Atomistic study of edge and screw textless c plus a textgreater dislocations in magnesium

The gamma surfaces in the pyramidal I {1 -1 0 1} and II {1 1 -2 2} planes for hexagonal close packed Mg have been calculated using two embedded-atom-method potentials and by ab initio methods, and reasonable agreement is obtained for key stacking fault energies. Screw and edge textless c + a textgreater dislocation core structures and Peierls stresses at 0 K and finite temperature have been examined using the embedded-atom-method potentials. Screw textless c + a textgreater dislocations glide in the {1 -1 0 1} pyramidal plane I, and in the prism plane for larger stresses, but not in the {1 1 -2 2} plane as observed in experiments. However, the preference for pyramidal I glide correlates well with the gamma surfaces. New low energy edge textless c + a textgreater dislocation cores were found in addition to the sessile Type I and Type III cores observed in previous simulations while the Type II core was not observed. The lowest energy core is a glissile core that lies in the {1 1 -2 2} plane and has a 3 nm long {1 1 -2 1} twin embryo, rather than the sessile Type III core found in previous simulations. As the temperature increases from 0 to 300 K, the Peierls stresses in compression/tension drop from -80 MPa/+140 MPa and -140 MPa/+220 MPa for the most glissile screw and edge dislocations to -5/+2.5 MPa and -27/+5 MPa, and dislocation glide changes from kink motion to face-centered-cubic-like motion. At 300 K and under an applied stress, almost all the edge cores found at low temperature transform into a glissile core denoted IT, which glides at low stresses. Thus, at 300 K both screw and edge textless c + a textgreater dislocations were found to glide at stresses smaller than the similar to 40 MPa measured experimentally. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Published in:
Acta Materialia, 58, 4332-4343

 Record created 2014-11-07, last modified 2018-12-03

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