A high-entropy rare earth boride ceramic material, a preparation method and application thereof

Abstract

The application discloses a high-entropy rare earth boride ceramic material and a preparation method and application thereof. The preparation method of the high-entropy rare earth boride ceramic material comprises the following steps: 1) mixing metal oxide powder and boron carbide powder, grinding to prepare mixed powder, and then pressing to prepare a green body; 2) embedding the green body into graphite felt, and then placing the green body in a protective atmosphere to perform electric field sintering to prepare a sintered material; 3) grinding the sintered material into powder, screening, taking the screened sintered material powder, pressing and cold isostatic pressing to form a sintered material blank; and 4) embedding the sintered material blank into graphite felt, and then placing the sintered material blank in a protective atmosphere to perform electric field sintering under normal pressure. The high-entropy rare earth boride ceramic material has the advantages of a huge component space, uniform metal element distribution, a composition content close to a designed proportion, excellent mechanical properties, adjustable performance and the like, and the preparation process is simple, the reaction time is short, the equipment requirement is low, and the preparation cost is low, so that the high-entropy rare earth boride ceramic material is beneficial to large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of high-entropy ceramics technology, specifically to a high-entropy rare-earth boride ceramic material, its preparation method, and its application. Background Technology

[0002] High-entropy boride ceramics are ultra-high temperature ceramics with high hardness, high melting point, and excellent oxidation resistance. Their properties have a huge range of adjustable properties, and they have great application potential in many fields such as high-speed cutting tools, aero-engine blades, bulletproof armor, microwave electronic devices, and optical sensors.

[0003] In recent years, rare earth elements have been proven to improve the mechanical and antioxidant properties of diborides. Introducing rare earth elements into high-entropy boride ceramic systems can effectively expand their compositional space, thus enabling the development of high-entropy rare earth boride ceramics with unique properties. The performance of high-entropy rare earth boride ceramics is greatly influenced by the composition of transition metal elements and the ratio between rare earth elements. It is hoped that compositional control can organically combine the effects of rare earth elements with the properties of high-entropy borides, thereby promoting the application of high-entropy boride ceramics in the field of ultra-high temperature structural materials. However, research on high-entropy rare earth boride ceramic materials is still in its early stages, with few related reports. Currently, high-entropy rare earth boride ceramics are mainly prepared by spark plasma sintering (SPS), which requires applying sufficiently high pressure (30MPa–50MPa) to promote sintering. This method suffers from many problems, such as long preparation cycle, high preparation cost, high equipment requirements, high energy consumption, and small compositional space of the prepared samples, which seriously restrict the performance control and practical application of high-entropy rare earth boride ceramics.

[0004] Therefore, it is of great significance to develop a high-entropy rare-earth boride ceramic preparation process that is simple, has a short preparation cycle, low equipment requirements, and low preparation cost, and to prepare high-entropy rare-earth boride ceramic materials with huge composition space, uniform distribution of metal elements, and controllable properties. Summary of the Invention

[0005] The purpose of this invention is to provide a high-entropy rare-earth boride ceramic material, its preparation method, and its application.

[0006] The technical solution adopted in this invention is:

[0007] A method for preparing a high-entropy rare-earth boride ceramic material includes the following steps:

[0008] 1) Metal oxide powder and boron carbide powder are mixed and ground to form a mixed powder. The metal oxide powder is composed of HfO2 powder, ZrO2 powder, Ta2O5 powder and rare earth oxide powder. The rare earth oxide powder is any one of Sm2O3 powder, Lu2O3 powder, Er2O3 powder, Ho2O3 powder, Y2O3 powder and Tm2O3 powder. Then, it is compressed into tablets to obtain a green body.

[0009] 2) The green blank is embedded inside the graphite felt and then sintered in an electric field under a protective atmosphere to obtain clinker;

[0010] 3) Grind the clinker into powder and sieve it. Then, take the clinker powder that passes through the sieve and press it into tablets. Finally, perform cold isostatic pressing to obtain the clinker blank.

[0011] 4) The clinker blank is embedded inside the graphite felt and then sintered in an electric field under normal pressure in a protective atmosphere to obtain high entropy rare earth boride ceramic material.

[0012] Preferably, the molar ratio of HfO2 powder, ZrO2 powder, and Ta2O5 powder in step 1) is 2:2:1.

[0013] Preferably, in step 1), the molar amount of rare earth elements in the metal oxide powder accounts for 5% to 25% of the total molar amount of Hf, Zr, Ta and rare earth elements.

[0014] Preferably, the boron carbide powder in step 1) is in excess by 20wt% to 25wt%. This excess boron carbide powder allows for a full reaction between the metal oxide and the boron carbide powder, and compensates for the loss of the boron source.

[0015] Preferably, the particle size of the HfO2 powder, ZrO2 powder, Ta2O5 powder, Sm2O3 powder, Lu2O3 powder, Er2O3 powder, Ho2O3 powder, Y2O3 powder, Tm2O3 powder, and boron carbide powder mentioned in step 1) is 1μm to 3μm, and the purity is ≥99.9%.

[0016] Preferably, the tablet compression in step 1) is carried out under a pressure of 8MPa to 12MPa and a holding time of 3min to 5min.

[0017] Preferably, the green blank in step 1) is in the shape of a round sheet with a diameter ≤16mm and a thickness ≤2mm.

[0018] Preferably, the graphite felt in step 2) has a length of 90mm to 110mm, a width of 18mm to 22mm, and a thickness of 4.75mm to 6.5mm.

[0019] Preferably, the protective atmosphere in step 2) is an argon atmosphere.

[0020] Preferably, in step 2), the green body is first wrapped with graphite paper coated with hexagonal boron nitride before being embedded with graphite felt. Wrapping the green body with graphite paper coated with hexagonal boron nitride can prevent the green body from reacting with the graphite paper and graphite felt during the sintering process.

[0021] Preferably, the specific operation of the electric field sintering in step 2) is as follows: connect the two ends of the graphite felt to AC power, first increase the current from 0 to 40A to 50A at a rate of 2A / s to 4A / s, then maintain it for 180s to 200s, and then decrease the current to 0 at a rate of 10A / s to 14A / s.

[0022] Preferably, the sieving in step 3) uses a 100-300 mesh nylon screen.

[0023] Preferably, the tablet compression in step 3) is carried out under a pressure of 6MPa to 8MPa and a holding time of 2min to 4min.

[0024] Preferably, the cold isostatic pressing in step 3) is carried out under a pressure of 280MPa to 300MPa and a holding time of 2min to 4min.

[0025] Preferably, the clinker blank in step 3) is in the shape of a round sheet with a diameter ≤10mm and a thickness ≤2mm.

[0026] Preferably, the graphite felt in step 4) has a length of 80mm to 100mm, a width of 13mm to 15mm, and a thickness of 4.75mm to 6.5mm.

[0027] Preferably, the protective atmosphere in step 4) is an argon atmosphere.

[0028] Preferably, in step 4), the clinker blank is first wrapped with graphite paper coated with hexagonal boron nitride before being embedded with graphite felt. Wrapping the clinker blank with graphite paper coated with hexagonal boron nitride can prevent the clinker blank from reacting with the graphite paper and graphite felt during sintering.

[0029] Preferably, the specific operation of the electric field sintering in step 4) is as follows: connect the two ends of the graphite felt to AC power, first increase the current from 0 to 40A to 50A at a rate of 3A / s to 5A / s, then hold it for 40s to 50s, then continue to increase the current to 70A to 80A at a rate of 1A / s to 3A / s, then hold it for 20s to 30s, and then decrease the current to 0 at a rate of 8A / s to 12A / s.

[0030] A high-entropy rare-earth boride ceramic material is prepared by the above-described method.

[0031] Application of a high-entropy rare-earth boride ceramic material as described above in the preparation of high-end tool coatings, bearing coatings, military armor, or helicopter belly ballistic protection layers.

[0032] The beneficial effects of this invention are: the high entropy rare earth boride ceramic material of this invention has the advantages of huge component space, uniform distribution of metal elements, component content close to the design ratio, excellent mechanical properties, and controllable performance. Moreover, its preparation process is simple, the reaction time is short, the equipment requirements are low, and the preparation cost is low, which is conducive to large-scale industrial production.

[0033] Specifically:

[0034] 1) This invention uses metal oxide powder and boron carbide powder as raw materials to prepare high-entropy rare earth boride ceramic materials containing several transition metal elements such as Hf, Zr and Ta, as well as any one rare earth element from Sm, Lu, Er, Ho, Y and Tm through a two-step rapid reaction method. The controllable space of element composition and ceramic material properties is huge, which greatly enriches the types of high-entropy rare earth boride ceramic materials.

[0035] 2) The high-entropy rare-earth boride ceramic material of the present invention has the advantages of uniform distribution of metal elements, composition content close to the design ratio, and excellent mechanical properties.

[0036] 3) The high-entropy rare-earth boride ceramic material of the present invention has ultra-high hardness and can be used to make high-end knife coatings, bearing coatings, military armor, and helicopter belly bulletproof layers, etc.

[0037] 4) The preparation method of the high entropy rare earth boride ceramic material of the present invention has the advantages of no pressure required in the sintering process, short reaction time (single sintering time is less than 5 min), low equipment requirements, simple process flow and low preparation cost, and high synthesis efficiency of high entropy rare earth boride ceramic material. Attached Figure Description

[0038] Figure 1 The images show the XRD patterns of the high-entropy rare-earth boride ceramic materials from Examples 1-3.

[0039] Figure 2 The images show the SEM image and EDS elemental distribution map of the high-entropy rare-earth boride ceramic material in Example 1.

[0040] Figure 3 The XRD patterns are for the high-entropy rare-earth boride ceramic materials of Comparative Examples 1-3. Detailed Implementation

[0041] The present invention will be further explained and described below with reference to specific embodiments.

[0042] The particle sizes of HfO2 powder, ZrO2 powder, Ta2O5 powder, Sm2O3 powder, Lu2O3 powder, Er2O3 powder, Ho2O3 powder, Y2O3 powder, Tm2O3 powder, and boron carbide powder in Examples 1-3 and Comparative Examples 1-3 were all 1 μm to 3 μm, and their purity was ≥99.9%.

[0043] Example 1:

[0044] A high-entropy rare-earth boride ceramic material is prepared by the following method:

[0045] 1) Add 0.92g of HfO2 powder, 0.54g of ZrO2 powder, 0.97g of Ta2O5 powder, 0.46g of Lu2O3 powder and 0.74g of boron carbide powder to an agate mortar and grind by hand for 30 minutes to obtain a mixed powder; weigh 1.5g of the mixed powder and put it into a mold, slowly pressurize it to 12MPa, hold the pressure for 5 minutes to obtain a green body (in the shape of a round disc, with a diameter of 16mm and a thickness of 2mm);

[0046] 2) Completely cover both sides of the green compact with graphite paper coated with hexagonal boron nitride. Cut a 25mm through hole in the middle of the side of a graphite felt (AvCarb, USA, model G475) measuring 110mm long, 22mm wide, and 4.75mm thick. Place the green compact, completely covered with hexagonal boron nitride-coated graphite paper, into the center of the graphite felt. Secure both ends of the graphite felt along its length between two molybdenum plates with screws. Suspend the green compact in the reaction chamber, seal the reaction chamber, and first use a mechanical pump to evacuate the reaction chamber until the vacuum pressure count reaches 10 Pa. Then, turn on the molecular pump to continue evacuating until the vacuum pressure count is less than 8 × 10⁻⁶ Pa. -3 Pa, then slowly introduce argon gas to atmospheric pressure, then turn on the power switch to connect the two ends of the graphite felt to AC power, increase the current from 0 to 50A at a rate of 4A / s, maintain it for 200s, then decrease the current to 0 at a rate of 14A / s, then turn off the power switch and let it cool naturally to obtain clinker.

[0047] 3) Add the calcined material to an agate mortar and grind it into powder by hand. Then pass it through a 300-mesh nylon sieve. Weigh 0.8g of the sieved calcined material powder and put it into a mold. Slowly press it to 8MPa and hold the pressure for 4 minutes. Then wrap it with layers of plastic wrap and put it into a plastic bag. After vacuum sealing, put it into a cold isostatic press and press it to 300MPa quickly. Hold the pressure for 4 minutes to obtain the calcined material blank (in the shape of a round plate with a diameter of 10mm and a thickness of 2mm).

[0048] 4) Completely cover both sides of the clinker blank with graphite paper coated with hexagonal boron nitride. Cut a 20mm through hole in the middle of the side of a graphite felt (AvCarb, USA, model G475) measuring 100mm long, 15mm wide, and 4.75mm thick. Place the clinker blank, completely covered with hexagonal boron nitride-coated graphite paper, into the center of the graphite felt. Secure both ends of the graphite felt along its length between two molybdenum plates with screws. Suspend the blank in the reaction chamber, seal the reaction chamber, and first use a mechanical pump to evacuate the reaction chamber until the vacuum pressure count reaches 10 Pa. Then, turn on the molecular pump to continue evacuating until the vacuum pressure count is less than 8 × 10⁻⁶ Pa. -3 Pa, then slowly introduce argon gas to atmospheric pressure, then turn on the power switch to connect the two ends of the graphite felt to AC power. Increase the current from 0 to 50A at a rate of 5A / s, hold for 40s, then increase the current to 80A at a rate of 3A / s, hold for 20s, then decrease the current to 0 at a rate of 12A / s. After turning off the power switch, allow it to cool naturally to obtain the high-entropy rare earth boride ceramic material (bulk); high-entropy rare earth boride (Hf 17 / 60 Zr 17 / 60 Ta 17 / 60 Lu 3 / 20 )B2, denoted as HEB2-Lu).

[0049] Performance testing:

[0050] The X-ray diffraction (XRD) pattern of the high-entropy rare-earth boride ceramic material (HEB2-Lu) in this embodiment is shown below. Figure 1 As shown, the scanning electron microscope (SEM) image and the elemental surface distribution map of the EDS energy dispersive spectroscopy are as follows: Figure 2 As shown.

[0051] Depend on Figure 1 It can be seen that the high-entropy rare-earth boride ceramic material in this embodiment is a single phase and does not contain other impurity phases.

[0052] Depend on Figure 2 It can be seen that the four constituent elements Hf, Zr, Ta and Lu in the high-entropy rare earth boride ceramic material of this embodiment are evenly distributed, the element composition content is close to the design ratio, and there is no obvious segregation.

[0053] Tests showed that the high-entropy rare-earth boride ceramic material of this embodiment has a density of 93% and a hardness of 34.1 GPa under a load of 0.49 N.

[0054] Example 2:

[0055] A high-entropy rare-earth boride ceramic material is prepared by the following method:

[0056] 1) Add 0.92g of HfO2 powder, 0.54g of ZrO2 powder, 0.97g of Ta2O5 powder, 0.44g of Er2O3 powder and 0.74g of boron carbide powder to an agate mortar and grind by hand for 30 minutes to obtain a mixed powder; weigh 1.5g of the mixed powder and put it into a mold, slowly pressurize it to 10MPa, hold the pressure for 4 minutes to obtain a green body (in the shape of a round disc, with a diameter of 16mm and a thickness of 1.8mm);

[0057] 2) Completely cover both sides of the green compact with graphite paper coated with hexagonal boron nitride. Cut a 25mm through hole in the middle of the side of a graphite felt (AvCarb, USA, model G475) measuring 100mm long, 20mm wide, and 4.75mm thick. Place the green compact, completely covered with hexagonal boron nitride-coated graphite paper, into the center of the graphite felt. Secure both ends of the graphite felt along its length between two molybdenum plates with screws. Suspend the green compact in the reaction chamber, seal the reaction chamber, and first use a mechanical pump to evacuate the reaction chamber until the vacuum pressure count reaches 10 Pa. Then, turn on the molecular pump to continue evacuating until the vacuum pressure count is less than 8 × 10⁻⁶ Pa. -3 Pa, then slowly introduce argon gas to atmospheric pressure, then turn on the power switch to connect the two ends of the graphite felt to AC power, increase the current from 0 to 45A at a rate of 3A / s, hold for 190s, then decrease the current to 0 at a rate of 12A / s, then turn off the power switch and let it cool naturally to obtain clinker.

[0058] 3) Add the calcined material to an agate mortar and grind it into powder by hand. Then pass it through a 200-mesh nylon sieve. Weigh 0.8g of the sieved calcined material powder and put it into a mold. Slowly apply pressure to 7MPa and hold the pressure for 3 minutes. Then wrap it layer by layer with plastic wrap and put it into a plastic bag. After vacuum sealing, put it into a cold isostatic press and quickly apply pressure to 290MPa. Hold the pressure for 3 minutes to obtain the calcined material blank (in the shape of a round plate with a diameter of 10mm and a thickness of 1.8mm).

[0059] 4) Completely cover both sides of the clinker blank with graphite paper coated with hexagonal boron nitride. Cut a 20mm through hole in the middle of the side of a graphite felt (AvCarb, USA, model G475) measuring 90mm long, 14mm wide, and 4.75mm thick. Place the clinker blank, completely covered with hexagonal boron nitride-coated graphite paper, into the center of the graphite felt. Secure both ends of the graphite felt along its length between two molybdenum plates with screws. Suspend the blank in the reaction chamber, seal the reaction chamber, and first use a mechanical pump to evacuate the reaction chamber until the vacuum pressure count reaches 10 Pa. Then, turn on the molecular pump to continue evacuating until the vacuum pressure count is less than 8 × 10⁻⁶ Pa. -3Pa, then slowly introduce argon gas to atmospheric pressure, then turn on the power switch to connect the two ends of the graphite felt to AC power, increase the current from 0 to 45A at a rate of 4A / s, hold for 45s, then increase the current to 75A at a rate of 2A / s, hold for 25s, then decrease the current to 0 at a rate of 10A / s, then turn off the power switch and allow it to cool naturally to obtain the high-entropy rare earth boride ceramic material (bulk); high-entropy rare earth boride (Hf 17 / 60 Zr 17 / 60 Ta 17 / 60 Er 3 / 20 )B2, denoted as HEB2-Er).

[0060] Performance testing:

[0061] The XRD pattern of the high-entropy rare-earth boride ceramic material (HEB2-Er) in this embodiment is shown below. Figure 1 As shown.

[0062] Depend on Figure 1 It can be seen that the high-entropy rare-earth boride ceramic material in this embodiment is a single phase and does not contain other impurity phases.

[0063] Tests (SEM and EDS) showed that the four constituent elements Hf, Zr, Ta, and Er in the high-entropy rare-earth boride ceramic material of this embodiment were uniformly distributed, with the elemental composition content close to the design ratio and no obvious segregation.

[0064] Tests showed that the high-entropy rare-earth boride ceramic material of this embodiment has a density of 91% and a hardness of 32.2 GPa under a load of 0.49 N.

[0065] Example 3:

[0066] A high-entropy rare-earth boride ceramic material is prepared by the following method:

[0067] 1) Add 0.92g of HfO2 powder, 0.54g of ZrO2 powder, 0.97g of Ta2O5 powder, 0.41g of Sm2O3 powder and 0.74g of boron carbide powder to an agate mortar and grind by hand for 30 minutes to obtain a mixed powder; weigh 1.5g of the mixed powder and put it into a mold, slowly pressurize it to 8MPa, hold the pressure for 3 minutes to obtain a green body (in the shape of a round disc, with a diameter of 16mm and a thickness of 1.9mm);

[0068] 2) Completely cover both sides of the green compact with graphite paper coated with hexagonal boron nitride. Cut a 25mm through hole in the middle of the side of a graphite felt (AvCarb, USA, model G475) measuring 90mm long, 18mm wide, and 4.75mm thick. Place the green compact, completely covered with hexagonal boron nitride-coated graphite paper, into the center of the graphite felt. Secure both ends of the graphite felt along its length between two molybdenum plates with screws. Suspend the green compact in the reaction chamber, seal the reaction chamber, and first use a mechanical pump to evacuate the reaction chamber until the vacuum pressure count reaches 10 Pa. Then, turn on the molecular pump to continue evacuating until the vacuum pressure count is less than 8 × 10⁻⁶ Pa. -3 Pa, then slowly introduce argon gas to atmospheric pressure, then turn on the power switch to connect the two ends of the graphite felt to AC power, increase the current from 0 to 40A at a rate of 2A / s, hold for 180s, then decrease the current to 0 at a rate of 10A / s, then turn off the power switch and let it cool naturally to obtain clinker.

[0069] 3) Add the calcined material to an agate mortar and grind it into powder by hand. Then pass it through a 100-mesh nylon sieve. Weigh 0.8g of the sieved calcined material powder and put it into a mold. Slowly press it to 6MPa and hold the pressure for 2 minutes. Then wrap it layer by layer with plastic wrap and put it into a plastic bag. Then vacuum seal it and put it into a cold isostatic press. Quickly press it to 280MPa and hold the pressure for 2 minutes to obtain the calcined material blank (in the shape of a round plate with a diameter of 10mm and a thickness of 1.9mm).

[0070] 4) Completely cover both sides of the clinker blank with graphite paper coated with hexagonal boron nitride. Cut a 20mm through hole in the middle of the side of a graphite felt (AvCarb, USA, model G475) measuring 80mm long, 13mm wide, and 4.75mm thick. Place the clinker blank, completely covered with hexagonal boron nitride-coated graphite paper, into the center of the graphite felt. Secure both ends of the graphite felt along its length between two molybdenum plates with screws. Suspend the blank in the reaction chamber, seal the reaction chamber, and first use a mechanical pump to evacuate the reaction chamber until the vacuum pressure count reaches 10 Pa. Then, turn on the molecular pump to continue evacuating until the vacuum pressure count is less than 8 × 10⁻⁶ Pa. -3 Pa, then slowly introduce argon gas to atmospheric pressure, then turn on the power switch to connect the two ends of the graphite felt to AC power, increase the current from 0 to 40A at a rate of 3A / s, hold for 50s, then increase the current to 70A at a rate of 1A / s, hold for 30s, then decrease the current to 0 at a rate of 8A / s, then turn off the power switch and allow it to cool naturally to obtain the high-entropy rare earth boride ceramic material (bulk); high-entropy rare earth boride (Hf 17 / 60 Zr 17 / 60 Ta 17 / 60 Sm3 / 20 )B2, denoted as HEB2-Sm).

[0071] Performance testing:

[0072] The XRD pattern of the high-entropy rare-earth boride ceramic material (HEB2-Sm) in this embodiment is shown below. Figure 1 As shown.

[0073] Depend on Figure 1 It can be seen that the high-entropy rare-earth boride ceramic material in this embodiment is a single phase and does not contain other impurity phases.

[0074] Tests (SEM and EDS) showed that the four constituent elements Hf, Zr, Ta, and Er in the high-entropy rare-earth boride ceramic material of this embodiment were uniformly distributed, with the elemental composition content close to the design ratio and no obvious segregation.

[0075] Tests showed that the high-entropy rare-earth boride ceramic material of this embodiment has a density of 91% and a hardness of 34.6 GPa under a load of 0.49 N.

[0076] Comparative Example 1:

[0077] A high-entropy rare-earth boride ceramic material is prepared by the following method:

[0078] 1) Add 0.92g of HfO2 powder, 0.54g of ZrO2 powder, 0.97g of Ta2O5 powder, 0.46g of Lu2O3 powder and 0.74g of boron carbide powder to an agate mortar and grind by hand for 30 minutes to obtain a mixed powder; weigh 0.8g of the mixed powder and put it into a mold, slowly pressurize it to 8MPa, hold the pressure for 4 minutes, then wrap it layer by layer with plastic wrap and put it into a plastic bag, then vacuum seal it and put it into a cold isostatic press, quickly pressurize it to 300MPa, and hold the pressure for 3 minutes to obtain a green body (in the shape of a round piece, with a diameter of 10mm and a thickness of 2mm);

[0079] 2) Completely cover both sides of the green compact with graphite paper coated with hexagonal boron nitride. Cut a 20mm through hole in the middle of the side of a graphite felt (AvCarb, USA, model G475) measuring 100mm long, 15mm wide, and 4.75mm thick. Place the green compact, completely covered with hexagonal boron nitride-coated graphite paper, into the center of the graphite felt. Secure both ends of the graphite felt along its length between two molybdenum plates with screws. Suspend the green compact in the reaction chamber, seal the reaction chamber, and first use a mechanical pump to evacuate the reaction chamber until the vacuum pressure count reaches 10 Pa. Then, turn on the molecular pump to continue evacuating until the vacuum pressure count is less than 8 × 10⁻⁶ Pa. -3Pa, then slowly introduce argon gas to atmospheric pressure, then turn on the power switch to connect the two ends of the graphite felt to AC power, increase the current from 0 to 50A at a rate of 5A / s, hold for 40s, then increase the current to 80A at a rate of 3A / s, hold for 20s, then decrease the current to 0 at a rate of 12A / s, then turn off the power switch and let it cool naturally to obtain the high-entropy rare earth boride ceramic material (denoted as HEB2-Lu-1).

[0080] Performance testing:

[0081] The XRD pattern of the high-entropy rare-earth boride ceramic material (HEB2-Lu-1) in this comparative example is shown below. Figure 3 As shown.

[0082] Depend on Figure 3 It can be seen that the actual product prepared in this comparative example is a multiphase rare earth boride solid solution, not a single-phase rare earth high-entropy boride ceramic material, and the density is only 72%. The reason is that the one-step rapid reaction cannot achieve sufficient solid solution of rare earth elements, and because the chemical properties of rare earth oxides are relatively active, unstable volatile compounds will be formed during the sintering process, which will lead to the formation of pores and by-products during the densification process.

[0083] Comparative Example 2:

[0084] A high-entropy rare-earth boride ceramic material (denoted as HEB2-Lu-2) is identical to Example 1 except that in step 4), the process of preparation is modified so that "the current is increased from 0 to 50A at a rate of 5A / s and then held for 40s" is changed to "the current is increased from 0 to 70A at a rate of 5A / s and then held for 30s".

[0085] Performance testing:

[0086] The XRD pattern of the high-entropy rare-earth boride ceramic material (HEB2-Lu-2) in this comparative example is shown below. Figure 3 As shown.

[0087] Depend on Figure 3 It can be seen that the actual product prepared in this comparative example is a multiphase rare earth boride solid solution, not a single-phase rare earth high-entropy boride ceramic material. The reason is that the rare earth elements were not fully dissolved during the second electric field sintering process, and the by-products were not completely eliminated during the densification process at higher temperatures (higher current and higher temperature).

[0088] Comparative Example 3:

[0089] A high-entropy rare-earth boride ceramic material (denoted as HEB2-Lu-3) is identical to Example 1 except that the step 2) in the preparation process is changed from "increasing the current from 0 to 50A at a rate of 4A / s and holding for 200s" to "increasing the current from 0 to 50A at a rate of 4A / s and holding for 120s".

[0090] Performance testing:

[0091] The XRD pattern of the high-entropy rare-earth boride ceramic material (HEB2-Lu-3) in this comparative example is shown below. Figure 3 As shown.

[0092] Depend on Figure 3 It can be seen that the actual product obtained in this comparative example is a multiphase rare earth boride solid solution, not a single-phase rare earth high-entropy boride ceramic material. The reason is that the first electric field sintering time was insufficient, which led to the generation of additional by-products during the reaction process, and these by-products could not be eliminated during the densification process of the second electric field sintering.

[0093] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-entropy rare-earth boride ceramic material, characterized in that, Includes the following steps: 1) Metal oxide powder and boron carbide powder are mixed and ground to form a mixed powder. The metal oxide powder is composed of HfO2 powder, ZrO2 powder, Ta2O5 powder and rare earth oxide powder. The rare earth oxide powder is any one of Sm2O3 powder, Lu2O3 powder, Er2O3 powder, Ho2O3 powder, Y2O3 powder and Tm2O3 powder. Then, it is compressed into tablets to obtain a green body. 2) The green blank is embedded inside the graphite felt and then sintered in an electric field under a protective atmosphere to obtain clinker; 3) Grind the clinker into powder and sieve it. Then, take the clinker powder that passes through the sieve and press it into tablets. Finally, perform cold isostatic pressing to obtain the clinker blank. 4) The clinker blank is embedded inside the graphite felt and then sintered in an electric field under normal pressure in a protective atmosphere to obtain high entropy rare earth boride ceramic material. In step 1), the molar ratio of HfO2 powder, ZrO2 powder, and Ta2O5 powder is 2:2:

1. Step 1) The percentage of rare earth elements in the metal oxide powder relative to the total molar amount of Hf, Zr, Ta and rare earth elements is 5% to 25%. The specific operation of the electric field sintering in step 2) is as follows: connect the two ends of the graphite felt to AC power, first increase the current from 0 to 40A to 50A at a rate of 2A / s to 4A / s, then maintain it for 180s to 200s, and then reduce the current to 0 at a rate of 10A / s to 14A / s. The specific operation of the electric field sintering in step 4) is as follows: connect the two ends of the graphite felt to AC power, first increase the current from 0 to 40A to 50A at a rate of 3A / s to 5A / s, then hold it for 40s to 50s, then continue to increase the current to 70A to 80A at a rate of 1A / s to 3A / s, then hold it for 20s to 30s, and then decrease the current to 0 at a rate of 8A / s to 12A / s.

2. The preparation method according to claim 1, characterized in that: Step 1) The boron carbide powder is in excess by 20wt% to 25wt%.

3. The preparation method according to claim 1 or 2, characterized in that: The particle size of the HfO2 powder, ZrO2 powder, Ta2O5 powder, Sm2O3 powder, Lu2O3 powder, Er2O3 powder, Ho2O3 powder, Y2O3 powder, Tm2O3 powder, and boron carbide powder mentioned in step 1) is 1μm to 3μm, and the purity is ≥99.9%.

4. The preparation method according to claim 1 or 2, characterized in that: Step 1) The pressing is carried out under a pressure of 8MPa to 12MPa and the holding time is 3min to 5min; Step 1) The green blank is in the shape of a round sheet with a diameter ≤16mm and a thickness ≤2mm; Step 2) The graphite felt has a length of 90mm to 110mm, a width of 18mm to 22mm, and a thickness of 4.75mm to 6.5mm.

5. The preparation method according to claim 1, characterized in that: Step 3) The sieving process uses a 100-300 mesh nylon screen; Step 3) The tableting is carried out under a pressure of 6MPa-8MPa for a holding time of 2-4 minutes; Step 3) The cold isostatic pressing is carried out under a pressure of 280MPa-300MPa for a holding time of 2-4 minutes; Step 3) The clinker blank is in the shape of a round sheet with a diameter ≤10mm and a thickness ≤2mm; Step 4) The graphite felt has a length of 80mm-100mm, a width of 13mm-15mm, and a thickness of 4.75mm-6.5mm.

6. The preparation method according to any one of claims 1, 2 and 5, characterized in that: The protective atmosphere in step 2) is an argon atmosphere; the protective atmosphere in step 4) is an argon atmosphere.

7. A high-entropy rare-earth boride ceramic material, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. The application of the high-entropy rare-earth boride ceramic material as described in claim 7 in the preparation of high-end tool coatings, bearing coatings, military armor, or helicopter belly ballistic protection layers.

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