Influence of long time post annealing on thermal stability and thermophysical properties of plasma sprayed La2Zr2O7 coatings

Abstract

Thermal barrier coatings (TBCs) were applied to gas turbines to function at higher gas temperatures. Extensive effort has been invested in identifying new materials with even better performance compared to yttria-stabilized zirconia (YSZ) being the industry standard up-to-date. La2Zr2O7 (LZ) with the pyrochlore structure has received attention and been identified as a new candidate material for TBCs. In this study, two different coatings produced with commercial and high-energy ball milled LZ powders were investigated. Coatings were annealed for 50 h, 100 h, 200 h and 500 h at 1150 degrees C. Microstructures of the coatings were examined with Scanning Electron Microscopy and thermal conductivities were investigated with laser flash measurements. Mercury porosimetry was used as well to identify pore size changes that might occur with annealing process. X-Ray diffraction analysis was used to determine any possible phase changes. The results showed a sintering effect leading to an increase in thermal conductivity, and after 500 h heat treatment time, phase decomposition occurred on LZ based coatings. (C) 2016 Elsevier B.V. All rights reserved.