Temperature dependence of phase relationships in different types of MCrAlY-coatings

The phase compositions of different MCrAlY-coatings were studied in the temperature range of 800 to 1100 °C. For this purpose free-standing coatings were quenched after different annealing treatments and subsequently characterized with respect to their microstructures using XRD, TEM and SEM/EDX. The experimental results were correlated with the calculations of phase equilibria using commercially available software (ThermoCalc) and dilatometric measurements of the physical coefficient of thermal expansion. The obtained results demonstrate that the thermal stability of the coating microstructure is sensitive to variations in major element contents in the range of just a few percent. Additionally, they can be used to estimate local temperature variations during service of real gas turbine components as well as for prediction of coating interdiffusion behavior with the superalloy components.