Microstructural examination of <scp>TGO</scp> formed during pre‐oxidation on Pt‐aluminized Ni‐based superalloy

Abstract

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.