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Materials Science and Engineering Seminar

Event Type
Department of Materials Science and Engineering
280 F. Seitz Materials Research Laboratory
Feb 24, 2014   8:30 am  
Robert Maass, Institute for Materials Physics, Georg-August University, Gottingen, Germany
Originating Calendar
MatSE Seminars

"Fast and Furious: Shear band dynamics in metallic glasses" - Bulk metallic glasses (BMG) are known to deform via shear localization and structural softening. This mode of deformation results in a quasi-brittle failure and undercuts their potential for engineering solutions. Shear-localization is confined to the nm-scale and results in intermittent flow that has very short

operating timescales. With the aim of improving room temperature malleability of BMGs, this talk focuses on understanding and eventually controlling shear-band dynamics. Shear-band dynamics will be divided into an initiation, propagation, and arrest phase, each providing insights on the fundamental mechanisms at play. It will be shown that i) shear-band initiation is a dilatational process reaching a volume expansion similar to values attained near the glass transition temperature [Phys. Rev. Lett. 107, 185502 (2011)], and ii) that the transition between serrated and non-serrated flow is directly linked to the propagation velocity of shear-bands [Acta.Mater. 59, 3205, (2009)]. Subsequently, the question “Why do shear-bands stop?” will be addressed in detail, and discussed on the basis of stop-and-go experiments. Here, time- and temperaturedependent stress decays and stress overshoots are observed. The view of an activated shear band being a shear-softened planar layer is adapted, and the findings are discussed with respect to stick-slip phenomena that arise in boundary lubrication processes of nanoscopically confined liquids. This framework provides access to characteristic time scales, which are in agreement with those obtained in earlier work on shearband propagation kinetics, and reveals first insights into how shear-bands arrest during inhomogeneous plastic flow [Appl. Phys. Lett. 100, 071904 (2012)].

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