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Severe plastic deformation (SPD) has been known for decades to provide microstructural refinement under a hydrostatic stress state by introducing a tremendous quantity of lattice defects, including vacancies, dislocations, and grain boundaries, leading to enhanced mechanical properties. Many SPD processes have been well studied and utilized for the processing of ultrafine-grained (UFG) metals and materials. One major challenge with SPD-processed UFG materials is their limited applicability, primarily due to their microstructural stability at elevated temperatures and the difficulty of scaling up to larger sizes or volumes. To first understand the thermal stability of UFG material, a copper prepared by high-pressure torsion, a technique that can achieve true nano-scale grains in bulk samples, was evaluated using two novel in situ techniques of micro-beam high-energy synchrotron X-ray diffraction. These are, namely, monochromatic X-ray beams that yield changes in microstructure with time and temperature, and a polychromatic X-ray beam that determines grain reorientation behavior during microstructural relaxation. Furthermore, a new processing technique named cold angular rolling process (CARP) demonstrated some promise as an SPD technique for producing theoretically unlimited lengths of strength-enhanced copper sheets at room temperature with a relatively low energy consumption. Additional miniature tensile testing incorporating digital image correlation (DIC) method and microstructural analysis utilizing high-energy X-ray diffraction determined the influence of CARP having higher shear strain hardening in comparison with other established techniques. This study highlights the significance of lattice-defect influenced mechanical properties and microstructure of UFG obtained across multi-length scales and volumes, which are critical for guiding the control and scalable production of advanced materials for commercialization. 

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. 

Al-Mg alloy disks were produced from Mg sandwiched between Al through 100 turns of high-pressure torsion (HPT) at 6.0 GPa at room temperature, resulting in high microhardness of Hv 300–350 in regions experiencing a nominal shear strain >  ~ 390. While compositional mapping using scanning electron microscopy energy-dispersive spectroscopy (EDS) showed a uniform distribution of Mg through the disk thickness at 1.5 mm and 3.0 mm from the disk center, transmission electron microscopy EDS showed a heterogeneous distribution of Mg remained on the nanoscale. Although HPT induces enough mixing to result in face-center-cubic Al with supersaturations of Mg of up to ~ 20 at.% near the disk surfaces, β-Al3Mg2, γ-Al12Mg17 and Al2Mg intermetallic phases were identified by electron diffraction throughout the disk thickness even in regions experiencing high shear strain. This study visually captures detailed compositional heterogeneity throughout the sample thickness following intense mechanical alloying, nanoscale re-structuring and phase transformations. 

Solid‐state welding of Al 1043 sheets is achieved via high‐pressure torsion (HPT) processing to produce bulk nanostructured Al disks. A homogeneous nanostructure without segregation is observed, with grain sizes of ≈430–470 nm. Miniature tensile testing, coupled with the digital image correlation (DIC) technique, is employed to determine the room‐temperature tensile deformation behavior, particularly the nonuniform behavior with necking, of the HPT‐bonded ultrafine‐grained (UFG) aluminum, comparing it with annealed coarse‐grained counterpart. The HPT‐bonded UFG Al exhibits a large fraction of post‐necking strain, which is supported by the estimated high strain rate sensitivity value ofm = 0.085, suggesting the delay of local necking leading to tensile fracture. Detailed DIC analysis reveals prolonged diffuse necking, thus delaying local necking, in the HPT‐bonded UFG Al, while the annealed samples show high fractions of local necking during the nonuniform deformation. Moreover, the DIC data illustrate that local necking predominantly occurred at a limited neck zone, maintaining a plateau strain distribution at the out‐of‐neck zone throughout necking deformation toward tensile failure for both annealed and UFG aluminum. The DIC method offers an alternative means to demonstrate the transition in necking behaviors of materials by estimating the plastic lateral contraction exponent. 

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.