PHASE FIELD CRYSTAL SIMULATION OF STRAIN EFFECTS ON DISLOCATION MOVEMENT OF PREMELTING GRAIN BOUNDRIES AT HIGH TEMPERATURE

Abstract

The properties of modern materials, especially superplastic, nanocrystalline or composite materials, depend critically on the properties of internal interfaces such as grain boundaries(GBs) and interphase boundaries(IBs). All processes which can change the properties of GBs and IBs affect drastically the behaviour of polycrystalline metals and ceramics. In this work, the annihilation processes of low-angle symmetric tilt GBs and dislocations during plastic deformation in the representative system of these materials near but below the melting point and the temperature at liquid-solid coexistence line were simulated using the phase-field crystal model, respectively. The results show that local premelting occurs around lattice dislocations near the melting point but the dislocation structure in the premelting region does not change, while the region become significantly larger when the system reaches the melting temperature. After premelting, deformation to the system causes dislocations in the premelting GB to begin to glide then annihilate with opposite Burgers vectors via the movement, finally the GB and the premelting region disappear. The annihilation mechanisms of dislocations are similar to those for premelting conditions. The more the temperature is closer to the melting point, the more obvious the atomic lattice around the premelting region is softened leading to the atomic binding strength around the dislocations being lowered. Only at this moment, the lattice atoms enable to reduce the resistance of the dislocation motion and accelerate its velocity during deformation. At the temperature reaching to the liquid-solid coexisting region in the simulation, the original premelting regions are induced to develop into bigger ones by the external strain acting. During this process, it can be seen some interactions including the multiplication dislocation pairs, the rotation of dislocation pairs and their annihilation. Furthermore, the shape of the premelting region changes with the variation of the interaction of dislocations inside the region, it is observed that the premelting regions approach each other and consolidate together,then decompose and segregate from each other. Although the shape of the premelting region changes with the applied strain, these regions do not disappear at the end of the simulation, totally different those in lower premelting temperature.