EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

During the operation of turbines in jet engines or in power plants, high thermal and intermittent mechanical loads appear, which can lead to high-temperature fatigue failure. Since Fatigue is a complex and time-consuming process, it is important to develop realistic numerical models to predict fatigue behaviour and to extrapolate the limited experimental results into a wider range of thermo-mechanical conditions.
To accomplish this, a reference volume element (RVE), mimicking the typical γ/γ′ microstructure of a nickel-based single crystal superalloy is introduced. This cubic RVE consists of one central cubic γ′ precipitate and surrounding six half-width channels of γ matrix. With the help of this RVE, the temperature and deformation-dependent internal stresses in the microstructure can be taken into account in a realistic manner. A phenomenological crystal plasticity/creep model is proposed that takes different mechanisms into account, including thermally activated dislocation slip, the internal stresses due to inhomogeneous strains in different regions of γ matrix channels and in γ′ precipitates, the softening effect due to dislocation climb, the formation of ⟨112⟩ dislocation ribbons for precipitate shearing, the Kear-Wilsdorf locks.
This constitutive law is parameterised based on experimental data for CMSX-4 single-crystal superalloy by applying an inverse analysis to identify the material parameters based on many low cycle fatigue tests in the intermediate temperature and high stress regime. The identified material parameters could predict low cycle fatigue behaviour at different temperatures.
The model does not only reliably reproduce the experimental results along different crystallographic loading directions, but it also increases our understanding of the relative importance of the different deformation mechanisms for the fatigue behaviour under various conditions.