Abstract
Nanolaminated structure with an average boundary spacing of 67 nm has been fabricated in copper by high-rate shear deformation at ambient temperature. The nanolaminated structure with an increased fraction of low angle grain boundaries exhibits a high microhardness of 2.1 GPa. The structure coarsening temperature is 180 K higher than that of its equiaxial nanograined counterpart. Formation of nanolaminated structure provides an alternative way to relax grain boundaries and to stabilize nanostructured metals with medium to low stacking faults energies besides activation of partial dislocations.
Highlights
Formation of laminated structure in nanoscale with low angle grain boundaries (GBs) provides an effective way to stabilize nanostructured metals and to achieve extraordinary grain refinement
Structure in Ni can be refined to a length scale as small as 20 nm [1], which is one order magnitude below the saturated grain size induced by traditional plastic deformations [2,3,4]
Extraordinary grain refinement and/or enhanced thermal stability has been achieved through the formation of NL structure in other metals or alloys with high stacking faults energies (SFE) such as pure Al [5], interstitial-free steel [6,7], Al-Cu [8,9] and Al alloy 5052 [10]
Summary
Formation of laminated structure in nanoscale (boundary spacing < 100 nm) with low angle grain boundaries (GBs) provides an effective way to stabilize nanostructured metals and to achieve extraordinary grain refinement. Even though the detailed mechanism remains ambiguous, formation of NL structure can be attributed to extensive dislocation activities during plastic deformation with high strain rates and strain gradients [5,9,11,12], where large amount of geometrically necessary dislocations (GNDs) would be generated and line up as laminated boundaries to accommodate increasing number of dislocations [4,13], forming laminated structure in nanoscale For those metals or alloys with medium to low SFE, pure Cu for example, NL structure can hardly be detected except for the localized regions in the shear bands [14]
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