Microstructure and thermo-physical properties of plasma sprayed LaTi₂Al₉O₁₉ thermal barrier coatings

Conventional thermal barrier coatings (TBCs) consisting of a yttria stabilized zirconia (YSZ) ceramic coat and a metallic bond coat for industrial application cannot work long above 1200°C. With aero-engines developing towards higher thrust-to-weight ratio, it is necessary to develop new ceramic coating materials with better thermal barrier performance for ultra-high temperature application. LaTi₂Al₉O₁₉ (LTA) was proposed as a promising candidate due to its excellent phase stability at temperatures above 1500°C. In this paper, the LTA coatings were produced by atmospheric plasma spraying (APS) and their microstructures and thermo-physical properties were investigated. There were some amorphous phases in the as-sprayed coatings and crystallization of the coatings occurred at 860°C and 1130°C, respectively. Due to the volatilization of La₂O₃ during spraying, the concentration of La in the sprayed coating was relatively lower than that in the powder, while the other elements didn't show apparent changes in the compositions. The thermal diffusivity of the LTA coatings ranged from 0.3 to 0.4 mm²·s^-1 at 1400°C and the corresponding thermal conductivity were in the range of 1.1 to 1.6 W·m^-1·K^-1. The coating porosity increased as the spraying power decreased, while the thermal conductivity decreased with increasing spraying power.