Recent development of the magnetic shape memory materials research in Finland
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Recent development of the magnetic shape memory materials research in Finland Outi Söderberg1, Ilkka Aaltio1, Yanling Ge1, Alexandr Soroka1,2, Raisa Niemi1, Xuwen Liu1, Simo-Pekka Hannula1 1 Department of Materials Science and Engineering, Helsinki University of Technology, POB 6200, FI-02015, TKK, Espoo, Finland. 2 AdaptaMat Ltd., Yrityspiha 5, FI-00390, Helsinki, Finland. ABSTRACT Ni-Mn-Ga based magnetic shape memory (MSM) materials have been studied since 1998 in Finland at the Helsinki University of Technology (TKK, previously HUT). The large HUTMSM-project resulted in MSM-alloys with high service temperature, 10 % field-induced-strain, as well as circumstances when and how a Ni-Mn-Ga alloy exhibits this phenomenon. The understanding of the structure and behavior of twin boundaries, and their role, for example, in the vibration damping and long-term actuation has been enhanced in the recent projects. Twin boundaries have been studied by XRD, by high-resolution transmission electron microscopy (HRTEM), and by in-situ straining in TEM, the last one in co-operation with the Institute of Physics in Prague (ASCR-IP), Czech Republic. The results obtained by neutron diffraction in cooperation with Hahn-Meitner-Institut Berlin, Institute for Metal Physics (IMP), Kiev, and Institut Laue-Langevin (ILL), Grenoble, have given new crystallographic information. Damping of NiMn-Ga polymer composites has been proved to be excellent at high stiffness levels with the loss factor δ = 0.6 at E ≈ 1 GPa. This research was carried out in co-operation with the University of California Los Angeles (UCLA), USA. In the long-term actuation, a fatigue life of 2x109 has been recorded for a five-layered modulated Ni-Mn-Ga structure in mechanical cycling. The evolution of the MSM parameters during the long-term use is recorded and used as an input data for the models developed in the European MAFESMA co-operation. The search for alloys with wide stable thermal property range showing MSM effect has continued and alloys that are stable down to 4 K have been established. Modeling based on Ginsburg-Landau theory has been applied to evaluate aging and thermal fluctuations in the modulated Ni-Mn-Ga structures. As a commercial target, AdaptaMat Ltd. develops technology to produce Ni-Mn-Ga magnetic shape memory material with improved quality, lower twinning stress, longer fatigue life as well as lower cost and better availability for use in research and development. INTRODUCTION The basis of the magnetic shape memory, MSM, research in Finland was set in 1995 with the studies of magnetic field induced martensite twin structure orientation in a Fe-Ni-C alloy by Ullakko and Aaltio [1]. This observation was confirmed in a Ni-Mn-Ga alloy at MIT by Ullakko [2]. The earlier material development of the Ni-Mn-Ga alloys in Ukraine provided this material with the preferential structure and anisotropic magnetic properties [3]. AdaptaMat Ltd. was founded in 1996 to serve the industrial purposes of fabricating and applying MSM materials. As the first r
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