Preparation Of High Emissivity Coating On Titanium Alloy Surface By Micro-arc Oxidation And Research Of Area Effect

The outer skin of aircraft surface temperature increased rapidly due to strongfriction between the atmosphere and outer covering when aircraft is flying at a highspeed. This fast elevated temperature has a major impact on normal flight of aircraft.The preparation of high emissivity coatings on metal surfaces can increase theantioxidant capacity of the metal, meanwhile remove numerous heat via infraredradiation radiated, reaching thermal protection purposes.In this paper, we select phosphate as the main salt electrolyte system, ceramiccoating on titanium alloy TC4is prepared by micro-arc oxidation method. In orderto improve the emissivity of coating, a small amount of aluminate and chromate isadded to phosphate electrolyte, we discuss the effects on coating’s morphology,phase, emissivity in these two components. At the same time, we also prepare amulti-component oxide film on eramic coating by sol-gel method, after sintering itcan form a composite coating with high emissivity. Taking account of the practicalapplication, we need to prepare larger alloy coating. Since changes of sample sizecan cause performance of coating changes under certain parameters, so we need toexamine the area effect on MAO coating during preparation, in order to providereference for preparing coating on larger sample size.Experimental results show that thickness and roughness of MAO coating whichobtained in pure micro-arc oxidation improve as the improvement of the operatingvoltage, while the emissivity of the coating rises as the surface roughness increases.Compared with emissivity of the MAO coating prepared in simple phosphateelectrolyte system, it has a significant growth when aluminate or chromate is addedto electrolyte system. The same phenomenon is produced on composite coatingwhen sol-gel film is scribbled on MAO coating. Shear strength of coatiings arelarger than15MPa, the emissivity at700℃of composite coating in3~8μm band is0.7, the maximum emission of coating in8~20μm is up to0.9. Full-band emissionrate is up to average0.85. Area effects on preparation of MAO coating shows, thethickness and the roughness of coating decreases as sample size increasing. And theincrease of power parameter is non-linear. Coating thickness uniformity underconstant amplification process is better than the constant amplification process.Moreover, the unevenness of thickness on larger sample area is reflected moreclearly.