Multilayered structure control for obtaining electrodeposited nanocrystalline iron–nickel alloy with high strength and ductility

Abstract

This study investigated the effect of a multilayered structure on the strength and ductility of a nanocrystalline iron (Fe)–nickel (Ni) alloy, in which an Fe–46 mass% Ni (non-Invar alloy) layer and an Fe–34 mass% Ni (Invar alloy) layer were alternately electrodeposited. The tensile strength of the multilayered nanocrystalline Fe–Ni alloy increased with decrease in the Invar alloy layer thickness ranging from 3.2 to 11.0 µm, following a Hall–Petch-type relationship. The tensile strength discontinuously decreased when the Invar alloy layer thickness decreased to less than 2.6 µm. By contrast, the elongation of the specimens increased with decrease in the Invar alloy layer thickness ranging from 2.6 to 1.5 µm. A specimen showing a high tensile strength of approximately 2 GPa and a high elongation of 15% was produced by the multilayering control of the Invar alloy layer thickness. The measurements of the chemical composition distribution and phase structure change near the interphase boundary revealed that the Ni content gradient layer was formed between the interphase boundaries and the next electrodeposited layer with a thickness of 2 µm. The strengthening mechanism and ductility improvement in the nanocrystalline Fe–Ni alloy by multilayering are discussed herein from the viewpoint of deformation restraint by the gradient layer in the Invar and non-Invar alloy layers via the interphase boundaries.