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

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 tran...

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Bibliographic Details
Published in:Journal of materials research 2017-10, Vol.32 (20), p.3822-3830
Main Authors: Niitsu, Kodai, Kimura, Yuta, Kainuma, Ryosuke
Format: Article
Language:English
Subjects:
Alloy systems
Alloys
Applied and Technical Physics
Behavior
Biomaterials
Entropy
Equilibrium
Heat
Heat of transformation
Inorganic Chemistry
Invited Paper
Latent heat
Martensitic transformations
Materials Engineering
Materials research
Materials Science
Nanotechnology
Nickel base alloys
Phase transitions
Precursors
Shape memory alloys
Specific heat
Stress-strain curves
Superelasticity
Temperature
Titanium base alloys
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Summary: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.
ISSN:0884-2914
2044-5326
DOI:10.1557/jmr.2017.377