Phase Field Crystal Simulation Of Dislocation Configuration At Gb And Its Evolution Under Applied Stress At High Temperature

Plastic deformation mechanism of crystalline materials at the nanoscale is one of the important directions in the field of traditional mechanics, exploring the structure evolution of crystalline deformation and explaining the various defects (point defects, dislocations, grain boundaries, etc.), microscopic stress, grain boundary state, and grain size of the crystalline, which influence the details of the deformation, is one of the core issues. However, due to the extremely complicated interaction of these factors during the plastic deformation which is limited and inconsistent with experimental evidence, thus-the development of computational simulation can compensate the drawbacks. In recent years, the phase field crystal model as one of the latest modeling techniques have been proposed and widely applied, which can perform an analysis on the atomic level in the diffusive time scale, such as defect with vacancy atoms and migration of grain boundaries (GBs), revealing atom effect. Based on this, in this paper the most simple twined structure of a hexagonal model were studied, using the phase field crystal model to separately study the role of GB dislocations for the high-temperature plastic deformation of crystalline materials. As to the low-angle GB under applied stress at high temperature, discussing the effects of different temperatures on the microstructure evolution of tensile deformation of grain boundary, noting that GB dislocations existed in the entire deformation process and as a main strain coordinated function, analyzing the elastic interaction of dislocations in the inner of premelted region, revealing the mechanism of structural changes of the premelted region. The main conclusions as follows:1. The simulation results of low-angle symmetric tilt GB at different temperatures show that GB is composed of two kinds of edge dislocations with the angle by Burgers vectors being around60°when the system temperature far from the melting point (Tm).As the temperature close to the melting point, a local premelting occurs around the lattice dislocations, but the dislocation structure has not changed. As the melting point is approached, structure transition occurs as follows, the dislocations form pairs and the original liquids are also combined a big "liquid pool". At this moment, GB converted from attractive to repulsive.2. As to the deformation for low-angle symmetric tilt GB with misorientation angle of4°at temperature far from the melting point, the same types of dislocations in low-angle symmetric GB move along two opposite directions, then meet and attract with the same type of dislocation in another GB leading to the annihilation of dislocations, finally a perfect single crystal is formed. As the temperature close to the melting point, the annihilation mechanisms of dislocations are similar for the lower temperature condition. But because of premelting occurs, it diminishes the resistance and leads to a faster movement of the dislocations, and it also causes more energy reduction of the system during the process of annihilation. As reach to the melting point, the atomic lattice around the premelted region appears to be softening, and thus to induce significantly larger premelted region. During the process of elastic interaction between dislocations in premelted region under the applied stress, it can be seen some phenomenon including the dislocation multiplication in pairs, the rotation of dislocation dipoles and their annihilation. What’s more, the shape of the premelted region changes as well, it is observed that the premelted region propagates in the opposite direction and consolidate together, then decompose and segregate from each other.3. As to the deformation for low-angle symmetric tilt GB with misorientation angle of8°at temperature far from the melting point, GB decomposed into four rows of sub-grain boundary (SGB) and moved to both sides, finally the SGB’s are annihilated and disappeared. As the temperature close to the melting point, the gliding mode of dislocation in the initial stage of deformation is similar with the lower temperature condition. But when the SGB’s are close to each other by gliding, the main strain coordinated function of deformation by dislocation gliding transformed into rotation. Note that the Burgers vectors of double-array dislocations which composed of dislocation dipoles rotate120°counterclockwise in the entire rotation process. By the end of the process, dislocation dipole segregates from each other and climbs across a short distance in the interior of the grain. When the strain reaches the critical value, each dislocation will break down into two dislocations with their Burgers vectors making an angle about120°, then these dislocations glide across a short distance in the premelted film to annihilate with the negative dislocations under applied stress, during the same time, the premelted film disappears as well.The above study for building the plastic deformation diagram of crystalline materials at high temperature and revealing the deformation mechanism associated with mechanical properties and guiding the mechanics design for super alloy material would be significant.