Tatsuhiko Ueki

Shape memory characteristics of sputter-deposited Ti-Ni-base thin films

Ti-Ni-Cu and Ti-Ni-Pd ternary shape memory alloy thin films were made by sputtering. They showed smaller temperature hysteresis and higher transformation temperatures, respectively, than those of Ti-Ni binary thin films; these characteristics are effective to achieve a high response actuator characteristic. The transformation temperatures and shape memory behavior were characterized by DSC measurement and thermal cycling tests under a variety of constant stresses, respectively. The Ti-Ni-Pd thin film showed a single stage transformation both upon cooling and heating similarly to a Ti-Ni binary alloy thin film which was also made in the present report; the transformation occurred between the parent B2 phase and martensite M(monoclinic)-phase. Correspondingly, they showed a single stage deformation both upon cooling and heating. The Ti-Ni-Cu thin film showed a two-stage transformation and hence a two-stage deformation; the first stage corresponds to the transformation between B2 and O(Orthorhombic)-phase and the second stage between the O- and M-phases. The first stage transformation was accompanied by a small temperature hysteresis. All these thin films showed perfect shape memory effect.

A new, automatic hydrothermal fluid sampler using a shape-memory alloy

A new hydrothermal fluid sampler has been developed to provide more maneuverability in underwater operation. The sampler characteristically employs a shape-memory alloy, which senses high temperature and actuates the suction mechanism. A shape-memory alloy is also used to switch the intake valve of the sampler, the intention being to avoid missampling when the inlet is in low temperature water. Prototype samplers were designed to collect the fluids hotter than 80°C. Test sampling was performed at hydrothermal vents (1372–1374 m deep) in the submarine volcano, Suiyo Seamount, Izu-Bonin Arc, northwestern Pacific. Observed fluid temperature was between 138 and 298°C, while the ambient seawater temperature was 3.1°C. Each prototype collected about 100 ml fluid as designed. The magnesium concentration in the samples indicated a seawater content of 47.5–90.8%, which indicates the entrainment of ambient seawater. Microscopic observatinn revealed the occurrence of microorganisms in the sample fluids at a population density of 105 to 106 cells ml−1, which is 2–3 orders of magnitude higher than those in seawater at that depth. The use of the newly developed fluid sampler will greatly facilitate the collection of vent-associated microorganisms, which are of potential biological and biotechnological interest.

Superelastic characteristics of Ni-Ti-Cu-X alloys

Transformation properties and superelastic characteristics were investigated in Ni-Ti-Cu ternary and Ni-Ti-Cu-X quaternary alloys, in order to provide a new superelastic alloy with smaller hysteresis for the application around room temperature. The Ms points of the Ni-Ti-Cu ternary alloys did not decrease below room temperature by changing the alloy composition or the heat treatment condition. The Ms point decreased linearly with the Cr and Fe contents as the forth element. The Ni-Ti-Cu-Cr alloys with the Cr content over 0.4% had Ms points below room temperature. Small hysteresis about 130MPa was measured in the Ni39.8Ti49.8Cu10Cr0.4 alloy at 310K, which was a quarter of that of the Ni50Ti50 alloy. This new superelastic alloy has an advantage over the Ni-Ti binary alloy in energy storage efficiency.