Grain-boundary activated pyramidal dislocations in nano-textured Mg by molecular dynamics simulation

The generation and structures of first- and second-order pyramidal 〈c + a  〉 dislocations, 1/3{1 0 1¯ 1} 〈1¯ 1¯ 2 3〉 and 1/3{1 1 2¯ 2} 〈1¯ 1¯ 2 3〉, are determined in pure magnesium using molecular dynamics simulation. In particular, simulations of [1 1 2¯ 0]- and [1 0 1¯ 0]-textured polycrystalline Mg display pyramidal 〈c + a  〉 slip nucleated at grain boundaries. Both the first- and second-order dislocations appear as a partial or extended edge type. In the [1 1 2¯ 0]-textured Mg, the first-order pyramidal 〈c + a  〉 slip occurs with 1/6〈2¯ 0 2 3〉 partials or 1/9[0 1¯ 1 3]+1/18[6¯ 2 4 3]+1/6[0 2¯ 2 3] extended dislocations. Secondary pyramidal dislocations are created with edge type from grain boundaries in the [1 0 1¯ 0]-texture. The pyramidal 〈c + a  〉 slip on the {1 1 2¯ 2} plane can extend to the basal plane, on which it is terminated by a screw dislocation on the {1 0 1¯ 1} plane.

► First- and second-order pyramidal 〈c + a〉 slip occurs in Mg. ► The first-order edge dislocation can take place with a long stacking fault (SF). ► The first-order edge dislocation has two phases at high stress. ► The second-order 〈c + a〉 edge dislocation core with edge type is sessile. ► The second-order 〈c + a〉 edge dislocation is difficult to have a long SF.