Comprehensive mapping of mechanical properties and martensitic transformation in Ti–Al–Mo standard ternary system: Integrating literature data and fabricating novel high-Al-content superelastic alloys

Abstract

Titanium alloys are increasingly used as structural and functional materials owing to their exceptional properties. This study aimed to develop β-Ti shape memory alloys by creating a compositional map of the phase constitution and mechanical properties of the Ti–Al–Mo ternary system at room temperature, particularly near the α″+β phase region. Data for 95 alloy compositions were collected from the literature, and the composition region of Ti–(7–14) mol% Al–(3–7) mol% Mo, which has rarely been reported, was experimentally investigated. The phase constitution of Ti–Al–Mo alloys primarily depends on the Mo concentration; however, at Al concentrations of 10 mol% or higher, the β phase region expands. The yield stress was found to be minimal around 6 mol% Mo on the low-Al side, and this minimum shifted to lower Mo concentrations as the Al content increased, corresponding to the β/(α″+β) boundary. The ultimate tensile strength increased marginally in low-Mo compositions because of the twinning-induced plasticity effect, with the optimal composition near Ti–11 mol% Al–4 mol% Mo. Superelasticity was observed in high-Al regions, particularly in the Ti–11 mol% Al–6 mol% Mo alloy, which exhibited a superelastic recovery strain of 3.2 % and a total shape recovery strain of 6 %. These findings highlight the potential for developing new room temperature superelastic alloys in the Ti–(10–14) mol% [Al]eq–(5–6) mol% [Mo]eq composition region.