**2. High strength two-phase titanium alloys**

Ti-6Al-2Mo-2Cr and Ti-6Al-5Mo-5V-1Cr-1Fe (Table 1).

The materials tested were high strength, two-phase α+β titanium alloys: Ti-6Al-4V,


**Table 1.** Chemical composition of the investigated titanium alloys.

Ti-6Al-4V – martensitic α+β alloy (Kβ = 0.3) – is the most widespread titanium alloy (>60% of all titanium alloys produced in USA and EU). Its high applicability results from good balance of mechanical properties and good castability, plastic workability, heat treatability and weldabil‐ ity. Aluminium addition stabilizes and strengthen α phase, increases α+β↔β transformation temperature and reduces alloy density. Vanadium – β-stabilizer – reduces α+β↔β transforma‐ tion temperature and facilitates hot working (higher volume fraction of β-phase). Depending on required mechanical properties following heat treatment can be applied to Ti-6Al-4V alloy: partial annealing (600÷650ºC / 1h), full annealing (700÷850ºC / furnace cooling to 600ºC / air cooling) or solutioning (880÷950ºC / water quenching) and ageing (400÷600ºC) [1,3].

Ti-6Al-2Mo-2Cr – martensitic α+β alloy – known as VT3-1, is one of the first widespread hightemperature titanium alloys used in Russia for aircraft engine elements. Amount of βstabilizers is similar to Ti-6Al-4V alloy but β-stabilizing factor is higher (Kβ = 0.6). Mo – stabilises and strengthens β-phase, in the presence of Si increases creep resistance, facilitates plastic working, Cr, Fe – eutectoid elements, stabilise β-phase and strengthen α and β phases in the low and medium temperature range [1].

The alloy is processed by forging, stamping, rolling and pressing. Depending on the applica‐ tion and required properties following heat treatment can be applied to the semiproducts: isothermal annealing (870ºC / 1h / furnace cooling to 650ºC / holding for 2 h / air cooling), duplex annealing (880ºC / 1h / air cooling and following heating 550ºC / 2÷5 h / air cooling) or hardening heat treatment (water quenching and ageing) [1,7].

Ti-6Al-2Mo-2Cr alloy retains its mechanical properties up to 300°C. At the temperature higher than 400°C mechanical properties are reduced due to partitioning of alloying elements proceeding by diffusion.

Ti-6Al-5Mo-5V-1Cr-1Fe transition α+β titanium alloy (Kβ = 1.2) is produced in Russia and Ukraine, where is known as VT22. It is characterized by very good mechanical properties thus is mainly used for large, heavy loaded, forged parts for long-term operation at elevated temperature up to 350÷400ºC and short-term up to 750÷800ºC. Typical applications include disks and blades of low pressure compressors, landing gear elements, engine mount struts and others [1,11].
