Classification of the main uses of pure titanium and titanium alloys
Titanium is an important structural metal developed in 1950s. Because of its high strength, good corrosion resistance and high heat resistance, titanium alloy has been widely used in various fields. Many countries in the world have recognized the importance of titanium alloy materials, and have studied and developed them successively, and have been applied in practice. In twentieth Century 50 to 60s, is the main structure of the titanium alloy used in aero engine development of high temperature titanium alloy airframe, 70s Kai issued a batch of titanium alloys, since 80s, titanium alloys and high strength titanium alloy has been further developed. Titanium alloys are mainly used to make aircraft engine compressor parts, followed by rockets, missiles and high-speed aircraft structures.
Titanium is allotrope, melting point of 1668 DEG C, at less than 882 DEG C when a dense row of six square lattice structure, called alpha titanium; a body centered cubic lattice structure at 882 DEG C, known as beta titanium. The titanium alloy (titanium alloys) with different microstructure was obtained by adding proper alloy elements to the different characteristics of the above two structures of titanium and gradually changing its phase transformation temperature and phase content. At room temperature, the titanium alloy has three kinds of matrix structure, and the titanium alloy is divided into the following three kinds: alpha alloy, (alpha + beta) alloy and beta alloy. China is represented by TA, TC and TB respectively.
Alpha titanium alloy
It is a single-phase alloy composed of alpha phase solid solution. It is a phase at both the general temperature and the higher applied temperature. The microstructure is stable, the wear resistance is higher than that of pure titanium, and the oxidation resistance is strong. At 500 ~ 600 DEG C, the strength and creep resistance are still maintained, but it can not be strengthened by heat treatment, and the room temperature is not high.
Beta titanium alloy
It is a beta phase solid solution consisting of single phase alloy, titanium alloy (3) without heat treatment which has high strength, Quenched and aged alloy has been further strengthened, the strength at room temperature is 1372 ~ 1666 MPa; but the poor thermal stability, should not be used at high temperature.
Alpha + beta titanium alloy
It is a double phase alloy, with good comprehensive performance, organizational stability, good toughness, ductility and deformation performance, better thermal pressure processing, can make the alloy quenching and aging strengthening. Strength than the annealed state after heat treatment is increased by 50% ~ 100; high temperature strength, can work at a temperature of 400 DEG to 500 DEG C under the long-term, the thermal stability in titanium alloy.
The most commonly used three kinds of titanium alloys are alpha titanium alloy and alpha + beta titanium alloy. The machinability of alpha titanium alloy Zui is good, alpha + beta titanium alloy is second, and beta titanium alloy is the worst. The alpha titanium alloy is TA, the beta titanium alloy is TB, and the alpha + beta titanium alloy is TC.
Titanium alloy can be divided into heat resistant alloy, high strength alloy, corrosion resisting alloy (titanium molybdenum, titanium palladium alloy, etc.), low temperature alloy and special functional alloy (titanium iron hydrogen storage material and Ti Ni memory alloy). The composition and properties of typical alloys are shown in table.
The phase composition and microstructure of the heat treated titanium alloy can be obtained by adjusting the heat treatment process. Generally fine equiaxed microstructure has plasticity, thermal stability and good fatigue strength; creep rupture strength, creep strength and fracture toughness of acicular structure has high; equiaxed and acicular mixed structure has good comprehensive performance.
Titanium alloy has the advantages of high strength, small density, good mechanical properties, good toughness and good corrosion resistance. In addition, titanium alloy has poor technological performance and difficult machining. It is easy to absorb hydrogen, nitrogen, carbon and other impurities in hot working. And poor abrasion resistance, complex production process. The industrial production of titanium began in 1948. The development of the aviation industry requires the titanium industry to grow at an average annual rate of about 8%. The annual output of titanium alloy processing materials has reached more than 4 tons, and nearly 30 grades of titanium alloy de have been produced. The most widely used titanium alloys are Ti-6Al-4V (TC4), Ti-5), Al-2.5Sn (TA7) and industrial pure titanium (TA1, TA2 and TA3).
Titanium alloys are mainly used to make aircraft engine compressor parts, followed by rockets, missiles and high-speed aircraft structures. In the mid 60s, titanium and its alloys have been used in general industries to produce electrodes for the electrolytic industry, condensers for power stations, heaters for petroleum refining and desalination, and environmental pollution control devices. Titanium and its alloys have become a kind of corrosion resistant structural materials. In addition, it is also used in the production of hydrogen storage materials and shape memory alloys.
China started titanium and titanium alloy research in 1956. In the middle of 60s, titanium alloy was industrialized and manufactured into TB2 alloy.
Titanium alloy is a new kind of important structural materials used in aerospace industry, the proportion between the strength and temperature between aluminum and steel, aluminum, steel and high strength but also has excellent anti-corrosion properties and low temperature properties. In 1950, the United States for the first time in the F-84 fighter bombers as a rear fuselage insulation panels, wind shield, tail cover and other non load components. In 60s, Kai started the use of titanium alloy parts from the rear fuselage moving to the central fuselage, and partially replaced the structural steel to make such important load-bearing components as bulkhead, beam, flap and slide rail. The amount of titanium alloy used in Jun aircraft increased rapidly, reaching 20% ~ 25% of the aircraft structure weight. Since 70s, civil aircraft began to use a large number of titanium alloys, such as Boeing 747 aircraft with titanium content of more than 3640 kilograms. The Maher number greater than 2.5 of the aircraft used titanium mainly to replace the steel, in order to reduce the structural weight. For example, the United States SR-71 high-altitude high-speed reconnaissance aircraft (flight Maher number 3, flying height 26212 meters), titanium accounted for 93% of the aircraft structure weight, known as the "full titanium" aircraft. When the aero engine thrust weight ratio from 4 to 6 to 8 to 10, the compressor outlet temperature correspondingly from 200 ~ 300 to 500 ~ 600 degrees C degrees C, originally made of aluminium low pressure compressor disk and blade must use titanium alloy, titanium alloy or stainless steel instead of high pressure compressor disk and blade. In order to reduce the structural weight. In 70s, the amount of titanium alloy in aviation engine in general accounted for the total weight of the structure from 20% to 30%, mainly used in the manufacture of compressor components, such as forging titanium fan and compressor disk and blade, titanium casting compressor casing, casing and bearing shell etc.. The spacecraft mainly use titanium alloy with high specific strength, corrosion resistance and low temperature resistance performance to make all kinds of pressure vessels, fuel tanks, fasteners, bandages, instrument frame and rocket shell. Man-made earth satellites, lunar module, manned spacecraft and space shuttle also use titanium alloy plate welding parts.