Titanium alloys are characterized by their relatively low density (4.42-4.76 g cm^-3, ~45% less than steels), high specific strength (226-282 kN m kg^-1) and excepcionally high corrosion resistance against most aqueous environments. Some Ti alloys can be used up to a maximum service temperature of 600ºC.

Pure Ti exists in two allotropic forms: α (<882ºC, HCP) and β phases (>882ºC, BCC). Alloying elements for Ti alloys are classified in α-stabilizers (Al, O, N, C), β-isomorphs (V, Mo, Nb, Ta), β-eutectoid (Fe, Mn, Cr, Ni, Cu, Si, H) and neutral (Zr, Sn), depending on the stability of α and β and the shape of the phase diagram. Ti alloys are classified into the categories α, α+β and β, which have an approximate market share of 26, 70 and 4%, respectively. 

Ti-6Al-4V alloy is the most common of the α+β group with a 56% share of the Ti market. This is due to its outstanding combination of mechanical strength, ductility, fatigue strength and toughness up to 300ºC.

The mechanical properties of α+β alloys have a complex relationship with the amount of β-isomorphs and the heat treatment (quenching, annealing, tempering and aging). As it can be seen in this section, the final microstructures (and, therefore, the mechanical properties) depend on the transformation of the β phase, which is mainly dictated by the cooling rate.   

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