Molecular dynamics simulations of cavitation in a Zr 50 Cu 50 metallic glass exhibit a waiting time dependent cavitation rate. On short time scales nucleation rates and critical cavity sizes are commensurate with a classical theory of nucleation that accounts for both the plastic dissipation during cavitation and the cavity size dependence of the surface energy. All but one parameter, the Tolman length, can be extracted directly from independent calculations or estimated from physical principles. On longer time scales strain aging in the form of shear relaxations results in a systematic decrease of cavitation rate. The high cavitation rates that arise due to the suppression of the surface energy in small cavities provide a possible explanation for the quasibrittle fracture observed in metallic glasses. DOI: 10.1103/PhysRevLett.110.185502 PACS numbers: 63.50.Lm, 62.20.mm, 64.70.pe Amorphous materials, commonly termed glasses when quenched from the melt, occur in every class of material including ceramics, metals, and polymers. While the shear response of amorphous solids has received a significant amount of attention in the theoretical physics and molecular simulation literature over the past decade [1-8], significantly less attention has been devoted to hydrostatic loading in such systems [9,10]. This omission appears significant since experimental studies in metallic glass (MG) and other amorphous solids reveal nanocavities [11,12] that form during or subsequent to deformation and strongly implicate cavitation in the physics of the fracture process zone, even when the fracture behavior is relatively brittle [13][14][15]. The importance of cavitation in fracture is supported by recent molecular dynamics (MD) simulations in glassy Cu 50 Zr 50 and Fe 80 P 20 [16].Theory and simulation studies have been applied to understand this process in liquids more commonly than in glasses. Two recent studies [17,18] simulated the process of homogeneous nucleation in liquids in comparison with experimental data. These studies observed evidence of the curvature dependence of the surface energy on the measured cavitation rate, an effect that has itself been the subject of a significant amount of study [19][20][21][22]. One particularly notable contribution from simulation was the mapping out of the point at which the gas-liquid spinodal dips below the glass line and the glass must become unstable to cavitation [23].Continuum mechanics approaches to modeling the kinetics of cavitation have been developed over many years by numerous researchers [6,[24][25][26][27][28][29][30]. Often preexisting cavities are assumed to exist due to voids, inclusions, or intersections of grains, and the effect of surface energy is neglected. Various assumptions have been considered regarding the plastic constitutive behavior around the cavity [6,[24][25][26][27][28][29][30]. In these cases, because plastic and elastic energy both scale with the volume of the void, above a critical stress cavity growth becomes unbounded. Here, as in some earlier ...

The electronic structures and stability of Co/Cu(100) superlattices have been investigated by a first-principles method based on density functional theory. The models 3Co/xCu (x = 1–8 monolayers) with different Cu layer thicknesses are investigated. The result shows that the stability increases with an increase in Cu layer thickness for odd (or even) Cu layer models. The charge transfer is prominent at the Co–Cu interface; the magnetic moment of atoms at the interfaces is larger than that of the interior Co layers, and the nonmagnetic Cu layer at the interface is slightly spin polarized under the influence of the ferromagnetic Co layers in the neighborhood. Finally, the Fermi energy, densities of states and structural energy are also discussed.

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The structure and property of Si2CN4(010) surface with different terminations were studied systemically by first principles calculation. The calculated cleavage energies of each possible surface showed that the Si—NⅡ bond located at the SiN layer was the strongest,while the Si—NⅠ bond connected with the carbodiimide was the weakest. As a result,the surface with the Si/NⅠ termination was the easiest to form. We have compared the atomic structure and electronic properties of un-optimized and optimized surface models. During the optimization of structure,the unsaturated surface atom,especially the NⅠ atoms at the surface would bond with each other to decrease the surface energies,since there are prominent density of states existing at the Fermi level of NⅠ atom. At the same time,the unsaturated C atoms do not have the tendency of bonding with each other,since their electronic state are more stable than NⅠ atom.

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