| この度、形状記憶材料について著名なテキサスA＆M大学・工学部准教授Ibrahim Karaman氏の講演会を開催することになりましたのでご案内申し上げます。是非ともご参加くださいますようお願い申し上げます。なお、講演は異なるトピックスについて東北大学多元物質科学研究所（20日）と工学研究科（21日）において2日にわたり行います。 | | | | １．日 時： | 2008年5月20日（火）15：00～16：30 | | ２．場 所： | 東北大学多元物質科学研究所
素材工学研究棟1号館 3階集会室 | | ３．演 題： | Magnetic Field-Induced Phase Transformation in NiMnGa and NiMnCoIn Shape Memory Alloys | | ４．講 師： | Ibrahim Karaman (Dept. Mech. Eng., Texas A&M Univ.,USA) | | | | ５．要 旨： | Magnetic shape memory alloys (MSMAs) have the ability to exhibit one order of magnitude higher magnetic field induced strain (MFIS) than magnetostrictive materials and few orders of magnitude faster dynamic response than conventional SMAs. Field-induced martensite variant reorientation (MVR) is the main governing mechanism for MFIS which results in low actuation stress levels in NiMnGa alloys. We have recently shown that stress-assisted magnetic field-induced phase transformation (FIPT) is possible in NiMnGa alloys and it can be reversible under low field magnitudes (<1 Tesla) depending on the magnitudes of assisting stress, stress hysteresis, magnetocrystalline anisotropy and saturation magnetization. Utilizing FIPT instead of MVR, more than one order of magnitude increase in stress levels is achieved in NiMnGa under which reversible MFIS can be obtained. Recently, a new family of MSMAs (NiMnIn, NiMnCoIn, NiMnSn) are discovered where FIPT can be triggered from an anti-ferromagnetic martensite to ferromagnetic austenite due to the large difference in their saturation magnetizations (Zeeman Energy). Such mechanism results in large actuation stress and work output, however, the requirement for large magnetic fields (~4T) restricts potential applications. We have conducted an extensive experimental program on NiMnGa and NiMnCoIn single crystals in quest for identifying physical and microstructural parameters critical for FIPT phenomena and how these parameters can be modified to reduce the field requirement. It will be shown that NiMnCoIn single crystals can exhibit actuation stress levels ranging from 20 to 120 MPa with MFIS levels in between 1 to 6%. Certain physical parameters such as orientation dependence of transformation strain and stress and temperature hysteresis are identified as critical in dictating the field requirement in addition to Zeeman energy. We will demonstrate how these parameters can possibly be engineered to decrease the required field magnitude for phase transformation. A thermodynamical framework based on microstructural, mechanical and magnetic requirements for FIPT is constructed and will be discussed to provide guidelines to increase the actuation stress levels further. | | | | ６．問合せ先： | 東北大学多元物質科学研究所 教授 貝沼亮介
TEL/FAX: 022-217-5815
E-mail: :kainuma@tagen.tohoku.ac.jp |
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