Classical molecular-dynamics potential for the mechanical strength of nanocrystalline composite fccAl+α−Fe2O3

Abstract

A classical molecular-dynamics potential for analyzing mechanical deformation in the ␣-Fe 2 O 3 + fcc-Al material system is developed. The potential includes an embedded atom method cluster functional, a Morsetype pair function, and a second-order electrostatic interaction function. It is fitted to the lattice constants, elastic constants, and cohesive energies of fcc Al, bcc Fe, ␣-Fe 2 O 3 , ␣-Al 2 O 3 , and B2-FeAl, accounting for the fact that mixtures of Al and Fe 2 O 3 are chemically reactive and deformation may cause the formation of these components as reaction products or intermediates. To obtain close approximations of the behavior of mixtures with any combination of the atomic elements, the potential is formulated and fitted such that the Al-Al, Fe-Fe, Al-Fe, O-O, Fe-O, and Al-O interactions are accounted for in an explicit and interdependent manner. In addition to being fitted to the lattice constants, elastic constants, and cohesive energies, the potential gives predictions of the surface and stacking fault energies for the crystalline components that compare well with the predictions of established potentials in the literature for the corresponding crystalline components. The potential is applied to analyze quasistatic tensile deformation in nanocrystalline Al, in nanocrystalline Fe 2 O 3 , and in nanocrystalline Al+ Fe 2 O 3 composites. Application of the potential to nanocrystalline Al reveals the features of mechanical deformation, such as the formation of unit dislocations, flow strength approaching ideal shear strength, and the Hall-Petch relationships, that are in close agreement with experiments and with the predictions of established potentials for Al in the literature. Analyses of deformation in nanocrystalline Fe 2 O 3 and in nanocrystalline Al+ Fe 2 O 3 composites point to the possibility that the strength of the nanocomposites can only be calculated using the mixture theory if the average grain size is above a critical value. Below the critical grain size, an accurate account of interfacial stresses is important to the prediction of the strength. For composites with grain sizes above the critical value, the observed dependence of strength on volume fraction is in agreement with experimental observations.

Atomistic modeling of interfaces and their impact on microstructure and properties

“…Several potentials have been proposed for ternary systems (see e.g. [113][114][115]). Unfortunately, the quality of ternary potentials remains far from the level currently achieved for pure metals and binary alloys.…”

Oxidation of nanocrystalline aluminum by variable charge molecular dynamics

“…Initially designed to simulate the properties of one metal (namely Al) interacting with oxygen, the Streitz and Mintmire potential was recently extended/modified to simulate many metals (Ti, Zr, Fe, Ni, Co,…) and alloys [12][13][14][15][16][17][18]. It was used to study nanocrystalline metal-oxide properties [16][17][18] or processes involved in the oxidation of metallic substrates [12,13,[19][20][21][22].…”

“…It was used to study nanocrystalline metal-oxide properties [16][17][18] or processes involved in the oxidation of metallic substrates [12,13,[19][20][21][22].…”

Ideal strength and structural instability of aluminum at finite temperatures

“…Despite numerous past studies 1,3,8,9,12,[16][17][18][19][20][21][22][23][24][25] , there remain questions on the fundamental properties of Al, such as how the temperature would affect the strength under various loading conditions and whether the lattice instability behaviors predicted at T=0 K would change with rising temperature. Previous first-principles calculations (at T=0 K) predict that under the <001>, <011>, <111> uniaxial tension and the {111} <112> shear deformation, dynamic phonon instabilities always precede the elastic instabilities determined by the peak stresses in ideal strength calculations 12 .…”