A preparation method of a high-entropy boride-silicon carbide composite ceramic

Abstract

The application belongs to the technical field of ceramics, and particularly relates to a preparation method of high-entropy boride-silicon carbide composite ceramics, which comprises the following steps: mixing high-entropy boride powder and carbon source powder, and then adopting a ceramic forming method to prepare a ceramic green body; embedding the ceramic green body with silicon powder, and performing liquid silicon infiltration treatment in a vacuum environment to obtain high-entropy boride-silicon carbide composite ceramics. The application mixes high-entropy boride and carbon source, and then performs liquid phase silicon infiltration, so that the process is simpler, the residual Si content is relatively less, and high-entropy boride-silicon carbide composite ceramics with a density of more than 99% can be obtained, which is suitable for large-scale production and application.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of ceramics, and particularly relates to a preparation method of high-entropy boride-silicon carbide composite ceramics. BACKGROUND

[0002] Hypersonic vehicles have a large flight speed, and the surface temperature of the nose cone or the leading edge of the wing rises sharply due to the impact of the airflow, resulting in serious ablation. In order to effectively protect the aircraft, the high-temperature resistance, high thermal conductivity and anti-oxidation ablation of the thermal protection material become particularly important. Among them, superhigh-temperature ceramics are widely used in thermal protection systems due to their high melting point, high thermal conductivity and ablation resistance, but in complex flight environments, superhigh-temperature ceramics are prone to oxidation and ablation, causing material failure. In order to further meet the needs of aircraft thermal protection materials, it is urgent to develop new materials.

[0003] High-entropy ceramics are single-phase solid solution compounds composed of equal molar or approximately equal molar anions or cations of not less than four elements. The unique high-entropy effect, lattice distortion effect, delayed diffusion effect and cocktail effect make it have better physical and chemical properties than single-component or two-component compounds. Among them, document 1 "Ye B, Fan C, et al. Synthesis of high-entropy diboride nanopowders via molten salt-mediated magnesiothermic reduction [J]. Journal of the American Ceramic Society, 2020, 103(9): 4738-4741." Beilin Ye et al. prepared (Ti 0.2 Hf 0.2 Zr 0.2 Nb 0.2 Ta 0.2)B2, etc. The results show that the oxidation onset temperature and the significant weight gain temperature of high-entropy boride ceramics are significantly higher than those of single-component borides. Literature 2“Gild J, Zhang Y, Harrington T, et al. High-entropy metal diborides: a new class of high-entropy materials and a new type of ultrahigh temperature ceramics[J]. Scientific reports, 2016, 6(1): 1-10.” Gild J et al. prepared (Ti 0.2 Hf 0.2 Zr 0.2 Nb 0.2 Ta 0.2 )B2, etc. The results show that the oxidation onset temperature and the significant weight gain temperature of high-entropy boride ceramics are significantly higher than those of single-component borides. Literature 2“Gild J, Zhang Y, Harrington T, et al. High-entropy metal diborides: a new class of high-entropy materials and a new type of ultrahigh temperature ceramics[J]. Scientific reports, 2016, 6(1): 1-10.” Gild J et al. prepared (Ti

[0004] To further improve the oxidation and ablation resistance of high-entropy borides, high-entropy boride-silicon carbide composite ceramics were prepared by introducing silicon carbide. During oxidation, SiC actively oxidizes and SiO diffuses outward to form a glassy SiO2 protective layer, preventing further oxygen erosion, which can effectively improve the oxidation and ablation resistance of the composite ceramics. So far, the main preparation methods of composite ceramics include pressureless sintering, pressure-assisted sintering, field-assisted sintering, etc. For example, patent CN109987941B A high-entropy ceramic composite material with oxidation resistance and a preparation method and application thereof, (Ti 0.2 Hf 0.2 Zr 0.2 Mo 0.2 Cr 0.2 )B2 powder and SiC powder are uniformly mixed in a certain proportion, and then sintered by SPS to make it dense. The relative density of the prepared composite ceramic can reach 95% ~ 99.9%, and the weight change after heat treatment is less. Patent CN112028635A An ultrahigh-temperature ceramic composite material and a preparation method, SiC is introduced as a sintering aid into (Ti 0.25 Hf 0.25 Zr 0.25 Ta 0.25)B2 in the ceramic body, and then using a gas phase silicon infiltration process to fill the pores with Si vapor, making the ceramic densified. This method uses four-component high-entropy boride mixed with SiC, and then molded into a sheet, and finally placed in a high-temperature atmosphere furnace for gas phase silicon infiltration. However, the above methods have high preparation process temperature, complex preparation principle, and many influencing factors, and are not suitable for large-scale production application. SUMMARY

[0005] To solve the above technical problems, the present application provides a preparation method of high-entropy boride-silicon carbide composite ceramic. The present application mixes high-entropy boride with carbon source, and then performs liquid silicon infiltration. The process is simpler, the residual Si content is relatively less, and high-entropy boride-silicon carbide composite ceramic with a density of more than 99% can be obtained. The preparation process and principle are simple, the temperature is low, and it is suitable for large-scale production application.

[0006] The present application is realized by the following technical solutions.

[0007] A preparation method of high-entropy boride-silicon carbide composite ceramic, comprising the following steps:

[0008] Mixing high-entropy boride powder with carbon source powder, and then using a ceramic forming method to prepare a ceramic body;

[0009] Embedding the ceramic body with silicon powder, and performing liquid silicon infiltration treatment in a vacuum environment to obtain high-entropy boride-silicon carbide composite ceramic.

[0010] Using the silicon powder embedding method, when the silicon reaches its melting point, liquid silicon and part of the gas silicon will penetrate into the ceramic interior from all directions, and form silicon carbide with the carbon source, which is uniformly distributed between the high-entropy boride.

[0011] In a preferred embodiment of the present application, the carbon source includes graphite, carbon black, and resin carbon, and the addition amount of the carbon source is 10-30wt.%.

[0012] In a preferred embodiment of the present application, the ceramic forming method includes dry pressing, isostatic pressing, slip casting, and hot-pressing casting.

[0013] In a preferred embodiment of the present application, the liquid silicon infiltration treatment conditions are: vacuum environment, pressure of 1-10 MPa, heating rate of 5-20℃ / min, holding temperature of 1500-1650℃, and holding time of 30-150 min.

[0014] In a preferred embodiment of the present application, the mixing step of high-entropy boride powder and carbon source powder is: mixing five-component high-entropy boride powder with carbon source, immersing in alcohol, then performing wet milling treatment, and drying.

[0015] In a preferred embodiment of the present application, the chemical formula of the five-component high-entropy boride is (D x1 E x2 F x3 G x4 H x5 )B2 or (D y1 E y2 F y3 G y4 )B2, wherein D, E, F, G, and H are any five of the nine metal elements Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, respectively; wherein x1+x2+x3+x4+x5=1, y1+y2+y3+y4=1, and the stoichiometric ratio between x1, x2, x3, x4, and x5 can be equimolar or non-equimolar; the stoichiometric ratio between y1, y2, y3, and y4 is equimolar or non-equimolar; preferably, x1+x2+x3+x4+x5=1, and 0.1≤x1≤0.5, 0.1≤x2≤0.5, 0.1≤x3≤0.5, 0.1≤x4≤0.5, 0.1≤x5≤0.5; y1+y2+y3+y4=1, and 0.1≤y1≤0.5, 0.1≤y2≤0.5, 0.1≤y3≤0.5, 0.1≤y4≤0.5. More preferably, the stoichiometric ratio between x1, x2, x3, x4, and x5 is equimolar; the stoichiometric ratio between y1, y2, y3, and y4 is equimolar. The average particle size of the high-entropy ceramic powder is 0.2-6 μm.

[0016] In a preferred embodiment of the present application, the high-entropy boride is prepared by a boron-carbon thermal reduction reaction method.

[0017] The metal oxide powder and the boron source are uniformly mixed, and then heat-treated at 1700-2000 °C. The heat-treated powder is ball-milled to obtain the desired high-entropy boride powder.

[0018] In a preferred embodiment of the present application, the purity of the metal oxide powder is higher than 90%, and the particle size is in the nanometer to micrometer range.

[0019] In a preferred embodiment of the present application, the boron source is boron carbide powder and / or boron powder, and the molar ratio of the total moles of metal oxides to the moles of boron source during batching is between 7.5 and 9, because the reduction rates of different oxides are different, and more boron source than the theoretical amount is needed when all the oxides are reduced.

[0020] In a preferred embodiment of the present application, the heat treatment time is 30-240 min; the rotation speed of the ball mill is 150-400 r / min, and the ball milling time is 5-40 h.

[0021] In the ceramic forming and sintering process of the present application, no binder or sintering aid is used.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] The present application first uses boron / carbon thermal reduction reaction to prepare high-entropy boride powder, mixes the high-entropy boride powder with carbon source powder, and then uses a ceramic forming method to prepare a ceramic green body. The ceramic green body is embedded with silicon powder, and then subjected to liquid silicon infiltration treatment in a vacuum environment to obtain high-entropy boride-silicon carbide composite ceramic. The present application can generate SiC in situ, and the prepared ceramic has a relatively uniform distribution of substances. In the sintering process, a large number of atomic migration phenomena occur in the ceramic, and the phases in the sintered ceramic are uniformly dispersed. The prepared ceramic block has high density (more than 99%), is not easy to change shape, can effectively improve the oxidation ablation resistance, and can be used to prepare components.

[0024] The present application solves the problems of complex preparation process and high preparation temperature of introducing silicon carbide into high-entropy boride, and can ensure that the prepared ceramic has a density of more than 99%, which is beneficial to further improve the oxidation ablation resistance of ultra-high temperature ceramic. In addition, the preparation temperature of the method of the present application is relatively low, the process is simple, the experimental environment requirement is not high, and the powder particle size and activity requirement is not high. The purity of the silicon powder used for embedding has no special requirement, and large-scale production at low cost can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a flowchart of the preparation method of high-entropy boride-silicon carbide composite ceramic of the present application.

[0026] Figure 2 It is the BSE and point scanning energy spectrum of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2-SiC composite ceramic prepared in Example 2.

[0027] Figure 3 It is the cross-sectional morphology and corresponding EDS spectrum of the sample of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2-SiC composite ceramic prepared in Example 2 after oxidation for 100h at 1550℃. DETAILED DESCRIPTION

[0028] In order to make the technical personnel of the present application better understand the technical solutions can be implemented, the following specific embodiments and the present application is further described with reference to the drawings, but the examples are not as a limitation of the present application.

[0029] The experimental methods and detection methods described in the following examples, such as no special instructions, are conventional methods; the reagents and materials, such as no special instructions, can be purchased on the market.

[0030] High-entropy boride combines the excellent oxidation ablation resistance of boride with the four high-entropy effects of high-entropy material, so that it has more excellent oxidation ablation resistance and high-temperature mechanical properties. The high-entropy boride-silicon carbide composite ceramic prepared by the RMI method has the advantages of high density, low cost and low sintering temperature, and is a fast and efficient method for preparing composite ceramics. Its principle is as follows:

[0031] Si melt is infiltrated into the ceramic body containing carbon source in a high temperature environment, and SiC is generated by the reaction of Si and C, thereby preparing high-entropy boride-silicon carbide composite ceramic. We propose to use boron / carbon thermal reduction reaction to prepare high-entropy boride powder, then mix the carbon source with the high-entropy boride powder, prepare the ceramic body, and finally use the RMI process to densify the ceramic body.

[0032] The preparation method of the present application comprises the following steps:

[0033] After mixing the high-entropy boride powder and the carbon source powder, a ceramic body is prepared by using a ceramic forming method;

[0034] The ceramic body is embedded with silicon powder, and liquid silicon infiltration treatment is carried out in a vacuum environment to obtain high-entropy boride-silicon carbide composite ceramic.

[0035] The present application adopts the method of embedding silicon powder. When the melting point of silicon is reached, liquid silicon and part of gaseous silicon will penetrate into the ceramic from all directions, and form silicon carbide with the carbon source, which is uniformly distributed between the high-entropy boride.

[0036] RMI method can be used to prepare high-entropy boride-silicon carbide composite ceramics with high density and good mechanical properties at low temperature using relatively simple equipment, but there are few reports on this method. Patent 3 "Liu Wei, Sun Tongchen, et al. A high-entropy ceramic matrix composite and a preparation method thereof [P]. Beijing: CN113321510B, 2022-06-03." Liu Wei et al. mixed high-entropy carbide powder with phenolic resin slurry, then impregnated it into semi-dense composite, and then treated with RMI process to obtain high-entropy ceramic matrix composite with excellent mechanical properties and high-temperature oxidation resistance. However, this method may have problems with the reaction of high-entropy carbide with silicon, while high-entropy boride does not react with silicon. The present invention uses RMI process to prepare high-entropy boride-silicon carbide ceramics with excellent mechanical properties and high-temperature ablation resistance at low cost.

[0037] In a preferred embodiment of the present application, the carbon source includes graphite, carbon black, and resin carbon, and the addition amount of the carbon source is 10-30 wt.%.

[0038] In a preferred embodiment of the present application, the ceramic forming method includes dry pressing, isostatic pressing, slip casting, and hot-pressing casting.

[0039] In a preferred embodiment of the present application, the liquid silicon infiltration treatment conditions are: vacuum environment, pressure 1-10 MPa, heating rate 5-20 ℃ / min, holding temperature 1500-1650 ℃, and holding time 30-150 min.

[0040] In a preferred embodiment of the present application, the mixing step of high-entropy boride powder and carbon source powder is: mixing five-component high-entropy boride powder and carbon source, then immersing in alcohol, followed by wet milling treatment, and drying.

[0041] In a preferred embodiment of the present application, the chemical formula of the high-entropy boride is (D x1 E x2 F x3 G x4 H x5 )B2 or (D y1 E y2 F y3 G y4B2, wherein D, E, F, G, H are respectively any five of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W; wherein x1, x2, x3, x4, x5 are the molar ratio of each element, y1, y2, y3, y4 are the molar ratio of each element, x1+x2+x3+x4+x5=1, y1+y2+y3+y4=1, and the stoichiometric ratio between x1, x2, x3, x4, x5 is equimolar ratio or non-equimolar ratio; the stoichiometric ratio between y1, y2, y3, y4 is equimolar ratio or non-equimolar ratio; preferably, x1+x2+x3+x4+x5=1, and 0.1≤x1≤0.5, 0.1≤x2≤0.5, 0.1≤x3≤0.5, 0.1≤x4≤0.5, 0.1≤x5≤0.5; y1+y2+y3+y4=1, and 0.1≤y1≤0.5, 0.1≤y2≤0.5, 0.1≤y3≤0.5, 0.1≤y4≤0.5. More preferably, the stoichiometric ratio between x1, x2, x3, x4, x5 is equimolar ratio; the stoichiometric ratio between y1, y2, y3, y4 is equimolar ratio. The average particle size of the high-entropy ceramic powder is 0.2-6 μm.

[0042] In the preferred embodiment of the present application, the high-entropy boride is prepared by a boron-carbon thermal reduction reaction method.

[0043] The metal oxide powder and the boron source are uniformly mixed, and then heat-treated at 1700-2000 ℃, and the heat-treated powder is ball milled to obtain the desired high-entropy boride powder.

[0044] In the preferred embodiment of the present application, the purity of the metal oxide powder is higher than 90%, and the particle size is in the nanometer to micron range.

[0045] In the preferred embodiment of the present application, the boron source is boron carbide powder and / or boron powder, and the molar ratio of the total number of moles of metal oxides to the number of moles of boron source is between 7.5-9, because the reduction rate of each oxide is different, more boron source than the theoretical amount is needed when all oxides are reduced.

[0046] In the preferred embodiment of the present application, the heat treatment time is 30-240 min, the rotation speed of the ball mill is 150-400 r / min, and the ball milling time is 5-40 h.

[0047] In the ceramic forming and sintering process of the present application, no binder or sintering aid is used.

[0048] The application first adopts boron / carbon thermal reduction reaction to prepare high-entropy boride powder, mixes the high-entropy boride powder with carbon source powder, and then adopts a ceramic forming method to prepare a ceramic body. The ceramic body is embedded with silicon powder, and liquid silicon infiltration treatment is performed in a vacuum environment to obtain high-entropy boride-silicon carbide composite ceramic. The ceramic block prepared by the method has high density (more than 99%) and is not easy to change shape. The method has low preparation temperature, simple process, low requirement for experimental environment, and low requirement for powder particle size and activity. The purity of the silicon powder used for embedding has no special requirement, and large-scale production at low cost can be realized. The application can generate SiC in situ, and the distribution of substances in the prepared ceramic is relatively uniform. In the sintering process, a large number of atomic migration phenomena occur in the ceramic, and the phases in the sintered ceramic are uniformly dispersed. The application solves the problems of high cost, high preparation temperature, and high requirement for experimental equipment, and makes the density of the prepared ceramic as high as 99% or more, and further improves the oxidation resistance and ablation resistance of the ultrahigh-temperature ceramic.

[0049] The content of the application will be specifically described below through the following examples and comparative examples.

[0050] Example 1

[0051] A preparation method of high-entropy boride-silicon carbide composite ceramic, in particular, a preparation method of a sample (S1) doped with 10wt.% of graphite, as shown in the following table, includes the following steps: Figure 1

[0052] Step 1, preparation of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder:

[0053] Five kinds of metal oxide powders (TiO2, ZrO2, HfO2, Nb2O5, Ta2O5) and boron carbide powder are added into a ball mill tank in a molar ratio of 1:1:1:1:1:8, and then uniformly mixed. Then, boron / carbon thermal reduction reaction is performed at a temperature of 1800℃, and the heat treatment time is 120 min. Finally, the powder after reaction is ball milled by using a planetary ball mill, and (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder is obtained. The rotation speed of the ball mill is 300 r / min, and the ball milling time is 24 h. The purity of the metal oxide powder is higher than 90%.

[0054] Step 2, preparation of a ceramic body:

[0055] ​Take 18 g of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 prepared in step 1 and 2 g of pure graphite powder, mix and granulate in an agate mortar, then take 5 g of the mixed powder and put it into a mold to obtain a green body by using a tablet press.

[0056] The mixing method is as follows: after weighing the high-entropy boride and carbon source according to the proportion, put them into a sealed bottle, add a large amount of alcohol to dissolve the powder in the alcohol, then put it into a drum ball mill for wet grinding treatment, and then take it out to dry in an oven.

[0057] Step 3, liquid silicon infiltration:

[0058] Embed the ceramic green body described in step 2 with silicon powder and place it in a graphite crucible, then put the ceramic green body wrapped with silicon powder into a silicon infiltration furnace for liquid silicon infiltration treatment in a vacuum environment, finally obtain (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2-SiC composite ceramic. The pressure is 10 MPa, the heating rate is 5 ℃ / min, the holding temperature is 1500 ℃, and the holding time is 60 min.

[0059] Example 2

[0060] A preparation method of a high-entropy boride-silicon carbide composite ceramic, specifically a preparation method of a sample (S2) doped with 20 wt.% graphite, comprising the following steps:

[0061] Step 1, preparation of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder:

[0062] Mix five kinds of metal oxide powders (TiO2, ZrO2, HfO2, Nb2O5, Ta2O5) and boron carbide powder in a ball mill jar according to the element molar ratio of 1:1:1:1:1:8, then perform boron / carbon thermal reduction reaction at a temperature of 1800 ℃, the heat treatment time is 120 min, finally the reacted powder is ball milled by using a planetary ball mill, and the desired (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2B2 powder. The rotation speed of the ball mill is 300 r / min, and the ball milling time is 24 h. The purity of the metal oxide powder is higher than 90%.

[0063] Step 2, preparation of a ceramic body:

[0064] Respectively, 16 g of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder prepared in step 1 and 4 g of pure graphite powder are placed in a agate mortar and mixed uniformly, granulated, and then 4.5 g of the mixed powder is weighed into a mold and a pressed body is obtained by using a tablet press; the mixing method is as follows: the high-entropy boride and the carbon source are weighed according to the proportion, placed in a sealed bottle, a large amount of alcohol is added, the powder is dissolved in the alcohol, and then placed in a drum ball mill for wet milling treatment, and then taken out and dried in an oven.

[0065] Step 3, liquid silicon infiltration:

[0066] The ceramic body described in step 2 is embedded with silicon powder and placed in a graphite crucible, and then the ceramic body wrapped with silicon powder is placed in a silicon infiltration furnace for liquid silicon infiltration treatment in a vacuum environment, and finally (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2-SiC composite ceramic is obtained. The pressure is 10 MPa, the holding temperature is 1500℃, the heating rate is 5℃ / min, and the holding time is 60 min.

[0067] Example 3

[0068] A preparation method of a high-entropy boride-silicon carbide composite ceramic, in particular, a preparation method of a sample (S3) doped with 30wt.% graphite, includes the following steps:

[0069] Step 1, preparation of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder:

[0070] Five kinds of metal oxide powders (TiO2, ZrO2, HfO2, Nb2O5, Ta2O5) and boron carbide powder are added to a ball mill tank and mixed uniformly according to the element molar ratio 1:1:1:1:1:8, and then a boron / carbon thermal reduction reaction is carried out at a temperature of 1800℃, the heat treatment time is 120 min, and finally the powder after reaction is ball milled by using a planetary ball mill, thereby obtaining the required (Ti 0.2 Zr0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder. The ball milling speed was 300 r / min, and the ball milling time was 24 h. The purity of the metal oxide powder was higher than 90%.

[0071] Step 2, preparation of a ceramic body:

[0072] 14 g of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 prepared in step 1 and 6 g of pure graphite powder were placed in a agate mortar and mixed uniformly, granulated, and then 4 g of the mixed powder was placed in a mold and a pressed body was obtained by using a tablet press; the mixing method was as follows: the high-entropy boride and the carbon source were weighed according to the proportion, placed in a sealed bottle, a large amount of alcohol was added, the powder was dissolved in the alcohol, and then placed in a drum ball mill for wet milling treatment, and then taken out and dried in an oven.

[0073] Step 3, liquid silicon infiltration:

[0074] The ceramic body described in step 2 was embedded with silicon powder and placed in a graphite crucible, and then the ceramic body wrapped with silicon powder was placed in a silicon infiltration furnace for liquid silicon infiltration treatment in a vacuum environment, and finally (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2-SiC composite ceramic was obtained. The pressure was 10 MPa, the holding temperature was 1500℃, the heating rate was 5℃ / min, and the holding time was 60 min.

[0075] Example 4

[0076] A preparation method of a high-entropy boride-silicon carbide composite ceramic, specifically a preparation of a sample (S3) doped with 30wt.% graphite, compared with example 3, the liquid silicon infiltration holding time was 30 min, including the following steps:

[0077] Step 1, preparation of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder:

[0078] Five metal oxide powders (TiO2, ZrO2, HfO2, Nb2O5, Ta2O5) and boron carbide powder were mixed in a ball mill tank at a molar ratio of 1:1:1:1:1:8, then boron / carbon thermal reduction reaction was carried out at a temperature of 1800°C, the heat treatment time was 120 min, and finally the reacted powder was ball milled by a planetary ball mill to obtain the required (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder. The rotation speed of the ball mill was 300 r / min, and the ball milling time was 24 h. The purity of the metal oxide powder was higher than 90%.

[0079] Step 2, preparation of ceramic green body:

[0080] 14 g of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 prepared in step 1 and 6 g of pure graphite powder were weighed and uniformly mixed in an agate mortar, then 4 g of the mixed powder was placed in a mold and a green body was obtained by using a tablet press; the mixing method was as follows: the high-entropy boride and the carbon source were weighed according to the proportion, then they were placed in a sealed bottle, a large amount of alcohol was added to dissolve the powder in the alcohol, and then the wet milling treatment was carried out in a drum ball mill, and then it was taken out and dried in an oven.

[0081] Step 3, liquid silicon infiltration:

[0082] The ceramic green body described in step 2 was embedded with silicon powder and placed in a graphite crucible, then the ceramic green body wrapped with silicon powder was placed in a silicon infiltration furnace, and liquid silicon infiltration treatment was carried out in a vacuum environment, finally (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2-SiC composite ceramic was obtained. The pressure was 10 MPa, the holding temperature was 1500°C, the heating rate was 5°C / min, and the holding time was 30 min.

[0083] Example 5

[0084] A preparation method of a high-entropy boride-silicon carbide composite ceramic, specifically the preparation of a sample (S3) doped with 30wt.% graphite, compared with example 3, the liquid silicon infiltration holding time was 150 min, including the following steps:

[0085] Step 1, (Ti 0.2 Zr 0.2 Hf0.2 Nb 0.2 Ta 0.2 )B2 powder preparation:

[0086] Five metal oxide powders (TiO2, ZrO2, HfO2, Nb2O5, Ta2O5) and boron carbide powder were mixed in a ball mill tank at a molar ratio of 1:1:1:1:1:8, and then subjected to boron / carbon thermal reduction reaction at a temperature of 1800°C for 120 min. Finally, the reacted powder was ball milled using a planetary ball mill to obtain the desired (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder. The rotation speed of the ball mill was 300 r / min, and the ball milling time was 24 h. The purity of the metal oxide powder was higher than 90%.

[0087] Step 2, preparation of ceramic green body:

[0088] 14 g of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 prepared in step 1 and 6 g of pure graphite powder were weighed into a maroon mortar and mixed evenly, granulated, and then 4 g of the mixed powder was weighed into a mold and a green body was obtained using a tablet press. The mixing method was as follows: the high-entropy boride and carbon source were weighed according to the proportion, placed in a sealed bottle, a large amount of alcohol was added to dissolve the powder in the alcohol, and then placed in a drum ball mill for wet milling treatment, and then taken out and dried in an oven.

[0089] Step 3, liquid silicon infiltration:

[0090] The ceramic green body described in step 2 was embedded with silicon powder and placed in a graphite crucible, and then the ceramic green body wrapped with silicon powder was placed in a silicon infiltration furnace for liquid silicon infiltration treatment in a vacuum environment, and finally (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2-SiC composite ceramic was obtained. The pressure was 10 MPa, the holding temperature was 1500°C, the heating rate was 5°C / min, and the holding time was 150 min.

[0091] Example 6

[0092] A preparation method of a high-entropy boride-silicon carbide composite ceramic, in particular, a sample (S3) doped with 30 wt.% graphite, compared with Example 3, the liquid silicon infiltration pressure is 1 MPa, comprising the following steps:

[0093] Step 1, preparation of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder:

[0094] Five kinds of metal oxide powders (TiO2, ZrO2, HfO2, Nb2O5, Ta2O5) and boron carbide powders are mixed in a ball mill tank according to the element molar ratio of 1:1:1:1:1:8, then boron / carbon thermal reduction reaction is carried out at a temperature of 1800 DEG C, the heat treatment time is 120 min, finally the powders after reaction are ball milled by using a planetary ball mill, and the desired (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 powder is obtained. The rotation speed of the ball mill is 300 r / min, and the ball milling time is 24 h. The purity of the metal oxide powder is higher than 90%.

[0095] Step 2, preparation of ceramic green body:

[0096] 14g of (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 )B2 prepared in step 1 and 6g of pure graphite powder are weighed and uniformly mixed in an agate mortar, granulated, then 4g of the mixed powder is weighed and placed in a mold, and a pressed green body is obtained by using a tablet press; the mixing method is as follows: the high-entropy boride and the carbon source are weighed according to the proportion, placed in a sealed bottle, a large amount of alcohol is added to dissolve the powders in the alcohol, then placed in a drum ball mill for wet milling treatment, and then taken out and dried in an oven.

[0097] Step 3, liquid silicon infiltration:

[0098] The ceramic green body described in step 2 is embedded with silicon powder and placed in a graphite crucible, then the ceramic green body wrapped with silicon powder is placed in a silicon infiltration furnace, and liquid silicon infiltration treatment is carried out in a vacuum environment, and finally (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2B2-SiC composite ceramics. The pressure is 1 MPa, the holding temperature is 1500 °C, the heating rate is 5 °C / min, and the holding time is 150 min.

[0099] The following describes the ceramics prepared in the above examples.

[0100] Figure 2 The BSE and point scanning energy spectrum of the HEB-SiC ceramics prepared in Example 2 are analyzed to find that the carbon graphitization degree is low and the reaction with silicon is not sufficient, resulting in a small amount of residual carbon and residual silicon. When the liquid silicon infiltrates into the ceramic, a molten salt environment is created, promoting the thermal motion of atoms. The further solid solution of high-entropy borides becomes a uniform single-phase solid solution, and a layer of free silicon is dispersed around the high-entropy borides. The diffusion rate of Si is slower than the reaction rate with carbon, and the graphitization degree of carbon is low, so a layer of SiC appears before Si reaches the surface of carbon, preventing Si from further reacting with the internal carbon. This results in a sandwich structure of SiC, with a silicon-rich SiC near the silicon area and a carbon-rich SiC near the carbon area.

[0101] Figure 3 The cross-sectional morphology and corresponding EDS spectrum of the sample after oxidation for 100 h at 1550 °C are shown in FIG. 10. Figure 3 It can be seen that the oxidation thickness is about 45 μm, and the upper surface of the oxidation layer is tightly combined, while the oxidation layer near the substrate is loosely combined. The holes left by the outflow of Si in the Si-rich area in the substrate indicate that the surface oxidation layer is mainly formed by the reaction of free Si diffusing to the surface of the sample with oxygen to form a glassy oxidation layer. The ceramics prepared in the other examples are similar to this result, and are not described one by one.

[0102] Through Figure 2 and Figure 3It can be seen that the high-entropy boride-silicon carbide composite ceramic is successfully prepared by the method, SiC is successfully generated in-situ in the ceramic, and SiC is introduced into the high-entropy boride. It should be noted that, compared with the prior art mentioned in the background art, the preparation method provided by the application is simpler: first, the high-entropy boride powder and the carbon source powder are mixed, then a ceramic blank is prepared by using a ceramic forming method, then the ceramic blank is embedded with silicon powder, and liquid silicon infiltration treatment is performed in a vacuum environment, thereby obtaining the high-entropy boride-silicon carbide composite ceramic. As can be seen from the preparation process, the method has low requirements for the experimental environment, the raw materials are easy to obtain, the powder particle size and activity are not high, the purity of the silicon powder used for embedding has no special requirements, and large-scale production at low cost can be realized. The preparation process principle is simple, and the reaction conditions are easy to control to regulate the product. From this point of view, it is also very suitable for large-scale production and application. In addition, high-density ceramic can be obtained by the simple preparation method provided by the application, and the density can be increased to more than 99%. Specifically, the density data of the ceramic prepared in the above embodiments of the application is shown in Table 1.

[0103] Table 1: Density data of ceramic prepared in each embodiment

[0104] Group Density Example 1 99.5％ Example 2 99.7％ Example 3 99.7％ Example 4 99.6％ Example 5 99.3％ Example 6 99.5％

[0105] In addition, the high-entropy boride powder and the carbon source powder are mixed, a ceramic blank is prepared by using a ceramic forming method, the ceramic blank is embedded with silicon powder, and liquid silicon infiltration treatment is performed in a vacuum environment to prepare the high-entropy boride-silicon carbide composite ceramic. In this process, the high-entropy boride powder and the carbon source powder are mixed by wet grinding, and the temperature during the liquid silicon infiltration process is 1500-1650 DEG C. As can be seen from the above embodiments and characterization results, high-quality ceramic can be prepared at 1500 DEG C.

[0106] In the prior art, the process route is complex, and the preparation temperature is high. For example, the publication number CN112028635A discloses an ultrahigh-temperature ceramic composite material and a preparation method, which directly mixes high-entropy boride and silicon carbide, then performs mold pressing, and finally prepares a composite ceramic by a gas phase silicon infiltration process. The temperature required by the gas phase silicon infiltration process is 2073-2273 K, which is significantly higher than 1500 DEG C in the present application.

[0107] The publication number CN109987941A discloses a high-entropy ceramic composite material with oxidation resistance and a preparation method and application thereof, which is to mix (Ti 0.2 Hf 0.2 Zr 0.2 Mo 0.2 Cr 0.2)B2 powder and SiC powder are uniformly mixed in a certain proportion, and then sintered by SPS, and the sintering temperature of the process is as high as 1800-2200 ℃, which is significantly higher than 1500 ℃ of the present application.

[0108] Therefore, under the premise of ensuring high density of the prepared composite ceramic and successful introduction of SiC into the high-entropy boride matrix, the present application can significantly reduce the required temperature in the preparation process, reduce energy consumption, and is conducive to reducing production cost, which is also very beneficial to large-scale production application from this aspect.

[0109] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, these modifications and variations are also intended to be included.

Claims

1. A method for preparing high-entropy boride-silicon carbide multiphase ceramics, characterized in that, Includes the following steps: After mixing high-entropy boride powder with carbon source powder, a ceramic green body is prepared by ceramic forming method; The ceramic green body was embedded with silicon powder and subjected to liquid silicon infiltration treatment in a vacuum environment to obtain high-entropy boride-silicon carbide multiphase ceramic. The conditions for the liquid silicon permeation treatment are as follows: in a vacuum environment, under a pressure of 1~10MPa, the temperature is raised to 1500~1650℃ at a heating rate of 5~20℃ / min, and held at 1500~1650℃ for 30~150min. The chemical formula of the high-entropy boride is (D x1 E x2 F x3 G x4 H x5 B2, wherein elements D, E, F, G, and H are any five of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W; wherein x1+x2+x3+x4+x5=1, and 0.1≤x1≤0.5, 0.1≤x2≤0.5, 0.1≤x3≤0.5, 0.1≤x4≤0.5, and 0.1≤x5≤0.5; Alternatively, the chemical formula of the high-entropy boride is (D y1 E y2 F y3 G y4 B2, wherein elements D, E, F and G are any four of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W; wherein y1+y2+y3+y4=1, and 0.1≤y1≤0.5, 0.1≤y2≤0.5, 0.1≤y3≤0.5, 0.1≤y4≤0.

5.

2. The preparation method according to claim 1, characterized in that, In the mixture of high-entropy boride powder and carbon source powder, the amount of carbon source added is 10~30 wt.%.

3. The preparation method according to claim 1, characterized in that, The carbon source is graphite, carbon black, or resin carbon.

4. The preparation method according to claim 1, characterized in that, The high-entropy boride powder has an average particle size of 0.2-6 μm.

5. The preparation method according to claim 1, characterized in that, High-entropy borides are prepared via a borocarbon thermal reduction reaction, comprising the following steps: The desired metal oxide powder is uniformly mixed with a boron source and heat-treated at 1700~2000℃. The heat-treated powder is then ball-milled to obtain the desired high-entropy boride powder.

6. The preparation method according to claim 5, characterized in that, The purity of the metal oxide powder is greater than 90%, and the particle size is in the nanometer to micrometer range.

7. The preparation method according to claim 5, characterized in that, The heat treatment time is 30~240 min.

8. The preparation method according to claim 5, characterized in that, The boron source is boron carbide powder and / or boron powder.

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