Study on the Microstructure and Properties of Electroless Deposition Nickel-base EMS Coating with Rare Earth Joined

Abstract: The preparation technology, electric-chemical properties of the bath and electromagnetic shielding effectiveness of the electroless deposition nickel-base alloy coatings with rare earth joined were studied. The optimum formulation of process of electroless deposition Ni-Fe-B-RE alloys was designed and tested using perpenpular method. The samples were prepared. The structure, micro morphology and corrosion performance were observed and analyzed. The electrochemical characteristic, mechanical, magnetic and electromagnetic shielding properties were measured.Such kind of changes can be described as the followings. The bath with a small amount of rare earth (less than 0.4g/L), the deposition velocity of the bath has no significant changes. Increasing the concentration of rare earth is added to bath, the plating rate is decreased obviously. The stability of bath, binding force and surface quality of coating can be improved by rare earth. The electric-chemical system of nickel base bath attribute to the unti-reversible process. With the concentration of metal salt and deducing agent improving, the polarization decreased, plating rate increased.Compared to the rare earth of Ce and La (there is no 4f electron in La but Ce), promotion action of Ce is more than La. Analyze the affection of Ce concentration on the cathode polarize curves, the results showed that the proper concentration of rare earth added into bath, will decrease the polarization and accelerate the speed of the cathode reaction. Confirmed the perfect quantity of rare earth Ce with 0.6g/L at working temperature is most excellent. When the concentration of rare earth (Ce and La) exceed 0.4 g/L, will increase the polarization of bath, improve the brightness and lubricity of coating. The rare earth can be co-deposited with nickel base alloy in water solution. The content of Fe and RE in alloy coating increase, Ni and B drop with the rare earth added into the bath. The structure of alloys changes into microcrystalline from amorphous. The rare earth elements Ce, La, make micro hardness of alloy coating improve, and the effect of Ce is superior to La.The content of Fe in coating can be improve by adding RE, can decrease the content of metalloid boron, and decrease the corrosion performance, the electrochemical impedance spectroscopy show the corrosion mode is controlled by electro-chemistry. Analysis based on datum form experiment, increasing the content of Fe in coating can improve the soft magnetism property. With Ce added can also improve its soft magnetism property. However with the content of Fe and Ce added, the corrosion performance will be influenced, the corrosion velocity was accelerated. The properties of coating with Ni~(2+):Fe~(2+)=5:l and Ce 0.6g/L is the most excellent…
Key words: electroless deposition; rare earth; amorphous; electromagnetic shielding; shielding effectiveness; Ni-Fe-B alloy

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