On the stress dependence of partial dislocation separation and deformation microstructure in austenitic stainless steels

In the austenitic stainless steels the separation of Shockley partial dislocations is known to play an important role in the plastic deformation and produces a variety of deformation microstructures depending on test and material conditions. Theoretical calculations have been carried out in an attempt to explain the origin of the deformation microstructures which include large stacking faults and twins. Force balance equations for the leading and trailing partials are established by considering the Peach-Koehler force from an applied stress field, repulsive force between leading and trailing partial dislocations, attractive force due to the stacking fault energy, and resistance (or damping) force to the glide of the partial dislocations. For a simple dislocation and stress arrangement, an expression for separation distance was derived from the force balance equations. The results indicate that the separation distance varies with the directional relationship between the applied stress and the Burgers vectors of glide dislocations. Also, the separation distance increases with the applied stress and can diverge when the applied stress exceeds a critical stress. The critical stress is readily achievable in the uniform strain range by strengthening measures like irradiation, lowering test temperature, and increasing strain or strain rate. Further, using a stress-based analysis, some predictions were attempted for the influence of radiation-induced defects on deformation microstructure in austenitic stainless steels.