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

► 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. 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.