Abstract
The onset of plastic yielding has been studied in samples of aluminum with near-micrometer average grain size using in situ tensile loading combined with synchrotron radiation. A white-beam Laue 3D micro-diffraction technique was used allowing the collection of diffraction signal from a volume with a resolution of 1 μm in all three dimensions. The orientation data obtained from the micro-diffraction are used to estimate the local variation in geometrically necessary dislocation density, and correction factors are suggested for voxels where neighbors are missing in either one or two dimensions. The results demonstrate a considerable heterogeneity in deformation in the early stages of plastic deformation.
Highlights
The process by which a polycrystalline metal undergoes plastic yielding, i.e. the transition from elastic to plastic behavior, is of fundamental importance for the understanding of mechanical properties, and yet there are many aspects of this transition that are still only poorly understood [1,2]
An alternative parameter that can be used is the geometrically necessary dislocation (GND) density [7,8]. This is not a direct measure of local plastic strain, increases in the GND density at a very low strain are a clear indicator of the transition from elastic to plastic deformation
The lattice orientation measurement at each voxel can further be used to determine the GND density using either a simple approach based on local kernel average misorientation [14], or a more detailed approach where all dislocations present can be described by the local dislocation density tensor iel l xk where ε is the Levi-Civita symbol, βiell is the elastic distortion tensor, which is the sum of the elastic strain tensor εiell and the lattice rotation tensor il = −òilm m
Summary
The process by which a polycrystalline metal undergoes plastic yielding, i.e. the transition from elastic to plastic behavior, is of fundamental importance for the understanding of mechanical properties, and yet there are many aspects of this transition that are still only poorly understood [1,2]. The GND density is calculated from local lattice curvature [7,8] and requires spatially resolved measurements of lattice orientation.
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