Hot-pressing sintered boron carbide ceramic and preparation method and application thereof

Abstract

This invention belongs to the field of ceramic preparation technology and provides a hot-pressed sintered multiphase boron carbide ceramic and its preparation method. The ceramic is based on boron carbide, with the addition of high-entropy diboride phases containing titanium, zirconium, hafnium, niobium, tungsten, and molybdenum, as well as a carbon phase. The ceramic may further contain corresponding high-entropy carbides. In the preparation process, multi-metal powder, amorphous boron powder, cobalt powder, and a process control agent are first subjected to high-energy ball milling and heat treatment under an inert atmosphere to obtain high-entropy diborides. Then, nanodiamond and cobalt powder are dispersed in ethanol, followed by ultrasonication, drying, and heat treatment to obtain the carbon phase. Subsequently, this carbon phase is mixed with boron carbide and granulated to obtain composite particle powder. Finally, it is hot-pressed and sintered in segments under vacuum conditions, with pressure pulses and pressure relief cycles applied during the high-temperature stage to obtain a dense multiphase ceramic, which can be applied to ceramic valves and ceramic cylinder valve plates.

Description

Technical Field

[0001] This invention belongs to the field of ceramic preparation technology, and relates to a hot-pressed sintered multiphase boron carbide ceramic, its preparation method and application. Background Technology

[0002] Boron carbide ceramics possess characteristics such as low density, high hardness, wear resistance, and corrosion resistance, making them well-suited for applications in wear-resistant sealing components and lightweight, high-strength parts. For special ceramic products such as ceramic valves and ceramic cylinder valve plates, their service life typically involves simultaneous exposure to media erosion, repeated opening and closing impacts, contact compression, edge friction, and cyclic stress. The material not only needs to maintain high surface hardness and wear resistance but also requires good crack resistance, edge integrity, and structural stability. Although boron carbide ceramics have high hardness, they are strongly covalently bonded ceramics with limited crystal slip ability and difficulty in dislocation movement. Under alternating loads and localized stress concentration conditions, they are prone to brittle fracture, especially at valve orifices, sealing edges, and thin-plate stress areas, where microcrack initiation, edge chipping, and rapid crack propagation are likely to occur, thus affecting sealing reliability and service life.

[0003] In existing technologies, to improve the brittleness of boron carbide ceramics, multiphase modification is typically achieved by introducing metallic phases, metal borides, carbides, or carbon-based phases, combined with pressure sintering processes such as hot pressing to improve density and interfacial bonding. While this approach can improve material properties to some extent, it still has several shortcomings. On the one hand, existing reinforcing phase systems are mostly single-component or have only a few components, resulting in limited grain boundary control capabilities and making it difficult to effectively control crack propagation behavior while maintaining the hardness advantage of boron carbide. On the other hand, different reinforcing phases differ from boron carbide in terms of interfacial bonding, high-temperature compatibility, and microstructure evolution. During sintering, local reaction imbalances, uneven grain boundary distribution, grain coarsening, or weak interfacial regions can easily occur, leading to significant performance fluctuations under repeated impacts and long-term friction conditions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a hot-pressed sintered multiphase boron carbide ceramic, its preparation method, and its application. High-entropy diborides are prepared by high-energy ball milling and heat treatment of multimetal powder, amorphous boron powder, and cobalt powder under an inert atmosphere. Nanodiamonds are dispersed in an alcohol medium and heat-treated to obtain a carbon phase. This carbon phase is then granulated with boron carbide and subjected to vacuum segmented hot pressing. Combined with pressure pulses and pressure relief pumping cycles, a dense ceramic with synergistic grain boundary strengthening and carbon phase toughening is obtained, thus meeting the needs of practical production.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a hot-pressed sintered multiphase boron carbide ceramic, wherein the multiphase boron carbide ceramic comprises boron carbide, high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2 and a carbon phase.

[0007] Preferably, the multiphase boron carbide ceramic further comprises high-entropy carbides.

[0008] Secondly, the present invention provides a method for preparing hot-pressed sintered multiphase boron carbide ceramics, specifically comprising:

[0009] S1, titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder are mixed, and the first part of cobalt powder and process control agent are added. The mixture is then subjected to high-energy ball milling and heat treatment under an inert atmosphere to obtain high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2.

[0010] S2, nanodiamond and a second cobalt powder are dispersed in anhydrous ethanol, ultrasonically dispersed, dried and heat-treated to obtain a carbon phase;

[0011] S3, Boron carbide, the high-entropy diboride and the carbon phase are mixed and made into a slurry with solvent and temporary binder, and composite particle powder is obtained by spray granulation;

[0012] S4, the composite particle powder is loaded into a mold and subjected to segmented hot pressing to obtain hot-pressed sintered multiphase boron carbide ceramic.

[0013] Preferably, the mass ratio of the titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder is 47.9:91.2:178.5:92.9:(55.2-147.1):(28.8-76.8).

[0014] Preferably, the amount of amorphous boron powder added is 11.3-21.4 parts based on 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder and molybdenum powder.

[0015] Preferably, the amount of the first cobalt powder added is 0.2-0.6 parts based on the total mass of 100 parts of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder.

[0016] Preferably, the process control agent is stearic acid or paraffin, and the amount added is 0.2-0.5 parts based on 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder.

[0017] Preferably, the ball-to-material mass ratio of the high-energy ball mill is (10:1)-(20:1), the rotation speed is 350-550 rpm, the total ball milling time is 20-40 h, and an intermittent operation mode is adopted, specifically, a 10-minute pause is taken after every 30 minutes of operation.

[0018] Preferably, the heat treatment is carried out under argon protection, with the temperature increased to 400-500℃ at 5℃ / min and held for 2 hours, followed by further heating to 1000-1100℃ and held for 6 hours, and then cooled to room temperature in the furnace.

[0019] Preferably, the mass ratio of the nanodiamond to the second cobalt powder is 100:(0.3-0.8).

[0020] Preferably, the heat treatment is performed in an argon atmosphere at 900-1000℃ for 0.5-3 hours.

[0021] Preferably, the mass ratio of boron carbide, high-entropy diboride to carbon phase is (70-88):(8-25):(1-8).

[0022] Preferably, the solvent is anhydrous ethanol, and the temporary binder is one or both of polyvinyl alcohol or phenolic resin. The amount of temporary binder added is 0.5-2.0 parts based on 100 parts of the total mass of boron carbide, high-entropy diboride and carbon phase. After spray granulation, the mixture is kept at 450-650℃ for 1-2 hours under an argon atmosphere.

[0023] Preferably, the segmented hot pressing specifically includes: in a vacuum degree ≤ 5 × 10 -2 Under Pa conditions,

[0024] Stage I was kept at 1100-1300℃ and 5-10MPa for 30-60 minutes;

[0025] Stage II involves heating to 1880-2000℃ and holding at 30-35MPa for 45-90 minutes;

[0026] In stage III, the temperature is reduced to 1500-1700℃ at a rate of 3-8℃ / min, and held at 20-35MPa for 1-4 hours, followed by furnace cooling to room temperature.

[0027] Preferably, at the end of stage I, a depressurization and pumping cycle is set, depressurizing from 5-10MPa to 2-4MPa and maintaining it for 3-10 minutes while maintaining vacuum pumping, and then restoring it to 5-10MPa before entering stage II.

[0028] During the Phase II heat preservation period, pressure pulses are applied. The pressure pulses alternate between high pressure maintenance and low pressure release in a cycle of 5-15 minutes. The high pressure is 30-35 MPa, maintained for 5-13 minutes, and the low pressure is 20-25 MPa, maintained for 0.5-5 minutes.

[0029] During ball milling and subsequent heat treatment, titanium, zirconium, hafnium, niobium, tungsten, molybdenum, and amorphous boron form numerous new surfaces and defect regions under repeated cold welding and crushing. The exposed metal surfaces, after the oxide film on the metal surface is sheared and broken, come into direct contact with boron. Boron atoms adsorb, embed, and diffuse near defects such as dislocations, grain boundaries, and stacking faults. During heat treatment, boron migrates into the crystal lattice along defect channels, nucleates at the interface, and transforms into a diboride crystal structure. Multiple metals randomly occupy the same lattice sites, resulting in a multi-metal diboride solid solution with a single structure. Cobalt is distributed at the metal-boron interface during ball milling, forming a cobalt-containing mixed layer and altering the atomic rearrangement path at the interface. During heat treatment, the dissolution and migration of boron by cobalt alters the interfacial diffusion flux, allowing diborides to continuously nucleate and grow at the multi-metal mixed interface.

[0030] After nanodiamonds and cobalt form an adherent contact in an alcohol medium, they undergo heat treatment. The dissolution of carbon by cobalt causes carbon atoms to migrate and diffuse from the nanodiamond surface into the cobalt phase, subsequently re-precipitating at the interface as a layered carbon structure. This precipitation and re-dissolution proceed along the interface curvature and interfacial energy gradient, resulting in multiple closed shells that stack and encapsulate residual carbon cores, forming a carbon phase dominated by an onion-like carbon structure. Vacancies retained in the carbon phase provide interfacial active sites, where cobalt adsorbs and forms a cobalt-rich interfacial layer.

[0031] During the composite mixing and granulation process, boron carbide, high-entropy diborides, and the carbon phase are located at the particle contact point and adjacent to the cobalt-enriched layer at the particle scale, thereby shortening the subsequent diffusion distance and reducing component segregation. During the vacuum hot-pressing heating stage, adsorbate desorption and organic residue pyrolysis migrate along the pores and are extracted. The carbon phase and residual oxides undergo solid-phase reduction to generate volatile products, which escape through the pores to form new solid-phase contacts. The depressurization and extraction cycle causes the closed pores to rebound and reduce the partial pressure within the pores during depressurization, allowing gas to diffuse outwards. Upon repressurization, the pore walls re-attach and neck growth occurs, and the pores undergo a sequence of opening, venting, and re-closing processes.

[0032] Upon entering the molten zone of cobalt, cobalt forms a continuous or semi-continuous liquid phase film at the particle contact points and permeates along grain boundaries and pore walls. Particles rearrange themselves with the participation of the liquid phase, and the liquid phase generates capillary action at the three-phase contact line, causing pore shrinkage and neck growth. Pressure pulses increase contact stress and effective contact area during the high-pressure phase, and redistribute the liquid phase channels and alter pore connectivity during the low-pressure phase. Subsequent repressurization continues to promote diffusion and neck evolution under the new contact geometry.

[0033] During the high-temperature holding stage, interfacial diffusion and liquid-phase dissolution-reprecipitation are the main processes. Boron migrates within the diboride phase through vacancies and antisite defects. The cobalt liquid phase carries the metal and boron for mass transfer at the interface. Solid phase necks between multiple particles grow and connect in the liquid phase. The carbon phase remains in contact with the cobalt liquid phase. Carbon dissolves and precipitates in cobalt, maintaining carbon activity near the interface. The carbon phase redistributes at the three grain boundaries and the grain interface, remaining as shells or dot-like clusters.

[0034] High-entropy carbides correspond to phase competition results when local carbon activity increases at high temperatures and boron supply is insufficient or boron diffusion is limited. At the interface between the diboride network and the carbon phase, there are channels for metal atoms to migrate into the liquid phase and defect regions. Metal and carbon undergo coordination rearrangement near the interface to form carbide nuclei. Multiple metals randomly occupy the same lattice sites, while the occupancy of carbon at interstitial sites exhibits non-stoichiometric variations controlled by local chemical potential and vacancies. Under solid-solution-limited conditions, cobalt tends to enrich on the carbon phase surface and at the diboride-boron carbide interface. After cooling and solidification of the liquid phase, it remains in the interfacial region as an enriched layer or dispersed micro-region. The adsorption layer alters the interfacial electronic states and bonding modes, affecting the interfacial connectivity.

[0035] Thirdly, this invention provides the application of hot-pressed sintered multiphase boron carbide ceramics in the preparation of ceramic valves and ceramic cylinder valve plates.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention adopts a multiphase design of boron carbide, high-entropy diboride and carbon phase to deflect and impede the crack propagation path; an interface transition region is formed between high-entropy diboride and boron carbide and between carbon phase and inorganic phase, which inhibits interface debonding and reduces the risk of brittle interface failure; cobalt element is enriched on the surface of carbon phase and in the interface region between high-entropy diboride and boron carbide, which improves the interphase connection state and stabilizes the interface structure, realizing the synergy of grain boundary strengthening and carbon phase toughening, thereby improving hardness, fracture toughness and bending strength. Attached Figure Description

[0037] Figure 1 This is a SEM image of hot-pressed sintered multiphase boron carbide ceramic provided in Embodiment 1 of the present invention. Detailed Implementation

[0038] The technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. The embodiments described herein are specific implementations of the present invention, used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary, and should not be construed as limiting the implementation methods or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can employ other obvious technical solutions based on the content disclosed in the claims and specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0039] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0040] Example 1

[0041] This embodiment provides a hot-pressed sintered multiphase boron carbide ceramic and its preparation method, specifically including:

[0042] The multiphase boron carbide ceramic comprises boron carbide, high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2, and a carbon phase, and the multiphase boron carbide ceramic further comprises high-entropy carbide.

[0043] The preparation method specifically includes:

[0044] S1, titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder, and amorphous boron powder are mixed, and a first portion of cobalt powder and a process control agent are added. The mixture is then subjected to high-energy ball milling and heat treatment under an inert atmosphere. The mass ratio of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder is 47.9:91.2:178.5:92.9:147.1:28.8. The amount of amorphous boron powder added is 11.3 parts per 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder. The amount of the first portion of cobalt powder added is calculated based on the mixture of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder, and amorphous boron powder. The total mass of the powder is 0.2 parts per 100 parts. The process control agent is stearic acid, and the amount added is 0.5 parts per 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder. The ball-to-material mass ratio of the high-energy ball mill is 20:1, the rotation speed is 550 rpm, the total ball milling time is 20 h, and the intermittent operation mode is adopted. The heat treatment is carried out under argon protection, heating to 400℃ at 5℃ / min and holding for 2 h, then heating to 1000℃ and holding for 6 h, and then cooling to room temperature with the furnace to obtain high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2.

[0045] S2, nanodiamond and a second part of cobalt powder are dispersed in anhydrous ethanol, wherein the mass ratio of nanodiamond to the second part of cobalt powder is 100:0.8. After ultrasonic dispersion, the mixture is dried and heat-treated. The heat treatment is carried out in an argon atmosphere at 900°C for 3 hours to obtain a carbon phase.

[0046] S3, Boron carbide, the high-entropy diboride, and the carbon phase are mixed and then mixed with a solvent and a temporary binder to form a slurry. The mass ratio of boron carbide, high-entropy diboride, and carbon phase is 88:8:1. The solvent is anhydrous ethanol, and the temporary binder is polyvinyl alcohol. The amount of temporary binder added is 0.5 parts based on 100 parts of the total mass of boron carbide, high-entropy diboride, and carbon phase. After spray granulation, the mixture is kept at 450°C for 2 hours under an argon atmosphere.

[0047] S4, the composite particle powder is loaded into a mold and subjected to segmented hot pressing, the segmented hot pressing specifically including: under a vacuum degree ≤5×10 -2 Under Pa conditions,

[0048] Stage I was kept at 1300℃ and 5MPa for 60 min;

[0049] Stage II: Heating to 2000℃ and holding at 30MPa for 45 minutes;

[0050] In Stage III, the temperature is reduced to 1500℃ at 8℃ / min and held at 20MPa for 4 hours. Then, the furnace is cooled to room temperature. At the end of Stage I, a pressure relief and vacuuming cycle is set up, from 5MPa to 4MPa and held for 3 minutes while maintaining vacuuming. After returning to 5MPa, Stage II begins.

[0051] During the heat preservation period of stage II, pressure pulses are applied. The pressure pulses alternate between high pressure holding and low pressure release in a 5-minute cycle. The high pressure is 30 MPa, held for 5 minutes, and the low pressure is 25 MPa, held for 0.5 minutes, to obtain hot-pressed sintered multiphase boron carbide ceramic.

[0052] Figure 1 The SEM image of the hot-pressed sintered multiphase boron carbide ceramic provided in this embodiment shows a multiphase composite structure.

[0053] Example 2

[0054] This embodiment provides a hot-pressed sintered multiphase boron carbide ceramic and its preparation method, specifically including:

[0055] The multiphase boron carbide ceramic comprises boron carbide, high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2, and a carbon phase, and the multiphase boron carbide ceramic further comprises high-entropy carbide.

[0056] The preparation method specifically includes:

[0057] S1, titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder, and amorphous boron powder are mixed, and a first portion of cobalt powder and a process control agent are added. The mixture is then subjected to high-energy ball milling and heat treatment under an inert atmosphere. The mass ratio of the titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder is 47.9:91.2:178.5:92.9:55.2:76.8. The amount of amorphous boron powder added is 21.4 parts per 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder. The amount of the first portion of cobalt powder added is calculated based on the mixture of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder, and amorphous boron powder. The total mass of the powder is 0.6 parts per 100 parts. The process control agent is paraffin wax, and the amount added is 0.2 parts per 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder. The ball-to-material mass ratio of the high-energy ball mill is 10:1, the rotation speed is 350 rpm, the total ball milling time is 40 h, and the intermittent operation mode is adopted. The heat treatment is carried out under argon protection, heating to 500℃ at 5℃ / min and holding for 2 h, then heating to 1100℃ and holding for 6 h, and then cooling to room temperature with the furnace to obtain high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2.

[0058] S2, nanodiamond and a second part of cobalt powder are dispersed in anhydrous ethanol, wherein the mass ratio of nanodiamond to the second part of cobalt powder is 100:0.3. After ultrasonic dispersion, the mixture is dried and heat-treated. The heat treatment is performed in an argon atmosphere at 1000℃ for 0.5h to obtain a carbon phase.

[0059] S3, Boron carbide, the high-entropy diboride, and the carbon phase are mixed and then mixed with a solvent and a temporary binder to form a slurry. The mass ratio of boron carbide, high-entropy diboride, and carbon phase is 70:25:8. The solvent is anhydrous ethanol, and the temporary binder is phenolic resin. The amount of temporary binder added is 2.0 parts based on 100 parts of the total mass of boron carbide, high-entropy diboride, and carbon phase. After spray granulation, the mixture is kept at 650°C for 1 hour under an argon atmosphere.

[0060] S4, the composite particle powder is loaded into a mold and subjected to segmented hot pressing, the segmented hot pressing specifically including: under a vacuum degree ≤5×10 -2 Under Pa conditions,

[0061] Stage I was kept at 1100℃ and 10MPa for 30 minutes;

[0062] Stage II: Heating to 1880℃ and holding at 35MPa for 90 minutes;

[0063] In Stage III, the temperature is reduced to 1700℃ at 3℃ / min and held at 35MPa for 1h. Then, the furnace is cooled to room temperature. At the end of Stage I, a depressurization and evacuation cycle is set, depressurizing from 10MPa to 2MPa and holding for 10min while maintaining vacuum evacuation. Then, the pressure is restored to 10MPa before entering Stage II.

[0064] During the heat preservation period of stage II, pressure pulses are applied. The pressure pulses alternate between high pressure holding and low pressure release in a cycle of 15 minutes. The high pressure is 35 MPa, held for 13 minutes, and the low pressure is 20 MPa, held for 2 minutes, to obtain hot-pressed sintered multiphase boron carbide ceramic.

[0065] Example 3

[0066] This embodiment provides a hot-pressed sintered multiphase boron carbide ceramic and its preparation method, specifically including:

[0067] The multiphase boron carbide ceramic comprises boron carbide, high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2, and a carbon phase, and the multiphase boron carbide ceramic further comprises high-entropy carbide.

[0068] The preparation method specifically includes:

[0069] S1, titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder, and amorphous boron powder are mixed, and a first portion of cobalt powder and a process control agent are added. The mixture is then subjected to high-energy ball milling and heat treatment under an inert atmosphere. The mass ratio of the titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder is 47.9:91.2:178.5:92.9:100:50. The amount of amorphous boron powder added is 15 parts per 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder. The amount of the first portion of cobalt powder added is based on the total mass of the titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder, and amorphous boron powder. 100 parts are counted as 0.4 parts, the process control agent is stearic acid, and the addition amount is 0.35 parts based on the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder of 100 parts. The ball-to-material mass ratio of the high-energy ball mill is 15:1, the rotation speed is 450 rpm, the total ball milling time is 30 h, and an intermittent operation mode is adopted. The heat treatment is carried out under argon protection, heating to 450℃ at 5℃ / min and holding for 2 h, then heating to 1050℃ and holding for 6 h, and then cooling to room temperature with the furnace to obtain high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2.

[0070] S2, nanodiamond and a second part of cobalt powder are dispersed in anhydrous ethanol, wherein the mass ratio of nanodiamond to the second part of cobalt powder is 100:0.5. After ultrasonic dispersion, the mixture is dried and heat-treated. The heat treatment is carried out in an argon atmosphere at 950°C for 1.5 hours to obtain a carbon phase.

[0071] S3, Boron carbide, the high-entropy diboride, and the carbon phase are mixed and then mixed with a solvent and a temporary binder to form a slurry. The mass ratio of boron carbide, high-entropy diboride, and carbon phase is 80:15:5. The solvent is anhydrous ethanol, and the temporary binder is polyvinyl alcohol and phenolic resin. The amount of temporary binder added is 1.2 parts based on 100 parts of the total mass of boron carbide, high-entropy diboride, and carbon phase. After spray granulation, the mixture is kept at 550°C for 1.5 hours under an argon atmosphere.

[0072] S4, the composite particle powder is loaded into a mold and subjected to segmented hot pressing, the segmented hot pressing specifically including: under a vacuum degree ≤5×10 -2 Under Pa conditions,

[0073] Stage I was kept at 1200℃ and 8MPa for 45 minutes;

[0074] Stage II: Heating to 1950℃ and holding at 32MPa for 70 minutes;

[0075] In Stage III, the temperature is reduced to 1600℃ at a rate of 5℃ / min and held at 28MPa for 2.5h. Then, the furnace is cooled to room temperature. At the end of Stage I, a depressurization and evacuation cycle is set up, depressurizing from 8MPa to 3MPa and holding for 6min while maintaining vacuum evacuation. After returning to 8MPa, Stage II begins.

[0076] During the heat preservation period of stage II, pressure pulses are applied. The pressure pulses alternate between high pressure holding and low pressure release in a cycle of 10 minutes. The high pressure is 32 MPa and held for 8 minutes, and the low pressure is 22 MPa and held for 2 minutes, resulting in hot-pressed sintered multiphase boron carbide ceramic.

[0077] Example 4

[0078] This embodiment provides a hot-pressed sintered multiphase boron carbide ceramic and its preparation method, specifically including:

[0079] The multiphase boron carbide ceramic comprises boron carbide, high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2, and a carbon phase, and the multiphase boron carbide ceramic further comprises high-entropy carbide.

[0080] The preparation method specifically includes:

[0081] S1, titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder, and amorphous boron powder are mixed, and a first portion of cobalt powder and a process control agent are added. The mixture is then subjected to high-energy ball milling and heat treatment under an inert atmosphere. The mass ratio of the titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder is 47.9:91.2:178.5:92.9:120:65. The amount of amorphous boron powder added is 18 parts per 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder. The amount of the first portion of cobalt powder added is based on the total mass of the titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder, and amorphous boron powder. The amount of material added is 0.5 parts per 100 parts, the process control agent is paraffin, and the amount added is 0.4 parts per 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder. The ball-to-material mass ratio of the high-energy ball mill is 18:1, the rotation speed is 400 rpm, the total ball milling time is 25 h, and the intermittent operation mode is adopted. The heat treatment is carried out under argon protection, heating to 480℃ at 5℃ / min and holding for 2 h, then heating to 1080℃ and holding for 6 h, and then cooling to room temperature with the furnace to obtain high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2.

[0082] S2, nanodiamond and a second part of cobalt powder are dispersed in anhydrous ethanol, wherein the mass ratio of nanodiamond to the second part of cobalt powder is 100:0.6. After ultrasonic dispersion, the mixture is dried and heat-treated. The heat treatment is carried out in an argon atmosphere at 920°C for 2 hours to obtain a carbon phase.

[0083] S3, Boron carbide, the high-entropy diboride, and the carbon phase are mixed and then mixed with a solvent and a temporary binder to form a slurry. The mass ratio of boron carbide, high-entropy diboride, and carbon phase is 75:20:3. The solvent is anhydrous ethanol, and the temporary binder is polyvinyl alcohol. The amount of temporary binder added is 0.5 parts based on 100 parts of the total mass of boron carbide, high-entropy diboride, and carbon phase. After spray granulation, the mixture is kept at 600°C for 1.2 hours under an argon atmosphere.

[0084] S4, the composite particle powder is loaded into a mold and subjected to segmented hot pressing, the segmented hot pressing specifically including: under a vacuum degree ≤5×10 -2 Under Pa conditions,

[0085] Stage I was kept at 1250℃ and 7MPa for 50 min;

[0086] Stage II: Heat to 1920℃ and hold at 34MPa for 60 minutes;

[0087] In Stage III, the temperature is reduced to 1650℃ at a rate of 6℃ / min and held at 30MPa for 3 hours. Then, the temperature is cooled to room temperature with the furnace. At the end of Stage I, a pressure relief and evacuation cycle is set up, which reduces the pressure from 7MPa to 3.5MPa and holds for 8 minutes while maintaining vacuum evacuation. Then, the pressure is restored to 7MPa before entering Stage II.

[0088] During the heat preservation period of stage II, pressure pulses are applied. The pressure pulses alternate between high pressure holding and low pressure release in a cycle of 12 minutes. The high pressure is 34 MPa and held for 7 minutes, and the low pressure is 24 MPa and held for 5 minutes, resulting in hot-pressed sintered multiphase boron carbide ceramic.

[0089] Comparative Example 1

[0090] This comparative example provides a hot-pressed sintered multiphase boron carbide ceramic and its preparation method. The difference between this example and Example 1 is that step S2 is not performed, and the composite particle powder contains only boron carbide and high-entropy diboride by mass, with 0 parts of carbon phase. Other process parameters and operating conditions are exactly the same as in Example 1.

[0091] Comparative Example 2

[0092] This comparative example provides a hot-pressed sintered multiphase boron carbide ceramic and its preparation method. The difference between this example and Example 1 is that S1 is not performed, and the composite particle powder contains only boron carbide and carbon phase by mass, with 0 parts of high-entropy diboride. Other process parameters and operating conditions are exactly the same as in Example 1.

[0093] Comparative Example 3

[0094] This comparative example provides a hot-pressed sintered multiphase boron carbide ceramic and its preparation method. The difference between this example and Example 1 is that no pressure pulse is applied during the heat preservation period of stage II in S4, and no pressure relief and pumping cycle is performed at the end of stage I. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0095] The hardness test method is GB / T 16534-2009; the fracture toughness test method is GB / T 23806-2025; and the bending strength test method is GB / T 6569-2006.

[0096] Table 1 shows the test results of hot-pressed sintered multiphase boron carbide ceramics from Examples 1-4 and Comparative Examples 1-3.

[0097] Table 1. Test results of hot-pressed sintered multiphase boron carbide ceramics in Examples 1-4 and Comparative Examples 1-3

[0098]

[0099] As shown in Table 1, compared with Example 1, the hardness, fracture toughness and bending strength of Comparative Example 1 decreased; the hardness, fracture toughness and bending strength of Comparative Example 2 decreased; and the hardness, fracture toughness and bending strength of Comparative Example 3 decreased.

[0100] This is because, in Comparative Example 1, the lack of carbon phase at grain boundaries allows stress to be transmitted more directly to boron carbide grains, making cracks more likely to propagate along the grain boundaries; the cobalt-enriched layer at the interface weakens the crack passivation effect, resulting in decreased fracture toughness and flexural strength. In Comparative Example 2, without the introduction of high-entropy diborides, the grain boundaries lack a continuous or semi-continuous network, and the load is mainly borne by boron carbide and carbon phases, reducing grain boundary strengthening and crack deflection paths; the interface transition zone is shortened, making cracks more likely to propagate linearly and form through defects, thus reducing fracture toughness and flexural strength. In Comparative Example 3, after eliminating pressure pulses and depressurization pumping cycles, pore gas migration is restricted, particle redistribution is insufficient, and neck growth and grain boundary contact area growth slow down; residual pores and weak bonding interfaces increase and form stress concentration sources, reducing crack initiation stress, leading to decreased hardness and flexural strength, and decreased fracture toughness.

[0101] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A hot-pressed sintered multiphase boron carbide ceramic, characterized in that, The multiphase boron carbide ceramic comprises boron carbide, high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2, and a carbon phase.

2. The hot-pressed sintered multiphase boron carbide ceramic according to claim 1, characterized in that, The multiphase boron carbide ceramic further comprises high-entropy carbides.

3. A method for preparing hot-pressed sintered multiphase boron carbide ceramic as described in claim 1, characterized in that, Specifically, it includes: S1, titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder are mixed, and the first part of cobalt powder and process control agent are added. The mixture is then subjected to high-energy ball milling and heat treatment under an inert atmosphere to obtain high-entropy diboride (Ti,Zr,Hf,Nb,W,Mo)B2. S2, nanodiamond and a second cobalt powder are dispersed in anhydrous ethanol, ultrasonically dispersed, dried and heat-treated to obtain a carbon phase; S3 involves mixing boron carbide, high-entropy diboride, and carbon phase, then preparing a slurry with solvent and temporary binder, and finally obtaining composite particle powder by spray granulation. S4, the composite particle powder is loaded into a mold and subjected to segmented hot pressing to obtain hot-pressed sintered multiphase boron carbide ceramic.

4. The method for preparing hot-pressed sintered multiphase boron carbide ceramic according to claim 3, characterized in that, In S1: The mass ratio of the titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, and molybdenum powder is 47.9:91.2:178.5:92.9:(55.2-147.1):(28.8-76.8). The amount of amorphous boron powder added is 11.3-21.4 parts based on 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder and molybdenum powder; The amount of cobalt powder added in the first part is 0.2-0.6 parts based on the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder of 100 parts; The process control agent is stearic acid or paraffin, and the amount added is 0.2-0.5 parts based on 100 parts of the total mass of titanium powder, zirconium powder, hafnium powder, niobium powder, tungsten powder, molybdenum powder and amorphous boron powder.

5. The method for preparing hot-pressed sintered multiphase boron carbide ceramic according to claim 3, characterized in that, In S1: The high-energy ball mill has a ball-to-material mass ratio of (10:1) to (20:1), a rotation speed of 350-550 rpm, a total ball milling time of 20-40 h, and adopts an intermittent operation mode.

6. The method for preparing hot-pressed sintered multiphase boron carbide ceramic according to claim 3, characterized in that, In S1: The heat treatment involves heating to 400-500℃ at a rate of 5℃ / min under argon protection, holding for 2 hours, then further heating to 1000-1100℃ and holding for 6 hours, followed by furnace cooling to room temperature.

7. The method for preparing hot-pressed sintered multiphase boron carbide ceramic according to claim 3, characterized in that, In S2: The mass ratio of the nanodiamond to the second cobalt powder is 100:(0.3-0.8). The heat treatment is performed in an argon atmosphere at 900-1000℃ for 0.5-3 hours.

8. The method for preparing hot-pressed sintered multiphase boron carbide ceramic according to claim 3, characterized in that, In S3: The mass ratio of boron carbide, high-entropy diboride to carbon phase is (70-88):(8-25):(1-8).

9. The method for preparing hot-pressed sintered multiphase boron carbide ceramic according to claim 3, characterized in that, In S3: The solvent is anhydrous ethanol, and the temporary binder is one or both of polyvinyl alcohol or phenolic resin. The amount of temporary binder added is 0.5-2.0 parts based on 100 parts of the total mass of boron carbide, high-entropy diboride and carbon phase. After spray granulation, the mixture is kept at 450-650℃ for 1-2 hours under an argon atmosphere.

10. The method for preparing hot-pressed sintered multiphase boron carbide ceramic according to claim 3, characterized in that, In S4: The segmented hot pressing specifically includes: under the condition of vacuum degree ≤ 5 × 10 -2 Pa, Stage I was kept at 1100-1300℃ and 5-10MPa for 30-60 minutes; Stage II involves heating to 1880-2000℃ and holding at 30-35MPa for 45-90 minutes; In stage III, the temperature is reduced to 1500-1700℃ at a rate of 3-8℃ / min, and held at 20-35MPa for 1-4 hours, followed by furnace cooling to room temperature.

11. The method for preparing hot-pressed sintered multiphase boron carbide ceramic according to claim 9, characterized in that: At the end of stage I, a depressurization and pumping cycle is set up, depressurizing from 5-10MPa to 2-4MPa and maintaining it for 3-10 minutes while maintaining vacuum pumping, and then restoring it to 5-10MPa before entering stage II; During the Phase II heat preservation period, pressure pulses are applied. The pressure pulses alternate between high pressure maintenance and low pressure release in a cycle of 5-15 minutes. The high pressure is 30-35 MPa, maintained for 5-13 minutes, and the low pressure is 20-25 MPa, maintained for 0.5-5 minutes.

12. The application of hot-pressed sintered multiphase boron carbide ceramics according to claim 1 or 2 in the preparation of ceramic valves and ceramic cylinder valve plates.

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