Modeling of interface failure in a thermal barrier coating system on Ni-based superalloys

In the present work, finite element modelling is employed to study interface cracking behaviour in a thermal barrier coating (TBC) on a singlecrystal Ni-based superalloy. The cohesive zone elements are implemented in the model to simulate interfacial debonding between the top-coat (TC), thermally grown oxide (TGO) and bond-coat (BC). To evaluate the effect of the interface geometry on the residual stress state and cracking behaviour, two periodic units of the TGO profile are analysed: a regular sinusoidal undulation with constant thickness and an irregular (unevenly thicker) TGO layer with symmetrical penetrations into the TC and BC layers. It has been found that the morphology of the TGO layer influences not only the magnitude and distribution of residual stresses but also governs the mechanisms of interfacial failure. For the regular TGO shape, the debonding cracks form at the peak of TGO/BC interface and at the valley of TC/TGO interface. Whereas only the TC/TGO interfacial debonding is observed in case of the irregular TGO profile. The debondings can induce the stress redistribution between the TBC layers that depends on which interface and to what extent is damaged. The TBC system with the regular TGO layer appears to be a more prone to interface failure than that one with the irregular TGO shape. However, much higher compressive stresses in the TGO layer are observed in the latter case. Possible scenarios of the TBC failure in terms of further cracks propagation are discussed. 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.orgilicenses/bv-ne-ndi4.01) Peer-review under responsibility of the First International Symposium on Risk and Safety of Complex Structures and Components organizers