Effect of Deposition Current Density and Annealing Temperature on the Microstructure, Hardness and Magnetic Properties of Nanostructured Nickel-Iron-Tungsten Alloys

Abstract

Nanostructured nickel-iron-tungsten alloy coatings were electrodeposited from an ammonia citrate bath on steel and copper substrates at current densities in the range of 50 to 300 mA cm−2. The contents of iron and tungsten in the alloy increase and that of nickel decreases with increasing deposition current density. At current densities below 100 mA cm−2, smooth shiny coatings with no cracks and craters are deposited. Higher current densities result in matte coatings developing cracks and craters. XRD analysis showed that the coatings contain nanocrystals of FCC structured solid solution of iron and tungsten in nickel embedded in an amorphous matrix. Increasing deposition current density leads to an increase in the amorphous phase content and a decrease in both the content and mean crystallite size of the FCC phase. The coatings with an increased amorphous phase content and a decreased mean FCC crystallite size exhibit lower magnetization and reduced hardness. During annealing at temperatures up to 400°C, the alloy undergoes structural relaxation along with short-range structural arrangement, resulting in increased magnetization and hardness. At temperatures above 500°C, annealing leads to amorphous phase crystallization and crystal grain growth in the FCC solid solution, thus leading to reduction in both magnetization and hardness.