2009 Volume 73 Issue 10 Pages 802-808
In order to understand the effect of microstructural change in bond coat (BC) layer on interfacial mechanical properties, heat treatment in a vacuum was performed in air plasma-sprayed thermal barrier coating system (APS-TBCs). TBC layer, BC layer and substrate were composed of 8 mass% Y2O3 partially stabilized ZrO2, NiCoCrAlY alloy and Inconel 738 Nickel base superalloy, respectively. Heat treatments were performed at 1413 K for 10 and 50 hours. Microstructural observation of TBCs was done from the transverse section of the specimens. Under the as-sprayed condition, the BC layer consists of a fine mixture of β and γ′ phases. The size of the both phases increased with the increase in heat treatment time. β phase near the BC/substrate interface disappeared during the heat treatment. This may be due to the diffusion of Al from the BC layer to the substrate and diffusion of Ni from substrate to BC layer. Yield stress of the BC layer decreased and interface delamination strain energy release rate Γi increased with the increase in the heat treatment time. The increase of Γi may be attributed to the increase of the size of the process zone ahead of the delamination front due to the decrease in yield stress of BC layer.
