Microstructure and Microhardness of Nickel Composite Electroforming Films under CO2 Supercritical Fluids

Abstract:

The experimental method of composite electroforming under CO2 supercritical fluids (SCF-CO2) was brief introduced. The experiment of nickel-Al2O3 and nickel-diamond composite electroforming were investigated using scanning electron microscope (SEM) and digital microscope hardness tester. The surface microstructures of nickel-Al2O3 and nickel-diamond composite electroforming films were analyzed. The effect of strengthening particles (nano Al2O3 particle and micro diamond particle) and pressure on microhardness of nickel-Al2O3 and nickel-diamond composite electroforming films were discussed. The results show that the bright and uniform surface of nickel-Al2O3 composite electroforming coating can be prepared under SCF-CO2 environment, and the dispersion of Al2O3 grains has optimal state. The microhardness of nickel-Al2O3 composite electroforming films gradually increases and then rapidly decreases with the increasing of Al2O3 addition. Its maximum can reach 11.4 GPa when the addition is 60 g/L and the pressure is 14 MPa, which is twice as much as that of the nickel-Al2O3 conventional composite electroforming layer. The content of Al2O3 grain in nickel-Al2O3 composite electroforming film under SCF-CO2 is 9.9 wt%. The microstructure of nickel-diamond composite electroforming films with black diamond grains and cellular distribution can be prepared under SCF-CO2. The microhardness of nickel-diamond composite electroforming films rises fast and then decreases gradually with the increasing of diamond particles. Its maximum can reach 9.1 GPa when the diamond grains content and working pressure are 60 g/L and 10 MPa respectively, but the microhardness will rapidly decrease when the pressure is higher than 14 MPa

Key words:nickel composite electroforming film; supercritical fluids; nano Al2O3 particle; diamond particle; microstructure