Introduction to Powder Metals - Titanium

1. Source of titanium

Titanium was first discovered in 1791 by an amateur mineralogist named Gregor in the UK. In 1795, German chemist Klaprous named this unknown metal substance after the Greek god Titans, which is translated into "titanium" in Chinese and English. Titanium is abundant on the earth. There are more than 140 known titanium minerals, but the main industrial applications are ilmenite and rutile. Among them, China's ilmenite reserves account for 28% of the global reserves, ranking first in the world.

Titanium is recognized as a non-toxic element in the world, with high mining and production costs and high prices. Due to a series of qualifications such as high and low temperature resistance, strong acid and alkali resistance, high strength, and low density, it has become a special material for NASA's rocket satellites, and has also been used in my country's Yutu, J-20, Shandong aircraft carrier and other super projects. After entering the civilian field in the 1980s, it has become the "honorary metal king" in the food industry with its natural antibacterial and biophilic properties.

2. The difference between pure titanium and titanium alloy

Pure titanium, also called industrial pure titanium or commercial pure titanium, is graded according to the content of impurity elements. It has excellent stamping process performance and welding performance, is insensitive to heat treatment and organizational type, and has a certain strength under satisfactory plastic conditions. Its strength mainly depends on the content of interstitial elements oxygen and nitrogen. The properties of 99.5% industrial pure titanium are: density P=4.5g/cm3, melting point is 1800°C, thermal conductivity coefficient λ=15.24W/(M.K), tensile strength σ b=539MPa, elongation: δ =25%, cross-sectional shrinkage ψ=25%, elastic modulus E=1.078×105MPa, hardness HB195. Titanium alloy Titanium alloy is an alloy composed of titanium and other elements. It is a relatively young metal with a history of only sixty or seventy years from its discovery to the present. Titanium alloy materials have the characteristics of light weight, high strength, low elasticity, high temperature resistance and corrosion resistance. They are mainly used in aircraft engines, rockets, missiles and other parts. Titanium has two isomorphs. Titanium is an isomer with a melting point of 1720°C. It has a close-packed hexagonal lattice structure below 882°C, called a titanium; above 882°C, it has a body-centered cubic lattice structure, called B titanium. By using the different characteristics of the above two structures of titanium, appropriate alloying elements are added to gradually change its phase transition temperature and phase content to obtain titanium alloys with different structures (itanium alloys). Titanium alloy elements can be divided into three categories according to their influence on the phase transition temperature:

①Elements that stabilize the a phase and increase the phase transition temperature are a stabilizing elements, including aluminum, magnesium, oxygen and nitrogen. Among them, aluminum is the main alloying element of titanium alloy, which has a significant effect on improving the room temperature and high temperature strength of the alloy, reducing the specific gravity and increasing the elastic modulus.

② Elements that stabilize the B phase and reduce the phase transition temperature are B stabilizing elements. It can be divided into isomorphous and eutectoid types. The former includes molybdenum, niobium, vanadium, etc.: the latter includes chromium, manganese, copper, silicon, etc.

③ Elements that have little effect on the phase transition temperature are neutral elements, such as zirconium and tin.

Common grades are explained in detail:

TA1 (American Standard Gr1)

TA1 (Gr1) titanium is the first of the four industrial pure titanium grades. It is the softest and most ductile of these grades. It has maximum formability, excellent corrosion resistance and high impact toughness. TA1 grade is the material of choice for any application that requires easy formability and is commonly used as titanium plates and titanium pipes.

TA2 (American Standard Gr2) grade

TA2 grade titanium is known as the "workhorse" of the commercial pure titanium industry due to its diverse availability and wide availability. It has many of the same qualities as TA1 grade titanium alloy, but is slightly stronger. Both are equally corrosion resistant. This grade has good weldability, strength, ductility and formability. This makes TA2 grade titanium rod and sheet the first choice for many applications in construction, power generation, medical industries, etc.

TA3 (ANSI Gr3) Grade        

This grade is the least used commercially pure titanium grade, but that does not make it any less valuable. TA3 grade is stronger than TA1 and TA2 grades, with similar ductility and only slight formability. But it has higher mechanical properties than its predecessors. TA3 grade is used in applications that require moderate strength and major corrosion resistance, such as aerospace, chemical processing, marine industries, etc.

TA4 (ANSI Gr4) Grade        

The TA4 grade is considered the strongest of the four commercially pure titanium grades. It is also known for its excellent corrosion resistance, good formability and weldability. It is used in some airframe components, cryogenic vessels, heat exchangers, etc. applications that require high definition.

TA9 (ANSI Gr7) Grade        

The TA9 grade is mechanically and physically equivalent to the TA2 grade, except for the addition of the interstitial element palladium, making it an alloy. Grade 7 has excellent weldability and properties and is the most corrosion resistant of all titanium alloys. In fact, it is the most corrosion resistant in reducing acids. Grade TA9 is used for chemical process and production equipment components. TA9 has extremely strong corrosion resistance, especially in reducing acid environments.

TA9-1 (American Standard Gr11) Grade

TA9-1 Grade is very similar to TA1 grade, except that a small amount of palladium is added to enhance the corrosion resistance and make it an alloy. This corrosion resistance can be used to prevent crevice corrosion and reduce acids in chloride environments. Other useful properties include optimal ductility, cold formability, useful strength, impact toughness, and excellent weldability. This alloy can be used in the same titanium applications as Grade 1, especially where corrosion resistance is required.

Ti 6Al-4V (National Standard TC4, American Standard Gr5)

Grade Known as the "workhorse" of titanium alloys, Ti6Al-4V or Grade 5 titanium is the most commonly used of all titanium alloys. It accounts for 50% of the total titanium used worldwide. Its availability lies in its many benefits. Ti6Al-4V can be heat treated to increase its strength. It can be used in welded structures at service temperatures up to 600°F. The alloy combines high strength with light weight, useful formability, and high corrosion resistance. The availability of Ti6AI-4V makes it an optimal alloy for use in several industries, such as the aerospace, medical, marine, and chemical processing industries. It can be used to create the following technical content: Aircraft turbine engine components Aircraft structural components Aerospace fasteners High-performance auto parts Marine applications Sports equipment

Ti 6AL-4V ELI (GB TC4ELI, ANSI Gr23) Grade

Ti 6AL-4V ELI or TC4ELI grade is a higher purity form of Ti 6Al-4V. It can be made into coils, strands, wires, or flat wires. It is the first choice for any situation where high strength, light weight, good corrosion resistance, and high toughness are required. It has excellent damage tolerance to other alloys. These advantages make TC4ELI grade the ultimate dental and medical titanium grade. Due to its biocompatibility, good fatigue strength, and low modulus, it can be used in biomedical applications such as implantable components. It can also be used in detailed surgical applications such as: Orthopedic pins and screws Orthopedic cables Ligature surgical implants Orthodontic appliances In joint replacements Cryogenic containers Bone fixation devices

TA10 (American Standard Gr12) Grade

TA10 grade titanium is given an "excellent" grade due to its high quality weldability. It is a highly durable alloy that provides great strength at high temperatures. TA10 grade titanium has similar properties to 300 series stainless steels. The alloy can be hot or cold formed using press forming, hydroforming, stretch forming, or drop hammer methods. Its ability to be formed in a variety of ways makes it useful in many applications. The high corrosion resistance of this alloy also makes it invaluable to those manufacturing equipment where crevice corrosion is a concern. TA10 grade can be used in the following industries and applications: Shells and heat exchangers Hydrometallurgical applications High temperature chemical manufacturing Marine and ticket components

Ti 5Al-2.5Sn     

Ti 5Al-2.5Sn is a non-heat-treatable alloy that can obtain good weldability and stability. It also has high temperature stability, high strength, good corrosion resistance and good creep resistance. Creep refers to the phenomenon of plastic strain occurring at high temperatures for a long time. Ti 5Al-2.5Sn is mainly used in aircraft and fuselage applications and low temperature applications.

3. Application of titanium and titanium alloys

Although titanium and titanium alloy materials are abundant in reserves, they are very expensive. This is because titanium has low chemical activity under high temperature conditions, and its smelting technology and operating environment are very harsh. It must be smelted under high temperature and vacuum conditions, and the temperature often reaches above 800℃, which is much more difficult than steel smelting. Therefore, whenever titanium alloy is mentioned, people think it is a high-grade metal material with low output and high price, and few applications.

At present, due to the excellent properties of titanium alloys, such as light weight, high strength and high temperature resistance, titanium and titanium alloy materials are widely used in the manufacture of cutting-edge weapons and national heavy equipment in various countries, such as being particularly suitable for use in the aerospace field. Examples of application areas are as follows: Chemical industry

1. Alkali industry

The emergence of titanium refrigerators in the alkali industry can effectively solve the problem of unqualified chlorine gas output due to unreasonable traditional cooling processes. At the same time, it has changed the production landscape of the chlor-alkali industry, and the life of the titanium alloy refrigerators invested can be as long as 20 years.

2. Salt industry

The most advanced salt production process is vacuum salt production, and the high-temperature concentrated brine produced in this process will cause serious damage to the carbon steel structure and cause equipment dripping. Using titanium-steel composite structures in heating chambers and evaporation chambers can effectively prevent salt scaling, improve the quality of salt production, and reduce the corrosion of high-concentration brine on the pipe wall during evaporation, extending the maintenance cycle. Aerospace 1. Aviation industry The application of titanium alloys in aviation is divided into aircraft structural titanium alloys and engine structural titanium alloys. The main application parts of aircraft titanium alloy structural parts are landing gear parts, frames, beams, fuselage skins, heat shields, etc. Russia's Il-76 aircraft uses high-strength BT22 titanium alloy to manufacture key components such as landing gear and load-bearing beams; the material of the Boeing 747 main landing gear transmission beam is Ti-6Al-4V, the forging is 6.20 meters long, 0.95 meters wide, and weighs 1545 kilograms; high-strength and high-toughness Ti-62222S titanium alloy is used in the key parts of the horizontal stabilizer shaft of the C-17 aircraft. In terms of aviation engines, titanium alloys are used in compressor discs, blades, drums, high-pressure compressor rotors, compressor casings, etc. The leading edge and tip of the fan blades of the Boeing 747-8GENX engine use titanium alloy protective sleeves, which have only been replaced three times during the 10-year service life.

2. Aerospace Industry

The working conditions of spacecraft are very extreme. In addition to the structural design of the material, which requires superb technology, the excellent characteristics and functions of the material itself are also very important. Therefore, titanium alloy stands out among many materials. In terms of aerospace equipment, in the 1960s, the wing beams and ribs of the double cabin and the closed cabin of the spacecraft in the Apollo program of the United States were made of Ti-5Al-2.5Sn, and the lining was made of pure titanium; the German MT Aerospace Company prepared a high-strength Ti-15V-3Cr alloy propulsion system tank and applied it to the giant platform of the European Alpha communication satellite; there are many examples of the application of Russian titanium alloys in aerospace engineering, such as the Energia launch vehicle using a 3.5t BT23 titanium alloy large die forging and forging. In addition, titanium alloys are also used in the fuel tank of liquid fuel rocket engines, cryogenic liquid storage tanks and liquid hydrogen delivery pump impellers, etc.

Similarly, with the rapid development of domestic aerospace engineering, titanium alloys have also been widely used. From the Dongfang-1 satellite in 1970 to the current Shenzhou series spacecraft and Chang'e probe, titanium alloys have been used. In addition, the low-temperature TA7ELI titanium alloy cylinders for use in liquid hydrogen environments developed by my country have been used in the Long March series of launch vehicles; Harbin Institute of Technology used TC4 titanium alloy to prepare the wheel rims of the lunar rover; in addition, my country also uses BT20 and other high-strength titanium alloys to manufacture missile engine casings, nozzles and other components. Ship field Titanium and titanium alloys are widely used in nuclear submarines, submersibles, atomic icebreakers, hydrofoil ships, hovercraft, minesweepers, as well as propeller thrusters, whip antennas, seawater pipelines, condensers, heat exchangers, acoustic devices, and fire-fighting equipment. For example, the US "Sea Cliff" submersible is equipped with a titanium observation cabin and control cabin, and its diving depth can reach 6100m; Japan's Toho Titanium Company and Fujishin Shipbuilding jointly built the "Marishiten II" all-titanium speedboat, which was very popular in the United States for a period of time; my country's first independently designed and independently integrated manned submersible "Jiaolong" also uses titanium alloys, and Jiaolong's working range covers 99.8% of the global ocean area.

4. Existing problems and prospects of titanium and titanium alloys

Although titanium and titanium alloys have made significant progress, the existing problems have also been exposed, and the development of titanium alloys is also facing considerable challenges. It is mainly reflected in the following three aspects:

• Production     

Although my country is a major titanium industry country, the number of high-quality products in production is not high, and the types of titanium products with special properties are few. Secondly, my country cannot produce titanium strips and titanium extruded profiles in batches and stably, which limits the development and utilization of titanium and titanium alloys in aerospace, ocean and other fields. It is still very difficult to further increase the titanium content of aircraft engines to about 50%.

2) Performance Since titanium metal has high chemical activity and is easily contaminated by other elements, the processing and manufacturing process of titanium alloy is very high. At the same time, the high-performance products processed need to comprehensively consider their mechanical, physical, chemical and process properties. The sharp decline of creep resistance and high-temperature oxidation resistance of existing titanium alloys above 600°C is the two main obstacles to the expansion of titanium alloy applications.

3) Cost At present, all countries are working hard to reduce the application cost of titanium alloys and have made many achievements. However, as far as the current situation in my country is concerned, my country's management and technical level have not yet reached the ideal height. The price of domestic titanium alloy products is less competitive in the international market, which is not conducive to further expansion of use.

At present, the main application areas of titanium alloys are still military industrial sectors such as aerospace. The development of new application areas, such as automobiles, trains, high-speed railways, and the application prospects of civilian fields commonly used in daily life are still very broad. In addition, replacing expensive alloy elements with lower-priced elements and reducing the cost of titanium alloy parts through process approaches are important topics in future titanium alloy research. After the titanium alloys used in high-end applications are manufactured at low cost in the future, titanium alloys will be applied to various fields.