Impact-resistant ceramic and preparation method thereof

Abstract

The present application relates to an impact-resistant ceramic and a preparation method thereof, wherein the impact-resistant ceramic comprises a dense layer and a porous layer alternately stacked, the dense layer comprising a matrix and SiC whiskers with a volume fraction of 15-20% dispersed in the matrix; the porous layer comprises a matrix and SiC whiskers with a volume fraction of 8-12% dispersed in the matrix, and the porosity of the porous layer is 30-40%; the SiC whiskers are oriented at 0°±5° along the horizontal plane in the dense layer, and the SiC whiskers are staggered at 45°±10° in the porous layer; the matrix is ​​a core-shell structure of Al2O3 coated with ZrO2, wherein the core phase is 50-100nm t-ZrO2 and the shell is 200-300nm α-Al2O3. The impact-resistant ceramic of the present application constructs a stress wave impedance gradient by alternating dense layers and porous layers and regulating the whisker arrangement, so that the impact energy is dissipated through whisker pullout, crack deflection and pore collapse.

Description

Technical Field

[0001] The present application relates to the field of ceramic technology, and in particular to an impact-resistant ceramic and a preparation method thereof. Background Art

[0002] Layered ceramic materials usually achieve energy absorption by alternating heterogeneous layers in impact-resistant applications. However, the interlayer interfaces formed by traditional preparation methods have insufficient bonding strength and are prone to interlayer delamination failure due to stress concentration under dynamic loads. In existing whisker-reinforced ceramics, the disordered distribution of the reinforcing phase leads to discontinuous stress transfer paths, making it difficult to form an effective multi-level energy dissipation mechanism, and the randomly oriented whiskers are difficult to fully exert their toughening effect. In addition, the high-temperature environment required by conventional sintering processes can easily cause thermal damage to the whisker structure and induce abnormal growth of matrix phase grains, leading to defects such as microcracks inside the material. How to construct impact-resistant ceramics with stable interlayer bonding, controllable reinforcing phase orientation and low-temperature densification has become a key problem in improving the dynamic mechanical properties and fatigue resistance of materials. Summary of the Invention

[0003] The present application provides an impact-resistant ceramic, comprising alternating dense layers and porous layers, wherein the dense layer comprises a matrix and SiC whiskers dispersed in the matrix at a volume fraction of 15-20%; the porous layer comprises a matrix and SiC whiskers dispersed in the matrix at a volume fraction of 8-12%, and the porosity of the porous layer is 30-40%; the SiC whiskers are oriented at 0°±5° along a horizontal plane in the dense layer, and are staggered at 45°±10° in the porous layer; the matrix is ​​a core-shell structure of Al2O3 coated with ZrO2, wherein the core phase is 50-100nm t-ZrO2 and the shell is 200-300nm α-Al2O3;

[0004] The surface of the SiC whisker is coated with a Fe3O4 nanolayer with a thickness of 10-30 nm, the diameter of the SiC whisker is 0.5-1 μm, and the aspect ratio of the SiC whisker is 20-50 μm.

[0005] In some embodiments, the mass ratio of the ZrO2 core to the Al2O3 shell in the matrix is ​​1:2-1:3.

[0006] In some embodiments, the thickness ratio of the dense layer to the porous layer is 1:1.2-1:1.5, and the thickness of each of the dense layer and the porous layer is 200-500 μm.

[0007] In some embodiments, the porous layer is distributed with through channels, the diameter of the through channels varies gradiently along the thickness direction, the through channels include surface channels and intermediate layer channels, the intermediate layer channels are 100-200 μm away from the surface layer, the diameter of the surface channels is 5-10 μm, and the diameter of the intermediate layer channels is 10-20 μm.

[0008] The present application also provides a method for preparing the impact-resistant ceramic as described in any one of the above items, comprising the following steps:

[0009] S10, Al2O3 coated ZrO2 core-shell powder and surface modified SiC whiskers are mixed in a mass ratio of 7:3, and an ethanol / glycerol mixed solvent is added, and a slurry is formed by adding 0.5-1wt% polyethyleneimine dispersant, wherein the volume ratio of the ethanol to the glycerol is 3:1; S20, a 3-5T pulsed magnetic field is applied in the vertical direction, and the whiskers are first horizontally oriented at a frequency of 0.1-1Hz for 30-60min, and then the magnetic field strength is gradually reduced at a rate of 5% / min; S30, 2 is injected in the process of gradually reducing the magnetic field strength. The wt% agarose solution is solidified in situ until the magnetic field strength drops to 1 T to form a green blank having a dense layer and a porous layer, the agarose solution is injected at a rate of 0.1-0.3 mL / s, and the slurry temperature is controlled at 25-35°C during injection; S40, steps S20-S30 are repeated multiple times to form alternating stacked dense layers and porous layers; S50, in an Ar / H2 mixed atmosphere, the temperature is first raised to 600°C at 1°C / min and kept for 2 hours for degreasing, and then the temperature is raised to 1350-1400°C at 5°C / min and sintered for 1 hour.

[0010] In some embodiments, in step S10, the molecular weight of the polyethyleneimine is 70,000.

[0011] In some embodiments, the direction of applying the pulsed magnetic field in step S20 forms an angle of 45° with the slurry casting direction.

[0012] In some embodiments, the H2 partial pressure is controlled to be 5-8 kPa during the sintering process in step S50, and the oxygen partial pressure in the furnace during the insulation stage is ≤10 -3 Pa.

[0013] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0014] 1. By alternately stacking dense and porous layers and regulating the arrangement of SiC whiskers, a stress wave impedance gradient is constructed, so that the impact energy can be dissipated in multiple stages through whisker pullout, crack deflection, and pore collapse.

[0015] 2. Through the core-shell structure design of Al2O3 coated ZrO2, the nano-t-ZrO2 core phase transformation toughening and the α-Al2O3 shell constraint work synergistically, improving toughness while maintaining high strength.

[0016] 3. By coating the surface of SiC whiskers with a Fe3O4 nanolayer and optimizing the aspect ratio, precise spatial orientation control of the whiskers can be achieved during magnetic field forming, forming a continuous stress transfer network.

[0017] 4. Through the design of a thickness ratio of dense layer to porous layer of 1:1.2-1:1.5 and a single layer of 200-500μm, the impact energy is dissipated in stages, avoiding stress concentration between layers and prolonging the absorption time.

[0018] 5. Through the porous layer gradient penetration channel (5-10μm in the surface layer to 10-20μm in the middle layer), the shock wave energy is absorbed in sequence according to the pore size gradient, inhibiting crack propagation and improving impact fatigue resistance.

[0019] 6. Through the coordinated control of the vertical pulse magnetic field and the 45° casting direction, the whiskers form a spiral arrangement structure, which enhances the bonding strength within the layer and disperses the propagation direction of the shock wave.

[0020] 7. By combining the ethanol / glycerol solvent system with the polyethyleneimine dispersant, the slurry has both flow stability and provides a uniform material basis for the directional arrangement of whiskers.

[0021] 8. By synchronously injecting agarose solution during gradient withdrawal, a bionic hinge structure is naturally formed at the interface between the dense layer and the porous layer, thereby improving the efficiency of interlayer stress transfer.

[0022] 9. Through the low-temperature sintering process in Ar / H2 atmosphere, the matrix is ​​densified while the decomposition of whiskers is suppressed, maintaining the integrity of the core-shell structure and the interface bonding strength.

[0023] 10. By synergistically controlling the H2 partial pressure and the oxygen partial pressure, the Fe3O4 layer can be controllably reduced to a metal interface layer, thereby enhancing the whisker-matrix bonding and preventing oxidation degradation of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0026] Figure 1 A flow chart of a method for preparing impact-resistant ceramics provided in an embodiment of the present application. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0028] Figure 1 A flow chart of a method for preparing impact-resistant ceramics provided in an embodiment of the present application is shown.

[0029] like Figure 1 As shown, the present application provides an impact-resistant ceramic, comprising alternating dense layers and porous layers, wherein the dense layer comprises a matrix and SiC whiskers dispersed in the matrix with a volume fraction of 15-20%; the porous layer comprises a matrix and SiC whiskers dispersed in the matrix with a volume fraction of 8-12%, and the porosity of the porous layer is 30-40%; the SiC whiskers are oriented at 0°±5° along a horizontal plane in the dense layer, and the SiC whiskers are staggered at 45°±10° in the porous layer; the matrix is ​​a core-shell structure of Al2O3 coated with ZrO2, wherein the core phase is 50-100nm t-ZrO2 and the shell is 200-300nm α-Al2O3;

[0030] The surface of the SiC whisker is coated with a Fe3O4 nanolayer with a thickness of 10-30 nm, the diameter of the SiC whisker is 0.5-1 μm, and the aspect ratio of the SiC whisker is 20-50 μm.

[0031] This impact-resistant ceramic creates a stress wave impedance gradient through alternating layers of dense and porous layers. Horizontally oriented SiC whiskers in the dense layer form a continuous reinforcement network, dissipating energy under impact loads through whisker pullout and crack deflection. Whiskers staggered at 45° in the porous layer work synergistically with the pore structure to absorb impact energy through elastic deformation and pore collapse. Within the core-shell Al2O3-coated ZrO2 matrix, the nanoscale t-ZrO2 core undergoes a martensitic transformation under stress to absorb energy. The α-Al2O3 shell maintains structural stability by limiting abnormal ZrO2 grain growth, while its high hardness provides fundamental load-bearing capacity.

[0032] The structural coupling of the dense layer and the porous layer enables the impact energy to be dissipated in multiple levels at the interface between the layers. The horizontally arranged whiskers increase the in-plane stiffness of the material, while the staggered whiskers hinder the cross-layer propagation of cracks. The core-shell structure improves the toughness while maintaining the high strength of the matrix through the synergistic effect of phase change toughening and interface strengthening. The gradient pores of the porous layer and the directional arrangement of the whiskers form a bionic structure, which enables the material to disperse stress concentration through a controllable layered failure mode when subjected to dynamic impact, thereby significantly improving the performance against multiple impacts.

[0033] By coating the surface of silicon carbide whiskers with a Fe3O4 nanolayer of specific thickness (10-30nm) and utilizing the magnetic response characteristics of Fe3O4, the whiskers can generate a directional magnetic moment response during the magnetic field forming process; at the same time, the whisker size design of 0.5-1μm diameter gives it suitable fluid mechanics properties in the slurry, and the geometric parameters of the aspect ratio of 20-50 not only ensure the effective rotational freedom of the whiskers under the action of the magnetic field, but also avoid the entanglement phenomenon caused by the excessively high aspect ratio, thereby realizing precise spatial orientation control of the whiskers in the matrix under magnetic field regulation. The synergistic effect of the magnetic response characteristics of the Fe3O4 nanolayer and the whisker geometric parameters enables the whiskers to quickly and stably complete directional arrangement during the magnetic field forming stage, forming a continuous stress transfer network; the matching relationship between the coating layer thickness and the whisker diameter not only maintains the mechanical properties of the whiskers themselves, but also ensures the accuracy of the orientation arrangement through the full response of the magnetic moment, and the optimized aspect ratio effectively balances the toughening effect and dispersion stability of the whiskers, ultimately constructing an enhanced phase distribution structure with multi-level energy dissipation paths in the matrix.

[0034] In some embodiments, the mass ratio of the ZrO2 core to the Al2O3 shell in the matrix is ​​1:2-1:3.

[0035] When impact-resistant ceramics are subjected to impact, the Al2O3 shell first bears the load and undergoes elastic deformation. Its high modulus effectively transfers stress to the ZrO2 core within. When the stress exceeds a critical value, the tetragonal phase (t-ZrO2) of the ZrO2 core undergoes a martensitic transformation (transforming to a monoclinic phase). The compressive stress generated by the volume expansion during this phase transformation, combined with the restraining effect of the Al2O3 shell, creates a synergistic effect. The differential deformation behavior of the core and shell phases under dynamic load can induce crack bifurcation. Simultaneously, the residual compressive stress generated by the phase transformation effectively closes microcracks, forming a multi-stage energy absorption mechanism when the material is impacted, significantly improving interlayer bond strength and resistance to multiple impacts. The 1:2-1:3 mass ratio ensures that the shell thickness effectively constrains the ZrO2 phase transformation expansion while avoiding a decrease in interfacial bond strength due to excessive shell thickness.

[0036] In some embodiments, the thickness ratio of the dense layer to the porous layer is 1:1.2-1:1.5, and the thickness of a single layer is 200-500 μm.

[0037] By limiting the thickness ratio of the dense layer to the porous layer to 1:1.2-1:1.5 and controlling the single layer thickness to 200-500μm, the material forms a staged energy dissipation mechanism when subjected to impact loads. The dense layer is thinner and has horizontally arranged whiskers, preferentially bearing the initial stress transfer of the impact, guiding the stress diffusion horizontally through the directional arrangement of the whiskers. The porous layer is thicker and has a staggered whisker arrangement. Its pore structure and whisker tilt angles are used to induce crack deflection, while absorbing the remaining energy through pore collapse. Controlling the single layer thickness within the range of 200-500μm ensures that each functional layer has sufficient structural integrity to maintain overall strength, while avoiding excessive interlayer stress gradients that could cause interfacial delamination due to excessive thickness.

[0038] Optimizing the thickness ratio ensures a gradient matching of the mechanical properties of the dense and porous layers. The dense layer rapidly disperses the impact energy peak, while the porous layer prolongs the energy absorption time through a multi-stage deformation mechanism. The synergistic effect of the two significantly enhances resistance to multiple impacts. A lower limit of 200μm ensures that each layer has independent functional space, while an upper limit of 500μm prevents excessive thickness from causing stress wave reflections and superposition. This creates a smooth stress transfer path on a macroscopic level, while the interfacial dislocation effect caused by the thickness difference between the layers further hinders crack propagation on a microscopic level.

[0039] In some embodiments, the porous layer is distributed with through channels, the diameter of the through channels varies gradiently along the thickness direction, the through channels include surface channels and intermediate layer channels, the intermediate layer channels are 100-200 μm away from the surface layer, the diameter of the surface channels is 5-10 μm, and the diameter of the intermediate layer channels is 10-20 μm.

[0040] During the initial propagation of the shock wave, the smaller pores (5-10 μm) in the surface layer absorb energy through the limited expansion of local microcracks, while the larger pores (10-20 μm) in the middle layer further dissipate stress through plastic deformation of the pore wall and crack deflection. At the same time, the continuous distribution of the through-pores guides crack propagation along the pore network, avoiding excessive stress concentration in a single direction. The gradient pore diameter matches the physical law of energy attenuation during shock wave propagation, allowing pores of different depths to participate in the energy absorption process in sequence. Through the synergistic effect of the gradient pore structure, the small pores in the surface layer preferentially disperse the impact energy and inhibit crack initiation, while the large pores in the middle layer extend the energy release time by expanding the crack propagation path. The spatial continuity of the through-pores ensures the integrity of the energy dissipation channel. This graded energy dissipation mechanism significantly improves the material's energy absorption efficiency under dynamic loads. At the same time, the gradient pore size variation avoids stress concentration caused by sudden changes in pore size, allowing the material to maintain a stable pore structure after multiple impacts, thereby enhancing its impact fatigue resistance.

[0041] The present application also provides a method for preparing the impact-resistant ceramic as described in any one of the above items, comprising the following steps:

[0042] S10. Al2O3-coated ZrO2 core-shell powder and surface-modified SiC whiskers are mixed in a mass ratio of 7:3, and an ethanol / glycerol mixed solvent is added, and a slurry formed by adding 0.5-1wt% polyethyleneimine dispersant is formed, wherein the volume ratio of ethanol to glycerol is 3:1.

[0043] S20. Apply a 3-5T pulsed magnetic field in the vertical direction, first align the whiskers horizontally at a frequency of 0.1-1 Hz for 30-60 minutes, and then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0044] S30. In the process of gradually decreasing the magnetic field strength, injecting 2 wt% agarose solution for in situ solidification until the magnetic field strength drops to 1 T, forming a blank having alternating dense layers and porous layers. The agarose solution is injected at a rate of 0.1-0.3 mL / s, and the slurry temperature is controlled at 25-35° C. during injection.

[0045] S40, repeating steps S20-S30 multiple times to form alternating stacked dense layers and porous layers.

[0046] S50. In an Ar / H2 mixed atmosphere, first heat to 600℃ at 1℃ / min and keep at this temperature for 2h for degreasing, then heat to 1350-1400℃ at 5℃ / min and sinter for 1h.

[0047] During the slurry preparation stage, the polyethyleneimine dispersant uniformly disperses the core-shell powder and the Fe3O4-coated SiC whiskers through electrostatic repulsion, forming a stable suspension system. When a vertical pulsed magnetic field is applied, the magnetic anisotropy of the Fe3O4 coating causes the SiC whiskers to align in the horizontal plane under the action of the Lorentz force, and the pulse frequency adjusts the vibration amplitude of the whiskers to eliminate local agglomeration. During the gradient reduction of the magnetic field intensity, the decreasing magnetic field intensity causes some whiskers to deflect angularly under the action of the residual magnetic field (45° arrangement in the porous layer). Simultaneously, the injection of agarose solution triggers solvent displacement, forming a three-dimensional network structure through hydrogen bonding. The oriented whiskers are fixed in the dense layer, while the deflected whisker area forms a porous layer due to solvent evaporation. During the low-temperature sintering stage, the Ar / H2 mixed atmosphere inhibits the oxidation of Fe3O3, and the surface activation energy of the core-shell powder is reduced, prompting the densification of the Al2O3 shell at 1350-1400℃ while preserving the structural integrity of the SiC whiskers.

[0048] This process uses the synergistic effect of dynamic magnetic field regulation and solvent replacement to simultaneously construct a dense layer of oriented whisker arrangement and a porous layer with a gradient pore structure in a single molding process, avoiding the interface defects of traditional mechanical stacking; the gradient field withdrawal strategy allows the whiskers to naturally form an interlayer bonding reinforcement zone as they transition from full orientation to partial deflection, while the in-situ solidification process spontaneously forms a pore gradient through differences in solvent evaporation rates; low-temperature sintering, while ensuring the densification of the matrix, utilizes the core-shell structure to reduce the sintering temperature, effectively inhibiting the thermal decomposition of SiC whiskers and abnormal growth of matrix grains, so that the material has both high whisker orientation and a complete pore structure.

[0049] Low-speed injection allows agarose molecules to fully penetrate the gaps between the whiskers and the matrix powder, combining with the hydroxyl groups in the slurry through hydrogen bonding. When the temperature is controlled between 25 and 35°C, the gelation rate of the agarose matches the speed of magnetic field removal, preventing premature solidification of the gel network due to excessively high temperatures, which would hinder the gradient orientation of the whiskers, while also preventing localized uneven gel concentration caused by excessively low temperatures. The synergistic effect of injection rate and temperature ensures the stable formation of a continuous gradient structure throughout the pores of the porous layer.

[0050] In some embodiments, in step S10, the molecular weight of the polyethyleneimine is 70,000.

[0051] The low viscosity of ethanol promotes the initial dispersion of powder particles, while the high viscosity of propylene glycol inhibits particle sedimentation. The ratio of the two controls the shear-thinning behavior of the slurry, making the slurry both fluid and stable during tape casting. Polyethyleneimine with a molecular weight of 70,000 is adsorbed on the surface of Al2O3-coated ZrO2 core-shell powder and SiC whiskers through its long-chain structure, forming a steric hindrance effect, preventing particle agglomeration and reducing interfacial energy. At the same time, its cationic properties neutralize the negative charge on the powder surface, eliminating flocculation caused by electrostatic attraction, thereby ensuring that the core-shell powder and whiskers are evenly distributed in the slurry.

[0052] The specific volume ratio of ethanol / glycerol enables the solvent system to form a dynamic hydrogen bond network, which can not only maintain the stability of the directional arrangement of the whiskers during the magnetic field forming stage, but also guide the gradient formation of the pore structure through viscosity changes when the gradient is removed; when the molecular weight of polyethyleneimine is limited to 70,000, its chain length matches the powder particle size, which can not only fully wrap the particle surface but also avoid excessive slurry viscosity due to excessive molecular chain length, thereby reducing the rotational resistance of the whiskers during the directional arrangement stage and ensuring that the whiskers are arranged at precise angles in the dense layer and the porous layer; the synergistic effect of the dispersant and the solvent enables the slurry to achieve optimal casting performance, providing a uniform material basis for the subsequent gradient magnetic field to control the spatial distribution of the whiskers.

[0053] In some embodiments, the direction of applying the pulsed magnetic field in step S20 forms an angle of 45° with the slurry casting direction.

[0054] When the slurry is cast along a specific direction, the whiskers produce an initial orientation trend under the action of the fluid shear force, and the 45° inclined pulse magnetic field direction forms a non-orthogonal vector superposition with the casting direction, causing the whiskers to rotate in three dimensions under the action of the magnetic field torque, and finally produce axial torsion on the basis of the directional arrangement in the horizontal plane; at the same time, the intermittent action of the pulsed magnetic field allows the whiskers to fine-tune their spatial position through fluid dynamics during the magnetic field off stage, thereby achieving precise angle control of the whiskers in dynamic balance.

[0055] The 45° angle design coordinates the coupling effect of magnetic field and fluid mechanics, so that the whiskers form an arrangement structure with spiral characteristics in the dense layer. This spatial orientation can not only enhance the bonding strength within the layer through mechanical interlocking between the whiskers, but also disperse the propagation direction of the shock wave through the torsion angle; at the same time, this angle matches the preset angle of staggered arrangement of whiskers in the porous layer, ensuring that the whisker ends at the interface between the dense layer and the porous layer form a bionic hinged structure, which dissipates energy through elastic bending and interface slip of the whiskers when subjected to impact loads, thereby improving the interlayer stress transfer efficiency and anti-delamination ability.

[0056] In some embodiments, the H2 partial pressure is controlled to be 5-8 kPa during the sintering process in step S50, and the oxygen partial pressure in the furnace during the insulation stage is ≤10 -3 Pa.

[0057] The H2 partial pressure effectively reduces potential oxide impurities on the substrate surface (such as adsorbed oxygen on the Al2O3 surface) and selectively reacts with the Fe3O4 coating on the SiC whisker surface to form an Fe metal phase, enhancing the interfacial bonding between the whisker and the substrate. Furthermore, the extremely low oxygen partial pressure inhibits the oxidative decomposition of the SiC whiskers at high temperatures (SiC + O2 → SiO2 + CO) and prevents lattice instability in the ZrO2 core phase due to excessive oxygen vacancy concentration, thereby maintaining the integrity of the core-shell structure. The coordinated control of the H2 and oxygen partial pressures ensures the controlled reduction of the Fe3O4 layer on the whisker surface (forming an Fe metal interface layer to enhance bonding strength) while avoiding thermal decomposition of the SiC whiskers and abnormal oxidation of the matrix phase. Under a strongly reducing atmosphere, the oxygen vacancy concentration in the ZrO2 core phase is limited to below a critical value, ensuring effective phase transformation toughening. Meanwhile, the α-Al2O3 shell maintains crystal structural stability at low oxygen partial pressures, ultimately achieving optimized interface and microstructural protection between the matrix and reinforcement phase.

[0058] The method of the present invention will be described in detail below with reference to embodiments, comparative examples and experimental data. Example

[0059] This embodiment provides a method for preparing impact-resistant ceramics, the method comprising the following steps:

[0060] Step 1: Mix 300 mL of anhydrous ethanol and 100 mL of glycerol to form a solvent system. Add 420 g of a core-shell powder consisting of an 80 nm tetragonal zirconia core and a 250 nm α-alumina shell (core-shell mass ratio of 1:2.5), 180 g of silicon carbide whiskers (0.8 μm diameter, aspect ratio 35) coated with a 20 nm Fe₃O₄ layer, and 6 g of a 70,000 molecular weight polyethyleneimine dispersant (total mass 0.8 wt%). Mix in a planetary ball mill at 200 rpm for 2 hours to obtain a uniform slurry.

[0061] Step 2: Pour the slurry into the casting machine trough, setting the casting direction at a 45° angle to the pulsed magnetic field generator. Start a vertical 3.5T pulsed magnetic field at 0.5Hz for 40 minutes, then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0062] Step 3: When the magnetic field strength is reduced to 2T, a 2wt% agarose solution at 30°C is injected into the slurry at a rate of 0.2mL / s. The slurry temperature is maintained at 30±1°C during the injection process. At the same time, the magnetic field strength is further reduced. After the magnetic field strength is reduced to 1T, a green blank with an alternating layer structure is formed.

[0063] Step 4: Repeat steps 2 and 3 multiple times to form alternating dense layers and porous layers.

[0064] Step 5: Place the green billet in an atmosphere sintering furnace, introduce 95% Ar + 5% H2 mixed gas, control the H2 partial pressure to 6kPa, heat up to 600℃ at 1℃ / min and keep warm for 2h, then heat up to 1380℃ at 5℃ / min, and maintain the oxygen partial pressure in the furnace at 5×10 -4 Pa, sintered for 1 hour and then cooled in the furnace to obtain impact-resistant ceramics. Example

[0065] This embodiment provides a method for preparing impact-resistant ceramics, the method comprising the following steps:

[0066] Step 1: Mix 300 mL of anhydrous ethanol and 100 mL of glycerol to form a solvent system. Add 420 g of a core-shell powder consisting of an 80 nm tetragonal zirconia core and a 250 nm α-alumina shell (core-shell mass ratio of 1:2), 180 g of silicon carbide whiskers (0.5 μm diameter, aspect ratio 20) coated with a 10 nm Fe₃O₄ layer, and 6 g of a 70,000 molecular weight polyethyleneimine dispersant (total mass 0.8 wt%). Mix in a planetary ball mill at 200 rpm for 2 hours to obtain a uniform slurry.

[0067] Step 2: Pour the slurry into the casting machine trough, setting the casting direction at a 45° angle to the pulsed magnetic field generator. Start a vertical 3T pulsed magnetic field at 0.5Hz for 40 minutes, then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0068] Step 3: When the magnetic field strength is reduced to 2T, a 2wt% agarose solution at 30°C is injected into the slurry at a rate of 0.1mL / s. The slurry temperature is maintained at 30±1°C during the injection process. At the same time, the magnetic field strength is further reduced. After the magnetic field strength is reduced to 1T, a green blank with an alternating layer structure is formed.

[0069] Step 4: Repeat steps 2 and 3 multiple times to form alternating dense layers and porous layers.

[0070] Step 5: Place the green billet in an atmosphere sintering furnace, introduce 95% Ar + 5% H2 mixed gas, control the H2 partial pressure to 5kPa, heat up to 600℃ at 1℃ / min and keep it for 2h, then heat up to 1350℃ at 5℃ / min, and maintain the oxygen partial pressure in the furnace at 5×10 -4 Pa, sintered for 1 hour and then cooled in the furnace to obtain impact-resistant ceramics. Example

[0071] This embodiment provides a method for preparing impact-resistant ceramics, the method comprising the following steps:

[0072] Step 1: Mix 300 mL of anhydrous ethanol and 100 mL of glycerol to form a solvent system. Add 420 g of a core-shell powder consisting of an 80 nm tetragonal zirconia core and a 250 nm α-alumina shell (core-shell mass ratio of 1:3), 180 g of silicon carbide whiskers (1 μm diameter, aspect ratio 50) coated with a 30 nm Fe₃O₄ layer, and 6 g of a 70,000 molecular weight polyethyleneimine dispersant (total mass 0.8 wt%). Mix in a planetary ball mill at 200 rpm for 2 hours to obtain a uniform slurry.

[0073] Step 2: Pour the slurry into the casting machine trough, setting the casting direction at a 45° angle to the pulsed magnetic field generator. Start a vertical 5T pulsed magnetic field at 0.5Hz for 40 minutes, then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0074] Step 3: When the magnetic field strength is reduced to 2T, a 2wt% agarose solution at 30°C is injected into the slurry at a rate of 0.3mL / s. The slurry temperature is maintained at 30±1°C during the injection process. At the same time, the magnetic field strength is further reduced. After the magnetic field strength is reduced to 1T, a green blank with an alternating layer structure is formed.

[0075] Step 4: Repeat steps 2 and 3 multiple times to form alternating dense layers and porous layers.

[0076] Step 5: Place the green billet in an atmosphere sintering furnace, introduce 95% Ar + 5% H2 mixed gas, control the H2 partial pressure to 8 kPa, heat up to 600℃ at 1℃ / min and keep it for 2h, then heat up to 1400℃ at 5℃ / min, and maintain the oxygen partial pressure at 5×10 -4 Pa, sintered for 1 hour and then cooled in the furnace to obtain impact-resistant ceramics.

[0077] Comparative Example 1

[0078] This comparative example provides a method for preparing an impact-resistant ceramic, the method comprising the following steps:

[0079] Step 1: Mix 300 mL of anhydrous ethanol and 100 mL of glycerol to form a solvent system. Add 420 g of a core-shell powder consisting of an 80 nm tetragonal zirconia core and a 250 nm α-alumina shell (core-shell mass ratio of 1:2.5), 180 g of silicon carbide whiskers (0.8 μm diameter, aspect ratio 35), and 6 g of a 70,000 molecular weight polyethyleneimine dispersant (total mass 0.8 wt%). Mix in a planetary ball mill at 200 rpm for 2 hours to obtain a uniform slurry.

[0080] Step 2: Pour the slurry into the casting machine trough, setting the casting direction at a 45° angle to the pulsed magnetic field generator. Start a vertical 3.5T pulsed magnetic field at 0.5Hz for 40 minutes, then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0081] Step 3: When the magnetic field strength is reduced to 2T, a 2wt% agarose solution at 30°C is injected into the slurry at a rate of 0.2mL / s. The slurry temperature is maintained at 30±1°C during the injection process. At the same time, the magnetic field strength is further reduced. After the magnetic field strength is reduced to 1T, a green blank with an alternating layer structure is formed.

[0082] Step 4: Repeat steps 2 and 3 multiple times to form alternating dense layers and porous layers.

[0083] Step 5: Place the green billet in an atmosphere sintering furnace, introduce 95% Ar + 5% H2 mixed gas, control the H2 partial pressure to 6kPa, heat up to 600℃ at 1℃ / min and keep warm for 2h, then heat up to 1380℃ at 5℃ / min, and maintain the oxygen partial pressure in the furnace at 5×10 -4 Pa, sintered for 1 hour and then cooled in the furnace to obtain impact-resistant ceramics.

[0084] Comparative Example 2

[0085] This comparative example provides a method for preparing an impact-resistant ceramic, the method comprising the following steps:

[0086] Step 1: Mix 300 mL of anhydrous ethanol and 100 mL of glycerol to form a solvent system. Add 420 g of a core-shell powder consisting of an 80 nm tetragonal zirconia core and a 250 nm α-alumina shell (core-shell mass ratio of 1:2.5), 180 g of silicon carbide whiskers (0.8 μm diameter, aspect ratio 35) coated with a 20 nm Fe₃O₄ layer, and 6 g of a 70,000 molecular weight polyethyleneimine dispersant (total mass 0.8 wt%). Mix in a planetary ball mill at 200 rpm for 2 hours to obtain a uniform slurry.

[0087] Step 2: Pour the slurry into the casting machine trough, setting the casting direction at a 45° angle to the pulsed magnetic field generator. Start a vertical 2T pulsed magnetic field at 0.5Hz for 40 minutes, then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0088] Step 3: When the magnetic field strength is reduced to 1 T, maintain the magnetic field strength and inject 2 wt% agarose solution at 30°C into the slurry at a rate of 0.2 mL / s. During the injection process, the slurry temperature is maintained at 30±1°C to form a green body with an alternating layer structure.

[0089] Step 4: Repeat steps 2 and 3 multiple times to form alternating dense layers and porous layers.

[0090] Step 5: Place the green billet in an atmosphere sintering furnace, introduce 95% Ar + 5% H2 mixed gas, control the H2 partial pressure to 6kPa, heat up to 600℃ at 1℃ / min and keep warm for 2h, then heat up to 1380℃ at 5℃ / min, and maintain the oxygen partial pressure in the furnace at 5×10 -4 Pa, sintered for 1 hour and then cooled in the furnace to obtain impact-resistant ceramics.

[0091] Comparative Example 3

[0092] This comparative example provides a method for preparing an impact-resistant ceramic, the method comprising the following steps:

[0093] Step 1: Mix 300 mL of anhydrous ethanol and 100 mL of glycerol to form a solvent system. Add 420 g of a core-shell powder consisting of an 80 nm tetragonal zirconia core and a 250 nm α-alumina shell (core-shell mass ratio of 1:2.5), 180 g of silicon carbide whiskers (1.2 μm diameter, aspect ratio 35) coated with a 20 nm Fe₃O₄ layer, and 6 g of a 70,000 molecular weight polyethyleneimine dispersant (total mass 0.8 wt%). Mix in a planetary ball mill at 200 rpm for 2 hours to obtain a uniform slurry.

[0094] Step 2: Pour the slurry into the casting machine trough, setting the casting direction at a 45° angle to the pulsed magnetic field generator. Start a vertical 3.5T pulsed magnetic field at 0.5Hz for 40 minutes, then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0095] Step 3: When the magnetic field strength is reduced to 2T, a 2wt% agarose solution at 30°C is injected into the slurry at a rate of 0.2mL / s. The slurry temperature is maintained at 30±1°C during the injection process. At the same time, the magnetic field strength is further reduced. After the magnetic field strength is reduced to 1T, a green blank with an alternating layer structure is formed.

[0096] Step 4: Repeat steps 2 and 3 multiple times to form alternating dense layers and porous layers.

[0097] Step 5: Place the green billet in an atmosphere sintering furnace, introduce 95% Ar + 5% H2 mixed gas, control the H2 partial pressure to 6kPa, heat up to 600℃ at 1℃ / min and keep warm for 2h, then heat up to 1380℃ at 5℃ / min, and maintain the oxygen partial pressure in the furnace at 5×10 -4 Pa, sintered for 1 hour and then cooled in the furnace to obtain impact-resistant ceramics.

[0098] Comparative Example 4

[0099] This comparative example provides a method for preparing an impact-resistant ceramic, the method comprising the following steps:

[0100] Step 1: Mix 200 mL of anhydrous ethanol and 100 mL of glycerol to form a solvent system. Add 420 g of a core-shell powder consisting of an 80 nm tetragonal zirconia core and a 250 nm α-alumina shell (core-shell mass ratio of 1:2.5), 180 g of silicon carbide whiskers (0.8 μm diameter, aspect ratio 35) coated with a 20 nm Fe₃O₄ layer, and 6 g of a 70,000 molecular weight polyethyleneimine dispersant (total mass 0.8 wt%). Mix in a planetary ball mill at 200 rpm for 2 hours to obtain a uniform slurry.

[0101] Step 2: Pour the slurry into the casting machine trough, setting the casting direction at a 45° angle to the pulsed magnetic field generator. Start a vertical 3.5T pulsed magnetic field at 0.5Hz for 40 minutes, then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0102] Step 3: When the magnetic field strength is reduced to 2T, a 2wt% agarose solution at 30°C is injected into the slurry at a rate of 0.2mL / s. The slurry temperature is maintained at 30±1°C during the injection process. At the same time, the magnetic field strength is further reduced. After the magnetic field strength is reduced to 1T, a green blank with an alternating layer structure is formed.

[0103] Step 4: Repeat steps 2 and 3 multiple times to form alternating dense layers and porous layers.

[0104] Step 5: Place the green billet in an atmosphere sintering furnace, introduce 95% Ar + 5% H2 mixed gas, control the H2 partial pressure to 6kPa, heat up to 600℃ at 1℃ / min and keep warm for 2h, then heat up to 1380℃ at 5℃ / min, and maintain the oxygen partial pressure in the furnace at 5×10 -4 Pa, sintered for 1 hour and then cooled in the furnace to obtain impact-resistant ceramics.

[0105] Comparative Example 5

[0106] This comparative example provides a method for preparing an impact-resistant ceramic, the method comprising the following steps:

[0107] Step 1: Mix 300 mL of anhydrous ethanol and 100 mL of glycerol to form a solvent system. Add 420 g of a core-shell powder consisting of an 80 nm tetragonal zirconia core and a 250 nm α-alumina shell (core-shell mass ratio of 1:2.5), 180 g of silicon carbide whiskers (0.8 μm diameter, aspect ratio 35) coated with a 20 nm Fe₃O₄ layer, and 6 g of a 70,000 molecular weight polyethyleneimine dispersant (total mass 0.8 wt%). Mix in a planetary ball mill at 200 rpm for 2 hours to obtain a uniform slurry.

[0108] Step 2: Pour the slurry into the casting machine trough, setting the casting direction at a 45° angle to the pulsed magnetic field generator. Start a vertical 3.5T pulsed magnetic field at 0.5Hz for 40 minutes, then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0109] Step 3: When the magnetic field strength is reduced to 2T, a 2wt% agarose solution at 30°C is injected into the slurry at a rate of 0.4mL / s. The slurry temperature is maintained at 30±1°C during the injection process. At the same time, the magnetic field strength is further reduced. After the magnetic field strength is reduced to 1T, a green blank with an alternating layer structure is formed.

[0110] Step 4: Repeat steps 2 and 3 multiple times to form alternating dense layers and porous layers.

[0111] Step 5: Place the green body in an atmosphere sintering furnace, introduce 95% Ar + 5% H2 mixed gas, control the H2 partial pressure to 6kPa, heat up to 600℃ at 1℃ / min and keep warm for 2h, then heat up to 1380℃ at 5℃ / min. During the insulation stage, the oxygen partial pressure in the furnace is maintained at 5×10⁻4Pa. After sintering for 1h, cool with the furnace to obtain impact-resistant ceramics.

[0112] Comparative Example 6

[0113] This comparative example provides a method for preparing an impact-resistant ceramic, the method comprising the following steps:

[0114] Step 1: Mix 300 mL of anhydrous ethanol and 100 mL of glycerol to form a solvent system. Add 420 g of a core-shell powder consisting of an 80 nm tetragonal zirconia core and a 250 nm α-alumina shell (core-shell mass ratio of 1:2.5), 180 g of silicon carbide whiskers (0.8 μm diameter, aspect ratio 35) coated with a 20 nm Fe₃O₄ layer, and 6 g of a 70,000 molecular weight polyethyleneimine dispersant (total mass 0.8 wt%). Mix in a planetary ball mill at 200 rpm for 2 hours to obtain a uniform slurry.

[0115] Step 2: Pour the slurry into the casting machine trough, setting the casting direction at a 45° angle to the pulsed magnetic field generator. Start a vertical 3.5T pulsed magnetic field at 0.5Hz for 40 minutes, then gradually reduce the magnetic field intensity at a rate of 5% / min.

[0116] Step 3: When the magnetic field strength is reduced to 2T, a 2wt% agarose solution at 30°C is injected into the slurry at a rate of 0.2mL / s. The slurry temperature is maintained at 30±1°C during the injection process. At the same time, the magnetic field strength is further reduced. After the magnetic field strength is reduced to 1T, a green blank with an alternating layer structure is formed.

[0117] Step 4: Repeat steps 2 and 3 multiple times to form alternating dense layers and porous layers.

[0118] Step 5: Place the green billet in an atmosphere sintering furnace, introduce 95% Ar + 5% H2 mixed gas, control the H2 partial pressure to 6kPa, heat up to 600℃ at 1℃ / min and keep it for 2h, then heat up to 1450℃ at 5℃ / min, and maintain the oxygen partial pressure in the furnace at 5×10 -4 Pa, sintered for 1 hour and then cooled in the furnace to obtain impact-resistant ceramics.

[0119] Experimental methods

[0120] 1. Whisker orientation: The X-ray diffraction (XRD) pole figure analysis method was used to measure the (002) crystal plane pole density distribution and calculate the orientation factor F = 1-Δθ / 90°, where Δθ is the half-height width angle.

[0121] 2. Interlaminar shear strength: Short beam shear test (span-to-thickness ratio 4:1) was conducted using a universal testing machine with a loading rate of 0.5 mm / min.

[0122] 3. Dynamic compression strength retention rate: 10 cycles of impact (strain rate 1000s) were performed using the Hopkinson pressure bar device. -1 ), calculate the ratio of the 10th intensity to the first intensity.

[0123] 4. Whisker thermal decomposition rate: The whisker mass loss before and after sintering was determined by thermogravimetric analysis (TGA).

[0124] 5. Pore structure: Micro-CT scanning (resolution 1 μm) was used to reconstruct the pore network in three dimensions and calculate the pore gradient coefficient.

[0125] The experimental results are shown in Table 1

[0126] Table 1 Comparison of key performance indicators of the examples and comparative examples

[0127] Group Whisker orientation (dense layer) Interlaminar shear strength (MPa) Dynamic compression strength retention rate Whisker thermal decomposition rate Pore ​​gradient coefficient Example 1 87% 158 92% 2.8% 0.85 Example 2 85% 146 89% 3.1% 0.82 Example 3 84% 152 90% 3.5% 0.79 Comparative Example 1 52% 89 68% 12.5% 0.42 Comparative Example 2 63% 105 75% 4.1% 0.58 Comparative Example 3 71% 122 81% 3.8% 0.67 Comparative Example 4 78% 136 84% 3.2% 0.63 Comparative Example 5 82% 143 87% 3.0% 0.52 Comparative Example 6 85% 127 78% 18.3% 0.81

[0128] Note: Porosity gradient coefficient = surface pore size / intermediate pore size.

[0129] Experimental results analysis

[0130] In the Example group, the optimized design of the core-shell structure mass ratio of 1:2-1:3 enables the Al2O3 shell to completely encapsulate the ZrO2 core phase. Significant phase transformation toughening was observed in shear tests, with cracks deflecting when they propagate to the core-shell interface. This explains the mechanism by which the interlaminar shear strengths of Examples 1-3 all exceed 145 MPa. The synergistic effect of the Fe3O4 coating thickness of 10-30 nm on the whisker surface and the magnetic field intensity of 3-5 T results in a highly oriented arrangement of the whiskers in the dense layer (orientation degree ≥ 84%). XRD pole figures show that the (002) crystal planes are concentrated within a range of ±5°. This oriented structure effectively disperses stress through the coordinated deformation of the whiskers during dynamic impact, resulting in a dynamic compressive strength retention rate of over 89% in the Example group.

[0131] In Comparative Example 1, the whiskers without Fe3O4 coating have a lack of magnetic responsiveness and their orientation degree drops sharply to 52%, resulting in an interlayer shear strength of only 89 MPa, which verifies the necessity of magnetically controlled orientation for interface strengthening.

[0132] In comparative example 2, after the magnetic field strength was reduced to 2 T, the whisker arrangement became disordered (orientation degree 63%) and the pore gradient coefficient dropped to 0.58, indicating that the 3-5 T magnetic field strength is the critical condition for the formation of a continuous energy dissipation channel.

[0133] When comparative example 3 used whiskers with a diameter of 1.2 μm, although the orientation degree reached 71%, the stress concentration effect of the coarse whiskers caused the dynamic compression retention rate to drop to 81%, indicating that the diameter range of 0.5-1 μm is crucial for balancing the toughening effect and dispersibility.

[0134] In Comparative Example 4, when the ethanol / glycerol volume ratio was adjusted to 2:1, the slurry viscosity was too high, causing the pore gradient coefficient to drop to 0.63, demonstrating that a 3:1 solvent ratio is the optimal solution for balancing tape casting and pore control. In Comparative Example 5, when the agarose injection rate was increased to 0.4 mL / s, the pore gradient coefficient significantly deteriorated (to 0.52), indicating that an injection rate of 0.1-0.3 mL / s can precisely control the continuity of the pore structure.

[0135] When the sintering temperature of comparative example 6 was raised to 1450°C, although the whisker orientation remained at 85%, the whisker thermal decomposition rate soared to 18.3%, and the interlaminar shear strength decreased by 21%, highlighting the protective effect of low-temperature sintering on the stability of the interface phase.

[0136] In summary, the parameters in the examples, through the synergistic effects of magnetically responsive whisker design, gradient magnetic field formation, solvent system optimization, and low-temperature sintering, achieve multiple advantages in whisker orientation, interlayer bond strength, impact fatigue resistance, and structural stability. Experimental data validate the necessity of the parameter ranges in the technical solution, demonstrating that deviations from any single parameter disrupt the material's multi-level energy dissipation mechanism, leading to significant performance degradation.

[0137] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations are intended to cover non-exclusive inclusion, so that a process, method, article, or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of additional identical elements in the process, method, article, or device that includes the element.

[0138] The foregoing description is intended only to provide specific embodiments of the present invention, which will enable those skilled in the art to understand and implement the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not intended to be limited to the embodiments shown herein, but is intended to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. An impact-resistant ceramic, characterized in that: The invention comprises a dense layer and a porous layer stacked alternately, wherein the dense layer comprises a matrix and SiC whiskers dispersed in the matrix with a volume fraction of 15-20%; the porous layer comprises a matrix and SiC whiskers dispersed in the matrix with a volume fraction of 8-12%, and the porosity of the porous layer is 30-40%; the SiC whiskers are oriented at 0°±5° along a horizontal plane in the dense layer, and the SiC whiskers are staggered at 45°±10° in the porous layer; the matrix is ​​a core-shell structure of Al2O3 coated with ZrO2, wherein the core phase is 50-100nm t-ZrO2 and the shell is 200-300nm α-Al2O3; The surface of the SiC whisker is coated with a Fe3O4 nanolayer with a thickness of 10-30 nm, the diameter of the SiC whisker is 0.5-1 μm, and the aspect ratio of the SiC whisker is 20-50 μm.

2. The impact-resistant ceramic according to claim 1, characterized in that: The mass ratio of the ZrO2 core to the Al2O3 shell in the matrix is ​​1:2-1:

3.

3. The impact-resistant ceramic according to claim 1, characterized in that: The thickness ratio of the dense layer to the porous layer is 1:1.2-1:1.5, and the thickness of each layer of the dense layer and the porous layer is 200-500 μm.

4. The impact-resistant ceramic according to claim 1, characterized in that: The porous layer is distributed with through channels, including surface channels and middle channel. The middle channel is 100-200 μm away from the surface layer. The diameter of the surface channel is 5-10 μm, and the diameter of the middle channel is 10-20 μm.

5. A method for preparing the impact-resistant ceramic according to any one of claims 1 to 4, characterized in that: The following steps are involved: S10, mixing Al2O3-coated ZrO2 core-shell powder and surface-modified SiC whiskers in a mass ratio of 7:3, adding an ethanol / glycerol mixed solvent, and adding 0.5-1wt% polyethyleneimine dispersant to form a slurry, wherein the volume ratio of ethanol to glycerol is 3:1; S20, applying a 3-5T pulsed magnetic field in the vertical direction, first aligning the whiskers horizontally at a frequency of 0.1-1Hz for 30-60min, and then gradually reducing the magnetic field intensity at a rate of 5% / min; S30, injecting 2 wt % agarose solution in the process of gradually decreasing the magnetic field strength for in-situ solidification to form a green body having alternating dense layers and porous layers, until the magnetic field strength is reduced to 1 T, the agarose solution is injected at a rate of 0.1-0.3 mL / s, and the slurry temperature is controlled at 25-35° C. during injection; S40, repeating steps S20-S30 multiple times to form alternating stacked dense layers and porous layers; S50. In an Ar / H2 mixed atmosphere, first heat to 600℃ at 1℃ / min and keep at this temperature for 2h for degreasing, then heat to 1350-1400℃ at 5℃ / min and sinter for 1h.

6. The method according to claim 5, characterized in that In the step S10, the molecular weight of the polyethyleneimine is 70,000.

7. The method according to claim 5, characterized in that In the step S20, the direction of applying the pulsed magnetic field forms an angle of 45° with the slurry casting direction.

8. The method according to claim 5, characterized in that During the sintering process of step S50, the H2 partial pressure is controlled to be 5-8 kPa, and the oxygen partial pressure in the furnace during the insulation stage is ≤10 -3 Pa.

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