Electrodeposition, Microstructure and Magnetic Properties of Nickel-Cobalt-Copper Alloy Powders

Abstract

Powders of Ni-Co alloys containing small amounts of Cu were produced by electrodeposition from an ammonium bath. Cathodic polarization curves were recorded and partial current densities for alloy deposition and hydrogen evolution were determined. At a current density of 100 mA cm−2, the electrodeposition process resulted in Ni79.1Co18.6Cu2.3 powder with an average grain size of 6.8 nm, composed of an amorphous matrix and FCC nanocrystals. The deposition of Cu with Ni and Co led to a higher proportion of the amorphous phase, smaller nanocrystals and smaller powder particles in the electrodeposit than in the alloy without copper. During annealing at temperatures ranging from 25°C to 160°C, no structural changes occurred in the powder. Upon structural relaxation in the temperature range of 160–350°C, the powders cooled at 25°C showed greater magnetic permeability. At temperatures between 350°C and 430°C, the amorphous phase exhibiting relatively lower magnetization underwent crystallization, accompanied by the formation of small-sized FCC nanocrystals, which had relatively higher magnetization values, leading to an increase in the magnetic permeability of the cooled powder. At temperatures above 430°C, the formation of large crystalline grains at the expense of small ones caused a decrease in magnetization.