Chemical diffusion increases thermal expansion gradients enhancing compressive stress cracking at the TGO interface

Abstract Micrographs of TBCs heated at 1125 °C revealed delamination cracks occurring along areas of compressed and undulated TGO as well as diffusion of Ni, Co, and Cr through the thermally grown oxide layer (TGO). In order to characterize the compressive stress mechanism, undulation and compression of the TGO were measured through factors of displacement, wavelength, and amplitude. The significant diffusion displayed around the TGO layer magnified the thermal expansion gradients of the area. When heated, these gradients created significant compressive stress leading to the areas where delamination cracks occurred. Thus, the diffusion of elements from the bond coat to the topcoat catalyzes compressive stress cracking incident to the TGO layer.