Hafnium foil for an electric vacuum device and a method of manufacturing the same

Abstract

The present application relates to a kind of hafnium foil for electric vacuum device and its preparation method, belong to microwave vacuum electron technology and refractory metal powder metallurgy field.The hafnium foil main content (hafnium+zirconium) ≥99.9wt%, thickness 0.01mm~0.15mm, size tolerance ≤±5 μm, tensile strength ≥450MPa, elongation after breaking ≥15%, main texture is <10‑10> / / RD.Preparation method includes: iodization purification, electron beam melting obtains high-purity hafnium ingot, is obtained foil material blank by hot forging breakdown, cross hot rolling, cross cold rolling, finally by vacuum stress relief annealing, cutting inspection and is prepared hafnium foil.The hafnium foil of the present application is high in purity, high in dimensional accuracy, strong and tough, isotropic degree is good, can be used for grid traveling wave tube spherical structure grid and other electric vacuum devices.

Description

Technical Field

[0001] This invention relates to a hafnium foil for electro-vacuum devices and its preparation method, belonging to the fields of microwave vacuum electronics technology and refractory metal powder metallurgy. Background Technology

[0002] To meet the requirements of high current control, grid modulation is often used to control the cathode current in modern microwave vacuum devices. Grid-controlled traveling wave tubes (TWTs) employ a grid-controlled electron gun, which involves placing a control grid in front of the cathode and a shadow grid between the control grid and the cathode. This allows for the control of a large injection current with relatively low modulation voltage and power during pulsed applications. Therefore, the grid is one of the key components of a TWT, playing a crucial role in achieving its electrical performance. Because the grid is close to the hot cathode and operates at temperatures no lower than 800°C, the grid material is typically a refractory metal foil with high high-temperature strength and high work function, such as molybdenum. However, during TWT operation, the cathode active material (Ba, BaO) evaporates at high temperatures and gradually deposits on the grid surface, reducing its work function and causing grid emission, thus disrupting normal operation. Currently, there are two common methods for suppressing grid emission:

[0003] (1) A film layer with a relatively high work function (such as hafnium) is deposited on the surface of the molybdenum grid after interacting with the active material. However, after long-term operation, the gate emission will be significantly enhanced again as the hafnium film is gradually worn away, which will limit the reliability and service life of the device.

[0004] (2) Hafnium foil is used directly to process the grid. Hafnium grid can suppress grid emission and avoid the film loss problem caused by hafnium plating on molybdenum grid, meet the long-term working requirements of traveling wave tube, and ensure the overall efficiency and life of high duty cycle pulse traveling wave tube.

[0005] The grid components require high purity and dimensional accuracy of raw materials, and the processing involves hydraulic or stamping blanking, high aspect ratio hydraulic spherical cap forming, laser or EDM machining, etc. Hafnium itself has gas-absorbing properties, and its processing performance is highly sensitive to deformation amount and deformation temperature. During foil preparation, it is prone to absorbing large amounts of gas impurities and improper control of deformation process parameters. Therefore, conventional hafnium sheets / foils often have low purity, insufficient strength-plasticity matching, high anisotropy, and poor dimensional accuracy and defect control, leading to delamination, cracking, and breakage during hydraulic / stamping, making it difficult to meet the requirements of grid processing and service. The lack of high-performance hafnium foil materials has hindered the development of new traveling wave tube devices and subsequent finalized production.

[0006] Regarding the preparation of hafnium plates / sheets / foils, Chinese patent ZL 202110146658.3 discloses a processing method for hafnium plates, involving the preparation of hafnium plates with a thickness of 3mm to 7mm by forging and hot rolling using hafnium ingots as raw materials; Chinese patent 202311384732.0 discloses a preparation method for improving the microstructure and properties of hafnium plates, involving controlling the composition of ingots through secondary electron beam melting, adjusting hot rolling / cold rolling / heat treatment processes and parameters to improve the strength and microstructure uniformity of hafnium plates, and preparing hafnium plates with a tensile strength higher than 400MPa and a thickness difference of 0.03mm within the same plate; currently, no patents or literature on hafnium foils with a thickness δ≤0.15mm have been found. Regarding hafnium-plated grids, Chinese patent ZL 201010155311.7 discloses a method for hafnium deposition via magnetron sputtering, involving the formation of a dense, uniform hafnium film with a thickness of 1μm to 3μm on the grid surface using magnetron sputtering to reduce grid emission and increase the operational stability of traveling wave tubes. No relevant patents or literature have been found regarding hafnium foil materials and their preparation methods for use in vacuum electronic devices. Therefore, it is necessary to develop a high-performance hafnium foil material for vacuum electronic devices with high purity, dimensional accuracy, and good processing performance, as well as its preparation method. Summary of the Invention

[0007] The purpose of this invention is to provide a hafnium foil for electro-vacuum devices and its preparation method, so as to solve the problems that hafnium foil cannot be used for the processing of key parts of electro-vacuum devices due to its unique gas absorption and processing characteristics, such as low purity, insufficient strength-plasticity matching, high anisotropy, and poor dimensional accuracy and defect control.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A hafnium foil for an electrovacuum device, characterized in that:

[0010] The hafnium foil has a main content (hafnium + zirconium) ≥ 99.9 wt%, of which zirconium ≤ 0.9 wt%, and an interstitial impurity content (oxygen + nitrogen + carbon) ≤ 200 ppm;

[0011] Thickness ranges from 0.01mm to 0.15mm, with dimensional tolerances ≤ ±5μm;

[0012] Tensile strength ≥450MPa, yield strength ≥300MPa, elongation after fracture ≥15%;

[0013] The difference in tensile strength between the longitudinal and transverse directions shall not exceed 10%;

[0014] The main texture is <10-10> / / RD, and it contains <11-20> / / RD texture components;

[0015] The microstructure consists of flattened fibrous grains, or flattened fibrous grains and fine equiaxed grains are uniformly interwoven, with the area of ​​flattened fibrous grains accounting for ≥60%, or the area of ​​equiaxed grains accounting for ≥60%.

[0016] A method for preparing hafnium foil for vacuum electronic devices as described above, characterized by comprising the following steps:

[0017] (1) Hafnium ingot purification: Hafnium metal raw materials are purified by surface activation and iodination to obtain low-impurity hafnium crystal rods;

[0018] (2) Electron beam melting: The crystal rod obtained by iodization purification is melted under the bombardment of high-energy electron beam to obtain high-purity metal hafnium ingot;

[0019] (3) Hot forging: High-purity metal hafnium ingots are forged in multiple directions at a forging temperature of 850℃~950℃;

[0020] (4) Cross hot rolling: The hafnium billet after forging is hot rolled in multiple passes and multiple directions; after hot rolling, it is vacuum intermediate annealed;

[0021] (5) Cross-cold rolling: The hot-rolled hafnium sheets are cold-rolled in multiple passes with a 90° reversal to obtain hafnium foil of the required thickness;

[0022] (6) Stress-relief annealing: The cold-rolled hafnium foil is subjected to stress-relief annealing under vacuum conditions;

[0023] (7) Cutting inspection: The stress-relief annealed hafnium foil is cut to the final size and inspected to obtain hafnium foil for vacuum electronic devices.

[0024] Furthermore, the feature is that, in step (1), the main content (hafnium + zirconium) of the metal hafnium raw material is ≥99.5wt%; the purity of the hafnium wire used for iodization purification is ≥99.9%, and the purity of the iodine is ≥99.5%.

[0025] Furthermore, the surface activation condition in step (1) is as follows: The vacuum level and temperature gradient of 300℃~500℃; the iodination purification conditions are to cut off the vacuum system, selective synthesis temperature of 300℃~500℃, and selective decomposition deposition temperature of 1300℃~1500℃.

[0026] Furthermore, the feature is that, in step (2), the vacuum degree of the electron beam melting is... The electron gun power is 60~70kW.

[0027] Furthermore, the feature is that, in step (3), the final forging temperature is 550℃~650℃; the multi-directional forging is alternating forging along three mutually perpendicular directions, and the single-pass reduction is 25%~35%.

[0028] Further, the feature is that, in step (4), the total deformation of the cross-hot rolling is 95%~99%, and the number of reversals is 3~7; the vacuum intermediate annealing temperature is 750~850℃, the holding time is 0.5~2h, and the vacuum degree is... .

[0029] Furthermore, the feature is that in step (5), a high-precision multi-roll mill is used for cold rolling, the roll crown is 4~10μm, and the total deformation is 70%~98%.

[0030] Furthermore, the characteristic feature is that, in step (6), the stress-relief annealing temperature is 500~1000℃, the holding time is 0.5~1h, and the vacuum degree is... A stepped heating method is adopted.

[0031] The beneficial effects of this invention are:

[0032] In the preparation method of this invention, the hafnium material raw material is activated, degassed, and purified by iodination. During the degasing stage, the solid solution elements and interstitial impurity elements in a semi-combined state with hafnium form a large partial pressure difference in the internal and external environments of the metal under high vacuum. During the iodination purification stage, iodine selectively synthesizes, selectively decomposes, and deposits hafnium metal, thereby partially removing interstitial gas impurity elements (carbon, nitrogen, oxygen, hydrogen) and refractory metal impurity elements (tungsten, molybdenum, tantalum, niobium) from the hafnium material, resulting in a low-impurity hafnium crystal rod.

[0033] In the preparation method of this invention, electron beam melting is used to further remove impurities from the hafnium crystal rod. Under the high vacuum environment of the electron beam melting process, some impurity elements with lower melting points and higher saturated vapor pressures than hafnium can be removed by volatilization while the metal is melting.

[0034] In the preparation method of this invention, a multi-directional hot forging process is used to open the hafnium ingot. Large deformation forging is carried out at an opening temperature of 850℃~950℃ to break up the preferred texture of the coarse columnar crystals in the molten state and transform it into a grain refinement texture with no obvious preferred texture that is more suitable for subsequent rolling deformation. This ensures the uniformity of the microstructure in the center and periphery of the hafnium ingot and avoids cracking of the billet. At the same time, the dynamic recovery and recrystallization strength of hafnium are moderate, which can retain a certain amount of deformation processing microstructure, thereby obtaining better mechanical properties after hot rolling.

[0035] In the preparation method of this invention, cross-hot rolling and cold rolling processes are used in conjunction with vacuum stress-relief annealing to ensure the fineness, uniformity, and texture of the microstructure in the in-plane and thickness directions of the foil. This results in a hafnium foil with near isotropic properties, strong plasticity matching, a main texture of <10-10> / / RD, and a microstructure dominated by flat, elongated fibrous grains or equiaxed grains, fundamentally solving the problems of cracking and delamination encountered in the application of hafnium foil.

[0036] In the preparation method of this invention, the inter-pass annealing of hot rolling and the inter-pass stress-relief annealing of cold rolling are at a temperature not less than [amount missing]. The process is carried out under high vacuum to avoid introducing gaseous impurities such as C, N, O, and H; the temperature is increased in stages and the temperature is maintained in the low-temperature zone for a longer period of time to ensure that nitrogen and oxygen are extracted by the vacuum system in a timely manner.

[0037] The hafnium foil for vacuum electronic devices prepared by this invention has advantages such as high strength and toughness matching, high dimensional accuracy, and good molding performance. It can be used to prepare spherical structure grids for grid-controlled traveling wave tubes, among other things. Attached Figure Description

[0038] Figure 1 This is a process flow diagram of the present invention.

[0039] Figure 2 This is a 500x magnified metallographic image of the rolled cross section of hafnium foil for electro-vacuum devices according to Embodiment 1 of the present invention.

[0040] Figure 3 This is a 2000x scanning electron microscope image of the rolled cross section of hafnium foil for electro-vacuum devices according to Embodiment 1 of the present invention.

[0041] Figure 4 This is a 2000x orientation image of typical texture components of hafnium foil for electro-vacuum devices according to Embodiment 1 of the present invention. Detailed Implementation

[0042] The following description is merely an embodiment of preferred processing parameters for the preparation process of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

[0043] The process flow of the method for preparing hafnium foil for vacuum electronic devices of the present invention is as follows: Figure 1 As shown.

[0044] The method for preparing hafnium foil for vacuum electronic devices of the present invention uses metallic hafnium (Hf+Zr≥99.5%, Zr≤0.9%) with a purity ≥99.5% as the main raw material, hafnium wire (Hf+Zr≥99.9%, Zr≤0.9%) with a purity ≥99.9% and elemental iodine with a purity ≥99.5% as auxiliary raw materials. The process involves iodization purification, electron beam melting, hot forging, cross-hot rolling, and cross-cold rolling to obtain a foil blank. Finally, vacuum stress-relief annealing and cutting inspection are performed to obtain a high-performance hafnium foil material for vacuum electronic devices with high purity and dimensional accuracy, near isotropic properties, strong-plasticity matching, and good molding performance. Specific steps include:

[0045] (1) Iodination purification: After being cleaned and dried, the metallic hafnium raw material is loaded into the raw material area of ​​a specially designed iodination purification reactor. Metallic hafnium wires are arranged in specific areas of the reactor as the master wire for hafnium deposition, and elemental iodine is used as the reaction medium. In a vacuum within a range of 300℃ to 500℃, the surface of metallic hafnium raw material is activated, and interstitial impurity elements are initially removed. Subsequently, the vacuum system is cut off, allowing gaseous elemental iodine to selectively synthesize with the target metal on the raw material in the low-temperature region of 300℃ to 500℃, and to undergo selective decomposition and deposition reaction on the mother wire in the high-temperature region of 1300℃ to 1500℃, to obtain low-impurity hafnium crystal rods.

[0046] (2) Electron beam melting: under a vacuum degree not lower than Under the condition of an initial electron gun power of 60kW~70kW, the hafnium crystal rod is melted, dripped and solidified on the hafnium bottom ingot below by bombardment with a high-energy electron beam to obtain a high-purity metal hafnium ingot; the hafnium ingot is repeatedly smelted 1~2 times as needed to ensure the uniformity of composition and structure.

[0047] (3) Hot forging: After heating the hafnium ingot to 850℃~950℃, take it out and place it under the forging machine for multi-directional forging. Forge along the first, second and third directions of the hafnium ingot (the first direction is the solidification axis of the hafnium ingot, and the three are perpendicular to each other). The single-pass reduction should not exceed 25%~35%, and the final forging temperature should not be lower than 550℃~650℃. If necessary, it can be heated again and the above forging process can be repeated once.

[0048] (4) Cross-hot rolling:

[0049] After forging, the hafnium billet is cut into 20mm~30mm slabs in the thickness direction;

[0050] ① 1 heat 3~4 passes: The slab is preheated to 850℃~900℃, and the rolls are preheated to 400℃~500℃. Hot rolling is carried out to widen the slab along the width direction. The total processing deformation in this step is 60%~73%, and the thickness is reduced to about 8mm.

[0051] ② 1~2 heats and 4~6 passes: The slab is heated to 800℃~850℃, and rolled after a 90° reversal. The reversal can be performed once every 2~3 passes of subsequent rolling. The total processing deformation in this step is about 75%, and the thickness is reduced to about 2mm.

[0052] ③ 1 heat 3~4 passes: The slab is preheated to 750℃~800℃, rolled after 90° reversal, and subsequent reversals can be made as needed; the total processing deformation in this step is about 60%, and the thickness is reduced to about 0.8mm;

[0053] ④ 1 heat, 2 passes: Raise the temperature to above 700℃~750℃. The direction can be reversed as needed. The total processing deformation in this step is about 38%, and the thickness is reduced to about 0.5mm.

[0054] ⑤ Finishing: After each hot rolling, the hafnium slab is ground and trimmed as needed; as needed, defects such as indentations, residual oxide scale, and local micro-cracks on the surface of the hafnium sheet after hot rolling are ground and the hafnium semi-finished product is trimmed to a fixed size.

[0055] ⑥ Intermediate annealing: Intermediate annealing is required after each hot rolling process, at a temperature of 750℃~850℃ for 0.5h~2h, with a vacuum degree not lower than [missing value]. .

[0056] The hot rolling process ends when the hafnium plate thickness is rolled to about 0.5 mm, with a total deformation of about 97%; the process involves about 3 to 7 cross-directional changes.

[0057] (5) Cross-rolling: After a 90° reversal, a high-precision multi-roll mill with roll crowns of 4μm~10μm is used to roll the 0.5mm hafnium sheet semi-finished product sequentially to 0.3mm, 0.2mm, 0.15mm~0.10mm, 0.10mm~0.07mm, 0.07mm~0.05mm, 0.05mm~0.03mm, and 0.03mm~0.01mm, for a total of 3~7 passes; mineral oil lubricant can be used if necessary. The total deformation during the cold rolling process is about 70%~98%, and the cross-reversal occurs about once during the cold rolling process.

[0058] (6) Vacuum stress-relief annealing: After surface degreasing and cleaning, hafnium foil of semi-finished and finished product thicknesses is subjected to vacuum annealing treatment, with step heating to 500℃~1000℃ (staying in the low temperature zone for a longer time), holding at that temperature for 0.5h~1h, and the vacuum degree not lower than After cooling in the furnace, it is taken out of the furnace.

[0059] (7) Cutting inspection: The stress-relief annealed hafnium foil is cut to the final size and inspected to obtain high-performance hafnium foil material for vacuum electronic devices.

[0060] Example 1

[0061] Hafnium feedstock with a purity of 99.73% was cleaned and dried before being loaded into the feed section of the iodination purification reactor. Hafnium wire with a purity of 99.92% was arranged as the hafnium deposition master wire, and elemental iodine with a purity of 99.65% was used as the reaction medium. Surface activation of metallic hafnium raw materials was performed under vacuum and a temperature gradient of 300℃~500℃. Subsequently, the vacuum system was disconnected, allowing gaseous elemental iodine to selectively synthesize with the target metal on the raw material in the 500℃ low-temperature region, followed by selective decomposition and deposition on a mother wire in the 1400℃ high-temperature region to obtain low-impurity hafnium crystal rods. Under vacuum conditions and an initial electron gun power of 70kW, high-purity hafnium ingots were obtained by electron beam melting of hafnium crystal rods. The hafnium ingots were heated to 950℃ and then subjected to multi-directional forging along the first, second, and third directions, with a single-pass reduction of 30% and a final forging temperature not lower than 550℃. The forged hafnium billets were then cut into 30mm slabs in the thickness direction and preheated to 900℃. The rolls were preheated to 500℃, and the slabs were then subjected to 1 pass along the width direction. The slab is first hot-rolled four times to widen the thickness to 8.0 mm; then preheated to 850°C, rolled six times after a 90° reversal, with a reversal every two passes, reducing the thickness to 2.0 mm; then preheated to 800°C, rolled four times after a 90° reversal, with a reversal every two passes, reducing the thickness to approximately 0.82 mm; finally, preheated to 750°C, rolled two times after a reversal, reducing the thickness to 0.52 mm. After each hot rolling pass, an intermediate annealing temperature of 850°C is maintained for 0.5 hours under vacuum. After surface grinding and edge trimming, the hafnium sheets are cut to a fixed size and annealed at 750℃ for 0.5 hours. Following a 90° reversal, the hafnium sheet semi-finished product is sequentially cold-rolled to 0.3mm, 0.2mm, 0.15mm, and 0.10mm using 4μm crown rolls, for a total of four cold rolling passes. Between each pass, a vacuum stress-relief annealing process is performed at 700℃ for 0.5 hours. The hafnium foil rolled to 0.10mm thickness is then degreased and cleaned, and then stepped up to 700℃. The material was subjected to stress-relief annealing for 0.5 hours and then cooled in the furnace before being removed from the furnace. The final product was a high-performance hafnium foil material for electro-vacuum devices with a (hafnium + zirconium) content of 99.96 wt% (including 0.7 wt% zirconium), a (oxygen + nitrogen + carbon) content of 180 ppm, a thickness of 0.10 mm, a dimensional tolerance of +3 μm, a transverse tensile strength of 650 MPa, a yield strength of 586 MPa, an elongation after fracture of 21%, and a rolling tensile strength of 606 MPa, a yield strength of 547 MPa, and an elongation after fracture of 25%. This material meets the requirements for grid processing and service.

[0062] A micrograph of the rolled section of the hafnium foil is shown below. Figure 2 , Figure 3 As shown. It can be seen that the microstructure ( Figure 2It has a layered fibrous structure, which is dominated by long, flat strip-shaped grains (accounting for 87.9%), with fine equiaxed grains distributed around its grain boundaries. Figure 3 ).

[0063] The typical texture component orientation imaging of this hafnium foil by electron backscatter diffraction (EBSD) is shown in the figure below. Figure 4 As shown, the main texture of this hafnium foil is <10-10> / / RD, and it contains a certain amount of <11-20> / / RD texture components; it also contains a small amount of... <0001> / / ND、 <0001> / / TD and other components.

[0064] Example 2

[0065] Hafnium feedstock with a purity ≥99.73% was cleaned and dried before being loaded into the feed section of the iodination purification reactor. Metallic hafnium wire with a purity of 99.92% was arranged as the hafnium deposition master wire, and elemental iodine with a purity of 99.65% was used as the reaction medium. Surface activation of metallic hafnium raw materials was performed under vacuum and a temperature gradient of 300℃~500℃. Subsequently, the vacuum system was shut off, allowing gaseous elemental iodine to selectively synthesize with the target metal on the raw material in the 300℃ low-temperature region, followed by selective decomposition and deposition on a mother wire in the 1300℃ high-temperature region to obtain low-impurity hafnium crystal rods. Under vacuum conditions and an initial electron gun power of 60kW, high-purity hafnium ingots were obtained by electron beam melting of hafnium crystal rods. The hafnium ingots were heated to 850℃ and then subjected to multi-directional forging along the first, second, and third directions, with a single-pass reduction of 25% and a final forging temperature not lower than 650℃. The forged hafnium billets were then cut into 30mm slabs in the thickness direction and preheated to 850℃. The rolls were preheated to 400℃, and the slabs were then subjected to 1 pass along the width direction. The slab is first hot-rolled four times to widen the thickness to 8.2 mm; then preheated to 800℃, rolled six times after a 90° reversal, with a reversal every three passes, reducing the thickness to 2.3 mm; then preheated to 750℃, rolled five times after a 90° reversal, with a reversal every two passes, reducing the thickness to approximately 0.75 mm; finally preheated to 700℃, rolled two times after a reversal, reducing the thickness to 0.49 mm. After each hot rolling pass, an intermediate annealing temperature of 750℃ is maintained for 2 hours under vacuum. After surface grinding and edge trimming, the hafnium sheets are cut to a fixed size and annealed at 750℃ for 0.5 hours. Following a 90° reversal, the hafnium sheet semi-finished product is sequentially cold-rolled to 0.3mm, 0.2mm, 0.13mm, 0.08mm, 0.05mm, and 0.03mm using 10μm crown rolls, for a total of 6 cold rolling cycles. Between these cycles, a vacuum stress-relief annealing process is performed at 500℃ for 1 hour. The hafnium foil rolled to 0.03mm thickness is then degreased and cleaned, and then stepped up to 500℃. The material was subjected to stress-relief annealing for 1 hour, followed by furnace cooling before being removed from the furnace. The final product was a high-performance hafnium foil material for electro-vacuum devices with an oxygen + nitrogen + carbon content of 60 ppm, a thickness of 0.03 mm, a dimensional tolerance of +2 μm, a transverse tensile strength of 586 MPa, a yield strength of 542 MPa, and an elongation after fracture of 32%, and a longitudinal tensile strength of 535 MPa, a yield strength of 497 MPa, and an elongation after fracture of 36%.

[0066] Example 3

[0067] Hafnium feedstock with a purity ≥ 99.57% was cleaned and dried before being loaded into the feed section of the iodination purification reactor. Metallic hafnium wire with a purity of 99.92% was arranged as the hafnium deposition master wire, and elemental iodine with a purity of 99.53% was used as the reaction medium. Surface activation of metallic hafnium raw materials was performed under vacuum and a temperature gradient of 300℃~500℃. Subsequently, the vacuum system was disconnected, allowing gaseous elemental iodine to selectively synthesize with the target metal on the raw material in the 500℃ low-temperature region, followed by selective decomposition and deposition on a mother wire in the 1500℃ high-temperature region to obtain low-impurity hafnium crystal rods. Under vacuum conditions and an initial electron gun power of 70kW, high-purity hafnium ingots were obtained by electron beam melting of hafnium crystal rods. The hafnium ingots were heated to 950℃ and then subjected to multi-directional forging along the first, second, and third directions, with a single-pass reduction of 35% and a final forging temperature not lower than 650℃. The forged hafnium billets were then cut into 30mm slabs in the thickness direction and preheated to 900℃. The rolls were preheated to 500℃, and the slabs were then subjected to 1 pass along the width direction. The slab is first hot-rolled four times to widen the thickness to 8.1 mm; then preheated to 850°C, rolled six times after a 90° reversal, with a reversal every three passes, reducing the thickness to 2.1 mm; then preheated to 800°C, rolled four times after a 90° reversal, with a reversal every two passes, reducing the thickness to approximately 0.73 mm; finally, preheated to 750°C, rolled two times after a reversal, reducing the thickness to 0.47 mm. After each hot rolling pass, an intermediate annealing temperature of 800°C is maintained for 1.5 hours under vacuum. After surface grinding and edge trimming, the hafnium sheets are cut to a fixed size and annealed at 800℃ for 0.5 hours. Following a 90° reversal, the hafnium sheet semi-finished product is sequentially cold-rolled to 0.3mm, 0.2mm, 0.13mm, 0.08mm, 0.05mm, 0.03mm, and 0.01mm using 6μm crown rolls, for a total of 7 cold rolling cycles. Between these cycles, a vacuum stress-relief annealing process is performed at 500℃ for 0.5 hours. The hafnium foil rolled to 0.01mm thickness is then degreased and cleaned, and then stepped up to 500℃. The material was subjected to stress-reducing annealing for 0.5 hours and then cooled in the furnace before being removed from the furnace. The final product was a high-performance hafnium foil material for electro-vacuum devices with an oxygen + nitrogen + carbon content of 100 ppm, a thickness of 0.01 mm, a dimensional tolerance of +2 μm, a rolling tensile strength of 508 MPa, a yield strength of 425 MPa, and an elongation after fracture of 16%, and a transverse tensile strength of 453 MPa, a yield strength of 371 MPa, and an elongation after fracture of 18%.

[0068] Comparative Example 1

[0069] Hafnium foil with a thickness of 0.10 mm was prepared using commercially available hafnium ingots of ordinary purity as raw material through multi-directional hot forging, slab slitting, and cross-hot / cold rolling processes. Except for the raw material used, which differed from Example 1, all other processes were the same as in Example 1. During the deformation process, cracking and tearing occurred, making it impossible to prepare hafnium foil with a thickness of 0.10 mm.

[0070] Comparative Example 2

[0071] Using 99.73% pure metallic hafnium as the main raw material, and 99.92% pure hafnium wire and 99.65% pure elemental iodine as auxiliary raw materials, hafnium ingots were obtained through iodination purification and electron beam melting. Then, conventional hot forging and unidirectional 850℃ hot forging were employed. A unidirectional hot rolling / cold rolling process was used, namely hot rolling at 750℃~900℃ and cold rolling in four passes. Except for the hot forging and rolling processes used, which differed from Example 1, the process was identical to Example 1. The final product was a hafnium foil material with a thickness of 0.10mm, a dimensional tolerance of +4μm, a transverse tensile strength of 636MPa, a yield strength of 575MPa, and an elongation at break of 5%, and a rolling tensile strength of 502MPa, a yield strength of 433MPa, and an elongation at break of 8%. However, during hydroforming, cracking occurred at the root of the spherical cap, failing to meet the requirements for grid processing.

Claims

1. A hafnium foil for an electrovacuum device, characterized in that: The hafnium foil has a main content of hafnium + zirconium ≥ 99.9 wt%, of which zirconium ≤ 0.9 wt%, and an interstitial impurity content of oxygen + nitrogen + carbon ≤ 200 ppm; Thickness ranges from 0.01mm to 0.15mm, with dimensional tolerances ≤ ±5μm; Tensile strength ≥450MPa, yield strength ≥300MPa, elongation after fracture ≥15%; The difference in tensile strength between the longitudinal and transverse directions shall not exceed 10%; The main texture is <10-10> / / RD, and it contains <11-20> / / RD texture components; The microstructure consists of flattened fibrous grains, or flattened fibrous grains and fine equiaxed grains are uniformly interwoven, with the area of ​​flattened fibrous grains accounting for ≥60%, or the area of ​​equiaxed grains accounting for ≥60%.

2. A method for preparing hafnium foil for an electrovacuum device as described in claim 1, characterized in that, Includes the following steps: (1) Hafnium ingot purification: Hafnium metal raw materials are purified by surface activation and iodination to obtain low-impurity hafnium crystal rods; (2) Electron beam melting: The crystal rod obtained by iodization purification is melted under the bombardment of high-energy electron beam to obtain high-purity metal hafnium ingot; (3) Hot forging: High-purity metal hafnium ingots are forged in multiple directions at a forging temperature of 850℃~950℃; (4) Cross hot rolling: The hafnium billet after forging is hot rolled in multiple passes and multiple directions; after hot rolling, it is vacuum intermediate annealed; (5) Cross-cold rolling: The hot-rolled hafnium sheets are cold-rolled in multiple passes with a 90° reversal to obtain hafnium foil of the required thickness; (6) Stress-relief annealing: The cold-rolled hafnium foil is subjected to stress-relief annealing under vacuum conditions; (7) Cutting inspection: The stress-relief annealed hafnium foil is cut to the final size and inspected to obtain hafnium foil for vacuum electronic devices.

3. The preparation method according to claim 2, characterized in that, In step (1), the main content of the metal hafnium raw material is hafnium + zirconium ≥ 99.5 wt%; the purity of the hafnium wire used for iodization purification is ≥ 99.9%, and the purity of iodine is ≥ 99.5%.

4. The preparation method according to claim 2, characterized in that, In step (1), the surface activation conditions are as follows: The vacuum level and temperature gradient of 300℃~500℃; the iodination purification conditions are to cut off the vacuum system, selective synthesis temperature of 300℃~500℃, and selective decomposition deposition temperature of 1300℃~1500℃.

5. The preparation method according to claim 2, characterized in that, In step (2), the vacuum degree of electron beam melting The electron gun power is 60~70kW.

6. The preparation method according to claim 2, characterized in that, In step (3), the final forging temperature is 550℃~650℃; the multi-directional forging is alternating forging along three mutually perpendicular directions, and the single-pass reduction is 25%~35%.

7. The preparation method according to claim 2, characterized in that, In step (4), the total deformation of the cross-hot rolling is 95%~99%, and the number of reversals is 3~7; the vacuum intermediate annealing temperature is 750~850℃, the holding time is 0.5~2h, and the vacuum degree is... .

8. The preparation method according to claim 2, characterized in that, In step (5), a high-precision multi-roll mill is used for cold rolling, with roll crown of 4~10μm and total deformation of 70%~98%.

9. The preparation method according to claim 2, characterized in that, In step (6), the stress-relief annealing temperature is 500~1000℃, the holding time is 0.5~1h, and the vacuum degree is... A stepped heating method is adopted.

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