Preparation method of high-density Ti-Nb alloy

Abstract

The application belongs to the technical field of titanium alloy powder preparation, and more particularly relates to a preparation method of a high-density Ti-Nb alloy. First, Ti powder and Nb powder are mixed and pressed, and then first vacuum sintering is performed to obtain a Ti-Nb preliminary homogenized alloy; then, after slicing, hydrogenation treatment is performed, and after ball milling, a hydrogenated Ti-Nb alloy powder is obtained; finally, the hydrogenated Ti-Nb alloy powder is pressed and then second vacuum dehydrogenation sintering is performed, and a large number of defects are generated by dehydrogenation, which is beneficial to element diffusion and sintering densification, and finally a homogenized and high-quality Ti-Nb alloy is prepared, thereby solving the bottleneck of low density of an alloy prepared by traditional powder metallurgy technology, the melting point of which is greatly different.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy powder preparation technology, and more specifically, relates to a method for preparing a high-density Ti-Nb alloy. Background Technology

[0002] In the development of powder metallurgy technology, Ti-Nb alloys have attracted widespread attention due to their unique mechanical properties and biocompatibility, particularly in applications such as medical implants and aerospace. However, the difference in melting points between Ti and Nb poses numerous challenges to densification during the synthesis process using traditional sintering methods. Specifically, Ti and Nb have melting points of 1668°C and 2477°C, respectively, a significant difference. Due to its high melting point, Nb often fails to completely dissolve in the Ti matrix, forming undissolved Nb particles. These undissolved Nb particles not only affect the alloy's microstructure but also lead to inhomogeneities in mechanical properties, thus limiting its potential for practical applications. Furthermore, undissolved Nb particles result in uneven phase distribution in the alloy, affecting properties such as strength, ductility, and corrosion resistance. Therefore, addressing the melting point difference between Ti and Nb and the resulting densification difficulties is crucial for optimizing the performance of Ti-Nb alloys. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing high-density Ti-Nb alloys, which aims to solve the technical problem of low density in alloys with large differences in melting points prepared by traditional powder metallurgy technology, and is especially suitable for the preparation of high-density Ti-Nb alloys with high Nb content.

[0004] To achieve the above objectives, the present invention provides a method for preparing a high-density Ti-Nb alloy, comprising the following steps:

[0005] (1) Ti powder and Nb powder are mixed in an inert atmosphere and then pressed to obtain a pressed green body.

[0006] (2) The pressed green blank is subjected to a first vacuum sintering to obtain a Ti-Nb alloy with preliminary homogenization;

[0007] (3) The pre-homogenized alloy slices are then subjected to hydrogenation treatment to obtain hydrogenated Ti-Nb alloy;

[0008] (4) After grinding the hydrogenated Ti-Nb alloy, hydrogenated Ti-Nb alloy powder is obtained;

[0009] (5) The hydrogenated Ti-Nb alloy powder is pressed and then subjected to a second vacuum dehydrogenation sintering to obtain a densified Ti-Nb alloy.

[0010] Preferably, the Ti-Nb alloy is a Ti-35Nb alloy, a Ti-40Nb alloy, or a Ti-45Nb alloy.

[0011] Preferably, in step (2), the first vacuum sintering is performed by evacuating the vacuum to 10... -3 Pa or below, then heat to a sintering temperature of 1150-1250℃ and hold for 3-5 hours.

[0012] Preferably, during the hydrogenation process in step (3), the hydrogen pressure is maintained at -30~-50 kPa, and the hydrogenation time is 1.5-2.5 h.

[0013] Preferably, the second vacuum dehydrogenation sintering in step (5) is performed by evacuating to a vacuum level of 10. -3 Pa or below, then heat to a sintering temperature of 1150-1250℃ and hold for 3-5 hours.

[0014] Preferably, in step (5), the second vacuum dehydrogenation sintering is first performed by setting multiple heat preservation sections at 400~800℃ to ensure that hydrogen in the sample is completely removed; then the temperature is raised to a maximum of 1200℃ and held at the maximum temperature for 3-5 hours to achieve sintering densification and uniform element diffusion, followed by furnace cooling; wherein during the heating process, the heating rate is set to 4-5℃ / min when the temperature is below 1000℃, and the heating rate is set to 2-3℃ / min when the temperature is above 1000℃.

[0015] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0016] 1. This invention provides a method for preparing a high-density Ti-Nb alloy, which is a powder metallurgy preparation method. First, Ti powder and Nb powder are mixed and pressed, then subjected to a first vacuum sintering to obtain a preliminarily homogenized Ti-Nb alloy. Next, the mixture is sliced ​​and subjected to hydrogenation treatment, followed by ball milling to obtain hydrogenated Ti-Nb alloy powder containing a large amount of H. Finally, the hydrogenated Ti-Nb alloy powder is pressed and subjected to a second vacuum dehydrogenation sintering. Dehydrogenation generates numerous defects, which is beneficial for sintering densification, ultimately resulting in a dense Ti-Nb alloy.

[0017] 2. This invention provides a method for preparing a high-density Ti-Nb alloy, achieving a density of over 99% and uniform element distribution. This method overcomes the densification difficulties caused by the melting point difference between Ti and Nb, and is key to optimizing the performance of Ti-Nb alloys. The preparation method is simple and provides an effective solution for preparing high-density and homogeneous Ti-Nb alloys, promoting their application in the field of high-performance materials and bringing new opportunities and development directions to related industries. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process for preparing Ti-Nb high-density alloys using powder metallurgy according to the present invention;

[0019] Figure 2 Comparative Example 1 shows the microstructure of the Ti-35Nb alloy prepared by the conventional powder metallurgy method.

[0020] Figure 3 Comparative Example 2 shows the microstructure of the Ti-10Nb alloy prepared by the conventional powder metallurgy method.

[0021] Figure 4 Comparative Example 3 shows the microstructure of the Ti-20Nb alloy prepared by the conventional powder metallurgy method.

[0022] Figure 5 Contents (a) and (b) are photographs of Ti-35Nb sintered samples before and after hydrogenation in Example 1, respectively.

[0023] Figure 6 This is a particle size distribution diagram of hydrogenated crushed Ti-35Nb powder from Example 1;

[0024] Figure 7 The results of SEM and EDS of the surface and internal cross-section of hydrogenated crushed Ti-35Nb powder in Example 1 are shown.

[0025] Figure 8 The XRD patterns of the mixed powder (Ti-35Nb) before sintering in step (1) of Comparative Example 1, the mixed powder (TiH2-35NbH) before sintering in Comparative Example 6, and the alloy powder (Secondaryhydrogenation) after hydrogenation in step (4) of Example 1 and before the second vacuum sintering are shown.

[0026] Figure 9 The microstructure of the hydrogenated Ti-35Nb alloy powder secondary sintering sample prepared in Example 1 is shown in the SEM electronic image and EDS results.

[0027] Figure 10 The images show the microstructures of the Ti-35Nb alloys prepared in Comparative Examples 1, 4, 5, and 6. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0030] Furthermore, the reference to "an embodiment" throughout this specification; "an embodiment," "an example," or similar language indicates that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. Therefore, the appearance of the phrase "in one embodiment" throughout this specification and similar language may, but not necessarily, refer to the same embodiment.

[0031] The melting points of Ti and Nb are 1668℃ and 2477℃, respectively, a significant difference. Due to its high melting point, Nb often fails to completely dissolve in the Ti matrix, forming undissolved Nb particles. These undissolved Nb particles not only affect the microstructure of the alloy but also lead to inhomogeneities in mechanical properties, thus limiting its potential for practical applications. Some literature indicates that pre-alloying powders can solve these problems, but pre-alloying powders typically require multiple melting processes. Therefore, developing a low-energy powder metallurgy method for preparing high-density TiNb alloys is of great significance. This invention combines pre-alloying, hydrogenation, and secondary sintering after hydrogenation to achieve a process for preparing high-density, highly homogeneous TiNb alloys using powder metallurgy.

[0032] Specifically, such as Figure 1 As shown, the present invention provides a powder metallurgy preparation method for a high-density Ti-Nb alloy, comprising the following steps:

[0033] (1) Ti powder and Nb powder are mixed in an inert atmosphere and then pressed to obtain a pressed green body.

[0034] (2) The pressed green blank is subjected to a first vacuum sintering to obtain a Ti-Nb alloy with preliminary homogenization;

[0035] (3) The pre-homogenized alloy slices are then subjected to hydrogenation treatment to obtain hydrogenated Ti-Nb alloy;

[0036] (4) After grinding the hydrogenated Ti-Nb alloy, hydrogenated Ti-Nb alloy powder is obtained;

[0037] (5) The hydrogenated Ti-Nb alloy powder is pressed and then subjected to a second vacuum dehydrogenation sintering to obtain a densified Ti-Nb alloy.

[0038] In some embodiments of this invention, Ti powder and Nb powder with low oxygen content (0-150 μm) are mixed, pressed, and then subjected to a first vacuum sintering. The purpose of the first vacuum sintering is to form a TiNb alloy with a relatively uniform composition. The first vacuum sintering has two functions: First, it enables the HCP structure Ti and BCC structure Nb to form an alloy with a single β-phase structure. Although undissolved Nb particles exist, most of the alloy has formed a homogeneous TiNb alloy, which helps to obtain hydrogenated powder with uniform elemental distribution in the subsequent process. Second, the blocky alloy formed in the first sintering step has more internal pores, resulting in a larger specific surface area. Compared with the high-density alloy formed by melting, it is easier to hydrogenate, and theoretically, the hydrogen pressure and time during the hydrogenation step are reduced.

[0039] The alloy obtained from the first vacuum sintering is hydrogenated and crushed to obtain hydrogenated alloy powder with uniform elemental distribution. After pressing, it undergoes a second vacuum sintering. The hydrogenated pre-alloyed powder is brittle. Grinding, such as ball milling, yields brittle hydrogenated pre-alloyed powder, which is easily broken and fills the pores during pressing, resulting in high pressing density. The hydrogenated pre-alloyed powder generates a large number of defects during dehydrogenation during sintering, which is beneficial for densification. The pre-alloyed powder is already in a state of uniform elemental distribution, so very high sintering temperatures are not required. In some embodiments, the highest sintering temperature for the second vacuum sintering is 1200℃, which is sufficient to achieve densification and homogenization. Sintering yields a high-density (99.32±0.02%) TiNb alloy with uniform elemental distribution (no segregation or undissolved particles).

[0040] The method for preparing high-density Ti-Nb alloys using powder metallurgy of the present invention is mainly aimed at Ti-Nb alloys with high Nb content that are prone to segregation, such as Ti-Nb alloys with an Nb mass percentage greater than or equal to 30%. In some embodiments, the Ti-Nb alloy is a Ti-35Nb alloy, a Ti-40Nb alloy, or a Ti-45Nb alloy. Step (1) Weigh Ti powder and Nb powder according to the elemental ratio of the target Ti-Nb alloy, and then mix them. In some embodiments, the particle size of the Ti powder and Nb powder in step (1) is less than 200 μm, more preferably less than 150 μm.

[0041] The inert atmosphere or protective atmosphere described in this invention includes, but is not limited to, helium, neon, or argon, with argon being preferred.

[0042] In some embodiments, the pressing in step (1) is cold isostatic pressing, with a pressure of 250-300 MPa and a holding time of 1000-1500 seconds. The first vacuum sintering in step (2) involves evacuating the vacuum to 10... -3Pa or below, then heated to a sintering temperature of 1150-1250℃ and held for 3-5 hours. During the hydrogenation process described in step (3), the hydrogen pressure is maintained at -30~-50 kPa, and hydrogenation lasts for 1.5-2.5 hours. In this embodiment of the invention, the hydrogenation process is carried out in a high-vacuum sintering furnace to avoid elements such as oxygen and hydrogen from entering the material at high temperatures and causing a decrease in mechanical properties. The initial pressure inside the sintering furnace is -102 kPa. During the hydrogenation process, hydrogen is introduced to control the pressure at -30~-50 kPa for the hydrogenation operation.

[0043] In some embodiments, step (4) is performed in a protective atmosphere, with the ball milling speed set to 400-600 RPM and the ball milling time to be 3-8 min. The protective atmosphere is an inert gas such as argon.

[0044] In some embodiments, the pressing in step (5) is cold isostatic pressing, with a pressure of 250-300 MPa and a holding time of 1000-1500 seconds. The second vacuum dehydrogenation sintering in step (5) involves evacuating to 10... -3 Pa or below, then heat to a sintering temperature of 1150-1250℃ and hold for 3-5 hours.

[0045] In some embodiments, the second vacuum dehydrogenation sintering in step (5) involves first setting multiple heat preservation sections at 400~800℃ to dehydrogenate the sample and ensure that the hydrogen is completely removed; then the temperature is raised to a maximum of 1200℃ and held at the maximum temperature for 3-5 hours to achieve sintering densification and uniform element diffusion, followed by furnace cooling; during the heating process, the heating rate is set to 4-5℃ / min when the temperature is below 1000℃ and 2-3℃ / min when the temperature is above 1000℃.

[0046] This invention proposes an improved hydrogenation sintering process, namely a method for preparing high-density, high-uniformity Ti-Nb alloys. In some examples, the density of the sintered samples reached 99.32%, overcoming the bottleneck of low density in the preparation of alloys with large melting point differences using traditional powder metallurgy technology.

[0047] The following are comparative examples and embodiments:

[0048] Comparative Example 1

[0049] The traditional metallurgical method for preparing Ti-35Nb alloy follows these steps:

[0050] (1) Ti powder and Nb powder with a particle size of less than 150 μm are loaded into a mixer in a mass ratio of 65:35. After washing the gas, argon gas is introduced for protection to prevent the oxygen content from increasing.

[0051] (2) After mixing the powder, it is compacted in a cylindrical rubber sleeve with a diameter of φ15×80mm in a vacuum glove box, and then subjected to cold isostatic pressing.

[0052] (3) The cold isostatic pressing parameters are 280MPa and held for 1200s to obtain a cylindrical blank.

[0053] (4) Place the pressed green body into a vacuum sintering furnace and evacuate it to 10°C. -3 After Pa, the sample was heated to 1200℃ and held for 4 hours. The heating rate was 5℃ / min below 1000℃ and 3℃ / min above 1000℃. The sample was then cooled in the furnace to obtain a Ti-35Nb one-time sintered sample.

[0054] Comparative Example 1: The microstructure of Ti-35Nb alloy prepared by conventional metallurgical methods is as follows. Figure 2 As shown.

[0055] Comparative Example 2

[0056] The other steps are the same as in Comparative Example 1, except that the prepared Ti-Nb alloy is Ti-10Nb, corresponding to step (1) where Ti powder and Nb powder with a particle size less than 150 μm are loaded into the mixer at a mass ratio of 90:10. The microstructure of the prepared Ti-10Nb alloy is as follows. Figure 3 As shown.

[0057] Comparative Example 3

[0058] The other steps are the same as in Comparative Example 1, except that the prepared Ti-Nb alloy is Ti-20Nb, corresponding to step (1) where Ti powder and Nb powder with a particle size less than 150 μm are loaded into the mixer at a mass ratio of 80:20. The microstructure of the prepared Ti-20Nb alloy is as follows. Figure 4 As shown.

[0059] By comparing the microstructures of Ti-35Nb, Ti-10Nb, and Ti-20Nb prepared in Comparative Examples 1 to 3, it can be found that Ti-10Nb and Ti-20Nb have relatively lower Nb content and less segregation compared to Ti-35Nb. Therefore, the secondary hydrogenation sintering improvement of this invention is mainly aimed at Ti-Nb alloys with higher Nb content, in order to improve their density and uniformity.

[0060] The following examples and comparative examples, using high Nb content Ti-35Nb as an example, propose a method for secondary hydrogenation sintering to solve the problems of low density and segregation in TiNb alloys prepared by powder metallurgy.

[0061] Example 1

[0062] The preparation method of Ti-35Nb alloy with high Nb content and high density is carried out according to the following steps:

[0063] (1) Ti and Nb powders with a particle size of less than 150 μm were loaded into a mixer at a mass ratio of 65:35 for mixing. Before mixing, the mixer was purged to ensure that the powders were mixed under an argon atmosphere to prevent the oxygen content from increasing. After mixing, the powders were compacted in a cylindrical rubber sleeve with a diameter of φ15×80 mm, and then subjected to cold isostatic pressing. The cold isostatic pressing parameters were 280 MPa and 1200 s to obtain a cylindrical compact.

[0064] (2) Place the pressed green body into a vacuum sintering furnace and evacuate it to 10°C. -3 After Pa, the sample was heated to 1200℃ and held for 4 hours, then cooled in the furnace. The resulting Ti-35Nb sample was a single-sintering sample with poor density and uniformity.

[0065] (3) Cut the first sintered sample into 3mm round pieces using a cutting machine, such as Figure 5 Content (a): The oxide layer on the surface is removed by sanding with sandpaper, and then ultrasonically cleaned in an ethanol solution. It is then placed in a sintering furnace for hydrogenation, first under vacuum of 10... -3 After Pa, heating begins, maintaining a vacuum and raising the temperature to 800℃, then lowering it to 600℃. Hydrogen gas is then introduced at 600℃, with the pressure maintained within the range of -30 to -50 kPa, and hydrogenation is carried out for 2 hours. This yields extremely fragile, saturated hydrogenated Ti-35Nb wafers, such as... Figure 5 Content (b).

[0066] (4) Then Figure 5 The hydrogenated sample from content (b) was placed in a vacuum ball mill jar, purged with argon gas, with a ball-to-powder ratio of 5:1 and a milling speed of 500 RPM. After milling for 5 minutes, the sample was passed through a 100-mesh sieve to obtain Ti-35Nb alloy powder with uniform elemental distribution. The particle size distribution of the alloy powder is as follows: Figure 6 As shown, the powder particle size ranges from 0 to 150 μm. EDS elemental analysis was performed on the surface and internal cross-sections of the powder particles, and the results are as follows. Figure 7 Contents (a), (b), (c), (d), (e), and (f) show that the hydrogenated alloy powder achieved a uniform distribution of the Ti-35Nb alloy. XRD results are shown below. Figure 8 As shown, the sample Secondaryhydrogenation is the XRD pattern of Ti-35Nb alloy powder after ball milling in this step, indicating that the alloy powder is a single δ phase.

[0067] (5) The hydrogenated and crushed Ti-35Nb alloy powder was placed in a ∅15*80mm cylindrical rubber sleeve in a vacuum glove box and compacted, followed by cold isostatic pressing; the cold isostatic pressing parameters were 280MPa and held for 1200s to obtain a cylindrical compact. The pressed green compact was placed in a vacuum sintering furnace and evacuated to 10 -3 After Pa, the sample was heated; the temperature was raised to 450℃ and held for 1 hour, then raised to 600℃ and held for 1 hour, and finally raised to 800℃ and held for 1 hour. Multiple holding periods were used to ensure complete removal of hydrogen from the sample. The temperature was then raised further to 1200℃ and held for 4 hours, followed by furnace cooling. The heating rate was 5℃ / min below 1000℃ and 3℃ / min above 1000℃, resulting in a Ti-35Nb secondary sintered sample.

[0068] Compared to the method of preparing pre-alloyed powder through multiple melting processes, the above method significantly reduces the number of process steps and energy consumption. Furthermore, the Ti-35Nb secondary sintered samples obtained using this method achieved a density of 99.32% (specifically, the density ρ1 (g / cm³) of the sintered samples measured using the Archimedes' displacement method) 3 Then, the density ρ2 (g / cm³) of the sample prepared by multiple arc melting processes was measured. 3 Alloys prepared by arc melting are non-porous, and the density of such samples is usually considered ideal. Then, by calculation (ρ1 / ρ2 = 99.32%), the microstructure and elemental distribution of the sintered samples are shown below. Figure 9 As shown in contents (a), (b) and (c), it is easy to see that the element distribution is uniform and the sintering density is high, which solves the bottleneck of low density in the preparation of alloys with large differences in melting point by traditional powder metallurgy technology.

[0069] During the experiment, the traditional powder metallurgy method of Comparative Example 1 was also attempted, but different Ti and Nb sources were replaced to prepare Ti-35Nb alloy.

[0070] Comparative Example 4

[0071] The other steps are the same as in Comparative Example 1, except that in step (1), TiH2 powder and Nb powder with a particle size of less than 150 μm are loaded into a mixer for subsequent steps, wherein the mass ratio of Ti to Nb is 65:35. The microstructure of the prepared Ti-35Nb alloy is as follows. Figure 10 As shown, its density was 93.09% as measured by the Archimedes displacement method.

[0072] Comparative Example 5

[0073] The other steps are the same as in Comparative Example 1, except that in step (1), Ti powder and NbH powder with a particle size of less than 150 μm are loaded into a mixer for subsequent steps, wherein the mass ratio of Ti to Nb is 65:35. The microstructure of the prepared Ti-35Nb alloy is as follows. Figure 10 As shown, its density was 91.78% as measured by the Archimedes displacement method.

[0074] Comparative Example 6

[0075] The other steps are the same as in Comparative Example 1, except that in step (1), TiH2 powder and NbH powder with a particle size of less than 150 μm are loaded into a mixer for subsequent steps, wherein the mass ratio of Ti to Nb is 65:35. The microstructure of the prepared Ti-35Nb alloy is as follows. Figure 10 As shown, its density was measured to be 92.26% using the Archimedes displacement method.

[0076] from Figure 10 It can be seen that the traditional powder metallurgy method using one-time sintering, even if TiH2 powder is used directly to replace Ti powder or NbH powder is used directly to replace Nb powder as in Comparative Examples 4 to 6, results in a low density of the prepared Ti-35Nb alloy, which is significantly lower than the density of the Ti-35Nb alloy obtained by two sintering in Example 1.

[0077] Figure 8 The samples Ti-35Nb and TiH2-35NbH represent the XRD patterns of the raw material mixed powders obtained by mixing powders in step (1) of Comparative Example 1 and Comparative Example 6, respectively. It can be seen that the phase of the initial powder (single δ phase) before densification sintering in Example 1 is completely different from the phase of the initial mixed powder of Comparative Example 1 and Comparative Example 6 by the traditional powder metallurgy method.

[0078] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-density Ti-Nb alloy, characterized in that, Includes the following steps: (1) Ti powder and Nb powder are mixed in an inert atmosphere and then pressed to obtain a pressed green body. (2) The pressed green blank is subjected to a first vacuum sintering to obtain a Ti-Nb alloy with preliminary homogenization; the first vacuum sintering specifically involves: evacuating the vacuum to 10 -3 Below Pa, then heat to a sintering temperature of 1150-1250℃ and hold for 3-5 hours; (3) The alloy slices that have been initially homogenized are then subjected to hydrogenation treatment to obtain hydrogenated Ti-Nb alloy; during the hydrogenation treatment, the pressure of hydrogen is maintained at -30~-50kPa and the hydrogenation time is 1.5-2.5 h; (4) After grinding the hydrogenated Ti-Nb alloy, hydrogenated Ti-Nb alloy powder is obtained; (5) The hydrogenated Ti-Nb alloy powder is pressed and then subjected to a second vacuum dehydrogenation sintering to obtain a densified Ti-Nb alloy; the second vacuum dehydrogenation sintering specifically involves: evacuating to 10... -3 The temperature is below Pa, then heated to a sintering temperature of 1150-1250℃ and held for 3-5 hours.

2. The preparation method according to claim 1, characterized in that, The Ti-Nb alloy is a Ti-35Nb alloy, a Ti-40Nb alloy, or a Ti-45Nb alloy.

3. The preparation method according to claim 1, characterized in that, The particle size of both Ti powder and Nb powder in step (1) is less than 200 μm.

4. The preparation method according to claim 1, characterized in that, The pressing in step (1) is cold isostatic pressing, with a pressure of 250-300 MPa and a holding time of 1000-1500 seconds.

5. The preparation method according to claim 1, characterized in that, Step (4) Perform ball milling under a protective atmosphere, with the ball milling speed set to 400-600 rpm and the ball milling time to 3-8 min.

6. The preparation method according to claim 1, characterized in that, The pressing in step (5) is cold isostatic pressing, with a pressure of 250-300 MPa and a holding time of 1000-1500 seconds.

7. The preparation method according to claim 1, characterized in that, In step (5), the second vacuum dehydrogenation sintering is first carried out in multiple heat preservation sections at 400~800℃ to ensure that hydrogen in the sample is completely removed; then the temperature is raised to a maximum of 1200℃ and held at the maximum temperature for 3-5 hours to achieve sintering densification and uniform diffusion of elements, followed by furnace cooling. During the heating process, the heating rate is set to 4-5℃ / min when the temperature is below 1000℃, and to 2-3℃ / min when the temperature is above 1000℃.

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