Methods to reduce the thermal conductivity of EB-PVD TBCs

This paper reviews the advantages and disadvantages of various thermal barrier coating (TBC) systems, with the aim of custom designing a TBC system to be both strain tolerant and have a low thermal conductivity. Methods of heat transfer within zirconia based ceramics are discussed, including the influence of coating microstructure and ceramic composition. It is shown the addition of dopant atoms (colouring) is effective in reducing ‘phonon’ transport and that layered microstructures are effective in reducing ‘photon’ transport. Advanced processing, using EB-PVD coating methods has allowed both coloured and layered ceramic coatings to be produced. Measured thermal conductivities of 1.0 W mK−1 have been achieved using these methods, much lower than current commercial EB-PVD coatings at 1.5–1.9 W mK−1.