Structure and Infrared Emissivity Properties of the MAO Coatings Formed on TC4 Alloys in K₂ZrF₆-Based Solution

Micro-arc oxidation (MAO) ceramic coatings were formed on TC4 alloy surface in silicate and metaphosphate electrolytes based with K₂ZrF₆ for various concentrations. X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) were used to characterize the phase composition, microstructure and chemical compositions of the coatings. The infrared emissivity of the coatings was measured at 50 °C in a wavelength range of 8-20 µm. The microstructural observations all revealed the typical porousstructures. Moreover, adecline in roughness and thickness of the prepared coatings can be observed when the concentration of K₂ZrF₆ increases. Combined with the results of XRD and XPS, it was found that all the oxides existed as the amorphous form in the coatings except the TiO₂ phase. The coatings exhibited the highest infrared emissivity value (about 0.89) when the concentration of K₂ZrF₆ was 6 g/L, which was possibly attributed to the defect microstructure and the optimal role of ZrO₂.