金属玻璃的高压退火改性及其结构起源

发布时间：2018-03-02 11:37

本文选题：金属玻璃　切入点：高压退火　出处：《中国科学院大学(中国科学院物理研究所)》2017年博士论文　论文类型：学位论文

【摘要】：不同于晶体材料的周期性结构,玻璃态物质中原子排列长程无序,利用传统的固体物理理论和实验手段很难表征其结构特征,理解玻璃态物质的结构是凝聚态物理领域最具挑战也是最迷人的问题之一。金属玻璃是典型的简单无序体系,为研究玻璃态物质的结构提供了很好的模型体系。最近的研究结果表明金属玻璃在结构上存在着纳米尺度的结构不均匀性,由原子排列松散的“类液区”和原子排列紧密的弹性基体组成。但是金属玻璃的无序结构十分复杂,是否还有其他形式的非均匀性存在?本文针对这一问题展开系统研究。高压处理和退火处理都可以显著改变金属玻璃的结构。本文结合这两种处理手段,首先利用高压退火的方法调控金属玻璃的结构。在高温和高压的耦合作用下,高压退火后的金属玻璃同时具有高能量状态和高密度,但塑性下降,该现象无法用传统的结构非均匀性来理解。随后的研究发现,在高压退火样品中存在着反常结构不均匀性:具有高原子堆积密度的区域散布在具有相对较低原子堆积密度的弹性基体中。利用反自由体积模型和激活能垒理论解释了这种反常结构非均匀性的形成原因和在外加温度下的演化。高压退火可以向金属玻璃中有效引入反常结构非均匀性,为研究其独特结构和对金属玻璃性能影响提供了有效手段。本文进一步研究了反常结构非均匀性对金属玻璃玻色峰这一玻璃态材料的本征性质的影响。在更致密的玻璃体系中观察到了玻色峰升高的现象,并且随着致密化程度的增加玻色峰连续增强。我们利用分子动力学模拟分析了玻色峰增强的结构起源,建立了玻色峰和结构不均匀性之间的联系,并揭示出玻色峰所反映的快原子振动和慢弛豫过程密切相关。最后,本文研究了反常结构不均匀性对金属玻璃动力学的影响。通过研究不同温度退火样品焓弛豫的演化和动态力学分析不同频率下β弛豫峰位置的变化,发现具有反常结构不均匀性的金属玻璃弛豫激活能显著提高,并提出了“负流变单元”的概念以解释其基本动力学特征。总之,本文提出高压退火这种可以向金属玻璃中引入反常结构非均匀性的方法,利用该方法对金属玻璃进行了系统的调控,并表征了调控后的金属玻璃的结构特征,这对理解玻璃态材料的不均匀结构具有重大意义。此外,本文研究了反常结构不均匀性对金属玻璃热力学性质、动力学性质和玻色峰的影响,这对认识金属玻璃的弛豫机制及探索新的有特殊功能的金属玻璃具有指导意义。
[Abstract]:Different from the periodic structure of crystal materials, the atoms in glass materials are disordered for a long time, so it is difficult to characterize their structural characteristics by using the traditional solid physics theory and experimental methods. Understanding the structure of glassy matter is one of the most challenging and fascinating problems in condensed matter physics. It provides a good model system for studying the structure of glass-state materials. Recent results show that there is structural heterogeneity in the structure of metallic glass at nanoscale. It is composed of "liquid like zone" with loose atomic arrangement and elastic matrix with compact atomic arrangement. However, the disordered structure of metallic glass is very complicated. Is there any other form of inhomogeneity? In this paper, the structure of metallic glass can be significantly changed by high pressure treatment and annealing treatment. Firstly, the structure of metallic glass is regulated by high pressure annealing. Under the coupling of high temperature and high pressure, the metal glass annealed at high pressure has both high energy state and high density, but the plasticity decreases. This phenomenon cannot be understood in terms of traditional structural heterogeneity. There is anomalous structural inhomogeneity in high pressure annealed samples: the region with high atomic packing density is scattered in elastic matrix with relatively low atomic packing density. The inverse free volume model and activation barrier theory are used. The formation of the anomalous structure inhomogeneity and the evolution at the applied temperature are explained. The anomalous structure inhomogeneity can be effectively introduced into metallic glass by high pressure annealing. It provides an effective means to study its unique structure and influence on the properties of metallic glass. The influence of anomalous structure inhomogeneity on the intrinsic properties of metallic glass Bose peak is further studied in this paper. The rise of the boson peak has been observed in glass system, With the increase of the densification degree, the Bose peak is continuously enhanced. The molecular dynamics simulation is used to analyze the structure origin of the Bose peak enhancement, and the relation between the Bose peak and the structure inhomogeneity is established. It is also revealed that the fast atomic vibration reflected by the boson peak is closely related to the slow relaxation process. In this paper, the effect of anomalous structure inhomogeneity on the kinetics of metallic glass is studied. The evolution of enthalpy relaxation of annealed samples at different temperatures and the change of the position of 尾 relaxation peak at different frequencies are studied. It is found that the relaxation activation energy of metallic glass with anomalous structure inhomogeneity is significantly increased, and the concept of "negative rheological unit" is proposed to explain its basic dynamic characteristics. In this paper, the method of high pressure annealing, which can introduce anomalous structure inhomogeneity into metallic glass, is proposed. The system is used to control the metallic glass, and the structural characteristics of the regulated metallic glass are characterized. In addition, the influence of anomalous structure on the thermodynamic properties, kinetic properties and boson peaks of metallic glass is studied. It is helpful to understand the relaxation mechanism of metallic glass and to explore new metallic glass with special function.
【学位授予单位】：中国科学院大学(中国科学院物理研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG139.8

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