Method for preparing high-density Nb3Al block through spark plasma sintering

Abstract

The invention provides a method for preparing a high-density Nb3Al block through spark plasma sintering, and relates to the technical field of superconducting material preparation. The method comprises the steps that firstly, pure Nb and pure Al are subjected to powder blending in proportion and placed in a planetary ball mill to be subjected to ball milling, and Nbss (Al) powder is obtained; then, Nbss (Al) powder obtained after ball milling is pressed into a block through a mold and then put into a tubular furnace to be sintered, and an Nb3Al block is obtained; the Nb3Al block obtained through sintering is crushed through a tungsten carbide mortar, and then the crushed Nb3Al powder is wrapped with tantalum foil and placed in a graphite mold to be sealed; and finally, the sealed mold is put into a discharge plasma sintering furnace to be sintered, and the high-density Nb3Al block is obtained. The method is convenient in process flow, short in period, low in energy consumption and simple in equipment, and has good process universality and large-scale expansion potential.

Description

Technical Field

[0001] This invention relates to the field of superconducting material preparation technology, and in particular to a method for preparing high-density Nb3Al bulk materials by spark plasma sintering. Background Technology

[0002] Due to its excellent comprehensive properties, Nb3Al has broad application prospects in the fields of superconductivity and high-temperature alloys. However, this intermetallic compound has a high phase formation temperature. As the temperature decreases, stoichiometric Nb3Al decomposes into Nb-rich Nb3Al and Al-rich Nb2Al phases, greatly increasing the difficulty of preparing standard stoichiometric Nb3Al without impurity phases. Currently, the more mature preparation processes are mainly divided into two categories: one is the rapid heating and cooling method, mainly used to prepare Nb3Al superconducting wires, but the process is complex, costly, and limited by the wire shape, making it difficult to use for structural parts or complex components; the other is the mechanical alloying-heat treatment method, which is suitable for preparing bulk materials. Although it is superior to wires in terms of shape freedom, the resulting bulk materials generally have low density, and their performance cannot meet the requirements of high-end applications.

[0003] To overcome the limitations of existing processes in terms of shape and performance, achieving Nb3Al bulk materials with high density, single-phase structure, and standard stoichiometry has become an important research direction. However, the preparation methods reported in academic literature and existing patents for high-density, single-phase, and standard stoichiometric Nb3Al bulk materials still have many shortcomings. The mechanical alloying-tube furnace sintering method, which sinterstensibly ball-milled Nb3Al powder at 800–900℃, produces samples with a loose structure and no obvious sintering necks between particles. The mechanical alloying-SPS sintering method, while producing bulk materials with significant porosity at 800℃, results in a basically dense bulk material at 1000℃, although the presence of the impurity Nb2Al phase is present. Patent CN 114182123 describes a method for preparing Nb3Al containing impurity phases by sintering and ball-milling Nbss(Al) powder using SPS at 1200–1400℃. Although subsequent low-temperature heat treatment at 850–950℃ reduced the impurity phase content, single-phase Nb3Al could not be obtained. Previously, our research group's CN 113249604 A prepared Nb3Al, which, while achieving a single phase, had a stoichiometric ratio deviating from the standard value, affecting the superconducting properties of Nb3Al. Therefore, developing a bulk Nb3Al preparation technology that balances high density, single-phase structure, and standard stoichiometric ratio is crucial for expanding its practical applications. Summary of the Invention

[0004] To address the aforementioned technical problems in existing technologies, this invention provides a method for preparing high-density Nb3Al bulk materials via spark plasma sintering, resulting in Nb3Al bulk materials with high density, single-phase structure, and conforming to standard stoichiometry. This method first prepares a microscale Nb-25at.%Al precursor through mechanical alloying; then, diffusion phase formation is performed at low temperature to obtain single-phase Nb3Al conforming to standard stoichiometry; finally, high density is achieved in the bulk material through crushing combined with spark plasma sintering technology. This method effectively solves the common problems of porous structure, stoichiometry deviation, and non-uniform phases in existing Nb3Al bulk materials.

[0005] The technical solution is as follows: A method for preparing high-density Nb3Al bulk by spark plasma sintering, the method comprising: S1. Pure Nb powder and pure Al powder are mixed in proportion and then ball-milled in a planetary ball mill to obtain Nbss(Al) powder. S2. The Nb3Al powder obtained after ball milling is pressed into blocks using a mold and then sintered in a tube furnace to obtain Nb3Al blocks; S3. The sintered Nb3Al block is crushed using a tungsten carbide mortar to ensure that the particle size is <50μm; S4. Wrap the crushed Nb3Al powder from S3 in tantalum foil and seal it in a graphite mold. S5. Place the sealed mold into a spark plasma sintering furnace for sintering to obtain a high-density Nb3Al bulk material.

[0006] When preparing the powder in S1, the ratio is 74.5~75.5 at% Nb and 24.5~25.5 at% Al.

[0007] The ball-to-material ratio in the planetary ball mill in S1 is (9~11):1.

[0008] In step S1, ball milling is carried out in a planetary ball mill filled with argon gas for 4 to 6 hours.

[0009] The sintering in S2 is carried out under an argon protective atmosphere.

[0010] The sintering time in S2 is 10h~12h, and the sintering temperature is 800~900℃.

[0011] The sintering temperature in S5 is 1500~1550℃, the pressure is 40~45MPa, and the sintering time is 3~5min.

[0012] The density of the high-density Nb3Al bulk obtained in S5 is not less than 97%.

[0013] The beneficial effects of the technical solutions provided in the embodiments of the present invention include at least the following: 1. This invention provides a method for preparing Nb3Al bulk materials based on an integrated process of "mechanical alloying—low-temperature heat treatment—mechanical crushing—SPS sintering". This process combines the synergistic advantages of low-temperature heat treatment to promote the full diffusion of Nb / Al elements and achieve long-range ordered formation of the Nb3Al phase, and discharge plasma activated sintering to achieve rapid bonding of powder interfaces, successfully preparing high-density Nb3Al bulk materials with pure phase composition and conforming to stoichiometry.

[0014] 2. In the sintering process, the present invention uses tantalum foil to fully encapsulate Nb3Al powder, which effectively isolates the powder from contact with the graphite mold, eliminates carbon diffusion pollution, avoids the formation of impurity phases (such as carbides), and ensures that the sintered bulk structure is simple, uniform and dense.

[0015] 3. To address the limitations of existing Nb3Al wires in terms of component shape and the low density of traditional bulk materials, the preparation method proposed in this invention achieves a balance between near-net-shape forming of complex shapes and high internal density. Furthermore, this process is convenient, has a short cycle time, low energy consumption, and requires simple equipment, exhibiting good process versatility and potential for large-scale scalability. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the sintered Nb3Al block in Embodiment 1 of the present invention, wherein (a) is a physical image of the sintered block product and (b) is a SEM image of the sintered block; Figure 2 This is the XRD pattern of the sintered Nb3Al block in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the sintered Nb3Al block in Comparative Example 1 of the present invention, wherein (a) is a physical picture of the sintered block product, (b) is a SEM image of the sintered block, and (c) is a surface scan image of the sintered block. Figure 4 This is a macroscopic view of the sintered Nb3Al block in Comparative Example 2 of this invention. Detailed Implementation

[0018] The technical solution of the present invention will now be described with reference to the accompanying drawings.

[0019] In embodiments of the present invention, words such as "exemplarily," "for example," etc., are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" in the present invention should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the word "exemplary" is intended to present the concept in a concrete manner. Furthermore, in embodiments of the present invention, the meaning expressed by "and / or" can be both, or either one.

[0020] In this embodiment of the invention, sometimes a subscript such as W1 may be written in a non-subscript form such as W1. When the difference is not emphasized, the meaning they express is the same.

[0021] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0022] This invention provides a method for preparing high-density Nb3Al bulk materials by spark plasma sintering. The method may include the following steps: S1. Pure Nb powder and pure Al powder are mixed in proportion and then ball-milled in a planetary ball mill to obtain Nbss(Al) powder. S2. The Nb3Al powder obtained after ball milling is pressed into blocks using a mold and then sintered in a tube furnace to obtain Nb3Al blocks; S3. The sintered Nb3Al block is crushed using a tungsten carbide mortar to ensure that the particle size is <50μm; S4. Wrap the crushed Nb3Al powder from S3 in tantalum foil and seal it in a graphite mold. S5. Place the sealed mold into a spark plasma sintering furnace for sintering to obtain a high-density Nb3Al bulk material.

[0023] The following description, in conjunction with specific embodiments, illustrates this point.

[0024] Example 1

[0025] Step 1: Prepare powder according to 75 at% Nb and 25 at% Al, with a ball-to-powder ratio of 10:1, and ball mill in a planetary ball mill filled with argon for 5 hours to obtain Nbss(Al) powder.

[0026] Step 2: After ball milling, the Nb3Al powder is pressed into blocks using a mold and then placed in a tube furnace for sintering under argon protection for 10 hours at a sintering temperature of 800℃ to obtain Nb3Al blocks.

[0027] Step 3: Crush the sintered Nb3Al blocks using a tungsten carbide mortar and sieve them through a 300-mesh sieve to ensure that the particle size is <50μm.

[0028] Step 4: Wrap the Nb3Al powder in tantalum foil and seal it in a graphite mold.

[0029] Step 5: Place the sealed mold into a spark plasma sintering furnace for sintering. Sintering temperature: 1500℃, pressure: 45MPa, sintering time: 5min.

[0030] like Figure 1 As shown in (a), the Nb3Al bulk material prepared by this process has a distinct metallic luster on its surface. Figure 1 The block shown in (b) has few internal pores and is sintered densely.

[0031] Figure 2 The image shows the XRD pattern of the sintered bulk material, which is a single-phase Nb3Al.

[0032] Comparative Example 1

[0033] Step 1: Prepare powder according to 75 at% Nb and 25 at% Al, with a ball-to-powder ratio of 10:1, and ball mill in a planetary ball mill filled with argon for 5 hours to obtain Nbss(Al) powder.

[0034] Step 2: After ball milling, the Nb3Al powder is pressed into blocks using a mold and then placed in a tube furnace for sintering under argon protection for 10 hours at a sintering temperature of 800℃ to obtain Nb3Al blocks.

[0035] Step 3: Crush the sintered Nb3Al blocks using a tungsten carbide mortar and sieve them through a 300-mesh sieve to ensure that the particle size is <50μm.

[0036] Step 4: Wrap the Nb3Al powder in carbon foil and seal it in a graphite mold.

[0037] Step 5: Place the sealed mold into a spark plasma sintering furnace for sintering. Sintering temperature: 1500℃, pressure: 45MPa, sintering time: 5min.

[0038] like Figure 3 As shown in (a), the Nb3Al bulk material produced by this process does not exhibit a molten metallic luster to the naked eye. Figure 3 A large number of pores are visible in (b), and the pores contain impurity phases. Figure 3 In the middle (c) is a surface scan image, the impurity phase is mainly carbides.

[0039] Comparative Example 2

[0040] Step 1: Prepare powder according to 75 at% Nb and 25 at% Al, with a ball-to-powder ratio of 10:1, and ball mill in a planetary ball mill filled with argon for 5 hours to obtain Nbss(Al) powder.

[0041] Step 2: After ball milling, the Nb3Al powder is pressed into blocks using a mold and then placed in a tube furnace for sintering under argon protection for 10 hours at a sintering temperature of 800℃ to obtain Nb3Al blocks.

[0042] Step 3: Crush the sintered Nb3Al blocks using a tungsten carbide mortar and sieve them through a 300-mesh sieve to ensure that the particle size is <50μm.

[0043] Step 4: Wrap the Nb3Al powder in carbon foil and seal it in a graphite mold.

[0044] Step 5: Place the sealed mold into a spark plasma sintering furnace for sintering. Sintering temperature: 1350℃, pressure: 30MPa, sintering time: 5min.

[0045] like Figure 4 As shown, the Nb3Al blocks produced by this process have visible pores, no traces of melting connection between particles, and powder is easily removed when ground by hand.

[0046] Density test: The samples from Example 1, Comparative Examples 1 and 2 were cut into three pieces. The density of the cut samples was measured using Archimedes' method of water displacement, and then divided by the theoretical density to obtain the density percentage. The statistical results are shown in Table 1.

[0047] Table 1 Statistical results of Nb3Al bulk density

[0048] As shown in Table 1, the Nb3Al bulk material prepared using the process described in this invention (Example 1) has a density as high as 99%. In contrast, the Nb3Al bulk materials prepared by changing the Nb3Al powder coating method (Comparative Examples 1 and 2) or adjusting the spark plasma process parameters (Comparative Example 2) exhibited a significant decrease in density. These results demonstrate that the tantalum foil coating method and optimized sintering parameters employed in this invention are crucial for ensuring high density and a single-phase structure in the Nb3Al bulk material.

[0049] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing high-density Nb3Al bulk by spark plasma sintering, characterized in that, The method includes: S1. Pure Nb powder and pure Al powder are mixed in proportion and then ball-milled in a planetary ball mill to obtain Nbss(Al) powder. S2. The Nb3Al powder obtained after ball milling is pressed into blocks using a mold and then sintered in a tube furnace to obtain Nb3Al blocks; S3. The sintered Nb3Al block is crushed using a tungsten carbide mortar to ensure that the particle size is <50μm; S4. Wrap the crushed Nb3Al powder from S3 in tantalum foil and seal it in a graphite mold. S5. Place the sealed mold into a spark plasma sintering furnace for sintering to obtain a high-density Nb3Al bulk material.

2. The method for preparing high-density Nb3Al bulk by spark plasma sintering according to claim 1, characterized in that, When preparing the powder in S1, the ratio is 74.5~75.5 at% Nb and 24.5~25.5 at% Al.

3. The method for preparing high-density Nb3Al bulk by spark plasma sintering according to claim 1, characterized in that, The ball-to-material ratio in the planetary ball mill in S1 is (9~11):

1.

4. The method for preparing high-density Nb3Al bulk by spark plasma sintering according to claim 1, characterized in that, In step S1, ball milling is carried out in a planetary ball mill filled with argon gas for 4 to 6 hours.

5. The method for preparing high-density Nb3Al bulk by spark plasma sintering according to claim 1, characterized in that, The sintering in S2 is carried out under an argon protective atmosphere.

6. The method for preparing high-density Nb3Al bulk by spark plasma sintering according to claim 1, characterized in that, The sintering time in S2 is 10h~12h, and the sintering temperature is 800~900℃.

7. The method for preparing high-density Nb3Al bulk by spark plasma sintering according to claim 1, characterized in that, The sintering temperature in S5 is 1500~1550℃, the pressure is 40~45MPa, and the sintering time is 3~5min.

8. The method for preparing high-density Nb3Al bulk by spark plasma sintering according to claim 1, characterized in that, The density of the high-density Nb3Al bulk obtained in S5 is not less than 97%.

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