Boron carbide-titanium diboride composite powder, boron carbide-titanium diboride composite ceramic and preparation methods of boron carbide-titanium diboride composite powder and boron carbide-titanium diboride composite ceramic

Abstract

The invention relates to the technical field of boron carbide ceramics, in particular to boron carbide-titanium diboride composite powder, boron carbide-titanium diboride composite ceramic and a preparation method of the boron carbide-titanium diboride composite powder and the boron carbide-titanium diboride composite ceramic. The method comprises the following steps: uniformly dispersing an organic titanium compound and boron carbide into an organic solvent to obtain boron carbide-organic titanium compound slurry; adding pure water into the boron carbide-organic titanium compound slurry for complete hydrolysis reaction, and then carrying out suction filtration and drying to obtain a boron carbide-titanium dioxide precursor; and carrying out in-situ calcination on the boron carbide-titanium dioxide precursor to obtain the boron carbide-titanium diboride composite powder. According to the invention, the B4C composite powder is prepared by an organic titanium compound hydrolysis method, the powder is subjected to high-temperature calcination and converted into B4C-TiB2 powder, and then the powder is subjected to ball milling dispersion and hot pressed sintering, so that uniform dispersion of TiB2 particles and great improvement of mechanical properties are realized.

Description

Technical Field

[0001] This invention relates to the field of boron carbide ceramics technology, and in particular to a boron carbide-titanium diboride composite powder, a boron carbide-titanium diboride composite ceramic, and a method for preparing the same. Background Technology

[0002] Boron carbide ceramics, as an important component of advanced structural ceramics, possess extremely high hardness, low density, and very high chemical stability, making them prominently used in wear resistance, metallurgy, and safety protection. Furthermore, the high boron content of boron carbide makes it an effective neutron absorber for use as a control rod, safety rod, and other neutron absorbers in nuclear reactor core assemblies. However, as a type of non-oxide ceramic with an extremely high covalent bond fraction, boron carbide's high melting point and low self-diffusion coefficient make sintering and densification very difficult, typically requiring sintering at temperatures above 2000 °C and pressures exceeding 30 MPa. Simultaneously, boron carbide ceramics exhibit high brittleness and low fracture toughness (typically 2~3 MPa·m). 0.5 This seriously affects its engineering service and limits its wide application.

[0003] Chinese patent CN 110759735A discloses a boron carbide ceramic composite material and its preparation method. The method uses ball milling to mix boron carbide and titanium diboride powders, and then prepares the boron carbide ceramic composite material by high temperature and pressure sintering. However, due to the low purity and coarse particle size of commercially available titanium diboride powder, the prepared boron carbide ceramic has poor performance, with a flexural strength of only 450~550 MPa.

[0004] Therefore, it is necessary to propose a new method for preparing boron carbide composite powder and its ceramics to solve the technical problems of low strength and poor toughness of boron carbide composite ceramics. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a boron carbide-titanium diboride composite powder, a boron carbide-titanium diboride composite ceramic, and a method for preparing the same.

[0006] This invention provides the following technical solution: In a first aspect of the present invention, a method for preparing boron carbide-titanium diboride composite powder is provided, the method comprising: The organotitanium compound and boron carbide were uniformly dispersed in an organic solvent to obtain a boron carbide-organotitanium compound slurry. After the hydrolysis reaction is complete by adding pure water to the boron carbide-organotitanium compound slurry, the mixture is filtered and dried to obtain the boron carbide-titanium dioxide precursor. The boron carbide-titanium dioxide precursor was calcined in situ to obtain boron carbide-titanium diboride composite powder.

[0007] Furthermore, the boron carbide has a particle size of 2–5 μm and a specific surface area of ​​5–9 m². 2 / g; The molar ratio of organotitanium compounds, boron carbide, and water is 1~5:2.7~24:1~5; Furthermore, the organotitanium compound is selected from one or more of tetrabutyl titanate, tetramethyl titanate, tetraethyl titanate, and tetraisopropyl titanate; The organic solvent is selected from one or more of lower alcohols, toluene, or tetrahydrofuran; The lower alcohol is selected from one or more of methanol, ethanol, or isopropanol.

[0008] Furthermore, after adding pure water to the boron carbide-organotitanium compound slurry to carry out the hydrolysis reaction completely, stirring is continued for a predetermined time to obtain the hydrolyzed solution. The hydrolyzed solution was then vacuum filtered to obtain a filter cake. The filter cake was dried in an oven at 65-95 ℃ for 12-24 h to obtain the boron carbide-titanium dioxide precursor.

[0009] Furthermore, the boron carbide-titanium dioxide precursor is a core-shell structure in which boron carbide is coated with titanium dioxide.

[0010] Furthermore, the conditions for in-situ calcination are: 1000~1500 ℃, held at a vacuum or inert atmosphere for 0.5~3 hours.

[0011] In a second embodiment of the present invention, a boron carbide-titanium diboride composite powder is prepared by the method described above, wherein the titanium diboride in the boron carbide-titanium diboride composite powder is uniformly composited on the surface of the boron carbide powder, and wherein the molar ratio of the titanium diboride to the boron carbide is 1~5:2.7~24.

[0012] Furthermore, the boron carbide-titanium diboride composite powder has a particle size of 2~6 μm and a specific surface area of ​​5~13 m². 2 / g.

[0013] In a third embodiment of the present invention, a boron carbide-titanium diboride composite ceramic is provided, the raw material components of which include boron carbide-titanium diboride composite powder obtained by the above preparation method or the above boron carbide-titanium diboride composite powder.

[0014] Furthermore, the bulk density of the boron carbide-titanium diboride composite ceramic is 2.63~3.03 g / cm³. 3 It has a relative density of 99%~99.8%, a flexural strength of 727~955 MPa, and a fracture toughness of 5.34~6.9 MPa·m. 0.5 Its Vickers hardness is 33~36 GPa.

[0015] In the fourth embodiment of the present invention, a method for preparing the boron carbide-titanium diboride composite ceramic as described above is provided, comprising: The boron carbide-titanium diboride ceramic powder was sieved. The sieved boron carbide-titanium diboride ceramic powder is transferred into a graphite mold and hot-pressed and sintered to obtain boron carbide-titanium diboride composite ceramic.

[0016] Furthermore, the hot pressing sintering conditions are: 1900~1950 ℃, 20~60MPa hot pressing sintering, holding at the temperature for 30~60 min and then naturally cooling down.

[0017] The technical effects and advantages of this invention are as follows: This invention uses an organotitanium compound as a TiO2 precursor. The precursor is prepared by hydrolysis and composite with boron carbide to form a boron carbide-titanium dioxide (B4C-TiO2) precursor. This precursor is then reacted in situ under vacuum conditions to obtain boron carbide-titanium diboride (B4C-TiB2) composite powder. This powder is then ball-milled, dispersed, and sieved, and hot-pressed to prepare boron carbide-titanium diboride composite ceramics with high density, few cross-sectional defects, and excellent mechanical properties. The innovation of this invention lies in using an organotitanium compound to hydrolyze and obtain the TiO2 precursor, which simultaneously coats the surface of the boron carbide powder, forming a well-bonded coating layer structure. Through vacuum calcination, a highly active B4C-TiB2 composite powder is synthesized in situ. This process not only removes oxygen from the raw materials but also minimizes the impact of volatile gases (CO) on density and flexural strength during hot-pressing sintering.

[0018] This invention uses the tetrabutyl titanate hydrolysis method to prepare B4C-TiO2 precursor, and converts the powder into B4C-TiB2 composite powder by high-temperature calcination. Then, the powder is ball-milled and dispersed and hot-pressed and sintered to achieve uniform dispersion of TiB2 particles and a significant improvement in performance.

[0019] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description and the drawings. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of boron carbide powder provided in an embodiment of this application; Figure 2a This is a scanning electron microscope image of the boron carbide-titanium dioxide precursor in Example 1 provided in this application; Figure 2b These are two scanning electron microscope images of the boron carbide-titanium dioxide precursor in Example 1 provided in this application; Figure 3 This is a scanning electron microscope image of boron carbide-titanium diboride in Example 1 provided in this application; Figure 4a This is a transmission scanning electron microscope (TEM) image of boron carbide-titanium diboride in Example 1 provided in this application. Figure 4b This is provided by the embodiments of this application. Figure 4a Mapping of B corresponding to the transmission scan of boron carbide-titanium diboride; Figure 4c This is provided by the embodiments of this application. Figure 4a The mapping diagram of C corresponding to the transmission scan of boron carbide-titanium diboride; Figure 4d This is provided by the embodiments of this application. Figure 4a The mapping diagram of Ti corresponding to the boron carbide-titanium diboride transmission scanning pattern; Figure 5 This is the cross-sectional backscatter scanning electron microscope morphology of the boron carbide-titanium diboride composite ceramic in Example 1 provided in this application; Figure 6 These are the phase XRD patterns of the composite ceramics after hot pressing and sintering in Examples 1-4 of this application; Figure 7 This is the cross-sectional backscatter scanning electron microscope morphology of the boron carbide-titanium diboride composite ceramic in Example 2 provided in this application; Figure 8 This is the cross-sectional backscatter scanning electron microscope morphology of the boron carbide-titanium diboride composite ceramic in Example 3 provided in this application; Figure 9 This is the cross-sectional backscatter scanning electron microscope morphology of the boron carbide-titanium diboride composite ceramic in Comparative Example 1 provided in this application; Figure 10 This is the cross-sectional backscatter scanning electron microscope morphology of the boron carbide-titanium diboride composite ceramic in Comparative Example 2 provided in this application; Figure 11 This is the cross-sectional backscatter scanning electron microscope morphology of the boron carbide-titanium diboride composite ceramic in Comparative Example 3 provided in this application. Figure 12 This is the cross-sectional backscatter scanning electron microscope morphology of the boron carbide-titanium diboride composite ceramic in Comparative Example 4 provided in this application. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] To address the shortcomings of existing technologies, this invention discloses a method for preparing boron carbide-titanium diboride composite powder, the method comprising: Step 1: The organotitanium compound and boron carbide are uniformly dispersed in an organic solvent to obtain a boron carbide-organotitanium compound slurry; wherein the boron carbide has a particle size of 2~5μm and a specific surface area of ​​5~9 m². 2 / g; the organotitanium compound is selected from one or more of tetrabutyl titanate, tetramethyl titanate, tetraethyl titanate, and tetraisopropyl titanate; the organic solvent is selected from one or more of lower alcohols, toluene, or tetrahydrofuran; the lower alcohol is selected from one or more of methanol, ethanol, or isopropanol.

[0023] Step 2: After the hydrolysis reaction is complete by adding pure water to the boron carbide-organotitanium compound slurry, the mixture is filtered and dried to obtain the boron carbide-titanium dioxide precursor; the molar ratio of the organotitanium compound, boron carbide and water is 1~5:2.7~24:1~5. Step 3: After in-situ calcination of the boron carbide-titanium dioxide precursor, boron carbide-titanium diboride ceramic powder is obtained.

[0024] In a specific embodiment of the present invention, for step 1: the organotitanium compound and boron carbide are uniformly dispersed in an organic solvent to obtain a boron carbide-organotitanium compound slurry; by obtaining a uniformly dispersed boron carbide-organotitanium compound slurry through this step, the hydrolysis products are uniformly coated on the surface of the boron carbide particles.

[0025] The specific operating steps are as follows: Step 101: The organotitanium compound is uniformly dispersed in a first organic solvent to obtain an organotitanium compound solution. The uniformly dispersed organotitanium compound solution is a clear, pale yellow solution. For example, the uniform dispersion method in this step includes stirring, sonication, etc.

[0026] Step 102: Add boron carbide ( Figure 1The boron carbide slurry is uniformly dispersed in a second organic solvent to obtain a boron carbide slurry. Exemplarily, the uniform dispersion method in this step includes stirring, ultrasonication, ball milling, sand milling, etc. For example, ball milling is used to uniformly disperse boron carbide in a second organic solvent to obtain a boron carbide slurry, including: adding boron carbide and a second organic solvent to a ball milling jar for ball milling, with a ball-to-material ratio of 4~10:1; filtering the discharged material after ball milling to obtain the boron carbide slurry.

[0027] Step 103: After uniformly mixing the organotitanium compound solution and the boron carbide slurry, a boron carbide-organotitanium compound slurry is obtained. Exemplary methods for uniform dispersion in this step include stirring, ultrasonication, ball milling, and sand milling.

[0028] The first organic solvent and the second organic solvent may be the same or different; the first organic solvent is selected from one or more of lower alcohols, toluene, or tetrahydrofuran; the second organic solvent is selected from one or more of lower alcohols, toluene, or tetrahydrofuran; the lower alcohol is selected from one or more of methanol, ethanol, or isopropanol.

[0029] In a specific embodiment of the present invention, the purpose of steps 101-103 is to uniformly disperse the organotitanium compound solution and the boron carbide slurry. To further achieve uniform dispersion of the raw materials, the method of this application may also perform filtration after uniform dispersion in each step to remove large particles in the organotitanium compound solution, boron carbide slurry or boron carbide-organotitanium compound slurry.

[0030] In a specific embodiment of the present invention, for step 2: after adding pure water to the boron carbide-organotitanium compound slurry to carry out the hydrolysis reaction completely, the mixture is filtered and dried to obtain the boron carbide-titanium dioxide precursor, specifically: Step 201: After the hydrolysis reaction is complete by adding pure water to the boron carbide-organotitanium compound slurry at a dropping rate of 5-10 ml / min, continue stirring for a predetermined time to obtain the hydrolyzed solution; for example, a peristaltic pump is used to add pure water at a rate of 5-10 ml / min. During this process, the organotitanium compound undergoes a hydrolysis reaction with water, and the product after the hydrolysis reaction is uniformly coated on the surface of the boron carbide by controlling the dropping rate of water.

[0031] Step 202: Vacuum filter the reacted solution to obtain a filter cake; Step 203: Place the filter cake in an oven and dry at 65~95℃ for 12~24h to obtain the boron carbide-titanium dioxide precursor. Figure 2a , Figure 2b The boron carbide-titanium dioxide precursor is a core-shell structure in which boron carbide is coated with titanium dioxide; the particle size of the boron carbide-titanium dioxide precursor is 3-6 μm, and the specific surface area is 90-125 m².2 / g.

[0032] In a specific embodiment of the present invention, for step 3: the in-situ calcination conditions are: 1000~1500 ℃, held at this temperature for 0.5~3 hours under vacuum or inert atmosphere (e.g., argon or helium) protection. For example, to prevent powder from scattering during vacuum or ventilation, contaminating the furnace and causing equipment damage, the dried filter cake can be crushed through a 50-mesh sieve and then dry-pressed into blocks using a tablet press. This not only increases the amount of calcined powder, thereby improving production efficiency, but also prevents powder from scattering in the calcination furnace during the calcination process.

[0033] Boron carbide-titanium diboride composite powder is prepared by the method of the present invention. In the boron carbide-titanium diboride composite powder, titanium diboride is uniformly composited on the surface of boron carbide matrix, wherein the molar ratio of titanium diboride to boron carbide is 1~5:2.7~24.

[0034] The boron carbide-titanium diboride composite powder has a particle size of 2~6μm and a specific surface area of ​​5~13 m². 2 / g.

[0035] This invention also provides a boron carbide-titanium diboride composite ceramic, the raw material of which includes boron carbide-titanium diboride composite powder obtained by the preparation method of this invention, wherein the bulk density of the boron carbide-titanium diboride composite ceramic is 2.63~3.03 g / cm³. 3 It has a relative density of 99%~99.8%, a flexural strength of 727~955 MPa, and a fracture toughness of 5.34~6.9 MPa·m. 0.5 Its Vickers hardness is 33~36 GPa.

[0036] The preparation method of the boron carbide-titanium diboride composite ceramic includes the following steps: The boron carbide-titanium diboride ceramic powder is sieved, preferably through a sieve of 100-200 mesh. The purpose is to break up agglomerated powder or soft agglomerates and avoid agglomeration and internal defects caused by uneven pressing of large powder pieces. The sieved boron carbide-titanium diboride ceramic powder was transferred into a graphite mold and hot-pressed to obtain boron carbide-titanium diboride composite ceramic. The hot-pressing conditions were: 1850~1950 ℃, 20~60MPa, and then held at that temperature for 30~60 min before natural cooling.

[0037] This invention uses the hydrolysis of organic titanium compounds and boron carbide powder to prepare boron carbide-titanium dioxide precursor. The precursor is then reacted in situ under vacuum conditions to obtain boron carbide-titanium diboride composite powder. The boron carbide-titanium diboride composite powder is then ball-milled, dispersed, and sieved. Finally, a boron carbide-titanium diboride composite ceramic with high density, few cross-sectional defects, and excellent mechanical properties is prepared by hot pressing and sintering process.

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0039] Example 1 Weigh 152.2 g of tetrabutyl titanate solution and pour it into anhydrous ethanol solvent, stirring until a clear, pale yellow solution is obtained. Then weigh boron carbide (particle size D). 50 300g of boron carbide powder (2.1μm, 97.8% purity) was poured into a ball mill jar and ball-milled at a ball-to-powder ratio of 5:1 for 2 hours using ethanol solvent. After ball milling, the output was filtered through a 200-mesh filter. The boron carbide slurry was poured into a tetrabutyl titanate ethanol solution and stirred for 1 hour. 60g of pure water was added using a peristaltic pump at a dropping rate of 5ml / min to completely hydrolyze the tetrabutyl titanate. Stirring continued for 2 hours. The solvent was removed by vacuum filtration, and the filter cake was dried in an oven at 75℃ for 24 hours to obtain the boron carbide-titanium dioxide precursor. Figure 2a and 2b As shown in the figure, the surface of boron carbide is uniformly coated with titanium dioxide produced after hydrolysis. The dried filter cake (boron carbide-titanium dioxide precursor) was crushed and passed through a 50-mesh sieve. It was first dry-pressed into blocks using a tablet press, and then calcined in a vacuum furnace at 1300℃ for 1 hour to obtain boron carbide-titanium diboride composite powder, such as... Figure 3 As shown, according to Figure 3 It can be seen that titanium dioxide coated on the surface of boron carbide is converted into titanium diboride in situ, and titanium diboride is uniformly distributed on the surface of boron carbide. Boron carbide-titanium diboride composite powder was dispersed by ball milling, dried by rotary evaporation, crushed and passed through a 200-mesh sieve, transferred into a graphite mold, and sintered by hot pressing at 1950℃-30MPa. After holding at the temperature for 40 minutes, it was naturally cooled to obtain boron carbide-titanium diboride composite ceramic.

[0040] Figure 1 Here is a scanning electron microscope (SEM) image of boron carbide powder, combined with... Figure 2a and 2b The scanning electron microscope (SEM) image of the boron carbide-titanium dioxide precursor in Example 1 is shown. As can be seen from the image, the product after hydrolysis of tetrabutyl titanate is coated on the surface of B4C, and the coating layer is about 30-50 nm thick.

[0041] Figure 3The image shows a scanning electron microscope (SEM) image of the boron carbide-titanium diboride composite powder in Example 1. The image shows that during calcination, TiO2 reacts in situ to form nano-TiB2 fine grains that are uniformly distributed within the B4C powder. Combined with... Figures 4a-4d Transmission electron microscopy (TEM) images and mapping diagrams of boron carbide-titanium diboride composite powders were obtained, further revealing that fine TiB2 nanoparticles are uniformly distributed in the B4C powder, with a particle size of 20-40 nm.

[0042] Figure 5 The cross-sectional backscatter scanning electron microscope morphology of the boron carbide-titanium diboride composite ceramic prepared in Example 1 is shown. The white particles in the figure are TiB2 phase with a narrow particle size distribution (1~3μm) and are uniformly dispersed in the boron carbide matrix.

[0043] Table 1

[0044] Table 1 shows the particle size and specific surface area of ​​the powders prepared at different stages. According to Table 1, the increase in specific surface area of ​​the boron carbide-titanium dioxide precursor powder prepared after hydrolysis of tetrabutyl titanate is attributed to the loose colloidal structure of the TiO2 layer coating the surface of B4C particles. However, the specific surface area of ​​the boron carbide-titanium diboride composite powder after calcination is not significantly increased compared to that of B4C, indicating that the porous and loose structure of the hydrolysis product TiO2 is transformed into dispersed nanocrystalline TiB2 particles.

[0045] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 2.63 g / cm³. 3 With a relative density of 99.3%, its three-point bending strength, fracture toughness, and hardness are 727 MPa, 5.34 MPa·m, and 1, respectively. 0.5 33.1 GPa.

[0046] Example 2 Weigh 315.5g of tetrabutyl titanate solution and pour it into anhydrous ethanol solvent, stirring until a clear, pale yellow solution is obtained. Then weigh boron carbide (particle size D). 50300g of boron carbide powder (2.8μm, purity 98.3%) was poured into a ball mill jar and ball-milled at a ball-to-powder ratio of 5:1 for 3 hours using ethanol solvent. After ball milling, the output was filtered through a 200-mesh filter. The boron carbide slurry was poured into a tetrabutyl titanate ethanol solution and stirred for 2 hours. 120g of pure water was added using a peristaltic pump at a dropping rate of 6ml / min to completely hydrolyze the tetrabutyl titanate. After stirring for another 2 hours, the solvent was removed by vacuum filtration. The filter cake was placed in an oven and dried at 75℃ for 24 hours to obtain the boron carbide-titanium dioxide precursor. The dried filter cake was crushed and passed through a 50-mesh sieve. It was first pressed into blocks using a tablet press, and then calcined in a vacuum furnace at 1400 ℃ for 1 hour to obtain boron carbide-titanium diboride composite powder. The calcined boron carbide-titanium diboride composite powder was ball-milled and dispersed, dried by rotary evaporation, crushed and passed through a 200-mesh sieve, transferred into a graphite mold, and hot-pressed and sintered at 1950℃-30MPa. After holding at the temperature for 30 minutes, it was naturally cooled to obtain boron carbide-titanium diboride composite ceramic.

[0047] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 2.76 g / cm³. 3 With a relative density of 99.5%, its three-point bending strength, fracture toughness, and hardness are 860 MPa, 5.49 MPa·m, and 1, respectively. 0.5 33.8 GPa.

[0048] Example 3 Weigh 491.3 g of tetrabutyl titanate solution and pour it into anhydrous ethanol solvent, stirring until a clear, pale yellow solution is obtained. Then weigh boron carbide (particle size D). 50 300g of boron carbide powder (2.1μm, purity 97.8%) was poured into a ball mill jar and ball-milled at a ball-to-powder ratio of 5:1 for 4 hours using ethanol solvent. After ball milling, the output was filtered through a 200-mesh filter. The boron carbide slurry was poured into a tetrabutyl titanate ethanol solution and stirred for 2 hours. 150g of pure water was added by a peristaltic pump to completely hydrolyze the slurry. After stirring for another 3 hours, the solvent was removed by vacuum filtration. The filter cake was then placed in an oven and dried at 75°C for 24 hours to obtain the boron carbide-titanium dioxide precursor. The dried filter cake was crushed and passed through a 50-mesh sieve. It was first pressed into blocks using a tablet press, and then calcined in a vacuum furnace at 1500 ℃ for 0.5 h to obtain boron carbide-titanium diboride composite powder. The calcined boron carbide-titanium diboride composite powder was ball-milled and dispersed, dried by rotary evaporation, crushed and passed through a 200-mesh sieve, transferred into a graphite mold, and hot-pressed and sintered at 1930 ℃-30 MPa. After holding at the temperature for 30 min, it was naturally cooled to obtain boron carbide-titanium diboride composite ceramic.

[0049] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 2.91 g / cm³. 3 With a relative density of 99.4%, its three-point bending strength, fracture toughness, and hardness are 934 MPa, 6.5 MPa·m, and 934 MPa, 6.5 MPa·m, respectively.0.5 33.4 GPa.

[0050] Example 4 Weigh 342.17 g of tetramethyl titanate solution and pour it into anhydrous ethanol solvent, stirring until a clear, pale yellow solution is obtained. Then weigh boron carbide (particle size D). 50 300g of boron carbide powder (2.8μm, purity 98.3%) was poured into a ball mill jar and ball-milled at a ball-to-powder ratio of 5:1 for 4 hours using ethanol solvent. After ball milling, the output was filtered through a 200-mesh filter. The boron carbide slurry was poured into a tetramethyl titanate ethanol solution and stirred for 2 hours. 160g of pure water was added using a peristaltic pump to completely hydrolyze the slurry. After stirring for another 5 hours, the solvent was removed by vacuum filtration. The filter cake was then placed in an oven and dried at 75 ℃ for 24 hours to obtain the boron carbide-titanium dioxide precursor. The dried filter cake was crushed and passed through a 50-mesh sieve. It was first pressed into blocks using a tablet press, and then calcined in a vacuum furnace at 1500 ℃ for 0.5 h to obtain boron carbide-titanium diboride composite powder. The calcined boron carbide-titanium diboride composite powder was ball-milled and dispersed, dried by rotary evaporation, crushed and passed through a 100-mesh sieve, transferred into a graphite mold, and hot-pressed and sintered at 1930 ℃-30 MPa. After holding at the temperature for 30 min, it was naturally cooled to obtain boron carbide-titanium diboride composite ceramic.

[0051] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 3.03 g / cm³. 3 With a relative density of 99.6%, its three-point bending strength, fracture toughness, and hardness are 955 MPa, 6.9 MPa·m, and 955 MPa, respectively. 0.5 34 GPa.

[0052] Example 5 Weigh 159.3 g of tetramethyl titanate solution and pour it into anhydrous ethanol solvent, stirring until a clear, pale yellow solution is obtained. Then weigh boron carbide (particle size D). 50 300g of boron carbide powder (2.8μm, purity 98.3%) was poured into a ball mill jar and ball-milled at a ball-to-powder ratio of 5:1 for 3 hours using ethanol solvent. After ball milling, the output was filtered through a 200-mesh filter. The boron carbide slurry was poured into a tetramethyl titanate ethanol solution and stirred for 2 hours. 120g of pure water was added using a peristaltic pump at a dropping rate of 5ml / min to completely hydrolyze the solution. After stirring for another 2 hours, the solvent was removed by vacuum filtration. The filter cake was then placed in an oven and dried at 75℃ for 24 hours to obtain the boron carbide-titanium dioxide precursor. The dried filter cake was crushed and passed through a 50-mesh sieve. It was first pressed into blocks using a tablet press, and then calcined in a vacuum furnace at 1400 ℃ for 1 hour to obtain boron carbide-titanium diboride composite powder. The calcined boron carbide-titanium diboride composite powder was ball-milled and dispersed, dried by rotary evaporation, crushed and passed through a 200-mesh sieve, transferred into a graphite mold, and hot-pressed and sintered at 1930℃-30 MPa. After holding at the temperature for 30 minutes, it was naturally cooled to obtain boron carbide-titanium diboride composite ceramic.

[0053] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 2.758 g / cm³. 3 With a relative density of 99.6%, its three-point bending strength, fracture toughness, and hardness are 848 MPa, 5.29 MPa·m, and 1, respectively. 0.5 33.4 GPa.

[0054] Example 6 Weigh 328.4 g of tetraethyl titanate solution and pour it into anhydrous ethanol solvent, stirring until a clear, pale yellow solution is obtained. Then weigh boron carbide (particle size D). 50 300g of boron carbide powder (2.1μm, purity 97.8%) was poured into a ball mill jar and ball-milled at a ball-to-powder ratio of 5:1 for 4 hours using ethanol solvent. After ball milling, the output was filtered through a 200-mesh filter. The boron carbide slurry was poured into a tetraethyl titanate ethanol solution and stirred for 2 hours. 170g of pure water was added by a peristaltic pump to completely hydrolyze the slurry. After stirring for another 3 hours, the solvent was removed by vacuum filtration. The filter cake was then placed in an oven and dried at 75°C for 24 hours to obtain the boron carbide-titanium dioxide precursor. The dried filter cake was crushed and passed through a 50-mesh sieve. It was first pressed into blocks using a tablet press, and then calcined in a vacuum furnace at 1500 ℃ for 0.5 h to obtain boron carbide-titanium diboride composite powder. The calcined boron carbide-titanium diboride composite powder was ball-milled and dispersed, dried by rotary evaporation, crushed and passed through a 200-mesh sieve, transferred into a graphite mold, and hot-pressed and sintered at 1930 ℃-30 MPa. After holding at the temperature for 30 min, it was naturally cooled to obtain boron carbide-titanium diboride composite ceramic.

[0055] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 2.923 g / cm³. 3 With a relative density of 99.1%, its three-point bending strength, fracture toughness, and hardness are 932 MPa, 6.7 MPa·m, and 932 MPa, respectively. 0.5 33.0 GPa.

[0056] Figure 6The XRD phase diagrams of the boron carbide composite ceramics after hot pressing and sintering in Examples 1-4 are shown. The diagrams reveal that the hot-pressed and sintered phases consist only of boron carbide and titanium diboride, with no other impurities. Furthermore, the titanium dioxide content in the precursor for the boron carbide-titanium dioxide composite powder prepared by hydrolysis in this invention ranges from 0 to 40 wt%, with titanium diboride loading of 10% in Example 1, 20% in Example 2, 30% in Example 3, and 40% in Example 4. Based on the mechanical property tests corresponding to Examples 1-6, it is evident that the mechanical properties of the boron carbide-titanium diboride composite ceramics increase sequentially with increasing TiO2 content, indicating that TiB2 is an excellent and highly efficient reinforcing and toughening additive for boron carbide ceramics.

[0057] Figures 7-8 The images show the cross-sectional backscattered electron microscopy (SEM) morphology of the boron carbide-titanium diboride composite ceramics prepared in Examples 2 and 3. The white particles in the images represent the TiB2 phase, and the particle size distribution is narrow, indicating uniform dispersion within the boron carbide matrix without significant coarse particle formation or agglomeration. The excellent particle dispersibility is primarily due to the uniform dispersion preparation method of the powder. This also demonstrates that the boron carbide-titanium dioxide composite powder precursor obtained by the hydrolysis method employed in this invention possesses excellent dispersibility, thus avoiding the potential decrease in material mechanical properties caused by the agglomeration of titanium diboride at high content.

[0058] Comparative Example 1 Comparative Example 1 was prepared by directly sieving the precursor product after hydrolysis and placing it into a graphite mold based on Example 2. The product was then hot-pressed and sintered at 1950℃-30 MPa and held at that temperature for 30 minutes before naturally cooling to obtain boron carbide-titanium diboride composite ceramic.

[0059] Figure 9 The cross-sectional backscattered electron microscope morphology of the boron carbide-titanium diboride composite ceramic prepared in Comparative Example 1 is shown. The white particles are TiB2 phase, and agglomerates are present. On the one hand, agglomerates lead to stress concentration in the material; on the other hand, since the thermal expansion coefficient of TiB2 is very different from that of B4C, microcracks are easily formed at its interface, which leads to a decrease in the performance of the ceramic.

[0060] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 2.725 g / cm³. 3 With a relative density of 99.0%, its three-point bending strength, fracture toughness, and hardness are 638 MPa, 5.14 MPa·m, and 100 MPa·m, respectively. 0.5 32.5 GPa.

[0061] Comparative Example 2 Weigh out boron carbide powder (particle size D) 50200g of TiB2 (particle size D: 2.8μm, purity 98.3%) and TiB2 (particle size D: 2.8μm, purity 98.3%) 50 50g of boron carbide-titanium diboride composite ceramic was obtained by mixing boron carbide with a particle size of 4~7μm and a purity of 97% and placing it into a ball mill jar with a ball-to-material ratio of 5:1. 500g of ethanol solvent was added and the mixture was ball-milled for 6 hours. After discharge, the mixture was filtered through a 200-mesh filter and dried using a rotary evaporator to remove the solvent. The obtained powder was then placed in an oven and dried at 65 ℃ for 2 hours. After drying, the powder was passed through a 200-mesh sieve and transferred into a graphite mold. The mixture was then hot-pressed and sintered at 1950℃-30 MPa and held at that temperature for 30 minutes before naturally cooling. Figure 10 The cross-sectional backscattered electron microscopy morphology of the boron carbide-titanium diboride composite ceramic prepared in Comparative Example 2 is shown. The white particles are TiB2 phase, with a wide particle size distribution and large grain size.

[0062] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 2.73 g / cm³. 3 With a relative density of 98.9%, its three-point bending strength, fracture toughness, and hardness are 593 MPa, 5.37 MPa·m, and 5.37 MPa·m, respectively. 0.5 , 33.3GPpa.

[0063] Comparative Example 3 Weigh 315.5g of tetrabutyl titanate solution and pour it into anhydrous ethanol solvent, stirring until a clear, pale yellow solution is obtained. Then weigh boron carbide (particle size D). 50 300g of boron carbide powder (0.8μm, purity 97.5%) was poured into a ball mill jar and ball-milled at a ball-to-powder ratio of 5:1 for 3 hours using ethanol solvent. After ball milling, the output was filtered through a 200-mesh filter. The boron carbide slurry was poured into a tetrabutyl titanate ethanol solution and stirred for 2 hours. 30g of pure water was added using a peristaltic pump to completely hydrolyze the boron carbide, and stirring was continued for 2 hours. The solvent was removed by vacuum filtration, and the filter cake was placed in an oven and dried at 75℃ for 24 hours to obtain the boron carbide-titanium dioxide precursor. The dried filter cake was crushed and passed through a 50-mesh sieve. It was first pressed into blocks using a tablet press, and then calcined in a vacuum furnace at 1300 ℃ for 1 hour to obtain boron carbide-titanium diboride composite powder. The calcined boron carbide-titanium diboride composite powder was ball-milled and dispersed, dried by rotary evaporation, crushed and passed through a 200-mesh sieve, transferred into a graphite mold, and hot-pressed and sintered at 1950 ℃-30 MPa. After holding at the temperature for 30 minutes, it was naturally cooled to obtain boron carbide-titanium diboride composite ceramic. Figure 11 The cross-sectional backscattered electron microscopy morphology of the boron carbide-titanium diboride composite ceramic prepared in Comparative Example 3 is shown. The white particles are TiB2 phase, and the particle size distribution is widened, with larger grain size appearing.

[0064] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 2.72 g / cm³. 3With a relative density of 98.5%, its three-point bending strength, fracture toughness, and hardness are 711 MPa, 4.31 MPa·m, and 4.31 MPa·m, respectively. 0.5 32.3 GPa.

[0065] Comparative Example 4 Weigh out boron carbide powder (particle size D) 50 200g of 2.8μm (purity 98.3%) and TiO2 (particle size D) 50 94g of boron carbide-titanium diboride composite powder (100nm, 99% purity) was poured into a ball mill jar at a ball-to-powder ratio of 5:1. 400g of ethanol solvent was added and the powder was ball-milled for 4 hours. After discharge, the powder was filtered through a 200-mesh filter and dried using a rotary evaporator to remove the solvent. The resulting powder was then dried in an oven at 65°C for 12 hours. After being removed, the powder was crushed and passed through a 50-mesh sieve. The powder was first pressed into blocks using a tablet press and then calcined in a vacuum furnace at 1400°C for 40 minutes to obtain boron carbide-titanium diboride composite powder. The calcined boron carbide-titanium diboride composite powder was then ball-milled and dispersed, dried by rotary evaporation, crushed and passed through a 200-mesh sieve, transferred into a graphite mold, and hot-pressed at 1950°C -30 MPa. After holding at the temperature for 30 minutes, the powder was allowed to cool naturally to obtain boron carbide-titanium diboride composite ceramic. Figure 12 The cross-sectional backscattered electron microscope morphology of the boron carbide-titanium diboride composite ceramic prepared in Comparative Example 4 is shown. The white particles are TiB2 phase with a wide particle size distribution. A small number of pores and interconnected TiB2 grains are observed in the cross-section.

[0066] The bulk density of the boron carbide-titanium diboride composite ceramic, determined using Archimedes' displacement method, was 2.89 g / cm³. 3 With a relative density of 98.7%, its three-point bending strength, fracture toughness, and hardness are 624 MPa, 4.72 MPa·m, and 1, respectively. 0.5 32.4 GPa.

[0067] Table 2

[0068] As shown in Table 2, the difference between Comparative Example 1 and Example 2 is that the boron carbide-titanium dioxide precursor was not calcined in Comparative Example 1, which directly hot-pressed the boron carbide-titanium dioxide precursor to obtain the boron carbide-titanium diboride composite ceramic. According to the test data of the boron carbide-titanium diboride composite ceramic in Comparative Example 1, its bending strength, fracture toughness, and hardness are all lower than those in Example 1. This indicates that calcination converts TiO2 into TiB2 in situ, reducing the influence of volatile gases on high-temperature densification during hot-pressing sintering. At the same time, after calcination, the composite TiB2 particles are dispersed, reducing the contact area between TiB2 particles and avoiding rapid growth and agglomeration of TiB2 particles at high temperatures.

[0069] Compared with Example 2, Comparative Example 2 differs in that the boron carbide-titanium diboride composite powder generated in situ in Example 2 is used. The composite ceramic prepared using the boron carbide-titanium diboride composite powder generated in situ has higher three-point bending strength, fracture toughness and hardness than the composite ceramic prepared by ordinary titanium diboride and boron carbide mixture (prepared in Comparative Example 2).

[0070] Compared with Example 2, Comparative Example 3 differs in the particle size of the boron carbide powder. A finer boron carbide raw material is used. The boron carbide particle size in Comparative Example 3 is 0.8 μm, while the boron carbide particle size in Example 2 is 2.8 μm. Due to the increase in the specific surface area of ​​the powder, the contact area of ​​the titanium diboride particles on the surface of the powder increases after calcination. During the high-temperature and high-pressure sintering process, the titanium diboride particles in contact with each other are more likely to grow at the grain boundaries, resulting in larger grain size and a decrease in the performance of the ceramic material.

[0071] Compared with Example 3, Comparative Example 4 differs in that the boron carbide-titanium dioxide precursor is prepared by hydrolysis and the boron carbide and titanium dioxide are mixed by direct ball milling. Due to the large specific surface area of ​​nano-titanium dioxide and the nano-sized grains, self-agglomeration is likely to occur at high content, and the viscosity of the slurry increases rapidly after mixing, which is not conducive to the uniform dispersion of the slurry.

[0072] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing boron carbide-titanium diboride composite powder, characterized in that, The method includes: The organotitanium compound and boron carbide were uniformly dispersed in an organic solvent to obtain a boron carbide-organotitanium compound slurry. After the hydrolysis reaction is complete by adding pure water to the boron carbide-organotitanium compound slurry, the mixture is filtered and dried to obtain the boron carbide-titanium dioxide precursor. The boron carbide-titanium dioxide precursor was calcined in situ to obtain boron carbide-titanium diboride composite powder.

2. The method for preparing boron carbide-titanium diboride composite powder according to claim 1, characterized in that, Boron carbide has a particle size of 2–5 μm and a specific surface area of ​​5–9 m². 2 / g; The molar ratio of organotitanium compounds, boron carbide, and water is 1~5:2.7~24:1~5.

3. The method for preparing boron carbide-titanium diboride composite powder according to claim 1, characterized in that, The organotitanium compound is selected from one or more of tetrabutyl titanate, tetramethyl titanate, tetraethyl titanate, and tetraisopropyl titanate; and / or, The organic solvent is selected from one or more of lower alcohols, toluene, or tetrahydrofuran; The lower alcohol is selected from one or more of methanol, ethanol, or isopropanol.

4. The method for preparing boron carbide-titanium diboride composite powder according to claim 1, characterized in that, After adding pure water to the boron carbide-organotitanium compound slurry and allowing the hydrolysis reaction to complete, continue stirring for a predetermined time to obtain the hydrolyzed solution. The hydrolyzed solution was then vacuum filtered to obtain a filter cake. The filter cake was dried in an oven at 65-95 ℃ for 12-24 h to obtain the boron carbide-titanium dioxide precursor.

5. The method for preparing boron carbide-titanium diboride composite powder according to claim 1, characterized in that, The boron carbide-titanium dioxide precursor is a core-shell structure in which boron carbide is coated with titanium dioxide.

6. The method for preparing boron carbide-titanium diboride composite powder according to claim 1, characterized in that, The conditions for in-situ calcination are: 1000~1500 ℃, and heat preservation for 0.5~3 hours under vacuum or inert atmosphere protection.

7. The boron carbide-titanium diboride composite powder obtained by the preparation method according to any one of claims 1-6, characterized in that, In the boron carbide-titanium diboride composite powder, titanium diboride is uniformly composited on the surface of boron carbide powder, wherein the molar ratio of titanium diboride to boron carbide is 1~5:2.7~24.

8. The boron carbide-titanium diboride composite powder according to claim 7, characterized in that, The boron carbide-titanium diboride composite powder has a particle size of 2~6μm and a specific surface area of ​​5~13 m². 2 / g.

9. A boron carbide-titanium diboride composite ceramic, characterized in that, Its raw material components include boron carbide-titanium diboride composite powder obtained by the preparation method according to any one of claims 1-6 or boron carbide-titanium diboride composite powder according to any one of claims 7-8.

10. The boron carbide-titanium diboride composite ceramic according to claim 9, characterized in that, The bulk density of the boron carbide-titanium diboride composite ceramic is 2.63~3.03 g / cm³. 3 It has a relative density of 99%~99.8%, a flexural strength of 727~955 MPa, and a fracture toughness of 5.34~6.9 MPa·m. 0.5 Its Vickers hardness is 33~36 GPa.

11. The method for preparing boron carbide-titanium diboride composite ceramics as described in claim 9 or 10, characterized in that, include: The boron carbide-titanium diboride ceramic powder was sieved. The sieved boron carbide-titanium diboride ceramic powder is transferred into a graphite mold and hot-pressed to obtain boron carbide-titanium diboride composite ceramic. The hot-pressing conditions are: 1900~1950 ℃, 20~60 MPa hot-pressing, and holding at the temperature for 30~60 min followed by natural cooling.

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