Electroless Ni-P Plating On The Diamond Particles And Properties To Study

Due to high interfacial energy between diamond and general metals or alloys, diamond can not be infiltrated by the general welding alloys, the diamond particles only embedded in the matrix mechanically with a combination of low intensity, in the process of use, diamond is easy to fall off from the tools and fracture while in the Process of work, utilization rate of diamond is only50%to60%or so. Heat resistance of diamond is not high, easily oxidized or graphite at high temperature will reduce the efficiency use of tools. So it is essential to modify the diamond surface. Adoption of electroless plating technique, dense, good adhesion, a certain thickness of chemical coating will be formed on the diamond surface, to enhance the bonding strength with the metal substrate, to improve the surface quality of the tool and to extend its life. Because electroless plating doesn’t need special huge equipment, low cost, and has no limit to material shape, it is a best choice to coat metals on micro-meter diamond by electroless plating method.The advanced testing methods such as optical microscope, scanning electron microscopy(SEM), EDS (EDS), X-ray diffraction(XRD)and so on are adopted to analyze surface morphology of Ni-P coating, phase structures and ingredient of the surface layer of diamond, related to performance analysis, after plating, a preliminary study of the diamond surface metallic coating layer formation mechanism.Through experimental research, selected the appropriate pre-plating process, calculated the deposition rate using weighing method, by analysis of effect of the concentration of each component of Ni-P electroless plating solution on the deposition rate, obtained the best coating conditions:nickel sulfate30g/L, sodium hypophosphite25g/L, citric acid20g/L, thiourea0.22mg/L, the main salt and sub-optimal molar concentration ratio of sodium should be controlled between0.4to0.5, pH4.8～5.5, temperature88±1℃, plating time1.5h.The results show that diamond by the Ni-P plating, the surface is silvery white with metallic luster, the coating is dense and uniform with good adhesion. Ni-P coating of diamond surface has the characteristics of amorphous without heat treatment; after heat treatment, Ni-P coating structure is crystal structure, phase composition of coatings are Ni3P and Ni, Ni12P5, as carried out in the air heat treatment, NiO generated. After heat treatment, the bonding strength between diamond and coating increased substantially. After electroless Ni-P plating, heat resistance of diamond has been greatly improved. Corrosion of the surface of diamond without coating is very serious after heated at high temperature and its heat resistance is poor. Due to protective effect of the coating after plating, so that heat resistance of diamond enhanced. The coating has low porosity, which indicated good density of electroless coating on diamond.Electroless plating on diamond surface has high practical value, increasing service life of diamond tools, reducing application cost.