High temperature strength retention of Cu/Nb nanolaminates through dynamic strain ageing

Abstract

The mechanical properties of Cu/Nb metallic nanolaminates with different layer thickness (7, 16, 34 and 63 nm) were studied by means of micropillar compression tests from room temperature to 400 • C. Both strain-rate jump and constant strain rate tests were carried out and they showed evidence of dynamic strain ageing in the nanolaminates with 7, 16 and 34 nm layer thickness deformed at 200 • C. Dynamic strain ageing was accompanied by a reduction of the strain rate sensitivity to 0, high strength retention at 200 • C and the development of shear localization of the deformation at low strains (5%-6%) that took place along the Nb layers in the nanolaminates. Atom probe tomography of the deformed specimens revealed the presence of O in solid solution in the Nb layers but not in the Cu layers. Thus, diffusion of O atoms to the mobile dislocations in Nb was found to be the origin of the dynamic strain ageing in the Cu/Nb nanolaminates around 200 • C. This mechanism was not found at higher temperature (400 • C) because deformation was mainly controlled by stress-assisted diffusion in the Cu layers. This discovery shows a novel strategy to enhance the strength retention at high temperature of metallic nanolaminates through dynamic strain ageing of one the phases.

Crystallographic Anisotropy Dependence of Interfacial Sliding Phenomenon in a Cu(16)/Nb(16) ARB (Accumulated Rolling Bonding) Nanolaminate

“…Nanolaminates are studied both theoretically and experimentally on the virtue of their unique properties such as high strength [ 1 , 2 ], high fracture toughness [ 3 , 4 , 5 ], extreme deformability [ 3 , 6 , 7 ], shock resistance [ 8 ], electrical conductivity [ 9 ], high temperature strength retention [ 10 ], high-temperature creep [ 11 ] and high resistance to radiation damage [ 12 ]. These nanolaminates have been used for radiation damage protection [ 13 ], and potential applications include hybrid diffusive–displacive helium outgassing [ 14 ] and structural materials [ 10 , 13 ]. These nanolaminates typically do not follow the rule of mixtures, i.e., the volume fraction of each component does not determine their properties, but rather their individual layer thickness and interfacial structure [ 15 , 16 ].…”

Texture Evolution and Nanohardness in Cu-Nb Composite Wires

“…Over the past two decades, Cu-Nb microcomposites have been widely used in defense, aerospace, and magnetic applications for their excellent combination of mechanical properties, high conductivity, and thermal stability [1][2][3][4]. Several techniques have been used to fabricate these materials, including accumulative drawing and bonding (ADB) [5,6], melt and deform [7,8], accumulative roll bonding (ARB) [9][10][11], and magnetron sputtering [12,13]. Compared with other techniques, the ADB process enables the production of Cu-Nb microcomposite wires more than 100 m in length [14].…”