Effect of K2ZrF6 concentration on thermal ablation resistance of ZrO2/TiO2 composite ceramic coatings on TC4 alloy

The poor thermal ablation resistance of TC4 alloy limits its use in critical high-temperature applications. In this work, ZrO2/TiO2 composite ceramic coatings were prepared by plasma electrolytic oxidation (PEO) to enhance the ablation resistance of TC4 alloy. The phase compositions, microstructure and ablation resistance of the coatings are significantly influenced by the addition of various concentrations of K2ZrF6 to the electrolyte. The X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDS) techniques were employed to investigate the phase composition, chemical compositions, microstructure, and elemental distribution of the PEO ceramic coatings. The results showed that ZrO2/TiO2 composite ceramic coatings formed on substrate consisted of t-ZrO2, ZrTiO4, R-TiO2, and A-TiO2 phases. These coatings also exhibited a volcanic-like porous structure. The thermal ablation resistance tests were carried out at 1300 °C for 3000 s, which indicated that the presence of t-ZrO2 in the coating could improve the ablation resistance of TC4 alloys by inhibiting crack propagation. Moreover, the thermal ablation resistance of the PEO coating prepared with 15 g/L K2ZrF6 was superior to that of other coatings, as indicated by the crack density and weight loss.