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

Modeling Displacive–Diffusional Coupled Dislocation Shearing of γ′ Precipitates in Ni-Base Superalloys. N.Zhou, C.Shen, M.J.Mills, J.Li, Y.Wang: Acta Materialia, 2011, 59[9], 3484-97