Preparation method for in-situ generation of tungsten carbide coating on surface of tungsten-rhenium alloy

Abstract

The invention provides a preparation method for in-situ generation of a tungsten carbide coating on the surface of a tungsten-rhenium alloy, which comprises the following steps: S1, mixing a tungsten source and a rhenium source according to a target ratio, spray-drying, and carrying out hydrogen reduction treatment to obtain a tungsten-rhenium pre-alloy; and S2, after the tungsten-rhenium pre-alloy prepared in the step S1 is transferred into a mold containing graphite, hot pressed sintering is conducted in the inert atmosphere at the temperature of 1800-2000 DEG C and the pressure of 50-100 MPa, and then the tungsten carbide coating can be generated on the surface of the tungsten-rhenium alloy in situ. According to the method, the tungsten-rhenium pre-alloy obtained through hydrogenation reduction is directly subjected to hot pressed sintering in a graphite-containing mold, and the tungsten carbide coating is prepared on the surface of the tungsten-rhenium alloy in situ. And the tungsten carbide coating which has excellent binding force with the tungsten-rhenium alloy and is high in hardness can be prepared. Wherein the binding force between the coating and the matrix is greater than or equal to 20MPa; the hardness of the tungsten-rhenium alloy with the tungsten carbide coating on the surface is larger than or equal to 1000 HV. The wear-resisting property is excellent.

Description

Technical Field

[0001] This invention relates to the field of alloy materials technology, and in particular to a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy. Background Technology

[0002] Tungsten (W), a refractory metal, plays an irreplaceable role in cutting-edge fields such as defense, aerospace, and nuclear industries due to its excellent properties, including high melting point, high density, high hardness, low sputtering rate, and low coefficient of thermal expansion. Specifically, its high-temperature and high-strength characteristics make it a core material for critical components such as jet engine nozzles; its excellent hardness and wear resistance make it the preferred material for friction stir welding heads and metal forming dies; and its low sputtering rate and low coefficient of thermal expansion make it the preferred material for the plasma-facing first wall in fusion reactors. However, pure tungsten materials suffer from fatal defects such as poor room-temperature ductility and toughness, and high-temperature recrystallization embrittlement, which severely limit its reliable application under extreme conditions.

[0003] To address the aforementioned technical bottlenecks, the materials science community generally employs alloying strategies, introducing rhenium (Re) to construct W-Re alloys. Studies have shown that the solid solution strengthening effect of Re can significantly improve the room-temperature plasticity and high-temperature strength of materials, but its low hardness still results in insufficient wear resistance. Applying a coating to the surface of tungsten-rhenium alloys can improve both hardness and wear resistance. Traditional coating preparation processes employ methods such as thermal spraying and magnetron sputtering. These methods only provide a mechanical bond between the coating and the substrate, resulting in poor adhesion, and the coating is prone to peeling off under heavy loads.

[0004] Therefore, it is necessary to develop a new preparation technology that can prepare high-performance coatings on the surface of tungsten-rhenium alloys in a short process, improve the surface hardness and wear resistance of tungsten-rhenium alloys, extend the service life of tungsten-rhenium alloys in extreme environments, and expand the application scenarios of tungsten-rhenium alloys. Summary of the Invention

[0005] The purpose of this invention is to address the technical bottlenecks in the existing technology of complex two-step processes for preparing tungsten-rhenium alloys based on tungsten-rhenium alloy substrates and coatings, and insufficient bonding strength at the coating / substrate interface, by providing a method for in-situ generation of tungsten carbide coatings on the surface of tungsten-rhenium alloys.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten source and rhenium source are mixed in the target ratio, spray dried, and then subjected to hydrogen reduction treatment to obtain tungsten-rhenium pre-alloy; S2: After transferring the tungsten-rhenium pre-alloy prepared in step S1 into a graphite-containing mold, hot pressing sintering is carried out in an inert atmosphere at 1800~2000℃ and 50~100MPa to generate a tungsten carbide coating in situ on the surface of the tungsten-rhenium alloy.

[0007] As an embodiment of the present invention, the tungsten source includes ammonium metatungstate.

[0008] As an embodiment of the present invention, the rhenium source includes ammonium rhenium oxide.

[0009] As an embodiment of the present invention, in the tungsten-rhenium pre-alloy described in step S1, the mass percentage content of rhenium is 3-25%.

[0010] As an embodiment of the present invention, the hydrogen reduction treatment process in step S1 is as follows: treatment at 900~1100℃ for 3~5 hours in a hydrogen atmosphere.

[0011] As an embodiment of the present invention, the graphite-containing mold mentioned in step S2 is a ceramic mold with graphite paper lining its inner wall, or a mold made of graphite material; the thickness of the graphite paper is ≥0.5mm, and the purity of the graphite paper is ≥99%.

[0012] As an embodiment of the present invention, the inert atmosphere described in step S2 includes at least one gas selected from helium, neon, and argon.

[0013] As an embodiment of the present invention, the hot pressing sintering time in step S2 is 0.5~1h.

[0014] As an embodiment of the present invention, the product of hot pressing sintering in step S2 includes, from the inside out: a tungsten-rhenium alloy substrate layer and a tungsten carbide coating layer.

[0015] As an embodiment of the present invention, the thickness of the tungsten carbide coating is 50~500μm.

[0016] As an embodiment of the present invention, in the product of hot pressing sintering in step S2, the tungsten rhenium alloy with a tungsten carbide coating on the surface has a hardness ≥1000HV.

[0017] As an embodiment of the present invention, in the product of hot pressing sintering in step S2, the bonding force between the tungsten carbide coating and the tungsten-rhenium alloy is ≥20MPa.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention improves the coating preparation process by directly hot-pressing and sintering the tungsten-rhenium pre-alloy obtained through hydrogenation reduction in a graphite-containing mold, thereby preparing a tungsten carbide coating in situ on the surface of the tungsten-rhenium alloy. This yields a tungsten carbide coating with excellent adhesion to the tungsten-rhenium alloy and high hardness. Specifically, the adhesion between the coating and the substrate is ≥20 MPa; the hardness of the tungsten-rhenium alloy with the tungsten carbide coating is ≥1000 HV; and it exhibits excellent wear resistance. Attached Figure Description

[0019] Figure 1 The image shows the metallographic diagram of the coating on the tungsten-rhenium alloy with a tungsten carbide coating prepared in Example 1. Detailed Implementation

[0020] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0021] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0022] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0023] Unless otherwise specified, all reagents or instruments used in this invention are commercially available products.

[0024] This invention provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten source and rhenium source are mixed in the target ratio, spray dried, and then subjected to hydrogen reduction treatment to obtain tungsten-rhenium pre-alloy; S2: After transferring the tungsten-rhenium pre-alloy prepared in step S1 into a graphite-containing mold, hot pressing sintering is carried out in an inert atmosphere at 1800~2000℃ and 50~100MPa to generate a tungsten carbide coating in situ on the surface of the tungsten-rhenium alloy.

[0025] This invention improves the coating preparation process by directly hot-pressing and sintering the tungsten-rhenium pre-alloy obtained by hydrogenation reduction in a graphite-containing mold, thereby preparing a tungsten carbide coating in situ on the surface of the tungsten-rhenium alloy. This allows for the preparation of a tungsten carbide coating with excellent adhesion to the tungsten-rhenium alloy and high hardness.

[0026] During the hot pressing sintering process of tungsten rhenium pre-alloy in a graphite-containing mold: (1) As the temperature rises, the graphite first undergoes "activation" - the number of defects (such as vacancies and dislocations) inside the crystal increases, the interlayer bonding force weakens, and some carbon atoms detach from the original layered structure and become "active carbon" with high migration ability; the tungsten rhenium pre-alloy particles undergo plastic deformation under the action of hot pressing pressure, the pores between the particles are compressed, and the contact surface gradually forms a dense metal matrix. The tungsten rhenium pre-alloy obtained by hydrogen reduction treatment has finer grains and higher purity, and larger grain boundary area, providing more pathways for the diffusion of carbon in the alloy metal matrix. (2) As the temperature continues to rise, under the influence of pressure and the concentration difference of carbon elements inside and outside the alloy, the contact surface between graphite and the alloy matrix remains tightly attached, eliminating the interfacial gap, shortening the diffusion distance of carbon, and promoting the rapid migration of active carbon along the grain boundary. When carbon diffuses to the surface of the tungsten-rhenium alloy, it will react with tungsten atoms in the matrix in situ to form tungsten carbide (WC). In this process, the role of rhenium atoms is to "adjust the crystal structure" - after rhenium is incorporated into the tungsten lattice as a solid solution element, it will slightly increase the tungsten lattice constant, providing more space for the insertion of carbon atoms, while reducing the activation energy of WC phase formation and accelerating the reaction. (3) When the target temperature is reached, during the hot-pressing and heat-preservation stage, the WC phase on the surface continues to grow and gradually "densifies": on the one hand, the unreacted activated carbon continues to diffuse into the matrix and react with the tungsten atoms in the deeper layers, causing the thickness of the WC coating to increase slowly; on the other hand, the WC grains that have been generated undergo "grain growth" at high temperature, the pores between the particles are filled, and the density of the coating is increased; more importantly, a "metallurgical bonding interface" is formed at this stage - the interface between the WC coating and the tungsten-rhenium matrix is ​​not a simple physical adhesion, but a "transition layer". The transition layer includes intermediate carbides and tungsten-rhenium alloy, and the three elements of carbon, tungsten and rhenium diffuse into each other: carbon extends into the matrix, tungsten migrates from the matrix to the coating, and rhenium is partially dissolved in the WC lattice. This mutual penetration of elements eliminates the interfacial tension, making the coating and the matrix a continuous whole, which is also the core reason for the coating's "good bonding performance". Meanwhile, WC itself has extremely high hardness, and the densified coating has no obvious defects, ultimately achieving the dual advantages of "high hardness" and "high adhesion".

[0027] In some embodiments of the present invention, the tungsten source comprises ammonium metatungstate. Ammonium metatungstate undergoes a stepwise decomposition-reduction process during hydrogen reduction ((NH4)6H2W). 12 O 40→WO3→W), ultimately producing fine-grained tungsten powder.

[0028] In some embodiments of the present invention, the rhenium source comprises ammonium perrylate. The ammonium perrylate is reduced to form rhenium powder with a finer particle size.

[0029] Ammonium metatungstate and ammonium rhenium, as tungsten and rhenium sources, provide ideal matrix conditions for the in-situ formation of tungsten carbide coatings by improving the compositional uniformity, purity, reactivity and process adaptability of the pre-alloyed material. Ultimately, this helps to obtain tungsten carbide coatings with strong adhesion, high hardness and stable performance.

[0030] Ammonium metatungstate and ammonium rhenium are both water-soluble salts, which can be uniformly dispersed at the atomic level through solution mixing. During spray drying, the two salts co-precipitate at the molecular scale to form composite particles. In the tungsten-rhenium pre-alloy obtained after hydrogen reduction, the hydrogen reduction process further removes residual nitrogen, oxygen, and other elements, resulting in a tungsten-rhenium pre-alloy with higher purity. Furthermore, the distribution of tungsten and rhenium in the prepared tungsten-rhenium pre-alloy is extremely uniform, which can avoid abnormal growth of tungsten carbide grains caused by local enrichment of tungsten, ensuring uniform coating thickness. The surfaces of the reduction products of ammonium metatungstate and ammonium rhenium have a certain amount of residual active sites (such as unsaturated bonds and lattice defects), which have a stronger adsorption capacity for carbon.

[0031] In some embodiments of the present invention, the rhenium content in the tungsten-rhenium pre-alloy described in step S1 is 3-25% by mass. The hardness of the tungsten carbide coating mainly depends on the purity, grain size, and density of the WC phase, while the rhenium content indirectly affects the coating hardness by regulating the carbide reaction efficiency and the WC grain growth process. Rhenium uniformly integrates into the tungsten lattice in solid solution form, which slightly increases the lattice constant of tungsten. This change reduces the resistance to carbon atoms embedding into the tungsten lattice, making it easier for the carbide reaction to generate a high-purity WC phase (reducing the generation of metastable phases such as W2C); at the same time, rhenium can refine the WC grains—rhenium atoms adsorb on the surface of the WC grains, hindering abnormal grain growth at high temperatures, forming a fine-grained WC coating. With increasing rhenium content, the high purity and density of the WC phase can be maintained within a certain range, and the coating surface has good smoothness, without obvious pores or cracks, which is beneficial to improving the hardness of the coating. However, when the rhenium content is further increased, rhenium will "preempt" tungsten atom lattice sites during carbonization, causing some tungsten atoms to fail to react fully with carbon, resulting in a decrease in the purity of the generated WC phase. Therefore, in tungsten-rhenium pre-alloys, the rhenium content needs to be controlled within the aforementioned suitable range.

[0032] In some embodiments of the present invention, the hydrogen reduction treatment in step S1 is performed by treating the material at 900-1100°C for 3-5 hours in a hydrogen atmosphere. Under these conditions, hydrogen reduction treatment can produce a tungsten-rhenium alloy with uniform elemental distribution and small grain size, providing favorable conditions for subsequent in-situ hot pressing sintering to prepare a tungsten carbide coating.

[0033] In some embodiments of the present invention, the inert atmosphere described in step S2 includes, but is not limited to, at least one gas selected from helium, neon, and argon, as long as an inert atmosphere can be formed. The core function of the inert atmosphere is to isolate oxygen, prevent graphite from being oxidized to CO or CO2, and at the same time prevent the formation of an oxide layer on the surface of the tungsten-rhenium alloy.

[0034] In some embodiments of the present invention, the graphite mold mentioned in step S2 is a ceramic mold with graphite paper laid on the inner wall, or a mold made of graphite material; the thickness of the graphite paper is ≥0.5mm, and the purity of the graphite paper is ≥99%.

[0035] In some embodiments of the present invention, the hot pressing sintering time in step S2 is 0.5~1h.

[0036] The temperature of hot-pressing sintering is a key factor affecting the thermodynamics and kinetics of the carbide reaction, directly determining the formation efficiency of the WC phase and the coating density. The hot-pressing sintering time affects the coating thickness by controlling the carbon diffusion depth and reaction sufficiency, and together with temperature, influences the coating density and interfacial bonding state. The hot-pressing sintering pressure indirectly improves carbon diffusion efficiency and coating density by improving the contact state between the tungsten-rhenium pre-alloy and graphite and promoting particle plastic deformation. Therefore, the in-situ hot-pressing sintering of tungsten carbide coatings relies on "temperature-dominant, time-matched, pressure-assisted, and carbon content-appropriate" factors to jointly determine the coating's performance and the bonding strength between the coating and the substrate, thus determining the wear resistance of the tungsten-rhenium alloy composite material with a tungsten carbide coating.

[0037] In some embodiments of the present invention, the product of hot pressing sintering in step S2 includes, from the inside out: a tungsten-rhenium alloy substrate layer and a tungsten carbide coating.

[0038] In some embodiments of the present invention, the product of hot pressing sintering in step S2 is a tungsten-rhenium alloy with a tungsten carbide coating on its surface, wherein the hardness of the tungsten-rhenium alloy with a tungsten carbide coating on its surface is ≥1000HV.

[0039] In some embodiments of the present invention, the bonding strength between the tungsten carbide coating and the tungsten-rhenium alloy in the product of hot pressing sintering in step S2 is ≥20MPa.

[0040] The following are specific embodiments of the present invention.

[0041] Example 1 This embodiment provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten-based ammonium metatungstate and rhenium-based ammonium rhenium are mixed in a W:Re mass ratio of 75:25. After spray drying, tungsten-rhenium precursor powder is obtained. The precursor powder is then subjected to hydrogen reduction at 1000℃ in an H2 atmosphere for 5 hours to obtain W-25Re pre-alloy powder. W-25Re indicates that the mass percentage of rhenium (Re) in the tungsten-rhenium pre-alloy is 25%. S2: Place the W-25Re pre-alloy powder prepared in step S1 into a graphite mold. After loading, place the graphite mold in an argon atmosphere for hot pressing sintering. The hot pressing sintering process parameters are: temperature 1900℃, time 1h, and pressure 70MPa. After sintering, a tungsten carbide coating can be generated in situ on the surface of the tungsten-rhenium alloy, resulting in a tungsten-rhenium alloy with a tungsten carbide coating on the surface.

[0042] Example 2 This embodiment provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten-based ammonium metatungstate and rhenium-based ammonium rhenium are mixed in a W:Re mass ratio of 75:25. After spray drying, tungsten-rhenium precursor powder is obtained. The precursor powder is then subjected to hydrogen reduction at 1000℃ in an H2 atmosphere for 5 hours to obtain W-25Re pre-alloy powder. W-25Re indicates that the mass percentage of rhenium (Re) in the tungsten-rhenium pre-alloy is 25%. S2: Place the W-25Re pre-alloy powder prepared in step S1 into a graphite mold. After loading, place the graphite mold in an argon atmosphere for hot pressing sintering. The hot pressing sintering process parameters are: temperature 1800℃, time 1h, and pressure 70MPa. After sintering, a tungsten carbide coating can be generated in situ on the surface of the tungsten-rhenium alloy, resulting in a tungsten-rhenium alloy with a tungsten carbide coating on the surface.

[0043] Example 3 This embodiment provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten-based ammonium metatungstate and rhenium-based ammonium rhenium are mixed in a W:Re mass ratio of 75:25. After spray drying, tungsten-rhenium precursor powder is obtained. The precursor powder is then subjected to hydrogen reduction at 1000℃ in an H2 atmosphere for 5 hours to obtain W-25Re pre-alloy powder. W-25Re indicates that the mass percentage of rhenium (Re) in the tungsten-rhenium pre-alloy is 25%. S2: Place the W-25Re pre-alloy powder prepared in step S1 into a graphite mold. After loading, place the graphite mold in an argon atmosphere for hot pressing sintering. The hot pressing sintering process parameters are: temperature 2000℃, time 1h, and pressure 70MPa. After sintering, a tungsten carbide coating can be generated in situ on the surface of the tungsten-rhenium alloy, resulting in a tungsten-rhenium alloy with a tungsten carbide coating on the surface.

[0044] Example 4 This embodiment provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten-based ammonium metatungstate and rhenium-based ammonium rhenium are mixed in a W:Re mass ratio of 75:25. After spray drying, tungsten-rhenium precursor powder is obtained. The precursor powder is then subjected to hydrogen reduction at 1000℃ in an H2 atmosphere for 5 hours to obtain W-25Re pre-alloy powder. W-25Re indicates that the mass percentage of rhenium (Re) in the tungsten-rhenium pre-alloy is 25%. S2: The W-25Re pre-alloy powder prepared in step S1 is placed in a ZrO2 ceramic mold with graphite paper (the thickness of the graphite paper is 1.0 mm and the purity of the graphite paper is ≥99%). After loading, the graphite mold is placed in an argon atmosphere for hot pressing sintering. The process parameters for hot pressing sintering are: temperature 1900℃, time 1h, and pressure 70MPa. After sintering, a tungsten carbide coating can be generated in situ on the surface of the tungsten-rhenium alloy, resulting in a tungsten-rhenium alloy with a tungsten carbide coating on the surface.

[0045] Example 5 This embodiment provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten-based ammonium metatungstate and rhenium-based ammonium rhenium are mixed in a W:Re mass ratio of 75:25. After spray drying, tungsten-rhenium precursor powder is obtained. The precursor powder is then subjected to hydrogen reduction at 1000℃ in an H2 atmosphere for 5 hours to obtain W-25Re pre-alloy powder. W-25Re indicates that the mass percentage of rhenium (Re) in the tungsten-rhenium pre-alloy is 25%. S2: The W-25Re pre-alloy powder prepared in step S1 is placed in a ZrO2 ceramic mold with graphite paper (the thickness of the graphite paper is 0.5 mm and the purity of the graphite paper is ≥99%). After loading, the graphite mold is placed in an argon atmosphere for hot pressing sintering. The process parameters for hot pressing sintering are: temperature 1800℃, time 1h, and pressure 70MPa. After sintering, a tungsten carbide coating can be generated in situ on the surface of the tungsten-rhenium alloy, resulting in a tungsten-rhenium alloy with a tungsten carbide coating on the surface.

[0046] Example 6 This embodiment provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten-based ammonium metatungstate and rhenium-based ammonium rhenium are mixed in a W:Re mass ratio of 75:25. After spray drying, tungsten-rhenium precursor powder is obtained. The precursor powder is then subjected to hydrogen reduction at 1000℃ in an H2 atmosphere for 5 hours to obtain W-25Re pre-alloy powder. W-25Re indicates that the mass percentage of rhenium (Re) in the tungsten-rhenium pre-alloy is 25%. S2: The W-25Re pre-alloy powder prepared in step S1 is placed in a ZrO2 ceramic mold with graphite paper (the thickness of the graphite paper is 0.5 mm and the purity of the graphite paper is ≥99%). After loading, the graphite mold is placed in an argon atmosphere for hot pressing sintering. The process parameters for hot pressing sintering are: temperature 2000℃, time 1h, and pressure 70MPa. After sintering, a tungsten carbide coating can be generated in situ on the surface of the tungsten-rhenium alloy, resulting in a tungsten-rhenium alloy with a tungsten carbide coating on the surface.

[0047] Example 7 This embodiment provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten-based ammonium metatungstate and rhenium-based ammonium rhenium are mixed in a W:Re mass ratio of 75:25. After spray drying, tungsten-rhenium precursor powder is obtained. The precursor powder is then subjected to hydrogen reduction at 1000℃ in an H2 atmosphere for 5 hours to obtain W-25Re pre-alloy powder. W-25Re indicates that the mass percentage of rhenium (Re) in the tungsten-rhenium pre-alloy is 25%. S2: Place the W-25Re pre-alloy powder prepared in step S1 into a graphite mold. After loading, place the graphite mold in an argon atmosphere for hot pressing sintering. The hot pressing sintering process parameters are: temperature 1900℃, time 1h, and pressure 100MPa. After sintering, a tungsten carbide coating can be generated in situ on the surface of the tungsten-rhenium alloy, resulting in a tungsten-rhenium alloy with a tungsten carbide coating on the surface.

[0048] Example 8 This embodiment provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten-based ammonium metatungstate and rhenium-based ammonium rhenium are mixed in a W:Re mass ratio of 75:25. After spray drying, tungsten-rhenium precursor powder is obtained. The precursor powder is then subjected to hydrogen reduction at 1000℃ in an H2 atmosphere for 5 hours to obtain W-25Re pre-alloy powder. W-25Re indicates that the mass percentage of rhenium (Re) in the tungsten-rhenium pre-alloy is 25%. S2: Place the W-25Re pre-alloy powder prepared in step S1 into a graphite mold. After loading, place the graphite mold in an argon atmosphere for hot pressing sintering. The hot pressing sintering process parameters are: temperature 1900℃, time 1h, and pressure 50MPa. After sintering, a tungsten carbide coating can be generated in situ on the surface of the tungsten-rhenium alloy, resulting in a tungsten-rhenium alloy with a tungsten carbide coating on the surface.

[0049] Example 9 This embodiment provides a method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, comprising the following steps: S1: Tungsten-based ammonium metatungstate and rhenium-based ammonium rhenium are mixed in a W:Re mass ratio of 75:25. After spray drying, tungsten-rhenium precursor powder is obtained. The precursor powder is then subjected to hydrogen reduction at 1000℃ in an H2 atmosphere for 5 hours to obtain W-25Re pre-alloy powder. W-25Re indicates that the mass percentage of rhenium (Re) in the tungsten-rhenium pre-alloy is 25%. S2: Place the W-25Re pre-alloy powder prepared in step S1 into a graphite mold. After loading, place the graphite mold in an argon atmosphere for hot pressing sintering. The hot pressing sintering process parameters are: temperature 1900℃, time 0.5h, and pressure 70MPa. After sintering, a tungsten carbide coating can be generated in situ on the surface of the tungsten-rhenium alloy, resulting in a tungsten-rhenium alloy with a tungsten carbide coating on the surface.

[0050] Comparative Example 1 This comparative example provides a method for preparing a tungsten carbide coating on the surface of a tungsten-rhenium alloy. The preparation is carried out according to the method of Example 1, except that the sintering temperature in S2 is 1500℃, the time is 1h, and the pressure is 70MPa.

[0051] Comparative Example 2 This comparative example provides a method for preparing a tungsten carbide coating on the surface of a tungsten-rhenium alloy. The preparation is carried out according to the method of Example 1, except that the sintering temperature in S2 is 2500℃, the time is 0.5h, and the pressure is 70MPa.

[0052] Comparative Example 3 This comparative example provides a method for preparing a tungsten carbide coating on the surface of a tungsten-rhenium alloy. The preparation is carried out according to the method of Example 1, except that the sintering temperature in S2 is 1900℃, the time is 5h, and the pressure is 0.1MPa (standard atmospheric pressure).

[0053] Comparative Example 4 This comparative example provides a method for preparing a tungsten-rhenium alloy, which is prepared according to the method of Example 1. The difference from Example 1 is that a ZrO2 ceramic mold is used in S2 and no graphite paper is laid on it.

[0054] Performance testing The tungsten-rhenium alloys with tungsten carbide coatings or uncoated tungsten-rhenium alloys (such as Comparative Example 2) prepared in the above embodiments and comparative examples were used as test samples, and the following performance tests were conducted. The test results are shown in Table 1.

[0055] 1. Metallographic structure analysis of the coating After the interface of the sample to be tested is polished, it is placed under a metallographic microscope, such as... Figure 1 As shown, the metallographic image of the sample coating of Example 1 is shown (the metallographic images of the coatings of other examples are similar). It can be seen that the coating includes a tungsten carbide surface layer, an intermediate transition layer, and a tungsten-rhenium alloy core layer from the outside to the inside. The thickness of each layer is detailed in Table 1.

[0056] 2. Test of adhesion between tungsten carbide coating and tungsten-rhenium alloy substrate According to the standard ASTM D4541-22, a portable adhesion tester was used to bond the test fixture to the coating surface with adhesive, and then a vertical tensile force was applied. The adhesion strength of the coating was determined based on the adhesive strength. The test results are detailed in Table 1.

[0057] 3. Coating hardness (Vickers hardness) The Vickers hardness (HV) of the sample under a 1kg load for 15s was tested using a Vickers hardness tester. The test results are shown in Table 1.

[0058] 4. Abrasion resistance A reciprocating friction testing machine was used, and the friction conditions were: pressure 50N, Si3N4 grinding balls with a diameter of 5mm, reciprocating frequency of 500 times per minute, friction distance of 5mm, time of 30min, and test temperature of room temperature (25±5℃). The wear volume was then calculated.

[0059] Table 1 The results above show that: The results of Examples 1-3 show that when the hot pressing sintering temperature is low, the coating is thinner, but the thickness exceeds 170 μm. However, as the temperature increases, the coating grains grow, the hardness decreases, and the wear rate decreases.

[0060] The results of Examples 4-6 show that during hot pressing sintering, a coating can be formed by laying graphite paper on the surface of the ceramic mold. Since there is less carbon source in the graphite paper, the coating thickness is thinner than that of the graphite mold used directly, but it still exhibits high hardness and low wear volume, and its behavior is consistent with that of the graphite mold.

[0061] The results of Examples 1 and 7-8 show that under high pressure, the element diffusion rate slows down and the coating thickness becomes thinner, but the density increases, which in turn increases the hardness of the coating and reduces the wear volume.

[0062] The results of Examples 1 and 9 show that although reducing the heat preservation time makes the coating thinner, the grain size in the coating is finer, which also increases the coating hardness and reduces the wear volume.

[0063] The results of Example 1 and Comparative Example 1 show that excessively low temperatures lead to thinning of the coating, while the density of both the substrate and the coating decreases, resulting in reduced coating hardness and increased wear.

[0064] The results of Examples 1, 4 and Comparative Example 2 show that if graphite molds are not used or graphite paper is laid on the surface of non-graphite molds, a carbide coating cannot be formed on the surface of the prepared tungsten-rhenium alloy, resulting in low hardness and poor wear resistance of the samples.

[0065] This invention improves the coating preparation process by directly hot-pressing and sintering the tungsten-rhenium pre-alloy obtained through hydrogenation reduction in a graphite-containing mold, thereby preparing a tungsten carbide coating in situ on the surface of the tungsten-rhenium alloy. This yields a tungsten carbide coating with excellent adhesion to the tungsten-rhenium alloy and high hardness. Specifically, the adhesion between the coating and the substrate is ≥20 MPa; the hardness of the tungsten-rhenium alloy with the tungsten carbide coating is ≥1000 HV; and it exhibits excellent wear resistance.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy, characterized in that, Includes the following steps: S1: Mix tungsten source and rhenium source in the target ratio, spray dry, and then perform hydrogen reduction treatment to obtain tungsten-rhenium pre-alloy; S2: After transferring the tungsten-rhenium pre-alloy prepared in step S1 into a graphite-containing mold, hot pressing sintering is carried out in an inert atmosphere at 1800~2000℃ and 50~100MPa to generate a tungsten carbide coating in situ on the surface of the tungsten-rhenium alloy.

2. The method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy according to claim 1, characterized in that, The tungsten source includes ammonium metatungstate; and / or, the rhenium source includes ammonium rhenium.

3. The method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy according to claim 1, characterized in that, In the tungsten-rhenium pre-alloy described in step S1, the mass percentage of rhenium is 3-25%.

4. The method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy according to claim 1, characterized in that, The hydrogen reduction process described in step S1 is as follows: treatment at 900~1100℃ for 3~5 hours in a hydrogen atmosphere.

5. The method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy according to claim 1, characterized in that, The graphite-containing mold mentioned in step S2 is a ceramic mold with graphite paper lining its inner wall, or a mold made of graphite material; the thickness of the graphite paper is ≥0.5mm, and the purity of the graphite paper is ≥99%.

6. The method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy according to claim 1, characterized in that, The inert atmosphere described in step S2 includes at least one gas selected from helium, neon, and argon.

7. The method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy according to claim 1, characterized in that, The hot pressing sintering time in step S2 is 0.5~1h.

8. The method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy according to claim 1, characterized in that, The product of hot pressing sintering in step S2 includes, from the inside out: a tungsten-rhenium alloy matrix and a tungsten carbide coating.

9. The method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy according to claim 8, characterized in that, The thickness of the tungsten carbide coating is 50~500μm.

10. The method for preparing an in-situ tungsten carbide coating on the surface of a tungsten-rhenium alloy according to claim 1, characterized in that, In the product of hot pressing sintering in step S2, the hardness of the tungsten-rhenium alloy with a tungsten carbide coating on the surface is ≥1000HV; the bonding force between the tungsten carbide coating and the tungsten-rhenium alloy is ≥20MPa.

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