非晶合金在复杂应力场下的剪切带形成及扩展机制研究

This proposal aims to obtain the formation of a sigle shear band in Cu64Zr36 metallic glass (MG) under designed complex stress fields, and give more insight into the shear-band formation and propagation mechanisms based on in-situ TEM observations and molecular dynamics simulations. Complex stress fields will firstly be designed using Finite Element Modeling (FEM) analysis through tailoring the size, shape and distance of notches. The corresponding specimens will then be fabricated using Focused Ion beam (FIB), and tested using in-situ TEM to obtain the formation of a single shear band. By studying the effect of complex stress fields on the formation and propagation of shear bands as well as the movement of atoms within the shear band, such as the shear band width, the density of atoms and crystallization, relationships between the complex stress fields and the formation and propagation of shear bands will be established. The formation and propagation of shear bands will then be tailored by tuning the complex stress fields. On the other hand, the formation and propagation of shear bands as well as the movement of atoms within the shear bands will be modeled using molecular dynamics simulations using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) software. The simulation output parameters, such as the Voronoi volume and bond pair analysis, will be employed to characterize the formation and propagation of shear bands, such as the shear band width and the density of atoms within the shear bands, providing more evidence and explanations for the experimental observations. Finally, the shear-band formation and propagation mechanisms of MGs under complex stress fields will be proposed based on both the experimental and simulation results, providing more understandings for further investigations of the plastic deformation mechanisms of MGs.

本项目拟通过设计复杂应力场在Cu64Zr36非晶合金中获得单一的剪切带，结合原位TEM观测及分子动力学程序模拟，研究剪切带的形成及扩展机制。首先通过引入缺口的大小、形状及相对位置，利用有限元分析设计复杂应力场，用聚焦离子束（FIB）制备非晶合金样品，并在原位TEM下获得单一的剪切带。然后观察应力场的变化对剪切带形成、扩展及内部原子流动的影响，如剪切带的宽度、剪切带内部原子密度及晶化现象，建立不同应力场同剪切带形成及扩展之间的联系，实现通过改变应力场对非晶合金中剪切带形成及扩展的调控。同时用LAMMPS 分子动力学程序模拟非晶合金在复杂应力场下剪切带的形成、扩展以及内部原子流动，通过计算Voronoi原子体积、键对分析等表征剪切带宽度以及内部原子密度等，为实验结果提供理论解释。最后综合实验及模拟结果，提出复杂应力场下非晶合金中剪切带形成及扩展机制，为研究非晶合金的塑性变形机理奠定基础。

揭示非晶合金剪切带形成及扩展机制、塑性流变机理对丰富非晶合金塑性变形理论具有重要意义。本项目采用有限元方法，基于缺口形状和位置对复杂应力场进行设计。在纳米尺度下，通过设计微区复杂应力场（Localized complex stress fields, LCSFs）获得了单一的剪切带，采用LAMMPS分子动力学（Molecular dynamics, MD）程序研究了复杂应力场对剪切带形成及扩展的影响规律，具体包括剪切带中原子的富集和流动，峰值应力、流变应力以及变形能量的释放过程，剪切带宽度演变等，揭示了微区复杂应力场下剪切带形成过程中原子流动、剪切带形成及扩展机制。在宏观尺度下，剪切带的形成和扩展在应力-应变等曲线上展现出锯齿流变行为。通过复杂应力场设计获得了稳定的塑性（锯齿）流变阶段，采用三参数韦伯分布等统计学方法研究了锯齿流变中弹性能量累积速率的变化规律，揭示了弹性能量累积与释放过程之间的联系规律，丰富了非晶合金塑性变形理论。基于非晶合金复合材料锯齿流变中弹性能量累积与释放阶段的分形研究，进一步揭示了非晶合金材料中锯齿流变体系的演化规律。在完成非晶合金塑性变形机理等既定目标基础上，开展了非晶合金先进制造技术相关研究，包括切削加工、电火花加工工艺及相关机理等。研究发现在低速切削条件下可获得较好的表面质量，其表面粗糙度值达到了精密加工水平；虽然非晶合金因其具有高强度、高硬度等特性被归类于难加工材料，但在电火花加工过程中却容易获得较高的加工效率，而且通过工艺参数设计、优化可以有效的降低非晶合金电火花加工表面晶化现象，相关研究成果可为非晶合金的工程应用提供理论支撑和技术指导。