Elastic properties of crystal surfaces are useful in understanding mechanical properties of nanostructures. This paper presents a fully nonlinear treatment of surface stress and surface elastic constants. A method for the determination of surface elastic properties from atomistic simulations is developed. This method is illustrated with examples of several crystal faces of some fcc metals modeled with embedded atom potentials. The key finding in this study is the importance of accounting for the additional relaxations of atoms at the crystal surface due to strain. Although these relaxations do not affect the values of surface stress (as had been determined in previousworks), they have a profound effect on the surface elastic constants.Failure to account for these relaxations can lead to values of elastic constants that are incorrect not only in magnitude but also in sign. A possible method for the experimental determination of the surface elastic constants is outlined.

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Atomistic calculations of elastic properties of metallic fcc crystal surfaces

The behaviour of copper atoms in dilute solution in α-iron is important for the microstructural changes that occur in ferritic pressure vessel steels under fastneutron irradiation. To investigate the properties of atomic defects that control this behaviour, a set of many-body interatomic potentials has been developed for the Fe—Cu system. The procedures employed, including modifications to ensure suitability for simulating atomic collisions at high energy, are described. The effect of copper on the lattice parameter of iron in the new model is in good agreement with experiment. The phonon properties of the pure crystals and, in particular, the influence of the instability of the metastable, bcc phase of copper that precipitates during irradiation are discussed. The properties of point defects have been investigated. It is found that the vacancy has lower formation and migration energy in bcc copper than in α-iron, and the self-interstitial atom has very low formation energy in this phase of coppe...

Computer simulation of point defect properties in dilute Fe—Cu alloy using a many-body interatomic potential

The requirements for fitting bcc metals within the EAM format are discussed and, for comparative purposes, the EAM format is cast in a normalized form. A general embedding function is defined and an analytic first- and second-neighbor model is presented. The parameters in the model are determined from the cohesive energy, the equilibrium lattice constant, the three elastic constants, and the unrelaxed vacancy formation energy. Increasing the elastic constants, increasing the elastic anisotropy ratio, and decreasing the unrelaxed vacancy formation energy favor stability of a close-packed lattice over bcc. A stable bcc lattice relative to close packing is found for nine bcc metals, but this scheme cannot generate a model for Cr because the elastic constants of Cr require a negative curvature of the embedding function.

Analytic embedded atom method model for bcc metals

Interfaces act as obstacles to slip and sinks for radiation-induced defects. Hence, nanolayered composites that contain a large volume fraction of interfaces provide over an order of magnitude increase in strength and enhanced radiation damage tolerance compared to bulk materials. This paper shows the experimental and atomistic modeling results from a Cu-Nb nanolayered composite to highlight the roles of nanostructuring length scales and the response of interfaces to ion collision cascades in designing composite materials with high radiation damage tolerance.

The radiation damage tolerance of ultra-high strength nanolayered composites

Recent advances in the fundamental understanding of the deformation mechanisms in metallic multilayers are reviewed. The strength of metallic multilayers increases with decreasing layer thickness and reaches a maximum at layer thickness of a couple of nanometers. The unit processes of slip transmission across the interphase boundary, without the mechanical advantage of a dislocation pile-up, are critical in determining the maximum flow strengths of multilayers. For the case of non-coherent fcc–bcc nanolayered composites such as Cu–Nb, we show that the atomic structure of the interface leads to low interface shear strength. The stress field of a glide dislocation approaching the interface locally shears the interface, resulting in dislocation core spreading and trapping in the interface plane. Glide dislocation trapping at the weak interface via core spreading is thus the key unit process that determines the interface barrier to slip transmission. The maximum strength achieved in a non-coherent multilayer can be tailored by the shear strength of the interface. The role of the atomic structure of the interface in promoting room temperature climb at interfaces and its implications in dislocation recovery is highlighted. Experimental validation of the model predictions is discussed.

An overview of interface-dominated deformation mechanisms in metallic multilayers

A procedure based on the embedded atom method (EAM) is presented for developing atomistic models for use in computer simulation calculations, with an emphasis on simple but general schemes for matching experimental data with fitting parameters. Both the electron density function and the two-body potential are taken as exponentially decreasing functions and the model is derived for any choice of cutoff distance. The model has been applied successfully to seven fcc and three hcp metals, but the extension to bcc metals was unsuccessful because of difficulty in matching the shear anisotropy ratio.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/66C95CA93C651BA72FCF320BE0183AEF/S0884291400002697a.pdf/div-class-title-simple-embedded-atom-method-model-for-fec-and-hcp-metals-div.pdf

D. J. Oh

Papers

Analytic embedded atom method model for bcc metals

Simple embedded atom method model for fcc and hcp metals