Study Of Ni-Cu Coating And Corrosion Behavior Prepared By Low Hydrogen Permeation Electroplating

Electroplating is a commonly used surface treatment technology in the industry.This method is less expensive to use and does not affect the dimensional precision of mechanical parts,while improving the functionality and corrosion resistance of the material.However,the pickling pre-treatment and plating processes are often accompanied by hydrogen evolution reactions,resulting in the entry of some hydrogen atoms into the substrate,leading to bubbling.substrate cracking,or hydrogen embrittlement of the coating.This problem in industry is solved by employing a 24 h annealing post-treatment of plated parts at 200～230℃ to eliminate the potential for hydrogen embrittlement.However,the long time of dehydrogenation not only reduces the production efficiency,but also consumes a large amount of fossil energy,which is not conducive to the strategic policy of "carbon neutrality and peak carbon dioxide emissions"proposed by the Chinese government.Based on the above background,this study was inspired by the hydrogen permeation "poisoning agent" and carried out a series of work on how to reduce the hydrogen atoms permeated into the coating by the hydrogen permeation during electroplating process.This study aimed to reduce the post-treatment time of hydrogen removal and produce "low permeation plating".First,the effect of plating parameters on the hydrogen permeation behavior during electroplating was investigated using a modified Devanathan-Stachurski double electrolytic cell technique.Experimental results show that the higher the current density during plating.the more hydrogen atoms diffuse into the coating and the metal matrix.At the same current density.the pulse current also reduces the amount of hydrogen permeation in the plating process compared with direct current.The hydrogen permeation curves of the coating and substrate bilayer metals in the electroplating process differ from the general single-layer metal hydrogen permeation.Therefore,the mathematical model of hydrogen atom distribution in the coating and substrate and the transient hydrogen permeation current of the bilayer metal during the electroplating process was re-derived based on the hydrogen permeation current density curves and Fick’s law of diffusion.Compared with the actual hydrogen permeation curve during plating,the theoretical fit and actual curve are highly consistent.Moreover,based on on the application of cerium oxide 4f/5d vacant orbitals in catalysis,exploring whether Ce salts as additives in the electroplating process affect the electrodeposition cathodic hydrogen evolution reactions(HER).In other words,it aims to determine whether Ce salts can promote the binding of hydrogen atoms to generate hydrogen molecules,thereby reducing the chance of entering the substrate.Different concentrations of Ce salts were added to Ni-Cu and Zn-Ni plating solution to investigate their effect and mechanism on hydrogen permeation during electroplating.Ce salts can remarkably reduce the hydrogen permeation current density in both cathodic coating and anodic coating.The effect of Ce on the kinetic parameters of HER in electroplating was calculated using the Iyer-Pickering-Zamanzadeh(IPZ)model.and the fitting results show that Ce slightly affected the kinetic parameters of Volmer reaction in HER but significantly improved the kinetic parameters of Tafel reaction.As an additive,Ce ions will be adsorbed at the substrate or coating interface.The lower electronegativity of the outer electron structure of Ce promotes the migration and sharing of electrons and reduces the strength of the Ni-H.Cu-H,and Zn-H bonds.Ce can also provide electrons for the Heyrovsky reaction in HER,and the synergistic effect of the two reactions promotes the desorption of adsorbed hydrogen atoms(Hads)to escape as hydrogen gas,reducing the hydrogen atoms that permeate into the coating.Therefore.Ce salts can be used as an efficient anti hydrogen permeation agent to inhibit hydrogen permeation during electroplating.Consequently,it reduces the post-treatment time and reduces the use of fossil fuels,thus providing a new idea and method for energy saving and emission reduction in the electroplating industry.Electroplating parts need to be used in the actual service environment,and the corrosion resistance of the material needs to be ensured.Therefore,the effects of Ce on the microscopic morphology,phase structure,composition,and corrosion resistance of Ni-Cu coatings prepared by DC and PC electroplating techniques were investigated using focused ion beam-transmission electron microscopy(FIB-TEM),scanning electron microscopy(SEM),X-ray diffractometer(XRD),X-ray photoelectron spectroscopy(XPS),atomic force microscopy(AFM).electrochemical impedance(EIS),and polarization curves.Ce salt did not affect the phase structure of the coatings,which are all face-centered cubic crystals,but the addition of Ce reduced the surface defects of and improved the pitting resistance of the coatings.FIB-TEM results show that the enrichment of Ce at the Ni-Cu coating/passive film interface formed a "site-blocking" effect.The enrichment of Ce at the boundary of passive film occupied the formation sites of oxygen vacancies,hindered the formation of oxygen vacancies,and filled the voids formed by the aggregation of cation vacancies,thus reducing the diffusion rate of point defects and decreasing the density of point defects.Ultimately,the corrosion resistance of Ni-Cu coatings was improved.