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Computational modeling sheds light on structural evolution in metallic glasses and supercooled liquids(计算模拟揭示了金属玻璃和过冷液体的结构演化)
发布时间:2017-03-17

Computational modeling sheds light on structural evolution in metallic glasses and supercooled liquids(计算模拟揭示了金属玻璃和过冷液体的结构演化)
Jun Ding & En Ma
npj Computational Materials 3, Article number: 9 (2017)
doi:10.1038/s41524-017-0007-1
Published online:01 March 2017
Abstract| Full Text | PDF OPEN

摘要:本文概述了目前金属玻璃及其母体过冷液体中无定形结构的演变,涉及该领域三大挑战性问题,重点介绍了近来通过计算分析得出、并有实验结果支持的重要见解。第一个问题是,用局部结构顺序作为指标,尤其用过冷期间局部结构顺序的演化作为指标,来解释实验观察到的粘度随温度的变化,从而提出液体脆性结构可能的起源。第二个问题涉及金属熔体的平均最近-相邻距离在受热时收缩而不是膨胀,并伴有配位数减少的问题。然而,这一看法的依据是分布函数的第一峰最大值的偏移,以及用距离截止指定的最近邻域法确定的平均键长。可是这一现象也可以是相邻原子不对称分布受热恶化时,加宽的第一峰偏斜的结果,因为这些相邻原子可以在非谐性原子间相互作用电位下受激活后移动较短和较长距离。第三个问题涉及金属玻璃的配对分布函数中,类晶体峰值位置。这些峰值位置可以用配位多面体的各种连接方案来解释,并可在亦已存在的无隐藏晶体顺序的高温液体中找到。本文还指出了该领域的发展方向,并呼吁对该领域开展更深入的计算研究,以期最终建立更强的非晶合金的结构-性能关系。   

Abstract: This article presents an overview of three challenging issues that are currently being debated in the community researching on the evolution of amorphous structures in metallic glasses and their parent supercooled liquids. Our emphasis is on the valuable insights acquired in recent computational analyses that have supplemented experimental investigations. The first idea is to use the local structural order developed, and in particular its evolution during undercooling, as a signature indicator to rationalize the experimentally observed temperature-dependence of viscosity, hence suggesting a possible structural origin of liquid fragility. The second issue concerns with the claim that the average nearest-neighbor distance in metallic melts contracts rather than expands upon heating, concurrent with a reduced coordination number. This postulate is, however, based on the shift of the first peak maximum in the pair distribution function and an average bond length determined from nearest neighbors designated using a distance cutoff. These can instead be a result of increasing skewness of the broad first peak, upon thermally exacerbated asymmetric distribution of neighboring atoms activated to shorter and longer distances under the anharmonic interatomic interaction potential. The third topic deals with crystal-like peak positions in the pair distribution function of metallic glasses. These peak locations can be explained using various connection schemes of coordination polyhedra, and found to be present already in high-temperature liquids without hidden crystal order. We also present an outlook to invite more in-depth computational research to fully settle these issues in future, and to establish more robust structure-property relations in amorphous alloys. 

 
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