Correlation between microstructure,chemical components and tribological properties of plasma-sprayed Cr2O3-based coatings

The wear resistance of chromium oxide (Cr₂O₃) coatings could be improved by doping modification and changing the structural scale, etc. In this study, micrometric Cr₂O₃ coatings were doped with different additives, CeO₂ and Nb₂O₅. Moreover, Cr₂O₃ coatings were deposited from nanostructured feedstock by the combination process of plasma spraying and dry-ice blasting. The correlation between the microstructure, chemical components and tribological properties of plasma-sprayed Cr₂O₃-based coatings was discussed based on the investigation of their porosity, hardness and friction behaviors. The results showed that the composite coatings doped with additives exhibited a higher microhardness, corresponding to a lower porosity than pure Cr₂O₃ coating under the identical plasma-spray condition. CeO₂ constituent was found to improve the wear resistance of Cr₂O₃ coating while Nb₂O₅ incorporation corresponds to a steep rise in the friction coefficient. The mismatch of coefficient of thermal expansion (CTE) between Cr₂O₃ and Nb₂O₅ lamellae facilitated the origin of fatigue cracks and the formation of microfracture pits. Although the combination process promotes a porosity reduction, the nanostructured Cr₂O₃ (n-Cr₂O₃) coatings present a lower microhardness than micrometric coatings, due to their loosen microstructure from insufficient plasma power compared to microscaled coatings. The wear mechanisms of both the micro- and nanometric Cr₂O₃ coatings are fatigue cracks and material transfer.