Unconventional {101¯2} twinning assisted by pyramidal II stacking faults

Twinning significantly affects the deformation behavior of hexagonal close-packed Mg, so a thorough understanding of twin nucleation and growth mechanisms is required for enhancing the properties of Mg-based materials. The commonly observed <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>{</mml:mo> <mml:mn>10</mml:mn> <mml:mrow><mml:mover><mml:mn>1</mml:mn> <mml:mo>¯</mml:mo></mml:mover> </mml:mrow> <mml:mn>2</mml:mn> <mml:mo>}</mml:mo></mml:mrow> </mml:math> tension twins have been traditionally linked to 〈c + a〉 dislocation dissociation, which results in zonal dislocations with large Burgers vectors several times that of a single twinning dislocation and some residual dislocations. Contrarily, our molecular dynamics simulations reveal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>{</mml:mo> <mml:mn>10</mml:mn> <mml:mrow><mml:mover><mml:mn>1</mml:mn> <mml:mo>¯</mml:mo></mml:mover> </mml:mrow> <mml:mn>2</mml:mn> <mml:mo>}</mml:mo></mml:mrow> </mml:math> twin nucleation from pyramidal II stacking faults through atomic shuffling without shear displacements. This introduces an alternative twin nucleation mechanism, different from the classically accepted mechanism of dislocation dissociation.