Microstructural examination of TGO formed during pre-oxidation on Pt-aluminized Ni-based superalloy



The study concerns electron beam physical deposition (EB-PVD) of yttria stabilized zirconia (YSZ) deposited on pre-oxidized Pt-modified aluminide bond coating. The coating was prepared by the means of Pt galvanizing followed by vapor phase aluminizing at 1050 °C. During annealing at 1100 °C in air atmosphere for 4 h a 1 µm thick layer of thermally grown oxide (TGO) consisting of equiaxed α-alumina grains was formed. Focused ion beam and scanning/transmission electron microscopy analysis revealed the presence of nanoscale Cr-rich precipitates distributed in the TGO as well as Cr precipitation in the grain boundaries of the β phase at the interface between the TGO and bond coat. Deposition of the YSZ on a pre-oxidized substrate provided mechanical keying with the TGO. Void formation was observed at the TGO and bondcoat interface presumably due to initial transient alumina formation.