Electrodeposited Re-ni-wp - Sic Composites Basic Theory Research And Applications

Process and basic theory of electrodeposited RE-Ni-W-P-SiC multifunctional composite composite coating have been studied, including some contents as follows:E-pH patterns of Ni-P-H₂O and Ni-C-H₂O systems were drown out on the basis of thermodynamic analysis, and results show that Ni and P can co-deposit on the cathode in the form of Ni₃P; there are some Ni₃C phases in the coating, and C comes from organic compound which was added in the bath and CO₂ in the air that was dissolved in water.Experimental results of process parameters indicate that a series of RE-Ni-W-P-SiC composite coatings with different contents were obtained by means of appropriate parameters, and component scopes of the coatings are SiC 5～30wt%, Ni 50～60wt%, W 10～25wt%, P 5～15wt% and RE 5～10wt%. The contents of W , P and SiC in the composite coatings were increased when chloride, oxide and sulfate rare earth was added in the bath respectively or together. The addition of sodium hypophosphate must be appropriate, if added much, W and SiC contents in the coatings were decreased , So the addition of sodium hypophosphate must be controlled 10～15 g/l. Current density, temperature and pH value have considerable effects on the contents of W, P and SiC in the composite coatings. Generally, current density (Dk) must be controlled 5～10 A/dm², pH 6.0～6.5 and temperature 55～65°C. Besides, Dk and pH have a great effect on the surface morphologies of the coatings, and the composite coatings get coarse when Dk and pH were high, on the contrary, the composites gain fine crystal when Dk and pH were low. The agitating interval time has little effect on Ni, W and P contents, while it has considerable effect on SiC content in the deposits. Extension of agitation and interval time will decrease SiC content in the composites, so interval and agitating time must be controlled 3 mins and 4～5 mins respectively.Curves of cathodic polarization display that when SiC particles and rare earth (RE) were added in the bath, cathodic depositing current density of the composites increases, and it is profitable for Ni-W-P coating to deposit in the cathode, forming Ni-W-P-SiC and RE-Ni-W-P-SiC composites. On the contrary, the addition of PTFE in the bath decreases cathodic depositing current density of the coatings. The current density increases a little when the amount of rare earth(RE)is 7～9 g/l; however, the density increases greatly with increasing amount of RE, and it reaches peak value when the amount of RE is 11～13 g/l. But if the amount of RE is raised further, the current density decreases.Mechanism of SiC particles and Ni-W-P coating co-deposition is: SiC particles carry about negative electric charge itself, and they may adsorb positive electric charge around when SiC particles are added in the bath. They move to the surface of cathode and form weak adsorption under the effects of fluid dynamics and electric field force; secondly, SiC particles on the cathodic surface dehydrate...