Silicon carbide whisker toughened boron carbide composite material based on gel casting

Abstract

The invention belongs to the technical field of inorganic non-metallic materials, and relates to a silicon carbide whisker toughened boron carbide composite material based on gel casting. The invention discloses a silicon carbide whisker toughened boron carbide composite material based on gel casting molding, the silicon carbide whisker toughened boron carbide composite material has a dumbbell-shaped B4C-SiCw-B4C structure, and the structure is characterized in that two ends of silicon carbide whiskers with the length-diameter ratio of more than 50: 1 are connected with boron carbide particles; the silicon carbide whisker toughened boron carbide composite material based on gel casting is prepared by the following steps: performing ball milling, gelatinization, carbonization treatment and siliconizing treatment on composite powder obtained by premixing silicon carbide whiskers and boron carbide of which the length-diameter ratio is greater than 50: 1 and a gel mixture. A small amount of silicon carbide whiskers with a high length-diameter ratio are introduced into boron carbide, so that the silicon carbide whiskers with the high length-diameter ratio in the obtained silicon carbide whisker toughened boron carbide composite material are promoted to be connected with B4C particles, a dumbbell-shaped B4C-SiCw-B4C structure is formed, crack propagation is effectively hindered, cracks are deflected or bridged, and effective toughening is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of inorganic non-metallic materials, and relates to a silicon carbide whisker toughened boron carbide composite based on gel casting. BACKGROUND

[0002] Boron carbide (B4C) ceramics have important application value in the fields of armor protection, nuclear industry, etc. due to their high hardness, low density and excellent neutron absorption capacity. However, the low intrinsic toughness and poor thermal shock resistance of boron carbide seriously restrict its reliability under extreme working conditions. In order to improve the toughness, researchers mainly add toughening phases to improve the toughness of boron carbide materials to meet the application requirements. The toughening methods of boron carbide ceramics include particle toughening, fiber toughening and whisker toughening, etc. Among the above methods, silicon carbide whisker (SiCw) is widely considered as an efficient toughening phase due to its excellent mechanical / thermal / chemical properties and relatively simple process feasibility, which can significantly improve the fracture toughness of ceramic matrix composites through whisker pull-out and crack deflection mechanisms.

[0003] However, silicon carbide whisker toughening still faces two key challenges in practical application: on the one hand, SiCw is prone to agglomeration due to its special one-dimensional nanostructure and surface chemical inertness during mixing, resulting in stress concentration points or even crack initiation sources in the composite; on the other hand, in traditional dry pressing or slip casting processes, the slurry flowability is often deteriorated due to insufficient shear field and difficult rheological property control, resulting in high porosity and uneven distribution of whiskers in the sintered body. In view of these technical problems, existing research mainly uses ultrasonic dispersion or surface chemical modification methods to improve the dispersion of SiCw, but these methods have obvious limitations in industrial application: ultrasonic treatment is difficult to apply to high solid content systems and is prone to cause whisker fracture; surface modification may introduce impurity phases affecting the high temperature performance of the material; although gel casting technology can effectively fix the position of the dispersed phase through in-situ polymerization reaction, it is crucial to accurately match the polymerization kinetics of organic monomers with the whisker sedimentation behavior. Once the matching is out of control, serious macroscopic component segregation will occur, resulting in uneven improvement of material performance. SUMMARY

[0004] The present application aims to solve the above problems in the prior art, and provides a silicon carbide whisker toughened boron carbide composite based on gel casting. w The silicon carbide whisker toughened boron carbide composite has a "dumbbell type" B4C-SiC

[0005] One object of the present application is achieved by the following technical solutions: A silicon carbide whisker toughened boron carbide composite material based on gel-casting has a "dumbbell type" B4C-SiC structure w The B4C structure is connected with boron carbide particles at both ends of silicon carbide whiskers with an aspect ratio of >50:1; The silicon carbide whisker toughened boron carbide composite material based on gel-casting is prepared by mixing a composite powder obtained by premixing silicon carbide whiskers with an aspect ratio of >50:1 and boron carbide with a gel mixture, ball milling, gelling, carbonizing, and siliconizing.

[0006] In the present application, the silicon carbide whiskers are uniformly distributed in the composite powder and are in-situ "fixed" by a porous carbon network after molding and carbonization by the gel system. Under high temperature conditions, the oxygen element on the surface of the silicon carbide whiskers diffuses with the boron element in the boron carbide, so that the boron carbide particles B4C and the silicon carbide whiskers SiC w are connected with each other, and further form a "dumbbell type" B4C-SiC w structure.

[0007] Preferably, the silicon carbide whiskers are needle-shaped, with a diameter of <100 nm and a length of 5-10 μm.

[0008] Preferably, the silicon carbide whiskers have an aspect ratio of (50-100):1.

[0009] Preferably, the silicon carbide whiskers include 3C-SiC phase, 6H-SiC phase, and SiO2 phase.

[0010] Preferably, the aspect ratio of the silicon carbide whiskers is basically unchanged before and after premixing and before and after ball milling.

[0011] Further preferably, the aspect ratio of the silicon carbide whiskers is >50:1 before premixing and >50:1 after premixing.

[0012] Further preferably, the aspect ratio of the silicon carbide whiskers is >50:1 before ball milling and >50:1 after ball milling.

[0013] Preferably, the silicon carbide whiskers and the boron carbide are uniformly mixed after premixing.

[0014] Preferably, the premixing is dry premixing, including one or both of mechanical premixing and airflow premixing.

[0015] Further preferably, the premixing is intermittent dry premixing.

[0016] Still further preferably, the intermittent dry premixing includes: using a cell disruptor, starting for 2-15 s, stopping for 30-300 s, and repeating for 5-20 times.

[0017] Further preferably, the intermittent dry premixing comprises: using an air flow mixer, air flow pressure is 0.2-0.5 MPa, starting for 5-10 min, stopping for 10-30 min, and repeating for 3-5 times.

[0018] Preferably, the boron carbide is particle graded by mass ratio, average particle size of 40-60 μm: average particle size of 5-15 μm: average particle size of 1-5 μm = (5-7):1:(2-4).

[0019] Further preferably, the boron carbide is particle graded by mass ratio, average particle size of 50 μm: average particle size of 10 μm: average particle size of 2 μm = 6:1:3.

[0020] Preferably, the proportion of silicon carbide whiskers in the composite powder is 0.5-5 wt%.

[0021] Preferably, the components of the gel mixture comprise, by mass percentage: resorcinol 10-30 wt%, formaldehyde 15-40 wt%, water 20-50 wt%, basic salt 0.01-0.1 wt%, and tetramethylammonium hydroxide 0.1-1 wt%.

[0022] Further preferably, the basic salt comprises one or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate.

[0023] Preferably, the ball milling uses zirconium oxide balls as grinding medium, rotation speed is 100-300 r / min, and time is 4-24 h.

[0024] Preferably, the temperature of the gelation is 60-90 °C, and time is 4-48 h.

[0025] Preferably, the heating rate of the carbonization treatment is 1-5 °C / min, carbonization temperature is 700-1000 °C, and carbonization time is 1-12 h.

[0026] Preferably, the preform obtained after the carbonization treatment has a compressive strength >41 MPa and a bending strength >17 MPa.

[0027] Preferably, the heating rate of the silicon infiltration treatment is 1-10 °C / min, silicon infiltration temperature is 1450-1750 °C, and silicon infiltration time is 0.1-6 h.

[0028] In the silicon infiltration treatment, the molten silicon infiltrates the porous preform and reacts with the internal carbon to form silicon carbide, and the excess silicon fills the remaining pores to form residual silicon.

[0029] As preferred, in the gel-casting based silicon carbide whisker toughened boron carbide composite material, the boron carbide particles are dispersed in the continuous network structure formed by silicon carbide, the residual silicon of the siliconizing treatment fills the pores in the continuous phase and exists in the whole silicon carbide whisker toughened boron carbide composite material; and the silicon carbide whisker toughened boron carbide composite material has a "dumbbell type" B4C-SiC w B4C structure, the structure is a silicon carbide whisker SiC w connected with boron carbide B4C particles at both ends, wherein the silicon carbide whisker SiC w has an aspect ratio of (50-100):1.

[0030] As preferred, in the gel-casting based silicon carbide whisker toughened boron carbide composite material, the aspect ratio of the silicon carbide whisker is (50-100):1.

[0031] As preferred, in the gel-casting based silicon carbide whisker toughened boron carbide composite material, the "dumbbell type" B4C-SiC w B4C structure has a length of 5-10 μm.

[0032] As preferred, in the gel-casting based silicon carbide whisker toughened boron carbide composite material, the silicon content is 5-20 vol%.

[0033] The second object of the present application is achieved by the following technical scheme: A preparation method of a gel-casting based silicon carbide whisker toughened boron carbide composite material, comprising: (1) mixing silicon carbide whiskers with an aspect ratio >50:1 and boron carbide to obtain a composite powder; (2) preparing a gel mixture, and ball-milling the composite powder and the gel mixture to obtain a ceramic slurry; (3) injecting the ceramic slurry into a mold, and performing gelation and normal pressure drying to obtain a gel solidification body; (4) placing the gel solidification body in a high-temperature furnace for carbonization treatment to obtain a preform; (5) placing a silicon block above the preform, and performing siliconizing treatment in a graphite furnace to obtain a silicon carbide whisker toughened boron carbide composite material with B4C-SiC w B4C structure.

[0034] As preferred, in the (1), the proportion of the silicon carbide whisker in the composite powder is 0.5-5 wt%.

[0035] Further preferably, in the (1), the proportion of the silicon carbide whisker in the composite powder is 1.5 wt%.

[0036] As preferred, in the (2), the viscosity of the ceramic slurry is 100-1000 Pa•s.

[0037] Preferably, the mass ratio of the composite powder and the gel mixture in (2) is (60-75):(40-25).

[0038] Further preferably, the amount of the composite powder added in the ceramic slurry in (2) is 65-75wt%.

[0039] Preferably, the mold in (3) comprises one of high-temperature-resistant plastic, glass or metal.

[0040] Preferably, the temperature for the normal-pressure drying in (3) is 100-150℃, and the time is 1-48h.

[0041] Preferably, the atmosphere in the high-temperature furnace in (4) is vacuum or inert gas atmosphere.

[0042] Preferably, the silicon carbide whiskers in the preform in (4) are in single filament form and are wrapped by the porous carbon network skeleton.

[0043] Further preferably, the porous carbon network skeleton is prepared after the carbonization treatment of the gel mixture.

[0044] Preferably, the compressive strength of the preform in (4) is >41MPa, and the bending strength is >17MPa.

[0045] Preferably, the average particle size of the silicon block in (5) is <1cm.

[0046] Preferably, the amount of the silicon block used in (5) is 1.5-2 times the theoretical required silicon mass.

[0047] Preferably, the bending strength of the silicon carbide whisker toughened boron carbide composite material in (5) is >300MPa, and the fracture toughness is >4.2 MPa•m 1 / 2 .

[0048] Further preferably, the bending strength of the silicon carbide whisker toughened boron carbide composite material in (5) is >340MPa, and the fracture toughness is >4.6 MPa•m 1 / 2 .

[0049] Preferably, the volume density of the silicon carbide whisker toughened boron carbide composite material in (5) is 2.5-2.6 g•cm -3 ; and the open porosity is lower than 0.3%.

[0050] Compared with the prior art, the present application has the following beneficial effects: 1、The present application introduces a small amount of high aspect ratio silicon carbide whiskers into boron carbide, and the high aspect ratio silicon carbide whiskers exist throughout the entire preparation process, which promotes the high aspect ratio silicon carbide whiskers in the silicon carbide whisker toughened boron carbide composite to connect the boron carbide particles, forming a "dumbbell type" B4C-SiC w B4C structure, effectively hinders crack propagation, causes "deflection" or "bridging" of the crack, and realizes effective toughening.

[0051] 2、The present application realizes three-dimensional uniform dispersion of silicon carbide whiskers in the preform and boron carbide composite through the synergistic dispersion of intermittent premixing and tetramethylammonium hydroxide dispersant.

[0052] 3、The present application prepares a ceramic preform with high compressive strength and high bending strength through composite powder premixing and gel casting molding process. The preform has excellent processability, which provides an effective way for near-net-shape forming of ceramic special-shaped structural parts and subsequent high-precision machining. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 SEM image of the silicon carbide whisker used in the present application.

[0054] Figure 2 XRD pattern of the silicon carbide whisker used in the present application.

[0055] Figure 3 SEM image of the preform in Example 1 of the present application.

[0056] Figure 4 SEM image of the silicon carbide whisker toughened boron carbide composite based on gel casting molding in Example 1 of the present application.

[0057] Figure 5 Low magnification SEM image of the silicon carbide whisker toughened boron carbide composite based on gel casting molding in Example 1 of the present application after acid etching to remove silicon.

[0058] Figure 6 High magnification SEM image of the silicon carbide whisker toughened boron carbide composite based on gel casting molding in Example 1 of the present application after acid etching to remove silicon.

[0059] Figure 7 SEM image of the silicon carbide whisker toughened boron carbide composite based on gel casting molding in Example 1 of the present application during crack propagation. DETAILED DESCRIPTION

[0060] The technical solutions of the present application will be further described and explained by specific examples, it should be understood that the specific examples described herein are only used to help understand the present application, and are not used to limit the specific application of the present application.

[0061] If no special description, the raw materials used in the examples of the present application are all the raw materials commonly used in the art, and the methods used in the examples are all the conventional methods in the art.

[0062] In this paper, the raw materials include: boron carbide B4C powder with an average particle size of 50 μm, Dalian Jinma Boron Industry Technology Group Co., Ltd.; boron carbide B4C powder with an average particle size of 10 μm, Dalian Jinma Boron Industry Technology Group Co., Ltd.; boron carbide B4C powder with an average particle size of 2 μm, Dalian Jinma Boron Industry Technology Group Co., Ltd.; resorcinol (C6H6O2), analytical pure, National Pharmaceutical Group Chemical Reagent Co., Ltd.; formaldehyde (CH2O), analytical pure, National Pharmaceutical Group Chemical Reagent Co., Ltd.; anhydrous sodium carbonate (Na2CO3), analytical pure, National Pharmaceutical Group Chemical Reagent Co., Ltd.; tetramethylammonium hydroxide, analytical pure, 25 wt% aqueous solution, National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0063] In this paper, the silicon carbide whiskers SiC used in the present application w The SEM image and XRD pattern of Figure 1 , 2 The silicon carbide whiskers SiC w are needle-shaped, with a diameter less than 100 nm and a length of 5-10 μm, and a length-diameter ratio > 50:1; they are mainly composed of 3C-SiC and contain a small amount of 6H-SiC and SiO2 phase.

[0064] In this paper, the test methods include: The test method for bending strength is the three-point bending strength method, and the electronic universal testing machine is AG-Xplus100kN electronic universal testing machine manufactured by Japan Corporation; The test method for fracture toughness is the SENB method, and the electronic universal testing machine is AG-Xplus100kN electronic universal testing machine manufactured by Japan Corporation; The test method for open porosity and bulk density is the Archimedes drainage method; The compression strength is AG-Xplus100kN electronic universal testing machine manufactured by Japan Corporation.

[0065] In this paper, the silicon carbide whiskers described in the present application are introduced into boron carbide, and the preparation method of the silicon carbide whisker toughened boron carbide composite material based on gel injection molding of the present application is used, and the silicon carbide whisker toughened boron carbide composite material prepared has a "dumbbell-shaped" B4C-SiCw B4C structure.

[0066] In this paper, the premixing is intermittent dry method premixing, including: using a blender, starting 2-15 s, stopping 30-300 s, and repeating 5-20 times; to ensure that the silicon carbide whiskers in the composite powder remain as the initial high aspect ratio silicon carbide whiskers. If the premixing is non-intermittent or other mechanical force is too large, such as the blender is started for 60-6000 s without stopping in between, the silicon carbide whiskers in the obtained composite powder cannot maintain an aspect ratio of >50:1, resulting in few or no "dumbbell-shaped" B4C-SiC w B4C structure is generated, making it difficult to effectively toughen the material.

[0067] In this paper, tetramethylammonium hydroxide is used as a dispersant, and its addition amount affects the dispersibility of the slurry; if the addition amount is too small, the dispersant cannot completely adhere to the surface of the powder, making it difficult to produce an electrostatic potential barrier effect and thus difficult to achieve effective dispersion; if the addition amount is too large, the dispersibility will not further improve, but the shrinkage during the curing stage of the preform will be large, which is easy to cause delamination and cracking defects. Moreover, other dispersants with large molecular chains, such as polyvinyl alcohol and polyethyleneimine, are prone to grafting reactions with the resorcinol formaldehyde reaction product, increasing the viscosity of the slurry and affecting the dispersion effect.

[0068] In this paper, the gel mixture has a certain viscosity, and the gel mixture is mixed with the composite powder and ball milled to make the gel mixture completely adhere to the surface of the composite powder. By controlling the ball milling parameters, the influence on the aspect ratio of the silicon carbide whiskers can be reduced, but the effect of promoting the uniform dispersion of the composite powder is not good; if the ball milling time is too long, it will affect the aspect ratio of the silicon carbide whiskers; if the ball milling time is too short, it will affect the uniformity of the gel mixture adhering to the surface of the composite powder, thereby affecting the generation of "dumbbell-shaped" B4C-SiC w B4C structure and the generation of three-dimensional continuous network.

[0069] In this paper, the mass ratio of the composite powder to the gel mixture is (60-75):(40-25); if the gel is too small, the viscosity of the slurry is too high, which is not conducive to molding, and the material after silicon infiltration has a large amount of residual silicon, resulting in low density, poor strength and toughness; if the gel is too much, the carbon content in the preform is too high, making it difficult to penetrate during silicon infiltration, resulting in a large amount of pores and residual carbon in the material, which makes the material have low density, high porosity, poor strength and toughness.

[0070] In this paper, the preparation method of the silicon carbide whisker toughened boron carbide composite material based on gel casting molding includes: (1) premixing 0.5-5 wt% of silicon carbide whiskers with the remaining amount of boron carbide to obtain a composite powder; The boron carbide is particle graded by mass ratio, and the average particle size is 40-60 μm: the average particle size is 5-15 μm: the average particle size is 1-5 μm = (5-7):1:(2-4); The premixing is intermittent dry premixing, and the intermittent dry premixing comprises: using a cell disruptor, starting for 2-15 s, stopping for 30-300 s, and circulating for 5-20 times; The aspect ratio of the silicon carbide whisker is greater than 50:1 before and after premixing. (2) A gel mixture is prepared according to 10-30 wt% of resorcinol, 15-40 wt% of formaldehyde, 20-50 wt% of water, 0.01-0.1 wt% of basic salt, and 0.1-1 wt% of tetramethylammonium hydroxide, and 65-75 wt% of the composite powder is ball milled with the remaining gel mixture to obtain a ceramic slurry; The aspect ratio of the silicon carbide whisker is greater than 50:1 before and after ball milling. (3) The ceramic slurry is injected into a mold, gelled at 60-90 °C, and dried at normal pressure at 100-150 °C to obtain a gel solidification body; (4) The gel solidification body is placed in a high-temperature furnace, heated to 800-1200 °C in a vacuum environment for carbonization treatment to obtain a preform; (5) A silicon block is placed above the preform, and the silicon block is heated to 1400-1750 °C in a vacuum graphite furnace for silicon infiltration treatment to obtain a silicon carbide whisker toughened boron carbide composite material based on gel casting; In the silicon carbide whisker toughened boron carbide composite material based on gel casting, the boron carbide particles are dispersed in a continuous network structure formed by silicon carbide, the residual silicon of the silicon infiltration treatment fills the pores in a continuous phase and exists in the entire silicon carbide whisker toughened boron carbide composite material, and a "dumbbell type" B4C-SiC w structure exists in the silicon carbide whisker toughened boron carbide composite material. w The two ends are connected to boron carbide B4C particles, and the silicon carbide whisker SiC w has an aspect ratio of (50-100):1.

[0071] Example 1 (1) 1.5 wt% of a silicon carbide whisker SiC w with an aspect ratio of (50-100):1, 59.1 wt% of B4C powder with an average particle size of 50 μm, 9.85 wt% of B4C powder with an average particle size of 10 μm, and 29.55 wt% of B4C powder with an average particle size of 2 μm are added to a cell disruptor, sealed, and intermittently dry premixed, the cell disruptor is started for 10 s, stopped for 60 s, and circulated for 10 times to obtain a composite powder; The aspect ratio of the silicon carbide whisker in the composite powder is still (50-100): 1.

[0072] (2) 6.9wt% resorcinol, 10.3wt% formaldehyde, 13.7wt% water, 0.02wt% sodium carbonate and 0.08wt% tetramethylammonium hydroxide were weighed respectively and mixed to obtain a gel mixture, then 69wt% of the composite powder was mixed with the gel mixture, and the mixture was poured into a ball mill tank, zirconium oxide balls were used as the grinding medium, the rotation speed was 200r / min, and the ball milling was performed for 12h, then the slurry after ball milling was vacuum degassed to obtain a ceramic slurry; The aspect ratio of the silicon carbide whisker in the ceramic slurry is still (50-100): 1.

[0073] (3) The ceramic slurry was poured into a mold and sealed, and then gelled in a 85℃ air drying oven for 12h; then the mold was demolded and transferred to a 120℃ air drying oven for normal pressure drying for 12h to obtain a solidified body.

[0074] (4) The solidified body was placed in a high-temperature furnace, heated to 900℃ at a heating rate of 2℃ / min in a vacuum environment, and kept for 3h, and then cooled to obtain a B4C / C preform.

[0075] The properties of the preform are shown in Table 1.

[0076] (5) In a graphite crucible coated with boron nitride coating, silicon blocks were placed on the B4C / C preform (the amount of silicon blocks was 1.5 times the theoretical amount of silicon required), and the graphite crucible was placed in a vacuum graphite furnace and heated to 1500℃ at a heating rate of 5℃ / min, and kept for 30min, and then cooled with the furnace to obtain a silicon carbide whisker toughened boron carbide composite material based on gel casting.

[0077] The properties of the silicon carbide whisker toughened boron carbide composite material based on gel casting are shown in Table 1.

[0078] Example 2 (1) 0.5wt% silicon carbide whisker (aspect ratio (50-100): 1), 59.7wt% B4C powder (average particle size 50μm), 9.95wt% B4C powder (average particle size 10μm) and 29.85wt% B4C powder (average particle size 2μm) were weighed respectively and added to a blender, sealed, and pre-mixed by intermittent dry method, the blender was started for 10s, stopped for 60s, and the cycle was repeated for 10 times to obtain a composite powder; The aspect ratio of the silicon carbide whisker in the composite powder is still (50-100): 1.

[0079] (2-5) The same as steps (2-5) in Example 1.

[0080] The properties of the preform, the silicon carbide whisker toughened boron carbide composite based on gelcasting are shown in Table 1.

[0081] Example 3 (1) 5wt% silicon carbide whisker (aspect ratio of (50-100):1), 57.0wt% B4C powder (average particle size of 50 μm), 9.5wt% B4C powder (average particle size of 10 μm) and 28.5wt% B4C powder (average particle size of 2 μm) were weighed respectively into a blender, sealed, and pre-mixed by intermittent dry method. The blender was started for 10 s and stopped for 60 s, and the cycle was repeated for 10 times to obtain the composite powder; The aspect ratio of the silicon carbide whisker in the composite powder was still (50-100):1.

[0082] (2-5) The same as steps (2-5) in Example 1.

[0083] The properties of the preform, the silicon carbide whisker toughened boron carbide composite based on gelcasting are shown in Table 1.

[0084] Example 4 (1) 1.5wt% silicon carbide whisker (aspect ratio of (50-100):1) and the rest B4C powder (average particle size of 50 μm) were weighed into a blender, sealed, and pre-mixed by intermittent dry method. The blender was started for 10 s and stopped for 60 s, and the cycle was repeated for 10 times to obtain the composite powder; The aspect ratio of the silicon carbide whisker in the composite powder was still (50-100):1.

[0085] (2-5) The same as steps (2-5) in Example 1.

[0086] The properties of the preform, the silicon carbide whisker toughened boron carbide composite based on gelcasting are shown in Table 1.

[0087] Example 5 (1) 1.5wt% silicon carbide whisker (aspect ratio of (50-100):1) and the rest B4C powder (average particle size of 2 μm) were weighed into a blender, sealed, and pre-mixed by intermittent dry method. The blender was started for 10 s and stopped for 60 s, and the cycle was repeated for 10 times to obtain the composite powder; The aspect ratio of the silicon carbide whisker in the composite powder was still (50-100):1.

[0088] (2-5) The same as steps (2-5) in Example 1.

[0089] The properties of the preform, the silicon carbide whisker toughened boron carbide composite based on gelcasting are shown in Table 1.

[0090] Example 6 (1) The same as step (1) in Example 1.

[0091] (2) 25wt% of the gel mixture was weighed, wherein the proportions of resorcinol, formaldehyde, water, sodium carbonate and tetramethylammonium hydroxide were the same as in Example 1, and 75wt% of the composite powder was weighed and mixed therewith, poured into a ball mill tank, zirconium oxide balls were used as the grinding medium, the rotation speed was 200r / min, and ball milling was performed for 12h. After vacuum degassing of the slurry after ball milling, a ceramic slurry was obtained. The aspect ratio of the silicon carbide whiskers in the ceramic slurry was still (50-100):1.

[0092] (3-5) The same as steps (3-5) in Example 1.

[0093] The properties of the preform and the silicon carbide whisker toughened boron carbide composite based on gel casting were as shown in Table 1.

[0094] Example 7 (1) The same as step (1) in Example 1.

[0095] (2) 40wt% of the gel mixture was weighed, wherein the proportions of resorcinol, formaldehyde, water, sodium carbonate and tetramethylammonium hydroxide were the same as in Example 1, and 60wt% of the composite powder was weighed and mixed therewith, poured into a ball mill tank, zirconium oxide balls were used as the grinding medium, the rotation speed was 200r / min, and ball milling was performed for 12h. After vacuum degassing of the slurry after ball milling, a ceramic slurry was obtained. The aspect ratio of the silicon carbide whiskers in the ceramic slurry was still (50-100):1.

[0096] (3-5) The same as steps (3-5) in Example 1.

[0097] The properties of the preform and the silicon carbide whisker toughened boron carbide composite based on gel casting were as shown in Table 1.

[0098] Comparative Example 1 (1) 60wt% of B4C powder (average particle size 50μm), 10wt% of B4C powder (average particle size 10μm) and 30wt% of B4C powder (average particle size 2μm) were weighed into a blender, sealed, and pre-mixed by intermittent dry method, i.e. the blender was started for 10s and stopped for 60s, and the cycle was repeated for 10 times, to obtain a composite powder; (2-5) The same as steps (2-5) in Example 1.

[0099] There was no "dumbbell-shaped" B4C-SiC structure in the boron carbide composite of the present comparative example. w

[0100] The properties of the preform and the boron carbide composite were as shown in Table 1. ​

[0101] Comparative Example 2 (1) 1.5wt% silicon carbide whiskers (aspect ratio of (50-100):1), 59.1wt% B4C powder (average particle size of 50μm), 9.85wt% B4C powder (average particle size of 10μm) and 29.55wt% B4C powder (average particle size of 2μm) were weighed respectively and put into a container without pre-mixing to obtain a composite powder; (2-5) Same as steps (2-5) in Example 1.

[0102] The boron carbide composite material of the present comparative example is partially agglomerated, and most of the silicon carbide whiskers are embedded in the in-situ generated silicon carbide and boron carbide particles, and there are few "dumbbell type" B4C-SiC w B4C structure is generated, and it is difficult to achieve effective toughening of the material.

[0103] The properties of the preform and the boron carbide composite material are shown in Table 1.

[0104] Comparative Example 3 (1) Same as step (1) in Example 1.

[0105] (2) 31wt% of a gel mixture was weighed, the gel mixture including resorcinol, formaldehyde, water and sodium carbonate, and the proportions of the four were the same as in Example 1; 69wt% of the composite powder was then mixed with the aforementioned gel mixture, poured into a ball mill jar, and zirconia balls were used as the grinding medium at a speed of 200r / min for 12h. After the slurry was vacuum degassed, a ceramic slurry was obtained; The aspect ratio of the silicon carbide whiskers in the ceramic slurry was still (50-100):1.

[0106] (3-5) Same as steps (3-5) in Example 1.

[0107] The boron carbide composite material of the present comparative example is partially agglomerated, and most of the silicon carbide whiskers are embedded in the in-situ generated silicon carbide and boron carbide particles, and there are few "dumbbell type" B4C-SiC w B4C structure is generated, and it is difficult to achieve effective toughening of the material.

[0108] The properties of the preform and the boron carbide composite material are shown in Table 1.

[0109] Comparative Example 4 (1) 1.5wt% SiC w(20~40):1, 59.1wt% of B4C powder (average particle size of 50 μm), 9.85wt% of B4C powder (average particle size of 10 μm) and 29.55wt% of B4C powder (average particle size of 2 μm) were added into a blender, sealed, and pre-mixed by intermittent dry method. The blender was started for 10 s and stopped for 60 s, and the cycle was repeated for 10 times to obtain the composite powder; The aspect ratio of the silicon carbide whisker in the composite powder was (20~40):1.

[0110] (2~5) was the same as that in step (2~5) of Example 1.

[0111] There were few "dumbbell-shaped" B4C-SiC structures in the boron carbide composite material of the present comparative example. w The B4C structure was difficult to be generated, and the effective toughening of the material was difficult to be achieved.

[0112] The properties of the preform and the boron carbide composite material were shown in Table 1.

[0113] Table 1, Properties of the preform and the silicon carbide whisker toughened boron carbide composite material According to the above table, within a certain range, with the increase of the amount of the silicon carbide whisker, the flexural strength and the fracture toughness of the silicon carbide whisker toughened boron carbide composite material first increased and then decreased. The mechanical properties of the boron carbide composite material in Comparative Examples 1 and 4, which did not add the silicon carbide whisker or used the silicon carbide whisker with a short aspect ratio, decreased.

[0114] According to Figure 3 , it can be seen that the silicon carbide whisker in the preform was distributed in a single filament shape and was tightly wrapped by the porous carbon network skeleton formed by the polycondensation reaction of resorcinol and formaldehyde. According to Figure 4 , it can be seen that in the silicon carbide whisker toughened boron carbide composite material, the boron carbide particles (black area) were uniformly dispersed in the continuous network structure formed by small size silicon carbide particles (dark gray area), and the residual silicon remaining after the silicon infiltration treatment filled the pores of the boron carbide composite material and existed in the entire boron carbide composite material. According to Figures 5-6 , it can be seen that after the silicon carbide whisker toughened boron carbide composite material was etched by mixed acid to remove silicon, the "dumbbell-shaped" B4C-SiC w structure was observed, in which the silicon carbide whisker was connected with the boron carbide particle. According to Figure 7 , it can be seen that during the fracture process of the boron carbide composite material, when the micro-crack propagation path encountered the silicon carbide whisker, the effective dissipation of the fracture energy at the tip of the main crack was achieved through multiple mechanisms such as whisker extraction, whisker fracture and crack deflection, and the toughening and reinforcing effect of the composite material was significantly improved.

[0115] In summary, the present application builds a "dumbbell type" B4C-SiC in the boron carbide B4C matrix by introducing high aspect ratio silicon carbide whiskers w The B4C bridging structure cooperates with crack deflection and bridging mechanism to achieve efficient toughening; in combination with intermittent mechanical premixing and synergistic dispersion technology of dispersants, the uniform dispersion of nanometer whiskers in micron boron carbide system is solved; the bending strength of the composite material is also significantly improved, and the process repeatability is excellent, which is suitable for high-end manufacturing field.

[0116] Aspects, embodiments, features of the present application should be considered illustrative in all aspects and not limiting the present application, the scope of the present application is only defined by the claims. Other embodiments, modifications and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed application.

[0117] In the preparation method of the present application, the order of each step is not limited to the order listed, and for those skilled in the art, the change of the order of each step without creative labor is also within the protection scope of the present application. In addition, two or more steps or actions can be carried out simultaneously.

[0118] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the embodiments of the present application. Those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, and here it is not necessary and also impossible to fully exemplify all the embodiments. Any obvious changes or variations derived from the essential spirit of the present application still belong to the protection scope of the present application, and any additional limitation is contrary to the spirit of the present application.

Claims

1. A silicon carbide whisker toughened boron carbide composite based on gelcasting, characterized in that, having a "dumbbell" B4C-SiC w - a B4C structure, said structure being a boron carbide particle connected to silicon carbide whiskers having an aspect ratio > 50:1 at both ends; The gel injection molding based silicon carbide whisker toughened boron carbide composite material is prepared by mixing a composite powder obtained by premixing silicon carbide whiskers with a length-diameter ratio of greater than 50:1 and boron carbide with a gel mixture, ball milling, gelling, carbonizing, and siliconizing.

2. The gelation mold-based, silicon carbide whisker toughened boron carbide composite material of claim 1, wherein, The silicon carbide whiskers are needle-shaped, have a diameter of less than 100 nm, and a length of 5-10 microns.

3. The gelation mold-based, silicon carbide whisker toughened boron carbide composite material of claim 1, wherein, The proportion of the silicon carbide whiskers in the composite powder is 0.5-5wt%.

4. The gelation mold-based, silicon carbide whisker toughened boron carbide composite of claim 1, wherein, After the premixing, the silicon carbide whiskers and the boron carbide are uniformly mixed; the premixing is dry premixing, including one or both of mechanical premixing and airflow premixing.

5. The gelation mold forming based silicon carbide whisker toughened boron carbide composite material according to claim 1, characterized in that, The components of the gel mixture include, by mass percentage, 10-30wt% of resorcinol, 15-40wt% of formaldehyde, 20-50wt% of water, 0.01-0.1wt% of an alkaline salt, and 0.1-1wt% of tetramethylammonium hydroxide.

6. The gelation mold forming based silicon carbide whisker toughened boron carbide composite material of claim 1, wherein, The gel-molding-based silicon carbide whisker toughened boron carbide composite material has boron carbide particles dispersed in a continuous network structure formed by silicon carbide, residual silicon of the silicon infiltration treatment fills the pores in a continuous phase; and the silicon carbide whisker toughened boron carbide composite material has "dumbbell-shaped" B4C-SiC w The B4C structure is a silicon carbide whisker SiC w Connected with boron carbide B4C particles at both ends.

7. A method of making a gelation casting based silicon carbide whisker toughened boron carbide composite material as claimed in claim 1, wherein, The preparation method includes: (1) premixing silicon carbide whiskers with a length-diameter ratio of greater than 50:1 and boron carbide to obtain a composite powder; (2) preparing a gel mixture and ball milling the composite powder and the gel mixture to obtain a ceramic slurry; (3) injecting the ceramic slurry into a mold, gelling and drying at normal pressure to obtain a gel solidification body; (4) placing the gel solidification body in a high-temperature furnace for carbonization treatment to obtain a preform; (5) The silicon block is placed above the preform, and silicon infiltration treatment is performed in a graphite furnace to obtain a "dumbbell-shaped" B4C-SiC w Silicon carbide whisker toughened boron carbide composite of B4C structure.

8. The method of making a gelation casting based silicon carbide whisker toughened boron carbide composite material according to claim 7, wherein, In the (2), the mass ratio of the composite powder to the gel mixture is (60-75):(40-25).

9. The method of making a gelation casting based silicon carbide whisker toughened boron carbide composite material of claim 7, wherein, In the (4), the silicon carbide whiskers in the preform are single filaments and are wrapped by a porous carbon network skeleton; the compressive strength of the preform is greater than 41 MPa, and the bending strength is greater than 17 MPa.

10. The method of making a gelation casting based silicon carbide whisker toughened boron carbide composite material of claim 7, wherein, The bending strength of the silicon carbide whisker toughened boron carbide composite material in (5) is > 300 MPa, and the fracture toughness is > 4.2 MPa•m 1 / 2 .

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