The Studies Of Electrodeposition And Properties Of Ni-Co-Fe Alloys On Copper

With the development of science and technology,more and more fields which put forward higher requirements on the properties of the coating,are involved in electroplating industrial.Trivalent chromium ions and hexavalent chromium ions in chromium electroplating for traditional,are toxic,serious pollution to the environment.Therefore,the generation of chromium plating has become the developing direction of the future.Ni-Co-Fe alloy coatings with decorative appearance,high thermal stability,high hardness,high wear resistance,good corrosion resistance and the recycled plating solution,green environmental protection performance was favored for a substitute for chrome plating.Cathodic polarization curves were tested though electrochemical workstation CHI660E under different process conditions in this paper,the influence of process conditions on electrodeposition was studied systematically.Through the measurement of coating thickness,roughness,hardness,binding force and other properties,processing conditions of Ni-Co-Fe alloy were determined that was 55?,the cathodic current density for 4 A/dm2,4 for pH.Through the Tafel curves and electrochemical impedance spectroscopy(EIS),electrochemical behavior of corrosion resistance of electrodeposition of Ni-Co-Fe alloy was studied,under different process conditions in 3.5%NaCl solution.The binding force of the surface coating and copper substrate was determined by scratch test,it showed that under the copper substrate surface roughness of 0.4 ?m,the maximum critical load of coating and copper substrate was 93.65 N,which was the best combination of force.Under the above conditions,the coating was thickness of 100 ?m,less surface cracks,surface brightness,hardness of 818.77 HV100,roughness of 0.3 ?m.Its content is Ni 49.7%,Co 31.5%,Fe 18.5%.its XRD spectrum analysis shows that the alloy coatings is the substitutional solid solution,which has a small amount of amorphous structure,between the amorphous and crystalline structure of nanocrystalline,based on Ni as solvent,Co,Fe as solute,Ni-Co-Fe(?)as the main crystal face,a small amount of Ni-Co-Fe(200)(220)(311)crystal face.Effect of cathodic polarization curves for different concentration of sodium citrate were determined,sodium citrate could increase the buffering capacity of plating solution by hydrolysis.Instead of nickel cobalt and iron hydrated ions discharging in the plating process,the metal ions combined with citrate can discharge directly because of the complexation.The measurements of coating thickness,hardness and corrosion resistance under different concentration of sodium citrate illustrated that the coating performance is best when the concentration of sodium citrate becoming 40 g/L.But the coating became thinner due to the hydrogen evolution reaction.From SEM and XRD images,we concluded that the amorphous component increased,the crystallization became thinner,and the grain size was smaller when the concentration of sodium citrate becoming 40 g/L.Researching the cyclic voltammograms curves during the electrodeposition process,we found that the electroplating Ni-Co-Fe reduction process is a three-dimensional nucleation process controlled by the diffusion,which was an irreversible process.The charge and discharge process of electric double layer was cut after adding sodium citrate.The nucleation was close to instantaneous nucleation process,and the electrical crystallization process may be controlled by the electrochemical and diffusion.This was advantageous to the nucleation.