Influence of KMnO₄ Concentrationon Infrared Emissivity of Coatings Formed on TC4 Alloys by Micro-Arc Oxidation

Ceramic coatings with high emissivity were fabricated on TC4 alloys by micro-arc oxidation technique (MAO) in mixed silicate and phosphate electrolytes with varying KMnO₄ addition. The microstructure, phase and chemical composition were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), and the infrared emissivity of the MAO coatings was measured in a waveband of 5-20 μm. The results show that the thickness of the coatings increased with the addition of KMnO₄, but the roughness of the coatings first decreased and then increased slightly due to the inhibitory effect of KMnO₄ on Na₂SiO₃ deposition. The main phase composition of the coatings was anatase and rutile TiO₂, amorphous form of SiO₂ and MnO₂. The infrared emissivity value of the coatings strongly depended on KMnO₄ concentration, the coating formed at the concentration of 0.8 g/L KMnO₄ reached the highest and an average of up to 0.87 was observed.