Aging behavior of the Ti-29Nb-13Ta-4.6Zr new beta alloy for medical implants
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TITANIUM and its alloys are attractive materials for surgical implantations because of their high specific strength, high corrosion resistance, and good biocompatibility.[1–4] Ti6Al-4V, an ␣ ⫹  alloy, is actively used for the surgical applications, e.g., the stem of a hip implant.[1,4] Recently, there has been a trend toward the use of nontoxic metallic alloying elements in titanium for application in the human body. Vanadium, the most widely used -stabilizing alloying element in titanium, is a potentially toxic element,[5] and there is also concern with the widely ␣-stabilizing element, aluminum, because of its possible relation to Alzheimer’s disease.[6] Therefore, the new titanium alloys for biomaterials use should contain only nontoxic metallic alloying elements such as Nb, Ta, and Zr,[7] which are important alloying elements for Ti alloys.[6] Recently, many researchers have actively investigated  Ti alloys[8,9,10] with a low modulus as medical implants using Nb, Ta, Zr, Mo, and Fe as alloying elements, e.g., for artificial bone materials. For instance, the Ti-35.3Nb-5.1Ta-7.1Zr  alloy,[8] which was first developed as the Ti-Nb-Ta-Zr alloy for medical applications, and the Ti-13Nb-13Zr near- alloy[9] were developed in the United States and have a low modulus and excellent mechanical properties, i.e., high yield and tensile strength and good fatigue strength in the annealed state. Under the guidance of the DV-X␣ cluster method,[11] used to find a lower elastic modulus than those of developed beta Ti alloys, a new  titanium alloy for surgical implants MASAHIKO IKEDA, Associate Professor, and SHIN-YA KOMATSU, Professor, are with the Department of Materials Science and Engineering, Faculty of Engineering, Kansai University, Osaka 564-8680, Japan. ISAO SOWA, formerly Undergraduate Student, Department of Materials Science and Engineering, Kansai University, is Engineer, Kyoei Steel Ltd., Osaka 530-0004, Japan. MITSUO NIINOMI, Professor, is with the Department of Production Systems Engineering, Toyohashi University of Technology, Toyohashi 441-8580, Japan. Manuscript submitted April 5, 2001. METALLURGICAL AND MATERIALS TRANSACTIONS A
developed by Professor Ninomi’s group at Toyohashi University of Technology.[12] This alloy contains nontoxic alloying elements, i.e., Nb, Ta, and Zr, and has a relatively lower Young’s modulus than other Ti alloys. The mechanical properties of the Ti-29Nb-13Ta-4.6Zr alloy, e.g., its tensile and fatigue properties, are currently being investigated by Professor Niinomi’s group.[13] Some investigators have reported that the elastic modulus of beta Ti alloys increases with aging.[14,15] Therefore, if Ti-29Nb-13Ta-4.6Zr is applied to bone materials, it is not necessary to perform aging treatments in this alloy. This alloy also has good heat-treatability. Thus, if this alloy is applied to other applications for medical implants, e.g., a bone plate that has a higher elastic modulus and mechanical strength than artificial bone,[16] it is expected that high strength is easily obtained by
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