Boron carbide graphite composite ceramic material and preparation method thereof

Abstract

The invention discloses a boron carbide graphite composite ceramic material and a preparation method thereof, and belongs to the technical field of advanced structure / function integrated ceramic composite materials. The material is composed of a boron carbide matrix phase, a multi-element solid solution reinforced phase, an in-situ generated graphite phase and an environmental durability phase, and by accurately regulating and controlling the volume fraction and atomic proportion of each phase and adopting a spark plasma sintering technology for segmented sintering densification, the synergistic improvement of high strength and toughness, excellent wave-absorbing performance and environmental durability of the material is realized. The relative density of the prepared composite material is greater than or equal to 98.0%, the bending strength is greater than or equal to 600MPa, and the prepared composite material has excellent high-temperature oxidation resistance and corrosion resistance at the same time.

Description

Technical Field

[0001] This invention belongs to the field of advanced structural / functional integrated ceramic composite materials technology, and relates to a boron carbide-graphite composite ceramic material and its preparation method, specifically involving a B4C-(Ti) composite ceramic material. x Cr 1-x B2-graphite composite ceramic materials and their preparation methods. Background Technology

[0002] Boron carbide ceramics, due to their high hardness, low density, and excellent neutron absorption capacity, have long been considered ideal materials for armor protection and the nuclear industry. However, their inherent brittleness, poor sintering performance, and limited functional properties have severely restricted their widespread application in modern high-end equipment. With the increasing demands for material performance in aerospace, marine engineering, and other fields, the development of multifunctional ceramic composite materials that combine high strength and toughness, excellent wave absorption performance, and environmental durability has become an urgent need.

[0003] In existing technologies, toughening boron carbide by introducing a second-phase reinforcement is the mainstream research direction. For example, using TiB2 or SiC as a reinforcing phase can improve the fracture toughness of B4C to some extent, but often at the cost of hardness or other properties. In recent years, the design concept of synthesizing multiphase composite materials through in-situ reaction has attracted attention. A representative example is the one-step synthesis of (TiB2) multiphase composite materials by reacting B4C with TiC and Cr3C2 using spark plasma sintering (SPS) technology. x Cr 1-x A multiphase composite material of B2 solid solution and graphite phase. This scheme achieves a preliminary balance between mechanical properties and microwave absorption properties by adjusting the Ti / Cr ratio (x = 0.48-0.89). Typical properties include flexural strength ≥ 520 MPa and fracture toughness ≥ 5.3 MPa·m. 1 / 2 And absorption characteristics with a minimum reflection loss ≤ -13dB in the 2~18GHz frequency band. Related characterization results (such as X-ray diffraction patterns and scanning electron microscope images) confirm that (Ti... x Cr 1-x The formation of B2 solid solutions and the uniformity of their microstructure.

[0004] Nevertheless, this existing technology still has significant limitations. Firstly, the material lacks high-temperature stability and environmental adaptability; the B4C matrix is ​​prone to oxidation above 600℃, while (Ti... x Cr 1-xFirst, B2 solid solutions may undergo phase transitions under long-term high-temperature environments, leading to performance degradation. Second, the bandwidth of its microwave absorption performance is limited, with the minimum reflection loss mainly concentrated in the X-band (8~12.4GHz), resulting in insufficient coverage of wider frequency bands and making it difficult to meet the requirements of modern stealth materials for being "thin, light, wide, and strong." Third, there is a bottleneck in improving mechanical properties. While existing technologies can achieve a balance between strength and toughness by adjusting the Ti / Cr ratio, it is difficult to simultaneously achieve the goals of ultra-high hardness and high fracture toughness. Finally, the material's functional dimensions are relatively simple, lacking the introduction of antioxidant or corrosion-resistant components, which limits its application in harsh environments such as marine climates and alternating high and low temperatures. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a boron carbide graphite composite ceramic material and its preparation method that improves the hardness, wear resistance and high temperature stability of the material.

[0006] The technical solution adopted by the present invention to solve its technical problem is: a boron carbide graphite composite ceramic material, wherein the composite material comprises a boron carbide matrix phase, a multi-component solid solution reinforcing phase, a graphite phase and an environmentally durable phase; the multi-component solid solution reinforcing phase is (Ti,Cr,M)B2 solid solution, wherein M is at least one transition metal element selected from tungsten (W) and molybdenum (Mo); the environmentally durable phase is at least one of silicon carbide (SiC) or alumina (Al2O3).

[0007] The composite material of this invention generates the aforementioned multi-component solid solution reinforcing phase and graphite phase through in-situ reaction, and combines them with the environmentally durable phase to achieve a synergistic effect of high strength and toughness, excellent microwave absorption performance, and environmental durability. The beneficial effects of this combination design are as follows: by introducing a third transition metal element (such as W or Mo) to form a multi-component solid solution, the solid solution strengthening effect significantly improves hardness and high-temperature stability. The high melting point of W (approximately 3422℃) and strong bond energy enhance the phase stability of the material above 1000℃, while Mo reduces crack propagation at high temperatures by improving grain boundary toughness. The addition of the environmentally durable phase (SiC or Al2O3) provides oxidation and corrosion resistance. SiC can form a silica protective layer at high temperatures, delaying the oxidation of the B4C matrix, while Al2O3 imparts resistance to salt spray corrosion in marine environments. The in-situ reaction ensures uniform distribution of each phase and high interfacial bonding strength, thereby synergistically improving flexural strength and fracture toughness. Simultaneously, the graphite phase optimizes dielectric properties, resulting in a minimum reflection loss ≤-15dB. This design enables the material to have a longer service life in extreme environments such as hot-end components of aero engines, and its overall performance is superior to traditional single toughening systems.

[0008] Preferably, in the multi-component solid solution reinforcing phase, the atomic ratio of titanium (Ti), chromium (Cr), and M satisfies: (Ti x Cry M z TiB2 is a solid solution with x ranging from 0.40 to 0.85, y ranging from 0.10 to 0.50, and z ranging from 0.05 to 0.20, where x + y + z = 1. By precisely controlling the ratio of Ti, Cr, and M elements, an optimized balance of the solid solution structure is achieved. When the x value is high, increasing the Ti content helps improve hardness and density because the TiB2 phase has a high modulus; while when the y value is moderately increased, the introduction of Cr element can enhance toughness and microwave absorption performance because CrB2 can improve interfacial bonding and electromagnetic loss characteristics. The z value ensures that the solid solution strengthening effect of M element (W or Mo) is not excessively diluted; the addition of W can further improve wear resistance, while Mo contributes to phase stability at high temperatures.

[0009] Preferably, when x = 0.65~0.75, y = 0.20~0.30, and z = 0.10~0.15, the material can simultaneously achieve high hardness (≥34GPa) and high toughness (≥6.8MPa·m). 1 / 2 Furthermore, the absorption bandwidth is extended to over 3.5 GHz. This proportional design avoids performance imbalances caused by an excess of a single element. For example, an excessively high Ti content may cause brittleness, while an excessively high Cr content will reduce hardness, thus ensuring the material's performance stability over a wide temperature range.

[0010] Preferably, the volume fractions of each phase in the composite material are: boron carbide matrix phase 60 vol%~70 vol%, multi-component solid solution reinforcing phase 15 vol%~25 vol%, graphite phase 8 vol%~12 vol%, and environmentally durable phase 2 vol%~5 vol%. This volume fraction, through optimizing the content of each phase, achieves an ideal balance between mechanical properties, microwave absorption performance, and environmental durability. The proportion of the boron carbide matrix phase ensures that the material maintains a low density and high hardness foundation; the proportion of the multi-component solid solution reinforcing phase provides effective second-phase toughening, but too low a volume fraction will result in insufficient reinforcement, while too high a volume fraction may lead to matrix discontinuity failure. The controlled proportion of the graphite phase can optimize microwave absorption performance through its lubrication and dielectric regulation effects, while avoiding strength reduction caused by excessive amounts. A small amount of environmentally durable phase is sufficient to form a protective network, and SiC or Al2O3 generates an oxide layer at high temperatures, raising the oxidation initiation temperature to above 800°C without significantly affecting density.

[0011] Preferably, when the boron carbide matrix phase is 65 vol%, the multi-component solid solution reinforcing phase is 20 vol%, the graphite phase is 10 vol%, and the environmentally durable phase is 3 vol%, the material exhibits the best comprehensive performance, with a flexural strength of up to 650 MPa, while its corrosion resistance in marine environments is improved by more than 30%.

[0012] Preferably, the performance indicators of the composite material include: relative density ≥ 98.0%; flexural strength ≥ 600 MPa; fracture toughness ≥ 6.5 MPa·m. 1 / 2 Vickers hardness ≥32GPa; minimum reflection loss ≤-15dB and effective absorption bandwidth ≥3.0GHz in the frequency range of 2GHz~18GHz.

[0013] Preferably, the graphite phase is in-situ generated flake graphite with an average sheet thickness of 0.1 μm to 1.0 μm, and is uniformly distributed at the interface between the boron carbide matrix phase and the multi-component solid solution reinforcing phase. In-situ generated flake graphite exhibits excellent anisotropy and interfacial compatibility, and its dielectric constant and impedance matching can be effectively adjusted within the sheet thickness range, thereby enhancing electromagnetic wave absorption efficiency. Thinner sheets provide a larger specific surface area, promoting multiple scattering and loss mechanisms, while thicker sheets help maintain mechanical stability.

[0014] Preferably, when the average layer thickness is 0.3 μm to 0.7 μm, the graphite phase not only optimizes the microwave absorption performance but also acts as a solid lubricant to reduce the coefficient of friction, thereby reducing the wear rate of the material under high-temperature frictional conditions. This structural design is achieved through in-situ reaction in the SPS process, eliminating the need for external graphite and avoiding the problem of interface weakening.

[0015] A method for preparing the above-mentioned boron carbide-graphite composite ceramic material includes the following steps:

[0016] Raw material preparation: Boron carbide (B4C) powder, titanium carbide (TiC) powder, chromium carbide (Cr3C2) powder, transition metal carbide powder, and environmental durability phase powder are prepared according to the specified proportions. The transition metal carbide powder is selected from at least one of tungsten carbide (WC) or molybdenum carbide (Mo2C), and the environmental durability phase powder is selected from at least one of silicon carbide (SiC) or alumina (Al2O3).

[0017] Mixing and drying: The prepared raw material powder is mixed with ball milling media and dispersant, and then wet ball milled and dried to obtain a uniformly mixed powder;

[0018] Sintering densification: The dried mixed powder is loaded into a mold and subjected to spark plasma sintering (SPS) technology. Under vacuum or inert atmosphere protection, pressure is applied and the mixture is heated to the sintering temperature. After holding at the temperature, it is cooled to obtain the composite ceramic material.

[0019] The mixing and drying steps employ wet ball milling, achieving nanoscale dispersion and avoiding component segregation. The SPS sintering technology utilizes rapid heating and field-assisted activation to achieve densification at a lower temperature, inhibiting grain growth and enabling the material to obtain a fine-grained structure, thereby improving mechanical properties.

[0020] Preferably, in the raw material preparation step, the average particle size and purity of each raw material powder are as follows: boron carbide (B4C) powder has an average particle size of 0.1 μm to 1.0 μm and a purity ≥ 99.5%; titanium carbide (TiC) powder and chromium carbide (Cr3C2) powder have an average particle size of 0.5 μm to 3.0 μm and a purity ≥ 99.0%; transition metal carbide powder has an average particle size of 0.5 μm to 2.0 μm and a purity ≥ 99.0%; and environmentally durable phase powder has an average particle size of 0.2 μm to 1.0 μm and a purity ≥ 99.5%. The fine particle size of B4C powder provides a high specific surface area, which promotes diffusion and reaction kinetics during sintering, thereby reducing the densification temperature; the particle size of transition metal carbide powder is controlled in the range of 0.5~2.0μm, which helps to match the particle size of B4C powder and achieve uniform solid solution formation; the fine particle size of environmental durability phase powder enables it to be dispersed and effectively exert its antioxidant effect.

[0021] Preferably, in the mixing and drying steps, wet ball milling uses zirconia grinding beads at a speed of 80 r / min to 120 r / min for a time of 12 h to 16 h; drying is performed using rotary evaporation with a water bath temperature controlled at 40 °C to 50 °C. Zirconia grinding beads possess high hardness and chemical inertness, avoiding grinding contamination; the grinding speed ensures sufficient shear force and collision energy, achieving nanoscale mixing of the powder without excessive wear; the grinding time ensures sufficient dispersion of the reaction precursors, laying the foundation for in-situ reaction. Rotary evaporation drying is carried out in a 40-50 °C water bath, avoiding component oxidation or agglomeration caused by high temperatures, resulting in a dry powder with good flowability, which is beneficial for the filling density in subsequent sintering.

[0022] Preferably, in the sintering densification step, the process parameters of spark plasma sintering include: sintering temperature 1850℃~2000℃; holding time 5min~20min; applied pressure: 40MPa~80MPa; heating rate: 50℃ / min~150℃ / min; and argon or nitrogen protective atmosphere. The sintering temperature is lower than the traditional sintering temperature (>2200℃), reducing energy consumption and the risk of abnormal grain growth; the holding time ensures complete reaction without excessive grain growth; the pressure promotes particle rearrangement and plastic flow, increasing density; the rapid heating rate utilizes the field effect of SPS to activate the powder surface and reduce the sintering activation energy; and the inert atmosphere protection avoids high-temperature oxidation.

[0023] Preferably, when the sintering temperature is 1950℃, the holding time is 10min, the pressure is 60MPa, and the heating rate is 100℃ / min, the material can obtain a near-fully dense structure while maintaining a fine grain size, thereby simultaneously improving hardness and toughness.

[0024] Preferably, the sintering densification step adopts a segmented sintering strategy: first, pre-holding at 1600℃~1700℃ for 5min~10min promotes in-situ reaction, then raising the temperature to 1850℃~2000℃ and holding for 5min~15min to complete densification; after sintering, hot isostatic pressing (HIP) post-treatment is performed under the following conditions: temperature 1700℃~1800℃, pressure 80MPa~120MPa, time 20min~40min. The pre-holding stage allows raw materials such as TiC and Cr3C2 to undergo preliminary reaction with B4C to generate a (Ti,Cr,M)B2 solid solution core, avoiding uneven reaction under direct high temperature; subsequently, the temperature is raised to complete densification, ensuring density and strength; the HIP post-treatment eliminates residual porosity through high temperature and high pressure, increases relative density, and heals microcracks, thereby improving fracture toughness.

[0025] Preferably, the pre-insulation temperature is 1650℃ for 8 minutes, and the HIP conditions are 1750℃, 100MPa for 30 minutes, to achieve optimal microstructure control and performance stability.

[0026] Compared with existing technologies, this invention has the following beneficial effects: This invention achieves a breakthrough improvement in the performance of boron carbide-based composite materials through a multi-component solid solution design and multifunctional phase composite. By introducing a third transition metal element to form a multi-component solid solution, the hardness and high-temperature stability of the material are significantly enhanced, while the addition of an environmentally durable phase imparts excellent oxidation and corrosion resistance. The in-situ reaction-generated flake graphite is uniformly distributed at the interface, optimizing dielectric properties and achieving broadband absorption characteristics. By precisely controlling the proportion and volume fraction of each phase, the mechanical properties of the material are synergistically improved, achieving an ideal balance between strength, toughness, and density. The innovative sintering process, combined with a segmented strategy and post-processing technology, effectively suppresses grain growth, resulting in a highly dense fine-grained structure. This multi-phase synergistic design enables the material to exhibit excellent comprehensive performance under extreme environments, significantly extending its service life and fully meeting the stringent requirements of modern high-end equipment for multifunctional ceramic materials. Attached Figure Description

[0027] Figure 1 This is a scanning electron microscope image of the polished surface of the composite material prepared in Example 1 of the present invention.

[0028] Figure 2 This is a scanning electron microscope image of the polished surface of the composite material prepared in Example 2 of the present invention.

[0029] Figure 3 This is a scanning electron microscope image of the polished surface of the composite material prepared in Example 5 of the present invention.

[0030] Figure 4This is a scanning electron microscope image of the polished surface of the composite material prepared in Example 6 of the present invention.

[0031] Figure 5 This is a scanning electron microscope image of the polished surface of the composite material prepared in Example 8 of the present invention. Detailed Implementation

[0032] The present invention will be specifically described below through examples. Unless otherwise stated, all raw materials used are commercially available. The amounts or process conditions not explicitly stated in the examples are the same as in Example 1.

[0033] Example 1

[0034] Raw material preparation steps

[0035] First, the raw material ratio is calculated based on the phase composition of the target composite material. The target product is: boron carbide matrix phase 65 vol%, multi-component solid solution reinforcing phase 20 vol% (corresponding to (Ti 0.7 Cr 0.25 W 0.05 (B2 solid solution), graphite phase 10 vol%, SiC environmentally durable phase 3 vol%. The raw material mass is deduced by back-calculating the chemical reaction ratios. The reaction equations for B4C with TiC, Cr3C2, and WC are as follows:

[0036] B4C + 2TiC → 2TiB2 + 3C (forming TiB2 and free carbon);

[0037] 3B4C + 2Cr3C2 → 6CrB2 + 7C (forming CrB2 and free carbon);

[0038] B4C + 2WC → 2WB2 + 3C (WB2 and free carbon are generated, and a solid solution is actually formed).

[0039] The reaction must ensure the complete formation of the (Ti,Cr,W)B2 solid solution and graphite, and the composite SiC phase. Specific raw material weighings are as follows:

[0040] Boron carbide (B4C) powder: average particle size 0.5μm, purity ≥99.5%, weighing out 68.5% of the total raw material mass;

[0041] Titanium carbide (TiC) powder: average particle size 1.0 μm, purity ≥99.0%, weighing 15.2% by mass;

[0042] Chromium carbide (Cr3C2) powder: average particle size 1.0μm, purity ≥99.0%, weighing accounts for 8.1% by mass;

[0043] Tungsten carbide (WC) powder: average particle size 1.0 μm, purity ≥99.0%, weighed as 3.5% by mass (as a transition metal M source);

[0044] Silicon carbide (SiC) powder: average particle size 0.5μm, purity ≥99.5%, weighing 4.7% by mass.

[0045] All raw material powders were obtained from commercially available high-purity products and dried at 110℃ for 2 hours to remove moisture before weighing.

[0046] Mixing and drying steps

[0047] The weighed raw material powder was loaded into a polypropylene ball mill jar, and zirconia grinding beads and anhydrous ethanol were added as dispersants. The ball-to-powder mass ratio was 5:1, and the powder-to-ethanol mass ratio was 1:2. After sealing the ball mill jar, it was placed on a drum ball mill and ball-milled at 100 r / min for 14 h to ensure uniform dispersion and nanoscale mixing. After ball milling, the slurry was transferred to a rotary evaporator, and the water bath temperature was controlled at 45℃, the vacuum degree was -0.09 MPa, and the mixture was rotary evaporated and dried for 4 h to obtain dried powder. The dried powder was then sieved through a 200-mesh sieve.

[0048] Sintering densification steps

[0049] Densification was achieved using spark plasma sintering (SPS) technology. The sieved mixed powder was loaded into a graphite mold with an inner diameter of 30 mm, with 0.1 mm thick carbon paper separating the powder from the mold to facilitate demolding. The mold was then placed in an SPS furnace (FCT Systeme GmbH model) and evacuated to 10 °C. -2 Pa, then high-purity argon gas is introduced as a protective atmosphere. The sintering process adopts a segmented strategy:

[0050] First stage preheating: Heat to 1650℃ at a heating rate of 100°C / min, apply a pressure of 60MPa, and hold for 8min to promote the in-situ reaction of B4C with TiC, Cr3C2, and WC to generate a (Ti,Cr,W)B2 solid solution core and free carbon (graphite phase).

[0051] Second stage densification: Continue heating at the same rate to 1950℃, maintain pressure at 60MPa, hold for 10min to complete full densification of the material and ensure uniform distribution of SiC phase.

[0052] After sintering, the sample was cooled to room temperature in the furnace, demolded, and the surface carbon paper was polished to obtain a dense ceramic disc with a diameter of 30 mm and a thickness of 5 mm. The sintered sample was then subjected to hot isostatic pressing (HIP) post-treatment: held at 1750℃ and 100 MPa argon pressure for 30 min to eliminate residual porosity.

[0053] Example 2

[0054] The composite material consists of: 60 vol% boron carbide matrix phase and 25 vol% multi-component solid solution reinforcing phase (corresponding to (Ti) 0.4 Cr 0.5 Mo 0.1 The raw material composition consisted of 8 vol% B2 solid solution, 8 vol% graphite phase, and 2 vol% silicon carbide environmentally durable phase. In the raw material preparation, B4C powder with an average particle size of 0.1 μm and a purity ≥99.5% accounted for 65.8% of the total raw material mass; TiC powder with an average particle size of 3.0 μm and a purity ≥99.0% accounted for 12.1% of the total raw material mass; Cr3C2 powder accounted for 10.5% of the total raw material mass; molybdenum carbide powder with an average particle size of 2.0 μm and a purity ≥99.0% accounted for 4.2% of the total raw material mass; and SiC powder with an average particle size of 1.0 μm and a purity ≥99.5% accounted for 7.4% of the total raw material mass. The mixing and drying steps involved ball milling with zirconia beads at 80 r / min for 12 h to ensure uniform powder dispersion. During drying, the water bath temperature was controlled at 40℃, and rotary evaporation was performed for 4 h to obtain the dried powder. Sintering densification was carried out in a spark plasma sintering furnace. First, the temperature was raised to 1600℃ at 50℃ / min and held for 5 min at a pressure of 40MPa to promote in-situ reaction and generate a solid solution core. Then, the temperature was raised to 1850℃ and held for 5 min at a pressure of 40MPa to complete densification. Subsequently, hot isostatic pressing was performed at 1700℃, 80MPa, and 20 min.

[0055] Example 3

[0056] The material composition is set as follows: boron carbide matrix phase 70 vol.%, multi-component solid solution reinforcing phase 15 vol.% (corresponding to (Ti 0.85 Cr 0.1 W 0.05 The raw material formulation consisted of 12 vol.% B2 solid solution, 12 vol.% graphite phase, and 5 vol.% Al2O3 environmentally durable phase. In the raw material formulation, B4C powder with an average particle size of 1.0 μm and a purity ≥99.5% accounted for 71.2%; TiC powder and Cr3C2 powder with an average particle size of 0.5 μm and a purity ≥99.0% accounted for 14.8% and 5.1% respectively; WC powder with an average particle size of 0.5 μm and a purity ≥99.0% accounted for 2.1%; and Al2O3 powder with an average particle size of 0.2 μm and a purity ≥99.5% accounted for 6.8%. The mixing and drying steps involved ball milling at 120 r / min for 16 h to enhance shear force to cope with the high hardness of Al2O3; the drying water bath temperature was 50℃ to avoid thermal damage to the components. The sintering densification parameters are: rapid heating to 2000℃ at 150℃ / min, holding for 20min, and pressure of 80MPa, without segmentation to simplify the process; however, the subsequent HIP treatment at 1800℃, 120MPa, and 40min ensures the elimination of pores.

[0057] Example 4

[0058] The composition is the same as in Example 1, but the atomic ratios are adjusted to x=0.65, y=0.25, z=0.10 to balance performance. The powder particle sizes in the raw material formulation are as follows: B4C powder average particle size 0.1 μm, TiC / Cr3C2 powder average particle size 0.5 μm, WC powder average particle size 0.5 μm, SiC powder average particle size 0.2 μm, utilizing fine particle sizes to promote graphite flake formation. The mixing and drying steps involve extending ball milling to 16 h at a speed of 100 r / min to increase dispersion; the drying temperature is 45 °C. Sintering densification uses a slow heating rate of 50 °C / min to 1900 °C, holding at 15 min under a pressure of 60 MPa, followed by slow cooling to induce graphite flake refinement; HIP treatment at 1750 °C, 100 MPa, and 30 min assists in densification.

[0059] Example 5

[0060] Material composition: matrix phase 65 vol%, reinforcing phase 20 vol% (Ti 0.7 Cr 0.25 W 0.05 (B2) Graphite phase 10 vol.%, SiC phase 3 vol.%. Powder particle size: B4C 0.5 μm, TiC / Cr3C 21.0 μm, WC 1.0 μm, SiC 0.5 μm. Mixing and drying steps: ball milling speed limit 120 r / min, time 12 h, drying water bath 40℃, to achieve efficient mixing. Sintering densification parameters: heating to 1600℃ at 150℃ / min, pre-holding at 80 MPa, then heating to 1850℃ and holding at 80 MPa; HIP post-treatment omitted.

[0061] Example 6

[0062] Composition: Boron carbide matrix phase 60 vol%, multi-component solid solution reinforcing phase 25 vol% (corresponding to (Ti 0.4 Cr 0.5 Mo 0.1 The raw material formulation consisted of 10 vol% graphite phase and 5 vol% Al2O3 environmentally durable phase. The raw material composition included 63.5% B4C powder (0.5 μm particle size), 10.8% TiC powder (1.0 μm particle size), 13.2% Cr3C2 powder (1.0 μm particle size), 4.5% Mo2C powder (1.0 μm particle size), and 8.0% Al2O3 powder (0.5 μm particle size). Mixing and drying were performed by ball milling at 100 r / min for 14 h, followed by drying in a 45℃ water bath. Sintering and densification employed a segmented strategy: pre-holding at 1700℃ / 10 min and 60 MPa pressure, main sintering at 2000℃ / 10 min and 60 MPa pressure, and HIP treatment at 1800℃ / 120 MPa / 20 min.

[0063] Example 7

[0064] Atomic proportions (x=0.70, y=0.20, z=0.10) and volume fractions (65 vol.% boron carbide matrix phase, 20 vol.% multi-component solid solution reinforcing phase) correspond to (Ti 0.7 Cr 0.2 Mo 0.1 B2 and graphite phases (10 vol.%) and alumina environmental durability phase (3 vol.%) were used for high toughness optimization. In the raw material preparation, B4C powder with an average particle size of 0.5 μm and a purity ≥99.5% accounted for 68.0% of the total raw material mass; TiC powder with an average particle size of 1.0 μm and a purity ≥99.0% accounted for 14.8% of the total raw material mass; Cr3C2 powder accounted for 7.9% of the total raw material mass; molybdenum carbide powder with an average particle size of 1.0 μm and a purity ≥99.0% accounted for 3.8% of the total raw material mass; and Al2O3 powder with an average particle size of 0.5 μm and a purity ≥99.5% accounted for 5.5% of the total raw material mass. Mixing and drying process: Zirconia ball milling beads were used to ball mill at 100 r / min for 14 h to achieve nanoscale dispersion; the water bath temperature was controlled at 45℃ during rotary evaporation drying, and drying for 4 h yielded a powder with good flowability. The sintering densification adopts a segmented strategy: first, the temperature is raised to 1650℃ at 100℃ / min and held for 8 min at a pressure of 60MPa to promote in-situ reaction and form a solid solution; then, the temperature is raised to 1950℃ and held for 10 min at a pressure of 60MPa to complete densification; after sintering, hot isostatic pressing is performed at 1750℃, 100MPa, and 30 min to eliminate micropores.

[0065] Example 8

[0066] Boron carbide matrix phase 70 vol%, multi-component solid solution reinforcing phase 15 vol% (corresponding to (Ti 0.75 Cr 0.20 W 0.05 The raw material formulation consisted of 10 vol% graphite phase and 3 vol% SiC environmentally durable phase. In the raw material preparation, B4C powder with an average particle size of 1.0 μm and a purity ≥99.5% accounted for 71.5% of the total raw material mass; TiC powder with an average particle size of 0.5 μm and a purity ≥99.0% accounted for 13.2% of the total raw material mass; Cr3C2 powder with an average particle size of 0.5 μm and a purity ≥99.0% accounted for 5.6% of the total raw material mass; WC powder with an average particle size of 0.5 μm and a purity ≥99.0% accounted for 2.8% of the total raw material mass; and SiC powder with an average particle size of 0.2 μm and a purity ≥99.5% accounted for 6.9% of the total raw material mass. The mixing and drying steps were performed under the following conditions: ball milling speed 100 r / min, time 14 h, to ensure uniform powder mixing; drying water bath temperature 45℃ to avoid component oxidation. Sintering densification parameters: heating to 1950℃ at 100℃ / min, holding for 10 min, and pressure of 60MPa; subsequent HIP treatment: 1750℃, 100MPa, 30 min to increase density.

[0067] Example 9

[0068] Material composition by volume fraction: boron carbide matrix phase 65 vol.%, multi-component solid solution reinforcing phase 20 vol.%, corresponding to (Ti 0.65 Cr 0.25 W 0.10 The raw material formulation included 10 vol% graphite phase and 3 vol% Al2O3 durable phase. All powders were selected for their small particle size to promote flake formation: B4C powder had an average particle size of 0.1 μm, TiC / Cr3C2 powder had an average particle size of 0.5 μm, WC powder had an average particle size of 0.5 μm, and Al2O3 powder had an average particle size of 0.2 μm. The mixing and drying steps involved extending ball milling to 16 h at a speed of 100 r / min to enhance dispersion; drying was performed in a 40℃ water bath. Sintering and densification were performed using the following parameters: rapid heating to 2000℃ at 150℃ / min, holding for 5 min, and a pressure of 80 MPa, utilizing high-temperature short-time sintering to refine the graphite flake layers; HIP post-treatment: 1800℃, 120 MPa, 20 min to ensure structural integrity.

[0069] Example 10

[0070] Material composition: 65 vol% matrix phase, 20 vol% reinforcing phase (corresponding to Ti) 0.70 Cr 0.20 Mo 0.10 (B2) Graphite phase 10 vol%, SiC durable phase 3 vol%. The raw material formulation uses high-purity powder with a purity ≥99.0%, particle size: B4C 0.5 μm, TiC / Cr3C 21.0 μm, Mo2C 1.0 μm, SiC 0.5 μm. Mixing and drying steps: ball milling speed 100 r / min, time 14 h, drying water bath 45℃. Sintering densification process: segmented sintering 1650℃ pre-holding 8 min, 1950℃ main sintering 10 min, pressure 60 MPa, heating rate 100℃ / min; combined with HIP post-treatment: 1750℃, 100 MPa, 30 min.

[0071] Comparative Example 1

[0072] The traditional single TiB2 reinforcing phase is adopted, omitting the multi-component solid solution and environmentally durable phase, and only retaining the B4C matrix and the added graphite phase.

[0073] Preparation method:

[0074] Raw materials: 75 vol.% B4C powder (0.5 μm, 99.5%) + 15 vol.% TiB2 powder (1.0 μm, 99.0%) + flake graphite powder (10 vol.%).

[0075] Mixed drying and sintering process: same as in Example 1.

[0076] Comparative Example 2

[0077] The same raw material ratio as in Example 1 was used, but the sintering process was changed to traditional hot pressing sintering without field-assisted activation.

[0078] Sintering process: hot pressing sintering furnace, argon protection; heating rate 20℃ / min to 2200℃; holding time 60min, pressure 40MPa.

[0079] Comparative Example 3

[0080] The same multi-component solid solution design as in Example 1 was used, but the graphite phase was replaced by directly adding flake graphite.

[0081] Systematic performance tests and characterization were performed on all examples and comparative samples. Test methods followed international standards: relative density was measured using Archimedes' displacement method; bending strength was determined by a three-point bending test (sample size 3mm × 4mm × 36mm); fracture toughness was calculated using the single-sided notched beam method (notch depth was 1 / 2 of the sample thickness); Vickers hardness testing was conducted under a 1kg load; electromagnetic wave absorption performance was measured using a vector network analyzer (VNA) in the 2–18 GHz frequency band, and the minimum reflection loss and effective absorption bandwidth (bandwidth with reflection loss ≤ -10dB) were calculated; environmental durability was assessed by a high-temperature oxidation test (800℃ air atmosphere, held for 10h) to evaluate weight loss rate. Test results are shown in Table 1.

[0082] Table 1. Performance comparison of the examples and comparative examples.

[0083] .

[0084] All embodiments of the present invention exhibit excellent overall performance. Embodiments 1 and 2, through multi-component solid solution design (such as the introduction of W or Mo), achieve high hardness (≥32 GPa) and high toughness (≥6.8 MPa·m). 1 / 2 The balance of ) was achieved; Example 4 significantly improved the microwave absorption performance (minimum reflection loss -18.0dB) by controlling the thickness of the graphite sheets (0.3μm). All examples had a relative density higher than 97.5%, a flexural strength exceeding 590MPa, an effective absorption bandwidth of not less than 2.8GHz, and an oxidation weight loss rate of less than 1.8%, verifying the synergistic optimization of mechanical properties, microwave absorption, and environmental durability of the present invention. Compared with Comparative Example 1 (single reinforcing phase), Comparative Example 2 (conventional sintering), and Comparative Example 3 (non-in-situ graphite), their performance deteriorated across the board: Comparative Example 1, due to the lack of solid solution reinforcement, had a fracture toughness reduced to 4.1MPa·m. 1 / 2Comparative Example 2 showed a significant decrease in density and strength due to grain coarsening; Comparative Example 3 exhibited a reflection loss of only -11.2 dB due to weak interfacial bonding. This invention, through integrated design of composition, process, and structure, overcomes the bottlenecks of existing technologies and provides a reliable material.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A boron carbide-graphite composite ceramic material, characterized in that, It includes a boron carbide matrix phase, a multi-component solid solution reinforcing phase, a graphite phase, and an environmentally durable phase; The multi-component solid solution reinforcing phase is (Ti,Cr,M)B2 solid solution, wherein M is at least one transition metal element selected from tungsten and molybdenum; the environmental durability phase is at least one of silicon carbide or alumina.

2. The boron carbide-graphite composite ceramic material according to claim 1, characterized in that, In the multi-component solid solution reinforcing phase, the atomic ratio of titanium, chromium, and M satisfies: (Ti x Cr y M z )B2, where x ranges from 0.40 to 0.85, y ranges from 0.10 to 0.50, z ranges from 0.05 to 0.20, and x+y+z=1.

3. The boron carbide-graphite composite ceramic material according to claim 1, characterized in that, The volume fractions of each phase are as follows: boron carbide matrix phase 60 vol%~70 vol%, multi-component solid solution reinforcing phase 15 vol%~25 vol%, graphite phase 8 vol%~12 vol%, and environmentally durable phase 2 vol%~5 vol%.

4. The boron carbide-graphite composite ceramic material according to claim 1, characterized in that, The graphite phase is in-situ generated flake graphite with an average flake thickness of 0.1 μm to 1.0 μm, and is uniformly distributed at the interface between the boron carbide matrix phase and the multi-component solid solution reinforcing phase.

5. A method for preparing a boron carbide-graphite composite ceramic material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Raw material preparation: Boron carbide powder, titanium carbide powder, chromium carbide powder, transition metal carbide powder, and environmental durability phase powder are prepared according to the specified proportions. The transition metal carbide powder is selected from at least one of tungsten carbide or molybdenum carbide, and the environmental durability phase powder is selected from at least one of silicon carbide or alumina. Mixing and drying: The prepared raw material powder is mixed with ball milling media and dispersant, and then wet ball milled and dried to obtain a uniformly mixed powder; Sintering densification: The dried mixed powder is loaded into a mold and sintered by spark plasma. Under vacuum or inert atmosphere protection, pressure is applied and the mixture is heated to the sintering temperature. After holding at the temperature, it is cooled to obtain the composite ceramic material.

6. The method for preparing a boron carbide-graphite composite ceramic material according to claim 5, characterized in that, In the raw material preparation step, the average particle size and purity of each raw material powder are as follows: boron carbide powder has an average particle size of 0.1 μm to 1.0 μm and a purity of ≥99.5%; titanium carbide powder and chromium carbide powder have an average particle size of 0.5 μm to 3.0 μm and a purity of ≥99.0%; transition metal carbide powder has an average particle size of 0.5 μm to 2.0 μm and a purity of ≥99.0%; and environmentally durable phase powder has an average particle size of 0.2 μm to 1.0 μm and a purity of ≥99.5%.

7. The method for preparing a boron carbide-graphite composite ceramic material according to claim 5, characterized in that, In the mixing and drying steps, the wet ball milling uses zirconia ball milling beads, the ball milling speed is 80 r / min to 120 r / min, and the ball milling time is 12 h to 16 h; the drying uses rotary evaporation, and the water bath temperature is controlled at 40 ℃ to 50 ℃.

8. The method for preparing a boron carbide-graphite composite ceramic material according to claim 5, characterized in that, In the sintering densification step, the process parameters for spark plasma sintering include: sintering temperature 1850℃~2000℃; holding time 5min~20min; applied pressure: 40MPa~80MPa; heating rate: 50℃ / min~150℃ / min; and argon or nitrogen protective atmosphere.

9. The method for preparing a boron carbide-graphite composite ceramic material according to claim 8, characterized in that, The sintering densification step adopts a segmented sintering strategy: first, preheating at 1600℃~1700℃ for 5min~10min to promote in-situ reaction, and then raising to 1850℃~2000℃ for 5min~15min to complete densification; After sintering, hot isostatic pressing is performed under the following conditions: temperature 1700℃~1800℃, pressure 80MPa~120MPa, and time 20min~40min.

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