Frontiers of Materials Award Symposium: Intermetallic Alloys at the Edge of Complexity: Structural and Kinetic Aspects: Session I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee, TMS: Solidification Committee
Program Organizers: Ashwin Shahani, University Of Michigan
Wednesday 2:00 PM
March 22, 2023
Room: 28C
Location: SDCC
Session Chair: Ashwin Shahani, University Of Michigan
2:00 PM Keynote
Capturing the Growth of Quasicrystals Near- and Far-from-Equilibrium: Ashwin Shahani1; 1University of Michigan
Since their discovery around forty years ago, quasicrystals (QCs) have attracted substantial research interest due to their unique structure. Even so, there are still remaining questions in terms of why and how they form in the first place. Here, we present our efforts on tracking the nucleation and growth of QCs near- and far-from-equilibrium, by leveraging state-of-the-art dynamic imaging techniques. Our research was conducted with the aid of time-resolved synchrotron-based X-ray microscopy and dynamic transmission electron microscopy. By coupling these two techniques, we have investigated a broad range of length-scales (from tens of nm to hundreds of ěm) and solidification pathways (1 K/s to 106 K/s cooling rates). The results provide a wealth of knowledge on the emergence of QCs in deeply undercooled melts; the influence of phasons on QC coalescence; and the growth mode of the QCs from a liquid (solidification) and from a solid phase (precipitation).
2:40 PM Invited
Simulating Complex Crystal Structures and Their Assembly in Hard and Soft Condensed Materials: Julia Dshemuchadse1; 1Cornell University
Intermetallic compounds and ordered mesoscopic systems (i.e., "hard" and "soft" condensed matter) share structural properties on both ends of the complexity spectrum: while their simplest representatives are trivial sphere packings, their structural diversity has proven to be immense and extends all the way to aperiodic structures, such as quasicrystals. We study the assembly and structural features of complex crystals via numerical simulations, in order to investigate the emergence of long-range order from short-range interactions. By employing simple coarse-grained models, we gain systematic insights into the phenomena that lead to the crystallization and stabilization of the same intricate crystal structure types across length scales and materials systems. Ultimately, we aim to deduce general principles of structure formation that will allow for the design of tailored, functional materials in the future.
3:20 PM Break
3:40 PM Invited
Influence of Icosahedral Short-range Order in the Liquid on Solidification Morphologies: Michel Rappaz1; 1École Polytechnique Fédérale de Lausanne
Icosahedral Short-Ranger Order (ISRO) of atoms in liquid, first conjectured by Frank in 1952 to explain the large undercoolings measured by Turnbull in fcc or hcp metals, has been confirmed by several observations (formation of quasicrystals, atomic structure of many intermetallic phases, neutron small angle scattering) and by atomistic simulations. In contrast to the original idea of Frank, however, ISRO can act as a precursor for the formation of fcc grains, so-called "iQC- or ISRO-mediated nucleation". Localized covalent bonding associated with ISRO can also affect diffusion in the liquid as well as the attachment kinetics of atoms at solid-liquid interfaces. An “ISRO-induced stacking fault” mechanism is believed to be responsible for the formation of twinned dendrites in Al alloys and can compete with solid-liquid interfacial energy anisotropy to modify dendrite growth direction. This keynote presentation will try to summarize the recent findings and open questions on the influence of ISRO on solidification morphologies.
4:20 PM Invited
Intermetallic Compounds from Metallic-glass Precursors: A. Lindsay Greer1; 1University of Cambridge
Devitrification of metallic glasses (MGs) upon heating has seen much study over half a century. Intermetallic compounds (IMCs), including quasicrystals, are among the phases that form. Quasicrystals are of particular interest as their icosahedral ordering is also prominent in at least some metallic liquids and glasses. The kinetics of growth of IMCs in MGs is complex, and includes unusual combinations such as interface-limited rates with strong solute partitioning. Only with modern analytical techniques are such combinations being understood in terms of the very different diffusivities of different atomic species. Materials that are formed by devitrification can have attractive properties, and recent work shows that these composites can show good plasticity despite containing phases that are profoundly brittle, challenging our current understanding. Finally, we note that bulk MGs, with very narrow compositional ranges for their formation, might themselves be regarded as a type of IMC!