| Nickel has been widely applied in the fields of aviation, spaceflight, manufacturing of machinery, electronic material and military national defense with the property of high strength and corrosion resistance. In order to meet the increasing property demanding for engineering materials, the process of making metal plating through the electricity deposition have been widely studied by electrochemical workers worldwide, electroplating process has characteristics such as simple equipment, less investment, without changing the performance of metal matrix and shape size, etc. The traits of the good stability of plating bath, easy-controlling and the excellent plating property made the nickel-based or nickel alloy composite plating become the focus of research.Compared with the DC electroplating, pulse electro plating can get better plating with finer grains, higher compactness and less porosity. Meanwhile, the appearance of the plating, corrosion resistance and the property of material surface can also be much improved. In this paper, a modified watt’s bath was used to prepare nickel plating on the surface of pure copper. The rare earth modified platings were made by adding LaCl3.7H2O in the plating bath during the single pulse electroplating, and the properties of pure nickel plating and rare earth modified plating were compared according to the surface morphology, microstructure, porosity, the strength combined with matrix, microhardness, wear resistance, corrosion resistance and the high temperature oxidation resistance. Five factors as LaCl3.7H2O concentration, pH value, bath temperature, cathodic current density and pulse frequency are selected to carry out the orthogonal experiment with five factors four levels. The platings’Tafel corrosion potential in3.5%NaCl solution of20℃were choosed as the orthogonal experiment criteria, and then the best plating parameters were determined by the anti-corrosion property in the orthogonal experiment, they are LaCl3.7H2O1.0g/L, pH value4.0, electroplating temperature30℃, cathodic current density1.5A/dm2, pulse frequency1000Hz. And on those parameter basis, the influence of the above five factors on the plating’s deposition rate, surface brightness, microhardness and corrosion resistance were studied by single factor analysis method respectively.Results showed the rare earth modified plating prepared through2hours electrical deposition under the above optimized orthogonal parameters have good combining strength with matrix; The scanning electron microscopy (SEM) was used to observe the surface morphology of platings, and it was found that the surface of rare earth modified plating are more smooth and the organization are more compact and well-distributed; according to observe the transmission electron microscopy (TEM) images of the prepare platings, it was found the average grain size of rare earth modified plating is about35to45nm, nearly half that of the pure nickel plating; at the same time, the energy dispersive spectrum (EDS) analysis showed that nickel atomic content in the rare earth modified plating was about99.73%, only a little amount of lanthanum atoms entered into the plating; Through the X-Ray Diffraction (XRD) analysis, lanthanum atoms entered into the plating and formed the ni-based rare earth alloy as the La2Ni7phase, it was also found that the additive rare earth LaCl3.7H2O significantly boost the preferred growth direction of nickel’s (200) crystal face; Contrast with pure nickel plating, the microhardness of rare earth modified plating increased about60HV; the corrosion potential of rare earth modified plating was raised to-0.368V; By measuring the friction weight-loss speed, the wear weight-loss rate of the rare earth modified plating was only half of the pure nickel plating; Through800℃,4hours high temperature oxidation, it was found that the oxide film of rare earth modified plating have better integrity and adhesion indicating its better oxidation resistance. |
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