High-strength composite ceramic rod and method of making same

Abstract

The application provides a high-strength composite ceramic rod and a preparation method thereof, and belongs to the technical field of ceramic materials. The ceramic rod is a coaxial three-layer gradient structure, and sequentially comprises a core, a transition layer and an outer surface layer from inside to outside. The content of zirconium oxide in the core is higher than that in the outer surface layer, and the total content of aluminum oxide and titanium carbide or titanium boride in the outer surface layer is higher than that in the core, so that residual compressive stress is formed in the outer surface layer after sintering and cooling. Composition continuously transitions between adjacent layers during cold isostatic pressing. The application realizes the synergistic optimization of high toughness of the core and high hardness of the outer surface layer by constructing the coaxial three-layer gradient structure, finally obtains the high-strength composite ceramic rod with fine-grained structure, high density and excellent mechanical properties, and meets the application requirements under high temperature, high load and high wear working conditions.

Description

Technical Field

[0001] This application relates to the field of ceramic materials technology, and in particular to a high-strength composite ceramic rod and its preparation method. Background Technology

[0002] Alumina ceramics possess advantages such as high hardness, high temperature resistance, wear resistance, and good chemical stability, making them widely used as structural ceramics in fields such as high-temperature rollers, wear-resistant shafts, high-temperature supports, and protective tubes. However, alumina ceramics have relatively low fracture toughness and are prone to brittle fracture under impact or thermal stress, limiting their application in high-reliability operating conditions.

[0003] To improve the toughness of alumina-based ceramics, existing technologies often introduce zirconium oxide (such as 3Y-ZrO2 powder) to form ZTA ceramics, utilizing stress-induced phase transformation to toughen and improve fracture toughness. Simultaneously, silicon carbide whiskers are also used for toughening, improving strength and toughness through mechanisms such as pull-out, bridging, and crack deflection. However, in practical applications, single-structure, homogeneous ZTA or whisker-toughened ceramics struggle to balance surface hardness and core toughness: a high content of surface toughening phase leads to decreased hardness; a low content of core toughening phase results in insufficient overall toughness. Furthermore, silicon carbide whiskers are prone to interfacial reactions with the alumina matrix during high-temperature sintering, leading to whisker damage or excessively strong interfacial bonding, significantly reducing the toughening effect.

[0004] To improve the distribution of mechanical properties, existing technologies have proposed layered or gradient structural designs, such as setting a high-hardness layer on the ceramic surface and retaining a high-toughness layer in the core. However, when there is a large difference in the coefficient of thermal expansion between the layers, tensile stress concentration is easily generated at the interface during cooling, causing interlayer cracking or spalling, which affects reliability. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a high-strength composite ceramic rod and a method for preparing the same.

[0006] Specifically, the first aspect of this application provides a high-strength composite ceramic rod, wherein the ceramic rod has a coaxial three-layer gradient structure, consisting of a core, a transition layer and an outer layer from the inside out. The core material is composed of the following components by mass percentage: 55%–68% alumina, 18%–28% 3Y-ZrO2 powder, 8%–15% silicon carbide whiskers, 0.5%–2% magnesium oxide, 0.5%–2% yttrium oxide, and 0.5%–2% lanthanum oxide; The raw material of the transition layer is composed of the following components by mass percentage: 65%–75% alumina, 12%–20% 3Y-ZrO2 powder, 5%–12% silicon carbide whiskers, 2%–6% titanium carbide or titanium boride, 0.5%–2% magnesium oxide, 0.5%–1.5% yttrium oxide, and 0.5%–1.5% lanthanum oxide; The raw material of the outer layer is composed of the following components in mass percentage: 72%–80% alumina, 5%–12% 3Y-ZrO2 powder, 5%–10% silicon carbide whiskers or silicon carbide particles, 3%–8% titanium carbide or titanium boride, 0.5%–1.5% magnesium oxide, 0.5%–1.5% yttrium oxide, and 0.5%–1.5% lanthanum oxide.

[0007] The zirconium oxide content in the core is higher than that in the outer layer, and the total content of alumina and titanium carbide or titanium boride in the outer layer is higher than that in the core, so that residual compressive stress is formed in the outer layer after sintering and cooling.

[0008] Furthermore, the average thickness of the core accounts for 50% to 70% of the total diameter of the ceramic rod, the average thickness of the transition layer accounts for 15% to 25% of the total diameter of the ceramic rod, and the average thickness of the outer layer accounts for 10% to 25% of the total diameter of the ceramic rod.

[0009] Furthermore, an organic pore-forming agent, accounting for 0.5% to 3% of the total mass of the powder in each layer, is additionally added to the raw materials of the core, transition layer and outer layer.

[0010] Furthermore, the organic pore-forming agent is cross-linked polymethyl methacrylate microspheres with a particle size of 1–10 μm.

[0011] Furthermore, the surface of the silicon carbide whisker has a double coating layer of SiO2 / Al2O3, wherein the inner layer is SiO2 and the outer layer is Al2O3.

[0012] A second aspect of this application provides a method for preparing the high-strength composite ceramic rod described above, comprising the following steps: (1) Mix each layer of raw materials with dispersant, binder and deionized water according to the formula and ball mill to prepare core slurry, transition layer slurry and outer layer slurry with solid content of 55% to 65%; the organic pore-forming agent is added within 30 minutes before the end of ball milling; (2) The core slurry is formed into a mandrel, and the surface of the mandrel is roughened after drying; a transition layer slurry is coated on the surface of the mandrel and dried, and an outer layer slurry is coated on the surface of the transition layer and dried to obtain a three-layer composite green body; the three-layer composite green body is subjected to cold isostatic pressing at a pressure of 250-300 MPa and held for 5-15 min. (3) The green blank after cold isostatic pressing is degreased in an inert atmosphere, with a heating rate of 0.2 to 1℃ / min, and the temperature is raised to 600 to 800℃ and held for 1 to 3 hours; (4) The degreased green body is pre-sintered in an inert atmosphere to obtain a pre-sintered body; (5) Place the pre-sintered body in an organic precursor solution of polycarbosilane or polysilazane and perform 2 to 4 rounds of vacuum pressure impregnation-pyrolysis cycle; (6) The pre-sintered body after impregnation-pyrolysis is subjected to stepwise hot isostatic pressing; (7) The ceramic rod after hot isostatic pressing is annealed in an inert atmosphere to obtain a high-strength composite ceramic rod.

[0013] Furthermore, step (1) also includes pre-treating the silicon carbide whiskers with a double-layer coating: first coating the surface of the whiskers with a SiO2 layer using a sol-gel method, and then coating with an Al2O3 layer; the coated whiskers are then heat-treated at 600-800℃ for 0.5-2 hours.

[0014] Furthermore, in step (5), different concentrations of precursor solutions are used for each round of impregnation: the concentration is 15-20 wt% for the first round, 20-25 wt% for the second round, and 25-30 wt% for the third round and subsequent rounds; Each round includes: first, evacuating to a vacuum level of ≤0.08 MPa and maintaining it for 0.5 to 1 hour; then, introducing inert gas and pressurizing to 0.5 to 2 MPa and maintaining it for 0.5 to 1 hour; and finally, drying and then pyrolyzing in an inert atmosphere at 900 to 1100℃ for 1 to 2 hours.

[0015] Furthermore, in step (4), the pre-sintering temperature is 1300-1400℃, and the holding time is 0.5-1.5 hours.

[0016] Further, in step (6), the stepwise hot isostatic pressing is as follows: first, the temperature is raised to 1200-1300℃ and held for 30-60 min with a pressure ≤10 MPa, then the pressure is gradually increased to 160-180 MPa at a rate of 1-3 MPa / min, and the final temperature is 1530-1570℃, and the temperature is held for 0.5-1.5 hours.

[0017] Furthermore, in step (7), the annealing temperature is 1300-1400℃, the holding time is 2-3 hours, and the temperature is cooled to 800℃ at a rate of 1.5-2℃ / min before being cooled in the furnace. Annealing is followed by a centerless grinding process to the final dimensions.

[0018] The present invention has the following beneficial effects: This invention achieves synergistic optimization of high toughness in the core and high hardness in the outer layer by constructing a coaxial three-layer gradient structure. The high content of zirconium oxide and silicon carbide whiskers in the core utilizes phase transformation toughening and whisker pull-out / bridging mechanisms to significantly improve the fracture toughness and impact resistance of the ceramic rod. The high content of alumina and titanium carbide / titanium boride in the outer layer endows the material with excellent surface hardness, wear resistance, and high-temperature stability. Simultaneously, the transition layer effectively alleviates interfacial stress concentration caused by differences in the thermal expansion coefficients of the layers, preventing interlayer cracking or spalling and ensuring the integrity and reliability of the structure.

[0019] Furthermore, by applying a SiO2 / Al2O3 double-layer coating to the silicon carbide whiskers, harmful interfacial reactions between the whiskers and the matrix during high-temperature sintering were effectively suppressed, preserving the whiskers' aspect ratio and toughening activity, thus further enhancing the toughening effect. The introduction of an organic pore-forming agent, which was then eliminated in subsequent processes, combined with the precursor-derived ceramic phase introduced by vacuum pressure impregnation-pyrolysis cycles, filled the micropores and improved density. The stepwise hot isostatic pressing process promoted full densification of the green body while controlling abnormal grain growth, ultimately yielding a high-strength composite ceramic rod with a fine-grained structure, high density, and excellent mechanical properties, meeting the application requirements under high-temperature, high-load, and high-wear conditions. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following description and illustration are provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0021] Obviously, the following description is merely some examples or embodiments of this application. Those skilled in the art can apply this application to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this application, any changes to design, manufacturing, or production based on the technical content disclosed in this application are merely conventional technical means and should not be construed as insufficient disclosure of the content of this application.

[0022] An embodiment of the first aspect of this application provides a high-strength composite ceramic rod, wherein the ceramic rod has a coaxial three-layer gradient structure, consisting of a core, a transition layer and an outer layer from the inside out. The core material is composed of the following components by mass percentage: 55%–68% alumina, 18%–28% 3Y-ZrO2 powder, 8%–15% silicon carbide whiskers, 0.5%–2% magnesium oxide, 0.5%–2% yttrium oxide, 0.5%–2% lanthanum oxide, and 2.0%–3.0% cross-linked polymethyl methacrylate (PMMA) microspheres (added separately). The high zirconium oxide content in the core provides stress-induced phase transformation toughening; the silicon carbide whiskers enhance the toughening effect; and magnesium oxide, yttrium oxide, and lanthanum oxide act as sintering aids, promoting liquid-phase sintering and refining the grain size.

[0023] The transition layer is composed of the following components by mass percentage: 65%–75% alumina, 12%–20% 3Y-ZrO2 powder, 5%–12% silicon carbide whiskers, 2%–6% titanium carbide or titanium boride, 0.5%–2% magnesium oxide, 0.5%–1.5% yttrium oxide, 0.5%–1.5% lanthanum oxide, and 1.5%–2.5% cross-linked polymethyl methacrylate (PMMA) microspheres (added separately). The introduction of TiC / TiB2 into the transition layer improves hardness and thermal conductivity, reduces the coefficient of thermal expansion, and also buffers the difference in the coefficient of thermal expansion between the core and the outer surface layer, reducing interfacial stress concentration.

[0024] The outer surface layer is composed of the following components by mass percentage: 72%–80% alumina, 5%–12% 3Y-ZrO2 powder, 5%–10% silicon carbide whiskers or silicon carbide particles, 3%–8% titanium carbide or titanium boride, 0.5%–1.5% magnesium oxide, 0.5%–1.5% yttrium oxide, 0.5%–1.5% lanthanum oxide, and 1.5%–2.5% cross-linked PMMA microspheres (added separately). The high alumina and TiC / TiB2 content in the outer surface layer results in a low coefficient of thermal expansion, leading to residual compressive stress on the surface after cooling, further improving surface hardness and wear resistance. The addition of silicon carbide whiskers or particles enhances the fracture toughness of the outer surface layer, preventing the propagation of surface microcracks.

[0025] The alumina powder has a D50 of 0.2–0.8 μm; the 3Y-ZrO2 powder has a D50 of 0.1–0.5 μm; the silicon carbide whiskers have a diameter of 0.1–1.0 μm and an aspect ratio of 10–40; the TiC or TiB2 powder has a D50 of 0.5–1.5 μm; and the magnesium oxide, yttrium oxide, and lanthanum oxide powders have a D50 ≤ 1 μm.

[0026] 3Y-ZrO2 powder is a 3 mol% yttrium oxide-stabilized tetragonal zirconia polycrystalline material, mainly composed of 94.7% ZrO2 and 5.3% Y2O3 (wt%), with an average particle size of 30 nm. The CAS number for this material is 1314-23-4.

[0027] In some embodiments, the average thickness of the core accounts for 50% to 70% of the total diameter of the ceramic rod, the average thickness of the transition layer accounts for 15% to 25% of the total diameter of the ceramic rod, and the average thickness of the outer layer accounts for 10% to 25% of the total diameter of the ceramic rod. This structural design enables the core to possess excellent toughness to resist the propagation of internal cracks, while the outer layer provides high hardness and wear resistance to cope with surface contact stress, and the transition layer smoothly connects the two, avoiding interface failure caused by abrupt performance changes.

[0028] In some embodiments, an organic pore-forming agent, comprising 0.5% to 3% of the total mass of the powder in each of the core, transition layer, and outer surface layer, is additionally added to the raw materials. The organic pore-forming agent is cross-linked polymethyl methacrylate microspheres with a particle size of 1 to 10 μm. This pore-forming agent is burned off during the degreasing stage, leaving spherical channels and stably controlling the porosity of the pre-sintered body.

[0029] An embodiment of the second aspect of this application provides a method for preparing the high-strength composite ceramic rod, comprising the following steps: (1) Mix each layer of raw materials with dispersant, binder and deionized water according to the formula and ball mill to prepare core slurry, transition layer slurry and outer layer slurry with solid content of 55% to 65%; the organic pore-forming agent is added within 30 minutes before the end of ball milling; (2) The core slurry is formed into a mandrel, and the surface of the mandrel is roughened after drying; a transition layer slurry is coated on the surface of the mandrel and dried, and an outer layer slurry is coated on the surface of the transition layer and dried to obtain a three-layer composite green body; the three-layer composite green body is subjected to cold isostatic pressing at a pressure of 250-300 MPa and held for 5-15 min. (3) The green blank after cold isostatic pressing is degreased in an inert atmosphere, with a heating rate of 0.2 to 1℃ / min, and the temperature is raised to 600 to 800℃ and held for 1 to 3 hours to completely remove organic matter and organic pore-forming agent. (4) The degreased green body is pre-sintered in an inert atmosphere to obtain a pre-sintered body; (5) Place the pre-sintered body in an organic precursor solution of polycarbosilane or polysilazane and perform 2 to 4 rounds of vacuum pressure impregnation-pyrolysis cycle; (6) The pre-sintered body after impregnation-pyrolysis is subjected to stepwise hot isostatic pressing; (7) The ceramic rod after hot isostatic pressing is annealed in an inert atmosphere to obtain a high-strength composite ceramic rod.

[0030] In some embodiments, in step (1), the surface of the silicon carbide whisker has a SiO2 / Al2O3 double coating layer, wherein the inner layer is SiO2 and the outer layer is Al2O3.

[0031] The method for pre-treating silicon carbide whiskers with double-layer coating is as follows: the silicon carbide whiskers are first washed with dilute hydrochloric acid (5 wt%) for 30 min, ultrasonically cleaned with deionized water 3 times, and then dried. SiO2 inner layer coating: Whiskers were dispersed in an ethanol solution of tetraethyl orthosilicate (TEOS) at a mass ratio of 0.5:100 to 1:100. Ammonia was added dropwise to adjust the pH to 9-10, and the mixture was stirred at 60°C for 4 hours. After centrifugation and drying, the mixture was heat-treated at 600°C in nitrogen for 1 hour to obtain the SiO2 coating layer. Al2O3 outer coating: SiO2-coated whiskers were dispersed in an isopropanol solution of aluminum isopropoxide, with an aluminum source to whisker mass ratio of 1:100 to 2:100. A small amount of water was added dropwise to promote hydrolysis, and the reaction was stirred at 80°C for 4 hours. After centrifugation and drying, the mixture was heat-treated in air at 600–800°C for 0.5–2 hours to obtain the Al2O3 outer layer.

[0032] The Al2O3 on the surface of the whiskers after double coating has good compatibility with the substrate, while the inner SiO2 layer blocks the direct reaction between silicon carbide and alumina.

[0033] The dispersion medium in step (1) is deionized water; the dispersant is ammonium polyacrylate (molecular weight 3000-5000), and the amount added is 0.8%-1.5% of the total mass of the powder; the binder is polyvinyl alcohol (PVA-1788), and the amount added is 1.5%-2.5% of the total mass of the powder; the plasticizer (optional) is polyethylene glycol 400, and the amount added is 0.5%-1% of the total mass of the powder; the defoamer is n-butanol, and the amount added is 0.1%-0.3% of the slurry volume.

[0034] The solid content of the slurry was controlled at 58%–62%. The ball milling conditions were: zirconia ball milling beads (5 mm diameter), ball-to-material ratio 3:1, rotation speed 200–300 r / min, and milling time 5–8 hours. Cross-linked PMMA microspheres were added 30 minutes before the end of ball milling and mixed uniformly at low speed (100 r / min) to avoid microsphere breakage. After ball milling, vacuum degassing was performed at a vacuum degree of 0.07–0.09 MPa for 15–30 min.

[0035] In some embodiments, in step (2), the core slurry is extruded into a cylindrical mandrel at an extrusion pressure of 2–5 MPa and an extrusion speed of 10–30 mm / s. The mandrel diameter is determined based on the total diameter of the target rod and the layer thickness ratio of the three layers. After extrusion, the mandrel is dried at room temperature until the moisture content is ≤1%, and then dried at 60°C for 4 hours. The surface of the mandrel is sandblasted to achieve a surface roughness Ra = 0.8–1.5 μm.

[0036] Transition layer coating: The transition layer slurry is evenly coated onto the mandrel surface by dip-coating or brushing. After the first coating dries, another coating is applied, repeating 2-3 times until the designed thickness is achieved. Each coating is dried at 60°C for 1 hour.

[0037] Surface coating: Apply the surface coating slurry by dip-coating or brushing, repeating 2-3 times until the designed thickness is achieved.

[0038] The dried three-layer composite green body is placed into a rubber mold and subjected to cold isostatic pressing at a pressure of 270–300 MPa for 8–12 minutes.

[0039] In some embodiments, in step (3), the degreasing is carried out in flowing nitrogen (purity ≥99.9%) at a flow rate of 1–3 L / min. First, the temperature is increased from room temperature to 220°C at a rate of 0.3°C / min and held for 2 hours to slowly remove moisture and low-molecular-weight organic matter. Then, the temperature is increased to 400°C at a rate of 1°C / min and held for 3 hours to completely pyrolyze and burn off the cross-linked PMMA microspheres, leaving spherical channels. Finally, the temperature is increased to 750°C at a rate of 0.5°C / min and held for 2 hours to fully remove the binder and other organic matter. After degreasing, the sample shows no cracks or deformation, and the mass loss rate is consistent with the total amount of organic matter added.

[0040] In some embodiments, in step (4), the degreased green body is pre-sintered in flowing argon gas (purity ≥99.99%). The heating rate is 4-6℃ / min, the pre-sintering temperature is 1300-1400℃, and the holding time is 0.5-1.5 hours. After pre-sintering, the green body has a certain mechanical strength (flexural strength 135-145 MPa), and the porosity is controlled at 8%-12%, which facilitates the impregnation and penetration of the precursor solution. During the pre-sintering process, neck connections are initially formed between the matrix particles, but densification sintering has not yet occurred, and a sufficient interconnected pore network is retained.

[0041] In some embodiments, in step (5), a xylene solution of polycarbosilane (PCS, number average molecular weight 800-1500) is used as a precursor. The precursor is prepared by dissolving 20.0 g of polycarbosilane powder in 80.0 g of xylene solvent, heating to 40-60°C, and stirring until completely dissolved to obtain a clear and transparent precursor solution.

[0042] The cyclic impregnation-pyrolysis process is carried out in three rounds, with different concentrations and processes used in each round: The first-round precursor concentration is 15-20 wt% (low viscosity, which is conducive to deep penetration). First, a vacuum is drawn to a vacuum degree of ≤0.08 MPa and held for 1 hour. Then, high-purity argon gas is introduced to pressurize to 1.0 MPa and held for 1 hour. Then, it is dried at 80℃ for 2 hours and at 120℃ for 2 hours. Under an argon atmosphere, it is pyrolyzed at 950℃ at a rate of 2℃ / min and held for 1 hour.

[0043] The second-round precursor concentration was 20–25 wt%, the vacuum degree was ≤0.08 MPa, and the impregnation was maintained for 1 hour; the pressure was increased to 1.5 MPa, and the impregnation was maintained for 1 hour; under an argon atmosphere, the temperature was increased to 1000℃ at 2℃ / min and held for 1 hour.

[0044] The third round of precursor concentration was 25–30 wt% (high ceramic yield, sealing residual surface porosity); vacuum degree ≤0.08 MPa, impregnation held for 1 hour; pressure increased to 2.0 MPa, impregnation held for 1 hour; pyrolysis was performed under argon atmosphere, heating to 1050℃ at 3℃ / min, and held for 1 hour. Weight gain (relative to the mass of the pre-sintered body) was measured after each pyrolysis round. After 3 cycles, the cumulative weight gain reached 3.5%–5.0%. If the weight gain in the third round was less than 0.8%, a fourth round was added, with the same process as the third round. The nano-SiC generated by pyrolysis filled the spherical channels and interparticle gaps left in the pre-sintered body, significantly reducing the open porosity of the green body and improving its overall density and strength, laying a good foundation for complete densification in the subsequent hot isostatic pressing process.

[0045] In some embodiments, in step (6), the sample after cyclic impregnation-pyrolysis is placed in a hot isostatic pressing furnace under an argon atmosphere. The stepwise hot isostatic pressing is as follows: first, the temperature is increased to 1200-1300℃ at a rate of 5-6℃ / min and held for 30-60 min with a pressure ≤10MPa. During this stage, the surface pores are partially healed through surface diffusion, but the internal pores remain connected to prevent the subsequent high pressure from failing to be transmitted to the interior; then, the pressure is gradually increased to 160-180 MPa at a rate of 1-3 MPa / min, with a final temperature of 1530-1570℃, and held for 0.5-1.5 hours. This step, through the synergistic effect of high temperature and high pressure, promotes the closure of residual pores, grain boundary migration, and material diffusion inside the billet, thereby achieving complete densification of the material. During this process, the nano-SiC generated by the pyrolysis of the precursor further undergoes solid-phase reaction or liquid-phase assisted sintering with components such as alumina and zirconium oxide in the matrix, refining the grain structure and eliminating microscopic defects. The step-by-step pressurization strategy effectively avoids the problem of premature surface densification and closure of internal exhaust channels due to sudden pressure increases, ensuring the consistency of the densification process of the inner and outer layers.

[0046] In some embodiments, in step (7), after hot isostatic pressing, the material is annealed in an argon atmosphere, heated to 1300-1400°C at a heating rate of 5°C / min, held for 2-3 hours, and then cooled to 800°C at a rate of 1.5-2°C / min before being cooled in the furnace. This step aims to eliminate residual stress generated during hot isostatic pressing, stabilize the grain boundary structure, and optimize the phase composition of zirconia. Annealing helps to release internal stress caused by rapid cooling or phase transformation within the material, preventing spontaneous cracking during subsequent processing or use, while also promoting the homogenization of the grain structure, thereby further improving the overall mechanical properties and reliability of the ceramic rod.

[0047] The annealed ceramic rods were centerlessly ground to their final dimensions (surface roughness Ra≤0.4μm), and then ultrasonically cleaned and dried.

[0048] Example The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight. Unless otherwise stated, all reagents used in the examples are available commercially or synthesized using conventional methods and are ready for use without further processing. Unless otherwise stated, all instruments used in the examples are available commercially.

[0049] Example 1 A high-strength composite ceramic rod, wherein the ceramic rod has a coaxial three-layer gradient structure, consisting of a core, a transition layer and an outer layer from the inside out; The core material is composed of the following components by mass percentage: 62% alumina, 24% 3Y-ZrO2, 10% silicon carbide whiskers, 1.5% MgO, 1.5% Y2O3, 1% La2O3, and an additional 2.5% cross-linked PMMA microspheres; The raw material of the transition layer is composed of the following components by mass percentage: 69% alumina, 18% 3Y-ZrO2, 8% silicon carbide whiskers, 3% TiC, 1% MgO, 0.5% Y2O3, 0.5% La2O3, and an additional 2.0% cross-linked PMMA microspheres; The outer surface layer is composed of the following components by mass percentage: 76% alumina, 10% 3Y-ZrO2, 8% silicon carbide whiskers, 4% TiC, 1% MgO, 0.5% Y2O3, 0.5% La2O3, and an additional 2.0% cross-linked PMMA microspheres.

[0050] The method for preparing the high-strength composite ceramic rod includes the following steps: (1) The method for pre-coating silicon carbide whiskers with a double layer is as follows: The silicon carbide whiskers are first washed with dilute hydrochloric acid (5 wt%) for 30 min, ultrasonically cleaned with deionized water 3 times, and dried. The whiskers are dispersed in an ethanol solution of tetraethyl orthosilicate (TEOS) with a mass ratio of TEOS to whiskers of 1:100. Ammonia is added dropwise to adjust the pH to 9.5, and the mixture is stirred at 60°C for 4 hours. After centrifugation and drying, the mixture is heat-treated at 600°C in nitrogen for 1 hour to obtain a SiO2 coating layer. The SiO2-coated whiskers are dispersed in an isopropanol solution of aluminum isopropoxide with a mass ratio of aluminum source to whiskers of 1.5:100. A small amount of water is added dropwise to promote hydrolysis, and the mixture is stirred at 80°C for 4 hours. After centrifugation and drying, the mixture is heat-treated at 800°C in air for 1 hour to obtain an Al2O3 outer layer. Each layer was ball-milled for 6 hours according to the specified ratio. The ball milling medium was deionized water with a solid content of 60%. The dispersant was ammonium polyacrylate (1.0%), the binder was PVA (2.0%), and the PMMA microspheres were added 30 minutes before the end of the ball milling. (2) The core slurry was extruded into a mandrel, dried, and then sandblasted to Ra=1.0μm. The transition layer slurry was applied twice and the outer layer slurry was applied twice in sequence. After each application, the mandrel was dried at 60℃ for 1 hour. The mandrel was then subjected to cold isostatic pressing at 280 MPa for 10 min. (3) Degreasing is carried out in flowing nitrogen: heating to 220℃ at 0.3℃ / min and holding for 2 hours, heating to 400℃ at 0.5℃ / min and holding for 3 hours, heating to 750℃ at 1℃ / min and holding for 2 hours; (4) The degreased green body was pre-sintered in flowing argon gas (purity ≥99.99%), heated to 1350℃ at 5℃ / min and held for 1 hour. The measured porosity was 10.3% and the bending strength was 142 MPa. (5) Cyclic impregnation-pyrolysis using polycarbosilane xylene solution as precursor: In the first round, the concentration was 15 wt%, and the pressure was maintained at 0.08 MPa for 1 hour, followed by argon gas to pressurize to 1 MPa and maintaining for 1 hour. After drying, the solution was pyrolyzed at 950℃ for 1 hour, with a weight gain of 1.6%. In the second round, the concentration was 22 wt%, the pressure was 1.5 MPa, and the solution was pyrolyzed at 1000℃ for 1 hour, with a cumulative weight gain of 3.1%. In the third round, the concentration was 30 wt%, the pressure was 2 MPa, and the solution was pyrolyzed at 1050℃ for 1 hour, with a cumulative weight gain of 4.5%. (6) The sample after cyclic impregnation-pyrolysis is placed into a hot isostatic press furnace under an argon atmosphere. First, the temperature is increased to 1250℃ at 5℃ / min and held for 30 min (pressure ≤10 MPa). Then, the temperature is increased to 1550℃ at 3℃ / min, and the pressure is increased to 160 MPa at 1 MPa / min. The temperature is held for 1 hour.

[0051] (7) Annealing: Heat to 1200℃ in argon at 5℃ / min and hold for 3 hours, then cool to 800℃ at 1.5℃ / min and cool with the furnace. Centerless grinding to the final size.

[0052] Example 2 This embodiment is basically the same as embodiment 1, except that: Core: 60% alumina, 25% 3Y-ZrO2, 11% silicon carbide whiskers, 1.2% MgO, 1.5% Y2O3, 1.3% La2O3, with an additional 3.0% PMMA microspheres; Transition layer: 71.5% alumina, 16% 3Y-ZrO2, 7% silicon carbide whiskers, 3% TiC, 0.8% MgO, 1.0% Y2O3, 0.7% La2O3, with an additional 2.5% PMMA microspheres; Outer layer: 76% alumina, 8% 3Y-ZrO2, 8% silicon carbide whiskers, 5.5% TiC, 0.8% MgO, 1.0% Y2O3, 0.7% La2O3, with an additional 2.5% PMMA microspheres.

[0053] The preparation method is basically the same as in Example 1, but the cold isostatic pressing pressure is 300 MPa and held for 8 min; the pre-sintering temperature is 1380℃ and held for 1 hour, the measured porosity is 10.5%, and the flexural strength is 135 MPa; the concentration of the first round of cyclic impregnation is 18 wt%, the second round is 24 wt%, and the third round is 28 wt%, with a cumulative weight gain of 4.1%; the stepwise HIP final temperature is 1530℃, the pressure is 170 MPa, and the holding time is 1 hour; the annealing temperature is 1180℃ and the holding time is 2 hours.

[0054] Example 3 This embodiment is basically the same as embodiment 1, except that: Core: 65% alumina, 22% 3Y-ZrO2, 9% silicon carbide whiskers, 1.6% MgO, 1.2% Y2O3, 1.2% La2O3, with an additional 2.0% PMMA microspheres; Transition layer: 68% alumina, 19% 3Y-ZrO2, 9% silicon carbide whiskers, 1.5% TiB2, 1.0% MgO, 0.8% Y2O3, 0.7% La2O3, with an additional 1.8% PMMA microspheres; Outer layer: 74% alumina, 12% 3Y-ZrO2, 7% silicon carbide whiskers, 25% TiB, 0.5% MgO, 0.8% Y2O3, 0.7% La2O3, with an additional 1.8% PMMA microspheres.

[0055] The preparation method is basically the same as in Example 1, except that TiC in the transition layer and outer surface layer is replaced with TiB2; the pre-sintering temperature is 1320℃ and held for 1 hour, the measured porosity is 11.0%, and the flexural strength is 148 MPa; the cyclic impregnation uses a polysilazane precursor, with a concentration of 16 wt% in the first round, 22 wt% in the second round, and 26 wt% in the third round, with a cumulative weight gain of 3.8%; the stepwise HIP final temperature is 1570℃, the pressure is 150 MPa, and the holding time is 1 hour; the annealing temperature is 1220℃ and the holding time is 3 hours.

[0056] Example 4 This embodiment is basically the same as embodiment 1, except that: Core: 58% alumina, 26% 3Y-ZrO2, 12% silicon carbide whiskers, 1.2% MgO, 1.6% Y2O3, 1.2% La2O3, with an additional 2.8% PMMA microspheres; Transition layer: 70% alumina, 16% 3Y-ZrO2, 8% silicon carbide whiskers, 3% TiC, 1.5% MgO, 1.0% Y2O3, 0.5% La2O3, with an additional 2.2% PMMA microspheres; Outer layer: 76% alumina, 10% 3Y-ZrO2, 8% silicon carbide particles, 4% TiC, 0.8% MgO, 0.8% Y2O3, 0.4% La2O3, with an additional 2.2% PMMA microspheres.

[0057] The preparation method is basically the same as in Example 1, but the pre-sintering temperature is 1300℃ and held for 1 hour, the porosity is 11.6%, the flexural strength is 139 MPa, the cumulative weight gain of cyclic impregnation is 4.3%, the stepwise HIP is 1550℃, 160 MPa and held for 1.5 hours, and the annealing temperature is 1200℃ and held for 3 hours.

[0058] Example 5 This embodiment is basically the same as embodiment 1, except that: Core: 63% alumina, 23% 3Y-ZrO2, 10% silicon carbide whiskers, 1.5% MgO, 1.3% Y2O3, 1.2% La2O3, with an additional 2.5% PMMA microspheres; Transition layer: 70% alumina, 17% 3Y-ZrO2, 8% silicon carbide whiskers, 2.5% TiC, 1.0% MgO, 0.8% Y2O3, 0.7% La2O3, with an additional 2.0% PMMA microspheres; Outer layer: 77% aluminum oxide, 9% 3Y-ZrO, 7% silicon carbide whiskers, 4% TiC, 0.7% MgO, 0.6% Y2O3, 0.7% La2O3, with an additional 2.0% PMMA microspheres.

[0059] The preparation method is basically the same as in Example 1, but the pre-sintering temperature is 1340℃, the porosity is 10.5%, the strength is 140 MPa, and the cyclic impregnation is carried out for 4 rounds. The concentration in the 4th round is 30 wt%, and the cumulative weight gain is 5.0%. In the second stage of stepwise HIP, the temperature is raised to 1560℃, the pressure is 180 MPa, and the holding time is 0.8 hours. Annealing is carried out at 1200℃ for 2.5 hours, and the cooling rate is 2℃ / min to 800℃.

[0060] Comparative Example 1 This comparative example is basically the same as Example 1, except that PMMA microspheres are not added to the components.

[0061] Comparative Example 2 This comparative example is basically the same as Example 1, except that the hot isostatic pressing adopts the traditional one-step pressurization: the temperature is directly increased to 1550℃ at 5℃ / min, and the pressure is simultaneously increased to 160 MPa, and the temperature is held for 1 hour, without the 1250℃ low temperature micro-pressure heat preservation stage.

[0062] Comparative Example 3 This comparative example is basically the same as Example 1, except that the silicon carbide whiskers are only coated with a single layer of SiO2 with a coating amount of 2.0%, and there is no outer layer of Al2O3 coating.

[0063] Comparative Example 4 This comparative example is basically the same as Example 1, except that: all three impregnations were performed using a 20 wt% polycarbosilane solution.

[0064] Comparative Example 5 This comparative example is basically the same as Example 1, except that: a ceramic rod with a single uniform structure is prepared without gradient layering of core, transition layer and outer surface layer. The preparation process does not include layered coating and cold isostatic pressing interlayer infiltration steps, and the remaining pre-sintering, impregnation pyrolysis, stepwise HIP and annealing conditions are the same as in Example 1.

[0065] Experimental Case The following tests were conducted on the samples prepared in Examples 1-5 and Comparative Examples 1-5: Bending strength: tested using the three-point bending method (span 30 mm, specimen size 3 mm × 4 mm × 36 mm). Fracture toughness: tested using the single-sided notched beam method (SENB); Hardness: Tested using a Vickers hardness tester (load 10 kgf); Density: determined by Archimedes' displacement method; The test results are shown in Table 1.

[0066] Table 1 Test results of Examples 1-5 and Comparative Examples 1-5

[0067] As shown in Table 1, the high-strength composite ceramic rods prepared in Examples 1-5 all exhibited excellent mechanical properties, with a density exceeding 99.1%, a flexural strength exceeding 940 MPa, and a fracture toughness greater than 10.5 MPa·m. 1 / 2 The outer layer has a Vickers hardness higher than 1880 HV10. In Example 5, by increasing the number of impregnation wheels to 4 and optimizing the hot isostatic pressing parameters, the highest density (99.5%) and the best combination of mechanical properties were obtained, indicating that sufficient precursor infiltration and a stepwise densification strategy are crucial for improving material properties.

[0068] In contrast, Comparative Example 1, lacking PMMA pore-forming agent, had a low pre-sintered body with poor pore connectivity, making it difficult for the precursor solution to penetrate deeply. This resulted in insufficient filling of nano-SiC generated by pyrolysis, ultimately leading to significantly lower density and mechanical properties compared to Example 1. This demonstrates that a controllable spherical pore network is a prerequisite for achieving efficient impregnation toughening. Comparative Example 2 employed a traditional one-step pressurized hot isostatic pressing process, lacking a low-temperature micro-pressure insulation stage. This caused premature sealing of the internal venting channels, preventing complete elimination of residual pores. Consequently, both density and strength were lower than in Example 1, which used stepwise hot isostatic pressing. This verifies the advantages of the stepwise pressurization strategy in eliminating internal defects and achieving uniform densification. In Comparative Example 3, the silicon carbide whiskers were only coated with a single layer of SiO2, lacking an outer layer of Al2O3. This resulted in weak interfacial bonding between the whiskers and the alumina matrix, and made them prone to adverse reactions at high temperatures. Consequently, the fracture toughness and hardness were slightly lower than those of Example 1, which had a double-layer coating. This demonstrates the role of the SiO2 / Al2O3 double-layer coating structure in improving interfacial compatibility and enhancing toughness. Comparative Example 4 used a precursor solution of constant concentration for impregnation, failing to achieve a gradient filling from shallow to deep. This led to premature sealing of surface pores and insufficient internal filling, resulting in a lower cumulative weight gain and final performance compared to Example 1, which had a gradient concentration impregnation. Comparative Example 5 had a single, uniform structure, lacking a gradient design. It could not simultaneously achieve high toughness in the core and high hardness and wear resistance in the outer layer. Furthermore, due to the uniformity of properties in each part, the overall bending strength and fracture toughness were significantly lower than those of Example 1, which had a gradient structure. This highlights the superiority of the coaxial three-layer gradient structure design in synergistically improving comprehensive mechanical properties.

[0069] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A high-strength composite ceramic rod, characterized in that, The ceramic rod has a coaxial three-layer gradient structure, consisting of a core, a transition layer, and an outer layer from the inside out. The core material is composed of the following components by mass percentage: 55%–68% alumina, 18%–28% 3Y-ZrO2 powder, 8%–15% silicon carbide whiskers, 0.5%–2% magnesium oxide, 0.5%–2% yttrium oxide, and 0.5%–2% lanthanum oxide; The raw material of the transition layer is composed of the following components by mass percentage: 65%–75% alumina, 12%–20% 3Y-ZrO2 powder, 5%–12% silicon carbide whiskers, 2%–6% titanium carbide or titanium boride, 0.5%–2% magnesium oxide, 0.5%–1.5% yttrium oxide, and 0.5%–1.5% lanthanum oxide; The raw material of the outer layer is composed of the following components in mass percentage: 72%–80% alumina, 5%–12% 3Y-ZrO2 powder, 5%–10% silicon carbide whiskers or silicon carbide particles, 3%–8% titanium carbide or titanium boride, 0.5%–1.5% magnesium oxide, 0.5%–1.5% yttrium oxide, and 0.5%–1.5% lanthanum oxide.

2. The high-strength composite ceramic rod according to claim 1, characterized in that, The average thickness of the core is 50% to 70% of the total diameter of the ceramic rod, the average thickness of the transition layer is 15% to 25% of the total diameter of the ceramic rod, and the average thickness of the outer layer is 10% to 25% of the total diameter of the ceramic rod.

3. The high-strength composite ceramic rod according to claim 1, characterized in that, The raw materials of the core, transition layer and outer layer are also supplemented with an organic pore-forming agent accounting for 0.5% to 3% of the total mass of the powder in each layer; And / or, the organic pore-forming agent is cross-linked polymethyl methacrylate microspheres with a particle size of 1–10 μm.

4. The high-strength composite ceramic rod according to claim 1, characterized in that, The surface of the silicon carbide whiskers has a double coating layer of SiO2 / Al2O3, wherein the inner layer is SiO2 and the outer layer is Al2O3.

5. A method for preparing a high-strength composite ceramic rod according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Mix each layer of raw materials with dispersant, binder and deionized water according to the formula and ball mill to prepare core slurry, transition layer slurry and outer layer slurry with solid content of 55% to 65%; the organic pore-forming agent is added within 30 minutes before the end of ball milling; (2) The core slurry is formed into a mandrel, and the surface of the mandrel is roughened after drying; a transition layer slurry is coated on the surface of the mandrel and dried, and an outer layer slurry is coated on the surface of the transition layer and dried to obtain a three-layer composite green body; the three-layer composite green body is subjected to cold isostatic pressing at a pressure of 250-300 MPa and held for 5-15 min. (3) The green blank after cold isostatic pressing is degreased in an inert atmosphere, with a heating rate of 0.2 to 1℃ / min, and the temperature is raised to 600 to 800℃ and held for 1 to 3 hours; (4) The degreased green body is pre-sintered in an inert atmosphere to obtain a pre-sintered body; (5) Place the pre-sintered body in an organic precursor solution of polycarbosilane or polysilazane and perform 2 to 4 rounds of vacuum pressure impregnation-pyrolysis cycle; (6) The pre-sintered body after impregnation-pyrolysis is subjected to stepwise hot isostatic pressing; (7) The ceramic rod after hot isostatic pressing is annealed in an inert atmosphere to obtain a high-strength composite ceramic rod.

6. The method for preparing the high-strength composite ceramic rod according to claim 5, characterized in that, Step (1) also includes pre-coating the silicon carbide whiskers with a double layer: first, a SiO2 layer is coated on the surface of the whiskers using the sol-gel method, and then an Al2O3 layer is coated; the coated whiskers are then heat-treated at 600-800℃ for 0.5-2 hours.

7. The method for preparing the high-strength composite ceramic rod according to claim 5, characterized in that, In step (5), different concentrations of precursor solutions are used for each round of impregnation: the concentration is 15-20 wt% for the first round, 20-25 wt% for the second round, and 25-30 wt% for the third round and subsequent rounds. And / or, each round includes: first, evacuating to a vacuum degree ≤0.08 MPa and holding for 0.5 to 1 hour, then introducing inert gas and pressurizing to 0.5 to 2 MPa and holding for 0.5 to 1 hour, and then drying and pyrolyzing in an inert atmosphere at 900 to 1100℃ for 1 to 2 hours.

8. The method for preparing the high-strength composite ceramic rod according to claim 5, characterized in that, In step (4), the pre-sintering temperature is 1300-1400℃ and the holding time is 0.5-1.5 hours.

9. The method for preparing the high-strength composite ceramic rod according to claim 5, characterized in that, In step (6), the stepwise hot isostatic pressing is as follows: first, heat to 1200-1300℃ and hold for 30-60 min with a pressure ≤10 MPa, then gradually increase the pressure to 160-180 MPa at a rate of 1-3 MPa / min, and finally the temperature is 1530-1570℃, and hold for 0.5-1.5 hours.

10. The method for preparing the high-strength composite ceramic rod according to claim 5, characterized in that, In step (7), the annealing temperature is 1300-1400℃, the holding time is 2-3 hours, and the temperature is cooled to 800℃ at a rate of 1.5-2℃ / min before being cooled in the furnace. Annealing is followed by a centerless grinding process to the final dimensions.

Images