A fully discrete Peierls model for the screw dislocation in Ta

Abstract

ABSTRACT The discrete Peierls model is generalised to be able to study the nonplanar dislocations as well as the planar dislocations. In the discrete model, the six-fold screw dislocation that is widely studied in numerical simulation and analytical theory splits into two different cores: the six-fold B core and the six-fold O core. The six-fold B core has the lowest energy and is the most stable while the six-fold O core has about 38 meV more energy in a period length. Because local dislocation hopping can only occur along the folds and hopping to sites out of the folds is not allowed, the dislocation movement is realised by transforming itself into a planar one in the model. The Peierls stress associated with this transition tunnel is , which is much higher than that obtained in simulations. Limitations of the model can be removed by using the two-dimensional energy landscape that is a natural consequence of the concept of the nonplanar dislocation. In the leading terms approximation of the two dimensional energy landscape, the non-Schmid behaviour of the screw dislocation in Ta is quantitatively predicted based on the model.