Dislocation constriction and cross-slip in Al and Ag an ab initio study.pdf

a r X i v : c o n d - m a t / 0 2 0 2 4 8 8 v 1 [ c o n d - m a t .m t r l - s c i ] 2 6 F e b 2 0 0 2 Dislocation constriction and cross-slip in Al and Ag: an ab initio study Gang Lu,1 Vasily V. Bulatov,2 and Nicholas Kioussis3 1Department of Physics and Division of Engineering and Applied Science, Harvard University, Cambridge, MA 02138 2Lawrence Livermore National Laboratory, Livermore, CA 94550 3Department of Physics, California State University Northridge, Northridge, CA 91330 Abstract A novel model based on the Peierls framework of dislocations is developed. The new theory can deal with a dislocation spreading at more than one slip planes. As an example, we study dislocation cross-slip and constriction process of two fcc metals, Al and Ag. The energetic parameters entering the model are determined from ab initio calculations. We find that the screw dislocation in Al can cross-slip spontaneously in contrast with that in Ag, which splits into partials and cannot cross-slip without first being constricted. The dislocation response to an external stress is examined in detail. We determine dislocation constriction energy and critical stress for cross-slip, and from the latter, we estimate the cross-slip energy barrier for the straight screw dislocations. 1 The cross-slip process by which a screw dislocation moves from one slip plane to an- other, plays an important role for plastic deformation in materials. For example, cross-slip is responsible for the onset of stage III of the stress-strain work-hardening curve; it is also responsible for the anomalous high temperature yield stress peak observed in L12 inter- metallic alloys. However cross-slip has been a tough problem to tackle because it contains both long-ranged elastic interactions between dislocation segments and short-ranged atomic interactions due to the constriction process, in which the two partial dislocations have to be recombined into a screw dislocation before cross-slip takes place. There ar