Microstructure and cyclic lifetime of Gd and Dy-containing EB-PVD TBCs deposited as single and double-layer on various bond coats

Abstract

Gadolinium zirconate (GdZ) and dysprosia stabilized zirconia (DySZ) are known for their lower thermal conductivity and higher thermal stability. In the present study, Electron Beam Physical Vapor deposited (EB-PVD) GdZ and DySZ are coated on different bond coats and the TBC systems are investigated for their lifetimes by thermal cycling at 1100°C. Lifetime values of these new TBC systems are then compared with their standard 7YSZ counterparts. GdZ top coats on NiCoCrAlY bond coats show a longer lifetime than the standard 7YSZ systems. However, on the (Ni, Pt)–Al bond coat lifetimes are generally short and 7YSZ shows a longer lifetime than the GdZ based systems. On NiCoCrAlY bond coats, single layer TBCs show longer lifetimes than their double layer counterparts. During thermal cycling, a chemical reaction between GdZ and the thermally grown oxide occurs, however, it has not been found detrimental for the lifetime of TBC systems. Besides lifetime investigations of different TBC systems, their failure patterns, diffusion of elements, phase changes and sintering of the TBC materials due to thermal cycling are also discussed.