MRS Bulletin

Technical Feature

Technical Feature

Structural Aspects of Metallic Glasses

Daniel B. Miracle, Takeshi Egami, Katharine M. Flores and Kenneth F. Kelton

Abstract

A recent structural model reconciles apparently conflicting features of randomness, short-range order, and medium-range order that coexist in metallic glasses. In this efficient cluster packing model, short-range order can be described by efficiently packed solute-centered clusters, producing more than a dozen established atomic clusters, including icosahedra. The observed preference for icosahedral short-range order in metallic glasses is consistent with the theme of efficient atomic packing and is further favored by solvent-centered clusters. Driven by solute—solute avoidance, medium-range order results from the organization in space of overlapping, percolating (via connected pathways), quasi-equivalent clusters. Cubic-like and icosahedral-like organization of these clusters are consistent with measured medium-range order. New techniques such as fluctuation electron microscopy now provide more detailed experimental studies of medium-range order for comparison with model predictions. Microscopic free volume in the efficient cluster packing model is able to represent experimental and computational results, showing free volume complexes ranging from subatomic to atomic-level sizes. Free volume connects static structural models to dynamic processes such as diffusion and deformation. New approaches dealing with “free” and “anti-free” microscopic volume and coordinated atomic motion show promise for modeling the complex dynamics of structural relaxations such as the glass transition. Future work unifying static and dynamic structural views is suggested.

Daniel B. Miracle is a Senior Scientist in the Materials and Manufacturing Directorate of the Air Force Research Laboratory (AFRL). He received his PhD degree from Ohio State University and an Honorary Doctor of Science degree from the Institute of Metal Physics, Ukrainian Academy of Sciences. Miracle has been a senior visiting fellow at the University of Cambridge and a scientific officer at the Air Force Office of Scientific Research. His current research interests include amorphous and nanocrystalline metals and boron-modified titanium.

Miracle is a fellow of ASM International and of the AFRL. He has been honored by the Air Force with the Basic Research Award and the Scientific Achievement Award. Miracle has authored or co-authored 130 articles and six book chapters and is co-editor of five books, including Composites Volume 21 of the ASM Handbook series.

Miracle can be reached at the Air Force Research Laboratory, Materials and Manufacturing Directorate, 2230 Tenth St., Wright-Patterson Air Force Base, OH 45433, USA; tel. 937-255-9833 and e-mail [email protected].

Takeshi Egami is a Distinguished Professor at the University of Tennessee and a Distinguished Scientist at Oak Ridge National Laboratory. He received his BS degree in applied physics from the University of Tokyo in 1968 and his PhD degree in materials science from the University of Pennsylvania in 1971.

Egami's research interests include local atomic structure and dynamics of functional materials using neutron and x-ray scattering and pair distribution function analysis; electronic oxides including super-conducting, ferroelectric, and magnetic oxides; and the theory of metallic glasses and liquids. Egami received the B.E.Warren Diffraction Physics Award from the American Crystallographic Association in 2003 and is a fellow of the American Physical Society.

Egami can be reached at South College, 1413 Circle Dr., Knoxville, TN 37996, USA; tel. 865-974-7204, fax 865-974-3949, and e-mail [email protected].

Katharine M. Flores is an assistant professor of materials science and engineering at Ohio State University. She received her PhD degree from Stanford University in 2000, where her thesis work focused on the mechanical behavior of bulk metallic glasses. Her group's work at OSU has expanded to include developing novel metallic glass processing techniques, as well as understanding the relationship between glass structure and deformation. Flores' work in this area has been recognized with an NSF CAREER Award and an ONR Young Investigator Award, both in 2005. Flores has active research interests in other structural materials systems, particularly hightemperature superalloys and structural biomaterials such as bone.

Flores can be reached at the Dept. of Materials Science and Engineering, Ohio State University, 2041 College Rd., Columbus, OH 43210 USA; tel. 614-292-9548, fax 614-292-1537, and e-mail [email protected].

Kenneth F. Kelton is the Arthur Holly Compton Professor in Arts and Sciences at Washington University in St. Louis, Missouri. He received his PhD degree from Harvard University in 1983 and joined the physics faculty at Washington University in 1985.

Kelton has spent extended periods at the University of Cambridge, most recently as an overseas visiting scholar in St. Johns College. Kelton's primary research interests are nucleation in condensed systems and the formation and structures of complex phases. Kelton is a fellow of the American Physical Society and the U.S. regional editor for the Journal of Non-Crystalline Solids.

Kelton can be reached at the Physics Dept., CB 1105, Washington University, 1 Brookings Dr., St. Louis, MO 63130-4899, USA; tel. 314-935-6228, fax 314-935-6219, and e-mail [email protected] wustl.edu.

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