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Bulk nanostructured metals introduced by severe plastic deformation contain an excess of lattice defects. A nanostructured copper (Cu) processed by a high-pressure torsion technique was examined during in situ heating to investigate microstructural relaxation and quantify the evolution of microstructural parameters using high-energy synchrotron microbeam X-ray diffraction. While general microstructural relaxations, such as recovery, recrystallization, and subsequent grain growth, were observed, the key microstructural parameters, including grain size, microstrain, dislocation density, and thermal expansion coefficient, and their changes at critical temperatures were uniquely described and quantified through diffraction data. Based on this analysis, the stored energies driving thermally activated microstructural changes were estimated for individual defect types — grain boundaries, dislocations, and vacancies — that are expected to significantly influence the relaxation behavior of nanostructured Cu. This study demonstrates the effectiveness of diffraction characterization techniques for gaining a comprehensive understanding of the thermal stability of bulk nanostructured materials. 

Abstract The magnesium alloy AZ31, which has undergone high-pressure torsion processing, was subjected to in situ annealing microbeam synchrotron high-energy X-ray diffraction and compared to the as-received rolled sheet material that was investigated through in situ neutron diffraction. While the latter only exhibits thermal expansion and minor recovery, the nanostructured specimen displays a complex evolution, including recovery, strong recrystallization, phase transformations, and various regimes of grain growth. Nanometer-scale grain sizes, determined using Williamson–Hall analysis, exhibit seamless growth, aligning with the transition to larger grains, as assessed through the occupancy of single-grain reflections on the diffraction rings. The study uncovers strain anomalies resulting from thermal expansion, segregation of Al atoms, and the kinetics of vacancy creation and annihilation. Notably, a substantial number of excess vacancies were generated through high-pressure torsion and maintained for driving the recrystallization and forming highly activated volumes for diffusion and phase precipitation during heating. The unsystematic scatter observed in the Williamson–Hall plot indicates high dislocation densities following severe plastic deformation, which significantly decrease during recrystallization. Subsequently, dislocations reappear during grain growth, likely in response to torque gradients in larger grains. It is worth noting that the characteristics of unsystematic scatter differ for dislocations created at high and low temperatures, underscoring the strong temperature dependence of slip system activation. Graphical Abstract 

The cold angular rolling process (CARP) is being developed as a continuous severe plastic deformation technique, which can process metal sheets without any length limitations at room temperature. CARP contains cold rolling and equal‐channel angular process components. The sheet thickness is kept consistent before and after CARP, allowing multiple passes of the sheet. The desired microstructure and mechanical properties can be achieved in the processed metallic sheets. The current study is aimed to evaluate the capability of CARP by processing copper sheets with different sheet widths for repetitive passes. The CARP‐treated sheets are examined by lab‐scale X‐ray and high‐energy synchrotron X‐ray diffraction to investigate the evolution in dislocation density, texture, and strain anisotropy, and by tensile testing to identify the bulk mechanical properties. The digital image correlation method is applied to tensile testing so that strain localization within the sample gauge is visualized and deformation behavior is evaluated after yielding till postnecking by estimating the hardening exponent and strain hardening rate of the CARP‐treated sheet. Comparing the reported continuous and multiple‐step processes on Cu and its alloys, the present study confirms that the CARP is potentially a useful sheet process for strengthening ductile metals.