Borride high-entropy ceramic and preparation method thereof

Abstract

The invention belongs to the technical field of high-entropy ceramics, and particularly relates to a boride high-entropy ceramic and a preparation method thereof. The preparation method comprises the following steps: adding a simple substance raw material, a dispersing agent and grinding balls into a ball-milling tank, performing mechanical ball-milling and mixing to obtain a turbid liquid, and then drying, grinding and sieving to obtain powder to be sintered; and pre-pressing the to-be-sintered powder into blocks, putting the blocks into a silicon carbide crucible, then putting the silicon carbide crucible into a microwave sintering furnace, carrying out microwave sintering on the blocks under the protection of an inert atmosphere, cooling and grinding to obtain the high-entropy boride ceramic. The microwave sintering technology is adopted for preparing the six-element high-entropy boride ceramic (VCrMoWTiNi) B for the first time, the element segregation problem caused by the thermal gradient in the sample sintering process is avoided, the sintering temperature is reduced, the uniformity of the sample is effectively improved, preparation of the high-performance six-element high-entropy boride is promoted, the preparation period is shortened, and energy is saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high entropy ceramics, and in particular relates to a monoboride high entropy ceramic and a preparation method thereof. Background Art

[0002] High-entropy ceramics primarily consist of five or more dominant elements randomly sharing the same cation or anion position, with the content of each element ranging from 5% to 35%. High-entropy ceramics offer many unexpected advantages in structure and performance. Monoboride high-entropy ceramics, in particular, exhibit exceptional hardness and are expected to be used in wear resistance, precision machining, and other fields.

[0003] At present, there are few studies on ultra-hard high-entropy monoboride ceramics. In the existing technology, hot pressing sintering, spark plasma sintering and traditional pressureless sintering are mainly used to prepare high-entropy monoboride. 0.2 Ta 0.2 Ni 0.2 Cr 0.2 W 0.2 )B with superhardness andlow thermal conductivity 46(2020)26626–26631”, dense, ultra-high hardness five-element high-entropy monoboride ceramics were prepared by ball milling and hot pressing sintering. However, hot pressing sintering relies on heat conduction heating, and the sintered body is easily impure due to uneven heating. In the literature “Theoretical and experimental investigations on the phase stability and fabrication of high-entropy monoborides. Journal of the European Ceramic Society 43(2023)2320–2330”, superhard five-element high-entropy monoboride ceramics were also prepared by spark plasma sintering. Although the rapid sintering and cooling of spark plasma sintering are conducive to regulating atomic diffusion, the monoboride is very easy to react with the graphite mold, which makes the high-entropy monoboride face the problem of carbon element contamination caused by the heating body. In the literature “Influence of molten-salt-synthesised high-entropy(V 0.2 Cr 0.2 Mo 0.2 W 0.2 Ni 0.2)B powder characteristics on superhard mechanism during sparkplasma sintering”, a five-element high entropy monoboride (V) was prepared by conventional pressureless sintering technology at 1500℃ for more than 5h. 0.2 Cr 0.2 Mo 0.2 W 0.2 Ni 0.2 )B powder, however, long-term heating prolongs the preparation cycle of the material, reduces the synthetic yield of the material, and greatly limits the practical application of the material. In addition, the existing technical methods only obtain five-element high-entropy ceramics, and the research on six-element high-entropy monoborides is still blank. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a boride high-entropy ceramic and a preparation method thereof.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The preparation method of monoboride high entropy ceramics comprises the following steps:

[0007] (1) Add the elemental raw materials, dispersant, and grinding balls into a ball mill, mix them into a suspension through mechanical ball milling, and then dry, grind, and sieve to obtain a powder to be sintered;

[0008] (2) The powder to be sintered in step (1) is pre-pressed into a block, placed in a silicon carbide crucible, and then placed in a microwave sintering furnace. The block is microwave sintered in an inert atmosphere, cooled, and ground to obtain a high entropy monoboride ceramic.

[0009] Preferably, the single-element raw materials are V powder, Cr powder, Mo powder, W powder, Ti powder, Ni powder and B powder.

[0010] Preferably, the molar ratio of the V powder, Cr powder, Mo powder, W powder, Ti powder, Ni powder and B powder is 1:1:1:1:1:1:1:5-7.

[0011] Preferably, the dispersant is anhydrous ethanol, and the mass ratio of the dispersant to the raw material is 2-10:1.

[0012] Preferably, the ball-to-material ratio in the ball mill is 2-10:1.

[0013] Preferably, the mechanical ball milling rate is 300-500 r / min, and the ball milling time is 6-12 h.

[0014] Preferably, the pre-compression pressure of the powder to be sintered is 10-30 MPa, and the holding time is 1-5 min.

[0015] Preferably, the to-be-sintered powder is pre-pressed into a cylindrical blank with a diameter of ≤50 mm and a thickness of 1-5 mm.

[0016] Preferably, the microwave sintering power is 0.6-5 kW, the microwave sintering temperature is 1000-1400℃, and the holding time is 5-15 min.

[0017] A boride high-entropy ceramic prepared by the above preparation method.

[0018] The positive beneficial effects of the present application are:

[0019] 1. The boride ceramic has mechanical properties such as hardness, strength, and wear resistance far higher than alloys due to the existence of covalent bonds and ionic bonds, but due to the low diffusion coefficient of boron element, long-time holding at high temperature is often required, the existing high-entropy boride ceramics are prepared by hot pressing or spark plasma sintering, the sintering temperature is generally higher than 1500℃, the holding time is usually more than 20 min, and the lower the temperature, the longer the holding time required, and there is no related research on the preparation of six-element high-entropy boride ceramics by microwave sintering technology, which is based on the research on five-element high-entropy boride ceramics. The present application first uses microwave sintering technology to prepare six-element high-entropy boride ceramics (VCrMoWTiNi)B with equal molar ratio, creatively uses the high penetration ability and spatial heating characteristics of microwave sintering, uses the dielectric loss of substances to generate heat under the action of microwaves, converts electromagnetic energy into heat energy, and does not use any holding structure, has the advantages of rapid heating, uniform heat field distribution, and energy saving, avoids the element segregation problem caused by thermal gradient in the sample sintering process, reduces the sintering temperature, effectively improves the uniformity of the sample, promotes the preparation of high-performance six-element high-entropy boride, shortens the preparation period, saves energy, fills the research gap of microwave sintering technology for super-hard six-element high-entropy boride, and provides a very effective reference for the development of new materials, which has very important significance.

[0020] 2. According to the formula ΔG = ΔH-TΔS, the increase of entropy will significantly reduce the sintering temperature, the present application increases the number of components of high-entropy ceramics and improves the configurational entropy of high-entropy ceramics to realize the synthesis and preparation at a lower temperature, in addition, the increase of entropy can improve the physical and chemical compatibility between metal elements, increase the solid solubility of metal cations, increase the Peierls stress of dislocation loop opening, increase the hardness of the material, and improve the uniformity of cation distribution.

[0021] 3. The present invention adds the element Ti. Ti is a high-hardness metal, and the corresponding TiB hardness is significantly greater than NiB. The addition of Ti is beneficial to improving the hardness of the high-entropy monoboride. In addition, the atomic radius of Ti in the transition metal is between Mo, W and Ni, close to Ni, which can effectively reduce the size difference between metal elements, weaken the phase phenomenon caused by size difference, improve the mutual solid solubility between the elements, promote the uniform distribution of Ni atoms, and solve the agglomeration problem of Ni atoms with small atomic radius, thereby realizing the preparation of high-entropy monoboride.

[0022] 4. The microwave sintering technology used in the present invention is combined with a silicon carbide crucible to prepare high-entropy boride ceramics (VCrMoWTiNi)B. Without any insulation device, it can completely avoid the carbon environment caused by the use of graphite molds in traditional hot pressing sintering and spark plasma sintering. It also avoids the pollution problem of chemical reaction between the titanium element with a strong affinity for carbon and the carbon element introduced by the sintering environment to produce a large amount of TiC, thereby improving the physical purity. In addition, the silicon carbide crucible can achieve efficient heat generation and heat transfer during the microwave sintering process, greatly improving the material heating rate and shortening the sintering time. This provides a new technical reference for promoting the preparation of single-phase high-entropy boride ceramics and has a good application prospect in the preparation of high-entropy boride ceramics. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is an optical photograph of the monoboride high entropy ceramic prepared in Example 1.

[0024] Figure 2 XRD patterns of the monoboride high entropy ceramics prepared in Examples 1-3.

[0025] Figure 3 This is the element surface scanning distribution diagram of the boride high entropy ceramic prepared in Example 1. DETAILED DESCRIPTION

[0026] The present invention is further described below with reference to some specific embodiments.

[0027] Example 1

[0028] A method for preparing a boride high entropy ceramic (VCrMoWTiNi)B comprises the following steps:

[0029] (1) preparing a mixed raw material by mixing metal elements V, Cr, Mo, W, Ti, Ni and non-metal element B powders in a molar ratio of V:Cr:Mo:W:Ti:Ni:B=1:1:1:1:1:1:6;

[0030] V powder has a purity of 99.95% and a particle size of 45μm; Cr powder has a purity of 99.9% and a particle size of 75μm; Mo powder has a purity of 99% and a particle size of 0.5μm; W powder has a purity of 99.95% and a particle size of 45μm; Ti powder has a purity of 99.8% and a particle size of 45μm; Ni powder has a purity of 99.8% and a particle size of 45μm; B powder has a purity of 99% and a particle size of 1-5μm;

[0031] (2) The mixed powder in step (1) was placed in a polytetrafluoroethylene ball mill, and anhydrous ethanol and zirconium oxide grinding balls were added, with the mass ratio of anhydrous ethanol to raw materials being 2:1 and the mass ratio of balls to materials being 2:1; the materials were wet mixed using a planetary ball mill at a speed of 300 r / min and a ball milling time of 12 h to obtain a uniformly mixed suspension;

[0032] (3) The suspension in step (2) is fully dried, and then ground and sieved through a 100-mesh sieve to obtain a powder to be calcined;

[0033] (4) Pre-pressing the powder to be sintered described in step (3) into a circular green body with a diameter of 30 mm and a thickness of 4 mm, with a pre-pressing pressure of 30 MPa and a holding time of 2 min;

[0034] (5) The circular blank described in step (4) is placed in a silicon carbide crucible and placed in a microwave oven for microwave sintering. The protective atmosphere is Ar gas. The sintering process parameters are regulated: sintering power is 4 kW, sintering temperature is 1400°C, and holding time is 10 min. The blank is then cooled in the furnace and ground in an agate mortar to obtain a boride high-entropy ceramic.

[0035] Depend on Figure 1 It can be seen that after sintering, the shape of the sample is regular and still round, with a diameter of about 30 mm. There is collapse at the edge of the sample and slight cracks on the surface, indicating that a solid solution reaction occurs during sintering, causing the green body to become loose.

[0036] Depend on Figure 2 It can be seen from the XRD characterization that the high-entropy (VCrMoWTiNi)B is a single-phase orthorhombic structure, (VCrMoWTiNi)B has good solid solubility, and there are slight diffraction peaks of other phases, mainly W2B, CrB2 and metal V. This is mainly due to the large diameter of the W, Cr, and V raw material particles, and the intermediate products or metal elements left due to incomplete reaction. However, the diffraction peak intensity is significantly weakened compared with the high-entropy monoboride, indicating that the content of the second phase is extremely small, and the synthesized product is mainly high-entropy monoboride.

[0037] like Figure 3 As shown in the figure, SEM-EDS detection shows that there is no obvious element segregation phenomenon.

[0038] Example 2

[0039] A method for preparing a boride high entropy ceramic (VCrMoWTiNi)B comprises the following steps:

[0040] (1) preparing a mixed raw material by mixing metal elements V, Cr, Mo, W, Ti, Ni and non-metal element B powders in a molar ratio of V:Cr:Mo:W:Ti:Ni:B=1:1:1:1:1:1:5;

[0041] V powder has a purity of 99.95% and a particle size of 45μm; Cr powder has a purity of 99.9% and a particle size of 75μm; Mo powder has a purity of 99% and a particle size of 0.5μm; W powder has a purity of 99.95% and a particle size of 45μm; Ti powder has a purity of 99.8% and a particle size of 45μm; Ni powder has a purity of 99.8% and a particle size of 45μm; B powder has a purity of 99% and a particle size of 1-5μm;

[0042] (2) The mixed powder in step (1) was placed in a polytetrafluoroethylene ball mill, and anhydrous ethanol and zirconium oxide grinding balls were added, with the mass ratio of anhydrous ethanol to raw materials being 6:1 and the mass ratio of balls to materials being 5:1; the materials were wet mixed using a planetary ball mill at a speed of 300 r / min and a ball milling time of 9 h to obtain a uniformly mixed suspension;

[0043] (3) The suspension in step (2) is fully dried, and then ground and sieved through a 100-mesh sieve to obtain a powder to be calcined;

[0044] (4) Pre-pressing the powder to be sintered described in step (3) into a circular green body with a diameter of 15 mm and a thickness of 2 mm, with a pre-pressing pressure of 20 MPa and a holding time of 1 min;

[0045] (5) The circular blank described in step (4) is placed in a silicon carbide crucible and placed together in a tube furnace for microwave sintering. The protective atmosphere is Ar gas. The sintering process parameters are regulated as follows: sintering power is 4 kW, sintering temperature is 1300°C, and holding time is 10 min. The blank is then cooled in the furnace and ground in an agate mortar to obtain a boride high-entropy ceramic.

[0046] Depend on Figure 2 It can be seen from the XRD characterization that the high entropy (VCrMoWTiNi)B is a single-phase orthorhombic structure, (VCrMoWTiNi)B has good solid solution, and there is a slight diffraction peak of the second phase.

[0047] Example 3

[0048] A method for preparing a boride high entropy ceramic (VCrMoWTiNi)B comprises the following steps:

[0049] (1) preparing a mixed raw material by mixing metal elements V, Cr, Mo, W, Ti, Ni and non-metal element B powders in a molar ratio of V:Cr:Mo:W:Ti:Ni:B=1:1:1:1:1:1:7;

[0050] V powder has a purity of 99.95% and a particle size of 45μm; Cr powder has a purity of 99.9% and a particle size of 75μm; Mo powder has a purity of 99% and a particle size of 0.5μm; W powder has a purity of 99.95% and a particle size of 45μm; Ti powder has a purity of 99.8% and a particle size of 45μm; Ni powder has a purity of 99.8% and a particle size of 45μm; B powder has a purity of 99% and a particle size of 1-5μm;

[0051] (2) The mixed powder in step (1) was placed in a polytetrafluoroethylene ball mill, and anhydrous ethanol and zirconium oxide grinding balls were added, with the mass ratio of anhydrous ethanol to raw materials being 10:1 and the mass ratio of balls to materials being 2:1; the materials were wet mixed using a planetary ball mill at a speed of 300 r / min and a ball milling time of 10 h to obtain a uniformly mixed suspension;

[0052] (3) The suspension in step (2) is fully dried, and then ground and sieved through a 100-mesh sieve to obtain a powder to be calcined;

[0053] (4) Pre-pressing the powder to be sintered described in step (3) into a circular green body with a diameter of 20 mm and a thickness of 5 mm, with a pre-pressing pressure of 30 MPa and a holding time of 1 min;

[0054] (5) The circular blank described in step (4) is placed in an alumina porcelain boat and placed together in a tube furnace for microwave sintering. The protective atmosphere is Ar gas. The sintering process parameters are regulated: sintering power is 4 kW, sintering temperature is 1200°C, and holding time is 10 min. The blank is then cooled in the furnace and ground in an agate mortar to obtain a high entropy monoboride ceramic.

[0055] Depend on Figure 2 It can be seen from the XRD characterization that the high entropy (VCrMoWTiNi)B is a single-phase orthorhombic structure, (VCrMoWTiNi)B has good solid solution, and there is a slight diffraction peak of the second phase.

[0056] A boride high-entropy ceramic (VCrMoWTiNi) B prepared by the preparation method described in any one of Examples 1-3, wherein the high-entropy (VCrMoWTiNi) B has a single-phase orthorhombic structure.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention and are not limiting. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in this field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing a boride high entropy ceramic, characterized in that: The steps include: (1) Add the elemental raw materials, dispersant, and grinding balls into a ball mill, mix them into a suspension through mechanical ball milling, and then dry, grind, and sieve to obtain a powder to be sintered; (2) The powder to be sintered in step (1) is pre-pressed into a block, placed in a silicon carbide crucible, and then placed in a microwave sintering furnace. The block is microwave sintered in an inert atmosphere, cooled, and ground to obtain a high entropy monoboride ceramic.

2. The method for preparing a boride high entropy ceramic according to claim 1, wherein: The single-substance raw materials are V powder, Cr powder, Mo powder, W powder, Ti powder, Ni powder and B powder.

3. The method for preparing a monoboride high entropy ceramic according to claim 2, wherein: The molar ratio of the V powder, Cr powder, Mo powder, W powder, Ti powder, Ni powder and B powder is 1:1:1:1:1:1:1:5-7.

4. The method for preparing a monoboride high entropy ceramic according to claim 1, wherein: The dispersant is anhydrous ethanol, and the mass ratio of the dispersant to the raw material is 2-10:

1.

5. The method for preparing a boride high entropy ceramic according to claim 1, wherein: The ball-to-material ratio in the ball mill is 2-10:

1.

6. The method for preparing a boride high entropy ceramic according to claim 1, wherein: The mechanical ball milling rate is 300-500 r / min, and the ball milling time is 6-12 h.

7. The method for preparing a monoboride high entropy ceramic according to claim 1, wherein: The pre-compression pressure of the powder to be sintered is 10-30 MPa, and the holding time is 1-5 minutes.

8. The method for preparing a monoboride high entropy ceramic according to claim 1, wherein: The powder to be sintered is pre-pressed into a cylindrical green body, wherein the cylindrical green body has a diameter of ≤50 mm and a thickness of 1-5 mm.

9. The method for preparing a boride high entropy ceramic according to claim 1, wherein: The microwave sintering power is 0.6-5kW, the microwave sintering temperature is 1000-1400°C, and the heat preservation time is 5-15 minutes.

10. A boride high entropy ceramic prepared by the preparation method according to any one of claims 1 to 9.

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