No abstract

No abstract

The nanocrystalline nickel coating was synthesized by pulse-jet electrodeposition from modified Watts bath. Pulse and jet plating was employed to increase the deposition current density, decrease diffusion layer, increase the nucleation rate and in this case the prepared method would result in fine-grained deposits. Transmission and scanning electron microscopy and X-ray diffraction (XRD) were used to study the microstructure, the surface morphology, the crystal preferred orientation and the variety of the lattice parameter respectively. The influence of pulse parameters, namely peak current density, the duty cycle and pulse frequency on the grain size, surface morphology, crystal orientation and microstructure was studied. The results showed that with increasing peak current density, the deposit grain size was found to decrease markedly in other parameters at constant. However, in our experiment it was found that the grain size increased slightly with increasing pulse frequency. For higher peak current density, the surface morphology was smoother. The crystal orientation progressively changed from an almost random distribution to a strong (111) texture. This means that the peak current density was the dominated parameter to effect the microstructure of electrodeposited nanocrystalline nickel coating. In addition, the lattice parameter for the deposited nickel is calculated from XRD and it is found that the calculated value is less than the lattice parameter for the perfect nickel single crystal. This phenomenon is explained by the crystal lattice mismatch.

In order to enhance the corrosion resistance of a drill pipe for an offshore platform, micro-arc oxidation (MAO) coatings were deposited on the surface of an aluminum alloy drill pipe by MAO technology. The microstructure and anticorrosion performance of the MAO coatings were investigated experimentally. This paper mainly focuses on the experimental work to determine the influence of cathode voltage on the structural characteristics and corrosion resistance of MAO coatings. The results show that the cathode voltage has a significant effect on the preparation of MAO coating during the process. The surface of the coating becomes more compact and smooth with the increase of the cathode voltage. Furthermore, the anticorrosion performance of MAO coatings can effectively be improved with the increase of cathode voltage.

No abstract