What is titanium and why was it chosen?

Why can titanium become the best among metals?

Since its discovery in the early 20th century, titanium and its alloys have been widely studied and applied because of its low density, good heat and corrosion resistance and high structural strength. Titanium alloys have more and better properties than pure metals, so they are used in a variety of scenarios. And with the progress of science and technology, titanium alloy has become an indispensable material for new technology, new equipment and new process, and its related industries have entered a new period of historical development.

Properties and applications of titanium

Titanium is a silver-white metal that is classified as a rare light metal in the classification of metals. The melting point is 1668℃, and the transition point is 882°C from the β phase of the body-centered cubic lattice to the α phase of the close-packed hexagonal lattice, or from α to β phase. Compared to other metals, titanium has its own characteristics in terms of chemical and mechanical properties.

1. Low density and high specific strength

The density of titanium is 4.51g/cm³, higher than aluminum but lower than steel, copper, nickel, but higher specific strength than aluminum alloy and high-strength alloy steel. High specific strength indicates that the metal material is light and high strength, so titanium is a kind of light and high strength metal structural material. The high specific strength of titanium makes it widely used in the development of cutting-edge technologies such as aviation, aerospace, missiles and weapons. In the general industry, such as high-speed rotating generator protection ring, steam turbine blade, high-grade bicycles, golf clubs, high jump with the use of titanium and titanium alloy.

2. Low elastic modulus

The elastic modulus of titanium is 106.4GMPa at room temperature, which is 57% of that of steel. This indicates that the resistance of titanium to positive strain is lower than that of steel, so the use of titanium is limited and it is not suitable for rigid structural components. However, in the titanium long tube bundle heat exchanger, the baffle design overcomes the disadvantage of extreme stiffness, and the effect is good even under the condition of vibration.

3. Low thermal conductivity

The heat transfer mechanism of titanium metal is mainly electron heat conduction, followed by lattice heat conduction. The actual test results show that the thermal conductivity of titanium is 0.1507J, which is 1/5 of low carbon steel, 1/25 of copper, and similar to stainless steel. Although the thermal conductivity of titanium is small, it can be used to make rock nails for climbing. The titanium nails are not only light and do not friction and heat conduction, which is the ideal material chosen by mountaineers.

4. The tensile strength is close to the yield strength

The high yield strength ratio (tensile strength/yield strength) of titanium leads to poor plastic deformation during forming. In addition, the yield limit of titanium is larger than the ratio of elastic modulus, so the springback ability of titanium molding is larger.

This characteristic of titanium leads us to find the best processing and forming conditions -- warm forming, which avoids the stress and stress cracking caused by the high resilience and yield ratio of titanium, and avoids the hydrogen absorption higher than 400°C caused by titanium in hydrogen embrittlement. This is one of the reasons for specifying ambient temperatures of no more than 315°C when titanium equipment is used in general industry.

5. Non-magnetic and non-toxic

Titanium is a non-magnetic metal and will not be magnetized in a large magnetic field. The pacemaker made of titanium is not affected by thunderstorms and has a good compatibility with human tissues and blood, so it is used in the medical field.

6. Strong damping resistance [ii]

Titanium is subjected to mechanical vibration, electrical vibration, compared with steel, copper, its own vibration attenuation time is the longest. Using this property of titanium can be used as tuning fork, vibrating element of ultrasonic mill in medicine and vibrating film of high quality sound speaker.

7. Good heat resistance

The new titanium alloy can be used at 600℃ or higher for a long time. With the development of aviation and aerospace industry, its engine disk, blade, rear fuselage, guide, air intake turns and other components use heat-resistant titanium alloy.

8. Good low temperature resistance

The strength of titanium alloys such as TA7 (Ti-5Al-2.5Sn),Grade 5(Ti-6Al-4V) and Ti-2.5Zr-1.5Mo increases with the decrease of temperature, but the plasticity changes little. It maintains good ductility and toughness at -196-253℃ to avoid cold brittleness of metal. It is an ideal material for low temperature containers, storage tanks and other equipment.

9. Strong inspiratory performance

Titanium is a chemically active metal that reacts with many elements and compounds at high temperatures. Titanium aspiration mainly refers to the reaction with carbon, hydrogen, nitrogen and oxygen at high temperature.

10. Strong corrosion resistance

Titanium is a very active metal with low equilibrium potential and high thermodynamic corrosion tendency in medium. But in fact titanium is very stable in many media, such as titanium in oxidizing, neutral and weak reducing media is corrosion resistant. This is because titanium and oxygen have a great affinity. In the air or oxygen-containing medium, titanium surface generates a layer of dense, strong adhesion and inert oxide film, which protects the titanium matrix from corrosion. Even due to mechanical wear, titanium quickly heals or regenerates, which indicates that titanium is a metal with strong passivation tendency.

At present, titanium has become one of the indispensable metal materials for enterprises to adopt new technology, new technology, and large-scale, automatic, safe and reliable production equipment and long-term operation.