Papers by Keyword: Ti-Ni

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Authors: M. Tomozawa, K. Okutsu, Hee Young Kim, Shuichi Miyazaki
Abstract: Dynamic actuation properties of two types of high-speed microactuators utilizing Ti-Ni-based thin films were investigated. One type is a microactuator utilizing a Ti-Ni-Pd thin film which has high transformation temperatures. Cooling rate of a microactuator increases with increasing temperature difference between transformation and atmosphere temperatures, thus the increase in transformation temperature is effective to increase the actuation response. The other type is a microactuator using R-phase transformation of a Ti-Ni thin film which has a narrow transformation temperature hysteresis. The narrow transformation temperature hysteresis of the R-phase transformation is effective to increase the actuation response. Both types of actuators are promising for high response applications. The working frequency of the microactuators reached 100Hz in the two types of microactuators utilizing the martensitic transformation of the Ti-Ni-Pd thin film and the R-phase transformation of the Ti-Ni thin film.
Authors: I. Yoshida, S. Yoshida
Authors: Hongyang Xing, Anak Khantachawana, Hee Young Kim, Shuichi Miyazaki
Abstract: The microstructure and shape memory behavior of Ti-rich Ti-Ni melt-spun ribbons with various Ni-contents were investigated. Ti-xNi(x=40~48at%) ribbons were fabricated by the melt-spinning method at the rotation speed of 5000rpm. They were heat-treated at 1073K for 3.6ks. It was found that the Ti-40at%Ni as-spun ribbon exhibited almost complete amorphous structure, while the specimen with more Ni-content, such as 48at%Ni ribbon exhibited the coexistence of amorphous and crystalline structures. It was also found that the maximum shape recovery strain increased with increasing Ni-content. The Ti-40at%Ni ribbon was very brittle because of many Ti2Ni precipitates formed.
Authors: Hiroki Cho, Takaei Yamamoto, Akihiko Suzuki, Toshio Sakuma, Kiyoshi Yamauchi
Abstract: It is well-known that the Ti-Ni shape memory alloy (SMA) is applicable to the medical stent. The repeated heat-treatment under the constrained strain is necessary for the manufacturing process of the laser-cut SMA stent. In this research, the effect of heat-treatment under the constrained strain on mechanical properties of the Ti-Ni shape memory alloy wire was investigated. The applied strain at single heat-treatment (εap) was 4, 5 and 8%, and the heat-treatment is repeated so as to became total applied strain 40%. In the case of εap=4 and 5%, partial transformation occurs in the SMA wire, and so a necking appears in the SMA wire. Due to this necking, multi-step martensitic transformation, and decreasing of breaking strength / breaking strain are caused. The necking does not occur because the whole of the SMA wire is transformed for εap=8%. The mechanical properties are improved by increasing of εap. Nevertheless, the mechanical properties of each sample are inappropriate for the medical stent. However, the mechanical properties of the as-manufactured sample are improved greatly by training. In addition, it is desirable that the applied strain during training is slightly larger than the requested strain for application.
Authors: Hong Yan Xing, Hee Young Kim, Shuichi Miyazaki
Abstract: Effects of rotation speed on the microstructure and transformation behavior were investigated for Ti-48at%Ni melt-spun ribbons. The Ti-48at%Ni shape memory alloy ribbons were fabricated by the melt-spinning method with various rotation speeds ranging from 2500rpm to 7500rpm. The melt-spun ribbons were completely crystallized to TiNi B2 phase during solidification at lower rotation speeds less than 4000rpm. Amorphous and B2 phase coexisted in the melt-spun ribbons fabricated at higher rotation speeds of 5000rpm and 7500rpm. The martensitic transformation behavior was investigated both in the as-spun and heat-treated ribbons. The transformation temperature increased with decreasing cooling rate and increasing heat-treatment temperature.
Authors: Takaei Yamamoto, Hiroki Cho, Toshio Sakuma
Abstract: This study describes the effect of temperature on critical stress for slip of Ti-Ni shape memory alloy. Tensile loading-unloading tests has been carried out using Ti-50.3at%Ni in the temperature range from 193K to 423K in order to investigate the temperature dependence of critical stress for slip of Ti-Ni shape memory alloy. The critical stress for slip is different in the three regions which are the martensitic single phase state in the range of 193K-273K, the mixture state of the martensitic and parent phases in the range of 273K-373K and the parent single phase state in the range of 373K-423K. The critical stress for slip of the martensitic single phase is about 200MPa. In the case of the mixture state of the martensitic and parent phases, the critical stress for slip increases with increasing temperature, and reaches the maximum stress of 652MPa at 373K. The critical stress for slip of the parent phase decreases with increasing temperature.
Authors: Hideki Hosoda, M. Tsuji, Y. Takahashi, Tomonari Inamura, Kenji Wakashima, Yoko Yamabe-Mitarai, Shuichi Miyazaki, Kanryu Inoue
Authors: Yu Wang, Xiao Bing Ren, Kazuhiro Otsuka
Abstract: “Glass”, a frozen disordered-state, has been found in areas as diverse as amorphous solids, magnetic alloys, ferroelectrics, superconductors, and even in models of biological evolutions. In the present review we introduce a new class of glass–the “strain-glass”, which was discovered very recently. Strain glass is derived from a martensitic system, where the local-strain is frozen in disordered configuration. The first example of strain glass was found in the well-studied Ni-rich Ti50-xNi50+x martensitic system in its “non-transforming” composition regime (x>1.5). Contrasting to the familiar martensitic transition, the strain glass transition is not accompanied by a change in the average structure, or a thermal peak in the DSC measurement. It involves a dynamic freezing process with broken ergodicity, during which nano-sized martensite domains are frozen. More interestingly, the seemingly “non-martensitic” strain glass exhibits unexpected properties: shape memory effect and superelasticity, like a normal martensitic alloy. Strain glass bears a striking similarity with other two classes of glasses: cluster-spin glass and ferroelectric relaxor. These ferroic-transition-derived glasses can be considered as a more general class of glass: ferroic glass. The finding of strain glass may provide new opportunities for martensite research from both fundamental side and application side.
Authors: E. López Cuellar, Gérard Guénin, Michel Morin
Abstract: The strain-resistivity behavior of Ti-45.0Ni-%.0Cu wires has been measured during superelastic cycling. The results are in good agreement with previous results, showing that the main changes of resistivity during superelastic cycling are due to Austenite ↔ Martensite phase changes and anisotropic variant orientation. The true plastic strain (dislocations) does not seem to play an important role for this alloy.
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