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Nanostructural Coating of Al2O3 on NiTi Alloy Via Electrochemical Method for Improvement of Biomedical and Surface Properties

Mahloujchi, Raziyeh | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45605 (07)
  4. University: Sharif University of Technology
  5. Department: Material Science and Engineering
  6. Advisor(s): Sadrnezhaad, Khatiboleslam
  7. Abstract:
  8. Nitinol alloy is important and increasingly used in medicine and industry due to its unique properties such as shape memory and superelasticity. Plasma Electrolytic Oxidation (PEO) is a relatively new method which in electrical discharge occurrence and formation of small plasma arcs on the anode surface and the electrochemical and thermochemical reactions in plasma environment prepare ceramic coating on the substrate. This method is taken into consideration because of its simplicity and effectiveness in the preparation of oxide ceramic coatings with porous structure on the surface of certain metals and alloys to improve their corrosion and wear properties. In this study, to improve the surface properties and enhance the biocompatibility of this alloy, the Plasma Electrolytic Oxidation (PEO) method was used in galvanostatic mode and Al2O3 nanostructured coating prepared on the surface of the alloy. For this purpose, aqueous electrolyte containing sodium aluminate and sodium hypophosphite with 0.15 and 0.01 mol.lit-1 constant concentrations was used. Firstly, the 0.1, 0.2 and 0.3 A.cm-2 current densitie were used for 4 minutes constant time and voltage-time curves, surface morphology, thickness, elemental and phase composition and corrosion resistance were studied for the obtained coatings. As regards the coatings of 0.2 A.cm-2 current density showed better surface structure and corrosion resistance, this current density was used for further studies. Then, the coating process was performed for 6 and 8 minutes, and in addition to the previous tests, line scan, mapping and wear tests were carried out on the coatings. The results showed that up to 6 minutes operation time, the coating properties were improved. But afterwards with increasing the operation time, some microcracks formed on the surface of coatings due to the increased sparks energy that led to deterioration of the coatings properties
  9. Keywords:
  10. Nitinol Alloy ; Plasma Electrolytic Oxidation ; Galvano Static ; Nanostructured Coating ; Electrochemical Method ; Nanostructured Alumina Coating

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