Measurement of Diffusion Coefficients in the bcc Phase of the Ti-Sn and Zr-Sn Binary Systems
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nd its alloys have attracted significant attention for biomedical applications, especially for use in load-bearing implants—for which there is a rapidly growing need in order to keep pace with the increased worldwide demand of the aging population.[1–5] To reduce the so-called stress shielding around implants, biomaterials with a low Young’s modulus equivalent, or close to, that of natural bone are highly desirable.[6,7] However, the current generation of bio-Ti alloys still generally has a higher Young’s modulus than human bones (20 to 30 GPa). Accordingly, advanced bio-Ti alloys are being pursued worldwide to further decrease the apparent elastic modulus.
LILONG ZHU, GEMEI CAI, and ZHANPENG JIN are with the School of Materials Science and Engineering, Central South University, Changsha 410083, Hunan, P.R. China. Contact e-mail: [email protected] ZHANGQI CHEN, WEI ZHONG, CHANGDONG WEI, and JI-CHENG ZHAO are with the Department of Materials Science and Engineering, The Ohio State University, 2041 College Road, Columbus, OH, 43210. Contact e-mail: [email protected] LIANG JIANG is with the State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, Hunan, P.R. China. Manuscript submitted July 28, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
Over the past six decades, many novel types of Ti alloys have been developed and commercially available for biomedical applications, which are generally grouped into a, (a + b) and b Ti alloys according to their primary constitutional phase(s) formed through an allotropic phase transformation between the low-temperature a (hcp) phase and the high-temperature b (bcc) phase at 882 C. Compared to a and (a + b) alloys, b Ti alloys display superior mechanical biocompatibility, especially lower elastic modulus, which makes b Ti alloys highly desirable for biomedical applications.[8,9] Various low-modulus b Ti alloys have been developed and studied, such as Ti-24Nb-4Zr-7.9Sn (with a Young’s modulus of 42 GPa),[10] Ti-35Nb-4Sn (with a Young’s modulus of 40 GPa),[11] and Ti-25Nb-11Sn (with a Young’s modulus of 45 GPa).[12] These Ti alloys contain high concentration of b-stabilizing elements such as Cr, Mo, Nb, Ta, and V, as well as neutral elements such as Sn, Hf, and Zr.[3,4,13–15] Among those elements, Sn and Zr are two of the most important alloying additions. Belonging to the same periodic group as Ti, Zr presents almost the same structural stability (the a to b phase transformation at 863 C) and mechanical biocompatibility as Ti, and thus has been investigated as the next-generation biomedical materials.[16–18] Sn is one of the major alloying additions for Zr-based alloys in nuclear industry.[19–21] Besides, the recent studies suggest
Zn-Sn-based alloys are also promising for biomedical applications.[22–24] The phase transformation in bio-Ti and bio-Zr alloys is quite complicated.[25] Phase stability, phase transformation, and microstructure evolution predictions based on reliable thermodynamic and kinetic databases are very fundamental information f
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