Flexible Bamboo-Structured NiCoMnIn Microfibers with Magnetic-Field-Induced Reverse Martensite Transformation
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gnetic-field-induced strain (MFIS) observed in ferromagnetic shape memory alloys (FSMAs) is attributed to two main mechanisms, i.e., the magneticfield-induced reorientation of martensite variants (MFIRMV) and magnetic-field-induced phase transformation (MFI-PT).[1–3] The off-stoichiometric NiMnGa alloys with a Heusler crystal structure exhibit a giant MFIS through MFI-RMV, which have been widely explored in the past decades.[2–4] However, the output stress of the NiMnGa alloys is restricted to 2 to 5 MPa due to the limited magnetic anisotropy energy of the martensite.[5–7] A large output stress up to 100 MPa was achieved in the NiCoMnIn alloy system with the transformation from paramagnetic/antiferromagnetic (PM/AF) martensite to ferromagnetic austenite under an application of magnetic Y.Z. JI, Z. CHEN, and D.M. LIU, Graduate Students, G. WANG, Associate Professor, and L. ZUO, Professor, are with the Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819, People’s Republic of China. Z.H. NIE, Lecturer, is with the School of Materials Science and Engineering, Beijing Institute of Technology, Beijing 100081, People’s Republic of China. Y.D. WANG, Professor, is with the School of Materials Science and Engineering, Beijing Institute of Technology, and is also with the Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University. Contact e-mail: [email protected] D.W. XING, Associate Professor, and J.F. SUN, Professor, are with the School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, People’s Republic of China. Manuscript submitted July 26, 2011. Article published online September 16, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
field.[1] Due to the giant MFIS, together with a high output stress, the NiCoMnIn FSMAs have attracted great attention.[1,8,9] However, for bulk polycrystalline and monocrystalline NiCoMnIn FSMAs, the intrinsic brittleness limits their practical applications. Here, bamboo-structured NiCoMnIn microfibers were fabricated, showing a high flexibility and magnetic-field-driven functional behavior at room temperature. The excellent mechanical and functional performance makes them potential candidates for magnetic-field-controlled biomedicine devices, such as microscale surgical detectors and artificial vessels. In addition, the bamboo structure has less pinnings from grain boundaries. Therefore, the NiCoMnIn microfibers would generate a high localized MFIS having the same functional behavior as in the single crystal,[10] which makes them promising in fabricating the microscale magnetic-field-driven actuators. An ingot button of 60 g in nominal composition of Ni45Co5Mn36.8In13.2 was fabricated by arc-melting under an argon atmosphere. The ingot was then melted by induction and slowly elevated to touch a copper wheel rotating at a surface velocity of 30 to 35 m/min. The fibers with ~40 lm in diameter and ~4 mm in length were finally spun. As the heat treatments obviousl
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