Zr-ta based low-activation refractory high-entropy alloy and preparation method thereof

Abstract

This invention discloses a Zr-Ta-based low-activation refractory high-entropy alloy and its preparation method. After preparation, the microstructure of the Zr-Ta-based low-activation refractory high-entropy alloy transforms from a single-phase structure to a nano-network structure. This nano-network structure consists of a bulk nanophase and a matrix phase, and its unique microstructure synergistically endows the alloy with excellent comprehensive properties: a yield strength of up to 980 MPa, while maintaining a compressive elongation of over 60%, successfully achieving synergistic optimization of mechanical properties and radiation resistance. This preparation method effectively expands the application boundaries of Zr-Ta-based low-activation refractory high-entropy alloys in the field of nuclear structural materials, and the process has advantages such as simple operation, strong controllability, and readily available heat treatment equipment, possessing significant potential for engineering applications.

Description

Technical Field

[0001] This invention relates to the field of high-entropy alloy preparation and heat treatment technology, and more particularly to a Zr-Ta-based low-activation refractory high-entropy alloy and its preparation method. Background Technology

[0002] With the continuous evolution of nuclear energy technology, the service conditions faced by structural materials in the operation of advanced reactors are becoming increasingly stringent. Nuclear structural materials need to withstand extreme conditions such as high temperature, high pressure, and high dose radiation, which places extremely high demands on the mechanical properties and radiation resistance of the materials.

[0003] High-entropy alloys, as a novel type of metallic material, exhibit numerous superior properties due to their unique compositional design, such as high strength, high hardness, good wear resistance, and excellent corrosion resistance. Refractory high-entropy alloys, as an important branch of high-entropy alloys, have broad application prospects in high-temperature environments due to their high melting point. Among them, refractory high-entropy alloys composed of low-activation elements have become a research hotspot in the field of nuclear materials due to their excellent high-temperature stability and high strength.

[0004] The network structure composed of a bulk nanophase and a matrix phase plays a crucial role in the regulation of material properties as a special microstructure. Studies have shown that introducing such a network structure into alloys allows the bulk nanophase to form effective "mechanical barrier units" through spatial dispersion, significantly hindering dislocation movement and suppressing grain boundary migration, thereby greatly improving the material's strength and hardness. Simultaneously, this network structure, composed of two synergistic phases, can also function as an "irradiation defect trap." The interface between the bulk nanophase and the matrix phase, as well as the bulk nanophase itself, can efficiently capture irradiated point defects and dislocation loops, effectively suppressing irradiation swelling and hardening, and significantly improving the material's radiation resistance. However, current methods for regulating the network structure composed of the bulk nanophase and the matrix phase in low-activation refractory high-entropy alloys are still imperfect. It is difficult to achieve synergistic optimization of the material's mechanical properties and radiation resistance by precisely controlling the morphology, size, distribution, and interfacial characteristics of this structure, which to some extent limits the application of such alloys in the field of nuclear materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a Zr-Ta-based low-activation refractory high-entropy alloy.

[0006] Another object of the present invention is to provide a Zr-Ta-based low-activation refractory high-entropy alloy prepared by the above preparation method.

[0007] To achieve the above objectives, the present invention is accomplished through the following technical solutions.

[0008] A Zr-Ta-based low-activation refractory high-entropy alloy with the general structural formula Cr a Hf b Ta c Ti d V e W f Zr g 1%≤a≤5%, 5%≤b≤15%, 50%≤c<70%, 0≤d≤15%, 4%≤e<24%, 5%≤f≤10%, 15%≤g≤35%, and a+b+c+d+e+f+g=100%, where a, b, c, d, e, f, and g are molar percentages; c+g≥66%.

[0009] In the above technical solution, the Zr-Ta-based low-activation refractory high-entropy alloy is a nano-network structure, which is a two-phase body-centered cubic structure or a body-centered cubic matrix + δ phase.

[0010] In the above technical solution, the micro Vickers hardness of the Zr-Ta-based low-activation refractory high-entropy alloy is 280~340HV.

[0011] In the above technical solution, the yield strength of the Zr-Ta-based low-activation refractory high-entropy alloy is 900~1300MPa, and the compressive elongation is greater than 60%.

[0012] A method for preparing a Zr-Ta-based low-activation refractory high-entropy alloy includes the following steps:

[0013] Step 1: Pre-treat the metal raw material to remove impurities, wherein the metal raw material is one or more of Cr, Hf, Ta, Ti, V, W and Zr; In step 1, the pretreatment operation consists of sequentially performing acid washing, alcohol washing, water washing, and drying.

[0014] In step 1, the pickling solution is a mixture of hydrofluoric acid, nitric acid and deionized water, and the ratio of hydrofluoric acid, nitric acid and deionized water by volume is 1:(2.8~3.2):(5.7~6.3).

[0015] In step 1, the purity of the pretreated metal raw material is ≥99%.

[0016] Step 2: According to the atomic percentage of each element in the Zr-Ta-based low-activation refractory high-entropy alloy, weigh the required metal raw materials and put them into the vacuum electric arc furnace crucible in order of melting point from low to high to carry out at least 8 melting operations to ensure that each element is evenly distributed in the button-shaped high-entropy alloy sample. After at least 8 melting operations, a high-entropy alloy ingot is obtained. In step 2, each melting operation includes: melting the metal to be melted (metal raw material or button-shaped high-entropy alloy sample) at 3000~3500℃ for 3~5 min, cooling, and obtaining a button-shaped high-entropy alloy sample.

[0017] Step 3: Cut the high-entropy alloy ingot into cuboids and perform low-temperature preheating pretreatment to prevent rolling cracks in the high-entropy alloy ingot. After low-temperature preheating pretreatment, roll the high-entropy alloy ingot at room temperature to obtain a high-entropy alloy sample. The low-temperature preheating pretreatment includes: heating to 180-220℃ at a heating rate of 5-10℃ / min under a protective gas and holding for 20-40 min to slowly expel internal adsorbed water and pore gas, avoiding gas expansion and internal cracking caused by rapid heating; then heating to 450-650℃ at a heating rate of 10-20℃ / min and holding for 40-60 min to uniformly heat the billet so that the temperature difference between the inside and outside of the billet is ≤30℃, eliminating residual stress in the casting state and avoiding thermal shock. In step 3, the length × width × height of the cuboid is (25 ± 5) mm × (25 ± 5) mm × (30 ± 5) mm.

[0018] In step 3, the number of rolling passes is 5 to 8, the single reduction rate is 3% to 5%, the low-speed rolling speed is 0.1 to 0.3 m / s, and the rolling is completed within 15 minutes after low-temperature preheating.

[0019] In step 3, the total reduction rate of the rolling process is ≥20%.

[0020] Step 4: Under protective gas and a certain pressure, the high-entropy alloy sample is held at 390~410℃ for 0.5~1 h, and then held at 630~1500℃ for 5~7 h. After the holding is completed, the sample is furnace cooled to 180~220℃ and then air cooled to room temperature to obtain Zr-Ta-based low-activation refractory high-entropy alloy.

[0021] In step 4, the high-entropy alloy sample needs to be tightly wrapped with an aluminum film and then kept warm.

[0022] In step 4, the pressure is 0.05~0.16 MPa, and the protective gas is argon.

[0023] In step 4, the vacuum level inside the furnace is evacuated to 1×10⁻⁶. -5 ~1×10 -4 Pa, then backfill with protective gas until the pressure inside the furnace reaches 0.05~0.16 MPa.

[0024] In step 4, the temperature inside the tubular furnace is raised to 390-410°C at a heating rate of 20-25°C / min.

[0025] In step 4, the temperature inside the tubular furnace is raised to 630-1500℃ at a heating rate of 25-35℃ / min.

[0026] In step 4, it is preferable to heat the high-entropy alloy sample at 390~410℃ for 0.5~1 h, and then heat it at 780~820℃ for 5~7 h.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Microstructure Optimization: This invention achieves the transformation of Zr-Ta-based low-activation refractory high-entropy alloys from a single-phase structure to a network structure composed of nano-bulk phases and matrix phases through heat treatment. Existing Zr-Ta-based low-activation refractory high-entropy alloys are mostly single-phase structures or single-phase structures with precipitated phases. The preparation method provided by this invention allows for the control of the size and distribution of the nano-network structure in Zr-Ta-based low-activation refractory high-entropy alloys, thereby improving their mechanical properties and radiation resistance.

[0028] 2. Mechanical Property Optimization: The network structure composed of the nanobulk phase and the matrix phase acts as a reinforcing phase in the alloy. When the alloy is subjected to external forces, this nanonetwork structure can effectively hinder dislocation movement and increase the resistance to dislocation slip, thereby improving the strength and hardness of the alloy. This nanonetwork structure can also further improve the mechanical properties of the alloy by refining grains and inhibiting grain boundary migration. Simultaneously, the precipitated nanoscale second phase and the matrix phase maintain a coherent structure with continuous lattice matching at the interface. This coherent state results in extremely low interfacial energy, significantly improving the strength and toughness of the material. The Zr-Ta-based low-activation refractory high-entropy alloy obtained by the preparation method of this invention has a yield strength of 980 MPa and a compressive elongation greater than 60%.

[0029] 3. Radiation Resistance Optimization: Under nuclear irradiation, materials develop numerous point defects and dislocation loops, resulting in radiation damage. The network structure composed of a bulk nanophase and a matrix phase can act as a trap for radiation damage, effectively capturing these defects and reducing radiation swelling and hardening. The size, morphology, and distribution of the nanonetwork structure significantly influence its radiation resistance. This invention modulates the nanonetwork structure through a preparation method, achieving suitable size and distribution to more effectively capture radiation defects, improve the alloy's radiation resistance (Vickers hardness of 320 HV), and further reduce the impact of radiation on material properties. Attached Figure Description

[0030] Figure 1 The XRD diffraction pattern of the as-cast Zr-Ta-based low-activation refractory high-entropy alloy prepared in Comparative Example 1; Figure 2Microstructure of the as-cast Zr-Ta-based low-activation refractory high-entropy alloy prepared in Comparative Example 1; Figure 3 The image shows the microstructure of the Zr-Ta-based low-activation refractory high-entropy alloy prepared in Example 1. Figure 4 The engineering stress-strain curve of the Zr-Ta-based low-activation refractory high-entropy alloy prepared in Example 1 at room temperature; Figure 5 The image shows the microstructure of the Zr-Ta-based low-activation refractory high-entropy alloy prepared in Example 2. Detailed Implementation

[0031] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0032] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0033] In the following examples, the pickling solution was a mixture of hydrofluoric acid, nitric acid and deionized water, with a volume ratio of 1:3:6; the alcohol used for alcohol washing had a purity of 99%.

[0034] Example 1 A method for preparing a Zr-Ta-based low-activation refractory high-entropy alloy, wherein the general structural formula of the Zr-Ta-based low-activation refractory high-entropy alloy is Cr3Hf5Ta. 50 V 15 W5Zr 22 This includes the following steps: Step 1: The metal raw materials are sequentially pickled, washed with alcohol, washed with water, and dried to remove impurities and ensure that the purity of the metal raw materials is higher than 99%. The metal raw materials are Cr, Hf, Ta, V, W, and Zr.

[0035] Step 2: Based on the atomic percentages of each element in the Zr-Ta-based low-activation refractory high-entropy alloy, weigh the required metal raw materials and place them into a vacuum arc furnace crucible in order of melting point from low to high. Perform eight melting operations in the vacuum arc furnace to ensure uniform distribution of each element within the button-shaped high-entropy alloy sample. After eight melting operations, a high-entropy alloy ingot is obtained. Each melting operation includes: melting the metal to be melted (metal raw materials or button-shaped high-entropy alloy sample) at 3400℃ for 5 minutes, followed by cooling to obtain the button-shaped high-entropy alloy sample.

[0036] Step 3: The high-entropy alloy ingot is cut into cuboids with dimensions of 27 mm × 28 mm × 30 mm and subjected to low-temperature preheating pretreatment to prevent rolling cracks. After low-temperature preheating pretreatment, the high-entropy alloy ingot is rolled at room temperature to obtain a high-entropy alloy sample. The low-temperature preheating pretreatment includes: under argon protection, the high-entropy alloy ingot is heated from room temperature to 200°C at a heating rate of 10°C / min and held at 200°C for 30 min to slowly expel adsorbed water and pore gases from the billet (high-entropy alloy ingot) and avoid gas expansion and internal cracking caused by rapid heating; then, the temperature is increased to 500°C at a heating rate of 20°C / min and held at 200°C for 60 min to ensure uniform heating, so that the temperature difference between the inside and outside of the billet is ≤30°C, eliminating residual stress in the casting state and avoiding thermal shock; the rolling passes are 7, the single reduction rate is 3%, the low-speed rolling speed is 0.3 m / s, and the total reduction rate is 21%.

[0037] Step 4: After tightly wrapping the high-entropy alloy sample with an aluminum film, place it into a tube furnace and evacuate the furnace to a vacuum level of 1×10⁻⁶. -4 Pa, then backfill with argon gas until the pressure inside the furnace reaches 0.1 MPa. Under the pressure of 0.1 MPa, the temperature inside the tubular furnace is raised to 410℃ at a heating rate of 25℃ / min and held at 410℃ for 0.5 h. Then, the temperature inside the tubular furnace is raised to 810℃ at a heating rate of 30℃ / min and held at 810℃ for 5.5 h. After the holding period, the furnace is cooled to 200℃ and then air-cooled to room temperature to obtain a Zr-Ta-based low-activation refractory high-entropy alloy.

[0038] Example 2 A method for preparing a Zr-Ta-based low-activation refractory high-entropy alloy, wherein the general structural formula of the Zr-Ta-based low-activation refractory high-entropy alloy is Cr2Hf3Ta. 53 Ti2V 10 W6Zr 24 This includes the following steps: Step 1: The metal raw materials are sequentially pickled, washed with alcohol, washed with water, and dried to remove impurities and ensure that the purity of the metal raw materials is higher than 99%. The metal raw materials are Cr, Hf, Ta, Ti, V, W, and Zr.

[0039] Step 2: Based on the atomic percentages of each element in the Zr-Ta-based low-activation refractory high-entropy alloy, weigh the required metal raw materials and place them into a vacuum arc furnace crucible in order of melting point from low to high. Perform eight melting operations in the vacuum arc furnace to ensure uniform distribution of each element within the button-shaped high-entropy alloy sample. After eight melting operations, a high-entropy alloy ingot is obtained. Each melting operation includes: melting the metal to be melted (metal raw materials or button-shaped high-entropy alloy sample) at approximately 3400℃ for 4 minutes, followed by cooling to obtain the button-shaped high-entropy alloy sample.

[0040] Step 3: Cut the high-entropy alloy ingot into a cuboid with a length × width × height of 26 mm × 28 mm × 28 mm and perform low-temperature preheating pretreatment to prevent the high-entropy alloy ingot from cracking during rolling. After low-temperature preheating pretreatment, roll the high-entropy alloy ingot at room temperature to obtain a high-entropy alloy sample. The low-temperature preheating and pretreatment process includes: low-temperature preheating and pretreatment under argon protection; under argon protection, the high-entropy alloy ingot is heated from room temperature to 200℃ at a heating rate of 10℃ / min, and held at 200℃ for 30 min to slowly expel adsorbed water and pore gas inside the billet (high-entropy alloy ingot) to avoid gas expansion and internal cracking caused by rapid heating; then the temperature is increased to 500℃ at a heating rate of 20℃ / min, and held at 200℃ for 50 min to ensure uniform heating, so that the temperature difference between the inside and outside of the billet is ≤30℃, eliminating residual stress in the casting state and avoiding thermal shock; the rolling passes are 6, the single reduction rate is 4%, the low-speed rolling speed is 0.3 m / s, and the total reduction rate is 24%.

[0041] Step 4: After tightly wrapping the high-entropy alloy sample with an aluminum film, place it into a tube furnace and evacuate the furnace to a vacuum level of 1×10⁻⁶. -4 Pa, then backfill with argon gas until the pressure inside the furnace reaches 0.1 MPa. Under the pressure of 0.1 MPa, the temperature inside the tubular furnace is raised to 400℃ at a heating rate of 20℃ / min and held at 400℃ for 0.5 h. Then, the temperature inside the tubular furnace is raised to 800℃ at a heating rate of 30℃ / min and held at 800℃ for 5 h. After the holding period, the furnace is cooled to 200℃ and then air-cooled to room temperature to obtain a Zr-Ta-based low-activation refractory high-entropy alloy.

[0042] Comparative Example 1 A cast Zr-Ta-based low-activation refractory high-entropy alloy is the high-entropy alloy ingot in step 2 of Example 1.

[0043] Comparative Example 2 A cast Zr-Ta-based low-activation refractory high-entropy alloy is the high-entropy alloy ingot in step 2 of Example 2.

[0044] Figure 1 The image shows the XRD diffraction pattern of the as-cast Zr-Ta-based low-activation refractory high-entropy alloy of Comparative Example 1. Figure 1 It can be seen that only body-centered cubic diffraction peaks appear in the as-cast Zr-Ta-based low-activation refractory high-entropy alloy of Comparative Example 1.

[0045] Figure 2 The image shows the microstructure of the as-cast Zr-Ta-based low-activation refractory high-entropy alloy of Comparative Example 1. Figure 2It can be seen that the microstructure of the as-cast Zr-Ta-based low-activation refractory high-entropy alloy in Comparative Example 1 is dendritic, and no second phase is present. Combined with the XRD diffraction analysis pattern, the as-cast Zr-Ta-based low-activation refractory high-entropy alloy in Comparative Example 1 has a single-phase body-centered cubic structure.

[0046] Figure 3 The image shows the microstructure of the Zr-Ta-based low-activation refractory high-entropy alloy prepared in Example 1. The Zr-Ta-based low-activation refractory high-entropy alloy prepared in Example 1 exhibits a uniform network structure composed of a nanobulk phase and a matrix phase. This network structure is a two-phase body-centered cubic structure with a volume ratio of approximately 2:3 between the two phases.

[0047] Figure 4 The figures show the engineering stress-strain curves at room temperature for the Zr-Ta-based low-activation refractory high-entropy alloy prepared in Example 1. Figure 4 As can be seen, the Zr-Ta-based low-activation refractory high-entropy alloy prepared in Example 1 has a high compressive elongation, exceeding 60%. No fracture occurred in the alloy specimen during the compression test. Furthermore, the alloy exhibits a high yield strength of 980 MPa and a Vickers hardness of 320 HV.

[0048] Figure 5 The image shows the microstructure of the Zr-Ta-based low-activation refractory high-entropy alloy prepared in Example 2. This alloy has a body-centered cubic matrix and a δ phase.

[0049] Testing revealed that the Zr-Ta-based low-activation refractory high-entropy alloy (Cr2Hf3Ta) prepared in Example 2... 53 Ti2V 10 W6Zr 24 (and the Zr-Ta-based low-activation refractory high-entropy alloy (Cr3Hf5Ta) prepared in Example 1) 50 V 15 W5Zr 22 It also possesses outstanding comprehensive mechanical properties and potential radiation resistance. Its elongation is greater than 60%, yield strength reaches 940 MPa, and Vickers hardness is 304 HV. In summary, the Zr-Ta-based low-activation refractory high-entropy alloy prepared by the method of the present invention has a network structure composed of a nano-bulk phase and a matrix phase, exhibiting outstanding comprehensive mechanical properties and potential radiation resistance.

[0050] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A Zr-Ta-based low-activation refractory high-entropy alloy, characterized in that, Its general structural formula is Cr a Hf b Ta c Ti d V e W f Zr g 1%≤a≤5%, 5%≤b≤15%, 50%≤c<70%, 0≤d≤15%, 4%≤e<24%, 5%≤f≤10%, 15%≤g≤35%, and a+b+c+d+e+f+g=100%, where a, b, c, d, e, f, and g are molar percentages; c+g≥66%.

2. The Zr-Ta-based low-activation refractory high-entropy alloy according to claim 1, characterized in that, The Zr-Ta-based low-activation refractory high-entropy alloy has a nano-network structure, which is a two-phase body-centered cubic structure or a body-centered cubic matrix + δ phase.

3. The Zr-Ta-based low-activation refractory high-entropy alloy according to claim 1, characterized in that, The Zr-Ta-based low-activation refractory high-entropy alloy has a micro Vickers hardness of 280~340 HV, a yield strength of 900~1300 MPa, and a compressive elongation greater than 60%.

4. The method for preparing the Zr-Ta-based low-activation refractory high-entropy alloy according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step 1: Pre-treat the metal raw material to remove impurities, wherein the metal raw material is one or more of Cr, Hf, Ta, Ti, V, W and Zr; Step 2: Calculate the atomic percentage of each element in the Zr-Ta-based low-activation refractory high-entropy alloy, weigh the required metal raw materials, add them in order of melting point from low to high and perform at least 8 melting operations to ensure that each element is evenly distributed in the button-shaped high-entropy alloy sample. After at least 8 melting operations, a high-entropy alloy ingot is obtained. Step 3: Cut the high-entropy alloy ingot into a cuboid and perform low-temperature preheating pretreatment to prevent the high-entropy alloy ingot from cracking during rolling. After low-temperature preheating pretreatment, roll the high-entropy alloy ingot at room temperature to obtain a high-entropy alloy sample. The low-temperature preheating pretreatment includes: heating to 180-220℃ at a heating rate of 5-10℃ / min and holding for 20-40 min under a protective gas; then heating to 460-650℃ at a heating rate of 10-20℃ / min and holding for 40-60 min. Step 4: Under protective gas and a certain pressure, the high-entropy alloy sample is held at 390~410℃ for 0.5~1 h, and then held at 630~1500℃ for 5~7 h. After the holding is completed, the sample is furnace cooled to 180~220℃ and then air cooled to room temperature to obtain Zr-Ta-based low-activation refractory high-entropy alloy.

5. The preparation method according to claim 4, characterized in that, The pretreatment process involves sequentially performing pickling, alcohol washing, water washing, and drying; the purity of the pretreated metal raw material is ≥99%.

6. The preparation method according to claim 4, characterized in that, Each melting operation includes: melting the metal to be melted at 3000~3500℃ for 3~5 min, cooling, and obtaining a button-shaped high-entropy alloy sample; The rolling passes are 5 to 8, the single-pass reduction rate is 3% to 5%, and the low-speed rolling speed is 0.1 to 0.3 m / s; The total reduction rate of the rolling process is ≥20%.

7. The preparation method according to claim 4, characterized in that, The high-entropy alloy sample was held at 390~410℃ for 0.5~1 h, and then held at 780~820℃ for 5~7 h.

8. The preparation method according to claim 4, characterized in that, The high-entropy alloy sample needs to be tightly wrapped in aluminum film and then kept warm.

9. The preparation method according to claim 4, characterized in that, The pressure is 0.05~0.16 MPa, and the protective gas is argon. The vacuum level inside the furnace was evacuated to 1×10⁻⁶. -5 ~1×10 -4 Pa, then backfill with protective gas until the pressure inside the furnace reaches 0.05~0.16 MPa.

10. The preparation method according to claim 4, characterized in that, The temperature inside the tube furnace is raised to 390-410℃ at a heating rate of 20-25℃ / min. The temperature inside the tubular furnace is raised to 630-1500℃ at a heating rate of 25-35℃ / min.

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