Electroless Ni-W-Mo-P Process And Properties

In this thesis, Ni-W-Mo-P alloy coating was deposited by electless plating using alkaline plating solution on the surface of Q235carbon steel. By using modern analytical tools such as environmental scanning electron microscopy (ESEM), energy dispersive spectroscopy (EDS) and four-point probe resistivity tester, quaternary alloy plating layer on the surface morphology, the deposition rate, hardness, resistance and other properties were analyzed. We explored each component of the bath impact on the deposition rate, the coating hardness. On this basis, the electroless Ni-W-Mo-P process was optimized.By selecting the coating deposition rate and microhardness as the evaluation indexes, we obtained the optimal operating conditions in the optimal design test of the process:the concentrations of nickel sulfate, sodium hypophosphite, sodium tungstate, sodium molybdate, sodium citrate, lactic acid, ammonium acetate and lead ions are35g/L,35g/L,30g/L,0.3g/L,30g/L,25ml/L,15g/L and1mg/L. The bath pH is9.5, plating temperature is88℃, plating time is2h.By the surface topography scanning electron microscope we found that the coating surface of Ni-W-Mo-P is formed by a plurality of mutually independent and more uniform cell structure, and has a typical cauliflower-like morphology. By optical microscope observing the coatings’ tissue, the microhardness is concerned with the coating surfaceunit cell size and density related.The Ni-W-Mo-P coating resistivity was determinated and was found generally high. Since W is added, the scattering probability of free electrons is increased, and refined grains and increase the number of grain boundaries per unit volume, as a result increases the resistivity of the alloy. The conditions are met the requirements of the Thin film resistors, so it can be said that Ni-W-Mo-P plating layer is preferably a thin film resistive material.