The α2 phase exist between 22-39 at.% aluminum (Al) (23) and the structure stays ordered until a temperature of 1180 °C and Al content of 32 at.%, before it transform to a disordered hcp structure (25). The structural α2 based alloys developed up to now are two phased, consisting of α2 and β phase (9). β phase is a disordered body centered cubic Ti phase (25) with a Ti content of between 0 to 47.5 at.% Al (23). These two phase alloys have approximately two times the strength of single phase α2 (9).
To create the two phases a β stabilizing element in addition to niobium (Nb), for example molybdenum (Mo), chromium (Cr) or tantalum (Ta) (2), is often present and the alloys also contains around 11 to 18 at.% Nb. The Nb, with retained Al concentration, enhances most of the material properties, but could in too high concentrations increase the creep sensibility. Other alloying elements can be added to improve this performance and tailor the material properties. However, the most important thing is to maintain control of the microstructure (9).