Study On Nano - Diamond Composite Electroforming Technology In Supercritical State

Composite electroforming technology based on electrodepositing principlein supercritical fluid has been a new precision forming technology to prepare composite material and micro-parts with perfect performance.The simulation of experimental process as well as researches and analysis of experimental process were studied by supercritical CO2 fluids composite electroforming technology.Three-dimensional electroforming models were built and the coupling field of fluid and electric current was simulated by Comsol Multiphysics software as well as the growth of electroforming layers and distribution of Ni+concentration on the surface of cathode. The results show that for plane electroforming, the distribution of electric current is uniform and similar to catholic electric current in the middle of cathode, but in the boundary of cathode the electric current rise sharply due to the shape change. For micro-electroforming, the bending degree and consistency of electric wires at the entrance of microstructure gradually increase; the electric field wires in the middle of microstructure are less, electric field wires in edge of microstructure are dense, and the electric field wires in the microstructure have the same direction, it shows that the distributionof electric field in the microstructure is steady uniform and orderly.Growthsimulating value ofelectroforming layer is similar todistribution of current density, the Ni+ concentration ofcathode surface first reducesand thenincreases.The optimizing process of nano-diamond composite electroforming in supercritical fluidwas put forward.The test was carried out by supercritical electrodepositing device developed by our group and the influence onperformance ofelectroforming layer were obtained. Through orthogonal experiment, the influence order of various process parameters to micro-hardness of composite electroforming layer and the optimal value of process parameters are determined respectively(from big to small): current density(9A/dm2), diamond content(60g/L), supercritical pressure(14MPa) and supercritical temperature(40℃).Through single factor experiment, the influence of various process parameters on the microstructure and micro-hardness of electroforming layer were analyzedand the error of thicknessof electroforming layer between test value and prediction value is 0.227%. The researchshows that the hardness of Ni-diamond electrodepositing layer prepared in SCF-CO2 can reach to 954HV(200g), increased 80% compared to ordinary condition. The uniformity of composite particles in electroforming layer significantly improves. It means that preparation of Ni-diamond composite electroforming layer under supercritical conditions has advantage of mechanical performance. It can be found from XRD spectrum thatcomparingto ordinary environment,diffraction peak of nickel crystal face(111) is inhibited and the diffraction peak of crystal face(200) is promotedin supercritical conditions.Basic applied research of SCF-CO2 composite electroforming was carried out and fine composite electroforming layer was prepared successfully.Based on parameters of flat electroforming process, the composite electroforming process of the "cross" micro-structure was studiedto analyze the effects of various process parameters on the surface morphology, which laid a good foundation for further engineering application.