(1) Classification of titanium alloys

Titanium alloy is an alloy composed of titanium as a matrix and adding alloying elements such as aluminum, tin, chromium, molybdenum, and manganese.

Titanium alloys in practical applications, especially ferrous alloys strengthened by heat treatment, are usually in a non-equilibrium state. The method of classification of titanium alloys according to the phase composition of the metastable state is a more scientific classification method, which provides a good scientific basis for the selection of titanium alloys in production.

According to the organization classification of the alloy in use state, it can be divided into three types: α type, β type, and α + β type. Titanium alloy grades are represented by "T+alloy category code + sequence number", T is the pinyin prefix of titanium, and alloy category codes are represented by A, B, and C respectively for α-type, β-type, and α+β-type titanium alloy. For example, TA6 means No. 6 α-type titanium alloy, and TC4 means No. 4 α+β-type titanium alloy.

1. α type titanium alloy

The main components of the α-type titanium alloy are the addition of aluminum, tin and zirconium to the titanium. The structure in the annealed state is a single-phase α solid solution. This type of alloy cannot be strengthened by heat treatment. It can maintain good high temperature strength when used at 500℃~600℃. The main advantages of this type of alloy are good welding performance, high castability and pressure workability, no cold brittleness and high structural stability. The disadvantage is lower process plasticity and sensitivity to hydrogen embrittlement.

2. β-type titanium alloy

The main component of β-type titanium alloy is the addition of chromium, molybdenum, vanadium and other alloying elements to titanium. After quenching, this type of alloy has a β-solid solution structure, which has high strength and impact toughness, and good pressure processing performance and welding performance. The disadvantage is that the organization and performance are not stable, and the smelting process is more complicated, so there are fewer applications.

3.α+β titanium alloy

The room temperature structure is an α+β two-phase structure, which is an α+β titanium alloy containing 5% to 25% of the β phase in a stable state and the α-type martensite phase formed by rapid cooling from the β zone. It can be quenched by heat treatment. Enhanced aging treatment. The α+β titanium alloy has a wide range of mechanical properties, has good comprehensive properties in a wide temperature range, and can be adapted to various different uses. Among them, the titanium-aluminum-vanadium alloy (TC4) is the most widely used, and it has higher Strength and toughness, it has good heat resistance when used at 100℃~400℃, and its forging performance, stamping performance and welding performance are good.

Titanium alloys can also be divided into structural titanium alloys and high-temperature titanium alloys according to their applications. The service temperature of structural titanium alloys is generally below 400℃, and high-temperature titanium alloys usually work around 500℃, and the current service temperature does not exceed 600℃.

The grades and main components of titanium alloys are listed below.

Titanium alloy grades and main components:

Alloy grades Main chemical composition

TAD Iodine Titanium

TA0 Industrial Pure Titanium

TA1 Industrial Pure Titanium

TA2 Industrial Pure Titanium

TA3 industrial pure iron

TA4 Ti-3A1

TA5 Ti-4Al-0.005B

TA6 Ti-5Al

TA7 Ti-5Al-2.5Sn

TA8 Ti-5Al-2.5Sn-3Cu

TA9 Ti-0.2Pd

TA10 Ti-0.3Mo-0.8Ni

TB1 Ti-3Al-8Mo-11Cr

TB2 Ti-5Mo-5V-8Cr-3Al

TB3 Ti-3.5Al-10Mo-8V-1Fe

TB4 Ti-4Al-7Mo-10V-2Fe-1Zr

TC1 Ti-2Al-1.5Mn

TC2 Ti-4Al-1.5Mn

TC3 Ti-5Al-4V

TC4 Ti-6Al-4V

TC5 Ti-5Al-2.5Cr

TC6 6Al-1.5Cr-2.5Mo-0.5Fe-0.3Si

TC7 Ti-6Al-0.6Cr-0.4Fe-0.4Si-0.01B

TC8 Ti-6.5Al-3.5Mo-0.25Si

TC9 Ti-6.5Al-3.5Mo-2.5Sn-0.3Si

TC10 Ti-6Al-6V-2Sn0.5Cu-0.5Fe

TC11 Ti-6.5Al-3.5Mn-1.5Zr-0.3Si

TC12 Ti-5Al-4Mo-4Cr-2Zr-2Sn-1Nb


(2) The function of titanium alloy

Functional materials are engineering materials with main physical properties, that is, materials that have special properties in terms of electricity, magnetism, sound, light, and heat, or exhibit special functions under their action.

Research on titanium alloy found that it has three major functions.

1. Memory function

Among titanium alloys, there are many excellent memory properties. For example, titanium-nickel alloy has one-way, two-way and omnidirectional memory effects at a certain ambient temperature, and is recognized as the best memory alloy. Pipe joints are made in engineering for the hydraulic system of fighter jets; the oil pipeline system of oil complexes; a 500mm diameter parabolic mesh antenna made of 0.5mm diameter wire is used on aerospace vehicles; used in medical engineering for production Treatment of the disease; made into screws for fracture healing and so on. The above applications have achieved obvious results.

2. Hydrogen storage function

Titanium-iron alloy has the characteristic of absorbing hydrogen, storing a large amount of hydrogen safely, and releasing hydrogen in a certain environment. This is very promising in hydrogen separation, hydrogen purification, hydrogen storage and transportation, and the manufacture of heat pumps and batteries that use hydrogen as energy.

3. Superconducting function

The niobium-titanium alloy exhibits a zero-resistance superconducting function when the temperature is lower than the critical temperature.

(3) Characteristics of titanium alloy

Titanium alloy has special properties such as electricity, magnetism, sound, light and heat, or a material that can exhibit special functions under its action.

1. Low density and high specific strength

The density of titanium metal is 4.51g/cm³, which is higher than that of aluminum and magnesium, but lower than that of steel, copper, and nickel, but its specific strength is higher than that of aluminum alloy and high-strength alloy steel.

2. Low modulus of elasticity

The elastic modulus of titanium is 106.4GPa at room temperature, which is 57% of steel.

3. Low thermal conductivity

The thermal conductivity of titanium is small, 1/5 of low carbon steel and 1/25 of copper.

4. The tensile strength is close to its yield strength

This performance of titanium shows that its yield ratio (tensile strength/yield strength) is high, which means that the plastic deformation of metallic titanium materials is poor during forming. Due to the large ratio of the yield limit of titanium to the modulus of elasticity, the resilience of titanium during forming is large.

5. Non-magnetic, non-toxic

Titanium is a non-magnetic metal and will not be magnetized in a large magnetic field. It is non-toxic and has good compatibility with human tissues and blood, so it is adopted by the medical profession.

6. Strong anti-damping performance

Compared with steel and copper metal, titanium metal has the longest vibration decay time after being subjected to mechanical vibration and electrical vibration. This performance of titanium can be used as a tuning fork, medical ultrasonic pulverizer vibrating element and high-end acoustic speaker vibrating film, etc.

7. Good heat resistance

The new titanium alloy can be used for a long time at a temperature of 600°C or higher.

8. Good low temperature resistance

Low temperature titanium alloys represented by titanium alloy TA7 (T-5Ai-2.5Sn), TC4 (Ti-6Al-4V) and Ti-2.5Zr-1.5Mo, etc., whose strength increases with the decrease of temperature, but the plastic change is not big. It maintains good ductility and toughness at low temperatures of -196℃~253℃, avoids cold brittleness of metals, and is an ideal material for equipment such as cryogenic containers and storage tanks.

9. Inspiratory performance

Titanium is a chemically very active metal, which can react with many elements and compounds at high temperatures. The gettering property of titanium mainly refers to the reaction with carbon, hydrogen, nitrogen, and oxygen at high temperatures.

10. Corrosion resistance

Titanium is a very active metal, its equilibrium potential is very low, and the thermodynamic corrosion tendency in the medium is high. But in fact, titanium is very stable in many media. For example, titanium is corrosion-resistant in oxidizing, neutral and weak reducing media. This is because titanium and oxygen have a great affinity. In the air or in an oxygen-containing medium, a dense, strong adhesion and inert oxide film is formed on the surface of titanium, which protects the titanium matrix from corrosion. Even due to mechanical wear, it will quickly heal itself or regenerate. This shows that titanium is a metal with a strong tendency to passivation. The titanium oxide film always maintains this characteristic when the medium temperature is below 315℃.

In order to improve the corrosion resistance of titanium, surface treatment technologies such as oxidation, electroplating, conversion coating, plasma spraying, ion nitriding, ion implantation and laser treatment have been studied, which have enhanced the protective effect of the titanium oxide film and obtained the hope The corrosion resistance effect. In response to the needs of metal materials in the production of sulfuric acid, hydrochloric acid, methylamine solution, high-temperature wet chlorine and high-temperature chloride, a series of corrosion-resistant titanium alloys such as titanium-molybdenum, titanium-palladium, and titanium-molybdenum-nickel have been developed. Titanium castings use titanium-32 molybdenum alloy, titanium-0.3 molybdenum-0.8 nickel alloy is used for environments where crevice corrosion or pitting corrosion often occurs, and titanium-0.2 palladium alloy is partially used for titanium equipment, all of which are well used Effect.