Study Of Brush Plated Nanocrystalline Ni-Fe Alloy Coating Using Soluble Anode

In this paper, nanocrystalline Ni-Co alloy coatings were synthesized by brush platingusing soluble anode. The composition of Ni-Co electrolyte was designed and the technicsoptimized.The relationship among grain-size, hardness, corrosion-resistance as well aswear-resistance was studied extensively. The effect of element Co on the performance ofNi-Co alloy coatings was discussed. The influence of low-temperature annealing on thestructure and properties of Ni-Co alloy coatings was investigated. The experimental resultsindicate that:According to the experiments the optimized brushing technics was that: the main saltused Sulphamate system, the velocity of plated pen is9m/min, the brushing voltage is7V,the plating time is60min.Ni-Co alloy coatings with varied Co content were typical nanocrystalline.The Cocontent of coating is far higher than the concentrations of Co2+in plating solution, areabnormal codeposition. In these coatings, the Ni-44.16%Co has minimum grain size of12.7nm. The coating hardness increased with the Co content increasing, is due to Co atomicsolid solution. The wear resistance of Ni-Co coating increased with the Co content increasing.The main wear mechanism of Ni-36.14%Co coating is adhesive wear, while the wearmechanism of Ni-44.16%Co is abrasive wear. Nanocrystalline Ni-Co alloy coating on3.5wt.%NaCl solution and5wt.%HCl solution has a better corrosion resistance. Thecorrosion rate of coating in the5wt.%HCl solution in was significantly higher than that inthe3.5wt.%NaCl solution. When the Co content of coating more than40%, the increase ofinternal stress leading to the destruction of protective film. The coating surface showsstress corrosion cracking, corrosion resistance of the coating to reduce.As the temperature of low-temperature annealing rised to500℃, the grain-size ofnanocrystalline Ni-44.16%Co coating increased from12.7nm to micro-grainsize. Themicro-hardness of Ni-44.16%Co coating reached maximum at300℃, then maintain a highhardness in the range of300℃~400℃. After400℃~500℃annealing the hardness dropped drastically.Before400℃annealing, the wear resistance of nano-crystalline Ni-44.16%Co alloycoating increased with the annealing temperature rised. It shows the best wear resistanceafter annealing at400℃and then decreases rapidly since500℃, which is closely related tothe changes in microhardness.With the coating dislocation reducted and coating grains turned to uniform the corrosionresistance of nano-crystalline Ni-44.16%Co alloy coating after annealing below300℃shows better with the temperature rised. At the range of300℃~400℃annealing thecorrosion resistance decreased slightly. When annealed above400℃the coating grains grewup quickly then it is difficult to generate protective oxide film over coating that lead to thecorrosion resistance dropped sharply.