Molybdenum alloy with high strength and toughness for high temperature and preparation method thereof

Abstract

The invention relates to the technical field of refractory metal powder metallurgy and deformation processing, in particular to a high-temperature high-strength and high-toughness molybdenum alloy and a preparation method thereof.The molybdenum alloy comprises, by mass, 0.1%-2% of HfC, 0.05%-0.2% of C and the balance Mo; molybdenum powder, hafnium carbide powder and carbon powder are used as raw materials, the warm-use high-toughness molybdenum alloy is prepared through the procedures of fusion coating, purification reduction, compression molding, high-temperature sintering, deformation machining, alkali washing coping and annealing treatment, the oxygen content of the alloy is smaller than or equal to 100 ppm, the room-temperature tensile strength is larger than or equal to 1000 MPa, the ductility is larger than or equal to 30%, the 1400-DEG C tensile strength is larger than or equal to 350 MPa, and good toughness matching and high-temperature stability are shown.

Description

Technical Field

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

[0002] Molybdenum and its alloys have the advantages of 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, strong corrosion resistance, etc. They are widely used as high-temperature structural materials and engine nozzle materials in aerospace, emitter materials for thermionic reactor diodes, rotating anode materials in medical devices, etc. With the continuous development of high-temperature application fields such as aerospace, equipment manufacturing, and nuclear industry, many high-end application scenarios have higher and higher requirements for material strength and toughness matching, high-temperature service stability, etc. Further improving the room temperature / high temperature mechanical properties of materials has become the focus of research and development of the new generation of molybdenum alloys.

[0003] The traditional method of improving the room temperature / high temperature performance of molybdenum alloys is mainly to dope Ti, Zr, Hf and other metal elements for solid solution strengthening, dope aluminum silicate potassium salt for potassium bubble strengthening, and dope rare earth oxides for second phase strengthening. With the continuous development of modern industrial high temperature application fields, traditional single mechanism strengthened molybdenum alloy materials can no longer meet the needs of high-end application scenarios. The development and preparation of multi-mechanism strengthened molybdenum alloys with excellent comprehensive properties such as room temperature / high temperature mechanical properties and high temperature structural stability is very necessary and urgent.

[0004] Hafnium carbide (HfC) is the substance with the highest melting point (3900°C) among all known single compounds, and has good chemical stability and relatively low vapor pressure. HfC is an ideal strengthener for molybdenum materials used in high-temperature applications. In high-temperature applications, strengthening molybdenum with HfC has obvious advantages. Molybdenum hafnium carbon (MHC) alloy with added Hf source and C source is also an upgraded product of titanium zirconium molybdenum (TZM) alloy, which is expected to replace traditional molybdenum alloys in key scenarios such as high-temperature die-casting molds and X-ray tube rotating anodes.

[0005] The MHC alloy is usually prepared by powder metallurgy by adding hafnium hydride and graphite or carbon black to molybdenum powder, and then sintering in hydrogen or vacuum after mixing and pressing. Since hafnium is easily combined 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 crack source. In addition, the graphite particles are relatively large and randomly and evenly distributed after mixing. Hf atoms need a long time to diffuse to react and 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 view of the problems existing in the above-mentioned prior art of uneven distribution of strengthening phase of molybdenum alloy, 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 and a preparation method thereof.

[0007] To achieve the above object, the technical solution of the present invention is as follows: A high-strength and high-toughness molybdenum alloy for high temperature use comprises the following components in terms of 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 1400°C tensile strength of ≥350 MPa.

[0008] The present invention also includes the following technical solutions: A method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use comprises the following steps: (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 for cold isostatic pressing to obtain a refined molybdenum alloy compact; (4) High temperature sintering: Place the refined molybdenum alloy blank into a sintering furnace and sinter 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 -3Pa, 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, the billet opening temperature is 1300-1800°C, and the total deformation amount is 75-95%, thereby obtaining a deformed molybdenum alloy; (6) Alkali washing and grinding: The deformed molybdenum alloy is surface washed with molten sodium hydroxide, and then rinsed with water and then 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 toughness molybdenum alloy for high temperature use.

[0009] Furthermore, in step (1), the molybdenum powder has a Fischer-Tropsch particle size of 2-8 μm, the hafnium carbide powder has a Fischer-Tropsch particle size of 10-500 nm, and the carbon powder has a Fischer-Tropsch particle size of 10-100 nm.

[0010] 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.

[0011] Furthermore, in step (2), the purification temperature is 200-700°C, and the purification time is 1-10 h.

[0012] Furthermore, in step (3), the cold isostatic pressing pressure is 100-300 MPa, and the pressing time is 5-30 min.

[0013] Furthermore, in step (3), the mold is a soft rubber mold, and the soft rubber mold is fixed by a rigid sleeve with holes.

[0014] Furthermore, in step (4), the sintering temperature is 1800-2300° C., and the sintering time is 4-14 h.

[0015] Furthermore, in step (7), the annealing temperature is 800-1600° C., and the annealing time is 0.5-4 h.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 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 uniformly 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 material cracking, 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 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 provided by the present invention has excellent comprehensive performance, oxygen content ≤100ppm, room temperature tensile strength ≥1000 MPa, elongation ≥30%, and 1400℃ tensile strength ≥350 MPa, showing good strength-toughness matching and high temperature stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which: Figure 1 The process flow chart of the preparation method of high-strength and high-toughness molybdenum alloy for high temperature is shown; Figure 2 The stress-strain curve of high-strength and high-toughness molybdenum alloy Example 1 for high temperature use is shown; Figure 3 The metallographic photograph of high-strength and high-toughness molybdenum alloy Example 3 for high temperature use is shown; 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

[0018] In order to make the purpose, technical solution 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 used to limit the present invention.

[0019] 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 shown in the attached figure. Figure 1 As shown, the following steps are included: (1) fusion coating; (2) purification and reduction; (3) pressing and forming; (4) high temperature sintering; (5) deformation processing; (6) alkali washing and grinding; (7) annealing treatment; the details are as follows: (1) Fusion coating: Molybdenum powder with a purity of not less than 99.95% and a Fisher particle size of 2-8 μm, hafnium carbide powder with a Fisher particle size of 10-500 nm, and carbon powder with a Fisher 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 treatment time is 1-5 min; the high-speed fusion speed of mechanical fusion is 2000-5000 rpm, and the treatment time is 10-60 min; to obtain a molybdenum alloy mixed powder; (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; purification temperature is 200-700℃, purification time is 1-10 h; (3) Pressing: Put 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; (4) High temperature sintering: The refined molybdenum alloy compact is placed in a sintering furnace, and the sintering furnace is heated to the sintering temperature by step-by-step heating in a hydrogen atmosphere or vacuum environment to 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 billet; (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; Y-type hot rolling processing helps to improve the uniformity of the organizational structure and mechanical properties of the deformed molybdenum alloy, thereby ensuring the high strength and toughness of the molybdenum alloy.

[0020] (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; (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, 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 tough 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 to 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 tough 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

[0021] Molybdenum powder with a Fisher particle size of 2 μm and a purity of not less than 99.95%, hafnium carbide powder with a Fisher particle size of 10 nm, and carbon powder with a Fisher 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, and then put into a mechanical fusion equipment. The pretreatment speed of 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℃ for 10 h; the purified molybdenum alloy mixed powder was placed in a soft rubber mold for pressing and molding, and the soft rubber film was fixed and limited by a rigid sleeve and tied with iron wire at 200 MPa pressure for 10 minutes to obtain a refined molybdenum alloy billet with regular shape, uniform size and qualified grain size; the refined molybdenum alloy billet 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 the deformation process 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-grinded, and then annealed at 800℃ for 2 hours in a vacuum environment to eliminate the residual stress of deformation and adjust the strength and toughness of the molybdenum alloy, and the oxygen content of the high-strength and toughness molybdenum alloy for high temperature use was 90 ppm, the room temperature tensile strength was 1086 MPa, the elongation was 42%, and the stress-strain curve was as shown in the attached figure Figure 2 As shown, the tensile strength at 1400℃ is 364 MPa. Example 2

[0022] 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 the molybdenum powder 978 g, hafnium carbide powder 20 g, and carbon powder 2 g were weighed and put into the mechanical fusion equipment. The pretreatment speed of 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, and the soft rubber film was fixed and limited by a rigid sleeve and tied with iron wire at 300 MPa pressure for 30 minutes to obtain a refined molybdenum alloy billet with regular shape, uniform size and qualified grain size; the refined molybdenum alloy billet was sintered in a vacuum environment at a sintering temperature of 2300℃ and kept warm for 14 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 1800℃, and the heating before or during deformation was carried out in a hydrogen atmosphere with a total deformation of 90% to obtain a deformed molybdenum alloy; after the molybdenum alloy was surface-washed with molten sodium hydroxide, washed with water and defect-grinded, it was annealed in a hydrogen atmosphere at 1000℃ for 2 hours to eliminate deformation residual stress and adjust the strength and toughness of the molybdenum alloy, and the high-strength and toughness molybdenum alloy for high temperature use had an oxygen content of 10 ppm, a room temperature tensile strength of 1375 MPa, an elongation of 35%, and a 1400℃ tensile strength of 408 MPa. Example 3

[0023] 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 the molybdenum powder 989 g, hafnium carbide powder 10 g and carbon powder 1 g were weighed and put into a mechanical fusion equipment. The pretreatment speed of 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℃ for 6 h; the purified molybdenum alloy mixed powder was placed in a soft rubber mold for pressing and molding, and the soft rubber film was fixed and limited by a rigid sleeve and tied with iron wire at 250 MPa pressure for 20 minutes to obtain a refined molybdenum alloy billet with regular shape, uniform size and qualified grain size; the refined molybdenum alloy billet 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 billet opening temperature of 1600℃, and the heating before or during the deformation process was carried out in a hydrogen atmosphere, with a total deformation of 95%, to obtain a deformed molybdenum alloy; the molybdenum alloy was surface-washed with molten sodium hydroxide, washed with water and defect-grinded, and then annealed at 1600℃ for 1 hour in a vacuum environment to eliminate the residual stress of deformation and adjust the strength and toughness of the molybdenum alloy, and the oxygen content of the high-strength and toughness molybdenum alloy for high temperature use was 28 ppm, the room temperature tensile strength was 1020 MPa, the elongation was 50%, the 1400℃ tensile strength was 384 MPa, and the metallographic photos and SEM pictures are as attached Figure 3 and 4 shown.

[0024] Comparative Example 1 Commercially available molybdenum powder with a Fisher particle size of 12 μm and a purity of not less than 99.95%, hafnium carbide powder with a Fisher particle size of 100 nm, and carbon powder with a Fisher particle size of 50 nm are used as raw materials, and mechanical fusion treatment is performed according to 998.5 g of molybdenum powder, 1 g of hafnium carbide powder, and 0.5 g of carbon powder; the other steps are the same as those in Example 1; the tensile strength of the final molybdenum alloy is 730 MPa, and the elongation is 26%.

[0025] Comparative Example 2 In the deformation process, rotary forging is used to reduce the diameter of the molybdenum alloy sintered blank, and the other steps are the same as those in Example 2; finally, a molybdenum alloy material with a diameter of 10 mm is obtained by rotary forging, and the total deformation amount is 80%, but the density and mechanical properties show large inhomogeneity. The relative density of the head is 99.8%, the tensile strength is 880 MPa, and the elongation is 22%; the relative density of the middle part is 99.3%, the tensile strength is 830 MPa, and the elongation is 25%; the relative density of the tail is 99.5%, the tensile strength is 854 MPa, and the elongation is 20%.

[0026] Comparative Example 3 In the deformation process, the blanking temperature of the Y-type hot rolling is 1100°C, the total deformation is 85%, the molybdenum alloy is vacuum annealed at 1000°C for 1 h, and the rest is the same as in Example 3; the final molybdenum alloy material has a room temperature tensile strength of 989 MPa and an elongation of 14%.

[0027] In summary, in Comparative Example 1, the molybdenum alloy prepared using commercially available molybdenum powder with a particle size of 12 μm as raw material has a significantly lower strength than that of Example 1 due to the larger raw material powder particles. In Comparative Example 2, the molybdenum alloy material structure and performance obtained by rotary forging for diameter reduction processing have large inhomogeneity, making it difficult to achieve the advantage of uniform Y-type hot rolling structure. In Comparative Example 3, the cogging temperature of Y-type hot rolling is relatively low, which makes the material strength high and the toughness reduced, and rolling cracks are 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.

[0028] 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 uniformly 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 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 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, reduce the probability of oxide inclusions, and deeply reduce 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 molybdenum alloys, reduces the tendency of material cracking, and significantly improves the recrystallization temperature and high-temperature strength of molybdenum alloys. 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 blank is evenly stressed, and a fine and uniform microstructure is obtained through continuous deformation. The high-strength and toughness molybdenum alloy for high temperature provided by the present invention has excellent comprehensive performance, oxygen content ≤100ppm, room temperature tensile strength ≥1000 MPa, elongation ≥30%, and 1400℃ tensile strength ≥350 MPa, showing good strength-toughness matching and high temperature stability.

[0029] Some exemplary embodiments of the present invention are described above. It can be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention. The features in these embodiments can be recombined in a suitable manner, and the scheme obtained thereby is still within the protection scope required 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 protection scope required by the present invention.

Claims

1. A high-strength and tough molybdenum alloy for high temperature use, characterized in that: The alloy comprises the following components in percentage by mass: HfC 0.1-2%, C 0.05-0.2%, and the balance is Mo; the oxygen content of the alloy is ≤100 ppm, the room temperature tensile strength is ≥1000 MPa, the elongation is ≥30%, and the tensile strength at 1400°C is ≥350 MPa.

2. A method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 1, 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 and molding: placing the purified and reduced molybdenum alloy mixed powder into a mold for cold isostatic pressing to obtain a refined molybdenum alloy compact; (4) High temperature sintering: Place the refined molybdenum alloy blank into a sintering furnace and sinter 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, 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, the billet opening temperature is 1300-1800°C, and the total deformation amount is 75-95%, thereby obtaining a deformed molybdenum alloy; (6) Alkali washing and grinding: The deformed molybdenum alloy is surface washed with molten sodium hydroxide, and then rinsed with water and then 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 toughness molybdenum alloy for high temperature use.

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

4. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 2 or 3, characterized in that: 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.

5. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 2, characterized in that: In step (2), the purification temperature is 200-700°C and the purification time is 1-10 h.

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

7. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 2 or 6, 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.

8. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 2, characterized in that: In step (4), the sintering temperature is 1800-2300°C and the sintering time is 4-14 h.

9. The method for preparing a high-strength and high-toughness molybdenum alloy for high temperature use according to claim 2, 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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