金属玻璃因独特的原子结构，兼具玻璃和金属的双重特性，展现出接近理想极限的高强度以及卓越的加工性能。然而，金属玻璃的室温塑性变形极易局域化形成纳米尺度的剪切带，剪切带的不稳定快速扩展通常导致材料发生宏观脆性破坏。更严重的是，亚稳态金属玻璃具有自发物理老化的趋势，即从高能量无序态向低能量有序态的弛豫转变，这一动力学过程将进一步削弱金属玻璃在服役过程中的塑性变形能力。近来，大量研究表明，结构年轻化通过外部能量的输入能够使金属玻璃达到在拓扑上更加无序的高焓状态，可以有效改善金属玻璃的塑性变形能力。极端年轻化甚至可使金属玻璃具有完全不同的力学行为，例如发生应变硬化。然而，金属玻璃的结构年轻化极限还缺乏系统深入的研究，年轻化的上限在哪还不清楚。本论文基于研究组前期的工作，结合热力学、动力学以及高能同步辐射 X 射线全散射等手段，以典型锆基金属玻璃为研究对象，揭示了老化金属玻璃结构年轻化的新机制，更新了对年轻化下限的认识，首次确定了结构年轻化的上限是“冻结”的稳态流动状态，明确了结构年轻化存在应变率极限，指出了变形路径对年轻化极限的影响。通过有限元模拟，设计实现了初始结构分布相关的金属玻璃变形强塑化，定量分析了结构年轻化对金属玻璃变形的影响。

本论文的主要工作概括如下：

（一）在玻璃态转变温度附近，通过对严重老化至无弛豫焓的金属玻璃进行不同变形程度的均匀压缩变形实验，揭示了结构年轻化的新机制。不同于目前普遍认为的玻璃年轻化源于在外部能量激励下局域结构重排导致的自由体积增加。研究发现，通过局域结构重排使自由体积在空间重分布，进而降低结构的力学稳定性也可以实现玻璃年轻化，而玻璃的整体能量水平并不一定增加。通过定量分析玻璃态转变前的热焓释放、玻璃态转变过程中的有效热焓变化以及原子振动玻色峰这三个参数随结构年轻化的演化，首次确定了玻璃结构年轻化的上限是“冻结”的稳态流动状态。

（二）不同应变率下的高温均匀单轴压缩实验分析表明，低应变率的牛顿流动通过降低金属玻璃的力学稳定性也可以使严重老化的金属玻璃年轻化。由于结构重排的影响，年轻化的应变率下限不再是牛顿流动到非牛顿流动的转变应变率。从热力学、低频振动“玻色峰”与多尺度结构这几个角度，明确了在发生局域剪切破坏之前结构年轻化存在应变率上限。当应变率超过该上限时，玻璃的整体能态下降而力学稳定性和结构无序度没有明显变化。这一结果进一步证实了能态无法全面的表征结构年轻化。

（三）通过应变率跳跃实验，设计了不同的变形路径，最终都使金属玻璃进入相同的稳定流动应变率。结果显示，尽管金属玻璃的宏观流动应力都进入了相同的水平，但其结构年轻化水平却不相同。分析表明，结构年轻化的差异主要由力学稳定性贡献，而玻璃的整体能量水平变化并不明显。多步跳跃降低了稳态流动时金属玻璃的力学稳定性，使其结构更加无序，并观察到饱和现象。说明改变变形路径在一定程度上能提高金属玻璃的结构年轻化上限。根据拓扑结构信息，该过程涉及复杂的短程及中程结构变化。

（四）基于剪切转变和自由体积相互作用的非晶塑性本构模型，利用有限元，分别从能态增加以及结构更加无序这两种物理机制下定量分析了结构年轻化对金属玻璃力学行为的影响。前者通过调控自由体积含量实现，后者通过调控自由体积统计分布的标准差实现。模拟结果显示，在通过提高能态实现的结构年轻化体系中，年轻化程度越高，体系越软，系统能承受的塑性变形越大，其塑性越强，但以牺牲强度为代价。在通过增加无序度实现的结构年轻化体系中，年轻化程度越高，系统塑性增强，峰值强度先降低后反向升高，实现了强度与塑性的共赢。在塑性流动后，观察到自由体积以及剪切转变数密度的含量与各自的标准差之间呈负相关。进一步分析发现这是由于在变形过程中它们的统计分布逐渐形成了双峰分布，硬区的出现降低了它们的平均含量。此外，还观察到在初始无序度较大的年轻化体系中，变形表现出明显的两阶段过程：屈服前，由软区的自由体积湮灭主控，贡献塑性；屈服后，由硬区的自由体积增多主控，贡献强度。

Due to its unique atomic structure, metallic glass possesses the dual characteristics of both glass and metal. It exhibits high strength close to the ideal limit, coupled with excellent processability. However, room-temperature plastic deformation in metallic glass tends to localize into nanoscale shear bands. The unstable and rapid expansion of these shear bands often leads to macroscopic brittle failure of the material. More importantly, metastable metallic glasses are prone to spontaneous physical aging, a transition from a high-energy disordered state to a low-energy ordered state. This kinetic process further diminishes the plastic deformation capacity of metallic glass during service, potentially leading to a ductile-to-brittle transition and loss of plasticity. Recent research indicates that structural rejuvenation, achieved through the input of external energy, can bring metallic glass into a topologically more disordered high-enthalpy state, effectively enhancing its plastic deformation ability. Extreme rejuvenation can even impart entirely different mechanical behaviors to metallic glass, such as strain hardening. However, the limit of structural rejuvenation in metallic glass is still not thoroughly understood, and the upper limit of rejuvenation remains unclear. Building upon the preliminary work of our research group, this thesis integrates thermodynamics, kinetics, and high-energy synchrotron X-ray total scattering, systematically investigates the limits of structural rejuvenation in a typical Zr-based metallic glass. It unveils new mechanisms of structural rejuvenation in well-aged metallic glass, updates the understanding of the rejuvenation lower limit, and identifies for the first time the upper limit of structural rejuvenation as a "frozen" steady flow state. It clarifies that there is a strain rate limit to structural rejuvenation and highlights the impact of deformation paths on this limit. Through finite element simulation, the deformation strength-plasticization of metallic glass related to the initial structure distribution was designed and realized, and the influence of structural rejuvenation on the deformation was quantitatively analyzed. The main contributions of this work are summarized as follows:

Near the glass transition temperature, by conducting uniform compression deformation experiments on well-aged metallic glass with no relaxation enthalpy, a new mechanism of structural rejuvenation was revealed. Contrary to the widely held belief that glass rejuvenation originates from the increase in free volume due to local structural rearrangements under external energy stimulation, our findings indicate that rejuvenation can also be achieved by spatial redistribution of free volume through local structural rearrangements, thereby reducing the mechanical stability of the structure, without necessarily increasing the overall energy level of the glass. By quantitatively analyzing three parameters—the release of thermal enthalpy before the glass transition, the effective thermal enthalpy changes during the glass transition, and the atomic vibrational boson peak—as they evolve with structural rejuvenation, for the first time, the upper limit of glass structural rejuvenation was determined to be a "frozen" steady-state flow condition.

High-temperature uniform uniaxial compression experiments under different strain rates indicate that Newtonian flow at low strain rates can rejuvenate severely aged metallic glasses by reducing their mechanical stability. Due to the impact of structural rearrangement, the lower limit of strain rate for rejuvenation is no longer the transition strain rate from Newtonian to non-Newtonian flow. From the perspectives of thermodynamics, low-frequency vibrations "boson peak", and multi-scale structure, the upper limit of strain rate for structural rejuvenation prior to local shear failure has been clarified. When the strain rate exceeds this upper limit, the overall energy state of the glass decreases while its mechanical stability and structural disorder do not show significant changes. This result further confirms that the energy state cannot comprehensively characterize structural rejuvenation.

Through strain rate jump experiments, various deformation paths were designed, all leading to the same final loading strain rate in the metallic glass. The results show that although the macroscopic flow stress of the metallic glasses reached the same level, their structural rejuvenation levels were different. Analysis indicates that the differences in structural rejuvenation are mainly contributed by mechanical stability, while changes in the overall energy level of the glass are not significant. Multi-step jumping reduces the mechanical stability of metallic glass in steady-state flow, makes its structure more disordered, and saturation phenomenon is observed. It shows that changing the deformation path can increase the upper limit of structural rejuvenation of metallic glass to a certain extent. Based on topological information, the process involves complex short - and medium-range structural changes.

Based on a constitutive model for amorphous plasticity that incorporates shear transformation and free volume interactions, the effects of structural rejuvenation on the mechanical behavior of metallic glass were quantitatively analyzed by using finite element under the two physical mechanisms of increasing energy state and increasing structure disorder respectively. The former is achieved by regulating the free volume content, while the latter is achieved by regulating the standard deviation of the free volume statistical distribution. The simulation results show that in the structural rejuvenation system achieved by improving the energy state, the higher the degree of rejuvenation, the softer the system, the greater the plastic deformation that the system can withstand, and the stronger the plasticity, but at the expense of strength. In the structural rejuvenation system achieved by increasing the degree of disorder, the higher the degree of rejuvenation, the better the plasticity of the system, and the peak strength decreases first and then increases, achieving a win-win situation between strength and plasticity. After plastic flow, it is observed that the content of the free volume and the population of STZ is negatively correlated with their respective standard deviations. Further analysis shows that this is due to their statistical distribution gradually forms a bimodal distribution during the deformation process, and the appearance of the hard region reduces their average content. It is also observed that in the rejuvenated system with large initial disorder, deformation shows a two-stage process: before yielding, the deformation is dominated by the free volume annihilation of the soft region, contributing plasticity; After yielding, the deformation is dominated by the increase of the free volume of the hard region, which contributes to the strength.