Processing of metals through the application of severe plastic deformation (SPD) is currently receiving much attention because it has the potential to refine the grain size to submicrometer or nanometer levels.[1] These ultrafine-grained materials have high strength through the Hall-Petch relationship but in practice their utility is generally restricted because they exhibit only limited ductility. [2] There is indirect evidence suggesting that grain-boundary sliding may occur more easily in metals processed by SPD and this may give high strength and a reasonable level of tensile ductility. [2][3][4][5] Here we report a direct demonstration of the occurrence of grain-boundary sliding in pure aluminum after SPD processing. Using high purity COMMUNICATIONS 34
The effect of Mg addition on the microstructural evolution and mechanical properties of high-purity aluminum was studied over a wide range of strain, up to ∼8. The high strains were achieved by applying the equal-channel angular pressing technique. The stress-strain relationship was related to the evolution of the microstructure investigated by transmission electron microscopy and X-ray diffraction peak profile analysis. In the early stages of plastic deformation the interaction between the dislocations and the Mg solute atoms results in an increase of the flow stress with temperature. The stable microstructure is developed at higher strains owing to the Mg addition resulting in the saturation of the proof stress at higher strains in Al-Mg alloys.
The microstructural and mechanical properties of an ultrafine-grained (UFG) Al-Zn alloy processed by high-pressure torsion (HPT) are investigated using depth-sensing indentations, focused ion beam, scanning electron microscopy and scanning transmission electron microscopy. Emphasis is placed on the microstructure and the effects of grain boundaries at room temperature. The experiments show the formation of Zn-rich layers at the Al/Al grain boundaries that enhance the role of grain boundary sliding leading to unique plastic behavior in this UFG material. The occurrence of significant grain boundary sliding at room temperature is demonstrated by deforming micro-pillars. Our results illustrate a potential for using UFG materials as advanced functional materials in electronic microdevices.
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