Observing formation and evolution of dislocation cells during plastic deformation

TL;DR

This study uses X-ray diffraction microscopy to visualize the formation and evolution of dislocation cells in aluminium during tensile deformation, revealing stochastic, isotropic processes and distribution patterns that inform dislocation dynamics modeling.

Contribution

It provides the first direct visualization of dislocation cell formation and evolution in bulk metal deformation, revealing stochastic processes and distribution patterns.

Findings

Cells form at 1% strain in a stochastic, isotropic manner.

Cell size and dislocation density follow log-normal and bi-modal Gaussian distributions.

Results support universal stochastic multiplicative processes in dislocation evolution.

Abstract

During plastic deformation of metals and alloys, dislocations self-organise in cells, which subsequently continuously decrease in size. How and when these processes take place has remained elusive, because observations of the structural dynamics in the bulk have not been feasible. We here present X-ray diffraction microscopy movies of the structural evolution during tensile deformation of a mm-sized aluminium (111) single crystal. The formation and subsequent development of 40,000 cells are visualised. We reveal that cells form in a stochastic and isotropic manner already at 1% strain. We show that the cell size and dislocation density distributions are log-normal and bi-modal Gaussian distributions, respectively, throughout. This insight leads to an interpretation of the formation and evolution steps in terms of universal stochastic multiplicative processes. This work will guide dislocation dynamics modelling, as it provides unique results on cell formation.