Influence of water vapour on structural and thermal conductivity of post-heat treated plasma sprayed LZ and YSZ coatings

In this work, the role of water vapour content during the post-heat treatment on the microstructure and thermal conductivity of atmospheric plasma sprayed lanthanum zirconate (LZ) and yttria stabilized zirconia (YSZ) coatings were studied. For this purpose free standing LZ and YSZ coatings with thickness about 300-400 μm were prepared and post-heat treated at 1100 °C for 50 h and 100 h with and without water vapour content. Phase stability and microstructure were investigated using X-ray diffraction and scanning electron microscope respectively. Thermal conductivity of as-sprayed and post-heat treated coatings were measured by laser-flash thermal diffusivity method and results obtained show that the thermal conductivity of post heat treated coatings increased significantly in both coatings. Further, the thermal conductivity of the coatings increased with increasing heat treatment time. Overall observations show that the presence of water vapour during the post-heat treatment has significantly influenced the microstructures as well as thermal conductivity in both coatings. Thermal conductivity of post-heat treated lanthanum zirconate and yttria stabilized zirconia coatings with presence of water vapour is 2.12 W m−1 K−1 and 2.48 W m−1 K−1 respectively which is 46% and 41% higher than as-sprayed coatings.