Grain boundary structure search by using an evolutionary algorithm with effective mutation methods

The role of grain boundary structure and crystal orientation on crack growth asymmetry in aluminum

Effect of grain boundary atomic density and temperature on <110> symmetric tilt grain boundaries in tungsten: An atomistic study

Using molecular dynamics (MD) simulations, the dislocation structures of symmetric tilt grain boundaries (STGBs) in hexagonal close packed (hcp) crystal structures are studied. STGBs over the entire range of possible rotation angles θ from 0° to 90° are found to have an ordered atomic structure. Formation energy calculations reveal four local minimum-energy boundaries that correspond to coherent grain boundaries (GBs). Deviations in tilt from the basal plane (θ = 0°, , prismatic plane (θ = 90°, , or one of these four minimum-energy boundaries, , result in the formation of a tilt wall (edge-type grain boundary dislocations, GBDs) superimposed on the nearest GB structure in θ-space. As θ deviates far from the rotation angle of one and draws closer to that of an adjacent , an abrupt transition in STGB base boundary structure and GBD Burgers vector occurs. For all θ, the sign and spacing of GBDs depend on θ, and their Burgers vector is either one or two times the interplanar spacing of PB. We present a simple model that generalizes the results to other c/a ratios. Subsequent MD simulations show that (1) the model forecasts the STGB structure to first-order and (2) STGBs with two distinct atomic structures can have remarkably different responses when interacting with basal lattice dislocations originating from the adjoining crystals.

Strontium Titanate is a prototypical perovskite oxide whose macroscopic electroceramic properties, like varistor and grain boundary barrier layer capacitor (GBBLC) behavior, are controlled by grain boundary (GB) phenomena. In this paper, we present a comparative analysis of the results of both experimental and theoretical investigations of the atomic structure of a (310) symmetrical tilt GB (a Σ=5 (310) [001] GB in the CSL notation) in SrTiO3. Bicrystals of SrTiO3 were procured from Shinkosha Ltd., and electron backscatter kikuchi pattern analysis as well as transmission electron diffraction studies confirm that the GB conforms to the Σ =5 misorientation. The atomic structure of this GB has been investigated using high resolution transmission electron microscopy (HRTEM) and associated image simulations, as well as by atomistic simulations using static iterative energy minimization schemes (“lattice-statics”).2

Using an interatomic potential that can capture the tetrahedral configuration of water molecules (H2O) in ice without the need to explicitly track the motion of the O and H atoms, coarse-grained (CG) atomistic simulations are performed here to characterize the structures, energy, cohesive strengths, and fracture resistance of the grain boundaries (GBs) in polycrystalline ice resulting from water freezing. Taking the symmetric tilt grain boundaries (STGBs) with a tilting axis of ⟨0001⟩ as an example, several main findings from our simulations are (i) the GB energy, EGB, exhibits a strong dependence on the GB misorientation angle, θ. The classical Read-Shockley model only predicts the EGB - θ relation reasonably well when θ < 20° or θ > 45° but fails when 20° < θ < 45°; (ii) two "valleys" appear in the EGB-θ landscape. One occurs at θ = 22° for Σ14(2̅31̅0) GB, and the other is at θ = 32° for Σ26(3̅41̅0) GB. These two GBs might be the most common in polycrystalline ice; (iii) all the STGB structures under consideration here are found to be a collection of edge dislocations with a Burgers vector of b = 1/3⟨112̅0⟩. The core structure of this edge dislocation is composed of a pentagon and a heptagon atomic ring. The separation and orientation of the structure units (SUs) at the GB exhibit a strong dependence on θ; (iv) the length of an atomic bond within the SUs, rather than EGB and θ which are often used in the literature, is identified as one controlling parameter that dictates the intrinsic GB cohesive strength; (v) characterization of the fracture resistance of the GB containing an initial crack is beyond the reach of nanoscale atomistic simulations but is feasible in concurrent atomistic-continuum (CAC) simulations that can simultaneously retain the atomic GB structure together with the long-range stress field within one model. The above findings provide researchers with a stepping stone to understand the complex microstructure of polycrystalline ice and its response to external forces from the bottom up. Such knowledge may be consolidated into constitutive rules and then transferred into the higher length scale models, such as cohesive zone finite element models (CZFEMs), for predicting how polycrystalline ice fractures at laboratory and even geophysical length scales.

Symmetrical tilt grain boundaries (STGBs) on the (10¯10), (¯2112), and (01¯18) planes in α‐Al2O3 have been investigated for their behavior with respect to yttrium doping by performing a combined study of high‐resolution transmission electron microscopy and spatially resolved energy dispersive X‐ray analysis. Bicrystals have been produced by diffusion bonding under ultrahigh vacuum; yttrium was introduced before the bonding process. The prismatic twin has a bulklike grain boundary (GB) structure and does not accommodate any yttrium at the GB. The yttrium at the Σ17 (¯2112) GB and the Σ37 (01¯18) GB changes the GB structure and the content of other impurities.

First-principles study of oxygen segregation and its effect on the embrittlement of molybdenum symmetrical tilt grain boundaries

Atomistic migration mechanisms of [formula omitted] symmetric tilt grain boundaries in magnesium

Atomic-scale analysis of liquid-gallium embrittlement of aluminum grain boundaries

The structure and energy of symmetric tilt grain boundaries in tungsten

The correlation between the structure and zero-temperature energy of symmetrical tilt grain boundaries (STGBs) in b.c.c. metals is investigated using a many-body potential of the Finnis-Sinclair type for Mo and Johnson's pair potential spline-fitted for α-Fe. As in free surfaces, the misorientation phase space associated with these simple planar defects consists of only two macroscopic degrees of freedom, namely those defining the grain-boundary (GB) plane normal. In a novel approach, the two-dimensional phase space is investigated in terms of a stereographic triangle and not in terms of the usual three parameters associated with the boundary misorientation. A comparison with similar calculations for free surfaces demonstrates the importance of the translational (microscopic) degrees of freedom in grain boundaries, while the comparison with STGBs in f.c.c. metals elucidates the important role played by the GB plane.

Structure‐composition-property correlations of symmetrical tilt grain boundaries in copper-based binary alloys

Effects of H segregation on shear-coupled motion of 〈110〉 grain boundaries in α-fe

Arrangement of polyhedral units for [0001]-symmetrical tilt grain boundaries in zinc oxide

A multiscale model of grain boundary structure and energy: From atomistics to a continuum description