Transformation entropy change and precursor phenomena in Ni-rich Ti-Ni shape memory alloys

Kodai Niitsu, Yuta Kimura, Ryosuke Kainuma

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


Many issues concerning the transformation behaviors in the Ni-rich Ti-Ni system remain unresolved, such as the isothermal nature of the B19′-martensitic and R-phase transformations and the precursor phenomena in the B2-parent phase. To clarify the origins of these behaviors, we investigated the transformation latent heat, specific heat, and superelastic behaviors of several Ni-rich Ti-Ni alloys in terms of the entropy change. An anomalous, very wide hump in the specific heat was detected for the B2-parent phase, which can likely be attributed to the precursor phenomenon in the B2-parent phase. In the critical region where the anomalous hump intersects the B19′-martensitic transformation, some evidences of the R-phase transformation were observed, such as a tweed-like microstructure and a specific heat peak with first-order-Transformation characteristics. These findings suggest a strong relationship between the R phase and the precursor state in the B2-parent phase.

Original languageEnglish
Pages (from-to)3822-3830
Number of pages9
JournalJournal of Materials Research
Issue number20
Publication statusPublished - 2017 Oct 27


  • phase equilibria
  • phase transformation
  • specific heat


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