Thermo-physical behavior of atmospheric plasma sprayed high porosity lanthanum zirconate coatings

Lanthanum zirconate (La2Zr2O7) is one of the potential thermal barrier top coat material due to its high melting point, phase stability and low thermal conductivity in comparison to the conventional yttria stabilized zirconia (YSZ) coatings. In this work, an attempt was made to further reduce the thermal conductivity of lanthanum zirconate from its bulk value by fabricating a highly porous microstructure. For this purpose, lanthanum zirconate top coating with different porosities (16, 21 and 28%) was prepared by atmospheric plasma spraying under selective operating conditions and their microstructure, permeability and thermo-physical properties were investigated. SEM micrographs of the porous lanthanum zirconate show the features of the coating microstructures and porosity percentage. The bond strength of the as-sprayed coatings linearly decreases while increasing the porosity in the coating microstructure. The gas permeability of the porous coating microstructure significantly increased with increase in the porosity. An increase in coating porosity, results in significant reduction of both thermal diffusivity and conductivity of the coating microstructure. (c) 2017 Elsevier B.V. All rights reserved.