Nanocomposite ceramic spring and microwave sintering method thereof

Abstract

This invention provides a nano-multiphase ceramic spring, the raw materials of which include inorganic powder and molding aids; the inorganic powder includes nano-α-silicon nitride powder, nano-α-alumina powder, nano-silicon carbide powder and / or aluminum nitride powder, rare earth oxides, and zirconium oxide. The molding aids include mixed sol binder, organic additives, dispersants, and plasticizers. This invention also proposes a method for preparing the above-mentioned ceramic spring, including slurry preparation, near-net-shape forming, debinding, microwave sintering, and post-treatment steps. This invention utilizes irregularly distributed long columnar β-silicon nitride to form a complex three-dimensional interlocking structure, thereby greatly enhancing the toughness of the ceramic material. Silicon nitride and alumina, as the main materials, are inherently stable, and the grain boundary phases formed by the rare earth oxides can absorb and accommodate irradiation defects, exhibiting excellent corrosion resistance and radiation resistance. Microwave sintering with a uniform temperature field ensures high grain uniformity and improves the product yield.

Description

Technical Field

[0001] This invention relates to the field of advanced structural ceramics and precision functional components, and in particular to a nano-multiphase ceramic spring and its microwave sintering preparation method. Background Technology

[0002] As a fundamental elastic element, the performance of springs directly determines the reliability and lifespan of a system under extreme operating conditions. In existing technology, springs are mainly classified into two categories based on their materials: metal springs and ceramic springs.

[0003] Metal springs are the most commonly used type of spring. Metal atoms are bonded together, allowing them to absorb energy through plastic deformation under stress. Under overload, they bend and deform as an early warning, rarely breaking suddenly, exhibiting excellent impact and fatigue resistance. Furthermore, the manufacturing process is mature (winding, heat treatment, stamping), enabling large-scale production at a much lower material and manufacturing cost than ceramics. They also offer a complete range of specifications and flexible customization. Through material selection, wire diameter, number of turns, and structural design, a stiffness range from extremely soft to extremely hard can be achieved to meet various load and deformation requirements. However, metal materials also have certain drawbacks. For example, they have a low temperature limit: long-term operating temperatures are generally below 750℃, and creep and oxidation occur at high temperatures, leading to relaxation of elasticity. They also have poor radiation resistance: neutron irradiation causes lattice defect aggregation, leading to swelling, hardening, and embrittlement (irradiation embrittlement), seriously threatening the safety of nuclear facilities. They also have insufficient corrosion resistance: stress corrosion cracking (SCC) easily occurs in high-temperature molten salts and acidic media. Finally, their high density increases system weight, hindering lightweighting in aerospace and other fields.

[0004] In comparison, ceramic materials possess advantages such as high temperature resistance, corrosion resistance, radiation resistance, and low density, perfectly addressing the aforementioned shortcomings of metallic materials. However, ceramic materials still face some serious problems in large-scale applications. For example, they exhibit high brittleness and low fracture toughness (K). IC Typically below 5 MPa·m 1 / 2 There is a risk of "catastrophic fracture" and a lack of damage warning. At the same time, dry pressing or isostatic pressing is mostly used for molding, which makes it difficult to manufacture complex spiral structures. The sintering temperature is high and the cycle is long, resulting in coarse grains and uneven performance.

[0005] Chinese invention patent application number 2024116055474 discloses a method for fiber-reinforced silicon nitride-based ceramic springs, belonging to the field of ceramic spring technology. The method comprises the following steps: preparing a slurry, preparing a spring preform, removing the mold, and firing. The slurry preparation involves placing *Xue Li Zi* seeds and deionized water into a mixer and stirring at 55-65°C for 58 hours, then filtering to obtain pectin. A dispersant, polyacrylamide, is added to the pectin solution and stirred until homogeneous to obtain a pectin premix. Silicon nitride powder is added to the pectin premix and stirred until homogeneous to obtain a silicon nitride premix. The silicon nitride premix is ​​stirred at 35-45°C while citric acid is added. After the addition is complete, a slurry is obtained. The fiber-reinforced silicon nitride-based ceramic spring prepared by this invention exhibits good toughness, high strength, and high stiffness.

[0006] The core technology of the aforementioned invention lies in adding *Xue Li Zi* seed gum as a binder to carbon fiber bundles, resulting in a tighter sintering of the carbon fiber bundles with silicon carbide powder, thereby improving the toughness of the ceramic material. Essentially, it still utilizes the principle of carbon fiber toughening. While this method of adding organic fiber materials can improve toughness, under extreme environments such as high temperature and high radiation, the internal microstructure is rapidly damaged, leading to a significant decrease in toughness. It is difficult to improve the lack of toughness while maintaining the original advantages of high temperature resistance, corrosion resistance, and radiation resistance. Therefore, this invention aims to provide a ceramic spring that combines high toughness, excellent resistance to environmental damage, precision molding, and high reliability. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a nano-multiphase ceramic spring and its microwave sintering preparation method, which solves the problem that existing ceramic springs are difficult to combine with the advantages of high toughness, excellent resistance to environmental damage, precision molding, and high reliability.

[0008] In a first aspect, the present invention proposes a nano-multiphase ceramic spring, the raw materials of which include inorganic powder and molding aids; the inorganic powder, calculated as 100% by weight, includes a matrix phase, a reinforcing phase, and sintering and grain boundary engineering aids; the molding aids are added additionally by weight percentage based on the total mass of the inorganic powder.

[0009] The matrix phase comprises: 35%-55% nano-α-silicon nitride powder and 15%-30% nano-α-alumina powder;

[0010] The reinforcing phase includes at least one of nano-silicon carbide powder and aluminum nitride powder, with a total content of 5%-15%; when the two are compounded, the mass ratio of nano-silicon carbide powder to aluminum nitride powder is 1:1-3:1.

[0011] The sintering and grain boundary engineering aids include: 4%-12% rare earth oxides and 2%-8% zirconium oxide;

[0012] The molding aids include, by weight percentage of inorganic powder: 6%-10% mixed sol binder, 1%-3% organic additives, 0.5%-1.5% dispersant, and 0.5%-1% plasticizer.

[0013] Preferably, the nano-α-silicon nitride powder has a particle size parameter of D50=30-80nm and a purity of ≥99.9%, and the nano-α-alumina powder has a particle size parameter of D50=40-100nm and a purity of ≥99.9%.

[0014] Preferably, the rare earth oxide includes one or a mixture of Y2O3, Yb2O3, and Lu2O3.

[0015] Preferably, 3 mol% Y2O3 is added to the zirconium oxide to form a metastable tetragonal zirconium oxide t-ZrO2 with a particle size of 0.2-0.8 μm.

[0016] Preferably, the mixed sol binder comprises a composite sol of aluminum sol and silica sol, wherein the aluminum sol contains 10-20 wt% Al2O3 and the silica sol contains 20-30 wt% SiO2.

[0017] Preferably, the organic additives include polyvinyl alcohol or polyvinyl butyral, the dispersant includes ammonium polyacrylate, and the plasticizer includes polyethylene glycol.

[0018] Secondly, the present invention also proposes a microwave sintering preparation method for the above-mentioned nano-multiphase ceramic spring, comprising the following steps:

[0019] S1. Slurry preparation: Inorganic powder and molding aid are added in proportion and mixed in a mixer at a vacuum degree of -0.1 to -0.09 MPa for 3 hours to obtain a uniform slurry;

[0020] S2. Near-net-shape forming: Using one of the following methods, namely precision injection molding, controlled extrusion molding or photopolymerization 3D printing, the slurry is prepared into a blank corresponding to the shape of a spring;

[0021] S3. Degreasing: In flowing air / nitrogen, heat to 600℃ at a rate of 0.2-0.5℃ / min and hold for 2 hours to completely remove organic matter and prevent the green body from cracking.

[0022] S4. Microwave Sintering: The green blank is placed in a microwave sintering furnace and sintered in a three-stage gradient temperature rise between 1150℃ and 1600℃ under a continuously flowing ammonia decomposition atmosphere. Specifically:

[0023] α-β phase transition period: Increase temperature at 5-8℃ / min to 1150-1250℃, and hold for 1.5-2.5 h;

[0024] Liquid phase densification period: Increase temperature at 3-5℃ / min to 1320-1420℃, and hold for 2.5-3.5 h;

[0025] Grain growth and toughening period: Increase temperature by 2-3℃ / min to 1500-1600℃ and hold for 1-2 hours;

[0026] S5. Post-processing: After furnace cooling to room temperature, the end faces are then precision ground to obtain the spring products.

[0027] Furthermore, in step S1, the obtained slurry is first tested for the following parameters: solid content > 52 vol%; according to the molding method in step S2, the controllable extrusion molding feed needs to meet the requirement of viscosity < 10 Pa·s at a shear rate of 10 s⁻¹, the precision injection molding feed needs to meet the requirement of viscosity < 1 Pa·s at a shear rate of 1000 s⁻¹, and the photopolymer 3D printing photosensitive resin needs to meet the requirement of viscosity < 5 Pa·s at a shear rate of 100 s⁻¹. Only after passing these requirements can the process proceed to step S2.

[0028] Furthermore, in step S2, the specific steps are as follows:

[0029] Precision injection molding: The slurry is dehydrated and granulated to form a feed material. The injection temperature is 80-100℃ and the pressure is 60-100 MPa. This method has a short molding cycle and is suitable for mass production of high-precision springs.

[0030] Controlled extrusion molding: Using a twin-screw extruder, the slurry is continuously extruded through the screw head. The pitch is controlled by matching the traction speed with the extrusion rate. This method is suitable for springs with a large length-to-diameter ratio and uniform cross-section.

[0031] Photopolymer 3D printing: 3-5 wt% photoinitiator is added to the slurry to form a ceramic photosensitive resin, and DLP technology is used to print layer by layer, controlling the layer thickness to 25-50 μm. This method is suitable for small batches, complex internal cavities, and personalized springs. The photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide or phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0032] Furthermore, in step S3, the degreasing atmosphere is selected according to the molding process: for photocurable preforms, flowing air is used to completely decompose the photosensitive resin; for injection molded and extruded preforms, flowing nitrogen is used to avoid powder oxidation.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention uses nano-α-silicon nitride powder as raw material, which undergoes phase transformation into a columnar structure of β-silicon nitride under high-temperature sintering. The irregularly distributed long columnar β-silicon nitride forms a complex three-dimensional interlocking structure, thereby greatly enhancing the toughness of the ceramic material. Furthermore, this invention also incorporates zirconium oxide, which, through the metastable tetragonal phase (t) transforming into a stable monoclinic phase (m) under stress, inhibits crack propagation through volume expansion, energy absorption, and crack shielding. This reduces the propagation of fine cracks, forcing cracks to overcome multiple resistances during propagation, including work done by grain pull-out, energy consumption during phase transformation, and grain deflection. This undoubtedly greatly increases the fracture toughness of the material.

[0035] 2. The silicon nitride and aluminum oxide used as the main materials in this invention are inherently stable, thus exhibiting excellent corrosion resistance and radiation resistance. Furthermore, the added rare earth oxides form grain boundary phases that absorb and accommodate radiation defects, enhancing radiation resistance. In corrosive media, a dense, chemically inert Re-Al-Si-O protective film can also be formed on the surface of the ceramic material, further improving corrosion resistance. Therefore, compared to traditional ceramic springs, this invention further enhances corrosion resistance and radiation resistance.

[0036] 3. This invention uses microwave sintering, which has a uniform temperature field and can effectively suppress abnormal grain growth, thereby ensuring high grain consistency and improving product yield. The sintering process uses a reducing atmosphere to clean the powder surface, which can promote mass transfer, achieve low-temperature rapid densification, and thus improve sintering efficiency. Attached Figure Description

[0037] Figure 1 This is a process flow diagram of an embodiment of the present invention. Detailed Implementation

[0038] Example 1:

[0039] This embodiment describes a spring used in the control rod drive mechanism of a high-temperature gas-cooled reactor. The technical objectives are to meet the requirements of high temperature (>1100℃), resistance to helium corrosion, radiation resistance, and long service life.

[0040] The raw material formula is as follows:

[0041] Inorganic powder (total mass 100%): 55% nano α-Si3N4 powder, 20% nano α-Al2O3; 5% nano β-SiC; 12% Y2O3; 28% t-ZrO.

[0042] Molding aids: 8 parts mixed sol binder (for bonding), 2 parts PVA, 0.5 parts ammonium polyacrylate, and 0.5 parts polyethylene glycol.

[0043] The nano-α-silicon nitride powder has a particle size parameter of D50 = 30-80 nm and a purity ≥ 99.9%, while the nano-α-alumina powder has a particle size parameter of D50 = 40-100 nm and a purity ≥ 99.9%. Zirconia is doped with 3 mol% Y₂O₃, forming a metastable tetragonal t-ZrO₂ with a particle size of 0.2-0.8 μm. The mixed sol binder comprises a composite sol of aluminum sol and silica sol, wherein the aluminum sol contains 10 wt% Al₂O₃ and the silica sol contains 20 wt% SiO₂.

[0044] The specific process steps are as follows:

[0045] (1) Slurry preparation: Inorganic powder and molding aids were added in proportion and mixed in a mixer under a vacuum of -0.1 to -0.09 MPa for 3 hours to obtain a solid content >52 vol% and a viscosity <10 Pa·s (shear rate 10 s). -1 A uniform slurry;

[0046] (2) Near-net-shape molding: Precision injection molding is adopted. The slurry is dehydrated and granulated to form feed material. The injection temperature is 90℃ and the pressure is 80 MPa.

[0047] (3) Degreasing: In flowing air / nitrogen, the temperature is raised to 600℃ at 0.3℃ / min and kept at that temperature for 2 hours to remove organic matter and prevent cracking;

[0048] (4) Microwave sintering: The green blank is placed in a microwave sintering furnace (frequency 2.45 GHz) and sintered in a three-stage gradient heating atmosphere (75% H2 + 25% N2, dew point < -60℃) under a continuously flowing ammonia decomposition atmosphere.

[0049] α-β phase transition period: 5℃ / min to 1150℃, hold for 1.5h; H2 reduces SiO2 on the powder surface, promotes the dissolution and precipitation of α-Si3N4, and transforms it into β-Si3N4 crystal nuclei;

[0050] Liquid-phase densification period: temperature increased to 1320℃ at 3℃ / min and held for 2.5 h; Re2O3-Al2O3-SiO2 formed a liquid phase, achieving rapid densification with a relative density of 99.2%;

[0051] Grain growth and toughening period: temperature increased from 2℃ / min to 1500℃ and held for 1 h; β-Si3N4 grains preferentially grow along the (001) plane into long columnar crystals (diameter 0.2-0.6 μm, aspect ratio 5-15), which together with t-ZrO3 particles form a microstructure of "bridging-pull-out-phase transformation" synergistic toughening. The flowing atmosphere inhibits the high-temperature decomposition of Si3N4, and the weight loss rate of the product after sintering is <0.2%;

[0052] (5) Post-processing: The furnace is cooled to room temperature, and then the end face is precision ground to obtain the spring product. A multilayer metallization layer of Ti / Ni / Au (total thickness 2-10 μm) can be deposited on the end by magnetron sputtering to be compatible with welding or mechanical connection.

[0053] The spring product performance of this embodiment is as follows: density 3.26 g / cm³. 3 fracture toughness K IC =10.8 MPa·m 1 / 2 The elasticity decay in helium at 1200℃ / 1000h is <3%. After simulated irradiation (1MeV neutron, room temperature, 5dPa), the dimensions are stable and the intensity retention rate is >92%.

[0054] Example 2:

[0055] This embodiment is an active control sealing spring for turbine blade tip clearance in aero-engines. The technical objectives are to meet the requirements of 1100℃ oxidizing atmosphere, high cycle fatigue, and lightweight design.

[0056] The raw material formula is as follows:

[0057] Inorganic powders: 45% nano-α-Si3N4 powder, 24% nano-α-Al2O3; 10% nano-β-SiC; 5% nano-AlN; 8% Yb2O3; 28% t-ZrO;

[0058] Molding aids: 6 parts mixed sol-bond (for bonding), 1 part PVB, 1 part ammonium polyacrylate, and 0.8 parts polyethylene glycol.

[0059] The nano-α-silicon nitride powder has a particle size parameter of D50 = 30-80 nm and a purity ≥ 99.9%, while the nano-α-alumina powder has a particle size parameter of D50 = 40-100 nm and a purity ≥ 99.9%. Zirconia is doped with 3 mol% Y₂O₃, forming a metastable tetragonal t-ZrO₂ with a particle size of 0.2-0.8 μm. The mixed sol binder comprises a composite sol of aluminum sol and silica sol, wherein the aluminum sol contains 15 wt% Al₂O₃ and the silica sol contains 25 wt% SiO₂.

[0060] The specific process steps are as follows:

[0061] (1) Slurry preparation: Inorganic powder and molding aids were added in proportion and mixed in a mixer under a vacuum of -0.1 to -0.09 MPa for 3 hours to obtain a solid content >52 vol% and a viscosity <10 Pa·s (shear rate 10 s). -1 A uniform slurry;

[0062] (2) Near-net-shape forming: It has cooling channels inside and is formed by photopolymerization 3D printing. The slurry is mixed with 4wt% photoinitiator to form a ceramic photosensitive resin. DLP technology is used to print layer by layer, and the layer thickness is controlled to 40μm.

[0063] (3) Degreasing: In flowing air / nitrogen, the temperature is raised to 600℃ at 0.4℃ / min and kept at that temperature for 2 hours to remove organic matter and prevent cracking;

[0064] (4) Microwave sintering: The green blank is placed in a microwave sintering furnace (frequency 2.45 GHz) and sintered in a three-stage gradient heating atmosphere (75% H2 + 25% N2, dew point < -60℃) under a continuously flowing ammonia decomposition atmosphere.

[0065] α-β phase transition period: 7℃ / min to 1200℃, hold for 2h; H2 reduces SiO2 on the powder surface, promotes the dissolution and precipitation of α-Si3N4, and transforms it into β-Si3N4 crystal nuclei;

[0066] Liquid-phase densification period: Temperature is increased to 1370℃ at a rate of 4℃ / min and held for 3 hours; Re2O3-Al2O3-SiO2 forms a liquid phase, achieving rapid densification with a relative density of 99.0%;

[0067] Grain growth and toughening period: temperature increased from 2.5℃ / min to 1550℃ and held for 1.5h; β-Si3N4 grains preferentially grow along the (001) plane into long columnar crystals (diameter 0.2-0.6μm, aspect ratio 5-15), which together with t-ZrO2 particles form a microstructure of "bridging-pull-phase transformation" synergistic toughening, and the weight loss rate of the product after sintering is <0.25%.

[0068] (5) Post-processing: The furnace is cooled to room temperature, and then the end face is precision ground to obtain the spring product. A multilayer metallization layer of Ti / Ni / Au (total thickness 2-10 μm) can be deposited on the end by magnetron sputtering to be compatible with welding or mechanical connection.

[0069] The spring product performance of this embodiment is as follows: density 3.18 g / cm³ 3 Fracture toughness K IC =12.0 MPa·m 1 / 2 After 500 cycles of cyclic oxidation in air at 1100℃, the weight gain is <0.3 mg / cm³. 2 High-cycle fatigue life at room temperature (Δσ=500MPa) > 1.75*10 7 Second-rate.

[0070] Example 3:

[0071] This embodiment describes an erosion-resistant spring for the main steam valve of a supercritical power plant. The technical objective is to meet the requirements of erosion resistance under 650℃ / 30 MPa supercritical steam and resistance to water vapor corrosion.

[0072] The raw material formula is as follows:

[0073] Inorganic powders: 35 parts nano α-Si3N4 powder, 30 parts nano α-Al2O3, 15% nano AlN, 12% Lu2O3, and 8 parts t-ZrO2;

[0074] Molding aids: 10 parts mixed sol binder (for bonding), 3 parts PVA, 1.5 parts ammonium polyacrylate, and 1 part polyethylene glycol.

[0075] The nano-α-silicon nitride powder has a particle size parameter of D50 = 30-80 nm and a purity ≥ 99.9%, while the nano-α-alumina powder has a particle size parameter of D50 = 40-100 nm and a purity ≥ 99.9%. Zirconia is doped with 3 mol% Y2O3, forming a metastable tetragonal t-ZrO2 phase with a particle size of 0.2-0.8 μm. The mixed sol binder includes a composite sol of aluminum sol and silica sol, wherein the aluminum sol contains 20 wt% Al2O3 and the silica sol contains 30 wt% SiO2.

[0076] The specific process steps are as follows:

[0077] (1) Slurry preparation: Inorganic powder and molding aids were added in proportion and mixed in a mixer under a vacuum of -0.1 to -0.09 MPa for 3 hours to obtain a solid content >52 vol% and a viscosity <10 Pa·s (shear rate 10 s). -1 A uniform slurry;

[0078] (2) Near net shape: Controllable extrusion molding is adopted, using a twin-screw extruder. The slurry is continuously extruded through the screw head, and the pitch is controlled by matching the traction speed and the extrusion rate.

[0079] (3) Degreasing: In flowing air / nitrogen, the temperature is raised to 600℃ at 0.5℃ / min and kept at that temperature for 2 hours to remove organic matter and prevent cracking;

[0080] (4) Microwave sintering: The green blank is placed in a microwave sintering furnace (frequency 2.45 GHz) and sintered in a three-stage gradient heating atmosphere (75% H2 + 25% N2, dew point < -60℃) under a continuously flowing ammonia decomposition atmosphere.

[0081] α-β phase transition period: 8℃ / min to 1250℃, hold for 2.5 h; H2 reduces SiO2 on the powder surface, promotes the dissolution and precipitation of α-Si3N4, and transforms it into β-Si3N4 crystal nuclei;

[0082] Liquid-phase densification period: temperature increased to 1420℃ at 5℃ / min and held for 3.5 h; Re2O3-Al2O3-SiO2 formed a liquid phase, achieving rapid densification with a relative density of 99.3%;

[0083] Grain growth and toughening period: temperature increased from 3℃ / min to 1600℃ and held for 2 h; β-Si3N4 grains preferentially grew along the (001) plane into long columnar crystals (diameter 0.2-0.6 μm, aspect ratio 5-15), which together with t-ZrO2 particles formed a microstructure of "bridging-pull-phase transformation" synergistic toughening. The flowing atmosphere suppressed the high-temperature decomposition of Si3N4, and the weight loss rate of the product after sintering was <0.3%;

[0084] (5) Post-processing: The furnace is cooled to room temperature, and then the end face is precision ground to obtain the spring product. A multilayer metallization layer of Ti / Ni / Au (total thickness 2-10 μm) can be deposited on the end by magnetron sputtering to be compatible with welding or mechanical connection.

[0085] The spring product performance of this embodiment is as follows: Vickers hardness 16.5 GPa, fracture toughness K IC =11.0 MPa·m 1 / 2 After being exposed to water vapor at 650℃ for 5000 hours, the surface showed no peeling, and the elasticity retention rate was >95%.

[0086] Comparative Example 1 (single variable, no zirconia phase transformation toughening):

[0087] This comparative example uses the exact same raw material ratios and preparation process as Example 1, the only difference being that t-ZrO2 was not added to the formula, and the corresponding reduction in mass was proportionally added to Y2O3. The fracture toughness K of the obtained product IC =6.0 MPa·m 1 / 2 Thermal shock resistance ΔT_c=280℃.

[0088] Comparative Example 2 (Single Variable, Traditional Atmospheric Pressure Sintering):

[0089] This comparative example uses the exact same raw material ratios, slurry preparation, molding, debinding, and post-treatment steps as Example 1. The only difference is that the sintering method is conventional molybdenum wire furnace sintering at atmospheric pressure, and the sintering process is completely consistent with Example 1 (three-stage heating regime, holding time, and ammonia decomposition atmosphere). The resulting product exhibits a significant hardness gradient in its cross-section (higher at the edges and lower at the center), abnormal grain growth, large performance dispersion, and low fracture toughness K. IC =7.5 MPa·m 1 / 2 .

[0090] Comparative Example 3 (Single Variable, Micron-sized Powder):

[0091] This comparative example used the exact same raw material ratios and preparation process as Example 1, the only difference being that all inorganic powders were micron-sized (D50 = 1-2 μm). The resulting product had coarse grains (average > 1.5 μm) and a fracture toughness K1c = 6.5 MPa·m. 1 / 2 .

[0092] Comparative Example 4 (closest to existing technology):

[0093] This comparative example refers to the technical solution disclosed in Chinese Invention Patent Application No. 2024116055474. A fiber-reinforced silicon nitride-based ceramic spring was prepared according to Example 1 of that patent, with the formula and process completely following the disclosure of that patent. The fracture toughness K of the obtained product... IC =7.2MPa·m 1 / 2 The elasticity decays by more than 15% after 1000 hours in helium at 1200℃, and the intensity retention rate is less than 65% after neutron irradiation at 5 dpa.

[0094] The performance parameters of the products from Examples 1-3 and Comparative Examples 1-4, as well as conventional hot-pressed silicon nitride springs and metal springs in the prior art, were compared, and the results are shown in Table 1:

[0095]

[0096] Table 1

[0097] Table 1 Test Standard Notes:

[0098] fracture toughness K IC The test method for fracture toughness of fine ceramics, GB / T23806-2009, was adopted, using the single-sided pre-cracked beam (SEPB) method.

[0099] Thermal shock resistance ΔT_c: The test method for thermal shock resistance of fine ceramics in GB / T 16535-2008 was adopted, using the water quenching method. The critical temperature difference was the maximum temperature difference at which the sample would crack.

[0100] Resistance to molten salt corrosion: Static immersion in 900℃ FLiNaK ternary molten salt (LiF:NaF:KF=46.5:11.5:42mol%) for 1000h;

[0101] Neutron irradiation resistance: room temperature, 1 MeV neutron irradiation, cumulative dose of 5 dpa;

[0102] High cycle fatigue life: GB / T 3075-2008 Metallic materials—Fatigue testing—Axial force control method—Stress ratio R=-1;

[0103] Energy consumption comparison: The comprehensive power consumption of sintering ceramic products per unit volume is based on 120 kWh / kg for traditional hot pressing sintering.

[0104] As can be seen from Table 1, the embodiments of the present invention have an absolute advantage over the prior art and comparative examples in terms of fracture toughness, maximum operating temperature, thermal shock resistance, resistance to molten salt corrosion, resistance to neutron irradiation, high-cycle fatigue life, and preparation energy consumption and cycle time, which fully demonstrates the technical superiority of the present invention.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A nano-composite ceramic spring, characterized in that: The raw materials include inorganic powder and molding aids; the inorganic powder, calculated as 100% by weight, includes a matrix phase, a reinforcing phase, and sintering and grain boundary engineering aids; the molding aids are added additionally by weight percentage based on the total mass of the inorganic powder. The matrix phase comprises: 35%-55% nano-α-silicon nitride powder and 15%-30% nano-α-alumina powder; The reinforcing phase includes at least one of nano-silicon carbide powder and aluminum nitride powder, with a total content of 5%-15%; when the two are compounded, the mass ratio of nano-silicon carbide powder to aluminum nitride powder is 1:1-3:

1. The sintering and grain boundary engineering aids include: 4%-12% rare earth oxides and 2%-8% zirconium oxide; The molding aids include, by weight percentage of inorganic powder: 6%-10% mixed sol binder, 1%-3% organic additives, 0.5%-1.5% dispersant, and 0.5%-1% plasticizer.

2. The nanocomposite ceramic spring as described in claim 1, characterized in that: The nano-α-silicon nitride powder has a particle size parameter of D50=30-80nm and a purity ≥99.9%, and the nano-α-alumina powder has a particle size parameter of D50=40-100nm and a purity ≥99.9%.

3. The nanocomposite ceramic spring as described in claim 1, characterized in that: The rare earth oxides include one or more of Y2O3, Yb2O3, and Lu2O3, or a mixture thereof.

4. The nanocomposite ceramic spring as described in claim 1, characterized in that: The zirconium oxide is mixed with 3 mol% Y2O3 to form a metastable tetragonal zirconium oxide t-ZrO2 with a powder particle size of 0.2-0.8 μm.

5. The nanocomposite ceramic spring as described in claim 1, characterized in that: The mixed sol binder includes a composite sol of aluminum sol and silica sol, wherein the aluminum sol contains 10-20 wt% Al2O3 and the silica sol contains 20-30 wt% SiO2.

6. The nanocomposite ceramic spring as described in claim 1, characterized in that: The organic additives include polyvinyl alcohol or polyvinyl butyral, the dispersant includes ammonium polyacrylate, and the plasticizer includes polyethylene glycol.

7. A microwave sintering preparation method for a nano-multiphase ceramic spring as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Slurry preparation: Inorganic powder and molding aid are added in proportion and mixed in a mixer at a vacuum degree of -0.1 to -0.09 MPa for 3 hours to obtain a uniform slurry; S2. Near-net-shape forming: Using one of the following methods, namely precision injection molding, controlled extrusion molding or photopolymerization 3D printing, the slurry is prepared into a blank corresponding to the shape of a spring; S3. Degreasing: In flowing air / nitrogen, heat to 600℃ at a rate of 0.2-0.5℃ / min and hold for 2 hours to completely remove organic matter and prevent the green body from cracking. S4. Microwave Sintering: The green blank is placed in a microwave sintering furnace and sintered in a three-stage gradient temperature rise between 1150℃ and 1600℃ under a continuously flowing ammonia decomposition atmosphere. Specifically: α-β phase transition period: Increase temperature at 5-8℃ / min to 1150-1250℃, and hold for 1.5-2.5 h; Liquid phase densification period: Increase temperature at 3-5℃ / min to 1320-1420℃, and hold for 2.5-3.5 h; Grain growth and toughening period: Increase temperature by 2-3℃ / min to 1500-1600℃ and hold for 1-2 hours; S5. Post-processing: After furnace cooling to room temperature, the end faces are then precision ground to obtain the spring products.

8. The microwave sintering preparation method according to claim 7, characterized in that, In step S1, the obtained slurry is first tested for the following parameters: solid content > 52 vol%; according to the molding method in step S2, the controllable extrusion molding feed needs to meet the requirement of viscosity < 10 Pa·s at a shear rate of 10 s⁻¹, the precision injection molding feed needs to meet the requirement of viscosity < 1 Pa·s at a shear rate of 1000 s⁻¹, and the photopolymer 3D printing photosensitive resin needs to meet the requirement of viscosity < 5 Pa·s at a shear rate of 100 s⁻¹. Only after passing the test can the slurry proceed to step S2.

9. The microwave sintering preparation method according to claim 7, characterized in that, In step S2, the specific steps are as follows: Precision injection molding: The slurry is dehydrated and granulated to form a feed material. The injection temperature is 80-100℃ and the pressure is 60-100 MPa. This method has a short molding cycle and is suitable for mass production of high-precision springs. Controlled extrusion molding: Using a twin-screw extruder, the slurry is continuously extruded through the screw head. The pitch is controlled by matching the traction speed with the extrusion rate. This method is suitable for springs with a large length-to-diameter ratio and uniform cross-section. Photopolymer 3D printing: 3-5wt% photoinitiator is added to the slurry to form a ceramic photosensitive resin, and DLP technology is used to print layer by layer, controlling the layer thickness to 25-50μm. This method is suitable for small batches, complex internal cavities, and personalized springs.

10. The microwave sintering preparation method according to claim 7, characterized in that: In step S3, the degreasing atmosphere is selected according to the molding process: for photocurable preforms, flowing air is used to completely decompose the photosensitive resin; for injection molded and extruded preforms, flowing nitrogen is used to avoid powder oxidation.

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