Optimization of Technology for W/Ni-P Electroless Plating of Artificial Diamond Powder and Study of Quality of the Composite Coating

Artificial diamond powder was sequentially coated with W coating and Ni-P coating by electroless plating to improve its properties.The parameters for electroless plating of W coating and Ni-P coating were optimized based on orthogonal tests and single factor tests.The microstructure and composition of the as- prepared W/Ni-P composite coating were analyzed by scanning electron microscopy and energy dispersive spectrometry,and the size distribution of the plated diamond powder was evaluated with a particle-size analyzer.As the results,the optimal composition of the bath for W electroless plating was suggested as 50 g/L sodium tungstate,32 g/L sodium hypophosphite,25 g/L trisodium citrate,and0.002 0 g/L thiourea;and the optimal electroless plating parameters were suggested as pH value of 8.5,temperature of 90 ℃,and time of 1 h.Besides,the optimal composition of the bath for Ni-P electroless plating was suggested as 35 g/L nickel sulfate,32 g/L sodium hypophosphite,25 g/L trisodium citrate,and0.002 0 g/L thiourea;and the optimal electroless plating parameters were suggested as pH value of 4.5,temperature of 80 ℃,and time of 1 h.As-obtained W/Ni-P composite coating was uniform and fine and exhibited good adhesion to the diamond powder.Moreover,the encapsulated artificial diamond powder exhibited more uniform grain size distribution.