Molybdenum-rhenium alloy easy to weld and preparation process thereof

Abstract

The invention relates to an easy-to-weld molybdenum-rhenium alloy and a preparation process thereof, ammonium tetramolybdate, Re powder and ZrC powder are uniformly mixed and then calcined, then hydrogen reduction is performed to obtain alloy composite powder, and the alloy composite powder is sequentially subjected to cold isostatic pressing, pressureless sintering, hot isostatic pressing sintering, high-temperature rolling and annealing to obtain a high-density easy-to-weld molybdenum-rhenium alloy plate. The ZrC particles are added into the molybdenum-rhenium alloy, the prepared molybdenum-rhenium-zirconium carbide composite powder particles are submicron and nearly spherical, the powder sintering activity is effectively improved, grain growth in the sintering process is effectively hindered through introduction of secondary phase zirconium carbide, and grains can be refined. Zirconium carbide is dispersed and distributed in a high-density and easy-to-weld molybdenum-rhenium alloy matrix, in the welding process, zirconium carbide can absorb oxygen at an alloy grain boundary, purify the grain boundary and generate zirconium oxide in situ, recrystallization embrittlement caused by rapid growth of grains in the welding process is inhibited, the strength, plasticity and toughness of the molybdenum-rhenium alloy can be effectively improved, and the welding performance of the molybdenum-rhenium alloy is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of alloy preparation, and in particular relates to an easily weldable molybdenum-rhenium alloy and a preparation process thereof. Background Art

[0002] Molybdenum-rhenium alloy has attracted wide attention due to its excellent toughness, ductility, and low ductile-brittle transition temperature. Under high temperature conditions, molybdenum-rhenium alloy has good compatibility with commonly used nuclear fuels such as UN, UC, and UO2, and can reduce the safety accidents caused by low weld strength during the launch phase of space nuclear reactors. The core structural material of a nuclear reactor is a thin-walled tube, and tungsten alloy has a high density and is brittle, so it cannot be used. Molybdenum-rhenium alloy is considered the best candidate for the core structural material of a nuclear reactor due to its small neutron absorption cross section and moderate density.

[0003] At present, Mo-14Re, Mo-30Re and Mo-47Re are commonly used in nuclear reactor cores. The higher the rhenium content, the better the welding performance of the molybdenum-rhenium alloy. However, the molybdenum-rhenium alloy is easily oxidized to form an oxide film under high temperature environment, which hinders the welding process. In addition, too high rhenium content is easy to generate brittle molybdenum-rhenium compounds at high temperature, which reduces the toughness of the molybdenum-rhenium alloy and is not conducive to welding. In addition, rhenium elements undergo transmutation after being irradiated by neutrons and react with neutrons at the same time, reducing the life of the nuclear reactor core. The low rhenium content leads to insufficient high-temperature plasticity and toughness of the molybdenum-rhenium alloy, and the low recrystallization temperature. During welding, the welding temperature is higher than the recrystallization temperature, resulting in embrittlement of the heat-affected zone, which greatly reduces the performance of the molybdenum-rhenium alloy. In summary, it is particularly important to design a molybdenum-rhenium alloy with a low rhenium content that does not affect the welding performance. Summary of the invention

[0004] The purpose of the present invention is to provide an easy-to-weld molybdenum-rhenium alloy and a preparation process thereof. ZrC particles are added to the molybdenum-rhenium alloy. ZrC can absorb oxygen at the grain boundaries of the molybdenum-rhenium alloy, generate ZrO2 in situ, and purify the grain boundaries, thereby effectively improving the strength and plastic toughness of the molybdenum-rhenium alloy and improving the welding performance of the molybdenum-rhenium alloy.

[0005] The present invention is specifically implemented by the following technical scheme. According to a preparation process of an easy-to-weld molybdenum-rhenium alloy proposed by the present invention, the following steps are included:

[0006] (1) placing ammonium tetramolybdate, Re powder and ZrC powder in a dual-power mixer and mixing them evenly to obtain a molybdenum-rhenium-zirconium carbide composite powder; wherein the Re powder accounts for 3% to 9% of the mass of the composite powder, the ZrC powder accounts for 0.3% to 0.6% of the mass of the composite powder, and the remainder is ammonium tetramolybdate;

[0007] (2) calcining the molybdenum-rhenium-zirconium carbide composite powder obtained in step (1) and then performing hydrogen reduction to obtain a molybdenum-rhenium alloy composite powder;

[0008] (3) The molybdenum-rhenium alloy composite powder obtained in step (2) is subjected to cold isostatic pressing, pressureless sintering, hot isostatic pressing, high-temperature rolling, and annealing in sequence to obtain a high-density and easily weldable molybdenum-rhenium alloy plate.

[0009] Preferably, in step (1), the speed of the dual-power mixer is 20 to 50 r / min, and the mixing time is 6 to 10 h.

[0010] Preferably, the calcination in step (2) is carried out in air at a temperature of 450-550°C for 4-6 hours. The hydrogen reduction comprises two stages of hydrogen reduction, wherein the first stage of hydrogen reduction is carried out at a temperature of 350-550°C and a hydrogen flow rate of 15-20 m 3 / h, keep warm for 5 to 10 hours; the second stage hydrogen reduction temperature is 750 to 900 ° C, the hydrogen flow rate is 20 to 25m 3 / h, keep warm for 8 to 12 hours.

[0011] Preferably, in step (3), the cold isostatic pressing of the pressed blank adopts a cold isostatic press with a pressure of 150-200 MPa and a holding pressure of 20-30 min; the pressureless sintering adopts a pressureless medium frequency furnace and introduces hydrogen, the sintering temperature is 2000-2200°C, the holding time is 6-12 h, and the hydrogen flow rate is 18-20 m 3 / h; the hot isostatic pressing sintering temperature is 1900-2000°C, the holding time is 1-3h, the heating rate is 10°C / min, and the peak pressure is 150-180MPa.

[0012] Preferably, the high temperature rolling in step (3) is carried out in a hydrogen atmosphere, the blanking temperature is 1300-1650°C, and the hydrogen flow rate is 10-15m 3 / h, single deformation is 20-30%, one fire and one pass, cross rolling, total deformation>60%.

[0013] Preferably, the annealing in step (3) is vacuum recrystallization annealing, the annealing temperature is 1200-1400°C, the holding time is 0.5-1h, and the vacuum degree is>10 -2 MPa, cooled with furnace.

[0014] The room temperature tensile strength of the easy-to-weld molybdenum-rhenium alloy prepared by the above method is greater than 200 MPa, and the elongation is greater than 12%. Vacuum electron beam welding is used during welding, and the vacuum degree is 10 -4 ~10 -5 Pa, voltage 100~150KV, beam intensity 5~16mA, welding speed 10~25mm / s.

[0015] Compared with the prior art, the present invention has obvious advantages and beneficial effects. By means of the above technical solution, the present invention can achieve considerable technical progress and practicality, and has a wide range of utilization value, and has at least the following advantages:

[0016] The present invention mixes zirconium carbide, molybdenum dioxide and rhenium powder, calcines and reduces the molybdenum-rhenium zirconium carbide precursor composite powder to obtain a molybdenum-rhenium alloy powder doped with zirconium carbide, and then performs cold isostatic pressing and pressureless sintering and then hot isostatic pressing for secondary sintering to obtain a molybdenum-rhenium alloy with higher density, and finally performs high-temperature rolling and vacuum recrystallization annealing to obtain a high-density and easy-to-weld molybdenum-rhenium alloy. The prepared molybdenum-rhenium-zrcarbon composite powder particles are submicron and nearly spherical, which can effectively improve the sintering activity of the powder. The introduction of the secondary phase zirconium carbide can effectively hinder the growth of grains during the sintering process, refine the grains, and improve the high-temperature strength of the molybdenum-rhenium alloy. In the easy-to-weld molybdenum-rhenium alloy, zirconium carbide particles are dispersed in the alloy matrix. During the welding process, zirconium carbide absorbs oxygen impurities at the grain boundaries, purifies the grain boundaries, and forms nano zirconium oxide in situ, thereby increasing the recrystallization temperature and high-temperature strength of the molybdenum-rhenium alloy, and inhibiting the rapid growth of grains during the welding process and causing recrystallization embrittlement. The structure of the molybdenum-rhenium alloy weld is uniform and dense, which significantly reduces the number of pores in the weld, reduces the area of ​​the weld heat-affected zone, and obtains a higher weld strength. The room temperature tensile strength of the prepared high-density and easy-to-weld molybdenum-rhenium alloy can reach 240MPa, and the elongation can reach more than 12%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a SEM image of the molybdenum-rhenium-zirconium carbide composite powder prepared in Example 1.

[0018] Figure 2 This is the EDS element distribution diagram of the molybdenum-rhenium-zirconium carbide composite powder prepared in Example 1.

[0019] Figure 3 This is a SEM image of the weld of the high-density and easy-to-weld molybdenum-rhenium alloy plate prepared in Example 1 after vacuum electron beam welding.

[0020] Figure 4 This is the EDS element distribution diagram of the high-density and easy-to-weld molybdenum-rhenium alloy plate prepared in Example 1.

[0021] Figure 5 yes Figure 3 A partial enlarged view of .

[0022] Figure 6 yes Figure 5 Point scan of the zirconium carbide particles at Point 1.

[0023] Figure 7 This is a SEM image of the weld of the molybdenum-rhenium alloy prepared in Comparative Example 1 after vacuum electron beam welding.

[0024] Figure 8 It is the room temperature tensile strength of the molybdenum-rhenium alloy weld prepared in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] The present invention is described in detail with specific examples below. If no specific conditions are specified in the following examples, they are all carried out according to conventional conditions or conditions recommended by the manufacturer. The raw materials and reagents used without specifying the manufacturer are all conventional products that can be purchased from the market.

[0027] Example 1

[0028] (1) ammonium tetramolybdate, Re powder and ZrC powder are placed in a dual-power mixer as composite powders and mixed evenly to obtain molybdenum-rhenium-zirconium carbide composite powders. The speed of the dual-power mixer is 30 r / min and the mixing time is 10 h. Among them, Re powder accounts for 3% of the mass of the composite powder, ZrC powder accounts for 0.4% of the mass of the composite powder, and the remainder is ammonium tetramolybdate;

[0029] (2) calcining the molybdenum-rhenium-zirconium carbide composite powder obtained in step (1) and then performing hydrogen reduction to obtain a zirconium carbide-reinforced molybdenum-rhenium alloy composite powder;

[0030] In this step, calcination is carried out in air at a temperature of 450°C for 4 hours; hydrogen reduction includes two stages of hydrogen reduction, the first stage of which is at a temperature of 400°C and a hydrogen flow rate of 16 m 3 / h, keep warm for 5h; the second stage hydrogen reduction temperature is 800℃, the hydrogen flow rate is 20m 3 / h, keep warm for 8h;

[0031] (3) The molybdenum-rhenium alloy composite powder obtained in step (2) is subjected to cold isostatic pressing, pressureless sintering, hot isostatic pressing, high-temperature rolling, and annealing in sequence to obtain a high-density and easily weldable molybdenum-rhenium alloy plate.

[0032] In this step, the cold isostatic pressing machine is used for the cold isostatic pressing of the compact, the pressure is 180 MPa, and the pressure is maintained for 20 min; the pressureless sintering is carried out by using a pressureless medium frequency furnace, the sintering temperature is 2100 ° C, the holding time is 6 h, and the hydrogen flow rate is 18 m 3 / h; the hot isostatic pressing sintering temperature is 1800℃, the holding time is 0.5h, the heating rate is 10℃ / min, and the peak pressure is 180MPa; the high-temperature rolling is carried out in a hydrogen atmosphere, the blanking temperature is 1350℃, and the hydrogen flow rate is 10m 3 / h, single deformation is 20%, one pass per heat, cross rolling, 4 passes, total deformation is 72%; annealing uses vacuum recrystallization annealing, annealing temperature is 1200℃, holding time is 0.5h, vacuum degree>10 -2 MPa, cooled with furnace.

[0033] The high-density and easy-to-weld molybdenum-rhenium alloy plate prepared in this embodiment is welded by vacuum electron beam welding with a vacuum degree of 10 -4 Pa, voltage 100KV, beam intensity 5mA, welding speed 10mm / s.

[0034] Figure 1 This is a SEM image of the molybdenum-rhenium-zirconium carbide composite powder prepared in Example 1. It can be seen that the molybdenum-rhenium-zirconium carbide composite powder is in the form of submicron nearly spherical particles, which are fine and uniform, with a particle size of about 0.3-1 μm.

[0035] Figure 2 This is the EDS element distribution diagram of the molybdenum-rhenium-zirconium carbide composite powder prepared in Example 1. It can be seen that the four elements of molybdenum, rhenium, carbon and zirconium are evenly distributed.

[0036] Figure 3 This is a SEM image of the weld of the high-density and easy-to-weld molybdenum-rhenium alloy plate prepared in Example 1 after vacuum electron beam welding. It can be seen that the organizational structure at the weld of the alloy plate is relatively uniform and the number of pores is relatively small.

[0037] Figure 4 : This is the EDS element distribution diagram of the high-density and easy-to-weld molybdenum-rhenium alloy plate prepared in Example 1. It can be seen that the Mo, Re, Zr, C, and O elements are evenly distributed in the molybdenum-rhenium alloy.

[0038] Figure 5 yes Figure 3 From the local enlarged image, it can be seen that the second phase particles are evenly distributed.

[0039] Figure 6 yes Figure 5 The point scan of the zirconium carbide particles at Point 1 shows that during the welding process, the zirconium carbide absorbs oxygen and generates zirconium oxide in situ, thus strengthening the weld structure.

[0040] Example 2

[0041] (1) ammonium tetramolybdate, Re powder and ZrC powder are placed in a dual-power mixer as composite powders and mixed evenly to obtain molybdenum-rhenium-zirconium carbide composite powders. The speed of the dual-power mixer is 40 r / min and the mixing time is 8 h. Among them, Re powder accounts for 5% of the mass of the composite powder, ZrC powder accounts for 0.6% of the mass of the composite powder, and the remainder is ammonium tetramolybdate;

[0042] (2) calcining the molybdenum-rhenium-zirconium carbide composite powder obtained in step (1) and then performing hydrogen reduction to obtain a zirconium carbide-reinforced molybdenum-rhenium alloy composite powder;

[0043] In this step, calcination is carried out in air at a temperature of 550°C for 5 hours; hydrogen reduction includes two stages of hydrogen reduction, the first stage of which is at a temperature of 350°C and a hydrogen flow rate of 18m 3 / h, keep warm for 6h; the second stage hydrogen reduction temperature is 750℃, the hydrogen flow rate is 25m 3 / h, keep warm for 12h;

[0044] (3) The molybdenum-rhenium alloy composite powder obtained in step (2) is subjected to cold isostatic pressing, pressureless sintering, hot isostatic pressing, high-temperature rolling, and annealing in sequence to obtain a high-density and easily weldable molybdenum-rhenium alloy plate.

[0045] In this step, the cold isostatic pressing of the billet adopts a cold isostatic press with a pressure of 200MPa and a holding pressure of 30min; the pressureless sintering adopts a pressureless medium frequency furnace with a sintering temperature of 2200℃, a holding time of 10h, and a hydrogen flow rate of 18℃ / min; the hot isostatic pressing sintering temperature is 1900℃, the holding time is 1h, the heating rate is 10℃ / min; the peak pressure is 150MPa; the high temperature rolling is carried out in a hydrogen atmosphere, the billet opening temperature is 1400℃, and the hydrogen flow rate is 12m 3 / h, single deformation is 30%, one pass per heat, cross rolling, 4 passes, total deformation is 76%; annealing uses vacuum recrystallization annealing, annealing temperature is 1300℃, holding time is 1h, vacuum degree>10 -2 MPa, cooled with furnace.

[0046] The high-density and easy-to-weld molybdenum-rhenium alloy plate prepared in this embodiment is welded by vacuum electron beam welding with a vacuum degree of 10 -5 Pa, voltage 120KV, beam intensity 10mA, welding speed 15mm / s.

[0047] Example 3

[0048] (1) ammonium tetramolybdate, Re powder and ZrC powder are placed in a dual-power mixer as composite powders and mixed evenly to obtain molybdenum-rhenium-zirconium carbide composite powders. The speed of the dual-power mixer is 50 r / min and the mixing time is 6 h. Among them, Re powder accounts for 9% of the mass of the composite powder, ZrC powder accounts for 0.3% of the mass of the composite powder, and the remainder is ammonium tetramolybdate;

[0049] (2) calcining the molybdenum-rhenium-zirconium carbide composite powder obtained in step (1) and then performing hydrogen reduction to obtain a zirconium carbide-reinforced molybdenum-rhenium alloy composite powder;

[0050] In this step, calcination is carried out in air at a temperature of 500°C for 6 hours; hydrogen reduction includes two stages of hydrogen reduction, the first stage of which is at a temperature of 550°C and a hydrogen flow rate of 16 m 3 / h, keep warm for 8h; the second stage hydrogen reduction temperature is 850℃, the hydrogen flow rate is 20m 3 / h, keep warm for 10h;

[0051] (3) The molybdenum-rhenium alloy composite powder obtained in step (2) is subjected to cold isostatic pressing, pressureless sintering, hot isostatic pressing, high-temperature rolling, and annealing in sequence to obtain a high-density and easily weldable molybdenum-rhenium alloy plate.

[0052] In this step, the cold isostatic pressing machine is used for cold isostatic pressing, the pressure is 150MPa, and the pressure is maintained for 30min; the pressureless sintering adopts a pressureless medium frequency furnace, the sintering temperature is 2000℃, the holding time is 10h, and the hydrogen flow rate is 20m 3 / h; the hot isostatic pressing sintering temperature is 2000℃, the holding time is 2h, the heating rate is 10℃ / min, and the peak pressure is 160MPa; the high temperature rolling is carried out in a hydrogen atmosphere, the blanking temperature is 1500℃, and the hydrogen flow rate is 15m 3 / h, single deformation is 25%, one pass per heat, cross rolling, 4 passes, total deformation is 69%; annealing uses vacuum recrystallization annealing, annealing temperature is 1400℃, holding time is 0.5h, vacuum degree>10 -2 MPa, cooled with furnace.

[0053] The high-density and easy-to-weld molybdenum-rhenium alloy plate prepared in this embodiment is welded by vacuum electron beam welding with a vacuum degree of 10 -4 Pa, voltage 150KV, beam intensity 16mA, welding speed 20mm / s.

[0054] Comparative Example 1

[0055] (1) placing ammonium tetramolybdate and Re powder as composite powders in a dual-power mixer and mixing them evenly to obtain molybdenum-rhenium composite powders, the speed of the dual-power mixer is 30 r / min, and the mixing time is 8 h; wherein the Re powder accounts for 4% of the mass of the composite powders, and the remainder is ammonium tetramolybdate;

[0056] (2) Same as Example 1;

[0057] (3) A molybdenum-rhenium alloy is obtained in the same manner as in Example 1. The welding process of the molybdenum-rhenium alloy in Comparative Example 1 is the same as in Example 1.

[0058] Figure 7 The SEM image of the weld of the molybdenum-rhenium alloy prepared in Example 1 after vacuum electron beam welding is shown in Figure 1. Figure 3 In comparison, it is obvious that the heat affected zone of the molybdenum-rhenium alloy prepared in Comparative Example 1 is more obvious, the structure at the weld is coarse and uneven, and the number of pores is significantly more than that in Example 1.

[0059] Figure 8 It is the room temperature tensile strength of the molybdenum-rhenium alloy weld prepared in Example 1 and Comparative Example 1. It can be seen that the room temperature tensile strength and elongation of the high-density and easy-to-weld molybdenum-rhenium alloy prepared in Example 1 are significantly higher than those of the molybdenum-rhenium alloy prepared in Comparative Example 1. The room temperature tensile strength of the molybdenum-rhenium alloy prepared in Comparative Example 1 is 135 MPa, and the elongation is 10.3%. The room temperature tensile strength of the high-density and easy-to-weld molybdenum-rhenium alloy prepared in Example 1 is 240 MPa, and the elongation is 12.8%.

[0060] The above is only an embodiment of the present invention, and does not limit the present invention in any form. The present invention can also have other forms of embodiments according to the above structures and functions, which are not listed one by one. Therefore, any simple modification, equivalent change and modification made by any technician familiar with the profession to the above embodiment according to the technical essence of the present invention without departing from the scope of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. An easily weldable molybdenum-rhenium alloy, characterized in that Prepare as follows: (1) placing ammonium tetramolybdate, Re powder and ZrC powder in a dual-power mixer and mixing them evenly to obtain a molybdenum-rhenium-zirconium carbide composite powder; wherein the Re powder accounts for 3% to 9% of the mass of the composite powder, the ZrC powder accounts for 0.3% to 0.6% of the mass of the composite powder, and the remainder is ammonium tetramolybdate; (2) calcining the molybdenum-rhenium-zirconium carbide composite powder obtained in step (1) and then performing hydrogen reduction to obtain a molybdenum-rhenium alloy composite powder; (3) The molybdenum-rhenium alloy composite powder obtained in step (2) is subjected to cold isostatic pressing, pressureless sintering, hot isostatic pressing, high-temperature rolling, and annealing in sequence to obtain a high-density and easily weldable molybdenum-rhenium alloy plate.

2. The easily weldable molybdenum-rhenium alloy according to claim 1, characterized in that In step (1), the speed of the dual-power mixer is 20 to 50 r / min, and the mixing time is 6 to 10 hours.

3. The easily weldable molybdenum-rhenium alloy according to claim 1, characterized in that In step (2), calcination is carried out in air at a temperature of 450 to 550° C. for 4 to 6 hours.

4. The easily weldable molybdenum-rhenium alloy according to claim 1, characterized in that The hydrogen reduction in step (2) includes two stages of hydrogen reduction. The first stage of hydrogen reduction is performed at a temperature of 350 to 550°C and a hydrogen flow rate of 15 to 20 m 3 / h, keep warm for 5 to 10 hours; the second stage hydrogen reduction temperature is 750 to 900 ° C, the hydrogen flow rate is 20 to 25m 3 / h, keep warm for 8 to 12 hours.

5. The easily weldable molybdenum-rhenium alloy according to claim 1, characterized in that In step (3), the cold isostatic pressing of the pressed blank is performed using a cold isostatic press at a pressure of 150-200 MPa for 20-30 min. The pressureless sintering is performed using a pressureless medium frequency furnace and hydrogen is introduced at a sintering temperature of 2000-2200°C for 6-12 h and a hydrogen flow rate of 18-20 m 3 / h; the hot isostatic pressing sintering temperature is 1900-2000°C, the holding time is 1-3h, the heating rate is 10°C / min, and the peak pressure is 150-180MPa.

6. The easily weldable molybdenum-rhenium alloy according to claim 1, characterized in that In step (3), high temperature rolling is carried out in a hydrogen atmosphere, the blanking temperature is 1300-1650°C, and the hydrogen flow rate is 10-15m 3 / h, single deformation is 20-30%, one fire and one pass, cross rolling, total deformation>60%.

7. The easily weldable molybdenum-rhenium alloy according to claim 1, characterized in that In step (3), vacuum recrystallization annealing is used, the annealing temperature is 1200-1400°C, the holding time is 0.5-1h, and the vacuum degree is>10 -2 MPa, cooled with furnace.

8. The easily weldable molybdenum-rhenium alloy according to claim 1, characterized in that The room temperature tensile strength is greater than 200 MPa and the elongation is greater than 12%.

9. The easily weldable molybdenum-rhenium alloy according to claim 1, characterized in that The molybdenum-rhenium alloy is welded by vacuum electron beam welding with a vacuum degree of 10 -4 ~10 -5 Pa, voltage 100~150KV, beam intensity 5~16mA, welding speed 10~25mm / s.

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