Method for preparing compact high-entropy carbide ceramic

Abstract

The invention relates to the technical field of preparation of high-entropy ceramics, and discloses a method for preparing compact high-entropy carbide ceramics, Ti3AlC2, TiC, VC, NbC, TaC and Mo2C are mixed and charged, then sintering is carried out, and the high-entropy carbide ceramics TiVNbTaMoCx are obtained after sintering is completed. In Ti3AlC2, TiC, VC, NbC, TaC and Mo2C, the molar ratio of Ti element to V element to Nb element to Ta element to Mo element is 1: 1: 1: 1: 1. According to the method, the density of the high-entropy carbide ceramic is improved by adopting a simple method, the process is simple and convenient, the production period is short, the raw materials do not need to be subjected to complex pretreatment, the preparation energy consumption and cost are remarkably reduced, and a new way is provided for large-scale preparation of the high-performance high-entropy ceramic material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-entropy ceramic preparation, and particularly relates to a method for preparing dense high-entropy carbide ceramic. BACKGROUND

[0002] Carbide ceramic has a wide range of applications in the fields of aerospace, advanced manufacturing, nuclear industry, etc. due to its high melting point, good mechanical properties, high thermal conductivity and good chemical corrosion resistance. High-entropy carbide ceramic is a single-phase solid solution carbide formed by five or more than five cations occupying the same point. Due to the existence of high-entropy effect, compared with traditional single-component carbide ceramic, high-entropy carbide ceramic has better thermodynamic stability and can maintain structural stability at a higher temperature. The slow diffusion effect of high-entropy ceramic can reduce the grain growth rate of the ceramic and obtain smaller grain size. Compared with the repeated lattice structure of single-component carbide ceramic, the crystal structure of high-entropy ceramic presents the characteristics of short-range order and long-range order due to the different atomic radii of atoms in the same Wyckoff position, and more lattice size fluctuations produce more lattice distortion. These effects can improve the mechanical properties of the ceramic. Moreover, the cocktail effect produced by the joint action of multiple factors can make high-entropy carbide ceramic have special properties that single-component carbide ceramic does not have. Current research has proved that high-entropy carbide exhibits better performance in mechanics, thermology, radiation resistance and wave absorption, which has important significance for occupying the strategic field of "deep space, deep sea and nuclear energy" in advance.

[0003] High-entropy carbide ceramic has strong covalent bonds and low self-diffusion coefficient. In the later stage of sintering, the migration rate of pores is much lower than the growth rate of crystals, so that the pores are difficult to be removed, and the ceramic has low density. Therefore, how to obtain high-entropy carbide ceramic with high density has become the focus of people's research.

[0004] Currently, the following four methods are mainly used to realize the densification of high-entropy ceramics: 1. Using high-quality ultra-fine powder to improve the sintering activity and densification efficiency, but the preparation process of ultra-fine powder is generally longer and the conversion efficiency is low, which will lead to an increase in economic cost and may also cause more environmental pollution; 2. Adjusting the carbon content, which has an important influence on the sintering behavior and final performance of high-entropy carbides, Tan et al. found that reducing the carbon content by 20% can reduce the sintering temperature by 300℃, but also leads to a decrease in mechanical properties; 3. Using advanced sintering processes, such as SPS and ultra-high temperature rapid sintering technology (with a heating rate of 1000℃ / min), to promote the densification of high-entropy ceramics, which still requires high sintering temperature or high sintering pressure to achieve the densification of ceramics, but the increase in sintering temperature will not only increase the preparation cost, but also lead to grain growth and cause a decrease in the mechanical properties of the material; 4. Introducing appropriate sintering aids, such as adding Co, Ni or silicon powder as raw materials, to achieve the densification of high-entropy ceramics at a lower temperature, which is simple and effective, but the mechanical properties, corrosion resistance and high-temperature resistance of the sintering aids themselves are lower than those of ceramic materials, and the introduction of sintering aids may lead to a decrease in the overall performance of the material.

[0005] Therefore, there is an urgent need for a method for preparing dense high-entropy carbide ceramics to solve the above technical problems. SUMMARY

[0006] The present application aims to solve the above technical problems and provides a method for preparing dense high-entropy carbide ceramics.

[0007] To achieve the above-mentioned purposes, the present application is implemented according to the following technical solutions:

[0008] A method for preparing dense high-entropy carbide ceramics, comprising the following steps: mixing Ti3AlC2, TiC, VC, NbC, TaC and Mo2C, then loading the mixture, and then sintering, to obtain high-entropy carbide ceramic TiVNbTaMoC x , wherein 4.43≤x≤4.49.

[0009] Preferably, the molar ratio of Ti elements, V elements, Nb elements, Ta elements and Mo elements in Ti3AlC2, TiC, VC, NbC, TaC and Mo2C is 1:1:1:1:1.

[0010] Preferably, the amount of Ti3AlC2 used is 3%-20% of the total Ti amount of Ti3AlC2 and TiC, calculated based on Ti.

[0011] The percentage of the amount of Ti used here is the molar percentage.

[0012] Ti3AlC2 is used as a titanium carbide in-situ generation source to generate TiC in-situ during sintering x The in-situ generated carbide raw material has higher sintering activity, and dense high-entropy carbide ceramics can be prepared at a lower temperature and pressure.

[0013] Preferably, the mixing process is: using a planetary ball mill or a drum ball mill, dry or wet mixing is adopted to obtain uniformly mixed raw materials.

[0014] Preferably, the loading process is: loading the uniformly mixed raw materials into a graphite mold.

[0015] Preferably, the sintering process is: using a pressure of 30 MPa or more and a temperature of 1550 DEG C or more, and holding for 15 min or more.

[0016] Preferably, the sintering process is: holding for 15 min at a pressure of 50 MPa and a temperature of 1550 DEG C.

[0017] The high-entropy carbide ceramic material TiVNbTaMoC of the application x During synthesis, the temperature and pressure are much lower than the common high-entropy carbide sintering conditions (common high-entropy carbide sintering conditions are generally above 1800 DEG C), the sintering temperature of the application is 1550 DEG C, and the sintering pressure is 50 MPa.

[0018] Preferably, after the sintering holding process is completed, the cooling and pressure relief are performed.

[0019] Specifically, the cooling and pressure relief process is: stopping heating, naturally cooling the sample in the mold to room temperature, and then relieving the pressure to normal pressure.

[0020] In the method, the sintering is performed by SPS (spark plasma sintering), the mixed raw materials are loaded into a graphite mold capable of bearing a pressure of 80 MPa; to ensure that the raw materials do not react with the graphite mold, carbon paper is added between the raw materials and the mold.

[0021] In the application, the Ti3AlC2, TiC, VC, NbC, TaC, and Mo2C used are raw materials directly purchased from the market, the particle size is ≤3 μm, and the purity is ≥99%.

[0022] Specifically, a method for preparing dense high-entropy carbide ceramics comprises the following steps:

[0023] Ti3AlC2, TiC, VC, NbC, TaC, and Mo2C were wet-mixed using a planetary ball mill with ethanol as the medium and tungsten carbide grinding balls as the abrasive to obtain a mixed slurry. The mixed slurry was dried to obtain a uniformly mixed raw material. The uniformly mixed raw material was placed in a graphite mold and subjected to spark plasma sintering. The sintering conditions were: 1550°C sintering temperature, 50MPa pressure, and holding time of 15min. After stopping heating, the material was naturally cooled to room temperature. After taking out the sample from the mold, the surface carburized layer was removed using a grinder to obtain high-entropy carbide ceramic TiVNbTaMoC x .

[0024] The present invention utilizes Ti3AlC2 to decompose the TiC generated in situ x Promote densification and achieve densification of high entropy carbide ceramics at lower temperature and pressure. The prepared high entropy carbide ceramics TiVNbTaMoC x It has high density and good mechanical properties.

[0025] Working principle:

[0026] The method of the present invention uses commercial Ti3AlC2 powder as the in-situ generation source of titanium carbide, adopts a simple and efficient process flow, and realizes the densification preparation of high-entropy carbide ceramics under relatively low temperature (1550°C) and pressure (50MPa) conditions through the steps of mixing, drying, loading, high-temperature and high-pressure reaction sintering and cooling and pressure relief.

[0027] The sintering process of the present invention utilizes a one-step process of spark plasma sintering to promote the decomposition of Ti3AlC2 during the sintering process to produce nano-scale TiC x , effectively promoting the subsequent diffusion and reaction of multi-component metal elements such as Ti, V, Nb, Ta, and Mo, and finally obtaining dense TiVNbTaMoC with excellent mechanical properties. x High-entropy carbide ceramic blocks. The present invention has a simple process, a short production cycle, and no need for complex pretreatment of raw materials, which significantly reduces preparation energy consumption and costs, providing a new approach for the large-scale preparation of high-performance high-entropy ceramic materials.

[0028] Ti3AlC2 will decompose to produce TiC at around 1360℃ in vacuum x This in-situ generated TiC x The in-situ decomposition of TiC can also be used as a sintering aid to accelerate the sintering process.

[0029] Beneficial effects:

[0030] The application has relatively low temperature and pressure, does not need complex process flow, and generates TiC in-situ through decomposition of Ti3AlC2 x Preparation of TiVNbTaMoC x The high-entropy carbide ceramic has a highest density of 99.6%, and a Vickers hardness of 41.10 GPa when the test load is 0.49 N. The method of the application improves the density of the high-entropy carbide ceramic by using a simple method, and has the advantages of simple process, short production cycle, no need for complex pretreatment of raw materials, and significant reduction of energy consumption and cost for preparation, thereby providing a new way for large-scale preparation of high-performance high-entropy ceramic materials. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is an XRD pattern of the ceramic prepared in Example 1 to Example 5, Comparative Example 1 and Comparative Example 2 of the application;

[0032] Figure 2 is TiVNbTaMoC prepared in Example 1 of the application 4.49 is a surface SEM image and an EDS element distribution map of the high-entropy carbide ceramic;

[0033] Figure 3 is TiVNbTaMoC prepared in Example 2 of the application 4.48 is a surface SEM image and an EDS element distribution map of the high-entropy carbide ceramic;

[0034] Figure 4 is TiVNbTaMoC prepared in Comparative Example 1 of the application 4.5 is a cross-sectional SEM image of the high-entropy carbide ceramic;

[0035] Figure 5 is TiVNbTaMoC prepared in Example 2 of the application 4.48 is a cross-sectional SEM image of the high-entropy carbide ceramic. DETAILED DESCRIPTION

[0036] The application will be further described in detail below with specific examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application.

[0037] All raw materials of the application are not particularly limited in purity, and the application uses conventional purity in the art.

[0038] The device used in the application is not particularly limited, and all devices commonly used in the art are used.

[0039] The sintering process involved in each of the following examples and comparative examples is completed by using an SPS-20T-10-1V type SPS discharge plasma hot pressing sintering furnace.

[0040] The Ti3AlC2, TiC, VC, NbC, TaC, Mo2C used in each of the following examples and comparative examples are raw materials directly purchased on the market, the particle size is ≤3 μm, and the purity is ≥99%.

[0041] Example 1

[0042] A method for preparing a dense high-entropy carbide ceramic, comprising the following steps:

[0043] 0.07 g of Ti3AlC2, 2.22 g of TiC, 2.41 g of VC, 4.01 g of NbC, 7.38 g of TaC, and 3.90 g of Mo2C powders are mixed using a planetary ball mill, with ethanol as the medium and tungsten carbide balls as the grinding material. After mixing for 480 min, a mixed slurry is obtained. The slurry is dried in a rotary evaporator to obtain a uniform mixed powder. The powder is placed in a graphite mold, and sintering is performed at a temperature of 1550°C, a pressure of 50 MPa, and a holding time of 15 min. After stopping heating, the sample is naturally cooled to room temperature. A surface carburized layer is removed using a grinding machine to obtain TiVNbTaMoC 4.49 The high-entropy carbide ceramic has a density of 97%, a Vickers hardness of 35.9 GPa at a test load of 0.49 N, a bending strength of 801 MPa, and a fracture toughness of 5.04 MPa·m 1 / 2 .

[0044] Example 2

[0045] A method for preparing a dense high-entropy carbide ceramic, comprising the following steps:

[0046] 0.12 g of Ti3AlC2, 2.17 g of TiC, 2.41 g of VC, 4.01 g of NbC, 7.38 g of TaC, and 3.90 g of Mo2C powders are mixed using a planetary ball mill, with ethanol as the medium and tungsten carbide balls as the grinding material. After mixing for 480 min, a mixed slurry is obtained. The slurry is dried in a rotary evaporator to obtain a uniform mixed powder. The powder is placed in a graphite mold, and sintering is performed at a temperature of 1550°C, a pressure of 50 MPa, and a holding time of 15 min. After stopping heating, the sample is naturally cooled to room temperature. A surface carburized layer is removed using a grinding machine to obtain TiVNbTaMoC 4.48 The high-entropy carbide ceramic has a density of 99.6%, a Vickers hardness of 41.10 GPa at a test load of 0.49 N, a bending strength of 1018.31 MPa, and a fracture toughness of 5.67 MPa·m 1 / 2 .

[0047] Example 3

[0048] A method for preparing a dense high-entropy carbide ceramic, comprising the following steps:

[0049] 0.25 g of Ti3AlC2, 2.06 g of TiC, 2.41 g of VC, 4.01 g of NbC, 7.38 g of TaC and 3.90 g of Mo2C powders were mixed by planetary ball milling with ethanol as medium and tungsten carbide balls as grinding material. After mixing for 480 min, a mixed slurry was obtained. The slurry was dried in a rotary evaporator to obtain a uniform mixed powder. The powder was placed in a graphite mold, and a TiVNbTaMoC ceramic was prepared by using a sintering temperature of 1550 °C, a pressure of 50 MPa, a holding time of 15 min, naturally cooling the sample to room temperature after stopping heating, and removing the surface carburized layer using a grinding machine. 4.46 The high-entropy carbide ceramic had a relative density of 99.2%, a Vickers hardness of 39.31 GPa when the test load was 0.49 N, a bending strength of 853 MPa, and a fracture toughness of 5.18 MPa·m 1 / 2 .

[0050] Example 4

[0051] A method for preparing a dense high-entropy carbide ceramic includes the following steps:

[0052] 0.25 g of Ti3AlC2, 2.06 g of TiC, 2.41 g of VC, 4.01 g of NbC, 7.38 g of TaC and 3.90 g of Mo2C powders were mixed by planetary ball milling with ethanol as medium and tungsten carbide balls as grinding material. After mixing for 480 min, a mixed slurry was obtained. The slurry was dried in a rotary evaporator to obtain a uniform mixed powder. The powder was placed in a graphite mold, and a TiVNbTaMoC ceramic was prepared by using a sintering temperature of 1550 °C, a pressure of 50 MPa, a holding time of 15 min, naturally cooling the sample to room temperature after stopping heating, and removing the surface carburized layer using a grinding machine. 4.45 The high-entropy carbide ceramic had a relative density of 97.3%, a Vickers hardness of 36.94 GPa when the test load was 0.49 N, a bending strength of 380 MPa, and a fracture toughness of 4.58 MPa·m 1 / 2 .

[0053] Example 5

[0054] A method for preparing a dense high-entropy carbide ceramic includes the following steps:

[0055] Ti3AlC2, 1.83 g of TiC, 2.41 g of VC, 4.01 g of NbC, 7.38 g of TaC and 3.90 g of Mo2C powders were mixed by planetary ball milling with ethanol as medium and tungsten carbide balls as milling media. After mixing for 480 min, the mixed slurry was obtained. The slurry was dried in a rotary evaporator to obtain a uniform mixed powder. The powder was placed in a graphite mold, and a sintering temperature of 1550 °C, a pressure of 50 MPa, and a holding time of 15 min were used. After stopping heating, the sample was naturally cooled to room temperature. A surface carburized layer was removed using a grinding machine to prepare TiVNbTaMoC 4.43 high-entropy carbide ceramic. The density was 96.9%, the Vickers hardness was 36.10 GPa when the test load was 0.49 N, the bending strength was 563 MPa, and the fracture toughness was 4.99 MPa-m 1 / 2 .

[0056] Comparative Example 1

[0057] TiC, 2.41 g of VC, 4.01 g of NbC, 7.38 g of TaC and 3.90 g of Mo2C powders were mixed by planetary ball milling with ethanol as medium and tungsten carbide balls as milling media. After mixing for 480 min, the mixed slurry was obtained. The slurry was dried in a rotary evaporator to obtain a uniform mixed powder. The powder was placed in a graphite mold, and a sintering temperature of 1550 °C, a pressure of 50 MPa, and a holding time of 15 min were used. After stopping heating, the sample was naturally cooled to room temperature. A surface carburized layer was removed using a grinding machine to prepare TiVNbTaMoC 4.5 high-entropy carbide ceramic.

[0058] TiVNbTaMoC prepared in the present comparative example 4.5 high-entropy carbide ceramic. The density reached 96.5%, the Vickers hardness reached 39.1 MPa when the test load was 0.49 N, the bending strength reached 813 MPa, and the fracture toughness was 4.57 MPa-m 1 / 2 .

[0059] Comparative Example 2

[0060] Ti3AlC2, 1.37 g of TiC, 2.41 g of VC, 4.01 g of NbC, 7.38 g of TaC and 3.90 g of Mo2C powders were mixed by planetary ball milling with ethanol as medium and tungsten carbide balls as milling media. After mixing for 480 min, the mixed slurry was obtained. The slurry was dried in a rotary evaporator to obtain a uniform mixed powder. The powder was placed in a graphite mold, and a sintering temperature of 1550 °C, a pressure of 50 MPa, and a holding time of 15 min were used. After stopping heating, the sample was naturally cooled to room temperature. A surface carburized layer was removed using a grinding machine to prepare the multiphase carbide ceramic.

[0061] As shown in Figure 1 , it is the XRD diagram of high-entropy carbide ceramic prepared by the present application embodiment 1 to embodiment 5, comparative example 1, comparative example 2;

[0062] As shown in Figure 2 , it is the TiVNbTaMoC 4.49 surface SEM diagram and EDS element distribution diagram of high-entropy carbide ceramic prepared by the present application embodiment 1;

[0063] As shown in Figure 3 , it is the TiVNbTaMoC 4.48 surface SEM diagram and EDS element distribution diagram of high-entropy carbide ceramic prepared by the present application embodiment 2;

[0064] As shown in Figure 4 , it is the TiVNbTaMoC 4.5 high-entropy carbide ceramic fracture SEM diagram prepared by the present application comparative example 1;

[0065] As shown in Figure 5 , it is the TiVNbTaMoC 4.48 high-entropy carbide ceramic fracture SEM diagram prepared by the present application embodiment 2;

[0066] It can be seen from Figure 1 : under the pressure of 50MPa, when the preparation temperature is 1550℃, using Ti3AlC2 instead of TiC as raw material, in-situ decomposition produces TiC x , the use amount of Ti3AlC2 is between 3%-20% of the total Ti amount of Ti3AlC2 and TiC, the prepared high-entropy carbide ceramic remains single phase; the use amount of Ti3AlC2 is greater than or equal to 40% of the total Ti amount of Ti3AlC2 and TiC (comparative example 2), the sample appears phase separation. It can be seen from Figure 5 the scanning electron microscope photos that the high-entropy carbide ceramic prepared by using part of Ti3AlC2 as raw material is more compact than Figure 4 , the use of TiC as the only titanium carbide source in comparative example 1 reduces the pores obviously, and the grains are more uniform.

[0067] It can be seen from embodiments 1-5 that using Ti3AlC2 as part of the titanium source of titanium carbide, in-situ decomposition produces TiC x , has higher sintering activity, and a small amount of addition can promote ceramic densification.

[0068] In the comparative example 1, by using commercial powder (≤3 μm) TiC, VC, NbC, TaC, Mo2C, TiVNbTaMoC can be prepared at 1550℃, 50MPa pressure 4.5 The high-entropy carbide ceramic has a density of 96.5%, a Vickers hardness of 39.1 MPa when the test load is 0.49 N, a bending strength of 813 MPa, and a fracture toughness of about 4.57 MPa·m 1 / 2 .

[0069] However, defects such as pores limit the further improvement of the mechanical properties of the material. If the TiVNbTaMoC 4.5 ceramic needs to be further improved, the preparation temperature needs to be improved, or a larger preparation pressure needs to be used. However, improving the sintering temperature will cause grain coarsening and reduce the mechanical properties of the TiVNbTaMoC 4.5 ceramic. Using a larger preparation pressure requires higher performance of the equipment and greatly increases the cost of material preparation. The present application uses Ti3AlC2 decomposition in situ to produce TiC x to prepare TiVNbTaMoC x high-entropy carbide ceramic, which realizes the densification of high-entropy ceramic at a lower temperature and lower pressure, has important practical significance for the industrial application of high-entropy carbide ceramic.

[0070] The technical scheme of the present application is not limited to the above specific embodiments, and any technical deformation made according to the technical scheme of the present application falls within the protection scope of the present application.

Claims

1. A method for preparing dense high-entropy carbide ceramics, characterized in that: The following steps are involved: Ti3AlC2, TiC, VC, NbC, TaC, and Mo2C are mixed and loaded, and then sintered to obtain high entropy carbide ceramics TiVNbTaMoC x , where 4.43≤x≤4.

49.

2. The method for preparing a dense high-entropy carbide ceramic according to claim 1, characterized in that: In Ti3AlC2, TiC, VC, NbC, TaC, and Mo2C, the molar ratio of Ti element, V element, Nb element, Ta element, and Mo element is 1:1:1:1:

1.

3. The method for preparing dense high-entropy carbide ceramics according to claim 1, characterized in that: The usage amount of Ti3AlC2 is calculated as Ti, accounting for 3%-20% of the total Ti amount of Ti3AlC2 and TiC.

4. The method for preparing dense high-entropy carbide ceramics according to claim 1, wherein: The mixing process is: using planetary ball milling or roller ball milling, adopting dry or wet mixing to obtain uniformly mixed raw materials.

5. The method for preparing dense high-entropy carbide ceramics according to claim 4, characterized in that: The loading process is as follows: loading the evenly mixed raw materials into the graphite mold.

6. The method for preparing dense high-entropy carbide ceramics according to claim 1, characterized in that: The sintering process is as follows: using a pressure of 30 MPa or above, a temperature of 1550° C. or above, and maintaining the temperature and pressure for 15 minutes or more.

7. The method for preparing dense high-entropy carbide ceramics according to claim 1, characterized in that: The sintering process is as follows: keeping the temperature and pressure at 50 MPa and 1550° C. for 15 minutes.

8. The method for preparing dense high-entropy carbide ceramics according to claim 6, characterized in that: After the heat preservation and pressure preservation process of sintering is completed, cooling and pressure relief are performed.

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