Modelling of the interdiffusion and oxidation of a multilayered chromia forming thermal barrier coating: Modelling of the interdiffusion and oxidation of a TBC

The stability of multilayered coatings is important in long-term use and thus accurate predictions of the effects of exposure at temperature are extremely important. In this paper, the prediction and validation of a multilayered thermal barrier coating with a bond coat based on the MCrAlY system is presented. The coating was a three layered bond coat consisting of a NiCrAlY layer with an aluminised outer region onto which a NiCr layer with 2 wt% Si had been deposited. Onto this an yttria partially stabilised zirconia topcoat was applied. The coating system was exposed to 800 °C for times up to 3000 h. The specimens were sectioned and scanning electron micrographs obtained. Energy dispersive spectroscopy, EDS, was used to provide compositional data on each of the layers in the starting condition and also to produce elemental profiles through the sections with increasing time at temperature. The oxidation kinetics were determined from oxide growth measurements over time. The variation of these elemental profiles with exposure time were compared with the ODIN finite-difference code, which also allowed for chromium depletion due to its selective oxidation. Generally, satisfactory agreement was found.