Two-Step SPD Processing of a Trimodal Al-Based Nano-Composite
An ultrafine-grained (UFG) aluminum nano-composite was fabricated using two severe plastic deformation steps: cryomilling of powders (and subsequent consolidation of blended powders by forging) followed by high-pressure torsion (HPT). The forged bulk composite featured a trimodal structure comprised of UFG, coarse grain (CG) regions, and ceramic particles. The additional HPT processing introduced finer grain sizes and altered the morphology and spatial distribution of the ductile CG regions. As a result, both strength and ductility increased substantially compared to those of the Al nano-composite prior to HPT. The increases were attributed to the more optimal shape and spacing of the CG regions which promoted uniform elongation and yielding during tensile loading. Microstructural changes were characterized at each processing step to establish the evolution of microstructure and to elucidate structure-property relationships. The toughening effect of the CG regions was documented via fracture analysis, providing a potential strategy for designing microstructures with enhanced strength and toughness.
KeywordsSevere Plastic Deformation Coarse Grain Severe Plastic Deformation Processing Kikuchi Pattern Severe Plastic Deformation Technique
The authors gratefully acknowledge M. Mecklenburg for his help in TEM. The images and data used in this article were generated at the Center for Electron Microscopy and Microanalysis (CEMMA), University of Southern California. The authors wish to acknowledge financial support provided by the Office of Naval Research under the guidance of Rod Peterson and Bill Golumbfskie (ONR Contract N00014-12-C-0241), the National Science Foundation of the United States under Grant No. DMR-1160966, and the European Research Council under ERC Grant Agreement No. 267464-SPDMETALS.
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