On the slip and twinning mechanisms on first order pyramidal plane of magnesium: Molecular dynamics simulations and first principal studies
Reza Namakian, George Z. Voyiadjis, P. Kwaśniak
Abstract
Molecular dynamics simulations and first-principles calculations are carried out on first order pyramidal plane (π1) of magnesium to study both compression twinning (CTW) and dislocation slip. To this end, a generalized stacking fault energy analysis is employed on dense (π1D) and loose spaced (π1L) π1 planes. The crystal shearing resistance is extracted by using a minimum-energy path (MEP) finder called the nudged elastic band (NEB) method. The MEP regarding 1¯012101¯1π1L slip system shows that the unfaulted crystal structure is recovered in the middle of the path with non-straight and pronounced curved slip trajectories. Besides, it will be revealed that metastable configurations on the half of the MEP for 1¯012101¯1π1L slip system are indeed related to a dissociated 〈c + a〉 extended dislocation of loose pyramidal-I 〈c + a〉 slip, 1/31¯1¯23101¯1π1L. Also, after extracting the dissociation mechanism related to this dislocation, it will be shown that loose pyramidal-I 〈c + a〉 slip can involve shuffling. Moreover, the MEP for dense pyramidal-I 〈a〉 slip, 1/31¯21¯0101¯1π1D, shows transmutation of this slip into CTW in the middle of the path. This transmutation process will be further examined on CTW growth, and it will be demonstrated that this CTW mechanism is energetically more favorable compared to other twinning mechanisms.