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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)

   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. Experimental evidence that shear bands in metallic glasses nucleate like cracks

   https://doi.org/10.1038/s41598-022-22548-8  

   Long, Alan A. ; Wright, Wendelin J. ; Gu, Xiaojun ; Thackray, Anna ; Nakib, Mayisha ; Uhl, Jonathan T. ; Dahmen, Karin A. ( November 2022 , Scientific Reports)

   Highly time-resolved mechanical measurements, modeling, and simulations show that large shear bands in bulk metallic glasses nucleate in a manner similar to cracks. When small slips reach a nucleation size, the dynamics changes and the shear band rapidly grows to span the entire sample. Smaller nucleation sizes imply lower ductility. Ductility can be increased by increasing the nucleation size relative to the maximum (“cutoff”) shear band size at the upper edge of the power law scaling range of their size distribution. This can be achieved in three ways: (1) by increasing the nucleation size beyond this cutoff size of the shear bands, (2) by keeping all shear bands smaller than the nucleation size, or (3) by choosing a sample size smaller than the nucleation size. The discussed methods can also be used to rapidly order metallic glasses according to ductility.

    

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4. Combinatorial measurement of critical cooling rates in aluminum-base metallic glass forming alloys

   https://doi.org/10.1038/s41598-021-83384-w  

   Liu, Naijia ; Ma, Tianxing ; Liao, Chaoqun ; Liu, Guannan ; Mota, Rodrigo Miguel Ojeda ; Liu, Jingbei ; Sohn, Sungwoo ; Kube, Sebastian ; Zhao, Shaofan ; Singer, Jonathan P. ; et al ( February 2021 , Scientific Reports)

   Direct measurement of critical cooling rates has been challenging and only determined for a minute fraction of the reported metallic glass forming alloys. Here, we report a method that directly measures critical cooling rate of thin film metallic glass forming alloys in a combinatorial fashion. Based on a universal heating architecture using indirect laser heating and a microstructure analysis this method offers itself as a rapid screening technique to quantify glass forming ability. We use this method to identify glass forming alloys and study the composition effect on the critical cooling rate in the Al–Ni–Ge system where we identified Al₅₁Ge₃₅Ni₁₄as the best glass forming composition with a critical cooling rate of 10⁴ K/s.

    

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5. Observation of an apparent first-order glass transition in ultrafragile Pt–Cu–P bulk metallic glasses

   https://doi.org/10.1073/pnas.1916371117  

   Na, Jong H. ; Corona, Sydney L. ; Hoff, Andrew ; Johnson, William L. ( January 2020 , Proceedings of the National Academy of Sciences)

   An experimental study of the configurational thermodynamics for a series of near-eutectic Pt_80-xCu_xP₂₀bulk metallic glass-forming alloys is reported where 14 <x< 27. The undercooled liquid alloys exhibit very high fragility that increases asxdecreases, resulting in an increasingly sharp glass transition. With decreasingx, the extrapolated Kauzmann temperature of the liquid,T_K, becomes indistinguishable from the conventionally defined glass transition temperature,T_g. Forx< 17, the observed liquid configurational enthalpy vs.Tdisplays a marked discontinuous drop or latent heat at a well-defined freezing temperature,T_gm. The entropy drop for this first-order liquid/glass transition is approximately two-thirds of the entropy of fusion of the crystallized eutectic alloy. BelowT_gm, the configurational entropy of the frozen glass continues to fall rapidly, approaching that of the crystallized eutectic solid in the low T limit. The so-called Kauzmann paradox, with negative liquid entropy (vs. the crystalline state), is averted and the liquid configurational entropy appears to comply with the third law of thermodynamics. Despite their ultrafragile character, the liquids atx= 14 and 16 are bulk glass formers, yielding fully glassy rods up to 2- and 3-mm diameter on water quenching in thin-wall silica tubes. The low Cu content alloys are definitive examples of glasses that exhibit first-order melting.

    

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