1014 Ti-Mo系形状記憶合金の機械的特性(S03-3 形状記憶合金の特性と応用技術(3),21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

Abstract

Although NiTi shape memory alloys are used extensively as biomedical applications such as stents and orthodontic wires, Ni is known as a toxic metal element. Thus, development of Ni-free shape memory alloys is required for biomedical applications. A candidate is Ti-base shape memory alloys. Although shape memory effect of Ti-Nb alloys has been widely investigated, comparably limited data has been obtained for Ti-Mo base alloys. It is known that the martensitic transformation temperature (M_S) from β parent phase to α" martensite phase is much lowered by Mo addition than by Nb addition, whereas few studies exist about the effect of ternary additions on M_S of Ti-Mo alloy. In order to clarify the effect of ternary additions on shape memory effect and mechanical properties comprehensively, Ti-Mo base alloys containing 3d transition metal elements were systematically investigated in terms of phase constitution and mechanical properties. It was found that the addition of 3d transition metal elements reduces M_S of the α"-martensitic transformation, and that all the ternary additions suppress the formation of the ω-phase which causes embrittlement. No alloy exhibited clear superelasticity. 1mol% addition of these 3d transition elements improves both the strength and ductility. Further additions of Co and Ni degrade the ductility due to large hardening. However, only Fe addition clearly improves strength without lowering ductility. Thus, Fe addition is effective to improve mechanical properties of Ti-Mo alloys.