The insufficient strength of pure tantalum metal necessitates the production of alloys with high strength in the temperature range of 1000℃-1900℃. These alloys can be formed into useful shapes and possess sufficient inherent oxidation resistance, or can be effectively protected by appropriate coatings, allowing operation within this temperature range without premature component failure. Considering economic costs, the research and development of new alloys is essential.
Tungsten has a melting point as high as 3450℃. Like tantalum, tungsten is a body-centered cubic metal and can form an infinite solid solution with tantalum. Therefore, adding tungsten to tantalum metal to form tantalum-tungsten alloys can overcome the insufficient strength of pure tantalum metal and significantly improve the tensile strength of the material. Rhenium metal has a melting point of 3186℃ and is one of the densest elements, possessing the second highest melting point among known pure metals. Rhenium metal has a low ductile-brittle transition temperature and does not form carbides. Rhenium has a close-packed hexagonal structure and a solubility of over 25% in tantalum. Rhenium metal plays a strong hardening role in tantalum-rhenium alloys. Among known refractory metals, it is the element with the best strengthening effect on tantalum-based alloys. Tantalum-rhenium alloys also have a low brittle-ductile transition temperature and good ductility (plasticity) at room temperature.
Tantalum alloy tubes are commonly used in rocket nozzles, high-temperature, corrosion-resistant heat exchangers in the field of atomic energy development, and infrared radiation tubes for infrared tracking. These applications require uniform wall thickness for tantalum alloy tubes. Currently, domestic and international standards for tantalum alloy tubes require a wall thickness tolerance of ±10%. However, tantalum metal has a relatively high density, reaching 16.6 g/cm³. Relaxing tolerances is very detrimental to material thinning and weight reduction. Therefore, it is essential to research and develop tantalum alloy tubes with a wall thickness tolerance ≤ ±5%.
This invention relates to tantalum alloys and their preparation methods, as well as seamless tantalum alloy tubes and their preparation methods. It addresses the problem of insufficient strength in equipment using pure tantalum metal in fields such as aviation, aerospace, and nuclear energy development. The tantalum alloy prepared by this invention has a Vickers hardness ≥150 at 1100℃, exhibiting good room temperature machinability, high high-temperature strength, and high-temperature hardness. The seamless tantalum alloy tubes prepared using this tantalum alloy possess excellent room temperature plasticity and good oxidation resistance, enabling application in harsh and extreme environments exceeding 1100℃.
The first tantalum alloy is vacuum recrystallized and annealed in a vacuum annealing furnace. The first tantalum alloy after vacuum recrystallization and annealing is then cooled to obtain a second tantalum alloy. The second tantalum alloy undergoes two cycles of the forging-vacuum recrystallization and annealing process to obtain a third tantalum alloy, ensuring that the grain size of the third tantalum alloy is ≤300µm. The selection of drill bit and spinning mandrel is determined, and holes are drilled into the third tantalum alloy. The inner walls of the drilled holes are polished. The drilled third tantalum alloy is then heated to 400-800℃ in a muffle furnace and held at that temperature. For 20-30 minutes, lubricate the spinning mandrel with oil, then attach the heated third tantalum alloy. Spin the third tantalum alloy multiple times using a die on a hydraulic press, ensuring that the deformation per pass is ≤10% and the total deformation is ≥50%, until the third tantalum alloy is suitable for rolling the tube. Remove the mandrel to obtain the first tube blank.
The first tube blank is then subjected to vacuum stress-relief annealing in a vacuum annealing furnace. After vacuum stress-relief annealing, the first tube blank is cooled to obtain the second tube blank. The second tube blank undergoes defect removal treatment, removing internal and external scratches and folds. The cracks are removed by grinding to obtain the third tube blank. The selection of rolls and cold-rolling mandrel is determined, and the third tube blank is cold-rolled multiple times using a three-roll mill, ensuring that the deformation per pass is 20-30% and the total deformation is ≥80%. The third tube blank is rolled to the finished size to obtain a tantalum alloy tube. The tantalum alloy tube is cleaned and cut to the required length to obtain a semi-finished tube.
The semi-finished tube is annealed in a vacuum annealing furnace and then cooled to obtain a seamless tantalum alloy tube. Furthermore, a seamless tantalum alloy tube is also provided, prepared using the above-described method. The seamless tantalum alloy tube has an outer diameter of 3-38 mm, a wall thickness of 0.2-5 mm, a length of 0-12000 mm, a wall thickness tolerance of ≤±4%, a grain size of 20-40 μm, a room temperature tensile strength ≥450 MPa, and an elongation ≥25%. By designing this tantalum alloy and its preparation method, tungsten and rhenium were added to tantalum. The resulting tantalum alloy had an oxygen content ≤80ppm, a carbon content ≤40ppm, and a nitrogen content ≤20ppm. After vacuum sintering, two electron beam melting processes, and thermomechanical processing, the tantalum alloy exhibited a Vickers hardness ≥200 at 1100℃, demonstrating good room temperature machinability, high high-temperature strength, and high high-temperature hardness.
Through the design of this seamless tantalum alloy tube and its preparation method, the tantalum alloy prepared above is subjected to multi-directional forging, which compacts the original segregation and porosity within the tantalum alloy, making its coarse structure finer and denser, thus improving the plasticity and mechanical properties of the tantalum alloy. The product has a dense microstructure and fine and uniform grains. A total of three annealing treatments are performed, and the vacuum annealing temperature and time are reasonably controlled to recrystallize the fragmented grains after each forging, making the grain structure uniform after each forging. The prepared seamless tantalum alloy tube has the following characteristics: outer diameter of 3-38mm, wall thickness of 0.2-5mm, length of 0-12000mm, wall thickness tolerance ≤±4%, grain size of 20-40um, room temperature tensile strength ≥450Mpa, elongation ≥25%, excellent room temperature plasticity and good oxidation resistance, and can be used in harsh extreme environments with ultra-high temperatures above 1100℃.
