Microstructure and infrared radiation of thermal barrier coating (La_0.2Nd_0.2Gd_0.2Sm_0.2Pr_0.2)MgAl₁₁O₁₉prepared by air plasma spraying

(La_0.2Nd_0.2Gd_0.2Sm_0.2Pr_0.2)MgAl₁₁O₁₉coating was prepared by atmospheric plasma spraying. Morphology of coatings varied with the velocity of primary gas and auxiliary gas, coating with highest gas velocity had the biggest area of unmelted zone, while the coating with lowest gas velocity had the smallest area of unmelted zone. Longer heating time of the powder in plasma jet led to a reduction in area of unmelted zone. The emissivity and bonding strength of the coatings were systematically evaluated. At room temperature, the average infrared emissivity in the 3–8 μm range reached 0.71–0.77, and Coating with lowest gas velocity exhibiting an 18.18 % enhancement over Coating with highest gas velocity. To enhance the bonding strength of the coatings, the spheroidization method was used.