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Structures and Dynamics in Condensed Systems

Synthesis
The research effort proposed here entails bringing simulation methods together with theory and critical experiments to investigate structural selection dynamics in highly driven systems. Building on our past efforts aimed at understanding the structure and properties of highly undercooled liquids and glasses, the structural dynamics of solidification and devitrification, and the fundamental behavior of interfaces, we are developing a research program that is focused on the multi-scale structural dynamics of metallic liquids, glasses, and crystalline phases under far-from-equilibrium conditions. By exploring this realm of material dynamics in earnest, we aim to open vast untapped domains of materials structures and physical behaviors, with an equally broad scope of potential functionality in magnetic, electric, elastic, thermal, and optical properties, and the critical coupled-response behaviors that may be strongly influenced by using far-from-equilibrium conditions to influence phase selection, crystallographic orientation, polycrystalline scale and texture, multiphase architectures, interface structure, solute distribution, and defect concentrations.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

Project Leader(s):

Key Scientific Personnel:

Postdoctoral Research Associate(s):

  • A unique combination of state-of-the-art experimental techniques—electrostatic levitation and high-energy X-ray diffraction—has led to the discovery of a short-lived intermediate step that facilitates the liquid to solid transition in a nickel-zirconium (Ni-Zr) alloy. A small charged bead of Ni-Zr was levitated using a controlled electric field. Electrostatic levitation creates an environment to study materials without the interference of a container, thus offering unique access to exploring phase transformations. Once floating, the sample was liquefied with a laser.

  • Glass is often described as being like a liquid, with randomly arranged atoms.New insights are emerging that show some distinct levels of order within the structure of glasses. Our rapidly evolving understanding arises from new structural information made possible because of advanced light sources like the U.S. Department of Energy’s Advanced Photon Source. The new theory fits experimental data better than the widely accepted model based on icosahedral-like clusters. The new model shows many crystal-like polyhedra as well as clustering of polyhedra — features not seen in previous models.

  • Liquids and glasses are often described as having “disordered” structures, but new methods are showing that there are some significant patterns hidden in the seemingly random arrangements of atoms. When applied to a glassy copper–zirconium alloy, “order mining” has revealed an unexpected similarity between metallic glasses and quasicrystals, among other novel features.

  • Researchers have found evidence of atomic-scale defect formation during crystal growth from the supercooled liquid. Researchers have long speculated that defects incorporate during growth, but until now had no evidence because they heal before they can be observed. Using high energy, high resolution in situ X-ray diffraction at the U.S. Department of Energy’s Advanced Photon Source, researchers overcame accuracy and data collection speed issues to make this discovery. The researchers found evidence of defects that involve swapping of the locations of the elements in Zr2Cu.

  • Scientists have discovered a way to make strong materials that are also ductile. One of life’s classic problems is that whenever a metal or alloy is altered to make it stronger, it loses its ability to deform – it becomes brittle, so its eventual failure is both unheralded and catastrophic. Nanostructured materials have shown great improvements in strength over their conventional counterparts, but until now, they have also typically been more brittle.

  • Prediction of the development of structural ordering associated with the glass transition in metallic liquids has eluded scientists since the discovery of metallic glasses in 1960. Indeed, this issue presents a fundamental problem of incommensurate time scales, since the cooling rates generally required for the formation of a metallic glass from a liquid (103 K/s) are too high to allow for direct experimental measurement of structural dynamics, but too low to permit direct simulation through molecular dynamics methods (generally limited to 108 K/s).

Publications


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