Titanium is an ideal structural material. Its density is not big, only 4.5g/m3, 43% lighter than steel, but its strength is twice as high as iron and almost 5 times higher than pure aluminum. It has low density and high strength. This combination of high strength and low density makes titanium technically important. At the same time, the corrosion resistance of titanium is close to or better than stainless steel, so it has been widely used in petroleum, chemical industry, pesticide, dye, paper, light industry, aviation, space development, Marine engineering and other aspects.
Titanium alloy has a very high specific strength (strength and density of the ratio), titanium alloy in aviation, military, shipbuilding, chemical industry, metallurgy, machinery, medical and other fields play an irreplaceable role. For example, titanium and aluminum, chromium, vanadium, molybdenum, manganese and other elements of the alloy, after heat treatment, the strength limit up to 1176.8-1471mpa, specific strength up to 27-33, and the same strength of alloy steel, its specific strength is only 15.5-19. Titanium alloy has not only high strength, but also corrosion resistance, so it is widely used in shipbuilding, chemical machinery and medical equipment. Among them, corrosion resistant titanium alloy is mainly used in various reactors, towers, autoclaves, heat exchangers, pumps, valves, centrifuges, pipelines, fittings, electrolytic cells, etc. However, due to the high price of titanium and its alloys, their application is limited.
Application of titanium and titanium alloys:
(1) titanium iodide, brand TAD
It is the high purity titanium obtained by iodization, so it is called iodization titanium, or chemical pure titanium. However, it still contains such interstitial impurities as oxygen, nitrogen and carbon, which have a great influence on the mechanical properties of pure titanium. With the increase of purity of titanium, the strength and hardness of titanium decreased obviously. So its characteristic is: chemical stability is good, but strength is very low.
Because of the low strength of high-purity titanium, it is of little significance as a structural material, so it is rarely used in industry. At present, pure titanium and titanium alloy are widely used in industry.
(2) industrial pure titanium
Different from chemical pure titanium, industrial pure titanium contains more oxygen, nitrogen, carbon and a variety of other impurities (such as iron, silicon, etc.), which is essentially a titanium alloy with low alloy content. Compared with pure titanium, its strength is greatly improved due to more impurity elements, and its mechanical and chemical properties are similar to stainless steel (but its strength is still lower compared with titanium alloy).
The characteristics of industrial pure titanium are: strength is not high, but good plasticity, easy to shape, stamping, welding, cutting performance is good; It has good corrosion resistance in atmosphere, seawater, wet chlorine and oxidizing, neutral and weakly reducing medium, and its oxidation resistance is better than most austenitic stainless steels. But the heat resistance is poor, the service temperature should not be too high.
According to the different impurity content, the industrial pure titanium can be divided into TA1, TA2 and TA3. The gap impurities of these three kinds of industrial pure titanium gradually increase, so their mechanical strength and hardness also gradually increase, but the plasticity and toughness decrease accordingly.
The commonly used industrial pure titanium is TA2, because of its moderate corrosion resistance and comprehensive mechanical properties. TA3 can be used when the wear resistance and strength requirements are higher. TA1 can be used when good forming performance is required.
Industrial pure titanium is mainly used for the working temperature below 350℃, the force is not big, but the requirements of good plastic stamping parts and corrosion resistant structural parts, such as: aircraft skeleton, skin, engine accessories; Seawater corrosion-resistant pipes, valves, pumps and parts of hydrofoil and desalination system for ships; Chemical heat exchanger, pump body, distillation tower, cooler, mixer, tee, impeller, fastener, ion pump, compressor valve and diesel engine piston, connecting rod, leaf spring, etc.
(3) alpha titanium alloy, grades TA4, TA5, TA6, TA7.
These alloys are ɑ single phase at room temperature and service temperature and cannot be strengthened by heat treatment (annealing is the only form of heat treatment). The strength at room temperature is generally lower than that of beta and alpha + beta titanium alloys (but higher than that of industrial pure titanium), while the strength and creep strength at high temperature (500-600℃) is the highest among the three titanium alloys. Moreover, it has good microstructure stability, oxidation resistance and welding performance, corrosion resistance and machinability, but low plasticity (thermoplasticity is still good), and poor stamping performance at room temperature. The most widely used is TA7, which has medium to high strength, sufficient plasticity and good weldability under annealing, and can be used under 500℃. When the content of interstice impurity elements (oxygen, hydrogen, nitrogen, etc.) is very low, it also has good toughness and comprehensive mechanical properties at ultra-low temperature, so it is one of the excellent ultra-low temperature alloys.
The tensile strength of TA4 is slightly higher than that of industrial pure titanium. Mainly used as welding wire in China.
TA5 and TA6 are used for parts and welding parts working in corrosive medium below 400℃, such as aircraft skin, skeleton parts, compressor shell, blade, ship parts, etc.
TA7 is used for long-term working structural parts and various forging parts under 500℃, and can be used up to 900℃ for short-term use. Also used for cryogenic (-253℃) components (such as cryogenic containers).
(4) titanium alloy beta, brand TB2.
The main alloy elements of this kind of alloy are molybdenum, chromium, vanadium and other stable beta elements. During normalizing and quenching, it is easy to retain the high-temperature beta phase to room temperature and obtain stable beta phase structure. Therefore, it is called titanium alloy beta.
Titanium alloy beta can be strengthened by heat treatment, with high strength, good welding performance and pressure processing performance. But the performance is not stable, melting process is complex, so it is not as widely used as alpha type and alpha + beta titanium alloy.
Can be used for 350℃ below the work of parts, mainly used for manufacturing a variety of overall heat treatment (solid solution, aging) plate stamping parts and welding parts; Such as compressor blade, wheel, shaft and other heavy load rotating parts and aircraft components. TB2 alloy is generally delivered in the state of solid solution treatment and used after solid solution and aging.
(5) alpha-beta titanium rods and titanium alloys commonly used brands TC6, TC9 and TC10
These alloys are called alpha + beta titanium alloys because of their alpha + beta two-phase structure at room temperature. It has good comprehensive mechanical properties, most of the heat treatment to strengthen (but of TC1, TC2, TC7 strengthening heat treatment), forging, stamping and welding performance is good, can be cutting, high strength at room temperature, 150-500 ℃ below has high heat resistance, some (such as TC1 and TC2 TC3, TC4) also has good low temperature toughness and good resistance to stress corrosion of sea water and thermal salt stress corrosion resistance; The disadvantage is that the organization is not stable enough.
TC4 is the most widely used of this kind of alloy. The alloy not only has good mechanical properties at room temperature, high temperature and low temperature, but also has excellent corrosion resistance in various media. So it is widely used in aerospace, ship and chemical industry.
TC1, TC2 can be used for working under 400℃ stamping parts, welding parts, die forging and bending processing of various parts. These two alloys can also be used as low temperature structural materials.
TC3 and TC4 can be used as long-term working parts, structural modules, various containers, pumps, low-temperature parts, vessel pressure shell, tank track, etc. The intensity is higher than TC1 and TC2.
TC6 can be used under 400℃ and is mainly used as structural material of aircraft engine. TC9 can be used to manufacture parts that work under 560℃ for a long time, mainly for compressor discs and blades of aircraft jet engines.
TC10 can be used to manufacture parts that work under 450℃ for a long time, such as aircraft structure parts, landing gear, honeycomb connections, missile engine casings, weapon structures, etc.