Investigation Of High Emissivity Coatings Prepared By Plasma Spraying

The rapid development of hypersonic vehicles has promoted the development ofthermal protective coatings with high infrared (IR) emissivity. These coatings cansignificantly enhance radiative heat transfer and then restrain the surface temperatureincrease of vehicles in hypersonic flight. Such kind of thermal protective coating with highIR emissivity can be applied not only to hypersonic vehicles, but also to civil industry. Forexample, they can be used in thermal furnaces and other high-temperature processing unitsfor the purposes of energy saving. In this article, the powder is deposited on the substrateby air plasma spraying, coatings obtained in this way have great advantage in bond strengthand thermal shock properties compared with paintings.High emissivity coating is prepared by the raw materials of chromium oxide,lanthanum oxide, calcium oxide and magnesium oxide, getting the ingredients inaccordance with the molecular formula La0.8Ca0.2CrO3and La0.9Ca0.1Cr0.9Mg0.1O3. The rawpowder is prepared by solid phase synthesis, then the powder is aggregated by spratdrying. The high emissivity coating is prepared on the super alloy substrate by air plasmaspraying. The phase of coating is studied by XRD, while the rate of infrared radiationis tested using IRE-2infrared radiometer, and the thermal shock resistance ofcoating is researched as well. The results shown that the prepared La0.8Ca0.2CrO3coating has high emissivity in full-wave band under600℃-800℃, the emission ratecan reach to0.88. The porosity of the coating is about14.8%, and the bonding strengthis20.8MPa. La0.9Ca0.1Cr0.9Mg0.1O3coating has high emissivity in full-wave bandunder600℃-800℃, the emission rate can reach to0.89. The porosity of the coating isabout39.7%, and the bonding strength is9.7MPa. Meanwhile, both of the coating hasgood resistance on thermal shock. It has no spalling failure after thermal shock testing bywater quenching from1100degrees to room temperature by10times.