Study On Microstructure Evolution Of Deformed Polycrystals

Nowadays,with the increasing complexity of engineering problems,people have higher requirements for the properties of materials,which are largely determined by the microstructure of materials.Research on microstructure evolution and influence factors of polycrystalline material microstructure can be designed to improve the material performance.At present,a large number of scholars observe and study the evolution characteristics of microstructure of materials in the processing process through experimental means,but it is difficult to observe the microbehavior evolution and orientation change of material deformation process by experiments alone.With the improvement of computer performance,using computer simulation method in the prediction of the material microstructure evolution behavior and its performance has important significance.Based on the basic principle of Voronoi diagram,the 3d polycrystalline microstructure geometric model was constructed in ABAQUS,a large-scale finite element software,by writing Python scripting language.On this basis,the geometric model of grain boundary was constructed,and the visualization of polycrystalline microstructure with different grain boundary thickness was realized.At the same time,with the aid of the GUI plug-in development assistant tool RSG dialog box constructor embedded in the software,the author wrote the Python kernel script program,designed the reasonable parameter dialog box and developed the material microstructure pre-processing modeling plug-in Polycrystal Toolkit.The effects of the number of polycrystalline grains and the initial orientation of the grains on the properties of polycrystalline materials were investigated by computer simulation and crystal plasticity theory.Then the secondary development of ABAQUS was carried out,and the subprogram of user-defined field variable VUSDFLD was written by Fortran language to extract the crystallographic orientation of each grain after deformation,and the evolution rule of grains orientation was studied.The research shows that:The surface of polycrystal with coarse grain presents obvious concave and convex phenomenon.In a certain volume,with the increasment of the number of grains,the polycrystalline deformation gradually tends to be uniform,and the more grain boundaries,the tighter between grains,showing good plasticity and toughness.Under the same deformation condition,the stress distribution and deformation of the two polycrystal models with different initial orientation are non-uniform,and the stress distribution and deformation degree of the same grain are very different.During the continuous deformation process of polycrystal,the orientation changes are more complex,and the orientation also changes with the rotation of grain.Some grain orientation changes greatly,some grain orientation changes slightly,and some grain orientation presents gradient distribution,but the difference is very small.When the orientation of grains rotates in the orientation space,they also begin to gather near a certain stable orientation.In the aggregation area,the orientation gradient of some grains also decreases.