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This work presents a multi-scale microstructural characterization of aluminum alloys processed by high-pressure torsion (HPT) and cold angular rolling process (CARP) to improve their mechanical properties. Mechanical properties such as microhardness and tensile strength were correlated with microstructural features. To understand the processing-structure-property relationships, characterization methods spanning nano- to millimeter scales were used, including X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) EDS. TEM and STEM EDS were used to show that HPT of a Mg sheet sandwiched between Al sheets successfully produced a supersaturated solid solution (SSSS) of Mg in Al and several Al-Mg intermetallic phases, leading to significant grain refinement and increases in microhardness over pure Al. Although CARP has potential to induce the severe plastic deformation (SPD), the CARP system used in this work was not able to achieve SPD aluminum alloys. However, SEM EBSD characterization shows that CARP achieves an increase of the low-angle grain boundaries (LAGBs) and geometrically necessary dislocation (GND) density in Al-1043,which improves the mechanical properties. Moreover, a preliminary study was conducted on CAPR processed Al-6061 alloys to understand the synergistic effects precipitation and CARP-processing on the microstructure and properties. This research provides the critical insights into the capabilities and current limitations of CARP as a continuous SPD technique for aluminum alloys, and demonstrate the importance of integrated multi-scale characterization in understanding advanced materials processing.
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This content will become publicly available on May 30, 2026
Advanced Characterization and Scalability of Severe Plastic Deformation Processes in Bulk Ultra-fined Grained Material
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.
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- Award ID(s):
- 2051205
- PAR ID:
- 10643563
- Publisher / Repository:
- Oregon State University
- Date Published:
- Format(s):
- Medium: X
- Institution:
- Oregon State University
- Sponsoring Org:
- National Science Foundation
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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.more » « less
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