M. Nishida, Kyushu University, Kasuga, Japan; Y. Iwanaga, S. Ushimaru, T. Maeshima, Kumamoto University, Kumamoto, Japan; K. Yamauchi, Tohoku University, Sendai, Japan
β-type Ti alloys are attracted attention due to their superior workability, low Young's modulus, specific strength and high toughness. Recently, these Ni-free alloys are expected as biomaterials in medical field due to their high biocompatibility. However, grain growth of β-type Ti alloys is very rapidly above the β transition temperature because of high diffusivity of bcc structure. Consequently intergranular fracture and cracking occur during the tube and wire processing for the usage of medical devices such as guide wire. Therefore, grain refinement is required for their practical application. In the present study, we have added a slight amount of rare earth elements such as Sc, Y and La to Ti-Mo-Sn system. The remarkable grain refinement has achieved by addition of the above elements. The mechanism of the grain refinement is due to the grain boundary pinning effect of rare earth oxide. It has been also observed that Vickers hardness and yield stress are remarkably decreased and elongation and superelasticity property are increased. The optimum quantity of each element for the grain refinement and the improvement of superelastic properties will be also reported.
Summary: The grain refinement is required for the practical application of Ni-free Ti-base shape memory alloys.In the present study, we have added a slight amount of rare earth elements such as Sc, Y and La to Ti-Mo-Sn systemand the remarkable grain refinement has achieved. The mechanism of the grain refinement and the improvement of superelastic property are discussed.
