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Electrodeposition of Ni-Co/SiC Composite Coatings

Bahadormanesh, Behrouz | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: English
  3. Document No: 39679 (57)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Dolati, Abolghasem
  7. Abstract:
  8. Ni-Co/SiC composite coatings with various contents of SiC nano particles were electrodeposited in a modified watt type of Ni-Co bath containing 20 nm SiC nano particles to be codeposited. The influences of the SiC concentration, current density, stirring rate of the deposition bath on the composition of the coatings were investigated and these parameters optimized for highest amount of SiC codeposition. The optimized deposition parameters were 40 g/l SiC and 480 rpm stirring rate and current density equal to 4 A/dm2. Ni-Co/SiC composite coating was deposited with the maximum particles content of 30.5 volume percent. Linear voltammetry demonstrates addition of the SiC to the Ni-Co deposition bath increased adsorption of Ni2+ and Co2+ ions (especially Co2+ ions) and consequently increased the transfer coefficient. Moreover, chronoamperometric analyses proves that codeposition of SiC particles with Ni2+ and Co2+ ions altered the nucleation mechanism from the mixed instantaneous and progressive to pure instantaneous. In the presence of SiC particles, anomalous behavior of Ni and Co deposition enhanced. Guglielmi’s model was modified for codeposition of high volume percentage of the second phase. The modified equations were verified by experimental results. SEM images clearly showed incorporation of the nano SiC particles altered the surface morphology of Ni-Co from dense irregular to cauliflower-like of Ni-Co/SiC. Nano-mechanical test instrument coupled to the AFM was employed for studying mechanical properties of the deposited coatings. Presence of 11 vol.% SiC in Ni-Co matrix increased the hardness from 2.1 GPa to 3.43 GPa. Average depth of scratch for mentioned composite coating was about 15% less than that of Ni-Co coating. Polarization method employed for investigation of corrosion resistance of deposits. Corrosion penetration rate (CPR) of the Ni-Co/SiC coating with 30.5 vol.% SiC was more than 17 times less than Ni-Co alloy in 3.5 wt% NaCl solution.

  9. Keywords:
  10. Hardness ; Nanocomposite ; Composite Coating ; Guglielmi Model ; Electrodeposition

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