Size-dependent deformation mechanisms and strain-rate sensitivity in nanostructured Cu/X (X = Cr, Zr) multilayer films

摘要: Abstract Hardness, activation volume and strain-rate sensitivity of Cu/Cr (face-centered cubic (fcc)/body-centered cubic) Cu/Zr (fcc/hexagonal close-packed) nanostructured multilayer films have been systematically measured as a function modulation period (L) ratio (η), respectively. Significant size effects were found for all the three plastic deformation characteristics, i.e. enhanced hardness but reduced with decreasing dimension length L. Microstructure evolution was statistically examined to rationalize these dependences. It crucially observed that abundant nanotwins existed in Cu grains, though nanotwin formation depressed smaller This inverse size-dependent is responsible reduction sensitivity, because negative effect induced by decreased predominates over positive coming from raised interfaces/boundaries. A mechanistic model modified account interface well effect, which yields calculations broad agreement experimental results when L larger than about 20 nm. Below this critical size, there are discrepancies between results, due change mechanism dislocation nucleation/slip confined layers crossing interfaces. layer slip also considering strengthening quantitatively describe L-dependent hardness. In addition, constituent phases their relative content on NMFs discussed regard variation η.