Method for preparing refractory high-entropy alloy diffusion couple sample based on duplex process

Abstract

The invention relates to a method for preparing a refractory high-entropy alloy diffusion couple sample based on a duplex process, and belongs to the technical field of alloys. According to the method, an electric arc melting method is adopted for carrying out semi-melting processing on a diffusion couple bonding surface of the refractory high-entropy alloy, the purpose of eliminating interface holes is achieved by softening a diffusion couple interface by adjusting current, and good bonding of high-melting-point diffusion couple samples of the refractory high-entropy alloy and pre-diffusion of components are achieved; and then a high-vacuum heat treatment furnace is used for conducting high-temperature diffusion treatment on the sample, and large-gradient component diffusion of the refractory elements is achieved. The problems that the refractory high-entropy alloy diffusion couple is poor in interface bonding degree, sensitive to impurities and prone to precipitation phase are effectively solved, the prepared refractory high-entropy alloy diffusion couple is high in quality and low in cost, a gradient component interval with hundreds of micrometers of continuous changes can be achieved on a millimeter-scale sample, and the method is suitable for industrial production. The method is suitable for ion irradiation mechanism research in the field of nuclear materials.

Description

Technical Field

[0001] This invention relates to a method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process, belonging to the field of alloy technology. Background Technology

[0002] A diffusion couple is a sample composed of two different metals or alloys bonded together. Heating causes interdiffusion, resulting in a continuously varying gradient composition region at the diffusion interface. Diffusion couple preparation technology is increasingly widely used in materials science and metallurgy, particularly in phase diagram determination and materials thermodynamics and kinetics. The diffusion couple method is currently the most applicable, efficient, and reliable method for determining alloy systems, especially solid-state relationships. This method can directly determine phase equilibrium relationships and compositions, and can obtain a wide range of alloy compositions from a single diffusion couple sample, significantly reducing experimental time and improving efficiency. It has been widely applied in areas such as determining diffusion coefficients and phase equilibrium studies in alloy systems, optimizing interfacial reactions and bonding strength between ceramics and metals, and controlling interfacial diffusion and performance of thin films and coatings. However, the traditional "fixture method" for preparing refractory high-entropy alloy diffusion couples faces two major challenges: First, refractory high-entropy alloys have a hysteresis diffusion effect, which makes element diffusion slow and makes it difficult to eliminate the original pores at the diffusion interface, resulting in poor interfacial bonding. Second, they are sensitive to impurities such as C, N, and O. Due to the limitations of the vacuum degree of the quartz tube and the maximum heat treatment temperature, the diffusion couple needs to be heat-treated for a long time, during which CNO-rich precipitates are easily generated. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process. This method is based on arc melting, and by controlling the current to heat the diffusion couple interface for cladding and pre-diffusion, it achieves metallurgical bonding of the interface and pre-diffusion of the compositional gradient through fusion-bonded voids. This results in small-sized diffusion couple samples with tight interfacial bonding and no impurity contamination, covering a wide research range. The gradient composition range continuously and uniformly varies within the atomic ratio range of 0-100; the range width can reach over 600 μm.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows.

[0005] A method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process, the method steps include:

[0006] S1. Sample preparation: Prepare metal elemental and alloy blocks for making diffusion couple samples; S2. Sample polishing: Polishing and ultrasonic cleaning of the surface of metal elements and alloy blocks; S3. Sample Preparation: Stack the ultrasonically cleaned elemental metals and alloy blocks, with the high-melting-point elemental metal or alloy block on top, and place them in an arc-melting copper crucible. Evacuate to a high vacuum of 2.5 × 10⁻⁶. -2 Below Pa; S4. Arc melting cladding-diffusion process: Control the current and heating time of arc melting, use an arc gun to heat high melting point metals or alloys to a semi-molten state, then stop heating and cool. S5. Repeat step 2-3 of S4. After the last cooling, polish the sample surface until it is shiny and then sonicate. S6. Place the sample in a high-vacuum heat treatment furnace and evacuate to a vacuum level of 2.5 × 10⁻⁶. -2 Below Pa, high-temperature heat treatment is used to further diffuse the sample; S7. After heat treatment and cooling, wire cutting is used to obtain regular samples. Then, the irradiated surface is polished to obtain refractory high-entropy alloy diffusion couple samples with good surface quality and low impurity content.

[0007] Preferably, in step S1, both the elemental metal and the alloy are homogenized samples.

[0008] Preferably, in step S1, the dimensions of the metallic element and alloy block are determined according to the material properties, with length and width ≤ 5 cm and thickness ≤ 1 cm.

[0009] Preferably, in step S2, during polishing, the surface is sanded to a mirror finish and then polished until complete grains are visible under a microscope; during ultrasonic cleaning, the process is carried out in acetone at a frequency of 100~200 kHz for 10~15 min.

[0010] Preferably, in step S3, during vacuuming, the mechanical pump is turned on to evacuate to 10 Pa, then the solenoid valve is turned on to evacuate to 5 Pa, and then the molecular pump is turned on to evacuate to a high vacuum of 2.5 × 10 Pa. -3 Below Pa.

[0011] Preferably, in step S4, the current and heating time for arc melting satisfy the following empirical formula:

[0012] U is the electric arc melting voltage (V), which ranges from 35 to 50V; I represents the arc current (A), with a value ranging from 50 to 100 A; t is the melting time (s), which ranges from 15 to 60 s; K is an empirical correction parameter with a value of 0.9; C is the specific heat capacity of low-melting-point metals or alloys (J / (kg)). ℃)); ρ is the density of a low-melting-point metal or alloy (kg / m³). 3 ); A is the sample contact area (m²) 2 ); δ represents the molten thickness (m) on the surface of a low-melting-point metal or alloy, with a value ranging from 0.5 to 1×10⁻⁶. -4 m; T H Melting point (°C) of high-melting-point metals or alloys; T L Melting point (°C) of low-melting-point metals or alloys; η is the arc thermal efficiency, with a value ranging from 0.7 to 0.9.

[0013] Preferably, in step S4, a heating compensation parameter t is introduced. loss The time required to compensate for the arc heating of high-melting-point metals or alloys to the melting point temperature of low-melting-point metals or alloys is 5~10s, that is, the heating time is extended by 5~10s based on the calculated heating time.

[0014] Preferably, in step S5, the heating time is shortened by 5-10 seconds each time.

[0015] Preferably, in step S6, the high-temperature heat treatment furnace is evacuated to a vacuum level of 2.5 × 10⁻⁶. -4 After the temperature drops below Pa, it is raised to 1600℃ and heat-treated for 20 hours. The entire heat treatment process is carried out under vacuum to maintain a pressure of 5 × 10⁻⁶ Pa. -4 Below Pa; during the heat treatment process, active elements such as Ti blocks are added to the crucible to remove impurities.

[0016] A refractory high-entropy alloy diffusion couple sample was prepared by the above method.

[0017] Beneficial effects This invention employs an electric arc melting method to partially melt the interface of a refractory high-entropy alloy diffusion couple. By adjusting the current, the interface of the diffusion couple is softened to eliminate interfacial porosity, achieving good bonding and pre-diffusion of components in the high-melting-point refractory high-entropy alloy diffusion couple sample. Subsequently, a high-vacuum heat treatment furnace is used to perform high-temperature diffusion treatment on the sample, achieving large-gradient diffusion of refractory elements. This invention effectively solves the problems of poor interfacial bonding and sensitivity to impurities and precipitation phases in refractory high-entropy alloy diffusion couples. The prepared refractory high-entropy alloy diffusion couples are of high quality, low cost, and can achieve a gradient composition range with continuous variations of hundreds of micrometers on millimeter-scale samples, making them suitable for ion irradiation mechanism research in the field of nuclear materials.

[0018] (1) The cladding-diffusion method ensures a high-quality interface: The electric arc melting cladding-pre-diffusion process effectively eliminates pores in the interface metallurgical bonding while realizing the pre-diffusion of the composition gradient, thus obtaining a sample with tight interface bonding, no impurity contamination and easy subsequent diffusion treatment, which significantly improves the excellent rate of preparing diffusion couples.

[0019] (2) High vacuum conditions and active element gettering ensure high purity samples: Diffusion samples are prepared by electric arc melting furnace and high vacuum heat treatment furnace to maintain high vacuum. Combined with high purity element gettering, the C, N and O contents of the obtained diffusion couple samples are all below 100 ppm, avoiding the generation of precipitated phases.

[0020] (3) High-temperature arc treatment ensures a large continuous diffusion range on small samples: the arc temperature can reach 3000℃, which enables the rapid diffusion of refractory elements, and finally obtains a diffusion couple sample with a small sample size but a large study area. The sample size can be as small as millimeters; its gradient composition range changes continuously and uniformly in the atomic ratio of 0-100, and the range width can reach more than 600μm. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the cladding-diffusion process for preparing the diffusion couple according to the present invention.

[0022] Figure 2 (a) is a physical image of the refractory high-entropy alloy diffusion couple obtained in Example 1; (b) is a SEM image of the diffusion interface and an EDS point scan result of the composition distribution.

[0023] Figure 3 (a) is a schematic diagram of the diffusion couple of the refractory high-entropy alloy obtained by the fixture method in Comparative Example 1; (b) is a SEM image of the diffusion couple interface.

[0024] Figure 4 (a) Schematic diagram of the diffusion couple fixture made of pure molybdenum; (b) SEM image of the diffusion boundary. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments.

[0026] Example 1: Preparation of V-VNbTa diffusion couples by cladding-diffusion dual process S1. Obtain a pure V and VNbTa uniform equiatomic ratio alloy bulk sample with a size of 20×17×2 mm using wire cutting; S2, pure V and VNbTa block samples were polished by sequentially grinding all surfaces with 400#, 800#, 1200# and 2000# sandpaper. The 20×17 mm surfaces of the two samples were sequentially ground to a mirror finish with 3000#, 5000# and 7000# sandpaper and then ultrasonically cleaned with acetone at a frequency of 100 kHz for 10 min. S3. Place the two ultrasonically cleaned blocks, mirror-side facing each other (VNbTa alloy on top), into an arc-melting copper crucible, and evacuate to a high vacuum of 2.5 × 10⁻⁶. -3 Below Pa; S4. Arc melting cladding-diffusion process: The alloy block is heated by an arc gun for cladding, eliminating porosity at the diffusion couple interface and performing pre-diffusion. S41. Control the current to 50A according to the empirical formula, heat the sample uniformly until the sample reaches a semi-molten state and maintain the heating for 60s. S42. Stop heating and cool the sample. Briefly repeat the heating step 3 times, each time with a current of 50A and a heating time reduced by 5s.

[0027] S5. After cladding, cool the sample to room temperature, polish the sample surface with an electric brush until it is shiny, and then sonicate. S6. Wrap the sample in Ta foil and place it in a molybdenum crucible in a high-vacuum heat treatment furnace along with the Ti block. Evacuate the furnace to a vacuum level of 2.5 × 10⁻⁶. -4 After Pa is below, it undergoes high-temperature heat treatment at 1600℃ for 20 hours; S7. After the heat treatment is completed and cooled to room temperature, the sample is wire-cut to obtain a sample of size 3×5×1mm. Then the irradiated surface is polished to obtain a refractory high-entropy alloy diffusion couple sample with good surface quality, low impurity content, and suitable for large-scale use in ion irradiation experiments.

[0028] The V-VNbTa alloy sample prepared as described above is as follows: Figure 2 As shown, its macroscopic interface quality is good. SEM microscopic images show that its diffusion interface is free of pores and precipitates. EDS spot scan shows that its V element content changes from 100 at% on the pure V side to 34 at% on the equiatomic VNbTa alloy side. The width of the entire gradient composition range is over 800 μm.

[0029] Table 1. C, N, and O content of diffusion couple sample in Example 1

[0030] Example 2: Preparation of Nb-NbZrTi diffusion couples by cladding-diffusion dual process S1. Obtain a pure Nb and NbZrTi uniform equiatomic ratio alloy bulk sample with a size of 20×17×2 mm using wire cutting; S2, pure Nb and NbZrTi bulk samples were polished by sequentially grinding all surfaces with 400#, 800#, 1200# and 2000# sandpaper. The 20×17 mm surfaces of the two samples were sequentially ground to a mirror finish with 3000#, 5000# and 7000# sandpaper and then ultrasonically cleaned with acetone at a frequency of 100 kHz for 10 min. S3. Place the two ultrasonically cleaned blocks mirror-side together (NbZrTi alloy on top) in an arc melting copper crucible, and evacuate to a high vacuum of 2.5 × 10⁻⁶. -3 Below Pa; S4. Arc melting cladding-diffusion process: The alloy block is heated by an arc gun for cladding, eliminating porosity at the diffusion couple interface and performing pre-diffusion. S41. Control the current to 40A according to the empirical formula, heat the sample uniformly until the sample reaches a semi-molten state and maintain the heating for 45s. S42. Stop heating and cool the sample. Briefly repeat the heating step 3 times, each time with a current of 40A and a heating time reduced by 5s.

[0031] S5. After cladding, cool the sample to room temperature, polish the sample surface with an electric brush until it is shiny, and then sonicate. S6. Wrap the sample in Ta foil and place it in a molybdenum crucible in a high-vacuum heat treatment furnace along with the Ti block. Evacuate the furnace to a vacuum level of 2.5 × 10⁻⁶. -4 After Pa is below, it undergoes high-temperature heat treatment at 1600℃ for 20 hours; S7. After the heat treatment is completed and cooled to room temperature, the sample is wire-cut to obtain a sample of size 3×5×1mm. Then the irradiated surface is polished to obtain a refractory high-entropy alloy diffusion couple sample with good surface quality, low impurity content, and suitable for large-scale use in ion irradiation experiments.

[0032] The Nb-NbZrTi alloy sample prepared as described above is as follows: Figure 3 As shown, its macroscopic interface quality is good. SEM microscopic images show that its diffusion interface is free of pores and precipitates. EDS spot scan shows that its Nb element content changes from 100 at% of pure Nb to 45 at% on the side of the equiatomic NbZrTi alloy. The width of the entire gradient composition range is more than 300 μm.

[0033] Table 2. C, N, and O content of diffusion couple sample in Example 2

[0034] Comparative Example 1: Preparation of V-VNbTa diffusion couples using the conventional fixture method The preparation process was carried out according to Example 1, except that the diffusion couple was prepared using the traditional clamp method, and in order to achieve the same diffusion distance of 800 μm, the high-temperature heat treatment time was extended to 40 hours. The specific steps are as follows: S1. Obtain a pure V and VNbTa uniform equiatomic ratio alloy bulk sample with a size of 20×17×2 mm using wire cutting; S2, pure V and VNbTa block samples were polished by sequentially grinding all surfaces with 400#, 800#, 1200# and 2000# sandpaper. The 20×17 mm surfaces of the two samples were sequentially ground to a mirror finish with 3000#, 5000# and 7000# sandpaper and then ultrasonically cleaned with acetone at a frequency of 100 kHz for 10 min. S3. Place the mirror sides of the two ultrasonically cleaned blocks together and put them on the ground. Figure 4 (a) shows a diffusion couple fixture made of pure molybdenum, with the fixture bolts tightened inside. S4. Arc melting cladding-diffusion process: The alloy block is heated by an arc gun for cladding, eliminating porosity at the diffusion couple interface and performing pre-diffusion. S5. Wrap the sample in Ta foil and place it in a molybdenum crucible in a high-vacuum heat treatment furnace along with the Ti block. Evacuate the furnace to a vacuum level of 2.5 × 10⁻⁶. -4 After Pa is below, it undergoes high-temperature heat treatment at 1600℃ for 40 hours; S6. After heat treatment, the sample was cooled to room temperature and then wire-cut to obtain a 3×5×1mm sample. The irradiated surface was then polished, and the diffusion interface was characterized by SEM. The results are as follows: Figure 4 As shown in (b), the diffusion interface of the two metals has a large number of pores and extremely poor bonding. Since the refractory high-entropy alloy is sensitive to C, N and O impurities, long-term heat treatment causes precipitates to form in the region near the diffusion interface.

[0035] Table 3. C, N, and O contents of the diffusion couple sample in Comparative Example 2

[0036] As can be seen from the above embodiments and comparative examples, whether or not the cladding-diffusion dual-process is used directly affects the quality of the diffusion couple. The process described in this invention can be used to prepare diffusion couple samples with tight interfacial bonding and large gradient composition space, suitable for large-scale ion irradiation experiments.

[0037] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A method for preparing refractory high-entropy alloy diffusion couple samples based on a duplex process, characterized in that: The method steps include: S1. Sample preparation: Prepare metal elemental and alloy blocks for making diffusion couple samples; S2. Sample polishing: Polishing and ultrasonic cleaning of the surface of metal elements and alloy blocks; S3. Sample Preparation: Stack the ultrasonically cleaned elemental metals and alloy blocks, with the high-melting-point elemental metal or alloy block on top, and place them in an arc-melting copper crucible. Evacuate to a high vacuum of 2.5 × 10⁻⁶. -2 Below Pa; S4. Arc melting cladding-diffusion process: Control the current and heating time of arc melting, use an arc gun to heat high melting point metals or alloys to a semi-molten state, then stop heating and cool. S5. Repeat step 2-3 of S4. After the last cooling, polish the sample surface until it is shiny and then sonicate. S6. Place the sample in a high-vacuum heat treatment furnace and evacuate to a vacuum level of 2.5 × 10⁻⁶. -2 Below Pa, high-temperature heat treatment is used to further diffuse the sample; S7. After heat treatment and cooling, a regular sample is obtained by wire cutting. Then, the irradiated surface is polished to obtain a refractory high-entropy alloy diffusion couple sample.

2. The method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process as described in claim 1, characterized in that: In step S1, both the metallic element and the alloy are homogenized samples.

3. The method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process as described in claim 1, characterized in that: In step S1, the dimensions of the metallic element and alloy block are determined according to the material properties, with length and width ≤ 5 cm and thickness ≤ 1 cm.

4. The method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process as described in claim 1, characterized in that: In step S2, during polishing, the surface is sanded to a mirror finish and then polished until complete grains are visible under a microscope; during ultrasonic cleaning, the process is carried out in acetone at a frequency of 100~200 kHz for 10~15 min.

5. The method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process as described in claim 1, characterized in that: In step S3, during vacuuming, the mechanical pump is turned on to evacuate to 10 Pa, then the solenoid valve is turned on to evacuate to 5 Pa, and finally the molecular pump is turned on to evacuate to a high vacuum of 2.5 × 10 Pa. -3 Below Pa.

6. The method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process as described in claim 1, characterized in that: In step S4, the current and heating time for arc melting satisfy the following empirical formula: ； U is the electric arc melting voltage (V), which ranges from 35 to 50V; I represents the arc current (A), with a value ranging from 50 to 100 A; t is the melting time (s), which ranges from 15 to 60 s; K is an empirical correction parameter with a value of 0.9; C is the specific heat capacity of a low-melting-point metal or alloy, in J / (kg). ℃); ρ is the density of a low-melting-point metal or alloy, in kg / m³. 3 ; A is the sample contact area, in m 2 ; δ represents the molten thickness on the surface of the low-melting-point metal or alloy, with a value ranging from 0.5 to 1×10⁻⁶. -4 m; T H The melting point of a high-melting-point metal or alloy is ℃; T L Melting point of low-melting-point metals or alloys, °C; η is the arc thermal efficiency, with a value ranging from 0.7 to 0.

9.

7. The method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process as described in claim 1, characterized in that: In step S4, the heating compensation parameter t is introduced. loss The time required to compensate for the arc heating of high-melting-point metals or alloys to the melting point temperature of low-melting-point metals or alloys is 5~10s, that is, the heating time is extended by 5~10s based on the calculated heating time.

8. The method for preparing refractory high-entropy alloy diffusion couple samples based on a duplex process as described in claim 1, characterized in that: In step S5, the heating time is shortened by 5-10 seconds each time.

9. The method for preparing refractory high-entropy alloy diffusion couple samples based on a dual-process as described in claim 1, characterized in that: In step S6, the high-temperature heat treatment furnace is evacuated to a vacuum level of 2.5 × 10⁻⁶. -4 After the temperature drops below Pa, it is raised to 1600℃ and heat-treated for 20 hours. The entire heat treatment process is carried out under vacuum to maintain a pressure of 5 × 10⁻⁶ Pa. -4 Below Pa; during the heat treatment process, active elements such as Ti blocks are added to the crucible to remove impurities.

10. A refractory high-entropy alloy diffusion couple sample, characterized in that: It is prepared by the method described in any one of claims 1 to 9.

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