SYNTHESIS AND CHARACTERIZATION OF ELECTRODEPOSITED NI–W ALLOYS WITH DIFFERENT LEVELS OF TUNGSTEN CONTENT

Abstract

Tungsten alloys are known for their excellent mechanical and tribological properties. Ni-W alloys exhibit enhanced properties such as corrosion resistance, wear resistance and catalytic activity for H₂, useful in practical applications. Pure tungsten cannot be electrodeposited from aqueous electrolytes, but can be codeposited with iron group elements such as nickel to form an alloy. The objective of the current work was to study the effect of bath chemistry and current density on chemical composition, microstructure and properties of Ni-W alloys deposited from citrate-containing baths, without stirring of the bath solution on copper substrate. The investigations include characterization of complex formation by UV-VIS spectrometry. the absorption spectrum of solutions with nickel in composition is similar and it shows the presence of four peaks. The current efficiency is increased with increased concentration of Ni²⁺ ions in bath. The layer thickness of the deposition obtained in NiW-1 bath is low, but increase with the current density. the homogeneous hardness of the Ni-W deposit may be attributed mainly to three factors: layer thickness, the deposition structure and deposit composition. All these tree factors are current density dependent. The micrograph of NiW coating, studied by scanning electron microscopy (SEM), shows the presence of cracks on a relatively uniform surface and the electron diffraction spectroscopy (EDS) analysis confirmed that Ni and W are uniformly distributed on the surface.