Delamination toughness of electron beam physical vapor deposition (EB-PVD) Y_2O_3-ZrO_2 thermal barrier coatings by the pushout method: Effect of thermal cycling temperature

摘要

A pushout test method was used to quantify effect of thermal cycling temperatures on the delamination toughness of an electron beam physical vapor deposited thermal barrier coating (EB-PVD TBC). The delamination toughness, Γ_i, was related to the maximum thermal cycling temperature, T_h, equal to 1000, 1025, 1050, and 1100 ℃. The measured delamination toughness varied from 9 to 95 J/m~2. At T_h = 1000 ℃, Γ_i attained a maximum value, larger than that of the as-deposited sample and decreasing with increased T_h. During the thermal cycling tests, the thermally grown oxide (TGO) was formed between the TBC and the bond coat deposited onto the superalloy substrate. Inside the TGO layer, mixture of Al_2O_3 and ZrO_2 oxides was observed close to the TBC side with nearly pure Al_2O_3 phases close to the bond-coat side. During the pushout test, delamination occurred at the interface of the mixture and pure Al_2O_3 layer with an exception for Th = 1100 ℃ specimens where delamination also occurred at the interface between the TGO and bond-coat layers. The effect of thermal cycling temperatures on the delamination toughness is discussed in terms of the microstructural change and delamination behavior.