Materials Research Lecture
Extending the Range of the Glassy State in Metals
Metallic glasses are ideally suited for exploration of the effects of deformation on the structure and properties of glasses. It is expected that plastic deformation can change the structure and properties, but is more surprising that there can be very significant effects even well within the (nominally) elastic regime. Such effects are related to the complex elastic response of metallic glasses, with local non-reversed configurational changes arising from non-affine displacements. Recent work suggests similar effects from thermal strains . Thermal cycling of metallic glasses (below 60% of the glass-transition temperature, so relaxation effects are negligible) induces rejuvenation, again interpreted in terms of non-affine strains, raising the question of whether glassy states can, strictly, be regarded as isoconfigurational. We explore the remarkably wide range of energy that can be achieved in the metallic glassy state, from high ('rejuvenated') to low ('relaxed' and even 'ultrastable') [2,3]. Rejuvenated metallic glasses are of interest for several reasons, but principally because they exhibit better plasticity. We also consider whether pure metals are glass-formers, and the wide range of glass-forming ability of metallic systems [4,5]. Interest in systems of poor glass-forming ability is currently high, because of their potential application in phase-change memory . There are aspects of induced anisotropy in metallic glasses and liquids that are still very far from understood , yet anisotropy may be critical in understanding the mechanisms of flow and deformation.
1. S. V. Ketov, Y. H. Sun, S. Nachum, Z. Lu, A. Checchi, A. R. Beraldin, H. Y. Bai, W. H. Wang, D. V. Louzguine-Luzgin, M. A. Carpenter and A. L. Greer, Nature 524, 200 (2015).
2. Y. H. Sun, A. Concustell and A. L. Greer, Thermomechanical processing of metallic glasses: extending the range of the glassy state, Nature Rev. Mater. 1, 16039 (2016).
3. A. L. Greer and Y. H. Sun, Stored energy in metallic glasses due to strains within the elastic limit, Philos. Mag. 96, 1643 (2016).
4. J. Orava and A. L. Greer, Fast and slow crystal growth kinetics in glass-forming melts, J. Chem. Phys. 140 214504 (2014).
5. A. L. Greer, Nature Mater. 14, 542 (2015).
6. Y. H. Sun, A. Concustell, M. A. Carpenter, J. C. Qiao, A. W. Rayment and A. L. Greer, Flow-induced elastic anisotropy of metallic glasses, Acta Mater. 112, 132 (2016).
More about the Speaker: At the University of Cambridge, Lindsay Greer is Head of the School of the Physical Sciences, and was (2006‒2013) Head of the Department of Materials Science & Metallurgy. He received his MA and PhD degrees from Cambridge, and holds an Honorary Doctorate from AGH University of Science & Technology, Cracow, Poland. He was a NATO Research Fellow and Assistant Professor of Applied Physics at Harvard University, and has held visiting positions at the CEA and INP Grenoble, Washington University (St Louis), and the Universities of Vienna and Turin. He is a Foreign PI of the Advanced Institute for Materials Research, Tohoku University (Sendai, Japan).
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