Improving Mechanical and Biological Behavior of Mg-2ag Alloy: Effects of Y Addition, Heat Treatment and Coating

Mohammadi Zerankeshi, Meysam | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 55890 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Alizadeh, Reza
  7. Abstract:
  8. Biodegradable Mg-Ag alloys are promising implants for bone tissue regeneration due to their unique ability to reduce inflammation and infection after implantation with the presence of silver. However, their biological performance, including biodegradability, needs further improvement. In this regard, the effects of adding yttrium element, solution heat treatment and coating on the microstructure, biodegradability behavior, mechanical properties and biological characteristics of a cast Mg-2Ag alloy were studied. Addition of 1 wt% of yttrium caused grain refinement in the microstructure and solid solution heat treatment led to a significant decrease in the volume fraction of secondary phases. Also, solid solution strengthening was the most important factor in increasing the ultimate shear strength of the Mg-2Ag alloy from 105 MPa to 122 MPa in the solution-treated Mg-2Ag-1Y alloy. Degradation tests showed the significant role of solution heat treatment in improving corrosion resistance by increasing the homogeneity of microstructure, reducing defects and volume fraction of secondary phases, as well as removing dendritic microstructure of Mg-2Ag alloy. The presence of a stable Y-rich surface film on the surface of the heat-treated Mg-2Ag-1Y alloy can effectively improve the corrosion resistance by inhibiting corrosion propagation, where the corrosion rate of the cast Mg-2Ag alloy decreased from 1.93 to 0.16 mm/year by adding yttrium and heat treatment. The results of cell culture experiments showed good cell adhesion and proliferation of MG63 osteoblast-like cell line on Mg-2Ag and Mg-2Ag-1Y alloys. In addition, the adhesion and viability of the cells were significantly increased by the incorporation of yttrium in the solution state of Mg-2Ag alloy due to the low volume of hydrogen gases produced and excellent corrosion resistance. In order to further reduce the corrosion rate of Mg-2Ag alloy, hydrothermal coating was implemented on its surface in both as-cast and solution states. The hydroxide coating formed on the Mg-2Ag solution-treated alloy demonstrated superior quality due to the almost complete elimination of secondary phases, which ultimately caused the corrosion rate to decrease to 0.04 mm per year, which is the lowest value in all studied alloys
  9. Keywords:
  10. Coating ; Mechanical Properties ; Biocompatibility ; Corrosion Rate ; Biodegradable Magnesium Alloys ; Antibacterial Alloys ; Heat Treatment ; Yttrium

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