The Synthesization Of Ni-Cu-P Coating And The Effect Of RE On Its Corrosion Property

Electroless plating technique was employed to synthesize Ni-Cu-P coatings on copperfrom an alkaline bath. Deposition rate was investigated by using the weight method. Themorphology, composition and microstructure of the coatings were characterized by ScanningElectron Microscopy (SEM), Energy Disperse Spectroscopy (EDS), Inductively CoupledPlasma Atomic Emission Spectrometer,(ICP-AES), X-ray Diffractometer (XRD) andTransmission Electron Microscopy (TEM) respectively. Potentiodynamic polarization curves,open circuit potential, and electrochemical impedance spectroscopy (EIS) techniques wereused to investigate corrosion behavior of the synthesized coatings.Electroless plating technique of Ni-Cu-P alloy coating was optimized in terms ofcorrosion resistance (in solutions containing3.5%NaCl). The effects of the concentration ofcopper sulfate in plating bath on the micro-morphology, composition and microstructure ofthe Ni-Cu-P alloy coatings were studied. The results demonstrated that with the increase ofcopper sulfate concentration (0.5~2.0g/L), the micro-morphology changed slightly; thecontent of Cu in coatings gradually raised, while that of Ni and P gradually decreased, whichindicated that the deposition of Cu was promoted and that of Ni and Cu was inhibited; thestructures of the coatiings were mixed crystal. It indicated that the as-deposited Ni-Cu-P alloycoating with better corrosion resistance and higher deposition rate (about9.6μm/h) wassynthesized by the optimized deposition parameters: ultrasonic power40W, temperature70~750C, concentration of Copper sulfate1.0g/L.On the basis of the optimization of deposition parameters, various amount of ceric (Ce)sulfate and lanthanum (La) chloride were added (0~150mg/L) in plating bath, respectively.The effects of rare earth (RE) compounds on the deposition rate, micro-morphology,composition, structure and corrosion resistance of Ni-Cu-P alloy coatings were investigated.The results manifested that with the increase of the RE addition amount, the deposition ratesightly raised first and then decreased obviously; the micro-morphology and compostionchanged notablely, the size of the cell on the surface of coatings became more fine and the REelements could codeposition with Ni, Cu and P; The structure was closer to amorphous withlow RE addition amount, and with the further increase of the RE addition amount, the newphase precipitated in the coatings and the content of crystal structure increased; The corrosion resistance increased first and then decreased; The right amount of RE addition could increasethe content of the amorphous structure of the mixed crystal structure of the coatings andhomogenize the size of the nanocrystalline particles, strenghten the ability to self-recovery ofpassive film after rupture and significantly enhance the corrosion resistance. There existed anoptimum value at20and10mg/L for Ce sulfate and La chloride, respectively. What’s more,the effect of trace addition of La chloride on improving the corrosion resistance of theNi-Cu-P coatings is more apparent than that of Ce sulfate.