H. Y. Kim, S. Miyazaki, University of Tsukuba, Tsukuba, Japan; Y. Ikehara, University of Tsukuba, Ibaraki, Japan; H. Hosoda, Tokyo Institute of Technology, Yokohama, Japan
Recently, β-type Ti alloys composed of non-toxic elements have attracted attention as biomedical superelastic materials. Ti-Nb alloys are attractive candidates for biomedical superelastic applications. A small recovery strain and a low critical stress for slip are major drawbacks of Ti-Nb superelastic alloys. Various attempts have been made to improve the superelastic properties of Ti-Nb alloys. Low temperature annealing and aging were effective to increase the critical stress for slip due to fine subgrain structure and precipitation hardening. It has also been reported that superelastic properties can be improved and tailored by texture control of the Ti-Nb superelastic alloys. A small superelastic strain of Ti-Nb is due to the small transformation strain in the compositions which reveal superelastic behavior. In this study, the effect of Nb and Zr contents on the transformation temperature, crystal structure and shape memory properties of Ti-Nb-Zr alloys was investigated. Many Ti-Nb-Zr alloys such as Ti-22Nb-6Zr, Ti-18Nb-12Zr, Ti-16Nb-16Zr and Ti-14Nb-18Zr alloys exhibited stable superelasticity at room temperature. The superelastic recovery strain increased with increasing Zr content when comparing different composition alloys which reveal similar transformation temperatures. The superelastic recovery strain of 6.4% was obtained in the Ti-14Nb-18Zr alloy. The effect of annealing temperature and aging condition on superelastic behavior will be discussed.
Summary: The effect of Nb and Zr contents on the transformation temperature, crystal structure and shape memory properties of Ti-Nb-Zr alloys was investigated in order to develop allergy free superelastic alloys.
