Titanium alloys are more suitable than alloy steel for use as materials in aerospace applications

Titanium alloys have the following advantages over general alloy steels: higher strength-to-density ratio; titanium alloys have a density of only 4.5g/cm³, which is much lower than that of iron, while their strength is similar to that of ordinary carbon steel. Excellent mechanical properties; the melting point of titanium alloys is 1660℃, which is higher than that of iron, and they have high thermal strength, capable of operating below 550℃, and usually show good toughness at low temperatures. Good corrosion resistance; below 550℃, titanium alloys easily form a dense oxide film on their surface, so they are not easily further oxidized, and they have high corrosion resistance to air, seawater, steam, and some acids, bases, and salt media.

High strength and toughness titanium alloys: A relatively successful example in this field 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 coordination, with room-temperature fracture strength and yield strength exceeding 1300MPa and 1200MPa respectively, and its high-temperature performance is also very good. In addition, Ti62222S has excellent fracture toughness and damage tolerance, comparable fatigue crack growth rate to alloy Ti6Al4V, and superior elastic modulus and superplastic forming properties to alloy Ti6Al4V, and can replace Ti6Al4V.

High-temperature titanium alloys: The research and development of supersonic cruise missiles, hypersonic cruise missiles, reusable launchers, and suborbital reusable cross-atmosphere aircraft require titanium alloys to be able to operate at temperatures above 600℃, which means titanium alloys must have excellent high-temperature performance. The first high-temperature titanium alloy in the world was developed by the United States, Ti6Al4V, which can be used at 300-350℃. The Ti6Al4V alloy has the characteristics of α+β, and is widely used in the aerospace field. To maximize the effect of Al solid solution strengthening, titanium alloys also contain elements such as Sn, Zr, Mo, and Si, and successively developed alloys such as IMI679, Ti6242 with a use temperature of 450℃, IMI685, Ti6242S with a use temperature of 500℃, IMI834, Ti1100, BT36 with a use temperature of 550-600℃.

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, N, and Al, the low-temperature performance of titanium alloys can be improved, allowing them to be used for a long time at 20K temperature environments.

Spacecraft operating under extreme conditions such as ultra-high temperature, ultra-low temperature, high vacuum, high stress, and strong corrosion requires not only excellent structural design but also the excellent characteristics and functions of the materials. Titanium alloys combine the required traits of aerospace products and are hailed as "cosmic metal" and "space metal". Titanium alloys, with their high strength, good mechanical properties, and corrosion resistance, have become ideal manufacturing materials for aircraft and engines, but due to their poor cutting processability, they have long been largely restricted in their application. With the development of processing technology, titanium alloys have been widely used in the manufacturing of parts such as the compressor section of aircraft engines, engine covers, exhaust devices, and structural frame components of aircraft in recent years. The titanium alloy parts of a new type of aircraft engine in our company account for approximately 11% of the total number of parts. This article is a summary of the understanding and experience in the cutting characteristics of titanium alloy materials and the specific characteristics exhibited under different processing methods during the trial production of this new aircraft engine.