Shape Memory and Superelasticity

, Volume 4, Issue 4, pp 417–427 | Cite as

The Effect of Low Temperature Aging and the Evolution of R-Phase in Ni-Rich NiTi

  • Ali ShamimiEmail author
  • Behnam Amin-Ahmadi
  • Aaron Stebner
  • Tom Duerig


This study investigates the thermal and mechanical properties that arise from aging Ni-rich Ni–Ti (Nitinol) at temperatures below 250 °C, well below those commonly used to fabricate medical devices. We demonstrate that the Ni50.8–Ti49.2 composition decomposes at temperatures as low as room temperature and discuss the unusual changes in thermal and mechanical behaviors compared to common aging treatments, such as separation of Martensite and R-phase transformations. Using such aging treatments, superelasticity can be achieved without the presence of austenite at body temperature (Af > 45 °C, well above the body temperature). Furthermore, the influence of R-phase on mechanical response and the disparity between thermal and mechanical behavior is discussed in detail.


Aging R-phase Low temperature aging Mechanical properties Heat treatment NiTi < materials Precipitation 


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Copyright information

© ASM International 2018

Authors and Affiliations

  • Ali Shamimi
    • 1
    Email author
  • Behnam Amin-Ahmadi
    • 2
  • Aaron Stebner
    • 2
  • Tom Duerig
    • 1
  1. 1.Confluent Medical Technologies Inc.FremontUSA
  2. 2.Colorado School of MinesGoldenUSA

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