Modeling displacive–diffusional coupled dislocation shearing of γ′ precipitates in Ni-base superalloys

Abstract In Ni-base superalloys, superlattice extrinsic stacking fault (SESF) shearing of γ′ precipitates involves coupled dislocation glide and atomic diffusion. A phase-field model is developed to study this process, in which the free energy of the system is formulated as a function of both displacement and long-range order parameter. The free energy surface is fitted to various fault energy data obtained from experiments and ab initio calculations. Three-dimensional simulations at experimentally relevant length scales are carried out to investigate systematically the influence of microstructural features on the critical resolved shear stress. The simulations reveal that the critical resolved shear stress for SESF shearing is determined not only by the SESF energy itself, but also by the complex stacking fault energy and by the shape (interface curvature) and spacing of γ′ precipitates. The effect of reordering kinetics (i.e. temperature effect) is also investigated. It is found that viscous deformation can only occur within certain domain of intermediate temperatures.