Due to their high strength, light weight and corrosion resistance titanium alloys are used in hydraulic systems of aerospace applications where pipe fittings are produced by welding or highly elastic pressing.

However, known titanium alloys have insufficient ductility to produce the fittings by elastic pressing.

One of known industrial titanium alloys, used in the hydraulic systems, is the alloy Ti-3A1-2. 5V. This alloy features high formability during cold rolling and allows to produce fittings by elastic pressing at minimum values of yield point 515 MPa and ultimate strength 620 MPa (AMS 4943D, Seamless Annealed Pipes for Hydraulic Systems, Made of Alloy Ti-3A1-2. 5V, UNSR56320).

Titanium alloy of the following composition in mass % is also known: Aluminum 2.5-4.5 Vanadium 2.0-3.0 Molybdenum 0.5-2.0 Zirconium 0.5-2.0 Iron 0.20 max Nitrogen 0.03 max Oxygen 0.15 max Ref. German patent application DE 19533743 Al, Int. Cl. C22C 14/00, published 13.03.97, as prior knowledge.

This alloy is applicable for hot working, may be used for manufacture of hot- worked and seamless cold-worked pipes, possesses a favorable combination of high strength, formability and corrosion resistance but its ductility is insufficient to flare the pipe or to produce fittings by elastic pressing.

The object of the invention is to propose titanium alloy possessing a combination of high strength, formability and corrosion resistance, suitable for manufacture of seamless cold-worked pipes for hydraulic systems of aerospace applications and sea vessels as well as for manufacture of pipe fittings by the elastic pressing method.

In accordance with the invention this is achieved by creation of titanium-base alloy containing aluminum, vanadium, molybdenum, zirconium, iron, nitrogen and additional carbon at the following content of components, mass %: Aluminum 2.5-4.0 Vanadium 2.5-4.0 Molybdenum 2.0-3.5 Zirconium 0.4-1.5 Iron 0.25 max Nitrogen 0.03 max Oxygen 0.15 max Carbon 0.01-0,1 Other impurities, total 0.3 max Titanium balance This titanium-base alloy may also additionally contain palladium or ruthenium in the following quantities, mass %: Palladium 0.03-0.1 Ruthenium 0.03-0.3 The lower limit of the alloying element content in mass %, i. e. AI (2.5), V (2.5), Mo (2.0), Zr (0. 4), of interstitial impurities Fe (0. 05), N (0. 005), 0 (0.05) and of carbon (0.01) is the minimum at which the high strength (cab= 690 MPa, Cy0. 2 = 530 MPa) and ductility (8 = 18.4%) are ensured when the pipe diameter is expanded by the factor of 1.43 in comparison with the initial outside diameter. The high ductility during cold rolling and expansion of the pipes is achieved due to higher content of the-phase

which increases the plasticity as a result of large number of sliding planes in the crystal lattice and of the deformation of the a-phase within the (3-phase under the isostatic compression.

The upper limit of the alloying element content in mass %, i. e. Al (4.0) and Zr (1. 5), in combination with the maximum content of (3-stabilizers V (4.0), Mo (3.5), interstitial impurities Fe (0. 25), N (0. 03), 0 (0.15), and carbon C (0. 1) allows to maintain sufficient ductility (8>17. 7%) when the pipe diameter is expanded by the factor of 1.4 at high strength of the material (aB = 932 MPa, ao. 2 = 738 MPa).

Further increase in aluminum, zirconium and interstitial impurities content causes the increase in the a-phase quantity and strength but reduces the ductility.

Increase in the (3-stabilizer content reduces the alloy stability, causes grain growth during the heat treatment which also reduces the alloy ductility.

Addition of 0.01-0. 1% of carbon increases the strength and ductility of the alloy and allows to use the same for manufacture of hydraulic system piping operating under severe conditions.

If the carbon content is below 0.01%, the yield point of the alloy is insufficient to ensure the performance capability of the piping in hydraulic systems. When the carbon content exceeds 0.1% the ductility of the alloy decreases at pipe expansion so that the pipe to fitting connection cannot be made by elastic pressing.

Additional alloying with palladium and ruthenium in the claimed limits increases the corrosion resistance of the alloy in the marine environment when the alloy is used in sea vessel piping.

Overalloying with the additional elements Pd and Ru in excess of the claimed limits will increase the alloy cost without any significant increase in the corrosion resistance, and underalloying below these limits cannot ensure the required corrosion resistance for long-term operation in marine environment.

Examples of the embodiment of the invention are given below.

To study the properties of the alloy, ingots with the composition shown in Table 1 have been melted in a vacuum arc furnace and pipes with the outside diameter of 1" and wall thickness of 0.051"were made from these ingots.

The mechanical and corrosion properties of the pipes are shown in Table 2.

As can be seen, the alloy with the claimed composition possesses high strength and ductility values in combination with high expansion and corrosion resistance and complies with the requirements for pipes used in hydraulic systems of aerospace applications and sea vessels.

Table 1 Example Al V Mo Zr Fe N C O Ti Ru Pd 1 2. 5 2. 5 2.0 0.5 0.05 0. 009 0.01 0.06 base 2 2. 5 4. 0 3.5 0.4 0.07 0.008 0.05 0.09 base 0.03 3 3. 4 3.6 2.8 1. 1 0.12 0.006 0.06 0. 1 base 4 3. 1 3. 0 2.7 1.1 0.19 0.006 0.07 0. 1 base-0.03 5 4. 0 4.0 3.5 1.5 0.08 0. 01 0. 1 0.15 base Table 2 Ultimate strength Yield point Elongation Outside Corrosion rate in at 20°C at 20°C 8, % diameter MgCI 37% Q, t aB, MPa GO. 2, MPa expansion solution at w 125°C, 300 h, mm/year mm/year 690 530 18.4 1.43 0.011 2 891 684 19. 4 1. 42 0. 0018 3 915 705 20. 4 1. 42 0. 011 4 902 709 21. 3 1. 46 0. 0016 5 932 738 17. 7 1. 40 0. 013

The outside diameter expansion was determined as the ratio of the outside diameter of the specimen after flaring to the initial outside diameter.

All specimens have sustained the test; the test was interrupted only because the support faces of the specimens lost the stability or the entire specimen lost the longitudinal stability.