Titanium machining workpiece, titanium alloy forging, titanium alloy pipe, etc
Properties and special work of titanium materials
1. Low density, high strength and high specific strength
The density of titanium is 4.51g/cm3, which is 57% of that of steel, just over half that of steel, less than twice that of aluminum, and three times stronger than aluminum.The specific strength of titanium alloy is the largest in common industrial alloys. The specific strength of titanium alloy is 3.5 times that of stainless steel, 1.3 times that of aluminum alloy, and 1.7 times that of magnesium alloy, so it is an essential structural material for aerospace industry.
The comparison of the density and specific strength of titanium with other metals is shown in table 1-1.
Table 1-1 comparison of the density and specific strength of titanium with other metals
|Metal||titanium （alloy）||iron||aluminum (alloy)||magnesium (alloy)||high strength steel|
|Density/(g · cm - 3) than intensity||4.5 （29）||7.87 --||2.7 （21）||1.74 （16）||-- 23|
2. Excellent corrosion resistance
The dullness of titanium depends on the presence of oxide film, and its corrosion resistance is much better in oxidizing medium than in reducing medium, where high rate corrosion can occur.Titanium is protected from corrosion in corrosive media such as seawater, wet chlorine, chlorite and hypochlorite solutions, nitric acid, chromic acid, metallic chlorides, sulfides and organic acids.However, in the media that react with titanium to produce hydrogen, such as hydrochloric acid and sulfuric acid, titanium usually has a higher corrosion rate.But if you add a small amount of oxidizer to the acid, the titanium will form a passivating film.So titanium is corrosion resistant in sulfur-nitric acid or hydrochloric-nitric acid mixtures, and even in hydrochloric acid with free chlorine.Titanium's protective oxide film is often formed when the metal encounters water, even in the presence of small amounts of water or water vapor.If exposed to a strong oxidizing environment with no water at all, titanium can undergo rapid oxidation and produce violent, often spontaneous combustion reactions.Titanium reacts with fuming nitric acid containing excess nitrogen oxide and titanium with dry chlorine gas.To prevent such a reaction, however, a certain amount of water must be present.
3. Good heat resistance
Usually aluminum at 150℃, stainless steel at 310℃ lost the original high mechanical properties, while titanium alloy at 500℃ still maintain good mechanical properties.When the aircraft speed reached 2.7 times of the speed of sound, the surface temperature of the aircraft mechanism reached 230℃, aluminum alloy and magnesium alloy could not be used, while titanium alloy could meet the requirements.Titanium has good heat resistance and is suitable for the turbine disc and blade of the aero-engine compressor and the skin of the rear fuselage of the aircraft.
4. Good low temperature performance
The strength of some titanium alloys (such as ti-5 al-2.5 SnELI) increases with the decrease of temperature, but the plasticity decreases little. It still has good ductility and toughness at low temperature, which is suitable for use at ultra-low temperature.Can be used in liquid hydrogen, liquid oxygen rocket engines, or in the manned spacecraft to make cryogenic containers and tanks.
Titanium is non-magnetic. It is used in submarine shells and does not cause mine explosions.
6. Low thermal conductivity
The thermal conductivity comparison between titanium and other metals is shown in the following table:
The thermal conductivity of titanium is only 1/5 that of steel, 1/13 that of aluminum and 1/25 that of copper.Poor thermal conductivity is a disadvantage of titanium, but it can be used in some situations.
7. Small elastic modulus
|Modulus of elasticity /GPa||108||72||196|
The modulus of elasticity of titanium is about 55% of that of iron. As a structural material, low modulus of elasticity is a disadvantage.
8. The tensile strength is close to the yield strength
The tensile strength of Ti-6Al-4V titanium alloy is 960mpa, the yield strength is 892mpa, and the difference between them is only 58mpa.
The comparison between tensile strength and yield strength of titanium and other metals is shown in the following table:
|strength||titanium alloy（Ti-6Al-4V）||18-8Stainless steel||Aluminium alloy|
9. Titanium is easy to be oxidized at high temperature
Titanium has a strong binding force with hydrogen and oxygen. Attention should be paid to prevent oxidation and hydrogen absorption. Titanium welding shall be carried out under the protection of argon to prevent pollution. Titanium tube and sheet should be heat treated in vacuum, and the atmosphere of micro oxidation should be controlled during heat treatment.
10. Low damping resistance
A clock of the same shape and size is made of titanium and other metal materials (copper and steel). When each clock is knocked once with the same force, it will be found that the vibration sound of the clock made of titanium lasts for a long time, that is, the energy given to the clock by knocking is not easy to disappear.
Special functions of titanium and titanium alloy processing materials:
11. Shape memory function
Ti-50% Ni (atomic fraction) alloy has the ability to restore its original shape under certain temperature conditions, so it is called titanium shape memory alloy.
12. Superconducting function
NbTi alloy, when the temperature drops to near absolute zero, the conductor made of NbTi alloy will lose resistance, which can make any large current pass through, the conductor will not heat up, and there is no energy consumption, so NbTi alloy is called superconducting material.
13. Hydrogen absorption function
Ti-50% Fe (atomic fraction) alloy has the ability to absorb a lot of hydrogen. By using this feature of Ti Fe alloy, hydrogen can be stored safely, that is to say, it is not necessary to use steel high pressure cylinder to store hydrogen. Under certain conditions, Ti Fe alloy can also release hydrogen, so it is called hydrogen storage material.