Ceramic coating and method for its production and application on the surface of a continuous casting mold

Abstract

The application provides a ceramic coating and a preparation method and application in a continuous casting crystallizer thereof, and relates to the technical field of ceramic coating of a continuous casting crystallizer.The ceramic coating preparation method comprises the following steps: mixing silicon carbide, silicon nitride and alloy powder, performing ball milling and then performing heat treatment to obtain ceramic powder; performing wet ball milling on the ceramic powder and graphene oxide, and then performing separation and drying to obtain composite powder; mixing the composite powder with metal oxide, and then covering the composite powder on the surface of a graphite element blank of a graphite crystallizer, and performing gradient sintering under high temperature and high pressure to obtain the ceramic coating.The application can effectively prolong the service life of the graphite crystallizer and improve the quality of the surface of a casting blank.

Description

Technical Field

[0001] This invention relates to the field of ceramic coating technology for continuous casting molds, and more particularly to a ceramic coating, its preparation method, and its application on the surface of a continuous casting mold. Background Technology

[0002] Continuous casting technology is a revolutionary forming process in modern metallurgical industry. Compared with traditional casting processes, continuous casting simplifies production processes, improves production efficiency, reduces production costs, and improves casting quality. Its core lies in the continuous pouring of high-temperature molten metal into a crystallizer, allowing the molten metal to form a billet with a specific cross-sectional shape, a liquid interior, and a nascent solidified shell on the outside, within a very short time. The billet is then continuously pulled out and subjected to secondary cooling until it completely solidifies. Continuous casting technology not only enables direct and uninterrupted production from liquid metal to solid billet, greatly improving metal forming efficiency, but also improves the internal microstructure of the billet during the metal cooling process, thereby enhancing product quality. It has been widely applied in the casting processes of steel and non-ferrous metals.

[0003] In continuous casting, the performance of the crystallizer directly affects the quality, output, and production efficiency of the cast billet. Depending on the material, crystallizers typically include copper alloy crystallizers, aluminum crystallizers, ceramic crystallizers, and graphite crystallizers. Among them, the most commonly used is the graphite crystallizer, which uses high-purity, high-density artificial graphite as the liner. Graphite's excellent thermal conductivity is used to quickly dissipate the heat of the molten metal, promoting the rapid formation of a uniform primary billet on the surface of the graphite liner. In addition, graphite's good lubricity helps reduce the frictional resistance between the solidified billet shell and the liner surface, thus facilitating the smooth demolding of the cast billet and improving its surface quality. Graphite also has high chemical stability and thermal shock resistance. Therefore, graphite crystallizers are widely used in the continuous casting industry.

[0004] However, graphite crystallizers are prone to surface oxidation at high temperatures, leading to continuous wear and tear. This not only reduces the lifespan of the crystallizer but also causes the oxide layer to contaminate the metal billet and affect the cooling process of the billet on the graphite crystallizer surface. In addition, graphite itself has low mechanical strength and insufficient toughness. When subjected to thermal shock from the molten metal, friction from the billet, and equipment vibration, cracks easily appear on the surface of the graphite crystallizer. Therefore, the surface properties of the graphite crystallizer are prone to change during long-term use, and there is an urgent need to provide a solution to improve the above problems. Summary of the Invention

[0005] The purpose of this invention is to provide a ceramic coating and its preparation method, as well as its application on the surface of a continuous casting crystallizer. By forming a dense and stable ceramic coating on the surface of a graphite continuous casting crystallizer, the stability of the graphite crystallizer during use is effectively improved, thereby increasing its service life.

[0006] In a first aspect, the present invention provides a method for preparing a ceramic coating, comprising the following steps: S1. Silicon carbide, silicon nitride and alloy powder are mixed, ball-milled and then heat-treated to obtain ceramic powder; S2. The ceramic powder and graphene oxide are wet-milled and then separated and dried to obtain the composite powder. S3. The composite powder is mixed with the metal oxide and then covered on the surface of the graphite blank in the graphite crystallizer. S4. A ceramic coating is obtained by gradient sintering under high temperature and high pressure.

[0007] Optionally, in step S1, the particle sizes of the silicon carbide, the silicon nitride, and the alloy powder are independently 20 μm-100 μm.

[0008] Optionally, the mass ratio of the silicon carbide, the silicon nitride, and the alloy powder is 2:(0.8-1.2):(0.4-0.6).

[0009] Optionally, the metallic elements in the alloy powder are selected from five of the following: Ni, Co, Cr, Y, Ti, Zr, and Ta.

[0010] Optionally, the mixture can be ball-milled at a speed of 50 rpm to 100 rpm.

[0011] Optionally, zirconium oxide can be used as the grinding ball for mixed ball milling.

[0012] Optionally, the ball-to-material ratio during ball milling is (2-5):1.

[0013] Optionally, wet mixing and ball milling are followed by drying and heat treatment.

[0014] Optionally, the mixture is ball-milled and then heat-treated at 1400℃-1600℃.

[0015] Alternatively, ceramic powder can be obtained by heat treatment under vacuum followed by cooling.

[0016] Optionally, the mass ratio of the ceramic powder to the graphene oxide is 1:(1-3).

[0017] Optionally, the graphene oxide has a particle size of 0.1 μm to 0.5 μm.

[0018] Optionally, the ceramic powder and graphene oxide are wet-milled in a solution containing a dispersant.

[0019] Optionally, the dispersant includes one of KH550 and KH560.

[0020] Optionally, the concentration of the dispersant in the solution containing the dispersant is 3%-8%; below 3%, the dispersion effect is poor and it is easy to cause powder agglomeration; above 8%, it will remain in the coating and reduce the density of the coating.

[0021] Optionally, the solid-liquid ratio is 0.04 g / mL to 0.08 g / mL.

[0022] Optionally, the particle size of the ceramic powder is 5μm-20μm.

[0023] Optionally, wet ball milling can be performed at a speed of 50 rpm to 100 rpm.

[0024] Optionally, the ball-to-material ratio in wet ball milling is (2-5):1.

[0025] Optionally, the mixture is separated after wet ball milling and dried at 80°C-120°C.

[0026] Optionally, wet ball milling can be performed for 1-5 hours.

[0027] Optionally, zirconium oxide can be used as the grinding ball for wet ball milling.

[0028] Optionally, the metal oxide includes one of aluminum oxide, zirconium oxide, titanium oxide, tungsten oxide, niobium oxide, and tantalum oxide.

[0029] Optionally, the mass ratio of the composite powder to the metal oxide is 1:(0.2-0.3).

[0030] Optionally, the particle size of the metal oxide is 5μm-15μm.

[0031] Optionally, the composite powder and the metal oxide are ball-milled together.

[0032] Optionally, gradient sintering can be performed at 1600℃-2200℃.

[0033] Optionally, the material is sintered under high pressure at a rate of 10°C / min to 50°C / min.

[0034] Optionally, gradient sintering can be performed at 20MPa-50MPa.

[0035] Optionally, two to five layers of gradient sintering are carried out under high temperature and high pressure, with the sintering temperature of each layer increasing by 100℃-300℃ and the pressure increasing by 5MPa-15MPa compared to the previous layer.

[0036] Optionally, the thickness of the ceramic coating is 0.3mm-0.8mm.

[0037] Secondly, the present invention also provides a ceramic coating prepared by any of the above-mentioned optional preparation methods, wherein the ceramic coating is formed on the surface of the graphite blank of a graphite crystallizer.

[0038] Thirdly, the present invention also provides an application of a ceramic coating prepared by any of the above-mentioned optional preparation methods on the surface of a continuous casting crystallizer.

[0039] Optionally, the continuous casting crystallizer is a graphite crystallizer, and the ceramic coating is formed on the surface of the graphite liner in the graphite crystallizer.

[0040] The method for preparing a ceramic coating provided by this invention has at least one of the following beneficial technical effects compared with the prior art: 1. By adding alloy powder and graphene oxide and sintering under high temperature and high pressure, it is beneficial to promote the formation of a dense structure of the metal phase. At the same time, the use of graphene oxide as a ceramic reinforcing phase improves the structural strength of the ceramic coating, thereby improving the fracture toughness of the ceramic coating and the bonding strength with the graphite matrix, and avoiding the problems of peeling and brittle fracture of the ceramic coating during continuous casting. 2. By mixing and sintering the composite powder with metal oxide, a stable ceramic-metal phase is formed between the metal oxide and alloy powder under high temperature and pressure, and a thermally conductive ceramic phase is formed with graphene. By combining the thermally conductive ceramic phase with the graphite crystallizer, the thermal expansion coefficients of the ceramic coating and the graphite crystallizer can be effectively balanced, thereby avoiding the problem of thermal stress concentration at the interface. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0042] This invention provides a method for preparing a ceramic coating, comprising the following steps: S1. Silicon carbide, silicon nitride and alloy powder are mixed, ball-milled and then heat-treated to obtain ceramic powder; S2. The ceramic powder and graphene oxide are wet-milled and then separated and dried to obtain the composite powder. S3. The composite powder is mixed with the metal oxide and then covered on the surface of the graphite blank in the graphite crystallizer. S4. A ceramic coating is obtained by gradient sintering under high temperature and high pressure.

[0043] In fact, in step S1, the silicon carbide, silicon nitride and alloy powder are subjected to ball milling heat treatment, which can promote the full mixing of ceramic phase materials and metal phase materials, and form ceramic powder through heat treatment sintering. In step S2, the ceramic powder and graphene oxide are wet ball milled and blended to promote the uniform dispersion of graphene oxide. Then, after sintering, the graphene oxide is used as a ceramic reinforcing phase, which can improve the structural strength of the ceramic coating. At the same time, graphene oxide can also form a thermally conductive ceramic phase with the ceramic metal phase, thereby improving the structural stability of the ceramic coating on the surface of the graphite crystallizer.

[0044] In some embodiments, the particle sizes of the silicon carbide, silicon nitride, and alloy powders used in step S1 are independently 20 μm-100 μm. In fact, using micron-sized raw materials ensures the uniformity of powder mixing during ball milling, preventing segregation of the metal components. Simultaneously, ball milling promotes the formation of a stable composite structure among the three powders, enhancing the interfacial bonding between them. This results in a ceramic powder with consistent composition after heat treatment and sintering, and improves the dispersion uniformity of the ceramic metal phase within the ceramic powder.

[0045] In some embodiments, the mass mixing ratio of silicon carbide, silicon nitride, and alloy powder in step S1 can be 2:(0.8-1.2):(0.4-0.6). In practice, using silicon carbide as the main skeleton of the coating can effectively improve the coating's hardness and wear resistance, while filling the coating with silicon nitride can improve its toughness and impact resistance. Furthermore, the added alloy powder forms a ceramic-metal phase during sintering, which not only improves the coating's density but also reduces thermal stress during sintering. Specifically, the mass ratio of silicon carbide, silicon nitride, and alloy powder can be set to one of 2:0.8:0.4, 2:1.2:0.6, 2:0.8:0.6, or 2:1.2:0.4, or any specific value within this range, all of which can achieve the purpose of this invention.

[0046] In some embodiments, the metallic elements in the alloy powder used in step S1 are selected from five of Ni, Co, Cr, Y, Ti, Zr, and Ta. Specifically, Ni and Co can improve the high-temperature strength and density of the coating after sintering; Cr can improve the oxidation and corrosion resistance of the coating during use; Y can improve the bonding strength of the coating on the graphite crystallizer surface; Ti and Zr can form a strengthening interface with silicon carbide, thereby refining the structure of the sintered coating and improving its density; and Ta can further improve the high-temperature stability of the coating. Specifically, the metallic elements in the alloy powder can be Ni, Co, Cr, Y, Ti, or a group of Ni, Co, Cr, Y, and Zr.

[0047] In some embodiments, in step S1, silicon carbide, silicon nitride, and alloy powders can be mixed and added into a ball mill jar, using 3mm zirconium oxide balls, controlling the ball-to-powder ratio at (2-5):1, and performing the mixing ball treatment at a speed of 50rpm-100rpm. In practice, the ball-to-powder ratio and ball milling speed used in the mixing ball milling process are necessary to ensure thorough mixing of the three raw material powders; these can be adjusted arbitrarily within the range to achieve the desired purpose of this invention.

[0048] In some embodiments, in step S1, silicon carbide, silicon nitride, and alloy powders can be dispersed in anhydrous ethanol and wet-milled, then dried. The dried powder is then transferred to a vacuum environment and heat-treated at 1400℃-1600℃, followed by cooling to room temperature to obtain ceramic powder. In practice, high-temperature heat treatment can sinter the powder into ceramic material, and the sintered ceramic material can then be ground and sieved to obtain ceramic powder with a particle size of 5μm-20μm. Specifically, the sintering temperature can be adjusted arbitrarily between 1400℃ and 1600℃ to achieve the desired objective of this invention.

[0049] In some embodiments, the mass ratio of ceramic powder to graphene oxide in step S2 is 1:(1-3), and the particle size of the graphene oxide used is 0.1μm-0.5μm. Simultaneously, the ceramic powder and graphene oxide can be wet-milled in a solution containing a dispersant. The dispersant improves the dispersion uniformity of the ceramic powder and graphene oxide during wet ball milling, preventing agglomeration and sedimentation that would lead to uneven milling. Specifically, the dispersant used includes one of KH550 and KH560, and the solid-liquid ratio during dispersion is 0.04g / mL-0.08g / mL, with the concentration of the dispersant in the solution being 3%-8%.

[0050] In some embodiments, when wet ball milling the ceramic powder and graphene oxide in step S2, 3mm zirconium oxide can also be used as the milling balls, and the ball-to-material ratio can be controlled at (2-5):1 before ball milling and mixing at 50rpm-100rpm. Furthermore, after ball milling, the material can be transferred to an environment of 80℃-120℃ to dry to constant weight to obtain the composite powder. Similarly, the ball milling parameters in step S2 can be adaptively adjusted within the range, and the drying temperature should be sufficient to fully dry the material.

[0051] In some embodiments, the metal oxide used in step S3 includes at least one of alumina, zirconium oxide, titanium oxide, tungsten oxide, niobium oxide, and tantalum oxide, and the particle size of the metal oxide can be 5 μm-15 μm. Specifically, the metal oxide can be one of the following combinations in a 1:1 mass ratio: tungsten oxide and niobium oxide, or a 1:1 mass ratio: alumina and zirconium oxide. Further, in step S3, the composite powder and the metal oxide can be mixed at a ratio of 1:(0.2-0.3) and then ball-milled to improve the dispersion uniformity between the two.

[0052] In some embodiments, gradient sintering can be performed in step S4 at 1600℃-2200℃ and 20MPa-50MPa. Specifically, gradient sintering refers to sintering the coating in multiple layers during the sintering process, and adjusting the sintering temperature and pressure sequentially during each layer sintering, and cooling to room temperature for shaping after each layer is sintered. For example, the temperature is 1600℃ and the pressure is 20MPa when sintering the first layer, and the temperature can be increased to 1800℃ and the pressure can be increased to 30MPa when sintering the second layer. Further, gradient sintering of 2 to 5 layers can be performed under high temperature and high pressure, and the temperature is increased at a rate of 10℃ / min-50℃ / min during the sintering process, with the sintering temperature of each layer increasing by 100℃-300℃ and the pressure increasing by 5MPa-15MPa compared to the previous layer.

[0053] Preparation Example 1 Example 1 of this preparation provides a method for preparing alloy powder, including the following steps: nickel sulfate, cobalt chloride, chromium chloride, yttrium chloride and titanium chloride are mixed and dissolved in an aqueous solution in a metal element ratio of 30:18:18:4:10 to obtain a mixed solution. N2H4 (molar ratio of N2H4 to metal element is 3:1) is added to the mixed solution, and the mixture is stirred at 80°C for 1 hour. After centrifugation, the precipitate is washed with anhydrous ethanol and deionized water, dried, ground and sieved to obtain alloy powder with an average particle size of 50 μm.

[0054] Preparation Example 2 Example 2 of this preparation provides a method for preparing alloy powder, including the following steps: nickel sulfate, cobalt chloride, chromium chloride, yttrium chloride, and zirconium nitrate are mixed and dissolved in an aqueous solution in a metal element ratio of 30:18:18:4:10 to obtain a mixed solution. N2H4 (molar ratio of N2H4 to metal element is 3:1) is added to the mixed solution, and the mixture is stirred at 80°C for 1 hour. After centrifugation, the precipitate is washed with anhydrous ethanol and deionized water, dried, ground, and sieved to obtain alloy powder with an average particle size of 50 μm.

[0055] Example 1

[0056] This embodiment 1 provides a method for forming a ceramic coating on the surface of a graphite crystallizer, including the following steps: S1. Silicon carbide with a particle size of 50 μm, silicon nitride with a particle size of 50 μm, and the alloy powder prepared in Preparation Example 1 were mixed at a mass ratio of 2:1:0.5 and then added to anhydrous ethanol for ultrasonic dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 2 hours using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation and drying at 80 °C to constant weight, the mixture was transferred to a vacuum furnace and evacuated. The furnace was heated to 1500 °C at a rate of 20 °C / min and sintered for 45 min. After cooling in the furnace, the mixture was ground and sieved to obtain ceramic powder with an average particle size of 10 μm. S2. Ceramic powder and graphene oxide with an average particle size of 0.3 μm were mixed at a mass ratio of 1:2 and then added to a 5% KH550 ethyl acetate solution at a solid-liquid ratio of 0.05 g / mL to obtain a dispersion. The dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 1 h using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation, the powder was dried at 100 °C to constant weight to obtain composite powder. S3. The composite powder is mixed with metal oxides (tungsten oxide and niobium oxide in a mass ratio of 1:1) with an average particle size of 10 μm. After ultrasonic dispersion in anhydrous ethanol, the mixture is transferred to a ball mill jar and ball milled at 80 rpm for 1 hour using 3 mm zirconium oxide grinding balls and a ball-to-material ratio of 3:1. After centrifugation, the mixture is dried at 100 °C to constant weight to obtain the mixed powder. S4. After cleaning the surface of the graphite crystallizer to be coated with ceramic powder, the mixed powder is thinly applied to the surface of the graphite crystallizer. Then, it is transferred to the sintering chamber, argon gas is introduced and pressurized to 20 MPa, and the temperature is raised to 1600℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the first coating layer. Then, it is transferred to the sintering chamber, and in an argon atmosphere of 30 MPa, the temperature is raised to 1800℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the second coating layer. Then, it is transferred to the sintering chamber again and sintered at 40 MPa and 2000℃ to form the third coating layer. After cooling to room temperature, the surface is polished to obtain a ceramic coating with a total coating thickness of 0.4 mm.

[0057] Example 2

[0058] This embodiment 2 provides a method for forming a ceramic coating on the surface of a graphite crystallizer, including the following steps: S1. Silicon carbide with a particle size of 50 μm, silicon nitride with a particle size of 50 μm, and the alloy powder prepared in Preparation Example 2 were mixed at a mass ratio of 2:1:0.5 and then added to anhydrous ethanol for ultrasonic dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 2 hours using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation and drying at 80 °C to constant weight, the mixture was transferred to a vacuum furnace and evacuated. The furnace was heated to 1500 °C at a rate of 20 °C / min and sintered for 45 min. After cooling in the furnace, the mixture was ground and sieved to obtain ceramic powder with an average particle size of 10 μm. S2. Ceramic powder and graphene oxide with an average particle size of 0.3 μm were mixed at a mass ratio of 1:2 and then added to a 5% KH550 ethyl acetate solution at a solid-liquid ratio of 0.05 g / mL to obtain a dispersion. The dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 1 h using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation, the powder was dried at 100 °C to constant weight to obtain composite powder. S3. The composite powder is mixed with metal oxides (tungsten oxide and niobium oxide in a mass ratio of 1:1) with an average particle size of 10 μm. After ultrasonic dispersion in anhydrous ethanol, the mixture is transferred to a ball mill jar and ball milled at 80 rpm for 1 hour using 3 mm zirconium oxide grinding balls and a ball-to-material ratio of 3:1. After centrifugation, the mixture is dried at 100 °C to constant weight to obtain the mixed powder. S4. After cleaning the surface of the graphite crystallizer to be coated with ceramic powder, the mixed powder is thinly applied to the surface of the graphite crystallizer. Then, it is transferred to the sintering chamber, argon gas is introduced and pressurized to 20 MPa, and the temperature is raised to 1600℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the first coating layer. Then, it is transferred to the sintering chamber, and in an argon atmosphere of 30 MPa, the temperature is raised to 1800℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the second coating layer. Then, it is transferred to the sintering chamber again and sintered at 40 MPa and 2000℃ to form the third coating layer. After cooling to room temperature, the surface is polished to obtain a ceramic coating with a total coating thickness of 0.4 mm.

[0059] Example 3

[0060] This embodiment 3 provides a method for forming a ceramic coating on the surface of a graphite crystallizer, including the following steps: S1. Silicon carbide with a particle size of 50 μm, silicon nitride with a particle size of 50 μm, and the alloy powder prepared in Preparation Example 1 were mixed at a mass ratio of 2:1:0.5 and then added to anhydrous ethanol for ultrasonic dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 2 hours using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation and drying at 80 °C to constant weight, the mixture was transferred to a vacuum furnace and evacuated. The furnace was heated to 1500 °C at a rate of 20 °C / min and sintered for 45 min. After cooling in the furnace, the mixture was ground and sieved to obtain ceramic powder with an average particle size of 10 μm. S2. Ceramic powder and graphene oxide with an average particle size of 0.3 μm were mixed at a mass ratio of 1:2 and then added to a 5% KH550 ethyl acetate solution at a solid-liquid ratio of 0.05 g / mL to obtain a dispersion. The dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 1 h using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation, the powder was dried at 100 °C to constant weight to obtain composite powder. S3. The composite powder is mixed with metal oxides (alumina and zirconium oxide in a mass ratio of 1:1) with an average particle size of 10 μm. After ultrasonic dispersion in anhydrous ethanol, the mixture is transferred to a ball mill jar and ball milled at 80 rpm for 1 hour using 3 mm zirconium oxide grinding balls and a ball-to-material ratio of 3:1. After centrifugation, the mixture is dried at 100℃ to constant weight to obtain the mixed powder. S4. After cleaning the surface of the graphite crystallizer to be coated with ceramic powder, the mixed powder is thinly applied to the surface of the graphite crystallizer. Then, it is transferred to the sintering chamber, argon gas is introduced and pressurized to 20 MPa, and the temperature is raised to 1600℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the first coating layer. Then, it is transferred to the sintering chamber, and in an argon atmosphere of 30 MPa, the temperature is raised to 1800℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the second coating layer. Then, it is transferred to the sintering chamber again and sintered at 40 MPa and 2000℃ to form the third coating layer. After cooling to room temperature, the surface is polished to obtain a ceramic coating with a total coating thickness of 0.4 mm.

[0061] Example 4

[0062] This embodiment 4 provides a method for forming a ceramic coating on the surface of a graphite crystallizer, including the following steps: S1. Silicon carbide with a particle size of 50 μm, silicon nitride with a particle size of 50 μm, and the alloy powder prepared in Preparation Example 1 were mixed at a mass ratio of 2:1:0.5 and then added to anhydrous ethanol for ultrasonic dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 2 hours using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation and drying at 80 °C to constant weight, the mixture was transferred to a vacuum furnace and evacuated. The furnace was heated to 1500 °C at a rate of 20 °C / min and sintered for 45 min. After cooling in the furnace, the mixture was ground and sieved to obtain ceramic powder with an average particle size of 10 μm. S2. Ceramic powder and graphene oxide with an average particle size of 0.3 μm were mixed at a mass ratio of 1:2 and then added to a 5% KH550 ethyl acetate solution at a solid-liquid ratio of 0.05 g / mL to obtain a dispersion. The dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 1 h using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation, the powder was dried at 100 °C to constant weight to obtain composite powder. S3. The composite powder is mixed with metal oxides (tungsten oxide and niobium oxide in a mass ratio of 1:1) with an average particle size of 10 μm. After ultrasonic dispersion in anhydrous ethanol, the mixture is transferred to a ball mill jar and ball milled at 80 rpm for 1 hour using 3 mm zirconium oxide grinding balls and a ball-to-material ratio of 3:1. After centrifugation, the mixture is dried at 100 °C to constant weight to obtain the mixed powder. S4. After cleaning the surface of the graphite crystallizer to be coated with ceramic, the mixed powder is thinly applied to the surface of the graphite crystallizer. It is then transferred to the sintering chamber, argon gas is introduced and pressurized to 20 MPa, and the temperature is raised to 1600℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the first coating layer. It is then transferred to the sintering chamber again, and in an argon atmosphere of 30 MPa, the temperature is raised to 1800℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the second coating layer. It is then transferred to the sintering chamber again, and sintered at 40 MPa and 2000℃ to form the third coating layer. After cooling to room temperature, the surface is polished to obtain a ceramic coating with a total thickness of 0.8 mm.

[0063] Example 5

[0064] This embodiment 5 provides a method for forming a ceramic coating on the surface of a graphite crystallizer, including the following steps: S1. Silicon carbide with a particle size of 20 μm, silicon nitride with a particle size of 20 μm, and the alloy powder prepared in Preparation Example 1 were mixed at a mass ratio of 2:1:0.5 and then added to anhydrous ethanol for ultrasonic dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 2 hours using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation and drying at 80 °C to constant weight, the mixture was transferred to a vacuum furnace and evacuated. The furnace was heated to 1500 °C at a rate of 20 °C / min and sintered for 45 min. After cooling in the furnace, the mixture was ground and sieved to obtain ceramic powder with an average particle size of 10 μm. S2. Ceramic powder and graphene oxide with an average particle size of 0.1 μm were mixed at a mass ratio of 1:2 and then added to a 5% KH550 ethyl acetate solution at a solid-liquid ratio of 0.05 g / mL to obtain a dispersion. The dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 1 h using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation, the powder was dried at 100 °C to constant weight to obtain composite powder. S3. The composite powder is mixed with metal oxides (tungsten oxide and niobium oxide in a mass ratio of 1:1) with an average particle size of 10 μm. After ultrasonic dispersion in anhydrous ethanol, the mixture is transferred to a ball mill jar and ball milled at 80 rpm for 1 hour using 3 mm zirconium oxide grinding balls and a ball-to-material ratio of 3:1. After centrifugation, the mixture is dried at 100 °C to constant weight to obtain the mixed powder. S4. After cleaning the surface of the graphite crystallizer to be coated with ceramic, the mixed powder is thinly applied to the surface of the graphite crystallizer. Then, it is transferred to the sintering chamber, argon gas is introduced and pressurized to 20 MPa, and the temperature is raised to 1600℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the first coating layer. Then, it is transferred to the sintering chamber again, and in an argon atmosphere of 30 MPa, the temperature is raised to 1800℃ at a rate of 50℃ / min and held for sintering for 30 min. After cooling to room temperature, the surface is polished to complete the sintering of the second coating layer. After cooling to room temperature and polishing the surface, a ceramic coating with a total thickness of 0.3 mm is obtained.

[0065] Example 6

[0066] This embodiment 6 provides a method for forming a ceramic coating on the surface of a graphite crystallizer, including the following steps: S1. Silicon carbide with a particle size of 100 μm, silicon nitride with a particle size of 100 μm, and the alloy powder prepared in Preparation Example 1 were mixed at a mass ratio of 2:1:0.5 and then added to anhydrous ethanol for ultrasonic dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 2 hours using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation and drying at 80 °C to constant weight, the mixture was transferred to a vacuum furnace and evacuated. The furnace was heated to 1500 °C at a rate of 20 °C / min and sintered for 45 min. After cooling in the furnace, the mixture was ground and sieved to obtain ceramic powder with an average particle size of 10 μm. S2. Ceramic powder and graphene oxide with an average particle size of 0.5 μm were mixed at a mass ratio of 1:2 and then added to a 5% KH550 ethyl acetate solution at a solid-liquid ratio of 0.05 g / mL to obtain a dispersion. The dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 1 h using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation, the powder was dried at 100 °C to constant weight to obtain composite powder. S3. The composite powder is mixed with metal oxides (tungsten oxide and niobium oxide in a mass ratio of 1:1) with an average particle size of 10 μm. After ultrasonic dispersion in anhydrous ethanol, the mixture is transferred to a ball mill jar and ball milled at 80 rpm for 1 hour using 3 mm zirconium oxide grinding balls and a ball-to-material ratio of 3:1. After centrifugation, the mixture is dried at 100 °C to constant weight to obtain the mixed powder. S4. After cleaning the surface of the graphite crystallizer to be coated with ceramic powder, a thin layer of mixed powder is applied to the surface of the graphite crystallizer. The crystallizer is then transferred to a sintering chamber, argon gas is introduced, and the pressure is increased to 20 MPa. The temperature is then raised to 1600℃ at a rate of 50℃ / min and held for 30 minutes. After cooling to room temperature, the surface is polished to complete the sintering of the first coating layer. The crystallizer is then transferred back to the sintering chamber, and in an argon atmosphere at 30 MPa, the temperature is raised to 1800℃ at a rate of 50℃ / min and held for 30 minutes. After cooling to room temperature, the surface is polished to complete the sintering of the second coating layer. Finally, the crystallizer is transferred back to the sintering chamber, and in an argon atmosphere at 40 MPa... The temperature was raised to 2000℃ at a rate of 50℃ / min and sintered at that temperature for 30 min. After cooling to room temperature and polishing the surface, the third coating layer was sintered. The coating was then transferred to a sintering chamber and heated to 2100℃ at a rate of 50℃ / min in an argon atmosphere of 45 MPa. After sintering at that temperature for 30 min, the coating was cooled to room temperature and polished to complete the sintering of the fourth coating layer. The coating was then transferred to a sintering chamber and heated to 2200℃ at a rate of 50℃ / min in an argon atmosphere of 50 MPa. After sintering at that temperature for 30 min, the coating was cooled to room temperature and polished to complete the sintering of the fifth coating layer, resulting in a ceramic coating with a total thickness of 0.8 mm.

[0067] Example 7

[0068] This embodiment 7 provides a method for forming a ceramic coating on the surface of a graphite crystallizer, including the following steps: S1. Silicon carbide with a particle size of 50 μm, silicon nitride with a particle size of 50 μm, and the alloy powder prepared in Preparation Example 1 were mixed at a mass ratio of 2:1:0.5 and then added to anhydrous ethanol for ultrasonic dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 2 hours using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation and drying at 80 °C to constant weight, the mixture was transferred to a vacuum furnace and evacuated. The furnace was heated to 1500 °C at a rate of 20 °C / min and sintered for 45 min. After cooling in the furnace, the mixture was ground and sieved to obtain ceramic powder with an average particle size of 10 μm. S2. Ceramic powder and graphene oxide with an average particle size of 0.3 μm were mixed at a mass ratio of 1:2 and then added to a 5% KH550 ethyl acetate solution at a solid-liquid ratio of 0.05 g / mL to obtain a dispersion. The dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 1 h using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation, the powder was dried at 100 °C to constant weight to obtain composite powder. S3. The composite powder is mixed with metal oxides (tungsten oxide and niobium oxide in a mass ratio of 1:1) with an average particle size of 10 μm. After ultrasonic dispersion in anhydrous ethanol, the mixture is transferred to a ball mill jar and ball milled at 80 rpm for 1 hour using 3 mm zirconium oxide grinding balls and a ball-to-material ratio of 3:1. After centrifugation, the mixture is dried at 100 °C to constant weight to obtain the mixed powder. S4. After cleaning the surface of the graphite crystallizer to be coated with ceramic powder, a thin layer of mixed powder is applied to the surface of the graphite crystallizer. The crystallizer is then transferred to a sintering chamber, argon gas is introduced, and the pressure is increased to 20 MPa. The temperature is then raised to 1600℃ at a rate of 50℃ / min and held for sintering for 30 minutes. After cooling to room temperature, the surface is polished to complete the sintering of the first coating layer. The crystallizer is then transferred back to the sintering chamber, and in an argon atmosphere at 30 MPa, the temperature is raised to 1800℃ at a rate of 50℃ / min and held for sintering for 30 minutes. After cooling to room temperature, the crystallizer is then sintered. The surface was polished to complete the sintering of the second coating layer; then it was transferred to the sintering chamber, heated to 2000℃ at a rate of 50℃ / min in an argon atmosphere of 40MPa and held for sintering for 30min, then cooled to room temperature and polished to complete the sintering of the third coating layer; then it was transferred to the sintering chamber again, heated to 2200℃ at a rate of 50℃ / min in an argon atmosphere of 50MPa and held for sintering for 30min, then cooled to room temperature and polished to complete the sintering of the fourth coating layer, resulting in a ceramic coating with a total thickness of 0.6mm.

[0069] Comparative Example 1 Comparative Example 1 provides a method for forming a ceramic coating on the surface of a graphite crystallizer, comprising the following steps: D1. Silicon carbide with a particle size of 50 μm, silicon nitride with a particle size of 50 μm, and the alloy powder prepared in Preparation Example 1 were mixed at a mass ratio of 2:1:0.5 and then added to anhydrous ethanol for ultrasonic dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 2 hours using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation and drying at 80 °C to constant weight, the mixture was transferred to a vacuum furnace and evacuated. The furnace was heated to 1500 °C at a rate of 20 °C / min and sintered for 45 min. After cooling in the furnace, the mixture was ground and sieved to obtain ceramic powder with an average particle size of 10 μm. D2. After mixing ceramic powder with metal oxides (tungsten oxide and niobium oxide in a mass ratio of 1:1) with an average particle size of 10 μm, the mixture was added to anhydrous ethanol and ultrasonically dispersed. The mixture was then transferred to a ball mill jar, ball-milled for 1 hour at 80 rpm using 3 mm zirconium oxide grinding balls and a ball-to-material ratio of 3:1. After centrifugation, the mixture was dried at 100 °C to constant weight to obtain the mixed powder. D3. After cleaning the surface of the graphite crystallizer to be coated with ceramic, the mixed powder is thinly applied to the surface of the graphite crystallizer and then transferred to the sintering chamber. Argon gas is introduced and pressurized to 45MPa. The temperature is raised to 1800℃ at a rate of 50℃ / min and sintered for 30min. After cooling to room temperature and polishing the surface, the process is repeated twice to obtain a ceramic coating with a thickness of 0.4mm.

[0070] Comparative Example 2 Comparative Example 2 provides a method for forming a ceramic coating on the surface of a graphite crystallizer, comprising the following steps: D1. Silicon carbide with a particle size of 50 μm, silicon nitride with a particle size of 50 μm, and the alloy powder prepared in Preparation Example 1 were mixed at a mass ratio of 2:1:0.5 and then added to anhydrous ethanol for ultrasonic dispersion to obtain a mixed dispersion. The mixed dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 2 hours using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation and drying at 80 °C to constant weight, the mixture was transferred to a vacuum furnace and evacuated. The furnace was heated to 1500 °C at a rate of 20 °C / min and sintered for 45 min. After cooling in the furnace, the mixture was ground and sieved to obtain ceramic powder with an average particle size of 10 μm. D2. Ceramic powder and graphene oxide with an average particle size of 0.3 μm were mixed at a mass ratio of 1:2 and then added to a 5% KH550 ethyl acetate solution at a solid-liquid ratio of 0.05 g / mL to obtain a dispersion. The dispersion was transferred to a ball mill jar and ball milled at 80 rpm for 1 h using 3 mm zirconia grinding balls at a ball-to-material ratio of 3:1. After centrifugation, the powder was dried at 100 °C to constant weight to obtain the composite powder. D3. After cleaning the surface of the graphite crystallizer to be coated with ceramic, the composite powder is thinly applied to the surface of the graphite crystallizer. Then, it is transferred to the sintering chamber, argon gas is introduced and pressurized to 45 MPa. The temperature is then raised to 1800℃ at a rate of 50℃ / min and sintered for 30 min. After cooling to room temperature and polishing the surface, the process is repeated twice to obtain a ceramic coating with a thickness of 0.4 mm.

[0071] Performance testing Graphite crystallizers of the same type as those used in Examples 1 to 7 and Comparative Examples 1 to 2 (without a ceramic coating on the surface) were used as blank examples. The graphite crystallizers from the blank group, Examples 1 to 7, and Comparative Examples 1 to 2 were installed in copper alloy production lines, and the actual production output per use of the graphite crystallizer was calculated in tons / set. The graphite crystallizers from the blank examples, Examples 1 to 7, and Comparative Examples 1 to 2 were kept at 1000°C and 20% oxygen concentration for 10 hours, and their weight loss rate after thermal oxidation was measured. The density of the ceramic coating on the surface of the graphite crystallizers from Examples 1 to 7 and Comparative Examples 1 to 2 was measured. The test results for the above items are shown in Table 1 below. The surface roughness, crack rate, and number of inclusion defects of the copper alloys obtained from the production lines equipped with the graphite crystallizers from the blank examples, Examples 1 to 7, and Comparative Examples 1 to 2 are shown in Table 2 below.

[0072] Table 1 Performance test data of graphite crystallizer

[0073] Table 2 Surface Quality Data of Copper Alloy

[0074] As can be seen from Table 1, the ceramic coating prepared by the method provided by the present invention can form a dense and stable structure on the surface of the graphite crystallizer, thereby improving the service life of graphite crystallization and the surface quality of the copper alloy produced during continuous casting.

[0075] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for preparing a ceramic coating, characterized in that, include: Silicon carbide, silicon nitride and alloy powder are mixed, ball-milled and then heat-treated to obtain ceramic powder; the ceramic powder and graphene oxide are wet-milled and then separated and dried to obtain composite powder; the composite powder is mixed with metal oxide and then coated on the surface of the graphite blank of the graphite crystallizer; the ceramic coating is obtained by gradient sintering under high temperature and high pressure.

2. The preparation method according to claim 1, characterized in that: The particle sizes of the silicon carbide, silicon nitride, and alloy powder are independently 20 μm-100 μm; and / or, the mass ratio of the silicon carbide, silicon nitride, and alloy powder is 2:(0.8-1.2):(0.4-0.6); and / or, the metal element in the alloy powder is selected from five of Ni, Co, Cr, Y, Ti, Zr, and Ta.

3. The preparation method according to claim 1, characterized in that: The mixture is ball-milled at a speed of 50 rpm to 100 rpm; and / or, ball-milled using zirconia as grinding balls; and / or, the ball-to-material ratio during ball-milling is (2-5):1; and / or, after wet ball-milling, the mixture is dried and heat-treated; and / or, after ball-milling, the mixture is heat-treated at 1400℃ to 1600℃; and / or, after heat-treatment under vacuum, the mixture is cooled to obtain ceramic powder.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the ceramic powder to the graphene oxide is 1:(1-3); and / or, the particle size of the graphene oxide is 0.1μm-0.5μm; and / or, the ceramic powder and the graphene oxide are wet-milled in a solution containing a dispersant, wherein the dispersant includes one of KH550 and KH560, the solid-liquid ratio is 0.04g / mL-0.08g / mL, and the concentration of the dispersant in the solution containing the dispersant is 3%-8%.

5. The preparation method according to claim 1, characterized in that: The ceramic powder has a particle size of 5μm-20μm; and / or, is wet ball milled at a speed of 50rpm-100rpm; and / or, the ball-to-material ratio during wet ball milling is (2-5):1; and / or, after wet ball milling, it is separated and dried at 80℃-120℃; and / or, wet ball milling is performed for 1h-5h; and / or, zirconium oxide is used as the grinding ball for wet ball milling.

6. The preparation method according to claim 1, characterized in that: The metal oxide includes at least one of aluminum oxide, zirconium oxide, titanium oxide, tungsten oxide, niobium oxide, and tantalum oxide; and / or, the mass ratio of the composite powder to the metal oxide is 1:(0.2-0.3); and / or, the particle size of the metal oxide is 5μm-15μm; and / or, the composite powder and the metal oxide are ball-milled and mixed.

7. The preparation method according to claim 1, characterized in that: Gradient sintering is performed at 1600℃-2200℃; and / or, sintering is performed under high pressure at a heating rate of 10℃ / min-50℃ / min. And / or, gradient sintering is performed at 20MPa-50MPa; and / or, two to five layers of gradient sintering are performed under high temperature and high pressure, with the sintering temperature of each layer increasing by 100℃-300℃ and the pressure increasing by 5MPa-15MPa compared to the previous layer; and / or, the thickness of the ceramic coating is 0.3mm-0.8mm.

8. A ceramic coating prepared by the preparation method according to any one of claims 1 to 7.

9. The application of a ceramic coating prepared by any one of claims 1 to 7 on the surface of a continuous casting crystallizer.

10. The application according to claim 9, characterized in that, The continuous casting crystallizer is a graphite crystallizer, and the ceramic coating is formed on the surface of the graphite lining in the graphite crystallizer.

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