Preparation method of MgO-MgA12O4-ZrO2 nano ceramic eutectic composite material

Abstract

The invention discloses a preparation method of a MgO-MgA12O4-ZrO2 nano ceramic eutectic composite material. The preparation method comprises the following steps: S1, preparing powder; s2, flash firing preparation; and S3, high-temperature melting preparation. According to the invention, two technologies of flash sintering and high-temperature melting are combined, the problems of high sintering temperature, easy growth of crystal grains, difficult densification and the like of the traditional eutectic ceramic are solved, and an excellent composite material with a nanoscale eutectic structure is finally obtained; a nanocrystalline blank obtained through flash sintering is crushed and then subjected to high-temperature melting, microdefects and air holes possibly existing in the flash sintering blank are eliminated, the chemical components and the microstructure of a final product are more uniform, and compared with traditional selective laser melting, the method is more convenient and faster to implement and lower in cost.

Description

Technical Field

[0001] This invention relates to the field of nanoceramic technology, specifically to a method for preparing a MgO-MgAl2O4-ZrO2 nanoceramic eutectic composite material. Background Technology

[0002] Nanoceramics, a branch of nanomaterials, refer to a class of ceramic materials where grains, grain boundaries, and the bonds between them are all at the nanoscale. This includes grain size, grain boundary width, second-phase distribution, pore size, and defect size, all within the nanometer range. Due to the refined grains and significantly increased number of grain boundaries in nanoceramics, the toughness and plasticity of the material are greatly improved, and it has a significant impact on the material's electrical, thermal, magnetic, and optical properties.

[0003] The preparation of nanoceramic powder is the first step in the preparation of nanoceramics. This is because the properties of the powder, such as chemical composition ratio, powder purity, particle size, particle size distribution, and agglomeration, have a significant impact on subsequent molding, sintering, and the final properties of the nanoceramics. Nanoceramic powder is a metastable intermediate substance with a nanometer size, existing between solids and molecules. As the powder becomes ultrafine, its surface electronic structure and crystal structure change, producing unique effects not found in ordinary powders.

[0004] The biggest challenge in the manufacturing process of nanopowders is solving the agglomeration problem. Agglomeration causes great trouble for sintering because agglomerated powder introduces a large number of defects and pores after sintering, which seriously affects the density and properties of the sintered product. Moreover, agglomerated powder is prone to forming large grains during sintering, making it difficult to obtain nano-ceramics.

[0005] Magnesium aluminum spinel (MgA12O4) belongs to the cubic crystal system and is a ceramic material with good chemical stability, wear resistance, corrosion resistance, low coefficient of thermal expansion, and good insulation properties. MgO-MgA12O4-ZrO2 nanoceramics possess excellent properties and broad application prospects. To prepare high-performance MgO-MgA12O4-ZrO2 nanoceramics, obtaining high-quality nanoparticle powder is crucial. Currently, obtaining "ideal powder"—that is, simultaneously meeting the stringent conditions of uniform composition, fine particle size, narrow particle size distribution, no agglomeration, and large specific surface area—remains challenging. Currently, selective laser melting is a commonly used method for preparing MgO-MgA12O4-ZrO2 nanoceramic eutectic composite materials, but its equipment cost is high, the process is complex, and it cannot produce large-size and complex-shaped components. Therefore, how to obtain high-quality powder at low cost and optimize the preparation method are urgent problems to be solved. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a method for preparing MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite materials.

[0007] The technical solution of this invention is: A method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material includes the following steps: S1. Powder preparation: A mixed powder of Al(OH)3 and MgSO4 is placed in a crucible, wherein the molar ratio of Al to Mg is 5~6:22. The crucible is placed in a sintering furnace for calcination at a temperature of 700~800℃ for 1.5~2h. After cooling down with the furnace, the crucible is removed, washed and dried to obtain MgAl2O4 nanopowder. S2. Flash sintering preparation: According to the weight, take 1±0.05 parts of MgO nanopowder, 1±0.05 parts of MgA12O4 nanopowder prepared in S1, and 1±0.05 parts of 3Y-TZP powder, place them in a mold and press them to obtain a green blank. Connect the green blank to a DC power supply through a platinum wire and apply an electric field of 800~900V / cm. At this time, the power supply control mode is voltage control mode. Then place it in a sintering furnace and heat the sintering furnace at a heating rate of 50~100℃ / min. When the temperature reaches the flash sintering temperature, the current of the green blank increases sharply to the limiting current, which is 80~120mA. At this time, the power supply control mode switches from voltage control mode to current limiting mode and continues to maintain it for 10~20s. Then turn off the power supply and the sintering furnace and let it cool naturally to room temperature to obtain the sintered green blank. S3. High-temperature melting and solidification preparation: After crushing the sintered billet prepared in S2, it is placed in a crucible and melted and solidified at high temperature in a high-temperature vacuum furnace under the protection of high-purity argon gas. The melting temperature is 1850~1950℃, held for 1~2h, slowly cooled to 1750~1800℃, held for 10~15min, and then cooled to room temperature to obtain the fused MgO-MgA12O4-ZrO2 nano-ceramic eutectic composite material.

[0008] Further, in S1, the method for preparing the mixed powder of Al(OH)3 and MgSO4 is as follows: 0.1±0.05g of polyethylene glycol is dissolved in 100±0.5mL of Al(NO3)3 solution to obtain a mixed solution. The solution is stirred for 10-15min, and then ammonia is gradually added dropwise until the pH of the mixed solution is 9. The stirring is continued for 10-12h, and then allowed to stand for 10-12h. The solution is filtered to obtain a wet gel. The wet gel is washed with distilled water 6-8 times, then washed with anhydrous ethanol 3-5 times, and then dried at 75-80℃ to obtain a dry gel. The dry gel is ground to obtain Al(OH)3 powder. The Al(OH)3 powder is added to the MgSO4 aqueous solution according to the ratio required in S1 to obtain a suspension. The suspension is then placed in an ultrasonic cleaner and ultrasonically treated for 15-20min. The suspension is then stirred in a water bath until the water in the suspension is completely evaporated to obtain MgAl2O4 nanoparticles.

[0009] Note: By using the sol-gel method and subsequent ultrasonic and water bath treatments, MgA12O4 nanoparticles with smaller particle size, more uniform distribution, and higher purity can be prepared. According to the optimized ratio, excess MgSO4 can be coated on the generated MgA12O4 nanoparticles, effectively preventing hard agglomeration between particles.

[0010] Furthermore, the polyethylene glycol is a mixture of PEG200 and PEG1000 in a 1:1 mass ratio, the ammonia solution has a molar concentration of 3-4 mol / L, the ultrasonic power of the ultrasonic treatment is 150-200 W, and the water bath stirring temperature is 80-90℃.

[0011] Note: Polyethylene glycol, as a dispersant, can effectively break up the agglomeration of powder particles through ultrasonic treatment and water bath stirring, resulting in powder with better dispersibility. This ensures the subsequent pressing of uniform green bodies and the obtaining of uniform sintered bodies.

[0012] Furthermore, in S1, the washing process involves washing with distilled water 3-4 times, and the drying temperature is 70-80℃.

[0013] Note: Washing removes residual sulfates from MgAl2O4 nanoparticles.

[0014] Furthermore, in S2, the particle size of MgO nanoparticles and 3Y-TZP powder is <20nm, wherein the content of Y2O3 in 3Y-TZP powder is 3mol%, and the balance is ZrO2.

[0015] Note: By limiting the size of the raw materials, we ensure that all raw materials are at the nanoscale.

[0016] Furthermore, in S2, during the heating process in the sintering furnace, a pressure of 20~40MPa is continuously applied to the green billet, and when the temperature reaches the flash firing temperature and during the subsequent holding process, a pressure of 40~60MPa is continuously applied to the green billet.

[0017] Note: Applying pressure during the heating stage helps to rearrange particles and reduce porosity in the green body; while increasing pressure during the critical flash firing stage can work synergistically with the electric field to greatly promote the densification process.

[0018] Furthermore, in S3, the sintered billet is crushed and then passed through a 300-320 mesh sieve.

[0019] Explanation: By crushing the sintered billet, the crushed particles have higher surface energy, which gives them higher diffusion and mass transfer driving force in the subsequent high-temperature melting process.

[0020] Furthermore, in S3, the volume fraction of high-purity argon is >99.99%, and the slow cooling rate is 2~4℃ / min.

[0021] Note: By controlling the slow cooling rate, the eutectic phase can be ensured to have enough time for nucleation and growth, thereby forming a fine and uniform eutectic structure. Cooling too fast may lead to amorphous state or structural disorder, while cooling too slow may lead to coarse grains.

[0022] Furthermore, in S2 and S3, the room temperature is 25~28℃.

[0023] Note: By controlling the final cooling temperature to room temperature, fluctuations in experimental results that may be caused by differences in ambient temperature were avoided.

[0024] The beneficial effects of this invention are: (1) The present invention provides a method for preparing a MgO-MgA12O4-ZrO2 nano-ceramic eutectic composite material, which combines two technologies: flash sintering and high-temperature melting. It aims to solve the problems of high sintering temperature, easy grain growth, and difficulty in densification of traditional eutectic ceramics, and finally obtains an excellent composite material with a nanoscale eutectic structure. At the same time, through the sol-gel method and subsequent ultrasonic and water bath treatment, MgA12O4 nanopowder with smaller particle size, more uniform distribution, and higher purity can be prepared. According to the optimized ratio, excess MgSO4 can be coated on the generated MgA12O4 nanopowder, which effectively prevents hard agglomeration between particles. After the nanocrystalline blank obtained by flash sintering is broken, it is subjected to high-temperature melting, which eliminates the microscopic defects and pores that may exist in the flash-sintered blank, making the chemical composition and microstructure of the final product more uniform. Compared with the traditional laser selective melting, it is more convenient and faster, and the cost is lower.

[0025] (2) The method for preparing a MgO-MgA12O4-ZrO2 nano-ceramic eutectic composite material of the present invention, by applying pressure during the flash calcination stage, helps the particles to rearrange and reduce the porosity in the green body; while increasing the pressure during the critical flash calcination stage can work synergistically with the electric field to greatly promote the densification process. Attached Figure Description

[0026] Figure 1 This is a hardness comparison chart of MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite materials prepared in different cases in the experimental examples of this invention; Figure 2 This is a comparison diagram of the fracture toughness of MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite materials prepared in different cases in the experimental examples of this invention. Detailed Implementation

[0027] Example 1 A method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material includes the following steps: S1. Powder preparation: A mixed powder of Al(OH)3 and MgSO4 was placed in a crucible, wherein the molar ratio of Al to Mg was 5:22. The crucible was placed in a sintering furnace and calcined at 750℃ for 2 hours. After cooling down in the furnace, the powder was removed, washed, and dried to obtain MgAl2O4 nanopowder. The powder was washed three times with distilled water and dried at 75℃. The method for preparing the mixed powder of Al(OH)3 and MgSO4 is as follows: 0.1 g of polyethylene glycol is dissolved in 100 mL of Al(NO3)3 solution to obtain a mixed solution. The polyethylene glycol is a mixture of PEG200 and PEG1000 in a 1:1 mass ratio. The mixture is stirred for 13 min, and then ammonia water with a molar concentration of 3.5 mol / L is gradually added dropwise until the pH of the mixed solution reaches 9. The mixture is stirred for 11 h, then allowed to stand for 11 h, and filtered to obtain a wet gel. The wet gel is first washed with distilled water. The mixture was washed 7 times, then washed 4 times with anhydrous ethanol, and then dried at 77°C to obtain a dry gel. The dry gel was ground to obtain Al(OH)3 powder. The Al(OH)3 powder was added to MgSO4 aqueous solution according to the ratio required in S1 to obtain a suspension. The suspension was then placed in an ultrasonic cleaner and ultrasonically treated for 18 minutes at an ultrasonic power of 175W. Then, it was stirred in a water bath at a temperature of 85°C until the water in the suspension was completely evaporated to obtain MgAl2O4 nanoparticles. S2. Flash sintering preparation: According to the weight, take 1 part of MgO nanopowder, 1 part of MgA12O4 nanopowder prepared in S1, and 1 part of 3Y-TZP powder. The particle size of MgO nanopowder and 3Y-TZP powder is <20nm, and the average particle size is 12nm. Among them, the content of Y2O3 in 3Y-TZP powder is 3mol%, and the balance is ZrO2. Press them in a mold to obtain a green blank. Connect the green blank to a DC power supply through a platinum wire and apply an electric field of 850V / cm. At this time, the power supply control mode is voltage control mode. Then place it in a sintering furnace and heat the sintering furnace at a heating rate of 75℃ / min. When the temperature reaches the flash sintering temperature, the current of the green blank increases sharply to the limiting current, which is 100mA. At this time, the power supply control mode switches from voltage control mode to current limiting mode and continues to maintain it for 15s. Then turn off the power supply and the sintering furnace and let it cool naturally to room temperature, which is 26℃, to obtain the sintered green blank. During the heating process in the sintering furnace, a pressure of 30 MPa is continuously applied to the green billet. When the temperature reaches the flash firing temperature and during the subsequent holding process, a pressure of 50 MPa is continuously applied to the green billet. S3. High-temperature melting and solidification preparation: The sintered billet prepared in S2 is crushed and passed through a 305-mesh sieve, placed in a crucible, and melted and solidified at high temperature in a high-temperature vacuum furnace under the protection of high-purity argon gas. The volume fraction of high-purity argon gas is >99.99%, the melting temperature is 1900℃, the holding temperature is 1.5h, and then it is slowly cooled to 1780℃ at a cooling rate of 3℃ / min. The holding temperature is 12min, and then it is cooled to room temperature of 26℃ to obtain the fused MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material.

[0028] Example 2 The difference between this embodiment and Embodiment 1 is that: In S1, the molar ratio of Al to Mg is 5.4:22.

[0029] Example 3 The difference between this embodiment and Embodiment 1 is that: In S1, the molar ratio of Al to Mg is 5.6:22.

[0030] Example 4 The difference between this embodiment and Embodiment 1 is that: In S1, the molar ratio of Al to Mg is 6:22.

[0031] Example 5 The difference between this embodiment and Embodiment 1 is that: The method for preparing the mixed powder of Al(OH)3 and MgSO4 is as follows: 0.95 g of polyethylene glycol is dissolved in 99.5 mL of Al(NO3)3 solution to obtain a mixed solution. The polyethylene glycol is a mixture of PEG200 and PEG1000 in a 1:1 mass ratio. The mixture is stirred for 10 min, and then ammonia water with a molar concentration of 3 mol / L is gradually added dropwise until the pH of the mixed solution reaches 9. The mixture is stirred for another 10 h, then allowed to stand for 10 h. The solution is then filtered to obtain a wet gel. The wet gel is first washed with distilled water. The solution was washed 6 times, then washed 3 times with anhydrous ethanol, and then dried at 75°C to obtain a dry gel. The dry gel was ground to obtain Al(OH)3 powder. The Al(OH)3 powder was added to MgSO4 aqueous solution according to the ratio required in S1 to obtain a suspension. The suspension was then placed in an ultrasonic cleaner and ultrasonically treated for 15 minutes at an ultrasonic power of 150W. Then, it was stirred in a water bath at a temperature of 80°C until the water in the suspension was completely evaporated to obtain MgAl2O4 nanoparticles.

[0032] Example 6 The difference between this embodiment and Embodiment 1 is that: The method for preparing the mixed powder of Al(OH)3 and MgSO4 is as follows: 0.15 g of polyethylene glycol is dissolved in 100.5 mL of Al(NO3)3 solution to obtain a mixed solution. The polyethylene glycol is a mixture of PEG200 and PEG1000 in a 1:1 mass ratio. The mixture is stirred for 15 min, and then ammonia water with a molar concentration of 4 mol / L is gradually added dropwise until the pH of the mixed solution reaches 9. The mixture is stirred for 12 h, then allowed to stand for 12 h, and filtered to obtain a wet gel. The wet gel is first washed with distilled water. The solution was washed 8 times, then washed 5 times with anhydrous ethanol, and then dried at 80°C to obtain a dry gel. The dry gel was ground to obtain Al(OH)3 powder. The Al(OH)3 powder was added to MgSO4 aqueous solution according to the ratio required in S1 to obtain a suspension. The suspension was then placed in an ultrasonic cleaner and ultrasonically treated for 20 minutes at an ultrasonic power of 200W. Then, it was stirred in a water bath at a temperature of 90°C until the water in the suspension was completely evaporated to obtain MgAl2O4 nanoparticles.

[0033] Example 7 The difference between this embodiment and Embodiment 1 is that: In S1, the calcination temperature is 700℃ and the calcination time is 1.5h. After cooling down in the furnace, the powder is taken out, washed and dried to obtain MgA12O4 nanoparticles. The powder is washed three times with distilled water and dried at 70℃.

[0034] Example 8 The difference between this embodiment and Embodiment 1 is that: In S1, the calcination temperature is 800℃ and the calcination time is 2h. After cooling down in the furnace, the powder is taken out, washed and dried to obtain MgA12O4 nanoparticles. The powder is washed 4 times with distilled water and dried at 80℃.

[0035] Example 9 The difference between this embodiment and Embodiment 1 is that: S2. Flash calcination preparation: According to the weight, take 0.95 parts of MgO nanopowder, 0.95 parts of MgA12O4 nanopowder prepared in S1, and 1.05 parts of 3Y-TZP powder. The particle size of MgO nanopowder and 3Y-TZP powder is <20nm, and the average particle size is 10nm.

[0036] Example 10 The difference between this embodiment and Embodiment 1 is that: S2, flash calcination preparation: According to the weight, take 0.95 parts of MgO nanopowder, 1.05 parts of MgA12O4 nanopowder prepared in S1, and 1.05 parts of 3Y-TZP powder. The particle size of MgO nanopowder and 3Y-TZP powder is <20nm, and the average particle size is 15nm.

[0037] Example 11 The difference between this embodiment and Embodiment 1 is that: In step S2, the green billet is connected to a DC power supply via a platinum wire, and an electric field of 800V / cm is applied. At this time, the power supply is controlled in voltage control mode. Then, it is placed in the sintering furnace, and the sintering furnace is heated at a rate of 50℃ / min. When the temperature reaches the flash firing temperature, the current of the green billet increases sharply to the limiting current, which is 120mA. At this time, the power supply control mode switches from voltage control mode to current limiting mode, and is maintained for 10 seconds. Then, the power supply and the sintering furnace are turned off, and the billet is allowed to cool naturally to room temperature, which is 25℃, thus obtaining the sintered billet.

[0038] Example 12 The difference between this embodiment and Embodiment 1 is that: In step S2, the green billet is connected to a DC power supply via a platinum wire, and an electric field of 900V / cm is applied. At this time, the power supply is controlled in voltage control mode. Then, it is placed in the sintering furnace, and the sintering furnace is heated at a rate of 100℃ / min. When the temperature reaches the flash firing temperature, the current of the green billet increases sharply to the limiting current, which is 80mA. At this time, the power supply control mode switches from voltage control mode to current limiting mode, and is maintained for 20 seconds. Then, the power supply and the sintering furnace are turned off, and the billet is allowed to cool naturally to room temperature, which is 28℃, thus obtaining the sintered billet.

[0039] Example 13 The difference between this embodiment and Embodiment 1 is that: During the heating process in the sintering furnace, a pressure of 20 MPa is continuously applied to the green billet. When the temperature reaches the flash firing temperature and during the subsequent holding process, a pressure of 40 MPa is continuously applied to the green billet.

[0040] Example 14 The difference between this embodiment and Embodiment 1 is that: During the heating process in the sintering furnace, a pressure of 40 MPa is continuously applied to the green billet. When the temperature reaches the flash firing temperature and during the subsequent holding process, a pressure of 60 MPa is continuously applied to the green billet.

[0041] Example 15 The difference between this embodiment and Embodiment 1 is that: S3. High-temperature melting and solidification preparation: The sintered billet prepared in S2 is crushed and passed through a 300-mesh sieve, placed in a crucible, and melted and solidified at high temperature in a high-temperature vacuum furnace under the protection of high-purity argon gas. The volume fraction of high-purity argon gas is >99.99%, the melting temperature is 1850℃, the holding temperature is 1h, and then it is slowly cooled to 1750℃ at a cooling rate of 2℃ / min. The holding temperature is 10min, and then it is cooled to room temperature of 25℃ to obtain the fused MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material.

[0042] Example 16 The difference between this embodiment and Embodiment 1 is that: S3. High-temperature melting and solidification preparation: The sintered billet prepared in S2 is crushed and passed through a 320-mesh sieve, placed in a crucible, and melted and solidified at high temperature in a high-temperature vacuum furnace under the protection of high-purity argon gas. The volume fraction of high-purity argon gas is >99.99%, the melting temperature is 1950℃, the holding temperature is 2h, and then it is slowly cooled to 1800℃ at a cooling rate of 4℃ / min. The holding temperature is 15min, and then it is cooled to room temperature of 28℃ to obtain the fused MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material.

[0043] Experimental Example First, we tested the furnace temperature during the flash firing process. During flash firing, the green billet generates Joule heat through the current, causing the actual temperature of the sample to be higher than the furnace temperature at which flash firing occurs. In Examples 1, 11, and 12, the applied voltage and the limiting current were different, resulting in different furnace temperatures at which flash firing occurred, as shown in Table 1.

[0044] Table 1 Furnace temperature under different limiting currents

[0045] It can be seen that as the limiting current increases, the furnace temperature rises. During flash calcination, although the actual temperature of the green blank is higher than the furnace temperature, it is still lower than the formation temperature of the ternary eutectic of the MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material, approximately 1710℃. During flash calcination, the localization of the current causes the temperature in some areas to be much higher than the melting point, resulting in melting of the sample. In the subsequent solidification process, a preliminary eutectic structure is formed.

[0046] Subsequently, we analyzed the effect of the molar ratio of Al to Mg in Examples 1 to 4 on the hardness and fracture toughness of the final prepared materials. Comparative examples were also set up: in Comparative Example 1, general MgAl₂O₄ nanoparticles were used; in Comparative Example 2, the molar ratio of Al to Mg was 1:3; in Comparative Example 3, the molar ratio of Al to Mg was 1:2; and in Comparative Example 4, no flash calcination was performed, but high-temperature melting and solidification were used directly. The results of each group are as follows: Figure 1 and Figure 2 As shown.

[0047] It can be seen that the hardness and fracture toughness of the MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite materials prepared in Examples 1 to 4 are much higher than those of other comparative examples. Therefore, this also confirms that the method of the present invention can effectively prevent hard agglomeration between particles, eliminate micro-defects and pores that may exist in the flash-sintered blank, and make the chemical composition and microstructure of the final product more uniform. Comparing Examples 1-4, it can be seen that increasing the molar percentage of Mg can further reduce the size of nano-MgAl2O4 particles and alleviate hard agglomeration. Due to particle contact and growth, hard agglomeration often occurs during the preparation of MgAl2O4 particles using solid-state reactions. In the process of preparing MgAl2O4 nanoparticles from calcined Al(OH)3 and MgSO4 mixed powders, excess MgSO4 particles coat the generated MgAl2O4 nanoparticles, preventing particle contact and thus preventing atomic diffusion, leading to hard agglomeration. Therefore, the content of MgSO4 in the mixed powder greatly affects the agglomeration of nanoparticles. At the same time, the MgSO4 content should not be too high, as this may lead to incomplete reaction. Therefore, the parameters used in Examples 1-4 all achieve good results.

[0048] In Comparative Example 1, ordinary MgAl2O4 nanoparticles were used. These particles are coarse and uneven in size and are prone to agglomeration. As a result, the agglomerated powder will introduce a large number of defects and pores after sintering, which will seriously affect the density and performance of the sintered product.

[0049] In Comparative Examples 2 and 3, the molar ratio of Al to Mg was relatively large, meaning that the molar ratio of Mg was relatively small. As a result, MgSO4 particles could not completely coat the generated MgAl2O4 nanoparticles or only a few were coated on them, which ultimately led to partial agglomeration.

[0050] In Comparative Example 4, flash calcination was not performed; instead, high-temperature melting and solidification were used directly. The final product's performance was inferior to that prepared by this method. This is because flash calcination completes densification within seconds to tens of seconds, significantly inhibiting grain growth. This is crucial for obtaining nanoscale grains (<100nm), whereas traditional methods, operating at high temperatures for extended periods, tend to coarsen the grains. Therefore, the method combining flash calcination and high-temperature melting and solidification not only reduces the overall sintering time but also lowers the sintering temperature, solving the problems of high sintering temperature, easy grain growth, and difficulty in densification in traditional eutectic ceramics. Ultimately, this yields an excellent composite material with a nanoscale eutectic structure.

Claims

1. A method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material, characterized in that, Includes the following steps: S1. Powder preparation: A mixed powder of Al(OH)3 and MgSO4 is placed in a crucible, wherein the molar ratio of Al to Mg is 5~6:

22. The crucible is placed in a sintering furnace for calcination at a temperature of 700~800℃ for 1.5~2h. After cooling down with the furnace, the crucible is removed, washed and dried to obtain MgAl2O4 nanopowder. S2. Flash sintering preparation: According to the weight, take 1±0.05 parts of MgO nanopowder, 1±0.05 parts of MgA12O4 nanopowder prepared in S1, and 1±0.05 parts of 3Y-TZP powder, place them in a mold and press them to obtain a green blank. Connect the green blank to a DC power supply through a platinum wire and apply an electric field of 800~900V / cm. At this time, the power supply control mode is voltage control mode. Then place it in a sintering furnace and heat the sintering furnace at a heating rate of 50~100℃ / min. When the temperature reaches the flash sintering temperature, the current of the green blank increases sharply to the limiting current, which is 80~120mA. At this time, the power supply control mode switches from voltage control mode to current limiting mode and continues to maintain it for 10~20s. Then turn off the power supply and the sintering furnace and let it cool naturally to room temperature to obtain the sintered green blank. S3. High-temperature melting and solidification preparation: After crushing the sintered billet prepared in S2, it is placed in a crucible and melted and solidified at high temperature in a high-temperature vacuum furnace under the protection of high-purity argon gas. The melting temperature is 1850~1950℃, held for 1~2h, slowly cooled to 1750~1800℃, held for 10~15min, and then cooled to room temperature to obtain the fused MgO-MgA12O4-ZrO2 nano-ceramic eutectic composite material.

2. The method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material according to claim 1, characterized in that, In S1, the preparation method of the mixed powder of Al(OH)3 and MgSO4 is as follows: 0.1±0.05g of polyethylene glycol is dissolved in 100±0.5mL of Al(NO3)3 solution to obtain a mixed solution. The solution is stirred for 10-15min, and then ammonia water is gradually added dropwise until the pH of the mixed solution is 9. The stirring is continued for 10-12h, and then allowed to stand for 10-12h. The solution is filtered to obtain a wet gel. The wet gel is washed with distilled water 6-8 times, and then washed with anhydrous ethanol 3-5 times. The gel is then dried at 75-80℃ to obtain a dry gel. The dry gel is ground to obtain Al(OH)3 powder. The Al(OH)3 powder is added to the MgSO4 aqueous solution according to the ratio required in S1 to obtain a suspension. The suspension is then placed in an ultrasonic cleaner and ultrasonically treated for 15-20min. The suspension is then stirred in a water bath until the water in the suspension is completely evaporated to obtain MgAl2O4 nanoparticles.

3. The method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material according to claim 2, characterized in that, The polyethylene glycol is a mixture of PEG200 and PEG1000 in a 1:1 mass ratio, the ammonia solution has a molar concentration of 3-4 mol / L, the ultrasonic power of the ultrasonic treatment is 150-200W, and the water bath stirring temperature is 80-90℃.

4. The method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material according to claim 1, characterized in that, In S1, the washing process involves washing with distilled water 3-4 times, and the drying temperature is 70-80℃.

5. The method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material according to claim 1, characterized in that, In S2, the particle size of MgO nanoparticles and 3Y-TZP powder is <20nm. Among them, the content of Y2O3 in 3Y-TZP powder is 3mol%, and the balance is ZrO2.

6. The method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material according to claim 1, characterized in that, In S2, during the heating process in the sintering furnace, a pressure of 20~40MPa is continuously applied to the green billet. When the temperature reaches the flash firing temperature and during the subsequent holding process, a pressure of 40~60MPa is continuously applied to the green billet.

7. The method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material according to claim 1, characterized in that, In S3, the sintered billet is crushed and then passed through a 300-320 mesh sieve.

8. The method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material according to claim 1, characterized in that, In S3, the volume fraction of high-purity argon gas is >99.99%, and the slow cooling rate is 2~4℃ / min.

9. The method for preparing a MgO-MgAl2O4-ZrO2 nano-ceramic eutectic composite material according to claim 1, characterized in that, In S2 and S3, the room temperature is 25~28℃.

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