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In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure , and tend to decrease the electrical and thermal conductivity of the material.
A linear variation has been observed between twin thickness, stacking fault energy and grain size, [47] and to a lesser degree, the stress state of the twinning grain (Schmid Factor). [48] The twin thickness saturated once a critical residual dislocations’ density reached the coherent twin-parent crystal boundary. [33] [49]
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
Twinning is a phenomenon somewhere between a crystallographic defect and a grain boundary. Like a grain boundary, a twin boundary has different crystal orientations on its two sides. But unlike a grain boundary, the orientations are not random, but related in a specific, mirror-image way. Mosaicity is a spread of crystal plane orientations.
This is also known as intercrystalline fracture or grain-boundary separation. More rapid diffusion along grain boundaries than along grain interiors; Faster nucleation and growth of precipitates at the grain boundaries; Quench cracking, or crack growth following a quenching process, is another example of intergranular fracture and almost always ...
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]
The absence of voids results from solid-state diffusive mass transfer, locally enhanced crystal plastic deformation, or solution and precipitation of a grain boundary fluid. [1] This mechanism operates at a low strain rate produced by neighbor switching. Grain boundary sliding is grain size- and temperature-dependent.
However, as the grain gets smaller, the interaction between grain and the dislocation inside impedes further process of grains. Among the grain boundaries, it is known that the twin boundaries, a special type of low-energy grain boundary has lower interaction energy with dislocation leading to much smaller saturation size of the grain. [13] The ...