金属玻璃的脆性由其处于脆-强转变温度时的状态决定
Brittleness of metallic glasses dictated by their state at the fragile-to-strong transition temperature
AI总结：
通过分子动力学模拟，研究发现金属玻璃的脆性由淬火温度是否跨越脆-强转变温度决定，强玻璃表现出更显著的剪切带和不对称流动，且脆性程度受熔体状态显著影响。
摘要：
通常，研究冷却对玻璃（尤其是块体金属玻璃（BMGs））脆性的影响时，采用连续变化的冷却速率；较慢的冷却速率比高冷却速率导致更硬、更刚且更脆的玻璃。这些方案掩盖了玻璃可能经历的潜在不连续性，这取决于其微观结构是类似于脆性还是强玻璃形成液体。本文利用大规模分子动力学模拟了模型BMG（Zr$_{0.6}$Cu$_{0.3}$Al$_{0.1}$）的纳米压痕行为，该模型通过从高于和低于脆-强转变温度$T_\ extrm{fst}$的平衡熔体快速淬火获得，分别产生脆性玻璃和强玻璃。虽然从压痕模拟中推导出的接触模量随淬火温度$T_\ ext{q}$平滑变化，但塑性响应在$T_\ ext{q}$通过$T_\ extrm{fst}$时准不连续地改变。特别是，强玻璃发展出高度不对称的流动轮廓和成熟的剪切带，与脆性玻璃形成对比。定量差异不仅通过正式的von Mises局部化参数分析揭示，还通过使用预训练人工智能模型对流动模式的图像分析揭示。此外，对于我们的压痕几何形状，看似不规则的流动轮廓产生了惊人可重复且因此确定性的特征。玻璃形成体的其他类别在多大程度上遵循我们的观察结果——即在玻璃转变温度下失去平衡时，脆性程度显著受熔体是脆性还是强的影响——仍有待确定。
英文摘要：
The effect of cooling on the brittleness of glasses in general, and bulk metallic glasses (BMGs) in particular, is usually studied with continuously varying cooling rates; slower cooling rates lead to stiffer, harder, and more brittle glasses than higher cooling rates. These protocols obscure any potential discontinuity that a glass might experience depending on whether its microstructure resembles that of a fragile or a strong glass-forming liquid. Here, we use large-scale molecular dynamics to simulate the nanoindentation behavior of model BMGs (Zr$_{0.6}$Cu$_{0.3}$Al$_{0.1}$) obtained by rapidly quenching equilibrium melts from temperatures above and below the fragile-to-strong transition temperature $T_\textrm{fst}$, leading to fragile and strong glasses, respectively. While the contact modulus deduced from the indentation simulation evolves smoothly with the temperature $T_\text{q}$ from which the melt is quenched, the plastic response changes quasi-discontinuously as $T_\text{q}$ passes through $T_\textrm{fst}$. In particular, strong glasses develop highly asymmetric flow profiles with mature shear bands, in contrast to fragile glasses. Quantitative differences reveal themselves not only through a formal von Mises localization parameter analysis but also through image analysis of flow patterns using pre-trained artificial intelligence models. Moreover, seemingly erratic flow profiles for our indentation geometry produced surprisingly reproducible and, thus, deterministic features. It remains to be determined to what extent other classes of glass formers follow our observation that the degree of brittleness is significantly influenced by whether the melt is fragile or strong when it falls out of equilibrium at the glass transition temperature.
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