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Abstract

Nickel based superalloys are precipitation strengthened materials that are widely used in gas turbines for applications including aerospace, electricity generation, gas and oil pumping and marine propulsion. Turbine blades of superalloy single crystals are lifetime-limited by their creep performance. Techniques such as thermal barrier coatings, internal cooling passages and laser-ablated effusion cooling holes produce the temperature distribution span several hundred Kelvin. Under these conditions the primary, tertiary and rafting creep regions may exist in a single blade cross section at the same time. This work focuses on the development of constitutive models adopting a unit cell (schematic microstructure) based on crystal plasticity finite element models (CPFEM). Most of the mechanisms mentioned above are being taken into account in a realistic, physically motivated manner. However, there remain some mechanisms for which simplified approaches have to be used. Within our model we consider local stresses of different phases due to external load, lattice misfit and dislocation deposition in matrix-precipitate interfaces, to predict dislocation filling processes in gamma channels. The probability of super-dislocation nucleation during the filling process has been investigated. The influence of rafting kinetics has been formulated by minimization of Gibb’s free energy in a unit cell including one precipitate and 3 matrix channels. Creep behaviours of superalloy single crystals in a wide range of temperatures and along different crystallographic orientations, rafting processes under different loading conditions and their influences on creep resistances as well as crack nucleation and propagation have been studied and compared with experiments to validate the model.