Study On Electroless Plating Ni-Sn-P Alloy Coating And Composite Coating

Besides the excellence in wearing and corrosion resistance, Ni-Sn-P electroless plating deposits have good properties in conductivity and solederability, etc, so that it has become one of the research hotspots in electroless plating for the moment, and has been widely applied in the industries. On the basis of predecessors'work, this paper mainly discussed the effect of three accelerants on the deposition rate and other performances of electroless plating Ni-Sn-P alloy coatings. Then micron-Si3N4 powders were incorporated into Ni-Sn-P alloy matrix by electroless deposition to obtain Ni-Sn-P/Si3N4 composite coatings.In this paper, the effect of three accelerants, which were GA, GB and GC, and their optimization on the deposition rate, wear resistance, micro-hardness and corrosion resistance of Ni-Sn-P alloy coatings was discussed. The analysis of microstructure and surface morphology of two tempered coatings at different temperature observed by the tools of scanning electron microscope(SEM) and X-ray diffraction (XRD). Tests of the wear resistance, micro-hardness and corrosion resistance of pre-heat-treatment coatings were also carried out.The results showed that, the three accelerants could increase the deposition rate of Ni-Sn-P alloy coatings with different degrees. The optimal combination of accelerants, which involved 80mg/L GA and 75ml/L GB, was educed. Adding the accelerants optimized into solution could make the deposition rate reach 18.0μm/h, and make the micro-hardness of Ni-Sn-P alloys advance to be 720HV.The corrosion resistance of Ni-Sn-P alloys in man-made seawater was better than Ni-P alloys and stainless steel. The micro-hardness of Ni-Sn-P alloys heated at 400℃reached 1182.8HV.Micron-Si3N4 powders were incorporated into Ni-Sn-P alloy matrix by electroless deposition to obtain Ni-Sn-P/Si3N4 composite coatings. The effect of pH value, temperature, concentration of Si3N4 in bath, stirring rate on the composition of deposits, deposition rate and other performances of composite coatings was also discussed. Experimental results showed that, the optimal process of electroless plating Ni-Sn-P/Si3N4 composite coatings contained the main parameters: stirring rate(600rpm), the concentration of Si3N4 (10g/L),the bath temperature was kept at 87~89℃,with the pH value in range of 4.8~5.0. The maximal Si3N4 content reached 24.0%. With Si3N4 joining in composite coatings, the wear resistance and the micro-hardness were developed. After heat-treated at 400℃, the composite coatings transformed from non-crystalline to crystalline structure. The micro-hardness was advanced markedly, and the wear resistance improved by nearly 10 times.