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Abstract
Magnesium-based bulk metallic glasses (BMGs) exhibit high specific strengths and excellent glass-forming ability compared to other metallic systems, making them suitable candidates for next-generation materials. However, current Mg-based BMGs tend to exhibit low thermal stability and are prone to structural relaxation and brittle failure. This study presents a range of new magnesium–precious metal-based BMGs from the ternary Mg–Ag–Ca, Mg–Ag–Yb, Mg–Pd–Ca and Mg–Pd–Yb alloy systems with Mg content greater than 67 at.%. These alloys were designed for high ductility by utilising atomic bond-band theory and a topological efficient atomic packing model. BMGs from the Mg–Pd–Ca alloy system exhibit high glass-forming ability with critical casting sizes of up to 3 mm in diameter, the highest glass transition temperatures (>200 °C) of any reported Mg-based BMG to date, and sustained compressive ductility. Alloys from the Mg–Pd–Yb family exhibit critical casting sizes of up to 4 mm in diameter, and the highest compressive plastic (1.59%) and total (3.78%) strain to failure of any so far reported Mg-based glass. The methods and theoretical approaches presented here demonstrate a significant step forward in the ongoing development of this extraordinary class of materials.
Highlights
The relative glass-forming ability of each alloy was initially determined using electron-based microscopy (Hitachi SU70 SEM) and verified on the central sections of castings using X-ray diffraction (XRD) with a Phillips MRD instrument equipped with a 0.5 mm micro-capillary tube and a Cu Kα radiation source
Thermophysical data were determined by differential scanning calorimetry (DSC) using a Mettler Toledo DSC1 calorimeter at a heating rate of 20 °C min−1
Based on these results, our observations and theoretical analysis, it is expected that ductility will be significantly improved in these and other BMGs if d- and f- band electron interactions can be constrained in participating alloy elements
Summary
Nominal alloy compositions (shown in Tables 1–4) were prepared using pure metals: Mg (99.95 wt.%), Ag (99.95 wt.%), Pd (99.95 wt.%), Ca (99.8 wt.%) and Yb (99.99 wt.%). These metals were alloyed in graphite crucibles using an induction furnace in an argon-purged (99.997 wt.%) atmosphere by completely dissolving the solute elements in the molten Mg balance at 750 °C. The relative glass-forming ability of each alloy was initially determined using electron-based microscopy (Hitachi SU70 SEM) and verified on the central sections of castings using X-ray diffraction (XRD) with a Phillips MRD instrument equipped with a 0.5 mm micro-capillary tube and a Cu Kα radiation source. Compression testing was carried out at room temperature using a screw-driven Schenck mechanical testing machine with a compliance of ∼10 nm/N at a strain rate of 10−4 s−1
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