Finite element simulation of stresses in a plasma-sprayed thermal barrier coating with an irregular top-coat/bond-coat interface

A three-dimensional finite element model of a conventional plasma-sprayed thermal barrier coating was set up with an irregular top-coat/bond-coat interface that was modelled based on the waviness data of a plasma-sprayed coating surface. The residual stresses upon cooling from a high-temperature stress-free state down to a room-temperature stressed state were studied as a function of thickness of the thermally grown oxide (TGO) layer taking into account the plasticity of the bond coat. The calculations indicate that the delamination cracks at the TGO/bond-coat are more likely to appear with progressive oxidation, and, conversely, the initiation of cracks in the top coat at the interfacial peaks in an intact thermal barrier coating is less probable because the tensile stresses in the top coat initially decrease and the tensile regions gradually become smaller and localized due to the observed stress conversion. Based on the obtained results and experimental evidence from the literature, a role of the interfacial topography in the failure sequence is discussed for oxidized and thermally-cycled coatings.