Molybdenum alloy single crystal containing dispersed carbide second phase and preparation method thereof

Abstract

The invention discloses a molybdenum alloy single crystal containing a dispersed carbide second phase and a preparation method of the molybdenum alloy single crystal, and belongs to the technical field of preparation of refractory metal single crystals. The alloy comprises the following components in percentage by weight: 5wt% of Re, 0.2-1wt% of NbC and the balance of Mo and other impurity elements, the specific preparation process comprises the steps that Mo metal, Re metal and NbC powder are premixed according to the alloy component proportion, then the premixed raw materials are subjected to electric arc melting through a vacuum non-consumable tungsten electrode melting furnace to obtain a molybdenum alloy ingot, and then the molybdenum alloy ingot is machined to prepare the molybdenum alloy bar. And finally, the molybdenum alloy single crystal containing the dispersed carbide second phase is prepared through electron beam floating zone smelting. The molybdenum alloy single crystal containing the dispersed carbide second phase is prepared by optimizing alloy component design and dispersed phase selection.

Description

Technical Field

[0001] The present invention belongs to the technical field of refractory metal single crystal preparation, and particularly relates to a molybdenum alloy single crystal containing a dispersed carbide second phase and a preparation method thereof. Background Art

[0002] Due to its high hardness, high melting point, low electron work function (4.2 eV), and excellent electrical conductivity, thermal conductivity, radiation resistance, and high-temperature stability, refractory metal molybdenum has important applications in fields such as advanced reactor fuel cladding materials, high-temperature electron emitters, X-ray targets, and power electronics packaging.

[0003] With the continuous expansion of the application fields of molybdenum alloys, especially in some cutting-edge technologies, higher requirements have been put forward for improving the performance of molybdenum-based materials. Through electron beam floating zone melting technology, molybdenum alloy single crystal materials with excellent high-temperature stability and no grain boundary defects can be prepared. However, limited by the complex grain boundary migration and coalescence processes during single crystal preparation, the performance optimization of molybdenum alloy single crystal materials is currently only limited to the solid solution of different types of elements, and the improvement of the performance of molybdenum alloy single crystal by lattice distortion caused by element solid solution is very limited. Therefore, it is extremely important to find new strengthening methods for molybdenum alloy single crystals.

[0004] By adding carbides with high melting points and high chemical stabilities (such as HfC, TiC, ZrC, NbC, etc.) to polycrystalline molybdenum alloys, the comprehensive mechanical properties of polycrystalline molybdenum alloy materials have been significantly improved under the action of dispersed carbide strengthening. Forming a dispersed carbide second phase has become an indispensable important means to strengthen polycrystalline molybdenum alloys. However, for molybdenum alloy single crystals, the presence of carbides will pin the grain boundaries and hinder the grain boundary migration and coalescence processes, thus affecting the successful preparation of single crystals during zone melting. 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 molybdenum alloy single crystal containing a dispersed carbide second phase and a preparation method thereof, so as to solve the problem that the presence of carbides affects the preparation of single crystals in the prior art for molybdenum alloy single crystals.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions: A preparation method of a molybdenum alloy single crystal containing a dispersed carbide second phase, comprising the following steps: Step 1, mix Mo metal, Re metal, and NbC powder and melt them to prepare a polycrystalline molybdenum alloy ingot, and process the polycrystalline molybdenum alloy ingot into a polycrystalline molybdenum alloy bar; Step 2: Place the polycrystalline molybdenum alloy rod and the molybdenum single crystal seed with a specific orientation in an electron beam floating zone melting furnace. The opposite ends of the polycrystalline molybdenum alloy rod and the molybdenum single crystal seed are in contact. A pre-melting zone is formed at the joint of the polycrystalline molybdenum alloy rod and the molybdenum single crystal seed by an electron gun. After increasing the power, the joint of the polycrystalline molybdenum alloy rod and the molybdenum single crystal seed is welded. Step 3: Move the electron gun and start melting at the molybdenum single crystal seed below the joint. After the melting zone is stable, move the electron gun upward for electron beam floating zone melting. After melting is completed and cooling is carried out, a molybdenum alloy single crystal is obtained. The molybdenum alloy single crystal includes Re and Mo, and Nb2C particles as the second phase are dispersed in the molybdenum alloy single crystal.

[0007] A further improvement of the present invention lies in: Preferably, in Step 1, in terms of mass fraction, the addition amount of Re metal is 5 wt.%, the addition amount of NbC powder is 0.2 - 1 wt.%, and the balance is Mo metal.

[0008] Preferably, in Step 1, when the Mo metal and the Re metal are in particulate form, first mix the Mo metal particles and the Re metal particles to form mixed particles, and then alternately lay the mixed particles and the NbC powder and carry out melting.

[0009] Preferably, in Step 1, when the Mo metal and the Re metal are in powder form, mix the Mo metal powder, the Re metal powder and the NbC powder evenly and then carry out melting.

[0010] Preferably, in Step 1, the polycrystalline molybdenum alloy ingot is obtained after multiple meltings.

[0011] Preferably, in Step 3, during the melting process, the melting power and the melting rate are adjusted according to the rod diameter.

[0012] Preferably, in Step 3, the cooling method is furnace cooling.

[0013] A molybdenum alloy single crystal containing a second phase of dispersed carbide prepared by any one of the above preparation methods. In terms of mass fraction, the molybdenum alloy single crystal includes Re and Mo, and Nb2C particles as the second phase are dispersed in the molybdenum alloy single crystal.

[0014] Preferably, the Nb2C particles are strip-shaped.

[0015] Preferably, in terms of mass fraction, in the molybdenum alloy single crystal, Re is 5 wt.%, the Nb2C particles are 0.2 - 1 wt.%, and the rest is Mo.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a molybdenum alloy single crystal containing a dispersed carbide second phase and a preparation method thereof. The alloy composition of the present invention is: Re: 5 wt.%, NbC: 0.2 - 1 wt.%, and the balance is Mo and other impurity elements; it is prepared by a melting process, and the preparation process is as follows: After vacuum drying, Mo metal, Re metal, and NbC powder are pre-mixed according to the alloy composition ratio, and then the pre-mixed raw materials are subjected to arc melting in a vacuum non-consumable tungsten electrode melting furnace to obtain a polycrystalline molybdenum alloy ingot. Then, the polycrystalline molybdenum alloy ingot is machined to prepare a polycrystalline molybdenum alloy rod, and finally, a molybdenum alloy single crystal containing a dispersed carbide second phase is prepared by electron beam floating zone melting. The present invention provides new ideas for optimizing the performance of refractory metal molybdenum alloy single crystals by optimizing alloy composition design and dispersed phase selection. In order to achieve the uniform distribution of NbC in the Mo-5Re alloy matrix, a vacuum non-consumable tungsten electrode melting furnace is selected to prepare a polycrystalline molybdenum alloy ingot containing a dispersed carbide second phase. In order to achieve the preparation of single crystals, the electron beam floating zone melting technology is selected to grow single crystals. By optimizing the alloy composition, reasonable dispersed phase selection, and appropriate preparation process, the carbide second phase can be dispersed in the molybdenum alloy single crystal, which is of great significance for the in-depth development of molybdenum alloy single crystals in structural and functional materials.

[0017] The method of the present invention realizes the uniform distribution of NbC powder in the Mo-5Re alloy through a vacuum non-consumable tungsten electrode melting furnace. According to the solubility of carbon element in the molybdenum matrix, the maximum addition amount of NbC is determined not to exceed 1 wt.%. The growth process of single crystals is completed through the electron beam floating zone melting technology. During the zone melting process, the NbC added to the Mo-5Re matrix melts during the zone melting process, thus ensuring that during the single crystal preparation process, the grain boundaries migrate and merge smoothly with the movement of the molten zone. The decomposed C element and Nb element combine to form the Nb2C phase during the subsequent cooling process. This method provides new ideas for improving the performance of molybdenum alloy single crystals by optimizing the alloy composition, reasonable dispersed phase selection, and appropriate preparation process, enabling the carbide second phase to be dispersed in the molybdenum alloy single crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the single crystal orientation map of a molybdenum alloy single crystal (Mo-5Re-0.5 wt.% NbC) containing a dispersed carbide second phase prepared by the present invention and a molybdenum seed crystal under EBSD orientation analysis; Among them, Figures (a) and (e) are the macroscopic views of molybdenum seeds and Mo-5Re-0.5wt.% NbC, respectively; Figures (b) and (f) are the single-crystal IPF Z maps of molybdenum seeds and Mo-5Re-0.5wt.% NbC, respectively; Figures (c) and (g) are the single-crystal pole figures of molybdenum seeds and Mo-5Re-0.5wt.% NbC, respectively; Figures (d) and (h) are the single-crystal inverse pole figures of molybdenum seeds and Mo-5Re-0.5wt.% NbC, respectively. Figure 2 are the schematic diagrams of the microstructures of a molybdenum alloy single crystal (Mo-5Re-0.5wt.% NbC) containing a dispersed carbide second phase and a Mo-5Re single crystal prepared by the present invention under an optical microscope; Among them, Figure (a) is the Mo-5Re single crystal; Figure (b) is Mo-5Re-0.5wt.% NbC. Figure 3 is the characteristic map of the second phase after EBSD phase analysis of a molybdenum alloy single crystal (Mo-5Re-0.5wt.% NbC) containing a dispersed carbide second phase prepared by the present invention; Among them, Figures (a) and (c) are the electron images of the second phase at different magnifications; Figures (b) and (d) are the corresponding distribution maps of the second phase, respectively. Figure 4 is the principle and schematic diagram of a key preparation method of a molybdenum alloy single crystal containing a dispersed carbide second phase prepared in the examples provided by the present invention. Detailed implementation manners

[0019] 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 phrases 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.

[0020] In this article, unless otherwise specified, "comprising", "including", "containing", "having" or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A only comprises a".

[0021] The present invention will be further illustrated with specific examples. It should be understood that these examples 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.

[0022] In the following examples, conventional instruments and equipment in the art are used. For the experimental methods without specific conditions noted in the following examples, they are generally carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following examples. Unless otherwise specified, commercially available products are used, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0023] The present invention discloses a method for preparing a molybdenum alloy single crystal containing a dispersed carbide second phase. The dispersed carbide second phase in the molybdenum alloy single crystal is a niobium carbide phase. The preparation method of the molybdenum alloy single crystal is an electron beam floating zone melting technology. Specifically, the method includes the following steps: (1) Weigh Mo metal (the balance) with a purity exceeding 99.95%, Re metal (5 wt.%), and NbC powder (0.2 - 1 wt.%) by mass percentage. After weighing, mix them evenly to obtain a mixed raw material, and place the mixed raw material in a water-cooled copper crucible of a vacuum non-consumable tungsten electrode melting furnace.

[0024] (2) Charge inert gas argon for purging, and adjust the vacuum degree in the furnace cavity of the vacuum non-consumable tungsten electrode melting furnace to meet the melting requirements.

[0025] (3) Regulate the melting current to 50 A to strike an arc, regulate the melting current, and under the protection of argon, carry out arc melting of the mixed raw material for 3 - 5 minutes. After one melting, cool the formed ingot in the furnace, and after cooling is completed, turn over the ingot. (4) In the furnace cavity environment mentioned in step (2), according to the operation process in step (3), repeat melting of the turned-over ingot. Repeat at least 6 times to ensure uniform composition, and then cool the ingot under vacuum to obtain a as-cast polycrystalline molybdenum alloy ingot. In this ingot, Mo and Re form a Mo-5Re solid solution. (5) Machine the obtained as-cast polycrystalline molybdenum alloy ingot to prepare an as-cast polycrystalline molybdenum alloy bar that meets the subsequent specifications.

[0026] (6) Open the door of the electron beam floating zone melting furnace, install an insulating platform and an electron gun, load the as-cast polycrystalline molybdenum alloy bar into the electron beam floating zone melting furnace. Place a Mo single crystal seed with a specific orientation at the bottom of the as-cast polycrystalline molybdenum alloy bar, and adjust the upper and lower feeders to make the as-cast polycrystalline molybdenum alloy bar contact and clamp with the Mo single crystal seed.

[0027] (7) Close the furnace door, turn on the mechanical pump to pre-pump the vacuum, and then turn on the molecular pump to adjust the vacuum degree in the furnace cavity of the electron beam floating zone melting furnace.

[0028] (8) Turn on the power supply of the electron beam floating zone melting furnace, turn on the filament, raise the filament current to 90 A, move the electron gun so that the pre-melting zone appears at the joint of the as-cast polycrystalline molybdenum alloy rod and the molybdenum single crystal seed crystal, turn on the high voltage, and slowly increase the power to about 1.0 word spectrum fart. Complete the welding at the joint of the as-cast polycrystalline molybdenum alloy rod and the molybdenum single crystal seed crystal.

[0029] (9) Move the electron gun so that the pre-melting zone appears on the molybdenum single crystal seed crystal 10 mm below the joint of the as-cast polycrystalline molybdenum alloy rod and the molybdenum single crystal seed crystal. Slowly increase the power. After the melting zone appears and stabilizes, set the zone melting rate, turn on the automatic movement of the electron gun, and carry out electron beam floating zone melting. During the process, always pay attention to the state of the melting zone, adjust the equipment power to maintain a stable melting zone, and prevent the collapse of the melting zone caused by too high power and the disappearance of the melting zone caused by too low power.

[0030] During the melting process of this process, the temperature and melting rate are adjusted with the adjustment of the rod diameter. The basic principle is to keep the melting zone stable.

[0031] (10) After electron beam floating zone melting, cool in the furnace for 3 h and then take out to obtain a molybdenum alloy single crystal containing a dispersed carbide second phase.

[0032] In some embodiments of the present invention, in step (1), different mixing methods are selected according to the morphologies of Mo and Re. When both Mo and Re are in powder form, since the particle sizes of Mo powder, Re powder and NbC powder are similar, they can be directly mixed evenly and then placed in the furnace for melting.

[0033] Furthermore, when Mo and Re are in granular form, since the particle sizes of Mo particles and Re particles are larger than the particle size of NbC powder, in order to make the NbC powder evenly distributed in the ingot, first mix the Mo particles and Re particles to form mixed particles, and then alternately lay the mixed particles and NbC powder for melting. Specifically, mix the Mo particles and Re particles evenly to form mixed particles, put half of the mixed particles into the water-cooled copper crucible of the vacuum non-consumable tungsten electrode melting furnace, evenly put a specific content of NbC powder above the mixed particles, and then put the remaining mixed particles and cover the NbC powder; specifically, the number of alternations can also be adjusted according to the actual situation.

[0034] The above two mixing methods are both for the NbC particles to be evenly distributed in the polycrystalline molybdenum alloy ingot.

[0035] In some embodiments of the present invention, the equipment used is a 20KW electron beam floating zone melting furnace, and during the single crystal preparation process, a molybdenum alloy single crystal with a specific orientation is prepared by the seed crystal method.

[0036] Furthermore, in step (2), the vacuum degree of the vacuum non-consumable tungsten electrode melting furnace is adjusted to 10-4 Magnitude, and argon is filled as the protective gas.

[0037] Further, in step (7), the mechanical pump evacuates the vacuum to below 2×10 -1 Pa, and then the molecular pump is turned on to evacuate the vacuum to 7×10 -3 Pa.

[0038] In the above preparation process, NbC particles are first introduced into the alloy ingot of Mo and Re. During the melting process, since the melting point of NbC is much higher than that of the refractory metal molybdenum, when preparing the polycrystalline ingot, Mo and Re can form the ingot in the target polycrystalline form, while NbC still remains distributed in the ingot in the form of particles. It is melted and homogenized by a vacuum non-consumable tungsten electrode melting furnace. During the preparation of single crystals by electron beam floating zone melting technology, due to the very high melting point of the local melting area, NbC particles dissolve in the Mo-5Re alloy matrix in the form of Nb element and C element. During the solidification process, Nb element and C element will precipitate as the temperature decreases, and then form niobium carbide (Nb2C) with a dispersed distribution.

[0039] During the polycrystalline melting process, since the melting point of NbC is much higher than that of the refractory metal molybdenum, and Nb and Mo can also form an infinite solid solution and will not segregate during the zone melting process. Therefore, in the Mo-5Re single crystal with 5% mass fraction of Re added, NbC powder is selected to form a carbide phase with a uniform and dispersed distribution. During the melting process, the content of NbC is limited to 0.2-1 wt.%, because the solubility of carbon element in molybdenum metal is not more than 1.2%. If the addition amount is too much, without affecting the preparation of single crystals, the addition amount of NbC does not exceed 1 wt.%. If it exceeds this content, NbC is difficult to decompose sufficiently during the subsequent dissolution process and still remains in the single crystal in the form of particles, affecting the formation of the single crystal.

[0040] This method is used to form single crystals with multiple specific orientations. By placing the selected single crystal with a specific orientation at the lower part of the as-cast polycrystalline molybdenum alloy bar, a molybdenum alloy single crystal containing a dispersed carbide second phase is prepared by the seed crystal method, which improves the single crystal preparation efficiency, and the orientation of the molybdenum alloy single crystal containing the dispersed carbide second phase is controlled by the seed crystal.

[0041] The second aspect of the present invention discloses a molybdenum alloy single crystal containing a dispersed carbide second phase. In terms of mass fraction, this single crystal includes Re: 5 wt.%, Nb2C: 0.2-1 wt.%, and the balance is Mo and other impurity elements, among which Nb2C is dispersed.

[0042] In some embodiments of the present invention, the second phase is in the form of strips with a size of 5 μm, and the second phase composition is Nb2C.

[0043] The following will be further described in conjunction with specific embodiments.

[0044] Example 1 A molybdenum alloy single crystal containing a dispersed carbide second phase and a preparation method thereof specifically include the following steps: (1) Weigh Re particles (5 wt.%), NbC powder (0.5 wt.%) with a purity exceeding 99.95% and Mo particles (the balance) by mass percentage; (2) Mix the Mo particles and Re particles evenly to form mixed particles. Put half of the mixed particles into a water-cooled copper crucible of a vacuum non-consumable tungsten electrode arc melting furnace. Put the NbC powder (0.5 wt.%) above half of the mixed particles in the water-cooled copper crucible, and put the other half of the mixed particles on and cover the NbC powder to ensure that the NbC powder can be evenly distributed after melting; (3) Charge inert gas argon for gas washing and adjust the vacuum degree in the furnace cavity of the vacuum non-consumable tungsten electrode melting furnace; (4) Regulate the melting current to 50 A to strike an arc, regulate the melting current, and remelt the mixed particles and NbC powder at least 6 times under argon protection to ensure the uniformity of the structure and composition. Each remelting must turn the ingot up and down; during the turning and remelting process, the current must gradually increase from small to large, and the time is 3 - 5 minutes until it is completely in a molten state. During this period, the melting state of the ingot must be constantly monitored to avoid explosion of the material.

[0045] (5) Under the furnace cavity environment mentioned in step (3), according to the operation process in step (4), repeat melting at least 6 times and then cool under vacuum to obtain a as-cast polycrystalline molybdenum alloy (Mo-5Re-0.5 wt.% NbC) ingot; (6) Machine the as-cast polycrystalline molybdenum alloy (Mo-5Re-0.5 wt.% NbC) ingot to obtain an as-cast polycrystalline molybdenum alloy (Mo-5Re-0.5 wt.% NbC) rod with a diameter of 8 mm; (7) Open the door of the electron beam floating zone melting furnace, install an insulating platform and an electron gun, put the as-cast polycrystalline molybdenum alloy (Mo-5Re-0.5 wt.% NbC) rod into the electron beam floating zone melting furnace. The seed crystal method is selected during the single crystal preparation process to improve the single crystal preparation efficiency and control the single crystal orientation. Place a Mo single crystal seed at the bottom end of the as-cast polycrystalline molybdenum alloy (Mo-5Re-0.5 wt.% NbC) rod. The orientation of the Mo single crystal seed is a bias

[001] orientation. Make the as-cast polycrystalline molybdenum alloy rod contact and clamp with the Mo single crystal seed by adjusting the upper and lower feeders; (8) Close the furnace door, turn on the mechanical pump to pre-pump the vacuum, and then turn on the molecular pump to adjust the vacuum degree in the furnace cavity of the electron beam floating zone melting furnace; (9) Turn on the power supply of the electron beam floating zone melting furnace, turn on the filament, raise the filament current to 90 A, move the electron gun so that the pre-melting zone appears at the joint of the as-cast polycrystalline molybdenum alloy rod and the molybdenum single crystal seed crystal, turn on the high voltage, and slowly increase the power to complete the welding at the joint of the as-cast polycrystalline molybdenum alloy rod and the molybdenum single crystal seed crystal.

[0046] (10) Move the electron gun so that the pre-melting zone appears on the molybdenum single crystal seed crystal 10 mm below the joint of the as-cast polycrystalline molybdenum alloy rod and the molybdenum single crystal seed crystal, ensure that the seed crystal orientation can be smoothly inherited, and the complex process of grain preferred selection and elimination in the preparation of single crystals by electron beam floating zone melting under natural conditions can be avoided by the seed crystal method. Using this process, molybdenum alloy (Mo-5Re-0.5 wt.% NbC) single crystals with a specific orientation can be prepared under the condition of one-time electron beam floating zone melting, improving the efficiency and quality of single crystal preparation.

[0047] (11) Slowly increase the power to 1.05 kw. After the melting zone appears and stabilizes, set the zone melting rate to 15 μm / s, turn on the automatic movement of the electron gun, and carry out electron beam floating zone melting. During the process, the state of the melting zone must be constantly monitored, and the power of the equipment should be adjusted to maintain a stable melting zone to prevent the collapse of the melting zone caused by too high power and the disappearance of the melting zone caused by too low power.

[0048] (12) After electron beam floating zone melting, take it out after furnace cooling for 3 h to obtain a molybdenum alloy single crystal (Mo-5Re-0.5 wt.% NbC) containing a dispersed carbide second phase.

[0049] The present invention prepares a molybdenum alloy single crystal containing a dispersed carbide second phase through a vacuum non-consumable tungsten electrode arc melting furnace and an electron beam floating zone melting technology. The seed crystal method is selected in the single crystal preparation process to improve the single crystal preparation efficiency and control the single crystal orientation. From Figure 1 the EBSD orientation analysis, it can be seen that the prepared molybdenum alloy containing a dispersed carbide second phase is a single crystal structure and the orientation is inherited from the seed crystal, both of which are biased towards the

[001] orientation.

[0050] Figure 2 Figure 18 is a schematic diagram of the microstructures of the prepared Mo-5Re single crystal and a molybdenum alloy single crystal (Mo-5Re-0.5 wt.% NbC) containing a dispersed carbide second phase under an optical microscope. It can be seen from the figure that Mo-5Re is a typical solid solution single crystal structure, while on the basis of the solid solution single crystal, a second phase with uniform dispersion is successfully introduced into the Mo-5Re-0.5 wt.% NbC single crystal. By magnifying the observation, it can be seen that the second phase is mainly in the shape of long strips about 5 μm, and the overall distribution characteristic of the second phase is uniform dispersion in a large area and concentrated aggregation in a small area. The reason is that the aggregated long strip second phase is formed by the melting of the original NbC powder during zone melting and then forming nearby during the subsequent cooling process.

[0051] The phase analysis of a molybdenum alloy single crystal containing a dispersed carbide second phase was carried out by EBSD orientation analysis technology. It was determined by EBSD orientation analysis technology that the carbide second phase was Nb2C phase. Figure 3 It shows that the added NbC powder melts during the arc melting and electron beam zone melting processes, and finally strips of Nb2C phase with a size of 5 μm are directly precipitated in the matrix during solidification, dispersedly distributed.

[0052] For molybdenum alloys, after solid solution strengthening reaches or approaches the limit level, in order to greatly improve the comprehensive mechanical properties of the material, a duplex structure with a dispersed second phase should be obtained, and the stability and thermal strength of the second phase should not be less than those of the matrix metal. However, for molybdenum alloy single crystals with harsh preparation conditions, the current methods for optimizing their comprehensive properties are only limited to single-phase solid solution strengthening. Therefore, the present invention provides a molybdenum alloy single crystal containing a dispersed carbide second phase and its preparation method. NbC with a relatively high melting point is selected as the second phase, and a molybdenum alloy single crystal containing a dispersed carbide second phase is prepared by arc melting and electron beam floating zone melting. The formation mechanism of the carbide in the single crystal is as Figure 4 shown. Due to the overheating phenomenon in the molten zone during the zone melting process, the added NbC particles melt at high temperature and transform into C element and Nb element. Since the C element in the molybdenum matrix does not exceed its maximum solid solubility at the melting temperature, it is ensured that the C element will not escape from the matrix. As the molten zone moves, because the C element and Nb element have a higher affinity, and the Nb2C phase has a lower Gibbs free energy, finally, a uniformly dispersed Nb2C second phase is formed in the Mo-5Re single crystal. The present invention has successfully realized the preparation of a molybdenum alloy single crystal containing a dispersed carbide second phase by optimizing the alloy composition design and the selection of the dispersed phase, providing a new idea for the performance optimization of refractory metal molybdenum alloy single crystals.

[0053] 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 in the protection scope of the present invention.

Claims

1. A method for preparing a single crystal molybdenum alloy containing a dispersed carbide second phase, characterized in that, It includes the following steps: Step 1: Mix Mo metal, Re metal and NbC powder and then melt them to obtain a polycrystalline molybdenum alloy ingot, and process the polycrystalline molybdenum alloy ingot into a polycrystalline molybdenum alloy rod; Step 2: Place the polycrystalline molybdenum alloy rod and a molybdenum single crystal seed with a specific orientation in an electron beam floating zone melting furnace. The opposite ends of the polycrystalline molybdenum alloy rod and the molybdenum single crystal seed with a specific orientation are in contact. A pre-melting zone is formed at the joint of the polycrystalline molybdenum alloy rod and the molybdenum single crystal seed through an electron gun. After raising the power, the joint of the polycrystalline molybdenum alloy rod and the molybdenum single crystal seed is welded; Step 3: Move the electron gun, start melting at the molybdenum single crystal seed below the joint. After the melting zone is stable, move the electron gun upward for electron beam floating zone melting. After melting and cooling, a molybdenum alloy single crystal is obtained; The molybdenum alloy single crystal includes Re and Mo, and Nb2C particles as the second phase are dispersed in the molybdenum alloy single crystal.

2. The preparation method of a molybdenum alloy single crystal containing a dispersed carbide second phase according to claim 1, characterized in that, In Step 1, by mass fraction, the addition amount of Re metal is 5 wt.%, the addition amount of NbC powder is 0.2 - 1 wt.%, and the balance is Mo metal.

3. The preparation method of a molybdenum alloy single crystal containing a dispersed carbide second phase according to claim 1, characterized in that, In Step 1, when Mo metal and Re metal are in granular form, first mix the Mo metal particles and Re metal particles to form mixed particles, and then alternately lay the mixed particles and NbC powder and then melt them.

4. The preparation method of a molybdenum alloy single crystal containing a dispersed carbide second phase according to claim 1, characterized in that, In Step 1, when Mo metal and Re metal are in powder form, mix the Mo metal powder, Re metal powder and NbC powder evenly and then melt them.

5. The preparation method of a molybdenum alloy single crystal containing a dispersed carbide second phase according to claim 1, characterized in that, In Step 1, the polycrystalline molybdenum alloy ingot is obtained through multiple meltings.

6. The preparation method of a molybdenum alloy single crystal containing a dispersed carbide second phase according to claim 1, characterized in that, In Step 3, during the melting process, the melting power and melting rate are adjusted according to the rod diameter.

7. The preparation method of a molybdenum alloy single crystal containing a dispersed carbide second phase according to claim 1, characterized in that, In Step 3, the cooling method is furnace cooling.

8. A molybdenum alloy single crystal containing a dispersed carbide second phase prepared by any one of the preparation methods, characterized in that, By mass fraction, the molybdenum alloy single crystal includes Re and Mo, and Nb2C particles as the second phase are dispersed in the molybdenum alloy single crystal.

9. A single crystal molybdenum alloy containing a dispersed carbide second phase according to claim 8, characterized in that The Nb2C particles are strip-shaped.

10. A molybdenum alloy single crystal containing a dispersed carbide second phase according to claim 8, characterized in that, By mass fraction, in the molybdenum alloy single crystal, Re is 5 wt.%, Nb2C particles are 0.2 - 1 wt.%, and the rest is Mo.

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