Phase Field Crystal Method For The Dislocation Reactions And The Annihilation Process Of The Low-angle Grain Boundary

With the rapid development of science and technology,nanocrystalline materials with specific structure and function have attracted more and more attention.Because the microstructure control of crystal materials has a great influence on the improvement of physical and chemical properties of materials,the study on the grain boundary structure has been a subject of concern for researchers.In terms of exploring the transformation of crystal structure,the phase field crystal model can describe the crystal defect structure and grain boundary migration movement in the diffusion scale and atom scale,so as to reflect the evolution process of grain boundary.In this paper,the grain boundary structure,grain boundary migration,dislocation reaction and system energy change of two-dimensional triangular crystal are described in detail by the single-mode phase field crystal model.During the study of the low-angle tilt grain boundary structure,it was found that a series of edge dislocations formed in the final solidified part of the system.There are 6 types of edge dislocations in the crystal system,and when the angle of edge dislocations is 60°,the dislocation pair structure can be formed.The symmetry of the grain boundary has no effect on the type of dislocation pairs that makes up the grain boundary.It can be found that the upper grain boundary in the crystal system is composed of n1n2 and n2n3 dislocation pairs,and the lower grain boundary is composed of n4n5 and n5n6 dislocation pairs.In the process of studying the influence of temperature on the low-angle symmetric tilt grain boundaries,it was found that the lower the temperature of the system during the relaxation phase,the faster the free energy curve decreases,and the crystal boundary structure can reach stable state in a short time and keep it all the time.Under the external stress,the lower the crystal temperature,the longer it takes for the dislocation pair to move from the beginning to the first encounter,and the longer the system takes to form a complete single crystal structure.The change trend of the free energy curve of the system is consistent under different temperature conditions.The lower the temperature,the free energy of the crystal system will rise and fall in multiple stages,the dislocation reaction process becomes more complicated,and the dislocation pair reaction tends to offset one pair after another at a low temperature.When simulating the low-angle asymmetric tilt grain boundary structure under different orientation angles,the n1n2 and n4n5 type dislocation pairs in the grain boundaries with increased orientation angle are more likely to appear.The increase in the orientation angle under external stress increases the number of decomposition reactions of the dislocation pairs,and only the n1n2 and n4n5 type dislocation pairs decompose.The increase in the orientation angle under external stress increases the number of decomposition reactions of dislocation pairs,and only the n1n2 and n4n5 type dislocation pairs decompose.It is further observed that increasing the orientation angle makes the process of annihilation of the grain boundaries form a single crystal.In this paper,the annihilation process of low-angle grain boundaries is studied in detail,and the influence of temperature and orientation angle on the formation of single crystals in the system is analyzed,which provides a reasonable reference for the design of structural functional materials.