The "phase field microelasticity theory of dislocations" has been used to study the propagation of dislocation ribbons with an overall Burgers vector of a 112 through a simulated Ni-base superalloy. The driving force for dislocation dissociation reactions and formation of planar faults is incorporated into the free energy using γ-surface functions specially fitted to ab initio data. The model shows that the mechanism of cutting of the γ precipitates by these ribbons exhibits significant dependence on stress magnitude, orientation and precipitate shape. In the case of mixed screw-edge ribbons a change of shearing mode is observed, from stacking fault shear to APB shear, when the applied stress approaches the yield of the material. This transition is absent in pure edge ribbons.