J. Phys. IV France
Volume 112, October 2003
Page(s) 685 - 688

J. Phys. IV France
112 (2003) 685
DOI: 10.1051/jp4:2003975

Stability of B2-type structure and martensitic transformation in Ti-Ni shape memory alloys

T. Fukuda1, T. Sakamoto1, T. Terai1, T. Kakeshita1 and K. Kishio2

1  Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan
2  Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8666, Japan

We have investigated electrical resistivity and magnetic susceptibility in a series of ${\rm Ti}- (50-x)$ ${\rm Ni}-x$Fe alloys, and observed their microstructure by electron microscopy, in order to know the phase stability of the B2-type structure. Following results were obtained: (i) The B2-R transformation temperature decreases as the iron content increases, and disappears in alloys with $x \geq 8$. (ii) The alloy with x=8 shows a negative temperature coefficient in electrical resistivity and an inflection point in the temperature dependence of magnetic susceptibility curve, and these anomalies are suppressed as iron content increases and disappear completely in alloys with $ x \geq 16$. (iii) The electron diffraction of the alloy with x=8 shows 1/3 <110 > diffuse scattering, and its intensity increases as temperature decreases. Furthermore, the dark field image obtained from the diffuse scattering show domain-like structure with its size smaller than 10mm. The results of (ii) and (iii) are related to the instability of the B2-type structure in Ti-Ni based alloys. As for such origin, the Fermi-surface-nesting of the B2-type structure with a vector $q=1/3[110]2\pi/a$ is considered.

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