Fluctuations in crystalline plasticity

Abstract

Recently acoustic signature of dislocation avalanches in HCP materials was found to be long tailed in size and energy, suggesting critical dynamics. Moreover, the intermittent plastic response was found to be generic for micro-and nano-sized systems independently of their crystallographic symmetry. These rather remarkable discoveries are reviewed in this paper in the perspective of the recent studies performed in our group. We discuss the physical origin and the scaling properties of plastic fluctuations and address the nature of their dependence on crystalline symmetry, system size, and disorder content. A particular emphasis is placed on the formation of dislocation structures, and on our ability to temper plastic fluctuations by alloying. We also discuss the "smaller is wilder" size effect that culminates in a paradoxical crack-free brittle behavior of very small, initially dislocation free crystals. We argue that the implied transition between different rheological behaviors is regulated by the ratio of length scales R = L/l , where L is the system size and l is the internal length. We link this size effect with size dependence of strength ("smaller is stronger") and the size-induced switch between different hardening mechanisms. We show that the task of taming the intermittency of plastic flow at ultra-small scales can be accomplished by generating tailored quenched disorder which allows one to control micro-and nano-forming and opens new perspectives in micro-metallurgy and structural engineering of miniature load-carrying elements. These insights were beyond the reach of conventional theoretical approaches that do not explicitly account for the stochastic nature of collective dislocation dynamics.

Statističke analogije između potresa, mikropotresa u metalima i lavina u 1D Burridge-Knopoff modelu

“…According to earlier investigations, fluctuations related to sudden local strain bursts undergo a so-called wild-to-mild transition depending on the sample size (Weiss et al, 2015). Even single crystalline metals are characterized by a length-scale due to internal mechanisms such as interactions between dislocations and solute atoms (Weiss et al, 2021;Zhang et al, 2017), which act like motion barriers for dislocation movement, restricting the dissipated energy and number of produced acoustic signals. Specimens smaller than this scale exhibit scale-free fluctuations reminiscent to critical phenomena (wild regime), whereas in larger samples these fluctuations become weak/subcritical (mild regime).…”

Dynamic Length Scale and Weakest Link Behavior in Crystal Plasticity

“…On the one hand, materials with HCP structure where practically single slip deformation takes place exhibit large, scalefree fluctuations [8][9][10]. On the other hand, upon the addition of solute atoms or changing the lattice structure to FCC or BCC fluctuations get bounded or may even disappear [23,24]. The reason for this behavior may be that, broadly speaking, the 1/r-type interaction of dislocations results a scale-free system whereas the introduction of short-range effects brings in a length-scale that also affects the critical dynamics.…”

Foreword: Plasticity and Solid State Physics

“…Several contributions in this volume report decisive advances in this field. A long-neglected aspect of the analysis of plasticity phenomena is the intermittency of plastic deformation, which results in fluctuations associated with dislocation avalanches and indicates critical dynamics, as discussed by Weiss et al [13]. This essential feature can be captured using the Landau-type mesoscopic continuum plasticity theory proposed by Salman et al [14].…”