<Emphasis Type="Italic">In-Situ</Emphasis> Synchrotron Characterization of Transformation Sequences in TiNi-Based Shape Memory Alloys during Thermal Cycling |
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Authors: | NG Jones SL Raghunathan D Dye |
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Affiliation: | (1) Department of Materials, Imperial College London, London, SW7 2AZ, U.K. |
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Abstract: | In-situ synchrotron radiation has been used to provide direct analysis of the transformation sequences in TiNi-based shape memory
alloys during thermal cycling. The high resolution, narrow peak width Debye–Scherrer diffraction spectra enabled positive
identification and quantification of the phase transformation sequences, which is not possible through normal laboratory studies.
The results facilitate a clearer understanding of the development and influence of intermediate phases such as R or B19 on
sequential martensitic transformations. Ti50.2Ni49.8 transformed predominately via a single-step B2 ↔ B19′ transformation, although evidence of the R phase was found during cooling in every cycle. The martensitic
start temperature was depressed by ~0.6 °C per cycle, while the R-phase start temperature was found to be unaffected. Ti50Ni41Cu9 transformed through a two-step B2 ↔ B19 ↔ B19′ sequence, with the B2 → B19 transformation reaching completion prior to the
formation of any B19′. The transformation temperatures of Ti50Ni41Cu9 were found to be insensitive to thermal cycling, remaining constant over the studied cycle range. |
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