1,721,018 research outputs found
Atomistic models of basal dislocation dipoles in proton-ordered hexagonal ice
No full textThere are 8 files in total
The files are LAMMPS-readable
Naming convention is (shape)_(set)_(character).data, where
- (shape) can be "straight" or "kinked"
- (set) can be "shuffle" or "glide"
- (character) can be "60deg" or "screw"
For example, kinked_shuffle_60deg.data contains a dipole of kinked dislocations residing on shuffle set planes and having 60 degree character
Hydrogen reverses the clustering tendency of carbon in amorphous silicon oxycarbide
No full textAmorphous silicon oxycarbide (SiOC) is of great technological interest. However, its atomic-level structure is not well understood. Using density functional theory calculations, we show that the clustering tendency of C atoms in SiOC is extremely sensitive to hydrogen (H): without H, the C-C interaction is attractive, leading to enrichment of aggregated SiC[subscript 4] tetrahedral units; with hydrogen, the C-C interaction is repulsive, leading to enrichment of randomly distributed SiCO[subscript 3] tetrahedral units. Our results suggest that conflicting experimental characterizations of C distributions may be due to differing amounts of H present in the samples investigated. Our work also opens a path for tailoring the properties of SiOC by using the total H content to control the C distribution.United States. Dept. of Energy. Office of Nuclear Energy (Nuclear Energy Enabling Technologies, Reactor Materials Program Contract DE-NE0000533
Non-coherent Cu grain boundaries driven by continuous vacancy loading
Get PDFWe use atomistic modeling to study the response of three non-coherent grain boundaries (GBs) in Cu to continuous loading with vacancies. Our simulations yield insights into the structure and properties of these boundaries both near and far from thermal equilibrium. We find that GB energies vary periodically as a function of the number of vacancies introduced. Each GB has a characteristic minimum energy state that recurs during continuous vacancy loading, but in general cannot be reached without removing atoms from the boundary. There is no clear correlation of GB energies with GB specific excess volumes or stresses during vacancy loading. However, GB stresses increase monotonically with specific excess volumes. Continuous vacancy loading gives rise to GB migration and shearing, despite the absence of applied loads. Successive vacancies introduced into some of the boundaries accumulate at the cores of what appear to be generalized vacancy dislocation loops. We discuss the implications of these findings for our understanding of grain boundary sink efficiencies under light ion irradiation.United States. Dept. of Energy. Office of Basic Energy Sciences. Center for Materials in Irradiation and Mechanical Extremes (Award 2008LANL1026
Formation, migration, and clustering of delocalized vacancies and interstitials at a solid-state semicoherent interface
No full textAtomistic simulations are used to study the formation, migration, and clustering of delocalized vacancies and interstitials at a model fcc-bcc semicoherent interface formed by adjacent layers of Cu and Nb. These defects migrate between interfacial trapping sites through a multistep mechanism that may be described using dislocation mechanics. Similar mechanisms operate in the formation, migration, and dissociation of interfacial point defect clusters. Effective migration rates may be computed using the harmonic approximation of transition state theory with a temperature-dependent prefactor. Our results demonstrate that delocalized vacancies and interstitials at some interfaces may be viewed as genuine defects, albeit governed by mechanisms of higher complexity than conventional point defects in crystalline solids.National Science Foundation (U.S.) (Grant No. OCI-1053575)United States. Dept. of Energy. Office of Basic Energy Sciences (Award No. 2008LANL1026
Healing of Nanocracks by Disclinations
No full textWe present a new mechanism—discovered using molecular dynamics simulations—that leads to complete healing of nanocracks. This mechanism relies on the generation of crystal defects known as disclinations by migrating grain boundaries. Crack healing by disclinations does not require any compressive loads applied normal to the crack faces and even occurs under monotonic tensile loading. By closing small cracks and suppressing the propagation of others, this mechanism may provide a novel way of mitigating internal damage that influences ductility in nanocrystalline metals.BP-MIT Materials and Corrosion Cente
Probing Interfaces in Metals Using Neutron Reflectometry
Get PDFSolid-state interfaces play a major role in a variety of material properties. They are especially important in determining the behavior of nano-structured materials, such as metallic multilayers. However, interface structure and properties remain poorly understood, in part because the experimental toolbox for characterizing them is limited. Neutron reflectometry (NR) offers unique opportunities for studying interfaces in metals due to the high penetration depth of neutrons and the non-monotonic dependence of their scattering cross-sections on atomic numbers. We review the basic physics of NR and outline the advantages that this method offers for investigating interface behavior in metals, especially under extreme environments. We then present several example NR studies to illustrate these advantages and discuss avenues for expanding the use of NR within the metals communityUnited States. Dept. of Energy. Office of Basic Energy Sciences. Center for Materials at Irradiation and Mechanical Extremes (Award 2008LANL1026
The role of interface structure in controlling high helium concentrations
No full textInterfaces are good traps for implanted He, but are also susceptible to He-induced embrittlement. Better understanding of the mechanisms of He interactions with interfaces may enable design of interfaces that control He while remaining mechanically sound. We review recent work that aims to gain such insight by determining how interface structure influences He trapping and the equation of state of He in interface bubbles as well as how He-induced hardening depends on interface area per unit volume in composite materials.United States. Dept. of Energy. Office of Basic Energy Sciences. Center for Materials in Irradiation and Mechanical Extremes (CMIME) (Award 2008LANL1026)Los Alamos National Laboratory. Laboratory Directed Research and Development Progra
The role of thermal spike compactness in radiation-induced disordering and Frenkel pair production in Ni[subscript 3]Al
No full textWe show that the shape of the kinetic energy distribution in radiation-induced thermal spikes may be described using a dimensionless number, proportional to (volume)[superscript 2/3]/(surface area), known as compactness. The disorder produced in thermal spikes in Ni[subscript 3]Al increases with compactness because the thermal spike cooling rate, which determines the time available for thermal disordering, decreases with compactness. On the other hand, Frenkel pair production is inversely correlated to compactness because longer thermal spike lifetimes enhance vacancy–interstitial recombination
Glass Transition by Gelation in a Phase Separating Binary Alloy
No full textWe use molecular dynamics simulations to show that glass transition in a model phase separating amorphous alloy, Cu50Nb50, occurs by gelation. At the glass transition, a mechanically stiff, percolating network of atoms with icosahedral local packing forms at the interfaces between compositionally enriched regions. This low-energy network halts coarsening of the phase-separated structure and imparts shear resistance. These features of glass transition are remarkably similar to gelation processes in polymeric and colloidal gels.National Science Foundation (U.S.) (Graduate Research Fellowship Grant No. 1122374
Determining the Burgers vectors and elastic strain energies of interface dislocation arrays using anisotropic elasticity theory
Get PDFA formalism for describing interface dislocation arrays linking the Frank–Bilby equation and anisotropic elasticity theory under the condition of vanishing far-field stresses is developed. The present approach enables the determination of a unique reference state for interface misfit dislocations, within which the Burgers vectors of individual dislocations are defined and allows for the unequal partitioning of elastic fields between neighboring crystals. The elastic strain energies of interface dislocation arrays are computed using solutions for short-range elastic fields. Examples of applications to simple interfaces are given, namely symmetric tilt and twist grain boundaries, as well as a pure misfit heterophase interface.United States. Dept. of Energy. Office of Basic Energy Sciences (Award 2008LANL1026)National Science Foundation (U.S.) (Grant 1150862
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