马恩:金属玻璃和过冷液体的结构演化

金属玻璃及其母体过冷液体的无定形结构的演变,涉及三个极具挑战的难题:1)液体脆性结构可能的起源,2)如何解释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,3)金属玻璃的配对分布函数中,类晶体峰值的位置如何。来自美国劳伦斯-伯克利国家实验室的Jun Ding和约翰-霍普金斯大学的马恩教授,综述了这一领域的最新进展,重点介绍了近来通过计算分析得出、并有实验结果支持的深刻洞见,进而指出了该领域未来的发展方向。他们还呼吁对此开展更深入的计算研究,期望能建立更强大的非晶合金的结构-性能关系。该文近期发表于npj Computational Materials 3:9 (2017),标题及摘要如下,点击此处下载原文/upload/201705/08/201705081032592618.pdf

原文链接:(http://www.nature.com/articles/s41524-017-0007-1)

Computational modeling sheds light on structural evolution in metallic glasses and supercooled liquids
Jun Ding & En Ma

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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