納米晶晶界演化行為的晶體相場(chǎng)法研究
發(fā)布時(shí)間：2018-08-05 13:22
【摘要】：納米晶材料作為新興的材料門(mén)類,因其具有獨(dú)特的機(jī)械、電磁及化學(xué)性質(zhì),在凝聚態(tài)物理、應(yīng)用化學(xué)、材料科學(xué)等研究領(lǐng)域受到了廣泛的重視。存在大量的晶界及三晶交線是納米晶材料的重要組織特征,晶界在曲率及外力驅(qū)動(dòng)條件下的演化行為,在很大程度上決定了納米晶材料的性能。納米晶晶界演化是一個(gè)涉及原子重排和界面擴(kuò)散的多尺度復(fù)雜物理過(guò)程。為從本質(zhì)上認(rèn)識(shí)晶界在不同條件下是如何運(yùn)動(dòng)進(jìn)而影響納米晶粒演化的,必須深入理解涉及空間和時(shí)間多尺度的晶界及三晶交線演化問(wèn)題。晶體相場(chǎng)模型是近年來(lái)興起的在原子尺度上描述材料微觀組織演化的模擬方法,這種基于密度泛函理論的原子尺度模擬方法最大優(yōu)勢(shì)在于能夠在反映材料原子尺度信息的基礎(chǔ)上描述其在擴(kuò)散時(shí)間尺度上的演化過(guò)程。本文采用標(biāo)準(zhǔn)和最小體耗散的晶體相場(chǎng)模型,以晶界原子尺度特征的準(zhǔn)確描述為基礎(chǔ),對(duì)BCC結(jié)構(gòu)納米晶中[001]傾斜晶界在曲率驅(qū)動(dòng)及外加剪切應(yīng)變條件下的演化行為以及三晶交線對(duì)晶界演化的影響等進(jìn)行了深入研究,這可為實(shí)現(xiàn)納米晶材料的組織調(diào)控提供理論基礎(chǔ)。論文獲得了如下主要結(jié)論:(1)基于所編制的晶體相場(chǎng)模型并行計(jì)算求解程序,成功實(shí)現(xiàn)了曲率驅(qū)動(dòng)及外加剪切應(yīng)變驅(qū)動(dòng)下納米晶晶界演化過(guò)程的數(shù)值模擬。成功獲得了BCC晶體中[001]傾斜晶界的平衡結(jié)構(gòu)、晶界能及其附近彈性應(yīng)變場(chǎng)等原子尺度特征的準(zhǔn)確表征,發(fā)現(xiàn)模擬所得晶界結(jié)構(gòu)符合位錯(cuò)理論描述,均由兩類刃位錯(cuò)(a100和a110/2)混合而成,單個(gè)位錯(cuò)附近的應(yīng)變場(chǎng)亦與各向異性的位錯(cuò)彈性理論定量相符。(2)獲得了純曲率驅(qū)動(dòng)、純耦合效應(yīng)及混合方式等晶界運(yùn)動(dòng)機(jī)制在BCC雙晶內(nèi)嵌系統(tǒng)中不同取向差下的適用性范圍。取向差在27.5度以上的晶界按照經(jīng)典純曲率驅(qū)動(dòng)方式做遷移運(yùn)動(dòng),內(nèi)嵌晶粒取向保持恒定,晶粒面積隨時(shí)間呈線性快速變化;取向差在20度以下的晶界按照純耦合方式運(yùn)動(dòng),內(nèi)嵌晶粒取向逐漸升高,而晶粒面積仍保持線性變化但演化速率較慢;而取向差在20-27.5度之間的晶界則按照部分曲率驅(qū)動(dòng)部分耦合效應(yīng)的混合方式運(yùn)動(dòng),中心晶粒取向變化小,而晶粒面積呈非線性緩慢變化。(3)闡明了極小取向差的彎曲晶界運(yùn)動(dòng)誘發(fā)晶粒轉(zhuǎn)動(dòng)現(xiàn)象的發(fā)生機(jī)制。當(dāng)晶界取向差較小時(shí),相鄰晶界位錯(cuò)間的共格區(qū)域內(nèi)存在明顯彈性畸變,從而導(dǎo)致晶界位錯(cuò)向晶粒中心徑向運(yùn)動(dòng),同時(shí)對(duì)內(nèi)部晶粒產(chǎn)生轉(zhuǎn)動(dòng)力矩,造成晶粒轉(zhuǎn)動(dòng);當(dāng)取向差較高時(shí),相鄰晶界位錯(cuò)的間距小,其間的彈性畸變也非常弱,位錯(cuò)湮滅、分解等反應(yīng)過(guò)程占主導(dǎo),整個(gè)晶界在純曲率驅(qū)動(dòng)下運(yùn)動(dòng),不會(huì)引起晶粒轉(zhuǎn)動(dòng)。從晶界原子結(jié)構(gòu)上而言,不同取向差下晶界表現(xiàn)出不同的演化行為可歸因于晶界內(nèi)多種位錯(cuò)的平衡間距隨取向差的變化不同步。(4)平直對(duì)稱傾斜晶界在外加剪切應(yīng)變條件下按照剪切耦合的方式遷移運(yùn)動(dòng),其微觀本質(zhì)是連錯(cuò)的形核及擴(kuò)展。連錯(cuò)對(duì)的存在對(duì)晶界遷移過(guò)程的影響顯著,連錯(cuò)的形核勢(shì)壘決定了晶界遷移的PN勢(shì),其同時(shí)具有的不全位錯(cuò)和臺(tái)階特征決定了晶界遷移的耦合因子。(5)晶界偏轉(zhuǎn)角對(duì)非對(duì)稱傾斜晶界剪切耦合運(yùn)動(dòng)的影響作用取決于兩類晶界位錯(cuò)的占比及其對(duì)剪切應(yīng)變的響應(yīng)。晶界偏轉(zhuǎn)角較小時(shí),一類位錯(cuò)承擔(dān)了變形主體,而另一類位錯(cuò)則隨之發(fā)生運(yùn)動(dòng),此時(shí)晶界的PN勢(shì)和耦合因子與對(duì)稱傾斜晶界相比變化不大;而當(dāng)偏轉(zhuǎn)角轉(zhuǎn)至兩類位錯(cuò)占比相近的角度時(shí),兩類位錯(cuò)共同作為變形主體,晶界開(kāi)啟運(yùn)動(dòng)和遷移都很困難,造成晶界PN勢(shì)和耦合因子的顯著提升。(6)獲得了納米晶中三晶交線對(duì)晶界演化的影響規(guī)律及機(jī)制,建立了三晶交線不連續(xù)遷移運(yùn)動(dòng)模型。三晶交線的拖拽作用改變了晶界位錯(cuò)的運(yùn)動(dòng)方式從而減緩了晶粒的演化動(dòng)力學(xué),三晶交線附近的位錯(cuò)釋放是由晶界的運(yùn)動(dòng)不協(xié)調(diào)造成;三晶系統(tǒng)在變形條件和曲率驅(qū)動(dòng)條件下表現(xiàn)出截然不同的穩(wěn)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.
【學(xué)位授予單位】：西北工業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB383.1
本文編號(hào)：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.
【學(xué)位授予單位】：西北工業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB383.1
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