A method for preparing eutectic oxide ceramics based on an amorphous crystallization process

Abstract

This invention discloses a method for preparing quasi-eutectic oxide ceramics based on an amorphous crystallization process, including the steps of obtaining amorphous powder with a specific eutectic composition and crystallizing the amorphous powder. The amorphous powder is obtained using a sol-gel method involving metal salt complexation; the amorphous powder is then rapidly hot-pressed and sintered using Joule hot pressing to crystallize and shape it, thus obtaining the quasi-eutectic oxide ceramic. Joule hot pressing causes rapid crystallization of the amorphous powder at a temperature much lower than the eutectic temperature. The precipitated grains are nested and intertwined to form a eutectic structure. Simultaneously, several grain boundaries are formed during the crystallization process due to the boundaries of the amorphous powder particles. This unique binary boundary structure has a strengthening and toughening effect on mechanical properties; therefore, the quasi-eutectic oxide ceramic of this invention exhibits excellent mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of ceramic material preparation technology, specifically to a method for preparing quasi-eutectic oxide ceramics based on an amorphous crystallization process. Background Technology

[0002] Oxide eutectic ceramics are ceramics with a uniform, fine eutectic structure formed in situ during melt solidification through eutectic reactions, exhibiting a three-dimensional interwoven distribution. They possess excellent mechanical properties, high-temperature structural stability, oxidation and corrosion resistance, and creep resistance, making them ideal high-temperature structural materials for long-term stable operation in oxygen-rich environments above 1400℃. For example, alumina-based oxide eutectic ceramics (such as Al2O3 / YAG and Al2O3 / GAP systems) have become candidate materials for hot-end components of aero-engines and nuclear energy systems due to their high-temperature strength, oxidation resistance, and excellent creep resistance.

[0003] The superior properties of oxide eutectic ceramics are highly dependent on their three-dimensional interwoven eutectic microstructure; therefore, the formation and control of the eutectic microstructure are crucial to their fabrication process. Currently, commonly used oxide eutectic ceramic fabrication techniques mainly rely on a series of directional solidification techniques based on the melt solidification process, including the Bridgman method, micro-pulling method, boundary epitaxial growth method, laser zone melting, electron beam zone melting, optical levitation zone melting, and laser levitation zone melting. Specifically: the Bridgman method uses an iridium or molybdenum crucible to complete a melting-solidification process exceeding 1800℃ in an inert atmosphere (Ar), with temperature gradient control achieved using a moving furnace; the laser levitation zone melting (LFZ) method utilizes a high-energy CO2 laser beam to locally melt the sample, achieving crucible-free growth through a rotating traction mechanism; the micro-pulling method, using a high-frequency induction furnace and capillary mold, can prepare single-crystal fibers with diameters below 5 mm. The methods described above based on directional solidification technology can effectively control the texture direction and microstructure characteristics of the solidified structure, thereby improving the mechanical properties of the material in specific directions and obtaining directional structures with high flexural strength and high fracture toughness. However, compared with traditional ceramic sintering methods, directional solidification technology usually requires operation at temperatures above 1820℃~2000℃, which has limitations such as complex equipment, equipment limitations due to high temperatures, difficulty in preparing complex eutectic ceramic components, slow preparation rate, and high cost.

[0004] To improve the preparation efficiency of oxide eutectic ceramics, researchers have combined directional solidification and powder sintering techniques to prepare a series of oxide eutectic ceramics. For example, Yao et al. successfully prepared Al2O3 / YAG binary eutectic ceramic blocks using directional solidification and hot pressing sintering techniques; Yu et al. prepared Al2O3 / 3YSZ binary eutectic ceramic blocks using combustion synthesis-gas phase atomization combined with vacuum hot pressing sintering techniques. However, oxide eutectic ceramics prepared by powder sintering methods all require solidification techniques as a pre-process to provide powder with a eutectic structure as raw material. That is, the sintering process itself does not form a eutectic structure; only powder sintering and grain growth occur, which plays a role in densification. Therefore, the above two-step method for preparing oxide eutectic ceramics is a sintering ceramic method based on obtaining eutectic structure powder through a pre-process. At the same time, a large number of grain boundaries exist in the eutectic powder particles during the sintering process, belonging to a quasi-eutectic oxide ceramic system in which eutectic structure and sintered grain boundary structure coexist. This method, which combines directional solidification and powder sintering, greatly improves the problem of difficult net-shape forming and complex component preparation of oxide eutectic ceramics prepared solely by directional solidification. However, it also increases the cost by adding a series of sintering processes such as ceramic crushing, grinding, granulation, and forming sintering.

[0005] In recent years, flash sintering technology has been developed for preparing oxide eutectic ceramics. This method eliminates the need for a pre-treatment step of eutectic structure powder, requiring only one step to obtain the oxide eutectic ceramic. For example, Sun et al. used flash sintering to prepare Al2O3-GdAlO3-ZrO2 ternary oxide eutectic ceramics. Flash sintering involves applying a high voltage to the material, generating a Joule heating effect through the flow of current within the material, causing a decrease in resistivity and a rapid increase in temperature when the material reaches its flash point, resulting in localized melting and solidification to form a eutectic. Flash sintering can complete densification within seconds, significantly shortening the sintering time. It requires materials with good electrical conductivity and high-temperature conductivity. Because flash sintering utilizes the rapid densification of materials at their flash point, the uncontrollable flashing (i.e., internal current) during flash sintering leads to random and localized microstructure distribution within the material. Therefore, the eutectic microstructure of flash sintering often exhibits uneven distribution, with the eutectic structure only partially forming at the channels, while the remaining parts exhibit characteristics of sintered ceramics. This uneven structural distribution limits its practical application.

[0006] The eutectic oxide ceramics or quasi-eutectic oxide ceramics prepared by the above-mentioned methods of directional solidification, sintering, or a combination of both share a common characteristic in their preparation process: a melting and resolidification process. This melting and resolidification process is crucial for forming the eutectic structure in these preparation techniques. However, ceramics generally have extremely high melting points, requiring sophisticated melting and solidification equipment, and the process is complex and costly. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to provide a method for preparing eutectic oxide ceramics based on an amorphous crystallization process. This method is a non-high-temperature melting and recooling solidification process, which has advantages such as simple process, low preparation temperature, short preparation time, simple equipment and operation, and excellent mechanical properties of the obtained ceramics.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution.

[0009] A method for preparing a quasi-eutectic oxide ceramic based on an amorphous crystallization process, the method comprising the following steps: Step S1 involves preparing an amorphous powder with a specific eutectic composition. The composition ratio of each component in the amorphous powder satisfies the eutectic composition ratio, which is the eutectic composition ratio corresponding to the composition system constituting the quasi-eutectic oxide ceramic. Preferably, this step uses a sol-gel method based on metal salt complexation reaction to prepare the amorphous powder.

[0010] Step S2 involves an amorphous crystallization process: the amorphous powder obtained in step S1 is rapidly hot-pressed and crystallized using a Joule hot-pressing device to obtain the quasi-eutectic oxide ceramic. The quasi-eutectic oxide ceramic exhibits eutectic structural morphology characteristics and also contains several grain boundaries formed by the sintering of amorphous powder particle boundaries. Therefore, the oxide ceramic obtained by amorphous crystallization in this invention belongs to the quasi-eutectic oxide ceramic category.

[0011] More specifically, the preparation method of the quasi-eutectic oxide ceramic includes the following steps: Step S11: The metal salt is dissolved in a deionized aqueous solution according to the eutectic composition ratio. Then, the complexing agent is dissolved in the solution at a ratio of 2:1 to 3:1. The mixed solution is heated in a 70°C water bath and stirred for 6 hours until it becomes a viscous gel. It is then placed in a 120°C oven to further remove moisture. After drying, it is ground into a precursor powder. The metal salt is typically a nitrate or chloride. The nitrate is selected from any two or three of aluminum nitrate, zirconium nitrate, yttrium nitrate, gadolinium nitrate, erbium nitrate, and lanthanum nitrate, and is proportioned according to the eutectic composition ratio.

[0012] The complexing agent is usually citric acid, ethylene glycol, etc.

[0013] Step S12: The obtained precursor powder is placed in a crucible and heated to 400-800°C in a muffle furnace at a heating rate of 5-10°C / min. After holding at this temperature for 2-3 hours, it is cooled with the furnace, ground, and sieved to obtain amorphous powder with the specific eutectic composition. The calcination temperature in this process is crucial for obtaining amorphous powder with a suitable morphology and for successfully preparing the quasi-eutectic oxide ceramic of this invention. If the calcination temperature is too low, the organic matter participating in the metal ion complexation process cannot be fully burned, thus affecting the subsequent amorphous crystallization reaction. If the temperature is too high, the amorphous powder will crystallize prematurely. The large number of nanocrystals formed by premature crystallization will grow into large grains as initial grains during the subsequent Joule hot pressing process, thus failing to form a quasi-eutectic morphology with three-dimensional interwoven structure, thereby losing its excellent mechanical properties.

[0014] Step S21: The amorphous powder is weighed and placed into a graphite mold with a diameter of 10-30 mm. It is then hot-pressed in a Joule hot-pressing apparatus, with the temperature increased to a first set temperature at a rate of 1-10 °C / s; then increased to a second set temperature at a rate of 0.5-1 °C / s, and held at the second set temperature for 0.5-2 hours. Afterward, it is cooled in the furnace to obtain the quasi-eutectic oxide ceramic. The pressure is increased to 30-60 MPa before the first heating and maintained until the cooling is complete. The second set temperature is 200 °C higher than the first set temperature, and the range of the second set temperature is 1200-1600 °C, adjusted according to the composition system of the quasi-eutectic oxide ceramic.

[0015] This invention produces a quasi-eutectic ceramic by hot-pressing amorphous powder and crystallizing it during the hot-pressing process. In this amorphous crystallization process, the formation mechanism of the eutectic structure is not a conventional liquid-to-solid solidification reaction, but rather a solid-to-solid crystallization reaction, rather than the melting and solidification process in existing technologies.

[0016] This invention also provides the aforementioned quasi-eutectic oxide ceramic prepared based on an amorphous crystallization process. The quasi-eutectic oxide ceramic is a fully crystallized blocky crystal, and its microstructure is characterized by being composed of numerous finely interwoven nanophase particles. The nanophase particles exhibit eutectic phase boundary structures within themselves and polycrystalline grain boundary structures at their boundaries, forming a unique multiphase interwoven structure with a binary boundary structure possessing both eutectic and polycrystalline grain boundary structures. The quasi-eutectic oxide ceramic prepared by this invention exhibits a unique binary boundary structure that enhances its mechanical properties, resulting in superior mechanical performance.

[0017] Furthermore, the quasi-eutectic oxide ceramic is an Al2O3-YSZ binary quasi-eutectic oxide ceramic, wherein YSZ is yttrium oxide-stabilized zirconium oxide ceramic.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a two-step method to prepare eutectic oxide ceramics, which has the advantages of simple preparation process, short preparation cycle and low cost, and no need for complicated pre-melting steps to prepare eutectic ceramic powder as sintering raw material.

[0019] (2) This invention is based on the amorphous crystallization process, which is different from the traditional high-temperature melting and then cooling solidification process. It does not require an extremely high temperature treatment process that exceeds the melting point of ceramics. It is a milder process for obtaining eutectic oxide ceramics from solid amorphous phase eutectoid.

[0020] (3) The present invention uses a Joule hot pressing device, which uses Joule radiation heating coupled with pressure to make amorphous powder crystallize rapidly. The crystallization temperature is much lower than the eutectic temperature. The precipitated grains are nested and intertwined to form a eutectic structure. The eutectic structure is uniform, with fine structure and excellent mechanical properties. Attached Figure Description

[0021] Figure 1 The image shows the XRD pattern of the Al2O3-3YSZ (alumina-3mol% yttrium-stabilized zirconium oxide) amorphous powder obtained in step 4 of the preparation process in Example 1 of this invention.

[0022] Figure 2 The images shown are SEM and EDS images of the Al2O3-3YSZ (alumina-3mol% yttrium-stabilized zirconium oxide) amorphous powder obtained in step 4 of the preparation process in Example 1 of this invention.

[0023] Figure 3 The image shows the XRD pattern of the Al2O3-3YSZ (alumina-3mol% yttrium-stabilized zirconium oxide) eutectic oxide ceramic prepared in Example 1 of this invention.

[0024] Figure 4 This is a SEM image of the Al2O3-3YSZ (alumina-3mol% yttrium-stabilized zirconium oxide) eutectic oxide ceramic prepared in Example 1 of the present invention.

[0025] Figure 5 This is an EDS image of the Al2O3-3YSZ (alumina-3mol% yttrium-stabilized zirconium oxide) eutectic oxide ceramic prepared in Example 1 of the present invention.

[0026] Figure 6 This is a SEM image of the conventional solidified eutectic oxide ceramic Al2O3-3YSZ (alumina-3mol% yttrium-stabilized zirconium oxide) prepared in Comparative Example 1 of this invention.

[0027] Figure 7The images show a comparison of Vickers indentation patterns on the oxide ceramics prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention.

[0028] Figure 8 The graph shows the change of loading force with increasing indentation depth in nanoindentation testing of the oxide ceramics prepared in Examples 1, 1, and 2 of this invention.

[0029] Figure 9 The images show nanoindentation test patterns of the oxide ceramics prepared in Examples 1, 1, and 2 of this invention.

[0030] Figure 10 The image shows the Vickers indentation test results of the oxide ceramics prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The present invention is a method for preparing quasi-eutectic oxide ceramics based on an amorphous crystallization process. It prepares quasi-eutectic oxide ceramic bulk materials through a two-step method of preparing amorphous powder by sol-gel, crystallization of amorphous powder by Joule hot pressing, and densification.

[0032] Example 1

[0033] This embodiment provides a method for preparing Al2O3-3YSZ binary eutectic oxide ceramics, including the following steps.

[0034] Step 1: Calculate the mass ratio of aluminum nitrate, zirconium nitrate, and yttrium nitrate according to the eutectic composition of the system composed of aluminum oxide and 3 mol% yttrium-stabilized zirconium oxide in the phase diagram, i.e., the molar ratio of the two is Al2O3:3YSZ = 62.5:37.5. Weigh out 20g of each of the three metal salt powders: aluminum nitrate, zirconium nitrate, and yttrium nitrate.

[0035] Step 2: Dissolve the weighed metal salt in 500mL of deionized water. According to the molar ratio of complexing agent to metal salt of 2:1, weigh citric acid and dissolve it in the above solution. Stir with a magnetic stirrer and keep in a 70℃ water bath for 6 hours until it becomes a viscous gel.

[0036] Step 3: Place the viscous gel-like sol in a 120℃ oven to further remove moisture, and then grind it into powder after drying.

[0037] Step 4: Place the powder obtained in Step 3 in a crucible, heat it to 800°C in a muffle furnace at a heating rate of 10°C / min, hold it at that temperature for 3 hours, and then cool it with the furnace. After grinding and sieving, obtain amorphous powder with a specific eutectic composition.

[0038] Step 5: Weigh the amorphous powder obtained in Step 2 and place it into a graphite mold with a diameter of 10-30 mm. Then, perform hot pressing treatment in a Joule hot pressing apparatus. The heating program is as follows: increase the temperature from room temperature to 1400℃ at a rate of 10℃ / s, increase it from 1400℃ to 1600℃ at a rate of 1℃ / s, hold at 1600℃ for 0.5 h, and then cool with the furnace. The pressure is increased to 30 MPa before the first heating and maintained until the cooling is completed, to obtain Al2O3-3YSZ binary eutectic oxide ceramic.

[0039] Example 2

[0040] This embodiment prepares Al2O3-3YSZ binary eutectic oxide ceramics, including the following steps.

[0041] Step 1: Calculate the mass ratio of aluminum nitrate, zirconium nitrate, and yttrium nitrate according to the eutectic composition of the system composed of aluminum oxide and 3 mol% yttrium-stabilized zirconium oxide in the phase diagram, i.e., the molar ratio of the two is Al2O3:3YSZ = 62.5:37.5. Weigh out 20g of each of the three metal salt powders: aluminum nitrate, zirconium nitrate, and yttrium nitrate.

[0042] Step 2: Dissolve the weighed metal salt in 500mL of deionized water. According to the molar ratio of complexing agent to metal salt of 2:1, weigh citric acid and dissolve it in the above solution. Stir with a magnetic stirrer and keep warm in a 70℃ water bath for 6 hours until it becomes a viscous gel.

[0043] Step 3: Place the viscous gel-like sol in a 120℃ oven to further remove moisture, and then grind it into powder after drying.

[0044] Step 4: Place the powder obtained in Step 3 in a crucible, heat it to 800°C in a muffle furnace at a heating rate of 5°C / min, hold it at that temperature for 3 hours, and then cool it with the furnace. After grinding and sieving, obtain amorphous powder with a specific eutectic composition.

[0045] Step 5: Weigh the amorphous powder obtained in Step 2 and place it into a graphite mold with a diameter of 10-30 mm. Then, perform hot pressing treatment in a Joule hot pressing apparatus. The heating program is as follows: increase the temperature from room temperature to 1400℃ at a rate of 10℃ / s, increase the temperature from 1400℃ to 1600℃ at a rate of 0.5℃ / s, hold at 1600℃ for 2 hours, and then cool with the furnace. The pressure is increased to 60 MPa before the first heating and maintained until the cooling is completed, to obtain Al2O3-3YSZ binary eutectic oxide ceramic.

[0046] Example 3

[0047] This embodiment prepares Al2O3-MgAl2O4-ZrO2 ternary eutectic oxide ceramics, including the following steps.

[0048] Step 1: Calculate the mass ratio of aluminum nitrate and gadolinium nitrate according to the eutectic composition of the composition system consisting of aluminum oxide, magnesium oxide and zirconium oxide in the phase diagram, that is, the molar ratio of the three Al2O3-MgO-ZrO2 = 42.1:17.4:40.5. Weigh out 20g of aluminum nitrate, magnesium nitrate and zirconium nitrate powder respectively.

[0049] Step 2: Dissolve the weighed metal salt in 500mL of deionized water. According to the molar ratio of complexing agent to metal salt of 2:1, weigh citric acid and dissolve it in the above solution. Stir with a magnetic stirrer and keep warm in a 70℃ water bath for 6 hours until it becomes a viscous gel.

[0050] Step 3: Place the viscous gel-like sol in a 120℃ oven to further remove moisture, and then grind it into powder after drying.

[0051] Step 4: Place the powder obtained in Step 3 in a crucible, heat it to 400°C in a muffle furnace at a heating rate of 5°C / min, hold it at that temperature for 3 hours, and then cool it with the furnace. After grinding and sieving, obtain amorphous powder with a specific eutectic composition.

[0052] Step 5: Weigh the amorphous powder obtained in Step 2 and place it into a graphite mold with a diameter of 10-30 mm. Then, perform hot pressing treatment in a Joule hot pressing apparatus. The heating program is as follows: increase the temperature from room temperature to 1000℃ at a rate of 10℃ / s, increase the temperature from 1000℃ to 1200℃ at a rate of 1℃ / s, hold at 1200℃ for 2 hours, and then cool with the furnace. The pressure is increased to 60 MPa before the first heating and maintained until the cooling is completed, to obtain Al2O3-MgAl2O4-ZrO2 ternary eutectic oxide ceramic.

[0053] Comparative Example 1

[0054] Step 1: Prepare a eutectic mixture based on the phase diagram of the alumina and 3 mol% yttrium-stabilized zirconium oxide (YZ) system, with a molar ratio of Al2O3:3YSZ = 62.5:37.5. Weigh out 20 g of Al2O3 and 3YSZ ceramic powders respectively. Add 200 mL of deionized water to the weighed ceramic powders and mix in a planetary ball mill at 300 rpm for 24 hours to form a slurry.

[0055] Step 2: The obtained slurry is dried to form ceramic agglomerates at 80℃ for 24 hours. The dried ceramic agglomerates are then ground into powder in an agate mortar. The powder is sieved through a 300-mesh metal sieve to obtain a uniformly sized mixed ceramic powder. The sieved mixed ceramic powder is then pressed into shape using a molding method: the powder is weighed and pressed into cylindrical green bodies with a diameter of 10mm and a length of 10cm.

[0056] Step 3: The cylindrical green body is melted and solidified by conventional laser zone melting to prepare Al2O3-3YSZ (alumina-3mol% yttrium-stabilized zirconium oxide) conventional solidified eutectic oxide ceramic.

[0057] Comparative Example 2

[0058] Step 1: Weigh 10g of 3mol% yttrium-stabilized zirconium oxide (3YSZ), add 200mL of deionized water, and mix in a planetary ball mill at a speed of 300r / min for 24h. After thorough ball milling and mixing, a slurry is formed.

[0059] Step 2: The obtained slurry is dried to form ceramic agglomerates at 80℃ for 24 hours. The dried ceramic agglomerates are then ground into powder in an agate mortar. The powder is sieved through a 300-mesh metal sieve to obtain a mixed ceramic powder with uniform particle size. The sieved mixed ceramic powder is then pressed into shape using a molding method: the powder is weighed and pressed into round green blanks with a diameter of 10mm.

[0060] Step 3: The circular green body was sintered in a muffle furnace at 1600℃ for 10h to prepare 3YSZ (3mol% yttrium oxide stabilized zirconium oxide) conventional sintered oxide ceramic.

[0061] Testing and Analysis: (1) First, the intermediate amorphous powders obtained in the preparation of eutectic oxide ceramics in the above embodiments were tested and analyzed. The crystal morphology, microstructure and elemental analysis of the amorphous powders were performed. The specific test and analysis results are as follows.

[0062] XRD analysis showed that the intermediate amorphous powders prepared in each embodiment had no obvious crystal diffraction peaks, indicating that completely amorphous powders were successfully prepared. Figure 1 The image shows the XRD pattern of the Al2O3-3YSZ amorphous powder prepared in Example 1 (i.e., the amorphous powder obtained in step 4 of Example 1). It can be clearly observed from the image that its XRD pattern curve has no obvious crystal diffraction peaks in the entire scanning range, only a diffuse scattering peak resembling a steamed bun in the range of 25-35°. This is the typical XRD characteristic peak shape of amorphous materials. This figure shows that the desired amorphous powder material was successfully prepared through step 4.

[0063] SEM and EDS analyses showed that the intermediate amorphous powder particles obtained in each embodiment were blocky and granular, with the three metallic elements aluminum, yttrium, and zirconium uniformly distributed. Figure 2The images show SEM and EDS images of the Al2O3-3YSZ amorphous powder prepared in Example 1. The SEM images show that the amorphous powder particles are blocky and granular. The EDS elemental mapping results show that the three metal elements are uniformly distributed on the prepared powder particles without elemental agglomeration, which is consistent with... Figure 1 The XRD patterns in the images corroborate each other, confirming that the desired amorphous powder material was successfully prepared through step 4.

[0064] (2) The crystal state, microstructure and elemental analysis of the quasi-eutectic oxide ceramics prepared in the above embodiments were tested and analyzed. The specific test and analysis results are as follows.

[0065] XRD analysis showed that the eutectic oxide ceramics prepared in each embodiment were all fully crystallized and contained only two phases: Al2O3 and ZrO2. Figure 3 The image shows the XRD pattern of the Al2O3-3YSZ (alumina-3 mol% yttrium-stabilized zirconium oxide) eutectic oxide ceramic prepared in Example 1. The XRD phase results show that the obtained Al2O3-3YSZ bulk ceramic possesses only two phases: Al2O3 and ZrO2. The ZrO2 characteristic peak at approximately 35° is divided into two XRD peaks, confirming that it is a Y-stabilized tetragonal ZrO2 phase, i.e., the YSZ phase. Simultaneously, the XRD results indicate that the amorphous powder was completely crystallized through the Joule hot-pressing process, with no amorphous residue remaining.

[0066] SEM and EDS analyses showed that the Al2O3-3YSZ-like eutectic oxide ceramics prepared in each embodiment exhibited a binary boundary structure: internal crystallization forming a typical eutectic phase boundary structure, and grain boundary crystallization forming a polycrystalline grain boundary structure. The three metal elements showed a segregated state in the eutectic oxide ceramic bulk material: Zr and Y elements were enriched together, while Al elements were enriched in the remaining regions, confirming that the interwoven two-phase structure is a typical eutectic structure. Specifically, as shown... Figure 4The image shows a SEM image of the Al2O3-3YSZ (alumina-3mol% yttrium-stabilized zirconium oxide) quasi-eutectic oxide ceramic prepared in Example 1. The SEM image reveals a fine interweaving of black and white phases, with most phases being nanoscale phases smaller than 1 micrometer. This fine interweaving of black and white phases results in an overall gray appearance. Numerous larger white phases are observed, typically surrounded by a layer of black phase. This is attributed to the sintering phenomenon at the particle boundaries during Joule hot pressing of the amorphous powder particles. These larger phases are usually formed by the aggregation of numerous homogeneous grains, which is the origin of the quasi-eutectic structure described in this invention. During crystallization, homogeneous grains at the boundaries of amorphous particles form a larger-sized homogeneous phase structure, thus resulting in numerous homogeneous grain boundaries. This invention forms a unique binary boundary structure through the amorphous crystallization process, where the internal crystallization of amorphous particles forms a typical eutectic phase boundary structure, and the crystallization of amorphous particle boundaries forms a polycrystalline grain boundary structure. This is why it is called a quasi-eutectic structure. This unique binary boundary structure has a strengthening and toughening effect on its mechanical properties, which is crucial for subsequent... Figures 8-10 This can be seen in the tests. For example... Figure 5 This is an EDS image of the Al2O3-3YSZ (alumina-3 mol% yttrium-stabilized zirconium oxide) quasi-eutectic oxide ceramic prepared in Example 1. The elemental mapping results from the EDS show the segregation of the three metal elements on the prepared quasi-eutectic oxide ceramic bulk: Zr and Y elements are enriched together, while Al is enriched in the remaining region. This corresponds to the white and black phases in the SEM image, respectively, and also to... Figure 3 The phase results obtained by XRD are consistent. Furthermore, it is also demonstrated that the interwoven microstructure of the two phases is a typical eutectic structure.

[0067] (3) The microstructure of the eutectic oxide ceramics prepared in the above comparative examples was tested and analyzed.

[0068] Specific test and analysis results show that the Al2O3-3YSZ eutectic oxide ceramics prepared in each comparative example all exhibit typical eutectic structures, distinct from the quasi-eutectic structures in the embodiments. Specifically, as follows... Figure 6 The image shows a SEM image of the Al2O3-3YSZ conventionally solidified eutectic oxide ceramic prepared in Comparative Example 1. The SEM results indicate that the eutectic ceramic prepared by the conventional solidification method has a fine two-phase interwoven structure, which is extremely similar to the structure formed by the amorphous crystallization of this invention. Meanwhile... Figure 6 It can be observed that it also has relatively large two-phase particles, but the difference is that the larger two-phase particles are still single crystals, and their grain boundaries are still phase boundaries, which is still a typical eutectic structure. This overall colony-like structure composed of fine and uniform grains and larger boundary grains may be due to the uneven distribution of internal cooling rate during solidification, which has been reported in many literatures.

[0069] (4) The mechanical properties of the above embodiments and comparative examples were compared and analyzed, as follows.

[0070] like Figure 7 The image shows a comparison of Vickers indentation results for the oxide ceramics prepared in Example 1, Comparative Examples 1 and 2. Vickers indentation tests were performed on the three samples, and the results show the indentation shape and crack condition of the three samples. Notably, the eutectic ceramic prepared by conventional solidification exhibited a relatively long crack in the Vickers indentation test, with almost no crack deflection. This indicates that the energy at the crack tip cannot be effectively dissipated by the eutectic microstructure, leading to transgranular fracture and resulting in poor fracture toughness. This can be further investigated in the following sections. Figures 8-10 As seen in the comparison.

[0071] like Figures 8-10 The figures show a comparison of the mechanical properties of the oxide ceramics prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively. The figures show that nanoindentation and Vickers indentation tests were performed on the three samples, and their fracture toughness was calculated. Figure 8 The graph shows the change in loading force with increasing indentation depth during nanoindentation testing. The graph indicates that the loading force of both the present invention and traditional solidified eutectic ceramics increases faster with increasing indentation depth, suggesting greater nanohardness and elastic modulus. Figure 9 The nanoindentation test results demonstrate that the nanomechanical properties of the quasi-eutectic ceramic of this invention are slightly better than those of traditional solidified eutectic ceramics. Figure 10 The Vickers indentation test results show that the quasi-eutectic ceramic of the present invention exhibits significantly superior macroscopic mechanical properties. Its Vickers hardness and fracture toughness combine the strengths of both other materials and surpass them. This simultaneous improvement in strength and toughness is attributed to the unique binary boundary structure of the quasi-eutectic structure. According to the Hall-Page relation, a dense internal typical eutectic phase boundary structure has more phase interfaces, which can accommodate more dislocation pile-up, resulting in higher strength and hardness. In contrast, the polycrystalline grain boundary structure formed by the crystallization of amorphous grain boundaries is mostly in-phase grain boundary, relatively thin, and acts as an energy depression during crack propagation, easily causing crack deflection, thereby dissipating energy and improving fracture toughness. Therefore, the quasi-eutectic ceramic prepared by the amorphous crystallization process of the present invention has superior mechanical properties, and its enhanced toughness performance has broad application prospects in the field of high-performance ceramics.

Claims

1. A method for preparing quasi-eutectic oxide ceramics based on an amorphous crystallization process, characterized in that, The preparation method includes the following steps: Step S1: Amorphous powder with a specific eutectic composition is obtained; Wherein, the specific eutectic component refers to the fact that the composition ratio of each component in the amorphous powder satisfies the eutectic composition ratio, wherein the eutectic composition ratio is the eutectic composition ratio corresponding to the composition system constituting the quasi-eutectic oxide ceramic; Step S2, perform amorphous crystallization process: use Joule hot pressing method to rapidly hot press and sinter the amorphous powder obtained in step S1 to crystallize the amorphous powder into shape, and obtain the quasi-eutectic oxide ceramic. The quasi-eutectic oxide ceramic refers to a ceramic whose microstructure has eutectic structure characteristics and also contains several grain boundaries formed by the boundaries of the amorphous powder particles during the crystallization process.

2. The method for preparing a quasi-eutectic oxide ceramic based on an amorphous crystallization process according to claim 1, characterized in that, The amorphous powder is prepared by a sol-gel method using a metal salt complexation reaction in step S1, and includes the following steps: Step S11: Dissolve the metal salt in a deionized aqueous solution according to the ratio of the eutectic composition, and then dissolve the complexing agent in the aqueous solution; heat the mixed solution in a water bath, stir until it becomes a viscous gel, then heat it in an oven to remove moisture, and then dry and grind it into precursor powder. Step S12: Place the obtained precursor powder in a crucible, heat it to 400-800°C in a muffle furnace at a heating rate of 5-10°C / min, hold it at that temperature for 2-3 hours, and then cool it with the furnace. After grinding and sieving, obtain an amorphous powder with the specific eutectic composition.

3. The method for preparing a quasi-eutectic oxide ceramic based on an amorphous crystallization process according to claim 2, characterized in that, The metal salt is a nitrate or a chloride, wherein the nitrate is selected from any two or three of aluminum nitrate, zirconium nitrate, yttrium nitrate, gadolinium nitrate, erbium nitrate, and lanthanum nitrate.

4. The method for preparing a quasi-eutectic oxide ceramic based on an amorphous crystallization process according to claim 2, characterized in that, The complexing agent is selected from citric acid or ethylene glycol, and the ratio of the complexing agent to the metal salt is 2:1 to 3:

1.

5. The method for preparing a quasi-eutectic oxide ceramic based on an amorphous crystallization process according to claim 1, characterized in that, The amorphous crystallization process in step S2 is as follows: Amorphous powder is loaded into a graphite mold and then hot-pressed in a Joule hot-pressing device. The temperature is raised to a first set temperature at a first heating rate; then raised to a second set temperature at a second heating rate; and then held at the second set temperature for 0.5 to 2 hours. After that, the powder is cooled in the furnace to obtain the quasi-eutectic oxide ceramic. The pressure is increased to 30 to 60 MPa before the first heating and is maintained until the cooling is completed.

6. The method for preparing a quasi-eutectic oxide ceramic based on an amorphous crystallization process according to claim 5, characterized in that: The second set temperature is determined according to the composition system of the quasi-eutectic oxide ceramic, and its range is 1200~1600℃; the second set temperature is 200℃ higher than the first set temperature.

7. The method for preparing a quasi-eutectic oxide ceramic based on an amorphous crystallization process according to claim 5, characterized in that: The first heating rate is 1~10℃ / s.

8. The method for preparing a quasi-eutectic oxide ceramic based on an amorphous crystallization process according to claim 5, characterized in that: The second heating rate is 0.5~1℃ / s.

9. A quasi-eutectic oxide ceramic prepared by the preparation method according to any one of claims 1-8, characterized in that, The quasi-eutectic oxide ceramic is a fully crystallized blocky crystal, and its microstructure is characterized by being composed of several finely interwoven nanophase particles. The nanophase particles have a eutectic phase boundary structure inside and a polycrystalline grain boundary structure at their boundaries, forming a multiphase interwoven structure with a binary boundary structure of eutectic phase boundary structure and polycrystalline grain boundary structure.

10. The quasi-eutectic oxide ceramic according to claim 9, characterized in that: The quasi-eutectic oxide ceramic is an Al2O3-YSZ binary quasi-eutectic oxide ceramic, wherein YSZ is yttrium oxide-stabilized zirconium oxide ceramic.

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