Temperature-activated dislocation avalanches signaling brittle-to-ductile transition in BCC micropillars

TL;DR

This study investigates the temperature-dependent transition from brittle to ductile behavior in tungsten micropillars, revealing a shift from uncorrelated dislocation activity to self-organized criticality as temperature increases.

Contribution

It combines in-situ experiments and simulations to elucidate the dislocation dynamics underlying the brittle-to-ductile transition in BCC metals.

Findings

Low-temperature deformation is smooth with uncorrelated dislocation activity.

High-temperature deformation shows correlated stress fluctuations and slip band formation.

The transition involves thermally activated surface nucleation processes.

Abstract

We carry out strain-controlled in-situ compression experiments of micron-sized tungsten (W) micropillars in the temperature range 300-900 K, together with simulations of three-dimensional discrete dislocation dynamics (DDD) at the same scale. Two distinct regimes are observed. At low temperatures, plastic deformation appears smooth, both temporally and spatially. Stress fluctuations are consistent with a Wiener stochastic process resulting from uncorrelated dislocation activity within the pillars. However, high-temperature stress fluctuations are highly correlated and exhibit features of self-organized criticality (SOC), with deformation located within well-defined slip bands. The high-temperature stress relaxation statistics are consistent with a thermally activated nucleation process from the surface. The nature of the transition between the two regimes is a manifestation of the brittle to ductile transition in BCC metals.