Effect of the monolayer thickness on the mechanical behavior of layered nanostructure Ni fabricated by electrodeposition

Abstract

Here five kinds of bulk layered nanostructured nickel (LNS Ni) composed of nano-sized grains (NG) layer and ultrafine grains (UFG) layer alternately according to the layer thickness ratio of 1:1 with the layer thickness spacing ranging from nearly 1 μm to 88 nm were prepared by electrodeposition to study the effect of monolayer thickness on the mechanical behavior of LNS Ni. Conventional continuous tension (CT) tests show that these five LNS Nis have greater plastic deformation ability than homogeneous nanostructured (NS) Ni and their mechanical behavior shows an obvious dependence on layer thickness. The strength of LNS Ni shows a linear upward trend with the decrease of layer thickness and furthermore exceeds that of homogeneous NS Ni after the layer thickness is reduced to 300 nm and the plasticity and toughness of LNS Ni decreases first and then increases with the decrease of layer thickness. As a result, an optimized mechanical property with high strength and high plasticity is obtained when the monolayer thickness is reduced to 88 nm. Such monolayer thickness-dependent mechanical behavior for LNS Ni should be attributed to the change of the contribution from interfacial coordinated deformation with the decrease of layer thickness due to the gradual increased proportion of the interface defects that affect dislocation activity. The tensile release and intermittent tension relaxation cycle (TRC) tests also illuminate that such layered structure can also effectively alleviate stress concentration during deformation, which should be another reason for the high plasticity and high toughness that LNS Ni holds.