The spacecraft operates under extreme conditions such as ultra-high temperature, ultra-low temperature, high vacuum, high stress, and strong corrosion. In addition to relying on excellent structural design, it also depends on the excellent characteristics and functions of the material. Titanium alloys combine the qualities required for aerospace products and are known as “cosmic metal” and “space metal”. Titanium alloy is an ideal manufacturing material for aircraft and engines due to its high strength, good mechanical properties and good corrosion resistance. However, due to its poor machinability, it has long restricted its application to a large extent. With the development of processing technology, in recent years, titanium alloys have been widely used in the manufacture of aircraft engine compressor sections, hoods, exhaust devices and other parts, as well as the manufacture of aircraft frame beams and other structural frame parts.
Titanium alloy has the following advantages over general alloy steel: the specific strength becomes higher: the density of titanium alloy is only 4.5g / cm3, which is much smaller than iron, and its strength is similar to ordinary carbon steel. Good mechanical properties: The melting point of titanium alloy is 1660 ℃, which is higher than that of iron and has higher thermal strength. It can work below 550 ℃, and usually shows better toughness at low temperatures. Good corrosion resistance: A dense oxide film is easily formed on the surface of the titanium alloy below 550 ° C, so it is not easy to be further oxidized, and it has high corrosion resistance to the atmosphere, seawater, steam, and some acid, alkali, and salt media.
- High-temperature titanium alloys: research and development of ultrasonic cruise bombs, hypersonic cruise bombs, reusable vehicles, and sub-orbital reusable transatmospheric vehicles, requiring titanium alloys to be able to be used at high temperatures of 600 ° C and above Titanium alloys must have excellent high temperature resistance. The first high-temperature titanium alloy in the world is Ti6Al4V developed by the United States, which can be used at 300 ～ 350 ℃. Ti6Al4V alloy has both α + β two-phase characteristics and is widely used in the aerospace field. In order to maximize the solid solution heat strengthening effect of Al, elements such as Sn, Zr, Mo, and Si were added to the titanium alloy, and IMI679, Ti6242 and other alloys with a use temperature of 450 ° C and IMI685, 500 ° C For alloys such as Ti6242S, IMI834, Ti1100, BT36 and other alloys with a temperature of 550 to 600 ° C are used.
- Low-temperature titanium alloy: With the rapid development of space technology, the application of titanium alloys in low-temperature and extremely low-temperature environments has increased, and the development of low-temperature titanium alloys is extremely important. It has been found through research that the low-temperature performance of titanium alloys can be improved by reducing the gap elements such as H, O, N, and Al, so that they can be used for a long time in a 20K temperature environment.
- High-strength and tough titanium alloy: The successful example in this regard is the α + β two-phase high-strength and high-toughness titanium alloy Ti62222S developed in the United States. This material has a good combination of strength and plasticity. The room temperature fracture strength and yield strength are greater than 1300MPa and 1200MPa, and its high temperature performance is also very good. In addition, Ti62222S also has higher fracture toughness and damage tolerance, a fatigue crack growth rate comparable to alloy Ti6Al4V, and an elastic modulus and superplastic formability superior to alloy Ti6Al4V, which can replace Ti6Al4V.
