Method for preparing a structural and functional integrated neutron absorption material composite plate with a layered structure

Abstract

The present invention discloses a method for preparing a structurally and functionally integrated neutron absorption material composite plate with a layered structure, belonging to the technical field of metal-based composite materials. The method comprises: S1. uniformly mixing pure aluminum powder, Al2O3 powder, and B4C powder; S2. using a cold spraying process to perform double-sided spraying on the surface of a B4C / 6061Al composite plate to obtain a (B4C+Al2O3) / Al composite coating; S3. annealing the coated plate; S4. stir-friction processing the annealed (B4C+Al2O3) / Al composite coating to finally obtain a neutron absorption material composite plate with a uniform surface structure and a fine-grained structure; S5. milling the obtained composite plate. This method prepares a sandwich structure composite plate with both high neutron absorption function and high-temperature strength, which can be used as a structurally and functionally integrated material.

Description

Technical Field

[0001] The present invention relates to the technical field of metal-based composite materials, and in particular to a method for preparing a structurally and functionally integrated neutron absorption material composite plate with a layered structure. Background Art

[0002] my country's nuclear power industry has flourished in recent years, generating significant amounts of spent fuel from nuclear power plants under construction or in operation. As a key development direction for spent fuel storage and transportation, dry storage and transportation of spent fuel places higher demands on the lightweight and high-temperature mechanical properties of neutron absorbers. The development of structurally integrated neutron-absorbing plates that combine neutron absorption with load-bearing capacity can reduce the use of structural materials with low heat dissipation capabilities, such as steel, improve the overall heat dissipation capacity of the equipment, and enable high-density storage and transportation of spent fuel.

[0003] The paper "Microstructure evolution and mechanical properties of B4C / 6061Al neutron absorber composite sheets fabricated by powder metallurgy" (Journal of Alloys and Compounds, 2018, 730:342-351) shows that a 30wt.% B4C / 6061Al composite can achieve a room-temperature strength of 268MPa after extrusion and rolling. The paper "Enhancing high-temperature strength of B4C–6061Al neutron absorber material by in-situ Mg(Al)B2" (Journal of Nuclear Materials, 2019, 526:151788) shows that a 26wt.% B4C-6061Al composite can achieve a room-temperature strength of 315MPa when hot-pressed at 630°C. The literature “Preparation and Performance Research of B4C / Al-based Composite Materials” (Shenyang University of Technology, 2018) shows that at 375°C, the strength of 31wt.% B4C-6061Al composite material is only 67MPa. This shows that B4C / 6061Al composite material has excellent mechanical properties at room temperature, but its mechanical properties decrease significantly at high temperatures. It can be seen from the document "Microstructure and mechanical properties of (B4C+Al2O3) / Al composites designed for neutron absorbing materials with both structural and functional usages" (Materials Science and Engineering: A, 2020, 773: 138840.) that the room temperature tensile strength of the (B4C+Al2O3) / Al composite material with a B4C content of 10wt.% is 209MPa, and the tensile strength at 350°C is 106MPa. Its high-temperature strength is significantly stronger than that of the B4C / 6061Al neutron absorbing material with a B4C content of 30wt.%, but due to limitations in the preparation process, the B4C content is difficult to further increase.

[0004] Cold spraying utilizes powder particles accelerated by high-pressure gas to impact a substrate in a completely solid state. After impact, the powder particles undergo significant plastic deformation and then deposit on the substrate to form a coating. This method can be used to deposit a (B4C+Al2O3) / Al composite on a B4C / 6061Al surface, resulting in a sandwich structure that combines high strength with high neutron absorption. However, the plastic deformation of the particles under high-speed impact often produces porosity defects and high dislocations in the coating, and the nano-Al2O3 particles are prone to agglomeration. Furthermore, the coating's microstructure is relatively heterogeneous, and poor interfacial bonding leads to low interlayer adhesion. To obtain defect-free, high-strength coatings, friction stir processing (FSP) can be used. By inserting a rotating tool with a needle and a shoulder into the coating, the overall microstructure is modified, eliminating defects and restoring dislocations. However, during FSP, the interface between the two materials undergoes significant differences in deformability, leading to turbulent material flow and mutual intrusion, resulting in the formation of voids at the interface. Solutions to these problems remain unresolved. Summary of the Invention

[0005] The present invention aims to provide a method for preparing a layered, structurally and functionally integrated neutron-absorbing composite sheet. This method utilizes cold spraying technology to coat the surface of a B4C / 6061Al composite with a (B4C+Al2O3) / Al composite. Friction stir processing is then used to improve the coating structure and properties. The resulting sandwich-structured composite sheet features a high B4C content within the B4C / 6061Al composite, exhibiting high neutron absorption and excellent room-temperature strength. The surface layer (B4C+Al2O3) / Al composite exhibits excellent high-temperature strength. The complementary advantages of these two materials make them suitable for use as a structurally and functionally integrated sheet.

[0006] To achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] A method for preparing a structurally and functionally integrated neutron absorption material composite plate having a layered structure, the method comprising the following steps:

[0008] S1: Pure Al powder, Al2O3 powder and B4C powder are uniformly mixed to obtain a mixed powder;

[0009] S2: Using a cold spray process, the mixed powder of step S1 is used to perform double-sided spraying on the surface of a B4C / 6061Al composite material plate with a thickness of 4 to 8 mm, thereby obtaining a (B4C+Al2O3) / Al composite coating on both sides of the plate;

[0010] S3: Annealing treatment of the B4C / 6061Al composite sheet with (B4C+Al2O3) / Al composite coating on both sides;

[0011] S4: Friction stir processing is performed on the (B4C+Al2O3) / Al composite coating on the surface of the composite plate after annealing treatment, and finally a neutron absorber composite plate with uniform surface structure and fine grain structure is obtained;

[0012] S5: Milling the obtained neutron absorber composite material plate to obtain a smooth surface.

[0013] The present invention uses a mixed powder of pure aluminum powder, Al2O3 powder and B4C as the cold spraying raw material. Among them, B4C powder has excellent physical properties, such as high hardness, high melting point and high thermal stability. In addition, B4C 10 The B element has a large neutron absorption cross section and good helium retention capacity, making the B4C / Al composite material an excellent neutron absorption material.

[0014] Preferably, the mixed powder is prepared in the proportion of 10 wt.% B4C, 5 wt.% Al2O3, and 85 wt.% pure aluminum powder and mixed evenly.

[0015] Preferably, in the prepared mixed powder, the particle diameter of the pure aluminum powder is 1 to 50 μm, the particle diameter of the Al 2 O 3 powder is 20 to 500 nm, and the particle diameter of the B 4 C powder is 3 to 100 μm.

[0016] Preferably, before step S2, the prepared mixed powder should be dried at a temperature of 120° C. to 180° C. for 15 to 30 minutes.

[0017] Preferably, before step S2, the B4C / 6061Al composite material plate is polished, then immersed in acetone and ultrasonically cleaned of surface stains and oil stains, and then dried.

[0018] Preferably, after the B4C / 6061Al composite material plate is cleaned, the drying temperature is 80-120° C. and the drying time is 10-20 minutes.

[0019] Preferably, in step S2, the spraying temperature is 200-450°C, the pressure of the spraying gas is 0.5-4 MPa, the powder feeding rate of the mixed powder is 15 g / min-35 g / min, the distance from the nozzle to the surface of the B4C / 6061Al composite material plate is 20-40 mm, and the coating thickness is 3-10 mm.

[0020] In the present invention, the spraying temperature is set to 200-450°C, which not only heats the mixed powder during the spraying process to improve the plasticity of the powder, but also increases the pressure of the spraying gas by utilizing the principle of thermal expansion and contraction.

[0021] In the present invention, the distance between the nozzle and the substrate surface is set to 20 to 40 mm. The reasons are: first, if the distance between the nozzle and the substrate surface is too large, the porosity of the sprayed coating may be high and the molding may not be dense. Second, if the distance between the nozzle and the substrate surface is too small, the powder particles ejected from the nozzle at high speed may cause erosion of the substrate surface.

[0022] In the present invention, the pressure of the spray gas is set to 0.5-4 MPa. The purpose is to ensure that the powder particles ejected from the nozzle at high speed have sufficient spraying speed and energy. It is worth mentioning that the spraying speed of the spray powder increases with the increase of pressure only within a certain range.

[0023] Preferably, the spraying gas is high-purity argon gas, the purity of which is greater than or equal to 99%.

[0024] Preferably, in step S3, the annealing temperature is 250-400° C., and the holding time is 1-4 hours.

[0025] Preferably, in step S4, during the friction stir processing, the feed speed of the stirring tool is 50 to 150 mm / min, and the rotation speed of the stirring tool is 200 to 800 r / min.

[0026] Preferably, the stirring tool is made of cermet, the stirring needle is 3 to 10 mm long, and the shoulder pressure is 0.1 to 0.5 mm, ensuring that the stirring needle penetrates the (B4C+Al2O3) / Al composite coating to a depth of 1.2 to 1.5 mm. The shoulder diameter is 20 to 25 mm, and the root diameter is 10 to 15 mm. The stirring needle is processed into a tapered shape, with no threads at the front 1.5 mm. The threads only exist in the area from 1.5 mm from the front to the root.

[0027] The composite plate prepared by the above method is a three-layer composite structure, the middle layer is a B4C / 6061Al composite substrate, and the two sides are (B4C+Al2O3) / Al composite coatings.

[0028] Preferably, the B4C content of the B4C / 6061Al composite material plate is 25-35 wt.%.

[0029] The thread design of the stirring needle in the present invention can not only enable the coating and the plate to be fully combined, but also effectively reduce the excessive mutual flow of the two materials at the interface of the processing area due to the huge difference in denaturation during the FSP process, thereby avoiding hole defects caused by the large difference in fluidity between the two materials.

[0030] Preferably, the matrix of the B4C / 6061Al composite material plate is 6061 aluminum alloy, and its chemical composition is: Cu 0.15-0.4wt.%, Mn 0.15wt.%, Mg 0.8-1.2wt.%, Zn 0.25wt.%, Cr 0.04-0.35wt.%, Ti 0.15wt.%, Si 0.4-0.8wt.%, Fe 0.7wt.%, and Al balance.

[0031] The present invention uses cold spraying technology to prepare a (B4C+Al2O3) / Al composite coating on the surface of a B4C / 6061Al composite material plate, and stir friction processing is performed on the composite material coating to obtain a structural and functional integrated neutron absorption material composite plate with a layered structure. Its advantages are that the process of cold spraying technology is relatively simple and the processing cost is low. Pure Al is used as the matrix of the coating, which effectively avoids the interface incompatibility problem between the coating and the B4C / 6061Al plate. Al2O3 is used as the coating reinforcement phase to improve the high-temperature performance of the composite plate. In addition, stir friction processing can eliminate pores and agglomeration defects in the coating, and the threaded design of the stirring needle can improve the interface bonding of the two composite materials and avoid the formation of holes. Cold spraying and stir friction processing, as solid-phase preparation and processing technologies, can effectively avoid the reaction between the Mg element in B4C / 6061Al and the Al2O3 in (B4C+Al2O3) / Al, and therefore have advantages that other processes cannot match. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to have a deeper understanding of the technical solutions in this application, the following is a relatively complete and clear explanation of the technical solutions in this application in conjunction with the embodiments. The embodiments described are only part of the embodiments in this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0033] Before cold spraying, the B4C / 6061Al composite sheet was polished to remove surface scale. Surface stains and oil were then cleaned using ultrasonic cleaning in acetone, followed by drying at a temperature of 80-120°C for 10-20 minutes.

[0034] In the embodiment of the present invention, the mixed powder is prepared by mixing 10 wt.% B₄C, 5 wt.% Al₂O₃, and 85 wt.% pure aluminum powder and uniformly blending the powder. The pure aluminum powder has a particle diameter of 1 to 50 μm, the Al₂O₃ powder has a particle diameter of 20 to 500 nm, and the B₄C powder has a particle diameter of 3 to 100 μm. The purity of all three powders is greater than 99.9%. The uniformly blended powder is then dried at a temperature of 120 to 180°C for 15 to 30 minutes.

[0035] Example 1:

[0036] This embodiment is a method for preparing a neutron absorption material composite plate having a layered structure and integrated functions, comprising the following steps:

[0037] S1. Pure aluminum powder, Al2O3 powder and B4C powder were mixed in a weight ratio of 85:5:10 to obtain a mixed powder, wherein the pure aluminum powder had a diameter of 50μm, the Al2O3 powder had a diameter of 500nm, and the B4C particle diameter was 100μm;

[0038] S2. A cold spray process was then performed on both sides of an 8 mm thick B4C / 6061Al composite sheet to obtain a (B4C+Al2O3) / Al composite coating. The coating was applied at a temperature of 450°C, a pressure of 4 MPa, a powder feed rate of 35 g / min, a distance of 40 mm from the nozzle to the B4C / 6061Al composite sheet surface, and a coating thickness of 10 mm.

[0039] S3. The B4C / 6061Al composite sheet with a (B4C+Al2O3) / Al composite coating on both sides was annealed to obtain a composite sheet at an annealing temperature of 400°C for 4 hours.

[0040] S4, stir friction processing is performed on the (B4C+Al2O3) / Al composite coating on the surface of the composite plate, and finally a neutron absorption material composite plate with uniform surface organization and ultrafine grain structure is obtained. The feed speed of the stirring tool is 150mm / min, the rotation speed of the stirring tool is 800r / min, the stirring needle length is 10mm, and the shoulder pressure is 0.5mm. Ensure that the stirring needle penetrates the (B4C+Al2O3) / Al composite coating to a depth of 1.5mm. The shoulder diameter is 25mm, and its root diameter is 15mm. The stirring needle is processed into a cone shape, and there is no thread at the front 1.5mm. The thread only exists in the area from 1.5mm from the front end to the root;

[0041] S5. Milling the obtained composite material plate to obtain a smooth surface.

[0042] The structural and functional integrated neutron absorption material composite plate with a layered structure obtained in this embodiment has a dense surface molding and good interface bonding. The B4C / 6061Al composite material plate with a B4C content of 30wt.% in the middle layer of the plate has a high neutron absorption function, and the tensile strength of the high-strength material layers on both sides at 350°C is 125MPa, with good wear resistance and load-bearing capacity.

[0043] Example 2:

[0044] This embodiment is a method for preparing a neutron absorption material composite plate having a layered structure and integrated functions, comprising the following steps:

[0045] S1. Pure aluminum powder, Al2O3 powder and B4C powder were mixed in a weight ratio of 94:1:5 to obtain a mixed powder, wherein the pure aluminum powder had a diameter of 1 μm, the Al2O3 powder had a diameter of 20 nm, and the B4C particles had a diameter of 3 μm.

[0046] S2. A cold spray process was then used to apply a (B4C+Al2O3) / Al composite coating to both sides of a 4 mm thick B4C / 6061Al composite sheet. The coating was applied at a temperature of 200°C, a spray gas pressure of 0.5 MPa, a mixed powder feed rate of 15 g / min, and a distance of 20 mm from the nozzle to the B4C / 6061Al composite sheet surface. The coating thickness was 3 mm.

[0047] S3. The B4C / 6061Al composite sheet with a (B4C+Al2O3) / Al composite coating on both sides was annealed to obtain a composite sheet at an annealing temperature of 250°C for 1 h.

[0048] S4, stir friction processing is performed on the (B4C+Al2O3) / Al composite coating on the surface of the composite plate, and finally a neutron absorption material composite plate with uniform surface organization and ultrafine grain structure is obtained. The feed speed of the stirring tool is 50mm / min, the rotation speed of the stirring tool is 200r / min, the stirring needle length is 3mm, and the shoulder pressure is 0.1mm. Ensure that the depth of the stirring needle penetrating the (B4C+Al2O3) / Al composite coating is 1.2mm. The shoulder diameter is 20mm, and its root diameter is 10mm. The stirring needle is processed into a cone shape, and there is no thread at the front 1.5mm. The thread only exists in the area from 1.5mm from the front end to the root;

[0049] S5. Milling the obtained composite material plate to obtain a smooth surface.

[0050] The structural and functional integrated neutron absorption material composite plate with a layered structure obtained in this embodiment has a dense surface molding and good interface bonding. The B4C / 6061Al composite material plate with a B4C content of 35wt.% in the middle layer of the plate has a high neutron absorption function, and the tensile strength of the high-strength material layers on both sides at 350°C is 108MPa, with good wear resistance and load-bearing capacity.

[0051] Comparative Example 1:

[0052] This example is a method for preparing a structurally and functionally integrated neutron absorption material composite plate having a layered structure, comprising the following steps:

[0053] S1. Pure aluminum powder, Al2O3 powder and B4C powder were mixed in a weight ratio of 85:5:10 to obtain a mixed powder, wherein the pure aluminum powder had a diameter of 100μm, the Al2O3 powder had a diameter of 1μm, and the B4C particle diameter was 500μm;

[0054] S2. A cold spray process was then used to apply a (B4C+Al2O3) / Al composite coating to both sides of an 8-mm-thick B4C / 6061Al composite sheet. The coating was applied at a temperature of 450°C, a pressure of 4 MPa, a powder feed rate of 35 g / min, and a distance of 40 mm from the nozzle to the B4C / 6061Al composite sheet surface. The resulting coating thickness was 10 mm.

[0055] S3. The B4C / 6061Al composite sheet with a (B4C+Al2O3) / Al composite coating on both sides was annealed to obtain a composite sheet at an annealing temperature of 400°C for 4 hours.

[0056] S4, stir friction processing is performed on the (B4C+Al2O3) / Al composite coating on the surface of the composite plate, and finally a neutron absorber composite plate with a uniform surface structure and an ultrafine grain structure is obtained. The feed speed of the stirring tool is 150mm / min, the rotation speed of the stirring tool is 800r / min, the stirring needle length is 10mm, and the shoulder pressure is 0.5mm. The depth of penetration of the stirring needle into the (B4C+Al2O3) / Al composite coating is ensured to be 1.5mm. The shoulder diameter is 25mm, and its root diameter is 15mm. The stirring needle is processed into a cone shape and all the stirring needles are threaded;

[0057] S5. Milling the obtained composite material plate to obtain a smooth surface.

[0058] In the composite material plate obtained in this example, since all the stirring pins have threads, the flow at the interface is turbulent during the stir friction processing, and there are defects in the interface bonding.

[0059] Comparative Example 2:

[0060] This example is a method for preparing a structurally and functionally integrated neutron absorption material composite plate having a layered structure, comprising the following steps:

[0061] S1. Pure aluminum powder, Al2O3 powder and B4C powder were mixed in a weight ratio of 85:5:10 to obtain a mixed powder, wherein the pure aluminum powder had a diameter of 50μm, the Al2O3 powder had a diameter of 500nm, and the B4C particle diameter was 100μm;

[0062] S2. A cold spray process was then used to apply a (B4C+Al2O3) / Al composite coating to both sides of an 8-mm-thick B4C / 6061Al composite sheet. The coating was applied at a temperature of 450°C, a pressure of 4 MPa, a powder feed rate of 35 g / min, and a distance of 40 mm from the nozzle to the B4C / 6061Al composite sheet surface. The resulting coating thickness was 10 mm.

[0063] S3. The B4C / 6061Al composite sheet with a (B4C+Al2O3) / Al composite coating on both sides was annealed to obtain a composite sheet at an annealing temperature of 400°C for 4 hours.

[0064] S4. Milling the obtained composite material plate to obtain a smooth surface.

[0065] The composite material plate obtained in this example had a large number of defects during the cold spraying process, resulting in poor material performance (surface strength less than 70 MPa), which could not meet the use requirements.

[0066] Comparative Example 3:

[0067] S1. Pure aluminum powder, Al2O3 powder and B4C powder were mixed in a weight ratio of 65:5:30 to obtain a mixed powder, wherein the pure aluminum powder had a diameter of 50μm, the Al2O3 powder had a diameter of 500nm, and the B4C particle diameter was 100μm;

[0068] S2. A cold spray process was then performed on both sides of an 8 mm thick B4C / 6061Al composite sheet to obtain a (B4C+Al2O3) / Al composite coating. The coating was applied at a temperature of 450°C, a pressure of 4 MPa, a powder feed rate of 35 g / min, a distance of 40 mm from the nozzle to the B4C / 6061Al composite sheet surface, and a coating thickness of 10 mm.

[0069] S3. The B4C / 6061Al composite sheet with a (B4C+Al2O3) / Al composite coating on both sides was annealed to obtain a composite sheet at an annealing temperature of 400°C for 4 hours.

[0070] S4, stir friction processing is performed on the (B4C+Al2O3) / Al composite coating on the surface of the composite plate, and finally a neutron absorption material composite plate with uniform surface organization and ultrafine grain structure is obtained. The feed speed of the stirring tool is 150mm / min, the rotation speed of the stirring tool is 800r / min, the stirring needle length is 10mm, and the shoulder pressure is 0.5mm. Ensure that the stirring needle penetrates the (B4C+Al2O3) / Al composite coating to a depth of 1.5mm. The shoulder diameter is 25mm, and its root diameter is 15mm. The stirring needle is processed into a cone shape, and there is no thread at the front 1.5mm. The thread only exists in the area from 1.5mm from the front end to the root;

[0071] S5. Milling the obtained composite material plate to obtain a smooth surface.

[0072] The composite material plate obtained in this example has extremely poor performance due to the excessively high B4C content.

[0073] Comparative Example 4:

[0074] S1. Pure aluminum powder, Al2O3 powder and B4C powder were mixed in a weight ratio of 85:5:10 to obtain a mixed powder, wherein the pure aluminum powder had a diameter of 50μm, the Al2O3 powder had a diameter of 500nm, and the B4C particle diameter was 100μm;

[0075] S2. A cold spray process was then performed on both sides of an 8 mm thick B4C / 6061Al composite sheet to obtain a (B4C+Al2O3) / Al composite coating. The coating was applied at a temperature of 450°C, a pressure of 4 MPa, a powder feed rate of 35 g / min, a distance of 40 mm from the nozzle to the B4C / 6061Al composite sheet surface, and a coating thickness of 10 mm.

[0076] S3. The B4C / 6061Al composite sheet with a (B4C+Al2O3) / Al composite coating on both sides was annealed to obtain a composite sheet at an annealing temperature of 400°C for 4 hours.

[0077] S4, stir friction processing is performed on the (B4C+Al2O3) / Al composite coating on the surface of the composite plate, and finally a neutron absorption material composite plate with uniform surface organization and ultrafine grain structure is obtained. The feed speed of the stirring tool is 20mm / min, the rotation speed of the stirring tool is 2000r / min, the stirring needle length is 10mm, and the shoulder pressure is 0.5mm. Ensure that the stirring needle penetrates the (B4C+Al2O3) / Al composite coating to a depth of 1.5mm. The shoulder diameter is 25mm, and its root diameter is 15mm. The stirring needle is processed into a cone shape, and there is no thread at the front 1.5mm. The thread only exists in the area from 1.5mm from the front end to the root;

[0078] S5. Milling the obtained composite material plate to obtain a smooth surface.

[0079] The composite material plate obtained in this example had low performance due to excessive heat input during the friction stir processing, which led to grain coarsening and excessive interfacial flow. The tensile strength of the surface composite material at 350°C was 80 MPa.

Claims

1. A method for preparing a neutron absorption material composite plate with a layered structure and integrated functions, characterized by: The method specifically comprises the following steps: S1: Pure Al powder, Al2O3 powder and B4C powder are uniformly mixed to obtain a mixed powder; S2: Using a cold spray process, the mixed powder of step S1 is used to perform double-sided spraying on the surface of a B4C / 6061Al composite material plate with a thickness of 4 to 8 mm, thereby obtaining a (B4C+Al2O3) / Al composite coating on both sides of the plate; S3: Annealing treatment of the B4C / 6061Al composite sheet with (B4C+Al2O3) / Al composite coating on both sides; S4: Friction stir processing is performed on the (B4C+Al2O3) / Al composite coating on the surface of the composite plate after annealing treatment, and finally a neutron absorber composite plate with uniform surface structure and fine grain structure is obtained; S5: Milling the obtained neutron absorber composite material plate to obtain a smooth surface.

2. The method for preparing the neutron absorbing material composite plate according to claim 1, characterized in that: In the mixed powder of step S1, B4C powder accounts for 5-10 wt.%, Al2O3 powder accounts for 1-5 wt.%, and pure Al powder accounts for 85-94 wt.%.

3. The method for preparing the neutron absorbing material composite plate according to claim 1 or 2, characterized in that: In the mixed powder of step S1, the particle diameter of pure Al powder is 1 to 50 μm, the particle diameter of Al 2 O 3 powder is 20 to 500 nm, and the particle diameter of B 4 C powder is 3 to 100 μm.

4. The method for preparing the neutron absorbing material composite plate according to claim 1, characterized in that: Before step S2, the mixed powder prepared in step S1 should be dried before step S2; the drying temperature is 120° C. to 180° C., and the drying time is 15 to 30 minutes.

5. The method for preparing the neutron absorbing material composite plate according to claim 1, characterized in that: In the cold spraying process of step S2, the spraying temperature is 200-450°C, the spraying gas pressure is 0.5-4 MPa, the powder feeding rate of the mixed powder is 15 g / min-35 g / min, the distance from the nozzle to the surface of the B4C / 6061Al composite material plate is 20-40 mm, and the coating thickness is 3-10 mm.

6. The method for preparing the neutron absorbing material composite plate according to claim 1, characterized in that: In step S3, the annealing temperature is 250-400° C., and the holding time is 1-4 hours.

7. The method for preparing a neutron absorbing material composite plate according to claim 1, characterized in that: In step S4, the friction stir processing parameters are: the stirring tool feed speed is 50-150 mm / min, and the stirring tool rotation speed is 200-800 r / min.

8. The method for preparing the neutron absorbing material composite plate according to claim 7, characterized in that: In the stir friction processing, the stirring tool is made of metal ceramic, the stirring needle length is 3 to 10 mm, the shoulder pressure is 0.1 to 0.5 mm, and the stirring needle penetrates the (B4C+Al2O3) / Al composite coating to a depth of 1.2 to 1.5 mm; the shoulder diameter is 20 to 25 mm, and the root diameter is 10 to 15 mm. The stirring needle is processed into a cone shape, and there is no thread at the front end 1.5 mm. The thread only exists in the area from 1.5 mm to the root.

9. The method for preparing a neutron absorbing material composite plate according to claim 1, characterized in that: The B4C content in the B4C / 6061Al composite material plate is 25-35 wt.%.

10. A neutron absorbing material composite plate prepared by the method according to any one of claims 1 to 9, characterized in that: The composite plate has a three-layer composite structure, with the middle layer being a B4C / 6061Al composite substrate and both sides being (B4C+Al2O3) / Al composite coatings.