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La30Ce30Al15Co25金属玻璃应力松弛行为

STRESS RELAXATION OF La30Ce30Al15Co25 METALLIC GLASS

  • 摘要: 作为潜在的工程材料, 金属玻璃在材料科学和凝聚态物理等领域引起广泛的研究兴趣. 金属玻璃结构与性能的关系表明, 金属玻璃的动态非均匀性与其黏弹性和塑性紧密相关. 然而, 宏观应力松弛行为与动态弛豫之间的物理图像并不清晰. 与传统金属材料不同, 金属玻璃的变形机理非常复杂. 应力松弛是一种表征玻璃体系黏弹性和塑性变形机制的有效手段, 从而探索结构和动态非均匀性. 本研究以La30Ce30Al15Co25金属玻璃为模型体系, 在较宽的温度窗口研究了其应力松弛行为. 研究结果表明, 与传统金属玻璃不同, La30Ce30Al15Co25金属玻璃具有明显的β弛豫行为. 基于Kohlarausch-Willams-Watts (KWW)方程的分析表明, 金属玻璃应力松弛为动态不均匀过程; 热动力学分析发现La30Ce30Al15Co25金属玻璃应力松弛存在显著的双阶段行为, 即从高应力条件下应力驱动为主导的松弛行为, 向低应力下热激活为主导的松弛行为发生转变. 通过激活能谱模型分析表明, 应力松弛单元的激活并非均匀, 而是存在能量上的起伏, 金属玻璃对于外力响应是一个渐进过程, 具有动力学不均匀性. 本研究进一步构建了金属玻璃的结构和动态非均匀性之间的关联, 为研究金属玻璃的α弛豫和β弛豫提供了强有力的支撑.

     

    Abstract: Metallic glass is a well-known engineering material that has been attracting tremendous research interest in materials science and condense matter physics. Early studies of the properties and structures of the metallic glasses showed that the dynamic heterogeneity is closely linked to the viscoelasticity and plasticity of metallic glasses. However, the physical landscape between the macroscopic stress relaxation behavior and the mechanical relaxation is still obscure. Different from the deformation mechanism of their crystalline counterparts, the deformation mechanism of metallic glasses is more complicated. To fully understand the mechanical properties of metallic glass, it is necessary to ascertain the structural characteristics of different spatial scales of metallic glass and evolution of structural characteristics with time. The significant importance is the connection between the macroscopic stress relaxation behavior and the dynamic mechanical relaxations (β relaxation, or α relaxation) in metallic glasses. Stress relaxation is a robust technique to characterize the viscoelastic and plastic mechanisms in glasses which can reflect their structural and dynamic heterogeneities. In the current research, La30Ce30Al15Co25 metallic glass was used as a model system, dynamic mechanical processes and stress relaxation behavior were studied. Compared with other traditional metallic glasses, La30Ce30Al15Co25 metallic glass shows a pronounced β relaxation process. The analysis based on the Kohlarausch-Willams-Watts (KWW) equation suggests that the stress relaxation process of metallic glass is a heterogeneous dynamic process. We observed an unusual two-stage stress relaxation phenomenon, consisting of the fast stress-driven event and the slow thermally activated event. The two-stage stress relaxation behavior is attributed the stress-driven event and thermally activated event to short-range atomic rearrangement, and long-range atomic diffusion, respectively. In addition, the analysis of the activation energy spectrum shows that the activation of the stress relaxation unit is not uniform, which corresponds to fluctuations in energy. This research is a step towards building a bridge linking the structural and dynamic heterogeneity of metallic glasses, and strongly supports the physical scenario of β to α relaxation.

     

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