3D Microstructural and Strain Evolution During the Early Stages of Tensile Deformation

TL;DR

This study uses advanced 3D imaging to observe early dislocation patterning in aluminum crystals during tensile deformation, revealing the evolution of dislocation boundaries and strain distribution at micro scales.

Contribution

It provides the first detailed 3D visualization of dislocation boundary evolution and strain fields during initial plastic deformation in single crystals.

Findings

Dislocation boundaries appear as planar structures at low strains.

Checkerboard patterning of boundaries emerges at higher strains.

Strain fluctuations occur at the microscale with average domain size of 3 μm.

Abstract

Dislocation patterning and self-organization during plastic deformation are associated with work hardening, but the exact mechanisms remain elusive. This is partly because studies of the structure and local strain during the initial stages of plastic deformation has been a challenge. Here we use Dark Field X-ray Microscopy to generate 3D maps of embedded $350 \times 900 \times 72 \,\mu\mathrm{m}^3$ volumes within three pure Al single crystals, all oriented for double slip on the primary and conjugate slip systems. These were tensile deformed by 0.6$\%$, 1.7$\%$ and 3.6$\%$, respectively. Orientation maps revealed the existence of two distinct types of planar dislocation boundaries both at 0.6$\%$ and 1.7$\%$ but no systematic patterning. At 3.6$\%$, these boundaries have evolved into a well-defined checkerboard pattern, characteristic of Geometrically Necessary Boundaries, GNBs. The GNB spacing is $\approx$ 14 $\mu$m and the misorientation $\approx$ 0.2{\deg}, in fair agreement with those at higher strains. By contrast to the sharp boundaries observed at higher strains, the boundaries are associated with a sinusoidal orientation gradient. Maps of the elastic strain along the (111) direction exhibit fluctuations of $\pm 0.0002 $ with an average domain size of 3 $\mu$m.