Mesentropic carbide ceramic materials by modulating carbon content synthesis and methods thereof

Abstract

This invention relates to the field of structural ceramics and high-temperature ceramic material preparation technology, and discloses a medium-entropy carbide ceramic material and its preparation method, comprising the following steps: 1) Weighing TiC powder, ZrC powder, Mo2C powder, HfC powder and carbon powder, and mixing them to obtain raw materials; 2) Adding excess carbon powder to the raw materials, mixing and grinding the above raw materials to obtain a mixed powder, wherein the total carbon content in the mixed powder is sufficient to form a single-phase solid solution and has free carbon; 3) Drying the mixed powder, sieving it, pressing it into a green body, and then sintering the green body to obtain the medium-entropy carbide ceramic material. This invention proposes a novel approach to synthesizing single-phase medium-entropy carbide ceramics—introducing excess carbon during the preparation process to promote the solid solution of metal elements, resulting in medium-entropy carbide ceramics with extremely low friction coefficients, i.e., good room temperature lubrication performance.

Description

Technical Field

[0001] This invention relates to the field of structural ceramics and high-temperature ceramic materials preparation technology, and in particular to a medium-entropy carbide ceramic material and its preparation method. Background Technology

[0002] Medium-entropy carbide ceramics, due to their high hardness, high melting point, low thermal conductivity, and excellent high-temperature stability, show broad application prospects in aerospace thermal protection and ultra-high temperature structural materials. Currently, the preparation of these ceramic materials mainly employs sintering methods such as pressureless sintering, spark plasma sintering, and hot pressing. Existing research largely focuses on modifying sintering process parameters, including the control of sintering temperature and pressure. Regarding temperature control, studies have shown that changing the sintering temperature can lead to a shift in the grain growth mechanism from surface diffusion to grain boundary diffusion, promoting the densification of ceramics and the uniform distribution of elements. However, excessively high temperatures can cause significant grain coarsening, reducing the mechanical properties of the material [Grain growth kinetics and densification mechanism of (TiZrHfVNbTa)C high-entropy ceramic underpressureless sintering [J]. Journal of Materials Science & Technology, 2022, 110: 57-64.]. Regarding pressure control, applying high pressure can promote the interdiffusion and homogenization of multi-component carbides, obtaining high-purity single-phase high-entropy carbides at relatively low temperatures, and exacerbating lattice distortion, thereby improving bulk modulus and strength. However, high-pressure conditions are difficult to be compatible with conventional sintering equipment, limiting engineering applications [The effect of pressure tuning on the structure and mechanical properties of high-entropy carbides [J]. ScriptaMaterialia, 2022, 216: 114755.].

[0003] Therefore, controlling the carbon content has become a research hotspot in recent years for the preparation of medium-to-high entropy carbide ceramic materials. However, it is worth noting that almost all studies on carbon content control focus on introducing carbon vacancies, i.e., reducing the stoichiometry of carbon. This method also has certain drawbacks. For example, reducing the carbon content (Mo...) 0.25 Nb 0.25 Ta 0.25 Ti 0.25 C 0.875However, it was found that carbon vacancies weaken the ability to remove oxygen impurities, leading to oxygen enrichment at grain boundaries and the formation of an amorphous phase, which significantly reduces its mechanical properties. [Influence of carbon deficiency on the mechanical and thermal properties of high-entropy carbide (Mo 0.25 Nb 0.25 Ta 0.25 Ti 0.25 C x [J]. Journal of the European Ceramic Society, 2026, 46(12): 118423.]. Similarly, in other high-entropy carbide systems, although carbon vacancies can regulate the structure and promote single-phase formation, this generally comes at the cost of sacrificing mechanical properties. It is evident that existing carbon regulation pathways are limited to a "carbon-deficient" approach and have certain limitations.

[0004] Therefore, a novel synthesis strategy is urgently needed to solve the above-mentioned technical problems. Summary of the Invention

[0005] The working principle of this invention: This invention discloses a method for synthesizing (Ti) through carbon excess. 0.25 Zr 0.25 Mo 0.25 Hf 0.25 Medium entropy carbide ceramic materials and their preparation methods are described. The method first weighs the corresponding transition metal carbide powder and excess graphite powder as starting materials. After thorough mixing via ball milling, the materials are sintered using spark plasma sintering technology to obtain bulk ceramic materials with excellent mechanical and lubrication properties. The preparation process is simple, efficient, and meets the requirements of green and energy-saving processes.

[0006] The (Ti) prepared by this invention 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C is a medium-entropy carbide ceramic material. Since the excess carbon exists in the form of free carbon, it can play a lubricating role. It exhibits a low coefficient of friction and wear rate at room temperature, and has better overall tribological properties. It can prevent material wear failure under harsh conditions.

[0007] The core innovation of this invention lies in the introduction of an additional excess of carbon. Since the Mo2C in the raw material has a hexagonal structure and its C / Mo atomic ratio is only 0.5, if the carbide raw material is weighed only according to the equimolar metal ratio, the total carbon content of the mixed powder will be severely insufficient, leading to severe elemental segregation in the sintered mass, the appearance of multiple impurity phases, and difficulty in obtaining a single-phase rock salt solid solution. This invention, after supplementing the carbon content to a stoichiometric ratio of 1 (C / M=1), further adds an excess of carbon powder. During the preparation process, a high carbon chemical potential is maintained. First, this drives the complete carbonization transformation of Mo2C, which reacts with carbon to transform into a rock salt structure and dissolves into a high-entropy lattice. Second, not only are there lattice oxygens in the transition metal carbides, but oxygen is also inevitably present in the furnace cavity during sintering. The excess carbon can act as a reducing agent to consume oxygen and remove oxide impurities. Finally, the excess carbon is dispersed throughout the material in the form of free carbon, forming a shear-friendly lubricating film and reducing the material's friction coefficient.

[0008] The synthesis mechanism of this invention is as follows: using transition metal carbide powder as raw material, based on 0.25TiC(s) + 0.25ZrC(s) + 0.25HfC(s) + 0.125Mo2C(s) + C(s) → (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 The reaction scheme of C+C(s) was used to synthesize a medium-entropy carbide ceramic material with uniform microstructure through grinding and spark plasma sintering. The amount of carbon added has a decisive influence on the microstructure and final properties of the carbide ceramic. If the carbon content is too low, elemental segregation or the appearance of a second phase will occur, the metal elements will not be completely dissolved, and sufficient densification will not be achieved. If the carbon content is too high, the hardness of the material will be reduced, and the mechanical properties cannot be guaranteed.

[0009] This invention employs spark plasma sintering (SPS) of mixed carbide powders as the optimal process route. SPS utilizes a DC pulsed current to excite plasma discharge and Joule heating effects between carbide particles, achieving extremely rapid heating rates and short-term densification. This effectively avoids the grain coarsening caused by the need for high-temperature, long-term sintering of medium- and high-entropy carbides due to severe lattice distortion and low diffusion rates. The strong electric field also reduces the atomic diffusion activation energy, accelerating the mixing and homogenization of multi-principal metal atoms.

[0010] The purpose of this invention is to overcome the aforementioned technical problems and propose a novel synthesis strategy—introducing excess carbon into the preparation process of carbide ceramics. Specifically, an excess of carbon source beyond the stoichiometric ratio is added to the raw materials. On the one hand, the reduction and deoxidation effect of carbon inhibits the formation of brittle phases at grain boundaries; on the other hand, the carbon chemical potential is maintained at a high level (i.e., the system has excess carbon), causing the hexagonal Mo2C structure to completely transform into a face-centered cubic structure (making the C / Mo ratio close to 1), thereby dissolving into the crystal lattice and achieving single-phase formation. This approach is drastically different from existing "carbon-deficient" technical routes and opens up a new direction for the preparation of medium-entropy carbide ceramic materials.

[0011] To achieve the above objectives, the present invention is implemented according to the following technical solution: A medium-entropy carbide ceramic material synthesized by controlling the carbon content, the ceramic material comprising a main crystalline phase and a free phase; the molecular formula of the main crystalline phase is (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C, belongs to a high-temperature resistant metal ceramic with a single face-centered cubic rock salt structure and equal proportion of metal elements; the free phase contains free carbon, which is dispersed in the form of a second phase at the grain boundaries or within the grains, and the content of the free carbon is 7.5 wt.%; the coefficient of friction of the ceramic material at room temperature is less than 0.3.

[0012] This invention also includes a method for preparing a medium-entropy carbide ceramic material synthesized by controlling the carbon content, comprising the following steps: 1) Weigh TiC powder, ZrC powder, Mo2C powder, HfC powder and carbon powder, mix them to obtain raw materials, wherein the molar ratio of Ti:Zr:Mo:Hf:C in the raw materials is 1:1:1:1:4; 2) Add an excess of carbon powder to the raw material, mix and grind to obtain a mixed powder, wherein the total carbon content in the mixed powder is sufficient to form a single-phase solid solution and has free carbon; 3) The mixed powder is dried, sieved, and pressed into a green body, which is then sintered to obtain a medium-entropy carbide ceramic material.

[0013] Preferably, in step 2), the mass of the carbon powder is 7.5 wt.% of the four transition metal carbide powders.

[0014] Preferably, in step 1), the purity of the transition metal carbide and the carbon powder is ≥99.5%, and the particle size is 1~3μm.

[0015] Preferably, in step 2), the grinding process is as follows: the mixed powder is placed in the grinding jar of a drum ball mill, and grinding media and grinding balls are added. The rotation speed of the drum ball mill is 100 rpm, and the grinding time is 24 h.

[0016] Preferably, the ball milling medium is anhydrous ethanol, and the amount used is equal to the total mass of the mixed powder.

[0017] Preferably, the grinding ball is made of tungsten carbide, and the mass ratio of the mixed powder is 3:1.

[0018] Preferably, in step 3), the drying temperature is 60~70 ℃ and the drying time is 10 h.

[0019] Preferably, in step 3), the sieve used for sieving is 200 mesh.

[0020] Preferably, in step 3), the sintering adopts discharge plasma sintering technology. The process is as follows: first, the temperature is raised to 1000 ℃ at a heating rate of 100 ℃ / min, then raised to 1600 ℃ at a heating rate of 30 ℃ / min, then raised to 2000 ℃ at a heating rate of 20 ℃ / min and held at that temperature for 15 min, and finally cooled to 1000 ℃ at a cooling rate of 50 ℃ / min and allowed to cool naturally to room temperature.

[0021] Preferably, the vacuum degree of the discharge plasma sintering is below 20 Pa.

[0022] Preferably, the pressure of the discharge plasma sintering is 40 MPa.

[0023] Beneficial effects The preparation process of this invention is simple and the raw materials are readily available. It innovatively employs a carbon excess strategy, which significantly promotes complete solid solution of metal elements and inhibits elemental agglomeration, resulting in a near-fully dense, uniformly proportioned (TiZrMoHf)C medium-entropy carbide ceramic. This design concept can be extended to other high-entropy carbide systems containing carbon-poor raw materials, possessing high universality and industrialization value, as detailed below: 1) Excess carbon drives the complete crystal transformation of Mo2C, enabling the rapid low-temperature formation of single-phase rock salt solid solution, breaking through the technical bottleneck of element segregation and multiphase coexistence in traditional processes. 2) "Excess carbon" also has the function of in-situ reduction and deoxygenation, which significantly purifies the grain boundaries and eliminates the amorphous grain boundary phase caused by oxygen enrichment in conventional carbon-deficient processes. This allows the material to maintain high density while exhibiting a non-linear increase in Vickers hardness. At the same time, the dispersed "free carbon" gives the material excellent room temperature lubrication properties. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Figure 1 XRD patterns of ceramic materials prepared in Examples 1 and 5 of this invention.

[0026] Figure 2 SEM images and EDS surface distribution diagrams of the ceramic materials prepared in Examples 1 and 5 of this invention.

[0027] Figure 3 Vickers hardness of ceramic materials prepared in Examples 1 and 5 of the present invention under different loads.

[0028] Figure 4 : The friction coefficient variation of the ceramic material prepared in Example 1 of this invention at room temperature. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] Unless otherwise specified, the apparatus used in this invention employs commonly used devices in the field.

[0031] In the following comparative examples and embodiments, the purity of TiC powder, ZrC powder, Mo2C powder, HfC powder and carbon powder used is ≥99.5%, and the particle size is 1~3 μm.

[0032] Example 1 A method for preparing a medium-entropy carbide ceramic material synthesized by controlling the carbon content includes the following steps: 1) Weigh TiC powder, ZrC powder, Mo2C powder, HfC powder and 0.1186 g carbon powder, mix them to obtain 9.1186 g of raw material, wherein the molar ratio of Ti:Zr:Mo:Hf:C is 1:1:1:1:4, add an additional 0.6750 g of carbon powder (7.5% of the total mass of transition metal carbides) to the raw material, mix and grind the above raw materials to obtain 9.7936 g of mixed powder; 2) Place the mixed powder into a ball mill jar, add anhydrous ethanol and tungsten carbide grinding balls, the mass ratio of anhydrous ethanol to mixed powder is 1:1, and the mass ratio of tungsten carbide grinding balls to mixed powder is 3:1. Place the ball mill jar in a drum ball mill and ball mill at 100 rpm for 24 h to obtain mixed powder.

[0033] 3) Place the mixed powder described in step 2) into a drying oven and dry it at 60 ℃ for 10 h. Then, sieve the dried mixed powder through a 200-mesh sieve.

[0034] 4) The dried mixed powder from step 3) is pressed into a green body, which is then subjected to discharge plasma sintering. The sintering is carried out in a vacuum environment. The sintering furnace is evacuated to a vacuum level of <20 Pa. The temperature is first increased to 1000 ℃ at a heating rate of 100 ℃ / min, then increased to 1600 ℃ at a heating rate of 30 ℃ / min, and then increased to 2000 ℃ at a heating rate of 20 ℃ / min and held at that temperature for 15 min. Finally, the temperature is reduced to 1000 ℃ at a cooling rate of 50 ℃ / min and then allowed to cool naturally to room temperature. The pressure throughout the sintering process is 40 MPa.

[0035] 5) The prepared medium-entropy carbide ceramic material was named (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C+7.5wt. %C ceramic (abbreviated as TZMHC-7.5C in the attached figure).

[0036] Comparative Example 1 (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C 0.875 A method for preparing carbide ceramic materials includes the following steps: 1) Weigh TiC powder, ZrC powder, Mo2C powder, and HfC powder, wherein the molar ratio of Ti:Zr:Mo:Hf:C is 1:1:1:1:3.5. Mix and grind the above raw materials to obtain 9 g of mixed powder. 2) Place the mixed powder into a ball mill jar, add anhydrous ethanol and tungsten carbide grinding balls, the mass ratio of anhydrous ethanol to mixed powder is 1:1, and the mass ratio of tungsten carbide grinding balls to mixed powder is 3:1. Place the ball mill jar in a drum ball mill and ball mill at 100 rpm for 24 h to obtain mixed powder.

[0037] 3) Place the mixed powder described in step 2) into a drying oven and dry it at 60 ℃ for 10 h. Then, sieve the dried mixed powder through a 200-mesh sieve.

[0038] 4) The dried mixed powder from step 3) is pressed into a green body, which is then subjected to discharge plasma sintering. The sintering is carried out in a vacuum environment. The sintering furnace is evacuated to a vacuum level of <20 Pa. The temperature is first increased to 1000 ℃ at a heating rate of 100 ℃ / min, then increased to 1600 ℃ at a heating rate of 30 ℃ / min, and then increased to 2000 ℃ at a heating rate of 20 ℃ / min and held at that temperature for 15 min. Finally, the temperature is reduced to 1000 ℃ at a cooling rate of 50 ℃ / min and then allowed to cool naturally to room temperature. The pressure throughout the sintering process is 40 MPa.

[0039] 5) The prepared carbide ceramic material was named (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C 0.875 Ceramics (abbreviated as TZMHC in the attached image) 0.875 ).

[0040] Comparative Example 2 (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 The preparation method of C carbide ceramic materials includes the following steps: 1) Weigh TiC powder, ZrC powder, Mo2C powder, HfC powder and 0.1186 g carbon powder, mix them to obtain 9.1186 g raw materials, wherein the molar ratio of Ti:Zr:Mo:Hf:C is 1:1:1:1:4. Mix and grind the above raw materials to obtain 9.1186 g mixed powder. 2) Place the mixed powder into a ball mill jar, add anhydrous ethanol and tungsten carbide grinding balls, the mass ratio of anhydrous ethanol to mixed powder is 1:1, and the mass ratio of tungsten carbide grinding balls to mixed powder is 3:1. Place the ball mill jar in a drum ball mill and ball mill at 100 rpm for 24 h to obtain mixed powder.

[0041] 3) Place the mixed powder described in step 2) into a drying oven and dry it at 60 ℃ for 10 h. Then, sieve the dried mixed powder through a 200-mesh sieve.

[0042] 4) The dried mixed powder from step 3) is pressed into a green body, which is then subjected to discharge plasma sintering. The sintering is carried out in a vacuum environment. The sintering furnace is evacuated to a vacuum level of <20 Pa. The temperature is first increased to 1000 ℃ at a heating rate of 100 ℃ / min, then increased to 1600 ℃ at a heating rate of 30 ℃ / min, and then increased to 2000 ℃ at a heating rate of 20 ℃ / min and held at that temperature for 15 min. Finally, the temperature is reduced to 1000 ℃ at a cooling rate of 50 ℃ / min and then allowed to cool naturally to room temperature. The pressure throughout the sintering process is 40 MPa.

[0043] 5) The prepared carbide ceramic material was named (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C ceramic (abbreviated as TZMHC in the attached diagram).

[0044] Comparative Example 3 (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 The preparation method of C-2C carbide ceramic materials includes the following steps: 1) Weigh TiC powder, ZrC powder, Mo2C powder, HfC powder and 0.1186 g carbon powder, mix them to obtain 9.1186 g of raw materials, wherein the molar ratio of Ti:Zr:Mo:Hf:C is 1:1:1:1:4. On this basis, add an additional 0.1800 g of carbon powder (2% of the total mass of transition metal carbide powder), mix and grind the above raw materials to obtain 9.2986 g of mixed powder; 2) Place the mixed powder into a ball mill jar, add anhydrous ethanol and tungsten carbide grinding balls, the mass ratio of anhydrous ethanol to mixed powder is 1:1, and the mass ratio of tungsten carbide grinding balls to mixed powder is 3:1. Place the ball mill jar in a drum ball mill and ball mill at 100 rpm for 24 h to obtain mixed powder.

[0045] 3) Place the mixed powder described in step 2) into a drying oven and dry it at 60 ℃ for 10 h. Then, sieve the dried mixed powder through a 200-mesh sieve.

[0046] 4) The dried mixed powder from step 3) is pressed into a green body, which is then subjected to discharge plasma sintering. The sintering is carried out in a vacuum environment. The sintering furnace is evacuated to a vacuum level of <20 Pa. The temperature is first increased to 1000 ℃ at a heating rate of 100 ℃ / min, then increased to 1600 ℃ at a heating rate of 30 ℃ / min, and then increased to 2000 ℃ at a heating rate of 20 ℃ / min and held at that temperature for 15 min. Finally, the temperature is reduced to 1000 ℃ at a cooling rate of 50 ℃ / min and then allowed to cool naturally to room temperature. The pressure throughout the sintering process is 40 MPa.

[0047] 5) The prepared carbide ceramic material was named (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C+2wt. %C ceramic (abbreviated as TZMHC-2C in the attached diagram).

[0048] Comparative Example 4 (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 The preparation method of C-5C carbide ceramic material includes the following steps: 1) Weigh TiC powder, ZrC powder, Mo2C powder, HfC powder and 0.1186 g carbon powder, mix them to obtain 9.1186 g of raw materials, wherein the molar ratio of Ti:Zr:Mo:Hf:C is 1:1:1:1:4. On this basis, add an additional 0.4500 g of carbon powder (5% of the total mass of transition metal carbide powder), mix and grind the above raw materials to obtain 9.5686 g of mixed powder; 2) Place the mixed powder into a ball mill jar, add anhydrous ethanol and tungsten carbide grinding balls, the mass ratio of anhydrous ethanol to mixed powder is 1:1, and the mass ratio of tungsten carbide grinding balls to mixed powder is 3:1. Place the ball mill jar in a drum ball mill and ball mill at 100 rpm for 24 h to obtain mixed powder.

[0049] 3) Place the mixed powder described in step 2) into a drying oven and dry it at 60 ℃ for 10 h. Then, sieve the dried mixed powder through a 200-mesh sieve.

[0050] 4) The dried mixed powder from step 3) is pressed into a green body, which is then subjected to discharge plasma sintering. The sintering is carried out in a vacuum environment. The sintering furnace is evacuated to a vacuum level of <20 Pa. The temperature is first increased to 1000 ℃ at a heating rate of 100 ℃ / min, then increased to 1600 ℃ at a heating rate of 30 ℃ / min, and then increased to 2000 ℃ at a heating rate of 20 ℃ / min and held at that temperature for 15 min. Finally, the temperature is reduced to 1000 ℃ at a cooling rate of 50 ℃ / min and then allowed to cool naturally to room temperature. The pressure throughout the sintering process is 40 MPa.

[0051] 5) The prepared carbide ceramic material was named (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C+5wt. %C ceramic (abbreviated as TZMHC-5C in the attached diagram).

[0052] Comparative Example 5 (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 The preparation method of C-10C carbide ceramic material includes the following steps: 1) Weigh TiC powder, ZrC powder, Mo2C powder, HfC powder and 0.1186 g carbon powder, mix them to obtain 9.1186 g of raw materials, wherein the molar ratio of Ti:Zr:Mo:Hf:C is 1:1:1:1:4. On this basis, add an additional 0.9000 g of carbon powder (10% of the total mass of transition metal carbide powder), mix and grind the above raw materials to obtain 10.0186 g of mixed powder; 2) Place the mixed powder into a ball mill jar, add anhydrous ethanol and tungsten carbide grinding balls, the mass ratio of anhydrous ethanol to mixed powder is 1:1, and the mass ratio of tungsten carbide grinding balls to mixed powder is 3:1. Place the ball mill jar in a drum ball mill and ball mill at 100 rpm for 24 h to obtain mixed powder.

[0053] 3) Place the mixed powder described in step 2) into a drying oven and dry it at 60 ℃ for 10 h. Then, sieve the dried mixed powder through a 200-mesh sieve.

[0054] 4) The dried mixed powder from step 3) is pressed into a green body, which is then subjected to discharge plasma sintering. The sintering is carried out in a vacuum environment. The sintering furnace is evacuated to a vacuum level of <20 Pa. The temperature is first increased to 1000 ℃ at a heating rate of 100 ℃ / min, then increased to 1600 ℃ at a heating rate of 30 ℃ / min, and then increased to 2000 ℃ at a heating rate of 20 ℃ / min and held at that temperature for 15 min. Finally, the temperature is reduced to 1000 ℃ at a cooling rate of 50 ℃ / min and then allowed to cool naturally to room temperature. The pressure throughout the sintering process is 40 MPa.

[0055] 5) The prepared carbide ceramic material was named (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C+10wt. %C ceramic (abbreviated as TZMHC-10C in the attached diagram).

[0056] Results Analysis like Figure 1 The figures show the XRD patterns of the ceramic materials prepared in Examples 1 and Comparative Examples 1-5 of this invention, which display the phase composition of the ceramic materials. As can be seen from the figures, Comparative Example 1 only used carbide powder for sintering, and the phase contained the impurity phase (ZrMo)C, and the elemental segregation was severe. As the amount of additional carbon added increased from 0% to 10%, the peak broadening and peak separation phenomenon gradually improved, indicating that the lattice distortion was weakened, the elemental segregation was suppressed, the metal elements gradually dissolved, and the material gradually tended to a face-centered cubic structure, until Example 1 (the amount of additional carbon added was 7.5 wt.%), which completely formed a single-phase carbide ceramic (except for the excess carbon).

[0057] like Figure 2 The figure shows the EDS surface distribution diagrams of the ceramic materials prepared in Example 1 and Comparative Examples 1 to 5 of the present invention, which show the elemental distribution of the ceramic materials. It can be observed from the figure that as the amount of carbon added increases, the elemental distribution tends to be more uniform and gradually tends to be single-phase.

[0058] like Figure 3 The figure shows the Vickers hardness diagrams of the ceramic materials prepared in Example 1 and Comparative Examples 1-5 of the present invention, which show the Vickers hardness of the ceramic materials under different loads. It can be observed from the figure that from Comparative Example 1 to Comparative Example 4 up to Example 1 (with an additional carbon addition of 7.5 wt.%), under the same load, the Vickers hardness of the material increases with the increase of the additional carbon addition. In Comparative Example 5, the carbon content is further increased, and the increase of free carbon leads to a decrease in the hardness of the material. The changes in microstructure and mechanical properties are taken into account.

[0059] like Figure 4As shown, the preferred embodiment 1 underwent tribological performance testing and found that the coefficient of friction was as low as 0.27, which is an excellent level among ceramic materials. This allows ceramic components to maintain long-term service capability under harsh operating conditions such as high speed, high temperature, and lack of oil, and has broad application prospects in fields such as high-end bearings.

[0060] The scope of protection of this invention is not limited to the specific embodiments described above. All equivalent modifications made based on the technical solutions of this invention fall within the scope of protection of this invention.

Claims

1. A medium-entropy carbide ceramic material synthesized by controlling the amount of carbon, characterized in that, The ceramic material comprises a main crystalline phase and a free phase; the molecular formula of the main crystalline phase is (Ti 0.25 Zr 0.25 Mo 0.25 Hf 0.25 C, has a single face-centered cubic rock salt structure, and the free phase contains free carbon, which is dispersed in the form of a second phase at the grain boundaries or within the grains.

2. The medium-entropy carbide ceramic material synthesized by controlling the carbon content according to claim 1, characterized in that, The coefficient of friction of the ceramic material at room temperature is less than 0.

3.

3. The medium-entropy carbide ceramic material synthesized by controlling the carbon content according to claim 1, characterized in that, The free carbon content is 7.5 wt.%.

4. A method for preparing a medium-entropy carbide ceramic material synthesized by controlling the carbon content according to claim 1 or 3, characterized in that, Includes the following steps: 1) Weigh TiC powder, ZrC powder, Mo2C powder, HfC powder and carbon powder, mix them to obtain raw materials, wherein the molar ratio of Ti:Zr:Mo:Hf:C in the raw materials is 1:1:1:1:4; 2) Add an excess of carbon powder to the raw material, mix and grind to obtain a mixed powder, wherein the total carbon content in the mixed powder is sufficient to form a single-phase solid solution and has free carbon; 3) The mixed powder is dried, sieved, and pressed into a green body, which is then sintered to obtain a medium-entropy carbide ceramic material.

5. The method for preparing a medium-entropy carbide ceramic material synthesized by controlling the carbon content according to claim 4, characterized in that, In step 2), the mass of the carbon powder is 7.5 wt.% of the four transition metal carbide powders.

6. The method for preparing a medium-entropy carbide ceramic material synthesized by controlling the carbon content according to claim 4, characterized in that, In step 2), the mixed powder is ground using a ball mill at 100 rpm for 24 hours. The grinding media is anhydrous ethanol, and the grinding balls are made of tungsten carbide.

7. The method for preparing a medium-entropy carbide ceramic material synthesized by controlling the carbon content according to claim 6, characterized in that, The mass ratio of anhydrous ethanol to the mixed powder is 1:1, and the mass ratio of the grinding ball to the mixed powder is 3:

1.

8. The method for preparing a medium-entropy carbide ceramic material synthesized by controlling the carbon content according to claim 4, characterized in that, In step 3), the sintering is performed using discharge plasma sintering technology, the sintering temperature is 2000 ℃, the heating rate to the sintering temperature is 20~100 ℃ / min, the holding time is 15 min, the vacuum degree is below 20 Pa, and the pressure is 40 MPa.

9. The method for preparing a medium-entropy carbide ceramic material synthesized by controlling the carbon content according to claim 4, characterized in that, In step 1), the purity of the transition metal carbide and the carbon powder is ≥99.5%, and the particle size is 1~3 μm.

Images