Multilayering process of electrodeposited nanocrystalline iron-nickel alloys for further strengthening

Effect of multilayering on the tensile property in nanocrystalline (nc) iron-nickel (Fe-Ni) alloys was studied to obtain a clue to further strengthening of nc materials. Multilayering electrodeposition process of nc Fe-Ni alloys with different Ni contents was investigated using an electrolyte which mainly composed of nickel sulfamate and iron chloride. The Ni content in the obtained nc Fe-Ni alloys increased with increasing current density of the electrodeposition. The multilayered structure with 3-11 layers composed of nc Fe-34 mass% Ni alloy (Invar alloy) and nc Fe-46 mass% Ni alloy (non-Invar alloy) were obtained alternatively applying two different current densities at predetermined time intervals. The average thickness of individual Invar alloy layer in the multilayered specimens with 3-11 layers was changed from 19.2 to 6.0 mu m. The tensile strength in the multilayered nc Fe-Ni alloy specimens was increased ranging from 1.47 to 2.24 GPa with decreasing thickness of Invar alloy layers and increasing number of multilayer interface. The possible mechanism of the strengthening in the multilayered nc Fe-Ni alloy specimens was discussed based on the results of the hardness-distance profile near the interface between the Invar alloy and non-Invar alloy layers.