The Research Of Dislocations Movement Process Of Small Angle Boundary In Nano- Crystalline Materials Under Thestress

Nanocrystalline materials have unique mechanical properties compareed with traditional materials, many nanocrystalline materials have good elastic-plastic in the process of mechanical loading, whose mechanisms of formation are being extensively studied. The microstructure of material determines the macroscopic properties of material, it is plays a very important role when grain of nanocrystalline materials at the nanometer level, grain size and grain boundary and the composition of grain boundary dislocations for the plastic deformation of nanomaterials. In general, plastic and superplastic mechanism of nanocrystalline materials can be divided into the following kinds: ordinary dislocation glide, diffusion creep along grain boundary, triple junctions, rotation deformation, grain boundary sliding and twinning. The activation of these mechanisms is substantially determined by grain size in nanocrystalline materials. In this paper, according to the two-dimensional dislocation-disclination dynamics, a theoretical model is describe the decay of a low-angle tile boundary in a deformed nanocrystalline. Critical external stresses are calculated by using the elastic dislocation theory and dislocation dynamics, which is the dislocation in the stress field of stress, and analysis in the process of decay of dislocation movement of the whole process. It is the first time to calculate and research the grain boundary dislocations movement by the x direction and y direction force. Through a series of research, this decay was found to result in the formation of an ensemble of mobile lattices dislocations, which can carry substantial plastic deformation. Aiming to understand the excellent plastic properties of nanocrystalline materials. In the process of numerical simulation of this paper, the following conclusions:1、Dislocation configuration for a single grain boundary, when grain boundary dislocations under the external stress, both ends of grain boundary will first launch dislocation, with the increase of stress, gradually extended to the grain boundary, eventually lead to the entire grain boundary decay. To the disclination increase, the decay of grain boundary is more difficulty.2、 In the single grain boundary, get a set of inclined dislocation configuration with vector and x axis into a 45 degree angle. When without the external force, grain boundary dislocations centered 45 degrees clockwise into a stable state. When applying force, with the increase of stress, all of the dislocation will slip against with vector direction.3、For double grain boundary model, can be divided into double grain boundary double dislocation configuration model and double grain boundary single dislocation configuration model. The two groups of model integrated research found that the existence of the adjacent boundary will result in the critical shear stress decreases of low angle grain boundary decay, in other words, the adjacent boundary will contribute to the decay of the small angle grain boundary.4、The same sign size double grain boundary single dislocation configuration model, the existence of the grain boundary can attract grain boundary dislocations movement, promote the disintegration of the adjacent boundary. The opposite sign size double grain boundary single dislocation configuration model, the presence of grain boundary has the trend to reject grain boundary dislocations movement, but also promote the disintegration of the adjacent boundary. With the increase of strength of disclination of grain boundary, the attraction or repulsion force to adjoining grain boundary dislocations is increase. When the length of two grain boundary equals, the critical shear stress for the decay grain boundary is the minimum value.