Numerical Simulation Of Grain Microstructural Evolution In Sintering Process Of Polycrystalline Materials

The mechanical,electrical,magnetic and other properties of the material are not only related to its chemical composition,but also depend on the microstructure distribution inside the material.By optimizing and designing the microstructure,the performance of the material can be greatly improved.The phenomenon of grain growth and microstructure evolution has an important influence on material properties.We study the grain growth process and its dynamics of polycrystalline materials.This research has important theoretical and engineering significance for the theory of material organization evolution and material performance prediction.This study deduced a simplified phase field model for the sintering process of porous polycrystalline ceramic materials by material thermodynamics.We have studied the pinning effect of different phase second phase particles by numerical simulation.We also studied pore deformation and grain boundary migration during sintering of porous ceramics.This study comprehensively analyzes the evolution and kinetics of grain structure in polycrystalline materials.Therefore,this study laid the foundation for the microstructure design of polycrystalline materials.(1)This study used phase field method to simulate the influence of hard phase particles with different shapes and volume fractions on the morphology evolution of grain structure.The results of this study show that the elliptical particles have a better retardation effect on grain growth during grain growth.Compared with unidirectional elliptical particles,bidirectional elliptical particles have a greater influence on grain boundary pinning and higher pinning efficiency.The unidirectional strip particles and the bidirectional strip particles have finer grain structure and smaller average grain radius,so the pinning effect is the best.When the elongated particles are located at the grain boundary and the direction is consistent with the direction of the grain boundary,the interface energy of the system is minimal.This is in line with the evolutionary trend of the system.For all types of particles,the pinning effect of the particles increases as the volume fraction increases.(2)This study is based on phase transition dynamics theory and Zener theory.We analyzed the difference in drag force between the second phase hard particles of different shapes relative to the grain boundaries of the ceramic grains,and determined the relationship between the grain size and the hard particles.Based on the Zener relationship,we describe and discuss the shape-dependent grain size constraints.Finally,we deduced the pinning forces caused by the second phase hard phase particles of different shapes,and used the pinning force to explain the different pinning efficiency of the second phase hard phase particles of different shapes for grain growth.The results of this study indicate that the critical grain size estimate(K,b)is highly correlated with the shape of the particles.The pinning effect is mainly due to the interaction of the particles with the grain boundaries,and the shape of the particles results in different contact patterns between the particles and the grain boundaries.This therefore produces different pinning forces for grain boundary migration.(3)The phase field method was used to simulate pore deformation and grain boundary migration.We introduce pores of different shapes and sizes into the simulation and simulate grain boundary migration and pore deformation during grain growth.We have also studied the interaction of pores and grain boundaries of different shapes and sizes during the sintering of porous materials.The results of this study indicate that the pore-grain microstructure is determined by the way of contact and that the contact pattern is closely related to pore size and shape.The efficiency of grain boundary migration and pore deformation is attributed to the pinning force at the grain-to-pore interface.The micropores at the grain boundary angle shrink as they age,which ultimately causes the boundary to terminate at the junction of the back surface.During grain growth,the pores will result in enhanced grain coarsening near the surface of the pore during sintering.The growth of the grains changes the shape of the holes,which causes the irregular polygonal holes to be surrounded by the grains.The reason why the grain boundaries intersecting the surface of the macropores are often perpendicular to the surface of the pores is the distortion of the grain boundaries.