Emerging medium-range order in deformed Zr-based bulk metallic glasses during sub-T_g relaxation

Abstract

The plasticity of bulk metallic glasses (BMGs) is closely correlated with the nature of shear bands; however, the structural origin of shear bands remains elusive due to the difficulty of obtaining direct observations. In this study, we investigated the microstructural evolution of shear bands during thermal relaxation by examining the local atomic-scale response to heating. Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ BMGs were subjected to two specifically designed deformation methods, namely, cold rolling and high-pressure torsion (HPT), to generate shear bands with varying volume fractions and rejuvenation states. In situ synchrotron diffraction results revealed a more pronounced growth of medium-range ordering at sub-T_g temperatures in the deformed BMGs than in the as-cast sample. The HPT-deformed BMG, with the highest volume fraction and distribution complexity of shear bands, demonstrated the most rapid increase in the ordering process. The transition of cluster connection modes possibly explained the anomalous emergence of medium-range order in the shear bands of deformed BMGs during sub-T_g relaxation or tension. Our study offers new insights into the atomic structure origins of shear bands, contributing to a deeper understanding of BMG plasticity.

Keywords

Bulk metallic glass / shear bands / local structure / relaxation

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