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Niobium alloys are usually divided into 6 categories according to their strength grades and functional properties: the first category of high-strength and low-plasticity niobium alloys, the second category of medium-strength and medium-plasticity niobium alloys, the third category of low-strength high-plasticity niobium alloys, and the fourth category Niobium oxide alloys, the fifth class of plastic oxidation-resistant niobium alloys and the sixth class of corrosion-resistant niobium alloys. According to the density, it can be divided into high-density and low-density niobium alloys. According to different functions, it is divided into structural alloys, functional precision alloys and corrosion-resistant alloys. Structural alloys are mainly used in the aerospace field. According to their strength, they are roughly divided into three categories: high strength, medium strength and low strength. Considering the factor of weight reduction, low-density niobium alloys have been developed. In order to continuously improve the comprehensive performance of niobium alloys, we have also developed High-strength niobium alloys strengthened by interstitial compounds (carbides, oxides and nitrides).
1.1 High strength, low plasticity niobium alloy
Generally, niobium alloys with high strength and low plasticity are mainly strengthened by adding alloying elements W, Mo and Ta, a small amount of Hf and Zr, and a small amount of C. Such niobium alloys include Cb-1, As-30, Cb-132M, F48, Su-31, etc., which are mainly used in gas turbine blades. The W, Mo and Ta elements in this type of alloy are solid solution strengthening, and Hf and Zr can form a dispersed second phase strengthening phase with C, so that the alloy has higher creep strength. Their solid phase temperature is higher than that of pure niobium, and their recrystallization temperature is also relatively high. Their high-temperature strength is significantly higher than that of medium-strength and low-strength niobium alloys. The working temperature is generally 1300~1600°C, and the short-term working temperature is higher. Because of containing W, Hf and other elements, the anti-oxidation performance has been improved to a certain extent. However, as the content of high melting point strengthening alloying elements such as W and Mo increases, the plastic-brittle transition temperature will also increase, and its plastic processing performance will deteriorate and deformation processing will be more difficult. In order to ensure a good match between high temperature strength and low temperature ductility, the thermomechanical processing of these alloys must be strictly controlled. In addition, high-strength niobium-like alloys mostly belong to the research and development stage, and most of the niobium alloys produced industrially are medium-strength and low-strength niobium alloys.
1.2 Medium strength, medium ductility niobium alloy
Medium-strength, medium-plastic niobium alloys are mainly composed of niobium as the matrix, adding no more than 10% of metal elements such as W, Mo, Ta, V, Ti, Zr, Hf and a small amount of C elements. This type of alloy has C-129Y , SCb-291, D31, D43, FS85, Cb-752, PWC-11, 5ВНЦ and Nb521, etc. The strength of these alloys at room temperature is 400~600MPa, and the elongation is 20~30%; they still have quite high strength at high temperatures of 1000~1400°C, and can work effectively. If the time is shorter, the working temperature can be higher. high. Since this type of alloy contains an appropriate amount of W, Ta, Ti, Zr, and Hf, the recrystallization temperature is increased to 1150~1250°C. At the same time, because the plastic-brittle transition temperature of this type of alloy is higher than that of pure niobium, the transition temperature in the welded state is generally above room temperature, and it is sensitive to interstitial elements such as O, N, and H, so it is necessary to strictly control O, N, and H. Pollution, the oxygen content in the alloy must be controlled below 80ppm. This type of alloy has certain plasticity and good workability
It has high performance and can be used to manufacture various parts, such as skins, bolts and nuts.
1.3 Low strength, high ductility niobium alloy
Low-strength, high-plasticity niobium alloy is based on niobium, adding metal elements such as Ti, Zr, Hf and other metal elements of group IV in the periodic table to form a solid solution strengthened alloy. This type of alloy includes Nb-1Zr for liquid metal containers and pipelines, niobium C-103 alloy for rocket engine thrust chambers, radiation sleeves and heat shields, and niobium Cb-752 alloy for honeycomb structures for ion engines. The recrystallization temperature of this type of niobium alloy is similar to that of pure niobium, generally 1000~1100°C. The room temperature strength of the alloy is generally 320~420MPa, and the elongation after fracture is 20~40%. This kind of alloy has good welding performance and low plastic-brittle transition temperature. In the range of (0.37~0.47)T melting temperature and vacuum state, the plastic-brittle transition temperature after aging treatment is still lower than room temperature. Compared with medium and high-strength alloys, this type of alloy has good plasticity at room temperature and excellent process performance, and can be made for liquid alkali metal transportation pipelines, turbo pumps for space and power generation equipment, satellites, and spacecraft And the thrust chamber body extension of the attitude control/orbit control engine of the missile and other components.