Phase-Field-Crystal Method Study Of Polycrystal Material Micro-Structure Evolution

The microscopic evolution of the real material has always been the direction in which people are interested,especially the defective movement in the nanoscale.Restricted by the limitations of the equipment,we have only through the experiment to get the pattern,combined with the data to forecast the behavior of the material.However,when the material structure is very complex,we should turn to computer simulation.The Phase-Field-Crystal(PFC)method is a research method proposed by Elder in 2002 to simulate the microstructure of material in nano-scale.By determining the density field of the object and minimizing the free energy function,the evolution process of the crystal material in the nano-scale can be simulated by combining the corresponding kinetic equation.Compared with the traditional Phase Field(PF)method,the PFC method can be used to describe the atomic scale structure and the large diffusion time scale and has been developed as a mature method for the simulation of nano-materials.Polycrystalline was widely used in engineering materials.In the material processing,the poly crystalline should be subject to various effects,such as extrusion,corrosion,high temperature,which directly affects the material within the micro-structure changes.Therefore,the plastic deformation of poly-crystalline has been widely concerned by people.In this paper,the PFC method was used to study the grain boundary evolution process of pure material poly-crystalline materials under dynamic and static loads.The relationship between the dislocation motion,dislocation reaction and the temperature,stress strain rate,direction,stress form etc.was studied and the change of internal distortion energy was analyzed,and the microscopic mechanism of stress effect of nano-scale poly-crystalline materials was revealed.And we get the following conclusions:1.Grain rotation,grain swallowing and grain boundary migration can be seen in the polycrystalline plastic deformation.The grain rotation mainly occurs between the two grains with smaller misorientation,and the grain swallowing occurs between the large grains and the small grains.2.The temperature change makes the grain boundary of different degrees of pre-melting.The grain rotation seem more difficult in low temperature.The dislocation easily slip into the grain inside at low temperature,compensating for the grain misorientation.The rate of grain boundary migration is faster when the temperature is high,more likely to appear grain swallowing phenomenon.3.The direction of the stress changes the grain growth direction also changes,grain growth tends to develop perpendicular to the direction of the pressure axis,while the grain boundary tends to parallel or perpendicular to the direction of the development of the pressure axis.4.Increase the strain rate,the grain boundary migration and dislocation movement rate faster.Under the applied static biaxial stress,the dislocation of the launch and decomposition can be seen in the early polycrystalline deformation.Compared with the applied dynamic biaxial stress,the static biaxial stress can form a higher dislocation density in the early stage.