PHASE FIELD CRYSTAL SIMULATION OF STRAIN EFFECTS ON DISLOCATION MOVEMENT OF PREMELTING GRAIN BOUNDRIES AT HIGH TEMPERATURE
GAO Yingjun1,2(), ZHOU Wenquan1, DENG Qianqian1, LUO Zhirong1, LIN Kui1, HUANG Chuanggao1,2
1 College of Physics Science and Engineering, Guangxi University, Nanning 530004 2 Guangxi Key Laboratory for Non-ferrous Metal and Featured Materials, Guangxi University, Nanning 530004 3 Institute of Physics Science and Engineering Technology, Yulin Normal University, Yulin 537000
Cite this article:
GAO Yingjun, ZHOU Wenquan, DENG Qianqian, LUO Zhirong, LIN Kui, HUANG Chuanggao. PHASE FIELD CRYSTAL SIMULATION OF STRAIN EFFECTS ON DISLOCATION MOVEMENT OF PREMELTING GRAIN BOUNDRIES AT HIGH TEMPERATURE. Acta Metall Sin, 2014, 50(7): 886-896.
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.
Fund: Supported by National Natural Science Foundation of China (Nos.51161003 and 50661001), Guangxi Natural Science Foundation (No.2012GXNSFDA053001) and Foundation of Guangxi Key Laboratory of Processing for Non-ferrous Metal and Featured Materials (No.GXKFJ12-01)
Fig. 1 Two-dimensional phase diagram[29,36] obtained by using one-mode approximation (L, T and S represent liquid phase, triangular phase, strip phase, respectively; φeqL and φeqS represent the atomic density located at the boundaries of solid-liquid coexistent region, respectively. r is the parameter of temperature, φ0 is the average atomic density )
(a) two-dimensional phase diagram of phase-field crystal (PFC) (b) magnified image of the box in Fig.1a
Sample
First stage at low temperature
Second stage at high temperature
r
φ0
r
φ0
A
-0.3
-0.180
-0.1
-0.180
B
-0.3
-0.195
-0.1
-0.195
C
-0.3
-0.199
-0.1
-0.199
Table 1 Parameters for sample preparation
Fig.2 Snapshots of low-angle grain boundaries for three samples (The black regions are the premelting region in Figs.2a~c, where the center is the core of the dislocation)
(a) sample A, at high temperature near melting point
(b) sample B, at high temperature close to melting point
(c) sample C, at high temperature in coexistent region of solid-liquid
(d) dislocation array model in grain boundaries for samples A, B and C
Fig.3 Atomic density distributions across the dislocation premelting region in the range of 512Dx×53Dy (Dx and Dy represent a grid size unit in x and y, respectively) for sample A (a), sample B (b) and sample C (c)
Fig.4 Simulations of annihilation process of grain boundaries (GBs) in sample A (a1~a5) and sample B (b1~b5) at different strains (ε) (The long arrow indicates that the dislocations movement and the arrow direction points to its moving direction)
Fig.5 Strain-energy curves of GB annihilation at different temperatures for sample A (a), sample B (b) and sample C (c)
Fig.6 Fig.6 Simulations of process evolution of dislocation of GB in sample C at different strains (ε) and time steps (t)
