Lifetime improvement of EB-PVD 7YSZ TBCs by doping of Hf or Zr in NiCoCrAlY bond coats

Abstract

Rare earth elements have a great positive influence on the oxidation behavior and thereby on the lifetime of TBC systems. A commonly used EB-PVD NiCoCrAlY bondcoat was doped by Hf and Zr in a range of 0.1-1 at.%. More than 3000 cycles were achieved by Hf-doping in a range of 0.15-0.6 at.% Hf which is a large improvement. Zr doped BCs provide high lifetimes of about 2800 cycles with a low doping content of 0.3 at.%. Microstructural changes, especially in the TGO, including formation of initially transient alumina, rare earth precipitates, and TGO evolution with time were examined in detail.