Short fiber toughened high-entropy carbide ceramic for ultra-high temperature extreme environment and preparation method and application thereof

Abstract

The present application relates to a kind of short fiber toughened high-entropy carbide ceramics for ultra-high temperature extreme environment and preparation method and application, short fiber toughened high-entropy carbide ceramics includes the volume fraction 5% to 20% of short fiber, matrix is high-entropy carbide.The present application uses short fiber to high-entropy carbide is toughened, SiC, W, C fiber all has high temperature resistance good, excellent mechanical properties and the like advantages, using short fiber form can ensure that preparation process is simple, toughening effect is good, there is no performance anisotropy etc.;The short fiber toughened high-entropy carbide ceramics prepared in the present application can reach 9.9446MPa.m ‑1 / 2 Left and right, excellent mechanical properties.

Description

Technical Field

[0001] This invention pertains to carbide ceramics and their preparation methods, specifically relating to a short-fiber toughened high-entropy carbide ceramic for use in ultra-high temperature extreme environments, its preparation method, and its application. Background Technology

[0002] High-entropy materials possess four unique effects: the high-entropy effect that enhances thermal performance, the lattice distortion effect that improves mechanical properties, the hysteresis diffusion effect that enhances high-temperature stability, and the synergistic cocktail effect that integrates the advantages of each component. They have great application potential in extreme environments.

[0003] In recent years, researchers have introduced the high-entropy effect into carbides, which have advantages such as high hardness, high melting point, and good high-temperature stability. This has given high-entropy carbides excellent comprehensive properties such as good high-temperature mechanical properties, high hardness, good radiation resistance (avoiding radiation amorphization), and resistance to steam oxidation. These properties make high-entropy carbides a promising candidate for development in nuclear structural materials and aerospace structural materials.

[0004] However, high-entropy carbide ceramics are inherently brittle and have low ductility, which greatly limits their engineering applications. At present, there is an urgent need to select a suitable toughening method to improve their toughness. The strong covalent bonds and low self-diffusion of high-entropy carbide ceramics themselves require extremely high temperatures for their preparation, which places extremely high demands on the toughening materials.

[0005] In recent years, the main toughening methods have included long fiber toughening, layered structure toughening, particle toughening, and whisker toughening. Long fiber toughening usually exhibits anisotropy in properties, layered structure toughening has poor shear strength, particle toughening has a relatively poor effect, and whisker toughening is too difficult to disperse. Therefore, the toughening methods currently used for high-entropy carbide ceramics all have shortcomings. Summary of the Invention

[0006] Technical problems to be solved

[0007] To avoid the shortcomings of existing technologies and to solve the problem of the difficulty in balancing the comprehensive mechanical properties and toughening effect of existing high-entropy carbide ceramic toughening methods, this invention proposes a short-fiber toughened high-entropy carbide ceramic for use in ultra-high temperature extreme environments, as well as its preparation method and application.

[0008] Technical solution

[0009] A short-fiber toughened high-entropy carbide ceramic for use in ultra-high temperature extreme environments is characterized by comprising 5%-20% by volume of short-fibers, and the matrix being a high-entropy carbide; the high-entropy carbide is a mixture of TiC, NbC, TaC, VC, Mo and C powders; the short-fibers include SiC, C and W.

[0010] The molar ratio of TiC, NbC, TaC, VC, Mo and C is 1:1:1:1:1:1.5-2.

[0011] The particle size range of TiC, NbC, TaC, VC, and Mo is 1-5 μm; the particle size range of the carbon powder is 10-50 nm.

[0012] The chopped fibers have a length of 1-10 mm, the SiC and C fibers have a diameter range of 1-20 μm, and the W fibers have a diameter range of 50-150 μm.

[0013] A method for preparing short-fiber toughened high-entropy carbide ceramics for ultra-high temperature extreme environments, characterized by the following steps:

[0014] Step 1: Mix TiC, NbC, TaC, VC, Mo and C powders and then ball mill them to obtain a mixed powder;

[0015] Step 2, Carbothermic Reduction: The powder is pre-pressed into blocks and subjected to carbothermic reduction reaction in a vacuum furnace under pressureless environment to remove a small amount of oxygen from the commercial powder, thereby obtaining the preform;

[0016] The carbothermic reduction process is as follows: the heating rate is 5-10℃ / min, the temperature is raised to 1500-1800℃, and the temperature is held for 2-3 hours; the cooling rate is 5-10℃ / min, the temperature is lowered to 500℃, and then the furnace is naturally cooled to room temperature to obtain ceramic products after carbothermic reduction reaction and initial diffusion.

[0017] Step 3: Grind the carbothermic reduction ceramic into powder;

[0018] Step 4, Fiber Deposition Interface and Mixing: Cut SiC or C fibers to 1-10 mm. Deposit BN interface on the short-cut C fibers using the CVI method; deposit PyC interface on the short-cut SiC fibers using the CVI method; deposit Y2O3 on W fibers using magnetron sputtering, and then cut them to 1-10 mm in length to obtain short-cut fibers.

[0019] Step 5: Mixing fibers and matrix powder: Mix the fibers and powder after the interface is deposited. C and SiC chopped fibers are mixed sequentially by stirring, wet ball milling, and vacuum precipitation. W chopped fibers are mixed in a natural state. Then, the two are mixed to obtain a mixed powder.

[0020] Step 6, SPS sintering: The mixed powder is placed in a graphite mold and sintered by the SPS method to obtain short-cut fiber toughened high-entropy carbide ceramics for use in ultra-high temperature extreme environments;

[0021] The SPS sintering process parameters are as follows: heating to 1800-2100℃ at a rate of 50-200℃ / min and increasing the pressure to 30-40MPa, holding at 1800-2100℃ and 30-40MPa for 10-20min; after holding, cooling down at a rate of 50-200℃ / min and allowing natural cooling in the furnace; thus obtaining short-cut fiber toughened high-entropy carbide ceramics for use in ultra-high temperature extreme environments.

[0022] In step 1: the powder is poured into an agate ball mill jar and tungsten carbide grinding balls are added. The ball mill speed is 300-400 r / min, and the ball milling is carried out for 12-24 hours. After the ball milling is completed, the powder is sieved through a sieve to obtain the matrix powder.

[0023] The mass ratio between the tungsten carbide grinding balls and the powder is 5-10:1; during wet grinding, the mass ratio of SiC, C short-cut fibers plus powder, ethanol, and grinding balls used is 1:5:5-10.

[0024] In step 3: during carbothermic reduction, the ambient pressure must be 95-98 MPa lower than the external atmospheric pressure.

[0025] In step 5: after pouring anhydrous ethanol into a beaker, slowly add the fiber and stir with a vertical stirrer at 400 r / min for 2 hours. Then pour the powder into the ethanol and fiber mixture, vacuum the mixture, and wet grind it at 300 r / min for 12-24 hours. After wet grinding, place it under vacuum negative pressure for 2 hours to allow the powder and fiber mixture to precipitate. Then dry it in an oven at 70℃ for 6-8 hours.

[0026] An application of the aforementioned chopped fiber-reinforced high-entropy carbide ceramic for ultra-high temperature extreme environments is characterized in that: the chopped fiber-reinforced high-entropy carbide ceramic achieves a strength of 9.9446 MPa. -1 / 2 It has excellent mechanical properties and is used in ultra-high temperature extreme environments.

[0027] Beneficial effects

[0028] This invention proposes a chopped fiber-toughened high-entropy carbide ceramic for use in ultra-high temperature extreme environments, its preparation method, and its application. The chopped fiber-toughened high-entropy carbide ceramic comprises 5%-20% by volume chopped fibers, with a high-entropy carbide matrix. This invention uses chopped fibers to toughen the high-entropy carbide. SiC, W, and C fibers all possess advantages such as good high-temperature resistance and excellent mechanical properties. Using chopped fibers ensures a simple preparation process, good toughening effect, and the absence of anisotropy in properties. The chopped fiber-toughened high-entropy carbide ceramic prepared by this invention can achieve a strength of 9.9446 MPa. -1 / 2 It has excellent mechanical properties.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] (1) This invention discloses a short-fiber toughened high-entropy carbide ceramic for use in ultra-high temperature extreme environments. The raw materials include 5%-20% by volume of short-fiber SiC, W, or C fibers, with the remainder being carbides, metals, and carbon powder. Currently, the toughening methods for high-entropy carbides using long fibers, layered structures, particles, and whiskers are difficult to achieve simultaneously in terms of toughening effect and ease of preparation, which greatly limits the application of high-entropy carbides. This invention uses short-fibers to toughen high-entropy carbides. SiC, W, and C fibers all have advantages such as good high-temperature resistance and excellent mechanical properties. Using short-fibers ensures a simple preparation process, good toughening effect, and no anisotropy in performance. The short-fiber toughened high-entropy carbide ceramic prepared by this invention can achieve a strength of 9.9446 MPa. -1 / 2 It has excellent mechanical properties.

[0031] (2) This invention discloses a method for preparing high-entropy carbide ceramics toughened with chopped fibers. The method involves heat-treating the raw material powder using a carbothermal reduction method, then mixing the powder with chopped fibers, and finally preparing the ceramics using an SPS sintering process. Currently, commercially available carbide powders have a high oxygen content. Direct mixing can easily lead to oxidation of the chopped fibers at high temperatures, causing them to lose their toughening effect. It can also cause elemental inhomogeneity or even a second phase in the matrix, resulting in poor matrix performance and reduced performance of the chopped fiber-toughened high-entropy carbide ceramics. This invention adds an excessive amount of carbon powder and uses a carbothermal reduction process to perform pressureless heat treatment on the powder. This allows the C and O to react and generate gas, which escapes, significantly reducing the oxygen content in the powder. This results in a uniform elemental distribution without segregation, reduces the content of low-density oxides, and increases density, ensuring a dense and uniform matrix. Attached Figure Description

[0032] Figure 1 This is a SEM image of the C-short fiber toughened high-entropy carbide ceramic prepared in Example 1 of the present invention.

[0033] Figure 2 The image shows the fracture morphology of the C-short fiber-toughened high-entropy carbide ceramic prepared in Example 1 of this invention after fracture toughness testing.

[0034] Figure 3 The fracture toughness test results are for the short-cut fiber toughened high-entropy carbide ceramics and pure ceramic (TiTaNbVMo)C prepared in Examples 1, 2 and 3 of this invention.

[0035] Figure 4 This is a schematic diagram of the SPS mold used in Embodiments 1, 2, and 3 of the present invention. Detailed Implementation

[0036] The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

[0037] To improve the toughness of high-entropy carbide ceramics by using short-chopped C fibers for toughening and to enable long-term service in ultra-high temperature extreme environments, this invention provides the following technical solution:

[0038] A short-fiber toughened high-entropy carbide ceramic for use in ultra-high temperature extreme environments is characterized by comprising 5%-20% by volume of short-fiber and a high-entropy carbide matrix.

[0039] Furthermore, the powders used in the matrix include TiC, NbC, TaC, VC, Mo, and C powders, with TiC, NbC, TaC, VC, and Mo having a particle size range of 1-5 μm, and carbon powder having a particle size range of 10-50 nm.

[0040] Furthermore, the short-cut fibers include three types: SiC, C, and W, with a length of 1-10 mm. The diameter of SiC and C fibers ranges from 1-20 μm, while the diameter of W fibers ranges from 50-150 μm.

[0041] Furthermore, the molar ratio of the powdered TiC, NbC, TaC, VC, Mo, and C is 1:1:1:1:1:1.5-2.

[0042] Meanwhile, this invention provides a method for preparing short-fiber toughened high-entropy carbide ceramics for ultra-high temperature extreme environments, characterized by the use of the aforementioned short-fiber and carbide powders, comprising the following steps:

[0043] Step 1: Powder preparation;

[0044] The six powders were mixed and then subjected to high-energy ball milling to make the powders uniform and fine.

[0045] Step 2, carbothermic reduction;

[0046] The powder was pre-compressed into blocks at 50 MPa, wrapped with a layer of graphite paper, and placed in a graphite crucible. The carbothermic reduction reaction was carried out in a vacuum furnace under pressureless conditions to remove trace amounts of oxygen from the commercial powder.

[0047] The heating rate is 5-10℃ / min, the temperature is raised to 1500-1800℃, and then held for 2-3 hours.

[0048] The cooling rate is 5-10℃ / min, and the temperature is reduced to 500℃. Then, the furnace is allowed to cool naturally to room temperature to obtain ceramic samples after carbothermic reduction reaction and initial diffusion.

[0049] Step 3: Grinding;

[0050] The carbothermic reduction of the ceramic sample is ground into powder for later mixing with fibers.

[0051] Step 4: Short-cut fiber deposition interface and mixing

[0052] SiC or C fibers were cut to a length of 1-10 mm. The chopped C fibers were deposited with a BN interface using the CVI method, and the chopped SiC fibers were deposited with a PyC interface using the CVI method. W fibers were deposited with Y2O3 using magnetron sputtering and then cut to a length of 1-10 mm.

[0053] Step 5: Mixing fibers and matrix powder

[0054] After the interface was deposited, the fibers and powder were mixed. The C and SiC short-cut fibers were mixed sequentially by stirring, wet ball milling, and vacuum precipitation, while the W short-cut fibers were mixed manually.

[0055] Step 6: SPS sintering

[0056] The powder was loaded into a graphite mold and sintered using the SPS method. After pre-pressing at a minimum pressure of 0.8t for 5 minutes, the temperature was increased to 1800℃ at a rate of 50-200℃ / min and the pressure was increased to 30-40MPa. The temperature was then held at 1800℃ and 30-40MPa for 10-20 minutes. After the holding period, the temperature was reduced to 600℃ at a rate of 50-200℃ / min and then allowed to cool naturally in the furnace.

[0057] Further, step 1 specifically involves: weighing the powder as raw material, pouring it into an agate ball mill jar and adding WC grinding balls, milling at a ball mill speed of 300 r / min for 12-24 h; after ball milling, sieving the obtained powder through a sieve to obtain matrix powder.

[0058] Furthermore, step 3 specifically requires that the ambient pressure be approximately 95 MPa lower than the external atmospheric pressure during carbothermic reduction.

[0059] Further, step 5 specifically involves: pouring anhydrous ethanol into a beaker, then slowly adding SiC or C chopped fibers, stirring at 400 rpm for 2 hours using a vertical stirrer, then adding the powder to the ethanol-fiber mixture, and wet milling at 300 rpm for 12-24 hours after vacuuming. After wet milling, place the mixture under vacuum for 2 hours to allow the powder-fiber mixture to precipitate, and then dry it in an oven at 70°C for 6-8 hours.

[0060] Furthermore, the mass ratio between WC grinding balls and powder during the ball milling process is 5-10:1.

[0061] Furthermore, the ratio of the mass of the SiC or C chopped fibers plus powder, the mass of ethanol, and the mass of the grinding balls is 1:5:5-10.

[0062] In this embodiment, the short-fiber toughened high-entropy carbide ceramic under ultra-high temperature extreme environment is characterized by comprising 5%-20% by volume of short-fibers, and the matrix being a high-entropy carbide. The powder used for the matrix includes TiC, NbC, TaC, VC, Mo, and C powders, with TiC, NbC, TaC, VC, and Mo having a particle size range of 1-5 μm, and the carbon powder having a particle size range of 10-50 nm. The short-fibers include SiC, C, and W, with a length range of 1-10 mm, SiC and C fibers having a diameter of 1-20 μm, and W fibers having a diameter of 50-150 μm.

[0063] Example 1

[0064] Step 1: Prepare powder;

[0065] Weigh out 0.0426 mol of carbide powder, 8.21 g of TaC powder, 2.55 g of TiC powder, 4.47 g of NbC powder, 2.68 g of VC powder, 4.08 g of Mo powder, and 0.77 g of C powder as equimolar pentagonal carbide matrix raw materials; the amount of C powder is 0.0639 mol, so that a carbothermic reduction reaction can be carried out in a vacuum furnace to remove the inherent oxygen content in the commercial carbide powder.

[0066] Place the powder into the agate grinding jar in sequence, and add 10mm, 5mm and 1mm tungsten carbide grinding balls in increasing quantities, with a total grinding ball mass of 120g. Then place the agate grinding jar into a stainless steel vacuum jar.

[0067] After vacuuming for 10 minutes, the powder was ball-milled in a planetary ball mill at 300 r / min for 24 hours. After the ball milling was completed, the powder was removed and passed through a 200-mesh sieve.

[0068] Step 2, carbothermic reduction;

[0069] The powder is pre-pressed into cylindrical blocks with a diameter of 25 mm in a tablet press, placed in a graphite crucible, and subjected to a carbothermic reduction reaction in a vacuum furnace under pressureless conditions. The process is started when the gas pressure inside the furnace reaches 95 MPa.

[0070] The heating rate is 5-10℃ / min, the temperature is raised to 1600℃, and then held for 3 hours.

[0071] The cooling rate is 5-10℃ / min, and the temperature is reduced to 500℃. Then, the furnace is allowed to cool naturally to room temperature to obtain ceramic samples after carbothermic reduction reaction and initial diffusion.

[0072] Step 3: Grinding;

[0073] The carbothermic reduction ceramic sample was ground into powder in an agate mortar with an agate grinding pestle. At this point, the powder was a high-entropy carbide powder with uneven element distribution after initial diffusion, and it was passed through a 200-mesh sieve.

[0074] Step 4, C fiber deposition interface;

[0075] C fibers were cut to a length of 2 mm and placed in a perforated graphite mold. An 800 nm thick BN interface was prepared in a deposition furnace using the CVI method.

[0076] Step 5: Mix the fibers with the matrix powder;

[0077] Take 22.5g of the ground powder, 0.298g of the calculated mass of 5% volume fraction of short-cut C fibers, and 110g of anhydrous ethanol, mix them, and stir with a vertical stirrer at 400r / min for 2h.

[0078] After stirring, pour the mixture into an agate ball mill jar, add 110g of carbide grinding balls of different sizes, vacuum, and use a planetary ball mill at 300r / min for 24h.

[0079] After ball milling, the mixture is poured into a clean beaker and precipitated in a vacuum environment using a vacuum pump until the powder fibers reach the bottom of the beaker and obvious stratification occurs, which takes about 2 hours. After precipitation, the mixture is placed in an oven and dried at 70°C for 6 hours. Then, the dried powder is slightly ground to prevent clumping.

[0080] Step 6: SPS sintering;

[0081] The powder is placed in the center of a circular cylindrical graphite mold. Graphite pads and cylindrical graphite molds are placed above and below the powder, respectively. Graphite paper is used to separate the powder from the molds and between the molds. The molds are then placed in an SPS furnace.

[0082] Waiting for the vacuum degree in the furnace to reach 1*10 -3 The subsequent operation process involves pre-pressing at a minimum pressure of 0.8t for 5 minutes, then raising the temperature to 2100℃ at 100℃ / min and increasing the pressure to 30-40MPa, and holding at 1800℃ and 30-40MPa for 10-20 minutes. After the holding period, the temperature is lowered to 600℃ at 100℃ / min, and then naturally cooled in the furnace.

[0083] Example 2

[0084] Step 1: Prepare powder;

[0085] Weigh out 0.0426 mol of carbide powder, 8.21 g of TaC powder, 2.55 g of TiC powder, 4.47 g of NbC powder, 2.68 g of VC powder, 4.08 g of Mo powder, and 0.77 g of C powder as equimolar pentagonal carbide matrix raw materials; the amount of C powder is 0.0639 mol, so that a carbothermic reduction reaction can be carried out in a vacuum furnace to remove the inherent oxygen content in the commercial carbide powder;

[0086] Place the powder into the agate ball milling jar in sequence, and add 10mm, 5mm and 1mm tungsten carbide grinding balls in increasing quantities, with a total mass of 120g. Then place the agate ball milling jar into a stainless steel vacuum jar.

[0087] After vacuuming for 10 minutes, the powder was ball-milled in a planetary ball mill at 300 r / min for 24 hours. After the ball milling was completed, the powder was removed and passed through a 200-mesh sieve.

[0088] Step 2, carbothermic reduction;

[0089] The powder is pre-pressed into cylindrical blocks with a diameter of 25 mm in a tablet press, placed in a graphite crucible, and subjected to a carbothermic reduction reaction in a vacuum furnace under pressureless conditions. The process is started when the gas pressure inside the furnace reaches 95 MPa.

[0090] The heating rate is 5-10℃ / min, the temperature is raised to 1600℃, and then held for 3 hours.

[0091] The cooling rate is 5-10℃ / min, and the temperature is reduced to 500℃. Then, the furnace is allowed to cool naturally to room temperature to obtain ceramic samples after carbothermic reduction reaction and initial diffusion.

[0092] Step 3: Grinding;

[0093] The carbothermic reduction ceramic sample was ground into powder in an agate mortar with an agate grinding pestle. At this point, the powder was a high-entropy carbide powder with uneven element distribution after initial diffusion, and it was passed through a 200-mesh sieve.

[0094] Step 4: SiC fiber deposition interface;

[0095] SiC fibers were cut to a length of 2 mm and placed in a perforated graphite mold. A 400 nm thick PyC interface was prepared in a deposition furnace using the CVI method.

[0096] Step 5: Mixing fibers and matrix powder

[0097] Take 22.5g of the ground powder, 0.476g of the calculated 5% volume fraction of chopped SiC fibers, and 110g of anhydrous ethanol, mix them, and stir with a vertical stirrer at 400r / min for 2h.

[0098] After stirring, pour the mixture into an agate ball mill jar, add 110g of carbide grinding balls of different sizes, vacuum, and use a planetary ball mill at 300r / min for 24h.

[0099] After ball milling, the mixture is poured into a clean beaker and precipitated in a vacuum environment using a vacuum pump until the powder fibers reach the bottom of the beaker and obvious stratification occurs, which takes about 2 hours. After precipitation, the mixture is placed in an oven and dried at 70°C for 6 hours. Then, the dried powder is slightly ground to prevent clumping.

[0100] Step 6: SPS sintering

[0101] The powder is placed in the center of a circular cylindrical graphite mold. Graphite pads and cylindrical graphite molds are placed above and below the powder, respectively. Graphite paper is used to separate the powder from the molds and between the molds themselves. The mold is then placed in an SPS furnace.

[0102] Waiting for the vacuum degree in the furnace to reach 1*10 -3 The subsequent operation process involves pre-pressing at a minimum pressure of 0.8t for 5 minutes, then raising the temperature to 2100℃ at 100℃ / min and increasing the pressure to 30-40MPa, and holding at 1800℃ and 30-40MPa for 10-20 minutes. After the holding period, the temperature is lowered to 600℃ at 100℃ / min, and then naturally cooled in the furnace.

[0103] Example 3

[0104] Step 1: Prepare powder;

[0105] Weigh out 0.0426 mol of carbide powder, 8.21 g of TaC powder, 2.55 g of TiC powder, 4.47 g of NbC powder, 2.68 g of VC powder, 4.08 g of Mo powder, and 0.77 g of C powder as equimolar pentagonal carbide matrix raw materials; the amount of C powder is 0.0639 mol, so that a carbothermic reduction reaction can be carried out in a vacuum furnace to remove the inherent oxygen content in the commercial carbide powder.

[0106] Place the powder into the agate grinding jar in sequence, and add 10mm, 5mm and 1mm tungsten carbide grinding balls in increasing quantities, with a total grinding ball mass of 120g. Then place the agate grinding jar into a stainless steel vacuum jar.

[0107] After vacuuming for 10 minutes, the powder was ball-milled in a planetary ball mill at 300 r / min for 24 hours. After the ball milling was completed, the powder was removed and passed through a 200-mesh sieve.

[0108] Step 2, carbothermic reduction;

[0109] The powder is pre-pressed into cylindrical blocks with a diameter of 25 mm in a tablet press, placed in a graphite crucible, and subjected to a carbothermic reduction reaction in a vacuum furnace under pressureless conditions. The process is started when the gas pressure inside the furnace reaches 95 MPa.

[0110] The heating rate is 5-10℃ / min, the temperature is raised to 1600℃, and then held for 3 hours.

[0111] The cooling rate is 5-10℃ / min, and the temperature is reduced to 500℃. Then, the furnace is allowed to cool naturally to room temperature to obtain ceramic samples after carbothermic reduction reaction and initial diffusion.

[0112] Step 3: Grinding;

[0113] The carbothermic reduction ceramic sample was ground into powder in an agate mortar with an agate grinding pestle. At this point, the powder was a high-entropy carbide powder with uneven element distribution after initial diffusion, and it was passed through a 200-mesh sieve.

[0114] Step 4: Deposition interface of W-cut fibers

[0115] W fibers were wound around a metal frame, and a 3 μm Y2O3 interface was deposited using reactive magnetron sputtering. The W fibers were then removed and cut to 2 mm.

[0116] Step 5: Mixing fibers and matrix powder

[0117] Take 22.5g of the ground powder and the calculated mass of 5% chopped W fiber should be 2.873g. Mix them by hand.

[0118] Step 6: SPS sintering

[0119] The powder is placed in the center of a circular cylindrical graphite mold. Graphite pads and cylindrical graphite molds are placed above and below the powder, respectively. Graphite paper is used to separate the powder from the molds and between the molds themselves. The mold is then placed in an SPS furnace.

[0120] Waiting for the vacuum degree in the furnace to reach 1*10 -3 The subsequent operation process involves pre-pressing at a minimum pressure of 0.8t for 5 minutes, then raising the temperature to 2100℃ at 100℃ / min and increasing the pressure to 30-40MPa, and holding at 1800℃ and 30-40MPa for 10-20 minutes. After the holding period, the temperature is lowered to 600℃ at 100℃ / min, and then naturally cooled in the furnace.

[0121] Figure 1 The image shows a SEM image of the sintered (TiTaNbVMo)C composite material with short-cut C fibers. The image indicates that the fibers retain their original shape after sintering, the matrix elements are uniform except for a small number of pores, and the fibers are well bonded to the matrix.

[0122] Figure 2 The image shows the fracture morphology of the C / (TiTaNbVMo)C composite sample after fracture toughness testing. Some fibers were pulled out and debonded in the image. The pulled-out fibers and the holes left in the matrix can be seen, indicating that the short-cut C fibers played a toughening role.

[0123] Figure 3The fracture toughness test results are for pure ceramic (TiTaNbVMo)C and those toughened with 5 vol.% C, SiC, and W short-cut fibers, respectively. Compared with pure ceramic, the fracture toughness of C / (TiTaNbVMo)C is improved by 2.7723 MPa·m. -1 / 2 The strength increased by 38.64%; the fracture toughness of SiC / (TiTaNbVMo)C increased by 0.2509 MPa·m. -1 / 2 The fracture toughness of W / (TiTaNbVMo)C increased by 3.49%; however, the fracture toughness of W / (TiTaNbVMo)C decreased.

[0124] The mechanical properties of the short-cut fiber-reinforced (TiTaNbVMo)C prepared in Examples 1, 2, and 3 above were evaluated by fracture toughness, and the results are as follows: Figure 3 This invention demonstrates that the method can yield fiber-reinforced ceramic composites with excellent mechanical properties. The best toughening effect is achieved when the volume fraction of chopped C fibers is 5 vol.%, with an average fracture toughness of 9.9446 MPa / m. 1 / 2 .

Claims

1. A method for preparing short-fiber toughened high-entropy carbide ceramics for use in ultra-high temperature extreme environments, characterized in that... The steps are as follows: Step 1: Mix TiC, NbC, TaC, VC, Mo and C powders and then perform high-energy ball milling to obtain mixed powder; the particle size range of TiC, NbC, TaC, VC and Mo is 1-5μm; the particle size range of carbon powder is 10-50nm; Step 2, Carbothermic Reduction: The powder is pre-pressed into blocks and subjected to carbothermic reduction reaction in a vacuum furnace under pressureless environment to remove a small amount of oxygen from the commercial powder, thereby obtaining the preform; The carbothermic reduction process is as follows: the heating rate is 5-10℃ / min, the temperature is raised to 1500-1800℃, and the temperature is held for 2-3 hours; the cooling rate is 5-10℃ / min, the temperature is lowered to 500℃, and then the furnace is naturally cooled to room temperature to obtain ceramic products after carbothermic reduction reaction and initial diffusion. Step 3: Grind the carbothermic reduction ceramic into powder; Step 4, Fiber Deposition Interface and Mixing: Cut SiC or C fibers to 1-10 mm. Deposit BN interface on the short-cut C fibers using the CVI method; deposit PyC interface on the short-cut SiC fibers using the CVI method; deposit Y2O3 on W fibers using magnetron sputtering, and then cut them to 1-10 mm in length to obtain short-cut fibers. Step 5: Mixing fibers and matrix powder: Mix the fibers and powder after the interface is deposited. C and SiC chopped fibers are mixed sequentially by stirring, wet ball milling, and vacuum precipitation. W chopped fibers are mixed in a natural state. Then, the two are mixed to obtain a mixed powder. Step 6, SPS sintering: The mixed powder is placed in a graphite mold and sintered by the SPS method to obtain short-cut fiber toughened high-entropy carbide ceramics for use in ultra-high temperature extreme environments; The SPS sintering process parameters are as follows: heat up to 1800-2100℃ at a rate of 50-200℃ / min, increase the pressure to 30-40MPa, hold at 1800-2100℃ and 30-40MPa for 10-20min; after holding, cool down at a rate of 50-200℃ / min and allow to cool naturally in the furnace. Short-cut fiber toughened high-entropy carbide ceramics for use in ultra-high temperature extreme environments were obtained.

2. The method according to claim 1, characterized in that: In step 1: the powder is poured into an agate ball mill jar and tungsten carbide grinding balls are added. The ball mill speed is 300-400 r / min, and the ball milling is carried out for 12-24 hours. After the ball milling is completed, the powder is sieved through a sieve to obtain the matrix powder.

3. The method according to claim 2, characterized in that: The mass ratio between the tungsten carbide grinding balls and the powder is 5-10:1; during the wet ball milling, the mass ratio of SiC and C short-cut fibers plus powder, the mass of ethanol, and the mass of grinding balls used is 1:5:5-10.

4. The method according to claim 1, characterized in that: In step 3: during carbothermic reduction, the ambient pressure must be 95-98 MPa lower than the external atmospheric pressure.

5. The method according to claim 1, characterized in that: In step 5: after pouring anhydrous ethanol into a beaker, slowly add the fiber and stir with a vertical stirrer at 400 r / min for 2 hours. Then pour the powder into the ethanol and fiber mixture, vacuum the mixture, and wet grind it at 300 r / min for 12-24 hours. After wet grinding, place it under vacuum negative pressure for 2 hours to allow the powder and fiber mixture to precipitate. Then dry it in an oven at 70℃ for 6-8 hours.

6. A short-fiber toughened high-entropy carbide ceramic for use in ultra-high temperature extreme environments, prepared by the method according to any one of claims 1 to 5, characterized in that... It comprises 5%-20% by volume of chopped fibers, and the matrix is ​​a high-entropy carbide; the high-entropy carbide is a mixture of TiC, NbC, TaC, VC, Mo and C powders; the chopped fibers include SiC, C and W.

7. The short-fiber toughened high-entropy carbide ceramic for ultra-high temperature extreme environments according to claim 6, characterized in that: The molar ratio of TiC, NbC, TaC, VC, Mo and C is 1:1:1:1:1:1.5-2.

8. The short-fiber toughened high-entropy carbide ceramic for ultra-high temperature extreme environments according to claim 6, characterized in that: The chopped fibers have a length of 1-10 mm, the SiC and C fibers have a diameter range of 1-20 μm, and the W fibers have a diameter range of 50-150 μm.

9. An application of a short-fiber toughened high-entropy carbide ceramic prepared by the method according to any one of claims 1 to 5 for use in ultra-high temperature extreme environments, characterized in that: The short-cutter fiber-reinforced high-entropy carbide ceramic achieves a strength of 9.9446 MPa. -1 / 2 It is used in ultra-high temperature extreme environments.

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