Achievement of Ultralow Elastic Modulus through Optimization of Phase Stability and Recrystallization Texture in Ti-Nb-Fe-Sn Alloys

Ti-Nb-Fe-Sn alloys with relatively low Nb content, located near the phase boundary of (& beta; + & omega;)/& beta;, are designed on the basis of electron-to-atom (e/a) ratio, d-electron alloy design concept, and Mo equivalent (Mo-eq) aiming at low Young's modulus comparable to human bone. The effect of Sn content and Nb content on the microstructure and the mechanical properties is investigated in Ti-5Nb-3Fe-(0-6)Sn (at%) and Ti-(3-9)Nb-3Fe-4Sn (at%) alloys. The composition dependence of Young's modulus and tensile strength of Ti-Nb-Fe-Sn alloys is analyzed in terms of the phase stability, & omega; phase, and recrystallization texture. Both Nb and Sn are effective in suppressing the athermal & omega; phase and stabilizing the & beta; phase. The recrystallization texture is strongly influenced by the content of Sn and Nb. A strong {110}(& beta;)(& beta;) Goss texture is formed in the Ti-5Nb-3Fe-(2-4)Sn and Ti-(3-5)Nb-3Fe-4Sn alloys. The Ti-5Nb-3Fe-4Sn alloy exhibits an exceptionally low Young's modulus of 30 GPa due to the combined effects of low stability of the & beta; phase, a small amount of & omega; phase, and a strong Goss texture.