Faculty of Engineering and Natural Sciences
Magnetic Field-Induced Structural Phase Transformation in Meta-magnetic Shape Memory Alloys
Ibrahim Karaman1, 2
The Dietz Career Development Associate Professor
1Department of Mechanical Engineering,
2Materials Science and Engineering Graduate Program,
Magnetic Shape Memory Alloys (MSMAs) have recently emerged as promising active materials due to their ability to combine the large strain output (~10%) of conventional SMAs with the high frequency response (>1 kHz) of magnetostrictive materials. They can also be used for sensing and power harvesting due to significant changes in magnetization upon the application of fluctuating mechanical forces or displacements making them truly multifunctional. Magnetic field-induced martensite variant reorientation has been the main governing mechanism for field-induced shape change which results in low actuation stress levels, especially in NiMnGa alloys. We have recently shown that magnetic field-induced phase transformation is also possible in new MSMAs, i.e. in meta-magnetic SMAs. Utilizing this mechanism, more than one order of magnitude increase in actuation stress can be achieved. An extensive experimental program is undertaken on NiMn(Co,X) (X=In, Sn,
Ga) single and polycrystals in quest for identifying physical and microstructural parameters critical for the field-induced phase transformation. The effects of applied field on the phase transformation temperatures, lattice parameters, magnetization, and superelastic response are systematically investigated and selected results will be presented. The magnetic work output of NiMnCoIn alloys is determined to be more than 1 MJm−3 per Tesla. Transformation strains and magnetostress levels are also determined as a function of crystal orientation. It is shown that crystals with a  orientation can demonstrate a magnetostress level of 140 MPa/Tesla with 1.2% strain under compression. These stress and strain levels are significantly higher than those from piezoelectric and magnetostrictive actuators. A thermodynamical framework is constructed and will be discussed to identify the effects of magnetic field on martensitic phase transformations. Using the thermodynamical model, guidelines to increase the actuation stress levels and possible future directions for research on meta-magnetic SMAs will be presented.
Ibrahim Karaman, VITA
Ibrahim Karaman received his Ph.D. from
Illinois at Urbana-Champaign in 2000. He joined the faculty of Department of Mechanical Engineering at
University in 2000. Currently, he is the The Dietz Career Development Associate Professor in the same department. He is also a member of the Faculty of Materials Science and Engineering Graduate Program. His main research interests are processing-microstructure-mechanical/functional property relationships in metallic materials including 1) ultrafine and nanocrystalline materials, and 2) conventional, high temperature and magnetic shape memory alloys; micro-mechanical constitutive modeling of crystal plasticity; twinning and martensitic phase transformation in metallic materials. Dr. Karaman received several national and international awards including the National Science Foundation CAREER Award in 2002, Office of Naval Research Young Investigator Award in 2005, The Robert Lansing Hardy Award from The Minerals, Metals and Materials Society in 2005, an Honorable Mention for the Early Career Faculty Fellow Award from The Minerals, Metals and
Materials Society in 2007, and Gary Anderson Early Achievement Award jointly from The American Society of Mechanical Engineers (ASME) and the American Institute of Aeronautics and Astronautics (AIAA). The Robert Lansing Hardy Award recognizes "outstanding promise for a successful career in the broad field of metallurgy by a metallurgist under the age of 35" and one award is given per year. He is an author or co-author more than 100 refereed journal articles.
July 7, 2009, 13:40,