C-Al₂O₃ coatings prepared by cathode plasma electrolytic deposition on TC4 substrate for better high temperature oxidation resistance

The Al2O3 coating prepared by cathode plasma electrolytic deposition (CPED) method usually has porous structure, which is not conductive to its application in the field of high temperature oxidation resistance. In this paper, carbon doped Al2O3 (C-Al2O3) coatings were prepared by adding glycerol to the electrolytes, and coatings with reduced porosity and better high temperature oxidation resistance were obtained. SEM, EDS, XRD, XPS, high temperature oxidation test and first-principles calculation were used to study the structures and performances of the coatings. The results show that by adding glycerol to the electrolytes, the porosity of the obtained coatings is reduced. The doping of carbon (C) causes the XRD peaks of Al2O3 and XPS spectrum of Al2p and O1s. to shift to the left. The decrease in porosity is closely related to the increase in electrical conductivity of the coating caused by the doping of C, which reduces the band-gap of Al2O3. The coating with low C content shows the best high temperature oxidation resistance, while high C content coatings exhibit poorer high temperature oxidation resistance. Related mechanism is disclosed in the paper.