金属玻璃形成液体的异常动力学行为研究

发布时间：2018-02-02 20:08

本文关键词： 金属玻璃液体动力学转变 sub-T_g弛豫团簇演变　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：金属玻璃是近几十年发展起来的一类新型材料,因其具有优异的综合性能以及明显的玻璃转变现象而受到科学家们的广泛关注。目前,尽管金属玻璃已应用于信息与电子器件、精密器械、航空航天器件等多个领域,但对其凝固过程中结构的演变规律及动力学机理仍缺乏研究。而研究金属玻璃形成液体的动力学行为及其结构演变机理对于深入理解和揭示金属玻璃液固遗传的微观本质、提高玻璃形成能力、促进金属玻璃制备和处理工艺的标准化等具有重要意义。基于以上背景,本文以研究金属玻璃形成液体为出发点,辅之以热力学测试和微观结构表征等手段,重点探究了金属玻璃形成液体的动力学行为,发现了与亚当-吉布斯(Adam-Gibbs)提出的"金属玻璃液体的动力学性质及其结构随温度的演变呈单调性"的传统理论不同的异常动力学现象,并探索了异常动力学转变过程中液体结构随温度的变化,揭示了部分金属玻璃液体微观团簇的演变规律。主要研究内容及结论如下:(1)通过对铁基高温熔体在远高于液相线温度的动力学行为研究,发现了铁基高温熔体黏度随温度变化的动力学转折现象以及第二次升温-降温过程中黏度的滞后现象。结合流体团簇模型和过冷液体脆性概念,提出了表征高温熔体动力学转变程度的参数F,建立了参数F与玻璃形成能力之间的联系,从而确定了该动力学转变对铁基非晶合金玻璃形成能力的影响。结合DSC测得的熔体热力学信号,探索了高温熔体动力学转变过程中的团簇演变规律。本文对探究铁基高温合金熔体性质,提高铁基非晶合金制备过程中的标准化程度具有重要意义。(2)选取超快冷制备的Cu46Zr42Al7Y5金属玻璃条带作为研究对象,通过采用热力学方法,研究了金属玻璃固体在sub-Tg热焓弛豫和晶化过程中所反映的过冷液体中的动力学行为。该金属玻璃条带的热流曲线表现为三个放热峰。其中,第一放热峰和第三放热峰分别是正常的sub-Tg焓弛豫峰和晶化峰。而本应表现为吸热玻璃转变峰的第二放热峰则是过冷液体中存在玻璃转变以外的动力学异常行为的表现。结合Cu46Zr42Al7Y5金属玻璃条带在连续升温和持续等温过程中的第二放热峰和晶化峰的变化以及它们分别对应的激活能的大小,揭示了第二放热峰的起源是发生在玻璃转变后期的团簇有序化行为引发的放热反应与玻璃转变引发的吸热反应相叠加的结果,该叠加过程是金属玻璃过冷液体中局域有序结构的演变和两种不同局域聚集结构互相竞争的体现。这种团簇有序化的异常动力学演变可能是锆-钇原子之间与铝-钇(或铜-钇)原子之间混合焓的巨大差异导致的。本文开辟了一种新思路,可以作为鉴别相分离和团簇理论争论的一种方法。
[Abstract]:Metallic glass is a new kind of material developed in recent decades. It has been widely concerned by scientists because of its excellent comprehensive properties and obvious glass transition phenomenon. Although metallic glass has been used in many fields, such as information and electronic devices, precision instruments, aerospace devices and so on. However, there is still a lack of research on the evolution law and kinetic mechanism of the structure during solidification. However, the study of the kinetic behavior of the formation of liquid and the evolution mechanism of the structure of metallic glass are helpful to understand and reveal the inheritance of liquid-solid in metallic glass. Microscopic nature. It is of great significance to improve the glass forming ability and to promote the standardization of the preparation and treatment of metallic glass. Based on the above background, this paper takes the study of metal glass forming liquid as the starting point. With the help of thermodynamics measurement and microstructure characterization, the kinetic behavior of metallic glass forming liquid was studied. Different from the traditional theory proposed by Adam-Gibbsof Adam-Gibbs' that the dynamic properties and structure of metallic glass liquids are monotonic with the evolution of temperature, the anomalous dynamic phenomena are found. The variation of liquid structure with temperature during abnormal dynamic transition is also explored. The evolution of some metallic glass liquid clusters was revealed. The main contents and conclusions are as follows: 1) the kinetic behavior of Fe-based high temperature melts is much higher than the liquid line temperature. The dynamic transition phenomenon of the viscosity of Fe-based high temperature melt with temperature and the lag phenomenon of viscosity in the second temperature-cooling process are found, which are combined with the fluid cluster model and the concept of supercooled liquid brittleness. The parameter F, which is used to characterize the degree of dynamic transition of high temperature melt, is proposed, and the relationship between the parameter F and the glass forming ability is established. The influence of the kinetic transformation on the glass forming ability of Fe-based amorphous alloy was determined. The thermodynamic signal of melt was measured by DSC. The evolution law of clusters in the process of dynamic transformation of high temperature melt was explored. The properties of Fe-base superalloy melt were investigated in this paper. It is of great significance to improve the standardization in the preparation of Fe-based amorphous alloys. (2) the Cu46Zr42Al7Y5 metal glass strips prepared by ultra-fast cooling are selected as the research object. By using thermodynamics. The kinetic behavior of metallic glass solids in supercooled liquid reflected in the process of sub-Tg enthalpy relaxation and crystallization has been studied. The heat flux curve of the metal glass strip shows three exothermic peaks. The first exothermic peak and the third exothermic peak are normal sub-Tg enthalpy relaxation peak and crystallization peak, respectively. The second exothermic peak, which should be shown as endothermic glass transition peak, is the kinetics other than glass transition in supercooled liquid. Abnormal behavior. Changes of the second exothermic peak and crystallization peak of the Cu46Zr42Al7Y5 metal glass strip during continuous heating and continuous isothermal process, and the magnitude of their corresponding activation energies, respectively. . It is revealed that the origin of the second exothermic peak is the superposition of the exothermic reaction caused by the ordering behavior of the cluster during the later period of glass transition and the endothermic reaction induced by the glass transition. The superposition process is the evolution of local ordered structure in metallic glass supercooled liquid and the competition between two different local aggregation structures. The anomalous dynamic evolution of this kind of cluster ordering may be between zirconium and yttrium atoms and aluminum. -yttrium. This paper opens up a new way of thinking due to the great difference in the enthalpy of mixing between copper and yttrium atoms. It can be used as a method to distinguish phase separation and cluster theory controversy.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG139.8

【相似文献】