Near-net forming method for diamond ceramic-based composite material

Abstract

The invention discloses a near-net forming method for a diamond ceramic matrix composite material, and belongs to the field of ceramic materials. The invention aims to solve the problems of high mold loss, difficulty in near-net forming and low diamond content in the prepared composite material in the existing diamond / silicon carbide preparation process. The method comprises: 1, raw material pretreatment; 2, preparing silicon-carbon coated diamond micro powder; 3, carrying out body temperature compression molding on the blank; 4, degreasing treatment; 5, multi-stage pseudo-vacuum graphite cavity molten silicon self-loss reactive sintering; and sixthly, step-by-step gradient grinding treatment is conducted. According to the method, a reusable multi-stage pseudo-vacuum graphite cavity is constructed based on the graphite mold to inhibit expansion of the diamond composite material caused by rapid volatilization of silicon steam in a vacuum environment, loss of silicon in a green body under high-temperature sintering is inhibited through graphite paper, and reaction of carbon and silicon is promoted to generate silicon carbide; the 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] The present application belongs to the field of ceramic materials, and particularly relates to a near-net-shaping method of diamond ceramic matrix composite material. BACKGROUND

[0002] With the rapid development of modern electronic information technology, new energy industry and aerospace field, electronic devices tend to develop in the direction of high integration and high power. This directly leads to the difficulty of heat flow dissipation of electronic devices, the temperature rise of electronic devices, and the performance decline and service life reduction of electronic devices. As the core carrier for heat dissipation, directional transport and precise regulation of electronic components, the performance of thermal management materials directly affects the operation efficiency, reliability and service life of the equipment. Among them, the substrate is the main carrier of electronic components. In order to improve the heat dissipation performance and avoid the short circuit risk of electronic components, the thermal conductivity and insulation performance of the substrate are crucial.

[0003] Diamond, as the material with the highest thermal conductivity in nature (up to more than 2000 W / (m×K)), its own and its composite materials have attracted much attention in the field of thermal management. However, due to the limitations of current preparation process, pure diamond material is usually difficult to meet the heat dissipation requirements of electronic components with large size and complex shape. Therefore, researchers regard diamond ceramic matrix composite materials (diamond / silicon carbide, diamond / nitride silicon, etc.) and diamond metal matrix composite materials (diamond / copper, diamond / aluminum, diamond / magnesium, etc.) as the next generation of thermal management materials. Among them, diamond / silicon carbide composite materials have attracted much attention due to their excellent thermal conductivity and insulation properties. However, the current preparation process of diamond / silicon carbide still has certain limitations, and there are still problems such as low density, difficult forming process and low performance in large-scale application.

[0004] Due to the characteristics of diamond itself that it is easy to graphitize at high temperature (in a vacuum environment, the temperature is higher than 1600℃, which will quickly graphitize), in order to avoid the decrease of the thermal conductivity of the composite material caused by the graphitization of diamond, reaction sintering is the mainstream process for the preparation of diamond / silicon carbide composite materials (the sintering temperature is generally between 1450℃-1650℃). Reaction sintering of diamond / silicon carbide is derived from reaction sintering of silicon carbide, which means that through high-temperature melting of silicon into silicon solution, the porous diamond / silicon carbide skeleton is infiltrated, and silicon reacts with carbon to form silicon carbide to fill the pores. There is also a way of densification by gas phase reaction sintering, which is to evaporate silicon at high temperature from the bottom of the blank to generate silicon vapor, and the silicon vapor enters the inside of the blank and reacts with carbon to form silicon carbide. No matter which way of reaction sintering, the essence of densification is to fill the pores inside the porous blank. In order to reduce the oxidation of silicon to form silicon oxide to hinder the filling of the blank by the subsequent silicon solution, researchers usually perform reaction sintering of diamond / silicon carbide in a vacuum environment.

[0005] However, in a vacuum reaction sintering environment, silicon becomes liquid at high temperature and volatilizes, causing the overall expansion of the diamond / silicon carbide blank to become larger, and the diamond usually cannot react with silicon in time to form a silicon carbide skeleton to inhibit the expansion of the blank, resulting in a significant increase in the internal silicon content and a decrease in the diamond content of the sintered diamond / silicon carbide, which seriously affects its thermal conductivity and insulation performance. More seriously, it can cause the blank to be unable to be formed. In order to solve this problem, researchers usually use a graphite mold to fix and limit the size of the diamond / silicon carbide blank. However, during the sintering process, the mold usually directly contacts the blank, and after sintering, the mold and the blank are large-area bonded, making the mold difficult to be used again, which inevitably causes the production cost of the diamond / silicon carbide to increase. Moreover, for diamond / silicon carbide composites with complex shapes, it is difficult to design the mold. Some researchers, such as Chinese patent CN1274341A, perform graphitization treatment on the diamond to improve the forming effect. However, separate graphitization treatment on the diamond will cause the processing cycle to be longer, reduce the diamond content of the internal composite material of the diamond / silicon carbide, and cause the production cost to increase. Moreover, in order to ensure the fullness of silicon during sintering, researchers usually use an excess of silicon, and the excess silicon usually forms a residue on the surface of the diamond / silicon carbide, increasing the difficulty of its post-processing. SUMMARY

[0006] The purpose of the present application is to solve the problems of large mold loss, difficulty in near-net forming, and low diamond content in the prepared composite material in the current diamond / silicon carbide preparation process, and to provide a near-net forming method for diamond ceramic matrix composite materials.

[0007] The present application reduces the production cost and processing cycle of diamond / silicon carbide composites, and provides a new idea for the large-scale and low-cost application of diamond / silicon carbide. The present application proposes a whole-process preparation method of "diamond coating layer design-wet mixing coating high diamond content blank warm compaction-multi-stage pseudo-vacuum graphite cavity molten silicon self-loss-gradient grinding", which realizes moldless loss, low-cost near-net forming of high-thermal-conductivity diamond / silicon carbide composites through optimization of the whole-process technology of diamond / silicon carbide preparation.

[0008] A near-net forming method for diamond ceramic matrix composite materials is realized by using a multi-stage pseudo-vacuum graphite cavity, comprising the following steps: I. Pretreatment of raw materials: The diamond micropowder with particle sizes of D1 and D2 is sequentially subjected to oil removal treatment and metal impurity removal treatment; the silicon carbide powder and the silicon powder are subjected to oxidation layer and impurity removal treatment; II. Preparation of silicon-carbon-coated diamond micropowder: Under the condition of water bath heating, the phenolic resin is dissolved in anhydrous ethanol, then the silicon powder, graphite powder and silicon carbide powder are added to stir into a slurry, the diamond micro powder with a particle size of D1 is added and uniformly mixed, and then dried, crushed and sieved to obtain the silicon-carbon-coated diamond micro powder; III. Warm compaction of the green body: The silicon-carbon-coated diamond micro powder is mixed with the diamond micro powder with a particle size of D2, sprayed with a solvent and stirred, and then introduced into a mold cavity to be warm-pressed into a green body. IV. Defatting treatment: The green body is placed in a vacuum sintering furnace, and the polymer is removed by stepwise temperature rising in the vacuum sintering furnace to obtain a diamond / silicon carbide green body. V. Multistage pseudo-vacuum graphite cavity melt silicon self-flowing reaction sintering: The porous graphite support is placed at the bottom of the first graphite mold, the graphite paper is laid above the porous graphite support, the diamond / silicon carbide green body is placed above the graphite paper, and the silicon powder is added on the top of the green body, and the first graphite mold cover is covered to form a first-stage pseudo-vacuum graphite cavity; the first-stage pseudo-vacuum graphite cavity is placed at the bottom of the N+1 graphite mold, and the N+1 graphite mold cover is covered to form an N+1-stage pseudo-vacuum graphite cavity, which is then transferred to a vacuum sintering furnace for stepwise temperature rising sintering to realize densification, thereby obtaining a densified composite material; the value of N is 1≤N≤4, and N is a positive integer. VI. Step-by-step gradient grinding treatment: The surface residual silicon of the composite material is removed and polished to obtain a diamond ceramic matrix composite material.

[0009] In the present application, the N+1-stage pseudo-vacuum graphite cavity is placed in a vacuum sintering furnace, and then the vacuum sintering furnace is evacuated. During the evacuation, the air in the graphite mold is evacuated from the gap between the graphite mold cover and the graphite mold, and then the temperature is raised. The silicon powder in the graphite mold melts and forms silicon vapor, which is partially evacuated from the gap between the graphite mold cover and the graphite mold, thereby slowing down the silicon powder loss rate in the vacuum environment, and further inhibiting the expansion of the diamond / silicon carbide green body during sintering. Since there is silicon vapor in the graphite mold, a pseudo-vacuum graphite cavity is formed.

[0010] Advantages of the present application: I. The present application is based on the graphite mold to construct a reusable multistage pseudo-vacuum graphite cavity to inhibit the expansion of the diamond composite material caused by the rapid evaporation of silicon vapor in the vacuum environment. The graphite paper inhibits the loss of silicon inside the green body under high temperature sintering, promotes the reaction of carbon and silicon to form silicon carbide, and realizes the near-net forming of the high-density diamond ceramic matrix composite material without mold damage. Secondly, the preparation efficiency of the silicon-carbon coated diamond micro powder is improved: the traditional method is to use grinding, which is time-consuming, and the present application increases the crushing process, and copper foil is used as the substrate during drying, so that the solvent is quickly removed, and the powder preparation time is shortened to about 1 / 3 of the traditional method. Thirdly, the present application ensures the uniformity of the distribution of different particle sizes of diamond, and further ensures the high content of diamond in the diamond composite material, reduces the mold loss in the forming process through the multi-stage pseudo-vacuum graphite cavity structure, reduces the preparation cost of the diamond composite material, ensures the high diamond content in the diamond composite material during the reaction sintering process, and the step-by-step gradient grinding method ensures the uniformity of the diamond composite material in the thickness direction. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 The polarized light microscope micro-morphology diagram of the silicon-carbon coated diamond micro powder obtained in step two of Example 1; Figure 2 The composition schematic diagram of the two-stage pseudo-vacuum graphite cavity described in step five of Example 1; Figure 3 The three-view diagram of the porous graphite support described in step five of Example 1; Figure 4 The schematic diagram of the multi-stage pseudo-vacuum graphite cavity melting silicon self-flowing reaction sintering in step five of Example 1; Figure 5 The diameter measurement data diagram of the densified composite material obtained in step five of Examples 1, 2, 3 and 4; Figure 6 The diameter measurement data diagram of the densified composite material obtained in step five of Comparative Examples 1-12; Figure 7 The content of diamond in the diamond ceramic matrix composite material prepared in Examples 1-4 and Comparative Examples 1-12; Figure 8 The micro-optical picture of the diamond ceramic matrix composite material prepared in Example 1; Figure 9 The micro-optical picture of the diamond ceramic matrix composite material prepared in Comparative Example 1; 1-1 is a first graphite mold, 1-2 is a first graphite mold cover, 2-1 is a second graphite mold, 2-2 is a 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 DESCRIPTION

[0012] Specific implementation method one: the present application is a near-net forming method for diamond ceramic matrix composite material, which is realized by using a multi-stage pseudo-vacuum graphite cavity, including the following steps: I. Raw material pretreatment: The diamond micropowder with particle size D1 and D2 is sequentially subjected to oil removal treatment and metal impurity removal treatment; the silicon carbide powder and the silicon powder are subjected to oxidation layer and impurity removal treatment; II. Preparation of silicon-carbon coated diamond micropowder Under water bath heating, the phenolic resin is dissolved in anhydrous ethanol, then the silicon powder, graphite powder and silicon carbide powder are added to form a slurry, the diamond micropowder with particle size D1 is added and mixed uniformly, and then dried and crushed and sieved to obtain the silicon-carbon coated diamond micropowder; III. Warm-pressing of the green body The silicon-carbon coated diamond micropowder and the diamond micropowder with particle size D2 are mixed, sprayed with a solvent and stirred, and then introduced into a mold cavity to form a green body by warm-pressing; IV. Defatting treatment The green body is placed in a vacuum sintering furnace, and the polymer is removed by stepwise temperature rising in the vacuum sintering furnace to obtain a diamond / silicon carbide green body; V. Multistage pseudo-vacuum graphite cavity melt silicon self-flowing reaction sintering A porous graphite support is placed at the bottom of a first graphite mold, graphite paper is laid above the porous graphite support, the diamond / silicon carbide green body is placed above the graphite paper, silicon powder is added on top of the green body, the first graphite mold cover is covered, and a first-stage pseudo-vacuum graphite cavity is formed; the first-stage pseudo-vacuum graphite cavity is placed at the bottom of an N+1 graphite mold, the N+1 graphite mold cover is covered, and an N+1-stage pseudo-vacuum graphite cavity is formed, and then transferred to a vacuum sintering furnace, and sintered by stepwise temperature rising in the vacuum sintering furnace to realize densification, to obtain a densified composite material; the value of N is 1≤N≤4, and N is a positive integer; VI. Step-by-step gradient grinding treatment The surface residual silicon of the composite material is removed and polished to obtain a diamond ceramic matrix composite material.

[0013] Specific implementation method two: the difference between this embodiment and specific implementation method one is that: in step one, the oil removal treatment of the diamond powder with particle size D1 and D2 is ultrasonic cleaning of the diamond particles 2-3 times using anhydrous ethanol or acetone as the solvent; the time for each ultrasonic cleaning is 10-30 min; in step one, the metal impurity removal treatment of the diamond powder with particle size D1 and D2 is static immersion of the diamond particles in dilute hydrochloric acid or dilute nitric acid for 2-4 h or heating and stirring at 60-70℃ for 1-2 h, and finally washing with deionized water to neutral; the oxidation layer and impurity removal treatment of the silicon carbide and silicon powder is heating and stirring of the silicon carbide and silicon powder respectively in a 5-10% sodium hydroxide solution at 60-70℃ for 30-60 min, then washing with deionized water to neutral, and then immersing in dilute hydrochloric acid for a period of time, and finally washing with deionized water to neutral. The other steps are the same as specific implementation method one.

[0014] Specific implementation method three: the difference between this embodiment and one of specific implementation method one or two is that: in step one, the size of the diamond powder with particle size D1 is 10-500 μm, and the size of the diamond powder with particle size D2 is 2-100 μm; the particle size of the silicon carbide is 1-50 μm, and the particle size of the silicon powder is 1-50 μm. The other steps are the same as specific implementation method one or two.

[0015] Specific implementation method four: the difference between this embodiment and one of specific implementation methods one to three is that: in step two, the mass-volume ratio of the phenolic resin, silicon powder, graphite powder, silicon carbide powder, diamond powder with particle size D1, and anhydrous ethanol is (1-500 g):(1-500 g):(1-500 g):(0-500 g):(1-500 g):(1-750 mL). The other steps are the same as specific implementation methods one to three.

[0016] Specific implementation method five: the difference between this embodiment and one of specific implementation methods one to four is that: in step two, the temperature of the water bath heating is 75-85℃; in step two, the drying is to pour the mixed slurry into a copper foil, and then place the copper foil in an oven for drying, the drying temperature is 80-150℃, and the drying time is 5-30 min; in step two, the aperture of the sieve is 10-500 μm. The other steps are the same as specific implementation methods one to four.

[0017] Embodiment six: the difference between this embodiment and one of the embodiments one to five is that the solvent in step three is anhydrous ethanol; the mass ratio of the silicon-carbon coated diamond micro-powder to the diamond micro-powder with a particle size of D2 in step three is (8-12):(3-6); the spraying amount of the solvent in step three is 5-20% of the mass of the silicon-carbon coated diamond micro-powder; the temperature of the warm-pressing forming in step three is 135-150℃, the pressure of the warm-pressing forming is 10-50 MPa, and the pressure maintaining time is 10-20 min; the mold cavity in step three is coated with polydimethylsiloxane. The other steps are the same as those in the embodiments one to five.

[0018] Embodiment seven: the difference between this embodiment and one of the embodiments one to six is that the process for removing the polymer by stepwise heating in step four is: the vacuum sintering furnace is vacuumized to a vacuum degree of 10 Pa or less, then heated to 800-1000℃ at a heating rate of 5-30℃ / min, kept warm for 30-90 min, then heated to 1000-1300℃ at a heating rate of 5-20℃ / min, kept warm for 10-90 min, and finally cooled to room temperature with the furnace. The other steps are the same as those in the embodiments one to six.

[0019] Embodiment eight: the difference between this embodiment and one of the embodiments one to seven is that the material of the porous graphite support in step five is graphite; the thickness of the graphite paper in step five is 50-500 μm, and the graphite paper completely covers the diamond / silicon carbide blank to inhibit the loss of molten silicon; the added mass of the silicon powder in step five is 1.5-3 times of the mass of the diamond / silicon carbide blank. The other steps are the same as those in the embodiments one to seven.

[0020] Embodiment nine: the difference between this embodiment and one of the embodiments one to eight is that the process for stepwise heating sintering in step five is: the vacuum sintering furnace is vacuumized to a vacuum degree of 10 Pa or less, then heated to 1350-1400℃ at a heating rate of 10-20℃ / min, kept warm for 0 min, then heated to 1450-1650℃ at a heating rate of 1-10℃ / min, kept warm for 10-120 min, and finally cooled to room temperature with the furnace. The other steps are the same as those in the embodiments one to eight.

[0021] Specific implementation ten: the difference between this embodiment and one of the specific implementation one to nine is that: in step six, the composite material is sand blasted to remove the residual silicon on the surface of the composite material, and then put into the grinding mold for grinding treatment, including: step (1), first single pressure block polishing: polishing at a speed of 5r / min~25r / min, changing the surface every 50~500 circles, repeating 2~5 times; step (2), polishing after increasing the number of pressure blocks: at least one pressure block is added, polishing at a speed of 5r / min~30r / min, changing the surface every 1000 circles, repeating 6~10 times. The other steps are the same as specific implementation one to nine.

[0022] The beneficial effects of the present application are verified by the following examples: Example 1: a near net shape forming method of diamond ceramic matrix composite is realized by adopting multi-stage pseudo vacuum graphite cavity, including the following steps: I. Pretreatment of raw materials: The diamond micropowder with particle size D1 and D2 is sequentially subjected to oil removal treatment and metal impurity removal treatment; the silicon carbide powder and the silicon powder are subjected to oxidation layer and impurity removal treatment; The oil removal treatment of the diamond micropowder with particle size D1 and D2 in step one is ultrasonic cleaning of the diamond particles by using anhydrous ethanol as a solvent for 3 times; the time for each ultrasonic cleaning is 30 min; The metal impurity removal treatment of the diamond micropowder with particle size D1 and D2 in step one is static immersion of the diamond particles by using dilute hydrochloric acid as a solvent for 2 h, and finally washing with deionized water to a pH value of 7; the dilute hydrochloric acid is a mixed solution of hydrochloric acid with a mass fraction of 37% and deionized water in a volume ratio of 1:1; The oxidation layer and impurity removal treatment of the silicon carbide and the silicon powder in step one is heating and stirring of the silicon carbide and the silicon powder at 60℃ for 30 min by using a sodium hydroxide solution with a mass fraction of 5% as a solvent, then washing with deionized water to a pH value of 7, and then immersing in dilute hydrochloric acid for stirring for 30 min, and finally washing with deionized water to a pH value of 7; the dilute hydrochloric acid is a mixed solution of hydrochloric acid with a mass fraction of 37% and deionized water in a volume ratio of 1:5; The particle size of the diamond micropowder with particle size D1 in step one is 80~100 mesh, and the particle size of the diamond micropowder with particle size D2 is 275~325 mesh; the particle size of the silicon carbide is 15 μm, and the particle size of the silicon powder is 15 μm; II. Preparation of silicon-carbon coated diamond micropowder: Under the conditions of heating and stirring at 80℃ water bath, 6.6g phenolic resin was dissolved in 25mL anhydrous ethanol, then 7g silicon powder, 6.75g graphite powder, 0.5g silicon carbide powder were added to form a slurry, 28.6g diamond micro-powder with particle size D1 was added and mixed uniformly, and the mixture was stirred for 30min, then the mixture was poured into a copper foil, the copper foil was placed in an oven and dried at 140℃ for 5min, then broken and sieved through an 80 mesh sieve to obtain silicon-carbon coated diamond micro-powder; III. Warm compaction of the green body: 10.5g silicon-carbon coated diamond micro-powder was mixed with 4.5g diamond micro-powder with particle size D2, 0.525mL anhydrous ethanol was sprayed 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 to form a green body with a diameter of 20mm by warm compaction; The temperature of the warm compaction in step three was 140℃, the pressure of the warm compaction was 30MPa, the holding time was 10min, and the green body was demolded after cooling to room temperature; The circular mold cavity in step three was coated with polydimethylsiloxane; IV. Debinding treatment: The green body obtained in step three was placed in a vacuum sintering furnace, and the polymer was removed by stepwise heating in the vacuum sintering furnace to obtain a diamond / silicon carbide green body; The stepwise heating process for removing the polymer in step four was as follows: the vacuum sintering furnace was evacuated to a vacuum degree of 10Pa or less, then heated to 900℃ at a heating rate of 15℃ / min, held for 60min, then heated to 1200℃ at a heating rate of 5℃ / min, held for 30min, and finally cooled to room temperature with the furnace; V. Two-stage pseudo-vacuum graphite cavity reaction sintering of molten silicon: A porous graphite support was placed at the bottom of the first graphite mold, graphite paper was laid on top of the porous graphite support, the diamond / silicon carbide green body was placed on top of the graphite paper, silicon powder was added on top of the green body, the first graphite mold cover was placed on top, and a one-stage pseudo-vacuum graphite cavity was formed; the one-stage pseudo-vacuum graphite cavity was then placed at the bottom of the second graphite mold, the second graphite mold cover was placed on top, and a two-stage pseudo-vacuum graphite cavity was formed, which was then transferred to a vacuum sintering furnace for stepwise heating and sintering to achieve densification, and a densified composite material was obtained; The material of the porous graphite support in step five was graphite; the thickness of the graphite paper in step five was 50μm, and the length and width were both 30mm; the graphite paper completely covered the diamond / silicon carbide green body to inhibit the loss of molten silicon; the added mass of silicon powder in step five was 2 times the mass of the diamond / silicon carbide green body; The process of the step five is: the vacuum sintering furnace is vacuumized to the vacuum degree of 10 Pa or less, then heated to 1400℃ at the heating rate of 17.5℃ / min, kept for 0 min, heated to 1450℃ at the heating rate of 5℃ / min, kept for 10 min, and finally cooled to room temperature with the furnace; Six, step-by-step gradient grinding treatment: The composite material is subjected to sand blasting treatment to remove residual silicon on the surface of the composite material, and then is placed into a grinding mold for grinding treatment, including: step (1), first single-press-block polishing: polishing at a speed of 10 r / min, surface changing every 200 revolutions, repeated for 3 times; step (2), polishing after increasing the number of press blocks: increasing 2 press blocks, polishing at a speed of 15 r / min, surface changing every 1000 revolutions, repeated for 7 times, the diamond ceramic matrix composite material surface has no obvious silicon residue, and the diamond ceramic matrix composite material is obtained.

[0023] Example 2: The difference between this example and example 1 is that the process of step five is: the vacuum sintering furnace is vacuumized to the vacuum degree of 10 Pa or less, then heated to 1400℃ at the heating rate of 17.5℃ / min, kept for 0 min, heated to 1500℃ at the heating rate of 5℃ / min, kept for 10 min, and finally cooled to room temperature with the furnace. The other steps and parameters are the same as those of example 1.

[0024] Example 3: The difference between this example and example 1 is that the process of step five is: the vacuum sintering furnace is vacuumized to the vacuum degree of 10 Pa or less, then heated to 1400℃ at the heating rate of 17.5℃ / min, kept for 0 min, heated to 1550℃ at the heating rate of 5℃ / min, kept for 10 min, and finally cooled to room temperature with the furnace. The other steps and parameters are the same as those of example 1.

[0025] Example 4: The difference between this example and example 1 is that the process of step five is: the vacuum sintering furnace is vacuumized to the vacuum degree of 10 Pa or less, then heated to 1400℃ at the heating rate of 17.5℃ / min, kept for 0 min, heated to 1600℃ at the heating rate of 5℃ / min, kept for 10 min, and finally cooled to room temperature with the furnace. The other steps and parameters are the same as those of example 1.

[0026] Comparative Example 1: The difference between this example and Example 1 is that a multi-stage pseudo-vacuum graphite cavity is not used, and the diamond / silicon carbide compact is exposed to the environment without the pseudo-vacuum graphite cavity; that is, step five is completed according to the following steps: the diamond / silicon carbide compact is transferred to a vacuum sintering furnace, and is sintered to densification in the vacuum sintering furnace at a stepwise heating rate to obtain a composite material; the stepwise heating sintering process in step five is as follows: the vacuum sintering furnace is vacuumed to a vacuum degree of 10 Pa or less, 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. The other steps and parameters are the same as in Example 1.

[0027] Comparative Example 2: The difference between this comparative example and Comparative Example 1 is that the stepwise heating sintering process in step five is as follows: the vacuum sintering furnace is vacuumed to a vacuum degree of 10 Pa or less, then heated to 1400 °C at a heating rate of 17.5 °C / min, held for 0 min, then heated to 1500 °C at a heating rate of 5 °C / min, held for 10 min, and finally cooled to room temperature with the furnace. The other steps and parameters are the same as in Comparative Example 1.

[0028] Comparative Example 3: The difference between this comparative example and Comparative Example 1 is that the stepwise heating sintering process in step five is as follows: the vacuum sintering furnace is vacuumed to a vacuum degree of 10 Pa or less, then heated to 1400 °C at a heating rate of 17.5 °C / min, held for 0 min, then heated to 1550 °C at a heating rate of 5 °C / min, held for 10 min, and finally cooled to room temperature with the furnace. The other steps and parameters are the same as in Comparative Example 1.

[0029] Comparative Example 4: The difference between this comparative example and Comparative Example 1 is that the stepwise heating sintering process in step five is as follows: the vacuum sintering furnace is vacuumed to a vacuum degree of 10 Pa or less, then heated to 1400 °C at a heating rate of 17.5 °C / min, held for 0 min, then heated to 1600 °C at a heating rate of 5 °C / min, held for 10 min, and finally cooled to room temperature with the furnace. The other steps and parameters are the same as in Comparative Example 1.

[0030] Comparative Example 5: The difference between this comparative example and Comparative Example 1 is that the stepwise heating sintering process in step five is as follows: the vacuum sintering furnace is vacuumed to a vacuum degree of 10 Pa or less, 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 20 min, and finally cooled to room temperature with the furnace. The other steps and parameters are the same as in Comparative Example 1.

[0031] Comparative Example 6: The difference between this comparative example and Comparative Example 2 is that the step five of the process of the stepwise temperature rising sintering is as follows: the vacuum sintering furnace is vacuumized to a vacuum degree of 10 Pa or less, then the temperature is raised to 1400 °C at a temperature rising rate of 17.5 °C / min, kept for 0 min, then the temperature is raised to 1500 °C at a temperature rising rate of 5 °C / min, kept for 20 min, and finally the furnace is cooled to room temperature. The other steps and parameters are the same as those of Comparative Example 2.

[0032] Comparative Example 7: The difference between this comparative example and Comparative Example 3 is that the step five of the process of the stepwise temperature rising sintering is as follows: the vacuum sintering furnace is vacuumized to a vacuum degree of 10 Pa or less, then the temperature is raised to 1400 °C at a temperature rising rate of 17.5 °C / min, kept for 0 min, then the temperature is raised to 1550 °C at a temperature rising rate of 5 °C / min, kept for 20 min, and finally the furnace is cooled to room temperature. The other steps and parameters are the same as those of Comparative Example 3.

[0033] Comparative Example 8: The difference between this comparative example and Comparative Example 4 is that the step five of the process of the stepwise temperature rising sintering is as follows: the vacuum sintering furnace is vacuumized to a vacuum degree of 10 Pa or less, then the temperature is raised to 1400 °C at a temperature rising rate of 17.5 °C / min, kept for 0 min, then the temperature is raised to 1600 °C at a temperature rising rate of 5 °C / min, kept for 20 min, and finally the furnace is cooled to room temperature. The other steps and parameters are the same as those of Comparative Example 4.

[0034] Comparative Example 9: The difference between this comparative example and Comparative Example 1 is that the step five of the process of the stepwise temperature rising sintering is as follows: the vacuum sintering furnace is vacuumized to a vacuum degree of 10 Pa or less, then the temperature is raised to 1400 °C at a temperature rising rate of 17.5 °C / min, kept for 0 min, then the temperature is raised to 1450 °C at a temperature rising rate of 5 °C / min, kept for 30 min, and finally the furnace is cooled to room temperature. The other steps and parameters are the same as those of Comparative Example 1.

[0035] Comparative Example 10: The difference between this comparative example and Comparative Example 2 is that the step five of the process of the stepwise temperature rising sintering is as follows: the vacuum sintering furnace is vacuumized to a vacuum degree of 10 Pa or less, then the temperature is raised to 1400 °C at a temperature rising rate of 17.5 °C / min, kept for 0 min, then the temperature is raised to 1500 °C at a temperature rising rate of 5 °C / min, kept for 30 min, and finally the furnace is cooled to room temperature. The other steps and parameters are the same as those of Comparative Example 2.

[0036] Comparative Example 11: The difference between this comparative example and Comparative Example 3 is that the process of the step five of the stepwise temperature rising sintering is: the vacuum sintering furnace is vacuumized to a vacuum degree of 10 Pa or less, then the temperature is raised to 1400℃ at a temperature rising rate of 17.5℃ / min, kept for 0 min, then the temperature is raised to 1550℃ at a temperature rising rate of 5℃ / min, kept for 30 min, and finally the furnace is cooled to room temperature. The other steps and parameters are the same as those of Comparative Example 3.

[0037] Comparative Example 12: The difference between this comparative example and Comparative Example 4 is that the process of the step five of the stepwise temperature rising sintering is: the vacuum sintering furnace is vacuumized to a vacuum degree of 10 Pa or less, then the temperature is raised to 1400℃ at a temperature rising rate of 17.5℃ / min, kept for 0 min, then the temperature is raised to 1600℃ at a temperature rising rate of 5℃ / min, kept for 30 min, and finally the furnace is cooled to room temperature. The other steps and parameters are the same as those of Comparative Example 4.

[0038] Comparative Example 13: The difference between this comparative example and Example 1 is that in the step three, 10.5 g of the silicon-carbon coated diamond micropowder is mixed with 4.5 g of the diamond micropowder with a particle size of D2, stirred for 10 min to obtain a mixture; 1.7 g of the mixture is introduced into a circular mold cavity with a diameter of 20 mm, and warm-pressed into a green body with a diameter of 20 mm; the temperature of the warm-pressing in the step three is 140℃, the pressure of the warm-pressing is 30 MPa, the holding time is 10 min, and the green body is cooled to room temperature and demolded; and the circular mold cavity in the step three is not coated with any substance. The other steps and parameters are the same as those of Example 1.

[0039] Figure 1 The polarized light microscope micro-morphology diagram of the silicon-carbon coated diamond micropowder obtained in the step two of Example 1; It can be seen that: Figure 1 the surface of the diamond powder is uniformly coated with a layer of graphite and silicon.

[0040] Figure 2 The composition schematic diagram of the two-stage pseudo-vacuum graphite cavity in the step five of Example 1; Figure 3 The three-view diagram of the porous graphite support in the step five of Example 1; Figure 4 The schematic diagram of the multi-stage pseudo-vacuum graphite cavity melt silicon self-flowing loss reaction sintering in the step five of Example 1; Figure 5 The diameter measurement data diagram of the densified composite material obtained in the step five of Example 1, 2, 3, and 4; Figure 5 The horizontal coordinate 1450℃ corresponds to Example 1, 1500℃ corresponds to Example 2, 1550℃ corresponds to Example 3, and 1600℃ corresponds to Example 4. From Figure 5 It can be known that, under different sintering process conditions, the sintered parts have no obvious expansion phenomenon and the diameters are about 20mm.

[0041] Figure 6 The diameter measurement data graph of the densified composite material obtained in step five of the comparative example 1-12; Figure 6 The comparative example 1 corresponds to 10min and 1450℃; the comparative example 2 corresponds to 10min and 1500℃; the comparative example 3 corresponds to 10min and 1550℃; the comparative example 4 corresponds to 10min and 1600℃; the comparative example 5 corresponds to 20min and 1450℃; the comparative example 6 corresponds to 20min and 1500℃; the comparative example 7 corresponds to 20min and 1550℃; the comparative example 8 corresponds to 20min and 1600℃; the comparative example 9 corresponds to 30min and 1450℃; the comparative example 10 corresponds to 30min and 1500℃; the comparative example 11 corresponds to 30min and 1550℃; and the comparative example 12 corresponds to 30min and 1600℃; From Figure 6 It can be known that, under different sintering process conditions, the sintered parts have obvious expansion phenomenon and the diameters are about 25mm.

[0042] Figure 7 The content of the internal diamond of the diamond ceramic matrix composite material prepared in the comparative examples 1-4 and the comparative examples 1-12; From Figure 7 It can be known that, the diamond volume fraction of the comparative examples 1-12 becomes smaller due to the expansion of the sintered parts, while the diamond volume fraction of the examples 1-4 does not become smaller due to the expansion of the sintered parts.

[0043] Figure 8 The micro-optical picture of the diamond ceramic matrix composite material prepared in the example 1; Figure 9 The micro-optical picture of the diamond ceramic matrix composite material prepared in the comparative example 1; From Figure 8 and Figure 9 It can be known by comparison that, the silicon proportion of the white area in the diamond ceramic matrix composite material of the example 1 is obviously less, the diamond is more dense, and the diamond content is higher.

Claims

1. A method of near-net-shaping of a diamond ceramic matrix composite material, characterized in that: The multi-stage pseudo-vacuum graphite cavity is realized, including the following steps: I. Pretreatment of raw materials: The diamond powder with particle size D1 and D2 is subjected to oil removal treatment and metal impurity removal treatment in sequence; the silicon carbide powder and silicon powder are subjected to oxidation layer and impurity removal treatment; II. Preparation of silicon-carbon coated diamond powder: Under water bath heating, phenolic resin is dissolved in anhydrous ethanol, then silicon powder, graphite powder and silicon carbide powder are added to form a slurry, and the diamond powder with particle size D1 is added and uniformly mixed, and then dried and crushed and sieved to obtain silicon-carbon coated diamond powder; III. Warm-pressing of green body: The silicon-carbon coated diamond powder and the diamond powder with particle size D2 are mixed, sprayed with solvent and stirred, and then introduced into a mold cavity to form a green body by warm-pressing; IV. Defatting treatment: The green body is placed in a vacuum sintering furnace, and the polymer is removed by stepwise temperature rising in the vacuum sintering furnace to obtain a diamond / silicon carbide green body; V. Multi-stage pseudo-vacuum graphite cavity melting silicon self-flowing reaction sintering: A porous graphite support is placed at the bottom of a first graphite mold, graphite paper is laid on the porous graphite support, the diamond / silicon carbide green body is placed on the graphite paper, silicon powder is added on the top of the green body, and a first graphite mold cover is covered to form a first-stage pseudo-vacuum graphite cavity; the first-stage pseudo-vacuum graphite cavity is placed at the bottom of an N+1 graphite mold, and an N+1 graphite mold cover is covered to form an N+1-stage pseudo-vacuum graphite cavity, which is then transferred to a vacuum sintering furnace for stepwise temperature rising and sintering to realize densification, thereby obtaining a densified composite material; the value of N is 1≤N≤4, and N is a positive integer; VI. Step-by-step gradient grinding treatment: The surface residual silicon of the composite material is removed and polished to obtain a diamond ceramic matrix composite material.

2. A method of near-net-shaping of a diamond ceramic matrix composite according to claim 1, characterized in that: In step I, the diamond powder with particle size D1 and D2 is subjected to oil removal treatment by ultrasonic cleaning 2-3 times using anhydrous ethanol or acetone as the solvent; each ultrasonic cleaning time is 10-30 min; in step I, the diamond powder with particle size D1 and D2 is subjected to metal impurity removal treatment by static immersion in dilute hydrochloric acid or dilute nitric acid for 2-4 h or by heating and stirring at 60-70℃ for 1-2 h, and finally washed with deionized water until neutral; the silicon carbide and silicon powder are subjected to oxidation layer and impurity removal treatment by heating and stirring at 60-70℃ for 30-60 min using a 5-10% sodium hydroxide solution as the solvent, then rinsing with deionized water until neutral, and then immersing in dilute hydrochloric acid for a period of time, and finally rinsing with deionized water until neutral.

3. The method of near-net-shaping of diamond ceramic matrix composites according to claim 1, characterized in that: In step I, the diamond powder with particle size D1 has a size of 10-500 μm, and the diamond powder with particle size D2 has a size of 2-100 μm; the silicon carbide has a particle size of 1-50 μm, and the silicon powder has a particle size of 1-50 μm.

4. The method of near-net-shaping of diamond ceramic matrix composites according to claim 1, characterized in that: The mass-volume ratio of the 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):(1g~500g):(1g~500g):(1mL~750mL).

5. The method of near-net-shaping of diamond ceramic matrix composites according to claim 1, characterized in that: The temperature of the water bath heating in step two is 75℃~85℃; the drying in step two is to pour the mixed slurry into a copper foil, and then put the copper foil into an oven for drying, the temperature of the drying is 80℃~150℃, and the time of the drying is 5min~30min; the aperture of the sieving in step two is 10μm~500μm.

6. The method of near-net-shaping of diamond ceramic matrix composites according to claim 1, characterized in that: The solvent in step three is anhydrous ethanol; the mass ratio of the silicon-carbon coated diamond micro-powder and the diamond micro-powder with a particle size of D2 in step three is (8~12):(3~6); the spraying amount of the solvent in step three is 5~20% of the mass of the silicon-carbon coated diamond micro-powder; the temperature of the warm-pressing in step three is 135℃~150℃, the pressure of the warm-pressing is 10MPa~50MPa, and the time of the pressure maintaining is 10min~20min; the mold cavity in step three is coated with polydimethylsiloxane.

7. The method of near-net-shaping of diamond ceramic matrix composites according to claim 1, characterized in that: The process of the stepwise temperature rising for removing the polymer in step four is: vacuumizing the vacuum sintering furnace to a vacuum degree of 10Pa or less, then rising the temperature to 800℃~1000℃ at a temperature rising rate of 5℃ / min~30℃ / min, maintaining the temperature for 30min~90min, then rising the temperature to 1000℃~1300℃ at a temperature rising rate of 5℃ / min~20℃ / min, maintaining the temperature for 10min~90min, and finally cooling to room temperature with the furnace.

8. The method of near-net-shaping of diamond ceramic matrix composites according to claim 1, characterized in that: The material of the porous graphite support in step five is graphite; the thickness of the graphite paper in step five is 50μm~500μm, and the graphite paper completely covers the diamond / silicon carbide blank to inhibit the loss of molten silicon; the added mass of the silicon powder in step five is 1.5~3 times of the mass of the diamond / silicon carbide blank.

9. The method of near-net-shaping of a diamond ceramic matrix composite material according to claim 1, characterized in that: The process of the stepwise temperature rising sintering in step five is: vacuumizing the vacuum sintering furnace to a vacuum degree of 10Pa or less, then rising the temperature to 1350℃~1400℃ at a temperature rising rate of 10℃ / min~20℃ / min, maintaining the temperature for 0min, then rising the temperature to 1450℃~1650℃ at a temperature rising rate of 1℃ / min~10℃ / min, maintaining the temperature for 10min~120min, and finally cooling to room temperature with the furnace.

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

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