A high-entropy alloy reinforced dip-type cathode and a preparation method thereof

Abstract

The application discloses a high-entropy alloy reinforced impregnated cathode and a preparation method thereof, and belongs to the field of refractory high-entropy alloys. The specific steps are as follows: 1) putting Os, Ir, Re, W and Ru raw material powders into a crucible and annealing in hydrogen; weighing and mixing the raw material powders; 2) uniformly mixing by using dry ball milling; 3) powder compression molding: putting the ball-milled powder into a mold and compressing, and keeping pressure for 20s-43s; 4) putting the compressed green body into a hydrogen furnace for sintering, introducing hydrogen, firstly, heating to 850 DEG C for 30min, then heating to 1380-1620 DEG C at a heating rate of 8.5 DEG C / min, and keeping temperature for 15-55min; and impregnating active salt at 1660-1690 DEG C. The impregnated cathode has a cathode matrix with a simple Hcp solid solution as a main structure, and has the advantages of high melting point, large impregnation amount, high temperature stability, high current emission density and the like.

Description

TECHNICAL FIELD

[0001] The application relates to a high-entropy alloy reinforced impregnated cathode and a preparation method thereof, and belongs to the field of refractory high-entropy alloys. BACKGROUND

[0002] A cathode is a core component of many vacuum electron devices such as cathode ray tubes, X-ray tubes and microwave tubes, and the research progress of cathode technology also largely determines the development process of vacuum electron devices. At present, vacuum electron devices mainly develop in the direction of high power, high efficiency, high reliability, high frequency and miniaturization. At present, the electron source in high-frequency high-power vacuum electron devices is mainly a barium tungsten-based diffusion cathode. The cathode usually works at a temperature below 1000 DEG C, and the emission current density is about 5 A / cm 2 . The W-Ir, W-Os and W-Re mixed matrix cathode with added noble metals has strong resistance to poisoning and certain resistance to ion bombardment, but the emission current density of the cathode is only about 10 A / cm 2 when working at 1000 DEG C. Although the cathode with added noble metals has lower emission work and stronger emission capacity, the current density is 5-10 A / cm 2 , and has a long service life of more than 20,000 hours. However, when the current density of more than 20 A / cm 2 is pursued, the working temperature of the cathode must be increased, and the high temperature causes excessive evaporation of the active material, which seriously shortens the service life of the cathode and greatly affects its practicability. In addition, the film-coated cathode coated with Os, Ir or Re and the like has emission performance equivalent to that of the mixed matrix cathode, but the composition changes due to interdiffusion between the matrix elements and the film elements in the process of long-time use, which causes the emission performance of the cathode to decrease, and the film-coated cathode also faces the problem of film peeling, which leads to unstable emission performance. Therefore, a new type of cathode is urgently needed to meet the development needs of high-power devices for cathodes. In addition, the toughness of the pure tungsten or the cathode with an intermetallic compound matrix is very poor, and the brittleness is large, which makes the cathode processing very difficult.

[0003] High-entropy alloys are a new type of alloy material developed in recent years. The characteristics are that 5 or more than 5 components are contained, and the content of each component is between 5% and 35%. Then, the composition range of the high-entropy alloy is further expanded to contain 4 or more than 4 components, and the content of each component is between 5% and 50%. After the high-entropy alloy is solidified, a large number of intermetallic compound phases are not formed, but a structure mainly composed of simple Fcc, Bcc or Hcp solid solution is formed. The formation of the solid solution matrix makes the high-entropy alloy overcome the inherent brittleness of the intermetallic compound and the amorphous alloy, so it is very promising to become an advanced engineering structural material.

[0004] Therefore, the high-entropy alloy is introduced into the cathode matrix, which is expected to improve the mechanical properties of the cathode and significantly improve the electron emission capacity of the cathode. SUMMARY

[0005] The present application provides a high-entropy alloy reinforced impregnated cathode and a preparation method thereof, which introduces high-entropy alloy into the cathode matrix to improve the microstructure of the cathode matrix, obtains a cathode matrix with a simple Hcp solid solution as the main structure, a cathode with high melting point and large impregnation amount, and finally obtains a high-entropy alloy reinforced impregnated cathode with high strength and high emission.

[0006] The present application provides an Os-Ir-Re-W-Ru high-temperature high-entropy alloy, which is composed of four or five elements of Os, Ir, Re, W and Ru in equal atomic ratio or non-equal atomic ratio, each element is matched in a molar percentage of 5-50, and the chemical formula is Os x Ir y Re z W k Ru n , wherein x+y+z+k+n=100, x, y, z, k and n are all 5-50, or any one of x, y, z, k and n is 0, and the others are 5-50;

[0007] A high-entropy alloy reinforced impregnated cathode and a preparation method thereof, the specific steps are:

[0008] (1) Put the Os, Ir, Re, W and Ru raw material powders into the crucible respectively, and pass hydrogen into the tube furnace for annealing treatment to ensure the purification of the original powder; according to the Os x Ir y Re z W k Ru n component, the required quality of Os, Ir, Re, W and Ru raw material powders is mixed according to the amount ratio of each element; Os powder with a particle size of 200 mesh, Ir powder with a particle size of 200 mesh, Re powder with a particle size of 200 mesh, W powder with a particle size of 2.3 microns and Ru powder with a particle size of 200 mesh are used for batching;

[0009] (2) The multi-component powders are uniformly mixed by using a ball milling method, and the dry milling method is adopted with inert gas protection or vacuum;

[0010] (3) Powder compaction: the powder after step (2) ball milling is put into a die (preferably with a diameter of 3mm) for compaction, and the pressure is maintained for 20s-43s;

[0011] (4) the green body pressed in step (3) is put into a hydrogen furnace for sintering, hydrogen is introduced as a protective gas, first, the temperature is raised to 850 DEG C for 30 min, then the sample is heated to 1380-1620 DEG C at a temperature rising rate of 8.5 DEG C / min, and is kept for 15-55 min; the active salt is immersed at 1660-1690 DEG C to obtain the high-entropy alloy reinforced impregnated cathode.

[0012] Further, the XRD spectrum of the high-entropy alloy reinforced impregnated cathode is composed of W and high-entropy alloy phase Hcp, and the cathode has the best thermoelectron emission performance and can further improve the current emission density.

[0013] The high-entropy alloy reinforced impregnated cathode prepared by the method has the advantages of high melting point, large impregnation amount, high temperature stability, high current emission density and the like, and finally obtains the high-entropy alloy reinforced impregnated cathode with high strength and high emission. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 XRD curve of Os 16 Ir 25 Re 24 W 35 and Os 17 Ir 35 Re 18 W 25 Ru5 cathode;

[0015] Figure 2 XRD curve of Os 25 Ir 25 Re 25 W 25 , Os 20 Ir 20 Re 20 W 20 Ru 20 and Os 30 Ir 35 Re 12 W 13 Ru 10 cathode;

[0016] Figure 3 SEM image of Os 20 Ir 20 Re 20 W 20 Ru 20 cathode surface morphology;

[0017] Figure 4 Macroscopic morphology of the high-entropy alloy reinforced impregnated cathode of the application;

[0018] Figure 5 Os for the present application 20 Ir 20 Re 20 W 20 Ru 20 Cathode emission current density

[0019] Table 1 is the component design parameter of the present application

[0020] Table 2 is the electron emission performance of the cathode of the present application involving five high-entropy alloy strengthened impregnated cathodes tested at 1000℃ b DETAILED DESCRIPTION

[0021] The present application will be further described in conjunction with specific embodiments, but the scope of protection of the present application is not limited to the content described.

[0022] Component design

[0023] (1) Put the Os, Ir, Re, W and Ru raw material powders into the crucible respectively, and perform annealing treatment in the hydrogen gas inlet tube furnace to ensure the purification of the original powder. Use metal powders with purity of 99.95% or above to prepare the ingredients, and mix the Os, Ir, Re, W and Ru raw material powders according to the proportion;

[0024] (2) Mix the multi-component powders uniformly by using the ball milling method, and adopt dry milling method and inert gas protection or vacuum;

[0025] (3) Powder compaction: put the powder after step 2 ball milling into a 3mm diameter mold and press it, and keep the pressure for 20s-43s;

[0026] (4) Put the green body after step 3 compaction into a hydrogen furnace for sintering, and inlet hydrogen as protective gas, first heat to 850℃ for 30min, then heat the sample to 1490℃ at a heating rate of 8.5℃ / min, and keep it for 30min; and the active ingredient 411 salt for electron emission is impregnated at 1660-1670℃.

[0027] (5) Put the cathode prepared by the above steps into a flat panel diode structure to test the pulse current emission density.

[0028] Table 1 is the component design parameter of the present application

[0029] Serial number Os Ir Re W Ru G1 16 25 24 35 0 G2 25 25 25 25 0 G3 17 35 18 25 5 G4 20 20 20 20 20 G5 30 35 12 13 10

[0030] Table 2 is the electron emission performance of the cathode of the present application involving five high-entropy alloy strengthened impregnated cathodes tested at 1000℃ b ​​

[0031] Serial number Porosity / % Immersion amount / % Current emission density (A / cm 2 ) G1 25.79 7.13 19.46 G2 26.48 7.41 5.43 G3 26.98 7.52 10.73 G4 25.83 7.68 20.53 G5 26.12 7.64 7.29 。

Claims

1. A method for preparing a high-temperature, high-entropy alloy-reinforced impregnated cathode, wherein the high-temperature, high-entropy alloy is composed of four or five elements selected from Os, Ir, Re, W, and Ru in equiatomic or non-equiatomic ratios, with each element in a molar percentage ratio of 5% to 50%, and the chemical formula is denoted as Os. x Ir y Re z W k Ru n Where x+y+z+k+n=100, x, y, z, k, and n are all 5-50, or any one of x, y, z, k, and n is 0, and the others are all 5-50; Its features are: Includes the following steps: (1) Place the Os, Ir, Re, W and Ru raw material powders into crucibles respectively, and anneal them in a tube furnace with hydrogen gas to ensure the purification of the original powders; according to Os x Ir y Re z W k Ru n Weigh out the required mass of Os, Ir, Re, W and Ru raw material powders and mix them according to the proportion of each element in the composition; use Os powder with a particle size of 200 mesh, Ir powder with a particle size of 200 mesh, Re powder with a particle size of 200 mesh, W powder with a particle size of 2.3 μm and Ru powder with a particle size of 200 mesh for ingredient preparation; (2) The multi-component powder is mixed evenly by ball milling, dry milling is used, and inert gas protection or vacuum is adopted; (3) Powder pressing and molding: The powder after ball milling in step (2) is placed into a mold and pressed, and the pressure is maintained for 20 s to 43 s; (4) Place the green blank pressed in step (3) into a hydrogen furnace for sintering, and introduce hydrogen as a protective gas. First, heat the sample to 850 °C for 30 min, and then heat it to 1380-1620 °C at a heating rate of 8.5 °C / min and hold it for 15-55 min. After impregnation with active salt at 1660-1690 °C, a high-entropy alloy-strengthened impregnated cathode is obtained.

2. The method according to claim 1, characterized in that, Os x Ir y Re z W k Ru n The XRD pattern of the high-entropy alloy-reinforced impregnated cathode consists of W and the high-entropy alloy phase Hcp. This impregnated cathode exhibits the best thermionic emission performance and can further improve the current emission density.

3. An impregnated cathode prepared according to the method of claim 1 or 2.

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