Abstract Scope |
Solute accelerated cross-slip of <c+a> dislocation from low-energy pyramidal II to high-energy pyramidal I plane has recently been discovered as critical in encouraging pyramidal <c+a> slip and enhancing ductility in certain solid solution Mg alloys. Favorable solutes, e.g. rare-earth elements, Ca, and Mn, reduce the cross-slip barrier by lowering the pyramidal I-II screw dislocation energy difference. Increasing the solute concentration can cause pyramidal I to become more stable than pyramidal II, modifying the cross-slip behavior and energetics. As pyramidal I becomes increasingly favorable, cross slip becomes difficult and the alloy may lose ductility. Here, the double cross-slip mechanism of <c+a> dislocation, when pyramidal I has lower energy than pyramidal II, is studied using transition path computations by employing a pure Mg MEAM potential. The mechanistic model of ductility is then extended to this regime and predicts an upper limit of solute concentration beyond which ductility of Mg alloy will deteriorate. |