A structure-function integrated shielding high-entropy alloy and its preparation method

Abstract

The present invention discloses a structural and functional integrated shielding high entropy alloy and a preparation method thereof, wherein the main components of the high entropy alloy are FeCrV(W y Ta z ) x Gd x , x =0.05~0.1, y =0~1, z =0~1, the main alloying elements Fe, Cr, V, W, and Ta are all alloying elements with low activation characteristics. During long-term service in the reactor, no long-lived nuclides will be produced due to irradiation transmutation by high-energy neutrons, thereby ensuring that the material has good low activation characteristics. The present invention designs and prepares a high-entropy alloy with low activation, corrosion resistance, and excellent shielding and mechanical properties by designing and optimizing the high-entropy alloy composition, laying a material foundation for the design and construction of modular small reactors. The preparation method described in the present invention is simple to operate and there is no obvious segregation inside the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of shielding alloys, and in particular relates to a structural and functional integrated shielding high-entropy alloy and a preparation method thereof. Background Art

[0002] As a new energy technology, small modular reactors (SMBRs) offer enhanced safety, greater adaptability, greater functionality and flexibility, and ease of transport and assembly. Currently, major nuclear power countries are conducting design and research on small modular lead-cooled fast reactors. Transportability is a key design objective for SMRs. While ensuring core life and nuclear safety, transportability requires that the entire reactor vessel be transportable by ship or road. Therefore, a small nuclear reactor weighs approximately 100 tons. Therefore, SMRs will utilize extensive innovative design research to achieve the safe design goals of "lightweight and miniaturization," i.e., "reduced volume and weight," and "integrated structure and functionality."

[0003] The reactor shielding system is an essential component of a nuclear reactor. Its purpose is to maintain a shielding layer of a certain thickness, ensuring that the target area remains within the control levels specified in the reactor's radiation safety design specifications. Reactor shielding involves placing a certain thickness of shielding material around the radiation source, which interacts with radiation particles through scattering and absorption, thereby attenuating and absorbing the radiation. Nuclear radiation primarily consists of neutrons, gamma rays, and alpha and beta rays. Neutrons and gamma rays have significantly greater penetrating power than alpha and beta rays. Generally speaking, shielding that protects against neutrons and gamma rays can also theoretically protect against other radiation. Therefore, neutrons and gamma rays are the primary radiation particles shielded by the reactor shielding system.

[0004] Generally speaking, the shielding system weighs over 20% of a small reactor. Compared to pressurized water reactors (PWRs), small modular reactors (SMRs) operate at higher temperatures, experience more corrosive media, and have higher neutron flux intensities. This means that while ensuring engineering feasibility and safety, the pursuit of lightweight and miniaturized SMRs places even higher demands on the shielding system to reduce weight and volume. Consequently, the shielding materials within SMRs must possess higher structural and shielding performance requirements.

[0005] At the same time, the neutron shielding properties are mainly achieved by adding B to the material. The high-boron steel and aluminum-based boron carbide composite materials used in nuclear power plants are typical "structure / function integration" shielding materials. However, the isotopes of B are 10 B and 11 B, 11 B has almost no thermal neutron absorption ability. 10The enrichment process of B is complicated and the cost is high, so the neutron shielding materials containing B are usually mainly added with natural B. In natural B, 10 The abundance of boron is 19.9%, and its equivalent thermal neutron absorption cross section is 764b. This affects the shielding effectiveness of a series of materials, resulting in these materials exposing many shortcomings in terms of shielding performance, structural strength, and radiation resistance, in order to adapt to the development trend of small modular reactors. Gd has the largest neutron absorption cross section, so doping alloys with Gd is a relatively easy idea to improve the shielding performance of existing in-core structural materials. However, in traditional single-element Fe-based alloys, the solubility of Gd in Fe is low, and it is easy to form an FeGd intermediate phase, which significantly reduces the performance of the material.

[0006] A high-entropy alloy (HEA), also known as a multi-principal-element high-disorder alloy, is an alloy composed of five or more components in approximately equiatomic ratios. HEAs combine multiple principal elements in high concentrations, greatly expanding the compositional space for alloy design. Upon solidification, HEAs do not form numerous intermetallic compound phases, but instead develop a microstructure dominated by simple FCC, BCC, or HCP solid solutions. The formation of a solid solution matrix enables HEAs to overcome the inherent brittleness of intermetallic compounds and amorphous alloys, making them very promising as advanced engineering structural materials. Summary of the Invention

[0007] The purpose of the present invention is to invent a Gd-doped structurally and functionally integrated shielding high-entropy alloy material based on the characteristics of high atomic solid solubility of multiple principal elements in high-entropy alloys. This high-entropy alloy has low activation, corrosion resistance, high strength and excellent neutron shielding performance, and has great application potential in small modular reactors.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A structural and functional integrated shielding high entropy alloy, characterized in that the main component of the high entropy alloy is FeCrV(W y Ta z ) x Gd x , where x=0.05~0.1, y=0~1, z=0~1.

[0010] Furthermore, the atomic percentage of the Cr content is greater than 20%.

[0011] A method for preparing a structurally and functionally integrated shielding high-entropy alloy, characterized in that the method for preparing the shielding high-entropy alloy is carried out according to the following steps:

[0012] First, place the weighed metal raw materials in the smelting furnace from top to bottom according to their melting points, with high melting point elements placed in the upper part of the crucible and low melting point elements placed in the lower part;

[0013] 2. Then vacuum the machine until the vacuum reaches 5×10 -3 Pa, pass argon gas to purge twice, then fill with argon gas protection, and start melting metal;

[0014] 3. After all the metal is melted, turn off the power and let the furnace cool to room temperature;

[0015] 4. Turn the ingot over and melt it again, repeat the process 8 times to reduce component segregation;

[0016] 5. After melting, the sample is placed in a vacuum of less than 5×10 -3 Pa vacuum heat treatment furnace, keep the temperature at 1000-1200° C. for 10-24 hours, then take out the sample and perform water cooling quenching to obtain the high entropy alloy.

[0017] Furthermore, the step begins with the preparation of ingredients, using Fe, Cr, V, W, and Gd elements with a purity of more than 99.5%, removing the oxide scale on the surface of the material by sandpaper polishing, and using ethanol ultrasonic vibration to clean the raw metal, and accurately weighing and proportioning the raw materials according to the molar ratio.

[0018] The beneficial effects of the present invention are:

[0019] 1. By optimizing the composition of high-entropy alloys, a high-entropy alloy with low activation, corrosion resistance, and excellent shielding and mechanical properties was designed and prepared. This laid the material foundation for the design and processing of modular small reactors.

[0020] 2. The preparation method of the present invention is simple to operate, safe and reliable, and there is no obvious segregation inside the material.

[0021] 3. Gd has the largest neutron absorption cross section, so doping alloys with Gd is a relatively straightforward approach to improving the shielding performance of existing in-core structural materials. However, in traditional single-element Fe-based alloys, Gd has a low solubility in Fe, which easily forms an FeGd interphase, significantly reducing the material's performance. This composition system has the following main features: the main alloying elements Fe, Cr, V, W, and Ta are all alloying elements with low activation characteristics. During long-term service in the reactor, they will not produce long-lived nuclides due to irradiation transmutation by high-energy neutrons, thereby ensuring that the material has good low activation characteristics; the higher Cr content in the material, atomic percentage >20%, can ensure that the material has good corrosion resistance, thereby ensuring that the material has good compatibility with the reactor coolant; Gd is the nuclide with the largest thermal neutron absorption cross-section. The equivalent thermal neutron absorption cross-section of natural Gd is 49163b. The addition of Gd can make the material have excellent neutron shielding performance; the addition of W and Ta can effectively shield the gamma rays generated by Gd after absorbing neutrons, thereby ensuring that the overall material has excellent in-pile shielding performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 XRD curves of four Gd-containing high entropy alloys;

[0023] Figure 2 FeCrV(WTaGd) 0.1 Microstructure and scanning energy spectrum of alloy;

[0024] Figure 3 The stress-strain curves of four high entropy alloys after thermal aging;

[0025] Figure 4 is the thermal neutron shielding efficiency of four high entropy alloys. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0027] The embodiment of the present invention provides a structural and functional integrated shielding high entropy alloy, characterized in that the main component of the high entropy alloy is FeCrV(W y Ta z ) x Gd x , where x=0.05~0.1, y=0~1, z=0~1.

[0028] As a further improvement of the present invention, the atomic percentage of the Cr content is greater than 20%.

[0029] A method for preparing a structurally and functionally integrated shielding high-entropy alloy, characterized in that the method for preparing the shielding high-entropy alloy is carried out according to the following steps:

[0030] First, place the weighed metal raw materials in the smelting furnace from top to bottom according to their melting points, with high melting point elements placed in the upper part of the crucible and low melting point elements placed in the lower part;

[0031] 2. Then vacuumize and when the vacuum reaches 5×10 -3 Pa, argon gas is passed through the gas for two times, and then argon gas protection is filled in to start smelting the metal;

[0032] 3. After all the metal is melted, turn off the power and let the furnace cool to room temperature;

[0033] 4. Turn the ingot over and melt it again, repeat the process 8 times to reduce component segregation;

[0034] 5. After melting, the sample is placed in a vacuum of less than 5×10 -3 Pa vacuum heat treatment furnace, keep the temperature at 1000-1200° C. for 10-24 hours, then take out the sample and perform water cooling quenching to obtain the high entropy alloy.

[0035] As a further improvement of the present invention, the step starts with the preparation of ingredients, using Fe, Cr, V, W, and Gd elements with a purity of more than 99.5%, removing the oxide scale on the surface of the material by sandpaper polishing, and using ethanol ultrasonic vibration to clean the raw metal, and accurately weighing and proportioning the raw materials according to the molar ratio.

[0036] Ingredient Design

[0037] Design of four different compositions of FeCrV(W y Ta z ) x Gd x , where the FeCrV atomic ratio is 1:1:1, and x = 0.05-0.1. The specific compositions of the four alloys are shown in Table 1. The main purpose of designing these four alloy compositions was to study the influence of each element on the alloy properties. The adjustment of the Ta and W content was mainly used to study their effects on gamma-ray and high-temperature mechanical properties.

[0038] Table 1. Composition ratio of four high entropy alloys

[0039]

[0040] Alloy preparation:

[0041] Ingredients: Fe, Cr, V, W, and Gd metals with a purity of more than 99.5% are used. The oxide scale on the surface of the material is removed by sandpaper polishing, and the raw metals are cleaned by ethanol ultrasonic vibration. The raw materials are accurately weighed and proportioned according to the molar ratio.

[0042] Preparation of button ingots: Use vacuum arc melting to melt the alloys. Place them in the melting furnace in descending order of melting point. High melting point elements are placed in the upper part of the crucible, and low melting point elements are placed in the lower part. Then vacuum is applied, with the vacuum degree not exceeding 5×10 -3 Pa. Purge the furnace twice with argon, then refill with argon protection at a pressure of 0.6 atmospheres. Begin smelting the metal. Once all the metal is melted, turn off the power and allow the furnace to cool to room temperature. Turn the ingot over and smelt again, repeating this process eight times.

[0043] After smelting, the button ingot was cut into two halves, half of the material was placed in a vacuum heat treatment furnace and kept warm at 1100℃ for 24h, and then the sample was taken out for water quenching.

[0044] 1. Alloy structure and performance test:

[0045] The phase composition of the samples was analyzed by X-ray diffractometer. The samples were tested using a Cu target XRD instrument with a scanning step size of 0.01° / min and a scanning range of 5° to 80°. Figure 1 Four types of FeCrV(WTa) x Gd x XRD curve of the alloy. It can be seen that the alloy is mainly BCC structure, and there is a small amount of undissolved oxygen in the Ta-containing high entropy alloy.

[0046] 2. Scanning Electron Microscope Analysis

[0047] The microstructure and composition distribution of alloys with different compositions were observed using scanning electron microscopy. Figure 2 The FeCrV(WTaGd) after solution treatment was realized 0.1 The alloy's microstructure and EDS scanning results show that the alloy is primarily a solid-solution FeCrVW alloy, with some Ta enriched at the FeCrVW grain boundaries. Gd is evenly distributed throughout the FeCrVW, with only a small amount of enrichment occurring in Ta-segregated areas.

[0048] 3. Mechanical properties

[0049] The compression test is used to evaluate the strength and toughness of the material. The sample is processed into a sample of φ3×5mm and compressed separately. The performance of the sample after compression is as follows Figure 3 As shown. It can be seen that the material with the highest yield strength is FeCrV(WTaGd) 0.1 About 1540MPa, the highest elongation is FeCrVW0.1 Gd 0.05 About 28%.

[0050] 4. Neutron shielding performance

[0051] Using MCNP neutronics software, a 0.0253eV parallel beam surface source was simulated to irradiate a target material with a thickness of about 2mm. The influence of different Gd contents on the neutron shielding performance was calculated by statistically analyzing the neutron flux at different thicknesses. The results were compared with the boron-containing 304 steel. Figure 4 As shown, it can be observed that the tenfold weakening thickness of the four high entropy alloys is lower than that of boron-containing 304 steel.

[0052] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the present invention.

Claims

1. A structural and functional integrated shielding high entropy alloy, characterized in that: The high entropy alloy composition is FeCrV(W y Ta z ) x Gd x , where x=0.05~0.1, y=0~1, z=0~1.

2. The structural and functional integrated shielding high entropy alloy according to claim 1, characterized in that: The percentage content of Cr atoms is greater than 20%.

3. A method for preparing a structurally and functionally integrated shielding high entropy alloy, characterized in that: The preparation method of the shielded high entropy alloy is carried out according to the following steps: First, place the weighed metal raw materials in the smelting furnace from top to bottom according to their melting points, with high melting point elements placed in the upper part of the crucible and low melting point elements placed in the lower part; 2. Then vacuum the machine and the vacuum degree reaches 5×10 -3 Pa, pass argon gas to purge twice, then fill with argon gas protection, and start melting metal; 3. After all the metal is melted, turn off the power and let the furnace cool to room temperature; 4. Turn the ingot over and melt it again, repeat the process 8 times to reduce component segregation; 5. After melting, the sample is placed in a vacuum of less than 5×10 -3 Pa vacuum heat treatment furnace, keep the temperature at 1000-1200° C. for 10-24 hours, then take out the sample and perform water cooling quenching to obtain the high entropy alloy.

4. The method for preparing a structural and functional integrated shielding high entropy alloy according to claim 3, characterized in that: The step begins with pre-mixing, using Fe, Cr, V, W, and Gd elements with a purity of more than 99.5%. The oxide scale on the surface of the material is removed by sandpaper polishing, and the raw metal is cleaned by ethanol ultrasonic vibration. The raw materials are accurately weighed and proportioned according to the molar ratio.

Images