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 solidified, and single crystalline (SX) substrate alloys were thermally cycled at 1100 degreesC. TBC spallation does not correlate solely to TGO thickness, but depends also very much on the substrate alloy The longest lifetimes are achieved on Hf-containing alloys while SX alloys suffer from early TBC spallation. The formation of the thermally grown oxide was investigated in detail by TEM. A mixed layer of alumina and zirconia exists in the as-coated condition. After initial slight thickening, the thickness of this mixed layer remains constant over a Iona period of time. During thermal exposure, a continuous layer of pure a-alumina forms and grows underneath the mixed zone by oxygen inward diffusion. (C) 2001 Elsevier Science B.V. All rights reserved.