非晶合金流变单元变形机制和操控性研究

Due to the absence of crystalline defects, the exploration of the deformation mechanism of metallic glasses is a big challenge, which is also one of hot topics in materials science. Previous study has already confirmed that some primary flow units could survive in metallic glasses. However, the geometric size, distribution and activation energy of the flow units are unclear so far. Regarding this, the project proposes to investigate the mechanical responses of the flow units when the glassy phase is influenced by the ion irradiation and the changes of the environmental temperature. The controllability of the flow units in metallic glasses will be studied. In the proposed project, the relaxation tests and the rheological experiments for the metallic glasses influenced by the ion irradiation and the environmental temperature will be carried out. The effects of the irradiation and the cryogenic temperature on the flow units will be observed. Based on the results from the transmission electron microscopic (TEM) observation and the synchrotronic source investigation, the degree of order, the expansion (shrinkage), the microstructural evolution of the glassy phase as functions of the irradiation dosage and the temperature will be constructed. The in-situ tension of the metallic glasses in TEM will be carried out to study the interaction between the flow units and the crack propagation and the shear-band formation. Based on the theory of potential energy landscape, the correlation between the flow units and the strain ability in the macroscale will be discussed, which may provide useful information for understanding the controllability of the flow unit. The operation of the proposed project will provide a solid knowledge for understanding the nature of brittleness of metallic glasses, which will be very useful for find a good way for improving the comprehensive mechanical properties of metallic glasses.

由于晶体缺陷的缺失，非晶合金塑性变形微观机理成为了当前本领域的研究难点和热点之一。前期研究已经发现非晶合金在特定条件下存在流变单元结构。然而对于流变单元的几何尺寸、分布以及激活能等性质和结构的研究依然处于起始阶段。为此，我们提出利用外场激发的方法，研究非晶合金中流变单元对外场作用的响应行为，进而探索操控流变单元的可行性。通过对非晶合金施加离子辐照和改变环境温度（室温至液氮温区），基于弛豫实验和低温流变测试，探索离子辐照和温度对流变单元结构和性能的影响规律。通过透射电镜和同步辐射研究，获取辐照计量和温度对非晶相有序度、结构膨胀（收缩）以及微观结构的影响。通过原位透射电镜拉伸实验，研究流变单元在裂纹扩展和剪切带形成过程中的作用。基于势能形貌理论阐述流变单元对宏观应变开动的影响，探索流变单元的可操纵性，为认知非晶合金的韧脆本质，从根本上提高其综合机械性能奠定理论基础。

在非晶合金应用探索的过程中，如何有效调控非晶合金的宏观机械性能，获得适合工程应用、综合性能优秀的非晶合金材料成为了当前研究的难点。只有突破与微观结构，特别是流动单元（非晶合金中最基本的变形单元结构）的观察和调控等相关的关键科学问题，非晶合金相关新材料研究开发才能够在强大应用背景的推动下得到持续发展。在过去4年里，我们开展了非晶合金的低温（液氮温区）结构演化的关联性研究。对选定的锆基非晶合金在室温至低温（－150度）区间内的原子结构行为进行了研究。在剪切塑性变形方面，我们考虑了多重剪切带的相互作用，通过数学方法，建立了非晶合金间歇性锯齿流变的时空动力学模型。基于该模型，通过行波解方法，获得了空间均匀性解。此外，通过在非晶合金中引入第二相，干扰非晶合金的锯齿流变行为，统计分析了纳米/非晶复合材料的锯齿流变行为。更进一步，我们开展了具有化学无序异质高熵合金的开发，第二纳米氧化相对高熵合金涂层的耐磨性影响研究；探索了剪切带扩展过程中，应变场的烟花行为，揭示了制备化学无序合金-异质高熵合金的方法，及变形机理。上述结果发表在NPG Asia Materials, Acta Materialia和Scripta Materialia等金属材料的顶级期刊上。其中一篇文章获得ESI高被引。