High-strength and high-toughness self-lubricating B4C-TiB2-graphite composite ceramic and preparation method thereof

Abstract

The application discloses high-strength and high-toughness self-lubricating graphite composite ceramic and a preparation method thereof, and belongs to the field of ceramic matrix composites. The ceramic is prepared from the following raw material components in mass fraction: boron carbide powder 73.5-96.2 %, titanium powder 3.2-22.3 %, and flaky graphite 0.6-4.2 %. TiB2 dispersed phase is generated in situ to refine grains, strengthen the matrix and induce crack deflection. Meanwhile, the flaky graphite is arranged along a specific direction by using the hot-pressing pressure to form a weak interface layer to promote crack deflection and bridging and provide self-lubricating function. The two phases work together to significantly improve the fracture toughness and endow the material with self-lubricating properties while maintaining high hardness.

Description

Technical Field

[0001] This invention pertains to ceramic matrix composites, and particularly relates to a high-strength, high-toughness, self-lubricating composite material. Graphite multiphase ceramics and their preparation methods. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Boron carbide ceramics possess extremely high hardness and extremely low density. Its hardness is second only to diamond and cubic boron nitride, and its theoretical density reaches 2.52 g / cm³. It also boasts advantages such as high elastic modulus, excellent neutron absorption capacity, good chemical stability, and high-temperature strength retention. Based on these advantages, boron carbide ceramics are widely used in lightweight ballistic armor (such as tank armor and individual soldier protective plates), neutron absorption and shielding components in the nuclear industry, high-wear-resistant nozzles and seals, high-temperature structural components in aerospace, and thermoelectric power generation devices.

[0004] However, Ceramics suffer from inherent brittleness, low fracture toughness, difficulty in sintering and densification, and poor lubrication properties, which severely restrict their engineering applications. Existing toughening modification systems often employ... Composite ceramics (such as CN112723889B) attempt to address the aforementioned issues; however, their toughness improvement is limited, and they often suffer from a significant decrease in hardness and a lack of self-lubricating properties. Furthermore, their preparation processes often rely on high-temperature, long-term sintering at ≥1900℃, resulting in high energy consumption and significant grain coarsening, making it difficult to achieve precise structural control.

[0005] Therefore, there is an urgent need for a composite boron carbide ceramic with high hardness, high fracture toughness, self-lubricating properties, and adjustable properties, as well as its preparation method. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a high-strength, high-toughness, self-lubricating material. Graphite multiphase ceramics and their preparation method: This technical solution generates TiB2 dispersed phase through in-situ reaction to refine grains, strengthen the matrix and induce crack deflection. At the same time, hot pressing pressure is used to orient the flake graphite along a specific direction to form a weak interface layer to promote crack deflection and bridging and provide self-lubricating function. The two phases work together to significantly improve fracture toughness and endow the material with self-lubricating properties while maintaining high hardness.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A high-strength, high-toughness self-lubricating agent Graphite multiphase ceramics, by mass fraction, consist of the following raw material components: boron carbide powder 73.5~96.2%, titanium powder 3.2~22.3%, and flake graphite 0.6~4.2%.

[0009] In some embodiments, the composition is 81.2-92.4% boron carbide powder, 6.4-16.0% titanium powder, and 1.2-3.2% flake graphite.

[0010] A high-strength, high-toughness self-lubricating agent of the above The preparation method of graphite multiphase ceramics includes the following steps:

[0011] S1. Ball mill boron carbide powder and titanium powder until they are evenly mixed, then add flake graphite and mix at low speed to prevent graphite breakage, and obtain a mixed slurry;

[0012] S2. The mixed slurry is subjected to solid-liquid separation, vacuum drying, sieving, and cold pressing to obtain a preform.

[0013] S3. Vacuum hot pressing sintering is performed on the preform to obtain boron carbide composite ceramic.

[0014] This invention uses Ti powder and A strong exothermic reaction occurs during hot pressing sintering, utilizing the heat of reaction to promote material diffusion and densification, achieving low-temperature sintering and higher density. Simultaneously, the hot pressing pressure induces the vertical orientation of the flake graphite, and the active C atoms generated in situ are deposited on the surface of the flake graphite, forming a synergistic effect between the graphite and... Constructing gradient interfaces between the matrix reduces interface energy, improves interface purity, and avoids strength reduction due to weak interfaces. With graphite The dispersed distribution of the crack within the matrix, with a significant difference in thermal expansion coefficient compared to the matrix, induces a deflection of the crack propagation path, prolonging the crack propagation path, increasing fracture energy dissipation, and thus improving fracture toughness. This can be achieved through the control of Ti powder. The fine-grained strengthening and crack deflection effect, and the lubrication and toughening functions of flake graphite, achieve simultaneous optimization of hardness, toughness and self-lubricating properties.

[0015] In some embodiments, the particle size of the flake graphite is 1~5μm and the aspect ratio is ≥5.

[0016] In some embodiments, the boron carbide powder has a particle size of 1-3 μm, and the titanium powder has a particle size of 1-10 μm.

[0017] In some embodiments, boron carbide powder and titanium powder are added to anhydrous ethanol, and the ball milling speed is 200-300 r / min for 10-12 h. Ball milling breaks up the agglomerates, further refines the boron nitride powder, and further flattens the tough titanium powder, resulting in a uniform distribution of Ti particles. Between particles; at the same time, the setting of this rotation speed avoids mechanical alloying of titanium and boron carbide at room temperature, ensuring that the exothermic effect of the reaction is released in a concentrated manner during the sintering stage, and achieving rapid densification at low temperature in conjunction with hot pressing pressure.

[0018] In some embodiments, when adding flake graphite and mixing at low speed, the ball milling speed is 50-150 r / min, and the ball milling time is 1-2 h. The purpose of low-speed mixing is to maintain the morphology of the flake graphite while achieving its properties... Uniform dispersion in mixed powders.

[0019] In some embodiments, in S2, the mixed slurry is vacuum dried, passed through a 150-250 mesh sieve, and cold-pressed to obtain a preform.

[0020] In some embodiments, the cold pressing process involves placing the dried and sieved mixed powder in a graphite mold, applying an axial pressure of 3-10 MPa for pre-pressing, and holding the pressure for 5-15 minutes.

[0021] In some embodiments, the vacuum hot pressing sintering involves heating to 1350-1450°C under vacuum conditions, holding at that temperature to allow the titanium and boron carbide to undergo an initial reaction; then introducing argon gas, applying pressure to 20-40 MPa, heating to 1750-1900°C, and holding at both temperature and pressure to achieve complete reaction and rapid densification.

[0022] In some embodiments, the vacuum hot pressing sintering involves heating to 1350-1450°C under vacuum conditions, holding at that temperature, then filling with argon gas, applying pressure to 25-35 MPa, heating to 1750-1850°C, and holding at both temperature and pressure.

[0023] In some implementations, both cold pressing and vacuum hot pressing sintering are performed in a vacuum hot press furnace. This ensures the initial density of the green body while avoiding contamination and loss during powder transfer. At the same time, maintaining low pressure in the low-temperature section facilitates the discharge of reaction gases, while increasing pressure in the high-temperature section synergistically promotes densification with the heat of reaction.

[0024] In some embodiments, in S3, the preform is vacuum hot-pressed and sintered, then cooled and demolded to obtain boron carbide composite ceramic.

[0025] The beneficial effects of this invention are as follows:

[0026] 1. This invention provides a high-strength, high-toughness self-lubricating material. Graphite multiphase ceramics, utilizing and The difference in thermal expansion coefficients induces crack deflection. Simultaneously, the added flake graphite and the generated graphite combine to comprehensively improve the mechanical properties of the composite ceramic of this invention. The relative density is above 98.5%, the Vickers hardness reaches 32.4~35.1 GPa, the flexural strength reaches 450~690 MPa, and the fracture toughness reaches [missing information]. It also endows the material with a unique self-lubricating function, with a friction coefficient of about 0.20~0.26, which solves the problems of high brittleness, low toughness and lack of lubrication of existing boron carbide ceramics. It is especially suitable for wear-resistant parts, sliding seals, oil-free lubricated bearings and other applications that are sensitive to the friction coefficient.

[0027] 2. The preparation method of the present invention is achieved through... The synergistic microstructure of uniformly dispersed pinned grain boundaries and highly oriented graphite along the perpendicular pressure direction, combined with the in-situ exothermic reaction of titanium and boron carbide, lowers the sintering temperature to 1800-1900℃ and reduces the holding time to 20-40 min. Compared with conventional boron carbide sintering processes, this reduces energy consumption by 100-200℃ and shortens the time by more than 50%, effectively suppressing... Grain coarsening solves the problems of easy agglomeration, poor interfacial bonding, and low density of added graphite in existing technologies.

[0028] 3. The gradient ball milling process of this invention is easy to operate, highly stable, and suitable for industrial mass production. Furthermore, the use of raw materials such as flake graphite and titanium powder lowers the sintering temperature, and the large reserves and ease of large-scale production of flake graphite significantly reduce energy consumption and production costs. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0030] Figure 1 This is a SEM image of the surface of the multiphase ceramic sample from Example 1 of the present invention;

[0031] Figure 2 The image shows the XRD pattern of the multiphase ceramic of Embodiment 1 of the present invention;

[0032] Figure 3 This is a SEM image of the surface of the multiphase ceramic sample from Example 2 of the present invention;

[0033] Figure 4 The image shows the XRD pattern of the multiphase ceramic of Embodiment 2 of the present invention;

[0034] Figure 5 This is a SEM image of the surface of the multiphase ceramic sample from Example 3 of the present invention;

[0035] Figure 6 The image shows the XRD pattern of the multiphase ceramic of Embodiment 3 of the present invention;

[0036] Figure 7 This is a SEM image of the surface of the multiphase ceramic sample from Example 4 of the present invention;

[0037] Figure 8 The image shown is the XRD pattern of the multiphase ceramic of Example 4 of the present invention.

[0038] Figure 9 This is a SEM image of the surface of the multiphase ceramic sample from Example 5 of the present invention;

[0039] Figure 10 This is Example 5 of the present invention. XRD pattern of graphite multiphase ceramics;

[0040] Figure 11 shows SEM images of the surface of the composite ceramic samples from Example 1 and Comparative Example 2.

[0041] Figure 11(a) is a SEM image of the sample surface of Example 1, and Figure 11(b) is a SEM image of the sample surface of Comparative Example 2. Detailed Implementation

[0042] To address the problem that existing composite boron carbide ceramics often suffer from a difficulty in simultaneously achieving high hardness, fracture toughness, and self-lubricating properties, this invention proposes a high-strength, high-toughness, self-lubricating ceramic. Graphite multiphase ceramics and their preparation methods.

[0043] The first aspect of this invention proposes a high-strength, high-toughness self-lubricating agent. Graphite multiphase ceramics, by mass fraction, consist of the following raw material components: boron carbide powder 73.5~96.2%, titanium powder 3.2~22.3%, and flake graphite 0.6~4.2%.

[0044] The first aspect of the present invention provides a high-strength, high-toughness self-lubricating agent as described above. The preparation method of graphite multiphase ceramics includes the following steps:

[0045] S1. Ball mill boron carbide powder and titanium powder until they are evenly mixed, then add flake graphite and mix at low speed to prevent graphite breakage, and obtain a mixed slurry;

[0046] S2. Vacuum dry the mixed slurry, sieve it, and cold press it to obtain a preform.

[0047] S3. Vacuum hot pressing sintering is performed on the preform to obtain boron carbide composite ceramic.

[0048] This invention uses Ti powder and As reactants, they undergo an in-situ reaction during hot pressing and sintering to produce... The reaction equation for activated carbon is:

[0049]

[0050] This reaction is strongly exothermic with a significant heat effect, generating localized high-temperature zones and creating a "self-heating" effect, thus reducing the temperature requirement for external heat sources. High-energy ball milling induces lattice distortion and amorphous layers on the surface of Ti powder particles, significantly reducing the temperature dependence of Ti on external heat sources. The activation energy of the reaction allows the reaction to start at a lower temperature; the axial pressure (20~40 MPa) promotes particle rearrangement and plastic flow, which, together with the heat of reaction, achieves rapid densification and shortens the holding time.

[0051] Compared to direct joining In comparison, the preparation method of this invention has a lower sintering temperature and higher densification. Meanwhile, Pinning grain boundaries achieves fine grain strengthening and dispersion strengthening, keeping the hardness and strength of composite ceramics at a high level.

[0052] In this invention, Ti and The active C atoms generated by the in-situ reaction deposit on the surface of flake graphite to form a carbon-carbon homogeneous transition layer. This transition layer repairs edge defects in the graphite and improves its intrinsic strength. Simultaneously, in the interaction between graphite and... A gradient interface is formed between the matrices, reducing interfacial energy and resulting in a purer bonding state, thus avoiding strength reduction due to an excessively weak interface. Simultaneously, pressure induces the sheet graphite to orient itself along the direction perpendicular to the pressure, forming a weak interfacial layer. Activated carbon ensures the stable orientation of the oriented graphite during hot pressing, achieving a self-lubricating function. This enables the synergistic utilization of added graphite and reaction byproduct carbon, toughening while maintaining hardness.

[0053] In-situ reaction products With flake graphite Dispersed distribution in the matrix, due to (The coefficient of thermal expansion is approximately ), graphite (c-axis thermal expansion coefficient approximately )and Matrix (coefficient of thermal expansion approximately) The significant difference in thermal expansion coefficients between these materials makes them prone to internal stress during cooling. During material fracture and failure, when the crack propagates to… In the region containing flake graphite, under the induction of the aforementioned internal stress, crack propagation is deflected, bridged, and bifurcated, which lengthens the crack propagation path, thereby consuming more energy and significantly improving fracture toughness.

[0054] Independent control of Ti powder particle size The fine-grain strengthening and crack deflection effect, combined with the lubrication and toughening function of independently controlled oriented weak interfaces by flake graphite, achieves decoupled design of two-phase morphology and content, thereby enabling... Constructing in matrix Graphite synergistic reinforcement network achieves simultaneous optimization of hardness, toughness and self-lubricating properties.

[0055] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0056] The raw materials and equipment used in the embodiments of the present invention are all commercially available.

[0057] Example 1

[0058] This embodiment provides a high-strength, high-toughness, self-lubricating... Graphite multiphase ceramics, comprising the following preparation steps:

[0059] 1. High-speed ball mill

[0060] Weigh out in proportion 20.3g of powder (particle size 2μm) and 4.0g of Ti powder (particle size 5μm) were mixed in a polytetrafluoroethylene ball mill jar. The grinding balls were SiC balls, and the ball-to-material ratio of SiC balls to raw material components was 5:1. The ball mill speed was 260rpm / min, the ball milling time was 12h, and the ball milling medium was anhydrous ethanol to achieve uniform mixing.

[0061] 2. Low-speed mixing

[0062] After the powder from step 1 has been ball-milled, add 0.8g of flake graphite (3μm particle size, aspect ratio 5) to the ball mill jar. At this point, adjust the ball mill speed to 100rpm / min, and mill for 2 hours using anhydrous ethanol as the milling medium to achieve uniform mixing. Filter out the grinding balls to obtain... A slurry of flake graphite.

[0063] 3. Dry and sieve

[0064] The slurry from step 2 was transferred to a rotary evaporator flask for rotary evaporation at a water bath of 65°C and a rotation speed of 50 rpm / min until the solvent was completely evaporated, yielding a mixed powder. The mixed powder was then placed in a vacuum drying oven and dried at 60°C for 24 hours to completely remove residual solvent. Finally, the dried mixed powder was passed through a 200-mesh sieve to obtain a uniformly dispersed mixed powder.

[0065] 4. Molding and hot-pressing reaction sintering

[0066] The mixed powder obtained in step 3 was placed in a graphite mold and then placed in a vacuum hot pressing sintering furnace. An axial pressure of 5 MPa was applied at room temperature for pre-pressing. Subsequently, the temperature was raised to 1400℃ at 20℃ / min under vacuum and held for 10 min to allow the titanium and boron carbide to undergo an initial reaction. Then, argon gas was introduced to increase the pressure to 30 MPa, and the temperature was further raised to 1850℃ at 10℃ / min and held for 30 min to achieve complete reaction and rapid densification.

[0067] 5. Cooling and demolding

[0068] After cooling in the furnace, the mold is removed for demolding, and the graphite paper on the surface of the sample is removed to obtain the multiphase ceramic product.

[0069] The composite ceramic prepared in this embodiment has the following properties after testing: relative density 99.4%, Vickers hardness 35.1 GPa, flexural strength 692 MPa, and fracture toughness. The coefficient of friction is 0.21.

[0070] Example 2

[0071] This embodiment provides a high-strength, high-toughness, self-lubricating... Graphite multiphase ceramics, comprising the following preparation steps:

[0072] 1. High-speed ball mill

[0073] Weigh out in proportion 23.1g of powder (particle size 2μm) and 1.6g of Ti powder (particle size 5μm) were mixed in a polytetrafluoroethylene ball mill jar. The grinding balls were SiC balls, and the ball-to-material ratio of SiC balls to raw material components was 5:1. The ball mill speed was 220rpm / min, the ball milling time was 8h, and the ball milling media was anhydrous ethanol to achieve uniform mixing.

[0074] 2. Low-speed mixing

[0075] After the powder from step 1 has been ball-milled, add 0.3g of flake graphite (3μm particle size, aspect ratio 5) to the ball mill jar. At this point, adjust the ball mill speed to 80rpm / min and mill for 2 hours using anhydrous ethanol as the milling medium to achieve uniform mixing. Filter out the grinding balls to obtain... A slurry of flake graphite.

[0076] 3. Dry and sieve

[0077] The slurry from step 2 was transferred to a rotary evaporator flask for rotary evaporation at a water bath of 65°C and a rotation speed of 50 rpm / min until the solvent was completely evaporated, yielding a mixed powder. The mixed powder was then placed in a vacuum drying oven and dried at 60°C for 24 hours to completely remove residual solvent. Finally, the dried mixed powder was passed through a 200-mesh sieve to obtain a uniformly dispersed mixed powder.

[0078] 4. Molding and hot-pressing reaction sintering

[0079] The mixed powder obtained in step 3 was placed in a graphite mold and then placed in a vacuum hot pressing sintering furnace. An axial pressure of 5 MPa was applied at room temperature for pre-pressing. Subsequently, the temperature was raised to 1380°C at 20°C / min under vacuum and held for 10 min to allow the titanium and boron carbide to undergo an initial reaction. Then, argon gas was introduced to increase the pressure to 30 MPa, and the temperature was further raised to 1850°C at 10°C / min and held for 30 min to achieve complete reaction and rapid densification.

[0080] 5. Cooling and demolding

[0081] After cooling in the furnace, the mold is removed for demolding, and the graphite paper on the surface of the sample is removed to obtain the multiphase ceramic product.

[0082] The composite ceramic prepared in this embodiment exhibits the following properties after testing: relative density 99.2%, Vickers hardness 34.3 GPa, flexural strength 604 MPa, and fracture toughness 5.2 MPa·m. 1 / 2 The coefficient of friction is 0.24.

[0083] Example 3

[0084] This embodiment provides a high-strength, high-toughness, self-lubricating... Graphite multiphase ceramics, comprising the following preparation steps:

[0085] 1. High-speed ball mill

[0086] Weigh out 24.0g of B4C powder (particle size 2μm) and 0.8g of Ti powder (particle size 5μm) according to the ratio, and mix them in a polytetrafluoroethylene ball mill jar. The grinding balls are SiC balls, and the ball-to-material ratio of SiC balls to raw material components is 5:1. The ball mill speed is 300rpm / min, the ball milling time is 12h, and the ball milling medium is anhydrous ethanol to achieve uniform mixing.

[0087] 2. Low-speed mixing

[0088] After the powder from step 1 has been ball-milled, add 0.2g of flake graphite (particle size 1μm, aspect ratio 5) to the ball mill jar. At this point, adjust the ball mill speed to 100rpm / min and mill for 2 hours using anhydrous ethanol as the milling medium to achieve uniform mixing. Filter out the grinding balls to obtain... A slurry of flake graphite.

[0089] 3. Dry and sieve

[0090] The slurry from step 2 was transferred to a rotary evaporator flask for rotary evaporation at a water bath of 65°C and a rotation speed of 50 rpm / min until the solvent was completely evaporated, yielding a mixed powder. The mixed powder was then placed in a vacuum drying oven and dried at 60°C for 24 hours to completely remove residual solvent. Finally, the dried mixed powder was passed through a 150-mesh sieve to obtain a uniformly dispersed mixed powder.

[0091] 4. Molding and hot-pressing reaction sintering

[0092] The mixed powder obtained in step 3 was placed in a graphite mold and then placed in a vacuum hot pressing sintering furnace. An axial pressure of 10 MPa was applied at room temperature for pre-pressing. Subsequently, the temperature was increased to 1350°C at 20°C / min under vacuum conditions and held for 10 min to allow the titanium and boron carbide to undergo an initial reaction. Then, argon gas was introduced to increase the pressure to 35 MPa, and the temperature was further increased to 1800°C at 10°C / min and held for 25 min to achieve complete reaction and rapid densification.

[0093] 5. Cooling and demolding

[0094] After cooling in the furnace, the mold is removed for demolding, and the graphite paper on the surface of the sample is removed to obtain the multiphase ceramic product.

[0095] The composite ceramic prepared in this embodiment has the following properties after testing: relative density 99.3%, Vickers hardness 33.7 GPa, flexural strength 560 MPa, and fracture toughness. The coefficient of friction is 0.25.

[0096] Example 4

[0097] This embodiment provides a high-strength, high-toughness, self-lubricating... Graphite multiphase ceramics, comprising the following preparation steps:

[0098] 1. High-speed ball mill

[0099] Weigh out in proportion 21.7g of powder (particle size 1μm) and 2.8g of Ti powder (particle size 1μm) were mixed in a polytetrafluoroethylene ball mill jar. The grinding balls were SiC balls, and the ball-to-material ratio of SiC balls to raw material components was 5:1. The ball mill speed was 300rpm / min, the ball milling time was 10h, and the ball milling medium was anhydrous ethanol to achieve uniform mixing.

[0100] 2. Low-speed mixing

[0101] After the powder from step 1 has been ball-milled, add 0.5g of flake graphite (5μm particle size, aspect ratio 6) to the ball mill jar. At this point, adjust the ball mill speed to 50rpm / min and mill for 2 hours using anhydrous ethanol as the milling medium to achieve uniform mixing. Filter out the grinding balls to obtain... A slurry of flake graphite.

[0102] 3. Dry and sieve

[0103] The slurry from step 2 was transferred to a rotary evaporator flask for rotary evaporation at a water bath of 65°C and a rotation speed of 50 rpm / min until the solvent was completely evaporated, yielding a mixed powder. The mixed powder was then placed in a vacuum drying oven and dried at 60°C for 24 hours to completely remove residual solvent. Finally, the dried mixed powder was passed through a 200-mesh sieve to obtain a uniformly dispersed mixed powder.

[0104] 4. Molding and hot-pressing reaction sintering

[0105] The mixed powder obtained in step 3 was placed in a graphite mold and then placed in a vacuum hot pressing sintering furnace. An axial pressure of 5 MPa was applied at room temperature for pre-pressing. Subsequently, the temperature was raised to 1400℃ at 20℃ / min under vacuum and held for 10 min to allow the titanium and boron carbide to undergo an initial reaction. Then, argon gas was introduced to increase the pressure to 30 MPa, and the temperature was further raised to 1850℃ at 10℃ / min and held for 30 min to achieve complete reaction and rapid densification.

[0106] 5. Cooling and demolding

[0107] After cooling in the furnace, the mold is removed for demolding, and the graphite paper on the surface of the sample is removed to obtain the multiphase ceramic product.

[0108] The composite ceramic prepared in this embodiment exhibits the following properties after testing: relative density of phase 99.0%, Vickers hardness 33.9 GPa, flexural strength 587 MPa, and fracture toughness 4.7 MPa·m. 1 / 2 The coefficient of friction is 0.23.

[0109] Example 5

[0110] This embodiment provides a high-strength, high-toughness, self-lubricating... Graphite multiphase ceramics, comprising the following preparation steps:

[0111] 1. High-speed ball mill

[0112] Weigh out 18.4g of B4C powder (3μm particle size) and 5.6g of Ti powder (10μm particle size) according to the proportion, and mix them in a polytetrafluoroethylene ball mill jar. The grinding balls are SiC balls, and the ball-to-material ratio of SiC balls to raw material components is 5:1. The ball mill speed is 300rpm / min, the ball milling time is 12h, and the ball milling medium is anhydrous ethanol to achieve uniform mixing.

[0113] 2. Low-speed mixing

[0114] After the powder from step 1 has been ball-milled, add 1.1g of flake graphite (3μm particle size, aspect ratio 8) to the ball mill jar. At this point, adjust the ball mill speed to 50rpm / min and mill for 2 hours using anhydrous ethanol as the milling medium to achieve uniform mixing. Filter out the grinding balls to obtain... A slurry of flake graphite.

[0115] 3. Dry and sieve

[0116] The slurry from step 2 was transferred to a rotary evaporator flask for rotary evaporation at a water bath of 65°C and a rotation speed of 50 rpm / min until the solvent was completely evaporated, yielding a mixed powder. The mixed powder was then placed in a vacuum drying oven and dried at 60°C for 24 hours to completely remove residual solvent. Finally, the dried mixed powder was passed through a 200-mesh sieve to obtain a uniformly dispersed mixed powder.

[0117] 4. Molding and hot-pressing reaction sintering

[0118] The mixed powder obtained in step 3 was placed in a graphite mold and then placed in a vacuum hot pressing sintering furnace. An axial pressure of 3 MPa was applied at room temperature for pre-pressing. Subsequently, the temperature was raised to 1400°C at 20°C / min under vacuum and held for 10 min to allow the titanium and boron carbide to undergo an initial reaction. Then, argon gas was introduced to increase the pressure to 30 MPa, and the temperature was further raised to 1800°C at 10°C / min and held for 25 min to achieve complete reaction and rapid densification.

[0119] 5. Cooling and demolding

[0120] After cooling in the furnace, the mold is removed for demolding, and the graphite paper on the surface of the sample is removed to obtain the multiphase ceramic product.

[0121] The composite ceramic prepared in this embodiment has the following properties after testing: relative density 98.5%, Vickers hardness 33.5 GPa, flexural strength 572 MPa, and fracture toughness 4.9 MPa·m.1 / 2 The coefficient of friction is 0.22.

[0122] Comparative Example 1

[0123] This comparative example provides a Ceramics, including the following preparation steps:

[0124] 1. High-speed ball mill

[0125] Weigh out in proportion 25g of powder (particle size 2μm) was placed in a polytetrafluoroethylene ball mill jar for mixing. The grinding balls were SiC balls, and the ball-to-material ratio of SiC balls to raw material components was 5:1. The ball mill speed was 260rpm / min, the ball milling time was 12h, and the ball milling medium was anhydrous ethanol to achieve uniform mixing. The grinding balls were then filtered out to obtain a mixed slurry.

[0126] 2. Drying and sieving

[0127] The slurry from step 2 was transferred to a rotary evaporator flask for rotary evaporation at a water bath of 65°C and a rotation speed of 50 rpm / min until the solvent was completely evaporated, yielding a mixed powder. The mixed powder was then placed in a vacuum drying oven and dried at 60°C for 24 hours to completely remove residual solvent. Finally, the dried mixed powder was passed through a 200-mesh sieve to obtain a uniformly dispersed mixed powder.

[0128] 4. Molding and hot-pressing reaction sintering: Same as in Example 1.

[0129] 5. Cooling and demolding: Same as in Example 1.

[0130] The composite ceramic prepared in this embodiment has the following properties after testing: relative density 96.0%, Vickers hardness 31.2 GPa, flexural strength 429 MPa, and fracture toughness. The coefficient of friction is 0.59.

[0131] Comparative Example 2

[0132] This comparative example provides a multiphase ceramic, which differs from Example 1 in that: The three materials, powder, Ti powder and flake graphite, were mixed in a polytetrafluoroethylene ball mill jar and then ball milled.

[0133] The composite ceramic sample prepared in this comparative example has the following properties: density 99.1%, hardness 34.2 GPa, flexural strength 648 MPa, and fracture toughness. The coefficient of friction is 0.42.

[0134] Comparative Example 3

[0135] This embodiment provides a multiphase ceramic, including the following preparation steps:

[0136] 1. High-speed ball mill

[0137] Weigh out in proportion 20.3g of powder (particle size 2μm) 3.1g of powder (particle size 5μm) and 0.3g of graphene were mixed in a polytetrafluoroethylene ball mill jar. The grinding balls were SiC balls, and the ratio of SiC balls to raw material components was 4:1. The ball mill speed was 200rpm / min, the ball milling time was 10h, and the ball milling medium was anhydrous ethanol to achieve uniform mixing. The grinding balls were then filtered out to obtain a mixed slurry.

[0138] 2. Drying and sieving

[0139] The mixed slurry was transferred to a rotary evaporator flask for rotary evaporation at a water bath of 65°C and a rotation speed of 50 rpm / min until the solvent was completely evaporated, yielding a mixed powder. The mixed powder was then placed in a vacuum drying oven and dried at 60°C for 24 hours to completely remove residual solvent. Finally, the dried mixed powder was passed through a 200-mesh sieve to obtain a uniformly dispersed mixed powder.

[0140] 3. Molding and hot-pressing reaction sintering

[0141] The mixed powder was placed in a graphite mold and hot-pressed in a hot press furnace. Under vacuum conditions, the temperature was first raised from room temperature to 1200°C at a heating rate of 20°C / min, Ar gas was introduced, and then the temperature was raised to 1850°C at a heating rate of 10°C / min and held for 60 min. The axial sintering pressure was controlled at 30 MPa during the sintering process.

[0142] 5. Cool in the furnace, remove the mold for demolding, and remove the graphite paper from the sample surface to obtain the multiphase ceramic product.

[0143] The composite ceramic prepared in this embodiment has the following properties after testing: relative density 98.2%, Vickers hardness 32.5 GPa, flexural strength 598 MPa, and fracture toughness. The coefficient of friction is 0.46.

[0144] like Figure 1 As shown, the product prepared in Example 1 The absence of obvious pores in the graphite multiphase ceramic indicates that the material has achieved extremely high density. The black phase in Example 1 is... The granular white phase is The tiny, white, stringy phases are graphite. These are produced by the in-situ reaction. The particles are evenly dispersed in Matrix, for Grain growth is inhibited, and this fine-grain strengthening mechanism can simultaneously improve the flexural strength and Vickers hardness of the material. Able to compare To bear higher loads, therefore The introduction of [something] can improve The flexural strength of the matrix. Additionally, from... Figure 1 The white phase region can be seen in the image. The presence of an uneven, rough fracture surface indicates... and Intergranular fracture occurs between grains, while The fracture surfaces of the grains appear relatively smooth and flat, indicating transgranular fracture. This hybrid fracture mode, combining intergranular and transgranular fracture, prolongs the crack propagation path, consumes more fracture energy, and improves the material's fracture toughness. These microstructural features lay a solid foundation for achieving the material's excellent comprehensive properties. Example 1 exhibits a relative density of 99.4%, Vickers hardness of 35.1 GPa, flexural strength of 692 MPa, and fracture toughness of 6.8 MPa·m. 1 / 2 .

[0145] like Figure 2 As shown, all phases in Example 1 are as follows: , And graphite, indicating that the raw material Ti and The reaction was completely completed. . It has the strongest diffraction peak, although The content is much smaller than However, the high atomic mass of Ti also indicates that the in-situ reaction produces... It exhibits good crystallinity. Obvious graphite diffraction peaks can also be observed in this figure, partly because the graphite in the sample has a certain degree of crystallinity, and partly because the amount of flake graphite added in Example 1 was relatively large, sufficient to be detected by XRD.

[0146] like Figure 3 As shown in Figure 5 / 7, due to the relatively small amount of Ti added, the white phase generated in the in-situ reaction... The amount of flake graphite added in Examples 2-4 is relatively small, resulting in a weaker toughening effect compared to Example 1. Additionally, as... Figure 4 As shown in Figure 6 / 8, the XRD test results only show... and The diffraction peaks of the phase are due to the fact that the amount of the introduced graphite phase is too small for XRD to detect.

[0147] like Figure 9As shown, when the amount of Ti introduced is too large, Graphite can form large agglomerates and defects in materials, leading to a deterioration in material properties. Therefore, although more graphite was introduced in Example 5... It contains graphite, but its overall performance is significantly lower than that of Example 1.

[0148] Figure 11(a) is a SEM image of the sample surface of Example 1. As shown in the figure, the yellow arrows indicate a considerable number of flake graphite structures, indicating that the gradient ball milling method maintains the flake morphology of the graphite. Figure 11(b) is a SEM image of the sample surface of Comparative Example 2. As shown in the figure, only a small amount of flake graphite exists, indicating that the method leads to the destruction of the graphite flake structure. Flake graphite has a multilayer structure, with layers stacked by van der Waals forces. This structure is conducive to inducing crack deflection and improving the fracture toughness of the material.

[0149] Comparing the data of Examples 1-5 and Comparative Example 2, it can be seen that the coefficient of friction of Examples 1-5 is significantly lower than that of Comparative Example 2, while the other properties are not much different. It can be seen that the addition of complete flake graphite enhances the lubrication performance of the composite ceramic.

[0150] Comparing the data from Examples 1-5 with Comparative Examples 1 and 3, it can be seen that the relative density of the composite ceramics in Examples 1-5 is all above 98.5%, and the Vickers hardness is all above 33.5 GPa, which is significantly better than that in Comparative Examples 1 and 3. This is due to the combination of Ti and... The in-situ exothermic reaction releases a large amount of heat, significantly promoting sintering densification; simultaneously, the in-situ generated... Graphite-co-stacking Grain boundaries effectively inhibit grain growth and reduce The grain size, especially in Example 1, achieved a Vickers hardness of up to 35.1 GPa, the highest among all examples.

[0151] In terms of strength and toughness, the fracture toughness and flexural strength of Examples 1-2 are superior to those of the comparative example, possibly due to... The combined action of granular and flake graphite in crack deflection, bridging, and pull-out mechanisms enhances fracture toughness; furthermore, in-situ reaction-generated... The clean surface of the particles and the strong metallurgical bonding interface with the matrix are conducive to the effective transfer of loads and improve the bending strength.

[0152] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 present invention.

Claims

1. A high-strength, high-toughness self-lubricating agent Graphite multiphase ceramics, characterized in that, By mass fraction, it comprises the following raw material components: boron carbide powder 73.5~96.2%, titanium powder 3.2~22.3%, and flake graphite 0.6~4.2%.

2. The high-strength, high-toughness self-lubricating material as described in claim 1 Graphite multiphase ceramics, characterized in that, Boron carbide powder 81.2-92.4%, titanium powder 6.4-16.0%, flake graphite 1.2-3.2%.

3. A device as described in claim 1 or claim 2 A method for preparing graphite multiphase ceramics, characterized in that, Includes the following steps: S1. Ball mill boron carbide powder and titanium powder until they are evenly mixed, then add flake graphite and mix at low speed to prevent graphite breakage, and obtain a mixed slurry. S2. The mixed slurry is subjected to solid-liquid separation, vacuum drying, sieving, and cold pressing to obtain a preform. S3. Vacuum hot pressing sintering is performed on the preform to obtain boron carbide composite ceramic.

4. As described in claim 3 A method for preparing graphite multiphase ceramics, characterized in that, The particle size of the flake graphite is 1~5μm, and the aspect ratio is ≥5.

5. As described in claim 3 A method for preparing graphite multiphase ceramics, characterized in that, The particle size of boron carbide powder is 1~3μm, and the particle size of titanium powder is 1~10μm.

6. As described in claim 3 A method for preparing graphite multiphase ceramics, characterized in that, Boron carbide powder and titanium powder were added to anhydrous ethanol, and the ball milling speed was 200~300 r / min, and the ball milling time was 10~12 h. Alternatively, when adding flake graphite and mixing at low speed, the ball mill speed should be 50~150 r / min and the ball milling time should be 1~2 h.

7. As described in claim 3 A method for preparing graphite multiphase ceramics, characterized in that, In S2, the mixed slurry is vacuum dried, passed through a 150-250 mesh sieve, and cold-pressed to obtain a green body; Preferably, the cold pressing process involves placing the dried and sieved mixed powder in a graphite mold, applying an axial pressure of 3-10 MPa for pre-pressing, and holding the pressure for 5-15 minutes.

8. As described in claim 3 A method for preparing graphite multiphase ceramics, characterized in that, The vacuum hot pressing sintering process involves heating to 1350-1450℃ in a vacuum, holding the temperature to allow titanium and boron carbide to undergo an initial reaction; then, argon gas is introduced, pressure is applied to 20-40 MPa, the temperature is raised to 1750-1900℃, and the temperature and pressure are maintained to achieve complete reaction and rapid densification. Preferably, the vacuum hot pressing sintering is performed by heating to 1350-1450°C under vacuum conditions, holding at that temperature, then filling with argon gas, applying pressure to 25-35 MPa, heating to 1750-1850°C, and holding at both temperature and pressure.

9. As described in claim 3 A method for preparing graphite multiphase ceramics, characterized in that, Both cold pressing and vacuum hot pressing sintering are carried out in a vacuum hot press furnace.

10. As described in claim 3 A method for preparing graphite multiphase ceramics, characterized in that, In S3, the preform is vacuum hot-pressed and sintered, then cooled and demolded to obtain boron carbide composite ceramic.

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