Abstract
Ceramic coatings with high emissivity were fabricated on TC4 alloys by micro-arc oxidation technique (MAO) in mixed silicate and phosphate electrolytes with varying KMnO&sub4; 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 KMnO&sub4;, but the roughness of the coatings first decreased and then increased slightly due to the inhibitory effect of KMnO&sub4; on Na&sub2;SiO&sub3; deposition. The main phase composition of the coatings was anatase and rutile TiO&sub2;, amorphous form of SiO&sub2; and MnO&sub2;. The infrared emissivity value of the coatings strongly depended on KMnO&sub4; concentration, the coating formed at the concentration of 0.8 g/L KMnO&sub4; reached the highest and an average of up to 0.87 was observed.