Novel Shape Memory Alloys: Session 4
Program Organizers: Othmane Benafan, NASA Glenn Research Center

Thursday 4:00 PM
July 13, 2017
Room: Wrigley
Location: Hyatt Regency Chicago

Session Chair: Shuichi Miyazaki, University of Tsukuba

4:00 PM  
Implications of Uniaxial and Torsional, Loading and Heating Paths on the Behavior of NiTi: Douglas Nicholson1; Santo Padula2; Othmane Benafan2; Raj Vaidyanathan1; 1University of Central Florida; 2NASA Glenn Research Center
    The overall objective of this work is to investigate the uniaxial and torsional behaviors of shape memory alloys (SMAs) under (i) isothermal (both uniaxial and torsional deformation at constant temperature), (ii) isobaric (thermal cycling to temperatures above and below the phase transformation temperatures under constant uniaxial stress), and (iii) isostrain (thermal cycling to temperatures above and below the phase transformation temperatures under constant uniaxial strain) conditions. This is accomplished by subjecting samples of polycrystalline NiTi to in situ neutron diffraction at Los Alamos National Laboratory and Oak Ridge National Laboratory at stress and temperature in carefully selected experiments. Additionally, spatially resolved information was obtained in the case of the torsion specimens. Analyses of the diffraction spectra for texture and strain information provided fundamental insight into deformation in NiTi.

4:20 PM  
An Overview of Functional Properties of Novel Ti-Ta-X High Temperature Shape Memory Alloys – Effect of Chemical Composition, Microstructure and Heat Treatment: Elvira Karsten1; Hans Jürgen Maier1; Thomas Niendorf2; Philipp Krooß2; Christian Lauhoff2; Alexander Paulsen3; Jan Frenzel3; Gunther Eggeler3; 1Institut für Werkstoffkunde (Materials Science), Leibniz Universität Hannover; 2Institut für Werkstofftechnik/Metallische Werkstoffe, Universität Kassel; 3Institut für Werkstoffe, Ruhr-Universität Bochum
    There is increasing interest from various industries for shape memory alloys with martensitic transformation start temperatures above 100 °C, so called high temperature shape memory alloys (HTSMAs), for applications at elevated temperatures. However, usage of the currently available HTSMAs results in several problems, e.g. poor cold workability or the need for high amounts of expensive noble elements. Ti-Ta-X alloys represent a promising alternative to overcome these issues. The functional cyclic degradation of these alloys is mainly caused by the formation of the α- and ω-phases, which hinder the reversible phase transformation. By suitable choice of alloy compositions and heat treatments, their formation can be suppressed or decelerated. This study presents results of functional and structural fatigue experiments on different Ti-Ta-X alloys and gives an overview of the influence of the chemical composition, microstructure and heat treatment on the functional stability. Concepts for fatigue life extension will be presented and discussed.

4:40 PM  
Effect of Heat-treatment Conditions on Microstructure and Shape Memory Properties of Ti-4.5Al-3V-2Fe-2Mo Alloy: Yuichi Matsuki1; Hirobumi Tobe2; Eiichi Sato2; 1The University of Tokyo; 2ISAS/JAXA
    Ti-4.5Al-3V-2Fe-2Mo alloy (SP-700) is known for its superior workability and superplasticity when compared to Ti-6Al-4V. Recently, our research group reported that SP-700 can exhibit shape memory properties at room temperature after heat-treatment at around 1073 K, although perfect shape recovery was not observed. At ISAS/JAXA, the application of shape memory properties of SP-700 is now under consideration for producing foldable structural components of rockets. To improve shape memory properties of SP-700, effects of heat-treatment conditions were investigated in this study. Mechanical tests and microstructure analysis revealed that shape memory effect and superelasticity of SP-700 highly depend on soaking, annealing temperatures and durations, and aging temperatures, which is attributed to precipitation states of α and ω phases. Soaking and subsequent annealing resulted in fine needle-shaped α phase precipitation. Aging increased the size of ω phase and strongly affected the martensitic transformation temperatures of SP-700.

4:55 PM  
Martensitic Transformation in Co-V-Ga Heusler Alloys: Xiao Xu1; Akihide Nagashima1; Makoto Nagasako1; Toshihiro Omori1; Takeshi Kanomata2; Ryosuke Kainuma1; 1Tohoku Univ.; 2Tohoku Gakuin Univ.
    Ferromagnetic and metamagnetic shape memory alloys have been widely studied in Ni-based Heusler alloys. Recently, in some Co-based Heusler alloys, such as Co2Cr(Ga,Si), Co2Cr(Al,Si) and Co2VSi, besides the well-known Co2NbSn, martensitic transformation behaviors have been reported. Moreover, a unique reentrant martensitic transformation behavior was found in the Co2Cr(Ga,Si) system. In this work, we present a novel Co-based Heusler system showing the martensitic transformation behavior. In Co-rich off-stoichiometric compositions, martensitic transformation was observed from L21 parent phase to L10 martensite phase. Two pseudo-binary sections were studied and the martensitic transformation starting temperatures (Ms) were found between around 250 to 500 K. The Ms was found to be above the Curie temperature and no reentrant martensitic transformation was found in this system.

5:15 PM  
Novel Long-period Stacking-ordered Structure of Martensite in Zirconium and Hafnium-based Alloys: Mitsuhiro Matsuda1; Ryo Matsuoka1; Kazuki Takashima1; Masatoshi Mitsuhara2; Minoru Nishida2; 1Kumamoto University; 2Kyushu University
    A novel long-period stacking ordered structure of a martensitic phase in a zirconium- and hafnium- based alloys were discovered and characterized by means of conventional transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy. The new phase in Zr-Co-Pd alloy had a 6O structure and its lattice parameters were estimated to be a = 0.34, b = 0.45 and c = 1.53 nm from the electron diffraction experiments. The space group of the LPSO structure was determined to be Immm on the basis of the extinction rule and symmetry. The orientation relationship between the B2 parent phase and 6O martensite is determined to be (010)B2 // (013)6O, (110)B2 // (001)6O and [001]B2 // [100]6O. Hf-Co-Pd alloy also had a martensite with a period of six layers.

5:35 PM Break