生体用Ti-29Nb-13Ta-4.6Zr合金の力学的特性に及ぼす時効処理の影響

Abstract

The relationships between mechanical properties and microstructure of Ti-29Nb-13Ta-4.6Zr in under aged, peak aged and over aged conditions at various aging temperatures were investigated. The maximum Vickers hardness values of Ti-29Nb-13Ta-4.6Zr aged at 573 K, 673 K and 723 K are obtained at aging times of around 2419.2 ks, 3024 ks and 1209.6 ks, respectively. ω phase precipitates in β phase of Ti-29Nb-13Ta-4.6Zr at relatively low aging temperature, 573 K, while α phase precipitates in β phase of Ti-29Nb-13Ta-4.6Zr at relatively higher aging temperature, 723 K. At an aging temperature of 673 K that lies between aging temperatures of 573 K and 723 K, ω phase precipitates at the early stage of aging, but α phase precipitates at relatively longer aging time. The precipitation site of α phase changes from intragrain to grain boundary at around peak aging time when Ti-29Nb-13Ta-4.6Zr is aged at 673 K and 723 K. The tensile strength of Ti-29Nb-13Ta-4.6Zr aged at 573 K, 673 K and 723 K increases up to a peak aging time with increasing aging time, but under over aging conditions, the tensile strength decreases. While the elongation decreases with increasing aging time at every aging temperature. The fatigue strength of Ti-29Nb-13Ta-4.6Zr increases greater when α phase precipitates than when ω phase precipitates. The fatigue strength of Ti-29Nb-13Ta-4.6Zr decreases a little due to the coarsening of α phase precipitated in β grain.