Enhanced plasticity in Zr-Cu-Ag-Al-Be bulk metallic glasses

分类： 物理学 >> 凝聚态:结构、力学和热性能 提交时间： 2017-03-23

Q. P. Cao J. B. Jin Y. Ma X. Z. Cao B. Y. Wang S. X. Qu X. D. Wang D. X. Zhang J. Z. Jiang

摘要： The dependences of bending plasticity on compositional adjustment and structural relaxation in Zr-Cu-Ag-Al-Be bulk metallic glasses (BMGs) were systematically studied. We reveal that with the increase in the Zr content, the plasticity is enhanced at the expense of glass forming ability and the shear transformation zone (STZ) volume becomes larger, while structural relaxation results in the embrittlement accompanied with the further enlarged STZ volume. Average positron lifetime, representing average free volume, drops with the increase in the Zr content and structural relaxation. The results indicate that neither STZ volume nor average positron lifetime can solely describe the plastic deformability of BMGs. Analyzing positron annihilation lifetime spectra, a bimodal distribution of open volume size is observed. The smaller open volume shrinks with increased concentration and the larger open volume expands with decreased concentration due to the increase in the Zr content, while structural elaxation only reduces the size of smaller open volume. The effects of open volume size distribution on the STZ activation and shear band propagation have been discussed. It has been demonstrated that combining the STZ volume with open volume size distribution can explain the plasticity evolution with the composition and structural relaxation, which sheds light on understanding the deformation mechanism of BMGs.

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