Microstructure and Wear Resistance of Plasma-Sprayed Al2O3-TiO2-CeO2/CNT Composite Coatings

To improve the wear resistance of 45 steel, nano-agglomerated Al2O3-TiO2-CeO2/carbon nanotubes (CNT) composite powders were prepared by spray drying and ball milling, followed by plasma spraying to fabricate coatings. The effect of CNT content on microstructure and wear resistance was investigated. The powders showed uniform size and high sphericity. Coatings mainly consisted of α-Al2O3, γ-Al2O3, and TiO2. CNT addition refined grain size to 18.3 ± 1.1 nm. The high thermal conductivity of CNT reduced unmelted particles, improving coating density and element uniformity. Average coating thickness was 200 μm. When the CNT content reached 3 wt.%, the coating porosity decreased to 5.01 ± 0.72%. TEM analysis indicated that CeO2 was mainly located at the grain boundaries. Moreover, the interfaces between CNT (002) and CeO2 (220) appeared clean and well-bonded. As CNT content increased, microhardness and wear resistance first increased then decreased. At 3 wt.% CNT, the volumetric wear rate was 0.87 ± 0.15 × 10−5 mm3·N−1·m−1, representing an 8.46-times improvement in wear resistance compared to the substrate. The presence of CeO2 enhanced the surface activity of CNT, facilitating the formation of lubricating films during friction and contributing to the superior wear resistance of the composite coating.