Effect of current density, temperature and bath pH on properties of Ni–W–Co alloys obtained by electrodeposition

Abstract

In this paper the effect of parameters such as current density, temperature, and electrolytic bath pH on the electrodeposition process of the Ni–W–Co ternary alloys was investigated. The morphological characteristics and chemical composition of the coatings were evaluated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray dispersive energy (EDX). A complete experimental design (CCD) was used to evaluate the resistance to corrosion of the Ni–W–Co ternary alloys in a medium containing chloride ions (3.5 % NaCl). Corrosion resistance was assessed using the techniques of potentiodynamic polarization (PP) and electrochemical impedance spectroscopy (EIS). Chemical composition results confirmed the formation of the Ni–W–Co ternary alloy. Different types of surface morphology were observed depending on the experimental conditions used. The alloys showed an amorphous character regardless of the W content. The highest current efficiency observed was 71.02 % for the alloy obtained under optimal conditions of 40 mA/cm2, 55 °C and pH 5. Under the condition of 100 mA/cm2, 55 °C and pH 8, the Ni50W41Co9 alloy was considered to be the most resistant to corrosion, which presented the lowest corrosion current density (5.817 × 10−6 A/cm2) and the highest resistance to polarization (5251 Ω cm2). Therefore, the results of this work show the importance of using optimization techniques to obtain metallic coatings with controlled properties for different types of applications.