High-entropy boride ceramic material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of high-entropy boride ceramic materials, in particular to a high-entropy boride ceramic material and a preparation method and application thereof. The invention provides a preparation method of a high-entropy boride ceramic material, which comprises the following steps: mixing transition metal oxide and boron carbide to obtain mixed powder; and sequentially carrying out heat treatment and sintering on the mixed powder to obtain the high-entropy boride ceramic material, the mass percent of the boron carbide in the transition metal oxide is 15-40%. The preparation method can solve the problem of abnormal grain size growth caused by high-temperature sintering, and meanwhile, the prepared high-entropy boride ceramic material is small in grain size, high in density, excellent in fracture toughness and bending strength and good in mechanical property.

Description

Technical Field

[0001] The invention relates to the technical field of high entropy boride ceramic materials, and in particular to a high entropy boride ceramic material and a preparation method and application thereof. Background Art

[0002] Ultra-high temperature ceramic materials generally refer to ceramic materials with a melting point above 3000℃ and can be used at high temperatures of 2000℃. Transition metal boride ceramics are representative ultra-high temperature ceramics with advantages such as high hardness, electrical conductivity, thermal conductivity and chemical stability. They can be widely used in high-temperature refractory materials, aerospace, catalysts and other fields. With the development of science and technology, transition metal borides are difficult to meet the requirements for material performance in extreme environments. Therefore, further improving the mechanical properties and reliability of materials is crucial to meet these extreme challenges.

[0003] High entropy ceramics have become a hot topic in the field of materials research. The concept was originally developed from high entropy alloys. High entropy ceramics are generally composed of five or more metal elements and one non-metal element. The content of the metal elements is an equimolar ratio or close to an equimolar ratio. High entropy ceramics usually include high entropy oxides, high entropy carbides, high entropy borides, high entropy nitrides and high entropy silicides.

[0004] The research on high entropy boride ceramics mainly focuses on diborides (MB 2 ), most of these high entropy boride ceramics have a hexagonal crystal structure, and have a high melting point, hardness, good thermal stability and electrical conductivity. They are often used in cutting tools, wear-resistant parts, and thermal protection systems for hypersonic missiles, space shuttles and other aircraft. Although high entropy boride ceramics have many advantages, they still face some technical challenges in practical applications. How to improve their fracture toughness and strength, and how to solve the problem of difficult densification and abnormal grain size growth caused by high temperature sintering. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a high entropy boride ceramic material and its preparation method and application. The preparation method of the present invention can solve the problem of abnormal grain size growth caused by high temperature sintering, and the prepared high entropy boride ceramic material has fine grain size, high density, excellent fracture toughness and flexural strength, and good mechanical properties.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a high entropy boride ceramic material, comprising the following steps:

[0008] mixing transition metal oxide and boron carbide to obtain mixed powder;

[0009] The mixed powder is subjected to heat treatment and sintering in sequence to obtain the high entropy boride ceramic material;

[0010] The mass percentage of the boron carbide to the transition metal oxide is 15-40%.

[0011] Preferably, the transition metal oxide comprises TiO 2 、ZrO 2 , Nb 2 O 5 、MoO 3 and Ta 2 O 5 .

[0012] Preferably, the mixing method is wet ball milling;

[0013] The ball milling medium of the wet ball milling is anhydrous ethanol, and the solid-liquid mass ratio of the wet ball milling is (1-3):1.

[0014] Preferably, the ball-to-material ratio of the wet ball milling is (3-6):1, the rotation speed is 100-300 rpm, and the time is 12-20 hours.

[0015] Preferably, the heat treatment temperature is 1000-1650° C., and the insulation time is 1-3 hours.

[0016] Preferably, the heat treatment process is to heat the temperature from room temperature to 1000°C at a heating rate of 5-10°C / min, then continue to heat the temperature to 1000-1650°C at a heating rate of 2-5°C / min, and keep the temperature.

[0017] Preferably, the sintering method is pressureless sintering, gas pressure sintering or spark plasma sintering;

[0018] When the sintering method is spark plasma sintering, the sintering pressure of the spark plasma sintering is 30-50 MPa.

[0019] Preferably, the sintering process is: heating from room temperature to 700°C at a heating rate of 100-150°C / min, and keeping warm for 1-5 minutes; heating from 700°C to 700-1200°C at a heating rate of 100-150°C / min, and keeping warm for 1-5 minutes; then heating from 700-1200°C to 1200-1650°C at a heating rate of 100-150°C / min, and keeping warm for 1-5 minutes; finally heating from 1200-1650°C to 1650-2200°C at a heating rate of 100-150°C / min, and keeping warm for 10-20 minutes.

[0020] The present invention also provides a high entropy boride ceramic material prepared by the preparation method described in the above technical solution.

[0021] The present invention also provides the application of the high entropy boride ceramic material described in the above technical solution in the fields of ultra-high temperature materials, superhard materials and ceramic cutting tools.

[0022] The present invention provides a method for preparing a high entropy boride ceramic material, comprising the following steps: mixing a transition metal oxide and boron carbide to obtain a mixed powder; sequentially heat treating and sintering the mixed powder to obtain the high entropy boride ceramic material; the mass percentage of the boron carbide in the transition metal oxide is 15-40%. The preparation method of the present invention uses transition metal oxide as a raw material and boron carbide as a reducing agent, which can avoid the generation of high entropy carbides and improve the relative density of the material. The presence of high entropy carbides will reduce the Vickers hardness and high temperature performance of the material; by controlling the amount of boron carbide, the carbon content and oxygen content are reduced, the purity and sintering activity of the high entropy boride ceramic material are improved, and the sintering temperature is reduced. The problem of abnormal grain size growth caused by high-temperature sintering is solved, and the grains are refined; and the refinement of the grain size is beneficial to the toughness of the high-entropy boride ceramic material (generally speaking, the smaller the grain size, the more obvious the hindering effect on crack propagation, thereby improving the fracture toughness of the high-entropy boride ceramic material), so that the prepared high-entropy boride ceramic material has a hexagonal crystal structure and a high relative density. The refinement of the grain size and the formation of a single solid solution synergistically improve the fracture toughness and flexural strength of the high-entropy boride ceramic material (the main reason is that a higher relative density means that there are fewer defects and pores inside the high-entropy boride ceramic material and a denser structure, thereby improving the flexural strength of the high-entropy boride ceramic material). BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The SEM images of the high entropy boride ceramic materials described in Examples 1 to 3 and Comparative Examples 1 to 3;

[0024] Figure 2 XRD diagrams of the high entropy boride ceramic materials described in Examples 1 to 3 and Comparative Examples 1 to 3;

[0025] Figure 3 The SEM images of the cross sections of the high entropy boride ceramic materials described in Examples 1 to 3 and Comparative Examples 1 to 3;

[0026] Figure 4 This is a SEM image of the indentation crack of the high entropy boride ceramic material described in Example 3. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing a high entropy boride ceramic material, comprising the following steps:

[0028] mixing transition metal oxide and boron carbide to obtain mixed powder;

[0029] The mixed powder is subjected to heat treatment and sintering in sequence to obtain the high entropy boride ceramic material;

[0030] The mass percentage of the boron carbide to the transition metal oxide is 15-40%.

[0031] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0032] In the present invention, the reaction in the preparation method is MO+B 4 C→MB 2 +B 2 O 3 (g) + CO(g), where MO is a transition metal oxide, MB is 2 It is a high entropy boride.

[0033] The present invention mixes transition metal oxide and boron carbide to obtain mixed powder.

[0034] In the present invention, the transition metal oxide preferably comprises TiO 2 、ZrO 2 , Nb 2 O 5 、MoO 3 and Ta 2 O 5 In the present invention, the purity of the transition metal oxide is preferably ≥ 99.9%. In the present invention, the particle size of the transition metal oxide is preferably 0.005 to 5 μm.

[0035] In the present invention, the purity of the boron carbide is preferably ≥ 99.9%. In the present invention, the particle size of the boron carbide is preferably 1 to 5 μm.

[0036] In the present invention, the mass percentage of boron carbide to the transition metal oxide is 15-40%, preferably 25-35%, more preferably 30-35%. In an embodiment of the present invention, the mass percentage of boron carbide to the transition metal oxide may be 33% or 15%.

[0037] In the present invention, the mixing method is preferably wet ball milling; the process of wet ball milling is preferably to put the mixture of transition metal oxide and boron carbide and ball milling beads into a ball milling jar, add ball milling media and mix them, and then perform wet ball milling.

[0038] In the present invention, the material of the ball mill is preferably nylon. In the present invention, the mesh number of the ball mill beads is preferably ≥ 200 meshes.

[0039] In the present invention, the ball milling medium of the wet ball milling is preferably anhydrous ethanol, and the solid-liquid mass ratio of the wet ball milling is preferably (1-3): 1. In an embodiment of the present invention, the solid-liquid ratio of the wet ball milling can be 1:1.

[0040] In the present invention, the ball-to-material ratio of the wet ball milling is preferably (3-6):1, more preferably (3.5-6):1, and most preferably (5-6):1. In an embodiment of the present invention, the ball-to-material ratio of the wet ball milling can be 6:1.

[0041] In the present invention, the speed of the wet ball milling is preferably 100-300 rpm, more preferably 200-300 rpm; the time of the wet ball milling is preferably 12-20 hours, more preferably 14-18 hours. In an embodiment of the present invention, the speed of the wet ball milling can be 300 rpm, and the time can be 14 hours.

[0042] In the present invention, the wet ball milling can refine and homogenize the mixed powder particles, thereby improving the sintering performance and mechanical properties of the high entropy boride ceramic material.

[0043] After the mixing is completed, the present invention also preferably includes rotary evaporation, drying and screening in sequence. The present invention does not have any special limitation on the process of rotary evaporation, and it can be carried out by a process well known to those skilled in the art and ensure the removal of anhydrous ethanol. In the present invention, the drying method is preferably vacuum drying; the temperature of the vacuum drying is preferably 50 to 80°C, more preferably 50 to 60°C; the present invention does not have any special limitation on the time of vacuum drying, and the time well known to those skilled in the art can be used. In an embodiment of the present invention, the temperature of the vacuum drying can be 60°C. In the present invention, the screening is preferably carried out using a sieve with a mesh size of 100 mesh. In the present invention, the function of the screening is to separate the ball mill beads.

[0044] After obtaining the mixed powder, the present invention sequentially performs heat treatment and sintering on the mixed powder to obtain the high entropy boride ceramic material.

[0045] In the present invention, the temperature of the heat treatment is preferably 1000-1650°C, and the holding time is preferably 1-3h. In the present invention, the process of the heat treatment is preferably to heat up from room temperature to 1000°C at a heating rate of 5-10°C / min, and then continue to heat up to 1000-1650°C at a heating rate of 2-5°C / min for insulation; more preferably, to heat up from room temperature to 1000°C at a heating rate of 5°C / min, and then continue to heat up to 1000-1650°C at a heating rate of 3°C / min for insulation. In the present invention, the insulation time is more preferably 2h. In an embodiment of the present invention, the process of the heat treatment can be: to heat up from room temperature to 1000°C at a heating rate of 5°C / min, and then continue to heat up to 1650°C at a heating rate of 3°C / min for 2h.

[0046] In the present invention, the above-mentioned heat treatment process can further ensure the preparation of high-purity high-entropy boride powder with fine grains, low oxygen content and low carbon content, thereby improving the purity and sintering activity of the high-entropy boride powder.

[0047] In the present invention, the sintering method is preferably pressureless sintering, gas pressure sintering or spark plasma sintering, and more preferably spark plasma sintering.

[0048] In the present invention, the sintering process is preferably: heating from room temperature to 700°C at a heating rate of 100-150°C / min, keeping warm for 1-5min; heating from 700°C to 700-1200°C at a heating rate of 100-150°C / min, keeping warm for 1-5min; then heating from 700-1200°C to 1200-1650°C at a heating rate of 100-150°C / min, keeping warm for 1-5min, and finally heating from 700-1200°C to 1200-1650°C at a heating rate of 100-150°C / min. The temperature is increased from 1200-1650°C to 1650-2200°C and kept warm for 10-20 min; more preferably, the temperature is increased to 700°C at a heating rate of 100°C / min, kept warm for 2 min, then the temperature is increased to 1200°C at a heating rate of 100°C / min and kept warm for 2 min, then the temperature is increased to 1650°C at a heating rate of 100°C / min and kept warm for 5 min, then the temperature is increased to 2000-2200°C at a heating rate of 100°C / min and kept warm for 10 min. In an embodiment of the present invention, the sintering may be spark plasma sintering; the process of the spark plasma sintering may be: firstly heating to 700°C at a heating rate of 100°C / min, keeping warm for 2min, then heating to 1200°C at a heating rate of 100°C / min and keeping warm for 2min, then heating to 1650°C at a heating rate of 100°C / min and keeping warm for 5min, then heating to 2200°C at a heating rate of 100°C / min and keeping warm for 10min, then cooling to 1200°C at a cooling rate of 100°C / min, and finally cooling to room temperature with the furnace; or firstly heating to 700°C at a heating rate of 100°C / min, keeping warm for 2min, then heating to 1200°C at a heating rate of 100°C / min and keeping warm for 2mi n, continue to heat up to 1650℃ at a heating rate of 100℃ / min and keep it for 5min, continue to heat up to 2100℃ at a heating rate of 100℃ / min and keep it for 10min, then cool down to 1200℃ at a cooling rate of 100℃ / min, and finally cool to room temperature with the furnace; or first heat up to 700℃ at a heating rate of 100℃ / min, keep it for 2min, then heat up to 1200℃ at a heating rate of 100℃ / min and keep it for 2min, continue to heat up to 1650℃ at a heating rate of 100℃ / min and keep it for 5min, continue to heat up to 2000℃ at a heating rate of 100℃ / min and keep it for 10min, then cool down to 1200℃ at a cooling rate of 100℃ / min, and finally cool to room temperature with the furnace.

[0049] In the present invention, when the sintering method is spark plasma sintering, the sintering pressure of the spark plasma sintering is preferably 30-50 MPa, more preferably 50 MPa. In an embodiment of the present invention, the sintering pressure of the spark plasma sintering can be 50 MPa.

[0050] In the present invention, controlling the sintering process within the above conditions can further promote the densification of the high entropy boride ceramic material and improve the Vickers hardness of the high entropy boride ceramic material.

[0051] After the sintering is completed, the present invention preferably further includes cooling, and the cooling includes sequential programmed cooling and furnace cooling; the degree cooling process is preferably cooling to 1200° C. at a cooling rate of 100° C. / min.

[0052] The present invention also provides a high entropy boride ceramic material prepared by the preparation method described in the above technical solution.

[0053] In the present invention, the relative density of the high entropy boride ceramic material is preferably greater than 93.6%, the Vickers hardness is preferably 22.19-26.31 GPa; the nanohardness is preferably 39.01-44.89 GPa; the elastic modulus is preferably 595.24-699.98 GPa; and the fracture toughness is preferably 3.97-6.11 MPa·m 1 / 2 ; The bending strength is preferably 385.21~632.687MPa.

[0054] The present invention also provides the application of the high entropy boride ceramic material described in the above technical solution in the fields of ultra-high temperature materials, superhard materials and ceramic cutting tools.

[0055] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Example 1

[0057] Add 33% of B in a molar ratio of 2:2:1:2:1 to titanium dioxide, zirconium dioxide, niobium pentoxide, molybdenum trioxide and tantalum pentoxide (the purity of the above transition metal oxides is ≥99.9%, and the particle sizes are 5nm, 1-5μm, 1μm, 1-5μm, 500nm, respectively) 4 C powder (purity ≥ 99.9%, particle size 1-5 μm) was used as a reducing agent, and then the powder and ball milling beads (the diameters of the ball milling beads were 5 mm and 10 mm, and the ratio of large and small balls was 1:1) were placed in a nylon ball ink tank, and 95 mL of anhydrous ethanol was added and wet ball milling was performed (the solid-liquid ratio of the wet ball milling was 1:1, the ball-to-material ratio was 6:1, the rotation speed was 300 rpm, and the time was 14 h) to obtain a wet mixed material;

[0058] The wet mixture is transferred to a flask and subjected to rotary evaporation to remove anhydrous ethanol, and then dried in a vacuum drying oven at 60° C., and the ball powder is separated through a 100-mesh sieve to obtain a uniform mixed powder;

[0059] The mixed powder is subjected to heat treatment, wherein the temperature is raised from room temperature to 1000° C. at a heating rate of 5° C. / min, and then further raised to 1650° C. at a heating rate of 3° C. / min, and kept at this temperature for 2 hours to obtain a heat-treated powder;

[0060] The heat-treated powder is subjected to spark plasma sintering at a pressure of 50 MPa, and the process is as follows: first, the temperature is increased to 700°C at a heating rate of 100°C / min, and the temperature is kept for 2 minutes. Then, the temperature is increased to 1200°C at a heating rate of 100°C / min and the temperature is kept for 2 minutes. Then, the temperature is increased to 1650°C at a heating rate of 100°C / min and the temperature is kept for 5 minutes. Then, the temperature is increased to 2000°C at a heating rate of 100°C / min and the temperature is kept for 10 minutes. Then, the temperature is decreased to 1200°C at a cooling rate of 100°C / min. Finally, the high entropy boride ceramic material is obtained.

[0061] Example 2

[0062] Add 33% of B in a molar ratio of 2:2:1:2:1 to titanium dioxide, zirconium dioxide, niobium pentoxide, molybdenum trioxide and tantalum pentoxide (the purity of the above transition metal oxides is ≥99.9%, and the particle sizes are 5nm, 1-5μm, 1μm, 1-5μm, 500nm, respectively) 4 C powder (purity ≥ 99.9%, particle size 1-5 μm) was used as a reducing agent, and then the powder and ball milling beads (the diameters of the ball milling beads were 5 mm and 10 mm, and the ratio of large and small balls was 1:1) were placed in a nylon ball ink tank, and 95 mL of anhydrous ethanol was added and wet ball milling was performed (the solid-liquid ratio of the wet ball milling was 1:1, the ball-to-material ratio was 6:1, the rotation speed was 300 rpm, and the time was 14 h) to obtain a wet mixed material;

[0063] The wet mixture is transferred to a flask and subjected to rotary evaporation to remove anhydrous ethanol, and then dried in a vacuum drying oven at 60° C., and the ball powder is separated through a 100-mesh sieve to obtain a uniform mixed powder;

[0064] The mixed powder is subjected to heat treatment, wherein the temperature is raised from room temperature to 1000° C. at a heating rate of 5° C. / min, and then further raised to 1650° C. at a heating rate of 3° C. / min, and kept at this temperature for 2 hours to obtain a heat-treated powder;

[0065] The heat-treated powder is subjected to spark plasma sintering at a pressure of 50 MPa, and the process is as follows: first, the temperature is increased to 700°C at a heating rate of 100°C / min, and the temperature is kept for 2 minutes. Then, the temperature is increased to 1200°C at a heating rate of 100°C / min and the temperature is kept for 2 minutes. Then, the temperature is increased to 1650°C at a heating rate of 100°C / min and the temperature is kept for 5 minutes. Then, the temperature is increased to 2100°C at a heating rate of 100°C / min and the temperature is kept for 10 minutes. Then, the temperature is decreased to 1200°C at a cooling rate of 100°C / min. Finally, the high entropy boride ceramic material is obtained.

[0066] Example 3

[0067] Add 15% of B in a molar ratio of 2:2:1:2:1 to titanium dioxide, zirconium dioxide, niobium pentoxide, molybdenum trioxide and tantalum pentoxide (the purity of the above transition metal oxides is ≥99.9%, and the particle sizes are 5nm, 1-5μm, 1μm, 1-5μm, 500nm, respectively) 4 C powder (purity ≥ 99.9%, particle size 1-5 μm) was used as a reducing agent, and then the powder and ball milling beads (the diameters of the ball milling beads were 5 mm and 10 mm, and the ratio of large and small balls was 1:1) were placed in a nylon ball ink tank, and 95 mL of anhydrous ethanol was added and wet ball milling was performed (the solid-liquid ratio of the wet ball milling was 1:1, the ball-to-material ratio was 6:1, the rotation speed was 300 rpm, and the time was 14 h) to obtain a wet mixed material;

[0068] The wet mixture is transferred to a flask and subjected to rotary evaporation to remove anhydrous ethanol, and then dried in a vacuum drying oven at 60° C., and the ball powder is separated through a 100-mesh sieve to obtain a uniform mixed powder;

[0069] The mixed powder is subjected to heat treatment, wherein the temperature is raised from room temperature to 1000° C. at a heating rate of 5° C. / min, and then further raised to 1650° C. at a heating rate of 3° C. / min, and kept at this temperature for 2 hours to obtain a heat-treated powder;

[0070] The heat-treated powder is subjected to spark plasma sintering at a pressure of 50 MPa, and the process is as follows: first, the temperature is increased to 700°C at a heating rate of 100°C / min, and the temperature is kept for 2 minutes. Then, the temperature is increased to 1200°C at a heating rate of 100°C / min and the temperature is kept for 2 minutes. Then, the temperature is increased to 1650°C at a heating rate of 100°C / min and the temperature is kept for 5 minutes. Then, the temperature is increased to 2200°C at a heating rate of 100°C / min and the temperature is kept for 10 minutes. Then, the temperature is decreased to 1200°C at a cooling rate of 100°C / min. Finally, the high entropy boride ceramic material is obtained.

[0071] Comparative Example 1

[0072] 5% of elemental boron powder (the elemental boron powder is 5% of the total mass of the diborides) is added to titanium diboride, zirconium diboride, niobium diboride, molybdenum diboride and tantalum diboride in a mass ratio of 2:2:1:2:1 to prevent volatilization of boron element during sintering to obtain a mixed material;

[0073] The mixture and ball milling beads were placed in a nylon ball milling jar, 95 mL of anhydrous ethanol was added and stirred thoroughly, and then the nylon ball milling jar was placed in a ball mill for ball milling. The solid-liquid ratio of the ball milling was 1:1, the ball-to-material ratio was 6:1, the rotation speed of the ball milling was 300 rpm, and the time was 14 h to obtain a wet mixture;

[0074] The wet mixed material is placed in a flask for rotary evaporation to evaporate the anhydrous ethanol, and then dried in a forced air drying oven at 60° C., and then passed through a 100-mesh sieve to obtain a uniform mixed powder;

[0075] The uniform mixed powder is subjected to spark plasma sintering with a spark plasma sintering pressure of 50 MPa, and the process is: firstly heating to 700°C at a heating rate of 100°C / min, keeping warm for 2 minutes, then heating to 1200°C at a heating rate of 100°C / min and keeping warm for 2 minutes, then heating to 1650°C at a heating rate of 100°C / min and keeping warm for 5 minutes, then heating to 2000°C at a heating rate of 100°C / min and keeping warm for 10 minutes, then cooling to 1200°C at a cooling rate of 100°C / min, and finally cooling to room temperature with the furnace to obtain a high entropy boride ceramic material.

[0076] Comparative Example 2

[0077] 5% of elemental boron powder (the elemental boron powder is 5% of the total mass of the diborides) is additionally added to titanium diboride, zirconium diboride, niobium diboride, molybdenum diboride and tantalum diboride in a mass ratio of 2:2:1:2:1 to prevent volatilization of the boron element during sintering, thereby obtaining a mixed material;

[0078] The mixture and ball milling beads were placed in a nylon ball milling jar, 95 mL of anhydrous ethanol was added and stirred thoroughly, and then the nylon ball milling jar was placed in a ball mill for ball milling. The solid-liquid ratio of the ball milling was 1:1, the ball-to-material ratio was 6:1, the rotation speed of the ball milling was 300 rpm, and the time was 14 h to obtain a wet mixture;

[0079] The wet mixed material is placed in a flask for rotary evaporation to evaporate the anhydrous ethanol, and then dried in a blast drying oven at 60° C., and then passed through a 100-mesh sieve to obtain a uniform mixed powder;

[0080] The uniform mixed powder is subjected to spark plasma sintering with a spark plasma sintering pressure of 50 MPa, and the process is: firstly heating to 700°C at a heating rate of 100°C / min, keeping warm for 2 minutes, then heating to 1200°C at a heating rate of 100°C / min and keeping warm for 2 minutes, then heating to 1650°C at a heating rate of 100°C / min and keeping warm for 5 minutes, then heating to 2100°C at a heating rate of 100°C / min and keeping warm for 10 minutes, then cooling to 1200°C at a cooling rate of 100°C / min, and finally cooling to room temperature with the furnace to obtain a high entropy boride ceramic material.

[0081] Comparative Example 3

[0082] 5% of elemental boron powder (the elemental boron powder is 5% of the total mass of the diborides) is additionally added to titanium diboride, zirconium diboride, niobium diboride, molybdenum diboride and tantalum diboride in a mass ratio of 2:2:1:2:1 to prevent volatilization of the boron element during sintering, thereby obtaining a mixed material;

[0083] The mixture and ball milling beads were placed in a nylon ball milling jar, 95 mL of anhydrous ethanol was added and stirred thoroughly, and then the nylon ball milling jar was placed in a ball mill for ball milling. The solid-liquid ratio of the ball milling was 1:1, the ball-to-material ratio was 6:1, the rotation speed of the ball milling was 300 rpm, and the time was 14 h to obtain a wet mixture;

[0084] The wet mixed material is placed in a flask for rotary evaporation to evaporate the anhydrous ethanol, and then dried in a forced air drying oven at 60° C., and then passed through a 100-mesh sieve to obtain a uniform mixed powder;

[0085] The uniform mixed powder is subjected to spark plasma sintering with a spark plasma sintering pressure of 50 MPa, and the process is: firstly heating to 700°C at a heating rate of 100°C / min, keeping the temperature for 2 minutes, then heating to 1200°C at a heating rate of 100°C / min and keeping the temperature for 2 minutes, then heating to 1650°C at a heating rate of 100°C / min and keeping the temperature for 5 minutes, then heating to 2200°C at a heating rate of 100°C / min and keeping the temperature for 10 minutes, then cooling to 1200°C at a cooling rate of 100°C / min, and finally cooling to room temperature with the furnace to obtain a high entropy boride ceramic material.

[0086] Test Case

[0087] Figure 1 The SEM images of the high entropy boride ceramic materials described in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in FIG. Figure 1It can be seen that the relative density of the high entropy boride ceramic materials prepared by the two methods increases with the increase of temperature, and the increase of relative density is conducive to the improvement of Vickers hardness. The relative density of the comparative examples is lower than 95%, which is difficult to be densified. The relative density of the embodiment can reach up to 97.4%, which is close to complete densification.

[0088] Figure 2 is the XRD diagram of the high entropy boride ceramic material described in Examples 1 to 3 and Comparative Examples 1 to 3, Figure 2 It can be seen that the high entropy boride ceramic material has a hexagonal crystal structure. 2 phase, failed to form a single solid solution;

[0089] Figure 3 The SEM images of the cross sections of the high entropy boride ceramic materials described in Examples 1 to 3 and Comparative Examples 1 to 3 are shown in FIG. Figure 3 It can be seen that the cross sections of the high entropy boride ceramic materials described in Examples 1 to 3 and Comparative Examples 1 to 3 can be observed to have ductile fracture and transgranular fracture.

[0090] Figure 4 is an SEM image of the indentation crack of the high entropy boride ceramic material described in Example 3 (both images are SEM images of the indentation crack of the high entropy boride ceramic material, where the left image reflects the bridging mechanism of the crack and the right image reflects the deflection mechanism of the crack), Figure 4 It can be seen that the indentation cracks of the high entropy boride ceramic material described in Example 3 have a toughening mechanism of crack deflection and crack bridging;

[0091] The density of high entropy boride ceramics was measured by Archimedes drainage method, and its relative density was calculated.

[0092] The Vickers hardness of high entropy boride ceramic materials was tested using a Vickers hardness tester (HV-30) with a load of 98N and maintained for 10s;

[0093] Nanoindentation tests were performed using a nanoindenter (Anton Paar STeP E400) with a load of 80 mN and a holding time of 10 s;

[0094] The fracture toughness test was carried out on an electronic universal testing machine (CMT6103 ZWICKInstron) using the single-edge notched beam method. The specimen size was 2 × 4 × 20 mm, the groove depth was 2 mm, the width was 0.2 mm, the span during the test was 16 mm, and the test loading rate was 0.05 mm / min;

[0095] A universal mechanical testing machine (DF-7000-MUGP) was used for the three-point bending test. The sample size was 2×4×20 mm, the span during the test was 16 mm, and the test loading rate was 0.5 mm / min.

[0096] Table 1 shows the performance parameters of the high entropy boride ceramic materials described in Examples 1 to 3 and Comparative Examples 1 to 3:

[0097] Table 1 Relative density, Vickers hardness, nanohardness, elastic modulus, fracture toughness and bending strength of the high entropy boride ceramic materials described in Examples 1 to 3 and Comparative Examples 1 to 3

[0098]

[0099] As can be seen from Table 1, Example 3 has higher toughness and strength, indicating that the high entropy boride ceramics prepared by the boron / carbon thermal reduction method have excellent mechanical properties without sacrificing hardness.

[0100] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a high entropy boride ceramic material, characterized in that: The following steps are involved: mixing transition metal oxide and boron carbide to obtain mixed powder; The mixed powder is subjected to heat treatment and sintering in sequence to obtain the high entropy boride ceramic material; The mass percentage of the boron carbide to the transition metal oxide is 15-40%.

2. The preparation method according to claim 1, characterized in that The transition metal oxides include TiO2, ZrO2, Nb2O5, MoO3 and Ta2O5 in a molar ratio of 2:2:1:2:

1.

3. The preparation method according to claim 1 or 2, characterized in that: The mixing method is wet ball milling; The ball milling medium of the wet ball milling is anhydrous ethanol, and the solid-liquid mass ratio of the wet ball milling is (1-3):

1.

4. The preparation method according to claim 3, characterized in that: The ball-to-material ratio of the wet ball mill is (3-6):1, the rotation speed is 100-300 rpm, and the time is 12-20 hours.

5. The preparation method according to claim 1, characterized in that: The heat treatment temperature is 1000-1650° C., and the heat preservation time is 1-3 hours.

6. The preparation method according to claim 5, characterized in that: The heat treatment process is to heat the temperature from room temperature to 1000°C at a heating rate of 5-10°C / min, then continue to heat the temperature to 1000-1650°C at a heating rate of 2-5°C / min, and keep the temperature.

7. The preparation method according to claim 1, characterized in that: The sintering method is pressureless sintering, gas pressure sintering or spark plasma sintering; When the sintering method is spark plasma sintering, the sintering pressure of the spark plasma sintering is 30-50 MPa.

8. The preparation method according to claim 7, characterized in that: The sintering process is as follows: heating from room temperature to 700°C at a heating rate of 100-150°C / min, and keeping the temperature for 1-5 minutes; heating from 700°C to 700-1200°C at a heating rate of 100-150°C / min, and keeping the temperature for 1-5 minutes; then heating from 700-1200°C to 1200-1650°C at a heating rate of 100-150°C / min, and keeping the temperature for 1-5 minutes; finally heating from 1200-1650°C to 1650-2200°C at a heating rate of 100-150°C / min, and keeping the temperature for 10-20 minutes.

9. The high entropy boride ceramic material prepared by the preparation method according to any one of claims 1 to 8.

10. Application of the high entropy boride ceramic material according to claim 9 in the fields of ultra-high temperature materials, superhard materials and ceramic cutting tools.

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