The thermally activated glide of edge and screw dislocations, with a Burgers vector of a/2(110), in Fe-Ni-Cr austenite (with or without N) was analyzed by using the conjugate gradient method to minimize the potential energy of the crystal, and the embedded-atom method to treat the atomic interactions. It was found that, in N-free austenite, the variation in crystal energy with dislocation position gave rise to a Peierls frictional stress. However, the magnitude of this stress was relatively low, and edge and screw dislocations could easily overcome it via thermal activation. On the other hand, the presence of N caused the core of a screw dislocation to dissociate onto two {111} planes that contained the dislocation line. This caused the screw dislocation to be sessile. The interaction of N with edge dislocations was found to give rise to both an athermal (long-range) and a thermal (short-range) component of the frictional stress. A detailed analysis of the interactions between N atoms and edge dislocations suggested that the athermal component of the frictional stress was more likely to be responsible for the experimentally observed athermal flow stress in polycrystalline Fe-Ni-Cr austenite. However, with the possible exception of very low temperatures, the strength contribution of the thermal frictional stress that was associated with the interaction of edge dislocations with N was expected to be small.

M.Grujicic, X.W.Zhou: Materials Science and Engineering A, 1995, 190[1-2], 87-98