Titanium has high durability, good corrosive resistance and has a relatively low mass. This makes its application necessary in those spheres where good mechanical properties and mass of products are important. This page contains the description of this metal: physical and chemical properties, applications, grades and its alloys, types of products.
Main information
Titanium (Ti) - chemical element with atomic number 22, atomic weight 47.88, light silver-white metal. Density - 4.51 g/cm3, Tmelt=1668+(-)5 °С, Tboil=3260 °С. This material is light, durable, very corrosive-resistant, has a low coefficient of thermal expansion, can be processed in a wide temperature range.
Discovery
TiO2 oxide was discovered in 1789 by English mineralogist William Gregor. When he was studying the magnetic iron sand, he found an oxide of an unknown metal and called it “manaccanite”. The first example of titanium specimen was obtained in 1825 by Swedish chemic and mineralogist J. J. Berzelius.
Titanium properties
In the periodic system of elements by D. I. Mendeleyev Ti is located in IV group of the 4th period under atomic number 22. This metal is quadrivalent in the most important and stable compositions. It looks like steel. Titanium is transition element. This metal melts under a very high temperature (1668±4 °С) and boils under 3300 °С; latent heat of melting and vaporization is twice as high than iron.
There are two allotropical titanium forms (two types of this metal with the same chemical composition, but different structure and properties). Low-temperature alpha form (stable under 882.5 °С) and high-temperature beta form (stable under 882.5 °С and the melting temperature).
By density and specific heat titanium takes up the intermediate position between aluminium and iron - the main construction metals. It should be also mentioned that its mechanical strength is as twice as higher than pure iron has and six time as high than aluminium has. But this material can take in oxygen, nitrogen and hydrogen actively that reduce the metal plasticity properties dramatically. Titanium forms hard-melting carbides with high hardness.
Titanium has a low heat conductivity that is 13 times less than aluminium has and 4 times less than iron has. The coefficient of thermal expansion under room temperature is relatively low, but it is positively related to the temperature.
Titanium has low elastic modulus and it shows a large anisotropy. Elastic moduli characterize the material property of elastic deformation after applying force. Anisotropy means different elasticity properties depending on the direction of applying the force. When the temperature rises to 350 °С, the elastic moduli reduce linearly. Low elastic modulus of Ti is a significant drawback as in some cases for making rather rigid structures products with larger section should be used if compared to those determined by the durability conditions.
Titanium has a high specific resistance (42·10-8-80·10-6 Ohm·cm depending on the content of additives). Under temperature below 0.45 K it becomes a superconductor.
Titanium is a paramagnetic metal. Usually paramagnetic materials demonstrate decrease of magnetizability when they are heated. Magnetizability characterizes the relation between the intensity of magnetization of a substance and its magnetic field. This material is an exception as its sensibility significantly increases when it is heated.
Physical and mechanical properties
Property
Value
Atomic number
22
Atomic weight
47,00
Density under 20°С, g/cm3
4,505
Melting temperature, °С
1668
Boiling temperature, °С
3260
Latent heat of melting, Jpg
358
Latent heat of vaporization, kJpg
8,97
Melting heat, kJ/mole
18,8
Vaporization heat, kJ/mole
422,6
Molecular volume, cm³/mole
10,6
Specific heat under 20°С, kJ/(kg·°С)
0,54
Specific heat conductivity under 20°С, W/(m·K)
18,85
TLEC under 25°С, 10-6 m/mK
8,15
Specific resistance under 20°С, Ohm·cm·10-6
45
Young's modulus, hPa
112
Shear modulus, hPa
41
Poisson's ratio
0,32
Hardness, НВ
130...150
Spark colour
Sharply white, long saturated spark bundle
Group of metals
Hard-melting, light metal
Chemical properties
Property
Value
Covalent radius, pm
132
Ionic radius, pm
(+4e) 68 (+2e) 94
Electronegativity (Pauling)
1,54
Electrolytic potential
- 1,63
Oxidation levels
2, 3, 4
Titanium and alloy grades
VT1-0, VT1-00, VT1-00sv are the most common titanium grades. Titanium of these grades is commercial. These grades do not contain addition agents, only some impurities. Ti content in VT1-0 grade is approximately 99.24-99.7%, in VT1-00 - 99.58-99.9%, VT1-00sv - 99.39-99.9%. VT1-0 and VT1-00 are supplied in form of sheets, slabs, rods and tubes. Wire is often used for different welding purposes and made of VT1-00sv grade.
Currently there are many mass-produced titanium alloys that differ in chemical composition, mechanical and technological properties. The most widely used addition agents in such materials are aluminium, vanadium, molybdenum, manganese, chrome, silicon, stannum, zirconium, iron.
VT5 titanium alloy contains 5% of aluminium. It has higher strength properties if compared to titanium, but it has low producibility. The alloy is forged, rolled, blanked and is well-weldable. VT5 grade is used for producing titanium rods (round bars), wire and pipes so as sheets. It is also used for producing parts working under temperature up to 400 °С.
VT5-1 titanium alloy contains 2-3% of stannum besides 5% of aluminium. Stannum improves its technological properties. VT5-1 grade is used for producing all types of semifinished products obtained by pressurizing: titanium slabs, sheets, forgings, stamped products, sections, pipes and wire. It is used for making products working in a wide temperature range: from cryogen (negative) to + 450 °С.
ОТ4 and ОТ4-1 titanium alloys contain such addition agents as aluminium and manganese. They have a high technological plasticity (they are well-deformable in hot and cold form) and are well-weldable. This material is usually used for producing titanium slabs, sheets, strips, flat bars, rods, round bars, forgings, sections and pipes. ОТ4 and ОТ4-1 titanium alloys are used for producing parts working under temperature up to 350 °С by welding, stamping and bending. These materials have some drawbacks: 1) relatively low durability and high temperature strength; 2) high tendency to hydrogen embrittlement. In PT3V alloy vanadium is used instead of manganese.
VT20 titanium alloy was designed as a more durable sheet material if compared to VT5-1. Hardening of VT20 grade is determined by its alloying with zirconium and small content of molybdenum and vanadium besides aluminium. Technological plasticity of VT20 alloy is low due to high aluminium content, but it has a good high temperature strength. This material is well-weldable and the weld durability is equal to the durability of the main metal. The alloy is used for making products with a long operation time under temperatures up to 500 °С.
VT3-1 titanium alloy is belongs to Ti - Al - Cr - Mo - Fe - Si system. It usually undergoes isothermal annealing. Such annealing provides the highest thermal stability and maximum plasticity. VT3-1 grade is one of the most widely-used alloys. It is used for long operation under temperature up to 400 - 450 °С; it is a heatproof material with high creep-rupture strength. This material is used for making rods (titanium round bars), sections, slabs, forgings and stamped products.
Advantages / drawbacks
Advantages:
low density (4500 kgpm3) allows increasing the mass of the products;
high mechanical strength. It should be mentioned that under high temperatures (250-500 °С) titanium alloys have a higher durability than high-durable aluminium and magnesium alloys;
really high corrosive resistance determined by the fact that Ti can create thin (5-15 μm) continuous films of ТiO2 oxides that are well-tied with the metal mass;
strength-to-density ratio of the best titanium alloys reaches 30-35 and higher; this is twice as high than the strength-to-density ratio of alloyed steels.
Drawbacks:
high cost of production; Ti is more expensive than iron, aluminium, copper, magnesium;
active reactivity under high temperatures (especially in liquid form) with all gases in the atmosphere, so Ti and its alloys can be melted in vacuum or inert gases only;
difficulties with organizing production of titanium waste;
bad antifriction properties determined by sticking of Ti to many materials; pair titanium-titanium cannot work for friction;
high tendency of Ti and many its alloys to hydrogen embrittlement and salt corrosion;
bad cutting machinability similar to machinability of stainless steels of austenite class;
high chemical activity, tendency to grain coarsening under high temperature and phase conversions during the welding cycle make welding titanium difficult.
Applications
Usually titanium is applied in aircraft and rocket engineering so as shipbuilding. Titanium and ferrotitanium are used as addition agents to high-quality steels and as a scavenger. Commercial titanium is used for creating containers, chemical reactors, pipelines, fittings, pumps, valves and other products that work in hostile environments. Compact titanium is used for making meshes and other components of vacuum-tube devices working under high temperatures.
As a construction material Ti holds the 4th place trailing Al, Fe and Mg only. Titanium aluminides are very resistant to oxidation and are very heatproof. This determines their use in aviation and automaking as construction materials. Biological harmlessness of this material makes it perfect for food industry and anaplasty.
Titanium and its alloys are widely used in engineering due to high mechanical strength that remains stable under high temperature, corrosion stability, high temperature strength, strength-to-density ratio, low density and other useful properties. High cost of this metal and material based on them is usually compensated by their high performance and sometimes they only serve as raw materials for making equipment or structures that can work in certain conditions.
Titanium alloys play a great role in aircraft engineering where the lightest structure combined with necessary durability is preferable. Ti is light if compared with other metals, but at the same time it can work under high temperature. Titanium-based materials are used for making fuselage skin, fasteners, framework, chassis components, different installations. Also these materials are applied for making structures of aircraft jet engines. This allows reducing their mass by 10-25%. Titanium alloys are used for compressor discs and blades, components of air intakes and engine guides, various fasteners.
Titanium is also applied in rocket engineering. Due to short-term engine operation and fast passing of drag-producing atmosphere titanium allows solving fatigue strength, static fatigue and (partially) creep problems in rocket engineering.
Due to insufficient heat strength commercial titanium can not be used in aircraft engineering, but due to high corrosive resistance in some cases it is a necessary component in chemical industry and shipbuilding. Thus it is used for producing compressors and pumps for pumping such aggressive media as sulphuric and hydrochloric acid and their salts, pipelines, isolation valves, autoclave presses, different containers, filters etc. Only Ti is corrosive-resistant in such media as liquid chlorine, water and acid chlorine solutions, so this metal is used for producing equipment for chlorine industry. Also it is used for making heat exchangers that work in corrosive active medias (e.g., in non-smoking nitric acid). In shipbuilding titanium is used for producing screw-propellers, ship plating, submarines, torpedoes. Mussels do not stick to this material and this significantly increases the ship resistance during the movement.
Titanium alloys are challenging for many other applications, but their use in engineering is limited by high cost and rareness of this metal.
Titanium compounds are also widely used in different industries. Carbide (TiC) is very hard and used in producing cutting instruments and abrasive materials. White dioxide (TiO2) is used for making paints (e.g., titanium whitewash) so as for producing paper and plastic. Titanium organic compounds (e.g., tetrabutoxytitanium) are applied as a catalyst and hardening agent in chemical and paint and coatings industry. Non-organic Ti compounds are applied in chemical electronic and fiber-optic industry as an additive. Diboride (TiB2) is an important component of super-hard materials for processing metals. Nitrides (TiN) are used for making tool coating.
Titanium products
Main types of products in the industry are sheets and slabs, rods and round bars, titanium pipes, titanium wire. All above-described products are applied in spheres with strict requirements to the product mass and simultaneously to their corrosive resistance and strength properties.