Non-basal slip systems in HCP metals and alloys: source mechanisms

A possible source mechanism for non-basal <c +a> slip dislocations is proposed based on the formation of an attractive junction between glissile <a> and sessile e dislocations from the prism plane into a pyramidal plane. The driving force for the junction formation, which comes from the long-range elastic interaction between c and <a>dislocations, is relatively large in most hexagonal close-packed (hcp) metals. Beryllium, which has an unusually low Poisson's ratio, is an exception to this rule. The cross-slip process is energetically unfavorable in Mg and Ti, from a viewpoint of the change in anisotropic elastic line tension, but it becomes favorable in Ti at elevated temperatures above 300degreesC. Discussion is given on intrinsic stacking fault energies and kinetic aspects of the cross slip. (C) 2001 Elsevier Science B.V. All rights reserved.