Why do Aviation Materials Have To Use Titanium Alloy?
4. Aviation Application of Titanium Alloy
Titanium alloy is mainly used in the manufacturing materials of aircraft and engines, such as forged titanium fans, compressor discs and blades, engine covers, exhaust devices and other parts, as well as structural frame parts such as aircraft girder partitions. Spacecraft mainly use the high specific strength, corrosion resistance and low temperature resistance of titanium alloy to manufacture a variety of pressure vessels, fuel tanks, fasteners, instrument straps, frames and rocket shells. Artificial earth satellites, lunar modules, manned spacecraft and space shuttles also use titanium alloy plate welding parts.
In 1950, the United States was first used as a rear fuselage heat shield, air guide cover, tail cover and other non-bearing components on the F-84 fighter-bomber. Since the 1960s, the use of titanium alloy has moved from the rear fuselage to the middle fuselage, partially replacing structural steel to make partitions, beams, flap rails and other important bearing components. Since the 1970s, titanium alloys have been used extensively in civil aircraft, such as Boeing 747 airliners with a titanium amount of more than 3,640 kg, accounting for 28% of the weight of the aircraft. With the development of processing technology, a large number of titanium alloys are also used on rockets, artificial satellites and spaceships.
The more advanced the aircraft,the more titanium is used. The titanium alloy used in the United States F—14A fighter jet accounts for about 25% of the weight of the aircraft; the F—15A fighter jet is 25.8%; the amount of titanium used in the fourth generation of the United States fighter jet is 41%, and the amount of titanium used in its F119 engine is 39%, which is currently the highest amount of titanium used in the aircraft.
5. The Reason Why Titanium Alloy is Widely Used in Aviation
The top 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 against the air and produce a lot of heat. When the flight speed reaches 2.2 times the speed of sound, aluminum alloy can't stand it. High temperature resistant titanium alloy must be used.
When the thrust-to-weight ratio of the aero-engine increases from 4 - 6 to 8 - 10, and the compressor outlet temperature increases correspondingly from 200 ~ 300 °C increased to 500 ~ 600 °C, the original low-pressure compressor discs and blades made of aluminum must be replaced with titanium alloy.
In recent years, scientists have made new progress in the research work on the properties of titanium alloys. The original titanium alloy composed of titanium, aluminum and vanadium has a maximum operating temperature of 550℃ ~ 600℃, while the newly developed aluminum titanate (Ti-Al) alloy has a maximum operating temperature of 1040℃.
Using titanium alloy instead of stainless steel to manufacture high-pressure compressor discs and blades can reduce structural weight. For each 10% weight reduction of the aircraft, fuel savings of 4% can be achieved. For rockets, every 1kg reduction in weight can increase the range of 15km.
6. Analysis of Machining Characteristics Of Titanium Alloy
First of all, titanium alloy has low thermal conductivity, which is only 1/4 of steel,1/13 of aluminum, and 1/25 of copper. Due to the slow heat dissipation in the cutting area, it is not conducive to thermal balance. During the cutting process, the heat dissipation and cooling effect are poor, and it is easy to form a high temperature in the cutting area. After processing, the deformation and rebound of the parts are large, resulting in increased torque of the cutting tool, fast edge wear, and reduced durability.
Secondly, the thermal conductivity of titanium alloy is low,so that the cutting heat accumulation in a small area near the cutting tool is not easy to emit, the friction on the front tool surface is increased, it is not easy to chip removal, cutting heat is not easy to emit, accelerate tool wear. Finally, titanium alloy has high chemical activity, and it is easy to react with the tool material at high temperatures, forming dissolution and diffusion, resulting in sticky knives, burning knives, broken knives and other phenomena.
