Titanium alloy is widely used in aerospace field because of its advantages such as high specific strength and good corrosion resistance. In this paper, the microstructure and mechanical properties of major titanium alloys in recent years are introduced, including high strength and high toughness titanium alloys (β 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 Alloy (α+β type, TC21 and TC4-DT) and flame retardant titanium alloy (Alloy C, BTT-l and BTT-3).
According to the influence of β transition temperature, the alloying elements of titanium can be divided into neutral elements, α phase stable elements and β phase stable elements. The α phase stable elements extend the α phase region to a higher temperature range, while the β phase stable elements make the β phase region move to a lower temperature, and the neutral elements have little effect on the β transition temperature.
Al is the most important alpha phase stable element, and the gap elements O, N, and C also belong to this group. β phase stable elements can be subdivided into β isomorphic and β eutectoid elements. Mo, V and Ta belong to β isomorphic elements, which have high solubility and are very important in β titanium. Fe, Mn, Cr, Co, Ni, Cu, Si and other eutectoid elements 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 the research and application of titanium alloys, especially the heat-treatment enhanced titanium alloys, non-equilibrium microstructure is often encountered, so it is more advisable to classify titanium alloys according to the phase composition of metastable states. According to the relationship between the quenching phase composition and the content of β-stable elements, titanium alloys can be divided into α type, near α type, α+β type, metastable β type, stable β type and so on.
Since the fracture toughness of titanium alloy is closely related to microstructure and aging conditions, there is no clear relationship between the composition of titanium alloy and fracture toughness, but the fracture toughness of coarse lamellar microstructure is higher than that of fine equiaxed microstructure. This is because the layered structure can deflect the propagation cracks along the different orientations of the lath beam, leading to the passivation of the crack front, and thus absorbing additional crack propagation energy.
