Preparation method of high-strength aluminum oxide ceramic substrate

Abstract

The invention discloses a preparation method of a high-strength aluminum oxide ceramic substrate, which comprises the following steps: firstly, modifying aluminum oxide powder by a liquid phase method, and coating a layer of nano magnesium oxide on the surface of the aluminum oxide powder; then carrying out ball milling treatment on the modified powder, rare earth metal oxide, metal oxide, an organic solvent, a binder, a plasticizer and a dispersing agent together, then carrying out defoaming, tape casting, drying and laminated hot pressing to obtain a ceramic green body, and finally carrying out sintering molding in an air atmosphere to obtain the ceramic. The nano magnesium oxide active coating layer constructed in situ and the added exogenous sintering aid act together, so that uniform growth of isometric crystals is promoted, development of a small amount of dominant oriented grains is directionally induced, a composite enhanced microstructure is formed, atomic scale super-uniform distribution and optimal interface combination of the nano magnesium oxide and the exogenous sintering aid are realized, and the nano magnesium oxide / exogenous sintering aid composite material is prepared. The bending strength of the obtained alumina ceramic can reach up to 881 MPa.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramic substrate preparation, and relates to a method for preparing a high-strength alumina ceramic substrate. Background Technology

[0002] Alumina ceramic substrates are key fundamental materials in electronic components, power modules, and high-temperature structural components. Their mechanical strength is a core indicator determining the long-term stability and reliability of these devices. With the rapid development of modern electronic technology towards higher power density and higher integration, more stringent requirements are being placed on the mechanical properties of alumina ceramic substrates.

[0003] Currently, the mainstream technique for improving the mechanical properties of alumina ceramics is to optimize the microstructure by adding sintering aids. Common techniques include adding single MgO, adding rare earth oxides (such as Y₂O₃, La₂O₃, etc.), or using a physical blending system of MgO and rare earth oxides. While these methods can improve sintering performance and increase material density to some extent, they still have significant shortcomings in achieving high strength. First, traditional physical blending methods have inherent limitations. Since the sintering aids and alumina matrix are only mechanically mixed, it is difficult to achieve uniform dispersion at the microscale, easily leading to local agglomeration. This uneven distribution directly results in an uneven densification process during sintering, limited grain boundary strengthening effect, and ultimately affects the mechanical strength of the material. Second, the interaction between MgO and rare earth oxides is not fully utilized. Although theoretical studies have confirmed that these two additives have complementary effects in grain boundary regulation and densification promotion, the traditional simple mixing method makes it difficult for the two components to establish an effective interaction mechanism. During sintering, MgO tends to prematurely form a high-temperature stable phase, while rare earth oxides tend to form localized enrichment zones, significantly limiting their interaction. Furthermore, physical mixing results in weak interfacial bonding between the additives and the matrix. Studies have shown that the interfacial bonding state of additives directly affects their diffusion behavior and grain boundary segregation during sintering. The weak interfacial bonding formed by traditional mixing methods is detrimental to the additives' ability to fully exert their role in grain boundary regulation. In addition, existing technologies suffer from narrow process windows and large performance fluctuations. Due to the uneven distribution of additives, material properties are extremely sensitive to sintering process parameters, leading to poor batch stability and difficulty in meeting the stringent consistency requirements of high-end applications.

[0004] While some improved techniques exist, such as co-precipitation or sol-gel methods for preparing composite powders, these methods suffer from drawbacks such as complex processes, high costs, or difficulty in large-scale production. Therefore, developing a method for preparing alumina ceramic substrates that can achieve ultra-uniform dispersion of additives, fully leverage synergistic effects, and is simple and suitable for large-scale production has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention aims to provide a method for preparing a high-strength alumina ceramic substrate. The high-strength alumina ceramic substrate is first modified by a liquid-phase method, and then coated with a layer of nano-magnesium oxide. Subsequently, the modified powder is ball-milled with rare earth metal oxides, metal oxides, organic solvents, binders, plasticizers, and dispersants. After degassing, casting, drying, and hot-pressing, a ceramic green body is obtained, which is finally sintered in an air atmosphere. The in-situ constructed nano-magnesium oxide active coating layer of this invention, together with the added exogenous sintering aids, promotes the uniform growth of equiaxed crystals and directionally induces the development of a small number of preferentially oriented grains, forming a composite reinforced microstructure. This achieves ultra-uniform atomic-scale distribution and optimal interfacial bonding of nano-magnesium oxide, significantly improving the density and mechanical strength of the alumina ceramic at low sintering temperatures.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a high-strength alumina ceramic substrate, comprising the following steps in sequence: S1. Preparation of surface-modified alumina powder Alumina powder was placed in a magnesium salt solution with a concentration of 0.01-0.05 mol / L to obtain a suspension. The pH of the suspension was adjusted to 4-6 using dilute nitric acid with a concentration of 0.1-0.5 mol / L. The suspension was stirred at 60-80℃ for 1-2 h. The pH of the suspension was then adjusted to 9-10 using ammonia water with a concentration of 0.1-0.5 mol / L. The suspension was stirred for another 2-4 h. The resulting suspension was filtered while hot. The filter cake was repeatedly washed with deionized water until the conductivity of the filtrate was below 10 μS / cm. The filtrate was dried at 90-120℃ for 12-24 h and then calcined to obtain surface-modified alumina powder. S2. Preparation of ceramic slurry Surface-modified alumina powder, rare earth metal oxide, metal oxide, anhydrous ethanol, polyvinyl butyral, dibutyl phthalate, and triethyl phosphate were placed together in a ball mill for ball milling to obtain ceramic slurry. S3, Preparation of high-strength alumina ceramic substrate The ceramic slurry is defoamed and cast in sequence, then dried, and then hot-pressed in layers to form a ceramic green body. The hot-pressing temperature is 80°C, the pressure is 1000 psi, and the holding time is 60 min. The ceramic green body is then sintered in an air atmosphere to obtain a high-strength alumina ceramic substrate.

[0007] As a limitation of the present invention, in step S1, the solid-liquid ratio of the alumina powder to the magnesium salt solution is 1:(50-100)g / mL; the magnesium salt solution is an aqueous solution of magnesium nitrate or an aqueous solution of magnesium chloride.

[0008] As another limitation of the present invention, in step S1, the calcination temperature is 400-500℃ and the time is 2-4 h.

[0009] As a third limitation of the present invention, in step S2, the rare earth metal oxide is one or more of erbium oxide, yttrium oxide, lanthanum oxide, and cerium oxide; the metal oxide is one or more of magnesium oxide, calcium oxide, zinc oxide, and titanium oxide. As a fourth limitation of the present invention, in step S2, the mass ratio between the surface-modified alumina powder and the rare earth metal oxide and metal oxide is 100:(0.05-0.15):(0.05-0.18).

[0010] As a fifth limitation of the present invention, in step S2, the mass ratio of the surface-modified alumina powder to anhydrous ethanol, polyvinyl butyral, dibutyl phthalate, and triethyl phosphate is 100:(58-65):(7.5-8.5):(4-5.5):(2.5-3.5).

[0011] As a sixth limitation of the present invention, in step S2, the ball milling process is as follows: stainless steel balls and materials with a ball-to-material ratio of (2-4):1 are placed in a ball mill and ball milled at 300-500 rpm for 20-28 h.

[0012] As a seventh limitation of the present invention, in step S3, the drying temperature is 60-80°C and the time is 1-2 h.

[0013] As an eighth limitation of the present invention, in step S3, the sintering process is performed in the following order: (a) In the first heating stage, the temperature was increased from room temperature to 600℃ at a heating rate of 5℃ / min and held for 6 hours; (b) In the second heating stage, the temperature is increased from 600℃ to 1500-1600℃ at a heating rate of 3℃ / min, and held for 1-4 hours; (c) In the first cooling stage, the temperature is reduced from 1500-1600℃ to 1000℃ at a cooling rate of 5℃ / min, and held for 0.5-2 hours. (d) In the third heating stage, the temperature is increased from 1000℃ to 1350℃ at a heating rate of 3℃ / min, and held for 0.5-4 h. (e) In the second cooling stage, the temperature is reduced from 1350℃ to 800℃ at a cooling rate of 3℃ / min, and held for 0.5-2 h, and then cooled to room temperature with the furnace.

[0014] The sintering process of this invention affects the microstructure and properties of the alumina ceramic substrate. When the temperature is increased from room temperature to 600°C at a heating rate of 5°C / min, the organic matter in the green body is slowly decomposed and discharged, thereby forming stable pore channels in the green body before the strength decreases to avoid cracking. Holding the temperature for 6 hours ensures that all organic matter is fully and completely decomposed and removed. When the temperature is increased from 600°C to 1500-1600°C at a heating rate of 3°C / min, rapid pre-sintering and densification of the alumina powder and efficient diffusion and network framework construction of nano-magnesium oxide and exogenous sintering aid components occur, thereby initially densifying the green body and laying the microstructure foundation for subsequent grain growth control. Holding the temperature for 1-4 hours... The holding time (h) is to allow the densification reaction and the interaction between nano-magnesium oxide and exogenous sintering aids in this stage to reach equilibrium and stability. After holding at this temperature, the temperature is lowered from 1500-1600℃ to 1000℃ at a rate of 5℃ / min. During this stage, the sintering driving force is drastically reduced and some reactions stop due to the rapid temperature decrease, causing the microstructure to transition from a high-temperature non-equilibrium state to a metastable state and temporarily "freeze." Holding at this temperature for 0.5-2 h allows for the release of internal thermal stress and optimization of the grain boundary structure through grain boundary diffusion and atomic rearrangement, achieving microscopic relaxation. Then, the temperature is increased from 1000℃ to 1350℃ at a rate of 3℃ / min. This stage is for more refined grain growth control and final densification within the pre-constructed network framework of nano-magnesium oxide and exogenous sintering aids, thereby further homogenizing the grain size distribution and ultimately achieving ultra-high density. Holding at this temperature for 0.5-4 h... h is to ensure that the refining process is fully completed, forming the final composite reinforced structure of "fine-grained matrix + ordered laminated plate-like crystals". After this stage, it is necessary to cool down from 1350℃ to 800℃ at a cooling rate of 3℃ / min. During this stage, the main crystal phase structure will be stabilized and the residual stress will be initially released, so that the ceramic substrate will transition from the sintered state to the room temperature stable state. Holding at this temperature for 0.5-2h is to balance the internal and external temperatures of the substrate, prevent micro-cracks from being generated due to excessive cooling, and ensure the structural integrity of the final product. Then, it is cooled to room temperature with the furnace.

[0015] As a ninth limitation of the present invention, in step S1, the surface-modified alumina powder obtained has a nano-magnesium oxide active coating layer formed on its surface by in-situ construction; the content of the nano-magnesium oxide coating in the surface-modified alumina powder is 0.02-0.04 wt.% of the mass of the alumina powder.

[0016] This invention constructs a nano-magnesium oxide active layer in situ on the surface of alumina powder using a liquid-phase method, enabling it to preferentially interact with the matrix during the initial sintering stage. This achieves three key effects: First, it forms a Mg-O-Al chemical bonding transition interface at the atomic scale, fundamentally solving the problems of weak interfacial bonding and uneven distribution in traditional physical blending. Second, it fills the gap in the role of sintering aids in traditional processes: In traditional external addition processes, alumina is in an unassisted sintering state before the temperature reaches the effective temperature of the aids, which easily leads to rapid local particle growth and abnormal grain coarsening. However, the intrinsic coating layer of this invention can act in the early stage of heating, providing a path for mass transport and constraining grain boundary migration, thus preventing abnormal grain growth in the initial stage. Third, it regulates the anisotropic crystallographic behavior of alumina particles. At low temperatures, nano-magnesium oxide preferentially adsorbs onto high-energy crystal planes, enhancing two-dimensional mass transfer and growth kinetics, while simultaneously inhibiting normal growth on low-energy basal planes, providing a thermodynamic driving force and kinetic pathway for the development of plate-like crystal orientation.

[0017] This intrinsic activation design, combined with a unique sintering process (high-temperature pre-activation - medium-temperature control - target temperature refining), constitutes the core of low-temperature high-performance sintering. Current research indicates that when the alumina sintering temperature is ≥1500℃, the grain growth mechanism shifts from grain boundary diffusion to bulk diffusion. The sintering process of this invention actively adapts to this shift: during the high-temperature pre-activation stage (e.g., short-term 1500℃), the high efficiency of bulk diffusion is utilized to rapidly construct a uniform and enhanced diffusion network framework; subsequently, during the holding at a lower target temperature (e.g., 1350℃), the established network framework is used to achieve material migration and orderly optimization of the microstructure, avoiding the bottleneck of incomplete densification or grain coarsening caused by insufficient bulk diffusion dynamics at low temperatures.

[0018] When the added exogenous sintering aids (rare earth oxides and metal oxides) begin to take effect, their target is not the alumina surface in a state without aids or in a simple mixture, but rather an optimized interface that has been pre-activated, uniformly modified, and preliminarily oriented by the nano-magnesium oxide layer. In this stage, the three components enter a deep synergistic phase: the exogenous rare earth oxides, with their strong diffusion-promoting ability, significantly enhance the bulk diffusion rate, especially at high temperatures, injecting powerful momentum into overall densification; while the exogenous metal oxides, in conjunction with the endogenous nano-magnesium oxide already "stationed" at the interface, form ultra-high concentrations of synergistic segregation at the grain boundaries, establishing an exceptionally strong grain boundary pinning network. This network not only effectively inhibits grain boundary migration at low temperatures but also, at high temperatures when intragranular diffusion becomes the main pathway for mass transport, maintains a strong inhibitory effect on grain growth achieved through grain boundary movement through the solute dragging effect, thereby achieving grain size control across the entire temperature range.

[0019] It is within this specific kinetic window created by strong dynamic densification and ultra-strong pinning inhibition that the "orientation template" effect pre-set by the surface modification layer manifests, ultimately giving rise to a composite structure of "fine-grained matrix + ordered stacked plate-like crystals". The formation mechanism is as follows: driven by rare-earth oxides, especially under the background of rapid material flow enhanced by high-temperature bulk diffusion, the vast majority of grains are locked into fine equiaxed crystals by the strong pinning effect of superimposed internal and external magnesium oxide, spanning different diffusion mechanism stages. Furthermore, at lower sintering temperatures, a few grains in the original powder with specific crystallographic orientations and initial stacked morphologies exhibit a unique evolutionary path: their high-energy sides (facets) preferentially adsorb and enrich sintering aids due to their higher surface energy, thus achieving local eutectic composition at the interface first, forming a nanoscale transition liquid phase. This liquid phase, as a rapid material transport channel, effectively promotes lateral diffusion and epitaxial attachment of atoms along the plate surface direction, driving the two-dimensional expansion growth of the plate-like crystals. Meanwhile, the low-energy basal planes of the plate-like crystals, due to their low enrichment of sintering aids and difficulty in forming a continuous liquid phase, coupled with their inherently high atomic adhesion barriers in crystallography, strongly inhibit their growth in the thickness direction (normal). This selective distribution of sintering aids, guided by surface energy differences, combined with the constrained diffusion kinetics at lower sintering temperatures, contributes to significant anisotropy in grain growth, allowing the plate-like morphology to be preserved and further enhanced during sintering. As sintering progresses, the fully developed plate-like crystals gradually form a layered stacking structure through geometric interlocking. This structure microscopically restricts grain rotation and rearrangement. Although the thermodynamic driving force always tends to reduce the total interfacial energy of the system by spheroidizing the grains through Oswald ripening, the long-range bulk diffusion and high-curvature interface dissolution processes necessary for this transformation are extremely slow at lower sintering temperatures. Therefore, the layered structure of the plate-like crystals is ultimately preserved as a kinetically frozen metastable state. Its exhibited layered order can be viewed as a self-organizing form achieved by the system through confined grain arrangement to locally reduce interfacial energy under non-equilibrium sintering conditions. This unique composite structure of embedded, layered, plate-like crystals within a uniform, fine-grained matrix is ​​the core of the leap in mechanical properties. The uniform, fine-grained matrix provides the foundation for high strength, while the ordered, layered plate-like crystals act as "micro-nano-scale reinforcing fibers." When cracks propagate, the plate-like crystals greatly dissipate fracture energy and blunt crack tips through various mechanisms such as crack deflection, bridging, pull-out, and their own transgranular fracture. In particular, its ordered, layered configuration makes this toughening effect more synergistic and efficient in space, thereby achieving a simultaneous and significant improvement in both strength and toughness.

[0020] The above technical solution has the following advantages or beneficial effects: 1. This invention employs a liquid-phase method to construct an in-situ nano-magnesium oxide active coating layer on the surface of alumina powder. This active coating layer, through interaction with exogenous sintering aids (rare earth oxides and metal oxides), promotes the uniform growth of equiaxed crystals while directionally inducing the development of a small number of preferentially oriented grains, thereby forming a composite reinforced microstructure. This not only achieves ultra-uniform atomic-scale distribution and optimal interfacial bonding of nano-magnesium oxide and exogenous sintering aids, but also significantly improves the density and mechanical strength of alumina ceramics while maintaining a low sintering temperature. 2. The alumina ceramic substrate prepared by this invention has a maximum bulk density of 3.902 g / cm³. 3 Its bending strength can reach up to 881 MPa; 3. The preparation method of this invention is simple, the process is easy to control, and it is suitable for large-scale industrial production.

[0021] This invention is applicable to the preparation of high-strength alumina ceramic substrates. The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0022] Figure 1 This is a SEM image of the oriented microstructure of the high-strength alumina ceramic substrate prepared in Example 1 of the present invention. Figure 2 This is a macroscopic SEM image of the high-strength alumina ceramic substrate prepared in Example 1 of the present invention; Figure 3 This is a cross-sectional microstructure SEM image of the alumina ceramic substrate prepared in Comparative Example 1 of the present invention. Detailed Implementation

[0023] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0025] Example 1 This embodiment prepares a high-strength alumina ceramic substrate, and the preparation process and steps are as follows: S1. Preparation of surface-modified alumina powder 100 g of alumina powder was placed in 7 L of 0.02 mol / L magnesium nitrate aqueous solution to obtain a suspension. The pH of the suspension was adjusted to 5 using 0.3 mol / L dilute nitric acid, and stirred at 70 °C for 1.5 h. Then, the pH of the suspension was adjusted to 9.5 using 0.3 mol / L ammonia solution, and stirring was continued for 3 h. The resulting suspension was filtered while hot, and the filter cake was repeatedly washed with deionized water until the conductivity of the filtrate was below 10 μS / cm. The filter cake was dried at 90 °C for 24 h and calcined at 450 °C for 2 h to obtain surface-modified alumina powder with a surface nano-magnesium oxide coating of approximately 0.03 wt.%. S2. Preparation of ceramic slurry 100 g of surface-modified alumina powder, 0.1 g of erbium oxide, 0.1 g of magnesium oxide, 60 g of anhydrous ethanol, 8 g of polyvinyl butyral, 5 g of dibutyl phthalate, and 3 g of triethyl phosphate were ball-milled together in a ball mill. The ball milling process was as follows: stainless steel balls with a ball-to-material ratio of 3:1 and the material were placed in the ball mill and ball-milled at 400 rpm for 24 h to obtain a ceramic slurry. S3, Preparation of high-strength alumina ceramic substrate The ceramic slurry was placed in a vacuum degassing machine and degassed at a pressure of 0.8 kPa for 30 min. The degassed slurry was then poured into the hopper of a casting machine. The casting thickness was set to 500 μm, and casting was performed to obtain a wet blank. The wet blank was then ventilated and dried at 70℃ for 1.5 h in the casting machine to form a green ceramic belt. The green ceramic strip was cut into four-inch square pieces, ten layers were stacked, and placed in a hot press. The press was held at 80°C and 1000 psi (approximately 6.9 MPa) for 60 minutes to obtain a dense alumina ceramic substrate green body. The alumina ceramic substrate green was placed in a high-temperature sintering furnace and sintered in air atmosphere: first, the temperature was increased from room temperature to 600℃ at a heating rate of 5℃ / min and held for 6 h; then, the temperature was increased from 600℃ to 1500℃ at a heating rate of 3℃ / min and held for 1 h; then, the temperature was decreased from 1500℃ to 1000℃ at a cooling rate of 5℃ / min and held for 2 h; then, the temperature was increased from 1000℃ to 1350℃ at a heating rate of 3℃ / min and held for 4 h; finally, the temperature was decreased from 1350℃ to 800℃ at a cooling rate of 3℃ / min and held for 1 h, and then cooled to room temperature with the furnace to obtain a high-strength alumina ceramic substrate.

[0026] Example 2 This embodiment prepares a high-strength alumina ceramic substrate, and the preparation process and steps are as follows: S1. Preparation of surface-modified alumina powder 100 g of alumina powder was placed in 5 L of 0.05 mol / L magnesium nitrate aqueous solution to obtain a suspension. The pH of the suspension was adjusted to 4 using 0.1 mol / L dilute nitric acid, and stirred at 80 °C for 1 h. Then, the pH of the suspension was adjusted to 9 using 0.1 mol / L ammonia solution, and stirring was continued for 2 h. The resulting suspension was filtered while hot, and the filter cake was repeatedly washed with deionized water until the conductivity of the filtrate was below 10 μS / cm. The powder was dried at 100 °C for 20 h and calcined at 400 °C for 2.5 h to obtain surface-modified alumina powder with a surface nano-magnesium oxide coating of approximately 0.04 wt.%. S2. Preparation of ceramic slurry 100 g of surface-modified alumina powder, 0.15 g of yttrium oxide, 0.05 g of calcium oxide, 65 g of anhydrous ethanol, 8.5 g of polyvinyl butyral, 4 g of dibutyl phthalate, and 2.5 g of triethyl phosphate were ball-milled together in a ball mill. The ball milling process was as follows: stainless steel balls with a ball-to-material ratio of 2:1 and the material were placed in the ball mill and ball-milled at 300 rpm for 28 h to obtain a ceramic slurry. S3, Preparation of high-strength alumina ceramic substrate The ceramic slurry was placed in a vacuum degassing machine and degassed at a pressure of 0.8 kPa for 30 min. The degassed slurry was then poured into the hopper of a casting machine. The casting thickness was set to 500 μm, and casting was performed to obtain a wet blank. The wet blank was then ventilated and dried at 60℃ for 2 h in the casting machine to form a green ceramic belt. The green ceramic strip was cut into four-inch square pieces, ten layers were stacked, and placed in a hot press. The press was held at 80°C and 1000 psi (approximately 6.9 MPa) for 60 minutes to obtain a dense alumina ceramic substrate green body. The alumina ceramic substrate green was placed in a high-temperature sintering furnace and sintered in air atmosphere: first, the temperature was increased from room temperature to 600℃ at a heating rate of 5℃ / min and held for 6 h; then, the temperature was increased from 600℃ to 1550℃ at a heating rate of 3℃ / min and held for 4 h; then, the temperature was decreased from 1550℃ to 1000℃ at a cooling rate of 5℃ / min and held for 1.5 h; then, the temperature was increased from 1000℃ to 1350℃ at a heating rate of 3℃ / min and held for 2.5 h; finally, the temperature was decreased from 1350℃ to 800℃ at a cooling rate of 3℃ / min and held for 0.5 h, and then cooled to room temperature with the furnace to obtain a high-strength alumina ceramic substrate.

[0027] Example 3 This embodiment prepares a high-strength alumina ceramic substrate, and the preparation process and steps are as follows: S1. Preparation of surface-modified alumina powder 100 g of alumina powder was placed in 10 L of 0.01 mol / L magnesium nitrate aqueous solution to obtain a suspension. The pH of the suspension was adjusted to 6 using 0.5 mol / L dilute nitric acid, and stirred at 60 °C for 2 h. Then, the pH of the suspension was adjusted to 10 using 0.5 mol / L ammonia solution, and stirring was continued for 4 h. The resulting suspension was filtered while hot, and the filter cake was repeatedly washed with deionized water until the conductivity of the filtrate was below 10 μS / cm. The powder was dried at 120 °C for 12 h and calcined at 500 °C for 4 h to obtain surface-modified alumina powder with a surface nano-magnesium oxide coating of approximately 0.02 wt.%. S2. Preparation of ceramic slurry 100 g of surface-modified alumina powder, 0.05 g of lanthanum oxide, 0.18 g of zinc oxide, 58 g of anhydrous ethanol, 7.5 g of polyvinyl butyral, 5.5 g of dibutyl phthalate, and 3.5 g of triethyl phosphate were ball-milled together in a ball mill. The ball milling process was as follows: stainless steel balls with a ball-to-material ratio of 4:1 and the material were placed in the ball mill and ball-milled at 500 rpm for 20 h to obtain a ceramic slurry. S3, Preparation of high-strength alumina ceramic substrate The ceramic slurry was placed in a vacuum degassing machine and degassed at a pressure of 0.8 kPa for 30 min. The degassed slurry was then poured into the hopper of a casting machine. The casting thickness was set to 500 μm, and casting was performed to obtain a wet blank. The wet blank was then ventilated and dried at 80℃ for 1 h in the casting machine to form a green ceramic belt. The green ceramic strip was cut into four-inch square pieces, ten layers were stacked, and placed in a hot press. The press was held at 80°C and 1000 psi (approximately 6.9 MPa) for 60 minutes to obtain a dense alumina ceramic substrate green body. The alumina ceramic substrate green was placed in a high-temperature sintering furnace and sintered in air atmosphere: first, the temperature was increased from room temperature to 600℃ at a heating rate of 5℃ / min and held for 6 h; then, the temperature was increased from 600℃ to 1600℃ at a heating rate of 3℃ / min and held for 2.5 h; then, the temperature was decreased from 1600℃ to 1000℃ at a cooling rate of 5℃ / min and held for 0.5 h; then, the temperature was increased from 1000℃ to 1350℃ at a heating rate of 3℃ / min and held for 0.5 h; finally, the temperature was decreased from 1350℃ to 800℃ at a cooling rate of 3℃ / min and held for 2 h, and then cooled to room temperature with the furnace to obtain a high-strength alumina ceramic substrate.

[0028] Comparative Example To investigate the influence of different preparation processes on the performance of the product of this invention, the following comparative experiments were conducted. Different alumina ceramic substrates were prepared in the following comparative examples: Comparative Example 1 This comparative example prepares an alumina ceramic substrate. The preparation process is similar to that of Example 1, except that step S1 is omitted. That is, unmodified alumina powder is directly ball-milled and mixed with erbium oxide, magnesium oxide, anhydrous ethanol, polyvinyl butyral, dibutyl phthalate, and triethyl phosphate before proceeding with the subsequent steps.

[0029] Comparative Example 2 This comparative example prepares an alumina ceramic substrate. The preparation process is similar to that of Example 1, except that magnesium oxide is not added in step S2.

[0030] Comparative Example 3 This comparative example prepares an alumina ceramic substrate. The preparation process is similar to that of Example 1, except that erbium oxide is not added in step S2.

[0031] Comparative Example 4 This comparative example prepares an alumina ceramic substrate. The preparation process is similar to that of Example 1. The only difference is that in step S3, when sintering the green blank, a segmented heating and cooling procedure is not used. Instead, the temperature is raised from room temperature to 1500°C at a heating rate of 5°C / min, held for 4 hours, and then cooled to room temperature with the furnace.

[0032] Comparative Example 5 This comparative example prepares an alumina ceramic substrate. The preparation process is similar to that of Example 1, except that in step S3, when sintering the green body, the first-stage cooling and third-stage heating processes are not used. The specific process is as follows: First, the temperature is increased from room temperature to 600℃ at a heating rate of 5℃ / min and held for 6 hours; then, the temperature is increased from 600℃ to 1500℃ at a heating rate of 3℃ / min and held for 1 hour; then, the temperature is decreased from 1500℃ to 800℃ at a cooling rate of 3℃ / min and held for 1.5 hours, and then cooled to room temperature with the furnace.

[0033] Comparative Example 6 This comparative example prepares an alumina ceramic substrate. The preparation process is similar to that of Example 1, except that in step S3, the second-stage cooling process is not used when sintering the green body. The specific process is as follows: First, the temperature is increased from room temperature to 600℃ at a heating rate of 5℃ / min and held for 6 hours. Then, the temperature is increased from 600℃ to 1500℃ at a heating rate of 3℃ / min and held for 1 hour. Next, the temperature is decreased from 1500℃ to 1000℃ at a cooling rate of 5℃ / min and held for 2 hours. Finally, the temperature is increased from 1000℃ to 1350℃ at a heating rate of 3℃ / min and held for 4 hours. After the holding period, the furnace is cooled directly to room temperature.

[0034] Performance testing The alumina ceramic substrates prepared in Examples 1-3 and Comparative Examples 1-6 of this invention were subjected to a series of tests, as detailed below: like Figure 1 The image shows a SEM image of the oriented microstructure of the high-strength alumina ceramic substrate prepared in Example 1 of this invention. As can be seen from the image, the alumina ceramic substrate has a typical "ordered stacked plate-like crystal" structure, which is formed by tightly stacked plate-like grains arranged in a highly oriented manner, constituting the core toughening unit.

[0035] like Figure 2 The image shows a macroscopic SEM image of the high-strength alumina ceramic substrate prepared in Example 1 of this invention. As can be seen from the image, the material has a precisely constructed composite strengthening structure of "fine-grained matrix + ordered laminated plate-like crystals". The uniform and fine equiaxed crystal matrix and the ordered plate-like crystals interlock synergistically to form a multi-scale strengthening and toughening network. The white circles represent the locally uniformly distributed "ordered laminated plate-like crystal" structure.

[0036] like Figure 3 The image shows a cross-sectional microstructure SEM image of the alumina ceramic substrate prepared in Comparative Example 1 of this invention. As can be seen from the image, its microstructure is in stark contrast to the optimized structure of this invention, exhibiting coarse and uneven grains, loose structure, numerous pores, and a complete lack of an ordered plate-like crystal structure.

[0037] The alumina ceramic substrates prepared in Examples 1-3 and Comparative Examples 1-6 of this invention were subjected to relevant mechanical property tests. The specific test results are shown in Table 1. Table 1. Performance test data of alumina ceramic substrates prepared in Examples 1-3 and Comparative Examples 1-6. As can be seen from the table above, the alumina ceramic substrates prepared in Examples 1-3 of this invention have higher bulk density and flexural strength than those in Comparative Examples 1-6. This is because this invention combines endogenous magnesium-modified interface pre-activation (nano-magnesium oxide) with exogenous sintering aids (rare earth oxides and metal oxides) and adopts a "multi-stage sintering process that actively adapts to the diffusion mechanism transformation". This achieves ultra-uniform distribution and optimal interface bonding of nano-magnesium oxide and exogenous sintering aids at the atomic scale, and precisely constructs a composite reinforced structure of "fine-grained matrix + ordered laminated plate-like crystals".

[0038] Each comparative example, due to not adopting the complete technical solution of this invention, has specific defects leading to performance degradation: Comparative Example 1, because it did not modify the alumina powder, resulted in the sintering aid and matrix being merely physically mixed and unevenly distributed, failing to form an effective grain boundary pinning network. Furthermore, the lack of pre-activation and directional control of the intrinsic active layer in the early stages of sintering made the grains prone to coarsening; Comparative Example 2, because it did not add magnesium oxide to the exogenous sintering aid, resulted in insufficient total pinning concentration at the grain boundaries, weakening the ability to inhibit grain boundary migration, especially at high temperatures where grains were prone to abnormal growth, failing to form a uniform fine-grained matrix; Comparative Example 3, because it did not add erbium oxide to the exogenous sintering aid, resulted in insufficient sintering driving force, slow and incomplete densification process, and reduced bulk diffusion efficiency, making it difficult to construct a well-developed strengthening and diffusion network framework at the grain boundaries; Comparative Example 4, because it did not modify the green blank... During sintering, the lack of a segmented heating and cooling process led to concentrated decomposition of organic matter, which easily resulted in defects. The sintering kinetics path was inaccurate, making it impossible to achieve the network construction, microstructure relaxation, and refining control of nano-magnesium oxide and exogenous sintering aids in stages. Ultimately, the resulting structure was coarse and uneven. In Comparative Example 5, the lack of a first-stage cooling and third-stage heating process during the sintering of the green blank resulted in the absence of necessary microstructure relaxation and target temperature refining stages during the sintering process. Internal stress was not fully released, and the final densification and grain refinement growth control were insufficient. In Comparative Example 6, the lack of a second-stage cooling process during the sintering of the green blank resulted in direct cooling from the refining temperature without a temperature buffer. The thermal stress generated by the excessively rapid cooling easily caused microcracks, damaging the integrity and final strength of the substrate.

[0039] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high-strength alumina ceramic substrate, characterized in that, Follow these steps in sequence: S1. Preparation of surface-modified alumina powder Alumina powder was placed in a magnesium salt solution with a concentration of 0.01-0.05 mol / L to obtain a suspension. The pH of the suspension was adjusted to 4-6 using dilute nitric acid with a concentration of 0.1-0.5 mol / L. The suspension was stirred at 60-80℃ for 1-2 h. The pH of the suspension was then adjusted to 9-10 using ammonia water with a concentration of 0.1-0.5 mol / L. The suspension was stirred for another 2-4 h. The resulting suspension was filtered while hot. The filter cake was repeatedly washed with deionized water until the conductivity of the filtrate was below 10 μS / cm. The filtrate was dried at 90-120℃ for 12-24 h and then calcined to obtain surface-modified alumina powder. S2, Preparation of ceramic slurry Surface-modified alumina powder, rare earth metal oxide, metal oxide, anhydrous ethanol, polyvinyl butyral, dibutyl phthalate, and triethyl phosphate were placed together in a ball mill for ball milling to obtain ceramic slurry. S3, Preparation of high-strength alumina ceramic substrate The ceramic slurry is defoamed and cast in sequence, then dried, and then hot-pressed in layers to form a ceramic green body. The hot-pressing temperature is 80°C, the pressure is 1000 psi, and the holding time is 60 min. The ceramic green body is then sintered in an air atmosphere to obtain a high-strength alumina ceramic substrate.

2. The method for preparing a high-strength alumina ceramic substrate according to claim 1, characterized in that, In step S1, the solid-liquid ratio of the alumina powder to the magnesium salt solution is 1:(50-100)g / mL; the magnesium salt solution is an aqueous solution of magnesium nitrate or magnesium chloride.

3. The method for preparing a high-strength alumina ceramic substrate according to claim 1, characterized in that, In step S1, the calcination temperature is 400-500℃ and the time is 2-4 h.

4. The method for preparing a high-strength alumina ceramic substrate according to claim 1, characterized in that, In step S2, the rare earth metal oxide is one or more of erbium oxide, yttrium oxide, lanthanum oxide, and cerium oxide; the metal oxide is one or more of magnesium oxide, calcium oxide, zinc oxide, and titanium oxide.

5. The method for preparing a high-strength alumina ceramic substrate according to claim 1, characterized in that, In step S2, the mass ratio of the surface-modified alumina powder to the rare earth metal oxide and the metal oxide is 100:(0.05-0.15):(0.05-0.18).

6. The method for preparing a high-strength alumina ceramic substrate according to claim 1, characterized in that, In step S2, the mass ratio of the surface-modified alumina powder to anhydrous ethanol, polyvinyl butyral, dibutyl phthalate, and triethyl phosphate is 100:(58-65):(7.5-8.5):(4-5.5):(2.5-3.5).

7. The method for preparing a high-strength alumina ceramic substrate according to claim 1, characterized in that, In step S2, the ball milling process is as follows: stainless steel balls with a ball-to-material ratio of (2-4):1 and the material are placed in a ball mill and milled at 300-500 rpm for 20-28 hours.

8. The method for preparing a high-strength alumina ceramic substrate according to claim 1, characterized in that, In step S3, the drying temperature is 60-80℃ and the time is 1-2 h.

9. The method for preparing a high-strength alumina ceramic substrate according to claim 1, characterized in that, In step S3, the sintering process is carried out in the following order: (a) In the first heating stage, the temperature was increased from room temperature to 600℃ at a heating rate of 5℃ / min and held for 6 h; (b) In the second heating stage, the temperature is increased from 600℃ to 1500-1600℃ at a heating rate of 3℃ / min, and held for 1-4 hours; (c) In the first cooling stage, the temperature is reduced from 1500-1600℃ to 1000℃ at a cooling rate of 5℃ / min, and held for 0.5-2 hours. (d) In the third heating stage, the temperature is increased from 1000℃ to 1350℃ at a heating rate of 3℃ / min, and held for 0.5-4 h. (e) In the second cooling stage, the temperature is reduced from 1350℃ to 800℃ at a cooling rate of 3℃ / min, and held for 0.5-2 h, and then cooled to room temperature with the furnace.

10. A method for preparing a high-strength alumina ceramic substrate according to any one of claims 1-9, characterized in that, In step S1, the surface-modified alumina powder obtained has a nano-magnesium oxide active coating layer formed on its surface through in-situ construction; the content of the nano-magnesium oxide coating in the surface-modified alumina powder is 0.02-0.04 wt.% of the mass of the alumina powder.

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