Deformation of Biomedical AuCuAl-Based Shape Memory Alloy Micropillars
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Deformation of Biomedical AuCuAl-Based Shape Memory Alloy Micropillars Akira Umise1,2㸩, Rui Serizawa1,2㸩, Sari Yanagida1,2㸩, Kenji Goto1,2㸩, Masaki Tahara1,2, Tso Fu Mark Chang1,2, Tomonari Inamura1,2, Masato Sone1,2 and Hideki Hosoda1,2 1
Laboratory for Materials and Structures (MS), Laboratory for Future Interdisciplinary Research of Science and Technology (FIRST), Institute of Innovative Research (IIR), Tokyo Institute of Technology, 4259-R2-27, Nagatsuta, Midori-ku, Yokohama 226-8503, Japan + Graduate students, Tokyo Institute of Technology 2
ABSTRACT The deformation behavior and shape recovery of an Fe-added AuCuAl shape memory alloy micropillar were investigated. XRD analysis revealed that Au-28Cu-22Al-2Fe (at.%) alloy contained a second phase which was evaluated to be α-Fe (bcc). SEM observation also confirmed the second phase at the surface of the micropillar specimen. A polycrystalline micropillar with 20 x 20 x 40μm rectangular was fabricated by a focused ion beam (FIB) system, and micro compress test was performed at room temperature. It was found that the yield stress of micropillar showed 50MPa, which must correspond to stress for inducing martensite. After the heating of the compressed micropillar, 1.75% shape recovery was recognized which is comparable to the transformation strain. Then, the Fe-added AuCuAl micropillar was concluded to possess good shape memory property, and thus this alloy may be suitable for small endovascular treatment which requires good X-ray radiography. INTRODUCTION Ti-Ni shape memory alloys are now widely used for minimally invasive procedures such as a stent for endovascular treatments. Since such devices are usually catheter-delivered, X-ray radiography is important for the endoscopic operation, and shape memory alloys containing heavy elements such as Au and Pt are fascinating in addition to good biocompatibility. Based on these background, we believe that AuCuAl-based alloy is a good candidate for those medical devices and have studied as biomaterials. The Au-Cu-Al shape memory alloys are known as “Spangold” which has been strongly developed for a use of jewelry by, for example, Wolff and Cortie from early 1990s [1, 2]. Recently, Buenconsejo and Ludwig have reported the martensitic transformation temperatures in a wide compositional range using a combinatorial method and concluded that this material is a good candidate as high temperature shape memory alloy [3]. In comparison with martensitic transformation behavior, the reports related to shape memory properties and mechanical properties in the literature are very limited. Battezzati and co-workers have reported that melt-spun AuCuAl thin film exhibits shape recovery by heating in a bold water [4]. Levey et al have reported Al concentration dependence of Vickers hardness [5]. Then, we have systematically investigated the mechanical properties of the polycrystalline alloys, and found that high ultimate tensile strength (UTS) of 600MPa and about good ductility of 10% are achieved when the chemical composition is around Au
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