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The twin thickness saturated once a critical residual dislocations’ density reached the coherent twin-parent crystal boundary. [ 33 ] [ 49 ] Significant attention has been paid to the crystallography , [ 50 ] morphology [ 51 ] and macro mechanical effects [ 52 ] of deformation twinning.
A twin boundary is a defect that introduces a plane of mirror symmetry in the ordering of a crystal. For example, in cubic close-packed crystals, the stacking sequence of a twin boundary would be ABCABCBACBA. On planes of single crystals, steps between atomically flat terraces can also be regarded as planar defects.
Grain boundaries are two-dimensional defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material. Most grain boundaries are preferred sites for the onset of corrosion [1] and for the precipitation of new phases from the solid. They are also important to many of the mechanisms of creep. [2]
The approach to model these is similar to the Winterbottom construction, now adding an extra facet of energy per unit area half that of the twin boundary -- half so the energy per unit area of the two adjacent segments sums to a full twin boundary energy, and the facets that for the twin boundary are identical for thee segments.
In mixed oxidation state materials like magnetite, antiphase domains and antiphase domain boundaries can occur as a result of charge-ordering even though there are no changes in atom locations. [4] For example, the reconstructed magnetite (100) surface contains alternating Fe II pairs and Fe III pairs in the first subsurface layer. [ 4 ]
In a TEM, bright field imaging is one technique used to identify the location of stacking faults. Typical image of stacking fault is dark with bright fringes near a low-angle grain boundary, sandwiched by dislocations at the end of the stacking fault. Fringes indicate that the stacking fault is at an incline with respect to the viewing plane. [3]
Grain boundary sliding (GBS) is a material deformation mechanism where grains slide against each other. This occurs in polycrystalline material under external stress at high homologous temperature (above ~0.4 [ 1 ] ) and low strain rate and is intertwined with creep .
Later Laurence D. Marks proposed a model using both experimental data and a theoretical analysis, which is based upon a modified Wulff construction which includes more surface facets, including Ino's {100} as well as re-entrant {111} surfaces at the twin boundaries with the possibility of others such as {110}, while retaining the decahedral ...