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Evaluation of Porous NTI SMA Formation Mechanism, Pore Characteristics and Thermo-Mechanical Properties Produced by Power Metallurgy for Biomedical Application

Ghasemi, Abbas | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41607 (07)
  4. University: Sharif University of Technology
  5. Department: Materials science and Engineering
  6. Advisor(s): Sadrnezhad, Khatiboleslam
  7. Abstract:
  8. Porous NiTi specimens were produced by elemental nickel and titanium powders and two different temporary space-holder consisting of NaCl and urea and conventional sintering method. Pore characteristic and morphology of porous NiTi specimens was investigated by optical and electron microscopy. Microstructure of specimens was probed using XRD and SEM. Suitable pore distribution and size for biomedical application was obtained using temporary space-holder method. Porosity content increases with increasing space holder powder. At 70 volume percent space-holder, best pore size and distribution with fully open pores, in size 200-500 µm, was obtained and pores are interconnected that suitable for biomedical application. In samples with NaCl space-holder, undesirable chlorine components in microstructure were detected. In other hand, homogenous NiTi was formed in urea space-holder similar to specimens without space-holder powder.
    The result show that the porous NiTi SMA has very good deformation recovery ability , in term of linear superelastcity as high as 4% under a high-cyclic strain level applied, the irrecoverable pore deformation occurs, which results in residual strain; and degradation of superelasticity effect only occurs in the first fatigue cycle, thereafter the good linear superelasticity is maintained. It has been shown that the fatigue of the porous NiTi SMA occurs at relatively lower strain level compared with the dense one.
  9. Keywords:
  10. Space Holder ; Powder Materials ; Biomaterials ; Shape Memory Alloy ; Porous Nitinol

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