Influence of Processes and Parameters on the Microstructure and Properties of Thermal Barrier Coatings Produced with a Nanostructured YSZ Powder

One approach to enhance the performance of thermal barrier coatings (TBC) lies within the application of nanostructured yttria stabilized zirconia (YSZ) powders. The nano-sized particles in the spray powders are usually prepared by chemical methods. In this study, YSZ powder (-90 +16 µm) was nanostructured by high energy ball milling. After being agglomerated, the powder was sprayed using a conventional plasma generator F4MB-XL and a modern three-cathode plasma generator Triplex Pro-200 both by Sulzer Metco. The parameters were varied to investigate their influence on the build-up, microstructures and properties of the TBC. The powders and TBC were characterized in terms of their morphologies, microstructures and phase compositions by means of light microscopy, electron scanning microscopy, transmission electron microscopy and X-ray diffraction analysis. The thermo-shock behavior of the TBC was evaluated using thermal cyclic tests at 1150 °C and 1300 °C. The results show that the milled powder contains nano-sized particles smaller than 100 nm. Appropriate process parameters had to be developed for the nanostructured powder in order to realize the desirable microstructure containing semi-molten particles. These semi-molten particles provide high porosities and fine pores in the TBC. This microstructure was realized more easily by Triplex Pro-200 than by F4MB-XL due to its special nozzle for high particle velocities and higher plasma stability. It resulted in significantly lower microhardness (600 HV0.1 compared to 848 HV0.1) and better thermo-shock resistance (47 cycles compared to 27 cycles at 1300 °C) of the TBC from the nanostructured powder than the reference TBC.