Pulsed electron beam treatment of MCrAlY bondcoats for EB-PVD TBC systems part 1 of 2: Coating production

Abstract

This is the first part of a two part paper discussing the influence of pulsed electron beam (PEB) treatment of thermal sprayed MCrAlY bondcoats on the cyclic life of thermal barrier coatings (TBCs). Part one describes the production of MCrAlY bondcoats via HVOF and VPS thermal spray methods. Some of these coatings were then modified by using a pulsed electron beam treatment before all the samples were coated with an EB-PVD 7–8 wt.% yttria partially stabilized zirconia topcoat. Part two describes the results obtained under cyclic oxidation conditions at 1150 °C with 1 h at temperature and 15 min cooling. The MCrAlY bondcoats manufactured with the two thermal spray methods show differences in microstructure, pore evaluation and surface roughness, these factors will be discussed along with details of the PEB treatment method in this paper. After PEB treatment the typical two phase (γ, β)structure of MCrAlY was no longer visible in the microsection near the surface of the bondcoat. The surface roughness of the HVOF sprayed sample was reduced by the treatment to an RZ below 4 μm and the porosity in the modified layer was completely removed. Some inclusions containing Y, Al and oxygen were found in and at the surface of the PEB treated layer. Their influence on the cyclic oxidation performance is further discussed in part 2 of this study.