Finite Element Analysis of Interface Undulation and Interface Delamination in the MCrAlY Coating System Under Thermal Cycling: Considering Oxide Thickness and Top-Coat Effects

Abstract

Thermal cycling is able to cause interface undulation and interface delamination in the MCrAlY coating system. A generalized plane strain finite element model was built in this work to analyze interface undulation and interface delamination. Increasing thermally grown oxide (TGO) thickness facilitates interface undulation. The possible reason for this is that increase in TGO thickness causes the TGO film to be subjected to larger bending moments. Nonetheless, interface undulation can be suppressed in the case of the existence of the top-coat. Simultaneously, the incorporation of the top-coat leads to an obvious reduction in the maximum tensile stresses within the bond-coat/TGO interface. Furthermore, whether the top-coat is incorporated into the coating system model or not, the bond-coat/TGO interface is subjected to compressive stresses, at its concave region and tensile stresses, at its convex region. Therefore, the convex region is thought to be the most likely place where cracks nucleate at the bond-coat/TGO interface. Additionally, the TGO thickness has a significant influence on the in-plane strain energy stored within the TGO film, and the in-plane strain energy is also thought to be one of the mechanisms for the interface delamination.