Thermal expansion behavior of new Co-based alloys and implications for coatings

In turbine applications, these alloys will be part of a multilayer system that generates thermal stresses due to the CTE mismatch between the components. To investigate this phenomenon, the CTE data was incorporated into a thermo-mechanical model to calculate the energy release rate (ERR) for the delamination of coatings from these alloys. The ERR of a thermally grown oxide (TGO) formed on the bare and bond coated Co-based alloys was determined as a function of superalloy and bond coat CTE. The ERR of a thermal barrier coating (TBC) was evaluated as a function of temperature, superalloy CTE, and coating thickness. The ERR was found to be about 1.5 × greater in Co-based superalloys compared to Ni-based superalloys cooled from T = 1100 °C to ambient. Strategies for reducing the driving force for delamination are discussed.