Differences between the R-phase and the commensurate phase in iron-doped Ti–Ni shape memory alloys

Abstract

A Ti–44Ni–6Fe (at. %) alloy was recently reported to exhibit a second order-like incommensurate–commensurate transformation. Whether or not the commensurate (C) phase and the R-phase in Ti–Ni alloys are the same phase has now been investigated. Transformation behaviour was examined in a series of Ti–(50 − x)Ni–xFe (at. %) alloys with x = 2.0, 4.0, 5.0, 5.5, 5.7, 6.0. Transformation temperature, entropy change and the transformation strain decrease continuously as x increases up to x = 5.7, where the product phase is apparently the R-phase. However, there is an obvious discontinuity in these values between x = 5.7 and x = 6.0. In addition, electron diffraction experiments have revealed that the intensity of satellite reflections of the C-phase is obviously weaker than that of the R-phase. These results strongly suggest that the C-phase is different from the R-phase.

Keywords:

• precursor phenomena
• incommensurate phase
• martensitic transformation

Acknowledgements

The present work was partly supported by grant-in-aid for scientific research (B) 18360331 from JSPS. This study was also supported by Priority Assistance for the Formation of Worldwide Renowned Centers of Research–The Global Century COE Program (Project: Center of Excellence for Advanced Structural and Functional Materials Design) from MEXT, Japan.