A Galvanostatic Modeling for Preparation of Electrodeposited Nanocrystalline Coatings by Control of Current Density
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The correlation between the grain size of electrodeposited coatings and the current densities was modeled by considering galvanostatic conditions. In order to test the model by experimental results, nanocrystalline (NC) nickel samples were deposited at different current densities using a Watts bath. The grain size of the deposits was evaluated by X-ray diffraction (XRD) technique. Model predictions were validated by finding a curve being the best-fit to the experimental results which were gathered from literature for different NC coatings in addition to those data measured in this research for NC nickel coatings. According to our model, the variation of grain size with the reciprocal of the current density follows a power law. A good agreement between the experimental results and model predictions was observed which indicated that the derived analytical model is applicable for producting the nanocrystalline electrodeposits with the desired grain size by controling current density.Keywords:
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In order to study the effects of pulse parameters on jet electrodeposition, Ni–Co–BN (h) nanocomposite coatings were prepared on the surface of steel C1045. The samples were analyzed and characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), laser scanning confocal microscopy (LSCM), microhardness tester, and electrochemical workstation. The experimental results showed that the contents of Co and BN (h) nanoparticles in the coatings changed with the variation of pulse parameters. When the pulse frequency was 4 kHz and the duty cycle was 0.7, their contents reached maxima of 27.34 wt % and 3.82 wt %, respectively. The XRD patterns of the coatings showed that the deposits had a face-centered cube (fcc) structure, and there was an obvious preferred orientation in (111) plane. With the increase in pulse parameters, the surface roughness of the coatings first decreased and then increased, with the minimum value obtained being 0.664 µm. The microhardness of the coatings first increased and then decreased with increase in pulse parameters. The maximum value of the microhardness reached 719.2 HV0.05 when the pulse frequency was 4 kHz and the duty cycle was 0.7. In the electrochemical test, the potentiodynamic polarization curves of the coatings after immersion in 3.5 wt % NaCl solution showed the pulse parameters had an obvious effect on the corrosion resistance of the Ni–Co–BN (h) nanocamposite coatings. The corrosion current density and polarization resistance indicated that the coatings had better corrosion resistance when the pulse frequency was 4 kHz and duty cycle was 0.7.
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Bulk nanocrystalline nickel was fabricated using the method of direct current deposition by changing the concentrations of the special additive C7H4NO3SNa·2H2O,current density and bath temperature.The microstructure of electrodeposits was evaluated by means of high-resolution transmission electron microscopy(HRTEM). The micro-hardness of electrodeposits was measured.Law of micro-hardness varying was studied.The results show that the bulk nanocrystalline nickel coatings of uniform structure are fabricated by changing parameters of technology.The micro-hardness increases with the increasing of the concentrations of the additive C7H4NO3SNa·2H2O.The micro-hardness increases with increasing of the current density.The micro-hardness almost doesn't increase with increasing of the current density between 700A·m-2 and 1100A·m2.The micro-hardness reduces with increasing of the temperature.
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The Ni-CeO2 nanocomposite coatings have been synthesized by pulse electrodeposition technique with different current densities (0.10, 0.30, 0.40, 0.50, 0.70 and 0.90 A/cm2) from a Watts-type electrolyte containing nano-sized ceria particles. The Ni-CeO2 coatings produced with different current densities have been characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) coupled with an energy dispersive spectrometer (EDS). The hardness of the coatings has been measured by Vickers microhardness tester (VMHT). It has been found that the crystallite size decreases and hardness increases with the increasing current density. However, the co-deposition of ceria in the nickel matrix increases up to the current density of 0.5 A/cm2, beyond which it decreases.
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