Evaluation of interfacial mechanical properties under shear loading in EB-PVD TBCs by the pushout method

A new simple pushout technique for evaluation of interfacial shear mechanical properties in thermal barrier coatings has been developed. The technique is similar to the pushout test of fiber-reinforced ceramics, except for the specimen shape and support method. The technique has been applied to evaluation of interfacial delamination toughness, Γi, of the electron beam physical vapor deposition (EB-PVD) ZrO2 thermal barrier coating (TBC) system. The change of Γi in the EB-PVD system with thermal exposure is measured and discussed in terms of microstructural change and delamination crack path. The measured delamination toughness varied from Γi = 10 to 115 J/m2. The delamination path and TGO growth were found to be closely related. The delamination toughness significantly decreases due to the formation and growth of a spinel phase in the TGO layer. The relation between delamination toughness and delamination behavior is discussed.