Preparation And Performance Of NiP Coatings By Electroforming Treatment

Electroforming process,which uses cathodic electrodeposition principle of metal ions to manufacture parts,has some characteristics,such as higher replication and repeatability precision.It is widely used in the fields of precise,special and complicated parts,and the micro/nano parts manufacturing.Though the electroforming has many advantages,the disadvantages,such aslow current density,long preparation time and larger internal stress,restrict further development of this technology.In this paper,the sulfate electroforming nickel phosphorus system was used to investigate the properties of electrolyte and the influence of process parameters on the surface morphology of electroforming layer,hardness,corrosion resistance and the internal stress.The effect of heat treatment and the effect of rare earth elements on the properties and surface morphology were also studied.The electric fielddistribution of hieroglyphic anode and uniformity anodewere studied by ANSYS method.The uniformity of electroforming layers was also studied in this paper.The study results of electrolyte showed that electrolyte had good ability of plating and dispersion.Through spectrophotometric method to detect the nickel and the titration method to detect phosphorus with sodium thiosulfate,the supplementary amount of nickel sulfate was 9g/3h and phosphorus was 3g/3h.The orthogonal test method was used to character the process parameters,which consisted of current density,temperature,p H values and connections of phosphorus.From the results of SEM,EDS and the electrochemical test,it was shown that with the increasing of temperature,current density and p H values,the electroforming rate increased.With the increasing of stirring speed,the electroforming rate increased to a high point,and then decreased when electroforming rate continue to increase.When the parameters exceeded a certain limit,the rate decreased.The phosphorus content of the electroforming layers increased with the increasing of phosphorous acid.The phosphorus content of the electroforming layers decreased with the increasing of current density and p H values.The surface topography of electroforming layers transformed cellular into mirror with the increasing of process parameters.The hardness decreased by the increasing of current density and p H values.With the increasing of temperature and phosphate,the hardness firstly increased then decreased gradually.The current density,p H values and the connection of Cl-lead to the increasing of the internal stress.The increasing of the temperature made the hardness decreased.The best corrosion resistance can be obtained when i was 1.5A/dm~2 andp H was 2 respectively.The electrochemical impedance spectrum fitting circuit parameter values and the electrochemical porosity results were consistent.The hardness of electroforming layers increased,while the resistance decreased after heat treatment.From the XRD results,it was shown that the layers turned microcrystalline into crystal of Ni and Ni3 P phases eventually with the increasing of temperature,and the saturation magnetization and coercive force increased.The electrolyte and electroforming layerwere investigated when added the Rare earth.The results show that the cathodic polarization curves of electrolyte when adding Rare earth elements shifted negative and the polarization degree increased.After added Rare earth elements,the peak current density of i-t curves of electrolyte increased under the same step potential,and the tm decreased corresponding.Through the analysis of Scharifker-Hill model,the entering of Rare earth elements didn’t change nickel phosphorus electro-crystallization behavior.The entering of Rare earth ions promoted nickel phosphorus electro-crystallization because the existence of rare earth ions debased over-potential of nickel phosphorus nucleation.The corrosion resistance and hardness of electroforming layer increased when added rare metals.But when the parameters exceed a certain limit,the hardness decreased.The cellular structures of electroforming layers with Rare earth elements existed were much smaller than that of without Rare earth elements.The EDS results showed that cerium and lanthanum had realized the co-deposition.While yttrium didn’t co-deposit with nickel phosphorus alloy.With increasing of the content of Rare earth,the magnetic of electroforming increased.Nickel phosphorus electroforming layers were obtained with the curved substrates.The simulation analysis of electric field was carried out using ANSYS analysis software.The results showed that the uniformity of pictographic anodic electric field was better than flat anode.The results of electroforming layers showed that the uniformity of hieroglyphic anode,which uniformity error was 14%,was significantly higher than plate anode,which uniformity error was 26%.