The history of titanium applications in aviation began in 1953 with the first usage of titanium in the engine pods and firewalls of the DC-T manufactured by Douglas in the United States. Since that time, titanium has been utilized in aircraft for almost 50 years. Because it has numerous beneficial qualities that are appropriate for aircraft applications, titanium is widely employed in aviation. We shall discuss the need for titanium in today's discussion on aircraft materials.
1.Titanium introduction
The first industrial manufacturing of titanium sponge, or titanium, began only in 1948 when the US DuPont Company manufactured tons of titanium sponge using the magnesium process. Because to its high specific strength, excellent corrosion resistance, and high heat resistance, the titanium alloy is utilized extensively across a variety of industries. Titanium ranks tenth in terms of abundance in the earth's crust, far greater than common metals like copper, zinc, and tin. Sand and clay are two types of rocks where titanium is particularly abundant.
2. the characteristics of titanium
High strength: 1.3 times that of aluminium alloy, 1.6 times that of magnesium alloy and 3.5 times that of stainless steel, the champion among metal materials.
High thermal strength: the use temperature is several hundred degrees higher than that of aluminium alloy, and can work for a long time at a temperature of 450 to 500°C.
Good corrosion resistance: resistant to acid, alkali and atmospheric corrosion, particularly strong resistance to pitting and stress corrosion.
Good low-temperature properties: titanium alloy TA7 with very low interstitial elements can maintain a certain degree of plasticity at -253°C.
High chemical activity: high chemical activity at high temperatures, easily reacting chemically with gaseous impurities such as hydrogen and oxygen in the air to produce a hardened layer.
Small thermal conductivity, small modulus of elasticity: the thermal conductivity is about 1/4 of nickel, 1/5 of iron and 1/14 of aluminium, while the thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The modulus of elasticity of titanium alloys is about 1/2 that of steel.
3.Classification and uses of titanium alloys
Heat-resistant alloys, high-strength alloys, corrosion-resistant alloys (titanium-molybdenum alloys, titanium-palladium alloys, etc.), low-temperature alloys, and unique functional alloys are some categories for titanium alloys based on their intended use (titanium-iron hydrogen storage materials and titanium-nickel memory alloys). Despite the fact that titanium and its alloys have not been used for a very long period, they have already received numerous major awards for their exceptional qualities. Because of its strength, low weight, and durability to high temperatures, it is especially well suited for the manufacturing of various spacecraft and airplanes. The aerospace sector currently uses about 75 percent of the titanium and titanium alloys produced worldwide. There are several components that were formerly constructed of titanium alloys but were originally built of aluminum alloys.
4. the titanium alloy of aviation applications
Titanium alloy is mainly used in aircraft and engine manufacturing materials, such as forging titanium fans, compressor discs and blades, engine cowlings, exhaust devices and other parts, as well as the aircraft beam spacer and other structural framework parts. Artificial earth satellites, moon modules, manned spacecraft and space shuttles also use titanium alloy plate welded parts.
In 1950 the United States for the first time in the F-84 fighter-bomber as the rear fuselage heat shield, wind shield, tail cowl and other non-load-bearing components. 60's began to use titanium alloy parts from the rear fuselage to the fuselage, partly instead of structural steel manufacturing spacer, beam, flap slide and other important load-bearing components. 70's onwards, civilian aircraft began to use titanium alloy in large quantities, such as the Boeing 747 passenger aircraft with titanium amounted to 3640 More than 28% of the weight of the aircraft. With the development of processing technology, in rockets, artificial satellites and spacecraft, also used a large number of titanium alloy.
The more advanced the aircraft, the more titanium is used. U.S. F-14A fighter aircraft use titanium alloy, accounting for about 25% of the weight of the aircraft; F-15A fighter aircraft for 25.8%; the fourth generation of U.S. fighter aircraft with 41% of the amount of titanium, its F119 engine with 39% of the amount of titanium, is currently the highest amount of titanium aircraft.
5. Reasons why titanium alloys are used in large numbers in aviation
The maximum speed of modern aircraft sailing 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 generate a lot of heat. When the speed of flight reaches 2.2 times the speed of sound, aluminium alloys can no longer withstand it. High temperature resistant titanium alloys must be used.
When the thrust-to-weight ratio of the aero-engine is increased from 4-6 to 8-10, the temperature of the compressor outlet is correspondingly increased from 200-300℃ to 500-600℃, the original low-pressure compressor disc and blade made of aluminium must be changed to titanium alloy.
In recent years scientists on titanium alloy performance research work, continue to make new progress. The original titanium alloy composed of titanium, aluminum, vanadium, the highest working temperature of 550 ℃ ~ 600 ℃, and the newly developed titanium aluminum (TiAl) alloy, the highest working temperature has been increased to 1040 ℃.
The use of titanium alloys instead of stainless steel to manufacture high-pressure compressor discs and blades can reduce the weight of the structure. For every 10 per cent weight reduction in an aircraft, fuel savings of 4 per cent can be achieved. For rockets, every 1kg weight reduction can increase the range by 15km.
6.titanium alloy machining characteristics analysis
First of all, titanium alloy thermal conductivity is low, only 1/4 of steel, aluminum 1/13, copper 1/25. because of the slow heat dissipation in the cutting area, is not conducive to thermal balance, in the cutting process, heat dissipation and cooling effect is very poor, easy to form a high temperature in the cutting area, after processing parts deformation rebound, resulting in increased torque cutting tool, edge wear fast, durability reduced.
Secondly, the titanium alloy thermal conductivity is low, so that cutting heat accumulates in the small area near the cutting tool is not easy to disperse, the front tool surface friction increases, not easy to chip, cutting heat is not easy to disperse, accelerating tool wear. Finally, titanium alloy chemical activity is high, processing at high temperatures is easy to react with the tool material, the formation of soluble, diffusion, resulting in sticky knife, burning knife, broken knife and other phenomena.
