Coupled modeling of rafting behaviour in nickel-based single crystal superalloys

Nickel-based single-crystal (NBSX) superalloys applied to turbine blades on advanced aero-engines, suffer from the creep degradation induced by microstructure evolution at high temperatures. Here, our experiments revealed a unique morphology change of γ' phase in NBSX superalloys during rafting, i.e. the fusion of adjacent γ' phase domains first appeared at both vertices of the vertical channel, rather than at the center of the channel. To comprehensively understand the mechanism of γ' phase domain evolution during creep, we integrate a cellular automata (CA) algorithm into a crystal plasticity finite element model (CPFEM) to simulate the evolution of γ' phase domains and creep deformation for NBSX superalloys. A microstructure evolution model is established to simultaneously capture the dissolution, coarsening, and rafting of γ' phase domains, which are implemented via a CA algorithm. The evolution rule of aluminum atomic equilibrium concentration driven by deformation energy, is introduced into the CPFEM-CA model to capture the unique γ' morphology evolution. The coupled model has been validated against experimental rafting data of NBSX superalloys. The results indicate that the observed unique rafting morphology is related to the element diffusion driven by deformation energy and leads to local stress concentration. The proposed CPFEM-CA model not only enhances the fundamental understanding of the γ' rafting behavior in NBSX superalloys, but also provides a powerful simulation tool for the creep behavior of γ'-strengthened superalloys.