A low-activation refractory multi-component alloy and preparation method thereof

Abstract

The present invention discloses a low-activation refractory multi-component alloy and a preparation method thereof. By introducing low-activation Cr and V solid solution elements on the basis of the high-melting-point W element, the alloy composition is W x Cr y V z , where x = 33 - 90, y = 5 - 33, z = 5 - 33, and x + y + z = 100, and x, y, and z are all atomic percentages. A powder metallurgy method with low energy consumption and near-net shaping is adopted to obtain an alloy structure with an ultrafine-grained BCC solid solution as the matrix and nanometer- and sub-micron-sized second phases dispersed therein. The low-activation W-Cr-V series alloys of the present invention exhibit excellent high-temperature thermal stability and high-temperature strength, and have more potential radiation resistance performance compared with the existing nuclear materials, and are expected to be applied to aerospace, nuclear industry and other high-temperature and radiation fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal materials and preparation thereof, and specifically relates to a low-activation, high-thermal-stability, high-strength, refractory W-Cr-V series multi-component alloy system and a preparation method thereof. Background Art

[0002] With the depletion of non-renewable fossil energy and the improvement of people's environmental awareness, human society's demand for clean energy is also increasing. Deuterium-tritium nuclear fusion, as a safe and controllable source of clean energy, is expected to become one of the main energy sources in the future. The common deuterium-tritium nuclear fusion reaction in fusion reactors will produce 3.5MeV high-energy He ions and 14.1MeV high-energy neutrons. The energy of the reaction products is much higher than that of the fission reactor nuclear reaction products, and the corresponding nuclear energy material radiation damage is also more severe. In order to avoid the generation of highly radioactive products after reaction with neutrons, the material also has a low activation requirement.

[0003] In traditional single-component alloys, atoms diffuse quickly, and the binding energy of defects such as interstitial rings is relatively high, which makes it easy to form more defects after irradiation. High-entropy alloys, as a new type of multi-component alloy developed in recent years, can effectively inhibit the formation of irradiation defects or promote the recombination of irradiation defects due to their lattice distortion effect in structure, hysteresis diffusion effect in kinetics, and cocktail effect in performance, and have shown good application prospects in the field of radiation resistance.

[0004] As one of the metals with high atomic number and highest melting point, tungsten can effectively shield high-energy particles such as gamma rays, and also has a good deceleration effect on fast neutrons. Combined with the cocktail effect on the performance of high-entropy alloys, tungsten-containing multi-component alloys are expected to achieve a good combination of high-temperature stability, high-temperature mechanical properties and radiation resistance. Low-activation tungsten-rich multi-component alloys have significant advantages in extreme environments such as high temperature, high heat load, and strong radiation, and are not easy to produce radioactive elements after service. They are a very promising new nuclear energy material and radiation shielding material. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] The present invention is proposed in view of the problems of poor high temperature thermal stability and insufficient high temperature strength of low-activated nuclear materials in the prior art.

[0007] Therefore, the object of the present invention is to overcome the deficiencies in the prior art and provide a low-activation refractory multi-component alloy.

[0008] To solve the above technical problems, the present invention provides the following technical solution: the low-activation refractory multi-component alloy is composed of three low-activation elements W, Cr, and V, and the alloy composition is WxCryVz, wherein x=33-90, y=5-33, z=5-33, x+y+z=100, wherein x, y, and z are all atomic percentages.

[0009] As a preferred solution of the preparation method of the present invention, the atomic percentage of W is greater than 30%, the sum of the contents of Cr and V elements is between 10% and 70%, and the sum of the atomic percentages of each component is 100%.

[0010] As a preferred solution of the preparation method of the present invention, the atomic percentage composition of the alloy is 60-94% W, 3-25% Cr, and 3-30% V.

[0011] As a preferred embodiment of the preparation method of the present invention, the low-activation refractory multi-component alloy has the following characteristics:

[0012] (a) It has an ultrafine grain structure, with BCC disordered solid solution as the matrix and dispersed second phase;

[0013] (b) It has high thermal stability, with an average grain size of less than 1 μm after heat treatment at 1200°C for 1 hour and an average grain size of less than 2 μm after heat treatment at 1500°C for 1 hour;

[0014] (c) The high temperature compressive strength at 1100°C is 1200-1800 MPa, and the compressive strain at 1100°C is greater than 5%;

[0015] (d) The high temperature compressive strength at 1200℃ is 400~600MPa, and the compressive strain at 1200℃ is greater than 30%.

[0016] Another object of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing a low-activated refractory multi-component alloy.

[0017] In order to solve the above technical problems, the present invention provides the following technical solutions: including preparing each component according to the atomic percentage of the alloy, high-energy ball milling under inert gas protection conditions, powder screening and then sintering in a mold.

[0018] As a preferred embodiment of the preparation method of the present invention, the high-energy ball mill uses cemented carbide balls and cemented carbide lined containers, the ball milling speed is 200-300 rpm, and the total ball milling time is 1500-3000 min.

[0019] As a preferred solution of the preparation method of the present invention, the mass ratio of the cemented carbide ball to all powders of each component of the alloy is 5:1 to 10:1.

[0020] As a preferred embodiment of the preparation method of the present invention, the initial vacuum degree during sintering is 0-40Pa.

[0021] As a preferred embodiment of the preparation method of the present invention, the sintering heating rate is greater than 50°C / min, and the sintering temperature is 1300-1700°C.

[0022] As a preferred embodiment of the preparation method of the present invention, the sintering heat preservation time is 1 to 30 minutes, and the pressure during sintering is 30 to 50 MPa.

[0023] Beneficial effects of the present invention:

[0024] (1) Compared with W-Re, W-Mo, WTaCrVHf and other alloys, the W-Cr-V multi-component alloy of the present invention uses all low-activation elements, produces fewer transmutation activation products, and has low activation characteristics. After serving in a nuclear reactor, its induced radioactivity is greatly reduced.

[0025] (2) W-Cr-V alloys have a multiphase, ultrafine grain structure, high room temperature strength, and good wear resistance. The alloy has excellent thermal stability and high temperature strength. It is expected to be used as a structural material, plasma-facing material, or coating for future fusion reactor systems.

[0026] (3) Aiming at the requirements of advanced nuclear energy systems for service materials, the present invention develops and prepares a W-Cr-V series multi-component alloy with low activation, high thermal stability and high strength in a low-energy consumption manner by screening low-activation elements, calculating thermodynamic phase diagrams, and combining powder metallurgy methods. The obtained nuclear materials are more suitable for fusion reactors and new generation fission reactors at higher service temperatures and service doses, solving the problems of insufficient high-temperature thermal stability, easy recrystallization, and insufficient high-temperature strength of traditional low-activation nuclear materials.

[0027] (4) The present invention provides a low-activation, high-thermal-stability, high-strength W-Cr-V multi-component alloy based on a powder metallurgy method. The element powders are mixed uniformly and preliminarily alloyed by a high-energy ball milling method, while reducing the grain size and powder particle size, and introducing high distortion energy. Subsequently, bulk ultrafine-grained materials are prepared by spark plasma sintering (SPS) or rapid hot pressing (FHP). BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for the description of the embodiments. The drawings described below are only representative pictures of the embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0029] Figure 1 It is a scanning electron microscope morphology image of the alloy powder after ball milling in Example 1 of the present invention and a particle size distribution curve of the powder.

[0030] Figure 2 It is the XRD spectrum of the ball-milled powder and the SPS sintered block of the alloy material in Example 1 of the present invention.

[0031] Figure 3 This is a scanning electron microscope morphology image and element distribution image of the alloy bulk material of Example 1 of the present invention.

[0032] Figure 4 This is a scanning electron microscope backscattering morphology image of the alloy material of Example 1 of the present invention after heat treatment at 1200, 1400, and 1500° C. for 1 hour.

[0033] Figure 5 It is a room temperature compression engineering stress-engineering strain curve diagram and a fracture morphology diagram of the alloy material of Example 1 of the present invention.

[0034] Figure 6 It is a high temperature compression engineering stress-engineering strain curve diagram of the alloy material of Example 1 of the present invention at 1100°C and 1200°C.

[0035] Figure 7 This is a scanning electron microscope morphology of the deformation structure of the alloy material of Example 1 of the present invention after high-temperature compression at 1200°C.

[0036] Figure 8 This is the XRD spectrum of the fast hot pressing (FHP) bulk material of the alloy material in Example 2 of the present invention.

[0037] Fig. 9 This is the SEM morphology and EDS element distribution of the alloy material of Example 2 of the present invention.

[0038] Fig.10 It is a room temperature compression engineering stress-engineering strain curve diagram and a fracture morphology diagram of the alloy material of Example 2 of the present invention.

[0039] Fig.11 It is a high temperature compression engineering stress-engineering strain curve diagram of the alloy material of Example 2 of the present invention at 1100°C and 1200°C.

[0040] Fig.12This is a scanning electron microscope morphology of the deformation structure of the alloy material of Example 2 of the present invention after high-temperature compression at 1200°C.

[0041] Fig.13 It is the XRD spectrum of the powder after ball milling and the bulk material after SPS sintering of the alloy material in Example 3 of the present invention.

[0042] Fig.14 It is the scanning electron microscope morphology and EDS element distribution of the alloy material of Example 3 of the present invention.

[0043] Fig.15 This is a scanning electron microscope backscattering morphology image of the alloy material of Example 3 of the present invention after heat treatment at 1200, 1400, and 1500° C. for 1 hour.

[0044] Fig.16 It is a room temperature compression engineering stress-engineering strain curve diagram and a fracture morphology diagram of the alloy material of Example 3 of the present invention.

[0045] Fig.17 It is the scanning electron microscope morphology image and EDS element distribution of the alloy material of comparative example 2 of the present invention.

[0046] Fig.18 It is a room temperature compression engineering stress-engineering strain curve diagram of the alloy material of comparative example 2 of the present invention. DETAILED DESCRIPTION

[0047] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0048] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0049] Unless otherwise specified, the experimental methods used in the examples are all conventional methods; the raw materials used in the examples are all commercially purchased.

[0050] The present invention provides a low activation, high thermal stability, high strength, refractory W-Cr-V series multi-component alloy material system. The W-Cr-V series multi-component alloy has the following atomic percentage components: W 90 Cr 5 V 5 , W 70 Cr 15 V15 .

[0051] Example 1

[0052] 1) Raw material powder weighing ratio and canning

[0053] Using W, Cr, and V element powders with a purity of more than 99.9% and particles less than 200 mesh as raw materials, the mixture was prepared in an argon-protected glove box according to the chemical formula W 70 Cr 15 V 15 The above powders are loaded into a carbide ball mill, and carbide balls are placed in a ball-to-material ratio of 5:1. The ball mill is sealed under argon protection, or the ball mill is repeatedly evacuated and filled with high-purity argon three times after sealing to ensure that the subsequent powder ball milling is carried out under argon protection.

[0054] 2) High energy ball milling

[0055] This step mainly uses the high-energy ball milling method to preliminarily alloy the element powder, while refining the powder and increasing the strain within the powder, thereby reducing the subsequent sintering temperature and shortening the sintering time.

[0056] Install the ball mill jar on the ball mill according to the equipment requirements, set the ball milling time to 2000min, and the ball milling speed to 300rpm (to reduce the temperature rise during the ball milling process, the machine can be stopped for 5-10 minutes for cooling after every 20-30 minutes of ball milling). After the ball milling is completed, the ball mill jar should be fully cooled at room temperature.

[0057] 3) Powder screening, storage and filling mold

[0058] Open the ball mill in air or under argon protection, pass the ball-milled powder through a 200-mesh standard sample sieve, and fill the powder into a mold or vacuum pack it / store it in inert gas for later use.

[0059] 4) Sintering

[0060] The pre-alloyed powder after ball milling and screening is loaded into a graphite mold protected and lubricated by graphite paper and pre-pressed at 40MPa. The powder is sintered into a dense bulk alloy material in a low-energy manner through spark plasma sintering (SPS) under vacuum (vacuum degree better than 40Pa). The heating rate is 100℃ / min, the sintering temperature is 1400℃, the holding time is 5min, and the pressure is maintained at 40MPa during sintering. After sintering, the temperature is lowered to below 400℃ with the furnace, and then the furnace door is opened to demould and take out the alloy sample.

[0061] Room temperature compression characterization method: The sample was processed into a Φ4*6mm cylindrical sample by electric spark wire cutting method, and the surface was descaled and polished smooth with sandpaper. The strain rate during room temperature compression was 0.001 / s.

[0062] High temperature compression characterization method: The sample was processed into a Φ6*9mm cylindrical sample by the electric spark wire cutting method, and the surface was descaled and polished with sandpaper. The thermocouple wire was welded to the center of the sample for accurate temperature measurement. Vacuum high temperature compression was performed using a Gleeble thermal simulator. The heating rate was 5℃ / s, the target temperature was kept for 1min, and the strain rate was 0.001 / s.

[0063] Heat treatment method: Cut the sample wire into appropriate size, polish the oxide skin and seal the quartz tube in vacuum. Put it into the muffle furnace and heat it up with the furnace or put it in after reaching the target temperature. After keeping the target temperature for 1 hour, take out the quartz tube, smash it and quench it with water, or take it out after cooling it with the furnace. The sample after polishing the oxide skin can also be placed in an atmosphere protection heat treatment furnace for heat treatment, or other methods can be used to avoid sample oxidation during the heat treatment process.

[0064] Depend on Figure 5-11 It can be seen that the powder obtained after ball milling of the alloy of this embodiment has been basically alloyed, locally rich in Cr and V elements, and the powder is refined to a D50 of 3.24μm. After SPS sintering, the matrix is ​​a BCC solid solution structure rich in W, Cr, and V, with an average grain size of about 0.43μm, and a nano- to submicron-sized second phase rich in Cr and V is dispersed on the matrix. The alloy has excellent thermal stability. After heat treatment at 1200, 1400 and 1500℃, the average grain sizes are 0.64, 1.17, and 1.41μm, respectively. The room temperature compressive strength of the alloy is as high as 2571MPa, and the fracture morphology shows a mixed fracture mode of transgranular fracture + intergranular fracture. The alloy has excellent high-temperature mechanical properties, with a compressive strength greater than 1500MPa at 1100℃ and a compressive strength greater than 500MPa at 1200℃. After high-temperature compression at 1200℃, the grain and second phase sizes remain stable, and no recrystallization and obvious grain growth occur.

[0065] Table 1 Carbon and oxygen content of low activation refractory multi-component alloy in Example 1 (alloy composition, including C and O impurities)

[0066]

[0067]

[0068] Example 2

[0069] The difference from Example 1 is that in step (4), rapid hot pressing (FHP) is performed after pre-pressing at 40 MPa.

[0070] Depend on Figure 14-18It can be seen that after FHP sintering, the alloy matrix is ​​a BCC solid solution structure rich in W, Cr, and V, with an average grain size of about 0.41μm, and nano- to micron-sized second phases rich in Cr and V are dispersed on the matrix. The room temperature compressive strength of the alloy is as high as 3719MPa, and the fracture morphology is mainly intergranular fracture. The alloy has excellent high-temperature mechanical properties, with a compressive strength of about 1300MPa at 1100℃ and a compressive strength of more than 400MPa at 1200℃. After high-temperature compression at 1200℃, the grain and second phase sizes remain stable, and no recrystallization or obvious grain growth occurs. The distribution direction of the large-sized strip-shaped second phase is perpendicular to the compression direction.

[0071] Example 3

[0072] The difference from Example 1 is that in step (1), according to the chemical formula W 90 Cr 5 V 5 (atomic percentage) for batching.

[0073] Depend on Figure 1-4 It can be seen that the alloy matrix obtained in this embodiment is a BCC solid solution structure rich in W, Cr, and V, with an average grain size of about 0.93μm, and a nano- to submicron-sized second phase rich in Cr and V is dispersed on the matrix. The alloy has good thermal stability. After heat treatment at 1200℃, the average grain size is less than 1μm, and the average grain size after heat treatment at 1400℃ and 1500℃ is less than 1.3μm. The room temperature compressive strength of the alloy is 1699MPa, the matrix grains are mainly fractured along the grain, and the large-sized second phase particles show transgranular fracture.

[0074] Comparative Example 1

[0075] According to the public literature Dhinisa Patel, Mark D. Richardson, Bethany Jim, et al. Radiation damage tolerance of a novel metastable refractory high entropy alloy V2.5Cr1.2WMoCo0.04. Journal of Nuclear Materials. 2020, 531: 152005 and O. El-Atwani, N. Li, M. Li, et al. Outstanding radiation resistance of tungsten-based high-entropy alloys [J]. Science Advances. 2019, 5 (3): v2002. At present, there are few refractory multi-component alloy systems that can be used in advanced nuclear reactors. After irradiation of VCrWMoCo high entropy alloy with 5MeV gold ions at room temperature for 40dpa, 96% of the structure remains stable, but the alloy contains highly activated elements Mo and Co, and the radioactivity problem after service needs to be considered. No irradiation dislocation rings were observed in the WTaCrV system low-activation alloy after an irradiation dose of 8 dpa. However, the alloy is a metastable film prepared by magnetron sputtering, which has high preparation cost and low thermal stability. It currently cannot meet the actual application requirements of advanced nuclear reactors.

[0076] Comparative Example 2

[0077] The difference from Example 1 is that in step (1), according to the chemical formula W 33 Cr 33 V 33 (atomic percentage) for batching.

[0078] Depend on Figure 12-13 It can be seen that the alloy is a multiphase heterogeneous structure, with a matrix of fine W-rich grains and a large number of strip-shaped and granular second phases rich in Cr and V. The room temperature compressive strength of the alloy is as high as 2549MPa, but the structure of the alloy after sintering is uneven.

[0079] Pure W and W-based composite materials have been applied to nuclear fusion reactors due to their advantages of high melting point, low activation, strong anti-sputtering ability, etc. However, such alloys also have the disadvantages of easy recrystallization at high temperature, insufficient high temperature thermal stability and high temperature strength, etc. The present invention adds low-activated Cr and V elements to pure W to form a high-concentration solid solution multi-component alloy, which further improves the thermal stability and high temperature mechanical properties of the alloy while maintaining the advantages of pure W basically unchanged.

[0080] It can be seen from the above embodiments that the W-Cr-V alloys prepared by the powder metallurgy method have a multiphase ultrafine grain structure, and the in-situ self-generated nano-submicron-sized Cr-rich and V-rich second phases are dispersed on the BCC matrix. With the increase of the content of Cr and V elements, the area fraction of the second phase in the alloy gradually increases, and the room temperature compressive strength shows an overall upward trend. It can be seen from Examples 1 and 2 that this series of alloys has excellent thermal stability, and the high temperature strength of the alloy in Example 1 is excellent, and the strength at 1100°C is greater than 1500MPa, which is much higher than the multi-component alloys reported so far. Therefore, through the alloy component system and preparation method provided by the present invention, low activation, high thermal stability, high temperature and high strength alloy materials can be obtained, which have excellent service potential in high temperature environments and provide new material options for the development of advanced nuclear reactors. It should be noted that although this series of alloys is designed for advanced nuclear reactors, it has the advantages of high melting point, high thermal stability, high temperature and high strength, and can also be applied to other fields.

[0081] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A low-activation refractory multi-component alloy, characterized in that: The low-activation refractory multi-component alloy is composed of three low-activation elements, W, Cr, and V. The atomic percentage composition of the alloy is 70-90% W, 5-15% Cr, and 5-15% V; The low activation refractory multi-component alloy has the following characteristics: (a) BCC disordered solid solution as the matrix with dispersed second phase; (b) The average grain size after heat treatment at 1200°C for 1 hour is less than 1 μm, and the average grain size after heat treatment at 1500°C for 1 hour is less than 2 μm; (c) The high temperature compressive strength at 1100°C is 1200-1800 MPa, and the compressive strain at 1100°C is greater than 5%; (d) The high temperature compressive strength at 1200℃ is 400~600MPa, and the compressive strain at 1200℃ is greater than 30%.

2. The method for preparing the low-activation refractory multi-component alloy as claimed in claim 1, characterized in that: The method comprises the following steps: preparing each component according to the atomic percentage of the alloy, high-energy ball milling under inert gas protection conditions, powder screening and then sintering in a mold.

3. The method for preparing a refractory multi-component alloy according to claim 2, characterized in that: The high-energy ball mill uses a cemented carbide ball and a cemented carbide lined container, the ball milling speed is 200-300 rpm, and the total ball milling time is 1500-3000 min.

4. The method for preparing a refractory multi-component alloy according to claim 3, characterized in that: The mass ratio of the cemented carbide ball to all powders of each component of the alloy is 5:1 to 10:

1.

5. The method for preparing a refractory multi-component alloy according to claim 2, wherein: The initial vacuum degree during the sintering is 0-40Pa.

6. The method for preparing a refractory multi-component alloy according to claim 5, characterized in that: The sintering heating rate is greater than 50°C / min, and the sintering temperature is 1300-1700°C.

7. The method for preparing a refractory multi-component alloy according to claim 6, characterized in that: The sintering heat preservation time is 1 to 30 minutes, and the pressure during sintering is 30 to 50 MPa.

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