The Feasibility Study Of Ni-Fe-W Alloy By The AC/DC Superimposed Electroplating

Direct current power, periodic reverse current power, pulsed current power and AC/DC superimposed power were used in plating production technical field in the current. Simple electroplating production can be met with Direct current power, but many problems still exist, such as concentration polarization phenomenon; Periodic reverse current means changing cyclically the direction of direct current. The concentration polarization phenomenon can be overcome with periodic reverse current, but the current efficiency is lower than the non-commutation current's; Although a better plating coating can be obtained with pulse current, but the equipment is very expensive and the one-time input cost is high; With AC/DC superimposed power not only concentration polarization phenomenon disappers, but also current density range of the cathode expands, such plating power and pulse power both have good prospects. At home and abroad, it has not been reported about electroplating Ni-Fe-W alloys with AC/DC superimposed power, but this power was used in this article. Amorphous alloy is better than the crystalline alloy in following aspects:corrosion resistance, hardness, etc. Therefore, how to obtain the amorphous alloy coatings is the focus content of this article.The optimum process parameters of AC/DC superimposed electroplating Ni-Fe-W amorphous alloy were obtained by studing influences of some factors on the hardness and the deposition rate of Ni-Fe-W alloy coating. The factors were as follow:the amplitude and frequency of AC/DC superimposed power, current density, test time, content of sodium citrate, pH value, temperature of the electroplating bath. The optimum process parameters were:NiSO4·7H2O 25g/L FeSO4·7H2O lOg/L, Na2WO4·2H2O 45g/L, H3BO330g/L, Na3C6H5O7·2H2O 40 g/L, SDS 0.1 g/L,1,4-butynediol 0.2g/L, pH of the bath was fixed 7-8 and the temperature of the bath was 60℃, plating time one hour. The composition, surface morphology and crystal structure of Ni-Fe-W alloy coating were characterized by EDS, SEM, XRD and other means. The results showed that when the concentration of tungsten sodium was 45g/L, crystalline of the coating presented amorphous clearly. The structure of Ni-Fe-W alloy coating was based on Ni-Fe-W solid solution phase which was formed by nickel as solvent, iron and tungsten as solute. The original lattice of nickel was not destroyed by the coating of tungsten and iron into the lattice, which was still Face-Centered cubic structure, only part of Ni atoms were replaced by tungsten and iron.With electrochemical impedance spectroscopy and Tafel polarization curves, the corrosion resistance of AC/DC superimposed plating and which of direct current electroplating was characterized and analyzed. Compared with direct current plating, the capacitive loop diameter of AC/DC superimposed plating significantly increased, which coincided with positive shift of corrosion potential in Tafel polarization curves and apparent decrease of corrosion current density. Tt's fully proved that corrosion resistance of AC/DC superimposed plating was better compared with which of direct current plating.As a more promising plating technology, AC/DC superimposed electroplating technology will be paied more and more attention. Though the technology is not very common in this area now, it will be generalizable with the understanding of AC/DC superimposed electroplating technology in the near future.