Atomistic Study on Medium-Range Order Structures in Amorphous Metals
Atomistic Study on Medium-Range Order Structures in Amorphous Metals
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DOI：
10.2472/jsms.64.156
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
M. Wakeda;Y. Shibutani;S. Ogata
中科院分区：
文献类型：
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作者：
M. Wakeda;Y. Shibutani;S. Ogata
非晶态金属具有弹性延伸率大、断裂韧性高、耐腐蚀等优良性能。这些性质可能源于它们的无序原子结构，这与具有长程周期有序的晶体结构完全不同。然而，非晶态金属的详细结构仍然是一个有争议的问题，因为实验衍射方法很难揭示非晶态金属的详细结构特征。本文采用分子动力学方法，结合二元Lennard-Jones Cu-Zr原子间相互作用势，研究了非晶态金属的中程有序（MRO）拓扑结构.我们进行了熔体淬火模拟，并构建了三个不同的Cu浓度的非晶合金模型。在构建的无定形结构中，发现了由互穿的二十面体链接组成的二十面体结构的MRO聚类。在无定形模型中，存在许多小的MRO团簇和少数大的MRO团簇，并且MRO团簇的数目随着团簇尺寸的增加而单调减少。在玻璃化转变温度Tg附近，随着二十面体数目的增加，MRO团簇的尺寸迅速增大。这意味着MRO集群规模的快速增长是由MRO集群之间的聚类以及每个MRO集群的增长引起的。具有更多二十面体团簇的非晶模型倾向于具有更大、更致密和更多的MRO团簇，并且二十面体MRO团簇的最大尺寸为约4 nm。通过回转半径和密度相关函数分析，发现二十面体MRO团簇的大小具有分形特征，其分形维数为1.46 ~ 1.80。
Amorphous metals have excellent properties, such as large elastic elongation, high fracture toughness and high corrosion resistance. These properties may arise from their disordered atomic structures, which are totally different from the crystalline structures with long-range periodic order. However, detailed structure of amorphous metals is still a controversial issue, because the experimental diffraction methods have a difficulty to reveal detailed structural features of amorphous metals. Using molecular dynamics methods with binary Lennard-Jones Cu-Zr interatomic potentials, we in this study investigated topological feature of amorphous metals focusing on a medium-range order (MRO). We conducted melt-quenching simulations and constructed amorphous alloy models with three different Cu concentrations. MRO clustering of icosahedra structures which consist of interpenetrating icosahedra links were found in a constructed amorphous structure. In the amorphous model, there are many small and a few large MRO clusters, and the number of MRO clusters monotonically decreases with increasing its size. During the melt-quenching process, the size of MRO cluster rapidly increases with increasing the number of icosahedra at around the glass transition temperature T g . It is implied that the rapid increase of the size of MRO cluster is caused by a clustering between MRO clusters as well as a growth of each MRO cluster. An amorphous model with more icosahedral clusters tends to have larger, denser and more MRO clusters, and a maximum size of the icosahedral MRO cluster is ~4nm. Based on both the radius of gyration and the density correlation function analyses, we found that the size of icosahedral MRO cluster has fractal feature, of which fractal dimension are 1.46 ～ 1.80.