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Preparation of Composite Coating with ZrO2 Nanoparticles on Mg alloy using AC Plasma Electrolyte Oxidation

Bahrami, Alireza | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50296 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Ghorbani, Mohammad
  7. Abstract:
  8. Plasma electrolytic oxidation (PEO) was implemented to produce a ceramic coating on AZ31 magnesium alloy, using an alternate power source (AC), in a silicate based electrolyte containing zirconia nanoparticles in different concentrations. Prior to adding nanoparticles to electrolyte, working parameters such as current density, frequency and coating duration were examined and studied concerning the equipment and coating conditions. And after reaching the optimized condition, ZrO2 nanoparticles were added to the electrolyte to create composite coatings. To examine the properties of the coatings before and after the creation of composite PEO coatings, scanning electron microscopy (SEM) was used to study the morphology and elemental analyses (EDS) and X-ray diffraction (XRD) were used to investigate the chemical and phase composition, respectively. Corrosion resistance of the specimens were evaluated by potentiodynamic polarization test. Moreover, coating hardness and its tribological properties were examined with microhardness and ball-on-disc tests. The results revealed that with producing PEO coatings with incorporation of zirconia nanoparticles into them, coating morphology became more homogenous and by filling the pores and defects with nanoparticles, porosity fell relatively from 41% to 15%. Therefore, corrosion resistance of composite coating was promoted in comparison with ordinary PEO coatingsCorrosion current density in the uncoated samples decreased from 1.20×103 in normal coated samples (non-composite) and after adding 8 g/l nanoparticles to electrolyte, current density decreased to 4.16×10-1. The smaller diameter of indenter mark and the narrower wear track of PEO coatings containing nanoparticles compared to non-composite coatings, proved improved hardness and tribological properties of nanocomposite coatings. It should be noted that the coefficient of friction in nanocomposite coatings was more stable than non-composite ones
  9. Keywords:
  10. Plasma Electrolytic Oxidation ; AZ31 Magnesium Alloy ; Zirconia Nanoparticles ; Abrasion Resistance ; Corrosion Resistance ; Composite Coating

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