Continuous chemical redistribution following amorphous-to-crystalline structural ordering in a Zr-Cu-Al bulk metallic glass

Bulk metallic glasses (BMGs) are thermodynamically metastable. As such, crystallization occurs when a BMG is thermally annealed at a temperature above the glass transition temperature. While extensive studies have been performed on the crystallization kinetics of BMGs, most of them have focused on the amorphous-to-crystalline structural ordering, and little attention has been paid to chemical distribution and its relationship with the structural ordering during the crystallization process. In this paper, a new approach, with simultaneous differential scanning calorimetry (DSC) and small angle neutron scattering (SANS) measurements, was applied to study in situ the crystallization of a Zr45.5Cu45.5Al9 BMG upon isothermal annealing at a temperature in the supercooled liquid region. Quantitative analysis of the DSC and SANS data showed that the structural evolution during isothermal annealing could be classified into three stages: (I) incubation; (II) amorphous-to-crystalline structural ordering; (III) continuous chemical redistribution. This finding was validated by composition analysis with atom probe tomography (APT), which further identified a transition region formed by expelling Al into the matrix. The transition region, with a composition of (Cu,Al)(50)Zr-50, served as an intermediate step facilitating the formation of a thermodynamically stable crystalline phase with a composition of (Cu,Al)(10)Zr-7. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

This paper presents a new approach to study the crystallization of Zr45.5Cu45.5Al9 bulk metallic glass (BMG) during isothermal annealing. By analyzing the data from simultaneous differential scanning calorimetry and small angle neutron scattering measurements, the authors identified three stages in the crystallization process: incubation, amorphous-to-crystalline structural ordering, and continuous chemical redistribution. The findings were further confirmed by composition analysis using atom probe tomography, which revealed the formation of a transition region where Al was expelled into the matrix.