Screw dislocation core structure in body-centred cubic iron

Abstract

The core structure of a screw dislocation with Burgers vector along [111] in body-centred cubic iron was evaluated numerically using an anharmonic potential matching the second and third-order elastic properties of the material. The core radius is found to be 3 to 4 Å and the corresponding core energy per identity distance along the dislocation line (three atom planes) is 0.25 to 0.35 ev. The core structure consists principally of three planar imperfections, corresponding to three intrinsic faults (of atomic dimensions) of the type 123456/56/123456 discussed by Frank and Nicholas (1953). There is a maximum energy barrier of 0.07 ev for motion of the screw dislocation in the [112] direction. The barrier is asymmetric and corresponds to ‘Peierls’ stresses at absolute zero of 4.1×10⁹ dynes/cm² and 2.7×10⁹ dynes/cm², respectively, for motion of the screw dislocation in the [112] and [112] directions.