Slurry vacuum suction and injection preparation method of oriented nano MAX phase ceramic

Abstract

The invention relates to the field of ceramic materials, in particular to a slurry vacuum suction and injection preparation method of oriented nano MAX phase ceramic. MAX-phase ceramic nanosheet layer powder is adopted as a raw material, the sheet layer length of MAX-phase ceramic nanosheet layer particles in the powder is 0.02-5 microns, the sheet layer thickness is 5-500 nanometers, and the oxygen content is 0.01%-20% by mass fraction; the MAX-phase ceramic is obtained after the blank formed through vacuum suction injection molding is sintered, and the microstructure MAX-phase crystal grains in the ceramic are in a lamellar shape or a fusiform shape. The preparation method comprises the following steps: orienting in a vacuum suction-injection molding process in a slurry suspension state by utilizing the special properties of nanosheet layered MAX powder to obtain an initial blank with a layered structure similar to that in a natural pearl shell, then molding and densifying through a pressureless sintering process, and further carrying out the action of a polymer additive, so as to obtain the MAX-based composite material. And densification improving processes such as cold isostatic pressing and hot isostatic pressing are adopted to improve the performance of the material.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials, specifically to a slurry vacuum impregnation method for preparing oriented nano-MAX phase ceramics. Background Technology

[0002] MAX phase ceramics (e.g., Ti3AlC) 2、 Ti3SiC2, Ti2AlC, Nb2AlC, etc., are a class of layered materials with a nano-ternary layered structure and properties combining ceramic and metallic characteristics. Their crystal structure can be described as follows: pure A atoms are inserted into densely packed M atoms, and X atoms fill the octahedral interstices formed by M atoms. Here, M atoms represent transition metal elements, A atoms are group A elements, and X atoms are C, N, or B elements. Unlike traditional structural ceramics (which are mainly composed of ionic or covalent bonds and suffer from low toughness and lack of plastic deformation), this alternating stacked ceramic-type MX layers and metallic-type MA layers exhibit comprehensive advantages such as high conductivity, excellent oxidation resistance, thermal shock resistance, self-healing ability, and ease of processing.

[0003] However, compared with the existing SiC used f / SiC and Al2O 3f Al2O3 (fracture toughness > 10 MPa•m) 1 / 2 Compared to advanced ceramic matrix composites, MAX phase ceramics have insufficient fracture toughness (7–8 MPa•m). 1 / 2 The difficulty in fabricating large-size Nb4AlC3 ceramics severely limits their widespread application as structural materials. To improve the fracture toughness of MAX phase ceramics, existing technologies mainly employ methods such as particle toughening, whisker / fiber toughening, and orientation toughening. Among these, orientation toughening significantly improves toughness by controlling the microscopic orientation of the material, and its mainstream fabrication techniques include strong magnetic field orientation (SMFA), hot forging (HF), nanosheet hot pressing (NFHP), and spark plasma sintering (SPS). For example, textured Nb4AlC3 ceramics were prepared using SMFA combined with SPS technology, resulting in a fracture toughness of 14.1 MPa•m. 1 / 2 It approaches the level of fiber-reinforced ceramic matrix composites.

[0004] Subsequently, research shifted to lower-cost SPS and its derivative technologies (such as SPS hot forging). However, these methods, relying on SPS sintering processes, often resulted in a significant decrease in the fracture toughness of the material, falling considerably below the level of SMFA technology. Until recently, our team's previous research developed the nanosheet hot pressing (HP) method, successfully overcoming the technical bottleneck of SPS and increasing the fracture toughness of Ti3AlC2 to 16.1 MPa•m. 1 / 2Nevertheless, the combination of SMFA and SPS technologies remains limited by high costs and difficulties in large-scale production; while NFHP has achieved a breakthrough in toughness at the laboratory scale, it still cannot match the large-scale fabrication capabilities of traditional ceramic slip casting or metal casting. Furthermore, although existing casting technologies (such as gel casting combined with alumina-rich pressureless sintering) can prepare MAX phase ceramics, the fracture toughness of the resulting materials (approximately 4.79 MPa•m) is limited. 1 / 2 The yield is still far below application requirements. These limitations indicate an urgent need to develop preparation methods that are both highly resilient, low-cost, and scalable. Summary of the Invention

[0005] The purpose of this invention is to provide a slurry vacuum casting method for preparing oriented nano-MAX phase ceramics, overcoming the shortcomings of existing oriented nano-MAX phase ceramic preparation processes which are complex and rely on costly magnetic field orientation and SPS sintering equipment. This method makes the preparation of oriented nano-MAX phase ceramics as convenient and simple as metal casting, enabling the formation of large sizes and complex shapes. Simultaneously, the sintering process is freed from the limitations of molds and sheaths, allowing for simple sintering similar to metal vacuum heat treatment to achieve very high performance.

[0006] The technical solution of this invention is: A slurry vacuum impregnation method for preparing oriented nano-MAX phase ceramics includes the following steps: (1) The raw material used is MAX phase ceramic nanosheet powder. The length of the nanosheet particles of MAX phase ceramic in the powder is between 0.02 and 5 micrometers, the thickness of the nanosheet is between 5 and 500 nanometers, and the mass fraction of oxygen content is between 0.01% and 20%. (2) After the raw material is vacuum-injected and sintered, nano-MAX phase ceramics are obtained. The MAX phase grains in the ceramics are lamellar or spindle-shaped, and the lamellar MAX phase grains have orientation.

[0007] The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation involves the nano-MAX phase ceramics being distributed in an orderly stacked manner, with MAX phase oxides distributed at the grain boundaries of the nano-MAX phase ceramic grains. The length of the MAX phase grain lamellars ranges from 0.05 to 20 micrometers, and the lamellar thickness ranges from 0.02 to 5 micrometers.

[0008] The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation of slurry, by mass percentage, is as follows: the content of MAX phase oxide in the nano-MAX phase ceramics is 0.02% to 40%, and the remainder is MAX phase ceramics.

[0009] The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation involves directly sintering the preform prepared from the nanosheet powder of MAX phase ceramics without pressure during sintering; or, the preform prepared from the nanosheet powder of MAX phase ceramics is subjected to a composite and sintering process, wherein the composite process is one or both of cold isostatic pressing and hot isostatic pressing.

[0010] The slurry vacuum impregnation preparation method for the oriented nano-MAX phase ceramics described above employs one of the following methods during the sintering process: (1) Direct pressureless sintering method The vacuum-injected preform is directly wrapped in graphite paper and placed in a crucible made of graphite, oxide ceramic or high-temperature resistant metal; the sintering temperature is 1000-1800℃, the holding time is 10-3600 minutes, the heating rate is 1-100℃ / minute, and the sintering is carried out in a vacuum or argon atmosphere. (2) Cold isostatic pressing pressureless sintering method First, the vacuum-injected preform is loaded into a polymer material sheath and isostatically pressed in a cold isostatic press. The isostatic pressing pressure is 80–300 MPa, and the holding time is 0.5–5 minutes. Then, it is sintered without pressure in a crucible at a temperature of 1000–1800℃, a holding time of 10–3600 minutes, and a heating rate of 1–100℃ / min. The sintering is carried out under a vacuum or argon atmosphere. (3) Direct pressureless sintering hot isostatic pressing method First, the block sintered by direct pressureless sintering method (1) is placed into a hot isostatic pressing (HIP) sintering liner. Then, the liner is evacuated and sealed. The block is then hot isostatically pressed in the liner, or hot isostatic pressing is performed directly without the liner. The hot isostatic pressing temperature is 1000-1600℃, the sintering pressure is 50-300MPa, the holding time is 10-3600 minutes, and the heating rate is 1-100℃ / minute. The hot isostatic pressing is performed in a vacuum or argon atmosphere. (4) Cold isostatic pressing, pressureless sintering, and hot isostatic pressing First, the block obtained by cold isostatic pressing pressureless sintering method (2) is loaded into a hot isostatic pressing sleeve. Then, the sleeve is evacuated and sealed. Hot isostatic pressing sintering is performed in the sleeve, or hot isostatic pressing sintering is performed directly without the sleeve. The hot isostatic pressing temperature is 1000-1600℃, the sintering pressure is 50-300MPa, the holding time is 10-3600 minutes, the heating rate is 1-100℃ / minute, and the hot isostatic pressing sintering is carried out in a vacuum or argon atmosphere.

[0011] The method for preparing oriented nano-MAX phase ceramics by vacuum casting includes the following steps: The nanosheet powder of MAX phase ceramics is vacuum cast to form a preform. (1) Prepare a slurry with a solid content of 35% to 55% by mixing the nanosheet powder of MAX phase ceramics with anhydrous ethanol solution or ethanol-polyethylene glycol solution. The method for preparing the slurry is any one or a combination of two or more of the following: ultrasonic vibration, magnetic stirring, electric stirring and ball milling. (2) Pour the prepared slurry into the vacuum filtration device. The filtration pressure is 0.02-0.2 MPa and the filtration time is 30-240 minutes. The filter screen is made of metal screen, polymer material screen, filter paper or filter membrane. The mesh size of the metal screen is 200-2000 mesh and the pore size of the polymer material screen, filter paper or filter membrane is 1-100 micrometers. (3) After vacuum filtration is completed and there is no liquid left, take it out and place it in a cool, ventilated and dry place to dry it completely into an embryo.

[0012] The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation involves adding polyethylene glycol (PEG), a polymeric material additive with a molecular weight of 600-1000, to an ethanol solvent to prepare an ethanol-PEG solution with a PEG mass fraction of 0.5-5%. To accelerate the dissolution of PEG, heating and stirring are performed during preparation. The heating temperature is 30-70°C, and the stirring time is 10-120 minutes.

[0013] The slurry vacuum injection preparation method for the oriented nano-MAX phase ceramics described above uses a muffle furnace, induction heating furnace, microwave heating furnace, or infrared heating furnace for sintering.

[0014] The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation of slurry involves controlling the oxide content in the MAX phase ceramics by adjusting the oxygen content of the nanosheet powder used to prepare the ceramics, controlling the grain size by adjusting the particle size of the nanosheet particles and the powder sintering parameters, and controlling the degree of orientation of the obtained ceramics by adjusting the different combinations and parameters of the pressurization method and sintering method.

[0015] The design concept of this invention is: First, the technical method for preparing oriented MAX phase ceramics in this invention utilizes a wet slurry forming process. However, unlike existing MAX phase ceramic slurry forming processes, this invention employs nanosheet-like MAX powder. This powder differs from the granular powder used in existing MAX phase ceramic slurry forming processes, exhibiting anisotropic geometry and a sheet-like structure. Therefore, it is possible to achieve orientation effects similar to hot pressing, SPS sintering, and hot forging during the slurry vacuum casting process. Second, to further reduce material preparation costs and overcome the limitations of hot pressing and SPS on the size and shape of the prepared material, a pressureless sintering forming process is adopted. To further improve material performance to the level of magnetic field orientation and SPS sintering, a combination of cold isostatic pressing and hot isostatic pressing is used to enhance performance.

[0016] This invention utilizes nanosheet powders with a large specific surface area. The loose powder structure makes the powder highly susceptible to cracking and defects during the injection molding process and the drying of the formed preform. Therefore, appropriate slurry solids content and polymeric additives are necessary. Insufficient solids content not only prolongs filtration time but also reduces preform density, leading to cracking. Conversely, excessive solids content causes a sharp increase in slurry viscosity, severely affecting flowability, making molding difficult, and increasing the frequency of air bubbles and defects in the preform. To further improve performance, this invention requires polymeric additives to help maintain good dispersion of the ceramic powder, stabilize the slurry system, and prevent sedimentation and agglomeration during material preparation. As plasticizers and binders, they also enhance the plasticity and flexibility of the ceramic slurry, reduce internal stress in the preform, and decrease the risk of cracking during molding and drying. To further improve the performance of the prepared material and achieve the very costly magnetic field orientation and SPS levels, this invention requires further cold isostatic pressing and hot isostatic pressing to eliminate internal defects in the material.

[0017] The present invention has the following advantages and beneficial effects: (1) The process route and preparation method of the present invention adopts slurry molding process, which not only has higher powder dispersibility and uniformity compared with dry powder process, but also can realize batch large-scale continuous preparation like metal casting process.

[0018] (2) The process flow and preparation method of the present invention can be flexibly expanded, demonstrating good technical adaptability and portability. It can prepare known MAX phase ceramic materials with orientation.

[0019] (3) The present invention can realize the preparation of MAX phase ceramics with complex shapes and curved surfaces, which can not only give full play to their material properties, but also meet the needs of diverse industrial applications and show broad application prospects.

[0020] (4) The present invention adopts a slurry molding process, which is more suitable for adding other second phases compared with the dry powder process, to obtain a uniformly distributed composite material effect.

[0021] (5) The present invention can improve the material density and reduce defects by combining cold isostatic pressing and hot isostatic pressing technologies, thereby improving the mechanical properties. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the preparation process of oriented nano-MAX phase ceramics in Example 1. In the figure, Ti3AlC2nanoflakes are Ti3AlC2 nano-MAX phase ceramic sheet powders, Ceramic slurry is ceramic slurry, Vacuumfiltration casting is vacuum casting, Green body is the green body, and Pressureless sintering is atmospheric pressure sintering (without external mechanical pressure).

[0023] Figure 2 This is a particle size distribution diagram of nano-Ti3AlC2 phase ceramic lamellar powder in Example 1. In the figure, the horizontal axis ParticleSize represents the particle size (μm), the left vertical axis Volume represents the volume percentage (%), and the right vertical axis CumulativeVolume represents the cumulative volume percentage (%) of powder particles smaller than or equal to that particle size.

[0024] Figure 3 This is a band contrast map image obtained by electron backscatter diffraction (EBSD) characterization of the vertical filter surface of the final sintered sample of Example 1.

[0025] Figure 4 for Figure 3 The pole figure of the 0001 crystal plane of the Ti3AlC2 phase crystal obtained by electron backscatter diffraction (EBSD) characterization of the sample is shown on the diffraction projection plane.

[0026] Figure 5This is a flowchart illustrating the preparation process of oriented nano-MAX phase ceramics in Example 2. In the diagram, Ti3AlC2 nanooflakes are Ti3AlC2 nano-MAX phase ceramic sheet powders, Ceramic slurry is ceramic slurry, Polyethylene glycol is polyethylene glycol, Vacuum filtration casting is vacuum filtration casting, Green body is the green body, Cold isostatic pressing is cold isostatic pressing, Pressureless sintering is atmospheric pressure sintering (without external mechanical pressure), and Hot isostatic pressing is hot isostatic pressing.

[0027] Figure 6 This is a scanning electron microscope (SEM) image of the oriented Ti3AlC2 ceramic prepared according to Scheme 1 in Example 2. In the image, the dark black part is the alumina phase, and the bright matrix is ​​the Ti3AlC2 ceramic phase.

[0028] Figure 7 This is a SEM image of the oriented Ti3AlC2 ceramic prepared according to Scheme 2 in Example 2. Detailed Implementation

[0029] In the specific implementation process, this invention proposes a method for preparing oriented MAX phase ceramics based on vacuum casting (VFC) and pressureless sintering (PS). This method uses nano-sheet MAX phase powder as raw material. Through the self-orientation arrangement of sheet particles during the vacuum casting process of slurry, a layered texture structure is formed. Combined with the low-temperature pressureless sintering process, grain refinement and densification are achieved.

[0030] I. Raw Material Selection and Characteristics: The raw material composition uses MAX phase ceramic nanosheet powder as the preparation material. Nanosheet particle characteristics: The length of the nanosheet particles ranges from 0.02 to 5 micrometers, and the thickness ranges from 5 to 500 nanometers. Oxygen content control: The mass fraction of oxygen in the powder ranges from 0.01% to 20%. Microstructure characteristics: After sintering, the MAX phase grains in the ceramic microstructure are lamellar or spindle-shaped and exhibit orientation.

[0031] II. Vacuum casting method for nanosheet powder of MAX phase ceramics 1. Preparation of polymer additive solution: Polyethylene glycol (molecular weight 600-1000) is added to ethanol solvent to prepare a polyethylene glycol solution with a mass fraction of 0-5%. To accelerate dissolution, heating (30-70℃) and stirring (10-120 minutes) are performed during preparation.

[0032] 2. Slurry preparation: The nanoparticles and ethanol-polyethylene glycol solution are prepared into a slurry with a solid content of 35%–55% by mass. Preparation methods can include ultrasonic vibration, magnetic stirring, electric stirring, or ball milling, or a combination of these methods.

[0033] 3. Vacuum Filtration and Forming: Pour the prepared slurry into a vacuum filtration device, with a filtration pressure of 0.02–0.2 MPa. The filter screen can be a metal filter screen (200–2000 mesh), a polymer material filter screen, or filter paper / membrane (pore size 1–100 micrometers), and the filtration time is 30–240 minutes.

[0034] 4. Drying treatment: After vacuum filtration is completed, take it out and place it in a ventilated place or other cool, ventilated and dry place to dry thoroughly to form an embryo.

[0035] III. Selection of Sintering Method The sintering method can be one of the following: direct pressureless sintering (without external mechanical pressure); nanopowder composite and sintering process; cold isostatic pressing pressureless sintering; pressureless sintering hot isostatic pressing; cold isostatic pressing pressureless sintering hot isostatic pressing.

[0036] 1. Direct pressureless sintering method The vacuum-injected preform is wrapped in graphite paper and placed in a crucible made of graphite, oxide ceramic, or high-temperature resistant metal. Sintering temperature: 1000–1800℃, holding time: 10–3600 minutes, heating rate: 1–100℃ / minute, sintering atmosphere: vacuum or argon.

[0037] 2. Cold isostatic pressing + pressureless sintering method The vacuum-injected preform is placed into a polymer material casing and isostatically pressed in a cold isostatic press. The isostatic pressing pressure is 80–300 MPa, and the holding time is 0.5–5 minutes. Pressureless sintering is then performed in the crucible, with the sintering temperature, holding time, heating rate, and atmosphere being the same as in the direct pressureless sintering method.

[0038] 3. Direct pressureless sintering + hot isostatic pressing The block sintered by the first method of direct pressureless sintering is placed in a hot isostatic pressing (HIP) sleeve, vacuumed and sealed, and then subjected to HIP sintering; alternatively, HIP can be performed directly without a sleeve. HIP temperature: 1000–1600℃, sintering pressure: 50–300 MPa, holding time: 10–3600 minutes, heating rate: 1–100℃ / minute, sintering atmosphere: vacuum or argon.

[0039] 4. Cold isostatic pressing + pressureless sintering + hot isostatic pressing method The block obtained by the second method of cold isostatic pressing + pressureless sintering is placed in a hot isostatic pressing (HIP) sleeve, vacuumed and sealed, and then subjected to HIP sintering; alternatively, HIP can be performed directly without a sleeve. The temperature, pressure, holding time, heating rate, and atmosphere of HIP are the same as those of the pressureless sintering HIP method.

[0040] 5. Sintering Equipment and Parameters: Sintering equipment can be a muffle furnace, induction heating furnace, microwave heating furnace, or infrared heating furnace. Sintering temperature: 1000~1800℃, sintering time: 10~3600 minutes.

[0041] IV. Microstructure of Nanoscale MAX Phase Ceramics Grain distribution: The nano-MAX phase ceramics exhibit an orderly, brick-like stacking distribution. Oxide distribution: MAX phase oxides are distributed at the grain boundaries of the nano-MAX phase ceramic grains. Grain size: The lamellar length of the MAX phase grains ranges from 0.05 to 20 micrometers, and the lamellar thickness ranges from 0.02 to 5 micrometers.

[0042] Oxide content: In oriented nano-MAX phase ceramics, the content of MAX phase oxides is 0.02% to 40% (mass percentage), and the remainder is MAX phase ceramics.

[0043] Performance control: Oxide content control; the oxide content in MAX phase ceramics is controlled by the oxygen content of the MAX phase ceramic nanosheet powder. Grain size control; the obtained grain size is jointly controlled by the particle size of the nanosheet particles and the powder sintering parameters. Orientation control; the degree of orientation of the ceramic is jointly controlled by different combinations of pressure application methods and sintering methods and their parameters.

[0044] V. Summary This invention provides a method for preparing oriented MAX phase ceramics. By precisely controlling the properties of nanosheet powders, sintering process parameters, and forming processes, MAX phase ceramics with specific microstructures and orientations are prepared. This method not only allows for the control of ceramic grain size and oxide content but also enables precise control of ceramic orientation through different sintering and pressurization methods, providing a new technical pathway for the preparation of high-performance ceramic materials.

[0045] Because this invention covers a wide range of technical methods and approaches, a clearer and more complete description is provided below in conjunction with specific embodiments to facilitate a further understanding of the purpose, solutions, and advantages of this discovery. It should also be noted that the embodiments described below are merely examples of some of the possible implementations and not all possible implementations. All technical methods using the scope of the claims of this invention should fall within the protection scope of this invention.

[0046] Example 1

[0047] In this embodiment, the preparation method of oriented nano-MAX phase ceramics is as follows ( Figure 1 ): 500 grams of Ti3AlC2 nano-MAX phase ceramic sheet powder with a particle size of 627 nm and an oxygen content of 7.75% by mass were weighed out. 500 grams of anhydrous ethanol were weighed out, and the Ti3AlC2 nano-MAX phase ceramic sheet powder was then added to the anhydrous ethanol solution. The mixture was mechanically stirred at 120 rpm while simultaneously ultrasonically dispersed for 60 minutes. The resulting slurry was then poured into a vacuum filtration apparatus using a 1000-mesh metal filter screen at a pressure of 0.1 MPa for 2 hours. After the liquid was completely removed, the formed sample was removed and air-dried in a fume hood for 48 hours. The completely dried sample was then wrapped in graphite paper and placed in a graphite crucible for pressureless sintering at 1300℃ for 120 minutes at a heating rate of 5℃ / min under an argon atmosphere. After sintering, in-situ self-generated Al2O3 phase-reinforced oriented Ti3AlC2 ceramics were obtained, with an Al2O3 content of 15% by mass. The oriented Ti3AlC2 ceramic material has a hardness of 5.5–6.5 GPa, a flexural strength of 630–730 MPa, significantly higher than that of ordinary Ti3AlC2 (300–400 MPa), and a fracture toughness of 9–11 MPa•m. 1 / 2 It is much higher than the fracture toughness of ordinary Ti3AlC2 (7~8 MPa•m). 1 / 2 ).

[0048] like Figure 2 As shown in the particle size distribution diagram of nano-Ti3AlC2 phase ceramic lamellar powder, the powder exhibits a distinct bimodal distribution, consisting of fine particles with a diameter of about 50 nanometers and coarse particles with a diameter of about 3 micrometers.

[0049] like Figure 3 As shown in the EBSD band contrast diagram of the oriented Ti3AlC2 ceramic, the material exhibits obvious grain lamellar characteristics and clear directionality.

[0050] like Figure 4 As shown, from the pole figure of the 0001 crystal plane of Ti3AlC2 phase crystal in the diffraction projection plane, it can be seen that the 0001 crystal plane of Ti3AlC2 phase crystal is highly concentrated at the north and south poles of the pole figure, reflecting the significant orientation of the material.

[0051] Example 2

[0052] In this embodiment, compared with Example 1, the addition of polymer materials and the hot and cold isostatic pressing process are added to improve the material properties. The preparation method of oriented nano-MAX phase ceramics is as follows ( Figure 5 ): 500 grams of Ti3AlC2 nano-MAX phase ceramic sheet powder with a particle size of 78 nm and an oxygen content of 7.75% by mass were weighed. 500 grams of anhydrous ethanol and 10 grams of polyethylene glycol with a molecular weight of 800 were weighed and ultrasonically dispersed and magnetically stirred for 30 minutes at 50°C until fully dissolved. The weighed Ti3AlC2 nano-MAX phase ceramic sheet powder was then added to the dissolved polyethylene glycol solution in anhydrous ethanol, mechanically stirred at 120 rpm, and simultaneously ultrasonically dispersed for 60 minutes. The resulting slurry was then poured into a vacuum filtration apparatus using a 1000-mesh metal filter screen at a pressure of 0.02 MPa for 2 hours. After the liquid was completely evaporated, the formed sample was removed and air-dried in a fume hood for 48 hours.

[0053] Option 1: The completely dried sample was then wrapped in graphite paper and placed in a graphite crucible for pressureless sintering at 1300℃ for 120 minutes at a heating rate of 5℃ / min. The sintering atmosphere was argon, resulting in in-situ self-generated Al2O3-reinforced oriented Ti3AlC2 ceramics with an Al2O3 content of 16% by mass. The oriented Ti3AlC2 ceramic material exhibited a flexural strength of 620–720 MPa, significantly higher than that of ordinary Ti3AlC2 (300–400 MPa), and a fracture toughness of 10–12 MPa•m. 1 / 2 It is much higher than the fracture toughness of ordinary Ti3AlC2 (7-8 MPa•m). 1 / 2 ).

[0054] Option 2: The completely dried sample was then wrapped and sealed in a polymer material sleeve and placed in a cold isostatic press for cold isostatic pressing at a pressure of 200 MPa for 120 seconds. The cold-isostatically pressed block was then wrapped in graphite paper and placed in a graphite crucible for pressureless sintering at a temperature of 1300℃ for 120 minutes, with a heating rate of 5℃ / min and an argon atmosphere. After sintering, the sample was placed in a hot isostatic pressing furnace for hot isostatic pressing at a temperature of 1200℃, a pressure of 130 MPa, and a holding time of 120 minutes. This resulted in in-situ self-generated Al2O3 phase-reinforced oriented Ti3AlC2 ceramic with an Al2O3 content of 16% by mass. The oriented Ti3AlC2 ceramic material exhibited a flexural strength of 850–950 MPa and a fracture toughness of 13–15 MPa·m. 1 / 2 The fracture toughness value of oriented Ti3AlC2 ceramics prepared by combining SMFA and SPS technology was achieved.

[0055] like Figure 6As shown in the SEM image of the oriented Ti3AlC2 ceramic prepared by Scheme 1, the prepared material is relatively dense, without obvious large pore defects, and the alumina second phase is uniformly distributed.

[0056] like Figure 7 As shown in the SEM image of the oriented Ti3AlC2 ceramic prepared by scheme 2, it can be seen that, compared with... Figure 6 In comparison, due to the addition of hot and cold isostatic pressing processes, the density of the prepared material is significantly increased and the porosity is significantly reduced.

[0057] Example 3

[0058] In this embodiment, the preparation method of oriented nano-MAX phase ceramics is as follows: 200 grams of Ti2AlC nano-MAX phase ceramic sheet powder with a particle size median of 180 nm and an oxygen content of 6.2% by mass were weighed. 200 grams of anhydrous ethanol and 4 grams of polyethylene glycol with a molecular weight of 600 were weighed and ultrasonically dispersed and magnetically stirred for 60 minutes at 60°C until fully dissolved. Then, the weighed Ti3AlC2 nano-MAX phase ceramic sheet powder was added to the anhydrous ethanol solution containing dissolved polyethylene glycol, mechanically stirred at 120 rpm, and simultaneously ultrasonically dispersed for 60 minutes. The resulting slurry was then poured into a vacuum filtration apparatus using a 500-mesh metal filter screen at a pressure of 0.05 MPa for 1 hour. After the liquid was completely evaporated, the formed sample was removed and air-dried in a fume hood for 36 hours. The completely dried sample was then wrapped in graphite paper and placed in an alumina crucible for pressureless sintering at 1300℃ for 120 minutes at a heating rate of 5℃ / min. The sintering atmosphere was argon. After sintering, in-situ self-generated Al2O3-reinforced oriented Ti2AlC ceramics were obtained, with an Al2O3 content of 12% by mass. The flexural strength of the oriented Ti2AlC ceramic material reached 530–630 MPa, significantly higher than that of ordinary Ti2AlC (250–350 MPa), and its fracture toughness was 10–11 MPa•m. 1 / 2 It is much higher than the fracture toughness of ordinary Ti2AlC (5-7 MPa•m). 1 / 2 ).

[0059] Example 4

[0060] In this embodiment, the preparation method of oriented nano-MAX phase ceramics is as follows: 300 grams of Cr2AlC nano-MAX phase ceramic sheet powder with a particle size of 720 nm and an oxygen content of 0.2% by mass were weighed. 300 grams of anhydrous ethanol and 10 grams of polyethylene glycol with a molecular weight of 1000 were weighed and ultrasonically dispersed and magnetically stirred for 90 minutes at 50°C until fully dissolved. The weighed Cr2AlC nano-MAX phase ceramic sheet powder was then added to the dissolved polyethylene glycol solution in anhydrous ethanol, mechanically stirred at 120 rpm, and simultaneously ultrasonically dispersed for 60 minutes. The resulting slurry was then poured into a vacuum filtration apparatus using a 2000-mesh metal filter screen at a pressure of 0.2 MPa for 4 hours. After the liquid was completely evaporated, the formed sample was removed and air-dried in a fume hood for 12 hours. The completely dried sample was then wrapped in graphite paper and placed in a molybdenum crucible for pressureless sintering at 1350℃ for 180 minutes at a heating rate of 2.5℃ / min. The sintering atmosphere was argon. The resulting oriented Cr2AlC ceramic had a low Al2O3 content (approximately 0.83%), attributed to the low oxygen content in the original powder. The oriented Cr2AlC ceramic material exhibited a flexural strength of 580–760 MPa, significantly higher than that of ordinary Cr2AlC (300–400 MPa), and a fracture toughness of 10–12 MPa•m. 1 / 2 It is much higher than the fracture toughness of ordinary Cr2AlC (5-8 MPa•m). 1 / 2 ).

[0061] Example 5

[0062] In this embodiment, the preparation method of oriented nano-MAX phase ceramics is as follows: 400 grams of Nb2AlC nano-MAX phase ceramic sheet powder with a particle size of 500 nm and an oxygen content of 5% by mass were weighed. 400 grams of anhydrous ethanol and 8 grams of polyethylene glycol with a molecular weight of 800 were weighed and ultrasonically dispersed and magnetically stirred for 120 minutes at 50°C until fully dissolved. The weighed Nb2AlC nano-MAX phase ceramic sheet powder was then added to the dissolved polyethylene glycol solution in anhydrous ethanol, mechanically stirred at 120 rpm, and simultaneously ultrasonically dispersed for 60 minutes. The resulting slurry was then poured into a vacuum filtration apparatus using a 1000-mesh metal filter screen at a pressure of 0.15 MPa for 2 hours. After the liquid was completely removed, the formed sample was removed and air-dried in a fume hood for 48 hours. The completely dried sample was then wrapped in graphite paper and placed in a graphite crucible for pressureless sintering at 1700℃ for 120 minutes at a heating rate of 5℃ / min. The sintering atmosphere was argon. After sintering, an in-situ self-generated Al2O3 phase-reinforced oriented Nb2AlC ceramic was produced, with an Al2O3 content of 10% by mass. The flexural strength of the oriented Nb2AlC ceramic material reached 750–850 MPa, significantly higher than that of ordinary Nb2AlC (300–400 MPa), and its fracture toughness was 11–13 MPa•m. 1 / 2 It is much higher than the fracture toughness of ordinary Nb2AlC (5-8 MPa•m). 1 / 2 ).

[0063] Example 6

[0064] In this embodiment, the preparation method of oriented nano-MAX phase ceramics is as follows: Weigh 500g of Ti3SiC2 nano-MAX phase ceramic sheet powder, with a particle size median of 320 nm and an oxygen content of 4% by mass. Weigh 500g of anhydrous ethanol and 10g of polyethylene glycol with a molecular weight of 800, and disperse them ultrasonically and magnetically for 60 minutes at 50℃ until fully dissolved. Then, add the weighed Ti3SiC2 nano-MAX phase ceramic sheet powder to the anhydrous ethanol solution containing dissolved polyethylene glycol, mechanically stir at 120 rpm while simultaneously dispersing ultrasonically for 60 minutes. The resulting slurry is then poured into a vacuum filtration device using an 800-mesh metal filter screen at a filtration pressure of 0.1 MPa for 2 hours. After the liquid is completely evaporated, remove the formed sample and air-dry it in a fume hood for 24 hours. The completely dried sample was then wrapped in graphite paper and placed in a graphite crucible for pressureless sintering at 1200℃ for 600 minutes at a heating rate of 5℃ / min. The sintering atmosphere was argon. After sintering, the resulting in-situ self-generated phase-reinforced oriented Ti3SiC2 ceramic had a SiO2 content of 7% by mass. The flexural strength of the oriented Ti3SiC2 ceramic material reached 560–660 MPa, significantly higher than that of ordinary Ti3SiC2 (250–350 MPa), and its fracture toughness was 10–12 MPa•m. 1 / 2 It is much higher than the fracture toughness of ordinary Ti3SiC2 (6-8 MPa•m). 1 / 2 ).

[0065] The results show that this invention utilizes the unique properties of layered MAX nanosheet powder, orienting it during vacuum casting in a slurry suspension state to obtain an initial green body with a layered structure similar to the shell of a natural pearl. This green body is then formed and densified through pressureless sintering, and further enhanced by the use of polymer additives and densification processes such as cold isostatic pressing and hot isostatic pressing to improve material properties. Compared to traditional methods, this technology not only significantly reduces sintering temperature and energy consumption but also improves the fracture toughness of the material through microstructure design. Preliminary experiments show that the MAX phase ceramics prepared based on this method possess both high toughness (fracture toughness > 10 MPa•m) and high strength. 1 / 2 With its excellent scalability, it breaks through the bottleneck of existing orientation toughening technology in the preparation of large-size samples, and provides a new way for the large-scale application of MAX phase ceramics in harsh environments such as aerospace and nuclear energy.

Claims

1. A method for preparing oriented nano-MAX phase ceramics by vacuum impregnation, characterized in that, Includes the following steps: (1) The raw material used is MAX phase ceramic nanosheet powder. The length of the nanosheet particles of MAX phase ceramic in the powder is between 0.02 and 5 micrometers, the thickness of the nanosheet is between 5 and 500 nanometers, and the mass fraction of oxygen content is between 0.01% and 20%. (2) After the raw material is vacuum-injected and sintered, nano-MAX phase ceramics are obtained. The MAX phase grains in the ceramics are lamellar or spindle-shaped, and the lamellar MAX phase grains have orientation.

2. The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation according to claim 1, characterized in that, The nano-MAX phase ceramics are distributed in an orderly stacked pattern, with MAX phase oxides distributed at the grain boundaries of the nano-MAX phase ceramic grains. The length of the MAX phase grain lamellars ranges from 0.05 to 20 micrometers, and the lamellar thickness ranges from 0.02 to 5 micrometers.

3. The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation according to claim 2, characterized in that, By mass percentage, the content of MAX phase oxide in nano-MAX phase ceramics is 0.02% to 40%, and the remainder is MAX phase ceramics.

4. The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation according to claim 1, characterized in that, During sintering, the preform prepared from the nanosheet powder of MAX phase ceramics is directly sintered without pressure; or, the preform prepared from the nanosheet powder of MAX phase ceramics is subjected to a composite and sintering process, wherein the composite process is one or both of cold isostatic pressing and hot isostatic pressing.

5. The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation according to claim 4, characterized in that, The sintering process employs one of the following methods: (1) Direct pressureless sintering method The vacuum-injected preform is directly wrapped in graphite paper and placed in a crucible made of graphite, oxide ceramic or high-temperature resistant metal; the sintering temperature is 1000-1800℃, the holding time is 10-3600 minutes, the heating rate is 1-100℃ / minute, and the sintering is carried out in a vacuum or argon atmosphere. (2) Cold isostatic pressing pressureless sintering method First, the vacuum-injected preform is loaded into a polymer material sheath and isostatically pressed in a cold isostatic press. The isostatic pressing pressure is 80–300 MPa, and the holding time is 0.5–5 minutes. Then, it is sintered without pressure in a crucible at a temperature of 1000–1800℃, a holding time of 10–3600 minutes, and a heating rate of 1–100℃ / min. The sintering is carried out under a vacuum or argon atmosphere. (3) Direct pressureless sintering hot isostatic pressing method First, the block sintered by direct pressureless sintering method (1) is placed into a hot isostatic pressing (HIP) sintering liner. Then, the liner is evacuated and sealed. The block is then hot isostatically pressed in the liner, or hot isostatic pressing is performed directly without the liner. The hot isostatic pressing temperature is 1000-1600℃, the sintering pressure is 50-300MPa, the holding time is 10-3600 minutes, and the heating rate is 1-100℃ / minute. The hot isostatic pressing is performed in a vacuum or argon atmosphere. (4) Cold isostatic pressing, pressureless sintering, and hot isostatic pressing First, the block obtained by cold isostatic pressing pressureless sintering method (2) is loaded into a hot isostatic pressing sleeve. Then, the sleeve is evacuated and sealed. Hot isostatic pressing sintering is performed in the sleeve, or hot isostatic pressing sintering is performed directly without the sleeve. The hot isostatic pressing temperature is 1000-1600℃, the sintering pressure is 50-300MPa, the holding time is 10-3600 minutes, the heating rate is 1-100℃ / minute, and the hot isostatic pressing sintering is carried out in a vacuum or argon atmosphere.

6. The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation according to claim 1, characterized in that, The nanosheet powder of MAX phase ceramics is prepared into a preform using vacuum casting, including the following steps: (1) Prepare a slurry with a solid content of 35% to 55% by mixing the nanosheet powder of MAX phase ceramics with anhydrous ethanol solution or ethanol-polyethylene glycol solution. The method for preparing the slurry is any one or a combination of two or more of the following: ultrasonic vibration, magnetic stirring, electric stirring and ball milling. (2) Pour the prepared slurry into the vacuum filtration device. The filtration pressure is 0.02-0.2 MPa and the filtration time is 30-240 minutes. The filter screen is made of metal screen, polymer material screen, filter paper or filter membrane. The mesh size of the metal screen is 200-2000 mesh and the pore size of the polymer material screen, filter paper or filter membrane is 1-100 micrometers. (3) After vacuum filtration is completed and there is no liquid left, take it out and place it in a cool, ventilated and dry place to dry it completely into an embryo.

7. The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation according to claim 6, characterized in that, Polyethylene glycol, a polymer additive with a molecular weight of 600-1000, is added to ethanol solvent to prepare an ethanol-polyethylene glycol solution with a mass fraction of 0.5-5%. To accelerate the dissolution of polyethylene glycol, heating and stirring are performed during preparation. The heating temperature is 30-70°C, and the stirring time is 10-120 minutes.

8. The method for preparing oriented nano-MAX phase ceramics by vacuum impregnation according to claim 1, characterized in that, The equipment used for sintering includes muffle furnaces, induction heating furnaces, microwave heating furnaces, or infrared heating furnaces.

9. A slurry vacuum impregnation method for preparing oriented nano-MAX phase ceramics according to any one of claims 1 to 8, characterized in that, When preparing oriented nano-MAX phase ceramics, the oxide content in the MAX phase ceramics is controlled by the oxygen content of the nanosheet powder of the MAX phase ceramics used to prepare the above ceramics. The obtained grain size is controlled by the particle size of the nanosheet particles and the powder sintering parameters. The degree of orientation of the obtained ceramics is jointly controlled by different combinations and parameters of the pressure application method and sintering method.

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