The research and development direction of titanium alloys for aerospace applications

Spacecraft operate under extreme conditions such as extremely high temperatures, extremely low temperatures, high vacuum, high stress, and strong corrosion. Besides relying on excellent structural design, the materials must possess outstanding properties and functions. Titanium alloys combine the necessary characteristics for space products and are thus known as "cosmic metals" and "space metals". According to the requirements of materials for space products, titanium alloys are developing in the following directions in the aerospace field:

※ High-strength and high-toughness titanium alloys
A successful example in this area is the α+β two-phase high-strength and high-toughness titanium alloy Ti62222S developed by the United States. This material has good strength and plasticity compatibility, with room-temperature fracture strength and yield strength exceeding 1300 MPa and 1200 MPa respectively, and its high-temperature performance is also excellent. In addition, Ti62222S has high fracture toughness and damage tolerance, and a fatigue crack growth rate comparable to that of alloy Ti6Al4V, as well as better elastic modulus and superplastic formability than alloy Ti6Al4V, which can replace Ti6Al4V.

※ High-temperature titanium alloys
The research and development of ultrasonic cruise missiles, hypersonic cruise missiles, reusable launchers, and suborbital reusable trans-atmospheric aircraft require titanium alloys to be able to operate at temperatures of 600°C and above. This demands that titanium alloys have excellent high-temperature resistance. The first high-temperature titanium alloy in the world was developed by the United States, Ti6Al4V, which can be used at 300-350°C. The Ti6Al4V alloy has the characteristics of α+β two phases and is widely used in the aerospace field. To maximize the effect of Al solid solution strengthening, elements such as Sn, Zr, Mo, and Si are added to the titanium alloy, and subsequently alloys such as IMI679, Ti6242, with a use temperature of 450°C, IMI685, Ti6242S, with a use temperature of 500°C, IMI834, Ti1100, and BT36, with a use temperature of 550-600°C, have been developed.

※ Low-temperature titanium alloys
With the rapid development of space technology, the application of titanium alloys in low-temperature and extremely low-temperature environments has increased. The development of low-temperature titanium alloys is extremely important. It has been found that by reducing the content of interstitial elements such as H, O, and N, as well as Al, the low-temperature performance of titanium alloys can be improved, allowing them to be used for a long time at 20K temperature.