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arXiv 0807.4926cond-mat.mtrl-scicond-mat.stat-mech
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晶界运动是玻璃形成液体动力学的表现

Grain Boundary Motion Exhibits the Dynamics of Glass-Forming Liquids

Hao Zhang, David J. Srolovitz, Jack F. Douglas*, James A. Warren

摘要:

多晶材料可以被视为由薄的非晶晶界(GB)区域彼此分离的晶体颗粒或晶粒的复合物。虽然GB已被详尽的研究在低温下,这些地区解决到复杂的有序结构的测量,更少的是知道他们在较高的温度下,GB可以表现出显着的流动性,结构紊乱,实验表征方法是有限的。分子动力学(MD)模拟的时间和空间尺度,使这种方法适用于调查在高温下的晶界的动力学和结构特性。在本研究中,我们使用MD模拟,以确定如何GB动态变化与温度和施加的应力。基于多晶材料的加工特性,长期以来一直假设GB具有与玻璃形成液体相同的特征。我们发现显着的支持这一建议,证明了弦状的集体运动,瞬态笼原子运动,和非Arbidius(Vogel-Fulcher)的GB迁移率的温度依赖性。显然,在GB区的原子不能同时有序相对于竞争晶粒造成的挫折是负责这种惊人的相似性。多晶材料中的晶粒被受抑流体包裹的范例提供了多晶材料的强大概念模型,指出了改善对其材料特性的控制的方法。

英文摘要:

Polycrystalline materials can be viewed as composites of crystalline particles or grains separated from one another by thin amorphous grain boundary (GB) regions. While GB have been exhaustively investigated at low temperatures, where these regions resolve into complex ordered structures accessible to measurement, much less is known about them at higher temperatures where the GB can exhibit significant mobility, structural disorder, and where experimental characterization methods are limited. The time and spatial scales accessible to molecular dynamics (MD) simulation make this method appropriate for investigating both the dynamical and structural properties of grain boundaries at elevated temperatures. In the present study, we use MD simulations to determine how the GB dynamics changes with temperature and applied stress. It has long been hypothesized that GB have features in common with glass-forming liquids based on the processing characteristics of polycrystalline materials. We find remarkable support for this suggestion, as evidenced by string-like collective motion, transient caging of atom motion, and non-Arrhenius (Vogel-Fulcher) temperature dependence of GB mobility. Evidently, the frustration caused by the inability of atoms in GB region to simultaneously order with respect to competing grains is responsible for this striking similarity. The paradigm that grains in a polycrystalline material are encapsulated by a frustrated fluid provides a powerful conceptual model of polycrystalline materials, pointing the way to improved control over their material properties.

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