Plating Ni- (W) -P Technology Research And Corrosion Resistance Coating

The electroless Ni-W-P alloy coating with strong corrosion resistance and good wear resistance can effectively prolong the life of materials and bring more economic benefits, which is gained by adding W on the basis of electroless Ni-P alloy coating.The major themes of this thesis are the process of the electroless Ni-(W)-P alloy coating and its corrosion resistance in H2SO4+HCl(etching solution A),(NH4)2S(etching solution B) and NaHCO3+CaCl2(etching solution C).By selecting the coating deposition rate and corrosion rate as the evaluation indexes, we obtained the optimal operating conditions in the optimal design test of the process:in etching solution A, the concentrations of nickel sulfate, sodium hypophosphite, sodium tungstate, citric acid, lactic acid, pH, temperature and time are24g/L,28g/L,20g/L,15g/L,27ml/L,5.4,88℃and2h; in etching solution B, the process formula contains:26g/L nickel sulfate,30g/L sodium hypophosphite,20g/L sodium tungstate,19g/L citric acid,27ml/L lactic acid while the pH, temperature and time are the same as etching solution A; in etching solution C, the concentrations of nickel sulfate, sodium hypophosphite, sodium tungstate, citric acid, lactic acid, pH, temperature and time are respectively24g/L,28g/L,20g/L,19g/L,27ml/L,6.4,88℃and2h.The surface morphologies, microstructures, chemical composition were detected. The results of scanning electron microscope showed that the electroless Ni-(W)-P alloy coating had the typical cauliflower shape topography with independent and relatively homogeneous spherical cellular particles; X-ray diffraction results showed that the coating was the amorphous structure which presented the typical "Steamed buns" diffraction peak and belonged to the uniform single-phase system in metastability state of thermodynamics.We studied the corrosion behavior of the coating in H2SO4+HCl(etching solution A),(NH4)2S(etching solution B) and NaHCO3+CaCl2(etching solution C) by the mean of comparing the optimized electroless Ni-W-P alloy coating with the coating which had poor corrosion resistance. The results of corrosion experiment showed that the corrosion resistance of the optimized electroless Ni-W-P alloy coating mainly depends on its amorphous structure and the growth way, the content of P, W, the nature of the corrosive medium and the influence of environmental factors, etc.