Microstructure degradation of EB-PVD TBCs on Pd-Pt-modified aluminide coatings under cyclic oxidation conditions

The study concerns Pd/Pt-modified aluminide bond coatings for EB-PVD TBCs on N5 superalloy in terms of microstructural evolution during cyclic oxidation tests.The coating was deposited by Pd. +. Pt electroplating, followed by high activity vapor phase aluminizing at 1050. °C and pre-oxidation heat treatment in order to form an α-alumina TGO. The 7. wt.% yttria stabilized zirconia TBC was deposited using electron beam physical vapor deposition. Cyclic oxidation tests of the coating were performed at 1100. °C in 1. h. cycles in laboratory air. The microstructure of the coatings in the as-deposited state as well as after cyclic oxidation test was studied using SEM. The evolution and phenomena occurring at the interface between the bond coating, thermally grown oxide and TBC during high temperature exposure were studied in detail using high resolution FEG-S/TEM. The samples for S/TEM analysis were prepared using FIB (Focused Ion Beam). The study is mostly focused on the growth of TGO during high temperature exposure and the overall performance of the Pd/Pt-modified aluminide coatings as a cost effective alternative to Pt-modified aluminide coatings commonly used as EB-PVD bond coats.