Evolution of interfacial toughness of a thermal barrier system with a Pt-diffused γ/γ′ bond coat

A strain-to-fail method has been employed to examine the interfacial adhesion of electron beam-physical vapor deposited thermal barrier coatings (TBCs) with a Pt-diffused γ/γ′ bond coat. Based on a previously established model, the estimated interfacial toughness decreases with oxidation time of TBCs. Furthermore, the interfacial toughness value varies considerably with the use of different Young's moduli in the model. It is believed that the modulus obtained from beam bending represents the columnar structure of the TBC. In this case, the mode I interfacial toughness was found to vary from 10 J m-2 for as-deposited TBCs to 0.79 J m-2 for the 60 h oxidized TBCs. The degradation of adhesion could be attributed to the defect formation and impurity segregation at the TGO/bond coat interface, which is associated with the diffusion of Pt. © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.