高频激励阵列调控块体金属玻璃拉伸塑性的机理研究

The lack of the tensile plasticity at room temperature fatally restricts structural applications of bulk metallic glasses. The reason behind the dilemma is the absence of accurate structural models and practical methods to tune the microstructure of the metallic glasses. Based on the structural model of flow units, this project plans to investigate the evolution of the flow units and tune the tensile plasticity of bulk metallic glasses, by the method of high frequency actuation. Firstly, to change the microstructure, the high frequency actuation will be applied on the samples through a probe. We will establish the correlation between the evolution of the flow units and the parameters of the high frequency actuation. The key factors which dominate the structural evolution will be analyzed. Then, based on the relationship between the radius of the array point and the radius of the crack tip curvature, high frequency actuation arrays will be designed. The properties between the array and the glassy matrix will be matched. The influence from the concentration of the flow units, the shape, size and distribution of the actuation arrays on the tensile plasticity will be revealed. Finally, combined with the molecular dynamics simulation and the theory of energy landscape, we will analysis the features of the fracture surface and the interaction of the shear bands during the deformation process. The mechanism of the effect from the high frequency actuation on the structural evolution and tensile plasticity will be discussed. Our results will provide a theoretical basis and practice guidance on the enhancement of the tensile plasticity of bulk metallic glasses.

室温拉伸塑性的缺失严重制约着块体金属玻璃作为高性能结构材料的应用。该问题的关键在于缺少合适的微观结构模型和实用的结构调控手段。本项目拟从金属玻璃流变单元结构模型出发，采用高频激励方法开展块体金属玻璃拉伸塑性调控机理的研究。通过探针对金属玻璃微区施加高频激励，诱导该区域微观结构发生改变，建立流变单元演化与高频激励参量的关联性，获得决定流变单元有效浓度等关键性质的主导因素；依据阵列点临界半径小于材料裂纹尖端塑性区半径原则，在样品表面设计高频激励阵列，合理匹配阵列与金属玻璃基体的性质，揭示流变单元有效浓度，阵列点形状、尺寸和分布等因素对块体金属玻璃拉伸塑性的影响规律；结合分子动力学模拟和能垒图理论，综合分析变形过程中剪切带的交互作用和断面形貌特征，阐明探针高频激励下块体金属玻璃流变单元的演化机制和阵列设计对拉伸塑性的调控机理。本项目研究成果可为块体金属玻璃拉伸塑性的改善提供理论依据和实践指导。

为了改善金属玻璃的室温拉伸塑性，本项目从剪切带的力学性质分布规律及高频激励对金属玻璃拉伸塑性的影响规律两个方面进行了深入研究。使用接触共振原子力显微镜，表征了剪切带纳米尺度的局部弹性模量，详细研究了剪切带交互作用处的弹性模量分布规律。实验结果揭示了金属玻璃剪切带交互作用处的准加工硬化效应。在分子动力学模拟的辅助下，通过构型演化深入讨论了该过程的理论机制。该结果有助于理解金属玻璃中剪切带相互作用下的变形机制和微观结构演化规律。为了进一步研究剪切带平面的力学性能，使用缠绕方法在Cu-Zr金属玻璃带中制备了具有简单图案的剪切带。使用振幅调制原子力显微镜测量了剪切带平面附近的拓扑形貌和能量耗散。首次测定了Zr基金属玻璃的剪切带平面附近的能量耗散分布规律，揭示了沿传播方向平面上的非均匀和波动能量耗散机制。该发现可以拓宽对剪切带动态特性的理解。最后，通过高频激励在Zr基金属玻璃中制备微米尺度非均匀结构阵列，该样品在室温准静态单轴拉伸载荷条件下表现出一定的拉伸塑性形变。通过有限元分析，超声振动微区阵列会改变阵点附近应力场分布，进而阻挡剪切带的扩展。分子动力学结果显示超声振动微米阵列可促进复合剪切带的产生，增加剪切带的扩展稳定性，改善金属玻璃的拉伸塑性。上述研究成果从微观剪切带和宏观高频激励处理，对金属玻璃的室温拉伸塑性变形机制和拉伸塑性的改善进行了深入研究，对金属玻璃室温拉伸塑性的提高提供了理论依据和实践参考。