Crystallography of dislocation networks in annealed iron

Abstract

Crystallographic analyses of dislocation networks in annealed b.c.c. iron observed in the electron microscope have been carried out by applying the kinematical theory of electron diffraction contrast at dislocations and Frank's formula for determining the dislocation content of a grain boundary from a crystallographic survey. From the analyses, the Burgers vectors of the individual dislocations, as well as the other crystallographic properties of the networks, have been determined uniquely. The majority of the networks observed so far lie in {110} planes. The Burgers vector of the short segments of dislocations produced at the junctions of the a/2 dislocations has been positively identified as being of a type, and these segments are pure screw dislocations. From the observed contrasts, the magnitude and the relative sign of the Burgers vectors of junction dislocations also have been determined. The observed crystallographic features are generally in good agreement with the grain boundary model predicted for the b.c.c. lattice. The angle between the a/2 dislocations in the network is found to be approximately 90°, while the angle predicted by minimizing the elastic energy is 103°.