Mild-to-wild plastic transition is governed by athermal screw dislocation slip in bcc Nb

Plastic deformation in crystals is mediated by the motion of line defects known as dislocations. For decades, dislocation activity has been treated as a homogeneous, smooth continuous process. However, it is now recognized that plasticity can be determined by long-range correlated and intermittent collective dislocation processes, known as avalanches. Here we demonstrate in body-centered cubic Nb how the long-range and scale-free dynamics at room temperature are progressively quenched out with decreasing temperature, eventually revealing intermittency with a characteristic length scale that approaches the Burgers vector itself. Plasticity is shown to be bimodal across the studied temperature regime, with conventional thermally-activated smooth plastic flow ('mild') coexisting with sporadic bursts ('wild') controlled by athermal screw dislocation activity, thereby violating the classical notion of temperature-dependent screw dislocation motion at low temperatures. An abrupt increase of the athermal avalanche component is identified at the critical temperature of the material. Our results indicate that plasticity at any scale can be understood in terms of the coexistence of these mild and wild modes of deformation, which could help design better alloys by suppressing one of the two modes in desired temperature windows. Recent studies have recognized that plasticity in metals can be controlled by dislocation avalanches. Here the authors examine temperature-dependent microplasticity in bcc Nb and reveal the dominance of athermal screw dislocation activity during intermittent slip.

Automated summary

Plastic deformation in crystals is mediated by the motion of line defects known as dislocations. The conventional understanding of plasticity as a homogeneous process has been challenged by the discovery of long-range correlated and intermittent collective dislocation processes, termed avalanches. In this study, the authors investigate the temperature-dependent microplasticity in body-centered cubic Nb and reveal the dominance of athermal screw dislocation activity during intermittent slip. The results suggest that plasticity can be understood in terms of the coexistence of mild and wild modes of deformation, providing insights for the design of better alloys.