Atomistic simulations were used to investigate how grain boundary structure influences dislocation nucleation under uniaxial tension and compression for a specific class of symmetric tilt grain boundaries that contained the E structural unit. After obtaining the minimum energy grain boundary structure, molecular dynamics was employed based upon an embedded-atom method potential for copper at 10K. Results showed several differences in dislocation nucleation with respect to uniaxial tension and compression. First, the average nucleation stress for all <110> symmetric tilt grain boundaries was over three times greater in compression than in tension for both the high strain rate and quasistatic simulations. Second, partial dislocations nucleate from the boundary on the {111} slip plane under uniaxial tension. However, partial and full dislocations nucleate from the boundary on the {100} and {111} slip planes under uniaxial compression. The full dislocation nucleation on the {100} plane for boundaries with misorientations near the coherent twin boundary was explained through the higher resolved shear stress on the {100} plane compared to the {111} plane. Last, individual dislocation nucleation mechanisms under uniaxial tension and compression were analyzed. For the vicinal twin boundary under tension, the grain boundary partial dislocation was emitted into the lattice on the same {111} plane that it dissociated onto. For compression of the vicinal twin, the 1/3<111> disconnection was removed through full dislocation emission on the {100} plane and partial dislocation emission parallel to the coherent twin boundary plane, restoring the boundary to the coherent twin. For the Σ19 boundary, the nearly simultaneous emission of numerous partial dislocations from the boundary resulted in the formation of the hexagonal close-packed phase.

Atomistic Simulations of Tension–Compression Asymmetry in Dislocation Nucleation for Copper Grain Boundaries. M.A.Tschopp, G.J.Tucker, D.L.McDowell: Computational Materials Science, 2008, 44[2], 351-62