Microstructural evolution and mechanical properties of nanostructured Cu/Ni multilayer fabricated by accumulative roll bonding

Abstract

In this paper, nanostructured multilayer with overall composition of Cu53Ni47 was fabricated by means of accumulative roll bonding (ARB) of pure Cu and Ni metal strips. In the first four ARB cycles, the thickness reduction of the Cu layer was slow and twin boundaries were formed. Necking and fracture of the harder Ni layer happened and the Ni island-like areas were therefore formed. After four ARB cycles, the thickness of both Cu and Ni single layers became homogeneous and finally the single layer thickness less than 100 nm was formed after seven ARB cycles, corresponding to an equivalent strain of 11.11. 3DAP element concentration analysis confirmed that Cu–Ni solid solution was formed due to the inter-diffusion of the constituent elements across the interface, which increased the bonding strength of the adjacent layers. Tensile tests revealed that the ultimate tensile strength of the multilayer was up to 950 MPa, which is approximately five times higher than that of the initial pure Cu metal. For all the tensile specimens with various ARB cycles, debonding of the layer interface formed during the last ARB cycle was observed. The plastic strain first increased to a maximum value of 9.1% after four ARB cycles due to the homogenization of deformation between Cu and Ni single layer. Then the plastic strain decreased to about 4.6% after seven ARB cycles due to the formation of nanoscale microstructure.