基于胶体模型原位研究非晶合金β弛豫的结构起源

Figuring out the structural origin of the β relaxation is the key to revealing the nature of β relaxation and its relevant physical problems，such as glass transition, plastic deformation and atomic diffusion. However, because of the limitation of the experimental methods, there is still a lack of more thorough and unified understanding about the structural origin of β relaxation. In situ observing the structural evolution of β relaxation in metallic glasses is the most direct and reliable way to reveal the structural origin of β relaxation. Recently, the colloidal system has been widely used as the model to investigate the basic scientific problems of metallic materials. In this project, the colloidal system is used as the model to simulate the evolution of the microstructure and microscopic dynamics of metallic glasses in the glass forming process. The confocal microscope is employed to in situ observe the structural evolution of β relaxation in the glass transition process. The packing structure, packing density and coordination number of particles corresponding to the β relaxation are statistically analyzed. The influence of free volume on the β relaxation is studied combined with the Voronoi volume and free volume model. The structural origin of β relaxation in amorphous alloys is clarified from the atomic scale. This study is expected to reveal the physical nature of β relaxation and of great significance to promote the development of material science of metallic glasses.

澄清非晶合金β弛豫的结构起源，是揭示β弛豫的本质和解决与其相关的玻璃转变机制、塑性形变机制以及原子扩散机制等问题的关键。然而，由于实验方法的限制，对非晶合金β弛豫的结构起源问题仍然缺乏较为深入和统一的认识。原位观测非晶合金β弛豫的结构演化过程，是揭示其结构起源的最直接和最可靠的途径。以胶体体系为模型，原位模拟研究金属材料的基本科学问题，是近来被广泛采用的新颖方法。本项目拟以胶体体系为模型，模拟非晶合金体系形成过程中微观动力学和微观结构的变化，并利用激光共聚焦显微镜，原位观测胶体体系在玻璃转变过程中β弛豫的结构演化；统计分析β弛豫对应粒子的堆垛结构、堆垛密度、配位数等空间构型信息；并结合Voronoi体积和自由体积模型，分析自由体积对β弛豫的影响机理；从原子尺度明确非晶合金β弛豫的结构起源。本项目的研究有望揭示β弛豫的物理本质，对于推动非晶合金材料科学的进一步发展具有重要的意义。

非晶合金中存在两种最主要的本征弛豫模式，即α弛豫和β弛豫。其中，β弛豫是固态非晶合金中存在的主要弛豫模式，其与非晶合金的玻璃转变、塑性形变以及原子扩散等机制密切相关。因此，澄清非晶合金β弛豫的结构起源，是揭示β弛豫的本质和解决与其相关的玻璃转变机制、塑性形变机制以及原子扩散机制等问题的关键。然而，由于实验方法的限制，对非晶合金β弛豫的结构起源问题仍然缺乏较为深入和统一的认识。原位观测非晶合金β弛豫的结构演化过程，是揭示其结构起源的最直接和最可靠的途径。以胶体体系为模型，原位模拟研究金属材料的基本科学问题，是近来被广泛采用的新颖方法。本课题以胶体玻璃体系为模型体系，模拟非晶合金体系形成过程中微观动力学和微观结构的变化，并利用激光共聚焦显微镜，原位观测胶体体系在玻璃转变过程中β弛豫的结构演化过程。研究主要发现：.(1)β弛豫的结构起源：β弛豫起源于非晶固态材料中类液区域粒子的集体运动； .(2)β弛豫与自由体积的关联：β弛豫事件容易在自由体积较大的区域优先发生；.(3)β弛豫之间的时空相关性：先发生的β弛豫事件容易在其附近激发新的β弛豫事件；.(4)冷却速率对β弛豫事件产生的影响：较高的冷却速率会促进β弛豫事件的发生，材料发生软化。