Life and FCT Failure of Yttria- and Ceria-Stabilized EBPVD TBC Systems on Ni-Base Substrates

The lifetime at 1100 °C of furnace oxidation tested TBC samples having YSZ (ZrO2-7 wt.% Y2O3) and CeSZ (ZrO2-25 wt.% CeO2-2.5 wt.% Y2O3) topcoats on four Ni-base alloys including a no-bond coat NiCrAl alloy were studied. The thermally grown oxide (TGO) was investigated by energy-dispersive spectroscopy. The outer zone of the TGO revealed preferred enrichment of Zr and of rare earth elements Ce and Y in dependence of the stage of life. The oxygen potential gradients in the TGO have been rated; they are stronger for the YSZ TBC systems than for the CeSZ systems and cause a more intensive interaction of the outer zone alias mixed zone with the metal substrate than with the ceramic topcoat. When comparing the chemical composition data of the mixed zone as a function of the test period, the average lifetime as well as the particular composition of the two topcoats and the refractory element content of the substrates allowed conclusions to be drawn about the mechanisms which influence the lifetime.