Tailored microstructure of EB-PVD 8YSZ thermal barrier coatings with low thermal conductivity and high thermal reflectivity for turbine applications

This paper discusses microstructural changes produced by two novel approaches using electron beam-physical vapor deposition (EB-PVD) in which periodic strain fields/microporosity was incorporated within the large columnar grains of ZrO2-8 wt.% Y2O3 (8YSZ). The traditional columnar microstructure of partially stabilized zirconia has been slightly modified to produce a lower thermal conductive thermal barrier coating (TBC) by periodically interrupting the condensing vapor resulting in microstructural modifications with diffuse or sharp interfaces and morphological changes on the submicron scale without changing the composition of the TBC. These microstructural modifications resulted in a 20-30% reduction in the thermal conductivity, 28-56% increase in hemispherical reflectance, improved oxidation cyclic life (over 100%), and better strain tolerance as compared to standard ZrO2-8 wt.% Y2O3 deposited on platinum-nickel-aluminide and CoNiCrAlY bond-coated MAR-M-247 test samples. The TBC with tailored microstructures were examined by various techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), steady-state laser heat flux technique, hemispherical reflectance and thermal cyclic oxidation tests.