Titanium and aviation have an unbreakable relationship. 1953, in the United States Douglas company produced DC-T machine engine pods and firewalls on the first use of titanium, thus opening the history of titanium aviation applications. 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 properties suitable for aircraft applications. Today we will talk about why titanium is necessary for aviation materials.
I. Introduction to Titanium
In 1948, the United States DuPont only with the magnesium method tons of production of titanium sponge - this marks the beginning of the industrial production of titanium sponge that titanium. Titanium alloy is widely used in various fields because of its high strength, good corrosion resistance, heat resistance and other characteristics.
Titanium is abundant in the earth's crust, ranking ninth in content, much higher than copper, zinc, tin and other common metals. Titanium is widely found in many rocks, especially in sand and clay.
Second, the properties of titanium
High strength: 1.3 times that of aluminum alloy, 1.6 times that of magnesium alloy, 3.5 times that of stainless steel, the champion of metal materials.
High thermal strength: the use temperature is several hundred degrees higher than aluminum alloy, can be in the temperature of 450-500 ℃ for long-term work.
Good corrosion resistance: resistant to acid, alkali and atmospheric corrosion, especially strong resistance to pitting and stress corrosion.
Good low-temperature performance: titanium alloy TA7 with very low interstitial elements can maintain a certain degree of plasticity at -253℃.
High chemical activity: high chemical activity at high temperatures, easily reacts chemically with hydrogen, oxygen and other gaseous impurities in the air to generate a hardened layer.
Small thermal conductivity, small modulus of elasticity: the thermal conductivity is about 1/4 of nickel, 1/5 of iron, 1/14 of aluminum, and various titanium alloys have a thermal conductivity of about 50% lower than that of titanium. The modulus of elasticity of titanium alloy is about 1/2 of steel.
Third, the classification and use of titanium alloy
Titanium alloys can be divided into: heat-resistant alloys, high-strength alloys, corrosion-resistant alloys (titanium - molybdenum, titanium - palladium alloys, etc.), low-temperature alloys, as well as special function alloys (titanium - iron hydrogen storage materials and titanium - nickel memory alloys) and so on.
Although titanium and its alloys have not been used for a long time, they have been awarded several honorable titles due to their outstanding performance. The first one is "Space Metal". Its light weight, high strength and high temperature resistance make it particularly suitable for the manufacture of airplanes 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 by titanium alloy.
Fourth, the aviation application of titanium alloy
Titanium alloy is mainly used for aircraft and engine manufacturing materials, such as forging titanium fan, pressurized air disk and blade, engine cover, exhaust device and other parts, as well as the aircraft's large beams frame and other structural frame parts. Spacecraft mainly use titanium alloys of high strength, corrosion resistance and low temperature resistance to manufacture a variety of pressure vessels, fuel storage tanks, fasteners, instrument straps, frames and rocket shells. Artificial Earth satellites, moon landing module, manned spacecraft and space shuttles also use titanium alloy plate welding parts.
In 1950, the United States for the first time in the F-84 fighter-bomber used as a rear fuselage heat shield, wind shield, tail cowl and other non-load-bearing components. 60's the beginning of the use of titanium alloys from the rear fuselage to the center fuselage, partially instead of structural steel manufacturing spacer frames, beams, flaps, slide rails, and other important load-bearing components. 70's, the civilian aircraft began to use titanium alloys in large quantities, such as the amount of titanium in the Boeing 747 aircraft amounted to 3640 kg or more, accounting for 28% of the weight of the aircraft. The amount of titanium used in Boeing 747 airliner is 3640 kilograms, accounting for 28% of the weight of the aircraft. With the development of processing technology, in rockets, satellites and spacecraft, also used a large number of titanium alloys.
The more advanced the airplane, the more titanium is used. U.S. F-14A fighter using titanium alloy, accounting for about 25% of the weight of the machine; F-15A fighter for 25.8%; U.S. fourth-generation fighters with titanium amount of 41% of the F119 engine with 39% of the amount of titanium, is the highest amount of titanium with the aircraft.
Fifth, titanium alloy in the aviation is a large number of reasons for application
The highest speed of modern aircraft navigation has reached the speed of sound more than 2.7 times. So fast supersonic flight, will make the airplane and air friction and produce a lot of heat. When the flight speed reaches 2.2 times the speed of sound, aluminum alloy can not withstand. A heat-resistant titanium alloy must be used.
When the thrust-to-weight ratio of the aero-engine is increased from 4 to 6 to 8 to 10, and the outlet temperature of the pressurizer is correspondingly increased from 200 to 300℃ to 500 to 600℃, the original low-pressure pressurizer discs and blades made of aluminum must be changed to titanium alloy.
In recent years, scientists on the performance of titanium alloys research work, and continue to make new progress. The original titanium alloy composed of titanium, aluminum, vanadium, the maximum operating temperature of 550 ° C to 600 ° C, and the newly developed titanium aluminum (TiAl) alloy, the maximum operating temperature has been increased to 1040 ° C.
Titanium alloy instead of stainless steel to manufacture high-pressure compressor disk and blade, can reduce the weight of the structure. Aircraft can save 4% of fuel for every 10% weight reduction. For rockets, for every 1kg of weight reduction, the range can be increased by 15km.
Six, titanium alloy machining characteristics analysis
First of all, the low thermal conductivity of titanium alloy, only 1/4 of steel, aluminum 1/13, copper 1/25. due to the slow heat dissipation in the cutting zone, not conducive to thermal balance, in the cutting process, the heat dissipation and cooling effect is very poor, easy to form a high temperature in the cutting zone, the deformation of the parts after machining rebound, resulting in increased torque on the cutting tool, the edge of the edge of the fast wear and reduced durability.
Secondly, the low thermal conductivity of titanium alloy, so that the cutting heat accumulated in the cutting knife near the small area area is not easy to disseminate, the friction of the front face increases, not easy to chip, cutting heat is not easy to disseminate, accelerate tool wear. Finally, titanium alloy chemical activity is high, processing at high temperatures is easy to react with the cutting tool material, the formation of dissolution, diffusion, resulting in sticky knife, burning knife, broken knife and other phenomena.
