Study Of The Craft Of Electroless Ni-P-Carbide Composite Plating

The electroless composite plating has got extensive application for its low costs,simple technique,homogeneous thickness of coating etc: As the micro-hardness of Ni-P coating is insufficiently high and the wear resistance is worse than expected, its performances can not satisfy the request of high speed of developing science and technology, which limited the range of application. In recent years, electroless composite plating has been paid more attention by scholars of domestic and foreign.The influence of technological parameters such as complexing agents on the depositing rate and the life of liquid of Ni-P-SiC composite coating has been studied. The orthogonal test method has been used to study the effects of the concentration of SiC, the speed of mixing, the temperature and the surfactants on depositing rate and micro-hardness, and obtained the optimized technological scheme and fine Ni-P-SiC composite coating. The effects of heat-treatment on microstructure and performance has been studied also. The mechanism of corrosion and wear resistance of coating has been discussed.The results showed that using citric acid-acetic acid as complexing agents can obtain high speed of depositing and homogeneous coating with SiC well-distributed. Among the technological parameters, the effects of temperature on depositing rate is biggest, and the mixing speed is next; the effects of the concentration of SiC particles on micro-hardness is biggest, and the mixing speed is next. Give consideration to depositing rate and stability of the liquid ,the temperature should be controlled at 90±2℃, the PH value should be controlled in 4.5～5.5.The research results showed that the Ni-P-SiC coating is superior to Ni-P coating in many performances, such as the micro-hardness and the wear resistance etc, except for corrosion resistance. The effects of heat-treatment on the performances of coatings are obvious. After heat-treatment at 400°C for 1 hour, the micro-hardness of composite coating can reach HV1258, with a minimum abrasion loss. The coating can complete crystallization at 550℃, alonge with the phase transition to stable phase of Ni-Ni3P-SiC. The higher the heat-treatment temperature is, the bigger the bond strength is and the corrosion resistance is worse. In view of all performances of the Ni-P-SiC coating, after depositing, the work piece should be heat-treated at 400℃ for one hour.