Previous experiments have revealed that the controllable introduction of structural gradients in metallic glasses (MGs) can endow the materials with extra plasticity due to the gradient-induced deflection of shear bands. However, the relation between the spatial structural gradient and the initiation of shear band deflection remains unclear. The current study has been focused on investigating the relationship between the improved mechanical properties of MGs and structural gradients specified by the distribution of the intrinsic free volume. Molecular dynamics (MD) simulations are firstly performed on homogeneous MG models containing various initial free volume values, showing that the shear band angle increases with decreasing free volume under uniaxial compression, whereas higher shear band angle is observed under uniaxial tension with increasing free volume. Based on the asymmetric behaviors of MGs under compression and tension, a theoretical model is developed to quantitatively characterize the influence of free volume on the mechanical response of MGs, which incorporates a failure criterion based on free volume generation during external loadings. The model can be further utilized to interpret and predict the fracture strain, shear band angle, maximum stress, and fracture surface morphology of gradient structured MGs in both simulations and experiments. The relationship between free volume gradient and shear band deflection induced extra plasticity established in this study provides valuable guidance for the structural design of MGs with enhanced mechanical properties.

中文翻译：

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揭示自由体积梯度和剪切带偏转之间的关系引起金属玻璃的额外塑性


先前的实验表明，由于梯度引起的剪切带偏转，在金属玻璃（MG）中可控地引入结构梯度可以赋予材料额外的塑性。然而，空间结构梯度与剪切带偏转起始之间的关系仍不清楚。当前的研究重点是研究 MG 改进的机械性能与由固有自由体积分布指定的结构梯度之间的关系。首先对包含不同初始自由体积值的均质 MG 模型进行分子动力学 (MD) 模拟，结果表明，在单轴压缩下，剪切带角随着自由体积的减小而增大，而在单轴拉伸下，随着自由体积的增大，剪切带角会增大。基于 MG 在压缩和拉伸下的不对称行为，开发了一个理论模型来定量表征自由体积对 MG 机械响应的影响，该模型包含基于外部载荷期间自由体积生成的失效准则。该模型可进一步用于解释和预测模拟和实验中梯度结构 MG 的断裂应变、剪切带角、最大应力和断裂表面形貌。本研究建立的自由体积梯度与剪切带偏转引起的额外塑性之间的关系为具有增强机械性能的 MG 的结构设计提供了有价值的指导。