An atomistic study of the strength of an extended-dislocation barrier

The stress dependence of a lock consisting of a a1÷3a[100] stair rod symmetrically located between two Shockley partials in face-centred cubic nickel was examined by atomistic simulation. The applied stress forced the partials into the stair rod. As the partials move into the lock with increasing strain, the separation distances are reasonably consistent with a linear elastic calculation of equilibrium separation except at the closest approach where the elastic calculation overestimates the separation. The overestimation is attributable to core overlap. The lock underwent several unstable transitions before becoming an inverted arrangement of its initial configuration. The sequence of transitions involves an asymmetric configuration at 2.3% strain containing an extrinsic fault, a transition at 4.8% strain that changes the stair rod to 1÷6a[011], and a transition that inverts the lock at 6% strain with the stair rod becoming 1÷6a[100]. The evolution of the lock is not reversible.