Effects of pH and Current Density on Microstructure and Hardness of the Cobalt-Tungsten Coating.

Abstract

In this study, cobalt-tungsten coatings were electrodeposited on copper substrates. Nanocrystalline and amorphous cobalt tungsten alloys were electrodeposited from citrate-boric acid baths. The characterization of the alloy coatings was carried out by scanning electron microscopy (SEM), X-ray fluorescence (XRF), and X-ray diffraction (XRD). The most significant factors, such as current density and pH of the electrolyte that affect the morphology, tungsten composition, and microhardness value, were studied. The tungsten content of the electrodeposits varied 11 to 46% by changing process variables. The microhardness value of the coatings was decreased dramatically when the tungsten composition exceeded 35%. Response surface methodology was used to construct models for predicting microhardness value and tungsten composition of the coating. The optimal conditions for the electrodeposition were found as follows: current density of 5A/dm2 and pH 6. Under optimal conditions, the coating exhibits a hardness of 570 HV.