Reasons for titanium alloy is used in aerospace materials

Titanium has an indissoluble bond with aviation. In 1953, titanium was first used on the engine pod and fire wall of DC-T aircraft produced by Douglas company, which opened the history of titanium aviation application. Since then, titanium has been used in aviation for more than half a century. Titanium can be widely used in aviation because it has many valuable characteristics suitable for aircraft applications.

In 1948, DuPont company of the United States produced sponge titanium by ton with magnesium method - which marked the beginning of industrialized production of sponge titanium, namely titanium. Titanium alloy is widely used in various fields because of its high specific strength, good corrosion resistance and high heat resistance.

Titanium is abundant in the earth's crust, ranking ninth, much higher than common metals such as copper, zinc and tin. Titanium is widely found in many rocks, especially in sand and clay.

High strength: 1.3 times of aluminum alloy, 1.6 times of magnesium alloy and 3.5 times of stainless steel. It is the champion in metal materials.

High thermal strength: the service temperature is several Baidu higher than that of aluminum alloy, and can work for a long time at the temperature of 450 ~ 500 ℃.

Good corrosion resistance: acid, alkali and atmospheric corrosion resistance, especially strong resistance to pitting corrosion and stress corrosion.

Good low temperature performance: titanium alloy TA7 with very low interstitial elements can maintain a certain plasticity at - 253 ℃.

High chemical activity: high chemical activity at high temperature, easy to react with hydrogen, oxygen and other gas impurities in the air to form a hardened layer.

Small thermal conductivity and elastic modulus: the thermal conductivity is about 1 / 4 of nickel, 1 / 5 of iron and 1 / 14 of aluminum, while the thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The elastic modulus of titanium alloy is about 1 / 2 of that of steel.

Classification and application of titanium alloys

Titanium alloys can be divided into heat-resistant alloys, high-strength alloys, corrosion-resistant alloys (titanium molybdenum, titanium palladium alloys, etc.), low-temperature alloys and special functional alloys (titanium iron hydrogen storage materials and titanium nickel memory alloys), etc.

Although the application history of titanium and its alloys is not long, it has won many glorious titles because of its extraordinary properties. The first title won is "space metal". It has the advantages of light weight, high strength and high temperature resistance. It is especially suitable for manufacturing aircraft and various spacecraft. At present, about three-quarters of the titanium and titanium alloys produced in the world are used in the aerospace industry. Many parts originally made of aluminum alloy have been replaced with titanium alloy.

Aviation application of titanium alloy

Titanium alloy is mainly used in aircraft and engine manufacturing materials, such as forged titanium fan, compressor disc and blade, hood, exhaust device and other parts, as well as structural frame parts such as girder spacer frame of aircraft. Spacecraft mainly use the high specific strength, corrosion resistance and low temperature resistance of titanium alloy to manufacture various pressure vessels, fuel tanks, fasteners, instrument straps, frames and rocket shells. Titanium alloy plate weldments are also used in artificial earth satellites, lunar modules, manned spacecraft and space shuttles.

In 1950, the United States first used F-84 fighter bomber as non load-bearing components such as rear fuselage heat shield, wind guide cover and tail cover. Since the 1960s, the use of titanium alloy has moved from the rear fuselage to the middle fuselage, partially replacing structural steel to manufacture important load-bearing components such as spacer frame, beam, flap slide rail and so on. Since the 1970s, a large number of titanium alloys have been used in civil aircraft. For example, the amount of titanium used in Boeing 747 aircraft has reached more than 3640 kg, accounting for 28% of the aircraft weight. With the development of processing technology, a large number of titanium alloys are also used in rockets, satellites and spacecraft.

The more advanced the aircraft, the more titanium is used. Titanium alloy used in American F-14A fighter aircraft accounts for about 25% of the aircraft weight; 25.8% for F-15A fighter; The titanium consumption of the fourth generation fighter of the United States is 41%, and the titanium consumption of its F119 engine is 39%, which is the aircraft with the highest titanium consumption at present.

The maximum speed of modern aircraft has reached more than 2.7 times the speed of sound. Such a fast supersonic flight will cause the aircraft to rub with the air and produce a lot of heat. When the flight speed reaches 2.2 times the speed of sound, the aluminum alloy can't stand it. High temperature resistant titanium alloy must be used.

When the thrust weight ratio of aeroengine is increased from 4 ~ 6 to 8 ~ 10, and the compressor outlet temperature is correspondingly increased from 200 ~ 300 ℃ to 500 ~ 600 ℃, the low-pressure compressor disk and blade originally made of aluminum must be replaced with titanium alloy.

In recent years, scientists have made new progress in the research on the properties of titanium alloys. The maximum working temperature of the original titanium alloy composed of titanium, aluminum and vanadium is 550 ℃ ~ 600 ℃, while the maximum working temperature of the newly developed aluminum titanium alloy has been increased to 1040 ℃.

Using titanium alloy instead of stainless steel to make high-pressure compressor disk and blade can reduce the structural weight. Fuel can be saved by 4% for every 10% reduction in weight of the aircraft. For rockets, every 1kg of weight reduced can increase the range of 15km.

Firstly, the thermal conductivity of titanium alloy is low, only 1 / 4 of steel, 1 / 13 of aluminum and 1 / 25 of copper. Due to the slow heat dissipation in the cutting area, which is not conducive to heat balance, the heat dissipation and cooling effect are very poor in the cutting process, which is easy to form high temperature in the cutting area, and the deformation and rebound of parts after processing are large, resulting in increased torque of cutting tools, rapid wear of cutting edges and reduced durability.