Investigation of reversible plasticity in a micron-sized, single crystalline copper bending beam by X-ray μLaue diffraction

Abstract

The observed mechanical behaviour of micron-sized samples raises fundamental questions about the influence of size on the underlying dislocation plasticity. In situ µLaue diffraction on a single crystalline copper bending beam was performed to study the feasibility of bending tests and their contribution to our understanding of size-dependent dislocation plasticity. Theoretical considerations lead to a minimum sample size where in situ µLaue experiments are useable. A critical size is evidenced below which, depending on Young's modulus and maximum stress, the elastic and plastic contributions to the lattice curvature cannot be separated. The experiment shows the increase in geometrically necessary dislocations during plastic deformation followed by a decrease during unloading. This can be explained by the formation and dissolution of a dislocation pile-up at the neutral axis of the bending cantilever. The dissolution of the dislocation pile-up is caused by the back stress of the pile-up and a direct observation of the Bauschinger effect, which is consistent with the non-purely elastic mechanical behaviour when unloading the sample.

Keywords:

• dislocation
• pile-up
• Bauschinger effect
• size effect
• Laue microdiffraction

Notes

Notes

1. Movement of the proved volume due to cantilever deflection can be neglected. The huge bending length, the small displacement of each loading sequence and the small distance to the fixation point leads to negligible movement of the primary synchrotron beam perpendicular to the neutral axis. Typically, the shift is less than 100 nm, which equals 10% of the synchrotron beam diameter.

2. Monochromatic beam experiments would be necessary to clarify if the totally stored dislocation density changed slightly, which is currently impossible during in situ deformation.