纳米晶晶界演化行为的晶体相场法研究
发布时间：2018-08-05 13:22
【摘要】：纳米晶材料作为新兴的材料门类,因其具有独特的机械、电磁及化学性质,在凝聚态物理、应用化学、材料科学等研究领域受到了广泛的重视。存在大量的晶界及三晶交线是纳米晶材料的重要组织特征,晶界在曲率及外力驱动条件下的演化行为,在很大程度上决定了纳米晶材料的性能。纳米晶晶界演化是一个涉及原子重排和界面扩散的多尺度复杂物理过程。为从本质上认识晶界在不同条件下是如何运动进而影响纳米晶粒演化的,必须深入理解涉及空间和时间多尺度的晶界及三晶交线演化问题。晶体相场模型是近年来兴起的在原子尺度上描述材料微观组织演化的模拟方法,这种基于密度泛函理论的原子尺度模拟方法最大优势在于能够在反映材料原子尺度信息的基础上描述其在扩散时间尺度上的演化过程。本文采用标准和最小体耗散的晶体相场模型,以晶界原子尺度特征的准确描述为基础,对BCC结构纳米晶中[001]倾斜晶界在曲率驱动及外加剪切应变条件下的演化行为以及三晶交线对晶界演化的影响等进行了深入研究,这可为实现纳米晶材料的组织调控提供理论基础。论文获得了如下主要结论:(1)基于所编制的晶体相场模型并行计算求解程序,成功实现了曲率驱动及外加剪切应变驱动下纳米晶晶界演化过程的数值模拟。成功获得了BCC晶体中[001]倾斜晶界的平衡结构、晶界能及其附近弹性应变场等原子尺度特征的准确表征,发现模拟所得晶界结构符合位错理论描述,均由两类刃位错(a100和a110/2)混合而成,单个位错附近的应变场亦与各向异性的位错弹性理论定量相符。(2)获得了纯曲率驱动、纯耦合效应及混合方式等晶界运动机制在BCC双晶内嵌系统中不同取向差下的适用性范围。取向差在27.5度以上的晶界按照经典纯曲率驱动方式做迁移运动,内嵌晶粒取向保持恒定,晶粒面积随时间呈线性快速变化;取向差在20度以下的晶界按照纯耦合方式运动,内嵌晶粒取向逐渐升高,而晶粒面积仍保持线性变化但演化速率较慢;而取向差在20-27.5度之间的晶界则按照部分曲率驱动部分耦合效应的混合方式运动,中心晶粒取向变化小,而晶粒面积呈非线性缓慢变化。(3)阐明了极小取向差的弯曲晶界运动诱发晶粒转动现象的发生机制。当晶界取向差较小时,相邻晶界位错间的共格区域内存在明显弹性畸变,从而导致晶界位错向晶粒中心径向运动,同时对内部晶粒产生转动力矩,造成晶粒转动;当取向差较高时,相邻晶界位错的间距小,其间的弹性畸变也非常弱,位错湮灭、分解等反应过程占主导,整个晶界在纯曲率驱动下运动,不会引起晶粒转动。从晶界原子结构上而言,不同取向差下晶界表现出不同的演化行为可归因于晶界内多种位错的平衡间距随取向差的变化不同步。(4)平直对称倾斜晶界在外加剪切应变条件下按照剪切耦合的方式迁移运动,其微观本质是连错的形核及扩展。连错对的存在对晶界迁移过程的影响显著,连错的形核势垒决定了晶界迁移的PN势,其同时具有的不全位错和台阶特征决定了晶界迁移的耦合因子。(5)晶界偏转角对非对称倾斜晶界剪切耦合运动的影响作用取决于两类晶界位错的占比及其对剪切应变的响应。晶界偏转角较小时,一类位错承担了变形主体,而另一类位错则随之发生运动,此时晶界的PN势和耦合因子与对称倾斜晶界相比变化不大;而当偏转角转至两类位错占比相近的角度时,两类位错共同作为变形主体,晶界开启运动和迁移都很困难,造成晶界PN势和耦合因子的显著提升。(6)获得了纳米晶中三晶交线对晶界演化的影响规律及机制,建立了三晶交线不连续迁移运动模型。三晶交线的拖拽作用改变了晶界位错的运动方式从而减缓了晶粒的演化动力学,三晶交线附近的位错释放是由晶界的运动不协调造成;三晶系统在变形条件和曲率驱动条件下表现出截然不同的稳定性。
[Abstract]:As a new type of material, nanocrystalline materials have been widely paid attention to in the fields of condensed matter physics, applied chemistry and material science because of their unique mechanical, electromagnetic and chemical properties. The existence of a large number of grain boundaries and intersecting lines is an important fabric of nanocrystalline materials, and the grain boundary is performed under the conditions of curvature and external force. The properties of nanocrystalline materials are largely determined by chemical behavior. The evolution of nanocrystalline boundary is a multi-scale and complex physical process involving atomic rearrangement and interface diffusion. It is necessary to understand how the grain boundary is moving in different conditions and influence the evolution of nanocrystalline grain in essence. It is necessary to understand the multiscale of space and time. The crystal phase field model is a new method to describe the evolution of microstructures on the atomic scale in recent years. The greatest advantage of the atomic scale simulation method based on density functional theory is that it can describe its diffusion time scale on the basis of reflecting the information of the atomic scale. Based on the accurate description of the atomic scale characteristics of the grain boundary, the evolution process of the crystal phase field of the standard and the minimum body dissipation is studied in this paper. The evolution behavior of the inclined grain boundary in the BCC structure nanocrystals under the conditions of curvature driven and external shear strain and the influence of the intersection of three crystals on the evolution of the grain boundary are studied. It can provide the theoretical basis for the organization and control of nanocrystalline materials. The main conclusions are obtained as follows: (1) a numerical simulation of the evolution of nanocrystalline boundaries driven by curvature driven and external shear strain was successfully realized on the basis of the parallel computation program of the crystal phase field model. The [001] tilt in BCC crystal has been successfully obtained. The equilibrium structure of grain boundary, the energy of the grain boundary and the elastic strain field near the grain boundary are accurately characterized. It is found that the grain boundary structure of the simulated grain conforms to the dislocation theory description, which is composed of two kinds of edge dislocations (A100 and a110/2), and the strain field near the single dislocation is also consistent with the anisotropic dislocation elasticity theory. (2) the pure curve is obtained. The grain boundary movement mechanism, such as rate driven, pure coupling effect and mixing mode, is applicable to the different orientation difference in the BCC embedded system. The grain boundary in the grain boundary is more than 27.5 degrees in the classical pure curvature driving mode. The grain orientation keeps constant, the grain surface product changes linearly with time, and the orientation difference is 20 degrees. The grain boundary in the following grain boundaries is moving in the pure coupling mode, and the grain orientation increases gradually, while the grain size remains linear but the evolution rate is slow, while the grain boundary between the orientation difference and the 20-27.5 degree is moving with the partial curvature which drives the partial coupling effect, and the orientation of the central grain is small and the grain area is nonlinear slowly. Slow change. (3) the mechanism of grain rotation induced by the curved grain boundary movement of the small orientation difference is clarified. When the grain boundary orientation difference is small, the common area between the adjacent grain boundary dislocations is obviously elastic, which leads to the grain boundary dislocation moving to the grain center, and the rotation moment of the grain at the same time, resulting in the grain rotation. When the orientation difference is high, the distance between the adjacent grain boundary dislocations is small, the elastic distortion is also very weak, the dislocation annihilation, the decomposition and other reaction processes dominate, the grain boundary is driven by pure curvature and does not cause the grain rotation. From the grain boundary structure, the different evolution behavior of the grain boundary under the different orientation difference can be attributed to the different evolution behavior. The equilibrium spacing of a variety of dislocation in grain boundary is not synchronized with the variation of orientation difference. (4) the vertical symmetry inclined grain boundary is migrated under the shear coupling mode under the external shear strain condition, and its microscopic nature is the nucleation and expansion of the dislocation, and the existence of the fault pair has a significant influence on the grain boundary migration process, and the grain boundary determines the grain boundary with the wrong nucleation barrier. The PN potential of the migration determines the coupling factor of grain boundary migration. (5) the influence of the grain boundary deflection angle on the shear coupling motion of the asymmetric slant grain boundary depends on the proportion of the two kinds of grain boundary dislocation and the response to the shear strain. The dislocation of grain boundary is small, and a class of dislocation bears the deformation body. The PN potential and coupling factor of the grain boundary have little change compared with the symmetrical slant grain boundary. When the deflection angle turns to the two kind of dislocation, the two kind of dislocation is the main body of deformation, and the movement and migration of grain boundary opening are very difficult, resulting in the remarkable enhancement of the grain boundary PN potential and the coupling factor. 6) the influence law and mechanism of the intersection of three crystals in nanocrystalline on the evolution of grain boundary was obtained. The movement model of discontinuous migration of intersecting lines was established. The drag and drop of the intersection of three crystals changed the movement mode of grain boundary dislocation and slowed the dynamics of grain evolution. The dislocation release near the intersection of three crystals was caused by the incoordination of grain boundary movement. The three crystal system shows a completely different stability under deformation conditions and curvature driving conditions.
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.1
本文编号：2165921
[Abstract]:As a new type of material, nanocrystalline materials have been widely paid attention to in the fields of condensed matter physics, applied chemistry and material science because of their unique mechanical, electromagnetic and chemical properties. The existence of a large number of grain boundaries and intersecting lines is an important fabric of nanocrystalline materials, and the grain boundary is performed under the conditions of curvature and external force. The properties of nanocrystalline materials are largely determined by chemical behavior. The evolution of nanocrystalline boundary is a multi-scale and complex physical process involving atomic rearrangement and interface diffusion. It is necessary to understand how the grain boundary is moving in different conditions and influence the evolution of nanocrystalline grain in essence. It is necessary to understand the multiscale of space and time. The crystal phase field model is a new method to describe the evolution of microstructures on the atomic scale in recent years. The greatest advantage of the atomic scale simulation method based on density functional theory is that it can describe its diffusion time scale on the basis of reflecting the information of the atomic scale. Based on the accurate description of the atomic scale characteristics of the grain boundary, the evolution process of the crystal phase field of the standard and the minimum body dissipation is studied in this paper. The evolution behavior of the inclined grain boundary in the BCC structure nanocrystals under the conditions of curvature driven and external shear strain and the influence of the intersection of three crystals on the evolution of the grain boundary are studied. It can provide the theoretical basis for the organization and control of nanocrystalline materials. The main conclusions are obtained as follows: (1) a numerical simulation of the evolution of nanocrystalline boundaries driven by curvature driven and external shear strain was successfully realized on the basis of the parallel computation program of the crystal phase field model. The [001] tilt in BCC crystal has been successfully obtained. The equilibrium structure of grain boundary, the energy of the grain boundary and the elastic strain field near the grain boundary are accurately characterized. It is found that the grain boundary structure of the simulated grain conforms to the dislocation theory description, which is composed of two kinds of edge dislocations (A100 and a110/2), and the strain field near the single dislocation is also consistent with the anisotropic dislocation elasticity theory. (2) the pure curve is obtained. The grain boundary movement mechanism, such as rate driven, pure coupling effect and mixing mode, is applicable to the different orientation difference in the BCC embedded system. The grain boundary in the grain boundary is more than 27.5 degrees in the classical pure curvature driving mode. The grain orientation keeps constant, the grain surface product changes linearly with time, and the orientation difference is 20 degrees. The grain boundary in the following grain boundaries is moving in the pure coupling mode, and the grain orientation increases gradually, while the grain size remains linear but the evolution rate is slow, while the grain boundary between the orientation difference and the 20-27.5 degree is moving with the partial curvature which drives the partial coupling effect, and the orientation of the central grain is small and the grain area is nonlinear slowly. Slow change. (3) the mechanism of grain rotation induced by the curved grain boundary movement of the small orientation difference is clarified. When the grain boundary orientation difference is small, the common area between the adjacent grain boundary dislocations is obviously elastic, which leads to the grain boundary dislocation moving to the grain center, and the rotation moment of the grain at the same time, resulting in the grain rotation. When the orientation difference is high, the distance between the adjacent grain boundary dislocations is small, the elastic distortion is also very weak, the dislocation annihilation, the decomposition and other reaction processes dominate, the grain boundary is driven by pure curvature and does not cause the grain rotation. From the grain boundary structure, the different evolution behavior of the grain boundary under the different orientation difference can be attributed to the different evolution behavior. The equilibrium spacing of a variety of dislocation in grain boundary is not synchronized with the variation of orientation difference. (4) the vertical symmetry inclined grain boundary is migrated under the shear coupling mode under the external shear strain condition, and its microscopic nature is the nucleation and expansion of the dislocation, and the existence of the fault pair has a significant influence on the grain boundary migration process, and the grain boundary determines the grain boundary with the wrong nucleation barrier. The PN potential of the migration determines the coupling factor of grain boundary migration. (5) the influence of the grain boundary deflection angle on the shear coupling motion of the asymmetric slant grain boundary depends on the proportion of the two kinds of grain boundary dislocation and the response to the shear strain. The dislocation of grain boundary is small, and a class of dislocation bears the deformation body. The PN potential and coupling factor of the grain boundary have little change compared with the symmetrical slant grain boundary. When the deflection angle turns to the two kind of dislocation, the two kind of dislocation is the main body of deformation, and the movement and migration of grain boundary opening are very difficult, resulting in the remarkable enhancement of the grain boundary PN potential and the coupling factor. 6) the influence law and mechanism of the intersection of three crystals in nanocrystalline on the evolution of grain boundary was obtained. The movement model of discontinuous migration of intersecting lines was established. The drag and drop of the intersection of three crystals changed the movement mode of grain boundary dislocation and slowed the dynamics of grain evolution. The dislocation release near the intersection of three crystals was caused by the incoordination of grain boundary movement. The three crystal system shows a completely different stability under deformation conditions and curvature driving conditions.
【学位授予单位】：西北工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.1
【相似文献】
相关期刊论文 前2条
1 孟祥敏，，李光来，张弗天，吴玉琨;9Ni钢中马氏体的小角倾斜晶界[J];金属学报;1996年07期
2 ;[J];;年期
相关会议论文 前1条
1 万亮;王绍青;;含∑9<110>{221}对称倾斜晶界的铜双晶在纯剪切载荷作用下形变行为的原子尺度模拟研究[A];中国核科学技术进展报告——中国核学会2009年学术年会论文集（第一卷·第6册）[C];2009年
相关博士学位论文 前1条
1 郭耀麟;纳米晶晶界演化行为的晶体相场法研究[D];西北工业大学;2015年
本文编号：2165921
本文链接：https://www.wllwen.com/kejilunwen/cailiaohuaxuelunwen/2165921.html
