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Abstract Investigating how solid matter behaves at enormous pressures, such as those found in the deep interiors of giant planets, is a great experimental challenge. Over the past decade, computational predictions have revealed that compression to terapascal pressures may bring about counter-intuitive changes in the structure and bonding of solids as quantum mechanical forces grow in influence 1–6 . Although this behaviour has been observed at modest pressures in the highly compressible light alkali metals 7,8 , it has not been established whether it is commonplace among high-pressure solids more broadly. We used shaped laser pulses at the National Ignition Facility to compress elemental Mg up to 1.3 TPa, which is approximately four times the pressure at the Earth’s core. By directly probing the crystal structure using nanosecond-duration X-ray diffraction, we found that Mg changes its crystal structure several times with non-close-packed phases emerging at the highest pressures. Our results demonstrate that phase transformations of extremely condensed matter, previously only accessible through theoretical calculations, can now be experimentally explored.
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Complexity and evolution of a three-phase eutectic during coarsening uncovered by 4D nano-imaging
We investigate the coarsening dynamics of the three-phase eutectic Al-Ag2Al-Al2Cu at 723 K via in situ transmission X-ray nano-tomography. Unlike previous investigations that compared observations between different samples annealed for different times, our three-dimensional measurement shows at nanoscale resolution the microstructural changes occurring in the same field-of-view, enabling new insight on the capillary-driven evolution of a ladder-like pattern. With the aid of a new reconstruction algorithm and machine learning segmentation, we trace the interfaces of the eutectic and observe significant structural changes within 4 hr. of aging. Even though the average length-scales of the eutectic solids follow a temporal power law, the microstructure is not self-similar. Instead, it evolves (in part) through the coalescence of neighboring Ag2Al solids at the expense of the intervening Al2Cu. By combining our X-ray data with electron diffraction to identify the common planes at the interphase boundaries, we show that coalescence leads to a decrease in lattice misfit, and hence, interfacial energy. At longer times, the interphase boundaries with low misfit compete for surface area, resulting in a ‘locking’ of the interfacial shape.
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- Award ID(s):
- 2203378
- PAR ID:
- 10529572
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Acta Materialia
- Volume:
- 266
- ISSN:
- 1359-6454
- Page Range / eLocation ID:
- 119684
- Subject(s) / Keyword(s):
- Coarsening Ostwald ripening Solid-state transformation Multi-phase eutectics Real-time imaging X-ray nano-tomography Crystallography
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.actamat.2024.119684
