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Molecular Dynamics Simulation of Phase Transformation and Shape Memory Effect of Ni-Ti Nanowires

Ebrahimi, Nazanin | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44158 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Simchi, Abdolreza; Akbarzadeh Changiz, Abbas
  7. Abstract:
  8. Phase transformation in Ni-Ti shape memory alloys (SAM) have been investigated quite frequently due to their shape recovery by thermal cycling. With emerging of nanotechnology, the martensitic/austenite phase transformation in SAM at nanoscale has become of interest for MEMS and NEMS applications. In this work, molecular dynamic simulation (MD) was utilized to study the phase transformation and shape memory effect in Ni-Ti nanowires. EAM/Alloy and EAM/FS potential functions were used. The potential energy versus temperature and time for the phase transformation was calculated and combined with the radius distribution function (RDF) in order to study the changes in the crystal structure. Effects of thermal rates, size of the nanowires, and loading cycles on the shape memory effect and strain recovery after pre-loading or deformation were studied. It was shown that an increase in the heating/cooling rate postpones the phase transformation of martensite to austenite or vise versa. In fact, the amount of thermal hysteresis was found to increase due to a shift in the transformation temperature to lower/higher temperatures. It was also shown that the phase transformation temperatures depend on the size of nanowires. We observed an increase in the temperature as the size of the system decrease to nanoscale. Studying of the shape memory effect determined that, in spite of bulk Ni-Ti alloys, the strain recovery in nanowires was dominated by the thermal fluctuations while the role of the phase transformation was less important
  9. Keywords:
  10. Molecular Dynamic Simulation ; Nanowire ; Martensitic Transformation ; Nitinol Alloy ; Shape Memory Effect

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