论文总字数：25333字

摘 要

非晶合金以其长程无序而短程有序的独特原子结构使其具有优异的性能。然而非晶合金有限的玻璃形成能力(GFA)是限制其实现工业应用的关键因素。研究非晶合金局域原子结构与GFA的关系，对于促进非晶合金发展与应用具有非常重要的意义。本论文以具有优异GFA的等原子比的Cu50Zr50(即CuZr)非晶合金为对象，利用分子动力学模拟的方法，研究CuZr非晶合金的中/短程有序结构与堆垛机制及该合金具有优异玻璃形成能力的结构起源。

径向分布函数分析表明CuZr熔体冷却形成非晶过程中各原子对间的偏对分布函数（PRDF）的第二峰均发生劈裂，且不同原子对间的PRDF开始发生劈裂的温度不尽相同。键对分析结果显示，非晶形成过程中二十面体结构短程序在非晶和液态中占主导地位。Voronoi多面体分析结果表明CuZr非晶合金中以Cu为中心的配位数主要为10-12，其配位多面体以具有五次对称的二十面体短程序为主，其中主要配位多面体为Cu₅Zr₇；而以Zr为中心的配位数主要集中在13-16，畸变二十面体和Frank-Kasper多面体为主要的配位短程序，其中含量最大的短程序为Zr₈Cu₇。CuZr非晶合金中的短程序通过共点、共线、共面、嵌套的连接方式扩展成中程序。

本论文从非晶形成过程中液态结构的稳定性与遗传性、非晶CuZr结构中占优势的多面体(Cu₅Zr₇和Zr₈Cu₇)与结晶先析出相(Cu₁₀Zr₇)结构对称的不相容性以及动力学角度三方面揭示了CuZr非晶合金具有优异玻璃形成能力的结构起源。

关键词：CuZr非晶合金 中/短程有序结构 玻璃形成能力 分子动力学模拟

The relationship between short- and medium-range order structure and glass forming ability in CuZr amorphous alloy

Abstract

Amorphous alloys possess a series of exellent physical, chemical and mechanical properties because of the unique atomic structure with long-range disorder and short-range oder (SRO). However, the limited glass forming ablility (GFA) hinderes the actual commercial applications. Therefore, it is vitally important for us to study the relationship between local atomic structure and GFA for promoting the application of amorphous alloys. In this thesis, the short- and medium-range oder (MRO), the packing mechanism for SRO and MRO and the structural origin with excellent GFA for CuZr alloy with have been systematically investigated by molecular dynamics (MD) simulations

The formation of CuZr binary amorphous alloys has been studied employing MD simulations. The resluts displayed that the second peak splits into two pronounced subpeaks on the partial radial distribution function(PRDF) curves of CuZr amorphous alloys. The temperature corresponding to the appearance of splitting for PRDF curves is different during the glass transition. The result of bond-pair analysis demonstrated that the icosahedral SRO is prevail in amorphous and liquid state during the glassformation. Furthermore, the result of Voronoi polyhedron analysis represented that the coordination number (CN) mainly distribute 10 to 12, whilst that of the Zr atoms ranges from 13 to 16. The structural analysis showed that the icosahedral-like with five-fold symmetry for Cu atoms is predominant while disorder icosahedra and Frank–Kasper polyhedra for Zr atoms is dominant in glass state. Furthermore, the major local structural units for the Cu- and Zr-centered clusters are Cu5Zr7 and Zr8Cu7 polyhedra are, respectively. The MRO was constructed by SRO via the linkage of vertex-, edge-, face-, and inter-crossed-shared atoms.

In this work, the stability and hereditary for the structure of liquid state, the structural incompatibility between the main competing crystalline phase and the major SRO in CuZr alloy and the kenetic properties were used to explored the structural origin with excellent GFA for CuZr alloy.

Keywords：CuZr amorphous alloy; Glass forming ability; short- and midium-range order; Molecular dynamics simulations

目 录

摘 要 I

Abstract II

第一章 绪论 1

1.1 非晶合金的发展 1

1.1.1 Cu基非晶合金的发展概述 1

1.1.2 Cu-Zr二元非晶合金的发展概述 2

1.2 非晶合金玻璃形成能力判据 3

1.2.1 临界冷却速率 3

1.2.2 约化玻璃温度 4

1.2.3 过冷液相区 4

1.2.4 参数 4

1.3 非晶合金的结构模型 4

1.3.1 密堆团簇堆垛模型 5

1.3.2. 准等同团簇堆垛模型 5

1.4 研究的目的与意义 6

第二章 分子动力学模拟与结构分析技术 7

2.1 分子动力学模拟的原理 7

2.1.1 分子动力学的基本原理 7

2.2.2 势函数 7

2.2.3 控温控压方法 7

2.2.4 系综 8

2.2.5 周期性边界条件 8

2.2 分子动力学模拟结构表征 8

2.2.1 径向分布函数 8

2.2.2 配位数 9

2.2.3键对分析 9

2.2.4 Voronoi多面体 9

2.3 模拟过程 10

2.4 研究内容 10

第三章 计算结果及数据分析 11

3.1 冷却速率对CuZr非晶合金室温结构的影响 11

3.2 冷却速率对玻璃转变温度的影响 13

3.3 非晶合金形成过程中的结构演变 14

3.4 CuZr非晶合金中/短程有序结构 16

3.5 非晶结构与玻璃形成能力之间的关系 20

第四章 结论及展望 24

4.1 结论 24

4.2 展望 24

参考文献 25

致 谢 27

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