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1. Fracture toughness of a metal–organic framework glass

   https://doi.org/10.1038/s41467-020-16382-7  

   To, Theany; Sørensen, Søren S.; Stepniewska, Malwina; Qiao, Ang; Jensen, Lars R.; Bauchy, Mathieu; Yue, Yuanzheng; Smedskjaer, Morten M. (May 2020, Nature Communications)

   Abstract Metal-organic framework glasses feature unique thermal, structural, and chemical properties compared to traditional metallic, organic, and oxide glasses. So far, there is a lack of knowledge of their mechanical properties, especially toughness and strength, owing to the challenge in preparing large bulk glass samples for mechanical testing. However, a recently developed melting method enables fabrication of large bulk glass samples (>25 mm³) from zeolitic imidazolate frameworks. Here, fracture toughness (K_Ic) of a representative glass, namely ZIF-62 glass (Zn(C₃H₃N₂)_1.75(C₇H₅N₂)_0.25), is measured using single-edge precracked beam method and simulated using reactive molecular dynamics.K_Icis determined to be ~0.1 MPa m^0.5, which is even lower than that of brittle oxide glasses due to the preferential breakage of the weak coordinative bonds (Zn-N). The glass is found to exhibit an anomalous brittle-to-ductile transition behavior, considering its low fracture surface energy despite similar Poisson’s ratio to that of many ductile metallic and organic glasses. 

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2. Review of Thermoplastic Drawing with Bulk Metallic Glasses

   https://doi.org/10.3390/met12030518  

   Jagdale, Shweta; Jabed, Akib; Theeda, Sumanth; Meduri, Chandra Sekhar; Hu, Zhonglue; Hasan, Molla; Kumar, Golden (March 2022, Metals)

   This study summarizes the recent progress in thermoplastic drawing of bulk metallic glasses. The integration of drawing with templated embossing enables the fabrication of arrays of high-aspect-ratio nanostructures whereas the earlier drawing methodologies are limited to a single fiber. The two-step drawing can produce metallic glass structures such as, vertically aligned nanowires on substrates, nanoscale tensile specimens, hollow microneedles, helical shafts, and micro-yarns, which are challenging to fabricate with other thermoplastic forming operations. These geometries will open new applications for bulk metallic glasses in the areas of sensors, optical absorption, transdermal drug-delivery, and high-throughput characterization of size-effects. In this article, we review the emergence of template-based thermoplastic drawing in bulk metallic glasses. The review focuses on the development of experimental set-up, the quantitative description of drawing process, and the versatility of drawing methodology. 

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3. Nontoxic, precious-metal-free titanium-based metallic glasses with exceptional glass-forming ability and high specific strength

   https://doi.org/10.1063/5.0191532  

   Chen, Lei; Thaiyanurak, Tittaya; Wang, Zhengming; Ayers, Madeline; Zaitseva, Natalia; Xu, Donghua (January 2024, Applied Physics Letters)

   Titanium-based metallic glasses (TBMGs) are attracting broad interest due to their simultaneous light weight, superhigh strength, and specific strength, exceptional wear- and corrosion-resistance and biocompatibility, desirable for electronic, biomedical, and aerospace applications. However, the glass-forming ability (GFA) of TBMGs, except some containing significant amount of toxic (Be) or precious (Pd, Ag) elements, is disappointingly low, as manifested by a critical casting diameter (dc) not more than 6 mm, which significantly restricts their manufacturing and applications. Here, we report our discovery of a series of TBMGs in the (TiZrHf)x(CuNi)y(SnSi)z pseudo-ternary system. These alloys possess an exceptionally large dc, reaching up to 12 mm, doubling the current record for Be and precious-metal free TBMGs. Moreover, these alloys exhibit a low density (7.0–7.3 g/cm3), high fracture-strength (up to ∼2700 MPa), high specific fracture-strength (up to ∼370 N m g−1), and even good plasticity with a plastic strain of up to 9.4% upon compression. They also possess high activation energy for crystallization and high atomic packing efficiency, which provide an initial physical account for their exceptional GFA and manufacturability. 

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4. Size-dependent vitrification in metallic glasses

   https://doi.org/10.1038/s41467-023-40417-4  

   Di Lisio, Valerio; Gallino, Isabella; Riegler, Sascha Sebastian; Frey, Maximilian; Neuber, Nico; Kumar, Golden; Schroers, Jan; Busch, Ralf; Cangialosi, Daniele (August 2023, Nature Communications)

   Abstract Reducing the sample size can profoundly impact properties of bulk metallic glasses. Here, we systematically reduce the length scale of Au and Pt-based metallic glasses and study their vitrification behavior and atomic mobility. For this purpose, we exploit fast scanning calorimetry (FSC) allowing to study glassy dynamics in an exceptionally wide range of cooling rates and frequencies. We show that the mainαrelaxation process remains size independent and bulk-like. In contrast, we observe pronounced size dependent vitrification kinetics in micrometer-sized glasses, which is more evident for the smallest samples and at low cooling rates, resulting in more than 40 K decrease in fictive temperature,T_f, with respect to the bulk. We discuss the deep implications on how this outcome can be used to convey glasses to low energy states. 

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5. Revisiting the Dependence of Poisson’s Ratio on Liquid Fragility and Atomic Packing Density in Oxide Glasses

   https://doi.org/10.3390/ma12152439  

   Østergaard, Martin B.; Hansen, Søren R.; Januchta, Kacper; To, Theany; Rzoska, Sylwester J.; Bockowski, Michal; Bauchy, Mathieu; Smedskjaer, Morten M. (August 2019, Materials)

   Poisson’s ratio (ν) defines a material’s propensity to laterally expand upon compression, or laterally shrink upon tension for non-auxetic materials. This fundamental metric has traditionally, in some fields, been assumed to be a material-independent constant, but it is clear that it varies with composition across glasses, ceramics, metals, and polymers. The intrinsically elastic metric has also been suggested to control a range of properties, even beyond the linear-elastic regime. Notably, metallic glasses show a striking brittle-to-ductile (BTD) transition for ν-values above ~0.32. The BTD transition has also been suggested to be valid for oxide glasses, but, unfortunately, direct prediction of Poisson’s ratio from chemical composition remains challenging. With the long-term goal to discover such high-ν oxide glasses, we here revisit whether previously proposed relationships between Poisson’s ratio and liquid fragility (m) and atomic packing density (Cg) hold for oxide glasses, since this would enable m and Cg to be used as surrogates for ν. To do so, we have performed an extensive literature review and synthesized new oxide glasses within the zinc borate and aluminoborate families that are found to exhibit high Poisson’s ratio values up to ~0.34. We are not able to unequivocally confirm the universality of the Novikov-Sokolov correlation between ν and m and that between ν and Cg for oxide glass-formers, nor for the organic, ionic, chalcogenide, halogenide, or metallic glasses. Despite significant scatter, we do, however, observe an overall increase in ν with increasing m and Cg, but it is clear that additional structural details besides m or Cg are needed to predict and understand the composition dependence of Poisson’s ratio. Finally, we also infer from literature data that, in addition to high ν, high Young’s modulus is also needed to obtain glasses with high fracture toughness. 

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