The phase-field crystal method is used to analysis the dislocation annihilation and grain boundary migration mechanism in the grain shrink process of the circular grain which has three different misorientations from the matrix grain. Results show that when the misorientation between the circular grain and the matrix grain is 17°, the structure of grain boundary is composed of dislocations whose cores is so near that can not find a single dislocation. This grain boundary can not be explained by the dislocation model. However the circular grain area decreases linearly with time, which is in good agreement with the classical boundary migration theory. When the misorientation is 4°, the grain boundary structure is composed of discrete dislocations. Dislocations climb along the radial dierction and the grain rotation occurs for the circular grain to adjust the space of dislocations in the process of circular grain shrinkage. Reactions may take place with the dislocatins becoming closer. For the misorientation of 10°, portion of the grain boundary is composed of discrete dislocations and portion of dislocations with cores overlapped. Dislocations climb along the radial direction and tangential motion occurs at the same time in the grain shrinkage process. The coupled motion lead to the dislocations becoming close and reacting with each other.
The two-mode phase-field-crystal (PFC) method is used to calculate two-dimensional phase diagram and to simulate the process of multistage microstructural evolution in the transformation from hexagonal phase to square phase, which is induced by deformation. And the effect of misorientation and deformation on dislocation, grain boundary, crystal structure and morphology of the new phase is carefully analyzed. Simulation results show that both the nucleation site and growth direction of the square phase are affected by the direction of deformation. Under a tensile deformation, the nucleation of the square phase occurs preferentially in the deformation zone; while under compression deformation, the nucleation of the square phase may begin at dislocations and grain boundary. Moreover, the new phase grows towards the direction along which the degree of atomic mismatch decreases, i.e. the vertical direction of tensile deformation and the parallel direction of compressive deformation. Besides, the free energy varies with misorientation. In small misorientation, the dislocation climbing, slipping and annihilating will result in an energy peak; while in a big misorientation, the dislocation annihilates in several stages and thus offsetting the energy caused by deformation. Furthermore, the process of phase transformation is complex: It is not a pure phase transformation but a composite change of phase transformation and dynamic recrystallization.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.