Research The Mechanism Of Magnetic Field On Ni-P-Diamond Electroless Composite Plating

Ni-P-diamond electroless composite coatings were manufactured by co-deposition of Ni-P with submicron diamond particles under the influence of magnetic field. For comparison, normal Ni-P-diamond composite coatings were prepared. The diamond particles were in a size range of 0.01 μm～0.5μm with a mean value of 0.25μm. The contents, forming and size of diamond particles in electroless composite coatings were measured by scanning electron microscope with spectrometer(SEM/EDS). The parameters of composite coatings such as the bonding strength, micro-hardness, friction coefficient were tested by coating adhesion test, friction tester and other test equipments. The magnetic field strength was measured by Tesla meter. And base the magnetic field strength, the solenoid internal space divided in different regions. We constructed the uniform magnetic field and gradient magnetic field in this work.The result indicated that the magnetic field has a significant impact on the electroless Ni-P-diamond composite coating. With the effect of uniform magnetic field, the deposition rate, micro-hardness and the bonding strength of Ni-P-diamond composite coatings showed a decreasing trend after the increase with the magnetic field strength increased. The rate of holds and coefficient of friction were increased with the magnetic field strength increase. The coefficient of friction of the sample which was manufactured in 4g/L diamond concentration and 10.60mT magnetic field strength, shown the lowest value. Each elements in the composite coatings were impacted by magnetic field strength varies, obviously. With the effect of gradient magnetic field, the micro-harness and bonding strength of composite coatings has relationship with the magnetic field gradient.Combined magnetic chemistry theory adsorption theory, we draw the following conclusions. (1) Magnetic field could accelerate the deposition rate of nickel ions through accelerate nickel ions and active hydrogen atoms free radicals conversion rate form triplet-phased to single-phased radical pairs; (2) The oxidation rate of hypophosphite increased with the deposition rate of nickel atoms; (3) A mount of hydrogen atoms, which can’t absorb on the catalytic surface, will escape from reaction interface as hydrogen gas, which has the effect of micro-stirring, thereby reducing the particles size of diamond reunion; (4) Too much strong magnetic field could formed amount of hydrogen gas, which could "scoured" the absorbed diamond particles and absorbed hydrogen atoms on the catalytic surface, the result is that, the concentration of diamond particles in the composite coatings was decreased and the surface of the coating became roughness.The result of micro-hardness test and bonding strength test of the samples which with the effect of gradient magnetic field indicate that, the influence of magnetic on composite coatings conform the analyzed based on magnetic chemical.