Abstract
Glasses boast high strength and hardness, but lack ductility at room temperature. A long-sought goal is therefore to impart ductility without conceding much strength. In this talk we advocate purposely enhanced inhomogeneities, in an otherwise compositionally uniform and single-phase amorphous structure, to promote distributed plastic flow. Four tactics (the 4 R’s) to improve deformability are highlighted. These strategies improve plasticity and toughness, and occasionally even tensile ductility with necking that is unusual for glasses at room temperature. Possibilities of strain hardening and strain rate hardening that are needed to stabilize uniform elongation will also be discussed. We also introduce “flexibility volume” as a universal indicator of the glassy state, to quantitatively calculate and predict the physical properties of glasses on both atomic and macroscopic levels. We show that this universal parameter deterministically predicts the shear modulus [1], which is at the heart of key properties of glasses such as metallic glasses, amorphous silicon and silica. The flexibility volume correlates strongly on the one hand with atomic packing topology, and on the other hand with the activation energy for thermally activated relaxation and the propensity for stress-driven shear transformations [1]. The quantitative correlations discovered are robust and prognostic for all glass compositions, processing conditions and length scales. These advantages advocate flexibility as a powerful single-parameter indicator, in lieu of the widely cited but ambiguous “free volume”, in characterizing the structural state of glasses and understanding their properties.
[1] J. Ding et al., Nature Communications 7 (2016) 13733.

Brief bio:
E. Ma did his undergraduate work at Tsinghua University and graduate work at Tsinghua University and Caltech, followed by postdoc sojourns at MIT and Univ. of Michigan. He is currently a professor in the Department of Materials Science and Engineering at Johns Hopkins University. Prof. Ma has published ~310 papers (w/ ~22,000 citations and h index=76, according to SCI; and ~28,500 citations and h index=87, according to Google Scholar) and presented ~125 invited talks at international conferences (and another ~83 at academic institutions). He is an elected Fellow of ASM, APS, and MRS. Dr. Ma has also been a professor at Xi’an Jiaotong Univ. since 2009. His current research interests include amorphous metals (metallic glasses), chalcogenide phase-change alloys for memory applications, ductility of nanostructured metals, plasticity mechanisms, and in situ transmission electron microscopy of materials exposed to mechanical, thermal and environmental stimuli.