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Tilt Boundaries (tilt + boundary)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Structure of Sapphire Bicrystal Boundaries Produced by Liquid-Phase Sintering

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003
Bernard J. Hockey
The structure and composition of sapphire bicrystal boundaries produced by liquid-phase sintering depended on the crystallographic misorientation of the crystals across the boundary and on the orientation of the boundary. Basal twist boundaries of 15° or 30° were not wetted by glass, but contained significant amounts of Ca and Si at the boundary. For tilt boundaries of 7° or 12°, the glass wetted segments of boundaries that contained the basal plane of either crystal. Boundary segments with orientations of 40° or more from the basal plane, however, were dewetted (i.e., "dry"). Boundary segments oriented less than ,40° from the basal orientation were partially wetted, consisting of segments of wetted and dry grain boundaries. For the 12° tilt boundary, Ca and Si could be detected on portions of the boundary that contained no glass. For bicrystal boundaries having tilts of ,4°, dewetting occurred for all observed boundary orientations. Basal-oriented segments in these small angle tilt boundaries contained noticeable concentrations of adsorbed Ca and Si, while nonbasal segments were apparently free of Ca and Si. Most results could be explained based on a combined Wulff plot construction, which predicts partially wetted grain boundaries and "missing" angles for unwetted grain boundaries. Results that could not be explained by the construction included growth step ledges bounded by nonequilibrium facet planes. [source]

Molecular dynamics simulation of crack tip blunting in opposing directions along a symmetrical tilt grain boundary of copper bicrystal

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2007
A. LUQUE
ABSTRACT Mode I crack growth along some grain boundaries of copper embrittled by solute segregation shows strong anisotropy. For instance, growth along the direction on the symmetrical tilt boundary has been reported to occur by intergranular brittle fracture, whereas growth along the opposite sense occurs in a ductile manner. In this paper, we simulate such crack configurations using molecular dynamics (embedded atom method [EAM]) in 3-dimensional perfect bicrystalline samples of pure copper of the aforementioned orientation at room temperature. In both cases the response is ductile, crack opening taking place by dislocation emission from the crack tip. The critical stress intensity factors (SIFs) for dislocation emission have been calculated by matching the displacement fields of the atoms in the tip neighbourhood with the continuum elastic fields. They are of the same order of magnitude for both growth senses despite the different morphology of their respective blunted crack tips and of the patterns of dislocations constituting their plastic zones. Thus, it seems that, in agreement with published results of continuum crystalline plasticity for the same problem, the plastic anisotropy associated with the different orientation of the slip systems with respect to the crack cannot in this case explain the experimental behaviour observed with solute embrittled bicrystals. [source]

Structure of Sapphire Bicrystal Boundaries Produced by Liquid-Phase Sintering

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2003
Bernard J. Hockey
The structure and composition of sapphire bicrystal boundaries produced by liquid-phase sintering depended on the crystallographic misorientation of the crystals across the boundary and on the orientation of the boundary. Basal twist boundaries of 15° or 30° were not wetted by glass, but contained significant amounts of Ca and Si at the boundary. For tilt boundaries of 7° or 12°, the glass wetted segments of boundaries that contained the basal plane of either crystal. Boundary segments with orientations of 40° or more from the basal plane, however, were dewetted (i.e., "dry"). Boundary segments oriented less than ,40° from the basal orientation were partially wetted, consisting of segments of wetted and dry grain boundaries. For the 12° tilt boundary, Ca and Si could be detected on portions of the boundary that contained no glass. For bicrystal boundaries having tilts of ,4°, dewetting occurred for all observed boundary orientations. Basal-oriented segments in these small angle tilt boundaries contained noticeable concentrations of adsorbed Ca and Si, while nonbasal segments were apparently free of Ca and Si. Most results could be explained based on a combined Wulff plot construction, which predicts partially wetted grain boundaries and "missing" angles for unwetted grain boundaries. Results that could not be explained by the construction included growth step ledges bounded by nonequilibrium facet planes. [source]