| Summary: | 碩士 === 國立中央大學 === 物理學系 === 102 === The cooperative structural rearrangement in the crystallization of a quenched 2D Yukawa liquid is investigated through molecular dynamics simulation. It is found that, in the grain coalescence, cracking the region in front of the grain boundary into smaller sub-grains co-rotating with small angle, followed by healing, is the key for aligning the lattice mis-orientation and inducing grain boundary stick-slip motion. Cracking is initiated from the weakly interlocked dislocation along its Burgers vector, which in turn causes dislocation motion along the crack. The recombination of two dislocations with 120$o$ Burgers vector angle difference through exciting three co-rotation sub-grains is the dominant process for defect reduction associated with grain boundary migration. A grain boundary with large curvature and roughness can support cascaded dislocation recombination process and induces high mobility of the grain boundary. Along the smooth grain boundary, the parallel Burgers vectors of the string of dislocations forbid defect reduction and induce coalescence stagnation.
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