An ultra-high performance aluminum nitride ceramic and a method of manufacturing the same

Abstract

The application discloses an ultrahigh-performance aluminum nitride ceramic and a preparation method thereof, and relates to the technical field of ceramic materials.The preparation method comprises the following steps: mixing coarse powder and fine powder alpha-AlN powder with different D50, adding the mixture into ethanol, and adding a silane coupling agent to perform in-situ surface modification; adding a bifunctional composite additive to the modified powder, performing ball milling, and drying to obtain mixed powder material, wherein the bifunctional composite additive comprises YbF3, ScF3 and beta-SiC nanowhiskers; performing debinding after shaping the mixed powder material; performing two-step atmosphere sintering and low-temperature hot isostatic pressing on the debound green body to obtain the ultrahigh-performance aluminum nitride ceramic; and the application realizes the synchronous improvement of the thermal conductivity and the bending strength of the aluminum nitride ceramic by designing a four-in-one collaborative preparation system of "powder bimodal grading + bifunctional composite additive + two-step atmosphere sintering + low-temperature hot isostatic pressing", and meanwhile, the application has excellent comprehensive performance and high reliability.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, specifically to an ultra-high performance aluminum nitride ceramic and its preparation method. Background Technology

[0002] Aluminum nitride (AlN) ceramics possess high theoretical thermal conductivity, low dielectric constant, a thermal expansion coefficient matching that of silicon, and excellent high-temperature stability, making them a core heat dissipation and insulation substrate for the third-generation semiconductor industry. Furthermore, the high hardness, wear resistance, corrosion resistance, high thermal conductivity, and strength of aluminum nitride ceramics make them ideal materials for manufacturing special ceramic products such as ceramic valves and ceramic cylinder valve plates. Simultaneously, aluminum nitride ceramics are non-toxic, high-purity, and possess good chemical stability, making them a high-performance, green, and special refractory ceramic. These properties give aluminum nitride ceramics broad application prospects in high-temperature refractory components, electronic packaging, semiconductor manufacturing, and optical devices.

[0003] However, the high thermal conductivity and high strength of aluminum nitride ceramics are negatively correlated and cannot be improved synergistically. This is mainly reflected in the following aspects: 1. To achieve high thermal conductivity, high-temperature long-time sintering is required to promote sufficient grain growth, reduce the number of grain boundaries, eliminate lattice oxygen defects, and reduce phonon scattering. However, grain coarsening leads to a decrease in grain boundary bonding force, easy crack propagation, and bending strength generally below 400 MPa, which cannot meet the mechanical reliability requirements under harsh working conditions. 2. To achieve high strength, grain refinement and second-phase toughening are required to suppress grain growth and obtain a fine-grained structure with an average grain size of <3 μm. However, a large number of grain boundaries will form severe phonon scattering, and the toughening phase will easily introduce new thermal resistance, resulting in thermal conductivity generally below 200 W / (m·K), which cannot meet the heat dissipation requirements of ultra-high power devices.

[0004] In existing technologies, traditional oxide additive systems (such as Y₂O₃) form a large amount of low thermal conductivity Y-Al-O grain boundary phases (YAG phase thermal conductivity is only 9 W / (m·K)), which not only fails to achieve deep deoxidation of the crystal lattice but also significantly increases grain boundary thermal resistance, with a thermal conductivity upper limit of only 220 W / (m·K). Existing toughening methods (such as ZrO₂ and Al₂O₃ second phases) will form a thermal conductivity mismatch with AlN, introducing strong phonon scattering, and the thermal conductivity will decrease by more than 30%, making it impossible to balance thermal conductivity and mechanical properties.

[0005] It is evident that existing technologies lack a mature industrial-scale solution to reliably achieve the dual high performance indicators of "thermal conductivity ≥250 W / (m·K) and flexural strength ≥500 MPa," indicating a clear technological gap. Therefore, developing a method for preparing aluminum nitride ceramics with both ultra-high thermal conductivity and ultra-high flexural strength has significant technological value and application prospects. Summary of the Invention

[0006] This invention aims to address the technical problem of lacking a mature industrial solution to stably achieve the dual high performance indicators of aluminum nitride ceramics: thermal conductivity ≥250W / (m·K) and flexural strength ≥500MPa. The goal is to provide an ultra-high performance aluminum nitride ceramic and its preparation method. By designing a four-in-one synergistic preparation system of "bimodal powder gradation + bifunctional composite additives + two-step atmosphere sintering + low-temperature hot isostatic pressing," the thermal conductivity and flexural strength of aluminum nitride ceramics are simultaneously improved. Furthermore, the ceramic exhibits excellent overall performance and high reliability.

[0007] This invention is achieved through the following technical solution:

[0008] The first objective of this invention is to provide a method for preparing ultra-high performance aluminum nitride ceramics, comprising:

[0009] α-AlN powders of different D50 coarse and fine powders were mixed, added to ethanol, and silane coupling agents were added for in-situ surface modification.

[0010] The bifunctional composite additives added to the modified powder are ball-milled and dried to obtain a mixed powder. The bifunctional composite additives include YbF3, ScF3 and β-SiC nanocrystals.

[0011] The mixed powder is degreased after being shaped;

[0012] The degreased green body is subjected to two-step atmosphere sintering and low-temperature hot isostatic pressing to obtain ultra-high performance aluminum nitride ceramics.

[0013] The α-AlN powder of the present invention adopts a bimodal gradation, with coarse powder as a thermally conductive skeleton and fine powder as a filler phase. This is a necessary condition for high density and low lattice oxygen preconditioning. The gradation powder is modified in situ on the surface using a silane coupling agent to form a monolayer coating on the surface of the AlN powder, which isolates oxygen erosion and improves the powder dispersibility and sintering activity.

[0014] This invention incorporates a bifunctional composite additive system into the powder, wherein YbF3 and ScF3 are deep deoxidation and sintering aid components. YbF3 reacts with Al2O3 on the AlN surface to generate a low-melting-point Yb-Al-OF liquid phase, promoting densification. - It can extract oxygen impurities from the AlN lattice, generating volatile AlF3 which is then discharged, achieving deep lattice deoxygenation; Sc 3+ With Al 3+With highly matched ionic radii, it can dissolve into the AlN lattice to suppress oxygen impurity solid solution, while refining grains and preventing abnormal grain growth. β-SiC nanowhiskers are grain boundary strengthening and toughening components with diameters of 50~100nm and aspect ratios of 10:1~20:1. SiC and AlN form an infinite solid solution system, and their thermal conductivity is highly matched with AlN, without introducing additional phonon scattering. At the same time, the whiskers are uniformly distributed at the AlN grain boundaries, achieving grain boundary pinning to suppress abnormal grain growth. Toughening is achieved through whisker pull-out and crack bridging effects, significantly improving bending strength.

[0015] This invention employs a two-step atmosphere sintering process to rapidly densify the green body at high temperatures, achieving a density of ≥97%. It also regulates grain size to suppress abnormal grain growth. Furthermore, it combines this with low-temperature hot isostatic pressing to further eliminate residual closed pores after sintering, increasing the density to over 99.5% without causing grain coarsening. This further optimizes grain boundary bonding and simultaneously improves thermal conductivity and flexural strength.

[0016] In summary, this invention, through the design of a four-in-one synergistic preparation system of "powder bimodal gradation + bifunctional composite additives + two-step atmosphere sintering + low-temperature hot isostatic pressing," achieves simultaneous control of four key elements—low lattice oxygen, fine grain homogenization, near-clean thin grain boundaries, and full density—through the synergistic effect across the entire chain from powder structure to additive components, grain boundary regulation, and sintering regime. This fundamentally reduces phonon scattering and enhances grain boundary mechanical properties, simultaneously achieving high thermal conductivity (≥250 W / (m·K)) and flexural strength (≥500 MPa) in aluminum nitride ceramics. Furthermore, it exhibits excellent overall performance: density ≥99.5%, breakdown strength ≥20 kV / mm, and insulation resistance ≥10... 16 Ω·cm, coefficient of thermal expansion <4.5×10 -6 / K is fully compatible with Si and SiC semiconductor materials and is suitable for use in extreme conditions. It has high reliability: after 1000 cycles of thermal cycling from -55℃ to 150℃, the performance degradation is less than 2%. After 1000 hours of high temperature and humidity testing at 85℃, there is no hydrolysis, and the insulation retention rate is ≥85%, while the thermal conductivity retention rate and strength retention rate are both greater than 90%. It is suitable for harsh scenarios such as new energy vehicles, aerospace, and outdoor base stations.

[0017] Furthermore, the D50 of coarse α-AlN powder is 2.0~3.0 μm, and the D50 of fine α-AlN powder is 0.3~0.5 μm.

[0018] Furthermore, the mass ratio of coarse powder to fine powder of α-AlN is (7:3) to (8:2).

[0019] Furthermore, the amount of silane coupling agent added is 0.1~0.3 wt% of the total mass of α-AlN powder.

[0020] Furthermore, YbF3 and ScF3 are compounded in a mass ratio of (3:1) to (5:1), and the total amount of both added is 0.8 to 1.5 wt% of the total mass of α-AlN powder.

[0021] Furthermore, the amount of β-SiC nanocrystals added is 0.2~0.3wt% of the total mass of α-AlN powder.

[0022] Furthermore, the β-SiC nanocrystals are surface-hydroxylated β-SiC nanocrystals, and the hydroxylation modification is performed using a mixed acid oxidation reflux method, the steps of which include:

[0023] The native β-SiC nanocrystals were added to anhydrous ethanol and ultrasonically dispersed to remove surface organic impurities and loose aggregates. After centrifugation and drying, purified whiskers were obtained.

[0024] The purified whiskers were added to a mixed acid system of concentrated sulfuric acid and concentrated nitric acid, and stirred until the whiskers were fully dispersed. The mixture was then stirred and refluxed at a constant temperature of 110-130℃ for 2-4 hours.

[0025] After the reaction was completed, the mixture was naturally cooled to room temperature. The reaction solution was then centrifuged to obtain a precipitate, which was dried to obtain surface-hydroxylated β-SiC nanocrystals.

[0026] In this invention, surface hydroxylation of β-SiC nanocrystals is a necessary pretreatment step before whisker feeding. The core of this process is the introduction of high-density active silanol groups (≡Si-OH) onto the whisker surface through controlled oxidative etching. This addresses the problems of strong chemical inertness of native SiC whisker surfaces, easy agglomeration and entanglement in slurries, and weak interfacial bonding with the AlN matrix / fluoride liquid phase. It is a crucial prerequisite for ensuring uniform dispersion of whiskers and fully realizing the "non-destructive toughening" effect. Hydroxylation of SiC whiskers is a conventional technique for surface modification of nano-inorganic materials, and any existing method can be used for the surface hydroxylation modification of β-SiC nanocrystals. This invention employs a mixed acid oxidation reflux method for modification.

[0027] Furthermore, the two-step atmosphere sintering is carried out under nitrogen protection, during which the green body is embedded in BN powder. The two-step atmosphere sintering includes:

[0028] High-temperature rapid densification sintering: heat from room temperature to 1780~1820℃ and hold for 1~2 hours;

[0029] Low-temperature grain-controlled sintering: After the previous holding step is completed, the temperature is lowered to 1680~1720℃, held for 4~6 hours, and then cooled to room temperature with the furnace.

[0030] In the two-step atmosphere sintering of this invention, the first step is high-temperature rapid densification sintering, which rapidly fills the pores with a low-melting-point liquid phase to achieve a green body density of ≥97% and a closed porosity of ≤2%, while simultaneously completing deep deoxidation of the crystal lattice, transferring oxygen impurities from the crystal lattice to the grain boundary phase. The second step is low-temperature grain control sintering, which inhibits abnormal grain growth and precisely controls the average grain size to 3~5μm, while promoting the spheroidization and volatilization of the grain boundary phase, reducing the content of the grain boundary phase, and forming a thin and continuous grain boundary structure.

[0031] Furthermore, the low-temperature hot isostatic pressing includes:

[0032] The sintered green blank is placed in a hot isostatic pressing furnace and held at 1600~1650℃ and 180~200MPa pressure for 2~3 hours with high-purity nitrogen as the pressure medium. The ultra-high performance aluminum nitride ceramic is then obtained by cooling in the furnace.

[0033] The second objective of this invention is to provide an ultra-high performance aluminum nitride ceramic, prepared by the aforementioned method.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] 1. This invention designs a four-in-one synergistic preparation system of "powder bimodal gradation + bifunctional composite additive + two-step atmosphere sintering + low-temperature hot isostatic pressing". It achieves full-chain synergy from powder structure to additive components to grain boundary control to sintering regime, and realizes simultaneous control of four key elements: low lattice oxygen, fine grain homogenization, near-clean thin grain boundaries, and full density. It reduces phonon scattering and enhances grain boundary mechanical properties from the source. At the same time, it achieves high thermal conductivity ≥250W / (m·K) and flexural strength ≥500MPa for aluminum nitride ceramics. The thermal conductivity can reach 278W / (m·K) and flexural strength 555MPa, which far exceeds the level of existing technology.

[0036] 2. The aluminum nitride ceramics prepared by this method exhibit excellent overall properties: density ≥99.5%, breakdown strength ≥20kV / mm, and insulation resistance ≥10 kV / mm. 16 Ω·cm, coefficient of thermal expansion <4.5×10 -6 / K is fully compatible with Si and SiC semiconductor materials and is suitable for use in extreme operating conditions.

[0037] 3. The aluminum nitride ceramics prepared by this method have high reliability: after 1000 cycles of thermal cycling from -55℃ to 150℃, the performance degradation is <2%; after 1000 hours of high temperature and humidity testing at double 85, there is no hydrolysis, the insulation retention rate is ≥85%, and the thermal conductivity retention rate and strength retention rate are both greater than 90%, making them suitable for harsh scenarios such as new energy vehicles, aerospace, and outdoor base stations. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0039] Figure 1 This is a SEM image of the cross-section of the ultra-high performance aluminum nitride ceramic of this invention. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0041] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0042] The "scope" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude end values, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0044] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0045] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other substances not listed may also be included, or that only the listed substances may be included.

[0046] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0047] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0048] It should be noted that, unless otherwise specified, the experimental methods used in the embodiments are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0049] Example 1

[0050] A method for preparing ultra-high performance aluminum nitride ceramics includes the following steps:

[0051] (1) Powder gradation and modification

[0052] Bimodal gradation of powder: Two types of ultra-high purity α-AlN powder were mixed at a mass ratio of 7.5:2.5. The coarse powder had a median particle size D50 of 2.5 μm, an oxygen content of 0.12 wt%, an α-phase content ≥99.5%, and a sphericity ≥0.9; the fine powder had a median particle size D50 of 0.4 μm, an oxygen content of 0.18 wt%, and an α-phase content ≥99.2%, serving as a filler phase. The tap density of the mixed powder was ≥1.8 g / cm³. 3 .

[0053] In-situ surface modification: The graded powder was added to anhydrous ethanol and ultrasonically dispersed for 30 min under nitrogen protection. Then, 0.2 wt% of silane coupling agent KH550 was added and stirred in a water bath at 50°C for 2 h.

[0054] (2) Compound addition of dual-function composite adjuvant system

[0055] In the modified AlN powder, 1.2 wt% of a composite additive was added, including 1.0 wt% of a deep deoxidation and sintering aid component (YbF3:ScF3=4:1) and 0.2 wt% of a grain boundary strengthening and toughening component (β-SiC nanocrystals). The mixture was ball-milled for 10 hours under nitrogen protection at a ball-to-powder ratio of 5:1. The ball milling media was high-purity AlN balls to avoid introducing impurities. After ball milling, the slurry was dried by rotary evaporation and passed through a 200-mesh sieve to obtain a mixed powder.

[0056] The specific modification steps for surface hydroxylation modification of β-SiC nanocrystals are as follows:

[0057] Whisker purification pretreatment: Native β-SiC nano whiskers were added to anhydrous ethanol at a solid-liquid ratio of 1g:10mL and ultrasonically dispersed for 20min under nitrogen protection to remove surface organic impurities and loose aggregates; after centrifugation, the precipitate was collected and dried in a vacuum drying oven at 100℃ for 6h to obtain purified whiskers.

[0058] Oxidative hydroxylation with mixed acid: The purified whiskers were added to a strong oxidizing mixed acid system of concentrated sulfuric acid (98wt%) and concentrated nitric acid (68wt%) in a solid-liquid ratio of 1g:12mL, and mechanically stirred until the whiskers were fully dispersed. The mixture was then transferred to an oil bath reaction apparatus with reflux condenser and stirred at 120℃ for 2-4 hours.

[0059] Post-processing purification and drying: After the reaction is completed, heating is stopped and the mixture is allowed to cool naturally to room temperature. The reaction solution is then slowly injected into 10 times its volume of deionized water for dilution. Subsequently, the mixture is centrifuged at 8000 r / min and repeatedly washed and centrifuged with deionized water until the pH of the supernatant is neutral (6.5~7.5) to completely remove residual acid radicals. The lower precipitate is collected and dried in a vacuum drying oven at 90℃ for 10 h. After light grinding, the surface hydroxylated β-SiC nanocrystals are obtained.

[0060] (3) Shaping and segmented degreasing

[0061] Molding: The mixed powder is first dry-pressed at 120MPa and held for 30s to obtain a green body; then it is cold isostatically pressed at 250MPa and held for 90s to obtain a ceramic green body with a density of 2.23g / cm³. 3 .

[0062] Segmented degreasing: The green billet is placed in a high-purity nitrogen atmosphere furnace for segmented degreasing, with a nitrogen flow rate of 1.0 L / min throughout the process to prevent oxidation of the green billet: room temperature to 300℃, heating rate 1℃ / min, holding for 30 min; 300~600℃, heating rate 0.5℃ / min, holding for 60 min; 600~800℃, heating rate 2℃ / min, holding for 30 min.

[0063] (4) Two-step atmosphere sintering

[0064] The nitrogen purity throughout the process is ≥99.999%. During sintering, the green body is embedded in high-purity BN powder for protection. Specific steps:

[0065] Step 1: High-Temperature Rapid Densification Sintering: The degreased green body is placed in a high-purity nitrogen atmosphere sintering furnace for atmospheric pressure sintering. The heating rate is 5℃ / min from room temperature to 1200℃; the heating rate is 3℃ / min from 1200℃ to 1800℃, and the holding time is 1.5h. In this stage, the low-melting-point liquid phase rapidly fills the pores, achieving a green body density of ≥97% and a closed porosity of ≤2%. At the same time, deep deoxidation of the crystal lattice is completed, transferring oxygen impurities from the crystal lattice to the grain boundary phase.

[0066] Step 2, Low-Temperature Grain Control Sintering: After the first holding step, the temperature is lowered to 1700℃ at a rate of 2℃ / min and held for 5 hours. Then, the temperature is lowered to 1200℃ at a rate of 3℃ / min and cooled to room temperature in the furnace. This stage inhibits abnormal grain growth, precisely controlling the average grain size to 3~5μm, while promoting the spheroidization and volatilization of grain boundary phases, reducing the content of grain boundary phases, and forming a thin and continuous grain boundary structure.

[0067] (5) Post-treatment of low-temperature hot isostatic pressing (HIP)

[0068] The sintered green blank is placed in a hot isostatic pressing furnace and held at 1600℃ and 180MPa pressure for 3 hours using high-purity nitrogen as the pressure medium, followed by furnace cooling to obtain the finished product. This stage eliminates residual closed pores after sintering, increasing the density to over 99.5% without causing grain coarsening, further optimizing grain boundary bonding, and simultaneously improving thermal conductivity and flexural strength. The product SEM image is shown below. Figure 1 As shown.

[0069] Example 2

[0070] The difference between this embodiment and Embodiment 1 is that:

[0071] 1. Powder gradation: coarse powder to fine powder mass ratio 8:2;

[0072] 2. Composite additives: Total addition amount 1.5wt%, including 1.25wt% deoxidizing component and 0.25wt% SiC whiskers;

[0073] 3. Sintering process: First step: hold at 1820℃ for 1 hour; second step: hold at 1720℃ for 4 hours.

[0074] 4. HIP process: 1650℃, 200MPa heat treatment for 2 hours.

[0075] Example 3

[0076] The difference between this embodiment and Embodiment 1 is that:

[0077] 1. Powder gradation: coarse powder to fine powder mass ratio 7:3;

[0078] 2. Composite additives: Total addition amount 1.0 wt%, including 0.8 wt% deoxidizing component and 0.2 wt% SiC whiskers;

[0079] 3. Sintering process: First step: hold at 1780℃ for 2 hours; second step: hold at 1680℃ for 6 hours.

[0080] 4. HIP process: 1600℃, 180MPa heat preservation for 3 hours.

[0081] Comparative Example 1

[0082] The difference between this comparative example and Example 1 is as follows:

[0083] 1. The AlN powder has no bimodal distribution and is entirely composed of a single coarse AlN component with a D50 of 2.5μm;

[0084] 2. The bifunctional composite additive in Example 1 was replaced with a traditional Y2O3 single oxide additive, with an additional 3wt% Y2O3.

[0085] 3. Sintering was carried out at 1850℃ under normal atmospheric pressure for 6 hours, without two-step sintering or HIP.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 1 is that no β-SiC whisker toughening component is added to the bifunctional composite additive.

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 1 is that only YbF3 is added to the bifunctional composite additive, without the addition of ScF3 and β-SiC whiskers.

[0090] Comparative Example 4

[0091] The difference between this comparative example and Example 1 is that the powder was not bimodalized, only a single coarse powder was used, and all of them were single components of coarse AlN with D50=2.5μm.

[0092] Comparative Example 5

[0093] The difference between this comparative example and Example 1 is that β-SiC whiskers are replaced with an equal amount of nano-ZrO2 for toughening, resulting in a mismatch in thermal conductivity with AlN.

[0094] Comparative Example 6

[0095] The difference between this comparative example and Example 1 is that the HIP process is omitted.

[0096] Comparative Example 7

[0097] The difference between this comparative example and Example 1 is that the graded mixed powder is not subjected to in-situ surface modification.

[0098] The products prepared in the above embodiments and comparative examples were tested using the following methods:

[0099] 1. Density

[0100] Test method: Archimedes' water displacement method (immersion method), test the dry weight, saturated wet weight and suspended weight of the sample, calculate the bulk density, and the ratio of the bulk density to the theoretical density of aluminum nitride (3.26 g / cm³) is the relative density.

[0101] Reference standards: GB / T 25995-2010 "Determination of density and apparent porosity of fine ceramics"; GB / T 39975-2021 "Specified test methods for aluminum nitride ceramic substrates".

[0102] 2. Average grain size

[0103] Detection method: After the sample surface is subjected to thermal etching treatment, the microstructure image is acquired by scanning electron microscopy (SEM). At least 300 grains are counted by linear intercept method, and the average grain size is calculated. The crystal size is verified by XRD Scherrer formula.

[0104] Reference standard: SEM cut-off method is commonly used in the electronic ceramics industry. Phase analysis is based on GB / T 19501-2013 "Microbeam analysis of electron backscatter diffraction phase identification".

[0105] 3. Lattice oxygen content

[0106] Detection method: Inert gas melting-infrared absorption method. The sample is melted in a high-temperature graphite crucible under a high-purity helium atmosphere. The lattice oxygen reacts with carbon to generate CO / CO2, which is then quantitatively converted into total oxygen content by an infrared detector.

[0107] Reference standard: General method for testing oxygen content in nitride ceramics, equivalent to GB / T 32651-2016 "Determination of oxygen content in silicon nitride powder - inert gas melting infrared absorption method".

[0108] 4. Room temperature thermal conductivity

[0109] Detection method: Laser flash method (laser pulse method), the thermal diffusivity of the sample at room temperature is tested, and the thermal conductivity is calculated by combining the material density and specific heat capacity at constant pressure using the formula λ=α·ρ·Cp.

[0110] Reference standards: GB / T 22588-2008 "Measuring thermal diffusivity or thermal conductivity by flash method"; GB / T 39975-2021 "Aluminum nitride ceramic substrates" specified test methods.

[0111] 5. Bending strength

[0112] Test method: Three-point bending method at room temperature, sample size 60mm×4mm×0.5mm, span 40mm, loading rate 0.5mm / min, record the fracture load and calculate the bending strength, and test at least 5 valid samples in each group and take the average value.

[0113] Reference standard: GB / T 6569-2015 "Test method for room temperature flexural strength of fine ceramics".

[0114] 6. Breakdown strength

[0115] Test method: The power frequency AC voltage uniform step-up method is used. A cylindrical-planar electrode system is adopted. The sample is immersed in insulating oil and the voltage is uniformly stepped up at a rate of 1kV / s until breakdown. The breakdown voltage is recorded and the breakdown strength per unit thickness is calculated.

[0116] Reference standard: GB / T 1408.1-2016 "Test methods for electrical strength of insulating materials - Part 1: Tests at power frequency".

[0117] 7. Insulation resistance

[0118] Detection method: DC high resistance meter method, using a three-electrode system, apply a DC test voltage of 1000V, charge for 60s and then read the volume insulation resistance value, which is converted into volume resistivity, in Ω·cm.

[0119] Reference standard: GB / T 1410-2006 "Test methods for volume resistivity and surface resistivity of solid insulating materials"

[0120] 8. Coefficient of thermal expansion (×10) -6 / K)

[0121] Test method: Push rod thermomechanical analysis (TMA), heating from room temperature to 150℃ at a heating rate of 5℃ / min, recording the elongation of the sample with temperature, and calculating the average linear thermal expansion coefficient within this temperature range.

[0122] Reference standard: GB / T 39975-2021 "Aluminum Nitride Ceramic Substrates" specifies the method, which is equivalent to the push rod method of ISO 17562 international standard.

[0123] 9. Thermal conductivity degradation test results show that after 1000 cycles of thermal cycling from -55℃ to 150℃, the performance degradation is less than 2%.

[0124] Test method: A high and low temperature impact test chamber was used, with the low temperature set to -55℃ and the high temperature to 150℃. Each temperature was held for 30 minutes, with a transition time of ≤5 minutes, and the cycle was repeated 1000 times. The thermal conductivity index before and after the cycle was tested, and the performance degradation rate was calculated.

[0125] Reference standards: GB / T 2423.22-2012 "Environmental testing - Part 2: Test methods - Test N: Temperature change"; General test specifications for automotive-grade substrates.

[0126] 10. Withstood 1000 hours of high temperature and humidity testing at 85°C, with no hydrolysis, insulation retention rate ≥85%, and thermal conductivity and strength retention rates both greater than 90%, making it suitable for harsh scenarios such as new energy vehicles, aerospace, and outdoor base stations.

[0127] Test method: Place the sample in a constant temperature and humidity test chamber, set the temperature to 85℃±2℃ and the relative humidity to 85% RH±5% RH, and place it continuously for 1000h; test the insulation resistance, thermal conductivity, and bending strength before and after, calculate the performance retention rate, and visually inspect the surface for hydrolysis, powdering, whitening, and cracking.

[0128] Reference standards: GB / T 2423.3-2016 Environmental testing - Part 2: Test methods - Test Cab: Constant damp heat test; GB / T 2423.50-2025 Environmental testing - Part 2: Test methods - Test Cy: Constant damp heat accelerated test (Double 85 Special Accelerated Test Standard).

[0129] The test results are shown in Table 1.

[0130] Table 1. Detection data of samples prepared in the examples and comparative examples.

[0131]

[0132]

[0133] As can be seen from the data in Table 1:

[0134] Comparative Example 1 uses a traditional Y2O3 single oxide additive. When the powder has no bimodal gradation, no two-step sintering, and no HIP, the performance is significantly reduced. The thermal conductivity at room temperature is only 185 W / (m·K), which is about 32% lower than that of Example 1. At the same time, the flexural strength is only 350 MPa, which is about 35.8% lower than that of Example 1.

[0135] When the powder in Comparative Example 4 was not bimodal, the green bulk density decreased significantly, the sintering porosity increased, and the grains coarsened, resulting in a simultaneous decline in thermal and mechanical properties. This proves that bimodal gradation is a necessary condition for high density and low lattice oxygen preconditioning.

[0136] In Comparative Examples 2 and 3, the bifunctional composite additives without β-SiC whisker toughening components resulted in flexural strength dropping below 500 MPa. Comparative Example 3, with only YbF3 added as a sintering aid, lacked β-SiC whisker toughening and ScF3, leading to incomplete deoxidation, coarse grains, and further deterioration of various properties. In Comparative Example 5, replacing β-SiC whiskers with an equal amount of nano-ZrO2 for toughening resulted in a significant decrease in thermal conductivity. Therefore, a comparison of Comparative Examples 2, 3, and 5 with Example 1 shows that only the bifunctional composite additive composed of YbF3 / ScF3 and β-SiC whiskers designed in this invention can achieve the technical effect of simultaneously achieving deoxidation and non-destructive toughening.

[0137] Comparative Example 6 showed that after removing HIP, residual closed pores remained, resulting in insufficient density, weak grain boundary bonding, and a significant decrease in the two core properties of room temperature thermal conductivity and flexural strength. This demonstrates that low-temperature nitrogen HIP is also a key process for achieving ≥99.5% density and simultaneously improving both properties.

[0138] In Comparative Example 7, after omitting the surface modification of the powder, the ash underwent oxidative hydrolysis during the mixing, drying, and degreasing processes. The lattice oxygen content increased from 0.21 wt% to 0.30 wt%, the phonon scattering of lattice point defects was significantly enhanced, the thermal conductivity decreased by 13.2%, the powder dispersibility decreased, the uniformity of the green body deteriorated, and the density and flexural strength decreased simultaneously.

[0139] Finally, it should be noted that the above specific embodiments are only used to describe the purpose, technical solution, and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions or improvements can be made to some or all of the technical features. These modifications, equivalent substitutions, and improvements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing ultra-high performance aluminum nitride ceramics, characterized in that, include: α-AlN powders of different D50 coarse and fine powders were mixed, added to ethanol, and silane coupling agents were added for in-situ surface modification. The bifunctional composite additives added to the modified powder are ball-milled and dried to obtain a mixed powder. The bifunctional composite additives include YbF3, ScF3 and β-SiC nanocrystals. The mixed powder is degreased after being shaped; The degreased green body is subjected to two-step atmosphere sintering and low-temperature hot isostatic pressing to obtain ultra-high performance aluminum nitride ceramics.

2. The method for preparing ultra-high performance aluminum nitride ceramic according to claim 1, characterized in that, The D50 of coarse α-AlN powder is 2.0~3.0μm, and the D50 of fine α-AlN powder is 0.3~0.5μm.

3. The method for preparing ultra-high performance aluminum nitride ceramic according to claim 1, characterized in that, The mass ratio of coarse powder to fine powder of α-AlN is (7:3) to (8:2).

4. The method for preparing ultra-high performance aluminum nitride ceramic according to claim 1, characterized in that, The amount of silane coupling agent added is 0.1~0.3wt% of the total mass of α-AlN powder.

5. The method for preparing ultra-high performance aluminum nitride ceramic according to claim 1, characterized in that, YbF3 and ScF3 are compounded in a mass ratio of (3:1) to (5:1), and the total amount of both added is 0.8 to 1.5 wt% of the total mass of α-AlN powder.

6. The method for preparing ultra-high performance aluminum nitride ceramic according to claim 1, characterized in that, The amount of β-SiC nanocrystals added is 0.2~0.3wt% of the total mass of α-AlN powder.

7. The method for preparing ultra-high performance aluminum nitride ceramic according to claim 1, characterized in that, β-SiC nanocrystals are surface-hydroxylated β-SiC nanocrystals. The hydroxylation modification is performed using a mixed acid oxidation reflux method, and the steps include: The native β-SiC nanocrystals were added to anhydrous ethanol and ultrasonically dispersed to remove surface organic impurities and loose aggregates. After centrifugation and drying, purified whiskers were obtained. The purified whiskers were added to a mixed acid system of concentrated sulfuric acid and concentrated nitric acid, and stirred until the whiskers were fully dispersed. The mixture was then stirred and refluxed at a constant temperature of 110-130℃ for 2-4 hours. After the reaction was completed, the mixture was naturally cooled to room temperature. The reaction solution was then centrifuged to obtain a precipitate, which was dried to obtain surface-hydroxylated β-SiC nanocrystals.

8. The method for preparing ultra-high performance aluminum nitride ceramic according to claim 1, characterized in that, The two-step atmosphere sintering is carried out under nitrogen protection, during which the green body is embedded in BN powder. The two-step atmosphere sintering includes: High-temperature rapid densification sintering: heat from room temperature to 1780~1820℃ and hold for 1~2 hours; Low-temperature grain-controlled sintering: After the previous holding step is completed, the temperature is lowered to 1680~1720℃, held for 4~6 hours, and then cooled to room temperature with the furnace.

9. The method for preparing ultra-high performance aluminum nitride ceramic according to claim 1, characterized in that, The low-temperature hot isostatic pressing includes: The sintered green blank is placed in a hot isostatic pressing furnace and held at 1600~1650℃ and 180~200MPa pressure for 2~3 hours with high-purity nitrogen as the pressure medium. The ultra-high performance aluminum nitride ceramic is then obtained by cooling in the furnace.

10. An ultra-high performance aluminum nitride ceramic, characterized in that, Prepared by the method described in any one of claims 1-9.

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