A TEM and SANS-Study for analysis of phase and morphology of alternative EB-PVD deposited TBC-compositions

Abstract

Electron-beam physical vapor deposition (EB-PVD) of standard (PYSZ) thermal barrier coatings produces tetragonal columnar structure with anisotropic pores. Long-term stability of the ceramic top coat of TBCs can be provided through the development of new materials having ultra-low thermal conductivity, excellent phase stability and improved sintering-resistance. For this purpose two alternative TBC-compositions were produced by EB-PVD-process: Fully yttria (14 wt.%) stabilised zirconia (FYSZ) and pyrochlore (LaZr2O7) both of which yield intrinsically low thermal conductivity values. As-coated and aged samples were analysed by the Laser-Flash technique for their thermal diffusivity which were correlated with the thermal derived changes of coatings. The anisotropic nano-sized pore morphology in FYSZ- and La2Zr2O7-TBCs were analysed by small angle neutron scattering (SANS) method. Pore morphology and phase changes were investigated by advanced SANS and TEM/SEM-analysis on FIB sections, indicating that production of pyrochlore phase by EB-PVD requires some process alteration. Cubic zirconia yields anisotropic pore morphology after high temperature treatment and is present already after coating. TEM and SANS investigations indicate that the pore morphology and microstructure of EB-PVD pyrochlore and fully stabilised zirconia differ significantly from those of PYSZ.