| Composite electrodeposition is a process that introduces some solid reinforcers into a plating bath, and the reinforcers will combine into the metal matrix when the metal ions reduce on the cathode. So composite deposits is a metal matrix composite material, which include a metal continuous phase and reinforcer discontinuous phase. The Nickel-carbon nanotubes composite synthesize the high-intensity, high modulus and excellent self-lubricating properties of carbon nanotubes and the pyrolytic stability and corrosion resistance of nickel, so this composite has been paid more attention in these years. But the existed references only gave some partial and simple researches on this composite. So, a systematic research about the effect of each factor on the composite electrodeposit was performed in this thesis. Base on this research, the tubular growth of nickel-carbon nanotubes was firstly found during the electrodeposition.A traditional Watts bath with treated carbon nanotubes was used as the plating cell. The cathodic E-i curve, surface morphology, elements analysis, hardness test, tensile test, polarization curve and electrochemical impedance spectrum (EIS) were performed to find out the relationship between the factors and the composite coating's properties. The results showed that the carbon nanotubes had been purified, shortened and actived after the treatment. The carbon nanotubes uniformly distributed in composite coatings and the dispersed carbon nanotubes combined with nickel matrix tightly. The resultant composite coating has a compact structure and uniform thickness. This composite coating also keeps higher hardness and cohesion ability than pure nickel coating. In the following experiments it has been found that the increasing of carbon nanotubes concentration is helpful to improve the sedimentation velocity, cohesion of the composite coatings but decreases its hardness and surface smoothness. The increasing of deposit current density makes the coating's surface coarser. The hardness, cohesion and corrosion resistance increase firstly with the increasing of current density, and decrease after reaching their peak values at 8A/dm~2. Higher bath temperature can improve the sedimentation velocity and coating's hardness. A smooth surface can be performed in either higher temperature or lower temperature bath. The agitation keeps weak effects on composite coating's properties, and the increasing of agitation can improve the coating's sedimentation velocity and hardness slightly.The pulse reverse process and Ni-CNTs composite was firstly utilized together to gain a perfect composite in this thesis. The relationship between pulse reverse parameters and the composite coating's properties was studied. The results showed that the increasing of both reverse ratio and frequency made the coating's surface smoother because the selective solution of nickel on the bumps. The carbon nanotubes content in composite coatings increases with higher reverse ratio and frequency because the increasing of reverse ratio can make more nickel dissolved and higher frequency give more opportunities to combine carbon nanotubes in composite coatings. Harder composite coatings can be gained at higher reverse ratio and lower frequency, which is mainly effected by the nickel matrix. The coating formed at 30% reverse ratio and 100Hz keeps the best cohesion to the carbon steel because the carbon nanotubes' reinforce. The effect of nickel matrix and carbon nanotubes make the coating formed at 30% reverse ratio and 100Hz keep the best corrosion resistance.The effect of anion surfactant and cation surfactant on the carbon nanotubes content, surface morphology, hardness, cohesion and corrosion resistance of composite coatings was studied and compared with the coatings without the assistance of surfactant. The results showed the addition of anion surfactant improved the composite coatings' mechanical properties but the cation surfactant made the coatings worse. The anion surfactant makes the carbon nanotubes charged with anions so it decrease the carbon nanotubes content in coatings because of the electrostatic repulsion, and the cation surfactant makes the carbon nanotubes charged with cations so it increase the carbon nanotubes content because of the electrostatic attraction. The nanotubes with anion surfactant can accelerate the nickel ions reduction on the cathode, which make the composite coatings coarser, and the cation surfactant can also make composite surfaces coarser by the more tangled carbon nanotubes. Both anion surfactant and cation surfactant can decrease the nickel grain size and change the texture coefficient of crystal plane. The anion can increase the cohesion between the and subsequently improve coating's hardness and the cohesion between the composite coating and the carbon steel. The cation makes the cohesion between carbon nanotubes and nickel deposits worse, so the composite coatings keep low hardness and poor cohesion to the carbon steel. Corrosion resistance of coatings with anion surfactant is not decreased but coatings with the assistance of cation surfactant loss its corrosion resistance and can not protect the parent metal effectively.The tubular growth of nickel-carbon nanotubes was firstly found during the electrodeposition in this thesis. This process is different from the existed template auxiliary deposition process about its complex procedures and the dependence on template material. The deposition mechanics of this nickel matrix composite was also discussed in this thesis. The research on this metal tube shows that the inner surface of this tube is smooth and the tube wall is compact. The outside diameter of this tubule is about 200-300μm with a wall thickness of about 10-20μm. The hydrogen bubbles play a great part in the metal tube formation. The absorption of carbon nanotubes on the interface between the bubble and electrolyte is the key procedure to stabilize the bubble on the electrode surface and act as the frame construction of nickel ions reduce.
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