金属玻璃弛豫行为与流动单元关系

The relaxation processes affect many properties of metallic glasses. However, nature and structural origin of the mechanical relaxations in metallic glasses are still not clear. It is necessary to study the relaxation behaviors and their structural origin due to their importance in understanding the glass transition phenomena,diffusion and mechanical properties in supercooling liquids. In the current work, lanthanum-, palladium- and zirconium-based bulk metallic glasses were selected as the model alloys. By means of dynamic mechanical analysis (DMA) and temperature-modulated differential scanning calorimetry (TMDSC), the relaxation behaviors were investigated. With the help of Cs-corrected transmission electron microscopy (TEM), the atomic structure at different states were characterized. Influence of the fragility on the dynamic mechanical relaxation behavior in metallic glasses were illustrated. The important influencing factors,such as physical aging below glass transition temperature, plastic deformation and different cooling rates，were considered to study the relaxation behaviors. The correlation between flow units and relaxation behaviors was established. In the framework of the physical models, the relation between main (alpha) relaxation and secondary (beta) relaxation in metallic glasses was discussed. The outcome of this research is of significance for understanding the structural origin of the relaxation behaviors in metallic glasses.

金属玻璃的弛豫行为影响着玻璃材料的诸多性能，然而，其弛豫本质及结构起源等基本物理问题尚不清晰。为了了解过冷液体的弛豫行为在玻璃转变、扩散、机械性能等充当的重要角色，就需要更加深入的研究弛豫及其物理本质。本项目拟采用典型的大块金属玻璃（La基、Pd基和Zr基）作为模型合金，利用动态力学分析仪和调制温度式差示扫描量热仪对弛豫行为进行研究。借助于球差校正扫描透射电子显微镜，对金属玻璃在不同的初始状态下的局域原子排布结构进行表征，进一步阐明金属玻璃的脆性对金属玻璃动态弛豫行为的影响。通过对金属玻璃在玻璃转变温度以下的物理时效、预加载应力处理和不同冷却速度等对弛豫行为的影响研究，探讨金属玻璃中的弛豫机制和微观结构的信息，建立金属玻璃中流动单元与弛豫行为之间的关联。利用相关的物理模型，揭示金属玻璃中主(alpha)弛豫与次(beta)弛豫之间的关系，为金属玻璃中弛豫可能的结构起源提供理论依据和实验数据。

金属玻璃的弛豫行为(alpha和beta 弛豫)与热力学和动力学机制紧密相关，比如扩散、晶化、玻璃转变及塑性变形行为等。尤其是beta弛豫联系着金属玻璃固有的微观结构非均匀性。故而，研究金属玻璃的动态弛豫机制就显得非常重要。.本项目以典型的金属玻璃作为研究载体，主要研究金属玻璃流动单元的演化机理。主要开展了以下四个方面的实验和理论研究：(1) 重点研究了La60Ni15Al25金属玻璃的高温压缩行为，揭示了beta弛豫与特殊原子排列之间的关系；(2) 系统研究了Cu46Zr47-xAl7Dyx (0≤x≤8)大块金属玻璃的动态弛豫机制与宏观力学性能的关联。结合非晶合金beta弛豫的测量结果，我们的研究表明正混合焓或组元间较大的混合焓涨落都会抑制非晶合金中的beta弛豫峰；而较强的混合焓（较强的组元之间的相互作用）且较小的混合焓涨落能增强非晶合金中beta弛豫峰的强度；(3)应力松弛手段架起了研究金属玻璃结构和动力不均匀的桥梁。我们详细讨论了金属玻璃在应力松弛过程中表现出的反常行为。以Cu46Zr46Al8金属玻璃作为研究载体，我们发现了应力松弛过程中的双阶段行为：低温下应力主导和高温下的热激活两个阶段；(4) 系统研究了不同典型金属玻璃的动态弛豫机制，借助于“准点缺陷模型”，我们对弛豫机制进行了描述。.通过本项目的研究，丰富了金属玻璃中流变单元的研究，为进一步理解金属玻璃的微观缺陷提供了思路。通过本项目的研究，发表SCI收录论文18篇，联合培养博士生4人，其中1人已毕业，在读硕士生1人，指导本科毕业论文2篇。项目负责人乔吉超副教授入选陕西省百人计划(青年项目)。