Abstract
The negative strain rate sensitivity (SRS) of metallic glasses is frequently observed. However, the physical essence involved is still not well understood. In the present work, small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM) reveal the strong structure heterogeneity at nanometer and tens of nanometer scales, respectively, in bulk metallic glass (BMG) Zr64.13Cu15.75Ni10.12Al10 subjected to fully confined compression processing. A transition of SRS of stress, from 0.012 in the as-cast specimen to −0.005 in compression processed specimen, was observed through nanoindentation. A qualitative formulation clarifies the critical role of internal stress induced by structural heterogeneity in this transition. It reveals the physical origin of this negative SRS frequently reported in structurally heterogeneous BMG alloys and its composites.
Highlights
W.; Liu, S.N.; Liu, Y.; Lan, S.; Wang, The strain rate has a significant effect on the flow stress during the deformation of bulk metallic glasses (BMGs), especially the serrated flow behavior [1,2,3]
This change agrees with the observations reported for various BMGs [22,23] and this is because at a high strain rate, a single shear band is difficult to adapt to rapid deformation, and only multiple shear bands can be activated at the same time, which leads to the decrease of the width of each serrated flow and disappears at a certain critical strain rate [22]
Negative strain rate sensitivity (SRS) is observed in monolithic Zr64.13 Cu15.75 Ni10.12 Al10 BMG after the fully confined compression deformation processing in the present study, as shown in Figure 2, together with the heterogeneous structure manifested by small-angle X-ray scattering (SAXS) and high-resolution transmission electron microscopy (HRTEM) observation, at scales from nano to tens of nanometers, as shown in Figures 3 and 4
Summary
W.; Liu, S.N.; Liu, Y.; Lan, S.; Wang, The strain rate has a significant effect on the flow stress during the deformation of bulk metallic glasses (BMGs), especially the serrated flow behavior [1,2,3]. A high positive value of strain rate sensitivity (SRS) for conventional crystalline metals represents more homogeneous deformation. Most of the monolithic BMGs have positive SRS [4,5,6,7,8,9], a few exhibit negative values [10,11,12]. It is noteworthy that most of the BMGs exhibiting negative SRS show significant structural heterogeneity. There is a significant negative SRS in BMGs containing extensive dendrite distribution [13]. Similar negative SRS has been reported in other MGs containing a composite structure [14,15,16]. It has been reported that Zr52.5 Cu17.9 Ni14.6 Al10 Ti5 (Vit105)
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