Influence of substrate material on oxidation behavior and cyclic lifetime of EB-PVD TBC systems

EB-PVD NiCoCrAlY/P-YSZ TBCs on several polycrystalline, directionally solid ified, and single crystalline (SX) substrate alloys were thermally cycled a t 1100 degreesC. TBC spallation does not correlate solely to TGO thickness, but depends also very much on the substrate alloy The longest lifetimes ar e achieved on Hf-containing alloys while SX alloys suffer from early TBC sp allation. The formation of the thermally grown oxide was investigated in de tail by TEM. A mixed layer of alumina and zirconia exists in the as-coated condition. After initial slight thickening, the thickness of this mixed lay er remains constant over a Iona period of time. During thermal exposure, a continuous layer of pure a-alumina forms and grows underneath the mixed zon e by oxygen inward diffusion. (C) 2001 Elsevier Science B.V. All rights res erved.