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Tribological and Corrosion Properties of Ni-SiC (FGM) Coatings

Daneshpour, Mohammad Javad | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45853 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. Ni-SiC nanocomposite coatings are considered as corrosion resistant coatings with better tribological properties. In order to get superior properties, the amount of added particles should be increased. But high concentration of particles has some drawbacks such as low adhesion to substrate, probability of cracking in coating due to heat expansion coefficient difference between substrate and coating and also embrittlement of coating and low elasticity. In this study, the possibility of producing Ni-SiC nanocomposite coatings with FGM structure was investigated. SiC particles concentration was 5 to 80 g/l and the current density was between 3 to 5 A/dm¬2. The pH of bath and temperature was adjusted to 4 and 50 respectively. Surface morphology, chemical composition and structure of coating were studied using SEM, EDS and XRD. Polarization and impedance tests and OCP monitoring were further carried out to evaluate corrosion behavior of coating and the results then compared with similar coating comprising uniform structure. It was observed that corrosion current density was decreased 5 times and corrosion potential showed a shift toward positive potentials for 114 mv in FGM coatings which shows significant improvement in corrosion behavior. The polarization resistance of coatings increased from 2394 to 5847(ohm). In order to investigating the surface properties, nanoindentation and scratch tests were done using AFM. Results clearly showed that by applying FGM structure, hardness and elastic modules were increased from 1.36 to 1.8(GPa) and 114.1 to 215.0(GPa) respectively and friction coefficient was decreased from 0.39 to 0.28. Eventually, with respect to analysis, it could be concluded that surface toughness of coating in FGM structure has lower value in comparison to regular structures
  9. Keywords:
  10. Functionally Graded Materials (FGM) ; Nano-Composite Coating ; Nickel-Silicon Carbide Coating ; Gradient Structure

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