The influence of Ni and Co concentration in the electroplating bath on Ni‐Co‐W alloys properties

Abstract

In this study, we evaluated the influence of nickel and cobalt concentrations in an electrochemical bath for a ternary Ni‐Co‐W coating alloy electrodeposition. The X‐ray diffraction indicated formation of amorphous coating alloys for higher Co concentration and a crystalline coating alloys for higher Ni concentration. Statistical evaluation showed a mathematical model connecting the increase of alloy deposition efficiency and the Ni and Co concentration in the electrochemical bath. Corrosion tests indicated that coating alloys with higher Ni concentration, which are crystalline alloys, showed higher polarization resistance (in NaCl 0.1 mol/L) indicating that composition can influence the corrosion resistance more than the crystallinity.

Parameters variation on Ni–Co–W coating electroplating to evaluate improvements in morphology and corrosion resistance

“…The value of current corrosion in experiment 6 was lower than others reported in Ni-Co-W literature which were evaluated under the same conditions [1,2,8], representing an improvement in the Ni-Co-W alloy characteristics. Table 2 shows the data of experiment 6, which had current corrosion density of 0.84•10 −2 A/m 2 in − 0.221 V corrosion potential attributing a high polarisation resistance (5.225 Ω m 2 ).…”

“…Anti-corrosive layers have the function of hinder electron diffusion through open pores or cracks [26]. Besides the absence of cracks in experiments 2 and 6, the increased corrosion resistance observed can be associated it with high Ni percentage in composition being an important feature of corrosion resistance influence [8]. Although experiments 1 and 5 present cracks, the roughness of its morphology suggests that the bigger grains prevented an increase in internal stress caused by grain reduction and provides reasonable performance in resistance to corrosion.…”

“…The synthetic bath produced was composed of sodium tungstate 0.03 mol L −1 , cobalt sulphate 0.01 mol L −1 , nickel sulphate 0.3 mol L −1 solutions and reagents of bath stabilisation, such as ammonium citrate, ammonium sulphate and borax. The metal masses were chosen based on an optimisation of the values found in the literature [1,2,8,9].…”

“…Statistical analysis was used to measure variable interactions, as it is considered an effective optimisation technique and is also a reliable method [1,8,10]. The alloys were deposited on copper substrate of 0.02 m on each side.…”

“…Table 1 shows that cathodic potential remained between 1.8 V and 2.9 V justifying the slight variation in final composition. In average composition, the amount of Ni contributed to an enhancement in faradic efficiency and corrosion resistance [8]. The Ni-Co-W alloys were analysed in SEM and showed cracks in all experiments, except in experiments 2 and 6.…”