TEM Characterization And Analysis Of Microstructure Evolution Of EB-PVD YSZ Coating Sintered At 1200℃

A standard 7 wt.% Y2O3-stabilized ZrO2(YSZ) prepared by electron-beam physical vapor deposition(EB-PVD) is mainly made of columnar grains. The micro pores of intra-column and inter-column gaps in EB-PVD TBC lead to low thermal conductivity and advantageous strain tolerance, which can effectively relieve the failure of thermal barrier coatings. Therefore, the EB-PVD TBC is widely used on the important components of aerospace turbine engines. When the EB-PVD TBC is exposed to 1100°C for some time, adjacent columns will sinter together due to high temperature. Densification of EB-PVD TBC caused by high-temperature sintering will lead to an accompany loss in strain tolerance, also resulting in a larger columnar gap. The adverse effects prompt the cracks of TBCs, which eventually result in the failure of the coatings. Thus, the characterization of the evolution of TBCs microstructure after high-temperature sintering is necessary for understanding coatings failures.In this paper, the samples are prepared by electron beam physical vapor deposition on the alumina substrate. Microstructure evolution of the EB-PVD TBCs sintered at 1200°C, especially a lot of grain boundary in YSZ coatings, are characterized and analyzed by applying TEM, SEM, STEM combined with XRD microscopic detection technology. The results obtained are as follows:(1) The microstructure of the as-coated YSZ coatings is mainly the feathery columnar grains structure. Among each column are the large tilting angle grain boundaries. After high-temperature sintering at 1200°C for 4 h, “feathery” features disappear with columnar grain coarsening. The grain scale at the top of the YSZ coatings is significantly greater than the bottom of the columnar grains.(2) The grain boundaries of the as-coated YSZ coatings is mainly large tilting angle grain boundaries. After high-temperature sintering, many small tilting angle grain boundaries are found in YSZ coatings. The grain interface is the {100} plane and tilting axis is <001> zone axis. The misorientation angles are measured to be 1.5o to 9o. The formation of these small tilting angle grain boundaries are closely relative to the disappearance of feathery columnar grains structure and the coarsening of columnar grain.(3) An experimental method is established determine the tilting grain boundaryand the twisting grain boundary by using high resolution image combined with electron diffraction.(4) The small tilting angle grain boundaries are composed of the orderly arrangement of edge dislocations. Therefore, so it is very likely that the proliferation, diffusion, regrouped and orderly arrangement of edge dislocations occur during the coarsening of columnar grains. The proliferation of dislocations will inevitably affect the mechanical properties of YSZ coatings. This may be one of the reasons for causing the YSZ coatings failure.