High-entropy alloy film-coated hot cathode with close-packed hexagonal structure and preparation method of high-entropy alloy film-coated hot cathode

Abstract

The invention discloses a high-entropy coated hot cathode with a close-packed hexagonal structure and a preparation method of the high-entropy coated hot cathode. The preparation method comprises the following steps: (1) mixing tungsten powder, rhenium powder, osmium powder, tantalum powder and molybdenum powder, then carrying out ball milling, and then carrying out sintering molding; (2) melting a product in the step (1) by adopting an electric arc melting technology, and cooling and solidifying to prepare a target material; and (3) coating the surface of a cathode material with the target material prepared in the step (2), and then performing annealing treatment to obtain the single-phase high-entropy alloy coated hot cathode material. The surface of a traditional diffusion cathode is covered with a high-entropy alloy film layer, the film layer is diffused into a base body through heat treatment to be further alloyed with tungsten or tungsten alloy, and the high-entropy film-coated cathode with the surface of a close-packed hexagonal structure is formed. The advantages of low diffusion coefficient, distortion of surface crystal lattices and the like of the high-entropy alloy film layer are effectively utilized, the function of reducing the work function of the surface of the cathode is realized, and the emission capability of the cathode is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of vacuum electronic device manufacturing, and in particular relates to a high entropy alloy coated hot cathode with a close-packed hexagonal structure and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of radar, communication, medical and other fields, vacuum electronic devices have also been continuously advancing towards high-band and high-power directions, which has put forward higher requirements on the performance of cathode materials. At present, the main way to improve the electron emission capability of hot cathodes is to reduce the surface work function of the cathode. The methods adopted include adjusting the mixing ratio of aluminates, coating the cathode surface with precious metal films (such as osmium, osmium-ruthenium, osmium-rhenium or osmium-iridium-aluminum, etc.), and impregnating the substrate with scandates, etc., to improve the bonding state of the atoms on the cathode surface and enhance the activity of the surface atoms.

[0003] The M-type cathode uses a sputtering method to coat a high work function metal film (Os, Ir, Re, etc.) on the emission surface. Taking osmium as an example, this metal film and the tungsten substrate gradually form a W-Os alloy under heating conditions, and the Ba-O dipole is attached to the cathode surface of the W-Os alloy in the form of a single atomic layer, forming a Ba-O / W-Os quaternary emission system, which makes the actual work function of the M-type cathode surface 0.2eV lower than that of the traditional barium tungsten cathode, or at the same current density, the operating temperature is reduced by 100°C. However, the film layer of this type of coated cathode is easy to fall off and has poor stability during long-term use, resulting in unstable emission performance. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a high entropy alloy coated hot cathode with a close-packed hexagonal structure and a preparation method thereof. The present invention forms a high entropy coated cathode with a close-packed hexagonal structure on the surface of a conventional diffusion cathode by coating a high entropy alloy film layer on the surface of the conventional diffusion cathode, and further alloying the film layer with tungsten or tungsten alloy by heat treatment. The advantages of the high entropy alloy film layer, such as low diffusion coefficient and surface lattice distortion, are effectively utilized to reduce the work function of the cathode surface and improve the electron emission capability of the cathode.

[0005] To achieve the above purpose, the technical solution adopted by the present invention to solve the technical problem is:

[0006] A method for preparing a high entropy film-coated hot cathode having a close-packed hexagonal structure comprises the following steps:

[0007] (1) mixing tungsten powder, rhenium powder, osmium powder, tantalum powder and molybdenum powder, ball milling and sintering;

[0008] (2) using arc melting technology to melt the product of step (1), and then cooling and solidifying it to form a target material;

[0009] (3) The target material prepared in step (2) is coated on the surface of the cathode material, and then annealed to obtain a hot cathode material coated with a single-phase high entropy alloy.

[0010] Furthermore, the weight percentages of the metal powders used in step (1) are as follows:

[0011] Tungsten powder 20-35wt%, rhenium powder 20-55wt%, osmium powder 10-55wt%, tantalum powder 1-5wt% and molybdenum powder 1-5wt%.

[0012] Furthermore, the ball milling process in step (1) is as follows:

[0013] The ball-to-material ratio is 8:1, the frequency is 25-30Hz; in bidirectional mode, the forward rotation time is 30min, the reverse rotation time is 30min, the interval is 10min, and the total ball milling time is 10-12h.

[0014] Furthermore, the sintering process in step (1) is:

[0015] The temperature was raised to 950°C at a rate of 10-15°C / min, kept at that temperature for 100-120 minutes, and then cooled along with the furnace. The hydrogen flow rate during the process was 40-50 mL / min.

[0016] Furthermore, the processing temperature of the arc melting technology in step (2) is 2000-2400° C., and a mixed gas of 98% argon and 2% hydrogen is used as the medium.

[0017] Furthermore, the cathode material in step (3) is obtained by impregnating a porous tungsten substrate with an active salt.

[0018] Furthermore, the preparation process of the cathode material is as follows:

[0019] The porous tungsten green body was placed in a hydrogen furnace, heated to 850°C in 30 minutes, and then heated to 1600-1700°C at a heating rate of 8.5°C / min to complete active salt impregnation to obtain a cathode material.

[0020] Furthermore, in step (3), magnetron sputtering is used to coat the target material on the surface of the cathode material.

[0021] A high entropy film-coated hot cathode with a close-packed hexagonal structure is prepared by the method.

[0022] Furthermore, it is an M-type cathode material.

[0023] Beneficial effects of the present invention:

[0024] 1. The present invention forms a high entropy film cathode with a close-packed hexagonal structure on the surface by coating a high entropy alloy film on the surface of a conventional diffusion cathode and further alloying the film with tungsten or tungsten alloy by heat treatment. The advantages of the high entropy alloy film layer, such as low diffusion coefficient and surface lattice distortion, are effectively utilized to reduce the work function of the cathode surface and improve the emission capacity of the cathode.

[0025] 2. The present invention adopts arc melting process to prepare high entropy alloy target material. Compared with traditional processes such as vacuum sintering, arc melting process can make the metal cool rapidly within 5 minutes after melting, and its cooling rate is increased by 60 times, so that the inclusion phase in the crystalline structure of the obtained target material is reduced, and a single HCP phase component is obtained, so that the composition of the target material is more uniform, the density is high, and the purity is high. Coating the target alloy to the surface of barium tungsten cathode can reduce the surface work function and improve the emission performance of the cathode.

[0026] 3. The cathode material prepared by the present invention has the characteristics of high current density, good electron beam uniformity, and the film layer is not easy to fall off during use. During operation, the active substance in the coated target material will diffuse to the cathode surface, reducing the work function of the cathode surface, thereby improving the emission capacity of the cathode, making the cathode have the characteristics of low temperature and large current. At the same time, the film layer will continue to penetrate and diffuse into the cathode matrix material to ensure the stability of the cathode matrix material.

[0027] 4. Hot cathode materials are mostly made of tungsten matrix. The present invention adds tungsten to the target material to avoid the diffusion effect between the matrix and the film layer. Osmium has the best emission performance and a relatively high content. Rhenium has an emission performance second only to osmium, but its economic benefits are more obvious than osmium. It can also enhance the physical properties of tungsten and improve the stability of the material at high temperatures, so that rhenium can partially replace osmium. Tantalum and molybdenum increase the density of the target material, have a high melting point, and have strong atomic bonding, which is conducive to obtaining hot cathode materials with better emission performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a process flow chart of the present invention;

[0029] Figure 2 A schematic diagram of a model of a high entropy alloy coated hot cathode prepared by the present invention;

[0030] Figure 3 The W prepared by the arc melting method of the present invention is 25 Re 20 Os 45 XRD spectrum of Ta5Mo5;

[0031] Figure 4 W is prepared by tungsten filament vacuum sintering method. 25 Re20 Os 45 XRD spectrum of Ta5Mo5;

[0032] Figure 5 This is a graph showing the electron emission performance of the high entropy alloy coated hot cathode prepared in the present invention. DETAILED DESCRIPTION

[0033] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0034] Example 1

[0035] A method for preparing a high entropy film-coated hot cathode having a close-packed hexagonal structure comprises the following steps:

[0036] (1) Weigh 57.5 g of tungsten powder, 23.25 g of rhenium powder, 130.625 g of osmium powder, 11.3125 g of tantalum powder and 5.998 g of molybdenum powder, all with a specification of 200 mesh, respectively, mix the powders and ball mill them for 12 h, and press them into shape by molding; the ball milling process is: ball-to-material ratio is 8:1, frequency is 30 Hz, bidirectional mode, forward rotation time is 30 min, reverse rotation time is 30 min, interval is 10 min, and the total ball milling time is 12 h;

[0037] (2) The formed sample was sintered in a tubular furnace at a temperature of 950°C for 120 min and cooled with the furnace. The hydrogen flow rate during the process was 40-50 mL / min.

[0038] (3) The sintered sample was melted by electron beam heating at 2400°C in a mixed atmosphere of argon and hydrogen, and after cooling and solidification, it was rolled and cut into approximately Alloy target;

[0039] (4) placing the porous tungsten green body into a hydrogen furnace, heating it to 850°C within 30 min, and then heating the sample to 1600°C at a heating rate of 8.5°C / min to complete the impregnation of 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain a barium tungsten cathode material;

[0040] (5) After cleaning the substrate and target, the vacuum degree of the sputtering chamber is better than 1×10 -4Pa, and the sputtering gas is high-purity argon. A high-entropy alloy target film with a thickness of about 1 micron is coated on the surface of the substrate. The deposited sample is annealed at 800°C in a hydrogen atmosphere for 120 minutes to obtain a high-entropy alloy coated tungsten cathode with a close-packed hexagonal structure.

[0041] Example 2

[0042] A method for preparing a high entropy film-coated hot cathode having a close-packed hexagonal structure comprises the following steps:

[0043] (1) Weigh 57.5 g of tungsten powder, 34.875 g of rhenium powder, 118.75 g of osmium powder, 11.3125 g of tantalum powder and 5.998 g of molybdenum powder, all with a specification of 200 mesh, respectively, mix the powders and ball mill them for 12 h, and press them into shape by molding; the ball milling process is: ball-to-material ratio is 8:1, frequency is 30 Hz, bidirectional mode, forward rotation time is 30 min, reverse rotation time is 30 min, interval is 10 min, and the total ball milling time is 12 h;

[0044] (2) The formed sample was sintered in a tubular furnace at a sintering temperature of 950°C for 120 minn and cooled with the furnace. The hydrogen flow rate during the process was 40-50 mL / min.

[0045] (3) The sintered sample was melted by electron beam heating at 2200°C in a mixed atmosphere of argon and hydrogen, and after cooling and solidification, it was rolled and cut into approximately Alloy target;

[0046] (4) placing the porous tungsten green body into a hydrogen furnace, heating it to 850°C within 30 min, and then heating the sample to 1600°C at a heating rate of 8.5°C / min to complete the impregnation of 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain a barium tungsten cathode material;

[0047] (5) After cleaning the substrate and target, the vacuum degree of the sputtering chamber is better than 1×10 -4 Pa, and the sputtering gas was high-purity argon. A high-entropy alloy target film with a thickness of about 1.1 microns was coated on the surface of the substrate. The deposited sample was annealed at 1000°C in a hydrogen atmosphere for 120 minutes to obtain a high-entropy alloy coated tungsten cathode.

[0048] Example 3

[0049] A method for preparing a high entropy film-coated hot cathode having a close-packed hexagonal structure comprises the following steps:

[0050] (1) Weigh 57.5 g of tungsten powder, 46.5 g of rhenium powder, 106.875 g of osmium powder, 11.3125 g of tantalum powder and 5.998 g of molybdenum powder, all of which are 200 mesh, respectively, ball mill the mixed powder for 10 h, and then press it into shape by molding; wherein the ball milling process is: ball-to-material ratio is 8:1, frequency is 28 Hz, bidirectional mode, forward rotation time is 30 min, reverse rotation time is 30 min, interval is 10 min, and the total ball milling time is 10 h;

[0051] (2) The formed sample was sintered in a tubular furnace at a sintering temperature of 950°C for 120 minn and cooled with the furnace. The hydrogen flow rate during the process was 40-50 mL / min.

[0052] (3) The sintered sample was melted by electron beam heating at 2200°C in a mixed atmosphere of argon and hydrogen, and after cooling and solidification, it was rolled and cut into approximately Alloy target;

[0053] (4) placing the porous tungsten green body into a hydrogen furnace, heating it to 850°C within 30 min, and then heating the sample to 1700°C at a heating rate of 8.5°C / min to complete the impregnation of 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain a barium tungsten cathode material;

[0054] (5) After cleaning the substrate and target, the vacuum degree of the sputtering chamber is better than 1×10 -4 Pa, and the sputtering gas was high-purity argon. A high-entropy alloy target film with a thickness of about 1.2 microns was plated on the surface of the substrate. The deposited sample was annealed at 900°C in a hydrogen atmosphere for 120 minutes to obtain a high-entropy alloy coated tungsten cathode.

[0055] Example 4

[0056] A method for preparing a high entropy film-coated hot cathode having a close-packed hexagonal structure comprises the following steps:

[0057] (1) Weigh 57.5 g of tungsten powder, 69.75 g of rhenium powder, 83.125 g of osmium powder, 11.3125 g of tantalum powder and 5.998 g of molybdenum powder, all of which are 200 mesh, respectively, mix the powders and ball mill them for 10 h, and press them into shape by molding; wherein the ball milling process is: ball-to-material ratio is 8:1, frequency is 25 Hz, bidirectional mode, forward rotation time is 30 min, reverse rotation time is 30 min, interval is 10 min, and the total ball milling time is 10 h;

[0058] (2) The formed sample was sintered in a tubular furnace at a sintering temperature of 950°C for 120 minn and cooled with the furnace. The hydrogen flow rate during the process was 40-50 mL / min.

[0059] (3) The sintered sample was melted by electron beam heating at 2000°C in a mixed atmosphere of argon and hydrogen, and after cooling and solidification, it was rolled and cut into approximately Alloy target;

[0060] (4) placing the porous tungsten green body into a hydrogen furnace, heating it to 850°C within 30 min, and then heating the sample to 1700°C at a heating rate of 8.5°C / min to complete the impregnation of 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain a barium tungsten cathode material;

[0061] (5) After cleaning the substrate and target, the vacuum degree of the sputtering chamber is better than 1×10 -4 Pa, and the sputtering gas was high-purity argon. A high-entropy alloy target film with a thickness of about 1.3 microns was coated on the surface of the substrate. The deposited sample was annealed at a high temperature of 600°C in a hydrogen atmosphere for 120 minutes to obtain a high-entropy alloy coated tungsten cathode.

[0062] Example 5

[0063] A method for preparing a high entropy film-coated hot cathode having a close-packed hexagonal structure comprises the following steps:

[0064] (1) Weigh 57.5 g of tungsten powder, 81.375 g of rhenium powder, 71.25 g of osmium powder, 11.3125 g of tantalum powder and 5.998 g of molybdenum powder, all of which are 200 mesh, respectively, mix the powders and ball mill them for 10 h, and press them into shape by molding; wherein the ball milling process is: ball-to-material ratio is 8:1, frequency is 30 Hz, bidirectional mode, forward rotation time is 30 min, reverse rotation time is 30 min, interval is 10 min, and the total ball milling time is 10 h;

[0065] (2) The formed sample was sintered in a tubular furnace at a sintering temperature of 950°C for 120 minn and cooled with the furnace. The hydrogen flow rate during the process was 40-50 mL / min.

[0066] (3) The sintered sample was melted by electron beam heating at 2000°C in a mixed atmosphere of argon and hydrogen, and after cooling and solidification, it was rolled and cut into approximately Alloy target;

[0067] (4) placing the porous tungsten green body into a hydrogen furnace, heating it to 850°C within 30 min, and then heating the sample to 1700°C at a heating rate of 8.5°C / min to complete the impregnation of 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain a barium tungsten cathode material;

[0068] (5) After cleaning the substrate and target, the vacuum degree of the sputtering chamber is better than 1×10 -4Pa, and the sputtering gas was high-purity argon. A high-entropy alloy target film with a thickness of about 1.4 microns was coated on the surface of the substrate. The deposited sample was annealed at 800°C in a hydrogen atmosphere for 120 minutes to obtain a high-entropy alloy coated tungsten cathode with a close-packed hexagonal structure.

[0069] Example 6

[0070] A method for preparing a film-coated hot cathode, as a control group, comprises the following steps:

[0071] (1) Weigh 57.5 g of tungsten powder, 81.375 g of rhenium powder, 71.25 g of osmium powder, 11.3125 g of tantalum powder and 5.998 g of molybdenum powder, all of which are 200 mesh, respectively, mix the powders and ball mill them for 10 h, and press them into shape by molding; wherein the ball milling process is: ball-to-material ratio is 8:1, frequency is 30 Hz, bidirectional mode, forward rotation time is 30 min, reverse rotation time is 30 min, interval is 10 min, and the total ball milling time is 10 h;

[0072] (2) The formed sample was sintered in a tubular furnace at a temperature of 950°C for 120 min and cooled with the furnace. The hydrogen flow rate during the process was 40-50 mL / min.

[0073] (3) The shaped sample was sintered in a 2200℃ vacuum tungsten wire sintering furnace, and the temperature was raised to 2200℃ at 10℃ / min. After keeping the temperature for 2h, the temperature was lowered to 600℃ at 10℃ / min and cooled in the furnace. After cooling and solidification, it was rolled and cut into approximately Alloy target;

[0074] (4) placing the porous tungsten green body into a hydrogen furnace, heating it to 850°C within 30 min, and then heating the sample to 1700°C at a heating rate of 8.5°C / min to complete the impregnation of 411 active salt (BaO:CaO:Al2O3 molar ratio 4:1:1) to obtain a barium tungsten cathode material;

[0075] (5) After cleaning the substrate and target, the vacuum degree of the sputtering chamber is better than 1×10 -4 Pa, under the condition that the sputtering gas is high-purity argon, the substrate surface is coated with an alloy target film with a thickness of about 1.4 microns. The deposited sample is high-temperature annealed in a hydrogen atmosphere at 800°C for 120 minutes to obtain an alloy-coated tungsten cathode.

[0076] Experimental example

[0077] 1. W prepared by the present invention 25 Re 20 Os 45 The XRD diffraction patterns of Ta5Mo5 high entropy alloy and the alloy prepared in Example 6 as a control group were analyzed. The results are shown in Figure 3 and Figure 4 .

[0078] according to Figure 3 From the XRD spectrum, it can be seen that the high entropy alloy prepared by the present invention has a single HCP phase component, which has a close-packed hexagonal structure. Figure 4 The test results show that the traditional vacuum sintering process cannot ultimately produce a high-entropy alloy with a single HCP phase component.

[0079] 2. The electron emission performance of the film-coated tungsten cathode material prepared by the present invention at 1000° C. is tested, and the results are shown in Table 1.

[0080] Table 1 Emission current density

[0081] Serial number <![CDATA[Emission current density (A / cm 2 )]]> Example 1 15.40 Example 2 17.90 Example 3 18.90 Example 4 16.53 Example 5 15.84 Example 6 12.5

[0082] 3. The emission performance of the film-coated tungsten cathode material prepared in Example 3 of the present invention was tested at different temperatures. The results are shown in Figure 5 .

[0083] According to Table 1 and Figure 5 It can be seen from the test results that the emission capacity of the coated tungsten cathode prepared by the technical solution of the present invention has been significantly improved, especially the cathode materials prepared in Examples 2 and 3, which have the best performance.

[0084] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a high entropy film-coated hot cathode having a close-packed hexagonal structure, characterized in that: The following steps are involved: (1) mixing tungsten powder, rhenium powder, osmium powder, tantalum powder and molybdenum powder, ball milling and sintering; (2) using arc melting technology to melt the product of step (1), and then cooling and solidifying it to form a target material; (3) The target material prepared in step (2) is coated on the surface of the cathode material, and then annealed to obtain a hot cathode material coated with a single-phase high entropy alloy.

2. The preparation method according to claim 1, characterized in that: The weight percentages of the metal powders used in step (1) are as follows: Tungsten powder 20-35wt%, rhenium powder 20-55wt%, osmium powder 10-55wt%, tantalum powder 1-5wt% and molybdenum powder 1-5wt%.

3. The preparation method according to claim 1, characterized in that: The process of ball milling in step (1) is as follows: The ball-to-material ratio is 8:1, the frequency is 25-30Hz; in bidirectional mode, the forward rotation time is 30min, the reverse rotation time is 30min, the interval is 10min, and the total ball milling time is 10-12h.

4. The preparation method according to claim 1, characterized in that: The sintering process in step (1) is: The temperature was raised to 950°C at a rate of 10-15°C / min, kept at that temperature for 100-120 minutes, and then cooled along with the furnace. The hydrogen flow rate during the process was 40-50 mL / min.

5. The preparation method according to claim 1, characterized in that: The processing temperature of the arc melting technology in step (2) is 2000-2400° C., and a mixed gas of 98% argon and 2% hydrogen is used as the medium.

6. The preparation method according to claim 1, characterized in that: The cathode material in step (3) is obtained by impregnating a porous tungsten substrate with an active salt.

7. The preparation method according to claim 1, characterized in that: In step (3), magnetron sputtering is used to coat the target material on the surface of the cathode material.

8. A high entropy film-coated hot cathode having a close-packed hexagonal structure, characterized in that: The method is prepared by any one of claims 1 to 7.

9. The high entropy film-coated hot cathode with a close-packed hexagonal structure according to claim 8, characterized in that: It is an M-type cathode material.

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