A tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating and a method for producing the same

Abstract

The application discloses a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating and a preparation method thereof, and belongs to the field of ceramic material preparation. The method is as follows: powder raw materials including modified silicon carbide, aluminum oxide, silicon dioxide and lead oxide are mixed with a solvent by ball milling, and ceramic slurry is obtained by removing bubbles; the ceramic slurry is brushed on the surface of a tungsten alloy substrate which has been pre-treated, and then dried and vacuum sintered. The application introduces a dense silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating on the surface of the tungsten alloy substrate, significantly improves the hardness, high-temperature oxidation resistance and high-temperature decarburization resistance of the tungsten alloy material, and the dispersed point-like silicon carbide can improve the stability of the coating, uniformly reduce the thermal expansion coefficient of the coating, reduce the difference between the thermal expansion coefficients of the composite ceramic coating and the tungsten alloy substrate, and improve the thermal shock resistance of the coating.

Description

TECHNICAL FIELD

[0001] The present application relates to a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating and a preparation method thereof, in particular to a method for preparing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating on the surface of a tungsten alloy material by slurry sintering, and belongs to the field of ceramic material preparation. BACKGROUND

[0002] Tungsten alloy has high strength, high hardness and excellent thermal stability, and plays an important role in the fields of national defense and military (such as armor-piercing bullet core, armor protection), energy and chemical industry (such as water coal slurry gasification furnace parts) and aerospace (such as high temperature engine components). In particular, in the water coal slurry gasification technology, tungsten alloy becomes the first choice for the burner shield due to its ability to withstand mechanical load and thermal shock under extreme working conditions. However, when the shield is long-term served in a high temperature environment of 1250-1400℃, it faces severe challenges of high temperature oxidation and carburization corrosion: on the one hand, high temperature oxidation leads to the formation of a loose and porous WO3 oxidation layer on the surface of the tungsten alloy, which is prone to cracking and peeling due to the repeated action of thermal stress, further accelerating the oxidation of the matrix; on the other hand, carbon atoms in the carbon-containing atmosphere diffuse into the tungsten alloy, forming a brittle carbide phase, which destroys the matrix structure and significantly reduces the strength and toughness. The coupling corrosion of oxidation-carburization seriously shortens the service life of the equipment.

[0003] In view of the above problems, it is crucial to prepare a high-performance ceramic coating on the surface of tungsten alloy. In the existing coating preparation technology, chemical vapor deposition (CVD), physical vapor deposition (PVD) and other methods have problems such as high equipment cost and complex process, while the slurry sintering method is the preferred process for preparing the composite ceramic coating due to its suitability for complex-shaped substrates, controllable microstructure (through dispersant to control particle distribution and phase composition) and low cost. If the slurry sintering technology can be introduced into the preparation of tungsten alloy material coating, it is expected to further improve the comprehensive performance of tungsten alloy workpieces.

[0004] Among them, the introduction of silicon carbide into the Al2O3-SiO2matrix to form a composite ceramic coating is expected to become an ideal choice for the tungsten alloy burner of the water coal slurry gasification furnace burner. However, there are two technical bottlenecks in the preparation process: first, micron-sized silicon carbide powder is prone to agglomeration in the ceramic slurry, resulting in poor slurry flowability and difficulty in forming; second, the difference in the coefficient of thermal expansion (CTE) between tungsten alloy and ceramic coating is significant, and the interfacial thermal stress is easy to cause the coating to crack and fall off, therefore, a preparation method that can perfectly solve the above difficulties must be found. SUMMARY

[0005] In view of the performance deficiency of tungsten alloy material in high temperature service environment in the prior art, which leads to shortening of service life of tungsten alloy material equipment and other problems, a first object of the present application is to provide a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating, which significantly improves the hardness, high temperature oxidation resistance and high temperature decarburization resistance of the tungsten alloy material by introducing a dense silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating on the surface of the tungsten alloy substrate, and the dispersed point-like distributed silicon carbide can improve the stability of the coating, uniformly reduce the thermal expansion coefficient of the coating, reduce the difference in thermal expansion coefficient between the composite ceramic coating and the tungsten alloy substrate, and improve the thermal shock resistance of the coating.

[0006] A second object of the present application is to provide a preparation method of a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating, which avoids the agglomeration problem of silicon carbide by using silane coupling agent and polyethylene imine grafting cooperative treatment of silicon carbide, promotes the formation of continuous interfacial phase of aluminosilicate liquid phase, significantly improves the interfacial bonding strength and density of the coating, and in addition, the slurry sintering method does not require complex molds and can meet the surface protection needs of special shaped parts.

[0007] In order to achieve the above technical objects, the present application provides a preparation method of a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating, which comprises: ball-milling and mixing powder raw materials including modified silicon carbide, aluminum oxide, silicon dioxide and lead oxide with a solvent to obtain ceramic slurry after defoaming; brushing the ceramic slurry on the surface of a tungsten alloy substrate after surface pretreatment, drying and then vacuum sintering to obtain the tungsten alloy material; the preparation process of the modified silicon carbide comprises: taking silicon carbide powder and sequentially subjecting it to spherical treatment, silane coupling agent treatment and polyethylene imine grafting treatment to obtain the modified silicon carbide; and the silicon carbide in the composite ceramic coating is dispersed in the Al2O3-SiO2 matrix in a dispersed point-like manner.

[0008] The key idea of the technical solution of the present application is to modify the silicon carbide first and then form a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating on the surface of the tungsten alloy substrate by slurry sintering method through metallurgical and mechanical bonding, so that the silicon carbide in the composite ceramic coating is dispersed in the Al2O3-SiO2 matrix in a dispersed point-like manner, forming a "SiC particle-matrix" composite structure, thereby significantly improving the stability of the coating, uniformly reducing the thermal expansion coefficient of the coating, reducing the difference in thermal expansion coefficient between the composite ceramic coating and the tungsten alloy substrate, improving the thermal shock resistance of the coating, and improving the high temperature comprehensive performance of the tungsten alloy material.

[0009] The present application first increases the stress uniformity and the density of the composite ceramic coating by utilizing the spherical morphology of the silicon carbide powder through the spheroidization treatment of the silicon carbide powder in the modification process of the silicon carbide, so as to reduce the occurrence of micro-cracks caused by stress concentration; secondly, the silicon carbide powder after the spheroidization treatment is subjected to silane coupling agent treatment and polyethylene imine grafting treatment in sequence, which has obvious synergistic effect and is the key to improve the overall performance of the tungsten alloy material, specifically: before sintering, the silane chain of the silane coupling agent and the amino chain of the polyethylene imine can be combined through hydrogen bond to form a more stable particle coating layer, which significantly improves the dispersibility of the silicon carbide, inhibits the sintering obstacle caused by agglomeration and improves the stability of the slurry; and as the sintering temperature is increased to 300 DEG C, the polyethylene imine will gradually decompose and release gases such as ammonia and hydrogen, the decomposition of the residual nitrogen-containing intermediates (such as amine derivatives) can react with lead oxide to form lead amine complex, which reduces the melting point (from 888 DEG C to 750 DEG C) and forms a liquid phase channel in advance. The coordination of the amino group with Al 3+ As the sintering temperature is increased to 600-800 DEG C, the organic chain segment (aminoalkane) of the silane coupling agent also gradually decomposes, but the silicon-oxygen skeleton (Si-O-Si) remaining after decomposition has high-temperature stability and can be used as an interface reaction site to pre-react with the surface hydroxyl groups of the alumina and silica particles in the slurry to form initial Si-O-Al or Si-O-Si bonds, providing reaction seeds for interface fusion in the high-temperature stage. At a higher sintering temperature, the silicon-oxygen structure remaining in the silane coupling agent can dissolve in the low-melting-point liquid phase formed by the decomposition of polyethylene imine, promote the penetration of the liquid phase into the interstitial space between the silicon carbide particles through the bridging action of the Si-O bond, and accelerate the particle rearrangement and densification. Reaction with alumina to form an aluminosilicate transition phase (such as mullite precursor 3 Al2O3•2SiO2), which has a thermal expansion coefficient between silicon carbide and Al2O3, can relieve interfacial thermal stress, reduce sintering cracking, anchor silicon carbide particles in the ceramic matrix, and improve interfacial bonding strength.

[0010] It is found through experiments that if lead oxide is not added to the slurry, sufficient low-melting-point liquid phase cannot be formed during high-temperature sintering, which will result in difficulty in sintering, insufficient densification, and a sharp increase in porosity of the material. The sintering in vacuum in the present application can also inhibit the oxidation of the tungsten alloy matrix to some extent, maintain the stability of the original composition of the coating and the matrix, isolate impurities (such as N2 and CO2) in the air, avoid the reaction of the impurities with the coating to form brittle phases (such as silicon nitride and carbonate), and maintain the interfacial bonding strength.

[0011] As a preferred scheme, the particle size of the silicon carbide in the composite ceramic coating is 1-5 μm.

[0012] As a preferred scheme, the mass ratio of modified silicon carbide, alumina, silicon dioxide and lead oxide in the ceramic slurry is (5-15):(15-21):(14-18):(2-5). When the amount of modified silicon carbide in the ceramic slurry is excessive, although the silicon carbide particles are still dispersed in the matrix in the form of dispersed points in the finally formed composite ceramic coating, due to the dense distribution of the silicon carbide particles, a small amount of silicon carbide particles may appear slight agglomeration, thereby reducing the overall performance of the coating. Meanwhile, the amount of alumina cannot be excessive, and when it is excessive, the lead silicate glass phase formed by alumina and silicon dioxide at high temperature is excessive, which may cause the overall hardness of the coating to drop sharply, and the wear resistance also decreases synchronously. Further preferably, the mass ratio of modified silicon carbide, alumina, silicon dioxide and lead oxide in the ceramic slurry is (5-10):(18-21):(16-18):(2-5).

[0013] As a preferred scheme, the powder raw material further comprises a dispersant, such as tetramethylammonium hydroxide and polyvinylpyrrolidone (PVP); and the solvent comprises at least one of methanol, ethanol, acetone and toluene.

[0014] As a preferred scheme, the spheroidization treatment is performed by immersing the silicon carbide powder in HF, then pre-oxidizing at 700-900°C in air for 2-4h, and then performing HF acid washing and drying treatment. The heat preservation in air during the spheroidization treatment is beneficial to the preferential oxidation of silicon carbide into silicon dioxide at sharp places on the surface of the silicon carbide, and then the silicon dioxide is removed by hydrofluoric acid, so that silicon carbide powder with higher sphericity can be obtained. Further, the pre-oxidation treatment and acid washing are repeated 2-4 times.

[0015] As a preferred scheme, the silane coupling agent treatment is performed by mixing at least one of KH792 and KH550, the silicon carbide powder after spheroidization treatment and water for 1-4h, and then washing with water, wherein the addition amount of the silane coupling agent is 5-15wt% relative to the total amount of the silane coupling agent, the silicon carbide powder after spheroidization treatment and water. The viscosity of the slurry decreases first and then tends to be stable with the increase of the addition amount of the silane coupling agent, and therefore, further preferably, the addition amount of the silane coupling agent is 10-15wt% relative to the total amount of the silane coupling agent, the silicon carbide powder after spheroidization treatment and water.

[0016] As a preferred scheme, the polyethyleneimine grafting treatment is performed by immersing the silicon carbide powder after silane coupling agent treatment in a polyethyleneimine aqueous solution with a pH of 3-4 for 1-3h, and the concentration of the polyethyleneimine aqueous solution is 6-8wt%.

[0017] As a preferred scheme, the spheroidization treatment further comprises an acid cleaning impurity removal treatment.

[0018] Further, the process of the acid cleaning and impurity removing treatment is as follows: the silicon carbide powder is soaked in hydrochloric acid, and ultrasonic operation is performed every 15-20 min, followed by filtration and water washing for several times to remove surface impurities such as Ca 2+ , Mg 2+ , Fe 3+ , etc.

[0019] As a preferred solution, the process of the vacuum sintering is as follows: first, the temperature is raised to 700-900 DEG C and kept for 20-40 min, then the temperature is raised to 1000-1200 DEG C at a rate of 1-5 DEG C / min and kept for 20-40 min, then the temperature is raised to 1300-1400 DEG C at a rate of 1-5 DEG C / min and kept for 1-2 h, then the temperature is lowered to 700-900 DEG C, and the furnace is cooled to room temperature, and the vacuum degree is 0.1-1 MPa.

[0020] As a preferred solution, the amount of the brushing is controlled to make the thickness of the silicon carbide reinforced Al2O3-SiO2-based composite ceramic layer after high-temperature vacuum sintering be 50-120 mu m.

[0021] The application further provides a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating, which is obtained by the above preparation method.

[0022] The dispersion of the silicon carbide in the Al2O3-SiO2 matrix in the composite ceramic coating of the tungsten alloy material obtained by the application has an important influence on the performance of the whole coating. It is found in experiments that if the dispersion state is broken, such as agglomeration or local segregation, the agglomerated SiC particles will hinder the liquid phase from fully filling the gaps, form a large number of pores and microcracks, and destroy the continuity of the coating; at the same time, the reinforcing effect of SiC is lost, the wear resistance is significantly reduced, and the agglomerates are easy to peel off from the matrix, aggravating the wear; most importantly, the thermal expansion coefficient matching is destroyed, and the thermal shock resistance is significantly reduced.

[0023] Compared with the prior art, the application has the following beneficial effects:

[0024] (1) The application avoids the agglomeration of silicon carbide by using silane coupling agent and polyethylene imine grafting to promote the formation of a continuous interfacial phase of the aluminosilicate liquid phase, significantly improving the interfacial bonding strength and density of the coating. In addition, the slurry of the application has good fluidity and can be uniformly coated on the surface of a tungsten alloy substrate with complex shape by spraying, brushing, dipping and other methods, without the need for complex molds, which can meet the surface protection needs of special-shaped parts, and the raw material utilization rate is high during the slurry coating process, the unsintered slurry can be recycled or recoated, reducing production costs and being suitable for industrialized mass production.

[0025] (2) The process of the present application is not only suitable for Al2O3-SiO2-based composite ceramic system, but also compatible with other ceramic matrix, and can flexibly add carbon fiber, nano particles and other reinforcing phases, further expanding the wear resistance, oxidation resistance, carburizing resistance and other properties of the coating.

[0026] (3) The tungsten alloy material of the present application, by introducing a dense silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating on the surface of the tungsten alloy matrix, significantly improves the hardness, high-temperature oxidation resistance and high-temperature carburizing resistance of the tungsten alloy material, and the dispersed point-like distribution of silicon carbide can improve the stability of the coating, uniformly reduce the thermal expansion coefficient of the coating, reduce the difference in thermal expansion coefficient between the composite ceramic coating and the tungsten alloy matrix, and improve the thermal shock resistance of the coating.

[0027] (4) The surface hardness of the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material of the present application is 1756HV, which is increased by 123% compared with the tungsten alloy bare sample (786HV); in the 1400℃ oxidation environment, the coating sample only increases by 0.006g, while the tungsten alloy bare sample increases by 0.563g, and the coating can effectively inhibit oxidation; in the 1400℃ carburizing experiment, the coating sample only increases by 0.092g (0.46%), and the bare sample increases by 1.116g (5.84%), and the coating can effectively block the penetration of carbon atoms. Before the introduction of silicon carbide powder, the surface hardness of the Al2O3-SiO2-based composite ceramic coating is 1324HV, and after the introduction of silicon carbide powder, it can reach 1756HV. The introduction of silicon carbide powder can reduce the thermal expansion coefficient of the coating, reduce the difference in thermal expansion coefficient between the coating and the tungsten alloy matrix, and improve the thermal shock resistance of the coating. In the 1400℃ air cooling thermal shock cycle experiment, the critical failure cycle number of the silicon carbide reinforced coating of the present application can reach 28 times, which is greatly improved compared with the un-reinforced coating (12 times), effectively delaying the damage evolution. And the coating of the present application is combined closely with the tungsten alloy matrix, and the surface flatness is good. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The a and b in FIG. 1 are the surface SEM images of the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating prepared in Example 1, wherein Figure 1 The b in FIG. 2 is Figure 1 The a in FIG. 2 is a partial enlarged view.

[0029] Figure 2 The XRD pattern of the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating prepared in Example 1.

[0030] Figure 3EDS point scan map of the surface of the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating prepared in Example 1.

[0031] Figure 4 The local enlarged view of a in FIG. 6. Figure 4 The local enlarged view of b in FIG. 6. Figure 1 The local enlarged view of a in FIG. 6.

[0032] Figure 5 XRD pattern of the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating prepared in Example 2.

[0033] Figure 6 SEM images of the surface of the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating prepared in Example 3, wherein, Figure 6 The local enlarged view of b in FIG. 8. Figure 6 The local enlarged view of a in FIG. 8.

[0034] Figure 7 XRD pattern of the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating prepared in Example 3.

[0035] Figure 8 Effect of the amount of coupling agent KH550 on the viscosity of the ceramic slurry.

[0036] Figure 9 Effect of the amount of coupling agent KH792 on the viscosity of the ceramic slurry.

[0037] Figure 10 Effect of the concentration of PEI on the viscosity of the ceramic slurry.

[0038] Figure 11 XRD pattern of the Al2O3-SiO2 matrix composite ceramic coating in the tungsten alloy material containing the Al2O3-SiO2 matrix composite ceramic coating prepared in Comparative Example 1.

[0039] Figure 12 SEM pattern of the surface of the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2 matrix composite ceramic coating prepared in Comparative Example 2.

[0040] Figure 13 SEM image of the surface of the SiC reinforced Al2O3-SiO2 based multiphase ceramic coating in the tungsten alloy material containing the SiC reinforced Al2O3-SiO2 based multiphase ceramic coating prepared in Comparative Example 3.

[0041] Figure 14 SEM image of the surface of the Al2O3-SiO2 based multiphase ceramic coating in the tungsten alloy material containing the Al2O3-SiO2 based multiphase ceramic coating prepared in Comparative Example 5. DETAILED DESCRIPTION

[0042] The application will be further described in conjunction with specific examples. It is apparent that the following described examples are only a part of the examples, and all other examples obtained by those skilled in the art without creative labor still belong to the protection scope of the application.

[0043] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the application can be purchased from the market or prepared by the existing method.

[0044] The tungsten alloy substrate used in the examples and comparative examples of the application is 95W-3Co-2Ni hard alloy, and other tungsten alloy substrates can also be used in the method of the application.

[0045] Example 1

[0046] The example provides a preparation method of a tungsten alloy material containing a SiC reinforced Al2O3-SiO2 based multiphase ceramic coating, comprising the following operation steps:

[0047] 1. Modification of SiC powder

[0048] (1) Surface pickling purification: the SiC powder is soaked in 15wt% hydrochloric acid for 1h, and ultrasonic treatment is performed every 15min during the soaking, and each ultrasonic treatment lasts for 15min, and then the SiC powder is filtered, washed with water twice and dried for standby, so as to remove surface impurities.

[0049] (2) Spherical treatment of SiC powder: the SiC powder is first soaked in 15wt% HF for 5min, and then filtered and dried, and then pre-oxidation treatment is performed on the SiC powder at 800℃ in air for 2h, and then HF acid washing and drying treatment are performed, and the pre-oxidation-acid washing is repeated for 3 times, so as to improve the sphericity of the powder and reduce the internal resistance of the slurry flow.

[0050] (3) Silane coupling agent treatment: the spheroidized silicon carbide powder, KH792 and deionized water were mixed by ultrasonic and stirring at a mass ratio of 9:2:9 for 1 h, and then left to stand. After that, the sample was washed with 5 times of deionized water, and then left to stand. The supernatant was taken and filtered. The process was repeated twice. The silicon carbide powder adsorbed with KH792 was obtained after drying.

[0051] (4) Polyethyleneimine (PEI) grafting treatment: under the condition of maintaining magnetic stirring, 10 g of the silicon carbide powder adsorbed with KH792 was added into a PEI aqueous solution (the concentration of PEI was 6 wt%, and the volume was 100 mL) with pH = 3. After soaking for 1 h, filtering and drying, the silicon carbide powder adsorbed with KH792 and grafted with PEI (i.e. modified silicon carbide powder) was prepared.

[0052] 2. Preparation of ceramic slurry

[0053] Under the condition of maintaining magnetic stirring, 5 g of the modified silicon carbide powder, 21 g of alumina powder, 18 g of silica powder, 6 g of tetramethylammonium hydroxide (TMAH) and 2 g of lead oxide were sequentially added into 100 mL of methanol. The mixture was ball milled in a XQM-2 type variable frequency planetary ball mill (self-rotation speed: 180 r / min, revolution speed: 200 r / min) for 6 h. The bubbles in the slurry were removed by using a ZKT-6020 type vacuum bubble remover, and the ceramic slurry was obtained.

[0054] 3. Pretreatment of tungsten alloy substrate

[0055] The tungsten alloy block (15 mm x 15 mm x 5 mm) was polished on 120#, 240#, 400# and 600# silicon carbide sandpaper in sequence, and then ultrasonically cleaned with anhydrous ethanol and acetone for 15 min, and dried by blowing.

[0056] 4. Surface brushing

[0057] The prepared ceramic slurry was uniformly brushed on the surface of the pretreated tungsten alloy substrate by using a brush, so as to ensure the uniform thickness of the coating. After brushing, the sample was placed in a constant temperature drying oven and dried at 80℃ for 2 h.

[0058] 5. Vacuum sintering

[0059] The dried sample was placed in a muffle furnace, and the vacuum degree was 0.5 MPa. The temperature was raised to 900℃ and maintained for 30 min, then raised to 1200℃ at a rate of 3℃ / min and maintained for 30 min, then raised to 1400℃ at a rate of 2℃ / min and maintained for 2 h, then cooled to 900℃, and then cooled to room temperature in the furnace. The tungsten alloy material containing silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating was obtained.

[0060] Figure 1SEM image of the silicon carbide reinforced Al2O3-SiO2 based composite ceramic coating in the tungsten alloy material with the silicon carbide reinforced Al2O3-SiO2 based composite ceramic coating prepared in the present example, wherein Figure 1 b in the above formula (I) is Figure 1 a in the above formula (I). In the figure, the black phase is silicon carbide (SiC) particles, and the gray-white matrix is the Al2O3-SiO2 composite ceramic matrix. As can be seen from a in the above formula (I), the SiC particles are distributed in the matrix in the form of dispersed points, forming a "SiC particle-matrix" composite structure. As can be seen from b in the above formula (I), the SiC particle size is mainly concentrated in the 1-5 μm interval, belonging to sub-micron-micron particles and part of the particles are irregular polyhedrons. The thickness of the silicon carbide reinforced Al2O3-SiO2 based composite ceramic layer is 100 μm. Figure 1 Figure 1

[0061] Figure 2 XRD pattern of the silicon carbide reinforced Al2O3-SiO2 based composite ceramic coating in the tungsten alloy material with the silicon carbide reinforced Al2O3-SiO2 based composite ceramic coating prepared in the present example, and the separate diffraction peaks appear in the pattern and their positions are the same as those in the standard PDF card of silicon carbide, indicating that the SiC particles are successfully introduced into the coating, and it is also confirmed that the silane coupling agent and PEI are decomposed in the sintering process.

[0062] Figure 3 EDS point scanning graph of the surface of the silicon carbide reinforced Al2O3-SiO2 based composite ceramic coating in the tungsten alloy material with the silicon carbide reinforced Al2O3-SiO2 based composite ceramic coating prepared in the present example. As can be seen from the figure, there is oxygen element in the element composition at point 1, which is caused by the diffusion of the matrix oxygen element into the silicon carbide particles during the high-temperature sintering process; the existence of carbon element at point 2 is also caused by the diffusion of the carbon element in the silicon carbide particles into the matrix during the high-temperature sintering process. Therefore, it is indicated that the silicon carbide particles and the Al2O3-SiO2 matrix have a significant interfacial interaction during the high-temperature sintering process. The carbon element in the silicon carbide particles diffuses into the matrix, and the oxygen element in the matrix diffuses into the silicon carbide particles. This diffusion is not a simple physical contact, but a chemical combination through atomic interpenetration, which directly proves that there is a close interfacial bonding between the silicon carbide and the matrix, rather than a loose mechanical stacking. This interfacial interdiffusion can effectively weaken the interfacial energy between the silicon carbide and the matrix, and relieve the stress concentration caused by the difference in thermal expansion coefficient between the two.

[0063] Example 2

[0064] ​​The difference between this example and example 1 is only in the amount of each component in the ceramic slurry: under the condition of keeping magnetic stirring, 10 g of modified silicon carbide powder, 18 g of alumina powder, 16 g of silica powder, 6 g of tetramethylammonium hydroxide (TMAH) and 2 g of lead oxide were sequentially added into 100 mL of methanol, and the remaining steps and conditions were consistent with example 1, to obtain a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating.

[0065] Figure 4 The surface SEM image of the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating prepared in this example is shown in FIG. 4, wherein Figure 4 b in FIG. 4 is Figure 4 a in FIG. 4 is a partial enlarged view. In the figure, the black phase is silicon carbide (SiC) particles, and the gray-white matrix is an Al2O3-SiO2 composite ceramic matrix. As can be seen from Figure 4 , the SiC particles are dispersed in the matrix in the form of dispersed points, and compared with Figure 1 , the SiC particles are more dense due to the increase in the amount of modified silicon carbide powder.

[0066] Figure 5 The XRD pattern of the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating prepared in this example is shown in FIG. 5, and the diffraction peak of silicon carbide also appears in the pattern and the relative intensity of the diffraction peak increases.

[0067] Example 3

[0068] The difference between this example and example 1 is only in the amount of each component in the ceramic slurry: under the condition of keeping magnetic stirring, 15 g of modified silicon carbide powder, 15 g of alumina powder, 14 g of silica powder, 6 g of tetramethylammonium hydroxide (TMAH) and 2 g of lead oxide were sequentially added into 100 mL of methanol, and the remaining steps and conditions were consistent with example 1, to obtain a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating.

[0069] Figure 6 The surface SEM image of the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating prepared in this example is shown in FIG. 4, wherein Figure 6 b in FIG. 4 is Figure 6 a in FIG. 4 is a partial enlarged view. In the figure, the black phase is silicon carbide (SiC) particles, and the gray-white matrix is an Al2O3-SiO2 composite ceramic matrix. As can be seen from Figure 6It can be seen that the SiC particles are dispersed in the matrix in the form of dispersed points and are very dense, but due to the large amount of silicon carbide, the silicon carbide particles appear a slight agglomeration phenomenon.

[0070] Figure 7 The XRD pattern of the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material prepared in this embodiment also shows the diffraction peak of silicon carbide, and the relative intensity of the diffraction peak is the largest.

[0071] Example 4 (exploring the amount of KH550 as silane coupling agent)

[0072] The silicon carbide powder was soaked in 15wt% hydrochloric acid for 1h, and ultrasonic was applied every 15min for 15min. Then, the silicon carbide powder was filtered, washed with water twice, and dried for standby. The silicon carbide powder was soaked in 15wt% HF for 5min, filtered and dried, and then pre-oxidized at 800℃ in air for 2h. Then, the pre-oxidized silicon carbide powder was washed with HF and dried. The pre-oxidation-acid washing was repeated for 3 times.

[0073] When the spheroidized silicon carbide powder, KH550 and deionized water were mixed, the effect of the amount of coupling agent KH550 on the viscosity of the ceramic slurry was investigated. The amount of KH550 was 5-15wt% of the total amount of spheroidized silicon carbide powder, KH550 and deionized water. The other conditions were the same as in Example 1, and the results are shown in Table 1. Figure 8

[0074] The results show that when the amount of KH550 is 0, the viscosity is 1452mPa•s. Under the same process conditions, the viscosity decreases with the increase of the amount of KH550. When the amount of KH550 is 10wt%, the viscosity decreases to about 1124mPa•s. The above results show that the viscosity of the ceramic slurry decreases significantly with the increase of the amount of KH550. With the increase of the amount of KH550, the dispersion effect of the system gradually increases, which leads to the decrease of the viscosity. Due to the limited data points, the viscosity does not show a stable stage, but it is speculated that with the continuous increase of the amount of KH550, the dispersion effect of the system will reach a relative saturation, and the change of the viscosity will tend to be flat.

[0075] Example 5 (exploring the amount of KH792 as silane coupling agent)

[0076] The silicon carbide powder was soaked in 15wt% hydrochloric acid for 1h, and ultrasonic was applied every 15min for 15min. Then, the silicon carbide powder was filtered, washed with water twice, and dried for standby. The silicon carbide powder was soaked in 15wt% HF for 5min, filtered and dried, and then pre-oxidized at 800℃ in air for 2h. Then, the pre-oxidized silicon carbide powder was washed with HF and dried. The pre-oxidation-acid washing was repeated for 3 times.​

[0077] The effect of the amount of coupling agent KH792 on the viscosity of the ceramic slurry was investigated when the spheroidized silicon carbide powder, KH792 and DW (deionized water) were mixed, the amount of KH792 was 5-15wt% relative to the total amount of spheroidized silicon carbide powder, KH792 and deionized water, and the other conditions were the same as in Example 1, and the results are shown in Table 1. Figure 9

[0078] The results show that when the amount of KH792 is 0, the viscosity is 1452 mPa•s. Under the same other process conditions, the viscosity decreases with the increase of the amount of KH792. When the amount of KH792 is 10wt%, the viscosity decreases to 892 mPa•s and tends to be stable. The above results show that the viscosity of the ceramic slurry decreases significantly first and then tends to be stable with the increase of the amount of KH792. When the amount of KH792 reaches a certain degree, the dispersion effect of the steric hindrance in the system reaches a relative saturation, and the viscosity tends to be stable. At the same time, it can be seen from Table 1 that the amount of KH792 needs to be greater than 10wt%, and the amount of KH792 is further preferably 10-15wt%. Figure 9

[0079] Example 6 (concentration of PEI)

[0080] Under the condition of magnetic stirring, 10g of the silicon carbide powder adsorbed with KH792 prepared in Example 1 was mixed with 100ml of PEI aqueous solution with different concentrations and pH=3, the effect of the concentration of PEI on the viscosity of the ceramic slurry was investigated, and the other conditions were the same as in Example 1, and the results are shown in Table 2. Figure 10

[0081] The results show that with the increase of the concentration of PEI, the viscosity of the ceramic slurry decreases significantly first, reaches the minimum when the concentration of PEI is 6wt%, and then increases slightly with the further increase of the concentration of PEI.

[0082] Example 7

[0083] The embodiment provides a preparation method of a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating, and the method comprises the following operation steps:

[0084] 1. Modification of silicon carbide powder

[0085] (1) Surface pickling purification: the silicon carbide powder is soaked in 15wt% hydrochloric acid for 1h, ultrasonic treatment is performed every 15min during the soaking, the ultrasonic treatment is performed for 15min each time, and then the silicon carbide powder is filtered, washed with water twice and dried for standby, so as to remove surface impurities.

[0086] ​​​(2) Spherical treatment of silicon carbide powder: The silicon carbide powder was first soaked in 15wt% HF for 5min, filtered and dried, and then pre-oxidized at 900°C in air for 1h, followed by HF acid washing and drying treatment, and the pre-oxidation-acid washing was repeated for 3 times to improve the sphericity of the powder and reduce the internal resistance of slurry flow.

[0087] (3) Silane coupling agent treatment: The silicon carbide powder after spheroidization treatment, KH792 and deionized water were mixed by ultrasonic and stirring at a mass ratio of 9:2:9 for 2h, and then left to stand. After that, it was washed with 5 times of deionized water, and after standing, the supernatant was taken and then filtered. This process was repeated twice, and then the silicon carbide powder adsorbed with KH792 was obtained after drying.

[0088] (4) Polyethyleneimine (PEI) grafting treatment: Under the condition of maintaining magnetic stirring, 10g of silicon carbide powder adsorbed with KH792 was added into the PEI aqueous solution (the concentration of PEI was 6wt%, and the volume was 100mL) with pH=3, and then soaked (the soaking time was 3h), filtered and dried to obtain the silicon carbide powder adsorbed with KH792 and grafted with PEI (i.e. modified silicon carbide powder).

[0089] 2. Preparation of ceramic slurry

[0090] Under the condition of maintaining magnetic stirring, 5g of modified silicon carbide powder, 20g of alumina powder, 18g of silica powder, 6g of polyvinylpyrrolidone (PVP) and 3g of lead oxide were sequentially added into 100mL of methanol, and then ball milled in a XQM-2 type variable frequency planetary ball mill (self-rotation 180r / min, revolution 200r / min) for 7h. ZKT-6020 type vacuum defoaming machine was used to remove the bubbles in the slurry to obtain the ceramic slurry.

[0091] 3. Pretreatment of tungsten alloy substrate

[0092] The tungsten alloy block (15mm×15mm×5mm) was polished on 120#, 240#, 400# and 600# silicon carbide sandpaper in sequence, and then ultrasonically cleaned with anhydrous ethanol and acetone for 15min, and then blown dry.

[0093] 4. Surface brushing

[0094] The prepared ceramic slurry was uniformly brushed on the surface of the pretreated tungsten alloy substrate with a brush to ensure the uniform thickness of the coating. After brushing, the sample was placed in a constant temperature drying oven and dried at 80°C for 2h.

[0095] 5. Vacuum sintering

[0096] The dried sample was placed in a muffle furnace, the vacuum degree was 0.5 MPa, the temperature was raised to 800 ℃ for 40 min, the temperature was raised to 1000 ℃ at a rate of 3 ℃ / min for 30 min, the temperature was raised to 1300 ℃ at a rate of 2 ℃ / min for 2 h, the temperature was lowered to 900 ℃, and then the furnace was cooled to room temperature, to obtain a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating.

[0097] Comparative Example 1

[0098] The difference between this comparative example and Example 1 is only that no silicon carbide powder is added in the ceramic slurry, and the rest of the steps and conditions are consistent, only an Al2O3-SiO2-based composite ceramic coating is combined on the tungsten alloy substrate, to obtain a tungsten alloy material containing an Al2O3-SiO2-based composite ceramic coating.

[0099] Figure 11 The XRD pattern of the Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material containing the Al2O3-SiO2-based composite ceramic coating prepared in this comparative example shows only one broad diffuse scattering peak, and the "halo peak" phenomenon appears, indicating that the coating is amorphous.

[0100] Comparative Example 2

[0101] The difference between this comparative example and Example 1 is only that the silicon carbide powder is not treated with a silane coupling agent during modification, and the rest of the steps and conditions are consistent, to obtain a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating.

[0102] Figure 12 The surface SEM image of the Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating prepared in this comparative example can be seen from the figure that the silicon carbide particles have serious agglomeration, and the coating has obvious cracks.

[0103] Comparative Example 3

[0104] The difference between this comparative example and Example 1 is only that the silicon carbide powder is not treated with polyethyleneimine (PEI) grafting during modification, and the rest of the steps and conditions are consistent, to obtain a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating.

[0105] Figure 13 The surface SEM image of the Al2O3-SiO2-based composite ceramic coating in the tungsten alloy material containing the silicon carbide reinforced Al2O3-SiO2-based composite ceramic coating prepared in this comparative example can be seen from the figure that the silicon carbide particles have serious agglomeration, and there are local loose areas.

[0106] Comparative Example 4

[0107] The difference between this comparative example and Example 1 is only that the vacuum sintering procedure is replaced by: treating for the same time at a sintering temperature of 600°C, the rest of the steps and conditions are consistent, the obtained SiC powder reinforced Al2O3-SiO2-based multiphase ceramic coating is not completely sintered, only a loose mechanical stack, the coating is loose and porous, can be easily scraped off with tweezers.

[0108] Comparative Example 5

[0109] The difference between this comparative example and Example 1 is only that the SiC powder is not modified, the rest of the steps and conditions are consistent, and a tungsten alloy material containing an Al2O3-SiO2-based multiphase ceramic coating is obtained.

[0110] Figure 14 The surface SEM image of the Al2O3-SiO2-based multiphase ceramic coating of the tungsten alloy material containing the Al2O3-SiO2-based multiphase ceramic coating prepared for this comparative example can be seen from the figure, the SiC particles appear serious agglomeration and the coating appears obvious cracks.

[0111] The surface and substrate hardness of the tungsten alloy materials containing SiC reinforced Al2O3-SiO2-based multiphase ceramic coatings prepared in Examples 1-3 and Example 7, tungsten alloy materials prepared in Comparative Examples 1-5, and tungsten alloy substrates (without vacuum sintering treatment) were tested, respectively, and the results are shown in Table 1.

[0112] ;

[0113] The thermal shock resistance of the tungsten alloy materials containing SiC reinforced Al2O3-SiO2-based multiphase ceramic coatings prepared in Example 1 and Comparative Example 1 under 1400°C air cooling thermal shock cycle was tested, respectively, and the results are shown in Table 2.

[0114] ;

[0115] The oxidation resistance of the tungsten alloy material containing SiC reinforced Al2O3-SiO2-based multiphase ceramic coating prepared in Example 1 and the tungsten alloy substrate bare sample coating surface under 1400°C, 15h oxidation environment and the carburization performance under 1400°C, 15h were tested, respectively, and the results are shown in Tables 3 and 4.

[0116] ;

[0117] .

Claims

1. A method of making a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2 based composite ceramic coating, characterized in that: A ceramic slurry is obtained by ball-milling a powder raw material including modified silicon carbide, alumina, silica and lead oxide with a solvent and then removing bubbles; the ceramic slurry is brush-coated on a surface of a tungsten alloy substrate after surface pretreatment, dried and then vacuum sintered to obtain the ceramic coating. The modified silicon carbide is prepared by sequentially subjecting silicon carbide powder to spheroidization treatment, silane coupling agent treatment and polyethylene imine grafting treatment. The silicon carbide is dispersed in the Al2O3-SiO2 matrix in the form of dispersed points.

2. A method of making a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2 based composite ceramic coating according to claim 1, characterized in that: The mass ratio of the modified silicon carbide, alumina, silica and lead oxide in the ceramic slurry is (5-15):(15-21):(14-18):(2-5).

3. A method of making a tungsten alloy material containing a SiC reinforced Al2O3-SiO2 based composite ceramic coating according to claim 2, characterized in that: The powder raw material further includes a dispersant, and the solvent includes at least one of methanol, ethanol, acetone and toluene.

4. The method of making a tungsten alloy material containing a SiC reinforced Al2O3-SiO2 based composite ceramic coating according to claim 1, characterized in that: The spheroidization treatment is performed by immersing the silicon carbide powder in HF, pre-oxidizing at 700-900°C in air for 1-2h, and then performing HF acid washing and drying.

5. A method of making a tungsten alloy material containing a silicon carbide reinforced Al2O3-SiO2 based composite ceramic coating according to claim 4, characterized in that: The silane coupling agent treatment is performed by mixing at least one of KH792 and KH550, the spheroidized silicon carbide powder and water for 1-4h, and then washing with water, wherein the silane coupling agent is added in an amount of 5-15wt% relative to the total amount of the silane coupling agent, the spheroidized silicon carbide powder and water. The polyethylene imine grafting treatment is performed by immersing the spheroidized silicon carbide powder treated with the silane coupling agent in a polyethylene imine aqueous solution with a pH of 3-4 for 1-3h, and the concentration of the polyethylene imine aqueous solution is 6-8wt%.

6. A method of producing a tungsten alloy material comprising a SiC reinforced Al2O3-SiO2 based composite ceramic coating according to any one of claims 2 to 5, characterized in that: The spheroidization treatment further includes acid washing and impurity removal.

7. A method of making a tungsten alloy material containing a SiC reinforced Al2O3-SiO2 based composite ceramic coating according to claim 6, characterized in that: The vacuum sintering procedure is as follows: first, heating to 700-900°C and maintaining for 20-40min, then heating to 1000-1200°C at a rate of 1-5°C / min and maintaining for 20-40min, then heating to 1300-1400°C at a rate of 1-5°C / min and maintaining for 1-2h, then cooling to room temperature after cooling to 700-900°C, and the vacuum degree is 0.1-1MPa.

8. A method of making a tungsten alloy material containing a SiC reinforced Al2O3-SiO2 based composite ceramic coating according to claim 7, characterized in that: The amount of the brush coating is controlled to obtain a thickness of 50-120μm of the Al2O3-SiO2 matrix ceramic layer reinforced with silicon carbide after high-temperature vacuum sintering.

9. A tungsten alloy material comprising a silicon carbide reinforced Al2O3-SiO2 based multiphase ceramic coating, characterized in that: The ceramic coating is prepared by the method of any one of claims 1-8.

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