Slurry filter-pressing forming and normal-pressure sintering preparation method of high-toughness low-orientation MAX-phase ceramic

Abstract

The invention belongs to the technical field of structural ceramic material preparation, and particularly relates to a slurry filter-pressing forming and normal-pressure sintering preparation method of high-toughness low-orientation MAX-phase ceramic. The method comprises the steps of raw material preparation, slurry preparation, filter-pressing forming, normal-pressure sintering and densification treatment, and specifically comprises the following steps: selecting MAX-phase nano lamella powder with the lamella length of 0.02-5 microns and the thickness of 5-500 nanometers, preparing the MAX-phase nano lamella powder into slurry with the solid content of 65-85%, carrying out filter-pressing forming under the pressure of 1-10 MPa, carrying out normal-pressure sintering at 1200-1800 DEG C, and carrying out cold isostatic pressing (80-300 MPa) and hot isostatic pressing (1000-1600 DEG C and 50-200 MPa) synergistic densification treatment. According to the method, grain orientation is inhibited through slurry filter pressing, pores are eliminated through cooperation with densification, and finally the Lotgering orientation factor flt is obtained; the density of the MAX-phase ceramic is greater than or equal to 99.5%, and the mechanical properties in all directions are uniform.

Description

Technical Field

[0001] This invention belongs to the field of structural ceramic material preparation technology, specifically relating to a method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering. Background Technology

[0002] MAX phase ceramics are a class of carbide or nitride ceramics with a layered structure, characterized by the simultaneous presence of covalent / ionic (MX) and metallic (MA) bonds in their unique crystal structure. This special chemical bonding allows them to successfully combine the excellent properties of ceramics (such as high melting point, high strength, good oxidation resistance, and thermal shock resistance) with the superior properties of metals (such as good thermal and electrical conductivity and machinability). To date, more than 300 MAX phases have been discovered or synthesized, showing broad application prospects in extreme environments such as aerospace, nuclear energy, and chemical engineering.

[0003] Despite the numerous advantages of MAX phase ceramics, their application as structural materials still faces significant challenges. Firstly, their compatibility with materials such as SiC... f Compared to advanced ceramic matrix composites such as SiC, traditional MAX phase ceramics still exhibit insufficient fracture toughness, limiting their application in load-bearing components. To overcome this bottleneck, orientation toughening has become an effective strategy. Currently, textured MAX phase ceramics with significant c-axis orientation can be prepared using techniques such as strong magnetic field orientation (SMFA), hot pressing (HP), and spark plasma sintering (SPS), resulting in a substantial improvement in their fracture toughness. For example, studies have reported that the fracture toughness of Nb4AlC3 ceramics was increased to 14.1 MPa•m using SMFA combined with SPS technology. 1 / 2 However, these processes typically rely on expensive equipment, and the harsh molding conditions severely limit their ability to produce large-sized or complex-shaped components, resulting in high costs and hindering their large-scale application.

[0004] To reduce manufacturing costs and achieve complex shape forming, research has shifted to atmospheric pressure sintering technology. Existing atmospheric pressure sintering technologies mainly fall into two categories: one involves uniaxially pressing MAX phase powder into shape before sintering; the other involves preparing the powder into a slurry, forming a green body through slip casting or vacuum casting, and then sintering. However, the former often requires extremely high forming pressure when preparing highly dense green bodies, making the process inconvenient; while the latter, although easy to form complex shapes, generally results in lower green body density due to reliance solely on gravity or capillary forces. This leads to the final sintered body's density and mechanical properties, especially fracture toughness, being difficult to match those of materials prepared by pressure-assisted sintering.

[0005] Furthermore, oriented MAX phase ceramics prepared by the aforementioned unidirectional pressure techniques such as hot pressing, hot forging, or SPS exhibit significant anisotropy in their mechanical properties. This anisotropy is a direct reflection of their highly textured microstructure: under pressure, the c-axis (basal plane normal) of the lamellar grains tends to align perpendicular to the pressure direction, forming a layered structure similar to the nacreous layer of a seashell. Although crack propagation requires passing through the grains or deflection in the two high-toughness directions, this results in excellent fracture toughness (often reaching 12–16 MPa•m). 1 / 2 However, in the other low-toughness direction, cracks are very likely to propagate along the basal surface with weaker bonding, resulting in a significant reduction in both flexural strength and fracture toughness.

[0006] Research data shows that in such highly oriented ceramics, the difference in fracture toughness between the high-toughness and low-toughness directions can be as high as 100%. For example, for textured Ti3AlC2 ceramics, the interlaminar fracture toughness may be less than half of the through-laminar toughness. This inherent performance limitation means that cracks initiating and propagating along the weak layer direction become a potential source of premature component failure under complex multi-directional stress or undefined stress directions (such as turbine blades and heat exchanger components), severely restricting the reliable application of such high-performance oriented ceramics in critical structural components. Therefore, how to eliminate or reduce the anisotropy of mechanical properties while retaining the inherent advantages of high strength and high toughness of MAX phase ceramics, and achieving a balance and predictability of material properties in three-dimensional space, has become a key scientific problem and technological challenge that must be solved to promote its wider application.

[0007] Patent CN106830971A discloses a method for preparing MAX phase porous ceramics. These ceramics have a porosity of 20.7%–35.3%, but low density, making them suitable only for non-load-bearing applications such as energy storage and adsorption, and unsuitable for structural components. An SPS sintering furnace is used, with a sintering pressure of 30–60 MPa. Patent CN109053206A discloses a short-fiber reinforced oriented MAX phase ceramic matrix composite material and its preparation method. The highly oriented MAX phase matrix with short fibers axially parallel to the sheets inevitably leads to significant anisotropy in mechanical properties, with cracking easily occurring in the low-toughness direction. Additional short fibers (carbon fiber, silicon carbide fiber, etc.) and particulate additives are required, potentially causing problems such as fiber-matrix interfacial reactions and uneven dispersion. The patent with publication number CN109180187A proposes a method for preparing highly oriented nano-MAX phase ceramics and MAX phase in-situ self-generated oxide nano-composite ceramics. By pressurizing and sintering (hot pressing, HIP, SPS), the nanosheet powder is forced to oriented and form a layered structure similar to nacre. Although it can improve the toughness in one direction, it exacerbates the anisotropy of mechanical properties. The fracture toughness in the low toughness direction is only about 50% of that in the high toughness direction.

[0008] In summary, there is an urgent need to develop a new method for preparing MAX phase ceramics that can take into account high density, high strength and toughness, low mechanical property anisotropy, and is suitable for low-cost, large-scale preparation of complex-shaped components. Summary of the Invention

[0009] In order to overcome the above-mentioned shortcomings of the prior art, the present invention aims to provide a slurry pressure filtration molding and atmospheric pressure sintering preparation method for high-strength and tough low-orientation MAX phase ceramics. This method aims to solve the technical bottlenecks in the prior art, such as the heavy reliance on expensive equipment, the difficulty in molding complex components, and the anisotropy of mechanical properties caused by high orientation in the preparation of high-performance MAX phase ceramics.

[0010] The technical solution of this invention is:

[0011] A method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering includes the following steps:

[0012] (1) Raw material preparation: MAX phase ceramic nanosheet powder is selected. The nanosheet length of the MAX phase ceramic nanosheet particles in the nanosheet powder is 0.02-5 micrometers, the thickness of the nanosheet is 5-500 nanometers, and the mass fraction of oxygen content is 0.01%-20%;

[0013] (2) Slurry preparation: Mix the nanosheet powder with the solvent to prepare a uniform slurry with a solid content of 65% to 85% by mass;

[0014] (3) Press filtration molding: Pour the slurry into a press filter containing filter media and press filter under a molding pressure of 1 to 10 MPa. After the liquid is completely discharged, the green body is obtained.

[0015] (4) Atmospheric pressure sintering and densification treatment: The green blank is sintered under a protective atmosphere at atmospheric pressure at a temperature of 1200-1800℃, a holding time of 60-360 minutes, and a heating rate of 1-10℃ / minute; densification treatment is carried out before and after atmospheric pressure sintering. The densification treatment is a combination of cold isostatic pressing before atmospheric pressure sintering and hot isostatic pressing after atmospheric pressure sintering.

[0016] After the above steps, a high-strength, low-orientation MAX phase ceramic bulk with a Lotgering orientation factor f value of less than 0.1 and a density of not less than 99.5% is obtained.

[0017] The method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering, in step (1), the MAX phase ceramics include any one or composite phase, solid solution, high-entropy body, or ordered phase among Ti3AlC2, Ti2AlC, Ti3SiC2, Cr2AlC, Nb2AlC, Nb4AlC3 and other synthesizable MAX phases.

[0018] In the method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering, in step (2), the solvent is anhydrous ethanol or acetone; when preparing the slurry, any one or more of the following methods are used for dispersion: ultrasonic vibration, magnetic stirring, electric stirring or ball milling.

[0019] In the method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering, in step (2), a polymeric dispersant or binder with a mass fraction of 0.1-5% is added to the solvent. The polymeric dispersant or binder is any one or a combination of two or more of polyvinyl alcohol, methyl cellulose, polymethyl methacrylate, polyethylene glycol, polyacrylamide, and polyacrylic acid.

[0020] In the method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering, in step (3), the filter medium is a metal filter screen, a polymer material filter screen, a filter paper, or a filter membrane; the mesh size of the metal filter screen is 200 to 2000 mesh, and the pore size of the polymer material filter screen, filter paper, or filter membrane is 1 to 100 micrometers.

[0021] In the method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering, the protective atmosphere in step (4) is argon or vacuum; atmospheric pressure sintering is carried out in a muffle furnace, induction heating furnace, microwave heating furnace or infrared heating furnace.

[0022] In the method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering, in step (4), the green body is subjected to cold isostatic pressing treatment before atmospheric pressure sintering, with a treatment pressure of 80-300 MPa and a holding time of 0.5-5 minutes.

[0023] In the method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering, in step (4), after atmospheric pressure sintering, the sintered body is subjected to hot isostatic pressing treatment at a temperature of 1000-1600℃, a pressure of 50-200MPa, and a holding time of 10-360 minutes.

[0024] The high-strength and low-orientation MAX phase ceramic described herein has MAX phase grains that are lamellar or spindle-shaped, with a Lotgering orientation factor f value of less than 0.1 and exhibiting isotropic characteristics. Its density is not less than 99.5%, its minimum flexural strength is not less than 630 MPa in the lowest direction, and its minimum fracture toughness is not less than 9 MPa·m in the lowest direction. 1 / 2 .

[0025] The high-strength, low-orientation MAX phase ceramic obtained in this way has its in-situ self-generated oxide content precisely controlled by the oxygen content of the raw material powder; the grain size of the ceramic is determined by the initial particle size of the nanosheet particles and the sintering parameters; and the degree of isotropy of the ceramic's microstructure is controlled by the combined synergistic control of the pressure filtration molding pressure and the subsequent densification treatment method.

[0026] The principles and design concepts of this invention:

[0027] This invention, while eliminating the need for expensive and complex pressure-assisted sintering processes, not only achieves high density and high strength and toughness but also overcomes the inherent anisotropic mechanical properties of traditional oriented materials. This invention provides a completely new technical approach, the core principle of which can be summarized as follows: through the synergistic process design of "nanosheet powder pressure filtration molding" and "atmospheric pressure sintering - pre- and post-densification," three-dimensional homogenization of the material is achieved macroscopically, while a fine-grained, dense, and nearly isotropic reinforced and toughened microstructure is constructed microscopically.

[0028] The core principles of this invention are embodied in the following aspects:

[0029] Microstructure Control Principle: From "Forced Orientation" to "Random Distribution". Traditional hot pressing or SPS technology forces nanosheet powders to orient themselves under unidirectional high pressure, forming a strong c-axis texture. While this structure achieves toughening in one direction, it also creates parallel weak interfaces, leading to performance limitations. The ingenuity of this invention lies in taking the opposite approach, utilizing the gentle pressurization process of filter pressing to suppress rather than promote orientation. By precisely controlling the high solids content and low molding pressure of the slurry, the fluidity of the slurry system is restricted under pressure, and the sheet-like particles are "frozen" in a random orientation state before they can undergo large-scale ordered arrangement. After sintering, the sheet-like grains in this disordered preform are randomly distributed in three-dimensional space, eliminating continuous weak bonding surfaces. This results in the material exhibiting balanced and predictable mechanical properties in different directions, with its Lotgering orientation factor successfully controlled below 0.1.

[0030] Secondly, the core of this invention lies in constructing a multi-stage synergistic densification and structure control system. Specifically, this system first obtains a green body with high initial density through pressure filtration molding, laying the foundation for subsequent processes; then, utilizing the high activity of nanosheet powder, it drives grain boundary migration and initial pore closure during atmospheric pressure sintering. Crucially, it creatively introduces cold isostatic pressing (CIP) and hot isostatic pressing (HIP) as optional "performance and structure controllers": CIP, by applying isotropic ultra-high hydrostatic pressure at room temperature, not only mechanically squeezes residual pores but also physically forces the initially oriented sheet particles that may have formed during pressure filtration to shift, rotate, or even break, thereby effectively destroying and dispersing their pre-texture and significantly reducing the overall orientation of the material; while subsequent HIP, at a higher temperature, promotes plastic flow and diffusion creep of the material through isostatic pressure. While completely eliminating closed micropores and pushing the density close to the theoretical value, this high-temperature, high-pressure process also further perturbs and homogenizes the grain orientation, consolidating and strengthening the randomized microstructure established by CIP. This makes it possible to prepare MAX phase ceramics that combine high strength, high toughness, and uniform three-dimensional properties.

[0031] The advantages and beneficial effects of this invention are:

[0032] (1) Achieving the unity of high strength and toughness with isotropy: This invention successfully prepared fine-grained MAX phase ceramics with low orientation by using a unique pressure filtration molding and post-processing technology for nanosheet MAX phase powder. It overcomes the inherent defect of weak performance in low fracture direction of materials obtained by traditional hot pressing, SPS and other technologies, and greatly improves the reliability and life of the material in complex multi-directional stress environment.

[0033] (2) It combines low cost and rapid prototyping capability: The core process of this invention adopts slurry pressure filtration and atmospheric pressure sintering, which eliminates the dependence on expensive and complex magnetic field orientation devices, hot pressing molds or SPS equipment, and significantly reduces equipment investment and production costs. The auxiliary pressure can drain the solvent more quickly, making the molding speed much faster than ordinary ceramic slurry molding methods.

[0034] (3) The present invention achieves excellent comprehensive performance through synergistic densification. The density of the material is successfully controlled to 0.1 through the synergistic densification of "pressure filtration + CIP + HIP". This makes the key mechanical properties of the material, such as hardness, flexural strength and fracture toughness, reach the level of the costly pressure-assisted sintering process, and the performance differences in bending and fracture toughness in each direction are small. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope (SEM) image of the microstructure of a high-strength, low-orientation Ti3AlC2 composite ceramic material.

[0036] Figure 2 SEM image of the fracture microstructure of high-strength, low-orientation Ti3AlC2 composite ceramic material.

[0037] Figure 3 The figures show the X-ray diffraction (XRD) patterns of the microstructure of high-strength, low-orientation Ti3AlC2 composite ceramic materials and the XRD patterns of oriented Ti3AlC2 composite ceramic materials. In the figures, the horizontal axis 2θ represents the diffraction angle (°), and the vertical axis Intensity represents the relative intensity (au). Detailed Implementation

[0038] In its specific implementation, this invention provides a method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering, which specifically includes the following steps:

[0039] (1) Raw material preparation: The raw material used is nanosheet powder of MAX phase ceramics. The length of the nanosheet particles of MAX phase ceramics in the nanosheet powder is between 0.02 and 5 micrometers, the thickness of the nanosheets is between 5 and 500 nanometers, and the mass fraction of oxygen content is between 0.01% and 20%. MAX phase ceramics include, but are not limited to, any one or a composite phase, solid solution, high entropy body, ordered phase, etc. among Ti3AlC2, Ti2AlC, Ti3SiC2, Cr2AlC, Nb2AlC, Nb4AlC3 and other synthesizable MAX phases.

[0040] (2) Slurry preparation: The above-mentioned nanosheet powder is prepared into a uniform slurry with a solid content of 65% to 85% by mass with a solvent. The solvent is anhydrous ethanol or acetone, or other liquids that do not react with the powder. The slurry can be prepared by any one or a combination of two or more of the following methods: ultrasonic vibration, magnetic stirring, electric stirring, and ball milling, to achieve sufficient dispersion. To further optimize the slurry performance, a polymeric dispersant or binder with a mass fraction of 0.1% to 5% can be added to the solvent. The polymeric dispersant or binder can be any one or a combination of two or more of the following: polyvinyl alcohol, methyl cellulose, polymethyl methacrylate, polyethylene glycol, polyacrylamide, and polyacrylic acid.

[0041] (3) Pressure filtration molding: The prepared slurry is poured into a pressure filter containing filter media and filtered under a molding pressure of 1–10 MPa. The filter media can be a metal filter screen, a polymer filter screen, filter paper, or a filter membrane. The mesh size of the metal filter screen is 200–2000 mesh, and the pore size of the polymer filter screen, filter paper, or filter membrane is 1–100 micrometers. After the liquid is completely discharged, a green body with a uniform structure is obtained.

[0042] (4) Atmospheric pressure sintering and densification treatment: To further improve performance, the green body is subjected to cold isostatic pressing (CIP, pressure 80-300 MPa, holding time 0.5-5 minutes) before atmospheric pressure sintering. The green body is then sintered at atmospheric pressure under a protective atmosphere (such as argon or vacuum) at a temperature of 1200-1800℃, a holding time of 60-360 minutes, and a heating rate of 1-10℃ / minute. Atmospheric pressure sintering can be carried out in conventional heating equipment such as muffle furnaces, induction furnaces, microwave furnaces, or infrared furnaces. After atmospheric pressure sintering, the sintered body is subjected to hot isostatic pressing (HIP, temperature 1000-1600℃, pressure 50-200 MPa, holding time 10-360 minutes). The combination of CIP and HIP can effectively eliminate porosity and disrupt the preferred orientation of grains.

[0043] (5) Obtaining the product: Through the above process, a high-density, low-orientation MAX phase ceramic bulk is finally obtained. In the microstructure of the ceramic, the MAX phase grains are lamellar or spindle-shaped, and the Lotgering orientation factor f value of the ceramic is less than 0.1, exhibiting isotropic characteristics. After HIP treatment, the density can reach more than 99.5%, and the mechanical properties in all directions are relatively uniform.

[0044] In the final MAX phase ceramic, the content of in-situ self-generated oxides is precisely controlled by the oxygen content of the raw material powder; the grain size of the ceramic is determined by the initial particle size of the nanosheet particles and the sintering parameters; and the degree of isotropy of the microstructure of the ceramic is controlled by the combination of pressure filtration molding pressure and subsequent densification treatment.

[0045] The present invention will be further described in detail below through embodiments.

[0046] Example 1

[0047] In this embodiment, the preparation method of high-strength and tough low-orientation MAX phase ceramic is as follows:

[0048] 200 grams of Ti3AlC2 nano-MAX phase ceramic sheet powder with a particle size of 89 nm and an oxygen content of 8.0% by mass were weighed out. 85 grams of anhydrous ethanol were weighed out, and then the weighed Ti3AlC2 nano-MAX phase ceramic sheet powder and 3 grams of polyethylene glycol were added to the anhydrous ethanol solution. The mixture was mechanically stirred at 150 rpm while simultaneously ultrasonically dispersed for 40 minutes to obtain a homogeneous slurry with a solid content of 70% by mass. The slurry was then poured into a vacuum filtration apparatus using a 1000-mesh metal filter screen at a pressure of 4 MPa for 1 hour. After the liquid was completely filtered out, the formed sample was removed and air-dried in a fume hood for 48 hours. 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 completely dried sample was then wrapped in graphite paper and placed in a graphite crucible for atmospheric pressure sintering at 1300℃ for 120 minutes at a heating rate of 5℃ / min. The sintering atmosphere was argon. After sintering, the sample was placed in a hot isostatic pressing furnace for hot isostatic pressing at 1200℃, 130 MPa, and 120 minutes. High-strength, low-orientation Ti3AlC2 ceramic was obtained after hot isostatic pressing, with an Al2O3 content of 16% by mass, a Lotgering orientation factor f=0.06, and a density of 99.7%. The high-strength, low-orientation Ti3AlC2 composite ceramic material exhibited a minimum flexural strength of 630 MPa, significantly higher than the flexural strength of ordinary Ti3AlC2 (300–400 MPa) and the minimum flexural strength of oriented Ti3AlC2 (400–500 MPa). High-strength, low-orientation Ti3AlC2 composite ceramic materials exhibit fracture toughness with a minimum direction of 9–10 MPa•m. 1 / 2 It is much higher than the fracture toughness of ordinary Ti3AlC2 (7-8 MPa•m). 1 / 2 ), and the lowest directional fracture toughness value of oriented Ti3AlC2 (4–6 MPa•m). 1 / 2 ).

[0049] like Figure 1 As shown in the SEM image of the microstructure of the high-strength, low-orientation Ti3AlC2 composite ceramic material, the bright and continuous areas represent the Ti3AlC2 matrix, while the dark and granular areas correspond to the Al2O3 phase. It can be seen that the grain size of the material is extremely small, similar to the nanosheet-oriented Ti3AlC2 reported in previously published papers.

[0050] like Figure 2As shown in the SEM image of the fracture microstructure of the high-strength, low-orientation Ti3AlC2 composite ceramic material, the lamellar structure in the image corresponds to the Ti3AlC2 matrix, while the granular structure corresponds to the Al2O3 phase. It can also be seen that the grain size of the material is extremely small.

[0051] like Figure 3 As shown in the XRD patterns of the high-strength, low-orientation Ti3AlC2 composite ceramic material and the oriented Ti3AlC2 composite ceramic material, it can be seen that the peaks in the image are near the main peak at 37-41 degrees 2θ, indicating an oriented nano-Ti3AlC2 layered structure. The 008 facet is significantly higher than the normal main peak at the 104 facet, exhibiting a distinct c-axis texture characteristic of the 00l facet. In contrast, the low-orientation Ti3AlC2 layered structure material prepared in this invention still has a main peak at the 104 facet, similar to the standard peak pattern of the non-oriented material.

[0052] Example 2

[0053] In this embodiment, the preparation method of high-strength and tough low-orientation MAX phase ceramic is as follows:

[0054] 200 grams of Nb4AlC3 nano-MAX phase ceramic sheet powder with a particle size of 102 nm and an oxygen content of 4.1% by mass were weighed out. 50 grams of acetone were weighed out, and then the Nb4AlC3 nano-MAX phase ceramic sheet powder and 3 grams of polyacrylamide were added to the acetone solution. The mixture was mechanically stirred at 100 rpm while simultaneously ultrasonically dispersed for 50 minutes to obtain a homogeneous slurry with a solid content of 80% by mass. The slurry was then poured into a vacuum filtration apparatus using an 800-mesh nylon filter screen at a pressure of 6 MPa for 1 hour. After the liquid was completely filtered out, the formed sample was removed and air-dried in a fume hood for 48 hours. The completely dried sample was then wrapped and sealed in a polymer material sleeve and placed in a cold isostatic press at a pressure of 220 MPa for 90 seconds. The completely dried sample was then wrapped in graphite paper and placed in a graphite crucible for atmospheric pressure sintering at 1700℃ for 120 minutes at a heating rate of 5℃ / min. The sintering atmosphere was argon. After sintering, the sample was placed in a hot isostatic pressing furnace for hot isostatic pressing at 1500℃, 120 MPa, and for 120 minutes. High-strength, low-orientation Nb4AlC3 ceramic was obtained after hot isostatic pressing, with an Al2O3 content of 7.2% by mass, a Lotgering orientation factor f=0.05, and a density of 99.5%. The high-strength, low-orientation Nb4AlC3 composite ceramic material exhibits a minimum flexural strength of 650 MPa and a minimum fracture toughness of 10–11 MPa•m. 1 / 2.

[0055] Example 3

[0056] In this embodiment, the preparation method of high-strength and tough low-orientation MAX phase ceramic is as follows:

[0057] 200 grams of Cr2AlC nano-MAX phase ceramic sheet powder with a particle size of 125 nm and an oxygen content of 6.4% by mass were weighed out. 70 grams of anhydrous ethanol were weighed out, and then the Cr2AlC nano-MAX phase ceramic sheet powder and 4 grams of polyvinyl alcohol were added to an acetone solution. The mixture was mechanically stirred at 150 rpm while simultaneously ultrasonically dispersed for 60 minutes to obtain a homogeneous slurry with a solid content of 74% by mass. The slurry was then poured into a vacuum filtration apparatus using a 1500-mesh metal filter screen at a pressure of 5 MPa for 1 hour. After the liquid was completely filtered out, the formed sample was removed and air-dried in a fume hood for 48 hours. 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 230 MPa for 100 seconds. The completely dried sample was then wrapped in graphite paper and placed in a graphite crucible for atmospheric pressure sintering at 1400℃ for 120 minutes at a heating rate of 5℃ / min. The sintering atmosphere was argon. After sintering, the sample was placed in a hot isostatic pressing furnace for hot isostatic pressing at 1200℃, 150 MPa, and 150 minutes. High-strength, low-orientation Cr2AlC ceramic was obtained after hot isostatic pressing, with an Al2O3 content of 9.5% by mass, a Lotgering orientation factor f=0.04, and a density of 99.6%. The high-strength, low-orientation Cr2AlC composite ceramic material exhibits a minimum flexural strength of 660 MPa. The minimum fracture toughness of the high-strength, low-orientation Cr2AlC composite ceramic material is 9–10 MPa•m. 1 / 2 .

[0058] The results show that this invention provides a method for preparing high-strength, low-orientation MAX phase ceramics. The core of this method lies in using nanosheet powder of MAX phase ceramics as raw material, preparing it into a slurry with a specific high solid content using a solvent, and then pressing and filtration it under low mechanical pressure to obtain a high-density green body with randomly oriented powder particles. After atmospheric pressure sintering, this green body directly yields low-orientation, high-density MAX phase ceramics. To further improve material properties and reduce orientation, densification processes such as cold isostatic pressing (CIP) or hot isostatic pressing (HIP) are introduced before or after the atmospheric pressure sintering process. Through their unique isotropic pressure fields, residual porosity is eliminated while the microstructure is destroyed and homogenized, ultimately producing a high-performance MAX phase ceramic material with high strength, high fracture toughness, and isotropic mechanical properties. This invention, through a series of innovative process combinations and precise parameter control, successfully combines low-cost slurry processes suitable for complex shape forming with the preparation requirements of high-performance, low-orientation MAX phase ceramics, providing a complete solution with clear principles and ingenious design to solve the bottleneck of large-scale application of this material system.

Claims

1. A method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering, characterized in that, Includes the following steps: (1) Raw material preparation: MAX phase ceramic nanosheet powder is selected. The nanosheet length of the MAX phase ceramic nanosheet particles in the nanosheet powder is 0.02-5 micrometers, the thickness of the nanosheet is 5-500 nanometers, and the mass fraction of oxygen content is 0.01%-20%; (2) Slurry preparation: Mix the nanosheet powder with the solvent to prepare a uniform slurry with a solid content of 65% to 85% by mass; (3) Press filtration molding: Pour the slurry into a press filter containing filter media and press filter under a molding pressure of 1 to 10 MPa. After the liquid is completely discharged, the green body is obtained. (4) Atmospheric pressure sintering and densification treatment: The green blank is sintered under a protective atmosphere at atmospheric pressure at a temperature of 1200-1800℃, a holding time of 60-360 minutes, and a heating rate of 1-10℃ / minute; densification treatment is carried out before and after atmospheric pressure sintering. The densification treatment is a combination of cold isostatic pressing before atmospheric pressure sintering and hot isostatic pressing after atmospheric pressure sintering. After the above steps, a high-strength, low-orientation MAX phase ceramic bulk with a Lotgering orientation factor f value of less than 0.1 and a density of not less than 99.5% is obtained.

2. The method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering according to claim 1, characterized in that, In step (1), the MAX phase ceramics include any one or a composite phase, solid solution, high entropy body, or ordered phase among Ti3AlC2, Ti2AlC, Ti3SiC2, Cr2AlC, Nb2AlC, Nb4AlC3 and other synthesizable MAX phases.

3. The method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering according to claim 1, characterized in that, In step (2), the solvent is anhydrous ethanol or acetone; when preparing the slurry, any one or a combination of two or more of the following methods are used for dispersion: ultrasonic vibration, magnetic stirring, electric stirring, or ball milling.

4. The method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering according to claim 1, characterized in that, In step (2), a polymeric dispersant or binder with a mass fraction of 0.1 to 5% is added to the solvent. The polymeric dispersant or binder is any one or a combination of two or more of polyvinyl alcohol, methyl cellulose, polymethyl methacrylate, polyethylene glycol, polyacrylamide, and polyacrylic acid.

5. The method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering according to claim 1, characterized in that, In step (3), the filter medium is a metal filter screen, a polymer filter screen, a filter paper, or a filter membrane; the mesh size of the metal filter screen is 200 to 2000 mesh, and the pore size of the polymer filter screen, filter paper, or filter membrane is 1 to 100 micrometers.

6. The method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering according to claim 1, characterized in that, In step (4), the protective atmosphere is argon or vacuum; atmospheric pressure sintering is carried out in a muffle furnace, induction heating furnace, microwave heating furnace or infrared heating furnace.

7. The method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering according to claim 1, characterized in that, In step (4), the green billet is subjected to cold isostatic pressing before atmospheric pressure sintering. The processing pressure is 80-300 MPa and the holding time is 0.5-5 minutes.

8. The method for preparing high-strength, low-orientation MAX phase ceramics by slurry pressure filtration molding and atmospheric pressure sintering according to claim 1, characterized in that, In step (4), after atmospheric pressure sintering, the sintered body is subjected to hot isostatic pressing treatment at a temperature of 1000-1600℃, a pressure of 50-200MPa, and a holding time of 10-360 minutes.

9. A high-strength, low-orientation MAX phase ceramic prepared by the method according to any one of claims 1 to 8, characterized in that, The MAX phase grains in the ceramic are lamellar or spindle-shaped, with a Lotgering orientation factor f value less than 0.1, exhibiting isotropic characteristics, a density of not less than 99.5%, a minimum flexural strength of not less than 630 MPa in the lowest direction, and a minimum fracture toughness of not less than 9 MPa·m in the lowest direction. 1 / 2 .

10. The high-strength, low-orientation MAX phase ceramic according to claim 9, characterized in that, In the final MAX phase ceramic, the content of in-situ self-generated oxides is precisely controlled by the oxygen content of the raw material powder; the grain size of the ceramic is determined by the initial particle size of the nanosheet particles and the sintering parameters; and the degree of isotropy of the microstructure of the ceramic is controlled by the combination of pressure filtration molding pressure and subsequent densification treatment.

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