Guiding shear bands in bulk metallic glasses using stress fields: A perspective from the activation of flow units

Abstract

Controlling shear band propagation is the key to obtain ductile metallic glasses. Here, we use a residual stress field to vary the direction of shear band propagation. We ascribe this behavior to the effect of the stress field on the activation of shear transformation zones (STZs) along their characteristic direction and we quantify this contribution to the energy of the process. Because of the progressively adverse orientation of the stress field, the energy stored as shear in the STZ decreases to a level where shear band propagation at alternative angles becomes energetically more favorable.

Rejuvenation engineering in metallic glasses by stress and structure modulation

“…1a and c, the elastic strains parallel and perpendicular to the loading direction ( 11 and 22 ) display a highly heterogeneous profile that seems to be stabilized even after releasing the external load. This behavior indicates a highly inhomogeneous deformation mechanism, i.e., shear banding [24,28,29] and, hence, it further confirms that, at low temperature, the shear bands are the only plastic carriers in MGs. HAADF-STEM images of random selected-areas along the shear fronts (of highest volumetric strain) and between the notch area highlight shear band activity.…”

“…It is well accepted that shear banding is not only confined to a narrow thin layer of about 20 nm but extends over a longer range (tens of micrometers) across the shear band [31,35,36]. Experimental observations of high-energy XRD across an individual shear band revealed that the strain at opposite sides of a shear band changes sign from compressive to tensile [24,29,31]. Likewise, the strains/stresses are created in an inhomogeneous manner during triaxial compression (see Fig.…”

“…Due to their very low thermal conductivities and the high cooling rates involved in the quenching process, MGs undergo differential cooling and large thermal gradients are generated across the sample leading to residual stress buildup [22,23]. Residual stresses and stress field gradients affect shear band dynamics and the overall plastic deformation [20,24], hardness [23,25] and even magnetic properties of MGs [26]. Recently, molecular dynamics (MD) simulations of stress modulated MG heterostructures revealed that strain hardening together with tensile ductility can be attained by only modulating the internal residual stress without altering the structure [27].…”

Ergodic Structural Diversity Predicts Dynamics in Amorphous Materials

“…This characteristic length scale is also commensurate with the critical size of soft regions that are responsible for triggering plastic shear transformations under thermal and/or mechanical stimuli. This is expected since the robust correlation between ΔQ and shear transformation has been well reported in the literature Kosiba et al (2020), Han et al (2020), andWei et al (2019). In this connection, local regions with a high level of S i can be identified as potential glassy defects.…”

Synthesis of Bulk Zr48Cu36Al8Ag8 Metallic Glass by Hot Pressing of Amorphous Powders

“…Monolithic BMGs show limited plasticity at room temperature due to the fact that plastic deformation in these materials occurs via the formation and propagation of highly localized shear bands [2]. Kosiba et al [40] reported that shear band propagation in ZrCu-based glassy specimens can be guided via the generation of designed elastic stress fields, suggesting that the current BMG may be made ductile. BMG composites containing secondary phases in the glassy matrix is another effective way to toughen the monolithic glass via a mechanism of shear band arrest and multiplication [41].…”