Effect of ultrasonic nanocrystal surface modification on fuel-lubricated wear mechanisms of thermal spray Al₂O₃-TiO₂ coating

In this study, an Al₂O₃-TiO₂ (87%–13 %) coating was deposited onto a hardened SAE 52100 bearing steel using a high-velocity oxygen fuel (HVOF) spraying deposition method to enhance surface durability. The Al₂O₃-TiO₂ composite coatings generally exhibit better properties than pure Al₂O₃ coatings. To further improve wear resistance, the Al₂O₃-TiO₂ coating was subjected to ultrasonic nanocrystal surface modification (UNSM) treatment. The effects of UNSM treatment on the microstructure and hardness of the coating were investigated by scanning electron microscopy (SEM), electron-backscattered diffraction (EBSD), X-ray diffraction (XRD), and nanoindentation. The sliding friction and wear resistance of the coatings were assessed using a reciprocating ball-on-disk micro-tribometer under fuel-lubricated (F-24 jet fuel) conditions against an SAE 52100 bearing steel ball. The experimental tribological test results indicated that UNSM-treated coatings exhibited a reduced friction coefficient and enhanced wear resistance compared to untreated coatings. Detailed wear track analysis provided insights into wear degradation mechanisms and elucidated the role of UNSM treatment in improving the fuel-lubricated wear behavior of Al₂O₃-TiO₂ coatings.