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Microstructure Features and Mechanical Properties Microtubes of WE43 Magnesium Alloys for Biodegradable Vascular Stent Application

Torabi Kafshgari, Mehran | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54552 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Akbarzadeh, Abbas
  7. Abstract:
  8. Magnesium and its alloys have gained much attention in medical applications, especially bio-degradable stents. However, they have not been used extensively due to their natural limitations, such as weak mechanical properties. WE43 magnesium alloy has gained attention as a bio-alloy due to its high temperature and good corrosion resistance. The present study aims to use a combination of ECAP and direct tube extrusion to fabricate thin wall tubes with good mechanical properties using WE43 magnesium alloy. In the first phase, the ECAP process at 370°C were conducted up to 4 passes on the homogenized samples to reach ultrafine grain structure. Subsequent to ECAP, direct tube extrusion at 230 °C, 250 °C, 270 °C, and 300 °C were conducted to evaluate a suitable temperature after the ECAP process and produce microtubes with final dimensions of 2.5mm and 2mm, outer and inner diameter, respectively. To investigate the effect of ECAP, an extrusion process was directly used on homogenized samples at 360 °C and 400 °C. Experimental results for most of the examples show a bimodal structure that did not receive a sufficient amount of activation energy for full dynamic recrystallization. Mean grain size after the extrusion process at 400 °C reached 3.1 micrometers and for other conditions reached one micrometer. A difference in the bimodal distribution, type, and distribution of precipitates for the microstructure of samples with the same grain size can be seen. Mechanical properties of samples were studied using tensile test, and microhardness has been reported. Extrusion at 300 °C from the ECAPed example shows the homogenized structure, yield strength, tensile strength, and elongation of 228 MPa, 282 MPa, 15.78%, respectively, which is a good criterion for stent applications
  9. Keywords:
  10. Dynamic Recrystallization ; Direct Extrusion ; Thin Walled Tube ; Equal Channel Angular Pressing (ECAP) ; Stent ; Ultra-Fine Grain Materials ; WE43 Magnesium Alloy

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