Mechanism transition of cross slip with stress and temperature in face-centered cubic metals

Abstract

A<110>/2 screw dislocation is commonly dissociated into two <112>/6 Shockley partial dislocations on {111} planes in face-centered cubic metals. As the two partials are not purely screw, different mechanisms of cross-slip could take place, depending on the stacking fault energy, applied stress and temperature. It is crucial to classify the mechanisms of cross-slip because each mechanism possesses its own reaction path with a special activation process. In this work, molecular dynamics simulations have been performed systematically to explore the cross-slip mechanism under different stresses and temperatures in three different metals Ag, Cu and Ni that have different stacking fault energies of 17.8, 44.4 and 126.8 mJ/m2, respectively. In Ag and Cu with low stacking fault energy, it is observed that the cross-slip mechanism of screw dislocations changes from the Fleischer obtuse angle (FLOA), to the Friedel-Escaig (FE), and then to the FL acute angle (FLAA) at low temperatures, with increasing the applied stress. However, when the temperature increases, the FE mechanism gradually becomes dominant, while the FLAA only occurs at the high stress region. In particular, the FLOA has not been observed in Ni because of its high stacking fault energy.