Lightness, high strength in temperature interval from cryogenic (-250 centigrade) till reasonably high (300-600 centigrade) and excellent corrosion resistance provide titanium alloys good prospect as construction material in many branches particularly in aviation and other branches of transport machine building.
Titanium alloys are brought with the help of alloying of titanium by the following elements (numbers in brackets are maximal concentration of inoculant by mass percentage for industrial alloys): �?1 (8), V (16), Mo (30), Mn (8), Sn (13), Zr (10), Cr (10), Cu (3), Fe (5), W (5), Ni (32), Si (0.5); rarely Nb (2) и Та (5). Pd (0.2) is used as microadditive for increasing of corrosion strength and В (0.01) –for grain’s pounding. Aluminum, as well as oxygen and nitrogen, better dissolving in alpha Ti, are increasing this temperature according its concentration’s increasing, which lead to enlargement of alpha modification area. Such elements are called alpha modificators. Sn and Zr are good dissolving in both allotropic modifications of titanium and impacting on the temperature of eutectic transformation in a very little range, they are considered among so called neutral hardeners.
Because of existence of polymorphism of titanium and its ability to make hard solutions and chemical combinations with many elements the diagrams of titanium alloys’ conditions are distinguishing by wide range of varieties. Yet, the concentration of inoculants in industrial titanium alloys, usually, is not exceeding the limits of hard solutions of alpha Ti, beta Ti phase is not usually applied.
Titanium alloys are divided on 3 groups according structural type. Alloys with Al, Sn, Zr and little quantity of beta stabilizators (0.5-2%) are considered among alloys based on alpha structure. Because of little quantity or even absence of beta structure they are not hardening by thermal treatment, so that they are considered among alloys with medium hardness. The advantages of alpha alloys are excellent bondability, high range of afterflow and absence of the necessity in thermal treatment, excellent casting characteristics as well, which is important for shaped castings.
Double phase alpha+beta alloys are the most numerous group of industrial titanium alloys. These alloys have higher technological plasticity than alpha alloys, and at same time can be thermally treated till very high hardness, they can have good high-temperature strength. Among the disadvantages of double phase alloys are worse bondability in comparison with alloys of previous group, because fragile zones and cracks can appear in the area of thermal impact, for prevention of which the special thermal treatment after welding is required. The other disadvantage of beta alloys is relatively low maximal working temperature approximately 300 centigrade; under higher temperatures the majority of these alloys are become fragile.
Titanium and its alloys can be forged, stamped (by volume and sheets), rolled, pressed and dragged. It is possible to get the same semis as from other construction metals, taking into consideration titanium’s inclination to oxidation during heating.
One of the disadvantages of titanium alloys is low antifriction characteristics, which require special covers’ and lubricants’ usage on friction surfaces.