Environmental requirements for storage of titanium rods

Principle of thermal spraying:

The particle stream atomized by the heat source and in the molten state hits the purified and rough substrate surface at a high speed to form the required coating. The particles will be deformed when they hit the surface of the substrate, relying on the so-called "embedding" effect to form a coating with a layered structure. With a large number of "overlapped continuous deposition" of plastic particles, the combination of particles should be mostly mechanical, and there must be a certain number of holes. At the same time, if spraying is carried out in the air, there may be oxide inclusions in the coating.
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Technical requirements for the production of titanium alloy sheet

Titanium rods and titanium alloys have high chemical activity. Titanium rods and titanium alloys easily react violently with oxygen, nitrogen and other oxygen-containing gases at high temperatures. When heated in the air, the surface of the blank forms an oxide scale and a surface gettering layer. Titanium rods and titanium alloys are easy to absorb hydrogen when heated, which causes difficulties in the processing of certain types of titanium alloy materials.

Titanium rods and titanium alloys have poor thermal conductivity. The thermal conductivity of titanium rods and titanium alloys is usually only 1/15 of that of alloys and 1/5 of that of steel. The lower thermal conductivity results in a large temperature difference between the ingot and billet section in the hot B inch, which produces a large thermal response, and cracks will form in severe cases. Therefore, the heating speed must be limited, and the temperature change, deformation speed, Deformation rate, deformation equipment.

Polycrystalline transformation of titanium rods and titanium alloys. Titanium has a-β phase transition. Heating to p temperature can significantly increase plasticity and reduce deformation resistance, but the deformation of β zone is not good enough to obtain a structure with good performance.

The cold deformation ability of titanium alloy is low. Cold working deformation of most titanium alloys is difficult. A little preheating (to 200~300T) can significantly reduce deformation resistance and improve plasticity.

Titanium is easy to bond and deform tools. This tendency tends to deteriorate the surface quality of the processed material, and puts forward more stringent requirements on the deformed tools and molds and process lubrication.

High yield ratio and low elastic modulus. Straightening in a cold state is very difficult.

The above processing characteristics should be fully considered when formulating the production process.
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High temperature oxidation of titanium

1.1 Oxidation of pure titanium

When the temperature is below 500℃, the performance of pure titanium is relatively stable. However, as the temperature continues to increase, oxygen continues to penetrate into the titanium lattice and react with the titanium matrix, forming a large amount of rutile structure on the surface of the titanium material. TiO2 oxide. The rutile TiO2 structure is loose and easy to crack and fall off, causing the titanium material to re-expose the fresh surface, that is, the high temperature oxidation behavior of the pure titanium material can be regarded as the repeated layered peeling of the surface oxide film.

1.2 The influence of alloying elements on the oxidation performance of titanium alloys

The addition of Al, Cr, Si and other alloying elements will not only change the mechanical properties of the titanium alloy, but also affect its resistance to high temperature oxidation. Among them, when the content of Al element in the titanium reaches a certain concentration, the oxyphilic Al element will preferentially react with oxygen, forming a continuous, dense and stable Al2O3 oxide film on the surface of the titanium base, which in turn has a better effect on the base material. Good resistance to high temperature oxidation. On the one hand, the existence of Cr element can promote the formation of Al2O3 oxide film. On the other hand, the miscible zone containing Cr phase can form a certain diffusion layer. When the titanium base is covered with Al protective coating, the diffusion layer can effectively inhibit Ti, Al The inter-diffusion of the elements prolongs the service life of the coating.
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Medical titanium rods, performance advantages and main applications of medical titanium materials

Titanium and titanium alloys are first widely used in aviation, aerospace, and other industries due to their low density (4.51g/cm3), high strength (some up to 1000MPa), high specific strength, and excellent high and low-temperature performance.的structural materials. In addition, titanium and titanium alloys have excellent corrosion resistance and other comprehensive properties in many chemical media and are widely accepted by civilian industries such as petroleum, chemical, medicine, sports, etc., gradually replacing various metal materials, in a short time Leaped to the third place in the use of metal materials.

Titanium was discovered in 1789. In 1908, Norway and the United States began to produce titanium dioxide by the sulfuric acid method. In 1910, the sodium method was used to prepare sponge titanium for the first time in a laboratory. In 1948, the United States DuPont (DUPONT) used the magnesium method to produce tons. The production of titanium sponges marked the beginning of the industrial production of titanium sponges.

It can be seen that the production process of titanium involves the highly toxic chemical medium chlorine gas (a chemical weapon in World War II) and the precious metal magnesium, and the reaction process requires a lot of energy, which is the reason why titanium is expensive. The titanium material smelted in this process cannot be used for production because it is still porous and loose, shaped like a sponge, called sponge titanium. Sponge titanium will be placed in a vacuum consumable electric arc furnace to smelt titanium ingots for use in titanium. Production of plates, rods, tubes, and other forms of titanium.

my country is rich in titanium resources, and the minerals are relatively concentrated. When converted into TiO2, the total reserves amount to more than 9 billion tons, ranking first in the world. Titanium ore is mainly distributed in provinces such as Sichuan, Yunnan, Guangdong, Guangxi, and Hainan, among which the reserves of the Panzhihua area account for 35% of the world's total reserves. However, compared with the world's major titanium deposits, my country's natural rutile (TiO2) resources are few, and there are few placers that can be easily exploited. Titanium ore is mostly titanium-vanadium-iron symbiotic rock ore, and the initial cost of beneficiation and smelting is high.

China's titanium industry started in the 1950s. In 1954, the Beijing Nonferrous Metals Research Institute began to conduct research on the preparation of sponge titanium. In 1956, the country included titanium as a strategic metal in its 12-year development plan, and it was implemented in the Fushun Aluminum Plant in 1958. It established the first titanium sponge production workshop in China and established the first titanium processing material production trial workshop in the Shenyang non-ferrous metal processing plant.

Around 1980, the production of titanium sponges in my country reached 2,800 tons. However, due to the lack of understanding of titanium metal by most people at that time, the high price of titanium materials also restricted the application of titanium. The output of titanium processed materials was only about 200 tons. In trouble.

In 2002, my country imported 2,147 tons of titanium sponge, exported 11 tons, and imported 2136 tons; from January to November 2003, my country imported 2609.9 tons of titanium sponge, exported 72.7 tons, and imported 2534.2 tons.

In 2002, my country produced 3328 tons of titanium sponges, and the actual sales were 3,079 tons; in 2003, my country produced 4,112 tons of titanium sponges and sold 4,128 tons. However, due to the large-scale development of the international chemical industry and aerospace industry, the international titanium materials have been in short supply, which has led to a situation in which my country's titanium materials have risen wildly since 2002.

The production capacity of titanium processing materials is determined by the production capacity of titanium ingots, that is, the country has the overall tonnage of vacuum consumable electric arc furnaces. my country basically has a production capacity of 20,000t/a of titanium ingots. With 70% converted into titanium, it basically has a production capacity of 14,000t/a.

According to preliminary statistics, my country actually produced about 6,000 tons of titanium in 2003, accounting for about 10% of the world's total output. It can be seen that China's titanium processing industry is not very developed, and it takes time and investment.
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Application of titanium alloy materials in the field of shipbuilding and its welding process requirements

The tensile strength of pure titanium is 265-353MPa, the general titanium alloy is 686-1176MPa, and the current maximum is 1764MPa. Titanium alloys have the same strength as many plates of steel but are much better than strength titanium alloys. The specific strength here refers to the strength of the material divided by its apparent density, which is also called the strength-to-weight ratio. The international unit of specific strength is (N/m2)/(kg/m3) or N·m/kg. The ratio of the tensile strength of the material to the apparent density of the material is called the specific strength. The ratio of the strength (stretch) to the density of the material at the breaking point.

The compressive strength of titanium and titanium alloys is not lower than its tensile strength. The compressive yield strength and tensile yield strength of industrial pure titanium are roughly equal, while the compressive strength of Ti-6Al-4V and Ti-5Al-2.5Sn alloys is slightly higher than the tensile strength. The shear strength is generally 60%-70% of the tensile strength. The bearing yield strength of titanium and titanium alloy sheets is 1.2-2.0 times the tensile strength.

Under a normal atmosphere, the durable strength of processed and annealed titanium and titanium alloys is (0.5-0.65) times the tensile strength. When performing 107 fatigue tests in the notched state (Kt=3.9), the endurance strength of annealed Ti-6Al-4V is 0.2 times the tensile strength.

The hardness of the highest purity grade of processed industrial pure titanium is usually less than 120HB, and the hardness of processed titanium of other purity is 200-295HB. The hardness of pure titanium castings is 200-220HB. The hardness value of titanium alloy in the annealed state is 32-38HRC, which is equivalent to 298-349HB. The hardness of as-cast Ti-5Al-2.5Sn and Ti-6Al-4V alloys is 320HB, and the hardness of Ti-6Al-4V castings with low gap impurities is 310HB.

The tensile elastic modulus of industrial pure titanium is 105-109GPa, and the tensile elastic modulus of most titanium alloys is 110-120GPa in the returned state. The age-hardened titanium alloy has a slightly higher tensile elastic modulus than in the annealed state, and the compressive elastic modulus is equal to or greater than the tensile elastic modulus. Although the stiffness of titanium and titanium alloys is much higher than that of aluminum and aluminum alloys, they are only 55% of iron. The specific elastic modulus of titanium alloy is comparable to that of aluminum alloy, second only to beryllium, molybdenum, and some high-temperature alloys.

The torsion or shear modulus of industrial pure titanium is 46 GPa, and the shear modulus of titanium alloy is 43-51 GPa.

In order to increase the strength of the titanium alloy, increasing the content of interstitial elements will have a harmful effect on the impact resistance and fracture toughness of the alloy. According to the different types and states of titanium alloys, the Charpy notched impact strength of industrial pure titanium is 15-54J/cm2, and the cast state is 4-10J/cm2. The impact strength of titanium alloy in the annealed state is 13-25.8J/cm2, which is slightly lower in the aging state. The Charpy V-notch impact strength of as-cast Ti-5Al-2.5Sn alloy is 10J/cm2, and that of Ti-6Al-4V alloy is 20-23J/cm2. The lower the oxygen content of titanium alloy processing materials, the higher this value.

Many titanium alloys have very high fracture toughness, or in other words, titanium alloys have good crack propagation resistance. The annealed Ti-6Al-4V alloy is a material with excellent toughness. When the notch concentration factor Kt=25.4mm, the ratio of notched tensile strength to non-notched tensile strength is greater than 1.

Titanium alloys can maintain certain properties at high temperatures. General industrial titanium alloys can maintain their useful properties at a temperature of 540°C, but they can only be used for short periods of time, and the temperature range for long-term use is 450-480°C. At present, a titanium alloy for use at a temperature of 600°C has been developed. As a missile material, titanium alloy can be used for a long time at a temperature of 540°C, and it can also be used for a short time at a temperature of 760°C.

Titanium and titanium alloy materials can still maintain their original mechanical properties at low and ultra-low temperatures. As the temperature decreases, the strength of titanium and titanium alloy materials continues to increase, while the ductility gradually deteriorates. Many annealed titanium alloy materials also have sufficient ductility and fracture toughness at -195.5°C. The Ti-5Al-2.5Sn alloy with very few interstitial elements can be used at a temperature of -252.7°C. The ratio of its notched tensile strength to non-notched tensile strength is 0.95-1.15 at a temperature of -25.7°C.

Liquid oxygen, liquid hydrogen, and liquid fluorine are important propellants in missiles and space devices. The low-temperature properties of the materials used to make low-temperature gas containers and low-temperature structural parts are very important. When the microstructure is equiaxed and the content of interstitial elements (oxygen, nitrogen, hydrogen, etc.) is very low, the ductility of the titanium alloy is still above 5%. Most titanium alloys have poor ductility at -252.7°C, while the elongation of Ti-6Al-4V alloy can reach 12%.
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Performance and characteristics of titanium heat exchanger and titanium reaction kettle heat control equipment

In the application of various titanium alloy products, titanium alloy forgings are mostly used in gas turbine compressor discs and medical artificial bones that require high strength, high toughness and high reliability. Therefore, not only high dimensional accuracy is required for titanium forgings, but also materials with excellent characteristics and high stability are required. The following mainly introduces 6 problems in titanium alloy flaw detection.

1. Segregation defects

In addition to β segregation, β spot, titanium-rich segregation and stripe α segregation, the most dangerous is interstitial α stable segregation (I type α segregation), which is often accompanied by small holes and cracks, containing oxygen, nitrogen and other gases. , The brittleness is greater. There are also aluminum-rich α stable segregation (type II α segregation), which is also accompanied by cracks and brittleness, which constitutes dangerous defects.

2. Inclusions

Most of them are metal inclusions with high melting point and high density. The high melting point and high density elements in the titanium alloy composition are not fully melted and left in the matrix (such as molybdenum inclusions). There are also cemented carbide tool chips mixed in the smelting raw materials (especially recycled materials) or improper electrode welding processes ( Titanium alloy smelting generally uses vacuum consumable electrode remelting method), such as tungsten arc welding, leaving high-density inclusions, such as tungsten inclusions, and titanium inclusions.

The existence of inclusions can easily lead to the occurrence and propagation of cracks, so it is a defect that is not allowed (for example, the Soviet Union's 1977 data stipulates that high-density inclusions with a diameter of 0.3 ~ 0.5 mm must be found in the X-ray inspection of titanium alloys. record).

3. Residual shrinkage

In the central area of ​​the acid leaching test piece (in most cases), there are irregular wrinkle cracks or cavities, and there are often serious looseness, inclusions (slag inclusions) and component segregation on or near them.

4. Holes

The holes do not necessarily exist individually, but may also exist in multiple dense ones, which will accelerate the growth of low-cycle fatigue cracks and cause premature fatigue failure.

5. Cracks

Mainly refers to forging cracks. Titanium alloy has high viscosity, poor fluidity, and poor thermal conductivity. Therefore, during the forging deformation process, due to the large surface friction, the obvious internal deformation unevenness and the large internal and external temperature difference, it is easy to produce shear bands inside the forging ( Strain line), which leads to cracking in severe cases, and its orientation is generally along the direction of maximum deformation stress.

6. Overheating

Titanium alloys have poor thermal conductivity. In addition to overheating of forgings or raw materials caused by improper heating during hot working, the forging process is also prone to overheating due to thermal effects during deformation, causing microstructure changes and generating overheated Widmanstatten structures.
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Application of titanium wire, titanium alloy wire and titanium nickel alloy wire in the fields of industrial and consumer goods

The Japan Institute of Atomic Energy (the original research) cooperated with the European Community, Russia, and the United States to establish the International Thermonuclear Experimental Reactor (ITER), and began engineering design activities (EDA) in 1992.

The EDA has carried out the technological development of various advanced devices, and the development of superconducting coils is one of them. The toroidal magnetic field coil (TF coil) is manufactured by the Efremov Institute of Electrical Physics and Engineering in Russia, and is designed and developed by the Japan Institute of Atomic Energy. The Nb3Sn superconducting wire is assembled with a titanium tube as a sheath. The following is a brief description of the advantages of using pure titanium tubes to assemble superconducting coils and their development results developed by the Japan Institute of Atomic Energy.

The superconducting coil for the test is composed of 1152 Nb3Sn superconducting wires (0.81mm in diameter) enclosed in a pure titanium tube (tube wall thickness 2mm, inner diameter 43mm), and a layer of 9 turns (height) is wound on the inner side of the support plate. 0.6m) composition (Figure 1). The overall outer diameter of the superconducting coil used in the test is 1.5m and the height is 2.8m. The stainless steel tube surrounding the support plate is used to cool the support plate. The superconducting coil is installed in the center of the prototype coil of the solenoid in the ITER. A current of 46kA flows through the prototype coil in a 13T magnetic field. Tests have verified that the superconducting coil meets the performance required by the IERTF coil. The critical current of the Nb3Sn superconducting wire will decrease under thermal or mechanical stress. In the past, the Nb3Sn superconducting wire was enclosed in a stainless steel tube. The difference in shrinkage (temperature change is 650C～-269C) will cause thermal stress, which will reduce the superconducting properties. For this reason, it is necessary to choose a material with the same thermal shrinkage rate as the Nb3Sn superconducting wire as the sealing tube. Such materials include Inconel 908 and titanium. Japan Harayan considered that pure titanium is superior to Inconel 908 in terms of non-magnetism, corrosion resistance, and processability, so it began experimental development work on titanium. According to the test results of the influence of the metal tube material on the critical current of the small Nb3Sn conductor; it can be seen that when a pure titanium tube is used when the magnetic field is 12T, the critical current value is twice that of a stainless steel tube. Based on this result, a pure titanium tube with a wall thickness of 2mm was used as the sealing tube of the superconducting coil for the test in Russia, and it was successfully energized in Japan Harayan, which increased the critical current of the conductor used in ITER by 30, making the same Cost has achieved higher operating performance.

Due to the very large electromagnetic force generated by the ITERTF coil, the metal tube is required to have sufficient strength. In addition, since the Nb3Sn superconducting material needs to be heat treated at 650C, 240h or more, the metal tube must also withstand this heat treatment. From the perspective of thermal shrinkage, pure titanium is a very ideal material, but it is necessary to study the effect of aging treatment on strength and toughness. Japan Haraken and Nippon Steel Corporation jointly studied the effect of the oxygen content of pure titanium after aging on the mechanical properties at liquid helium temperature (4K). The results show that the mechanical properties of pure titanium at 4K depend on the oxygen content in pure titanium. When the oxygen content is about 0.1, the necessary strength and toughness can be maintained after heat treatment (650C, 240h). Based on this result, the tube used for the superconducting coil used in the test is a pure titanium tube with an oxygen content of 0.106 produced in Russia.

This technology is also expected to be applied in fields such as power storage superconducting coils that require high magnetic fields and high current coils.
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