Abstract
This manuscript is based on an oral contribution to the TMS 2020 annual meeting and is dedicated to Prof. Peter Liaw, who for decades has shown great interest in serrated plastic flow. Here we will focus on the case of bulk metallic glasses, and begin with briefly summarizing some aspects of serrated and non-serrated inhomogeneous flow—a phenomenon that has perplexed materials scientists for decades. Four directions of research are identified that emerged out of the desire to fundamentally understand the intermittent inhomogeneous flow response. These research directions gear away from the phenomenological stress–strain behavior but put the underlying shear defect into focus. Unsolved problems and future research topics are discussed.
Highlights
Kimura and Masumoto recognized that the appearance of plastic flow in bulk metallic glasses (BMGs) at low homologous temperatures can be either smooth or intermittent, depending on the applied deformation rate and/or deformation temperature
Since an aspect-ratio reduction of a malleable BMG constitutes the extreme case of shear-band interaction due to an insufficient distance between free surfaces for unconstrained system-spanning shear-band formation, one may have expected a power-law scaling if the introduction of inhomogeneous stress fields is the sole factor determining the serration statistics
This manuscript discusses four research directions that go beyond the stress–strain signature of serrated flow in BMGs
Summary
IN the early two thousands, the topic of serrated versus non-serrated flow in bulk metallic glasses (BMGs) experienced a second wave of interest following the remarkable initial work by Kimura and Masumoto presented more than 20 years earlier.[1,2,3] Kimura and Masumoto recognized that the appearance of plastic flow in BMGs at low homologous temperatures (the inhomogeneous deformation regime) can be either smooth or intermittent, depending on the applied deformation rate and/or deformation temperature. We pursued this route and began to trace the time-resolved shear-band dynamics across temperature and various metallic glass alloys.[20,21,22] One of the central outcomes of this effort was that the logarithm of the average shear-band velocity, as derived from a simple linearization of the underlying displacement jump and by adopting a shear-displacement jump mechanism, scaled linearly when graphed vs 1=T This represented nothing else than the two decades earlier mapped transition between serrated and non-serrated flow by Kimura and Masumoto. The body of literature on serrated flow continues to grow for metallic glasses, and finds renewed interested in the novel area of multi-principle element alloys.[28,29,30] In contrast, our own continued efforts departed from the stress–strain signature of serrated flow, targeting fundamentals of strain localization in metallic glasses, some of which are contained in the following subsections that are organized according to the identified research areas A to D
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