Microstructure and Magnetic Properties of Electrodeposited Ni85.8Fe10.6W1.4Cu2.2 Alloy Powder

Abstract

Nanostructured 85.8 wt%Ni–10.6 wt%Fe–1.4 wt%W–2.2 wt%Cu alloy powder was deposited from an ammonium citrate bath at a current density of 600 mAcm−2. A cathodic polarization curve was recorded, and the current efficiency of the alloy was determined as a function of current density. The deposition of the alloy at current densities up to 400 mAcm−2 is an activation-controlled process. At higher densities, diffusion control is attained. At potentials more positive than −0.90 V, hydrogen evolution from NH4+ and (HCit)3− ions occurs in parallel with the alloy deposition. XRD analysis revealed an amorphous matrix embedded with nanocrystals of the FCC phase of the solid solution of iron, tungsten and copper in nickel. SEM micrographs showed the formation of two shapes of particles: large cauliflower-like particles and small dendritic particles with a large number of secondary and higher-order branches. The annealing of the as-deposited powder causes structural changes which consequently affect its magnetic properties. In the temperature range of 150°C–460°C, structural relaxation takes place, involving short-range ordering and an increase in the relative magnetic permeability of the cooled sample. At temperatures above 460°C, amorphous matrix crystallization and crystalline grain growth of the FCC solid solution occur, resulting in a decrease in the magnetic permeability of the powder.