Abstract
Strain hardening, originating from defects such as the dislocation, avails conventional metals of high engineering reliability in applications. However, the hardenability of metallic glass is a long-standing concern due to the lack of similar defects. In this work, we carefully examine the stress-strain relationship in three bulk monolithic metallic glasses. The results show that hardening is surely available in metallic glasses if the effective load-bearing area is considered instantly. The hardening is proposed to result from the remelting and ensuing solidification of the shear-band material under a hydrostatic pressure imposed by the normal stress during the shear banding event. This applied-pressure quenching densifies the metallic glass by discharging the free volume. On the other hand, as validated by molecular dynamics simulations, the pressure promotes the icosahedral short-range order. The densification and icosahedral clusters both contribute to the increase of the shear strength and therefore the hardening in metallic glasses.
Highlights
Strain hardening is a highly desired property for structural materials, especially for high-strength engineering metals and alloys[1]
For the metallic glasses (MGs) in which the plastic deformation proceeds via shear banding events[7], their capability to be hardened substantially depends on the shear band itself[13]
We propose that remelting and solidification under a hydrostatic pressure imposed by the normal stress result in the hardening of the shear band material
Summary
Strain hardening is a highly desired property for structural materials, especially for high-strength engineering metals and alloys[1]. It renders the strained material harder and increasingly difficult to deform further in the plastic regime, and enables the material to accommodate the plastic strain globally. The plastic strain cannot be spread out in the whole sample; instead, it is often localized into thin shear bands in MGs at room temperature[7,8,9]. If the shear bands has formed and developed during the plastic deformation of MGs, strain softening was frequently confirmed[15,16,17,18].
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