Knowledge Management System of Institue of Mechanics, CAS
| 金属熔化过程的分子动力学研究 | |
| 王暾 | |
| Thesis Advisor | 周富信 |
| 2001 | |
| Degree Grantor | 中国科学院研究生院 |
| Place of Conferral | 北京 |
| Subtype | 博士 |
| Degree Discipline | 一般力学与力学基础 |
| Other Abstract | 熔化是固相转化为液相的过程，揭示出金属熔化相变过程中原子尺度上的动力学规律，具有很大的理论意义和应用背景。本论文采用分子动力学方法和多体相互作用势，通过对内能、静态结构因子、径向分布函数、原子弛豫位形等进行分析，研究了金属铜和铝的单晶、双晶、表面、固液界面等系统的熔化过程及多体效应对熔化的影响。金属单晶熔化时结构发生有序一无序突变，具有均匀形核熔化特点，将导致晶体熔化过热。不同的非均匀形核条件使得晶体的熔点不同，但都低于理想单晶熔点。在较低的温度下双晶Σ5、Σ9、Σ11、Σ19、Σ33的晶界附近存在无序区。随着温度的升高，无序区逐渐扩展最终导致双晶熔化，具有非均匀形核熔化的特点。但晶界的存在并不一定导致非均匀形核熔化，例如艺3熔化前不存在无序区，它的熔化是由均匀形核控制的。表面的存在使得晶体熔化都以无序从表面向内部逐渐扩展而进行，即都以非均匀形核方式进行。并且表面能越大，表面预熔温度越低。对具有（110）和（111）表面的双晶的模拟表明表面和晶界在熔化时可以相互作用，其熔化并不是通过两个晶粒的同时熔化进行的，这与对称倾斜双晶中两个晶粒的同时熔化是不同的。固液系统的模拟可以较准确地确定晶体的熔点，其在熔点下的模拟表明固液原子间存在动态平衡交换。利用所扩展的EAM-LJ多体势研究表明，随着多体势强度的增加，熔点下降；而随着电子密度衰减指数的减小，熔点降低。总之，论文研究了多种条件下的熔化过程，给出了金属熔化相变的一些微观动力学机制。; Understanding melting, the transition from solid to liquid, on microscopic scale is a fundamental problem of condensed physics. How the structure changes in the transition is required to understand the transition better for both theoretical and applied purposes. In this paper, with molecular dynamics and EAM potentials, the melting of the single crystals, grain boundaries, surfaces and solid-liquid systems and the many-body effects are studied by the analysis of internal energy, static structural factor, radical distribution function and atomic configuration. When a single crystal melts, its structure changes abruptly, which is characterized as homogeneous nucleation for melting and makes the crystal superheated above its equilibrium melting point. On the other hand, heterogeneous nucleation makes a crystal melt at a temperature below the melting point of its corresponding single crystal, although different nucleation influences the melting point distinctively. Below their melting points, structural disorder exists in the neighborhood of grain boundaries of Σ5, Σ9, Σ11, Σ19 and Σ33 bicrystals. As the disorder propagates and makes the bicrystals finally melt with ever increasing temperature, their melting is dominated by heterogeneous nucleation. However, grain boundaries do not always lead to heterogeneous nucleation. For example, there is not any disordered area before Σ3 is melted homogeneously. Surfaces always make crystals melt heterogeneously with the propagation of disorder from surfaces to their interiors. It is showed that the premelting temperature decreases with increasing surface energy. The melting of the bicrystal with (110) and (111) surfaces does not proceed by the simultaneous melting of the two crystals, which is different from the simultaneous melting of symmetrical tilt bicrystals such as Σ9. With a system containing both crystal and liquid the melting point can be determined accurately. The crystal and liquid can coexist at its melting point with dynamic interchange of atoms between crystal and liquid. Using our extended EAM-LJ potential, we find that the melting point decreases with increasing many-body bonding and/or decreasing the decay of the electron density. In a word, in this paper, the melting is studied on microscopic scale for various systems, and some dynamics mechanisms for melting are presented. |
| Call Number | 29940 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://dspace.imech.ac.cn/handle/311007/23866 |
| Collection | 力学所知识产出(1956-2008) |
| Recommended Citation GB/T 7714 | 王暾. 金属熔化过程的分子动力学研究[D]. 北京. 中国科学院研究生院,2001. |
| Files in This Item: | ||||||
| File Name/Size | DocType | Version | Access | License | ||
| 11869.pdf（1872KB） | 学位论文 | 开放获取 | CC BY-NC-SA | Application Full Text | ||
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