Ten properties of titanium - Knowledge - Baoji Jufuti non-ferrous metals co,ltd.

Ten properties of titanium

Small density, high strenght, large specific strenght

The density of titanium is 4.51g/cm3, 57 percent of that of steel. Titanium is less than twice as heavy and three times as strong as aluminum. The specific strength (strength/density ratio) of titanium alloy is the largest among commonly used industrial alloys (see Table 2-1). The specific strength of titanium alloy is 3.5 times that of stainless steel. 1.3 times of aluminum alloy; Magnesium alloy is 1.7 times larger than magnesium alloy, so it is an essential structural material for the aerospace industry.
Table 2-1 Comparison of density and specific strength of titanium with other metals.

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Excellent corrosion resistance

The dullness of titanium depends on the presence of oxide film, and its corrosion resistance is much better in oxidizing media than in reducing media. High rate corrosion occurs in reducing media. Titanium is not corroded in some corrosive media, such as seawater, wet chlorine, chlorite and hypochlorite solution, nitric acid, chromic acid, metal chloride, sulfide and organic acids. However, titanium usually has a higher corrosion rate in the media in which it reacts to produce hydrogen, such as hydrochloric acid and sulfuric acid. But adding a small amount of oxidant to the acid will make a passivation film form on the titanium surface. So titanium is resistant to corrosion in mixtures of strong sulfuric acid to nitric acid or hydrochloric acid to nitric acid, even in hydrochloric acid containing free chlorine. The protective oxide film of titanium often forms when the metal hits water, even in small amounts of water or steam. If titanium is exposed to a strong oxidizing environment with no water at all, rapid oxidation and violent reactions occur, and even spontaneous combustion often occurs. This has happened with titanium reacting with fuming nitric acid containing excess nitrogen oxide and with dry chlorine gas. So to prevent this kind of reaction, there must be a certain amount of water.

Good heat resistance

Usually aluminum at 150℃, stainless steel at 310℃ that is lost the original performance, and titanium alloy at about 500℃ still maintain good mechanical properties. When the aircraft speed reaches 2.7 times the speed of sound and the surface temperature of the aircraft structure reaches 230℃, aluminum alloy and magnesium alloy can not be used, while titanium alloy can meet the requirements. Titanium has good heat resistance and is used in the plates and blades of aero-engine compressors and in the skin of the rear fuselage of aircraft.

Good low temperature performance

The strength of some titanium alloys (such as Ti-5AI-2.5Sneli) increases with the decrease of temperature, but the plasticity decreases little, and it still has good ductility and toughness at low temperature, which is suitable for use at ultra-low temperature. It can be used on dry liquid hydrogen and oxygen rocket engines or as cryogenic containers and storage tanks on manned spacecraft.

No magnetic

Titanium is non-magnetic, it is used in submarine housing, does not cause mine explosion.

Small thermal conductivity

The comparison of thermal conductivity between titanium and other metals is shown in Table 2-2.
Table 2-2 Comparison of thermal conductivity of titanium with other metals.

Titanium has a small thermal conductivity, only 1/5 of steel, 1/13 of aluminum, and 1/25 of copper. Poor thermal conductivity is a disadvantage of titanium, but it can be exploited in certain situations.

Low elastic modulus

The comparison of elastic modulus between titanium and other metals is shown in Table 2-3.
Table 2-3 Comparison of elastic modulus of titanium with other metals.

The elastic modulus of titanium is only 55% of that of steel, which is a disadvantage when used as a structural material.

The tensile strenght is close to the yield strenght

Ti-6ai-4v titanium alloy tensile strength is 960MPa, yield strength is 892MPa, the difference between the two is only 58MPa, as shown in Table 2-4.
Table 2-4 Comparison of tensile strength and yield strength between titanium and other metals.

Titanium is easily oxidized at high temperature

Titanium and hydrogen and oxygen bonding force is strong, attention should be paid to prevent oxidation and hydrogen absorption. Titanium welding should be carried out under the protection of argon to prevent pollution. Titanium tubes and thin plates should be heat treated under vacuum, and micro oxidation atmosphere should be controlled during heat treatment of titanium forgings.

Low damping performance

Using titanium and other metal materials (copper, steel) to make the same shape and size of the bell, with the same force to knock each bell, it will be found that the bell made of titanium oscillates long sound, that is, the energy given by knocking the bell is not easy to disappear, so we say that the damping performance of titanium is low.

Three special functions of titanium

(1) Shape memory function
It refers to the ability of Ti-50% Ni (atomic) alloy to restore its original shape under certain temperature conditions. This material is called shape memory alloy.

(2)Superconductivity

Refers to NbTi alloy, when the temperature drops to close to absolute zero, NbTi alloy made of wire, will lose resistance, any large current through, wire will not heat, no energy consumption, NbTi is called superconducting material.

(3) Hydrogen storage function

Refers to ti-50% Fe (atomic) alloy, which has the ability to absorb large amounts of hydrogen. Using this feature of TiFe, hydrogen can be stored safely, that is, it is not necessary to use steel high-pressure gas cylinders for hydrogen storage. Under certain conditions, hydrogen can be released by TiFe, which is called energy storage material.