Analysis of factors affecting the properties of G r.17 titanium-palladium alloy


Gr.17 is an alloy composed of Gr.1 (first-grade industrial pure titanium) + 0.04%~0.08% Pd. It belongs to α-type titanium alloy. Since Ti-Pd alloy not only retains the excellent corrosion resistance of industrial pure titanium in oxidizing media, but also has significantly improved corrosion resistance in reducing media, it is particularly important to resist localization in high temperature (above boiling point) chlorides. Ability to corrode. In addition, Pd is a slow eutectoid β-stable element. Increasing its content can reduce the susceptibility to hydrogen embrittlement. Therefore, Gr.17 titanium-palladium alloy is widely used in petroleum, chemical industry, metallurgy and other fields due to its strong corrosion resistance, hydrogen absorption resistance and crevice corrosion resistance.
This article mainly introduces the impact of the impurity elements Fe and O content and their heat treatment process and microstructure on the mechanical properties of Gr.17 titanium palladium alloy. It explores the corresponding rules and optimizes the reasonable heat treatment system, Fe, O content and its microstructure. The structure shape significantly reduces the yield strength and meets the requirements of technical standard 200629. It provides a technological basis for mass production of this alloy plate.


Experimental Method
The materials used for the test were Gr.17 alloy ingots melted in the vacuum electric arc furnace of the casting plant. They were opened and forged into square slabs in the forging plant. After grinding, the slabs were hot-rolled twice on a 3300 mm four-roller reversible rolling mill until the thickness reached the desired thickness. It is 8.0 mm hot rolled plate. The phase transformation point of the alloy is 880°C.
(1) Conduct mechanical property testing on 8.0 mm plates with impurity element Fe and O contents of 0.02%, 0.05%; 0.03%, 0.06%; 0.04%, and 0.08% respectively.
(2) 8.0 mm plates with the same chemical composition and the same processing technology were annealed at 680°C, 710°C, 740°C, 770°C, and 790°C for 1 hour respectively, and the mechanical properties were tested after annealing.
(3) Conduct mechanical property testing on 8.0 mm plates with different grain equiaxed structures (same chemical composition, same processing technology, annealing at different temperatures).

As the Fe and O content increases, the strength gradually increases and the elongation gradually decreases. The impurity elements Fe and O can form interstitial solid solutions with titanium, causing severe lattice distortion, strongly hindering dislocation movement, increasing strength, reducing plasticity, and also affecting fatigue performance, creep resistance, thermal stability, and notch sensitivity. Very harmful. Therefore, the contents of impurity elements Fe and O should be strictly controlled. In this study, due to the harsh yield strength σ 0.2 index, in order to further reduce the yield strength of the plate to meet the requirements of the technical standard 200629, the Fe and O content of the ingot and the oxidation and oxygenation during processing should be strictly controlled. , annealed in the range of 680~740°C. As the temperature increases, the strength decreases slightly, but the change amplitude is small. Between 680 and 740°C, the elongation gradually increases, but when the temperature increases to 770°C, the elongation decreases. This is the result of grain growth and coarsening, and should be avoided. On this basis, the preferred heat treatment temperature is 680~740°C. Under the same holding time, as the annealing temperature increases, the equiaxed α structure grains gradually increase. When the temperature increases to above 770°C, the grains coarsen significantly and product performance deteriorates. The yield strength of the plate corresponding to the equiaxed structure d does not meet the standard. This is because the higher the annealing temperature, the greater the degree of recovery. As a result, the stored energy after deformation is reduced and the grains are coarsened. The isometric structure a bc has a good match of strength and plasticity. The reason is that the difference in strain degree inside the fine grains and near the grain boundaries is small, which causes small stress concentration and can withstand large deformation. And the finer the grains, the more tortuous the grain boundaries are, which is not conducive to the propagation of cracks. It can be concluded that a uniform and fine equiaxed α structure is beneficial to the reduction of the yield strength and the improvement of the plasticity of the sheet. Therefore, a reasonable thermal processing process should be formulated to make the sheet have a uniform and fine equiaxed structure. In order to obtain better comprehensive mechanical properties.

Conclusion
(1) The content of impurity elements Fe and O is the main influencing factor on the yield strength of Gr.17 titanium-palladium alloy plate. The Fe and O content of the ingot and the oxidation and oxygenation during the processing must be strictly controlled.
(2) The preferred heat treatment temperature is 680~740℃.
(3) Uniform and fine equiaxed α structure is beneficial to reducing the yield strength and improving plasticity of the plate. Through the above analysis of factors affecting the yield strength of Gr.17 titanium-palladium alloy plates, the relevant relationships and rules were obtained. Based on this, the parameters were optimized and the reasonable chemical composition, thermal processing technology and heat treatment system were determined to make the finished product The yield strength of the plate is significantly reduced and the plasticity is improved. The mechanical properties of the plate meet the standard requirements of technical standard 200629. It provides a technological basis for mass production of this alloy plate in the future.

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Performance analysis and main application fields of titanium alloy forgings and titanium alloy castings

After metal is forged, its structure and mechanical properties can be improved. After the casting structure is deformed by hot processing by the forging method, due to the deformation and recrystallization of the metal, the original coarse dendrites and columnar grains change into an equiaxed recrystallization structure with finer grains and uniform size, causing the original segregation and recrystallization in the steel ingot. The compaction and welding of porosity, pores, slag inclusions, etc. make the structure more compact and improve the plasticity and mechanical properties of the metal.
Generally speaking, the mechanical properties of castings are lower than the mechanical properties of forgings of the same material. In addition, the forging process can ensure the continuity of the metal fiber structure, so that the fiber structure of the forging is consistent with the shape of the forging, and the metal streamlines are complete, ensuring that the parts have good mechanical properties and long service life. Precision die forging and cold extrusion are used Forgings produced by , warm extrusion and other processes are incomparable to castings.

  1. Aircraft forgings
    Calculated by weight, about 85% of the components on the aircraft are forgings. The aircraft engine’s turbine disk, rear journal (hollow shaft), blades, wing spars, fuselage rib plates, wheel brackets, and inner and outer cylinders of the landing gear are all important forgings related to aircraft safety. Aircraft forgings are mostly made of precious materials such as high-strength, wear-resistant and corrosion-resistant aluminum alloys, titanium alloys, and nickel-based alloys. In order to save materials and energy, most aircraft forgings are produced using die forging or multi-directional die forging presses. Car forging Calculated by weight, there are 1719% forgings on the car. A general car is composed of 15 parts such as body, trunk, engine, front axle, rear axle, frame, gearbox, drive shaft, steering system, etc. The characteristics of automobile forgings are complex appearance, light weight, poor working conditions, and safety. High standard. For example, the crankshaft, connecting rod, camshaft used in the automobile engine, the front beam required for the front axle, the steering knuckle, the half shaft used in the rear axle, the half axle sleeve, the transmission gear in the axle box, etc., are all related Security critical forgings for safe operation of automobiles.
  2. Diesel engine forgings
    Diesel engine is a type of power machinery, which is often used as an engine. Taking a large diesel engine as an example, the forgings used include cylinder head, main journal, crankshaft end flange output shaft, connecting rod, piston rod, piston head, crosshead pin, crankshaft transmission gear, ring gear, intermediate gear and dye oil pump. There are more than ten kinds of bodies.
  3. Marine forgings
    Marine forgings are divided into three categories: main engine forgings, shafting forgings and rudder forgings. The main engine forgings are the same as the diesel engine forgings. Shafting forgings include thrust shafts, intermediate shafts, stern shafts, etc. Rudder system forgings include rudder stock, rudder post, rudder pin, etc.
  4. Weapon forgings
    Forgings occupy an extremely important position in the weapons industry. By weight, 60% of the tank is forged parts. The barrel, muzzle brake and breech of artillery, the rifled barrel and triangular bayonet of infantry weapons, rocket and submarine depth bomb launchers and fixed seats, stainless steel valve bodies for high-pressure coolers of nuclear submarines, artillery shells, Guns, bullets, etc. are all forged products. In addition to steel forgings, other materials were used to create weapons.
  5. Petrochemical forgings
    Forgings are widely used in petrochemical equipment. Such as manholes and flanges of spherical storage tanks, various tube sheets required for heat exchangers, butt welding flanges, forged cylinders (pressure vessels) of catalytic cracking reactors, cylinder sections used in hydrogenation reactors, chemical fertilizers The top cover, bottom cover, head, etc. required for the equipment are all forged parts.
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Application of titanium alloy in aerospace field

The application of titanium in the aerospace industry mainly utilizes its low density, high strength, high temperature resistance, corrosion resistance and other properties.

The application of titanium in the aerospace industry also achieves the purpose of reducing launch weight, increasing range, and saving costs, and is a popular material in the aerospace industry. In the rocket, missile and aerospace industries, it can be used as pressure vessel, fuel storage tank, rocket engine casing, rocket nozzle sleeve, artificial satellite casing, manned spacecraft cabin (skin and structural skeleton), landing gear, moon landing cabin, propulsion system, etc.

In addition to the use of industrial pure titanium, Ti-6Al-4V, Ti-5Al-2.5Sn, Ti-6Al-4VELI and Ti-5Al-2.5SnELI in titanium and titanium alloys used in the aerospace industry, there is also Ti-7Al-4Mo , Ti-3Al-2.5V, Ti-13V-1Cr-Ti-15V-3Cr-3Sn-3Al and Ti/B-Al composite materials.

The space shuttle is the earliest manned spaceship in the world that can be used repeatedly. Development began in 1972, and the first flight was successful in 1981. The spaceship consists of an aircraft with small wings, a 47m long external fuel container and 2 solid fuel rocket boosters totaling 500t.

The orbital spacecraft is 37m long and weighs about 68t. This size is roughly the same as the jet transport aircraft DC-9. It is the largest manned spacecraft so far. Its cargo compartment is 18m long and 5m in diameter, and can transport 29.5t of cargo to Earth orbit.

The space shuttle can be launched like a rocket, and like a spaceship, it can fly on an orbit with a maximum altitude of 1000km, and can glide and land like an airplane without thrust. This space shuttle is essentially a space transport ship, so one of the parameters for judging its usefulness is the amount of payload transported between the earth and the earth’s orbit. To maximize this payload, titanium alloys are an important material for aerospace motor components.

The design life of the orbiting spacecraft is 100 flights, and each flight stays in space for 7 to 30 days. The spacecraft is manned, so it is designed to adapt to the space environment (vacuum, extreme temperature difference on the orbit, heat when re-entering the atmosphere, etc.), and used repeatedly.

     1. High pressure vessel

Titanium alloys are used in many places because they can reduce the overall weight of spacecraft orbiting vehicles. The main use part of titanium is the high-pressure container filled with the necessary fuel and gas. The lightweight titanium alloy container was successfully developed on NASA’s Gemini spacecraft and Apollo spacecraft, using Ti-6Al-4V alloy. The iron pressure vessel on the Apollo spacecraft has actually used an unprecedented design with a safety factor of 1.5, which was previously designed with a safety factor of about 4. In order to further reduce the weight of the high-pressure storage container of the orbital space shuttle, a method of adding white bird fiber (aromatic organic fiber produced by DuPont Company of the United States) on the surface of the thin-walled titanium container is adopted.

     Pressure vessel for storing compressed gas. The “Prowler” satellite and booster share 14 titanium containers, reducing the mass by 272kg.

     A pressure vessel for storing liquid propellants. About 50 pressure vessels were used on the “Apollo” spacecraft, 85% of which were made of titanium. Hercules Ⅲ transition stage engine, the weight is reduced by 35% after switching to titanium alloy propellant tank.

     2. Engine housing

Solid fuel rocket motor case. The second-stage rocket engine of the “Minuteman” intercontinental missile uses Ti64 alloy to reduce the weight by 30% to 40%.

     Liquid fuel rocket motor case. The pressure shell of the combustion chamber of the “Apollo” lunar module descending engine is made of Ti64 alloy.

     3. Various structural parts

     Titanium alloys are also widely used in various structural parts. The pressure chamber of the “Mercury” spacecraft is mainly made of titanium, accounting for 80% of the weight of the cabin. There are 7 types of titanium alloy grades used in the “Gemini” spacecraft, and 570kg of titanium parts are used, accounting for 84% of the structural weight. The brackets, fixtures and fasteners of the “Apollo” spacecraft are all made of titanium, using a total of 68t titanium.

     4. Hydraulic piping

     The oil pressure piping of the space shuttle uses seamless pipes made of Ti-3Al-2.5V alloy. Due to the use of this alloy, the weight can be reduced by more than 40%. In order to reduce the sensitivity to fatigue fracture and improve the actual life of the system, various The assembly of the tubes uses automatic forming.

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Longbai titanium sponge will reach 80,000-100,000 tons/year

At the 2022 China Panxi Vanadium and Titanium Forum, Li Jianjun of Longmang Sponge Titanium made a detailed report on the theme of “Building a World-Class Titanium Chemical Group Leading by ‘Double Carbon'”. He described it from four aspects: “International carbon progress, domestic carbon progress, Longbai empowerment, innovation leadership, and all employees working together to reduce carbon”. He said that around the titanium element, Longbai Group is focusing on creating products such as titanium dioxide, titanium sponge and titanium alloys, and lithium-ion battery materials, giving full play to its industrial advantages, realizing multi-industry coupling, and building an ecological circle with “Longbai characteristics”. A number of technological breakthroughs have been achieved in the comprehensive utilization of vanadium, iron, scandium, chromium, cobalt, nickel and other resources and industrialization has been achieved. Through technological innovation, the efficient recycling of various metal elements in raw material ores has been achieved, effectively promoting the green and low-carbon development of enterprises. , Circular development. The Honggebei mining area of ​​Longbai Panzhihua Company has become the largest production base of titanium raw materials in the country, which has proved the comprehensive strength of the enterprise in the integration of mineral resources, technological innovation, green industry development and efficient development and utilization of mineral products. Under the guidance of the “Double Carbon” strategy, Longbai Group adheres to the “big chemical industry” route, builds a high-quality, low-cost production process for the entire industrial chain, greatly improves the level of comprehensive resource utilization, and realizes circular economy to help reduce carbon. Focusing on mineral products, titanium and zirconium products, new energy products and rare and scattered metal products, Chen Jianjian introduced the industrial advantages of the group in detail. At present, the company’s titanium dioxide and sponge titanium production capacity has reached an annual output of 1.5 million tons and 50,000 tons respectively, both ranking first in the world; in terms of new energy products, it has formed an annual output of 100,000 tons of iron phosphate and 50,000 tons of iron phosphate Lithium + 100,000 tons of graphite anode material integrated new energy product industrial system; in terms of rare and scattered metal products, the company now has the world’s largest production base of scandium oxide and metal scandium, with an annual production capacity of 50 tons, ranking first in the world First, and form a production scale of 600 tons/year of vanadium series products, and plan to form a production line of 30,000 tons/year of vanadium series products in the future. He said that Longbai Group actively responded to the call of the national “double carbon” policy, paid attention to environmental and ecological protection, proposed and gradually implemented green electricity consumption, hydropower consumption, solar energy utilization, fossil fuel reduction and substitution, terminal energy electrification, industrial Taking measures such as utilization of surplus energy and improvement of equipment energy efficiency, we have continuously cultivated the titanium chemical industry, joined hands with all employees to reduce carbon, realized multi-industry coupling, and achieved remarkable results.

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Effect of Solution Cooling Method on Microstructure and Mechanical Properties of TB15 Titanium Alloy

The mechanical properties, fracture morphology and microstructure of TB15 titanium alloy after solution cooling at 900℃×2h and aging at 530℃×8h were investigated by scanning electron microscope observation, tensile test and fracture toughness test.
The results show that the effect of solution cooling on the strength and ductility of TB15 titanium alloy is relatively large, and the effect on fracture toughness is small. After solid solution, when refilled with 0.1MPa argon vacuum air cooling, the comprehensive mechanical properties of the alloy are the best. /2. With the increase of solution cooling rate, the fracture toughness of TB15 titanium alloy gradually decreases, but the change is not too large. Under different solution cooling methods, the number, thickness and interlamellar spacing of secondary α phase of TB15 titanium alloy after solution aging will change differently. Compared with air cooling, the number of lamellar secondary α-phases in backfilling 0.1MP argon vacuum air cooling increases, the thickness increases slightly, and the lamellar spacing increases.

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