局部塑性变形下铁基金属玻璃的致密化和非均匀性增强

Densification and heterogeneity enhancement of Fe-based metallic glass under local plastic flow

本文研究了经局部塑性变形后,Fe_(78)Si_(9)B_(13)金属玻璃在原子尺度上的结构演变及其对合金显微硬度的影响.借助砂纸作为传力的媒介,充分放大了作用于带材表面上的等效压力,发生塑性变形后合金表面产生了大量的剪切带.基于倒空间和实空间的同步辐射X射线衍射分析,在塑性变形后,合金结构的致密度增大,过剩自由体积被排出,并由此揭示了Fe_(78)Si_(9)B_(13)金属玻璃在短程及中程尺度上原子协同重排行为.结合高分辨透射电子显微镜观察的结果,Fe_(78)Si_(9)B_(13)金属玻璃在发生塑性变形后,结构不均匀的程度将会加剧.此外,不同于单轴加载下金属玻璃的加工软化,Fe_(78)Si_(9)B_(13)金属玻璃在发生局部塑性变形后,维氏硬度增大,表现出局部的加工硬化行为.从自由体积的角度看,合金表面的大量剪切带可能是由于剪切带影响区域的重叠和交叉发生相互作用,并加速原子迁移,使自由体积湮灭的速率大于产生速率.

The atomic-scale structure and concomitant mechanical property evolution of a ribbon-shaped Fe_(78)Si_(9)B_(13) metallic glass after local plastic flow are investigated.By using abrasive papers as a medium to transport the pressure,the equivalent pressure on the ribbon surface is sufficiently magnified.Multiple shear bands pervading along their surface are generated simultaneously after deformation.The densification processes triggered by the cooperative atomic rearrangements in the short and medium-range are revealed by analyzing the synchrotron diffraction patterns in reciprocal space and real space.Meanwhile,the local plastic flow enhances the structural heterogeneity.In contrast to the strain-softening under uniaxial loading,these structural changes contribute to the improvement of resistance to subsequent deformation.As a result,the Vickers hardness of the deformed Fe_(78)Si_(9)B_(13) metallic glass increases compared with the undeformed sample,manifesting a local strain-hardening behavior.