Phase Transformations of Ferromagnetic Fe-Pd-Pt-Based Shape Memory Alloys
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Phase Transformations of Ferromagnetic Fe-Pd-Pt-Based Shape Memory Alloys 2
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Gwon-seung Yang1, Reid Jonasson , Seung-nam Baek , Kinzo Murata , Shozo Inoue , Keiji 4
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Koterazawa , Soon-jong Jeong , Kiyoshi Mizuuchi and Kanryu Inoue 1
Materials Science and Engineering, Chosun University, Kwang Ju, Korea Materials Science and Engineering, University of Washington, WA 98195-2120, USA 3 Kobe Material Testing Lab. Co., Hyogo-ku, Kobe, Japan 4 Mechanical and Intelligent Engineering, Himeji Institute of Technology, Himeji, Hyogo 671-2201, Japan 5 Korean Electric and Magnetic Devices Group, Korea Electrotechnology Research Institute, P.O. Box 20, Changwon 641-120, Korea 6 Osaka Municipal Technical Research Institute, Osaka 536-8553, Japan 2
ABSTRACT Several ternary Fe-Pt-Pd alloys with the compositions of Fe-(25-x) at% Pt-x at% Pd and Fe-y at% Pt-(30-y) at% Pd were investigated to study their phase transformations in order to develop ductile ferromagnetic shape memory alloys appearing around room temperature. Alloys were prepared by vacuum floating induction melting, followed by hot rolling at 1000oC and homogenization at 900oC. Homogenized alloys were heat treated at 650oC for various periods of time in vacuum for atomic ordering in encapsulated quartz tubes, and quenched into iced water. It was found that in general the transformation temperatures changes with heat treatment time. In the case of Fe-23at.%Pt-2at.%Pd, Ms temperature increased and the difference between Ms and Mf increased with increasing heat treatment time, which was different from Fe3Pt where a degree of order becomes one. As heat treatment time increased, there was a tendency in that a strong first-order transformation in the disordered state was replaced by a weak first-order transformation. The Curie temperature of the alloys rose drastically with the addition of Pd, along with the transformation temperatures. Fe-23at.%Pt-2at.%Pd showed good shape memory effect after 8 hours of heat treatment at 650oC. This alloy showed much better shape recovery than any other binary Fe-Pt and Fe-Pd shape memory alloys. INTRODUCTION Ferromagnetic shape memory alloys (FSMAs) have received considerable attention in the past several years because of their potentiality as elements of high performance and power actuators due to their ferromagnetic nature of martensite phase. It is partly because FSMAs have an advantage over conventional shape memory alloys. The response times of conventional shape memory alloys can be slow due to the amount of time it takes to thermally cycle the alloy. FSMAs are expected to undergo a shape change by the application and removal of a magnetic field. The cycling of a magnetic field is much faster than thermal cycling, which will be described using a 3-D phase diagram for FSMAs, as shown in Figure 1 [1]. In the case of conventional shape memory alloys, the sample is firstly shape memorized and quenched below martensite finish temperature (Mf) to obtain the martensite phase. A stress is then applied to the sample an
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