非晶合金多重剪切带形成与演化动力学研究

Metallic glasses (MGs) have shown wide potential applications as advanced materials in fields such as defense applications, space projects, etc. However, plastic deformation in MGs at room temperature is prone to be localized into nanoscale shear bands and leads to catastrophic failure, accompanied with very limited plasticity. This greatly impedes their structural applications. Lately, the room-temperature plasticity in MGs have been greatly developed by triggering the interaction and multiplication of shear bands, via the introducation of the residual stress, the optimum design of material composites,and the presence of nanoscale or microscale heterogeneities. Nevertheless, the understanding of the behavior of multiple shear bands in MGs is still lacking, and the key proplem is the formation and evolution dynamics of multiple shear bands and their underlying mechanisms. Therefore, this research is aimed to investigate the formation mechanism and dynamic evolution process of multiple shear bands, via systematical experiments, numerical simulation, and theoretical analyses. The evolution of the shear band patterns will be characterized quantitatively and the inherent laws will be uncovered. Then, a new constitutive model of MGs will be established and the whole process of shear band multiplication will be numerically simulated. Finally, the mechanisms behind the collective behavior of multiple shear bands will be revealled. This research may increase our understanding of plastic mechanism as well as provide helpful guidelines for improving the room-temperature ductility in MGs.

非晶合金作为新型结构材料已在国防、空天等众多高新技术领域显示出广阔的应用前景。然而，该材料在室温下极易形成纳米尺度的剪切带，并迅速诱导材料断裂，伴随极低的宏观塑性，极大地限制了它作为结构材料的应用。近年来，研究发现，通过引入残余应力、优化设计材料成分、加入纳微米尺度的非均质等，可以促进非晶合金内部剪切带的相互交割和多重化，从而大大提高该材料的室温塑性。然而，对于非晶合金多重剪切带行为的认知目前还十分匮乏，其中的关键问题是多重剪切带的形成与演化动力学及其内在机理。为此，本项目拟通过实验研究、数值模拟和理论分析相结合，系统深入地研究非晶合金多重剪切带形成机制及演化动力学过程，定量表征多重剪切带形貌演化及考察其内在规律；并建立新的本构模型数值模拟剪切带多重化过程；揭示多重剪切带群体演化行为的控制机理。本项目的研究将有助于深入理解非晶合金的塑性变形机制，为改善非晶合金的室温塑性提供有益指导。

非晶合金（又称金属玻璃）因其优异的力学物理性能，在国防、空天等众多高新技术领域显示出广阔的应用前景。然而，该材料在室温下极易形成纳米尺度的剪切带，并迅速诱导材料断裂，伴随极低的宏观塑性，极大地限制了它作为结构材料的应用。近年来，研究发现，通过引入残余应力、优化设计材料成分、加入纳微米尺度的非均质等，可以促进非晶合金内部剪切带的相互交割和多重化，从而大大提高该材料的室温塑性。然而，对于非晶合金多重剪切带行为的认知目前还十分匮乏，其中的关键问题是多重剪切带的形成及演化动力学行为及其内在机理。基此，本项目通过系统的实验、数值模拟和理论研究，揭示了非晶合金多重剪切带形成机制及演化动力学过程：建立了新的非晶合金压力敏感-自由体积本构，结合分叉理论得到了复杂应力条件下非晶合金剪切带失稳的临界条件，揭示了材料参数如压力敏感系数、泊松比、结构序参量等对剪切带形成的影响，进一步，从理论上预测了剪切带的形成方向；通过开展准静态及动态压缩和弯曲实验，定量表征了非晶合金多重剪切带形貌演化及其随应变率、样品尺寸、第二相百分比等的变化规律，并阐明了多重剪切带诱导的动态破碎行为及其内在机理；基于能量守恒及动量扩散机理，建立了多重剪切带动力学演化的理论模型，得到了剪切带间距和剪切错动的解析表达式，很好的表征了剪切带间距及错动随试样几何尺寸及弯曲曲率的变化规律，同时反映了剪切带在拉压端的非对称行为；从能量耗散的角度，揭示了非晶合金多重剪切带行为是剪切带形核和扩展两个过程的能量竞争。本项目研究将有助于深入理解非晶合金的塑性变形机理，为改善非晶合金的室温塑性提供理论指导。