Abstract
Nanostructured (NS) and ultrafine-grained (UFG) materials have high strength and relatively low ductility. Their toughness has not been comprehensively investigated. Here we report the Charpy impact behavior and the corresponding microstructural evolutions in UFG Cu with equi-axed and elongated grains which were prepared by equal channel angular pressing (ECAP) for 2 and 16 passes at room temperature. It is found that their impact toughness (48 J/cm2) is almost comparable to that of coarse grained (CG) Cu: 55 J/cm2. The high strain rate during the Charpy impact was found to enhance the strain hardening capability of the UFG Cu due to the suppression of dynamic dislocation recovery. The crack in the CG Cu was blunted by dislocation-slip mediated plastic deformation, while the cracks in the UFG Cu were formed at grain boundaries and triple junctions due to their limited plasticity. Near the crack surfaces the elongated grains in ECAP-2 sample were refined by recrystallization, while equi-axed grains in the ECAP-16 sample grew larger.
Highlights
Nanostructured (NS) and ultrafine-grained (UFG) materials have high strength and relatively low ductility
After equal channel angular pressing (ECAP) for 2 passes, the coarse grains were divided into parallel elongated grains with boundaries parallel to {111} trace (Fig. 1b). This result suggests that the elongated boundaries are dislocation (111) slip plane with high density of dislocations and low-angle mis-orientation, which was further verified by selected area electron diffraction (SAED) and Electron Backscattered Diffraction (EBSD) results, as shown in the insets of Fig. 1b and c, respectively
UFG Cu samples were processed by ECAP process for 2 and[16] passes, producing elongated grain structure with low-angle grain boundary (GB) and equi-axed grain structure with high-angle GBs, respectively
Summary
Nanostructured (NS) and ultrafine-grained (UFG) materials have high strength and relatively low ductility. Their toughness has not been comprehensively investigated. We report the Charpy impact behavior and the corresponding microstructural evolutions in UFG Cu with equi-axed and elongated grains which were prepared by equal channel angular pressing (ECAP) for 2 and 16 passes at room temperature. A steel with low alloy contents and UFG elongated grains as well as nanometer-sized carbides was reported to have an impact energy of 226 J, which is significantly higher than that of its conventional CG counterpart (14 J) at room temperature[6,8]. The inset is SAED with a selected area of 5 μm in diameter. (e) Distribution of boundary mis-orientation angles measured using EBSD
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