Research On Nickel-tungsten Alloy Plating Process

With the industrial development and increase of p eople’s environmental awareness, the use of hard chrom plating technology has been greatly restricted. Research on the substituting for hard chrom plating technology has become a hot spot in surface treatment field. Amony the many techniques, Ni-W alloy coating due to its high hardness, high wear resistance and good corrosion resistance has been widespread concern. In this paper, we prepare nano nickel-tungsten alloy coating at a lower concentration which has a high tungsten content, high hardness and excellent corrosion resistance.Ni-W alloy coating is prepared by sulfate plating solution, effect of sodium tungstate was studied. The concentration of sodium tungstate should be 45 g/L, adding less amount will reduce the tungsten content and hardness, which can not reach the requirement of substituting for chrom; adding more amount will result in increased costs. Effects of complexing agent on the tungsten content and haidness were studied by single factor test, the concentration of citric acid should be 45 g/L. adding more amount will reduce the tungsten content and hardness. The effects of additives on coating performance were study by orthogonal test. Results show that sodium saccharin is the m ost important factor. adding more will ruduce the tungsten content and hardness, adding less will lead to non-uniform coating surface. The effects of conditions were studied by orthogonal test. The results show that temperature is the most important factor. Best bath temperature is 65 ℃. We also study the deposition process of pulse plating. We study the effect of heat treatment process by single factor experiments. It is confirm that gas for heat treatment has a great influence on coating surface morphology. The coating surface was uni form and meticulous, almost no cracks when the heat treatment process in argon atmosphere. Effect of the average current density, frequency, duty cycle on tungsten content and hardness were studied by single factor tests. We found that there will be cracks in the surface if the current density is too low. Frequency is too high or too low will reduce the tungsten content and the hardness of th e coating. The tungsten content of coating will reduce as increasing of the ducy cycle. Compared with direct current plated coating, pulse plating coating has higher tungsten content, higher hardness, finer grain and Superior corrosion resistance.We study the deposition mechanism by polarization curves, cyclic voltammetry curves and electrochemical impedance. The results verify that deposition process is only one step. With the complexing agent concentration increases, the potential negative shifts and the tungsten content decreases significantly.