Synchrotron X-Ray Microbeam Diffraction Measurements of Full Elastic Long Range Internal Strain and Stress Tensors in Commercial-Purity Aluminum Processed by Multiple Passes of Equal-Channel Angular Pressing.

Synchrotron X-ray microbeam diffraction was used to measure the full elastic long range internal strain and stress tensors of low dislocation density regions within the submicrometer grain/subgrain structure of equal-channel angular pressed (ECAP) AA1050 after 1, 2, and 8 passes. This is the first time that full tensors were measured in plastically deformed metals at this length scale. This work supplements previous studies that measured long range internal stresses (LRIS) in ECAP AA1050 of multiple passes, but only for a single direction. The maximum (most tensile or least compressive) principal elastic strain directions for the unloaded 1 pass sample for the grain/subgrain interiors align well with the pressing direction, and are more random for the 2 and 8 pass samples. The measurements reported here indicate that the local stresses and strains become increasingly isotropic (homogenized) with increasing ECAP passes using route BC. The average maximum (in magnitude) LRISs are -0.43 σa for 1 pass, -0.44 σa for 2 pass, and 0.14 σa for the 8 pass sample. These LRISs appear to be larger than LRISs reported by previous works (using single reflection measurements).

X-ray microbeam measurements of individual dislocation cell elastic strains in deformed single-crystal copper.

The distribution of elastic strains (and thus stresses) at the submicrometre length scale within deformed metal single crystals has remarkably broad implications for our understanding of important physical phenomena. These include the evolution of the complex dislocation structures that govern mechanical behaviour within individual grains, the transport of dislocations through such structures, changes in mechanical properties that occur during reverse loading (for example, sheet-metal forming and fatigue), and the analyses of diffraction line profiles for microstructural studies of these phenomena. We present the first direct, spatially resolved measurements of the elastic strains within individual dislocation cells in copper single crystals deformed in tension and compression along <001> axes. Broad distributions of elastic strains are found, with important implications for theories of dislocation structure evolution, dislocation transport, and the extraction of dislocation parameters from X-ray line profiles.