Disordered long-range internal stresses in deformed copper and the mechanisms underlying plastic deformation

The strength of wavy glide metals increases dramatically during deformation as dislocations multiply and entangle, forming dense dislocation wall structures. Numerous competing models have been proposed for this process but experimental validation and guidance for further model development require new experimental approaches capable of resolving local stresses within the dislocation microstructure. We use three-dimensional X-ray microscopy combining submicrometer spatial resolution with diffracted-beam masking to make direct measurements of axial elastic strain (and thus stress) in individual dislocation cell walls and their adjacent cell interiors in heavily deformed copper. These spatially resolved measurements show broad, asymmetric distributions of dipolar stresses that directly discriminate between long-standing deformation models and demonstrate that the distribution of local stresses is statistically connected to the global behavior through simple rules.

► Axial elastic strains were measured from numerous individual, contiguous dislocation cell walls and cell interiors.
► The mean stresses for the cell walls and cell interiors were of opposite sign, in agreement with theoretical predictions.
► The separation between the mean cell wall and cell interior stresses was about 20% of the flow stress.
► Broad distributions of dipolar stresses were observed that are consistent with a simple size-scaling model.