Preparation Of Electrodeposited Ni-w Alloy Coating Structure And Its Performance Study

Ni-W alloys which have unique performance of friction, self-lubrication, optical, magnetic, electrical, high hardness, excellent wear resistance, corrosion resistance and low stress have attract more and more focus in recent years. Ni-W alloy coatings'structure are dense and pyro-oxidation resistance, sometimes even comparable with graphite and ceramics. In this paper, because there are plenty of resource of tungsten and rare earth in south of Jiangxi Province, a Ni-W alloy which has good performance and can be used to replace hard chrome plating was investigated and prepared by electrodeposition which can reduce the environmental pollution. The main conclusions are as follows:The preparation process of Ni-W alloys were optimized by using the method of orthogonal design. The thickness, hardness and the tungsten content of the coatings were also determined by using the magnetic thickness instrument, microhardness tester, EDS and so on. At the same time, the range analysis of the experimental results were performed by using the range analysis method and the influence of various factors on the properties of Ni-W alloys were obtained. The result shows that the process parameters of current density, Na2SO4 concentration, NH₄Cl concentration and NaI concentration, have an important influence on the electrodeposition process. Ni-W alloy coatings and the properties of the Ni-W alloy coatings. And the NaI concentration was the most important factor on the electrodeposition process and the alloy coatings properties, because of the large polarization and the small electronegativity of NaI. The current density Dk of 14A/dm2, Na2SO4 concentration of 40 g/L, NH₄Cl concentration of 25 g/L and the NaI concentrationof 4g/L were the best electrodeposited preparation process, and the comprehensive properties of Ni-W alloy coatings were the best. The thickness, micro-hardness and the tungsten content of the Ni-W alloy coating can be up to 46.35μm, 619.61 HV and 37.42%, respectively.Heat treatments for Ni-W alloy coatings prepared by electroposition at different temperatures were carried out. The changes of the microstructure and properties of the coatings were discussed by microhardness, XRD, electrochemical workstation and optical microscopy. The results show that the temperature at 500℃and the holding time of 2 h was the best heat treatment process. The micro-hardness of Ni-W alloy coating increased from 619.61 HV to 1010.44 HV after the treatment, and the alloy coating corrosion resistance at 3.5% NaCl solution was good.Finally, a comprehensive and systematic study of the influence on the process of electrodeposited Ni-W alloy coatings and the properties of the alloy coatings with addition of rare earth oxides of Er₂O₃, Nd₂O₃, Eu₂O₃ and Dy₂O₃. Moreover, the regulation trends of the tungsten content, hardness, thickness, corrosion resistance and surface morphology and etc, following with the change of the addition amount of rare earth oxides were studied, and the effect mechanism was also discussed. The result shows that the addition of rare earth oxides can make the corrosion potential shift and significantly improve the hardness and corrosion resistance, and the effect of addition of rare earth oxides Er₂O₃ was the best.