双晶晶界在高温下的热稳定性的分子动力学研究

IMECH-IR > 力学所知识产出(1956-2008)

	双晶晶界在高温下的热稳定性的分子动力学研究
	吴勇义
导师	周富信
	1999
学位授予单位	中国科学院研究生院
学位授予地点	北京
学位类别	硕士
学位专业	一般力学与力学基础
关键词	分子动力学经验多体势晶界静态结构因子径向分布函数 Molecular Dynamics Empirical N-body Potential Grain Boundary Static Structure Factor Radial Distribution Function
英文摘要	晶界结构在高温下的热稳定性问题是一个长期争论而又未能解决的问题，其争论的焦点是：在远低于熔点的温度下，晶界结构是否发生了可观察到的无序化，即是否存在一个远低于熔点的结构转化温度。为了能澄清这一争论，本文系统地研究了晶界结构的热稳定性。为了消除相互作用势的影响和系统误差，本文首先采用Morse势和经验多体势分别对铝、铜单晶的熔化过程进行了分子动力学模拟。在平衡态下，通过计算表征结构无序化的静态结构因子、径向分布函数和单晶原子位形图，获得了铝、铜单晶的熔点，结果表明：多体势计算的铝和铜的单晶熔点更接近实验值。因此，采用经验多体势应用分子动力学方法分别模拟了铝、铜Σ3、Σ5、Σ9、Σ11、Σ19、Σ33六种对称倾侧双晶晶界晶界结构由有序向无序转化的过程，计算了平衡态下的表征结构无序化的静态结构因子、径向分布函数和晶界原子位形图并将多体势获得的铝、铜单晶熔点作为晶界结构转化温度的约化熔点，获得了铝、铜Σ3、Σ5、Σ9、Σ11、Σ19、Σ33六种对称倾侧双晶晶界结构的转化温度和熔点，结果表明：1．Σ5、Σ9、Σ11、Σ19、Σ33五种对称倾侧双晶晶界均在远低于单晶熔点温度时，晶界结构发生了可观察到的无序化，而且双晶晶界结构的转变温度相差不大，双晶晶界熔点也低于单晶熔点。2．Σ3晶界在温度远低于熔点时，其晶界结构没有发生可观察到的无序化；Σ3晶界的转化温度与单晶熔点接近。所以，可以认为Σ3晶界不存在转化温度。这是由于Σ3晶界为共格孪晶，具有较低的能量。综上所述，除Σ3共格孪晶外，在远低于熔点温度下，晶界结构发生了可观察到的无序化，即：存在一个远低于熔点的转化温度，此时其静态结构因子约为0.5左右；晶界结构的熔点均低于单晶熔点，此时其静态结构因子约为0.15左右。从全文模拟结果可以看出，静态结构因子、径向分布函数、晶界原子位形图三种方法在确定晶界的结构转化温度和熔点时，静态结构因子是最有效、最准确的定量方法。; The stability of grain boundary structure at high temperature has long been a problem in dispute. The main point of this dispute is whether the grain boundary can melt into a structure similar to that of super-cooled liquid or becomes disordered at a temperature much lower than the single-crystal melting point. To make the problem in this dispute clear, systematical study is performed in the thesis. In this thesis, to eliminate the effect of the interatomic potential and system error, the aluminium or copper single-crystal melting processes have been firstly studied through molecular dynamics simulations using the Morse interaction potential or the empirical N-body potential for Cu or Al. At equilibrium, the aluminium and copper melting temperatures are obtained by calculating the static structure factor, radial distribution function and plotting the detailed atomic configuration of single-crystal, which indicate a certain amount of structural disorder. The calculation results show that the melting temperatures obtained from the empirical N-body potential are more approximate to the experimental results. By using molecular dynamics simulations and the empirical N-body potential, the transformation process from order to disorder is studied for these six symmetrical tilt aluminium bicrystal or copper bicrystal boundaries Σ3、Σ5、Σ9、Σ11、Σ19、Σ33. By calculating such functions, which indicate a certain amount of structural disorder, as static structure factor, radial distribution function and detailed atomic configuration of grain boundary at equilibrium and by employing melting point of single-crystal obtained from the empirical N-body potential as the reduce temperature of the grain-boundary structural transformation temperature, we obtain the structural transformation temperature and the melting temperature of these six symmetrical tilt aluminium bicrystal or copper bicrystal boundaries Σ3、Σ5、Σ9、Σ11、Σ19、Σ33. The results clearly point out that: 1. A observable disordered structure transformations in these five symmetrical tilt aluminium bicrystal boundaries Σ5、Σ9、Σ11、Σ19、Σ33 occur well below the single-crystal melting point. Furthermore the difference among the transformation temperatures of different bicrystal grain boundary structures is small. The melting point of bicrystal grain boundary structures is below that of the single-crystal. 2. There occurs no observable disordered structure in the Σ3 grain boundary structure at temperature well below the melting point; the transformation temperature of the Σ3 grain boundary is close to the single-crystal melting point. Therefore it can be concluded that the transformation temperature does not exist in the Σ3 grain boundary because the Σ3 grain boundary is a twin-boundary structure and has a lower energy level. From above all, an observable disordered structure occurs at temperature well below the single-crystal melting point in all grain boundaries except in the Σ3 twin-boundary, which means that there exists a transformation temperature well below the melting point when the static structure factor is about 0.5 and that the grain boundary structure's melting points are all below the corresponding single-crystal melting point when the static structure factor is about 0.15. The simulation results show that the static structure factor is the most effective and most exact quantitative method for determining the transformation temperature among the three methods of the static structure factor, radical distribution function and atomic configuration of grain boundaries.
索取号	29857
语种	中文
文献类型	学位论文
条目标识符	http://dspace.imech.ac.cn/handle/311007/23972
专题	力学所知识产出(1956-2008)
推荐引用方式 GB/T 7714	吴勇义. 双晶晶界在高温下的热稳定性的分子动力学研究[D]. 北京. 中国科学院研究生院,1999.

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