Lead-bismuth-corrosion-resistant high-entropy alloy thin-wall pipe and preparation method thereof

Abstract

The invention relates to the technical field of lead-bismuth corrosion resistant thin-wall pipes, in particular to a lead-bismuth corrosion resistant high-entropy alloy thin-wall pipe and a preparation method thereof. The lead-bismuth corrosion resistant high-entropy alloy thin-wall pipe comprises the following chemical components in percentage by weight: 45-60% of Fe, 20-35% of Ni, 10-25% of Cr, 3-8% of Al, 3-5% of Ti and 1-3% of Si. According to the method, a high-entropy alloy cast ingot is prepared through high-vacuum induction melting, casting defects are eliminated and the grain size is refined through the forging process of high-temperature heat treatment and repeated upsetting and drawing, a face-centered cubic and body-centered cubic double-phase organization structure is obtained, and the alloy has excellent high-temperature resistance and corrosion resistance. And finally, the high-entropy alloy thin-wall pipe which is excellent in structure performance, uniform in wall thickness, good in surface quality, high in reliability and resistant to lead and bismuth corrosion is prepared through multi-pass cold machining, and a technical support is provided for material selection of a next-generation lead-cooled fast reactor cladding material.

Description

Technical Field

[0001] The invention relates to the technical field of lead-bismuth corrosion-resistant thin-walled pipes, and in particular to a lead-bismuth corrosion-resistant high-entropy alloy thin-walled pipe and a preparation method thereof. Background Art

[0002] In the lead-cooled fast reactor of the fourth-generation nuclear energy system, the cladding material is an important component of the fuel element. Its main function is to isolate the external coolant and the internal nuclear fuel, and at the same time prevent the escape of fission products.

[0003] Liquid lead-bismuth eutectic alloy (LBE) has excellent thermal conductivity, chemical stability, radiation resistance and neutronic properties, and is considered to be the preferred material for lead-cooled fast reactor coolants. However, when metal materials come into contact with LBE, corrosion behaviors such as oxidation, dissolution, embrittlement and erosion will occur. This is due to the difference in thermodynamic properties between metal materials and LBE, which can cause the metal elements in the material to gradually dissolve and migrate to LBE. At the same time, LBE will also diffuse into the material along the grain boundaries. The loss of elements will cause the material to undergo a phase change, and the diffused metal elements will undergo complex chemical reactions with dissolved O, leading to material failure. In addition, during the operation of the reactor, liquid LBE has a high flow rate, and its continuous scouring will also cause local corrosion of metal materials, resulting in the destruction of structural materials and affecting the safe operation of lead-cooled fast reactors.

[0004] High entropy alloys, due to the diversity of their composition design, have excellent high temperature resistance, oxidation resistance, corrosion resistance, radiation resistance and wear resistance. They have gradually become a hot spot in the forefront of material research and have been identified as one of the candidate materials for the cladding of lead-cooled fast reactor fuel elements. Due to the complex microstructure evolution and difficult performance regulation of high entropy alloys, the current existing tube drawing and preparation technology cannot achieve the forming of lead-bismuth corrosion-resistant high entropy alloy thin-walled tubes with excellent microstructure performance, uniform wall thickness, good surface quality and high reliability. At the same time, there are very few publicly available technologies for preparing lead-bismuth corrosion-resistant high entropy alloy thin-walled tubes, which seriously affects the rapid development of my country's fourth-generation nuclear energy system. Therefore, how to change the current situation of the difficulty in forming high-entropy alloy thin-walled tubes in the existing technology has become a problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0005] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube and a preparation method thereof. The prepared thin-walled tube has the advantages of excellent organizational properties, uniform wall thickness, good surface quality, and good high temperature resistance and corrosion resistance in a corrosive environment.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] A lead-bismuth corrosion-resistant high-entropy alloy thin-walled pipe, the chemical composition of the lead-bismuth corrosion-resistant high-entropy alloy thin-walled pipe is as follows by weight percentage:

[0008] Fe: 45-60%; Ni: 20-35%; Cr: 10-25%; Al: 3-8%; Ti: 3-5%; Si: 1-3%.

[0009] The method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube comprises the following steps:

[0010] (1) Weighing raw materials according to a preset composition ratio, preparing alloy ingots by vacuum induction melting, and then casting them into solid round ingots of Φ85 mm±5 mm;

[0011] (2) The solid round ingot is subjected to homogenization treatment and forging, and then machined to obtain a high entropy alloy tube with a thick-walled hollow columnar structure;

[0012] (3) The thick-walled hollow cylindrical high-entropy alloy tube blank is subjected to high-temperature heat treatment and then cold-drawn. During the processing, an intermediate annealing process is required to restore the plasticity of the alloy to ensure the cold working ability of the alloy tube;

[0013] (4) The cold-processed pipe is subjected to aging treatment, straightening, pickling and cleaning to obtain a finished high-entropy alloy thin-wall pipe resistant to lead-bismuth corrosion.

[0014] The method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube comprises the following steps: in step (1), the pressure of the induction melting vacuum chamber is 5×10 -3 ~7×10 -3 Pa, the smelting temperature is 1400~1700℃.

[0015] In the preparation method of the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube, in step (2), the homogenization treatment temperature is 1000-1200° C., the insulation time is 20-50 hours, and the furnace is cooled to room temperature.

[0016] The preparation method of the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube, in step (2), the forging blank adopts a four-upsetting and four-drawing upsetting and drawing process, the ingot is heated to 1000-1200°C, kept warm for 1-5h, the ingot is first upset, and the forging strain rate is 0.1-1s -1 The deformation of each upsetting is 30-40%, and then it is pulled to the original length; after each upsetting and pulling, it is returned to the furnace and heated to 1000-1200℃, kept warm for 1-5h, and air-cooled to room temperature after forging.

[0017] In the method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube, in step (2), the high-entropy alloy tube blank with a thick-walled hollow columnar structure has the following dimensions: outer diameter 18-25 mm, inner diameter 15-20 mm, wall thickness 1-5 mm, and length 100-300 mm.

[0018] The preparation method of the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube comprises the following steps: in step (3), when heat treating the high-entropy alloy tube blank with a thick-walled hollow columnar structure, the tube blank is heated to 1000-1200° C., kept at this temperature for 1-3 hours, and then cooled to room temperature with water; after 10-20 cold drawing processes, the tube blank is deformed by 5%-15% each time, and the heat treatment process of the high-entropy alloy tube blank with a thick-walled hollow columnar structure is repeated after each process.

[0019] In the method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube, in step (4), the aging treatment temperature of the cold-processed tube is 550-900° C., and the insulation time is 1-500 h.

[0020] In the method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube, in step (4), the finished lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube has dimensions of: outer diameter 5-8 mm, inner diameter 4-7 mm, wall thickness 0.3-1 mm, and length 500-2000 mm.

[0021] The design idea of ​​the present invention is:

[0022] The present invention selects relatively low-cost Fe and FCC structural stabilizing element Ni as matrix elements to ensure that the alloy has excellent plastic processing ability and reduce the alloy smelting cost and cold processing difficulty. In addition, by adding appropriate amounts of Cr, Al, Ti and Si elements to the matrix, these elements can form a uniform and dense multilayer oxide film in a corrosive environment by utilizing the characteristics of strong oxygen binding ability, effectively hindering the diffusion of alloy elements, lead, bismuth and oxygen, inhibiting the dissolution corrosion of the alloy matrix, and effectively improving the corrosion resistance of the high entropy alloy.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube of the present invention has a simple alloy system, processing technology and heat treatment process, which are easy to implement, making it have a high engineering application value in the field of nuclear structural materials.

[0025] 2. The lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube obtained by the present invention has the advantages of stable organizational properties and excellent corrosion resistance. A small amount of B2 phase is precipitated in the FCC matrix and grain boundaries, which significantly improves the high-temperature performance and LBE corrosion resistance of the high-entropy alloy.

[0026] 3. The present invention adopts a multi-pass cold working tube forming technology, combined with a subsequent recrystallization annealing process to eliminate stress, thereby obtaining a lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube with uniform wall thickness and good surface quality.

[0027] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an EBSD picture of an embodiment of the present invention.

[0029] Figure 2-Figure 3 This is a SEM picture of the surface morphology of an embodiment of the present invention. Figure 2 For forging state, Figure 3 It is in time-limited state.

[0030] Figure 4 In the embodiment of the present invention, at 550°C, the oxygen concentration is 1×10 -6 SEM image of the cross-sectional morphology of the corrosion layer after corrosion for 3000h in static liquid lead-bismuth eutectic with wt.%.

[0031] Figure 5-Figure 6 This is a picture of the appearance of the finished product of the lead-bismuth corrosion-resistant high-entropy alloy thin-walled pipe in the embodiment of the present invention. Figure 5 is the pipe cross section, Figure 6 For the side of the pipe. DETAILED DESCRIPTION

[0032] The following is a more detailed description of the specific embodiments of the present invention in conjunction with the accompanying drawings and examples, so that the scheme of the present invention and its advantages in various aspects can be better understood. However, the specific embodiments and examples described below are only for the purpose of illustration, rather than for limiting the present invention.

[0033] Example

[0034] In this embodiment, the chemical composition and specific preparation technology of a lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube are as follows:

[0035] 1. The chemical composition of the lead-bismuth corrosion-resistant high-entropy alloy thin-walled pipe is as follows, by weight percentage:

[0036] Fe: 50%; Ni: 25%; Cr: 12%; Al: 8%; Ti: 4%; Si: 1%.

[0037] 2. The method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube comprises the following steps:

[0038] (1) Raw materials were weighed according to the preset composition ratio, and alloy ingots were prepared by induction melting. The pressure in the vacuum induction melting furnace chamber was 6×10 -3 Pa, the melting temperature is 1500℃, after the melting and refining process, it is cast into a solid round ingot of Φ85mm;

[0039] (2) The solid round ingot is homogenized at 1100℃ for 24h. The furnace is cooled to room temperature. Then the ingot is hot forged. The four-upsetting and four-drawing process is adopted. The ingot is heated to 1100℃ and kept for 1h. The ingot is first roughened. The forging strain rate is 0.1s -1 , the deformation amount is 35%, and then drawn to the original length, and the heating, insulation and upsetting process are repeated four times, and then air-cooled to room temperature; the forging billet is then machined to obtain a thick-walled hollow cylindrical high-entropy alloy tube billet with an outer diameter of 20 mm, an inner diameter of 16 mm, a wall thickness of 2 mm, and a length of 120 mm;

[0040] (3) heat treating the thick-walled high-entropy alloy tube billet by heating it to 1100°C, holding it for 1 hour, and cooling it to room temperature with water; cold drawing is performed for 15 times, with a deformation of 10% in each time, and the heat treatment process of the thick-walled hollow columnar high-entropy alloy tube billet is repeated after each processing to restore the plasticity of the alloy to ensure the cold working ability of the alloy tube;

[0041] (4) The cold-processed pipe was subjected to aging treatment at 700°C for 50 hours, straightened, pickled and cleaned to obtain a finished lead-bismuth corrosion-resistant high-entropy alloy thin-walled pipe with an outer diameter of 6.5 mm, an inner diameter of 5.6 mm, a wall thickness of 0.45 mm and a length of 1000 mm.

[0042] like Figure 1 As shown in the figure, the high entropy alloy in the embodiment is an equiaxed crystal structure with an average grain size of about 45.56 μm. Figure 2-Figure 3 As shown, it is shown that the phase composition of the high entropy alloy in different states in the embodiment is a two-phase structure, including a face-centered cubic (FCC) matrix phase and an ordered body-centered cubic (B2) phase. Figure 4 As shown, at 550°C, the oxygen concentration is 1×10 -6 After being corroded in a static liquid lead-bismuth eutectic with a concentration of wt.% for 3000 h, the cross-sectional morphology of the corrosion layer of the high entropy alloy shows that the high entropy alloy of the embodiment of the present invention has no dissolution and erosion under such corrosion conditions, indicating that the high entropy alloy has excellent corrosion resistance. Figure 5-Figure 6 As shown, the wall thickness of the high entropy alloy thin-walled tube is relatively uniform and there are no obvious defects on the surface.

[0043] The implementation results show that the present invention prepares high entropy alloy ingots by induction melting and forging, eliminates casting defects and refines grain size through high temperature heat treatment and multiple upsetting forging processes, and obtains a two-phase microstructure with face-centered cubic and body-centered cubic. This special heterogeneous structure gives the alloy excellent high temperature resistance and corrosion resistance. Subsequently, a high entropy alloy thin-walled tube with excellent microstructure, uniform wall thickness, good surface quality and high reliability is prepared through multiple cold working, which provides new ideas for the selection and preparation of lead-cooled fast reactor cladding materials and further promotes the rapid development of my country's fourth-generation nuclear energy system.

[0044] The embodiments are preferred implementations of the present invention, but the present invention is not limited to the above-mentioned implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention belong to the protection scope of the present invention.

Claims

1. A high entropy alloy thin-walled pipe resistant to lead-bismuth corrosion, characterized in that: The chemical composition of the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube is as follows by weight percentage: Fe: 45-60%; Ni: 20-35%; Cr: 10-25%; Al: 3-8%; Ti: 3-5%; Si: 1-3%.

2. A method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube according to claim 1, characterized in that: The following steps are involved: (1) Weighing raw materials according to a preset composition ratio, preparing alloy ingots by vacuum induction melting, and then casting them into solid round ingots of Φ85 mm±5 mm; (2) The solid round ingot is subjected to homogenization treatment and forging, and then machined to obtain a high entropy alloy tube with a thick-walled hollow columnar structure; (3) The thick-walled hollow cylindrical high-entropy alloy tube blank is subjected to high-temperature heat treatment and then cold-drawn. During the processing, an intermediate annealing process is required to restore the plasticity of the alloy to ensure the cold working ability of the alloy tube; (4) The cold-processed pipe is subjected to aging treatment, straightening, pickling and cleaning to obtain a finished high-entropy alloy thin-wall pipe resistant to lead-bismuth corrosion.

3. The method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube according to claim 2, characterized in that: In step (1), the pressure of the induction melting vacuum chamber is 5×10 -3 ~7×10 -3 Pa, the smelting temperature is 1400~1700℃.

4. The method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube according to claim 2, characterized in that: In step (2), the homogenization treatment temperature is 1000-1200° C., the insulation time is 20-50 hours, and the furnace is cooled to room temperature.

5. The method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube according to claim 4, characterized in that: In step (2), the forging process adopts a four-upsetting and four-drawing upsetting process, the ingot is heated to 1000-1200°C, kept warm for 1-5 hours, the ingot is first upset, and the forging strain rate is 0.1-1s -1 The deformation of each upsetting is 30-40%, and then it is pulled to the original length; after each upsetting and pulling, it is returned to the furnace and heated to 1000-1200℃, kept warm for 1-5h, and air-cooled to room temperature after forging.

6. The method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube according to claim 5, characterized in that: In step (2), the dimensions of the thick-walled hollow columnar high-entropy alloy tube blank are: outer diameter 18-25 mm, inner diameter 15-20 mm, wall thickness 1-5 mm, and length 100-300 mm.

7. The method for preparing a lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube according to any one of claims 2 to 6, characterized in that: In step (3), when the high entropy alloy tube blank with a thick-walled hollow columnar structure is heat treated, it is heated to 1000-1200° C., kept at this temperature for 1-3 hours, and then water-cooled to room temperature; after 10-20 cold drawing processes, with a deformation amount of 5%-15% in each process, the heat treatment process of the high entropy alloy tube blank with a thick-walled hollow columnar structure is repeated after each process.

8. The method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube according to claim 2, characterized in that: In step (4), the aging treatment temperature of the cold-processed pipe is 550 to 900° C., and the insulation time is 1 to 500 hours.

9. The method for preparing the lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube according to claim 2, characterized in that: In step (4), the finished lead-bismuth corrosion-resistant high-entropy alloy thin-walled tube has the following dimensions: outer diameter 5-8 mm, inner diameter 4-7 mm, wall thickness 0.3-1 mm, and length 500-2000 mm.

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