fatigue wear. In contrast, the coatings with lower PM regions showed higher load-bearing capacity, but lower fracture toughness led to extensive droplet spalling, ultimately exacerbating the wear and failure of the coatings.