2007 Volume 47 Issue 5 Pages 745-752
Alloy designing and evaluation of various properties of new α+β type titanium alloy with excellent cold workability, superplasticity, and cytocompatibility were conducted. Alloy designing was performed by investigations of the effects of O, Al, Mo, Fe, and Nb contents on cold workability of the alloy with a basic composition of Ti–4.5%Al–4.5%Nb–2%Fe–2%Mo. Use of β stabilizing elements such as V, Ni, or Cu was avoided for biocompatibility. Cold workability was evaluated on the basis of a critical rolling reduction for onset of cracking, hardness under as solution treated condition and hardness variations with a cold rolling reduction. Excellent cold workability was obtained by enhanced thermal and mechanical stabilities of β phase and by lowered hardness of α phase in the α+β two-phase microstructure. Newly developed alloy Ti–4.5%Al–6%Nb–2%Fe–2Mo showed the β transus of 1156 K, a critical rolling reduction over 60%, and yield strength in recrystallization annealing of 910 MPa. An extremely fine α+β two-phase microstructure with α grain size of approximately 1 μm was evolved by annealing at 1048 to 1073 K, and a superplastic elongation value of around 3000% was obtained by tensile testing at these temperatures. New alloy showed an excellent cytocompatibility in a cell culture test using L929 cells, yielding a higher value of cell viability over Ti–6%Al–4%V and Ti–6%Al–7%Nb alloys.