High-resolution electron microscopy and molecular dynamics study of the (a/2)[111] screw dislocation in · molybdenum

Abstract

The structure of the (a/2)[111] screw dislocation in Mo is studied by high-resolution transmission electron microscopy (HRTEM) and by molecular dynamics (MD) simulation. Detailed analysis of HRTEM images reveals, for the first time, the nonplanar dissociation of the screw dislocation core which is responsible for the high flow stress of bcc metals at low temperatures. It is shown that image contrast is dominated by surface relaxations induced by the Eshelby twist. These relaxations do not exactly correspond to those given theoretically by Eshelby and Stroh but are influenced by the nonplanar core dissociation. It is concluded that MD simulations are important for the interpretation of HRTEM images of defects which lead to shear stress components on the surface.