金属玻璃应力松弛与蠕变多级动力学跨时间尺度计算机模拟

Metallic glasses are metastable structures in thermodynamics. Under the condition of specific stress and temperature, they are prone to undergo structural aging or rejuvenation, which affects their mechanical properties and service reliability. Metallic glasses usually present hierarchical dynamics characteristics due to their structural heterogeneity. It is of both scientific curiosity and engineering importance to build a temporal-spatial correlation between their hierarchical dynamics and the structural heterogeneity. Stress relaxation and creep can reflect the dynamic characteristics of materials which are relevant to their structures. However, the timescales of the microscopic processes accompanying stress relaxation and creep are usually of the order of experimental timescales, which are far from the usual molecular dynamics time window. This study is aimed at developing and using accelerated molecular dynamics to conduct multi-time-scale simulations of hierarchical dynamics of metallic glasses, which helps to completely describe the hierarchical characteristics of metallic glasses dynamics and benefits recognizing their structural origins and evolution accompanying the events of different timescales. Based on the proposed atomic-scale scenarios, we further establish a physics relevant constitutive relation to describe the temporal-spatial correlation between the structural and dynamic heterogeneities of metallic glasses. We also plan to conduct experiments of stress relaxation and creep on metallic glasses, then analyze the results through thermal activation theory, phenomenological model, and discrete analysis, which can confirm the multi-time-scale computer simulations and the constitutive relation between structure and dynamics. The study is targeted to provide physical insights into the microstructure-property relationship and manipulate this relationship to improve the mechanical performances and service reliability of metallic glasses.

金属玻璃处于热力学亚稳态，在应力和温度驱动下，结构趋于老化或年轻化，从而影响力学性能和服役可靠性。由于结构不均匀，金属玻璃呈现多级动力学特征。建立金属玻璃微观结构与多级动力学的时空关联，具有重要科学意义和潜在应用价值。应力松弛和蠕变可以反映多级动力学特征从而关联结构。但其所涉及的原子过程通常具有实验室时间尺度特征，远远超出经典分子动力学时间范畴。本研究将发展和应用加速分子动力学技术，实现金属玻璃应力松弛和蠕变多级动力学的跨时间尺度计算机模拟，完整描述金属玻璃多级动力学特征，并辨识不同时间尺度事件的微结构起源及其演化机理。结合原子图像，构建物理相关的本构关系，描述金属玻璃动力学与结构不均匀性的时空关联。开展应力松弛和蠕变实验，通过热激活理论、唯象模型和离散谱分析，验证跨时间尺度模拟和时空关联物理模型。本研究旨在认识和调控金属玻璃的微结构-性能关系，为改善力学性能和服役可靠性提供理论支持。

按照目标设定，项目发展和应用加速分子动力学技术，开展金属玻璃应力松弛和蠕变多级动力学的跨时间尺度计算机模拟研究，完整描述了金属玻璃多级动力学特征，并辨识不同时间尺度事件的微结构起源及其演化机理，从而实现了所有的研究目标。项目取得了多方面的研究进展，主要包括：实现了实验室时间尺度合金扩散行为和β弛豫的分子动力学模拟，揭示了扩散与玻璃转变的关联以及β弛豫的熵效应；提出玻璃结构决定动力学二性能的关键因素为结构特征的空间关联；提出玻璃转变的统计结构与动力学模型。以上进展，为在原子尺度理解无序物质结构—性能关联提供了物理基础。