Titanium alloy is widely used in aerospace field because of its high specific strength and corrosion resistance. This paper describes the microstructure and mechanical properties of major titanium alloys in recent years, including high strength and high toughness titanium alloys (β type or metastable β type, Ti-1023, Ti-15-3, β21S and BT-22), high temperature titanium alloys (above 500℃, near α type, IMI834, Ti-1100, BT36 and Ti-60), damage-tolerance titanium alloys (α+β, TC21 and TC4-DT) and flame retardant titanium alloys (Alloy C, BTT-l and BTT-3).
The alloying elements of titanium can be divided into neutral elements, α-phase stable elements and β-phase stable elements according to their effects on β transition temperature. The α-phase stable elements extend the α-phase region to a higher temperature range, while the β-phase stable elements move the β-phase region to a lower temperature, and the neutral elements have little effect on the β-transition temperature.
Al is the most important α-phase stable element, and the interstitial elements O, N and C also belong to this category. The β-phase stable elements can be subdivided into β-homomorphic elements and β-eutectic elements. Mo, V and Ta belong to β-homomorphic elements, which have high solubility and are very important in β-titanium. Fe, Mn, Cr, Co, Ni, Cu and Si are eutectomic elements, which are easy to form intermetallic compounds with Ti. Sn and Zr are neutral elements, but can significantly strengthen the α phase.
With the development of research and application of titanium alloys, especially titanium alloys strengthened by heat treatment, non-equilibrium microstructure is often encountered, so it is preferable to classify titanium alloys according to the phase composition of the metastable state. According to the relationship between phase composition of titanium alloy after quenching from β phase region and β-stable element content, titanium alloy can be divided into α type, nearly α type, α+β type, metastable β type, stable β type and so on.
