A high-strength and tough molybdenum alloy for high temperature and its preparation method

Abstract

The present invention relates to the technical field of refractory metal powder metallurgy and deformation processing, and particularly to a high-temperature high-strength and toughness molybdenum alloy and a preparation method thereof. The molybdenum alloy comprises the following components, by mass percentage: HfC 0.1-2%, C 0.05-0.2%, and the balance Mo. The high-strength and toughness molybdenum alloy for high temperature use is prepared using molybdenum powder, hafnium carbide powder, and carbon powder as raw materials through the steps of fusion coating, purification and reduction, press molding, high-temperature sintering, deformation processing, alkali washing and grinding, and annealing. The alloy has an oxygen content of ≤100 ppm, a room temperature tensile strength of ≥1000 MPa, an elongation of ≥30%, and a tensile strength of ≥350 MPa at 1400°C, exhibiting good strength-toughness matching and high-temperature stability.

Description

Technical Field

[0001] The present invention relates to the technical field of refractory metal powder metallurgy and deformation processing, and in particular to a high-temperature high-strength and toughness molybdenum alloy and a preparation method thereof. Background Art

[0002] Molybdenum and its alloys possess advantages such as high melting point, high hardness, high elastic modulus, low thermal expansion coefficient, excellent high-temperature strength and thermal shock resistance, wear resistance, excellent electrical and thermal conductivity, and strong corrosion resistance. They are widely used as high-temperature structural materials in aerospace, engine nozzle materials, emitter materials for thermionic reactor diodes, and rotating anode materials in medical devices. With the continuous development of high-temperature applications in aerospace, equipment manufacturing, nuclear industry, and other fields, many high-end applications have increasingly stringent requirements for material strength-toughness matching and high-temperature service stability. Further improving the room-temperature and high-temperature mechanical properties of these materials has become a key focus of research and development for the next generation of molybdenum alloys.

[0003] Traditional methods for improving the room temperature and high temperature properties of molybdenum alloys primarily involve solid solution strengthening through the addition of metallic elements such as Ti, Zr, and Hf, potassium bubble strengthening through the addition of potassium aluminum silicate salts, and second-phase strengthening through the addition of rare earth oxides. With the continuous development of modern industrial high-temperature applications, molybdenum alloys strengthened by a single mechanism are no longer sufficient for high-end applications. The development and preparation of multi-mechanism-strengthened molybdenum alloys with superior comprehensive performance, including room temperature and high temperature mechanical properties and high-temperature microstructure stability, is becoming increasingly necessary and urgent.

[0004] Hafnium carbide (HfC) has the highest melting point of any known single compound (3900°C), and possesses excellent chemical stability and a relatively low vapor pressure. HfC is an ideal strengthening agent for molybdenum materials used in high-temperature applications. Strengthening molybdenum with HfC offers significant advantages in high-temperature applications. Molybdenum-hafnium-carbon (MHC) alloys, which incorporate Hf and C sources, are an upgraded version of titanium-zirconium-molybdenum (TZM) alloys and are expected to replace traditional molybdenum alloys in critical applications such as high-temperature die-casting molds and rotating anodes for X-ray tubes.

[0005] The powder metallurgy method for preparing MHC alloys is usually to add hafnium hydride and graphite or carbon black to molybdenum powder, mix and press into shape, and then sinter in hydrogen or vacuum. Because hafnium easily combines with oxygen during the powder metallurgy preparation process to form larger hafnium oxide particles, it is difficult to disperse and distribute them evenly in the matrix. Not only can the strengthening effect not be achieved, but it is also easy to form a potential source of cracks. In addition, the graphite particles are relatively large and randomly and evenly distributed after mixing. Hf atoms need a long time to diffuse before they can react to form dispersed HfC. The number of second phases that can be formed is relatively small, resulting in low strength and plasticity of the alloy. In addition, in actual production, metal hydrides are flammable and explosive. When they come into contact with water in the air, they will react violently and may even cause an explosion. There are certain safety hazards in production and use. Summary of the Invention

[0006] In response to the problems in the above-mentioned prior art of uneven distribution of molybdenum alloy strengthening phases, difficulty in coordinated optimization of mechanical properties, poor high-temperature toughness and low strength, the present invention provides a high-strength and toughness molybdenum alloy for high temperature use and a preparation method thereof.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A high-strength and high-toughness molybdenum alloy for high temperature use comprises the following components, in percentage by mass: 0.1-2% HfC, 0.05-0.2% C, and the balance Mo. The alloy has an oxygen content of ≤100 ppm, a room temperature tensile strength of ≥1000 MPa, an elongation of ≥30%, and a tensile strength of ≥350 MPa at 1400°C.

[0009] The present invention also includes the following technical solutions:

[0010] A method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use comprises the following steps:

[0011] (1) Fusion coating: Molybdenum powder, hafnium carbide powder and carbon powder with a purity of not less than 99.95% are weighed in proportion, and the hafnium carbide powder and carbon powder are uniformly coated on the surface of the molybdenum powder particles by mechanical fusion method to obtain a molybdenum alloy mixed powder; the mechanical fusion method includes a pretreatment process and a high-speed fusion process;

[0012] (2) Purification and reduction: Place the molybdenum alloy mixed powder after mechanical fusion into a heating furnace and purify it in a hydrogen atmosphere or vacuum environment. The hydrogen dew point of the hydrogen atmosphere is not higher than -40 °C or the vacuum degree of the vacuum environment is less than 8×10 -3 Pa;

[0013] (3) Pressing: The purified and reduced molybdenum alloy mixed powder is placed in a mold for cold isostatic pressing to obtain a refined molybdenum alloy compact;

[0014] (4) High temperature sintering: Place the refined molybdenum alloy compact into a sintering furnace and sinter in a hydrogen atmosphere or vacuum environment. The hydrogen dew point of the hydrogen atmosphere is not higher than -40 °C or the vacuum degree of the vacuum environment is less than 8×10 -3 Pa, to obtain a molybdenum alloy sintered blank;

[0015] (5) Deformation processing: The molybdenum alloy sintered billet is subjected to Y-type hot rolling in a hydrogen atmosphere, with a billet opening temperature of 1300-1800°C and a total deformation of 75-95% to obtain a deformed molybdenum alloy;

[0016] (6) Alkali cleaning and grinding: The deformed molybdenum alloy is alkaline cleaned with molten sodium hydroxide, and then rinsed with water and then ground;

[0017] (7) Annealing treatment: The molybdenum alloy after grinding is annealed in a hydrogen atmosphere or vacuum environment. The hydrogen dew point of the hydrogen atmosphere is not higher than -40℃ or the vacuum degree of the vacuum environment is 10 -2 -10 -5 Pa, to obtain high strength and toughness molybdenum alloy for high temperature use.

[0018] Furthermore, in step (1), the molybdenum powder has a Fisher particle size of 2-8 μm, the hafnium carbide powder has a Fisher particle size of 10-500 nm, and the carbon powder has a Fisher particle size of 10-100 nm.

[0019] Furthermore, in step (1), the rotation speed of the pretreatment process is 1000-1500 rpm, and the processing time is 1-5 min; the rotation speed of the high-speed fusion process is 2000-5000 rpm, and the processing time is 10-60 min.

[0020] Furthermore, in step (2), the purification temperature is 200-700°C, and the purification time is 1-10 h.

[0021] Furthermore, in step (3), the cold isostatic pressing pressure is 100-300 MPa, and the pressing time is 5-30 min.

[0022] Furthermore, in step (3), the mold is a soft rubber mold, and the soft rubber mold is fixed by a rigid sleeve with holes.

[0023] Furthermore, in step (4), the sintering temperature is 1800-2300°C, and the sintering time is 4-14 h.

[0024] Furthermore, in step (7), the annealing temperature is 800-1600°C, and the annealing time is 0.5-4 h.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention provides a method for preparing high-strength and high-toughness molybdenum alloy for high temperature use. Through a mechanical fusion coating process, hafnium carbide powder and carbon powder are evenly coated on the surface of molybdenum powder particles to ensure that each molybdenum particle can fully contact with the reinforcing phase hafnium carbide powder and carbon powder, significantly improving the microscopic uniformity of the material. The uniform distribution of hafnium carbide in the molybdenum alloy plays a role in dispersion strengthening and second-phase strengthening, improving the room temperature and high-temperature toughness, hardness and high-temperature structural stability of the molybdenum alloy. The addition of hafnium carbide effectively avoids excessive enrichment or aggregation of hafnium elements, avoids the problem of excessive strengthening and insufficient toughness and plasticity, and ensures the good machinability of the alloy in subsequent deformation processing. Carbon powder can react with oxygen to generate CO or , reducing the probability of oxide inclusions, and deeply reducing the oxygen content in the molybdenum alloy. The synergistic effect of hafnium carbide and carbon significantly reduces the oxidation tendency and probability of the strengthening element hafnium, inhibits the generation of large-sized hafnium oxide particles, ensures the uniform dispersion distribution of micro-nanoscale hafnium carbide particles in the molybdenum matrix, plays a role in refining grains and strengthening grain boundaries, optimizes the microstructure and mechanical properties of the molybdenum alloy, reduces the tendency of the material to crack, and significantly improves the recrystallization temperature and high-temperature strength of the molybdenum alloy. In addition, the present invention effectively controls the oxygen / nitrogen content through purification and reduction treatment at the raw material end, significantly reduces the probability of generating hard and brittle oxygen / nitride particles, reduces the formation of oxygen / nitride impurities from the source, reduces the tough-brittle transition temperature of the material, and thus improves the sintering and deformation processing performance of the alloy. In the deformation processing stage, Y-type hot rolling with the advantages of no torsion and micro-tension is adopted to ensure that the billet is uniformly stressed, and a fine and uniform microstructure is obtained through continuous deformation. The high-strength and toughness molybdenum alloy for high temperature use provided by the present invention has excellent comprehensive performance, with an oxygen content of ≤100ppm, a room temperature tensile strength of ≥1000 MPa, an elongation of ≥30%, and a tensile strength of ≥350 MPa at 1400°C, showing good strength-toughness matching and high-temperature stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which:

[0028] Figure 1 The process flow chart of the preparation method of high-strength and high-toughness molybdenum alloy for high temperature is shown;

[0029] Figure 2 The stress-strain curve of Example 1 of the high-strength and tough molybdenum alloy for high temperature use is shown;

[0030] Figure 3 Shows a metallographic photograph of Example 3 of a high-strength and tough molybdenum alloy for high temperature use;

[0031] Figure 4 The SEM image of Example 3 of the high-strength and high-toughness molybdenum alloy for high temperature use is shown. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0033] The process flow of the preparation method of a high-strength and tough molybdenum alloy for high temperature use according to the present invention is as follows: Figure 1 As shown, it includes the following steps: (1) fusion coating; (2) purification and reduction; (3) pressing and forming; (4) high-temperature sintering; (5) deformation processing; (6) alkali cleaning and grinding; (7) annealing treatment; the details are as follows:

[0034] (1) Fusion coating: Molybdenum powder with a purity of not less than 99.95% and a Fisher's particle size of 2-8 μm, hafnium carbide powder with a Fisher's particle size of 10-500 nm, and carbon powder with a Fisher's particle size of 10-100 nm are weighed in proportion, and the hafnium carbide powder and carbon powder are uniformly coated on the surface of the molybdenum powder particles by mechanical fusion. The pretreatment speed of mechanical fusion is 1000-1500 rpm, and the processing time is 1-5 min; the high-speed fusion speed of mechanical fusion is 2000-5000 rpm, and the processing time is 10-60 min; and a molybdenum alloy mixed powder is obtained;

[0035] (2) Purification and reduction: Place the molybdenum alloy mixed powder after mechanical fusion into a heating furnace and purify it in a hydrogen atmosphere or vacuum environment. The hydrogen dew point of the hydrogen atmosphere is not higher than -40 °C or the vacuum degree of the vacuum environment is less than 8×10 -3 Pa; purification temperature is 200-700℃, purification time is 1-10 h;

[0036] (3) Pressing: Place the purified and reduced molybdenum alloy mixed powder into a mold and cold isostatically press it at 100-300 MPa for 5-30 min to obtain a refined molybdenum alloy compact with regular shape, uniform size and appropriate grain size;

[0037] (4) High temperature sintering: Place the refined molybdenum alloy compact into a sintering furnace, and heat the sintering furnace to the sintering temperature by step-by-step heating in a hydrogen atmosphere or vacuum environment. Sinter the refined molybdenum alloy compact. The hydrogen dew point of the hydrogen atmosphere is not higher than -40°C or the vacuum degree of the vacuum environment is less than 8×10 -3 Pa, sintering temperature is 1800-2300℃, sintering time is 4-14 h, and the density is 9.8±0.2 g / cm 3 Molybdenum alloy sintered blank;

[0038] (5) Deformation processing: The molybdenum alloy sintered billet is subjected to Y-type hot rolling in a hydrogen atmosphere, with a billet opening temperature of 1300-1800℃ and a total deformation of 75-95%, to obtain a deformed molybdenum alloy; Y-type hot rolling processing helps to improve the uniformity of the microstructure and mechanical properties of the deformed molybdenum alloy, thereby ensuring the high strength and toughness of the molybdenum alloy.

[0039] (6) Alkali cleaning and grinding: The deformed molybdenum alloy is alkaline cleaned with molten sodium hydroxide, and then rinsed with water and ground to remove surface defects such as surface indentations, residual oxide scale, and local microcracks as needed;

[0040] (7) Annealing treatment: The molybdenum alloy after grinding is annealed in a hydrogen atmosphere or vacuum environment. The hydrogen dew point of the hydrogen atmosphere is not higher than -40℃ or the vacuum degree of the vacuum environment is 10 -2 -10 -5 Pa, the annealing temperature is 800-1600℃, the annealing time is 0.5-4 h, and the alloy is cooled with the furnace to obtain a high-strength and toughness molybdenum alloy for high temperature use; the annealing treatment helps to reduce or eliminate the residual stress and distortion energy introduced in the deformation process, or achieve partial recrystallization, effectively regulate and balance the strength and toughness of the molybdenum alloy, and thus ensure that the oxygen content of the high-strength and toughness molybdenum alloy for high temperature use is ≤100 ppm, the room temperature tensile strength is ≥1000 MPa, the elongation is ≥30%, and the 1400℃ tensile strength is ≥350 MPa. Example 1

[0041] Molybdenum powder with a Fisher's particle size of 2 μm and a purity of not less than 99.95%, hafnium carbide powder with a Fisher's particle size of 10 nm, and carbon powder with a Fisher's particle size of 10 nm were selected and weighed according to the ratio of 998.5 g of molybdenum powder, 1 g of hafnium carbide powder, and 0.5 g of carbon powder. The mixture was then placed in a mechanical fusion device. The pretreatment speed of the mechanical fusion was 1000 rpm and the processing time was 2 min. The high-speed fusion speed was 2000 rpm and the processing time was 15 min to obtain a molybdenum alloy mixed powder. The molybdenum alloy mixed powder was placed in a reduction furnace and reduced under a hydrogen atmosphere at a reduction temperature of 700 ° C for 10 h. The purified molybdenum alloy mixed powder was placed in a soft rubber mold for pressing and molding. The soft rubber film was fixed and limited by a rigid sleeve and tied with iron wire. MPa pressure for 10 minutes to obtain a refined molybdenum alloy compact with regular shape, uniform size and qualified grain size; the refined molybdenum alloy compact was sintered in a hydrogen atmosphere at a sintering temperature of 1800℃ and kept warm for 10 hours to obtain a molybdenum alloy sintered billet with a density of 9.8±0.2 g / cm³; the molybdenum alloy sintered billet was Y-type hot rolled at a billet opening temperature of 1300℃, and the heating before or during deformation was carried out in a hydrogen atmosphere with a total deformation of 75% to obtain a deformed molybdenum alloy; the molybdenum alloy was surface washed with molten sodium hydroxide, washed with water and defect repaired, and then annealed at 800℃ for 2 hours in a vacuum environment to eliminate deformation residual stress and adjust the strength and toughness of the molybdenum alloy. The oxygen content of the high-temperature high-strength and toughness molybdenum alloy obtained was 90 ppm, the room temperature tensile strength was 1086 MPa, the elongation was 42%, and the stress-strain curve was shown in the attached figure. Figure 2 As shown, the tensile strength at 1400℃ is 364 MPa. Example 2

[0042] Molybdenum powder with a Fisher's particle size of 8 μm and a purity of not less than 99.95%, hafnium carbide powder with a Fisher's particle size of 500 nm, and carbon powder with a Fisher's particle size of 100 nm were selected and weighed according to the ratio of 978 g of molybdenum powder, 20 g of hafnium carbide powder, and 2 g of carbon powder. The mixture was then placed in a mechanical fusion device. The pretreatment speed of the mechanical fusion was 1500 rpm and the processing time was 5 min. The high-speed fusion speed was 5000 rpm and the processing time was 30 min to obtain a molybdenum alloy mixed powder. The molybdenum alloy mixed powder was placed in a reduction furnace and reduced under a hydrogen atmosphere at a reduction temperature of 200 °C for 2 h. The purified molybdenum alloy mixed powder was placed in a soft rubber mold for pressing and molding. The soft rubber film was fixed and limited by a rigid sleeve and tied with iron wire. MPa pressure for 30 min to obtain a refined molybdenum alloy compact with regular shape, uniform size and qualified grain size. The refined molybdenum alloy compact was sintered in a vacuum environment at a sintering temperature of 2300℃ for 14 h to obtain a molybdenum alloy sintered billet with a density of 9.8±0.2 g / cm³. The molybdenum alloy sintered billet was Y-type hot rolled at a billet opening temperature of 1800℃. Heating before and during deformation was carried out in a hydrogen atmosphere with a total deformation of 90%, thus obtaining a deformed molybdenum alloy. After surface alkaline washing with molten sodium hydroxide, water cleaning and defect grinding, the molybdenum alloy was annealed at 1000℃ for 2 h in a hydrogen atmosphere to eliminate deformation residual stress and adjust the strength and toughness of the molybdenum alloy. The obtained high-temperature high-strength and toughness molybdenum alloy has an oxygen content of 10 ppm, a room temperature tensile strength of 1375 MPa, an elongation of 35%, and a tensile strength of 408 MPa at 1400℃. Example 3

[0043] Molybdenum powder with a Fisher's particle size of 5 μm and a purity of not less than 99.95%, hafnium carbide powder with a Fisher's particle size of 50 nm, and carbon powder with a Fisher's particle size of 30 nm were selected and weighed according to the ratio of 989 g of molybdenum powder, 10 g of hafnium carbide powder, and 1 g of carbon powder. The mixture was then placed in a mechanical fusion device. The pretreatment speed of the mechanical fusion was 1500 rpm and the processing time was 3 min. The high-speed fusion speed was 3000 rpm and the processing time was 20 min to obtain a molybdenum alloy mixed powder. The molybdenum alloy mixed powder was placed in a reduction furnace and reduced under a vacuum environment at a reduction temperature of 500 °C for 6 h. The purified molybdenum alloy mixed powder was placed in a soft rubber mold for pressing and molding. The soft rubber film was fixed and limited by a rigid sleeve and tied with iron wire. MPa pressure for 20 minutes, and a refined molybdenum alloy compact with regular shape, uniform size and qualified grain size was obtained; the refined molybdenum alloy compact was sintered in a hydrogen atmosphere at a sintering temperature of 2000℃ and kept warm for 8 hours to obtain a molybdenum alloy sintered billet with a density of 9.8±0.2 g / cm³; the molybdenum alloy sintered billet was Y-type hot rolled at a blanking temperature of 1600℃, and the heating before or during deformation was carried out in a hydrogen atmosphere. The total deformation was 95%, and a deformed molybdenum alloy was obtained; after the molybdenum alloy was surface-washed with molten sodium hydroxide, washed with water and defect-grinded, it was annealed at 1600℃ for 1 hour in a vacuum environment to eliminate deformation residual stress and adjust the strength and toughness of the molybdenum alloy. The oxygen content of the high-temperature high-strength and toughness molybdenum alloy was 28 ppm, the room temperature tensile strength was 1020 MPa, the elongation was 50%, and the tensile strength at 1400℃ was 384 MPa. The metallographic photos and SEM images are shown in the attached Figure 3 and 4 shown.

[0044] Comparative Example 1

[0045] Commercially available molybdenum powder with a Fisher's particle size of 12 μm and a purity of not less than 99.95%, hafnium carbide powder with a Fisher's particle size of 100 nm, and carbon powder with a Fisher's particle size of 50 nm were used as raw materials. 998.5 g of molybdenum powder, 1 g of hafnium carbide powder, and 0.5 g of carbon powder were mechanically fused. The other steps were the same as in Example 1. The final molybdenum alloy had a tensile strength of 730 MPa and an elongation of 26%.

[0046] Comparative Example 2

[0047] During the deformation process, rotary swaging was used to reduce the diameter of the molybdenum alloy sintered blank, with all other processes being the same as in Example 2. Finally, the rotary swaging process yielded a molybdenum alloy material with a diameter of 10 mm and a total deformation of 80%. However, the density and mechanical properties exhibited significant heterogeneity. The head had a relative density of 99.8%, a tensile strength of 880 MPa, and an elongation of 22%. The middle had a relative density of 99.3%, a tensile strength of 830 MPa, and an elongation of 25%. The tail had a relative density of 99.5%, a tensile strength of 854 MPa, and an elongation of 20%.

[0048] Comparative Example 3

[0049] In the deformation process, the starting temperature of the Y-type hot rolling is 1100°C, the total deformation is 85%, and the molybdenum alloy is vacuum annealed at 1000°C for 1 hour. Other conditions are the same as those in Example 3. The final molybdenum alloy material has a room temperature tensile strength of 989 MPa and an elongation of 14%.

[0050] In summary, in Comparative Example 1, the molybdenum alloy prepared using commercially available molybdenum powder with a Fischer particle size of 12 μm as raw material had a significantly lower strength than that of Example 1 due to the larger raw powder particles. The molybdenum alloy material structure and performance obtained by rotary swaging for diameter reduction in Comparative Example 2 had large heterogeneity, making it difficult to achieve the advantage of uniform Y-type hot rolling structure. The cogging temperature of the Y-type hot rolling in Comparative Example 3 was low, resulting in high material strength and reduced toughness, making rolling cracks very likely to occur. Therefore, the above preparation methods are not suitable for the preparation and processing of high-strength and high-toughness molybdenum alloys for high temperatures.

[0051] The present invention provides a method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use. Through a mechanical fusion coating process, hafnium carbide powder and carbon powder are evenly coated on the surface of molybdenum powder particles, ensuring that each molybdenum particle can fully contact the reinforcing phase hafnium carbide powder and carbon powder, significantly improving the micro-uniformity of the material. The uniform distribution of hafnium carbide in the molybdenum alloy plays a role in dispersion strengthening and second-phase strengthening, improving the room temperature and high-temperature toughness, hardness and high-temperature structural stability of the molybdenum alloy. The addition of hafnium carbide effectively avoids excessive enrichment or aggregation of hafnium elements, avoids the problem of excessive strengthening and insufficient toughness and plasticity, and ensures the good machinability of the alloy in subsequent deformation processing. Carbon powder can react with oxygen to generate CO or CO2 during the high-temperature sintering stage, reducing the probability of oxide inclusions and deeply reducing the oxygen content in the molybdenum alloy. The synergistic effect of hafnium carbide and carbon significantly reduces the oxidation tendency and probability of the strengthening element hafnium, inhibits the formation of large-sized hafnium oxide particles, ensures the uniform dispersion distribution of micro-nanoscale hafnium carbide particles in the molybdenum matrix, plays a role in refining grains and strengthening grain boundaries, optimizes the microstructure and mechanical properties of the molybdenum alloy, reduces the tendency of the material to crack, and significantly improves the recrystallization temperature and high-temperature strength of the molybdenum alloy. In addition, the present invention effectively controls the oxygen / nitrogen content through purification and reduction treatment at the raw material end, significantly reduces the probability of generating hard and brittle oxygen / nitride particles, reduces the formation of oxygen / nitride impurities from the source, reduces the tough-brittle transition temperature of the material, and thus improves the sintering and deformation processing performance of the alloy. In the deformation processing stage, Y-type hot rolling with the advantages of no torsion and micro-tension is adopted to ensure that the billet is uniformly stressed, and a fine and uniform microstructure is obtained through continuous deformation. The high-strength and toughness molybdenum alloy for high temperature use provided by the present invention has excellent comprehensive performance, with an oxygen content of ≤100ppm, a room temperature tensile strength of ≥1000 MPa, an elongation of ≥30%, and a tensile strength of ≥350 MPa at 1400°C, showing good strength-toughness matching and high-temperature stability.

[0052] Some exemplary embodiments of the present invention are described above. It will be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention. The features in these embodiments can be recombined in an appropriate manner, and the solutions obtained thereby are still within the scope of protection claimed by the present invention. Based on the above embodiments, all other embodiments obtained by those skilled in the art without making creative work, that is, all modifications, equivalent substitutions and improvements made within the spirit and principles of this application, fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use, characterized in that: The steps include: (1) Fusion coating: Molybdenum powder, hafnium carbide powder, and carbon powder with a purity of not less than 99.95% are weighed in proportion, and the hafnium carbide powder and carbon powder are uniformly coated on the surface of the molybdenum powder particles by a mechanical fusion method to obtain a molybdenum alloy mixed powder; the mechanical fusion method includes a pretreatment process and a high-speed fusion process; (2) Purification and reduction: The molybdenum alloy mixed powder after mechanical fusion is placed in a heating furnace and purified in a hydrogen atmosphere or vacuum environment. The hydrogen dew point of the hydrogen atmosphere is not higher than -40 °C or the vacuum degree of the vacuum environment is less than 8×10 -3 Pa; (3) Pressing: placing the purified and reduced molybdenum alloy mixed powder into a mold and performing cold isostatic pressing to obtain a refined molybdenum alloy compact; (4) High temperature sintering: Place the refined molybdenum alloy compact into a sintering furnace and sinter in a hydrogen atmosphere or vacuum environment. The hydrogen dew point of the hydrogen atmosphere is not higher than -40 °C or the vacuum degree of the vacuum environment is less than 8 × 10 -3 Pa, to obtain a molybdenum alloy sintered blank; (5) Deformation processing: The molybdenum alloy sintered billet is subjected to Y-type hot rolling in a hydrogen atmosphere at a billet opening temperature of 1300-1800° C. and a total deformation of 75-95% to obtain a deformed molybdenum alloy; (6) Alkali cleaning and grinding: The deformed molybdenum alloy is alkaline cleaned with molten sodium hydroxide, and then rinsed with water and ground; (7) Annealing: The molybdenum alloy after grinding is annealed in a hydrogen atmosphere or vacuum environment. The hydrogen dew point of the hydrogen atmosphere is not higher than -40 ° C or the vacuum degree of the vacuum environment is 10 -2 ~10 -5 Pa, to obtain high-strength and tough molybdenum alloy for high temperature use; The alloy comprises the following components by mass percentage: HfC 0.1-2%, C 0.05-0.2%, and the balance Mo; the alloy has an oxygen content of ≤100 ppm, a room temperature tensile strength of ≥1000 MPa, an elongation of ≥30%, and a tensile strength at 1400°C of ≥350 MPa; In the step (1), the rotation speed of the pretreatment process is 1000-1500 rpm, and the processing time is 1-5 minutes; the rotation speed of the high-speed fusion process is 2000-5000 rpm, and the processing time is 10-60 minutes; In the step (2), the purification temperature is 200-700° C., and the purification time is 1-10 hours.

2. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 1, wherein: In step (1), the molybdenum powder has a Fisher particle size of 2 to 8 μm, the hafnium carbide powder has a Fisher particle size of 10 to 500 nm, and the carbon powder has a Fisher particle size of 10 to 100 nm.

3. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 2, wherein: In step (3), the cold isostatic pressing pressure is 100 to 300 MPa, and the pressing time is 5 to 30 minutes.

4. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 1 or 2, characterized in that: In step (3), the mold is a soft rubber mold, and the soft rubber mold is fixed by a rigid sleeve with holes.

5. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 4, characterized in that: In step (4), the sintering temperature is 1800-2300° C., and the sintering time is 4-14 hours.

6. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 5, characterized in that: In step (7), the annealing temperature is 800-1600° C., and the annealing time is 0.5-4 h.

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