A method for near-net-shaping of diamond ceramic matrix composites

Abstract

The application discloses a near-net forming method of diamond ceramic matrix composite, and belongs to the field of ceramic materials. The application aims to solve the problems of large mold loss in the preparation process of diamond / silicon carbide, difficult near-net forming and low diamond content in the prepared composite. The method comprises the following steps: 1, raw material pretreatment; 2, preparation of silicon-carbon coated diamond powder; 3, green body warm-pressing forming; 4, degreasing treatment; 5, multi-stage pseudo-vacuum graphite cavity molten silicon self-flowing loss reaction sintering; and 6, step-by-step gradient grinding treatment. The application constructs a reusable multi-stage pseudo-vacuum graphite cavity based on a graphite mold to inhibit the expansion of the diamond composite caused by the rapid volatilization of silicon vapor in a vacuum environment, and the loss of silicon in the green body under high-temperature sintering is inhibited through graphite paper, so that the reaction of carbon and silicon to generate silicon carbide is promoted, near-net forming of the high-density diamond ceramic matrix composite without mold damage is realized, the high diamond content is ensured, and the cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials, and specifically relates to a near-net-shape forming method for diamond ceramic matrix composite materials. Background Technology

[0002] With the rapid development of modern electronic information technology, new energy industries, and aerospace, electronic devices are trending towards higher integration and higher power. This directly leads to difficulties in timely heat dissipation, causing device temperatures to rise, resulting in decreased performance and reduced lifespan. Thermal management materials, as the core carriers for heat dissipation, directional transport, and precise control in electronic components, directly affect the operating efficiency, reliability, and lifespan of equipment. Among these, the substrate, as the primary carrier of electronic components, requires particularly high thermal conductivity and insulation properties to improve heat dissipation while mitigating the risk of short circuits.

[0003] Diamond, as the material with the highest thermal conductivity in nature (reaching over 2000 W / (m×K), has attracted much attention from researchers for its applications in thermal management, both directly and in its composites. However, due to current limitations in its fabrication processes, pure diamond materials often struggle to meet the heat dissipation requirements of large-sized, complex-shaped electronic components. Therefore, researchers consider diamond ceramic matrix composites (diamond / silicon carbide, diamond / silicon nitride, etc.) and diamond metal matrix composites (diamond / copper, diamond / aluminum, diamond / magnesium, etc.) as next-generation thermal management materials. Among these, diamond / silicon carbide composites have garnered significant attention due to their excellent thermal conductivity and insulation properties. However, current diamond / silicon carbide fabrication processes still have limitations, with issues such as low density, difficult molding processes, and poor performance hindering large-scale applications.

[0004] Due to the inherent high-temperature graphitization of diamond (rapid graphitization occurs above 1600℃ in a vacuum environment), reaction sintering is currently the mainstream process for preparing diamond / silicon carbide composites to avoid a decrease in the overall thermal conductivity of the composite material caused by diamond graphitization (sintering temperature is generally between 1450℃ and 1650℃). Reaction-sintered diamond / silicon carbide originates from reaction-sintered silicon carbide, which refers to a process where silicon is melted at high temperature to become a silicon solution, which is then impregnated into a porous diamond / silicon carbide preform framework. The silicon reacts with carbon to form silicon carbide, filling the pores. There is also a method of densification through gas-phase reaction sintering, where silicon vapor is generated by high-temperature evaporation beneath the preform, and the silicon vapor enters the preform and reacts with carbon to form silicon carbide. Regardless of the reaction sintering method, the densification essentially involves filling the voids inside the porous preform. To reduce the risk of silicon oxidation and the formation of silicon oxide, which hinders the subsequent filling of the preform by the silicon solution, researchers typically perform reaction sintering on diamond / silicon carbide under a vacuum environment.

[0005] However, in a vacuum reaction sintering environment, silicon becomes liquid and volatilizes at high temperatures, causing the diamond / silicon carbide preform to expand significantly. Diamond typically cannot react with silicon in time to form a silicon carbide framework to inhibit this expansion, resulting in an increase in silicon content and a decrease in diamond content after sintering, severely impacting its thermal conductivity and insulation properties. In more severe cases, it may even prevent the preform from being formed. To address this issue, researchers often use graphite molds to fix the dimensions of the diamond / silicon carbide preform. However, during sintering, the mold is usually in direct contact with the preform, leading to large-area adhesion after sintering. This makes the mold difficult to reuse and inevitably increases the manufacturing cost of diamond / silicon carbide. Furthermore, mold design is challenging for complex-shaped diamond / silicon carbide composites. Some researchers, such as those using Chinese patent CN1274341A, have used graphitization to improve the molding effect of diamond. However, graphitizing diamond alone leads to a longer processing cycle, reduces the diamond content in the diamond / silicon carbide composite material, and increases production costs. Moreover, to ensure sufficient silicon during sintering, researchers often use excess silicon, which usually leaves residues on the surface of the diamond / silicon carbide, increasing the difficulty of post-processing. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of high mold wear, difficulty in near-net-shape forming, and low diamond content in the prepared composite materials during the current diamond / silicon carbide preparation process, and to provide a near-net-shape forming method for diamond ceramic matrix composite materials.

[0007] This invention reduces the preparation cost and processing cycle of diamond / silicon carbide composite materials, providing a new approach for the large-scale, low-cost application of diamond / silicon carbide. The invention proposes a complete preparation method consisting of "diamond coating design - wet-mixed coating of high-diamond-content preform warm-pressing - multi-stage pseudo-vacuum graphite cavity molten silicon self-flow - gradient grinding." By optimizing the entire diamond / silicon carbide preparation process, it achieves near-net-shape forming of high thermal conductivity diamond / silicon carbide composite materials with zero mold loss and low cost.

[0008] A near-net-shape forming method for diamond ceramic matrix composites, which employs a multi-stage pseudo-vacuum graphite cavity, includes the following steps:

[0009] I. Raw material pretreatment:

[0010] Diamond micro powders with particle sizes D1 and D2 are subjected to degreasing and metal impurity removal treatments in sequence; silicon carbide powder and silicon powder are subjected to oxide layer and impurity removal treatments.

[0011] II. Preparation of silicon-carbon coated diamond micropowder:

[0012] Under water bath heating conditions, phenolic resin is dissolved in anhydrous ethanol, then silicon powder, graphite powder and silicon carbide powder are added and stirred into a slurry, then diamond micro powder with a particle size of D1 is added and mixed evenly, dried and crushed and sieved to obtain silicon carbide coated diamond micro powder.

[0013] III. Warm pressing of the billet:

[0014] Silicon carbide-coated diamond micro powder is mixed with diamond micro powder with a particle size of D2, solvent is sprayed and stirred, and then the mixture is poured into a mold cavity and warm-pressed into a blank.

[0015] IV. Degreasing treatment:

[0016] The preform is placed in a vacuum sintering furnace, and the polymer is removed by stepwise heating in the vacuum sintering furnace to obtain a diamond / silicon carbide preform.

[0017] V. Multi-stage pseudo-vacuum graphite cavity molten silicon self-flow reaction sintering:

[0018] A porous graphite support is placed at the bottom of the first graphite mold, graphite paper is laid on top of the porous graphite support, a diamond / silicon carbide blank is placed on top of the graphite paper, silicon powder is added to the top of the blank, and the first graphite mold cover is closed to form a primary pseudo-vacuum graphite cavity; then the primary pseudo-vacuum graphite cavity is placed at the bottom of the (N+1)th graphite mold, and the (N+1)th graphite mold cover is closed to form an (N+1)th pseudo-vacuum graphite cavity, which is then transferred to a vacuum sintering furnace, where it is sintered by step heating to achieve densification, resulting in a densified composite material; the value of N is 1≤N≤4, and N is a positive integer;

[0019] VI. Gradient Grinding Process:

[0020] Residual silicon was removed from the surface of the composite material and polished to obtain a diamond ceramic matrix composite material.

[0021] This invention places an N+1 level pseudo-vacuum graphite cavity into a vacuum sintering furnace, and then evacuates the furnace. During evacuation, air inside the graphite mold is drawn out through the gap between the graphite mold cover and the graphite mold. Then, the temperature is raised, and the silicon powder inside the graphite mold melts and forms silicon vapor. This vapor is slowly partially drawn out through the gap between the graphite mold cover and the graphite mold, slowing down the rate of silicon powder loss under vacuum conditions. This, in turn, inhibits the expansion of the diamond / silicon carbide blank during the sintering process. Because silicon vapor is present inside the graphite mold, a pseudo-vacuum graphite cavity is formed.

[0022] The beneficial effects of this invention are:

[0023] I. This invention constructs a reusable multi-level pseudo-vacuum graphite cavity based on a graphite mold to suppress the expansion of diamond composite materials caused by the rapid volatilization of silicon vapor in a vacuum environment. The graphite paper suppresses the loss of silicon inside the blank under high-temperature sintering and promotes the reaction of carbon and silicon to generate silicon carbide, thus realizing near-net-shape forming of high-density diamond ceramic matrix composite materials without mold damage.

[0024] II. This invention improves the preparation efficiency of silicon carbide coated diamond micro powder: the traditional method uses grinding, which is time-consuming, while this invention adds a crushing process and uses copper foil as a substrate during drying to quickly remove the solvent, shortening the powder preparation time to about 1 / 3 of the traditional method.

[0025] Third, this invention ensures the uniform distribution of diamonds of different particle sizes, thereby ensuring a high diamond content inside the diamond composite material. The multi-level pseudo-vacuum graphite cavity structure reduces mold wear during the molding process, lowers the preparation cost of the diamond composite material, ensures a high diamond content inside the diamond composite material during reaction sintering, and the step-by-step gradient grinding method ensures the uniformity of the diamond composite material in the thickness direction. Attached Figure Description

[0026] Figure 1 The image shows the microstructure of the silicon carbide-coated diamond powder obtained in step two of Example 1 under a polarizing microscope.

[0027] Figure 2 This is a schematic diagram of the composition of the secondary pseudo-vacuum graphite cavity described in step five of Example 1;

[0028] Figure 3 The three views are of the porous graphite support described in step five of Example 1;

[0029] Figure 4 This is a schematic diagram of the multi-stage pseudo-vacuum graphite cavity molten silicon self-flow reaction sintering in step five of Example 1;

[0030] Figure 5 The graph shows the diameter measurement data of the densified composite material obtained in step five of Examples 1, 2, 3, and 4.

[0031] Figure 6 This is a graph showing the diameter measurement data of the densified composite material obtained in step five of Comparative Examples 1-12;

[0032] Figure 7 The diamond content inside the diamond ceramic matrix composites prepared in Examples 1-4 and Comparative Examples 1-12;

[0033] Figure 8 Microscopic optical images of the diamond ceramic matrix composite material prepared in Example 1;

[0034] Figure 9 Microscopic optical images of the diamond ceramic matrix composite material prepared for Comparative Example 1;

[0035] 1-1 is the first graphite mold, 1-2 is the first graphite mold cover, 2-1 is the second graphite mold, 2-2 is the second graphite mold cover, 3 is a porous graphite support, 4 is graphite paper, 5 is a diamond / silicon carbide blank, and 6 is silicon powder. Detailed Implementation

[0036] Specific Implementation Method 1: This implementation method provides a near-net-shape forming method for diamond ceramic matrix composite materials, which utilizes a multi-stage pseudo-vacuum graphite cavity and includes the following steps:

[0037] I. Raw material pretreatment:

[0038] Diamond micro powders with particle sizes D1 and D2 are subjected to degreasing and metal impurity removal treatments in sequence; silicon carbide powder and silicon powder are subjected to oxide layer and impurity removal treatments.

[0039] II. Preparation of silicon-carbon coated diamond micropowder:

[0040] Under water bath heating conditions, phenolic resin is dissolved in anhydrous ethanol, then silicon powder, graphite powder and silicon carbide powder are added and stirred into a slurry, then diamond micro powder with a particle size of D1 is added and mixed evenly, dried and crushed and sieved to obtain silicon carbide coated diamond micro powder.

[0041] III. Warm pressing of the billet:

[0042] Silicon carbide-coated diamond micro powder is mixed with diamond micro powder with a particle size of D2, solvent is sprayed and stirred, and then the mixture is poured into a mold cavity and warm-pressed into a blank.

[0043] IV. Degreasing treatment:

[0044] The preform is placed in a vacuum sintering furnace, and the polymer is removed by stepwise heating in the vacuum sintering furnace to obtain a diamond / silicon carbide preform.

[0045] V. Multi-stage pseudo-vacuum graphite cavity molten silicon self-flow reaction sintering:

[0046] A porous graphite support is placed at the bottom of the first graphite mold, graphite paper is laid on top of the porous graphite support, a diamond / silicon carbide blank is placed on top of the graphite paper, silicon powder is added to the top of the blank, and the first graphite mold cover is closed to form a primary pseudo-vacuum graphite cavity; then the primary pseudo-vacuum graphite cavity is placed at the bottom of the (N+1)th graphite mold, and the (N+1)th graphite mold cover is closed to form an (N+1)th pseudo-vacuum graphite cavity, which is then transferred to a vacuum sintering furnace, where it is sintered by step heating to achieve densification, resulting in a densified composite material; the value of N is 1≤N≤4, and N is a positive integer;

[0047] VI. Gradient Grinding Process:

[0048] Residual silicon was removed from the surface of the composite material and polished to obtain a diamond ceramic matrix composite material.

[0049] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in the following ways: In step one, the degreasing treatment of diamond micropowder with particle sizes D1 and D2 involves ultrasonically cleaning the diamond particles 2-3 times using anhydrous ethanol or acetone as a solvent; each ultrasonic cleaning session lasts 10-30 minutes. In step one, the removal of metallic impurities from the diamond micropowder with particle sizes D1 and D2 involves soaking the diamond particles in dilute hydrochloric acid or dilute nitric acid for 2-4 hours or heating and stirring at 60-70°C for 1-2 hours, followed by rinsing with deionized water until neutral. For the removal of oxide layers and impurities from silicon carbide and silicon powder, a 5%-10% sodium hydroxide solution is used as a solvent, and the silicon carbide and silicon powder are heated and stirred at 60-70°C for 30-60 minutes, respectively, then rinsed with deionized water until neutral, and then immersed in dilute hydrochloric acid for a period of time, finally rinsed with deionized water until neutral. Other steps are the same as in Specific Implementation Method One.

[0050] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the diamond micropowder with a particle size of D1 mentioned in step one has a particle size of 10μm~500μm, and the diamond micropowder with a particle size of D2 has a particle size of 2μm~100μm; the silicon carbide has a particle size of 1μm~50μm, and the silicon powder has a particle size of 1μm~50μm. Other steps are the same as in Specific Implementation Method One or Two.

[0051] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the mass-to-volume ratio of phenolic resin, silicon powder, graphite powder, silicon carbide powder, diamond micron powder with a particle size of D1, and anhydrous ethanol in step two is (1g~500g):(1g~500g):(1g~500g):(0g~500g):(1g~500g):(1mL~750mL). The other steps are the same as in Specific Implementation Methods One to Three.

[0052] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in the following ways: the water bath heating temperature in step two is 75℃~85℃; the drying in step two involves pouring the mixed slurry into copper foil, then placing the copper foil in an oven to dry at a temperature of 80℃~150℃ for 5min~30min; and the sieve aperture in step two is 10μm~500μm. Other steps are the same as in Specific Implementation Methods One to Four.

[0053] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in the following ways: the solvent in step three is anhydrous ethanol; the mass ratio of silicon carbide-coated diamond micropowder to diamond micropowder with a particle size of D2 in step three is (8~12):(3~6); the amount of solvent sprayed in step three is 5~20% of the mass of silicon carbide-coated diamond micropowder; the temperature for warm pressing in step three is 135℃~150℃, the pressure for warm pressing is 10MPa~50MPa, and the holding time is 10min~20min; the mold cavity in step three is coated with polydimethylsiloxane. Other steps are the same as in Specific Implementation Methods One to Five.

[0054] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the stepwise heating process for polymer removal described in step four is as follows: The vacuum sintering furnace is evacuated to a vacuum level below 10 Pa. Then, the temperature is increased to 800℃~1000℃ at a heating rate of 5℃ / min~30℃ / min, held for 30min~90min, then increased to 1000℃~1300℃ at a heating rate of 5℃ / min~20℃ / min, held for 10min~90min, and finally cooled to room temperature with the furnace. Other steps are the same as in Specific Implementation Methods One to Six.

[0055] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the porous graphite support in step five is made of graphite; the thickness of the graphite paper in step five is 50μm to 500μm, and the graphite paper completely covers the diamond / silicon carbide preform to suppress molten silicon loss; the mass of silicon powder added in step five is 1.5 to 3 times the mass of the diamond / silicon carbide preform. Other steps are the same as in Specific Implementation Methods One to Seven.

[0056] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the stepped heating sintering process described in step five is as follows: The vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1350℃~1400℃ at a heating rate of 10℃ / min~20℃ / min, held for 0 min, then heated to 1450℃~1650℃ at a heating rate of 1℃ / min~10℃ / min, held for 10 min~120 min, and finally cooled to room temperature with the furnace. Other steps are the same as in Specific Implementation Methods One to Eight.

[0057] Specific Implementation Method 10: The difference between this implementation method and Specific Implementation Methods 1 to 9 is that in step 6, the composite material is sandblasted to remove residual silicon on the surface of the composite material, and then placed in a grinding mold for grinding, including: Step (1) Initial single-block polishing: Polishing is performed at a speed of 5r / min to 25r / min, changing the surface every 50 to 500 revolutions, and repeating 2 to 5 times; Step (2) Polishing after increasing the number of blocks: At least one more block is added, and polishing is performed at a speed of 5r / min to 30r / min, changing the surface every 1000 revolutions, and repeating 6 to 10 times. Other steps are the same as in Specific Implementation Methods 1 to 9.

[0058] The beneficial effects of the present invention are verified using the following embodiments:

[0059] Example 1: A near-net-shape forming method for diamond ceramic matrix composites is achieved using a multi-stage pseudo-vacuum graphite cavity, comprising the following steps:

[0060] I. Raw material pretreatment:

[0061] Diamond micro powders with particle sizes D1 and D2 are subjected to degreasing and metal impurity removal treatments in sequence; silicon carbide powder and silicon powder are subjected to oxide layer and impurity removal treatments.

[0062] In step one, the diamond micro powder with particle sizes D1 and D2 is degreased by using anhydrous ethanol as a solvent to ultrasonically clean the diamond particles three times; each ultrasonic cleaning takes 30 minutes.

[0063] In step one, the diamond micro powder with particle sizes D1 and D2 is treated to remove metal impurities by soaking the diamond particles in dilute hydrochloric acid for 2 hours, and then washing them with deionized water until the pH value is 7. The dilute hydrochloric acid is a mixture of 37% hydrochloric acid and deionized water in a volume ratio of 1:1.

[0064] In step one, the treatment of removing the oxide layer and impurities from silicon carbide and silicon powder is carried out using a 5% sodium hydroxide solution as a solvent. The silicon carbide and silicon powder are heated and stirred at 60°C for 30 minutes, then rinsed with deionized water until the pH value is 7. Next, they are immersed in dilute hydrochloric acid and stirred for 30 minutes. Finally, they are rinsed with deionized water until the pH value is 7. The dilute hydrochloric acid is a mixture of 37% hydrochloric acid and deionized water in a volume ratio of 1:5.

[0065] The diamond micro powder with particle size D1 mentioned in step one has a particle size of 80-100 mesh, and the diamond micro powder with particle size D2 has a particle size of 275-325 mesh; the silicon carbide has a particle size of 15 μm, and the silicon powder has a particle size of 15 μm.

[0066] II. Preparation of silicon-carbon coated diamond micropowder:

[0067] Under the conditions of heating and stirring in an 80℃ water bath, 6.6g of phenolic resin was dissolved in 25mL of anhydrous ethanol, and then 7g of silicon powder, 6.75g of graphite powder, and 0.5g of silicon carbide powder were added and stirred into a slurry. Then, 28.6g of diamond micro powder with a particle size of D1 was added and mixed evenly. The mixture was stirred for another 30min. The slurry was then poured into copper foil, which was placed in an oven and dried at 140℃ for 5min. The foil was then crushed and passed through an 80-mesh sieve to obtain silicon carbide coated diamond micro powder.

[0068] III. Warm pressing of the billet:

[0069] 10.5g of silicon carbide-coated diamond micro powder was mixed with 4.5g of diamond micro powder with a particle size of D2, and 0.525mL of anhydrous ethanol was sprayed on the mixture and stirred for 10min to obtain a mixture. 1.7g of the mixture was introduced into a circular mold cavity with a diameter of 20mm and warm-pressed into a blank with a diameter of 20mm.

[0070] The temperature for warm pressing in step three is 140℃, the pressure for warm pressing is 30MPa, the holding time is 10min, and after cooling to room temperature, the film is removed.

[0071] The circular mold cavity described in step three is coated with polydimethylsiloxane;

[0072] IV. Degreasing treatment:

[0073] The preform obtained in step 3 is placed in a vacuum sintering furnace, and the polymer is removed by step heating in the vacuum sintering furnace to obtain a diamond / silicon carbide preform.

[0074] The step-by-step heating process for removing polymers described in step four is as follows: the vacuum sintering furnace is evacuated to a vacuum level of less than 10 Pa, then heated to 900°C at a heating rate of 15°C / min and held for 60 min, then heated to 1200°C at a heating rate of 5°C / min and held for 30 min, and finally cooled to room temperature with the furnace.

[0075] V. Secondary pseudo-vacuum graphite cavity molten silicon self-flow reaction sintering:

[0076] A porous graphite support is placed at the bottom of the first graphite mold, graphite paper is laid on top of the porous graphite support, a diamond / silicon carbide blank is placed on top of the graphite paper, silicon powder is added to the top of the blank, and the first graphite mold cover is closed to form a primary pseudo-vacuum graphite cavity; then the primary pseudo-vacuum graphite cavity is placed at the bottom of the second graphite mold, and the second graphite mold cover is closed to form a secondary pseudo-vacuum graphite cavity, which is then transferred to a vacuum sintering furnace, where step heating sintering is performed to achieve densification, resulting in a densified composite material;

[0077] The porous graphite support mentioned in step five is made of graphite; the graphite paper mentioned in step five has a thickness of 50μm and a length and width of 30mm; the graphite paper completely covers the diamond / silicon carbide blank to suppress the loss of molten silicon; the mass of silicon powder added in step five is twice the mass of the diamond / silicon carbide blank.

[0078] The step-by-step heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree of less than 10 Pa, then heated to 1400°C at a heating rate of 17.5°C / min, held for 0 min, then heated to 1450°C at a heating rate of 5°C / min, held for 10 min, and finally cooled to room temperature with the furnace.

[0079] VI. Gradient Grinding Process:

[0080] The composite material was sandblasted to remove residual silicon on the surface of the composite material, and then placed in a grinding mold for grinding treatment, including: Step (1) First single-block polishing: polishing at a speed of 10 r / min, changing the surface every 200 revolutions, repeating 3 times; Step (2) Polishing after increasing the number of blocks: adding 2 blocks, polishing at a speed of 15 r / min, changing the surface every 1000 revolutions, repeating 7 times. There was no obvious silicon residue on the surface of the diamond ceramic matrix composite material, and the diamond ceramic matrix composite material was obtained.

[0081] Example 2: The difference between this example and Example 1 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400°C at a heating rate of 17.5°C / min, held at that temperature for 0 min, then heated to 1500°C at a heating rate of 5°C / min, held at that temperature for 10 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Example 1.

[0082] Example 3: The difference between this example and Example 1 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400°C at a heating rate of 17.5°C / min, held at that temperature for 0 min, then heated to 1550°C at a heating rate of 5°C / min, held at that temperature for 10 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Example 1.

[0083] Example 4: The difference between this example and Example 1 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400°C at a heating rate of 17.5°C / min, held at that temperature for 0 min, then heated to 1600°C at a heating rate of 5°C / min, held at that temperature for 10 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Example 1.

[0084] Comparative Example 1: The difference between this example and Example 1 is that a multi-stage pseudo-vacuum graphite cavity is not used, exposing the diamond / silicon carbide blank to an environment without a pseudo-vacuum graphite cavity; that is, step five is completed according to the following steps: the diamond / silicon carbide blank is transferred to a vacuum sintering furnace, and densification is achieved by step-by-step heating and sintering in the vacuum sintering furnace to obtain the composite material; the step-by-step heating and sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400°C at a heating rate of 17.5°C / min, held at 0 min, then heated to 1450°C at a heating rate of 5°C / min, held at 10 min, and finally cooled to room temperature with the furnace. Other steps and parameters are the same as in Example 1.

[0085] Comparative Example 2: The difference between this comparative example and Comparative Example 1 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5℃ / min, held at that temperature for 0 min, then heated to 1500℃ at a heating rate of 5℃ / min, held at that temperature for 10 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 1.

[0086] Comparative Example 3: The difference between this comparative example and Comparative Example 1 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5℃ / min, held for 0 min, then heated to 1550℃ at a heating rate of 5℃ / min, held for 10 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 1.

[0087] Comparative Example 4: The difference between this comparative example and Comparative Example 1 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5℃ / min, held for 0 min, then heated to 1600℃ at a heating rate of 5℃ / min, held for 10 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 1.

[0088] Comparative Example 5: The difference between this comparative example and Comparative Example 1 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5℃ / min, held for 0 min, then heated to 1450℃ at a heating rate of 5℃ / min, held for 20 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 1.

[0089] Comparative Example 6: The difference between this comparative example and Comparative Example 2 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5℃ / min, held for 0 min, then heated to 1500℃ at a heating rate of 5℃ / min, held for 20 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 2.

[0090] Comparative Example 7: The difference between this comparative example and Comparative Example 3 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5℃ / min, held at that temperature for 0 min, then heated to 1550℃ at a heating rate of 5℃ / min, held at that temperature for 20 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 3.

[0091] Comparative Example 8: The difference between this comparative example and Comparative Example 4 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5 ℃ / min, held for 0 min, then heated to 1600℃ at a heating rate of 5 ℃ / min, held for 20 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 4.

[0092] Comparative Example 9: The difference between this comparative example and Comparative Example 1 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5 ℃ / min, held for 0 min, then heated to 1450℃ at a heating rate of 5 ℃ / min, held for 30 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 1.

[0093] Comparative Example 10: The difference between this comparative example and Comparative Example 2 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5℃ / min, held for 0 min, then heated to 1500℃ at a heating rate of 5℃ / min, held for 30 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 2.

[0094] Comparative Example 11: The difference between this comparative example and Comparative Example 3 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5℃ / min, held for 0 min, then heated to 1550℃ at a heating rate of 5℃ / min, held for 30 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 3.

[0095] Comparative Example 12: The difference between this comparative example and Comparative Example 4 is that the stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree below 10 Pa, then heated to 1400℃ at a heating rate of 17.5℃ / min, held for 0 min, then heated to 1600℃ at a heating rate of 5℃ / min, held for 30 min, and finally cooled to room temperature with the furnace. All other steps and parameters are the same as in Comparative Example 4.

[0096] Comparative Example 13: The difference between this comparative example and Example 1 is as follows: In step three, 10.5g of silicon carbide-coated diamond micropowder is mixed with 4.5g of diamond micropowder with a particle size of D2 and stirred for 10 minutes to obtain a mixture; 1.7g of the mixture is introduced into a circular mold cavity with a diameter of 20mm and warm-pressed into a blank with a diameter of 20mm; the warm-pressing temperature in step three is 140℃, the warm-pressing pressure is 30MPa, the holding time is 10 minutes, and after cooling to room temperature, the mold is removed; no substance is coated inside the circular mold cavity in step three. Other steps and parameters are the same as in Example 1.

[0097] Figure 1 The image shows the microstructure of the silicon carbide-coated diamond powder obtained in step two of Example 1 under a polarizing microscope.

[0098] from Figure 1 It can be seen that the surface of diamond powder is uniformly coated with a layer of graphite and silicon.

[0099] Figure 2 This is a schematic diagram of the composition of the secondary pseudo-vacuum graphite cavity described in step five of Example 1;

[0100] Figure 3 The three views are of the porous graphite support described in step five of Example 1;

[0101] Figure 4 This is a schematic diagram of the multi-stage pseudo-vacuum graphite cavity molten silicon self-flow reaction sintering in step five of Example 1;

[0102] Figure 5 The graph shows the diameter measurement data of the densified composite material obtained in step five of Examples 1, 2, 3, and 4.

[0103] Figure 5 The horizontal axis 1450℃ corresponds to Example 1, 1500℃ corresponds to Example 2, 1550℃ corresponds to Example 3, and 1600℃ corresponds to Example 4;

[0104] from Figure 5 It can be seen that under different sintering process conditions, no obvious expansion of the green body occurs when the diameter is around 20mm after sintering.

[0105] Figure 6 This is a graph showing the diameter measurement data of the densified composite material obtained in step five of Comparative Examples 1-12;

[0106] Figure 6 The values ​​of 10 min and 1450℃ correspond to Comparative Example 1; 10 min and 1500℃ correspond to Comparative Example 2; 10 min and 1550℃ correspond to Comparative Example 3; 10 min and 1600℃ correspond to Comparative Example 4; 20 min and 1450℃ correspond to Comparative Example 5; 20 min and 1500℃ correspond to Comparative Example 6; 20 min and 1550℃ correspond to Comparative Example 7; 20 min and 1600℃ correspond to Comparative Example 8; 30 min and 1450℃ correspond to Comparative Example 9; 30 min and 1500℃ correspond to Comparative Example 10; 30 min and 1550℃ correspond to Comparative Example 11; and 30 min and 1600℃ correspond to Comparative Example 12.

[0107] from Figure 6 It can be seen that under different sintering process conditions, the diameter of the sintered parts all show obvious expansion and increase, with a diameter of about 25mm.

[0108] Figure 7 The diamond content inside the diamond ceramic matrix composites prepared in Examples 1-4 and Comparative Examples 1-12;

[0109] from Figure 7 It can be seen that in Comparative Examples 1-12, the diamond volume fraction decreased due to the expansion of the sintered parts, while in Examples 1-4, the diamond volume fraction did not decrease due to the expansion of the sintered parts.

[0110] Figure 8Microscopic optical images of the diamond ceramic matrix composite material prepared in Example 1;

[0111] Figure 9 Microscopic optical images of the diamond ceramic matrix composite material prepared for Comparative Example 1;

[0112] Depend on Figure 8 and Figure 9 The comparison shows that the silicon content in the white area of ​​the diamond ceramic matrix composite material of Example 1 of the present invention is significantly lower, the diamond is more concentrated, and the diamond content is higher.

Claims

1. A near-net-shape forming method for diamond ceramic matrix composite materials, characterized in that: This is achieved using a multi-stage pseudo-vacuum graphite cavity, and includes the following steps: I. Raw material pretreatment: Diamond micro powders with particle sizes D1 and D2 are subjected to degreasing and metal impurity removal treatments in sequence; silicon carbide powder and silicon powder are subjected to oxide layer and impurity removal treatments. II. Preparation of silicon carbide-coated diamond micropowder: Under water bath heating conditions, phenolic resin is dissolved in anhydrous ethanol, then silicon powder, graphite powder and silicon carbide powder are added and stirred into a slurry, then diamond micro powder with a particle size of D1 is added and mixed evenly, dried and crushed and sieved to obtain silicon carbide coated diamond micro powder. III. Warm pressing of the billet: Silicon carbide-coated diamond micro powder is mixed with diamond micro powder with a particle size of D2, solvent is sprayed and stirred, and then the mixture is poured into a mold cavity and warm-pressed into a blank. IV. Degreasing treatment: The preform is placed in a vacuum sintering furnace, and the polymer is removed by stepwise heating in the vacuum sintering furnace to obtain a diamond / silicon carbide preform. V. Multi-stage pseudo-vacuum graphite cavity molten silicon self-flow reaction sintering: A porous graphite support is placed at the bottom of the first graphite mold, graphite paper is laid on top of the porous graphite support, a diamond / silicon carbide blank is placed on top of the graphite paper, silicon powder is added to the top of the blank, and the first graphite mold cover is closed to form a primary pseudo-vacuum graphite cavity; then the primary pseudo-vacuum graphite cavity is placed at the bottom of the (N+1)th graphite mold, and the (N+1)th graphite mold cover is closed to form an (N+1)th pseudo-vacuum graphite cavity, which is then transferred to a vacuum sintering furnace, where it is sintered by step heating to achieve densification, resulting in a densified composite material; the value of N is 1≤N≤4, and N is a positive integer; VI. Gradient Grinding Process: Residual silicon was removed from the surface of the composite material and polished to obtain a diamond ceramic matrix composite material.

2. The near-net-shape forming method for diamond ceramic matrix composite materials according to claim 1, characterized in that: In step one, the degreasing treatment of diamond micron powder with particle sizes D1 and D2 involves ultrasonically cleaning the diamond particles 2 to 3 times using anhydrous ethanol or acetone as solvent, with each ultrasonic cleaning lasting 10 to 30 minutes. The removal of metallic impurities from the diamond micron powder with particle sizes D1 and D2 involves soaking the diamond particles in dilute hydrochloric acid or dilute nitric acid for 2 to 4 hours or heating and stirring at 60°C to 70°C for 1 to 2 hours, followed by rinsing with deionized water until neutral. The removal of oxide layers and impurities from silicon carbide and silicon powder involves heating and stirring the silicon carbide and silicon powder separately at 60°C to 70°C for 30 to 60 minutes using a 5% to 10% sodium hydroxide solution as solvent, followed by rinsing with deionized water until neutral, then immersing them separately in dilute hydrochloric acid and stirring for a period of time, and finally rinsing with deionized water until neutral.

3. The near-net-shape forming method for diamond ceramic matrix composite materials according to claim 1, characterized in that: The diamond micropowder with particle size D1 mentioned in step one has a size of 10μm~500μm, and the diamond micropowder with particle size D2 has a size of 2μm~100μm; the silicon carbide has a particle size of 1μm~50μm, and the silicon powder has a particle size of 1μm~50μm.

4. The near-net-shape forming method for diamond ceramic matrix composite materials according to claim 1, characterized in that: The mass-volume ratio of phenolic resin, silicon powder, graphite powder, silicon carbide powder, diamond micro powder with a particle size of D1 and anhydrous ethanol in step two is (1g~500g):(1g~500g):(1g~500g):(0g~500g):(1g~500g):(1mL~750mL).

5. The near-net-shape forming method for diamond ceramic matrix composite materials according to claim 1, characterized in that: The water bath heating temperature in step two is 75℃~85℃; the drying in step two involves pouring the mixed slurry into copper foil, then placing the copper foil in an oven to dry it at a temperature of 80℃~150℃ for a time of 5min~30min; the sieve aperture in step two is 10μm~500μm.

6. The near-net-shape forming method for diamond ceramic matrix composite materials according to claim 1, characterized in that: The solvent mentioned in step three is anhydrous ethanol; the mass ratio of silicon carbide-coated diamond micropowder to diamond micropowder with a particle size of D2 mentioned in step three is (8~12):(3~6); the amount of solvent sprayed in step three is 5~20% of the mass of silicon carbide-coated diamond micropowder; the temperature of warm pressing in step three is 135℃~150℃, the pressure of warm pressing is 10MPa~50MPa, and the holding time is 10min~20min; the mold cavity mentioned in step three is coated with polydimethylsiloxane.

7. The near-net-shape forming method for diamond ceramic matrix composite materials according to claim 1, characterized in that: The step-by-step heating process for polymer removal described in step four is as follows: the vacuum sintering furnace is evacuated to a vacuum level below 10 Pa, then heated to 800℃~1000℃ at a heating rate of 5℃ / min~30℃ / min, held for 30min~90min, then heated to 1000℃~1300℃ at a heating rate of 5℃ / min~20℃ / min, held for 10min~90min, and finally cooled to room temperature with the furnace.

8. The near-net-shape forming method for diamond ceramic matrix composite materials according to claim 1, characterized in that: The porous graphite support mentioned in step five is made of graphite; the graphite paper mentioned in step five has a thickness of 50μm to 500μm, and the graphite paper completely covers the diamond / silicon carbide preform to suppress the loss of molten silicon; the silicon powder added in step five has a mass of 1.5 to 3 times the mass of the diamond / silicon carbide preform.

9. The near-net-shape forming method for diamond ceramic matrix composite materials according to claim 1, characterized in that: The stepped heating sintering process described in step five is as follows: the vacuum sintering furnace is evacuated to a vacuum degree of less than 10 Pa, and then the temperature is increased to 1350℃~1400℃ at a heating rate of 10℃ / min~20℃ / min, held for 0 min, then increased to 1450℃~1650℃ at a heating rate of 1℃ / min~10℃ / min, held for 10 min~120 min, and finally cooled to room temperature with the furnace.

10. The near-net-shape forming method for diamond ceramic matrix composite materials according to claim 1, characterized in that: In step six, the composite material is sandblasted to remove residual silicon on the surface of the composite material, and then placed in a grinding mold for grinding, including: step (1) initial single-block polishing: polishing at a speed of 5r / min to 25r / min, changing the surface every 50 to 500 revolutions, repeating 2 to 5 times; step (2) polishing after increasing the number of blocks: at least one more block is added, polishing at a speed of 5r / min to 30r / min, changing the surface every 1000 revolutions, repeating 6 to 10 times.

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