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TheEffect of Hot Rolling Variables on the Shape Memory Properties of Ni-Ti Shape Memory Alloys

Ahadi, Aslan | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 39941 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Karimi Taheri, Ali; Abbasi, Mahdi
  7. Abstract:
  8. In the present study the hot deformation behavior and the effect of hor rolling variables on the shape memory properties of a Ni-Ti shape memory alloy was studied. In order to simulate the hot compression test Abaqus softeware was employd. The results proved the pronounced increase in the specimen temperature at high strain rates and low temperatures (47 °C at strain rate of 1 s-1 and temperature of 700 °C). Thus, the effect temperature rise due to deformation heating on the characterisitics of the flow curves was eliminated. Afterwards, the corrected constitutive equation of the alloy was obtained and the rolling plan was designed. Shape memory measurments showed that two-way shape memory effect is increased with increasing the height reduction and subsequently drops down. Microstructural observations revealed the presence of martensite variants with haphazard orientations in the annealed specimen causes the weak two-way shape memory effect. Also with increasing the height reduction the one-way shape memory effect increased. Evaluation of the stress-strain curves displays the increament of the stress required for martensite re-orientation with increasing the height reduction that caused the one-way shape memory effect to be increased. Microstructural observations also revealed the prescence of deformation twins with decreasing the rolling temperature. It was seen that the post-rolled grain size is far more sensitive to the height reduction than rolling temperature. DSC measurments was indicative of the decreament in the transformation temperatures with decreasing the rolling temperature. The thermal cycling behavior showed far more intensity of the R-phase in the specimen rolled at lower temperature and its reason needs further investigation.
  9. Keywords:
  10. Nickel-Titanium Shape Memory Alloy ; Recovery ; Martensitic Transformation ; Two-Way Shap Memory Property

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