Preparation method of a high-performance dense microporous sintered corundum material

Abstract

This application belongs to the technical field of new material preparation, and discloses a preparation method of a high-performance dense microporous sintered corundum material. In the present invention, sintered corundum fine powder is first prepared. This fine powder has characteristics such as large grains, many pores, small pores, and low thermal conductivity. Using this fine powder as the main raw material, the prepared high-performance dense microporous sintered corundum material has properties such as high temperature resistance, oxidation resistance, corrosion resistance, etc., and also has excellent thermal shock resistance, and can be used in harsh working environments, such as the guide vanes of aerospace engines. In addition, the corundum material obtained by the preparation method of the present invention can also be applied to other fields that require high temperature resistance, high mechanical strength, and good thermal stability, such as industrial furnace linings, high-temperature sensor protective covers, etc.

Description

Technical Field

[0001] This application belongs to the technical field of new material preparation, and specifically relates to a preparation method of a high-performance dense microporous sintered corundum material. Background Art

[0002] In an aeroengine, the guide vane is a key component located after the combustion chamber and before the turbine. Its main function is to guide the high-temperature and high-pressure gas flow to impact the turbine blades at the best angle, thereby maximizing the working efficiency of the turbine. In the combustion chamber of an aeroengine, after the fuel and oxidizer are mixed and ignited, the generated gas temperature can reach above 2000°C. The guide vane is directly exposed to this extremely high-temperature environment and needs to be able to withstand this high temperature for a long time without melting or significant deformation. In addition to the continuous high temperature, the engine also experiences frequent thermal cycles during startup, acceleration, deceleration, and shutdown. These thermal cycles will cause thermal stress to be generated inside the material, which may lead to crack formation and propagation, thereby affecting the service life of the blade.

[0003] Due to the extremely harsh working environment of the guide vane, including extremely high temperature, pressure, and particle erosion in the high-speed gas flow, very high requirements are put forward for the selection of the guide vane material.

[0004] In terms of mechanical properties: Tensile strength: The guide vane needs to have sufficient tensile strength to resist the impact force and centrifugal force of the gas flow. Abrasion resistance: The high-speed gas flow contains fine solid particles, which will cause wear on the blade surface. Therefore, the guide vane material needs to have good wear resistance. Creep resistance: Under the action of high temperature and stress, the material may undergo creep, that is, slow plastic deformation. This will affect the shape accuracy and structural integrity of the blade.

[0005] In terms of thermodynamic properties: Low thermal conductivity: In order to reduce the heat transfer to other parts of the engine, the guide vane material should have a low thermal conductivity to maintain good heat insulation effect. Thermal expansion coefficient: The thermal expansion coefficient of the material should be as low as possible to reduce the internal stress caused by temperature changes.

[0006] The materials used in the prior art all have their limitations. For example, nickel-based superalloys: Although the currently widely used nickel-based superalloys have good comprehensive properties, there are still certain limitations under extremely high-temperature conditions, such as the creep problem after long-term use. For example, ceramic materials: Traditional ceramic materials such as zirconia have good high-temperature resistance, but their brittleness and processing difficulty limit their application in complex-shaped components.

[0007] Existing materials and technologies still have deficiencies in meeting the stringent requirements of aerospace engine guide vanes. Therefore, developing a new type of high heat-resistant material, especially a material with excellent mechanical properties, thermodynamic properties, and chemical stability, is crucial for improving the overall performance and reliability of the engine. Summary of the Invention

[0008] Object of the Invention: Aiming at the deficiencies in the prior art, this application provides a preparation method of a high-performance dense microporous sintered corundum material. The sintered corundum material prepared by the method of the present invention has excellent mechanical properties, thermodynamic properties, and chemical stability, and can be applied to harsh working environments.

[0009] Technical Solution: The preparation method of the high-performance dense microporous sintered corundum material provided by the present invention uses sintered corundum fine powder as the main raw material. The sintered corundum fine powder has a bulk density of 3.65 - 3.69 g / cm 3 , a grain size of 100 - 300 μm, and a thermal conductivity less than 1.8 W / (m·K); silicon carbide fibers and sintering aids are added, and then uniformly mixed with a polyvinyl alcohol solution, and isostatically pressed into a preform; the preform is placed in a furnace, heated to 850 - 900 °C under a protective atmosphere, held for 2 - 2.5 hours, and then continuously heated to 1700 - 1800 °C, held for 4 - 5 hours, and after sintering is completed, it is naturally cooled to room temperature to obtain the dense microporous sintered corundum material.

[0010] Specifically, the sintered corundum fine powder is obtained by the following method: 94 - 96 parts of α - Al2O3 powder, 1 - 3 parts of aluminum hydroxide powder, 0.5 - 2 parts of metallic aluminum powder, and 0.2 - 0.8 parts of additive are mixed, and after being uniformly mixed, they are ground; the ground powder is made into balls to form ball blanks with a diameter of 30 ± 2 mm. The water content in the ball blanks is about 20%, and it is dried to a water content of less than 1%, calcined, cooled after calcination, broken, and ball milled to obtain the sintered corundum fine powder.

[0011] The raw materials for preparing sintered corundum fine powder contain a small amount of aluminum hydroxide, which will decompose into alumina and water vapor at high temperature. This process will occur before or during sintering. During the decomposition of aluminum hydroxide, certain gases (water vapor) will be generated, and these gases will form a tiny pressure between the powder particles, which helps the rearrangement of the material, thereby promoting densification during sintering. Due to the thermal decomposition characteristics of aluminum hydroxide, it can change the microstructure of the final product during the heating process, such as affecting the grain size, shape and distribution, and further affecting the mechanical properties and other physical and chemical properties of the material. However, the addition amount of aluminum hydroxide must be strictly controlled because excessive addition may lead to adverse consequences, such as generating too many pores or unwanted phase changes, etc. Therefore, for the present invention, the addition amount of aluminum hydroxide is preferably 1.5 to 2 parts.

[0012] At high temperature, when the trace amount of metallic aluminum powder in the raw materials contacts water vapor, in addition to forming alumina, hydrogen gas (H2) will also be generated, and these gases will expand inside the material to form pores. By adjusting the particle size, addition amount of aluminum powder, as well as the sintering temperature and time, the size, shape and distribution of the generated pores can be effectively controlled, so as to obtain the desired microstructure. The dosage of aluminum powder needs to be precisely controlled. Excessive addition may lead to too many pores and affect the mechanical properties of the product; while insufficient addition will not achieve the expected pore-forming effect. Fine particles are more likely to be evenly dispersed in the alumina powder, which helps to form a uniformly distributed pore structure. If the particles are too large, it may be difficult to disperse them evenly, resulting in too intense local reactions and generating uneven pores. At the same time, finer aluminum powder has a larger specific surface area, which increases its chance of contacting water vapor or oxygen, thereby increasing the reaction rate. However, overly fine aluminum powder may lead to difficult handling and increase safety risks (such as spontaneous combustion or explosion). Therefore, it is necessary to balance the reaction activity and operation safety. For the present invention, the preferred particle size of the metallic aluminum powder is between 10 and 50 microns, and its addition amount is preferably 0.8 - 1 part.

[0013] Specifically, the additives are: magnesium oxide and silicon dioxide. A trace amount of magnesium oxide is used to promote sintering densification, and a trace amount of SiO2 is used to improve the dispersibility of the fine powder. The addition amounts are 0.2 - 0.5 parts of magnesium oxide and 0.1 - 0.3 parts of silicon dioxide, preferably 0.2 parts of magnesium oxide and 0.1 part of silicon dioxide.

[0014] Specifically, the grinding is to grind the mixture to D50 of 5 ± 0.1 μm in a continuous ball mill.

[0015] Specifically, for the calcination, the heating process is as follows: It rises from room temperature to 250°C and is kept warm. The decomposition temperature of aluminum hydroxide is usually between about 200°C and 450°C. Then it is rapidly heated to 800°C and kept warm for [X] hours. The effective temperature range for the reaction between aluminum powder and water vapor is roughly between 700°C and 1000°C. This stage is crucial for metallic aluminum powder because within this temperature range, it can react with the remaining water vapor to form Al2O3. Therefore, the specific heating process is: rising from room temperature to 250°C, keeping warm for 1 - 3 hours, then rapidly heating to 800°C and keeping warm for 1 - 3 hours. More specifically, the heating process is: rising from room temperature to 250°C within 1 hour, keeping warm at 250°C for 2 hours, rapidly heating to 800°C within 30 minutes, keeping warm at 800°C for 2 hours, and heating to 1920°C within 6 hours.

[0016] Specifically, for the cooling, it is cooled with the kiln furnace until the temperature is below 80°C.

[0017] Specifically, the dosage ratios of the sintered corundum fine powder, silicon carbide fiber, sintering aid, and polyvinyl alcohol solution are as follows: 100 parts of sintered corundum fine powder, 5 - 10 parts of silicon carbide fiber, 1 - 3 parts of sintering aid, and 4 - 6 parts of polyvinyl alcohol solution. Preferably, 100 parts of sintered corundum fine powder, 8 parts of silicon carbide fiber, 2 parts of sintering aid, and 5 parts of polyvinyl alcohol solution.

[0018] Specifically, the sintering aid is titanium dioxide. The addition of titanium dioxide can promote particle bonding, improve the strength and wear resistance of the sintered product. At the same time, it can inhibit grain growth, improve the fine grain degree and uniformity of the sintered product. In addition, titanium dioxide can form a solid solution with the sintered material, reduce the sintering temperature, and accelerate the diffusion and sintering speed.

[0019] Beneficial effects: The sintered corundum material prepared by the method of the present invention performs excellently in an extremely high-temperature environment, can withstand temperatures exceeding 2000°C in the combustion chamber, and has excellent oxidation resistance and thermal corrosion resistance. It is not easy to react with oxygen to form oxides, and at the same time has high resistance to most acid-base solutions and gases. In addition, this material has enhanced mechanical properties, with extremely high hardness and strength, and can effectively resist particle erosion and wear in the gas flow; after introducing reinforcing phases such as silicon carbide fibers, the toughness of the material is significantly improved, and it can better absorb the energy generated by thermal shock, avoiding the rapid propagation of cracks. Moreover, the larger grain size helps to improve the creep resistance of the material, and it can still maintain its shape unchanged under continuous high temperature and stress.

[0020] The sintered corundum prepared by the method of the present invention also has excellent thermodynamic properties, including a low thermal conductivity and a low coefficient of thermal expansion, which can effectively isolate heat, reduce the heat transferred from the combustion chamber to other parts of the engine, protect the external structure from overheating damage, and reduce the internal stress caused by temperature changes to prevent the material from cracking. At the same time, it has good processability and can be made into complex geometric shapes through advanced forming techniques to meet the design requirements of the guide vane, and a reliable connection with other engine components can be ensured through appropriate joining techniques. Although the high-quality sintered corundum and its processing cost are relatively high, the optimization of the production process and the economies of scale contribute to gradually reducing the unit cost. Coupled with the long service life and high reliability of the material, the maintenance and replacement costs are reduced, making it economically viable. In addition, sintered corundum is a non-toxic and harmless material that can be recycled and reused, meeting the requirements of sustainable development.

[0021] In addition to the guide vanes of aerospace engines, this high-performance sintered corundum material can also be applied to other fields that require high temperature resistance, high mechanical strength, and good thermal stability, such as industrial furnace linings, high-temperature sensor protective covers, etc. In summary, the sintered corundum material and its preparation method provided by the present invention not only overcome the limitations of existing materials in high-temperature environments, but also greatly improve the comprehensive performance of the material through fiber reinforcement technology, providing strong technical support for the development of the aviation industry. Brief Description of the Drawings

[0022] Figure 1 SEM micrograph of the material obtained in Example 1 (100μm)

[0023] Figure 2 SEM micrograph of the material obtained in Example 1 (50μm)

[0024] Figure 3 SEM micrograph of the material obtained in Example 1 (10μm)

[0025] Figure 4 SEM micrograph of the sintered corundum in Comparative Example 1 (20μm)

[0026] Figure 5 SEM micrograph of the sintered corundum in Comparative Example 1 (10μm)

[0027] Figure 6 SEM micrograph of the sintered corundum in Comparative Example 2. Detailed Description of the Embodiments

[0028] The technical solutions of the present application will be described in detail below through examples, but the protection scope of the present application is not limited to the described examples. The parts mentioned in the present invention are all in parts by mass.

[0029] Example 1

[0030] Weigh 95 parts of high-purity (above 99.5%) α-Al2O3 powder, 1.8 parts of aluminum hydroxide powder, 0.9 parts of metallic aluminum powder, 0.2 parts of magnesium oxide, and 0.1 parts of silicon dioxide. Mix the above raw materials, and after mixing evenly, conduct grinding. Grind the mixture to a D50 of about 5 microns in a continuous ball mill; then form ball blanks with a diameter of about 30 mm in a pelletizer; dry at 90°C, controlling the water content to be below 1%; conduct calcination in an ultra-high-temperature vertical kiln. The heating process is as follows: rise from room temperature to 250°C within 1 hour, hold at 250°C for 2 hours, quickly rise to 800°C within 30 minutes, hold for 2 hours, rise to 1920°C within 6 hours, and the final calcination temperature is about 1920°C, hold for 4 hours, and then cool with the kiln, cooling to below 80°C; preliminarily crush the sintered block through a Barmac crusher, and then ball mill it with a ball mill to obtain the sintered corundum fine powder. Its SEM electron micrograph is as Figure 1 , Figure 2 , Figure 3 shown.

[0031] Comparative Example 1

[0032] Existing commercially available sintered corundum, its SEM electron micrograph is as Figure 4 , Figure 5 shown.

[0033] Comparative Example 2

[0034] Existing commercially available sintered corundum, its SEM electron micrograph is as Figure 6 shown.

[0035] From the comparison of the electron micrographs of the examples and the comparative examples, it can be seen that for the existing commercially available sintered corundum, the grain size is basically around 20 - 40 μm, and individual grains are about 50 μm; while the grains of the product obtained in this example are larger in size and more fully crystallized. It can also be seen that the existing sintered corundum has fewer pores, and the pore sizes are uneven. Due to looseness between the grain boundaries, pores are also commonly seen at the grain boundaries (such as Figure 5 ), and even in some grains, there is basically no pore distribution, thus losing the excellent thermal shock resistance characteristics of sintered corundum (such as Figure 6 ). While the product obtained in this example has a large number of fine pores, the pores are fine, and they are distributed in the grains. The crystal structure and pore distribution are as Figure 2 , Figure 3 shown. Due to having more fine pores, the thermal conductivity of this sintered corundum is reduced by more than 30% compared with that of the existing commercially available sintered corundum.

[0036] Example 2

[0037] Weigh 95 parts of high-purity (above 99.5%) α-Al2O3 powder, 1.8 parts of aluminum hydroxide powder, 0.9 part of metallic aluminum powder, 0.2 part of magnesium oxide, and 0.1 part of silicon dioxide. Mix the above raw materials, and after mixing evenly, carry out grinding. Grind the mixture to a D50 of about 5 microns in a continuous ball mill; then form ball blanks with a diameter of about 30 mm in a pelletizer; dry at 90°C and control the water content to be below 1%; carry out calcination in an ultra-high temperature shaft kiln. The heating process is as follows: rise from room temperature to 250°C within 1 hour, hold at 250°C for 2 hours, rise to 800°C within 2 hours, hold for 2 hours, and rise to 1920°C within 6 hours. The final calcination temperature is about 1920°C, hold for 4 hours, and then cool with the kiln, cool to below 80°C; preliminarily crush the sintered block by a Barmac crusher, and then ball mill it with a ball mill to obtain the sintered corundum fine powder.

[0038] Example 3

[0039] Weigh 95 parts of high-purity (above 99.5%) α-Al2O3 powder, 1.8 parts of aluminum hydroxide powder, 0.9 part of metallic aluminum powder, 0.2 part of magnesium oxide, and 0.1 part of silicon dioxide. Mix the above raw materials, and after mixing evenly, carry out grinding. Grind the mixture to a D50 of about 5 microns in a continuous ball mill; then form ball blanks with a diameter of about 30 mm in a pelletizer; dry at 90°C and control the water content to be below 1%; carry out calcination in an ultra-high temperature shaft kiln. The heating process is as follows: rise from room temperature to 250°C within 1 hour, then immediately rise to 800°C within 2 hours, hold for 2 hours, rise to 1920°C within 6 hours. The final calcination temperature is about 1920°C, hold for 4 hours, and then cool with the kiln, cool to below 80°C; preliminarily crush the sintered block by a Barmac crusher, and then ball mill it with a ball mill to obtain the sintered corundum fine powder.

[0040] The relevant test data of Examples 1 to 3 and Comparative Example 1 are shown in the following table:

[0041]

[0042]

[0043] It can be seen from the data in the table that compared with the existing sintered corundum, the examples of the present invention have a larger bulk density, larger grain size, and lower thermal conductivity.

[0044] In addition, it can be seen that the heating method will affect the thermal conductivity of the product. The reason is that the heating method affects the formation of pores. Example 1 can better form more fine pores. Therefore, its thermal conductivity is the lowest.

[0045] Example 4

[0046] Using the sintered corundum fine powder obtained in Example 1 as the main raw material, mix according to the following ratio: 100 parts of sintered corundum fine powder, 8 parts of silicon carbide fiber, 2 parts of titanium dioxide, and 5 parts of polyvinyl alcohol solution. Mix evenly, and press into a long strip-shaped guide vane preform under a pressure of 200 MPa by a cold isostatic press; place the preform in a furnace, heat it to 850 °C under a nitrogen protection atmosphere, hold for 2 hours, then continue to heat to 1750 °C, hold for 4 hours, and naturally cool to room temperature after sintering to obtain the dense microporous sintered corundum material.

[0047] Example 5

[0048] Using the sintered corundum in Example 2 as the main raw material, mix according to the following ratio: 100 parts of sintered corundum, 8 parts of silicon carbide fiber, 2 parts of titanium dioxide, and 5 parts of polyvinyl alcohol solution. Mix evenly, and press into a long strip-shaped guide vane preform under a pressure of 200 MPa by a cold isostatic press; place the preform in a furnace, heat it to 850 °C under a nitrogen protection atmosphere, hold for 2 hours, then continue to heat to 1750 °C, hold for 4 hours, and naturally cool to room temperature after sintering to obtain the dense microporous sintered corundum material.

[0049] Example 6

[0050] Using the sintered corundum fine powder obtained in Example 3 as the main raw material, mix according to the following ratio: 100 parts of sintered corundum fine powder, 8 parts of silicon carbide fiber, 2 parts of titanium dioxide, and 5 parts of polyvinyl alcohol solution. Mix evenly, and press into a long strip-shaped guide vane preform under a pressure of 200 MPa by a cold isostatic press; place the preform in a furnace, heat it to 850 °C under a nitrogen protection atmosphere, hold for 2 hours, then continue to heat to 1750 °C, hold for 4 hours, and naturally cool to room temperature after sintering to obtain the dense microporous sintered corundum material.

[0051] Example 7

[0052] Using the sintered corundum in Comparative Example 1 as the main raw material, mix according to the following ratio: 100 parts of sintered corundum fine powder, 8 parts of silicon carbide fiber, 2 parts of titanium dioxide, and 5 parts of polyvinyl alcohol solution. Mix evenly, and press into a long strip-shaped guide vane preform under a pressure of 200 MPa by a cold isostatic press; place the preform in a furnace, heat it to 850 °C under a nitrogen protection atmosphere, hold for 2 hours, then continue to heat to 1750 °C, hold for 4 hours, and naturally cool to room temperature after sintering to obtain the dense microporous sintered corundum material.

[0053] The samples obtained in Examples 4 to 7 were tested. Compressed air at 448 kPa was used to blow 1000 g ± 5 g of standard silicon carbide sand (36#) onto the samples within 450 s ± 15 s, and the weight loss rate was calculated. After soaking in a 10% NaOH solution at room temperature for 15 days, the weight loss rate was calculated. After holding in an oxygen atmosphere at 800 °C for 5 days, the weight gain rate was calculated. The specific results are shown in the following table:

[0054]

[0055] Examples 4 and 5 were tested. The specimens were placed in an electric furnace (1000 °C, 1500 °C, 2000 °C) and held for 15 min, then taken out and air-cooled. After 30 min, the specimens were put into the electric furnace again for heating, holding, and cooling, and repeated multiple times until cracks or fractures appeared in the specimens, and the number of thermal shock cycles before specimen failure was recorded.

[0056]

[0057] It can be seen that the materials of the present invention have excellent wear resistance, corrosion resistance, high temperature resistance, and thermal shock resistance. Further, by comparing between Examples 4 to 7, it can be found that the materials obtained in Examples 4 to 6 are significantly superior to Example 7 in terms of high temperature resistance and thermal shock resistance.

[0058] Through the optimized preparation process of the present invention, a large number of uniformly distributed and size-controllable micro-pores are formed inside the corundum material. The difference in thermal expansion coefficients between the air in the pores and the alumina matrix is small, enabling the two to expand or contract better synergistically during temperature changes, reducing the internal stress generated due to thermal expansion mismatch. When an external thermal shock causes cracks to propagate in the ceramic matrix, the cracks are prone to deflection, bifurcation, or pinning when encountering the pores. This phenomenon shortens the crack length, increases the number of cracks, and forms a complex network structure. This not only increases the energy required for material fracture but also effectively inhibits the further propagation of cracks. The uniformly distributed micro-pores can act as a "buffer zone" during rapid heating and cooling processes, effectively absorbing and dispersing the thermal stress caused by rapid temperature changes, thereby reducing the impact on the matrix structure and further enhancing the thermal shock resistance of the material.

[0059] The above description is only the preferred embodiments of the present application and is not intended to limit the present application.

Claims

1. A preparation method of a dense microporous sintered corundum material, characterized in that, Using sintered corundum fine powder as the main raw material, the sintered corundum fine powder has a bulk density of 3.65 - 3.69 g / cm 3 , the grain size is 100 - 300 μm, and the thermal conductivity is less than 1.8 W / (m·K); adding silicon carbide fibers and sintering aids, then mixing evenly with polyvinyl alcohol solution, and isostatically pressing into a preform; placing the preform in a furnace, heating to 850 - 900 °C under a protective atmosphere, holding for 2 - 2.5 hours, then continuing to heat to 1700 - 1800 °C, holding for 4 - 5 hours, and naturally cooling to room temperature after sintering to obtain the dense microporous sintered corundum material; The described sintered corundum fine powder is obtained by the following method: by mass parts, mix 94 - 96 parts of α - Al₂O₃ powder, 1 - 3 parts of aluminum hydroxide powder, 0.5 - 2 parts of metallic aluminum powder, and 0.3 - 0.8 parts of additive. After mixing evenly, carry out grinding; pelletize the ground powder to form pellets with a diameter of 30 ± 2 mm, dry them until the water content is below 1%, calcine, cool after calcination, crush and ball - mill to obtain the described sintered corundum fine powder; The particle size of the metallic aluminum powder is between 10 and 50 μm; for the described calcination, the heating process is as follows: rise from room temperature to 250 °C, hold for 1 - 3 hours, rapidly rise to 800 °C within 30 min, hold for 1 - 3 hours, and then rise to 1920 °C.

2. The preparation method of the dense microporous sintered corundum material according to claim 1, characterized in that, The described additive is: by mass parts, 0.2 - 0.5 parts of magnesium oxide and 0.1 - 0.3 parts of silicon dioxide.

3. The preparation method of the dense microporous sintered corundum material according to claim 1, characterized in that, The described grinding is to grind the mixture to D50 of 5.0 ± 0.1 μm in a continuous ball mill.

4. The preparation method of the dense microporous sintered corundum material according to claim 1, characterized in that, For the described calcination, the heating process is as follows: rise from room temperature to 250 °C within 1 hour, hold at 250 °C for 2 hours, rapidly rise to 800 °C within 30 min, hold for 2 hours, and rise to 1920 °C within 6 hours.

5. The preparation method of the dense microporous sintered corundum material according to claim 1, characterized in that, For the cooling after calcination, cool with the furnace until the temperature is below 80 °C.

6. The preparation method of the dense microporous sintered corundum material according to claim 1, characterized in that, The dosage ratio of the described sintered corundum fine powder, silicon carbide fiber, sintering aid, and polyvinyl alcohol solution is: by mass parts, 100 parts of sintered corundum fine powder, 5 - 10 parts of silicon carbide fiber, 1 - 3 parts of sintering aid, and 4 - 6 parts of polyvinyl alcohol solution.

7. The preparation method of the dense microporous sintered corundum material according to claim 6, characterized in that, The described sintering aid is titanium dioxide.

Images