• Baskes, M. I.

Abstract

Recent advances in computers and atomistic modeling have made the realistic simulation of materials behavior possible. Two decades ago, modeling of materials at the atomic level used simple pair potentials. These potentials did not provide an accurate description of the elastic properties of materials or of the formation of free surfaces, a phenomenon critical in the fracture process. This paper will review the evolution of the Embedded Atom Method (EAM), a modern theory of metallic cohesion that was developed to overcome the limitations of pair potentials. The EAM includes many body effects that are necessary to describe such processes as bond weakening (or strengthening) by impurities. We examine the effects of deformation on polycrystalline FCC metals. We perform simple shear molecular dynamics simulations using the EAM on nickel samples of -10000 atoms to study yield and work hardening. It is found that the deformation is always inhomogeneous when a grain boundary or free surface is present. The atomistic simulations reveal that dislocations nucleating at grain boundaries or free surfaces are critical to causing yielding in pristine material as observed in experiment. Detailed investigation shows that the grain boundaries are significantly weaker than the bulk material and yield at a lower stress. Even so, the yield stress of the polycrystalline samples with either low angle and high angle grain boundaries are found to be similar and only slightly lower than the yield stress of single crystals with the same characteristic dimensions. The local yield stress at the boundaries if found to be significantly less than the average yield stress.

Topics

• impedance spectroscopy
• surface
• single crystal
• grain
• nickel
• grain boundary
• theory
• experiment
• simulation
• molecular dynamics
• laser emission spectroscopy
• dislocation
• plasticity