Carbon-boron double-phase high-entropy ceramic composite material and preparation method thereof

Abstract

The invention discloses a carbon-boron double-phase high-entropy ceramic composite material and a preparation method thereof, and belongs to the technical field of high-entropy ceramic materials.The preparation method comprises the steps that TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, B4C and carbon black serve as raw materials, and carbon-boron double-phase high-entropy ceramic composite powder is formed through a boron-carbon thermal reduction reaction; and then heating and sintering. When the double-phase high-entropy composite powder is prepared by adopting a boron / carbon thermal reduction method, the synthesis temperature has decisive influence on phase formation and grain size. Along with the rising of the synthesis temperature, the oxide phase in the composite powder is gradually reduced, and when the synthesis temperature reaches 1800 DEG C, the carbon-boron double-phase high-entropy composite powder composed of a high-entropy carbide phase (HEC) and a high-entropy boride phase (HEB) is formed. After the carbon-boron double-phase high-entropy composite powder is subjected to spark plasma sintering, the ceramic density is obviously improved along with the increase of the synthesis temperature of the composite powder.

Description

Technical Field

[0001] This invention relates to the field of high-entropy ceramic materials technology, specifically to a carbon-boron dual-phase high-entropy ceramic composite material and its preparation method. Background Technology

[0002] In recent years, the concept of "high entropy" has been gradually introduced into the field of ultra-high temperature ceramics (UHTCs), forming high-entropy ceramic systems such as high-entropy carbides (HECs), high-entropy borides (HEBs), and high-entropy nitrides (HENs), constituting a new and important branch of high-entropy structural ceramics. With its groundbreaking component design concept and multi-component synergistic effect, high-entropy structural ceramics exhibit excellent high-temperature stability, high hardness, oxidation resistance, and radiation resistance, attracting widespread attention in extreme environment applications such as thermal barrier coatings for aero-engines and radiation-resistant components for nuclear reactors.

[0003] However, the mechanical properties of single-phase high-entropy ceramics are limited by their simple structure and composition, making it difficult to achieve a synergistic improvement in hardness and fracture toughness. For example, the (Ti,Zr,Hf,Nb,Ta)C system reported in the prior art uses TiO2, ZrO2, HfO2, Nb2O5, and Ta2O5 as raw material oxides, and calcium hydride (CaH2) as a reducing agent, employing a low-temperature calcium hydride reduction method to prepare high-entropy carbide ceramics (Ti, Zr, Hf, Nb, Ta)C, although achieving 4.2 MPa·m 1 / 2 While exhibiting good fracture toughness, its Vickers hardness is only 20.4 GPa under a load of 4.9 N, and even lower (16.2 GPa) under a load of 49 N. The (Hf,Zr,Ta,Nb,Ti)B2 material developed by Xu et al. achieved densification of high-entropy diboride-based composite materials at relatively low temperatures through novel sintering techniques or sintering aid strategies. It achieved a hardness of 24.9 GPa under a load of 1.96 N, but its fracture toughness plummeted to 2.79 MPa·m. 1 / 2 . Summary of the Invention

[0004] This invention provides a carbon-boron dual-phase high-entropy ceramic composite material and its preparation method, which effectively solves the technical problem that existing single-phase high-entropy ceramics cannot simultaneously achieve fracture toughness and hardness. This invention prepares dual-phase high-entropy powders at different synthesis temperatures through a boron / carbothermal reduction method, and then obtains a carbon-boron dual-phase high-entropy ceramic composite material with uniform microstructure and better mechanical properties through spark plasma sintering.

[0005] The first objective of this invention is to provide a carbon-boron dual-phase high-entropy ceramic composite material. This material is produced under a protective atmosphere using equimolar amounts of TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, B4C, and carbon black as raw materials. The temperature is raised to 1600℃–1800℃, and a boron-carbothermic reduction reaction is carried out to form high-entropy ceramic composite powders containing carbide and boride phases. The powders are then subjected to programmed temperature sintering to obtain the carbon-boron dual-phase high-entropy ceramic composite material.

[0006] All the raw materials used in this invention were purchased from Shanghai Xiangtian Nanomaterials Co., Ltd.

[0007] In a preferred embodiment, the carbide phase is (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 C; the boride phase is (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2.

[0008] As a preferred embodiment, the (Ti) 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 The grain size of C is 0.225 μm to 0.93 μm, and the (Ti) 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 The grain size of B2 is 0.706μm~1.87μm.

[0009] The second objective of this invention is to provide a method for preparing the above-described carbon-boron dual-phase high-entropy ceramic composite material, comprising the following steps: Using equimolar amounts of TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, B4C, and carbon black as raw materials, a mixed powder was obtained by grinding.

[0010] Under a protective atmosphere, the mixed powder is heated to 1600℃~1800℃ and a boron-carbothermic reduction reaction is carried out to form a carbon-boron dual-phase high-entropy ceramic composite powder.

[0011] The carbon-boron dual-phase high-entropy ceramic composite powder was subjected to programmed temperature sintering to obtain a carbon-boron dual-phase high-entropy ceramic composite material.

[0012] In the above technical solutions, when the sintering temperature exceeds 1800℃, excessive grain growth occurs, leading to a decrease in mechanical properties. When the temperature is 1600℃ or 1700℃, the presence of unreacted oxide phases in the composite material results in insufficient density, which in turn reduces its mechanical properties, such as Vickers hardness and fracture toughness. However, the mechanical properties of the carbon-boron dual-phase high-entropy ceramic composite materials prepared at both temperature values ​​are still superior to those of the single-phase high-entropy ceramics disclosed in the prior art.

[0013] As a preferred embodiment, the programmed temperature rise sintering method is as follows: at 40 MPa, the carbon boron dual-phase high-entropy ceramic composite powder is heated to 1600°C at a rate of 100°C / min to 120°C / min, and then heated to 2000°C at a rate of 80°C / min to 100°C / min, and held at that temperature for 10 min to 20 min.

[0014] In a preferred embodiment, the heating rate is 3℃ / min to 5℃ / min during the process of heating to 1600℃~1800℃.

[0015] In a preferred embodiment, the boron-carbon thermal reduction reaction takes 1 hour.

[0016] As a preferred embodiment, before the programmed heating and sintering, the carbon-boron dual-phase high-entropy ceramic composite powder is cooled, ground, and passed through a 200-mesh sieve.

[0017] In a preferred embodiment, the grinding process specifically involves using zirconium oxide with a diameter of 8 mm to 10 mm as the grinding media, and grinding at a ball-to-material ratio of 3:1 at a speed of 600 rpm to 800 rpm for 10 to 12 hours.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: To address the technical problem that existing single-phase high-entropy ceramics cannot simultaneously achieve both fracture toughness and hardness, this invention proposes a method combining boron-carbothermic reduction and heated sintering to prepare a two-phase high-entropy ceramic composite material containing carbide (HEC) and boride (HEB) phases. By controlling the synthesis temperature, this invention optimizes the phase composition, grain size, and elemental distribution of the powder, ultimately achieving high densification and excellent mechanical properties in the ceramic bulk.

[0019] This invention optimizes the phase composition of dual-phase high-entropy ceramics by controlling the synthesis temperature. As the temperature increases, residual oxides in the powder gradually decrease until they are completely eliminated, resulting in a pure dual-phase structure of carbide and boride phases at 1800℃. The elimination of oxide impurities significantly improves the density of the sintered body, increasing the relative density from 95.6% to 99.7%. Simultaneously, it avoids the adverse effects of brittle oxides at grain boundaries on mechanical properties, fully leveraging the synergistic enhancement effect of the high hardness of the carbide phase and the high toughness of the boride phase. This results in an increase in Vickers hardness from 17.62 GPa to 20.93 GPa and fracture toughness from 3.2 MPa·m¹ / ² to 4.1 MPa·m¹ / ², exhibiting relatively good comprehensive mechanical properties. The performance improvement is mainly attributed to increased density and reduced porosity, thus achieving simultaneous optimization of hardness and toughness in dual-phase high-entropy ceramics. Attached Figure Description

[0020] Figure 1 The images show the XRD patterns of carbon-boron dual-phase high-entropy composite powders prepared at different synthesis temperatures in Examples 1 to 3 of this invention.

[0021] Figure 2 The images show the SEM images of carbon-boron dual-phase high-entropy composite powders prepared at different synthesis temperatures in Examples 1 to 3 of this invention, where a represents 1600℃, b represents 1700℃, and c represents 1800℃.

[0022] Figure 3 This is an EDS surface scan image of the carbon-boron dual-phase high-entropy composite powder prepared at 1800℃ in Example 3 of the present invention, where a is the surface scan point and b~h are the element distribution maps.

[0023] Figure 4 This is a spot scan image of the carbon-boron dual-phase high-entropy composite powder prepared at 1800℃ in Example 3 of the present invention, wherein a is the first scan point selection image, b is the element distribution image of each scan point in a, c is the second scan point selection image, and d is the element distribution image of each scan point in c.

[0024] Figure 5 These are high-resolution transmission electron micrographs of the carbide and boride phases in the carbon-boron dual-phase high-entropy composite powder prepared at 1800℃ in Example 3 of the present invention. Among them, a is a high-resolution TEM image of the carbide phase, b is a high-resolution TEM image of the boride phase, c is an electron diffraction image of the carbide grains, and d is an electron diffraction image of the boride grains.

[0025] Figure 6 The XRD patterns are of carbon-boron dual-phase high-entropy ceramic composite materials prepared in Examples 1 to 3 of this invention at different synthesis temperatures and under the same SPS sintering environment (i.e., 2000℃, 40MPa).

[0026] Figure 7 The images show the SEM microstructures of carbon-boron dual-phase high-entropy ceramic composites prepared at different synthesis temperatures and under the same SPS sintering conditions in Examples 1 to 3 of this invention, where a represents 1600℃, b represents 1700℃, and c represents 1800℃.

[0027] Figure 8 The two-phase grain size distribution diagrams of the carbon-boron dual-phase high-entropy ceramic composite material prepared using powder synthesized at a synthesis temperature of 1600℃ in Example 1 of the present invention are shown, where a is the grain size distribution diagram of the HEC phase and b is the grain size distribution diagram of the HEB phase.

[0028] Figure 9 The two-phase grain size distribution diagrams of the carbon-boron dual-phase high-entropy ceramic composite material prepared using powder synthesized at a synthesis temperature of 1700℃ in Example 2 of the present invention are shown, where a is the grain size distribution diagram of the HEC phase and b is the grain size distribution diagram of the HEB phase.

[0029] Figure 10 The two-phase grain size distribution diagrams of the carbon-boron dual-phase high-entropy ceramic composite material prepared using powder synthesized at a synthesis temperature of 1800℃ in Example 3 of the present invention are shown, where a is the grain size distribution diagram of the HEC phase and b is the grain size distribution diagram of the HEB phase.

[0030] Figure 11 The image shows an EDS surface scan of the carbon-boron dual-phase high-entropy ceramic composite material synthesized at 1800℃ and prepared by SPS sintering in Example 3 of the present invention. In the image, a is a surface scan and b~h are element distribution maps.

[0031] Figure 12 The image shows an EDS surface scan of the carbon-boron dual-phase high-entropy ceramic composite material synthesized at 1700℃ and prepared by SPS sintering in Example 2 of this invention. In the image, a is a surface scan, and b~h are element distribution maps.

[0032] Figure 13 The image shows an EDS surface scan of the carbon-boron dual-phase high-entropy ceramic composite material synthesized at 1600℃ and prepared by SPS sintering in Example 1 of this invention. In the image, a is a surface scan, and b~h are element distribution maps.

[0033] Figure 14 The images show the indentation cracks of carbon-boron dual-phase high-entropy ceramic composite material blocks synthesized at different temperatures and prepared by SPS sintering in Examples 1 to 3 of this invention, where a is 1600℃, b is 1700℃, and c is 1800℃. Detailed Implementation

[0034] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0035] Existing technology 1: Yudin S, Volodko S, Moskovskikh D, et al. Fabrication of high-entropy carbide ceramics (Ti,Zr,Hf,Nb,Ta)C through low-temperature calcium-hydride reduction of oxides. J Eur Ceram Soc 2023, 43: 5108-16. This prior art uses TiO2, ZrO2, HfO2, Nb2O5, and Ta2O5 as raw material oxides, and calcium hydride (CaH2) as a reducing agent, employing a low-temperature calcium hydride reduction method to prepare high-entropy carbide ceramics (Ti, Zr, Hf, Nb, Ta)C, achieving a strength of 4.2 MPa·m. 1 / 2 It has good fracture toughness, but its Vickers hardness is only 20.4 GPa under a load of 4.9 N, and even lower (16.2 GPa) under a load of 49 N.

[0036] Prior Art 2: Xu L, Guo WM, Zou J, et al. Low-temperature densification of high entropy diboride based composites with fine grains and excellent mechanical properties. Compos B Eng 2022, 247. The (Hf,Zr,Ta,Nb,Ti)B2 material developed by the above prior art achieves densification of high-entropy diboride-based composites at relatively low temperatures by employing novel sintering techniques or sintering aid strategies. Its hardness reaches 24.9 GPa under a 1.96 N load, but its fracture toughness drops sharply to 2.79 MPa·m. 1 / 2 To address the technical problem in existing technologies where single-phase high-entropy ceramics cannot simultaneously achieve both fracture toughness and hardness, this invention provides a carbon-boron dual-phase high-entropy ceramic composite material and its preparation method.

[0037] The technical solution of the present invention will be analyzed below.

[0038] This invention provides a carbon-boron dual-phase high-entropy ceramic composite material. The carbon-boron dual-phase high-entropy ceramic composite material is produced under a protective atmosphere using equimolar amounts of TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, B4C, and carbon black as raw materials. The temperature is raised to 1600℃~1800℃, and a boron-carbothermic reduction reaction is carried out to form high-entropy ceramic composite powders containing carbide and boride phases. The powders are then subjected to programmed temperature sintering to obtain the carbon-boron dual-phase high-entropy ceramic composite material.

[0039] In this invention, the synthesis temperature has a decisive influence on phase formation and grain size when preparing biphase high-entropy composite powder using the boron-carbothermic reduction method. As the synthesis temperature increases, the oxide phase in the composite powder gradually decreases. When the synthesis temperature reaches 1800℃, a carbon-boron biphase high-entropy composite powder composed of high-entropy carbide (HEC) and high-entropy boride (HEB) phases is formed. After spark plasma sintering, the ceramic density of the carbon-boron biphase high-entropy composite powder significantly increases with increasing synthesis temperature. The carbon-boron biphase high-entropy ceramic composite material prepared by sintering the composite powder synthesized at 1800℃ exhibits near-complete elimination of internal pores, a relative density close to the theoretical density, and a uniform microstructure. With increasing synthesis temperature of composite powders, the Vickers hardness and fracture toughness of carbon-boron dual-phase high-entropy ceramic composites both show an upward trend. Among them, the ceramic prepared at 1800℃ exhibits the best comprehensive mechanical properties, with a relative density of up to 99.7%, a Vickers hardness of 20.93 GPa under a load of 98 N, and a fracture toughness of 4.1 MPa·m. 1 / 2 It exhibits relatively good comprehensive mechanical properties, and its performance improvement is mainly attributed to increased density and decreased porosity.

[0040] The technical effects of the present invention will be described below with reference to specific embodiments and comparative examples.

[0041] Example 1 A method for preparing a carbon-boron dual-phase high-entropy ceramic composite material includes the following steps: S1. Using equimolar amounts of TiO2 (50nm, 99% purity), ZrO2 (50nm, 99% purity), HfO2 (50nm, 99% purity), Nb2O5 (50nm, 99% purity), Ta2O5 (50nm, 99% purity), B4C (50nm, 99% purity) and carbon black (50nm, 99% purity) as raw materials, the raw materials were mechanically mixed using a planetary ball mill with 10mm diameter zirconium oxide as the ball milling medium. The ball-to-material ratio was 3:1, and the mixture was ball-milled at 600 rpm for 12 hours to obtain a mixed powder.

[0042] S2, the mixed powder is placed in a high-temperature furnace and heated to 1600℃ under an argon atmosphere, and subjected to a boron-carbothermic reduction reaction for 1 hour to ensure complete reaction. After cooling to room temperature, it is ground using an agate mortar and passed through a 200-mesh sieve to obtain carbon-boron dual-phase high-entropy ceramic composite powder.

[0043] S3. Carbon-boron dual-phase high-entropy ceramic composite powder was loaded into a graphite mold with an inner diameter of 20 mm and sintered and densified at 40 MPa using a spark plasma sintering furnace (SPS-4, Shanghai Chenhua Technology Co., Ltd.). Specifically, the carbon-boron dual-phase high-entropy ceramic composite powder was heated to 1600 °C at a rate of 120 °C / min, and then further heated to 2000 °C at a rate of 100 °C / min, and held for 10 min to obtain a carbon-boron dual-phase high-entropy ceramic composite material, denoted as (Ti). 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C-B2.

[0044] Example 2 A method for preparing a carbon-boron dual-phase high-entropy ceramic composite material includes the following steps: S1. Using equimolar amounts of TiO2 (50nm, 99% purity), ZrO2 (50nm, 99% purity), HfO2 (50nm, 99% purity), Nb2O5 (50nm, 99% purity), Ta2O5 (50nm, 99% purity), B4C (50nm, 99% purity) and carbon black (50nm, 99% purity) as raw materials, the raw materials were mechanically mixed using a planetary ball mill with 10mm diameter zirconium oxide as the ball milling medium. The ball-to-material ratio was 3:1, and the mixture was ball-milled at 600 rpm for 12 hours to obtain a mixed powder.

[0045] S2, the mixed powder is placed in a high-temperature furnace and heated to 1700℃ under an argon atmosphere, and subjected to a boron-carbothermic reduction reaction for 1 hour to ensure complete reaction. After cooling to room temperature, it is ground using an agate mortar and pestle and then sieved through a 200-mesh sieve to obtain carbon-boron dual-phase high-entropy ceramic composite powder.

[0046] S3. Carbon-boron dual-phase high-entropy ceramic composite powder was loaded into a graphite mold with an inner diameter of 20 mm and sintered and densified at 40 MPa using a spark plasma sintering furnace (SPS-4, Shanghai Chenhua Technology Co., Ltd.). Specifically, the carbon-boron dual-phase high-entropy ceramic composite powder was heated to 1600 °C at a rate of 120 °C / min, and then further heated to 2000 °C at a rate of 100 °C / min, and held for 10 min to obtain a carbon-boron dual-phase high-entropy ceramic composite material, denoted as (Ti). 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C-B2.

[0047] Example 3 A method for preparing a carbon-boron dual-phase high-entropy ceramic composite material includes the following steps: S1. Using equimolar amounts of TiO2 (50nm, 99% purity), ZrO2 (50nm, 99% purity), HfO2 (50nm, 99% purity), Nb2O5 (50nm, 99% purity), Ta2O5 (50nm, 99% purity), B4C (50nm, 99% purity) and carbon black (50nm, 99% purity) as raw materials, the raw materials were mechanically mixed using a planetary ball mill with 10mm diameter zirconium oxide as the ball milling medium. The ball-to-material ratio was 3:1, and the mixture was ball-milled at 600 rpm for 12 hours to obtain a mixed powder.

[0048] S2, the mixed powder is placed in a high-temperature furnace and heated to 1800°C under an argon atmosphere, and subjected to a boron-carbothermic reduction reaction for 1 hour to ensure complete reaction. After cooling to room temperature, it is ground using an agate mortar and passed through a 200-mesh sieve to obtain carbon-boron dual-phase high-entropy ceramic composite powder.

[0049] S3. Carbon-boron dual-phase high-entropy ceramic composite powder was loaded into a graphite mold with an inner diameter of 20 mm and sintered and densified at 40 MPa using a spark plasma sintering furnace (SPS-4, Shanghai Chenhua Technology Co., Ltd.). Specifically, the carbon-boron dual-phase high-entropy ceramic composite powder was heated to 1600 °C at a rate of 120 °C / min, and then further heated to 2000 °C at a rate of 100 °C / min, and held for 10 min to obtain a carbon-boron dual-phase high-entropy ceramic composite material, denoted as (Ti). 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )C-B2.

[0050] The morphology and properties of the carbon-boron dual-phase high-entropy ceramic composite materials prepared in Examples 1 to 3 of this invention were tested, and the results are as follows.

[0051] Figure 1 XRD patterns of carbon-boron dual-phase high-entropy composite powders prepared at different synthesis temperatures. Figure 1 It can be seen that when the synthesis temperature reaches 1600℃, the target phases (Ti,Zr,Hf,Nb,Ta)C, i.e., the high-entropy carbide phase (HEC), and (Ti,Zr,Hf,Nb,Ta)B2, i.e., the high-entropy boride phase (HEB), have been formed in the powder, indicating that the boron / carbothermic reduction method has occurred at this temperature, but oxide (TiO2) remains. When the temperature is increased to 1700℃, the intensity of the oxide characteristic peaks decreases significantly but still remains, and the target phases HEC and HEB still exhibit relatively broadened characteristics, which is presumably related to the small grain size or incomplete grains. Finally, when the temperature reaches 1800℃, all oxide impurity peaks in the XRD pattern disappear completely, leaving only the characteristic peaks of the target phases HEC and HEB.

[0052] Figure 2 SEM images of carbon-boron dual-phase high-entropy composite powders synthesized at different temperatures. Figure 2 As can be seen, the grain size of the sample increases with increasing synthesis temperature. The grain size at different synthesis temperatures was measured using ImageJ software. At 1600℃, the grain size of the HEC phase was approximately 0.225 μm, and the grain size of the HEB phase was approximately 0.706 μm. When the synthesis temperature reached 1800℃, the grain size of the HEC phase reached 0.93 μm, and the grain size of the HEB phase reached 1.87 μm.

[0053] Figure 3 This is an EDS surface scan of the carbon-boron dual-phase high-entropy composite powder synthesized at a temperature of 1800℃. The image clearly shows that Nb and Ti elements are mainly distributed in the boride grains, while Ta and Hf elements are enriched in the carbide grains. Zr elements are relatively uniformly distributed in both types of grains.

[0054] Figure 4 This is an EDS spot scan of the carbon-boron dual-phase high-entropy composite powder synthesized at 1800℃. The spot scan clearly shows that the smaller, spherical grains are carbide grains, while the larger, layered hexagonal grains are boride grains. This result also confirms the successful synthesis of the dual-phase powder. The step-like growth morphology is related to the liquid intermediate B₂O₃. It is speculated that during the boron-carbothermic reduction process, carbides continuously dissolve in the B₂O₃ liquid phase to react and form borides. The borides and carbides, due to their smooth interfaces, grow in a step-like manner.

[0055] Figure 5 Figures a and b show high-resolution transmission electron micrographs (HRTEM) of the carbide and boride phases in the carbon-boron dual-phase high-entropy composite powder prepared at a synthesis temperature of 1800℃. Figure 5 The characteristic lattice spacing observed in a is 2.106 Å, which is in high agreement with the theoretical value of the (200) plane spacing of the cubic carbide phase; Figure 5 In b, regular lattice fringes of 2.918 Å are observed, corresponding to the characteristic spacing of the (100) crystal plane of the hexagonal boride phase. Selected area electron diffraction (SAED) analysis further confirmed the phase composition: Figure 5 The diffraction spots obtained by performing a Fourier transform (FFT) on the characteristic region of a, such as Figure 5 c, after being identified, corresponds to the (200) and (111) crystal plane families of the carbide phase; Figure 5 The d-graph is Figure 5 The Fourier transform electron diffraction pattern at the corresponding position in b is used to identify the (100) and (101) crystal planes of the hexagonal boride crystal by calibrating the diffraction spots.

[0056] Figure 6 These are the XRD patterns of carbon-boron dual-phase high-entropy ceramic composite materials ((Ti,Zr,Hf,Nb,Ta)C-B2) prepared from powders synthesized at different temperatures under the same SPS sintering environment (i.e., 2000℃-40MPa). Figure 6 As can be seen, the phase composition of the composite powders synthesized at different temperatures did not change after sintering. The powders synthesized at 1600℃ and 1700℃ still had undissolved oxide phases after SPS densification treatment, indicating that the sintering densification process failed to further promote the solid solution of multi-component cations.

[0057] Figures 7-10 These are SEM microstructure images of carbon-boron dual-phase high-entropy ceramic composites ((Ti,Zr,Hf,Nb,Ta)C-B2) prepared by SPS sintering at different synthesis temperatures. Figure 7 As can be clearly seen in Figure a, after SPS sintering of the powder synthesized at 1600℃, the ceramic sample exhibits obvious porosity and a relative density of 95.6%. When the powder synthesis temperature reaches 1700℃, the porosity in the sintered ceramic sample is significantly reduced, with most of the remaining pores located at grain boundaries, and the relative density is also increased to 98.3%. Figure 7 b; Finally, after the synthesis temperature of the powder was increased to 1800℃, the pores in the sintered ceramic sample completely disappeared, and the relative density reached 99.7%, which is close to complete densification, such as Figure 7c. The particle size of the samples was measured and statistically analyzed using Imagej software, and grain size distribution diagrams of the two phases at various synthesis temperatures were plotted (blue bars represent the HEC phase grain size distribution, and red bars represent the HEB phase grain size distribution). Figures 8-10 As can be seen, the grain size of the high-entropy ceramics prepared is also increasing as the synthesis temperature continues to rise.

[0058] Figures 11-13 These are EDS surface scans of the carbon-boron dual-phase high-entropy ceramic composite material ((Ti,Zr,Hf,Nb,Ta)C-B2) prepared by SPS sintering at different synthesis temperatures according to this invention. The images clearly show that Ti, Nb, and Zr elements are mainly distributed in the boride grains of the (Ti,Zr,Hf,Nb,Ta)C-B2 dual-phase high-entropy ceramic grains; while Hf and Ta elements are enriched in the carbide grains. This indicates that the elemental distribution is not related to the synthesis temperature. The elemental distribution of the sintered ceramic bulk is compared with the previous... Figure 4 Comparing the elemental distribution of the powders, it was found that the Zr elements, which were relatively uniformly distributed before sintering, exhibited a phenomenon of aggregation into the borides after sintering.

[0059] Table 1 shows the mechanical properties of the carbon-boron dual-phase high-entropy ceramic composite material ((Ti,Zr,Hf,Nb,Ta)C-B2) prepared by spark plasma sintering at different synthesis temperatures according to this invention. The results show that the mechanical properties of the obtained carbon-boron dual-phase high-entropy ceramic composite material gradually improve with increasing powder synthesis temperature. Under a load of 98 N, the Vickers hardness of the carbon-boron dual-phase high-entropy ceramic composite material prepared in Example 1 of this invention reaches 20.93 GPa, and the fracture toughness reaches 4.1 MPa·m. 1 / 2 The increase in Vickers hardness is mainly attributed to the decrease in oxide content in the powder due to the increased synthesis temperature, which significantly improves the density of the sintered ceramic. On the other hand, the enhanced fracture toughness is due to the combined effect of two factors: first, the grain size of ceramics prepared using powder synthesized at 1800℃ is not significantly coarser compared to ceramics prepared using powder synthesized at 1700℃; second, the former has a significantly lower porosity than the latter. These changes in microstructural characteristics improve the material's resistance to crack propagation, making crack propagation require more energy.

[0060] Table 1 Mechanical properties of ceramics prepared by SPS sintering of powders at different synthesis temperatures Figure 14 The indentation cracks in the bulk carbon-boron dual-phase high-entropy ceramic composite material ((Ti,Zr,Hf,Nb,Ta)C-B2) prepared at different synthesis temperatures are shown in this invention. Figure 14 It can be clearly seen that the propagation mode of indentation cracks in carbon-boron dual-phase high-entropy ceramic composite samples prepared at all synthesis temperatures is a large amount of intergranular fracture plus some small amounts of transgranular fracture on the boride grains.

[0061] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A carbon-boron dual-phase high-entropy ceramic composite material, characterized in that, The carbon-boron dual-phase high-entropy ceramic composite material is obtained by using equimolar amounts of TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, B4C, and carbon black as raw materials under a protective atmosphere, heating to 1600℃~1800℃, and conducting a boron-carbothermic reduction reaction to form high-entropy ceramic composite powders of carbide and boride phases. Then, it is sintered by programmed temperature rise to obtain the carbon-boron dual-phase high-entropy ceramic composite material.

2. The carbon-boron dual-phase high-entropy ceramic composite material according to claim 1, characterized in that, The carbide phase is (Ti) 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 C; the boride phase is (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2.

3. The carbon-boron dual-phase high-entropy ceramic composite material according to claim 2, characterized in that, The (Ti) 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 The grain size of C is 0.225 μm to 0.93 μm, and the (Ti) 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 The grain size of B2 is 0.706μm~1.87μm.

4. A method for preparing the carbon-boron dual-phase high-entropy ceramic composite material according to claim 1, characterized in that, Includes the following steps: Using equimolar amounts of TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, B4C and carbon black as raw materials, a mixed powder was obtained by grinding. Under a protective atmosphere, the mixed powder is heated to 1600℃~1800℃ and a boron-carbothermic reduction reaction is carried out to form a carbon-boron dual-phase high-entropy ceramic composite powder. The carbon-boron dual-phase high-entropy ceramic composite powder was subjected to programmed temperature sintering to obtain a carbon-boron dual-phase high-entropy ceramic composite material.

5. The method for preparing carbon-boron dual-phase high-entropy ceramic composite material according to claim 4, characterized in that, The programmed temperature rise sintering method is as follows: at 40 MPa, the carbon boron dual-phase high-entropy ceramic composite powder is heated to 1600℃ at a rate of 100℃ / min~120℃ / min, and then heated to 2000℃ at a rate of 80℃ / min~100℃ / min, and held for 10min~20min.

6. The method for preparing carbon-boron dual-phase high-entropy ceramic composite material according to claim 4, characterized in that, During the process of heating to 1600℃~1800℃, the heating rate is 3℃ / min~5℃ / min.

7. The method for preparing carbon-boron dual-phase high-entropy ceramic composite material according to claim 4, characterized in that, The time for the boron-carbon thermal reduction reaction is 1 hour.

8. The method for preparing carbon-boron dual-phase high-entropy ceramic composite material according to claim 4, characterized in that, Before the programmed heating and sintering, the carbon-boron dual-phase high-entropy ceramic composite powder is cooled, ground, and passed through a 200-mesh sieve.

9. The method for preparing carbon-boron dual-phase high-entropy ceramic composite material according to claim 4, characterized in that, The grinding process specifically involves using zirconium oxide with a diameter of 8mm to 10mm as the grinding media, with a ball-to-material ratio of 3:1, and grinding at a speed of 600rpm to 800rpm for 10h to 12h.

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