Study On Technics & Performance Of Nano Electroless Composite Plating On 20~# Steel

Nano electroless composite coating was a kind of composite coatings with specific function. It not only had excellent characteristics of the matrix metal, but also had special features of the nano-particles. It was one of the most time-saving and economy way to make up wear-resistant coatings. Thus, the nano electroless composite coating had a broad application prospects in the surface modification of materials.Using the orthogonal experiments, firstly, the process parameters of nano electroless composite plating was optimized, secondly, the effect of solution temperature, heat treatment temperature, the types of complexing agent and nano-particles in the content on the properties of nano composite coatings was discussed. Finally, the nano-particles in the content on the properties of nano composite coatings and the abrasive resistance of the four kinds of nano composite coatings were analyzed. The results were summarized as follows:The best parameters of nano-Al2O3 and nano-TiO2 electroless composite plating were as follows:solution temperature 80℃-90℃, value of pH 4～5, heat treatment temperature 400℃, heat-treatment time 2h, main salt 25 g·L-1, reducing agent 25 g·L-1, complexing agents 20～25ml·L-1, stabilizing agents 2 g·L-1.The study on the solution temperature in the nano-Al2O3 composite plating showed that the solution temperature had a great impact on the performance of nano composite coating. With the solution temperature rising, the hardness of the composite coating increased at first, and then dropped. When it reached the best solution temperature 85±3℃, the performance of the nano-Al2O3 composite coatings were as follows:Hardness was 718.67HV, and abrasion loss was 21.6mg. The study on the heat treatment temperature in the nano-Al2O3 composite plating showed that the hardness of nano composite coatings were higher after the heat treatment. The best heat treatment temperature was 400℃, and meantime the hardness of nano composite coatings reached 949.06HV. The study on the types of the complexing agent showed that complex ions with nickel ions could be formed when using lactic acid which could effectively avoid separating out sediment, and could assure the stability of the solution. When the lactic acid in the content was 25ml·L-1, the hardness of the nano-SiC composite coating was 523.25HV. It was almost double more than the composite coating made by citric acid.The study on the nano-particles in the content showed that:With the content of the nano-particles increased, the nano-particles in the composite coatings became uniformity and dense, and the hardness of composite coatings increased. When the content of the nano materials was beyond the plane, the nano-particles reunited easily and the homogenization of the nano-materials and the hardness & wear resistance of the composite coatings began to decline. When the four kinds of nano-particles reached 6g·L-1(Al2O3),6g-L-1(TiO2), 8g·L-1(SiC),6g·L-1(SiO2), the surface of their composite coatings were smooth, and the nano-particles in the composite coatings distributed uniformity. At the moment the hardness were 953.10HV(Al2O3),536.01HV(TiO2),556.04HV(SiC),889.21HV(SiO2).The comparative study on the wear resistance of the four nano composite coatings showed that the type of the nano-particles had a great impact on the wear resistance of nano composite coatings. The Al2O3 composite coating had the best wear resistance and the SiO2 composite coating was the better one. The performance of the SiC one and the TiO2 one were less. Their wear losses were 16.4mg,20.6mg,28.7mg and 27.2mg.