Crystallography of dislocations and dislocation loops in deformed iron

Abstract

Crystallographic analyses of dislocations and dislocation loops in deformed b.c.c. iron observed in the electron microscope have been carried out by applying the electron diffraction theory of contrast at dislocations. Dislocations in deformed iron are in the form of tangles, with interspersed clusters of dislocation loops, from the very first stage of deformation. Crystallographic analyses show that the tangles consist of dislocations of two distinct Burgers vectors, in the ratio of approximately two to one. The dislocations of the primary system are composed of segments of both signs, in roughly equal proportion. The Burgers vector of a majority of dislocation loops is identical to that of the primary dislocations, and the rest of the loops belong to the secondary system. The loops are found to be pure edge prismatic dislocations lying in {111} planes, and are identified as being of vacancy type. From a consideration of the elastic theory of defect interaction, it is concluded that the interactions of dislocations with dislocations of dissimilar Burgers vectors and the formation of a cluster of small loops around the dislocations and junctions are responsible for formation of dislocation tangles.