Titanium alloy smelting technology is complex and difficult to process. At present, only four countries in the world, the United States, Russia, Japan, and China, have complete titanium industrial production technology. The titanium industry industry chain has two different branches, namely titanium material industry and titanium dioxide industry. In the titanium industry, starting from ilmenite and rutile mining, sponge titanium is manufactured, and then made into various metal products for aerospace, chemical, marine and other fields.
1 Titanium and titanium alloys
1.1 Titanium: a rare metal with abundant reserves and difficult processing
The abundance of titanium in the earth's crust is 0.56%, ranking 9th among all elements, and its reserves are much higher than many common metals, ranking third only after iron and aluminum. Due to the complex smelting technology and difficult processing of titanium, titanium is classified as a "rare" metal. At present, only the United States, Russia, Japan and China have mastered the complete titanium industrial production technology in the world.
The valuable titanium minerals are mainly ilmenite (FeTiO3) and rutile (TiO2). According to the "Mineral Commodity Summaries 2022" of the United States Geological Survey (USGS), as of the end of 2021, the global ilmenite reserves are 700 million tons, accounting for 93%, and the rutile reserves are 49 million tons, accounting for 7%. Global titanium resources are mainly distributed in Australia, South Africa, China, India and Kenya and other countries. China's ilmenite reserves are 230 million tons, accounting for 33% of the world's total reserves, ranking first in the world. However, in my country's titanium resources, there are more ilmenite ore and less rutile ore; more lean ore and less rich ore; no single titanium ore, all of which are polymetallic symbiotic ore, with high content of calcium and magnesium impurities, and difficult mining, beneficiation and smelting technology.
The titanium industry industry chain has two different branches, namely titanium material industry and titanium dioxide industry. In the titanium industry, starting from ilmenite and rutile mining, sponge titanium is manufactured, and then made into various metal products for aerospace, chemical, marine and other fields; in the titanium dioxide industry, from ilmenite and rutile mining At the beginning of the election, titanium dioxide, a chemical intermediate product, is generated through chemical processes, which are used in industries such as coatings, plastics and papermaking.
Titanium sponge is the basic raw material for the titanium industry, but different downstream application fields have different requirements for the quality grade of titanium sponge. According to the national standard of sponge titanium, according to the level of titanium content, impurity content and hardness from high to low, sponge titanium can be divided into 0A, 0, 1, 2, 3, 4, and 5; The particle size is generally 0.83mm-25.4mm, the small particle size is 0.83mm-12.7mm, and the fine particle size is 0.83mm-5.0mm.
The raw material for high-end titanium alloy production is mainly grade 0 sponge titanium. For example, the sponge titanium purchased by Western Superconductor is mainly grade 0 and grade 1 sponge titanium, mainly grade 0, small particles with a particle size of 3mm-12.7mm, and has special internal control technical standards for related parameters. The general civil titanium alloy related enterprises purchase standard sponge titanium, and the sponge titanium purchased by Western Titanium is mainly standard 1-grade sponge titanium and some 0-grade and 2-grade sponge titanium.
Domestic sponge titanium production has continued to grow in recent years. In 2020, according to the statistics of the titanium, zirconium and hafnium branch of China Nonferrous Metals Industry Association on the output of 12 domestic sponge titanium production enterprises, a total of 123,000 tons of sponge titanium were produced, a year-on-year increase of 44.9%.
1.2 Types of titanium and titanium alloys
Sponge titanium (or sponge titanium plus alloying elements) is smelted to form a titanium ingot, and then the ingot is processed into a material, that is, a titanium material, by plastic processing methods such as forging, rolling, and extrusion. According to data from the China Nonferrous Metals Industry Association Titanium, Zirconium and Hafnium Branch, in 2020, my country's titanium production will reach nearly 100,000 tons, accounting for more than 50% of global titanium production. There are various classification methods for titanium materials according to whether alloying elements are added, grades, shapes and uses.
Titanium alloy is an alloy formed by adding appropriate amount of other elements based on titanium to adjust the composition of the matrix phase and comprehensive physical and chemical properties. Titanium alloys can be divided into: α-type titanium alloys with close-packed hexagonal structure (including near-α-type alloys)—that is, domestic grades TA, and β-type titanium alloys with body-centered cubic structure (including near-β-type alloys)—that is, domestic grades TA. The grade is TB, a two-phase mixed α+β titanium alloy—that is, the domestic grade TC.
Alpha and near-alpha titanium alloys have good creep, durability and weldability and are suitable for use in high temperature environments. Beta-type and near-beta-type titanium alloys have high tensile strengths from room temperature to around 300°C, but at higher temperatures, the creep resistance and thermal stability of the alloys decrease sharply. α+β type titanium alloy not only has good hot working performance, but also has good comprehensive performance in medium and high temperature environment.
2 Domestic demand for titanium alloys: mainly in chemical and aerospace applications, aerospace demand is rapidly increasing
Titanium has outstanding characteristics such as low density, high specific strength, low thermal conductivity, good high temperature and low temperature resistance, and strong corrosion resistance. Seawater desalination, construction, daily utensils and other fields have expanded, and it is known as "modern metal" and "strategic metal".
The use of titanium materials in my country is mainly in the chemical industry. According to the statistics of the China Nonferrous Metals Industry Association Titanium, Zirconium and Hafnium Branch, the sales volume of the major domestic titanium material manufacturers in the chemical industry accounts for about 50% of the total sales volume. In recent years, the demand for titanium materials in the domestic aerospace field has grown rapidly, and the sales volume of major domestic titanium material manufacturers in the aerospace field has increased from 9.7% in 2010 to 18.4% in 2020.
The sales of titanium materials in the domestic aerospace industry maintained rapid growth. In 2020, the total sales volume of major domestic titanium material manufacturers in the aerospace field is about 17,228 tons, a year-on-year increase of 36.73%, and a compound growth rate of 16.94% compared with the sales volume of 3,603 tons in 2010.
Aviation titanium alloys are mainly used in aircraft structural parts, aero-engine structural parts and aviation fasteners. The operating temperature of titanium alloys for aircraft structures is generally below 350 °C, and it is required to have high specific strength, good toughness, excellent fatigue resistance, good welding process performance, etc. The main application parts are landing gear components, frames, beams, Fuselage skins, heat shields, etc. Titanium alloys for engines are required to have high specific strength, good thermal stability, good oxidation resistance and creep resistance. The main application fields are compressor discs, blades, drums, high-pressure compressor rotors, and compressor casings. Titanium alloys for aviation fasteners are required to have good processability, non-magnetic, corrosion resistance, etc., mainly including titanium alloy rivets, titanium alloy bolts, etc.
2.1 Aircraft fuselage structural parts: the consumption of titanium alloys for both military and civil aircraft continues to increase
2.1.1 Application of titanium alloy for fuselage structural parts: used for important structural parts such as wings, landing gear and tail
Titanium alloy has excellent properties such as low density, high specific strength, corrosion resistance, high temperature resistance, non-magnetic, weldable, wide operating temperature range (-269℃-600℃), and can be used for various parts forming, welding and machining. , which was soon widely used in the aviation field. In the early 1950s, military aircraft began to use industrial pure titanium to manufacture less stressed structural parts such as heat shields, tail covers, and speedbrakes of the rear fuselage. In the 1960s, titanium alloys were further applied to major stress-bearing structural parts such as aircraft flap slide rails, load-bearing bulkheads, mid-wing box beams, and landing gear beams.
Taking the American F14 fighter jet as an example, titanium alloys account for 26% of the structural weight of the F14 fighter jet. Components made of titanium include wing structures, landing gear components, tail structures, as well as small fasteners, springs and hydraulic pipes.
The use of titanium alloys as the fuselage material has many advantages: 1) Substituting steel and nickel-based superalloys can greatly reduce the quality of the aircraft; 2) It can meet the strength requirements of aircraft. Compared with aluminum alloys, titanium alloys with a mass of about 60% are sufficient. achieve the same intensity. 3) Good corrosion resistance, titanium alloy does not need surface anti-corrosion coating or coating. 4) Good electrochemical compatibility with polymer composites. 5) Meet the strength requirements in the confined space, for example, the titanium alloy landing gear beam of Boeing 747.
In terms of military aircraft, the amount of titanium used in foreign advanced fighter aircraft accounts for about 25% of the total mass of the airframe structure. The U.S. F-35 fighter uses 27% titanium, and the F-22 fighter uses 41% titanium. The main bearing beam and frame of the fuselage are forged from titanium alloys as a whole, setting a record for the highest amount of titanium used in fighter aircraft so far. The titanium alloy consumption of the US B1 bomber and B2 bomber is 21% and 26% respectively. The amount of titanium used in American transport aircraft has also increased from 6% of C5 in early service to 10.3% of C17, and the amount of titanium used in Russian Il 76 transport aircraft has reached 12%.
In terms of civil aircraft, due to the extensive use of composite materials, the amount of titanium alloys that are more compatible with composite materials is also gradually increasing. The titanium consumption of Airbus aircraft increased from 4.5% of the third generation A320 to 6% of the fourth generation A340, the titanium consumption of A380 increased to 10%, and the titanium consumption of A350 passenger aircraft was further increased to about 14%; Boeing aircraft used titanium The amount of titanium has gradually increased from 0.5% of the original Boeing 707 to 4% of the Boeing 747, and then to 7% of the Boeing 777. The amount of titanium used in the Boeing 787 has increased to about 15%, basically keeping pace with the Airbus aircraft. Russia's new passenger aircraft MS21 uses titanium alloys as high as 25%, which is currently the highest record for titanium use in civilian transport aircraft.
Domestically, military fighters have gradually increased from the J-8, which initially used only 2% of titanium, to the J-10, which used 4% of titanium, the J-11, and the J-20. The amount of titanium alloy used in the large military transport aircraft Y-20 is 10%, which is equivalent to that of the advanced C-17 transport aircraft in the United States. In civil aircraft, the amount of titanium alloy used in commercial passenger aircraft ARJ21 is 4.8%, while titanium alloy is widely used in C919 large passenger aircraft. .
2.1.2 Titanium alloy materials for fuselage structural parts: Ti-64 is the most widely used and is developing towards better processing performance
At present, the titanium alloy materials used in the aviation field mainly include TC4 (US Ti-64 alloy), TC18, TC21, TA15, TB6 (US Ti-1023 alloy) and so on. Ti-64 titanium alloy is the earliest and most classic titanium alloy, and it is designed to operate at temperatures up to 350°C. Ti-64 not only has high temperature resistance, but also has very good plastic workability, and is widely used in the aerospace field.
TC18 has greater hardenability and is suitable for the manufacture of large forgings. Russia has developed Ti-55531 titanium alloy on the basis of TC18 alloy according to the needs of civil aircraft such as Boeing and Airbus. Ti-55531 is stronger, with superior hardenability and a wider processing window, and has been used on parts such as A380 aircraft pylons and landing gear struts.
In terms of cast titanium alloys, the most widely used and most used cast titanium alloy in the aviation field is ZTC4 titanium alloy. Among the titanium alloy castings developed and produced in my country, the amount of ZTC4 and ZTA15 alloys accounts for 80%. In addition, the commonly used cast titanium alloys in China are ZTC3 and ZTC6. ZTC3, ZTC6 and ZTA15 are high-temperature cast titanium alloys and high-strength cast titanium alloys developed or imitated by the Aviation Materials Institute according to the development needs of the aviation industry. They can reduce the weight of the overall structure of the aircraft, meet the requirements of high temperature and high load and corrosive environment, and improve the life of the airframe. Play an important role.
2.2 Aeroengine Structural Parts: Mainly used for the cold end components of aerogenerators, and the application scope of new titanium alloy performance improvement has been continuously expanded
2.2.1 Titanium alloys are mainly used for aircraft cooling end components, and the proportion of the usage continues to increase
The use of titanium alloys is the key to improving the thrust-to-weight ratio of military aircraft. The thrust-to-weight ratio is an important performance indicator of aero-engines. The thrust-to-weight ratio of the earliest aeroengines was 2~3, and the thrust-to-weight ratio of the fourth-generation aeroengines exceeded 10. Titanium has good high temperature strength, creep resistance and oxidation resistance at 300~650℃, and it is light in weight and high in specific strength. Tweet weight ratio.
In terms of military aviation, titanium alloys are generally used for rotating parts such as fans, high-pressure compressor discs, blades, and stationary parts such as combustion chambers and tail nozzles of aero-engines. In foreign advanced aero-engines, the amount of titanium alloys has accounted for 25% to 40% of the total engine mass. The amount of titanium alloys used in the third-generation aviation engine F100 has reached 25%, and the amount of titanium alloys used in the fourth-generation aviation engine F119 has reached 40%.
In civil aircraft engines, titanium alloys are also used for fans, compressor discs, blades and other components. Taking the V2500 aero-engine as an example, its titanium alloy content reaches 31%, and the titanium alloy parts are mainly concentrated in the front of the engine and the position where the external working temperature is low. Alloy parts are used less. The use of titanium alloy parts covers many parts such as casing, rotor hub, rotor blade, stator blade, bearing support, pipeline, bracket, etc. The total price of the parts exceeds 7.5 million US dollars, which is about 15 million US dollars compared to the new V2500 price. than about 50%.
Figure 18: Application of titanium alloy in V2500 aero-engine
2.2.2 The performance requirements of aviation titanium alloys are high, and the new titanium alloys further expand the application scope
The application of titanium alloys in aero-engines requires that they have good instantaneous strength, heat resistance, durable strength, high temperature creep resistance and organizational stability in a higher temperature range. α-type, near-α-type and α+β-type titanium alloys have good comprehensive properties in medium and high temperature environments, and are widely used in aero-engines.
Titanium alloys used in active aero-engines mainly include TC4, TC11, TC17 and TA11, etc., which are used for blades, discs, casings and other parts that work in the low temperature section of engine fans and compressors.
TC4 has good plastic workability, and TC17 is a two-phase titanium alloy with high strength, high toughness and high hardenability. Due to its low operating temperature, it is widely used in the manufacture of low-temperature components such as aero-engine fan blades and compressor discs.
TC25 titanium alloy is a heat-strength titanium alloy (Russian brand BT25) developed by the former Soviet Union. The alloy contains high melting point elements such as molybdenum and tungsten. It has good thermal strength and heat resistance. , mainly used in the manufacture of aero-engine high-pressure compressor discs.
With the urgent demand for high-performance titanium alloys in advanced aerospace, 600 ℃ high-temperature titanium alloys, flame-retardant titanium alloys, TiAl and SiCf/Ti composite materials have become the focus of the development of new high-temperature titanium alloys.
600℃ high temperature titanium alloy is suitable for high-pressure compressor overall blisk, casing, etc. with a working temperature of 500℃-600℃; flame-retardant titanium alloy is suitable for high-pressure compressor casing, blades, etc.; TiAl alloy is suitable for working temperature of 700℃ ℃-850℃ high pressure compressor blades, turbine blades
