Application range of titanium and titanium alloy bellows

Titanium is called the metal of the 21st century due to its excellent comprehensive properties. Although the price ratio of titanium and titanium alloy bellows to stainless steel bellows is very high (about 10:1), the life of steel equipment is only 2 to 3 years. Titanium bellows The service life of the tube can reach more than 20a, and there is almost no need for repair costs. From the long-term and comprehensive economic benefits, the use of titanium bellows is still very cost-effective. At present, due to cost and manufacturing technology and other reasons, titanium and titanium alloy bellows can only be used in high-tech industries such as aviation, aerospace and high-energy physics in our country, while chemical and oil refining industries are rarely used. It can be expected that with the development of science and technology in our country, the application of titanium will become more and more extensive.

Titanium bellows are generally used in occasions with high-performance requirements, such as lightweight and high flexibility, and also used in fields with high corrosion resistance requirements. Titanium and titanium alloy bellows have broad application prospects in chemical plants such as saltworks, fertilizer plants, and alkali plants. The chemical industry has high requirements for the corrosion resistance of bellows. Stainless steel can no longer meet the actual production needs. The use of titanium and titanium alloy bellows is a development trend. For example, when alkali plants and chemical plants are used for mother liquor heat exchange, due to the high concentration of CL-in the medium, there is corrosion to stainless steel. The use of titanium bellows can effectively prevent corrosion. For example, a chemical plant in the United States used (254mm) hydroformed titanium wave expansion joints in the pipeline for transporting acetic acid; titanium bellows heat exchanger developed by a Beijing company for the salt chemical industry and marine chemical industry has been used in some chemical plants, The use effect is good.

In the oil refining industry, the most used bellows are the wave expansion joint. Bellows expansion joints are widely used in catalytic cracking units in the oil refining industry. The bellows (wave expansion joints) used in the oil refining industry have high requirements for corrosion resistance. The characteristic is that the pipe diameter is large, the bellows are easy to be corroded, and the damaging effect occurs. The main reason is corrosion damage, which accounts for about 80% of the damage loss of the bellows expansion joint. In recent years, with the increase in the content of corrosive media in crude oil, the development of heavy oil catalytic cracking technology, and the increase in the operating temperature of the device, the working conditions of the bellows have become more severe. The corrugated expansion joints in the catalytic cracking unit of an oil refinery often go through a production cycle. Corrosion damage occurs in a few months or even a few hours of operation and needs to be replaced. This seriously affects the safe operation of the equipment and the performance of economic benefits. An urgent problem for each refinery. Therefore, it should be a development trend to use titanium and titanium alloys to replace stainless steel. A Japanese company has used titanium wave expansion joints in the oil refining industry. Various performance experiments have shown satisfactory results, paving the way for practical applications.
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How does the shrinkage behavior of the titanium tube change?

Titanium tube is similar to other metals. The shrinkage behavior of titanium tube during casting also undergoes a change from liquid to solid state and then to solid-state. This shrinkage behavior is usually divided into volume shrinkage and linear shrinkage. The volume shrinkage reflects the change of the entire volume of the titanium tube during the casting process. Since the total volume shrinkage is equal to the volume of the concentrated shrinkage cavity of the casting plus the volume of the shrinkage porosity, the solidification shrinkage behavior of the alloy casting process is related to the volume shrinkage of the alloy. It determines the characteristics of the shrinkage cavity and shrinkage porosity of drill alloy, which is of great significance for understanding the formation of shrinkage cavity and shrinkage porosity defects of titanium pipe.

Important factors affecting the solidification and shrinkage of titanium tubes include alloying elements, mold materials and mold structures. Because alloying elements affect the crystallization temperature interval of the titanium tube, just like its influence on fluidity, the solidification shrinkage of the titanium tube firstly depends on the characteristics of the added alloying element, that is, the crystallization temperature formed between titanium and alloying elements The size of the interval is related. Eutectic titanium tubes with narrow crystallization temperature intervals have good fluidity and are easy to form concentrated shrinkage cavities, while titanium tubes with wide crystallization temperature intervals have poor fluidity and are easy to form dispersive shrinkage cavities, that is, shrinkage porosity.

Because titanium tube has a series of good physical properties, as an excellent structural material, it can compete with stainless steel and nickel alloy for the scope of application: in many sectors of the national economy, the use of titanium tube increases product life and improves The reliability and productivity of the equipment have speeded up the process and improved working conditions, all of which have achieved significant economic benefits.
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Classification of mechanical properties of titanium materials The properties of metal materials can be divided into:

Mechanical properties: The resistance of metal materials under different external forces, also called mechanical properties. Such as elasticity, plasticity, strength, hardness, toughness, etc. The mechanical properties are stipulated in the standard, you can see the standard, there are high-temperature performance, low-temperature performance, we usually say that the performance is normal temperature performance.

Physical properties: such as electrical conductivity, thermal conductivity, thermal expansion, melting point, magnetism, density, etc.

Chemical properties: such as acid and alkali resistance, corrosion resistance, and oxidation resistance.

The above three properties are collectively referred to as usability.

Process performance: The performance of the material in processing and manufacturing shows the degree of difficulty in processing and manufacturing, such as titanium castability, forge ability, weldability, machinability, heat treatment, etc., the bending of titanium plates, the bending of titanium tubes Flattening and flaring.

Some people confuse physical properties with mechanical properties. They often say that sampling is done for physical testing, but it is actually doing mechanical performance testing. His statement is wrong.

Note: Mechanical properties and physical properties are different concepts

The physical properties are inherent in itself and generally do not need to be tested.
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Clean technology of titanium alloy

Before welding titanium, it is important that the welding joints and welding wires do not have oxide scale, dust, grease, oil, moisture and other potential contaminants. Including these foreign substances in the titanium, weld metal will reduce performance and corrosion resistance. The welding wire packaged by the manufacturer is clean. If the wire looks dirty, it is best to wipe it with a non-chlorinated solvent before use. In severe cases, pickling may be required. All bonding surfaces and surfaces of the substrate must be cleaned at least one inch away from the joint.

The surface of ordinary pickling machines usually only needs to be scrubbed with household thinner or detergent, and then rinsed thoroughly with hot water and air drying. In addition, if there is no residue, use a clean lint-free cloth or cellulose sponge to wipe the weld and adjacent areas with a chlorine-free solvent such as toluene, toluene or methyl ethyl ketone (MEK). These solvents are particularly effective in removing trace amounts of grease and oil. A new stainless steel brush should be used for solvent cleaning. In any case, steel brushes or steel wool should not be used on titanium due to the risk of corrosion resistance caused by embedded iron particles.

The light oxide film, formed by heating in the range of 600°-800°F (316-427°), can be removed by brushing with a new stainless steel wire brush. Light grinding, filing and pickling are also effective. An acceptable acid bath for titanium is to use 35 vol% nitric acid (70% concentration) and 5% hydrofluoric acid (48% concentration) at room temperature. Soaking the welding area for 1 to 15 minutes (depending on the activity of the bathtub) should be sufficient.

Rinse with cold water to remove acid, then rinse with hot water to facilitate drying and complete the cleaning. Heavy scale and oxygen-contaminated surfaces that may exist after high-temperature heat treatment are best removed by mechanical methods. Grinding and sanding or sandblasting are usually used. Although useful, molten caustic baths require care to minimize the possibility of hydrogen absorption. After descaling, pickling should be used to remove all residues and improve surface appearance.

Once cleaned, joints should be carefully stored. Handling should be reduced as much as possible, and welding should be started as soon as possible after cleaning. When not working, the welds should be covered with paper or plastic to avoid the accumulation of contaminants.
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Application of titanium and titanium alloys in dental technology

Pure titanium is a silver-white metal with silver-grey luster. It can be used as a deoxidizer in steelmaking and a component of stainless steel and alloy steel. Titanium powder can be used as a raw material for pigments and paints. It can also be used as electrodes and condensers in power stations and environmental pollution control devices. But the intensity is low. The strength of the titanium alloy is very high. For example, the strength of commonly used titanium alloy Ti-6AI-4V has reached the level of general high-strength steel. Titanium alloy has higher heat resistance, toughness and fracture toughness at low temperature than its titanium material, so it can be used as many industrial parts, such as aircraft engine parts, as part of the original parts of rockets and missiles. In the petroleum industry, it is mainly used as various containers and reactors. Titanium-nickel shape memory alloys have been widely used in instruments. Titanium nitride is close to gold in color and can be used as a decorative material. Titanium and titanium alloys are widely used in the aviation industry and are known as "space metals"; in addition, they are increasingly widely used in the shipbuilding industry, chemical industry, manufacturing mechanical parts, telecommunications equipment, and cemented carbide. In addition, because titanium alloys have good compatibility with the human body, titanium alloys can also be used as artificial bones, dentures, porcelain teeth and medical appliances for fixing various bad bones. Titanium alloy has excellent properties such as light specific gravity, strong corrosion-resistance, strong high-temperature resistance and good weldability, and its application in the dental field is becoming more and more extensive.

Titanium and titanium alloys are widely used as dental implants because of their good mechanical properties and biocompatibility. The neck of the implant is made of titanium and titanium alloy with a smooth surface to facilitate the wrapping of fibrous tissue, forming a good epithelial cuff area and preventing the accumulation of plaque. The porous structure of the implant body increases the surface area of ​​the implant, provides conditions for the attachment and growth of bone tissue, and facilitates the retention of the implant. The cell test results of the ZnHA/TiO2 biological coating prepared in the experiment show that osteoblasts adhere well to the ZnHA/TiO2 coating, the cell proliferation ability is enhanced on the surface of the material, and the better cell attachment inhibits to a certain extent The attachment of bacteria on the surface of the implant.
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Factors of TC4 alloy rod die forging and material extrusion

1: Reasons for cracks in titanium rod extrusion

 Titanium rods and titanium alloy rod blanks have low thermal conductivity, which will cause a great temperature difference between the surface layer and the inner layer during hot extrusion. When the temperature of the extrusion cylinder is 400 degrees, the temperature difference can reach 200 to 250 degrees. Under the combined influence of suction strengthening and the large temperature difference of the blank section, the metal on the surface and the center of the blank produces very different strength and plastic properties, which will cause very uneven deformation during the extrusion process. Large additional tensile stress is generated in the extruded product, which becomes the source of cracks and cracks on the surface of the extruded product.

It can be divided into:

1) Extrusion method. Reverse extrusion is more uniform than forward extrusion, cold extrusion is more uniform than hot extrusion, and lubricated extrusion is more uniform than non-lubricated extrusion. The influence of the extrusion method is realized by changing the friction conditions.

2) Extrusion speed. As the extrusion speed increases, the unevenness of metal flow increases.

3) Extrusion temperature. When the extrusion temperature increases and the deformation resistance of the blank decreases, the uneven flow of the metal increases. During the extrusion process, if the heating temperature of the extrusion cylinder and the mold is too low, and the metal temperature difference between the outer layer and the center layer is large, the unevenness of the metal flow will increase. The better the thermal conductivity of the metal, the more uniform the temperature distribution on the end surface of the ingot.

4) Metal strength. When other conditions are the same, the higher the metal strength, the more uniform the metal flow.

5) Die angle. The larger the mold angle (that is, the angle between the end face of the mold and the central axis), the more uneven the metal fluidity. When a porous die is used for extrusion, the die hole arrangement is reasonable, and the metal flow tends to be uniform.

6) Degree of deformation. The degree of deformation is too large or too small, and the metal flows unevenly.

Solution:

1: When forging with a press under the same unit pressure as forging with a forging hammer. The heating temperature of the blank can be reduced by 50100℃. In this way, the interaction between the heated metal and the periodic gas and the temperature difference between the blank and the mold are correspondingly reduced, thereby improving the uniformity of deformation, the uniformity of the structure of the die forging is also greatly improved, and the consistency of mechanical properties is also improved. .

2: Increase the forging angle and fillet radius and use lubricant: The height of the burr bridge on the forging die is larger than that of steel, and the deformation of the titanium rod is characterized by more difficult to flow into the deep and narrow die groove than steel.

3: Reduce the deformation speed, the area shrinkage rate with the most obvious numerical increase, and the area shrinkage rate is the most sensitive to the structural defects caused by overheating.
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Use of corrosion inhibitor for titanium alloy plate

In reducing inorganic acid and some organic acids, the corrosion rate of titanium alloy plate is relatively fast because it cannot maintain the passive oxide film. Adding corrosion inhibitor is an effective measure to reduce corrosion. Candle inhibitors include precious metal ions, heavy metal ions, oxidizing inorganic foods, oxidizing organic compounds, complex organic corrosion inhibitors, etc. The price of precious metal ions is very high, and they are rarely used as corrosion inhibitors for reducing organic acids; to metal ions, copper ions and iron ions have very obvious corrosion inhibitors, but they need to reach a critical concentration before they can work; Oxidizing inorganic compounds include nitric acid, chlorine, potassium chlorate, potassium dichromate, potassium permanganate, hydrogen peroxide, etc.; oxidizing organic compounds include nitro or nitroso compounds, nitrogen compounds, etc.; complex organic retarders Corrosion agents are different from oxidizing organic compounds. They can inhibit corrosion at any concentration. There is no concept of critical concentration, but the effect is different.

The surface treatment is an effective way to improve the corrosion resistance of titanium alloy plates. Surface treatment methods include cathodic oxidation, thermal oxidation, nitriding and coating techniques. Anodizing, thermal oxidation and the influence of the Xu layer on the crevice corrosion time of the titanium alloy plate. The data shows that the effect of the coating on the corrosion resistance of the titanium alloy plate is the most obvious, even better than the corrosion resistance of Ti—0.15Pd.

The anodic oxidation of titanium alloy plate is usually carried out in 5%-10%(NH4)2sO solution and 25V direct current voltage is applied. The thickness of the anodic oxide film can reach 300-500nm. Anodizing treatment can effectively remove iron contamination on the surface, effectively prolong the passivation time of the titanium alloy plate, and prevent hydrogen absorption caused by ortho iron contamination. Therefore, foreign regulations require that all titanium equipment must be anodized. In order to improve the effect of anodizing, the anodizing solution uses sodium platinum to replace ammonium sulfate, so that the corrosion resistance is better.

The titanium alloy plate can be oxidized into a rutile-type thermal oxidation strand with a thicker and higher crystallinity than the anodized film in the air, and its corrosion resistance is better than that of the anodized film. The thermally oxidized strands of the titanium alloy plate are made at a temperature of 600-700°C and a time of 10-30 minutes. If the temperature is too high or the time is too long, the effect is not good.

Among the coating layers of the titanium alloy plate, the coating removal effect is the best. The coating containing palladium is usually an oxidation coating or a lead alloy coating. The typical preparation method of palladium oxide coating PdO-T102 is to apply PdCL4 and TiCL3 solution to the surface of the titanium alloy plate and heat it at 500-600℃ for 10-50 min. Repeat the operation several times to make the coating thickness reach 1g /M2 or more. The riveting alloying layer is first deposited by electroplating or vacuum deposition of a very thin layer, and surface alloying treatment techniques such as laser remelting surface or ion implantation are carried out, and its adhesion and corrosion resistance is better than that of the oxide coating.

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The application status of titanium alloy in golf clubs

Golf is largely affected by the materials of the golf equipment. Therefore, different clubs are required to be used in different places and situations on the golf course. The clubs are also designed into a variety of shapes of different lengths, which can be roughly divided into three categories. : Wood, iron and putter.

1. Titanium alloy wood club head

Wood rods are used for opening and long-distance shots. In order to make the ball hit more straight and farther, the weight of the wood head needs to be maintained at 200g, and the volume should be increased as much as possible to increase the ball and wood head. Contact area.

Titanium alloy has low density, high strength and good corrosion resistance. Under the same weight, the hollow ball head made of titanium alloy is 2-3 times larger than the stainless steel ball head, and the mass can be evenly distributed around the ball head, so that the player can hit the ball farther and straighter.

2. Titanium alloy iron head

Irons are mainly used for mid-range and precise shots, which require higher accuracy. When the ball is in contact with the striking surface, the striking surface must provide enough friction to increase the spin rate after the ball is hit. In this way, the rolling of the ball can be better controlled when hitting the ball, making the hitting more accurate.

Some companies add a titanium-diamond composite to the club’s striking surface to increase the coefficient of friction through diamond particles on and near the surface of the striking surface. But this will make the ball head overweight by nearly 30g, otherwise, the ball head will become smaller and even difficult to hit the ball. The iron head using titanium alloy as the body can be embedded with diamond composite on the same volume of the striking surface, while the quality remains unchanged.

3. Titanium alloy putter head

Putting is used to hit the ball into the hole on the green [i]. The titanium-tungsten putter series launched by a company uses titanium alloy in the middle body of the ball head, with counterweight tungsten at both ends [ii]. After the tungsten block is inlaid with the body, it can be made to reach Dense combination.

The density of titanium alloy is generally 4.51g/cm, and the density of weight tungsten is about 19g/cm so that 70% of the mass of the ball head is concentrated at the two ends. This design can increase the rotational inertia of the ball hitting surface by about 50%. The higher the rotational inertia, the putter head can prevent the twisting caused by not hitting the center of the ball head. This putter has more obvious advantages on the green than the traditional putter.

market expectation

With the rapid growth of China's economy and the rapid improvement of people's living standards, golf has been favored by the majority of sports enthusiasts. Especially for middle and high-level consumer groups, golf is also a way of business social interaction in addition to physical fitness. China will become another consumer market with huge potential besides the United States and Japan.

Titanium alloys have entered the golf equipment industry for more than 20 years, and various titanium materials have been used in golf heads in a comprehensive manner. But the price of titanium alloy ball heads is higher, almost three times that of stainless steel ball heads, so the ball head market is still dominated by stainless steel. How to improve titanium alloy casting technology and reduce costs will become the main research direction of golf head manufacturers in the future.

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Application function of titanium plate and titanium alloy plate in the petrochemical industry

Titanium alloy plates and titanium plates are mainly used to manufacture various containers, reactors, heat exchangers, distillation towers, pipes, pumps and valves in the petrochemical machinery manufacturing industry. Titanium can be used as a titanium cathode and condenser in power stations, as well as environmental pollution control devices. The hardness of steel is higher than that of titanium plate, but the specific strength or tensile strength of titanium alloy is higher than that of high-quality steel. Titanium alloy has good heat resistance, low-temperature toughness and fracture toughness, so it is mostly used as aircraft engine parts and rocket and missile structural parts. Titanium alloy can also be used as fuel and oxidant storage tanks and high-pressure vessels. Now there are automatic rifles, mortar seat plates and recoilless gun launch tubes made of titanium alloy.

1. Memory function

Titanium-nickel alloy has one-way, two-way and omnidirectional memory effects at a certain ambient temperature, and is recognized as the best memory titanium alloy. Pipe joints used in engineering for the hydraulic system of fighter jets; oil pipeline systems for oil complexes; 500mm diameter parabolic mesh antennas made of 0.5mm diameter wires for aerospace vehicles; used in medical engineering for snoring Treatment; Titanium plates are made into screws for fracture healing. The above applications have achieved obvious results.

2. Superconducting function

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

3. Hydrogen storage function

Titanium-iron alloy has the characteristic of absorbing hydrogen, which can store a large amount of hydrogen safely, and release the 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.

Titanium dioxide, the oxide of the titanium plate, is a white powder and a better white pigment, commonly known as titanium white. In the past, the main purpose of mining titanium ore was to obtain titanium dioxide. Titanium white has strong adhesion, is not easy to undergo chemical changes, and is always white. Especially valuable is that titanium dioxide is non-toxic. It has a high melting point and is used to make refractory glass, glaze, enamel, clay, high-temperature resistant laboratory utensils, etc.

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Analysis of heat transfer performance and market prospect of TC4 seamless titanium tube

TC4 titanium alloy is currently one of the most widely used titanium alloys. It has high strength and good corrosion resistance. However, it is difficult to see seamless titanium tubes made of TC4 in the seamless titanium tube market at home and abroad. The titanium tube is thinner than other traditional metal pipe fittings, and the heat exchange effect is better. The TC4 pipes on the market are mainly high-strength thick-walled pipes produced by hot extrusion or oblique perforation.

In order to solve the key technology of TC4 seamless tube cold-rolling forming, a series of researches were carried out jointly by schools and enterprises. For example, the direct cold-rolling forming process is used to produce high-strength titanium alloy tubes, which not only greatly reduces the production cost but also meets the requirements for high-performance titanium alloy applications.

The billeting method with different deformations is adopted, and the tube blank is rolled into a tube with a total deformation of 70% after two passes and three passes, respectively. Carry out 800℃×1h vacuum annealing between passes. The cooling method is furnace cooling to 500℃ and then air cooling to room temperature to observe the changes in structure and properties. Concluded: 

In the case of small deformation billeting, the wall thickness deviation is small, and the surface roughness is gradually reduced; for large deformation billeting, the wall thickness deviation is large, which will affect the wall thickness deviation of the pipes obtained by subsequent passes. In the case of the same total deformation, the more rolling passes, the greater the elongation and hardness of the pipe, and the higher the strength.

In summary, the small deformation billet has little effect on the anisotropy of the pipe; the anisotropy of the mechanical properties in multi-pass rolling has certain fluctuations, and the material flow is strip-shaped when rolling with large deformation. When rolling with small deformation, the material flow is in a bundle shape. Under the condition of the same heat treatment conditions between passes and subsequent rolling processes, the structural distortion of the pipe obtained from the large deformation billet is more serious.

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Titanium parts used in automobiles

The use of titanium in automobiles is mainly divided into two categories. The first category is to reduce the mass of internal combustion engine reciprocating parts (for internal combustion engine parts that reciprocate, even reducing the mass of a few grams is important); the second category It is used to reduce the total mass of the car. According to the design and material characteristics, titanium is mainly distributed in engine components and chassis parts in new-generation cars. In the engine system, titanium can be used to make parts such as valves, valve springs, valve spring holders and connecting rods; in the chassis parts are mainly springs, exhaust systems, half shafts and fasteners.

According to the information, in addition to the above mentioned key points, there are rocker arms, suspension springs, piston pins, turbocharger rotors, fasteners, lug nuts, car stop brackets, door projection beams, brakes Caliper piston, pin, clutch disc, pressure plate, shift button, etc.

Ways to reduce the cost of titanium alloys

Although titanium and titanium alloys entered the field of automobile manufacturing as early as the 1950s, the development was relatively slow. The main reason was the price factors. A lot of work. To meet the needs of the automotive industry.

Titanium has a high melting point and very active chemical properties. It has a strong chemical affinity with elements such as O, H, N, and C, which makes it difficult to extract pure titanium. The Kroll magnesium reduction method commonly used in industry produces sponge titanium.

With the advancement of titanium smelting technology, it is an effective method to reduce the cost of raw materials to add the leftovers and scraps generated during the production and processing of titanium as furnace charge after a series of treatments to achieve recycling. The practice has shown that every 1% of residual titanium used can reduce the production cost of titanium ingots by 0.8%. If an electron beam cooling bed furnace or a plasma beam cooling bed furnace is used for smelting, not only can the metallurgical quality of titanium ingots be improved, but also recycled charge can be used in large quantities, effectively reducing the cost of ingot casting.

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The rolling process of TC4 titanium alloy material for aviation

Titanium alloy materials have the characteristics of high specific strength, high yield ratio, high deformation resistance, excellent process plasticity and superplasticity. Titanium rod products are widely used in various fields of the national economy. There are titanium alloy rods in aerospace aircraft. Rivet connector made after cold heading. At present, the analysis of the heat treatment and microstructure of the small diameter titanium alloy bar (≤Φ10mm) hot continuous rolling and rolled bar is relatively lacking. In response to this problem, the technicians performed high-temperature compression tests on the TC4 titanium alloy on the Gleeble500 thermal simulator. Analyze the flow stress curves of TC4 titanium alloy at different temperatures and different strain rates, provide necessary process parameters for hot continuous rolling of titanium alloy bars, and analyze the structure and performance of the rolled products.

The results of the study found:

 1. From the perspective of reducing deformation resistance, improving material formability, and ensuring final rolling microstructure and performance, the best rolling temperature for TC4 titanium alloy bars is 950℃, which is slightly lower than the phase transformation temperature of TC4 titanium alloy; The best strain rate is 1s-1, so as to ensure that the work hardening caused by the strain and strain rate during the deformation process is small, and the plasticity of the material is fully utilized;

2. Φ12 and Φ6mm bars are obtained by hot continuous rolling of a three-high Y-shaped mill. The structure of Φ12mm bars is equiaxed primary α phase + α strip + β transformation structure, and the crystal grain diameter is about 3-10μm; Axis primary α phase + thin strip α phase + β transformation structure, the grain size does not exceed 1 μm. It can be seen that as the cumulative deformation increases, the grain size decreases significantly;

 3. The structure and mechanical properties of the TC4 titanium alloy bar obtained by the hot continuous rolling of the three-high Y-shaped mill meet the technical requirements. The rolling equipment, rolling process parameters and heat treatment system used in the test can produce titanium alloy bars that meet the requirements, thereby providing a technical basis for further industrial production.

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Application advantages of TC21 titanium alloy rods and forgings in the aviation field

In order to meet the requirements of damage tolerance design, the international community attaches great importance to the development of medium-strength or high-strength titanium alloys with high fracture toughness and very slow crack growth rate, namely high damage tolerance titanium alloys (or damage tolerance titanium alloys). At present, damage tolerance titanium alloys with high fracture toughness and low crack growth rate have been developed abroad, namely, low gap Ti-6Al-4V (β-ELI) and Ti-6-22-22S. A new two-phase high-strength and high-toughness TC21 alloy developed in China.

Ti-6Al-4V (β-ELI) belongs to the high damage tolerance type titanium alloy with 900MPa strength level. The content of interstitial elements C, O, N and impurity element Fe in the alloy is significantly less than that of Ti-6A1-4V alloy. Reduce the strength of the alloy, but improve the toughness of the alloy. The main performance of alloy forgings can reach: o.≥895MPa, 00.2≥ 795MPa, 8≥8%, w≥15%, ic≥75MPa·m1/2Ti-6Al-4V(β-ELI) alloy has been applied to Boeing 777 passenger aircraft The stabilizer is connected to the joint and the body of the F/A-22 aircraft.

Ti-6-22-22S (Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.2Si) alloy is a type of α+3 titanium alloy for aviation developed by RMI Corporation of the United States in the 1970s. By adding Si, the alloy can maintain high strength at medium temperature. The advantages of this alloy are: the typical toughness can reach 100mm in diameter; and the excellent superplastic forming performance. Ti-6-22-22S alloy has been selected by the US Air Force as the material for F-22 fighters. For example, the wing chord of the lower keel of the aircraft is Ti-6-22-22S alloy forgings, and the alloy is also planned to be used X-33 trainer, reusable launch vehicle and joint attack fighter.

TC21 (Ti-Al-Mo-Sn-Zr-Cr-Si-X series) titanium alloy is a new two-phase, high-strength, high-toughness, and high-damage-tolerant titanium alloy with my country's independent intellectual property rights. At present, the large bars of this alloy below D300mm have the conditions for stable batch supply. TC21 titanium alloy has the properties of high strength, high toughness, high weldability and low fatigue crack growth rate. Its comprehensive mechanical properties are more widely used than Ti-6-22-22S and Su-27 series aircraft used in American F-22 aircraft. The BT20 titanium alloy is more excellent, especially with very excellent electron beam welding performance, which is suitable for manufacturing important load-bearing components of large integral frame beams of aircraft.

Titanium has more than 30 years of experience in damage tolerance design abroad, but my country started late in damage tolerance design. With the rapid popularization of damage tolerance design technology for domestic aviation systems, the demand for high damage tolerance titanium alloys will become increasingly urgent. my country needs to deeply study the damage tolerance performance mechanism of titanium alloys and improve the characterization and evaluation technology of damage tolerance performance.

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