Parametric variations of the interatomic potential in atomistic analysis of nano-scale metal plasticity

Abstract

Atomistic simulations of plastic deformation in nano-scale copper crystals are carried out. Attention is devoted to adjusting interatomic potential parameters with the objective of gaining fundamental insight into the crystal defect processes in FCC metals. An initial point defect is utilized in the molecular statics model to trigger plasticity in a controlled manner. Two different potential models have been employed: Morse and Embedded Atom Method. With the Morse potential, the interaction range has been parameterized to view dislocation slip behavior and/or phase transformation without the influence of an unstable surface state of the specimen. We focus on tensile loading along a low-symmetry orientation where single slip prevails upon yielding. When the Morse interaction distance is small, dislocation slip is seen to be the dominant deformation mechanism. A slight increase in the interaction range results in phase transition from the FCC structure to a BCC structure when using the Morse potential. Re-orientation of the BCC lattice also occurs at later stages of the deformation via a twinning operation. When the atomic interaction range is increased further, the effect of surface stress becomes increasingly important. Plastic yielding occurs in the form of partial slip which creates stacking faults. The initial point defect plays a less significant role and phase transition during deformation is suppressed. Detailed mechanisms of these atomistic features, as well as comparisons between the two potentials, are discussed.