1, low density, high strength, than the strength of large

Titanium density is 4.51g/cm3, 57% of steel, just a little more than half of steel, less than twice the aluminum, strength than aluminum three times. Titanium alloy specific strength is commonly used in industrial alloys in the largest, titanium alloy specific strength is stainless steel 3.5 times, is 1.3 times the aluminum alloy, is 1.7 times the magnesium alloy, so is the aerospace industry is essential to the structure of the material.

Comparison of the density and specific strength of titanium with other metals is shown in Table 1-1.

Table 1-1 titanium and other metals density and specific strength comparison

Metal Titanium (alloy) Iron Aluminum (alloy) Magnesium (alloy) High-strength steel

Density / (g-cm-3) Specific strength 4.5 (29) 7.87 -- 2.7 (21) 1.74 (16) -- 23

2、Excellent corrosion resistance

The passivity of titanium depends on the presence of oxide film, it is in the oxidizing medium in the corrosion resistance than in the reducing medium is much better, in the reducing medium can occur in a high rate of corrosion. Titanium is not corroded in some corrosive media, such as seawater, wet chlorine gas, chlorite and hypochlorite solutions, nitric acid, chromic acid, metal chlorides, sulfides, and organic acids. However, in media that react with titanium to produce hydrogen (e.g. hydrochloric and sulfuric acids), titanium usually has a large corrosion rate. However, if a small amount of oxidizing agent is added to the acid, a passivation film is formed on titanium. Therefore, titanium is corrosion-resistant in sulfuric acid-nitric acid or hydrochloric acid-nitric acid mixtures, and even in hydrochloric acid containing free chlorine. The protective oxide film of titanium is often formed when the metal encounters water, even in small amounts or in the presence of water vapor. If titanium is exposed to a strongly oxidizing environment in the complete absence of water, rapid oxidation and a violent, often spontaneous combustion reaction can occur. Such behavior has occurred with titanium and fuming nitric acid containing excess nitrogen oxides, and with titanium and dry chlorine gas. However, a certain amount of moisture is necessary to prevent such reactions from occurring.

3、Good heat resistance

Usually aluminum at 150 ℃, stainless steel at 310 ℃ that is the loss of the original high mechanical properties, and titanium alloys at about 500 ℃ still maintain good mechanical properties. When the aircraft speed reaches 2.7 times the speed of sound, the surface temperature of the aircraft mechanism reaches 230 ℃, aluminum alloys and magnesium alloys can not be used, while titanium alloys can meet the requirements. Titanium's heat resistance is good, it is suitable for aero-engine compressor turbine disk and blade and the skin of the rear fuselage of the aircraft.

4, good low temperature performance

Certain titanium alloys (such as Ti-5Al-2.5SnELI) strength increases with the reduction of temperature, but the plasticity is not reduced much, there is still good ductility and toughness at low temperatures, suitable for use in ultra-low temperatures. Can be used for liquid hydrogen, liquid oxygen rocket engines, or in manned spacecraft to do ultra-low temperature containers and storage tanks.

5, non-magnetic

Titanium is non-magnetic, it is used in submarine shells, will not cause the explosion of mines.

6, small thermal conductivity

Comparison of the thermal conductivity of titanium and other metals is shown in the following table.

Metal Ti Al Fe Cu

Thermal conductivity / W - (m - K) 17 212 85 255

Titanium's thermal conductivity is small, only 1/5 of steel, aluminum 1/13, copper 1/25. poor thermal conductivity is a disadvantage of titanium, but in some cases you can use this feature of titanium.

7, small modulus of elasticity

Metal Ti Al Fe

Modulus of elasticity / GPa 108 72 196

The modulus of elasticity of titanium is about 55% of that of iron, and when used as a structural material, the low modulus of elasticity is a disadvantage.

8, tensile strength and yield strength is close to

Ti-6Al-4V titanium alloy tensile strength of 960Mpa, yield strength of 892MPa, the difference between the two is only 58Mpa.

Titanium and other metals in the tensile strength and yield strength of the comparison between the following table:

Strength Titanium alloy (Ti-6Al-4V) 18-8 stainless steel Aluminum alloy

Tensile strength 960 608 470

Yield strength 892 255 294

9. Titanium is easily oxidized at high temperatures.

Titanium with hydrogen, oxygen, strong bonding force, we must pay attention to prevent oxidation and hydrogen absorption. Titanium welding should be carried out under argon protection to prevent contamination. Titanium tubes and plates should be heat-treated under vacuum, titanium forgings in the heat treatment to control the micro-oxidizing atmosphere.

10, low damping resistance

Titanium and other metal materials (copper, steel) made of the same shape and size of the clock, with the same force to knock each clock will find that the clock made of titanium vibration up the sound lasts a long time, that is, by knocking to give the clock's energy is not easy to disappear.

The special function of titanium and titanium alloy processing materials:

11, shape memory function

Ti-50%Ni (atomic fraction) alloy, under certain temperature conditions, it has the ability to restore its original shape, so it is called titanium shape memory alloy.

12、Superconductivity

NbTi alloy, when the temperature drops to near absolute zero, NbTi alloy made of wire, will lose resistance, can make any large current through the wire will not heat, no energy consumption, so NbTi alloy is called superconducting materials.

13、Hydrogen absorption function

Ti-50% Fe (atomic fraction) alloy, with a large number of hydrogen absorption capabilities. The use of Ti-Fe alloy of this feature, hydrogen can be safely stored, that is, the storage of hydrogen does not necessarily use steel high-pressure cylinders. Under certain conditions, the Ti-Fe alloy can also be used to release hydrogen, so it is called a hydrogen storage material.