The orientations of dipolar dislocation structures produced by the cyclic deformation of B.C.C. metals

Abstract

The orientations of dipolar walls produced by cyclic deformation in a renitrogenized mild steel and in literature observations on b.c.c. metals are shown generally to agree well with the predictions of a geometrical model of the dipolar wall, based on dipole loop stacking and on the sweeping of such loops into the walls by edge dislocations. Ladder-like walls within persistent slip bands are found to be perpendicular to the primary Burgers vector, as predicted for the dislocation activity of dislocations of a single Burgers vector. Literature observations of slip-bands containing rung-like walls not perpendicular to the primary Burgers vector are shown to be compatible with the two slip systems reported. Evidence for the occurrence of mutually perpendicular {100}-{210} and {311}-{110} combinations of labyrinth-like walls is also presented, with each combination predicted for a pair of {110}〈111〉 slip systems, the occurrence of which is compatible with the observations. In contrast to observations previously analyzed in f.c.c. metals, consideration of the cross-slip systems generally does not appear necessary to explain the observed wall orientations. It is suggested that the role of cross slip on influencing the orientations of the dipolar walls produced should depend on the test temperature and strain rate.