npj：金属玻璃变形行为调节——软点的作用

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金属玻璃（MG）具有很高的强度，然而剪切带的出现极大降低了该类材料的拉伸塑性。来自阿拉巴马大学、劳伦斯伯克利国家实验室和加利福尼亚大学的一个研究小组，希望提高MG材料本征的空间异质性、促进分布式流动来提高和改善单片MG的空间延展性。

他们研究了非均质无定型构型（金属玻璃，特别是Cu₆₄Zr₃₆）引起的弹性各向异性对MG形变性能的影响，并利用多尺度模拟方法对体系延展性做了相关研究。通过对Cu₆₄Zr₃₆ MGs类部分材料作原子模拟，揭示了纳米尺度剪切形变转化为剪切带形变由局域剪切模量的空间异质性决定。为获得最佳拉伸延展性，他们定义了弹性异质性的临界空间相关长度。该临界长度与剪切带形成的转变节点相关。随着材料异质性之间空间关联性的增强，以及弹性软点和硬点的区域扩大，作者们观察到在材料软点处，软点数量的降低削弱了材料延展性，且应力诱导的成核生长和剪切带增长开始向应变渗透转变。作者认为，这一方法可通过调控材料本征的异质性来增强高强度金属合金的拉伸塑性，从而促进新型延性单片MG的设计和开发。该文近期发表于npj Computational Materials  4: 19 (2018)； doi:10.1038 /s41524-018-0077-8。英文标题与摘要如下，点击阅读原文可以自由获取论文PDF。

Spatial correlation of elastic heterogeneity tunes the deformation behavior of metallic glasses

Neng Wang, Jun Ding, Feng Yan, Mark Asta, Robert O.Ritchie & Lin Li

Metallic glasses (MGs) possess remarkably high strength but often display only minimal tensile ductility due to the formation of catastrophic shear bands. Purposely enhancing the inherent heterogeneity to promote distributed flow offers new possibilities in improving the ductility of monolithic MGs. Here, we report the effect of the spatial heterogeneity of elasticity, resulting from the inherently inhomogeneous amorphous structures, on the deformation behavior of MGs, specifically focusing on the ductility using multiscale modeling methods. A highly heterogeneous, Gaussian-type shear modulus distribution at the nanoscale is revealed by atomistic simulations in Cu₆₄Zr₃₆ MGs, in which the soft population of the distribution exhibits a marked propensity to undergo the inelastic shear transformation. By employing a mesoscale shear transformation zone dynamics model, we find that the organization of such nanometer-scale shear transformation events into shear-band patterns is dependent on the spatial heterogeneity of the local shear moduli. A critical spatial correlation length of elastic heterogeneity is identified for the simulated MGs to achieve the best tensile ductility, which is associated with a transition of shear-band formation mechanisms, from stress-dictated nucleation and growth to structure-dictated strain percolation, as well as a saturation of elastically soft sites participating in the plastic flow. This discovery is important for the fundamental understanding of the role of spatial heterogeneity in influencing the deformation behavior of MGs. We believe that this can facilitate the design and development of new ductile monolithic MGs by a process of tuning the inherent heterogeneity to achieve enhanced ductility in these high-strength metallic alloys.

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