论文总字数：23847字

摘 要

非晶合金以其优异的性能和独特的长程无序而短程有序原子结构成为材料工作者的研究热点。合金液体在足够高冷却速率下可以得到非晶，在慢冷条件下发生晶化，得到三维有序晶体。同时，由于冷速的影响即使同样得到非晶结构，但是由于冷速的不同，非晶合金的结构也会不同。众所周知，材料的结构决定材料的性能，因此研究不同冷速下非晶态合金的结构特别是原子层次的结构对于研究非晶合金的性能具有重要的意义。冷速对非晶结构的影响以及液态合金晶化过程中怎么实现无序到有序的转变是非常有必要的。

利用分子动力学模拟软件Lammps和结构表征手段对模拟计算结果进行分析和讨论，5E11K/s、1E12K/s、5E12K/s、1E13K/s冷速下非晶合金的第二峰发生劈裂，且随着冷速的降低，第二峰强度增加，原子有序性增加，1E11K/s冷速下发生晶化，径向分布函数呈现多峰的特征，为典型的结晶特性；从不同冷速下室温径向分布函数结果表明，异类原子间径向分布函数高，相互作用力强。非晶中二十面体短程序和密排六方/面心立方结构为主，晶化后1441和1661键对明显增高，对应的bcc结构增多，表明Cu₁₅Zr₈₅ 合金的晶化相主要为bcc结构。Voronoi多面体分析，晶化后室温以Cu为中心的配位数13、14，Voronoi多面体主要是lt;0,6,0,8gt;、lt;0,5,1,7gt;、lt;0,5,2,6gt;三类所典型多面体，以Zr原子为中心的配位数最多的是14、其次是13，Voronoi多面体最多的是lt;0,6,0,8gt;、其次是lt;0,5,1,7gt;。

本论文以Cu₁₅Zr₈₅合金为研究对象，研究冷却速率对合金室温结构的影响；非晶和晶体形成过程的结构转变及非晶结构中的中、短程序；液态合金无序到有序的转变的影响。揭示非晶形成和晶化过程中的结构演化以及非晶和晶体的室温结构。

关键词：非晶合金 分子动力学模拟 Voronoi多面体 结构表征

Effect of cooling rate on the structural evolution of Cu₁₅Zr₈₅ alloy during solidification

Abstract

Amorphous alloys have become a research hotspot for material workers because of their excellent properties and their unique long-range disorder and short-range ordering atomic structure. The alloy liquid can be made amorphous at a sufficiently high cooling rate and crystallized under slow cooling conditions to obtain three-dimensionally ordered crystals. At the same time, even if the amorphous structure is similarly obtained due to the influence of the cooling rate, the structure of the amorphous alloy will be different due to the difference in the cooling rate. It is well-known that the structure of the material determines the properties of the material, so studying the structure of the amorphous alloy at different cooling rates, especially the atomic level structure, is of great significance for the study of the properties of the amorphous alloy. The effect of the cooling rate on the amorphous structure and how to achieve disordered to ordered transformation during the crystallization of the liquid alloy are very necessary.

Analytical calculation results were analyzed and discussed using molecular dynamics simulation software Lammps and radial distribution functions, key pair analysis, Voronoi polyhedrons, and instantaneous configuration characterization methods, 5E11K/s, 1E12K/s, 5E12K/s, 1E13K/ s The second peak of the amorphous alloy splits during cooling, and as the cooling rate decreases, the intensity of the second peak increases, the atomic order increases, and the crystallization occurs at a cooling rate of 1E11K/s. The radial distribution function is exhibited. The characteristic of multimodality is a typical crystallization behavior. The radial distribution function at room temperature under different cooling velocities shows that the radial distribution function between heterogeneous atoms is high and the interaction force is strong. The icosahedral short process and densely packed hexagonal/face-centered cubic structure in amorphous are dominated. After the crystallization, the 1441 and 1661 bond pairs are significantly increased and the corresponding bcc structure is increased, indicating that the crystallization phase of Cu₁₅Zr₈₅ alloy is mainly bcc structure. The Voronoi polyhedron analysis shows that after crystallization, coordination numbers 13 and 14 of Cu centered at room temperature, Voronoi polyhedrons are mainly lt;0,6,0,8gt;, lt;0,5,1,7gt;, lt;0,5,2,6gt; The typical polyhedrons of the three types, with Zr atoms centered on the most number of coordination numbers 14, followed by 13, Voronoi polyhedrons with the most lt;0,6,0,8gt;, followed by lt;0,5,1 , 7gt;.

In this dissertation, the Cu₁₅Zr₈₅ alloy is studied to study the effect of cooling rate on the room temperature structure of the alloy, the structural transformation of the amorphous formation process, and the short and medium processes in the amorphous structure, and the disordered to ordered transformation of the liquid alloy. It reveals the structure evolution during amorphous formation and crystallization as well as the room temperature structure of amorphous and crystalline.

Keywords: amorphous alloy; molecular dynamics simulation; Voronoi polyhedron ;structural characterization

目 录

第一章 绪论 1

1.1非晶合金的发展及研究 1

1.1.1非晶合金的发展 1

1.1.2 CuZr二元非晶合金的发展 2

1.2非晶合金的简介 3

1.3非晶合金的结构模型 3

1.3.1硬球无规密堆模型 3

1.3.2微晶模型连续无规则网络模型 3

1.3.3准等同团簇模型 4

1.4非晶形成的判据 4

1.5研究的目的与意义 5

第二章 分子动力学模拟及结构表征 6

2.1分子动力学模拟方法 6

2.1.1分子动力学模拟 6

2.1.2系综 6

2.1.3周期性边界条件和非周期性边界条件 7

2.1.4势函数 7

2.1.5 温度控制和压力控制 7

2.2 结构表征手段 8

2.2.1径向分布函数(RDF) 8

2.2.2 配位数 8

2.2.3键对分析 8

2.2.4 Voronoi多面体 8

2.3 模拟过程 9

2.4 研究内容 9

第三章 计算结果与讨论 10

3.1液态构型的获得 10

3.2非晶和晶体形成过程中的结构演化 11

3.3 冷却速率对Cu15Zr85室温结构及的影响 17

第四章 结论 23

参考文献 24

致 谢 26

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