Displacement fields around 1/2[111] screw dislocations in bcc metals and their defocus convergent-beam electron diffraction patterns

Abstract

Displacement fields have been calculated around 1/2[111] screw dislocations with various types of core structures in bcc metals. Three types of cores are studied: two types of polarized cores with large and small extensions of the displacement fields and an isotropic core. The difference in the displacement along the [111] direction ∆uz from that for the elastic solution has been evaluated for each type of dislocation. In the outside of the core region, the Duz values are close to zero along the six directions and the regions with ∆uz > 0 and ∆uz <o are alternately arranged, lying between those directions. Appreciable difference in ∆uz has been detected between the polarized cores and the isotropic core up to large distance from the core region. The defocus convergent-beam electron diffraction patterns have been calculated for the dislocations with the incident beam parallel to the dislocation line. Winding and spiral features have been shown in the higher-order Laue zone (HOLZ) lines for the dislocated structures, which have been confirmed by a preliminary experiment. In addition, small shifts of the HOLZ lines have been shown by the calculation between the polarized cores and the isotropic one.