Specially oriented tungsten single crystal bar and preparation method thereof

Abstract

The invention discloses a specific orientation tungsten single crystal bar and a preparation method thereof, and belongs to the technical field of refractory metal single crystal preparation. In order to solve the problems that tungsten is high in melting point and crystal orientation is difficult to control, the method utilizes an electron beam floating zone melting technology and adopts a seed crystal method to prepare the tungsten single crystal. In the preparation process, the distance between a tungsten polycrystalline bar and a tungsten single crystal seed crystal is strictly controlled to be 1-1.5 mm while it is guaranteed that the coaxiality of the tungsten polycrystalline bar and the tungsten single crystal seed crystal is high; after a tungsten polycrystalline bar and a tungsten single crystal seed bar are welded, the center of an electronic gun is moved to the tungsten single crystal seed bar 10 mm below the welding position, the electronic gun is moved from bottom to top, and therefore the tungsten single crystal bar with the specific orientation is obtained. The preparation method is high in efficiency, easy to operate and high in repeatability, the prepared tungsten single crystal bar is uniform in size, specific in orientation and smooth and uniform in surface, and the crystal orientation of the tungsten single crystal and the crystal orientation of the single crystal seed crystal are basically consistent.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractory metal single crystal preparation, and particularly relates to a tungsten single crystal rod with a specific orientation and a preparation method thereof. Background Art

[0002] Tungsten has characteristics such as a high melting point, high density, strong anti-neutron radiation ability, good electrical conductivity and thermal conductivity, and strong resistance to acid and alkali erosion, and its chemical properties are stable. Therefore, tungsten is widely used in fields such as aerospace, nuclear industry, electronic information, and power machinery. Among them, tungsten single crystal is a high-tech new material with advantages such as no grain boundaries, a low ductile-brittle transition temperature, and high thermal-work conversion efficiency. Tungsten single crystals with specific orientations have important applications in the electronic field. For example, <001>-oriented tungsten single crystals are used for tungsten filaments in thermal field emission scanning electron microscopes, and <310>-oriented tungsten single crystals are used for tungsten filaments in cold field emission scanning electron microscopes. At present, the preparation of tungsten single crystals with specific orientations used in scanning electron microscopes mainly relies on developed countries, so it is necessary to independently develop technologies for preparing tungsten single crystals with specific orientations.

[0003] For the preparation of tungsten single crystals, due to its high melting point and great preparation difficulty, traditional melting methods cannot be used, and only methods such as crucible-free floating zone melting, plasma arc melting, and annealing and recrystallization can be used. The crucible-free floating zone melting method mainly includes electron beam floating zone melting, plasma arc induction zone melting, and optical floating zone melting. Among them, electron beam floating zone melting is a better method for preparing high-purity refractory metal single crystals.

[0004] The key to preparing refractory metal single crystals by electron beam floating zone melting lies in ensuring the stability of its molten zone. Tungsten has a high coefficient of thermal expansion, and during the melting process, the rod is prone to bending due to the thermal expansion of the material, resulting in poor straightness of the specimen and increasing the orientation deviation of the single crystal. In addition, when preparing tungsten single crystals by the method of free crystal selection, the crystal orientation is random, so it is necessary to conduct multiple experiments to prepare tungsten single crystals with specific orientations. Therefore, there is currently a lack of a suitable method for preparing tungsten single crystals with specific orientations. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned disadvantages of the prior art and provide a method for preparing a tungsten single crystal rod with a specific orientation to solve the problem of the lack of a suitable method for preparing tungsten single crystals with specific orientations in the prior art.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: A method for preparing a tungsten single crystal rod with a specific orientation, comprising the following steps: Step 1, obtaining a tungsten polycrystalline rod and a tungsten single crystal seed rod with a specific orientation, wherein the crystal orientation of the tungsten single crystal seed rod with a specific orientation is <001> or <310>; Step 2: The upper chuck of the electron beam floating zone furnace clamps the tungsten polycrystalline rod, and the lower chuck clamps the tungsten single crystal seed rod. The distance between the lower end of the tungsten polycrystalline rod and the upper end of the tungsten single crystal seed rod is 1 - 1.5 mm. Step 3: Evacuate the electron beam floating zone furnace to reach the target vacuum degree. Step 4: Apply the main high voltage of the electron beam to the electron beam floating zone furnace. The process of applying the main high voltage of the electron beam is divided into a first stage and a second stage. In the first stage, the main high voltage is applied from 0 KV to 10 KV, and in the second stage, the range of the applied main high voltage is 10 - 15 KV. During the interval between the first stage and the second stage, the annular electron gun is placed between the tungsten polycrystalline rod and the tungsten single crystal seed rod to complete the welding of the tungsten polycrystalline rod and the tungsten single crystal seed rod. Step 5: After welding, place the annular electron gun at the single crystal seed 10 mm below the welding point and apply the main high voltage. The tungsten single crystal seed rod melts. After the melting zone is stable, the annular electron gun moves upward to obtain a tungsten single crystal rod with a specific orientation grown by equal diameter zone melting.

[0007] A further improvement of the present invention lies in: Preferably, in Step 2, the coaxiality of the clamped tungsten polycrystalline rod and the clamped tungsten single crystal seed rod.

[0008] Preferably, in Step 3, the target vacuum degree is 6×10 -3 Pa.

[0009] Preferably, in Step 4, before applying the main high voltage of the electron beam to the electron beam floating zone furnace, increase the filament current. When the filament current is stable at 90 A, apply the main high voltage of the electron beam.

[0010] Preferably, in Step 4, in the first stage, the main high voltage is applied from 0 KV to 10 KV, and stop for 1 min after increasing by 2 KV each time.

[0011] Preferably, in Step 4, the value of the applied main high voltage is adjusted according to the width of the melting zone.

[0012] Preferably, in Step 5, during the upward movement of the annular electron gun, the moving speed is 20 μm / s.

[0013] Preferably, after Step 5, slice, electrochemically polish the tungsten single crystal rod, and judge the crystal orientation.

[0014] Preferably, in Step 1, before clamping the tungsten polycrystalline rod and the tungsten single crystal seed rod with a specific orientation, cut the end face, and perform grinding and cleaning treatment on the end face.

[0015] A tungsten single crystal rod with a specific orientation prepared by any one of the above preparation methods, and the crystal orientation of the tungsten single crystal rod with a specific orientation is <001> or <310>.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for preparing a tungsten single crystal rod with a specific orientation. Aiming at the problems of high melting point and difficult control of crystal orientation of tungsten, the electron beam floating zone melting technology is used, and the tungsten single crystal is prepared by the seed crystal method. During the preparation process, while ensuring a high coaxiality between the tungsten polycrystalline rod and the tungsten single crystal seed crystal, the distance between the two is strictly controlled to be between 1 - 1.5 mm. After welding the tungsten polycrystalline rod and the tungsten single crystal seed crystal rod, the center of the electron gun is moved to the tungsten single crystal seed crystal rod 10 mm below the welding point, and the electron gun is moved upward from bottom to top, thereby obtaining a tungsten single crystal rod with a specific orientation. The preparation method of the present invention has high efficiency, simple operation, and strong repeatability. The prepared tungsten single crystal rod has uniform size, a specific orientation, a smooth and uniform surface, and the crystal orientations of the tungsten single crystal and the single crystal seed crystal are basically the same. Moreover, this preparation method can quickly and effectively prepare a tungsten single crystal with a specific orientation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a physical diagram of the tungsten single crystal rod prepared in Example 1 provided by the present invention. The positions of the red square and the green square are the slicing positions of the tungsten single crystal seed crystal and the tungsten single crystal prepared by the present invention during crystal orientation analysis, respectively.

[0018] Figure 2 It is the IPF-Z diagram, corresponding pole figure and inverse pole figure of the (001) orientation single crystal seed crystal used in Example 1 provided by the present invention; Among them, Figure (a) is the IPF-Z diagram, Figure (b) is the corresponding pole figure, and Figure (c) is the corresponding inverse pole figure Figure 3 It is the IPF-Z diagram, corresponding pole figure and inverse pole figure of the tungsten single crystal prepared by the seed crystal method using the (001) orientation single crystal in Example 1 provided by the present invention; Among them, Figure (a) is the IPF-Z diagram, Figure (b) is the corresponding pole figure, and Figure (c) is the corresponding inverse pole figure Figure 4 It is the IPF-Z diagram, corresponding pole figure and inverse pole figure of the (310) orientation single crystal seed crystal used in Example 2 provided by the present invention; Among them, Figure (a) is the IPF-Z diagram, Figure (b) is the corresponding pole figure, and Figure (c) is the corresponding inverse pole figure Figure 5 It is the IPF-Z diagram, corresponding pole figure and inverse pole figure of the tungsten single crystal prepared by the seed crystal method using the (310) orientation single crystal in Example 2 provided by the present invention; Among them, Figure (a) is the IPF-Z diagram, Figure (b) is the corresponding pole figure, and Figure (c) is the corresponding inverse pole figure Figure 6Photographs of the welded bars in Comparative Examples 1 and 2 provided by the present invention; Among them, figure (a) is Comparative Example 1; figure (b) is Comparative Example 2.

[0019] Figure 7 Photograph of the stable melting zone provided by the present invention. Detailed Description of the Invention

[0020] The present invention will be further described in detail below with reference to the accompanying drawings: To enable those skilled in the art to understand the features and effects of the present invention, the following provides a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art for the present invention. In case of conflict, the definition in this specification shall prevail.

[0021] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar expressions encompass the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" encompasses the meanings of "A comprises a and others" and "A consists only of a".

[0022] The present invention will be further illustrated with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0023] Conventional instrument and equipment in the art are used in the following embodiments. The experimental methods without specific conditions noted in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratios represent weight ratios.

[0024] In view of the high melting point, high density, and difficult orientation control of tungsten, the present invention discloses a method for preparing tungsten single crystal bars with a specific orientation. Tungsten single crystal bars with a diameter of about 4 mm and a crystal orientation of <001> or <310> are prepared by the electron beam floating zone melting technique using the seed crystal method. At the same time, the orientation of the tungsten single crystal prepared by the seed crystal method is basically the same as that of the original single crystal seed crystal.

[0025] Specifically, the method for preparing tungsten single crystal bars with a specific orientation includes the following steps: Step 1: Polish and clean the surfaces and cut ends of the tungsten polycrystalline rod and the tungsten single crystal seed rod with a specific orientation. The diameters of both the tungsten polycrystalline rod and the tungsten single crystal seed rod are 4 mm, and the sample rods are required to have good straightness.

[0026] Step 2: Clamp the tungsten polycrystalline rod in Step 1 on the upper chuck in the chamber of the electron beam floating zone furnace, and install the tungsten single crystal seed rod on the lower chuck in the chamber. During the clamping process, ensure the coaxiality between the tungsten polycrystalline rod and the tungsten single crystal seed rod, and at the same time control the distance between the two within 1 - 1.5 mm. By controlling the distance between the two within this range, the growth orientation can be ensured to be consistent with the original orientation.

[0027] In this process, the tungsten polycrystalline rod and the tungsten single crystal seed rod with a specific orientation are respectively installed on the upper chuck and the lower chuck of the zone furnace. By rotating the upper and lower chucks, the coaxiality between the tungsten polycrystalline rod and the tungsten single crystal seed rod is ensured, so that the orientation of the tungsten single crystal seed has good inheritance.

[0028] Step 3: Close the furnace door of the electron beam floating zone furnace, turn on the equipment circulating water, and turn on the mechanical pump to pre-pump the vacuum. When the vacuum degree is higher than 1.0 Pa, turn on the molecular pump to further pump the vacuum. When the vacuum degree is higher than 6×10 -3 Pa, the required vacuum degree for melting is reached, and the mechanical pump and the molecular pump are ensured to run continuously during the melting process.

[0029] Step 4: Apply the filament current and the main high voltage. Slowly increase the filament current. When the filament current is increased to 70 A, wait for 2 minutes to complete the preheating of the filament, and then slowly increase the current to 90 A. When the filament current is stable at about 90 A, start to apply the main high voltage of the electron beam. The application of the main high voltage is divided into two stages. In the first stage, the main high voltage is increased from 0 KV to 10 KV in a stepped pressure application method, that is, after increasing the voltage value by 2 KV each time, stop for 1 min to stabilize the power of the equipment and at the same time play a role in preheating the material; when the main high voltage value reaches 10 KV, start the second stage of pressure application. There is no specific application standard in the second stage of pressure application, which needs to be based on the specific situation of the melting zone. The value of the main high voltage is between 10 - 15 KV.

[0030] Before applying the high voltage in the above-mentioned second stage, move the annular electron gun to the middle position between the tungsten polycrystalline rod and the tungsten single crystal seed rod, and then control the size of the electron beam power by adjusting the main high voltage. When the tungsten polycrystalline rod and the tungsten single crystal seed rod are melted and combined, the welding process is completed. During the welding process, the vacuum degree in the chamber of the electron beam floating zone furnace is at 6×10 -3 Pa.

[0031] During this process, there is no specific application standard for the second pressurization process, which depends on the specific situation of the melting zone. The main high voltage value is between 10 - 15 KV. If the main high voltage is too large, the width of the melting zone becomes smaller, and the melting zone is prone to collapse during the zone melting process, and the rod breaks from the melting zone. If the main high voltage is too small, there are unmelted solid phases in the material, and single crystals cannot be prepared.

[0032] Step 5, after the welding process, move the annular electron gun to a position about 10 mm below the welding joint of the tungsten polycrystalline rod and the tungsten single crystal seed rod at the single crystal seed position. By controlling the value of the main high voltage, melt the tungsten single crystal seed rod. After the melting zone is stable, move the electron gun automatically from bottom to top at a speed of 20 μm / s. It should be noted that, as Figure 7 shown, when the upper and lower rods are connected and necking occurs in the melting zone, and the width of the melting zone remains basically unchanged, the melting zone is considered stable. During the zone melting process, the melting zone is kept stable by regulating the electron beam power, so as to obtain a tungsten single crystal rod with equal diameter zone melting growth.

[0033] During the above process, move the electron gun to a position about 10 mm below the welding joint at the single crystal seed position, and then move the electron gun from bottom to top. If the distance is less than 10 mm, during the upward movement of the electron gun, it is easy for the orientation inheritance of the prepared tungsten single crystal to be poor due to the instability of the melting zone, or the single crystal preparation may fail.

[0034] Step 6, slice the tungsten single crystal seed and the tungsten single crystal prepared by the seed method. Grind the cut sample thin slice with diamond sandpaper, and then electro-polish it to ensure that the surface of the sample is smooth and has no scratches. Conduct electron backscatter diffraction analysis on the electro-polished sample, and compare and analyze the crystal orientation of the tungsten single crystal prepared by the seed method with the crystal orientation of the original single crystal seed.

[0035] Among them, the electro-polishing parameters are: the polishing solution is a solution of H 2 O : NaOH = 98 : 2 (wt. %), the voltage is 20 V, the polishing time is 50 s, and the temperature is 25 - 30 °C.

[0036] A tungsten single crystal with a specific orientation is prepared by the above method. The crystal orientation of the tungsten single crystal rod prepared by the seed method is basically the same as that of the original single crystal seed, and the crystal orientation has good inheritance. The crystal orientations are <001> and <310>. The orientation accuracy of the prepared single crystal is well verified by the results of EBSD. At the same time, the surface of the tungsten single crystal rod is smooth and uniform, and the straightness is good.

[0037] The key control points of the above method for preparing a tungsten single crystal with a specific orientation are: 1. In the method of the present invention, it is proposed to ensure the coaxiality between the tungsten polycrystalline rod and the tungsten single crystal seed crystal. If the coaxiality between the two is not precise enough, the two rods are likely to be misaligned during the welding process, thus affecting the orientation accuracy of the tungsten single crystal.

[0038] 2. In the method of the present invention, it is proposed to control the distance between the tungsten polycrystalline rod and the tungsten single crystal seed crystal to be 1 - 1.5 mm. Too large or too small a distance will affect the orientation accuracy of the single crystal. If the distance between the two is too small during the welding process, as the electron beam power increases, the temperature of the rod rises, and thermal expansion will cause the rod to be extruded and bent, affecting the straightness of the rod, and at the same time affecting the precision of the single crystal orientation. If the distance between the two is too large during the welding process, the rod is likely to collapse after melting, thus affecting the surface quality and smoothness of the rod. When the distance between the two is controlled between 1 - 1.5 mm, the surface of the prepared single crystal is smooth and the straightness is good.

[0039] 3. In the method of the present invention, there is no specific application standard for the second-stage pressurization process, which needs to be based on the specific situation of the melting zone, and the main high-voltage value is between 10 - 15 KV. If the main high voltage is too large, the width of the melting zone becomes smaller, and the melting zone is likely to collapse during the zone melting process, and the rod breaks from the melting zone. If the main high voltage is too small, the width of the melting zone becomes larger, resulting in unmelted solid phase in the melting zone, and a single crystal cannot be prepared.

[0040] 4. In the method of the present invention, it is proposed to move the electron gun to a position about 10 mm below the welding point at the position of the single crystal seed crystal, and then move the electron gun from bottom to top to ensure that the prepared single crystal has good seed crystal orientation inheritance. If the distance is less than 10 mm, during the upward movement of the electron gun, the orientation inheritance of the prepared tungsten single crystal is likely to be poor due to the instability of the melting zone, or the single crystal preparation may fail.

[0041] The following will describe the present invention in detail with specific embodiments.

[0042] Example 1 Step 1: Grind and clean the surfaces of the tungsten polycrystalline rod and the (001)-oriented tungsten single crystal seed crystal rod. The diameter of the tungsten polycrystalline rod is 4 mm and the length is 400 mm. The size of the tungsten single crystal seed crystal rod is a diameter of 4 mm and a length of 200 mm. Grind the surfaces of the tungsten polycrystalline rod and the tungsten single crystal seed crystal rod successively with sandpapers of 400 mesh, 600 mesh, 800 mesh, 1200 mesh, 1500 mesh, and 2000 mesh, and then clean the surface with alcohol and dry it for standby.

[0043] Step 2, sample installation. The polished and cleaned tungsten polycrystalline rod and tungsten single crystal seed rod are respectively installed on the upper chuck and the lower chuck in the furnace chamber. Since mechanical errors are inevitably introduced between the chuck and the rod during the installation process, the coaxiality between the tungsten polycrystalline rod and the tungsten single crystal seed rod is strictly controlled by rotating the upper and lower chucks. Then, the distance between the tungsten polycrystalline rod and the tungsten single crystal seed rod is made 1.2 mm by moving the upper and lower chucks. Because as the temperature rises, the tungsten polycrystalline rod and the tungsten single crystal seed will expand, and by controlling the distance between them, the bending of the rod caused by the thermal expansion of the material can be well avoided.

[0044] Step 3, evacuation. Close the furnace door of the electron beam floating zone melting furnace, turn on the equipment cooling circulating water, and turn on the mechanical pump for evacuation. When the vacuum degree is higher than 1.0 Pa, turn on the molecular pump for further evacuation. When the vacuum degree is higher than 6×10 -3 Pa, the required vacuum degree for melting is reached, and the mechanical pump and the molecular pump are ensured to be running during the melting process.

[0045] Step 4, applying filament current. After the vacuum degree is higher than 6×10 -3 Pa, start applying filament current and increase the current slowly. When the filament current reaches 70 A, wait for 2 minutes for the filament to complete the preheating process, and then increase the filament current to 90 A. After the filament current stabilizes at 90 A, the main high voltage can be applied.

[0046] Step 5, applying main high voltage. The electron gun is a ring-shaped electron gun. Move the center of the electron gun between the tungsten polycrystalline rod and the tungsten single crystal seed rod, and then start applying the main high voltage. The application of the main high voltage is divided into two steps. In the first step, it adopts a stepped increase mode, starting from 0 KV, increasing by 2 KV each time and stopping for 1 min. When the main high voltage reaches 10 KV. Start the second step of applying the main high voltage. The value of the main high voltage is between 10 - 15 KV, and the specific value needs to be adjusted according to the melting zone state during the melting process.

[0047] Step 6, rod welding. Before the degassing treatment, confirm the distance between the tungsten polycrystalline rod and the tungsten single crystal seed rod, and ensure that the center of the electron gun is at the middle gap position between the two rods. Gradually reduce the distance between the two rods by adjusting the magnitude of the main high voltage until the tungsten polycrystalline rod and the tungsten single crystal seed rod are melted and connected together, at which time the rod welding is completed. During the entire rod welding process, the vacuum degree inside the electron beam floating zone melting furnace is ensured to be higher than 6×10 -3 Pa.

[0048] Step 7, single crystal preparation. After the rod welding is completed, move the center of the electron gun to 10 mm below the welding joint of the tungsten polycrystalline rod and the tungsten single crystal seed rod on the tungsten single crystal seed, and then adjust the magnitude of the main high voltage to generate a stable melting zone in the tungsten single crystal seed rod. At this time, move the electron gun upward at a rate of 20 μm / s. During the smelting process, control the power of the electron beam to keep the melting zone stable. The surface of the smelted single crystal rod is smooth and uniform in thickness, as Figure 1 shown. The main process parameters during the zone melting process are: the main high voltage is 10.10 - 13.40 KV, the electron beam current is 0.09 - 0.15 A, the electron beam power is 1.00 - 1.17 KW, the filament voltage is 6.08 V, and the filament current is 90.54 A.

[0049] Step 8, sample detection. Cut the original tungsten single crystal seed rod and the tungsten single crystal rod prepared by the seed method (such as Figure 1 the green and red boxes in), and grind the sample slices with a thickness of about 2 mm in turn using 400#, 600#, 800#, 1200#, 1500#, 2000# diamond sandpaper, and then perform mechanical polishing with 3.5 - grit polishing paste until there are no obvious scratches on the surface. Prepare an electrolyte of H 2 O : NaOH = 98 : 2 (wt. %), and perform electrolytic polishing on the mechanically polished sample. The voltage is 20 V, the polishing time is 50 s, and the polishing temperature is 25°C. Perform EBSD analysis on the electrolytically polished single crystal seed and the tungsten single crystal prepared by the seed method. From Figure 2 and Figure 3 the results, it can be seen that the orientation of the tungsten single crystal prepared by the seed method is basically the same as that of the original (001) - oriented tungsten single crystal seed.

[0050] Example 2 Step 1, polish and clean the surfaces of the tungsten polycrystalline rod and the (310) - oriented tungsten single crystal seed rod. The diameter of the tungsten polycrystalline rod is 4 mm and the length is 400 mm. The size of the tungsten single crystal seed is a diameter of 4 mm and a length of 200 mm. Polish the surfaces of the tungsten polycrystalline rod and the tungsten single crystal seed rod in turn using 400 - mesh, 600 - mesh, 800 - mesh, 1200 - mesh, 1500 - mesh, 2000 - mesh sandpaper, and then clean the surface with alcohol and dry it for standby.

[0051] Step 2, sample installation. The polished and cleaned tungsten polycrystalline bar and tungsten single crystal seed bar are respectively installed on the upper chuck and the lower chuck in the furnace chamber. Since mechanical errors are inevitably introduced between the chuck and the bar during the installation process, the coaxiality between the tungsten polycrystalline bar and the tungsten single crystal seed bar is strictly controlled by rotating the upper and lower chucks. Then, the distance between the tungsten polycrystalline bar and the tungsten single crystal seed bar is set to 1.4 mm by moving the upper and lower chucks. Because the tungsten polycrystalline bar and the tungsten single crystal seed will expand as the temperature rises, controlling the distance between them can well avoid the bending of the bars caused by thermal expansion of the materials.

[0052] Step 3, evacuation. Close the furnace door of the electron beam floating zone melting furnace, turn on the equipment cooling circulating water, and start the mechanical pump for evacuation. When the vacuum degree is higher than 1.0 Pa, turn on the molecular pump for further evacuation. When the vacuum degree is higher than 6×10 -3 Pa, the required vacuum degree for melting is reached, and the mechanical pump and the molecular pump are ensured to be running during the melting process.

[0053] Step 4, applying filament current. After the vacuum degree is higher than 6×10 -3 Pa, start applying filament current and increase the current slowly. When the filament current reaches 70 A, wait for 2 minutes for the filament to complete the preheating process, and then increase the filament current to 90 A. After the filament current stabilizes at 90 A, the main high voltage can be applied.

[0054] Step 5, applying main high voltage. The electron gun is a ring-shaped electron gun. Move the center of the electron gun between the tungsten polycrystalline bar and the tungsten single crystal seed bar, and then start applying the main high voltage. The application of the main high voltage is divided into two steps. In the first step, it adopts a stepped increase mode, starting from 0 KV, increasing by 2 KV each time and stopping for 1 min. When the main high voltage reaches 10 KV, start the second step of applying the main high voltage. The value of the main high voltage is between 10 - 15 KV, and the specific value needs to be adjusted according to the melting zone state during the melting process.

[0055] Step 6, bar welding. Before the degassing treatment, confirm the distance between the tungsten polycrystalline bar and the tungsten single crystal seed bar, and ensure that the center of the electron gun is at the middle gap position between the two bars. Gradually reduce the distance between the two bars by adjusting the magnitude of the main high voltage until the tungsten polycrystalline bar and the tungsten single crystal seed bar are melted and connected together, at which point the bar welding is completed. During the entire bar welding process, the vacuum degree in the electron beam floating zone melting furnace is ensured to be higher than 6×10 -3 Pa.

[0056] Step 7, single crystal preparation. After the rod welding is completed, move the center of the electron gun to 10 mm below the welding joint of the tungsten polycrystalline rod and the tungsten single crystal seed rod on the tungsten single crystal seed. Then, adjust the magnitude of the main high voltage to generate a stable melting zone in the tungsten single crystal seed rod. At this time, move the electron gun upward at a rate of 20 μm / s. During the melting process, control the power of the electron beam to keep the melting zone stable. The obtained single crystal sample has a smooth surface and uniform thickness. The main process parameters during zone melting are: the main high voltage is 10.00 - 13.30 KV, the electron beam current is 0.10 - 0.15 A, the electron beam power is 1.00 - 1.35 KW, the filament voltage is 6.11 V, and the filament current is 90.85 A.

[0057] Step 8, sample detection. Cut the original tungsten single crystal seed rod and the tungsten single crystal rod prepared by the seed method. Grind the sample thin slices with a thickness of about 2 mm successively using 400#, 600#, 800#, 1200#, 1500#, and 2000# diamond sandpapers, and then perform mechanical polishing using 3.5-grit polishing paste until there are no obvious scratches on the surface. Prepare an electrolyte with H 2 O:NaOH = 98:2 (wt. %), and perform electrolytic polishing on the mechanically polished sample at a voltage of 20 V for a polishing time of 50 s and a polishing temperature of 27 °C. Perform EBSD analysis on the electrolytically polished single crystal seed and the tungsten single crystal prepared by the seed method. From Figure 4 and Figure 5 the results, it can be seen that the orientation of the tungsten single crystal prepared by the seed method is basically the same as that of the original tungsten single crystal seed with a (310) orientation.

[0058] Comparative Example 1: The difference between this comparative example and Examples 1 and 2 is that the distance between the tungsten polycrystalline rod and the tungsten single crystal seed rod is 0.8 mm (less than 1 - 1.5 mm).

[0059] In this comparative example, the distance between the tungsten polycrystalline rod and the tungsten single crystal seed rod is too small. During the welding process, the rod bends due to the thermal expansion of the material, affecting the straightness of the rod, as shown in Figure 6 Figure (a), thus affecting the crystal orientation of the single crystal.

[0060] Comparative Example 2: The difference between this comparative example and Examples 1 and 2 is that the distance between the tungsten polycrystalline rod and the tungsten single crystal seed rod is 1.7 mm (greater than 1 - 1.5 mm).

[0061] In this comparative example, the distance between the tungsten polycrystalline rod and the tungsten single crystal seed rod is too large. During the welding process, the rod is prone to collapse after melting, as shown in Figure 6As shown in Figure (b), it affects the surface quality and smoothness of the bar, and further affects the preparation of single crystals and crystal orientation.

[0062] Example 3 Step 1: Grind and clean the surfaces of the tungsten polycrystalline bar and the (001)-oriented tungsten single crystal seed bar. The diameter of the tungsten polycrystalline bar is 4 mm and the length is 400 mm. The size of the tungsten single crystal seed bar is a diameter of 4 mm and a length of 200 mm. Grind the surfaces of the tungsten polycrystalline bar and the tungsten single crystal seed bar successively with sandpapers of 400 mesh, 600 mesh, 800 mesh, 1200 mesh, 1500 mesh, and 2000 mesh, and then clean the surface with alcohol and dry it for standby.

[0063] Step 2: Specimen installation. Install the surface-ground and cleaned tungsten polycrystalline bar and tungsten single crystal seed bar on the upper chuck and lower chuck in the furnace chamber respectively. Since mechanical errors will inevitably be introduced between the chuck and the bar during the installation process, the coaxiality between the tungsten polycrystalline bar and the tungsten single crystal seed bar is strictly controlled by rotating the upper and lower chucks. Then, move the upper and lower chucks to make the distance between the tungsten polycrystalline bar and the tungsten single crystal seed bar 1 mm. Because as the temperature rises, the tungsten polycrystalline bar and the tungsten single crystal seed will expand, and by controlling the distance between them, the bending of the bar caused by thermal expansion of the material can be well avoided.

[0064] Step 3: Vacuum pumping. Close the furnace door of the electron beam floating zone melting furnace, turn on the equipment cooling circulating water, and start the mechanical pump for vacuum pumping. When the vacuum degree is higher than 1.0 Pa, turn on the molecular pump for further vacuum pumping. When the vacuum degree is higher than 6×10 -3 Pa, the required vacuum degree for melting is reached, and the mechanical pump and the molecular pump are ensured to be running during the melting process.

[0065] Step 4: Apply filament current. After the vacuum degree is higher than 6×10 -3 Pa, start applying filament current and increase the current slowly. When the filament current reaches 70 A, wait for 2 minutes for the filament to complete the preheating process, and then increase the filament current to 90 A. After the filament current stabilizes at 90 A, the main high voltage can be applied.

[0066] Step 5: Apply main high voltage. The electron gun is a ring-shaped electron gun. Move the center of the electron gun between the tungsten polycrystalline bar and the tungsten single crystal seed bar, and then start applying the main high voltage. The application of the main high voltage is divided into two steps. In the first step, it is increased in a stepped manner, starting from 0 KV, increasing by 2 KV each time and stopping for 1 min. When the main high voltage reaches 10 KV, start the second step of applying the main high voltage. The value of the main high voltage is between 10 - 15 KV, and the specific value needs to be adjusted according to the molten zone state during the melting process.

[0067] Step 6, bar welding. Before degassing treatment, confirm the distance between the tungsten polycrystalline bar and the tungsten single crystal seed bar, and determine that the center of the electron gun is at the middle gap position between the two bars. Gradually reduce the distance between the two bars by adjusting the magnitude of the main high voltage until the tungsten polycrystalline bar and the tungsten single crystal seed bar are melted and connected together, at which point the bar welding is completed. During the entire bar welding process, the vacuum degree inside the electron beam floating zone furnace is guaranteed to be higher than 6×10 -3 Pa.

[0068] Step 7, single crystal preparation. After the bar welding is completed, move the center of the electron gun to the tungsten single crystal seed at 10 mm below the welding joint of the tungsten polycrystalline bar and the tungsten single crystal seed bar, and then generate a stable melting zone on the tungsten single crystal seed bar by adjusting the magnitude of the main high voltage. At this time, move the electron gun upward at a rate of 20 μm / s. During the smelting process, control the power of the electron beam to keep the melting zone stable. The surface of the single crystal bar obtained by smelting is smooth and uniform in thickness, as Figure 1 shown. The main process parameters during the zone melting process are: the main high voltage is 10.10 - 13.40 KV, the electron beam current is 0.09 - 0.15 A, the electron beam power is 1.00 - 1.17 KW, the filament voltage is 6.08 V, and the filament current is 90.54 A.

[0069] Step 8, sample detection. Cut the original tungsten single crystal seed bar and the tungsten single crystal bar prepared by the seed method. Grind the sample thin slices with a thickness of about 2 mm in sequence using 400#, 600#, 800#, 1200#, 1500#, and 2000# diamond sandpapers, and then perform mechanical polishing using 3.5 - grit polishing paste until there are no obvious scratches on the surface. Prepare an electrolyte of H 2 O:NaOH = 98:2 (wt. %), perform electrolytic polishing on the mechanically polished sample, with a voltage of 20 V, a polishing time of 50 s, and a polishing temperature of 25°C. Perform EBSD analysis on the electrolytically polished single crystal seed and the tungsten single crystal prepared by the seed method, and it is found that the orientation of the tungsten single crystal prepared by the seed method is basically consistent with that of the original (001) - oriented tungsten single crystal seed.

[0070] Example 4 Step 1, polish and clean the surfaces of the tungsten polycrystalline bar and the (310) - oriented tungsten single crystal seed bar. The diameter of the tungsten polycrystalline bar is 4 mm and the length is 400 mm, and the size of the tungsten single crystal seed is a diameter of 4 mm and a length of 200 mm. Polish the surfaces of the tungsten polycrystalline bar and the tungsten single crystal seed bar in sequence using 400 - mesh, 600 - mesh, 800 - mesh, 1200 - mesh, 1500 - mesh, and 2000 - mesh sandpapers, and then clean the surface with alcohol and dry for standby.

[0071] Step 2, sample installation. The polished and cleaned tungsten polycrystalline rod and tungsten single crystal seed rod are respectively installed on the upper chuck and the lower chuck in the furnace chamber. Since mechanical errors are inevitably introduced between the chuck and the rod during the installation process, the coaxiality between the tungsten polycrystalline rod and the tungsten single crystal seed rod is strictly controlled by rotating the upper and lower chucks. Then, the distance between the tungsten polycrystalline rod and the tungsten single crystal seed rod is made 1.5 mm by moving the upper and lower chucks. Because the tungsten polycrystalline rod and the tungsten single crystal seed will expand as the temperature rises, controlling the distance between them can well avoid the bending of the rod caused by the thermal expansion of the material.

[0072] Step 3, evacuation. Close the furnace door of the electron beam floating zone melting furnace, turn on the equipment cooling circulating water, and turn on the mechanical pump for evacuation. When the vacuum degree is higher than 1.0 Pa, turn on the molecular pump for further evacuation. When the vacuum degree is higher than 6×10 -3 Pa, the required vacuum degree for melting is reached, and the mechanical pump and the molecular pump are ensured to be running during the melting process.

[0073] Step 4, applying filament current. After the vacuum degree is higher than 6×10 -3 Pa, start applying filament current and increase the current slowly. When the filament current reaches 70 A, wait for 2 minutes for the filament to complete the preheating process, and then increase the filament current to 90 A. After the filament current stabilizes at 90 A, the main high voltage can be applied.

[0074] Step 5, applying main high voltage. The electron gun is a ring-shaped electron gun. Move the center of the electron gun between the tungsten polycrystalline rod and the tungsten single crystal seed rod, and then start applying the main high voltage. The application of the main high voltage is divided into two steps. The first step is in a stepped increase mode, starting from 0 KV, increasing by 2 KV each time and stopping for 1 min. When the main high voltage reaches 10 KV, start the second step of applying the main high voltage. The value of the main high voltage is between 10 - 15 KV, and the specific value needs to be adjusted according to the melting zone state during the melting process.

[0075] Step 6, rod welding. Before the degassing treatment, confirm the distance between the tungsten polycrystalline rod and the tungsten single crystal seed rod, and ensure that the center of the electron gun is at the middle gap position between the two rods. Gradually reduce the distance between the two rods by adjusting the magnitude of the main high voltage until the tungsten polycrystalline rod and the tungsten single crystal seed rod are melted and connected together, at which time the rod welding is completed. During the entire rod welding process, the vacuum degree in the electron beam floating zone melting furnace is ensured to be higher than 6×10 -3 Pa.

[0076] Step 7, single crystal preparation. After the welding of the rod stock is completed, move the center of the electron gun to a position 10 mm below the welding joint of the tungsten polycrystalline rod and the tungsten single crystal seed rod on the tungsten single crystal seed. Then, by adjusting the magnitude of the main high voltage, a stable melting zone is generated on the tungsten single crystal seed rod. At this time, move the electron gun upward at a rate of 20 μm / s. During the melting process, the melting zone is stabilized by controlling the power of the electron beam. The surface of the single crystal sample obtained by melting is smooth and uniform in thickness. The main process parameters during zone melting are as follows: the main high voltage is 10.00 - 13.30 KV, the electron beam current is 0.10 - 0.15 A, the electron beam power is 1.00 - 1.35 KW, the filament voltage is 6.11 V, and the filament current is 90.85 A.

[0077] Step 8, sample detection. Cut the original tungsten single crystal seed rod and the tungsten single crystal rod prepared by the seed method. Grind the sample thin slices with a thickness of about 2 mm successively using 400#, 600#, 800#, 1200#, 1500#, and 2000# diamond sandpapers, and then perform mechanical polishing using 3.5-grit polishing paste until there are no obvious scratches on the surface. Prepare an electrolyte with H 2 O:NaOH = 98:2 (wt. %). Electrolytically polish the mechanically polished sample at a voltage of 20 V for a polishing time of 50 s and a polishing temperature of 27°C. Perform EBSD analysis on the electrolytically polished single crystal seed and the tungsten single crystal prepared by the seed method, and it is found that the orientation of the tungsten single crystal prepared by the seed method is basically the same as that of the original tungsten single crystal seed with a (310) orientation.

[0078] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a specifically oriented tungsten single crystal rod, characterized in that: The following steps are involved: Step 1, obtaining a tungsten polycrystalline rod and a tungsten single crystal seed crystal rod with a specific orientation, wherein the crystal orientation of the tungsten single crystal seed crystal rod with a specific orientation is <001> or <310> ; Step 2, the upper chuck of the electron beam suspension zone furnace clamps the tungsten polycrystalline rod, and the lower chuck clamps the tungsten single crystal seed crystal rod, and the distance between the lower end of the tungsten polycrystalline rod and the upper end of the tungsten single crystal seed crystal rod is 1-1.5 mm; Step 3, evacuating the electron beam suspension zone furnace to reach a target vacuum degree; Step 4, applying electron beam main high voltage to the electron beam suspension zone furnace, the process of applying electron beam main high voltage is divided into a first stage and a second stage, the first stage applies the main high voltage from 0KV to 10KV, and the second stage applies the main high voltage in the range of 10-15KV; In the interval between the first stage and the second stage, the annular electron gun is placed between the tungsten polycrystalline rod and the tungsten single crystal seed crystal rod to complete the welding of the tungsten polycrystalline rod and the tungsten single crystal seed crystal rod; Step 5, after welding, place the annular electron gun at the single crystal seed crystal 10 mm below the welding point, apply the main high voltage, melt the tungsten single crystal seed crystal rod, and after the molten zone is stable, move the annular electron gun upward to obtain a specific orientation tungsten single crystal rod grown by equal diameter zone melting.

2. The method for preparing a specifically oriented tungsten single crystal rod according to claim 1, characterized in that: In step 2, the clamped tungsten polycrystalline rod and the clamped tungsten single crystal seed crystal rod are coaxial.

3. The method for preparing a specifically oriented tungsten single crystal rod according to claim 1, characterized in that: In step 3, the target vacuum degree is 6×10 -3 Pa.

4. The method for preparing a specifically oriented tungsten single crystal rod according to claim 1, characterized in that: In step 4, before applying the electron beam main high voltage to the electron beam suspension zone furnace, the filament current is increased, and when the filament current is stabilized at 90A, the electron beam main high voltage is applied.

5. The method for preparing a specifically oriented tungsten single crystal rod according to claim 1, characterized in that: In step 4, the first stage applies the main high voltage from 0KV to 10KV, and stops for 1 minute after each increase of 2KV.

6. The method for preparing a specifically oriented tungsten single crystal rod according to claim 1, characterized in that: In step 4, the value of the main high pressure applied is adjusted according to the width of the molten zone.

7. The method for preparing a specifically oriented tungsten single crystal rod according to claim 1, characterized in that: In step 5, the annular electron gun moves upward at a speed of 20 μm / s.

8. The method for preparing a specifically oriented tungsten single crystal rod according to claim 1, characterized in that: After step 5, the tungsten single crystal rod is sliced ​​and electropolished to determine the crystal orientation.

9. The method for preparing a specifically oriented tungsten single crystal rod according to claim 1, characterized in that: In step 1, before clamping the tungsten polycrystalline rod and the tungsten single crystal seed crystal rod with a specific orientation, the end faces are cut, polished and cleaned.

10. A specifically oriented tungsten single crystal rod prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The crystal orientation of the specific oriented tungsten single crystal rod is <001> or <310> .

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