Perfect superelasticity by dispersion of effective precipitate routed through brittle phase in biomedical titanium alloy

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There is no effective method of microstructural control to suppress the slip deformation that competes with superelastic deformation inβ-Titanium superelastic alloy, though this alloy is a candidate biomedical superelastic alloy. The superelastic deformation in β-titanium alloy is, therefore, not a perfect one ; plastic strain remains after deformation. We propose a new heat-treatment method to precipitate fine α-phase for strengthening that is nucleated at fine ω-phase. The ω-phase brings extreme brittleness and is not used in usual heat-treatment of titanium alloy, whereas it is used as a medium for ω-phase nucleation in our new method. 800MPa in strength and perfect shape recovery are achieved by a three-step heat-treatment : 773K (fine ω precipitation)→1023K (fine α precipitation at ω)→1123K(erasing ω) in Ti-Mo-X (X=Al and Mn). In addition, a low-temperature heat-treatment around 373K as the fourth step improved mechanical property.