Novel Shape Memory Alloys: Poster Session
Program Organizers: Othmane Benafan, NASA Glenn Research Center
Tuesday 5:30 PM
July 11, 2017
Room: Crystal Ballroom A
Location: Hyatt Regency Chicago
P2-24: Aging Hardening Behaviors in Bcc-type Mg-Sc Alloy: Daisuke Ando1; Yukiko Ogawa1; Yuji Sutou1; Junichi Koike1; 1Tohoku University
Recently, our group discovered that a metastable bcc Mg-Sc alloy shows a shape memory behavior due to martensitic transformation . This discovery was led by a finding of very fine plate-like precipitates in bcc-type Mg-Sc alloy after aging. According to a Mg-Sc binary phase diagram, we could expect a metastable bcc phase transform to a stable hcp phase in low annealing temperature. Then, we recognized that the microstructure is much resemblance to that of Ti based shape memory alloy after aging. Therefore, we researched the alloy with considerable certainty that Mg-Sc alloys show shape memory effect. In this presentation, we would like to discuss the aging hardening behavior in bcc-type Mg-Sc alloy in detail. Y. Ogawa, D. Ando, Y. Sutou, J. Koike Science, 353 (2016) 368-370
P2-25: An Experimental Study on Strain Rate Sensitivity of Fe-28Mn-6Si-5Cr Shape Memory Alloy under Tensile Deformation: Bo Cao1; Takeshi Iwamoto1; 1Hiroshima University
Fe-28Mn-6Si-5Cr alloy, which is one of Fe-based shape memory alloys, shows the smaller shape memory effect (SME) compared with the widely-used Ni-Ti alloy. However, its production cost is much lower. Thus, the alloy is attempted to be applied to many engineering fields under different working environment loaded at various strain rates. It is necessary to evaluate tensile deformation behavior of the alloy in a wide range of strain rate including a measurement of an amount of martensite which can control such excellent performances as well as temperature for increasing a reliability of the alloy. In this study, tensile tests at various maximum strain are conducted from quasi-static to impact deformation. The rate sensitivity of volume resistivity and temperature in the alloy is estimated experimentally by using the assembled circuit of Kelvin double bridge with a higher precision and a thermocouple during tensile tests.
P2-26: Characterization of new Cu-based Shape Memory Alloys with very low transformation temperature: Patricia Lorenzo Garcia-Minguillán1; Iñaki López Ferreño1; Tomasz Breczewski1; Maria L. Nó1; Jose San Juan1; 1University of Basque Country
New Cu-based SMAs have been developed for cryogenic applications, these alloys have a temperature range between 20-400 K. Unfortunately, most of the commercial experimental equipment are usually working in temperature ranges down to about 100K.So in the present work, we describe first the design of a new electrical resistivity equipment with a closed cycle, based on four probe method, in order to measure the transformation temperatures down to liquid helium. The final operational performances are also described. Then in the second part of the work, we used this equipment to study a new family alloy exhibiting martensitic transformation at very low temperatures, down to 20 K. The dependence of the transformation temperatures on concentration is established. In the intermediate temperature range, resistivity results have been compared with those obtained by DSC in order to verify the reliability of all transformation temperatures range in these new alloys.
P2-27: Cryogenic Immersion Time of Influence on Thermal and Mechanical Properties of an Alloy with Shape Memory Ni48Ti52: Bartholomeu Cruz Filho1; 1Universidade de Brasília - UnB
Summary: Cryogenic processing has been used with relative success to increase the wear resistance of tool steels and high cycle fatigue life in ferrous materials. This study investigates the effects of cryogenic immersion on thermal and mechanical properties of an alloy with Ni48Ti52 shape memory. The treatments consist of a cryogenic cooling 24°C to -196°C with a heating and cooling rate of 18°C/h, the samples immersed for 12 hours, 18 hours and 24 hours at a temperature of -196 °C, respectively. The modulus of elasticity and damping obtained by the pulse excitation technique, the phase transformation temperature, latent heat of transformation obtained by differential scanning calorimetry and hardness C scale obtained by Hockwell a comparative analysis of the properties of their respective CP'S with and without DCT were performed using optical microscopy testing procedures, scanning electron microscopy and diffraction X-ray which allowed to assess how these properties they are affected.
P2-28: Crystallization and Martensitic Transformation Behavior of Ti-Ni-Si Alloys: Ju-wan Park1; Yeon-min Im1; Yeon-wook Kim2; Tae-hyun Nam1; 1Gyeongsang National University; 2Keimyung University
Ti-Ni-Si alloy ribbons were prepared by melt spinning and then crystallization temperature and activation energy for crystallization were investigated by differential scanning calorimetry(DSC). Crystal structure and microstructures of ribbons was examined by X-ray diffraction and electron microscopy. Ti-Ni-Si alloy ribbons with Si content less than 1.0 at% were crystalline, while those more than 3.0 at% were amorphous. Crystallization occurred in the sequence of amorphous → Ti2Ni + B2 → Ti2Ni + B2 + TiNi3 → Ti2Ni + B2 + TiNi3 + TiSi + Ti5Si4. Activation energy for crystallization was 189±8.6 kJ/mol for a Ti-47Ni-3Si alloy and 212±8.6 kJ/mol for a Ti-45Ni-5Si alloy. In a Ti-47Ni-3Si alloy, the B2-B19’ transformation occurred irrespective of crystallization temperature. In a Ti-45Ni-5Si alloy, the two-stage B2-R-B19’ transformation occurred when crystallization temperature was higher than 973 K, while the one-stage B2-R when it was lower than 893 K.
P2-29: Damping Rate Comparative Analyses of a Cu-14Al-4Ni SMA Subjected to Heat Treatment and Hot Rolling: Victor Barbosa1; Pedro Cunha de Lima1; Camila Aguiar Teixeira1; Emmanuel Pacheco Rocha Lima2; Nicole Oliveira de Araujo1; 1Federal Institute of Bahia; 2UNB
The present study aims to compare the damping rate of a Cu-14Al-4Ni treated thermally and one treated thermomechanically. Both alloys underwent heat treatment of betatization at 950oC during 30 minutes. Posteriorly, one alloy was hot rolled with 5% elongation. The damping rate, or internal friction, were obtained through Impulse Excitation Method based on the rule ASTM E1876, and also determined the Young Modulus. All alloys were subjected to Hardness Test, Scanning Electronic Microscopy (SEM) to analyze their microstructure and obtain grain size, and X-ray Diffraction (XRD) to investigate the martensitic phase. The results showed that the alloy thermomechanically treated presented a higher damping rate due to the martensitic phase (0,0,18)’when compared to the one only thermally treated. The hot rolled alloy also showed lower Young Modulus, hardness and grain size that give the structure a higher quantity of grain boundary to reduce vibration.
P2-30: Design of Fatigue-Resistant Shape Memory Alloys for Medical Applications: Chuan Liu1; Gregory Olson1; 1Northwestern University
NiTi-based shape memory alloys have been widely applied in biomedical devices. While low Ni composition is desirable to decrease Ni-hypersensitivity, long fatigue life is also of essential importance to fulfill new stringent performance requirements of artificial heart valve. Fatigue simulations modeling crack nucleation have identified the significance of increasing matrix yield strength and controlling inclusion size. The precipitation of coherent nanoscale L21 Heusler aluminides from a supersaturated B2 matrix is an effective approach to enhance its matrix yield strength. A system design approach is taken to develop high strength NiTi-based alloys with quaternary additions such as Pd and Zr. To control inclusion size, inclusion morphologies of NiTi tubes processed by different melting methods are characterized. Electron beam refining is confirmed to significantly decrease the average inclusion size.
P2-31: Effect of Magnetron Sputtered W Thin Film on the Surface Characteristics and Corrosion Behavior of NiTi Shape Memory Alloys: Ailian Liu1; Jiawen Xu1; Chao Liu2; Jiehe Sui3; 1Heilongjiang University of Science and Technology; 2 Northeast Petroleum University; 3Harbin Institute of Technology
NiTi shape memory alloys have been widely applyed in the medical field due to their unique shape memory effect and superelasticity as well as biocompatibility. However, excesses of Ni ion may cause allergic reactions and promote carcinogenesis and toxic reactions. Surface modification of NiTi is an effective way to improve the above problems. W thin film was deposited on NiTi alloy by magnetron sputtering in this paper and the surface characteristics and corrosion behavior of experimental alloys were researched. Results show that the W film with sputtering power 100W is uniformly dense, with the minimum roughness and maximum thickness. Sputtering W leads to the formation of W2O5 and inhibits the release of Ni ion effectively. The corrosion resistance of NiTi alloy in Hank's solution has been evidently improved by W sputtered. The NiTi alloy with a moderate magnetron sputtering power 100W exhibits the best corrosion resistance ability.
P2-32: Effect of Silver Addition on the Microstructure, Cytotoxicity and Corrosion Resistance of NiTi and NiTiCu Shape Memory Alloys: Prasanna Iyengar1; Sampath Vedamanickam1; 1Indian Institute of Technology, Madras
Among shape memory alloys (SMAs), Ni-Ti SMAs are extensively for medical devices. Though addition of silver enhances biocompatibility and antibacterial behaviour, it has not been explored on Ni-Ti alloys. In the present work, NiTiAgx and NiTiCuyAgx alloys were therefore prepared by vacuum induction melting, homogenized and rolled at 900ºC. Cytotoxicity was assessed by MTT assay using L6 myoblast cells and binary NiTi as positive control. The transformation temperatures were determined by DSC. Phase analysis was carried out by XRD and Rietveld method was used to refine data to obtain information on crystal structure and strain parameters. Corrosion studies were carried out on the alloys in Hank’s solution. SEM and EDX were used to characterize the microstructures and morphological changes during the assay. The results were correlated to assess the effect of addition of Ag on the properties of the NiTi alloys. Keywords: shape memory alloys, biocompatibility, cytotoxicity, MTT assay, corrosion,
P2-33: Effect of Testing Temperature on Deformation Behavior of a Ti-Au-Cr-Zr Superelastic Alloy
: Yuri Shinohara1; Masaki Tahara1; Tomonari Inamura1; Hideki Hosoda1; 1Tokyo Institute of Technology
A metastable β (bcc) Ti-Au-Cr-Zr alloy exhibits superelasticity at wide temperature range compared to conventional β-Ti alloys. Testing temperature dependence on microstructure and superelastic properties were revealed in this study to understand the mechanism of superelasticity of this alloy. Ti-4Au-5Cr-8Zr (mol %) was analyzed by transmission electron microscopy (TEM) observations at 93 - 297 K. In addition, the mechanical properties of this alloy were evaluated by tensile tests at 123 - 433 K. The fundamental reflection of β phase and diffuse scattering of athermal ω phase were recorded regardless of the testing temperature in selected area diffraction pattern. The yield stress was dependent on testing temperature as shown by the linear relationship with positive slope at 313 - 413 K. It is considered that the yield stress corresponds to stress for inducing martensite and follows Clausius-Clapeyron relationship at this temperature range.
P2-34: Effect of Thermal Cycle on Shape Memory Characteristics of Ti-(50.0, 50.3)Ni-(15-X)Hf-XZr Alloys: Jae Il Kim1; Aaron Stebner2; Ik Ha1; 1Dong-A University; 2Colorado school of mines
This study investigated the effect of theraml cycle on tranformation temeprature of Ti-[50.0, 50.3]Ni-(15-X)Hf-XZr(X=0~15). After melting, all ingots were homogenized at 1273K for 10hr in an argon atmosphere, followed by solution treatment at 1073K for 1hr and water quenching. Thermal cycle(~1000th) without loadong was carried out. As a result of DSC measurement with increasing Zr content, the martensitic transformation temperature(Ms) of Ti-(50.0, 50.3)Ni-(15-X)Hf-XZr alloys decreased. The Ms of Ti-50.0Ni-(15-X)Hf-XZr alloy is higher than that of Ti-50.3Ni-(15-X)Hf-XZr alloys in same Zr content. The Ms of Ti-50.3Ni-(15-X)Hf-XZr steeply decrease than Ms of Ti-50.0Ni-(15-X)Hf-XZr. With increasing thermal cycle(~1000th), the Ms decreases and saturates in low Zr conten alloys and decreases continuously in the high Zr content alloys. This means that the addition of Zr causes thermal stability to degrade. The Ms of Ti-50.0Ni-Hf alloys decrease more than that of Ti-50.3Ni-Hf alloys with increasing thermal cycle number at the same Zr content.
P2-35: Effects of Ageing on the Superelastic Properties of 50.3Ni-Ti-XHf (x = 6,8) Alloys: Joseph Pauza1; Aaron Stebner1; Jaeil Kim2; Tom Duerig3; Spencer Connor1; 1Colorado School of Mines; 2University of Dong-A; 3Confluent Medical
Traditional Nitinol alloys require a significant amount of cold-work in order to obtain strengths exhibited by precipitate hardened NiTiHf alloys. As a result, new NiTiHf alloys have been developed for 3D printing applications, where cold-work is not practical. We present an investigation of the effects of H-phase precipitation on the superelastic behavior of NiTiHf6 and NiTiHf8 as a result of variations in ageing treatments. In Nitinol alloys it is clear that the increase in precipitate volume increases the transformation temperatures, however the effect of precipitate growth on the transformation temperatures of these novel alloys is not as straightforward. Hafnium acts as transformation temperature promoter while Nickel is a demoter and H-phase precipitate depletes the matrix of both elements, consequently it is unclear how different precipitate growth will influence the transformation stresses seen in these novel alloys. We present an evaluation of these effects using mechanical testing, DSC, and microstructure analysis.
P2-36: Effects of Oxidation on the Transformation Behavior of Ti-Ta High Temperature Shape Memory Alloys: Dennis Langenkämper1; Alexander Paulsen1; Christoph Somsen1; Jan Frenzel1; Gunther Eggeler1; 1Ruhr-Universität Bochum
High temperature shape memory alloys (HT-SMAs) based on Ti-Ta show potential for actuator applications, where transformation temperatures are required, which are higher than what can be achieved with conventional NiTi-based SMAs. At these temperatures, there are a number of processes which affect the martensitic transformation, which governs all shape memory effects. These can include short range diffusion processes, precipitation processes and oxidation, which will be focused on in the present work. In this study, the oxidation behavior of a Ti80Ta20 alloy is investigated at temperatures of 335°C (< Mf), 455°C (> Af) and up to 850°C by using thermogravimetric analysis (TGA) for 100 hours. Oxide layers and microstructures are analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Special emphasis is placed on the effect of oxidation on the martensitic transformation behavior.
P2-37: Heating Rate-dependent Deterioration in Shape Memory Effect in a Co-Al Alloy Undergoing FCC⇌HCP Martensitic Transformation: Xiao Yang1; Yuhua Wen1; Huabei Peng1; 1College of Manufacturing Science and Engineering, Sichuan University
It is generally believed that an up/step-quenching treatment can suppress the deterioration of shape memory effect (SME) due to the martensitic stabilization in Cu-based alloys. However, our recent studies showed that the SME in an up-quenched Cu-Al-Mn alloy dropped drastically as lowering recovery heating rate (Acta Materialia 111 (2016): 348). Interestingly, our preliminary studies showed that a similar phenomenon also occurred in a solution-treated Co-8Al alloy undergoing FCC⇌HCP martensitic transformation. Its SME was 56% when directly heated at 973 K, but it significantly dropped to 18% when heated at a rate of 5 K/min. This phenomenon has never been reported in Co-based alloys, and it is not clear whether it is also ascribed to the martensitic stabilization or not. In this paper, we will investigate the effect of recovery heating rate on the HCP martensitic transformation and its relationship with the heating rate-dependent deterioration in SME in the Co-8Al alloy.
P2-38: Influence of Titanium Addition on the Microstructural Evolution of Cu-14Al-4.1Ni Alloy Subjected to Heat Treatment: LUCAS CARDOSO1; Nicole Oliveira Araujo1; Camila Aguiar Teixeira1; Emmanuel Pacheco Rocha Lima1; Pedro Cunha de Lima1; 1IFBA
The shape memory alloys (SMA) have been increasingly investigated due to their functional properties that make them applicable in several areas such as aeronautics, nuclear and medicine. This work evaluated the influence of the Titanium as the fourth element in a copper based SMA. The alloys were casted in a plasma furnace, raging the Ti in 0.5, 0.6 and 0.7wt.%, and the microstructure evolution was verified by X-Ray Diffractometry (XRD). The samples were subjected to heat treatment of betatization at 900°C for 15, 20 and 30 minutes, cooled in water at 25°C. Scanning Electron Microscopy (SEM) and XRD analyses assisted the identification of phases and precipitates, as well as, the verification of Ti performance as grain refiner and its influence in the increase of the phase transformation temperatures, obtained by Differential Scanning Calorimetry (DSC).
P2-39: Martensitic Transformation in bcc-type Mg-Sc Alloy: Yukiko Ogawa1; Daisuke Ando1; Yuji Sutou1; Junichi Koike1; 1Department of Materials Science, Graduate School of Engineering, Tohoku University
Conventional Mg alloys have a poor formability which arises from the anisotropic hcp structure, resulting to a utilization in a limited field. To improve the formability, our group has been focusing on Mg-Sc alloy because bcc phase with an isotropic structure can be obtained in a Mg-rich composition in Mg-Sc binary phase system. In fact, we already have reported that Mg-Sc alloy with bcc/hcp two-phase to show much a good valance of strength and elongation than conventional Mg alloys. Furthermore, very recently, a metastable bcc Mg-Sc alloy with a density of just 2 g/cm3 is newly discovered to show a shape memory behavior [*]. In this presentation, we will discuss about the shape memory behavior and the martensitic transformation in bcc-type Mg-Sc alloy.[*]Y. Ogawa et al., Science, 353 (2016) 368-370.
P2-40: Microstructure Behavior of a Cu-Al-Ni SMA with Chromium Addition: Camila Aguiar Teixeira1; Rodrigo Coelho Estevam1; Pedro Cunha de Lima1; Lucas Cardoso1; Victor Barbosa1; 1IFBA
In the present research, the influence of chromium on the microstructure and properties of a Cu-Al-Ni SMA were investigated. Alloys with a Cu-14Al-4Ni (wt.%) composition and different contents of chromium (0.2, 0.4 and 0.7wt.%) were casted in a plasma furnace. All samples underwent heat treatment of betatization at a temperature of 900ºC for 15 and 30 minutes, followed by water solution quenching at -10ºC. Posteriorly, all samples were analyzed through X-ray Fluorescence (XRF), Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC) and X-ray Diffraction (XRD). It was possible to verify, through the obtained SEM and XRD analyses, that Cr and the heat treatment duration have a fundamental role in the martensite structure evolution. DSC experiments showed a decrease of the phase transformation temperatures.
P2-41: Porous Ni-Ti-Nb Shape Memory Alloys with Tunable Damping Behavior Controlled by Martensitic Transformation: Shanshan Cao1; Yuanyuan Li1; Caiyou Zeng1; Xin Ping Zhang1; 1South China University of Technology
Porous Ni-Ti-Nb shape memory alloys with designed porosities and compositions were prepared by powder metallurgy. Thermal analysis and dynamic mechanical analysis were carried out to investigate the phase transformation and damping behavior of the porous alloys, respectively. Systematic microstructural study indicates that both the pore configuration and Nb distribution in the matrix of porous Ni-Ti-Nb alloys have significant influence on the martensitic transformation controlled damping behavior. Increasing pore size in micro-scale leads to linear decrease of the internal friction, while addition of Nb dramatically increases the damping capacity of the porous alloys. The internal friction can be optimized by adjusting Nb/NiTi ratio, which balances the competitive contribution of Nb/matrix and B2/B19’ interfaces to the damping capacity during martensitic transformation. Moreover, beta-Nb of nanolamellar structure in the matrix plays a greater role in the damping capacity than that of granular shape by offering large amount of interfaces.
P2-42: Precipitate Growth and Volume Fraction of Ni-rich NiTiHf HTSMA using High Energy X-ray Diffraction: Matthew Carl1; Brian Van Doren2; Marcus Young1; 1University of North Texas; 2ATI Specialty Alloys and Components
NiTiHf high temperature shape memory alloys (HTSMAs) have begun to show considerable progress in their ability to be manufactured and are now on the cusp of becoming viable alloys for use in the aerospace industry. However, precipitate phase evolution and growth has not yet been studied in-situ nor have the effects of previous thermo-mechanical processing on their formation. In this study, H-phase precipitate formation is observed experimentally in-situ during aging of a Ni-rich NiTiHf alloy using high energy synchrotron radiation X-ray diffraction (SR-XRD). The effects of prior thermo-mechanical treatments on its formation rate and volume fraction are compared. It is shown that growth of the H-phase can be observed in-situ using SR-XRD and the H-phase formation rate seems to exhibit linear growth when aging at 550 °C while increasing the temperature to 650 °C shows a logarithmic trend that plateaus after approximately 1 hour of aging.
P2-43: Studies on Influence of Aging on Shape Memory Characteristics of some Cu-Al-Mn Shape Memory Alloys: Canan AKSU CANBAY1; V. Sampath1; S. Gudeloglu1; 1Firat University
Shape memory alloys (SMAs) are used in numerous engineering and medical devices and it depends on their transformation temperatures. But these temperatures are ifluenced by their composition, microstructure, thermomechanical history, etc. Among SMAs, it is those based on Ni-Ti that are used extensively because of their good shape memory characteristics (recovery strain, recovery stress), biocompatibility and corrosion resistance. These days copper-based SMAs are being explored as an attractive alternative to Ni-Ti SMAs as they are easier and cheaper to produce and process and possess higher transformation temperatures. But they are prone for aging, leading to shifting of transformation tempertures. This affects the performance of the devices. In this paper, the effect of aging on shape memory properties of Cu-11.34Al-4.35Mn, Cu-13.38Al-3.14Mn, Cu-14.25Al-4.77Mn (% wt.) SMAs are being explored in light of of X-ray diffraction, differential thermal analysis and optical microscopy. Keywords: Shape memory alloys, transformation temperatures, aging, Ni-Ti SMAs, copper-based SMAs.
P2-44: Superelastic Response of Co-free Polycrystalline Fe-Ni-Al-Nb Shape Memory Alloys without Deformation Processing: Wenyi Peng1; Zhaoxia Chen1; Yongjiang Guo1; Lei Chen1; Aisheng Zhang1; Rui Zhu1; Yan Gong1; 1School of Materials Science and Engineering, Nanchang University
Our work investigate the superelasticity response of Co-free polycrystalline Fe-Ni-Al-Nb shape memory alloys at room temperature. And neither hot working nor cold working is applied in the fabrication of the samples. The nominal composition of the samples is Fe56.5Ni30Al10.5Nb3 (at. %). The samples were solute-treated and water quenched, for twice. And then they are aged at 873K for 20 h, 45 h, 70 h and 95 h, respectively. The compressive superelastic strain of them is 9.6%, 10.6%, 5.5% and 8.3%, respectively. To the samples aged for 70 h, two transformation plateaus can be observed. This indicates there are two types of martensitic transformation and the switching of them depends on the aging duration. X-ray diffraction analysis shows there are β-NiAl-typed phase with a B2 structure and Ni3Al-typed phase with a L12 structure precipitated during the aging and the latter forms when the aging duration is greater than 45h.
P2-45: Suppression of Martensitic Transformation in Co2Cr(Ga,Si) Heusler Alloys by Thermal Cycling: Xiao Liang1; Fei Xiao1; Xuejun Jin1; Takashi Fukuda2; Tomoyuki Kakeshita2; 1Shanghai Jiao Tong University; 2Osaka University
The influence of thermal cycles on martensitic transformation behavior and phase stability of a Co2Cr(Ga,Si) ferromagnetic Heusler alloy was investigated. The as-quenched specimen exhibits successive L21(L)–D022–L21(H) martensitic transformation in the cooling process, which is known as re-entrant martensitic transformation. However, heating up to 800 K for reverse D022–L21 transformation with a rate of 10 K/min stabilizes the parent phase, meaning that the martensitic transformation is suppressed by the thermal cycles. Precipitation was observed in the specimen after thermal cycles, and it will be the reason for the stabilization of parent phase.
P2-46: Transformation Behavior and Superelasticity of Rapidly Solidified Ti-(50-x)Ni-20Hf Alloys: Dong-jo Kim1; Yeon-wook Kim2; Tae-hyun Nam1; 1Gyeongsang National University; 2Keimyung University
Ti-(50-x)Ni-20Hf (x=0, 0.5, 1) (at.%) alloy ribbons were prepared by melt-spinning and then transformation behavior and superelasticity of them were investigated by means of scanning electron microscopy, differential scanning calorimetry, X-ray diffraction and tensile tests. All the as-spun ribbons were amorphous and the activation energy for crystallization was in the range of 167.8 kJ/mol and 182.7 kJ/mol, depending on Ni content. After annealing for crystallization, very small (Ti,Hf)2Ni particles with the size of 11 nm ~ 325 nm embedded in the B19’ martensite matrix, depending on annealing temperature, were observed. Volume fraction of (Ti,Hf)2Ni particles increased from 4.3 % to 13.6 %, with raising annealing temperature from 873 K to 1123 K, above which it decreased. Ms(the B2→B19' transformation start temperature) increased with raising annealing temperature. The crystalline alloy ribbons showed partial superelasticity, which was ascribed to the increase in the critical stress for slip by precipitation hardening.