42 43 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 2 / 2 3 Paving theway for stronger alloys Materials Engineering & Processes – Materials Science – Engineering & Technology - Metallurgy Understanding the formationofmicrostructures is critical toawide range of solidification procedures, including casting and welding. Research conducted by scientists at the University of Birmingham has expanded our understanding of alloys by exploring how microscopic crystals evolve in molten metals as they cool. Their breakthrough research has the potential to enhance the tensile strength of alloys utilised in aerospace and automobile applications. A microscopic examination will show faceted dendritic intermetallic crystals in all sorts of metal alloys, including nickel-based superalloys, steels and aluminium alloys. Although these crystals significantly affect the properties of alloys, there is a scarcity of research dedicated to studying their formation mechanisms. The classic view of dendrite formation is that as a spherical solid nucleus in undercooled liquid melt grows, the solid-liquid interphase becomes unstable. Perturbations form consequently, leading to the formation of dendrites. The research team was interested in whether this mechanism applies to the formation of faceted intermetallic dendrites. They built a furnace to melt an aluminium-copper (Al-Cu) alloy and control the cooling, and coupled it with high-speed tomography at Diamond’s I12 beamline. This setup allowed them to capture ‘snapshots’ in seconds, resolving the topological evolution of the crystals as they formed at high temperatures. The intermetallic Al 2 Cu in the Al-Cu alloy forms in many shapes, from simple rods to complicated faceted dendrites.The study shows that, in a cooling aluminium-copper alloy, the solidification processes with the formation of faceted dendrites. These dendrites form by a layer-by-layer stacking of small, micrometre-sized basic units. These units start L-shaped and stack on top of each other like building blocks. However, they change shape as they cool, first transforming into a U shape and finally a hollowed-out cube, while some stack together to form beautiful dendrites. These findings provide new insights into what happens at a micro level as an alloy cools, and show the shape of the basic building blocks of crystals in molten alloys. The results directly contrast with the classical view of dendrite formation in cooling alloys, opening the door to developing new approaches to predict and control intermetallic crystal formation. As crystal shape determines the strength of the final alloy, if we can make alloys with finer crystals, we can create stronger alloys. Dendrites also form in processes other than the solidification of metals. It’s possible that this mechanism may also explain the formation of dendrites in cooling magmas and cycling batteries. Related publication: Song, Z. et al. Revealing growth mechanisms of faceted Al2Cu intermetallic compounds via high-speed Synchrotron X-ray tomography. Acta Materialia 231 , (2022). DOI: 10.1016/j.actamat.2022.117903 Funding acknowledgement: EPSRC CDT Grant (No: EP/L016206/1) Alan Turing Fellowship (2018-2021) UKRI Future Leaders Fellowship (No. MR/W007967/1) Corresponding authors: Biao Cai, University of Birmingham,
[email protected] Imaging andMicroscopy Group Beamline I12 (a) the basic units of Al 2 Cu intermetallic compound, (b) dendrites of Al 2 Cu, and (c) the layer-by-layer growth mechanism for Al 2 Cu dendrites. Searching for life and for our origins are two sides of the same coin Earth Sciences & Environment – Geology – Geochemistry – Planetary Geology In 1996, researchers at NASA Johnson Space Center released a paper in Science entitled “Possible relic biogenic activity in Mars meteorite ALH84001”. This caused intense scientific examination of this meteorite, ultimately leading to the formation of the field of Astrobiology and renewed interest in sending missions to Mars. After several years, the scientific consensus was that there was no evidence of Martian life in the meteorite, but the question of organic material remained ambiguous. So the question remained for many years: if ALH84001 does not contain signs of martian life, what is the nature of organic material in this meteorite, and what is its origin? An international team of researchers undertook a series of investigations to spatially resolve the presence, nature and possible synthesis mechanisms for the organic material in ALH84001. They used a Focused Ion Beam (FIB) instrument to cut sections from the matrix and carbonate rosettes within the meteorite and performed Transmission Electron Microscopy (TEM), Scanning Transmission X-ray Microscopy (STXM) and D/H measurements on those sections. That enabled them to find the organic carbon and study its provenance and relationship to minerals in the meteorite. At Diamond’s I08 beamline, they carried out high spatial resolution STXM analysis across the C and N edges to look at the presence and bonding environment of the carbon present. The results revealed a high proportion of aromatic and oxygen functionality in the organic material. Finally, after completing these analyses, they measured the hydrogen isotopic signal of the analysed organic carbon to ensure its martian origin. From these analyses, the team were able to show that the organic carbon was synthesised in situ on Mars in two processes: serpentinisation and carbonation. These two organic synthesis mechanisms had not been seen on Mars before and are indicative of water-rock reactions 3.6 billion years ago. Water-rock interactions are relevant to planetary habitability, influencing mineralogical diversity and the production of organic molecules. This discovery has enabled them to set a non-life background for the detection of a non-terrain-based life form but also points to fundamental reactions between igneous rocks and brines that lead to the synthesis of abiotic/prebiotic organic material that produced life on early Earth. While the record of these interactions on early Earth has been destroyed by plate tectonics and overprinted by life on Earth, that record appears intact on Mars. Related publication: Steele, A. et al. Organic synthesis associated with serpentinization and carbonation on early Mars. Science 375 , 172-177 (2022). DOI: 10.1126/ science.abg7905 Funding acknowledgement: NASA grant 17-NAI8_2-0020 (principal investigator K.R. financial support through the Helmholtz Recruiting Initiative program) Corresponding author: A Steele, Carnegie Institution of Washington,
[email protected] Imaging andMicroscopy Group Beamline I08 Meteorite fragment ALH84001 found in Antarctica in 1984, Wikimedia commons.