Application status and Prospect of titanium alloy
The oceans, which account for about 71% of the earth’s surface area, are rich in resources. Developing and using the oceans to make them the source of our great wealth has become one of the directions of people’s efforts for many years. However, seawater is corrosive because it contains about 3.5% salt. In addition, some biological pollution in the ocean also accelerates the corrosion of seawater.
Titanium is a kind of material with excellent physical properties and stable chemical properties. Titanium and its titanium alloys have high strength, small specific gravity, seawater corrosion resistance and marine atmosphere corrosion resistance, which can well meet the requirements of people’s application in marine engineering. After years of efforts by people in the titanium industry and researchers in marine engineering applications, titanium has been widely used in marine oil and gas development, seaport construction, coastal power stations, seawater desalination, ships, marine fisheries and marine thermal energy conversion. Now, titanium for ocean engineering has become one of the main fields of titanium civil application.
Table of Contents
- 1 Application status
Prospect of titanium alloy
- 2.1 Market situation of titanium alloy civil health products
- 2.2 Application of titanium alloy building decoration materials
- 2.3 Research progress of titanium alloys for aviation
- 2.4 Development and application of titanium alloys for aviation
- 2.5 Existing problems and Prospects
Offshore oil and gas development
Oil is the lifeblood of a country’s economy. It is estimated that the world’s recoverable oil resource reserves are 300 billion tons, of which the seabed oil reserves are about 130 billion tons. The development of submarine oil began in the early 20th century. Its development has experienced the process from offshore to open sea, from shallow sea to deep sea. Limited by technical conditions and material development, only oil and natural gas deposits extending directly from the coast to the shallow sea can be exploited at first. Since the 1980s, stimulated by the energy crisis and technological progress, offshore oil exploration and development has developed rapidly, offshore oil development has advanced rapidly to the continental shelf, and a new offshore oil industry has gradually formed. Offshore drilling platform is a working base for seabed oil and gas exploration and production. It marks the level of seabed oil and gas development technology. Offshore oil production equipment mainly includes oil production platform and auxiliary equipment, including crude oil cooler, riser, pump, valve, joint and fixture. These equipment are in contact with sulfide, ammonia, chlorine and other media in seawater and crude oil. Because titanium has excellent corrosion resistance in these media, the United States used offshore oil platform pillars made of titanium in its oil fields in the early 1970s. At the same time, tubular heat exchangers and plate heat exchangers were made of titanium. The titanium tubular heat exchanger uses seawater as the cooling medium to cool the high-temperature steam / oil mixture extracted from the oil well. Titanium plate heat exchanger also uses seawater as cooling medium to cool the fresh water cooling crude oil in carbon steel heat exchanger. The United States uses about 100 titanium heat exchangers on the drilling platform of Beihai oilfield. The titanium parts ordered by hunting oilfield services in Aberdeen, Scotland, are said to be the world’s first titanium high-pressure riser shaft, which is used in the heidrum project of Conoco in Norway.
The service life of petroleum titanium alloy drilling pipe is long, and its weight is only half that of stainless steel, while its service flexibility is twice that of stainless steel, and its service life is 10 times that of steel. These excellent properties make titanium an excellent material for drilling near circular and deep oil wells with great difficulty. The combination drilling tool with titanium drilling pipe can greatly reduce the drilling time and the total drilling cost. Grantprideco, RTI energy systems and torch drilling services in the United States first used titanium drilling tubes for industrial applications in 2000. The titanium drilling pipes jointly produced and supplied by grantprideco and RTI energy systems are also equipped with steel tool joints provided by grantprideco anti fatigue. The joint has the advantages of light weight, good flexibility, and can make the titanium drilling pipe strong.
Seawater pipeline system is an indispensable part of seabed oil exploitation. Because titanium has high corrosion resistance to seawater and its service life is 10 times that of steel system, the cost of titanium pipeline system is cost-effective compared with Cu Ni system. American active metal company and precision tube technology company jointly set up a titanium tube technology company to produce a large-diameter titanium alloy tube. The alloy used for this pipe is Ti-3Al-2.5V alloy, with a diameter of 650mm, a wall thickness of 22 ~ 25mm, a length of 350m, and a pipe weighing 80 ~ 90t. It is planned to be used for seabed oil exploitation. Another company in the United States has used the seamless titanium alloy pipe with a length of 15m, an outer diameter of 600mm and a wall thickness of 25mm to make a shaft pipe with a length of nearly 500m by extrusion, which has been used in an offshore drilling platform. It is said that the weight of the shaft pipe can be reduced by half, which greatly reduces the ballast cost. In addition, it also has high fracture toughness and long fatigue life.
It is reported that in the North Sea oil field development project of the United States, the titanium consumption of floating body devices and seafloor fixed devices on board has increased than before. The demand for titanium materials for 24 floating body devices on board and 64 seafloor fixed devices is: 50 ~ 100t safety protection device, 50 ~ 100t connecting device, 400 ~ 1000t general lifting equipment and 1400 ~ 4200T drill pipe. The corrosion of structural parts caused by biological pollution of offshore oil production platform is quite serious. An American company used a long casing made of titanium pipe on the production platform to protect the parts on the platform.
In the past few years, the application of titanium alloy parts in oil drilling and coastal production has increased significantly. Titanium alloy parts enable oil drilling to enter deeper waters and deeper oil wells, including higher temperature and severely corrosive (i.e. multi salt) production environment.
For such applications, TC4 titanium rod (Ti-6Al-4V) based alloy is the most suitable and the lowest cost in terms of comprehensive properties. Seawater pipeline system is an indispensable part of seabed oil exploitation. Because titanium has high corrosion resistance to seawater and its service life is 10 times that of steel system, the cost of titanium pipeline system is cost-effective compared with Cu Ni system. American active metal company and precision tube technology company jointly set up a titanium tube technology company to produce a large-diameter titanium alloy tube. The alloy used for this pipe is ta18 (Ti-3Al-2.5V) alloy, with a diameter of 650mm, a wall thickness of 22 ~ 25mm, a length of 350m, and a pipe weighing 80 ~ 90t. It is planned to be used for seabed oil exploitation. Another company in the United States has used the seamless titanium alloy pipe with a length of 15m, an outer diameter of 600mm and a wall thickness of 25mm to make a shaft pipe with a length of nearly 500m by extrusion, which has been used in an offshore drilling platform. It is said that the weight of the shaft pipe can be reduced by half, which greatly reduces the ballast cost. In addition, it also has high fracture toughness and long fatigue life.
Practice has proved that Ti-6Al-4V (gr.5_tc4) alloy is the best material for drilling pipe. As a drilling application, yield strength and fatigue strength are the most important. Therefore, two gr.5 alloys with especially low gap elements are suitable for key dynamic lifting devices. When the service temperature exceeds 75 ~ 80 ℃, gr29 alloy containing ruthenium is used to prevent crevice corrosion or stress corrosion.
The most commonly used components include offshore drilling hoists, drilling pipes, tapered stress joints (TSJ) and titanium / steel hybrid hoists.
Small titanium components such as titanium pumps, valves, joints, fasteners, fixtures and spare parts have been widely used on oil production platforms. Titanium alloy is also widely used in the shell of offshore oil exploration logging tools abroad.
There is an oxide film with a thickness of no more than 10nm on the surface of titanium. It is very stable in corrosive environment and has excellent corrosion resistance to air, seawater and marine environment. It is the raw material that can best adapt to various marine environments at present. Japan vigorously carries out marine development, such as the bridge from Honshu to Shikoku, the cross road of Tokyo Bay, Kansai Airport, floating oil storage base, etc. The exposure tests conducted by the Japanese Ministry of construction and the iron and steel club on the ocean surface of otaikawa and the investigation reports of various anti-corrosion exposure tests conducted by the Ministry of transport and the steel pipe pile Association on the floating sand trestle in Boqi also show that titanium is the most suitable material. Titanium not only has excellent anti-corrosion performance, but also has the advantages of few dissolved ions in seawater environment, non-toxic and no need to worry about environmental pollution. Japan has also built a super large floating marine structure, and titanium steel composite materials are used at the scouring place of seawater; Titanium is used as the splash proof trunk of piers in the construction of Tokyo Bay Cross Highway, and the amount of titanium used for each pier is 0.9t. Large floating marine buildings that have been used or planned include airports, harbor logistics bases, sports facilities, etc.
Coastal power stations
The comprehensive utilization of seawater is one of the important projects in marine engineering. The condenser of coastal power station is a large amount of equipment using seawater. Titanium used in coastal power stations is mainly used for condensers. Because the condenser uses seawater as cooling water, and the seawater contains a large amount of mud and sand, suspended substances, marine organisms and various corrosive substances, the situation is more serious in the light brine with alternating changes of seawater and river water. The traditional condenser uses copper alloy pipe, which is often seriously damaged due to various corrosion in seawater. Titanium has good corrosion resistance in seawater, especially in polluted seawater, especially in high-speed scouring corrosion resistance of seawater.
Seawater desalination unit
“Water is the source of life”. At present, the lack of water resources has become a problem perplexing the whole world. About 25% of the world’s population does not have sufficient drinking water resources. The world’s land rivers and groundwater resources are far from meeting the needs of industrial development. Therefore, seawater desalination will be an effective way for human beings to solve freshwater resources in the future.
From the development of seawater desalination at home and abroad, there are mainly two methods: distillation and reverse osmosis. The former is to heat seawater to vaporize it, and then condense the steam to obtain fresh water. The latter is to pressurize the seawater to make the fresh water pass through a special membrane and retain the salt to obtain fresh water. Early seawater desalination units used copper alloy, carbon steel and other materials. Because these materials were not resistant to seawater corrosion and had low production efficiency, they were soon replaced by titanium with excellent seawater corrosion resistance. In seawater desalination, the main application of titanium is the heater heat transfer tube of desalination device. The main producing countries of seawater desalination units are the United States and Japan. By 2004, more than 15000 seawater desalination units have been built and under construction all over the world, with a daily output of about 32 million tons of fresh water. The Japanese company has built 10 distillation units with a daily output of 30000 tons of fresh water for Saudi Arabia, with 3200 tons of titanium pipes. The unit with an average daily output of 10000 tons needs 107 tons of titanium.
Seawater desalination plants have been built or are under construction in Tianjin, Shandong and other places in China. For example, the preliminary plan of seawater desalination in Tianjin is to produce 500000 tons of fresh water per day by 2007 and 700000 tons by 2010. It is estimated that the amount of titanium used in seawater desalination projects in Tianjin and Shandong is about 250 tons.
Titanium and its alloys are considered to be good ship materials because of their corrosion resistance in seawater and marine atmosphere, light specific gravity, high strength, impact resistance, non-magnetic, sound transmission and low expansion coefficient. In recent years, the application of titanium in ships has attracted much attention. The navies and shipbuilding industries of various countries also attach great importance to the application of titanium in ships, and many brands of marine titanium alloys have been developed. Titanium and its alloys are widely used in ships, such as hull structural parts, pressure hull of deep-sea survey ships and submarines, pipes, valves, rudders, shaft brackets, accessories, thrusters and propeller shafts in power driving devices, heat exchangers, coolers, Hull Sonar fairings, etc.
The first application of titanium in ship shell was made in the former Soviet Union α Class submarine. Subsequently, titanium was used in artificial or unmanned deep-sea research and deep-sea assistance submarines. Industrial pure titanium is used for general structural parts and Ti-6Al-4V alloy is used for pressure vessels. It is reported that titanium for hull structure can not only reduce the weight of the hull and increase the effective loading weight, but also reduce maintenance and prolong the service life of the ship. Aluminum alloy, mild steel and other hull structural materials generally need maintenance in 10 years, while titanium materials hardly need maintenance and repair, and the service life can be extended from about 20 years to 30 ~ 40 years.
Japan’s research on deep-sea investigation of marine titanium alloy is fruitful. Almost all titanium alloy materials are used in the pressure chamber of “deep-sea 6500” which can accommodate three operators. This is the result of the long efforts of the director of Mitsubishi Heavy Industries Kobe shipyard. The amount of titanium used by submarines is large. For example, the amount of titanium used by a nuclear submarine with a diving depth of 900m is as high as 3500t.
It is reported that Japan’s fishery has changed from fishing to fish farming, and lionfish, halibut and eel have been artificially cultured. In artificial culture technology, titanium metal mesh and titanium tubular heat exchanger maintaining a certain seawater temperature are widely used. The artificial culture of grouper has been realized in the coastal area of Fujian, China. The titanium plate culture basket has brought excellent benefits to the culture of grouper.
Ocean thermal energy conversion
The ocean contains huge energy, such as tidal energy, wave energy, temperature difference energy, ocean current energy, salt difference energy and so on. With the increasing shortage of energy in the world, people will be more interested in the development and utilization of marine energy. Thermal power generation and tidal power generation projects have been studied and developed. The principle of thermoelectric power generation is to use the seawater with higher temperature on the ocean surface to vaporize ammonia or freon to drive the turbine to rotate for power generation, and then use the low-temperature seawater in the deep ocean to cool the vaporized ammonia or freon to form a continuously circulating heat engine system.
The main equipment of thermoelectric power generation is evaporator, condenser, seawater suction pipe, loop, etc. the equipment is required to be resistant not only to corrosion, but also to ammonia and fluorine corrosion. Titanium and its alloys not only have good seawater corrosion resistance, but also to ammonia and fluorine corrosion, so titanium is the most ideal material.
Titanium tube evaporators and condensers have been used in thermoelectric power stations in the United States and Japan, and good results have been achieved.
Prospect of titanium alloy
As an emerging civil market of titanium, offshore engineering has developed rapidly in recent years. With the further intensification of the world energy crisis, countries all over the world will invest a lot of human and material resources to exploit seabed oil resources and other mineral resources; In the trend of global freshwater shortage, all coastal countries will use seawater to produce freshwater; Moreover, the competition of naval equipment among military powers is becoming increasingly fierce, which is inseparable from titanium and titanium alloy materials. Therefore, titanium and its alloys will be more and more widely used in marine engineering. It is expected that titanium for offshore engineering is expected to become a large application market of titanium materials.
Market situation of titanium alloy civil health products
1. Current market conditions
At present, iron, aluminum and stainless steel are widely used in tableware and cooking utensils at home and abroad, which will more or less produce some factors detrimental to human health:
① Iron pot: the iron in the dish is trivalent iron. The human body can’t absorb it. The human body can only absorb divalent iron.
② Aluminum pot: under the condition of high temperature acid and alkali, aluminum will dissolve out, causing aluminum poisoning, which is unsafe. The International Health Organization expressly prohibits the use of aluminum pots in contact with foods containing salts.
③ Non stick pot: most of them use “TEFLON”
Paint, the U. S. government accused it of being a carcinogen. Teflon will release more than ten kinds of harmful gases under high temperature, resulting in the death of some respiratory sensitive animals.
However, the toxic effect of these gases on human body has not been determined.
④ Enamel tableware: what is painted on the outer layer of enamel products is actually a layer of enamel, containing substances such as aluminum silicate. Because of the collision and friction of frying, it is very easy to cause damage, so that substances such as aluminum silicate will be transferred to food.
⑤ Pottery pot and casserole: there are two main potential hazards: one is the glaze of clay casserole, and the other is “pseudo purple sand”. “Pseudo purple sand” is prepared and processed by adding chemical pigments such as iron red powder and manganese dioxide, and is made by coloring with chemical agents, rather than real purple sand.
2. Advantages of titanium health products
The advantage of titanium health products is that there is a solid titanium oxide compound film on the surface of titanium metal, and its chemical properties are extremely stable. Even the “aqua regia” in acid can’t help it. Titanium pot does not react with food materials during cooking. Therefore, the pure titanium pot is the only metal pot that can be used to fry traditional Chinese medicine.
In the United States and Japan, people call titanium pot a delicious pot, and the original taste is a healthy element.
Titanium pot has excellent thermal function: it can cook green dishes at low temperature, quickly and low oil, and retain the nutritional components and taste of food materials to the greatest extent. High nutritional green food is a healthy element.
The advantages of titanium tableware and cooking utensils are reflected in the following aspects:
- (1) strong corrosion resistance: it is more corrosion resistant than stainless steel. Even if it contains the most corrosive “aqua regia” (the mixture of concentrated sulfuric acid and concentrated nitric acid), there is no rust. Cooking and storing acidic and alkaline food for a long time will not produce metal odor, and it can also be used to cook traditional Chinese medicine.
- Other metal pots can’t do this.
- (2) high hardness: much higher than that of stainless steel, wear-resistant, scratch resistant and semi permanent.
- (3) light weight: the wife is very easy to use. The weight is only half of that of an iron pot.
- (4) no maintenance: the husband can use it at ease. It can’t be burned or broken at high temperature. No maintenance is required.
- (5) antibacterial property: it has natural photocatalyst antibacterial effect, natural antibacterial effect under natural light, sanitation and no bacterial pollution.
- (6) non stick effect: good non stick effect, equivalent to that of iron pot, but not completely non stick.
- (7) energy saving: it saves time and energy. The heat transfer speed is 7 times that of iron pot and dozens of times that of composite bottom steel pot and alloy pot. Cooking saves energy.
- (8) biological affinity: the human body is compatible with metal and will not be allergic after long-term contact. In medical treatment, it has replaced stainless steel as “human bone” and implanted into the human body.
- (9) scope of application: stove and ceramic magnetic furnace can be used (10) health: 99.75% high-purity titanium metal is made of uncoated, which is the most healthy and safe metal pot.
- (11) non sticky surface: electrolytic grinding is more comprehensive and thorough, and there are no harmful dust particles left by mechanical polishing. The electrolytic grinding titanium pot presents a fine concave convex surface, which can improve the heat transfer speed and non sticky.
- (12) image in the eyes of the public: in the eyes of the public, titanium is used to make luxury goods such as space shuttle, nuclear reactor, jewelry, eye rack, golf club and so on.
Titanium has such excellent properties, and titanium is also a very difficult metal to process. The understanding and understanding of titanium processing technology and processing means restrict relevant enterprises from entering this field. So far, domestic titanium tableware and cooking utensils are still a virgin land, waiting for the development of people of insight. The titanium tableware and cooking utensils produced by the technology of the project overcome the difficulty of pure titanium in showing artistry and the stereotype of aesthetic feeling, and have bright colors, making the perfect combination of science and technology and living technology. So that thousands of families really realize “to be healthy, use titanium pot!”
Application of titanium alloy building decoration materials
Metal materials are used in buildings, especially roofs. The first application is copper, followed by surface treated steel plates, aluminum, stainless steel and titanium. With the continuous development of national economy and the continuous improvement of people’s living standards, people have higher and higher requirements for urban buildings, especially for the aesthetics of buildings.
In recent years, architects pursue the use of new building materials that are more advanced than traditional materials. Titanium has many excellent properties, which fully meet many special performance requirements of building materials, so it is favored by architects and construction industry.
Japan is the first country to apply titanium to buildings, and it is also the country that applies titanium most in buildings.
It is mainly applied to the roof of buildings, as well as building curtain walls, ports, bridges, tunnels, outer walls, doorplates, railings, pipes, etc. Britain, France, the United States, Spain, the Netherlands, Canada, Belgium and Switzerland all have examples of using titanium as roofs and curtain walls. Sweden, Singapore and Egypt also began to use titanium in some new buildings. In 1997, Guggenheim Museum in Bilbao, Spain used titanium plate to construct curved architectural modeling. Abu Dhabi airport also uses titanium, with a consumption of hundreds of tons. It is the first airport in the world to use titanium as building structural material.
The National Grand Theater is the first building to use titanium in China, and the Hangzhou Grand Theater is the first.
The buildings using titanium metal also include the gate Hall of China Nonferrous Metals engineering design and Research Institute, Donglai first Pavilion in Linping, Hangzhou, the roof of Shanghai Circus acrobatic field and Dalian Shengya polar world. The titanium sculpture “dolphin and man” in the riverside park of Baoji City, Shaanxi Province, the titanium sculpture “heaven and earth ball” in the central square of Xingtai City, Hebei Province, and the titanium sculpture “Rooster heralding the dawn” in the pedestrian street of Baoji City, Shaanxi Province are used for urban sculpture.
China’s titanium production technology is basically mature and the production design scale is large, but the sales market is small and the economic benefit is not ideal, mainly due to the lack of products with good technical and economic performance satisfactory to customers. The current situation of titanium for construction in China is as follows:
- 1. Single product: as a structural material, there are not enough varieties for users to choose. As a surface decoration material, China has not formed a large-scale production enterprise of titanium surface treatment, and the processing is still in the stage of manual workshop production mode, which is not conducive to the large-scale use of titanium as decoration material.
- 2. Low grade: there is no high-quality products, let alone a large supply of titanium and related composite materials. Only some models, city carvings, handicrafts, etc. can be produced, and there is no high-grade surface decoration materials and their production means.
- 3. High price: without stable high-quality products, it is impossible to have a wide range of applications, resulting in small use and high price, which is not conducive to promotion and use.
- 4. Designer factor: there is no similar vocational training system in China. After the invention of new materials, they are not stored in the thinking of architectural designers. As a result, titanium is rarely designed in the original architectural design drawings, so there are obviously few uses.
In recent years, with the progress of global oceanization and the continuous decline in the price of titanium raw materials, the demand and application scope of titanium in the field of construction and decoration are expanding. It is expected that the demand for titanium in the construction and decoration industry will reach more than 5000 tons in the next few years, the demand for titanium in marine engineering and island construction will reach more than 5000 tons, and the demand for titanium in shipbuilding industry will reach more than 5000 tons.
At present, there is no professional titanium material production enterprise engaged in building decoration in China, but simply applies industrial materials to the civil field, which has a large gap with the market and industry demand. It is urgent to establish a professional production line to meet the professional needs in this field.
Titanium is a metal that can be produced in large quantities, has the lowest price and is almost completely free from seawater corrosion. As a building material, titanium has low reflectivity, light silver gray and charming metal natural luster.
Baoji Titanium Industry Research Institute will produce titanium materials for building decoration, which are mainly applied to the roof of buildings, followed by curtain walls, harbor facilities, bridges, subsea tunnels, outer walls, decorations, small accessories, column decoration, exterior decoration, monuments, signs, doorplates, bars, pipes, anti-corrosion coatings, etc. The project uses the existing domestic titanium plate and titanium coil as raw materials and adopts shaping, polishing and embossing technology to make the plate surface bright, consistent color and metal pattern; Large area plate anodizing coloring technology is adopted to color the plate surface and form colorful colors to meet the needs of architectural and decorative materials.
Research progress of titanium alloys for aviation
Titanium is widely distributed, and its content exceeds 0.4% of the mass of the earth’s crust. The global proven reserves are about 3.4 billion tons, ranking 10th among all elements (oxygen, silicon, aluminum, iron, calcium, sodium, potassium, magnesium, hydrogen and titanium).
American scientists first obtained titanium by “sodium method” (sodium reduction of TiCl4) in 1910, but the titanium industry did not develop immediately with the discovery of titanium.
It was not until 1948 after the second world war that the “magnesium method” (magnesium reduction of TiCl4) invented by Luxembourg scientists was used for production in the United States that the titanium industry began to start.
The density of titanium is 40% less than that of steel, and the strength of titanium is equivalent to that of steel, which can improve the structural efficiency. At the same time, titanium has good heat resistance, corrosion resistance, elasticity, anti elasticity and formability. Because titanium has the above characteristics, titanium alloy has been used in aviation industry since its emergence. In 1953, titanium was first used on the fire wall and nacelle of DC-T engine produced by Douglas company of the United States, and the history of titanium alloy application in aviation began.
The space shuttle is the most important and widely used aircraft. Titanium is the main structural material of aircraft. It is also the preferred material for important components such as aeroengine fan, compressor disc and blade. It is known as “space metal”. The more advanced the aircraft, the more titanium is used. For example, the titanium content of the fourth generation aircraft of F22 in the United States is 41% (mass fraction), and the titanium content of F119 engine is 39%, which is the aircraft with the highest titanium content at present. The research of titanium alloy originated from aviation, and the development of aviation industry also promoted the development of titanium alloy. The research of titanium alloy for aviation has always been the most important and active branch in the field of titanium alloy, but its development is also extremely difficult. For example, people spend more than ten years to overcome the “thermal barrier” problem of titanium alloy for aviation engine.
In this paper, titanium alloys are classified from the perspective of alloy matrix phase composition. Taking aircraft as the representative of aircraft, this paper focuses on the application and research of titanium alloy in aeroengine, aircraft fuselage and aviation fasteners. Finally, the problems existing in the development of aviation titanium alloy are analyzed.
Classification of titanium alloys
The classification of titanium alloys in the United States, Britain, Russia, France, Japan and other countries is mostly determined by manufacturers. Some companies directly use the chemical symbols and numbers of elements instead of the added alloy elements and their content naming, such as Ti-6Al-4V (equivalent to TC4 in China). The brand comparison and chemical composition of various countries are listed in Table 1. According to the phase composition, titanium alloys can be divided into: close packed hexagonal structure (HCP) α Type titanium alloy (including near α Type alloy) – that is, domestic brand TA, two-phase mixed α+β Type titanium alloy – that is, the domestic brand TC and body centered cubic structure (BCC) β Type titanium alloy (including near β Type alloy) – that is, the domestic brand is TB.
α Type titanium alloy
Annealed to α Single phase solid solution alloy based on titanium α Type titanium alloy, which mainly contains Al, Sn and other elements. Al can increase the tensile and creep strength of the alloy, reduce the density of titanium alloy and improve the specific strength. It is an important alloying element in titanium alloy. In order to maximize the solid solution strengthening effect of aluminum and avoid alloy embrittlement caused by excessive Al, the alloying of high temperature titanium alloy should follow the equivalent empirical formula proposed by Rosenberg. Only in this way can the alloy maintain good thermal stability while improving heat resistance strength. α These elements in titanium alloys play a stabilizing role by inhibiting or increasing the phase transformation temperature at the phase transformation temperature. And β Compared with titanium alloy, α Type a alloy has good creep resistance, strength, weldability and toughness. It is the preferred alloy for use at high temperature. At the same time, α Type alloy has no cold brittleness. It is also suitable for low temperature environment, which expands its application range. α The forging property of type a alloy is poor and easy to produce forging defects. The forging defects can be controlled by reducing the processing rate of each pass and frequent heat treatment. α The matrix is a stable phase. For a given alloy, the change of its properties is mainly the change of grain size, because the yield strength and creep strength are related to grain size and energy stored during deformation. α T-type titanium alloy can not improve its strength by heat treatment, and the strength has little or no change after annealing. Some alloys contain more Al, Sn, Zr and a small amount of β Stable elements (generally less than 2%). Although these alloys contain β Phase, but the matrix is mainly composed of α The phase composition is similar to that in heat treatment sensitivity and processability α Type alloys are very close and are called near α Type titanium alloy. near α Type alloy is strengthened by solid solution alloy elements α The matrix can be developed on the basis of high creep strength, most of which are near α Because of its good thermal stability, p-type alloy has become an important kind of high temperature titanium alloy. Its strengthening mechanism is β The atoms in the phase diffuse rapidly and are prone to creep, β Stable elements and inhibition α Effect of phase embrittlement (i.e. delay) α The process of forming an ordered phase in.
common α Type titanium alloy (including near α Type alloys) include Ti811 (ti-8al-1mo-1v), Ti-6Al-2Zr-1Mo-1V, Ti-679 (ti-2.25al-11sn-5zr-1mo-0.25si), bt18 (ti-7.7al-11zr-0.6mo-1nb-0.3si) and ti6242s (ti-6al-2sn-4zr-2mo-0.1si). Their composition and properties are listed in Table 2.
α+β Type titanium alloy
In order to improve the strength and toughness of titanium alloy, people have developed α+β Type titanium alloy. Compared with other titanium alloys, α+β Simultaneous addition of α Stable elements and β Stabilize elements so that α and β The phase is strengthened. α+β The alloy has excellent comprehensive properties, such as room temperature strength higher than α The alloy has good hot working process performance and can be strengthened by heat treatment, so it is suitable for aviation structural parts. α+β The annealed microstructure of type I titanium alloy is α+β Phase, β The phase content is generally 5% ~ 40%. However, its structure is not stable enough, the maximum service temperature can only reach 500 ℃, and its welding performance and heat resistance are lower than α Type titanium alloy.
α+β Type titanium alloys mainly include TC4 (Ti-6Al-4V), TC6 (ti-6al-1.5cr-2.5mo-0.5fe-0.3si), TC11 (ti-6.5al-3.5mo-1.5zr-0.3si), TC17 (ti-5al-2sn-2zr-4mo-4cr), TC19 (ti-6al-2sn-4zr-6mo) and TC21 (ti-6.2al-2.8mo-2nb-2sn-2.1zr-1.3cr), etc. TC11 alloy is also called near alloy β Alloy.
Zhou proposed a processing technology of TC11 alloy. Firstly, the alloy is lower than β- A new microstructure was obtained by heat treatment at the transition temperature of 15 °, followed by rapid water cooling, high temperature and low temperature toughening and strengthening heat treatment. The new matrix consists of 15% equiaxed α Grain, 50% ~ 60% layered α Grains and transformed β Grain composition. The results show that the alloy shows high fatigue resistance, long creep fatigue life, high toughness and excellent high temperature service performance, and does not reduce plasticity and thermal stability.
The new process and the experimental principle of strengthening and toughening mechanism are discussed. The key problem in the practical application of this processing technology is the accurate control of temperature.
This TC11 titanium alloy processing technology has been applied to the production of reliable aeroengine compressor discs, rotators and other components.
β Type titanium alloy
β The content of stable elements is high enough and cooled quickly after solution treatment β The alloy obtained by keeping the phase at room temperature is called β Type titanium alloy. Classified by stable state organization type, β Titanium alloys can be divided into stable types β Titanium alloy, metastable β Titanium alloy, as shown in Figure 1. In Figure 1, MS is the martensitic transformation temperature line, β C is the of metastable alloy β Minimum content of stable elements, β S is a stable alloy β Minimum content of stable elements.
Figure 1 β Relationship between stabilizer content and phase composition of titanium alloy
β The alloy has good cold formability in solid solution state, and has excellent hardenability and heat treatment response.
The common heat treatment method is first solution treatment, and then aging at 450 ~ 650 ℃ β Fine particles will precipitate on the matrix α Phase, forming a dispersed second phase, which is β Strengthening mechanism of alloy. because β Titanium alloys precipitate more during aging than other types of titanium alloys α Phase, containing more α-β The phase interface hinders the dislocation movement, so β Titanium alloy has the highest strength at room temperature.
The ability of metal materials to absorb energy in the process of deformation and fracture is called toughness. The more energy a material absorbs, the better its toughness will be. Fracture toughness is an index of material toughness, which reflects the resistance of materials to crack and other sharp defect propagation. Generally speaking, the fracture toughness and strength of titanium alloys are inversely proportional, that is, the fracture toughness decreases with the increase of strength. Research β The application of titanium alloy in aerospace industry requires the design of microstructure, processing technology and heat treatment system with good strength and fracture toughness. Alloy composition and microstructure are the key factors β Two main factors of fracture toughness of titanium alloy. The alloy composition determines the composition of the alloy β The number of phases also determines the type and fracture toughness of the alloy. The morphology, quantity and volume of microstructure also affect the fracture toughness of the alloy. Fu Yanyan et al β Titanium alloy β Stable element and medium element Zr can improve the strength and reduce the fracture toughness of the alloy. Tiny β Grain can not effectively improve the aging state β The strength of titanium alloy will reduce the fracture toughness of Ti-15-3 alloy β- C and Ti-1023 have no obvious effect on the fracture toughness.
Aging state β The strength of titanium alloy mainly depends on the secondary precipitation of aging precipitation α The content and size of the phase contain the same primary phase α In the case of phase, fine secondary α Phase can significantly improve the strength of the alloy.
primary α The coarsening of phase and the transformation of primary phase from spherical to flake will lead to β The plasticity of titanium alloy decreases and the fracture toughness increases. β The bimodal structure of titanium alloy has a good match of strength, plasticity and toughness.
β The reason why titanium alloy is widely used is that it has the advantages of high strength and high plasticity unmatched by other types of titanium alloy after aging. At the same time, β Titanium alloy is gradually replaced by titanium alloy because of its heat treatment strengthening and deep quenching ability α+β Two phase titanium alloy has become the preferred structural material for aircraft fuselage and wing, and plays a more and more important role in aerospace industry.
Development and application of titanium alloys for aviation
In the 1950s, military aircraft entered the supersonic era, and the original aluminum and steel structures could not meet the new needs. At this time, titanium alloy entered the stage of industrial development. Titanium alloy has been widely used in the aviation field because of its excellent properties such as low density, high specific strength, corrosion resistance, high temperature resistance, non-magnetic, weldable, wide service temperature range (269 ~ 600 ℃), and can form, weld and machine various parts. In the early 1950s, military aircraft began to use industrial pure titanium to manufacture structural parts with less stress such as rear fuselage heat shield, tail cover and speed reducer. In the 1960s, titanium alloy was further applied to the main stressed structural parts such as aircraft flap sliding rolling, load-bearing spacer frame, middle wing box beam and landing gear beam. By the 1970s, the application of titanium alloy in aircraft structure was expanded from fighter aircraft to military large bombers and transport aircraft, and titanium alloy structure was also widely used in civil aircraft.
After entering the 1980s, titanium for civil aircraft has gradually increased and exceeded that for military aircraft. The more advanced the aircraft, the more titanium is used.
Titanium alloy for Aeroengine
The engine is the heart of an airplane. The rotating parts such as fan, high-pressure compressor disc and blade of engine should not only bear great stress, but also have certain heat resistance. Such working conditions are too high for aluminum; Too dense for steel. Titanium is the best choice. Titanium has good high temperature strength, creep resistance and oxidation resistance at 300 ~ 650 ℃. At the same time, an important performance index of the engine is the thrust weight ratio, that is, the ratio of the thrust generated by the engine to its mass. The thrust weight ratio of the earliest engine was 2 ~ 3, and now it can reach 10. The higher the thrust weight ratio, the better the engine performance. Using titanium alloy instead of nickel base superalloy can reduce the quality of engine and greatly improve the thrust weight ratio of aircraft engine. Titanium is used more and more in aircraft engines. In foreign advanced aeroengines, the amount of high-temperature titanium alloy has accounted for 25% ~ 40% of the total engine mass. For example, the amount of titanium alloy for the third generation engine F100 is 25%, and the amount of titanium alloy for the fourth generation engine F119 is 40%.
Titanium alloy is required to have good instantaneous strength, heat resistance, endurance strength, high temperature creep resistance and microstructure stability in the range of room temperature to high temperature. β Type and near β Although T-type titanium alloy has high tensile strength from room temperature to about 300 ℃, its creep resistance and heat resistance stability decrease sharply at higher temperature β Titanium alloys are rarely used in aircraft engines. α Type and near α Type titanium alloy has good creep, durability and weldability, and is suitable for use in high temperature environment.
α+β Type titanium alloy not only has good hot working properties, but also has good comprehensive properties in medium and high temperature environment. So, α Type, near α Type and α+β Ti alloys are widely used in aeroengines. Table 6 lists the titanium alloys for aircraft engines developed all over the world.
At present, the maximum working temperature of high temperature titanium alloy for Aeroengine has been increased from 350 ℃ to 600 ℃, which can meet the material requirements of advanced engines. Through the efforts of titanium alloy researchers all over the world for half a century, Ti811 (ti-8al-1mo-1v), Ti-6Al-2Zr-1Mo-1V, Ti-679 (ti-2.25al-11sn-5zr-1mo-0.25si), TC6 (ti-6al-1.5cr-2.5mo-0.5fe-0.3si), TC17 (ti-5al-4mo-4cr-2sn-2zr), TC19 (ti-6al-2sn-4zr-6mo), TC21 (ti-6.2al-2.8mo-2nb-2sn-2.1zr-1.3cr) and ti1100 have been developed (ti-6al-2.75sn-4zr-4mo-0.45si), imi834 (ti-5.8al-4sn-3.5zr-0.7nb-0.5mo-0.35si-0.06c) and other alloys.
Ti811（Ti-8Al-1Mo-1V） The alloy has many advantages, such as low density, high elastic modulus, excellent vibration damping performance, good thermal stability, good welding performance and forming performance, and its specific stiffness is the highest among all industrial titanium alloys. Zhao Yongqing and others conducted in-depth research on the thermal stability and high temperature fatigue properties of Ti811 Alloy, and studied the influence of microstructure and sample surface state on the thermal stability of Ti811 Alloy The results show that Ti811 Alloy with equiaxed structure and bimodal structure has good thermal stability, and the existence of acicular structure worsens the thermal stability of Ti811 Alloy. In addition, it is considered that the surface oxide layer and exposure time have no significant effect on the thermal stability of Ti811 Alloy under 425 ℃ thermal exposure.
Gao Guangrui and others studied the effects of temperature, displacement amplitude and contact pressure on the high temperature fretting fatigue (FF) behavior of Ti811 titanium alloy by using a high frequency fatigue tester and a self-made high temperature fretting fatigue device. The results show that:
At 350 ℃ and 500 ℃, the fretting fatigue sensitivity of Ti811 Alloy increases with the increase of temperature. Creep is an important factor affecting the FF failure of Ti811 Alloy at high temperature. The change of displacement amplitude affects the fatigue stress factor and the role and mechanism of wear in the FF process.
Ti-6Al-2Zr-1Mo-1V is a universal alloy developed by the former Soviet Union in the 1960s. The alloy can work at 300 ~ 500 ℃ and is mainly used to produce aircraft engine case.
Ouyang et al. Have done a lot of work on the recrystallization behavior of Ti-6Al-2Zr-1Mo-1V titanium alloy at different temperatures and strain rates. The results show that:
When the deformation temperature is higher than 1050 ℃ and the strain rate is lower than 0.01s-1, the dynamic recrystallization mechanism of the alloy is mainly discontinuous dynamic recrystallization; when the deformation temperature is lower than 1050 ℃ and the strain rate is higher than 0.01s-1, the dynamic recrystallization mechanism of the alloy is mainly continuous dynamic recrystallization, and there is a small amount of discontinuous dynamic recrystallization. In addition, the potential of Ti-6Al-2Zr-1Mo-1V alloy during phase transformation The results show that the external factors (such as deformation stress, strain rate and cooling rate) are β → α phase transition follows the burgers direction transition rule. However, the strain rate and cooling rate can significantly affect the phase transition α Morphology of precipitation phase.
Ti-679 alloy is obtained by adding zirconium, molybdenum, silicon and other alloy elements with low aluminum and high tin. It can be used as engine high-pressure compressor blades and discs. Among its alloy elements, aluminum is used to improve the alloy strength, but it is easy to lead to poor molding. Better molding and strength can be obtained by combining low aluminum and high tin; molybdenum is used to avoid excessive formation β Phase, so that the creep strength decreases, while the role of zirconium is to supplement and strengthen α Ti-679 alloy has good creep resistance and thermal stability, and its working temperature can reach 450 ℃.
TC6 titanium alloy has good thermal strength and thermal stability. Its mechanical behavior and microstructure change at high temperature have attracted extensive attention of researchers all over the world. Bai Xinfang et al. Carried out 990 ℃ heat preservation heat treatment on TC6 titanium alloy to study the effects of the distribution changes of oxygen atoms and alloy elements on the microstructure and hardness of the inner surface layer during the heat preservation process. The results show that the inner surface layer of the sample is rich after heat treatment at 990 ℃ oxygen α The microhardness of the layer from the edge to the inside of the substrate shows a low high low variation law, about 55 from the edge μ The maximum value reached 449hv1 at M. the change of microhardness of the inner surface layer was caused by the change of alloy element distribution and the enrichment of oxygen atoms in the inner surface layer due to oxidation. Sun Kun et al studied four typical TC6 titanium alloy samples under high strain rate loading conditions (1) × The results show that the flow stress of TC6 titanium alloy with different microstructure increases rapidly with the increase of strain.
TC17 titanium alloy is a kind of rich alloy β A transition two-phase titanium alloy with stable elements. The alloy has the advantages of high creep resistance, good hardenability and high fracture toughness at medium temperature (300 ~ 450 ℃), and is widely used in the manufacture of aeroengine fan disk and compressor disk. As a two-phase titanium alloy, TC17 can adjust its microstructure through heat treatment to improve its comprehensive mechanical properties. Its standard heat treatment process is: (840 ℃, 1hac) + (800 ℃, 4hwq) + (630 ℃, 8hacc4). Sun Xiaomin et al. Studied the microstructure of laser melt deposited TC17 titanium alloy in its original state and after solution aging. The results show that when the solution temperature increases from 800 ℃ to 835 ℃, the primary phase is formed α The phase volume fraction is reduced from 53% to 34%. After aging, the photo layer is significantly thicker and 0.7 ~ 0.8 wide μ m. Secondary α TC19 titanium alloy is a kind of rich titanium alloy developed in the United States in the 20th century β of α+β Ti-6242 alloy (ti-6al-2sn-4zr-2mo) It is a kind of titanium alloy with high strength and toughness. Compared with ti-6242 alloy, TC19 titanium alloy increases Mo content and improves room temperature and high temperature tensile properties. The addition of Sn and Zr makes the phase transformation behavior of the alloy very slow. Zhu Baohui and others studied TC19 titanium alloy bars prepared by different forging processes. The results show that the conventional forging process and high low high The forging process can be used to forge tcl9 alloy bars, but the mechanical properties of bars obtained by high low high forging process are better than those of conventional forging process.
TC21 alloy is a new two-phase high strength and toughness titanium alloy developed by China with independent intellectual property rights. It is used as an important structural material in the field of aviation and aerospace. People have carried out many studies on the relationship between cooling rate, heat treatment and microstructure and properties. Wang Yihong et al. Proposed that when the cooling rate is greater than 122e / s, β The phase transformation forms orthorhombic martensite. When the cooling rate is between 122 ~ 3 ℃ / s, the massive transformation occurs, the cooling rate continues to decrease, and the transformation is controlled by diffusion to form two different morphologies of widmanstatte lamellae. The research results of song Yinggang et al show that:
After shot peening strengthening, an elastic-plastic deformation layer is formed on the surface of TC21 titanium alloy. During the strengthening process, the dislocation density increases due to the actuation of the basal, cylindrical and conical slip system of close packed hexagonal crystals, and the dislocation morphology in phase a presents a network; the nano indentation hardness before strengthening is 3.2gpa, and after strengthening is 6.7gpa, which is more than twice as high. A high macro residual is formed in the strengthening layer Compressive stress, which is shown as a gradient change gradually decreasing inward from the surface. The depth of the strengthening layer reaches 370 μ m. Gong Xuhui et al. Studied the high temperature dynamic tensile mechanical behavior of TC21 titanium alloy. The results show that when the strain rate is 0.001 and 0.05s-1, there is a turning point in the yield stress temperature curve, and the turning point temperature increases with the increase of strain rate; when the temperature is lower than the turning point temperature, the yield stress of TC21 titanium alloy with the same oxygen content and polycrystalline pure titanium has a similar temperature correlation. After the compression test of TC21 titanium alloy with strain rate of 0.01 ~ 50s-1 and temperature of 973 ~ 1373k, Qu henglei et al. Concluded that there was uneven deformation structure in different parts of the sample, and the alloy recrystallized and dynamically recrystallized respectively in different temperature regions. Recrystallization led to grain coarsening (size about 100 ~ 200) μ m）。
Dynamic recrystallization leads to grain refinement (the minimum size is 1 ~ 2) μ m）。
The above alloys are titanium alloys for conventional aeroengines, and their service temperature is below 650 ℃.
At present, the practical heat-resistant titanium alloys are ti1100 and imi834, which have been applied to EJ2000 and 55-712 modified engines respectively With the emergence of accidents, flame retardant titanium alloys have attracted more and more attention. The United States, Russia and other countries have developed new titanium alloys with good flame retardant performance. The high-strength flame retardant titanium alloy alloyc developed by Pratt Whitney has been used as vector nozzle parts of F119 engine. The nominal composition of the alloy is Ti-35V-15Cr (mass fraction,%) , the alloy contains a large amount of expensive metal vanadium. In addition, some special equipment should be used in the hot deformation process of alloy-c alloy ingot, which further increases the material price. Russia has studied Ti Cu alloy with low cost, and reported BT25 and BT36 alloys. Chinese researchers have systematically summarized and evaluated the previous research work on titanium alloy for engine.
Titanium alloy for aircraft fuselage
The aircraft engine requires the alloy to have good thermal strength and specific strength, while the fuselage requires the alloy to have excellent characteristics such as good strength, corrosion resistance and light weight at medium temperature. Titanium alloy can well meet these requirements. Using titanium alloy as fuselage material has the following five advantages:
1) Replacing steel and nickel base superalloys can greatly reduce the quality of aircraft. The high thrust weight ratio enables titanium alloy to replace steel with better strength for aircraft parts.
2) It can meet the strength requirements of aircraft.
Compared with aluminum alloy, titanium alloy with about 60% mass can achieve the same strength. When the service temperature exceeds 130 ℃, titanium alloy can replace aluminum alloy, because this temperature is the limit applicable temperature of traditional aluminum alloy.
3) Good corrosion resistance. Most aircraft support mechanisms are under the kitchen and toilet, which is easy to cause corrosion. Titanium alloy does not need surface anti-corrosion coating or coating.
4) It has good electrochemical compatibility with polymer composites.
5) Space constraints replace steel and aluminum alloys. A typical example of using titanium alloy due to space constraints is the titanium alloy landing gear beam of Boeing 747. This beam is the largest titanium alloy forging. Although the cost of other alloys (such as 7075 aluminum alloy) is lower, the volume of aluminum alloy landing gear exceeds the wing range and does not meet the requirements when bearing the required mass. Steel is strong enough to carry mass, but it will greatly increase the mass of the aircraft.
β- 21s (ti-15mo-3al-2.7nb-0.25si) alloy is developed by American timet company for the national space shuttle. It can be made into strip with oxidation resistance and can be used as composite material.
It has better high temperature characteristics and better creep resistance than ti-6-4 (general) β The creep resistance of the alloy in high temperature environment is not good).
β- 21s has been used by Boeing and P & W in the instantaneous high temperature environment of 650 ℃, and its continuous working temperature is 480 ~ 565 ℃. β- The outstanding advantage of 21s alloy is that it can better resist the liquid corrosion of high temperature hydraulic press. This hydraulic press fluid is one of the few substances that can corrode titanium alloy in aerospace environment. When it exceeds 130 ℃, it will decompose and form an organic metal containing phosphoric acid, which will corrode titanium alloy. More importantly, it will cause serious embrittlement of engine pump containing a lot of hydrogen. β- 21s is the only metal that can resist this corrosive agent because β- 21s contains molybdenum and niobium and can be used in engine compartment and jet engine parts (previously steel or nickel base alloy). In addition, β- 21s can reduce the mass and is used to manufacture nozzles, plugs, skins and various longitudinal beam structures in three engines (P & w4084, GE90 and trent800) of Boeing 777, which can reduce the mass of 74kg per aircraft.
Ti-10-2-3 (ti-10v-2fe-3al) is one of the most widely used high-strength and toughening materials so far β Titanium alloy was first developed by American timet company in 1971. It is a forged titanium alloy with high structural benefit, high reliability and low cost to adapt to the damage tolerance design principle. V and Fe are the main components β Stable elements. In order to improve the forging properties and fracture toughness of the alloy, the content of Fe is less than 2%, and the content of O is limited to less than 0.13%.
The tensile strength of the forging can reach 11901mpa, and the mass of each aircraft can be reduced by 270Kg with ti-10-2-3.
Boeing selects high-strength alloy and minimizes the mass when producing aircraft. This titanium alloy is the most used in Boeing 777 β Titanium alloy. The landing gear of this kind of aircraft is almost made of this alloy, and only the inner and outer cylinders and axles are made of 4340m (strength 1895mpa). The main landing gear strut of Airbus A380 is also made of ti-10-2-3 alloy. The alloy also has good fatigue resistance and can eliminate stress corrosion cracking when using steel. McDonnell Douglas uses ti-10-2-3 (1105mpa) to make cargo doors, engine compartments, tail wings and other parts of C-17 transport aircraft. Ti-10-2-3 is also widely used in helicopters because of its advantages in fatigue strength. Bell, Westland, Sikorsky and Eurocopter all use ti-10-2-3 alloy as their rotor system.
Titanium alloy for aviation fasteners
In addition to metal components, there are many carbon fiber composites on both military and civil aircraft and spacecraft.
The electrode potential of titanium and carbon fiber composites is similar, and titanium alloy has become the only connecting material of composites. Therefore, with the increasing consumption of titanium alloy and composite materials for advanced military and civil aircraft, the demand for titanium alloy fasteners is increasing. Titanium alloy as aviation fastener has at least the following four advantages:
1) Good weight loss. A Russian il-96 aircraft has 142000 fasteners, which can reduce the mass by nearly 600kg. The use of titanium alloy fasteners in China’s aerospace system also has obvious weight reduction effect. After reducing the mass of aircraft and spacecraft, it can improve thrust, increase range, save fuel and reduce launch cost.
2) The excellent corrosion resistance of titanium alloy, especially its positive potential matching with carbon fiber composites, can effectively prevent galvanic corrosion of fasteners.
3) In the aircraft structure, due to the high temperature of fasteners, aluminum alloy can not be used, but titanium alloy can only be used.
4) Titanium has good elasticity and non magnetism, which is very important to prevent the loosening of fastening bolts and magnetic field interference.
Modern aircraft use a variety of titanium alloy fasteners, mainly including ordinary titanium bolts, interference bolts, special fasteners, etc. In the United States, France and other aviation developed countries, more than 95% of titanium alloy fasteners are made of Ti-6Al-4V (TC4). In addition, TB2 β 3. The typical performance parameters of ti-44.5, Ti-15-3 (TB5), TB8 and Tb3 are listed in Table 7.
Ti-6Al-4V (TC4) alloy β The stability coefficient is the lowest, 0.27. Its advantages are the lowest density, good strength and fatigue performance, simple alloy composition and the lowest cost of semi-finished products. However, because the plasticity at room temperature is not high enough, induction heating is needed for hot upsetting, vacuum solution treatment and aging treatment, and the processing cost is high.
TB2, Tb3, TB8 and TB16 are metastable β Titanium alloy, β The stability coefficient is higher than that of the alloy. The disadvantage is that the density is high. Although the strength is equivalent to that of Ti-6Al-4V, the fatigue performance is not as good as that of Ti-6Al-4V. Moreover, the composition is complex and the cost of semi-finished products is high. Since vacuum aging treatment is also required, the cost of finished fasteners is higher than that of Ti-6Al-4V.
Existing problems and Prospects
Titanium is a kind of metal with excellent performance and rich reserves. It is known as “modern metal”. After half a century of development, great progress has been made in the preparation technology and Application Research of titanium alloy, especially in the aviation field. However, some existing problems are gradually exposed. The further development of aviation titanium alloy is facing many challenges, mainly in the following three aspects:
- (1) Dosage. Whether in military and civil aircraft or aircraft, the amount of titanium alloy directly reflects the aviation level of a country. At present, the titanium consumption of aeroengines is low, and it is still very difficult to further increase to about 50%.
- (2) Performance. Like other aviation structural materials, high performance requires good performance matching, that is, its mechanical properties, physical properties, chemical properties, process properties and defect controllability must be comprehensively considered. When the existing titanium alloys are above 600 ℃, the sharp decline of creep resistance and high-temperature oxidation resistance are the two main obstacles to the expansion and application of titanium alloys.
- The author believes that in the whole process of development and application of aviation titanium alloy technology, new manufacturing technology will be the focus of development and research, such as near net shape processing such as superplastic forming, powder metallurgy forming, etc.
- (3) In terms of cost. At present, people have made some achievements in reducing the cost of aviation titanium alloy, but there are still many fields to be studied and developed. Taking the flame retardant titanium alloy as an example, alloy-c invented in the United States has excellent flame retardant properties and high-temperature mechanical properties, but it needs to add a lot of expensive V and poor malleability, resulting in high price. Therefore, it is only formally applied in F119 engine.
Due to backward management and technology, the price of domestic titanium alloy products is not competitive in the world, which is not conducive to further expand its application in China. Therefore, we must first seriously study the ways to reduce the cost of titanium products and determine the near, medium and long-term development plan. Secondly, China should establish its own titanium alloy system to ensure that there are a variety of alloy options for each use, gradually get rid of the long-term dependence of aviation key materials on foreign countries, and form backbone materials or general materials, so as to fundamentally lay the foundation for low-cost manufacturing. Finally, it is an important topic in the future research of titanium alloy to replace expensive alloy elements with lower price elements and reduce the cost of titanium alloy parts through technological means.
To sum up, titanium alloy has high thrust weight ratio, high toughness, good strength and weldability. It is an aviation material with excellent comprehensive properties. In the past decades, the alloying theory, comprehensive strengthening and toughening technology and heat treatment process of aviation titanium alloys have been greatly developed. At present, the research of titanium alloy mainly focuses on the thermal stability at high temperature, creep resistance and low-cost titanium alloy design and manufacturing process. With the deepening of research, the high-end aviation application will drive the technological progress of low-cost processing of titanium alloy, so as to fundamentally break through the cost bottleneck restricting the improvement of aviation titanium alloy consumption and application level. All titanium aircraft may become a reality in the near future.
Source: Network Arrangement – China Titanium Alloy Welded Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
If you want to have more information about the article or you want to share your opinion with us, contact us at email@example.com