Titanium materials can be used in the aerospace industry

As a new type of manufacturing method, additive manufacturing (also known as 3D printing) has the advantages of fast manufacturing, saving materials, and user-customizable. It has attracted more and more attention in the fields of aviation, aerospace, automobiles, and medical equipment. Due to the needs of industrial applications, the fatigue performance of additive manufacturing materials (especially the ultra-high cycle fatigue performance) and the corresponding fatigue mechanism have become one of the scientific problems that need to be solved urgently in the research field of additive manufacturing.

The Research Group of Metallic Materials Microstructure and Mechanical Properties of the Institute of Mechanics, Chinese Academy of Sciences has recently carried out a series of research work on the fatigue characteristics of additively manufactured titanium alloys (Ti-6Al-4V). The research team conducted fatigue performance tests on additively manufactured titanium alloys and obtained the high-cycle and ultra-high-cycle fatigue properties of the material. Through the observation of the fatigue fracture, it is reported that the high-cycle and ultra-high-cycle fatigue cracks of the additive-manufactured titanium alloy all originate in the internal holes and unfused defects of the material, and form a new phenomenon of "fish-eye" fracture morphology. This is quite different from the fatigue characteristics and cracks initiation mechanism of traditional forged metal materials. According to the distribution characteristics of crack source size, a statistical correlation between fatigue performance and crack size is constructed. Based on the fatigue life data of the material and the size of the fatigue crack defect, a probability statistical P-S-N analysis was carried out to obtain the relationship between the high-cycle and ultra-high-cycle fatigue failure probability of the material, the fatigue life, and the applied load. In addition, in order to further explore the characteristics of fatigue crack growth, the research team used an in-situ fatigue loading device to obtain Ti-6Al-4V crack growth rates at different temperatures and different preparation orientations, revealing the fatigue crack growth of titanium alloys with different orientations. Mechanisms.

This research not only provides effective fatigue performance data for engineering applications of additive manufacturing of titanium alloys. At the same time, it has laid a theoretical foundation for exploring the crack initiation and propagation mechanism of additive manufacturing of titanium alloys.
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What are the factors that affect the welding performance of titanium and titanium?

(1) High strength. The density of titanium alloy is generally about 4.5g/cm3, which is only 60% of steel. The strength of pure titanium is close to that of ordinary steel. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloy is much greater than that of other metal structural materials. See Table 7-1, which can produce parts and components with high unit strength, good rigidity, and light weight. At present, titanium alloys are used in aircraft engine components, skeletons, skins, fasteners, and landing gear.

(2) High thermal intensity. The service temperature is several hundred degrees higher than that of aluminum alloy. It can still maintain the required strength at medium temperature. It can work for a long time at a temperature of 450～500℃. These two types of titanium alloys are still very high in the range of 150℃～500℃. Specific strength, while the specific strength of aluminum alloy decreases significantly at 150°C. The working temperature of titanium alloy can reach 500℃, while that of aluminum alloy is below 200℃.

(3) Good corrosion resistance. Titanium alloy works in moist atmosphere and sea water medium, its corrosion resistance is far better than stainless steel; it is particularly resistant to pitting corrosion, acid corrosion, and stress corrosion; it is resistant to alkali, chloride, chlorine organic substances, nitric acid, sulfuric acid It has excellent corrosion resistance. However, titanium has poor corrosion resistance to reducing oxygen and chromium salt media.

(4) Good low temperature performance. Titanium alloys can still maintain their mechanical properties at low and ultra-low temperatures. Titanium alloys with good low temperature performance and extremely low interstitial elements, such as TA7, can maintain a certain degree of plasticity at -253°C. Therefore, titanium alloy is also an important low-temperature structural material.

(5) High chemical activity. Titanium has high chemical activity, and produces a strong chemical reaction with O, N, H, CO, CO2, water vapor, ammonia, etc. in the atmosphere. When the carbon content is more than 0.2%, it will form hard TiC in the titanium alloy; when the temperature is higher, it will also form a hard surface layer of TiN when it interacts with N; when the temperature is above 600℃, titanium absorbs oxygen to form a hardened layer with high hardness ; When the hydrogen content increases, an embrittlement layer will also be formed. The depth of the hard and brittle surface layer produced by absorbing gas can reach 0.1-0.15 mm, and the degree of hardening is 20%-30%. Titanium also has a high chemical affinity and is easy to adhere to the friction surface.

(6) The thermal conductivity is small, and the elastic modulus is small. The thermal conductivity of titanium λ=15.24W/(m.K) is about 1/4 of nickel, 1/5 of iron, and 1/14 of aluminum. The thermal conductivity of various titanium alloys is about 50% lower than that of titanium. The modulus of elasticity of titanium alloy is about 1/2 of that of steel, so its rigidity is poor and easy to deform. It is not suitable to make slender rods and thin-walled parts. The springback of the machined surface during cutting is very large, about 2～3 of stainless steel. Times, causing severe friction, adhesion, and adhesive wear on the flank of the tool. Alloying of Titanium Titanium alloy is an alloy composed of titanium as the base and adding other elements. Titanium has two isomorphs: close-packed hexagonal α titanium below 882°C, and body-centered cubic β titanium above 882°C.
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Advantages of titanium plate

Titanium tube is a highly active metal, and its activity increases with increasing temperature.

Titanium tubes and their alloys will interact with oxygen when heated in air or an oxygen-containing atmosphere. When heated below 428℃, a protective oxide film is formed. When the temperature rises, the thickness of the oxide film increases. When the temperature is above 538℃, the oxide film begins to lose its protective effect. Oxygen diffuses through the film into the metal, forming obvious gas infiltration. Floor. If it rises above 815°C, a loose oxide scale will form on the surface of the titanium alloy.

In order to prevent the titanium alloy from oxidizing, absorbing hydrogen, and other trace element pollution during superplastic forming, technical measures need to be taken to make the formed titanium alloy parts have excellent properties.

At present, the main measures are coating protection, vacuum heating, and inert gas (argon) protection.

1. Coating protection law

After cleaning, the surface of the formed blank is coated with a protective coating of a certain thickness. After the part is de-molded, the coating is removed by alkaline washing, acid washing, or sand blowing.

The coating should have the following main properties:

a. High temperature resistance, can be used under high temperature of 750-1050℃;

b. It should have a certain lubricating effect to prevent the blank from being scratched during forming;

c. The coating can be firmly attached to the surface of the blank under the working temperature;

d. Easy to remove after heating;

e. No harmful substances, no pollution to the environment and harm to human health.

The coatings that have been identified as suitable for superplastic forming of titanium tubes and titanium alloys are: Ti-2 alcohol-soluble preparations can be used in conjunction with Ti-3 graphite lubricants, suitable for hot forming at 750-1050°C; KBC-12 Water-soluble preparation, can be used in conjunction with graphite water agent.

2. Vacuum forming

For titanium pipes, vacuum forming is the most ideal for β-type titanium alloys with thinner parts, higher requirements for surface brightness, and stronger sensitivity to hydrogen embrittlement.

Vacuum forming does not necessarily require expensive vacuum heating equipment. As long as a sealed space is created between the blank and the upper and lower cavities of the mold, the air in the upper and lower cavities is gradually extracted by a vacuum unit during the heating process, especially when the temperature is above 400℃ to the forming temperature, the temperature of the upper and lower cavities of the mold When the vacuum degree is above 10^(-3) Torr, the valve of the pipeline is changed during forming, and the forming purpose is achieved by filling with argon gas. This method is used in the forming of the titanium foil corrugated board, and satisfactory results are obtained. When the vacuum degree is controlled at 10^(-3) Torr, the hydrogen content is lower than the standard requirement. When the vacuum degree reaches 10^(-5) Torr, a bright surface part can be obtained.

In addition, for parts with medium thickness and no higher requirements for surface and concave brightness, vacuum argon protection can also be used to test this aspect in the formation of spherical gas cylinders, and the effect is also good.
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Where is the application range of titanium standard parts?

With the further development of the aerospace industry and the continuous exploration of the deep space field, the performance requirements of cryogenic materials for spacecraft structural parts have further increased.

On the one hand, the spacecraft structural materials must have sufficient strength and toughness and excellent thermal properties at low temperatures; on the other hand, considering the complexity of the shape of the spacecraft structural parts, the materials must have good machinability.

Compared with traditional low temperature materials, titanium alloy has a higher yield strength at low temperatures, which is more than 3 times that of stainless steel, and its density is only 1/4 to 1/2 of that of stainless steel. In addition, titanium alloy also has a series of advantages such as low thermal conductivity, small expansion coefficient, and non-magnetic, so it is very suitable as a new low-temperature material in the aerospace field.

At present, low-temperature titanium alloys have been initially used in the field of liquid rocket engines, mainly as structural materials such as hydrogen-oxygen engine hydrogen storage tanks, hydrogen pump impellers, etc., greatly improving the thrust-to-weight ratio, working life and reliability of liquid rocket engines. The problem with the application of low-temperature titanium alloys is that the elongation and fracture toughness of titanium alloys are greatly reduced in low-temperature environments, and they show obvious low-temperature brittleness. Therefore, how to reduce the low-temperature brittleness of titanium alloys and improve the toughness and plasticity of titanium alloys under low-temperature conditions becomes low Titanium alloy research is the top priority.

Scholars at home and abroad have conducted a lot of research to solve this problem, and found that two methods of reducing the content of interstitial elements such as C, H, O and reducing the content of aluminum element can effectively improve the low-temperature performance of titanium alloys. Through these two methods, a series of new low-temperature titanium alloys with excellent properties have been developed at home and abroad.

The former Soviet Union was committed to the development and application of low-temperature titanium alloys. By reducing the content of aluminum, the former Soviet Union has developed a series of low-aluminum low-temperature titanium alloys, of which OT4 and BT5-1 are widely used. OT4 alloy has been used in spacecraft orbital docking parts, liquid rocket pipes and combustion chamber structural parts; BT5-1 alloy has been used in the manufacture of liquid hydrogen containers. In order to further improve the impulse driving ratio of liquid rocket engines, a Russian research institute conducted research and development of high-strength, high-plasticity, low-temperature titanium alloys suitable for extremely low temperature environments at -253 ℃.

The research on low-temperature titanium alloys in the United States has mainly focused on the α-type titanium alloy TA7 ELI (Extra low interstitial) and the α+β-type titanium alloy TC4 ELI. By reducing the content of interstitial elements, the strength and toughness of the two titanium alloys at extremely low temperatures have been significantly improved. TA7 ELI, as a near-α-type titanium alloy, still has good toughness, low thermal conductivity and notch sensitivity at low temperatures of 20 K. It has been successfully used in cryogenic vessels, cryogenic pipelines, and liquid rocket engine impellers. structure. In the Apollo project, TC4 ELI has been widely used as the main material of liquid hydrogen containers and liquid hydrogen pipes and has achieved good results. In addition, American scholars have also carried out basic research on a series of problems such as the fracture mechanism of low-temperature titanium alloys and hydrogen embrittlement, and obtained the mechanical properties and fracture mechanism data of various low-temperature titanium alloys such as TA7 ELI and TC4 ELI. The further development and application of titanium alloy laid the foundation.
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Application of titanium in transplantation

Because titanium alloy has the characteristics of high deformation resistance and poor plasticity, it is very difficult to use conventional plastic processing technology. For example, in the production of titanium alloy rods and titanium wires, due to their large variety and low output, it is difficult to organize the production with the continuous rolling of small bar and high-speed wire rod mills used in modern steel production. Due to the particularity of titanium alloy rod and titanium wire processing, compared with ordinary metals under the same conditions, its deformation resistance is high, widening is easy to be ears, the temperature range suitable for processing is narrow, and it is difficult to bite, so it adopts backward rows. In the production of high-speed rolling mills, it is difficult to guarantee the product quality in terms of product size or organization performance.

This production line implements low-temperature controlled rolling. Because the rolling temperature range of titanium alloys is narrow, the entire line is controlled by cooling the rolling piece and controlling the rolling speed. According to the rolling temperature range of the rolling piece, you can choose to perform water cooling or not. Perform water cooling. The production line adopts a special cooling system to control the temperature of the rolls and rolling pieces, and the closed-loop control is performed uniformly by the console, thereby ensuring the stability of the process and the quality of the rolled products. According to different steel grades, diameters and rolling speeds of the products produced, the console selects different cooling parameters, and adjusts the cooling temperature of the rolls and rolling pieces by adjusting the water volume.

At present, due to the backward processing methods, high-quality titanium alloy rods and titanium wires are scarce. Imports are mainly used to meet the domestic demand for high-quality titanium alloy rods and titanium wires. Therefore, it is of practical significance to establish a titanium alloy rod and titanium wire production line, and to introduce advanced new technology into the titanium alloy rod and titanium wire production line. It can meet the needs of materials such as titanium alloy rods, titanium wires and other materials in the fields of national defense, aerospace, and automobiles. Compared with conventional titanium wire and titanium bar rolling production lines, this production line has the following advantages:

1. It can obtain higher size and shape accuracy, thereby reducing the difficulty of finishing, reducing material consumption and processing costs, and meeting the needs of titanium alloy wire and rod in various fields. According to the user's dimensional accuracy requirements, different numbers of stands can be combined for rolling;

2. The process is flexible and the operation is convenient, and the process regulations can be changed according to the needs to improve the operation rate;

3. The production process is short, the number of holes and the number of frame replacements are reduced, and the operation rate is improved;

4. Rolled by a three-high Y-shaped rolling mill, the rolled piece is in a state of three-way compressive stress, and the deformation conditions are good;

5. The pass type has high commonality, realizes the free rolling of certain specifications, and increases the product specifications;

6. The surface quality of the rolled piece is good, with less cracking and less splitting, which reduces the accidents of continuous rolling stock, so the yield rate is high.

7. The frame is small in size, light in weight, easy to adjust and transport, can save roll changing time, compact structure layout, and small footprint;

8. The rolling speed output and feedback of the entire rolling process is controlled by PLC through the DC speed regulator, the control procedure is simplified, the rolling speed control precision is high, and the speed adjustment is simple and rapid;

9. Adopting modular design, the equipment is easy to manufacture and maintain, which reduces equipment cost and maintenance cost.

Therefore, it is possible to popularize and apply the continuous rolling technology of titanium alloy wire and titanium alloy bar.
ASTM B265 TA6V Titanium Plate     Titanium Rotary Sputtering Target     Ti 15333 Titanium Strip     Ti 7-4 Titanium Bar

What should be paid attention to in the design and manufacture of titanium heat exchangers?

Titanium and titanium alloy materials have high strength, good plasticity and toughness, and have sufficient corrosion resistance and high temperature strength. They are widely used in aerospace, shipbuilding, and chemical industries. Although the one-time investment of titanium equipment is huge, the reliability and service life of the equipment are greatly improved, and the economic benefits are obvious. At present, titanium alloy pipes are increasingly used in various industries, such as petroleum, chemical, energy and other industries, as applied materials in the field of ship equipment and seawater desalination technology. Research work on the weldability and welding process development of titanium and titanium alloys has received extensive attention.

my country's titanium industry has made great progress in the development process of the past few decades. Relevant departments attach great importance to the development and research of titanium and titanium alloy application technology, especially the application technology of marine titanium alloy, which has a significant increase in the consumption of titanium alloy. At present, the marine titanium alloys used in our country include TA2, TA16 and TA17, etc., which have been applied to a certain extent on ships. Most of the research on the performance of these titanium alloy products stays in the basic performance research, such as stretching, bending, etc., and there is no data that can be evaluated in depth. In addition, there are few reports on the research of titanium alloy pipelines, and it is necessary to continue to invest in titanium alloy scientific research. Funds, to carry out low-cost technical research, while ensuring that the product has good performance, can further reduce the processing and manufacturing costs of the product, and at the same time, it is necessary to conduct experimental research in a specific marine environment to accumulate more data to support the titanium alloy crafts improvement.

Application of titanium and titanium alloys in the field of ships

The superior performance of a ship indicates the strength of the navy's combat effectiveness. The ship is a platform for maritime transportation and combat, and is the most important equipment of the navy. Therefore, the material properties of the warship must be very good, while reducing the cost of service, ensuring the operation and maintenance of the ship system, and enhancing the combat capability of the ship. Titanium alloys have excellent mechanical properties, corrosion resistance, erosion and corrosion resistance, and high strength. They are used on ships to improve the reliability and effectiveness of ships and achieve weight reduction and load increase. At present, there have been a large number of experience in the use of pipeline materials in ships to prove that the service life of traditional materials is limited. Pipes made of steel pipes have a service life of only 1 to 2 years. Pipes made of copper-nickel alloy materials have a service life of only 1 to 2 years. 6 to 8 years, while the pipes made of titanium alloy materials have a service life of more than 40 years.

After decades of development, the level of titanium alloys for ships in China has been greatly improved, and a titanium alloy system for independent ships has been formed. Different ships have different strength requirements. Titanium alloys of different strengths are used in different parts, mainly for Heat-resistant and corrosion-resistant parts and special marine machinery in ship power engineering. Titanium alloys are widely used in ships, including hull structures, propulsion systems, power systems, auxiliary systems and special equipment. It can be said that titanium alloy materials can be used for all large equipment and components except for ship accessories and cabin facilities.
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Performance requirements for titanium containers and titanium alloy tubes for petrochemical industry

Titanium plate has the characteristics of low density, high specific strength, and corrosion resistance, and has great potential for application in the automotive industry. The use of titanium and titanium alloys on cars can save fuel, reduce engine noise and vibration, and improve life span. However, for a long time, automotive materials have always been the country for materials such as steel and Al. In order for Ti materials to enter the automotive market, in addition to its own functional advantages, costs must be further reduced to a level acceptable to the automotive industry. Ti titanium plate metallurgical parts for automobiles are a very promising category, but due to the current constraints of cost and other factors, the application and implementation of metallurgical parts are slow. Using leading titanium plate metallurgy technology to prepare Ti titanium plate metallurgical parts can not only greatly reduce the cost, but also help the promotion of Ti and its alloys in the automotive industry, making it another major application after the aerospace industry category. The development of low-cost titanium and its alloy titanium plates can provide low-cost materials for metallurgical parts of titanium and titanium plates for automobiles. Judging from the existing skills, the sponge Ti powder method, the hydrogenation dehydrogenation method and the metal hydride restoration method are mainly suitable for the automobile industry.

1. Sponge Ti powder method

This is currently a way to meet the needs of the automotive industry in terms of cost. The first step is to use the traditional production sponge Ti and the residual material in the process to crush it; the obtained titanium plates are often relatively coarse and rich in content. Cl element. U.S. Huachang Company chooses the gas phase method to introduce TiCl4 and Mg vapors into a tube furnace at 850°C successively to quickly produce fine Ti powder and MgCl2, but it is difficult to separate such fine powder from MgCl2, and the content of O is high; Japan creates one The spray response method sprays the gas onto the liquid Mg to generate particles. The test shows that about 100 grams of Ti powder with a particle size of tens of microns can be prepared for every 100 grams of Mg and 400 grams of TiCl4, and the production power has increased by 2 times. , The cost is reduced by 50%, and it is expected to be used as the material for titanium metallurgical Ti products.

2. Hydrodehydrogenation method

This method is due to the wide planning of the titanium plate size, low cost, less stringent requirements for materials, and easier technology to complete. Through years of improvement and implementation, it has become the primary method for preparing Ti powder at home and abroad. However, the titanium plates prepared by this method tend to have a high content of O, N, etc. The Northwest Research Institute of Nonferrous Metals in China selected hydrogenation and dehydrogenation technology to hydrogenate and dehydrogenate the ingots and produced high-quality titanium plates with low O, N, and Cl. It has outstanding functions and has been able to produce O content of less than 0.20%. Titanium plate has been mass-produced, and it is expected to supply stable titanium plate for metallurgical parts of automobile titanium plate.

3. Metal hydride restoration method

TiCl4 can be restored with hydrogen at 3500°C, and TiO2 can be restored with carbon heat above 1800°C. In order to reduce the reaction temperature, the former Soviet Union scientists proposed to use CaH2 to restore TiO2 and TiCl4, which can be carried out at a temperature of 1100 to 1200 ℃, the reaction generates TiH2, and then de-H to obtain Ti powder. Because this method does not have a Cl element to participate in the reaction, it is possible to obtain a titanium plate with extremely low Cl content. Although the Ti powder produced by this method has a higher H content, it is reported that the presence of a small amount of H is beneficial to the sintering of the titanium plate and the improvement of the microscopic arrangement, and can be completely removed in the subsequent vacuum sintering and annealing process.
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