A method for preparing high-density high-entropy rare earth hafnate ceramics by electric arc remelting
By combining non-equimolar composition design with arc remelting process, the preparation problem of high-entropy rare earth hafnium salt ceramics was solved, and high-density and single-phase stable high-entropy rare earth hafnium salt ceramics were realized, which are suitable for nuclear energy systems and high-temperature functional ceramics.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- XIAMEN UNIV
- Filing Date
- 2026-05-08
- Publication Date
- 2026-06-09
Smart Images
Figure CN122167161A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the technical field of special ceramics, specifically relating to a method for preparing high-density, high-entropy hafnium salt ceramics based on arc remelting. Background Technology
[0002] Rare-earth hafnium salt ceramics possess high melting points, excellent high-temperature stability, and radiation resistance potential, making them widely used in nuclear energy control materials and high-temperature functional ceramics. High-entropy ceramics have attracted attention due to the high configurational entropy effect, lattice distortion effect, and retarded diffusion effect resulting from multi-principal solid solution. By introducing multiple rare-earth elements into the A-site to construct a high-entropy system, the performance can be significantly improved by utilizing lattice distortion and retarded diffusion effects. The structural stability region of A₂B₂O₇ type ceramics is affected by r A / r B The ionic radius ratio is controlled; a lower radius ratio is conducive to the formation of disordered single-phase defect fluorite structures.
[0003] However, the preparation of existing high-entropy rare-earth hafnium salts faces the following significant bottlenecks:
[0004] First, the composition design lacks parameterized constraints for structural stability. Existing technologies mostly employ simple equimolar designs, only satisfying the configuration entropy threshold value while ignoring other effects. This leads to the easy precipitation of ordered pyrochlore phases or micro-phase separation during high-temperature cooling of the material.
[0005] Secondly, conventional solid-state sintering processes are constrained by the "hysteresis diffusion effect." When preparing high-entropy rare-earth hafnium salts using powder metallurgy methods (pressureless sintering, hot pressing, or SPS), atomic diffusion is extremely slow due to the multi-principal-element environment. Even with prolonged holding at ultra-high temperatures, it is difficult to eliminate atomic-level segregation and Kirkendall voids. This makes it difficult for the product density to exceed 95%, and the slow furnace cooling process cannot effectively preserve the ideal high-temperature disordered state.
[0006] To overcome diffusion lag during the preparation process, techniques that can generate a liquid phase, such as arc melting, are ideal. However, arc melting presents challenges in arc initiation and contamination when processing insulating oxides. Rare earth hafnium salt precursors are high-temperature insulators, making it difficult to directly form conductive channels. Furthermore, directly initiating an arc on loose powders can lead to severe spattering and significant stoichiometry imbalances, thereby affecting the final composition and properties of the material.
[0007] The aforementioned problems limit the stable preparation of high-density, high-phase-purity single-phase defect fluorite high-entropy rare-earth hafnium salt ceramics. Summary of the Invention
[0008] The purpose of this invention is to provide a method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by conductive arc-assisted vacuum arc remelting based on a composition-structure-process coupling design. This method addresses the problems of diffusion retardation, easy residual porosity, and phase segregation caused by the high-entropy effect in conventional solid-state sintering routes, which are difficult to overcome in existing technologies. It also solves the problems of difficult arc initiation, severe spatter, and oxygen depletion when directly arc-melting insulating oxide powders. This invention, through the design of a disorder formula based on non-equimolar components and the use of a rapid arc cooling process, prepares defective fluorite structure ceramics that possess both high density and single-phase stability.
[0009] A method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting includes the following steps:
[0010] S1, according to the target chemical formula (Dy) a Ho b Er c Yb d Lu e The raw materials are prepared by mixing 2Hf2O7, where a+b+c+d+e=1, 0.22≤a≤0.26, 0.20≤b≤0.24, 0.18≤c≤0.22, 0.16≤d≤0.20, and 0.14≤e≤0.18. The raw material powders include Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2, wherein the molar amount of HfO2 is less than the total molar amount of hafnium required for the target chemical formula.
[0011] S2. After mixing the raw material powders, pre-sinter them to obtain a porous skeleton;
[0012] S3. Place the porous framework in a water-cooled crucible of a vacuum arc melting furnace. Use metallic hafnium as an arc igniter to contact the porous framework. After evacuating the furnace cavity, introduce a protective gas. After igniting the arc, melt the metallic hafnium first, and then continue arc heating until the porous framework melts to obtain a liquid melt. Hold the melt at this temperature for 60–180 s, then extinguish the arc and cool to obtain an ingot. Turn the ingot over and repeat the melting process to obtain a remelted ingot. The sum of the molar amounts of metallic hafnium and HfO2 added is equal to the total molar amount of hafnium required for the target chemical formula.
[0013] S4. The remelted ingots are re-oxidized and annealed in an oxygen-containing atmosphere at 1100–1450 °C for 1–6 h to obtain high-density, high-entropy rare-earth hafnium salt ceramics.
[0014] Optionally, Dy, Ho, Er, Yb, and Lu are A-site components, and the non-equimolar ratio of the A-site components simultaneously satisfies the following configuration and disorder parameter constraints to establish a thermodynamic basis for the formation of defective fluorite structures:
[0015] (1) A-site configuration entropy ;
[0016] (2) Standardized entropy of position A ;
[0017] (3) Disorder of A-position size And it is within the range of inhibiting long-range ordered reconstruction;
[0018] (4) Average ionic radius at site A , ;
[0019] Where, x i r represents the mole fraction of each rare earth element at position A. i R represents the ionic radius of the corresponding rare earth element under 8 coordination, and R is the ideal gas constant.
[0020] During the powder preparation stage, the amount of HfO2 added is reduced by an equal amount based on the molar amount of hafnium in the hafnium arc igniter in subsequent steps, in order to achieve closed-loop component control. Optionally, the molar amount of HfO2 is 96.0% to 98.0% of the total molar amount of hafnium required for the target chemical formula.
[0021] Optionally, the relative density of the porous skeleton is 55% to 78%.
[0022] Optionally, in step S2, the raw material powder is wet ball milled and mixed, dried to obtain a mixed powder, and the mixed powder is pre-sintered in an air atmosphere at a temperature of 1480-1580°C for a holding time of 2-8 hours.
[0023] Wet ball milling achieves powder homogenization and refinement. The mixed powder is then directly pre-fired in a corundum crucible, or pre-pressed into a green blank before pre-firing, to form a porous framework with certain strength and interconnected pores. This achieves powder pre-reaction, deep degassing, and framework stabilization. Pre-sintering forms a porous framework with mechanical integrity and open pores, preventing loose insulating powder from splashing under subsequent arc impact and improving the overall melting efficiency during arc heating.
[0024] Preferably, the wet ball milling uses anhydrous ethanol as the medium, zirconia balls as the milling medium, a ball-to-material ratio of (6-15):1, a milling speed of 250-450 rpm, and a milling time of 8-20 h.
[0025] Preferably, the heating rate of the pre-sintering is 3 to 8 °C / min.
[0026] Optionally, in step S3, the furnace cavity is evacuated to a vacuum level not exceeding 5 × 10⁻⁶. -3 Pa, then backfill with argon gas to 0.03-0.08 MPa.
[0027] Optionally, in step S3, the arc-starting current is 180–320 A, the time to completely melt and obtain the liquid phase melt is 20–120 s, and the number of times the ingot is flipped and remelted is 3–6.
[0028] Optionally, the hafnium metal is a sheet with a thickness of 50–150 μm. Conductive arc ignition is achieved by using a hafnium metal arc igniter in contact with the skeleton. After arc ignition, the hafnium metal arc igniter is melted first to form a transient conductive wetting layer on the skeleton surface. This layer establishes a conductive path during the arc ignition stage, allowing the skeleton to complete liquid-phase melting. The compositional uniformity is improved by repeated ingot turning and remelting. After arc extinguishing, a water-cooled crucible is used to rapidly solidify the melt, thereby freezing the localized disordered state at high temperature and suppressing the formation of the pyrochlore phase.
[0029] Optionally, in step S4, the oxygen partial pressure of the oxygen-containing atmosphere is 10. -3 ~0.21 atm. The ingot obtained by arc remelting was subjected to oxygen-containing atmosphere re-oxidation annealing to compensate for the oxygen deficiency that may occur during the melting stage, stabilize the defective fluorite structure, and restore the oxygen / total metal atomic ratio of the resulting ceramic to 1.72~1.78.
[0030] A high-density, high-entropy rare-earth hafnium oxide ceramic is prepared by the above-mentioned method of preparing high-density, high-entropy rare-earth hafnium oxide ceramic by arc remelting; the ceramic has a single-phase defect fluorite structure with space group Fm-3m; its relative density is not less than 97.5%, and because it retains the local disordered state after liquid phase mixing, the total amount of the second phase measured by XRD-Rietveld refinement is not higher than 2 vol.%.
[0031] More preferably, the nominal chemical formula of the high-entropy rare earth hafnium salt is (Dy 0.24 Ho 0.22 Er 0.20 Yb 0.18 Lu 0.16 )2Hf2O7.
[0032] Compared with the prior art, the present invention has at least the following beneficial effects:
[0033] 1. Compared with conventional solid-state sintering which is constrained by the "delayed diffusion effect", this invention utilizes the rapid liquid-phase diffusion mechanism of arc remelting to achieve high homogeneity mixing of multi-principal-element systems and significantly reduce component segregation; by utilizing rapid solidification after arc interruption, the precipitation of long-range ordered phase (pyrochlore phase) is avoided kinetically, thereby preparing dense high-entropy ceramic materials with a relative density ≥97.5% and very few second phases.
[0034] 2. The non-equimolar heavy rare earth component design of the present invention establishes a strong thermodynamic tendency for the stability of the defective fluorite phase, while the rapid solidification process of electric arc remelting together ensures the high stability of the single-phase structure kinetically.
[0035] 3. Zero external contamination was achieved through homogeneous transient arc ignition technology. The hafnium metal arc igniter used in this invention ingeniously solves the industry problem that insulating oxide skeletons cannot directly ignite arcs. After completing conductive arc ignition, the homogeneous hafnium metal is integrated into the hafnium salt lattice through subsequent re-oxidation annealing and initial ingredient reduction, achieving stoichiometric closed-loop and avoiding the introduction of other impurities.
[0036] 4. The size disorder and mass fluctuations introduced by the non-equimolar design are retained in the crystal lattice by the arc-cooling process. This high degree of local mismatch can serve as a strong phonon scattering center. Compared with conventional equimolar materials, the single-phase defect fluorite ceramics prepared in this invention have more significant physical structural advantages in terms of thermal conductivity control and irradiation defect containment. They are suitable for applications such as nuclear reactor control materials, neutron absorption-related ceramic components in advanced nuclear energy systems, structural / functional ceramic components for high-irradiation environments, high-temperature insulation and thermal barrier-related functional ceramics, and integrated thermal structure ceramic components for extreme environments. Attached Figure Description
[0037] Figure 1 This is a schematic diagram of the process flow for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting, as an example.
[0038] Figure 2 The XRD patterns are of the high-entropy rare-earth hafnium salt ceramics prepared in Example 1 and Comparative Examples 1-4 of this invention.
[0039] Figure 3 Physical photos and SEM images of the high-entropy rare-earth hafnium salt ceramics prepared in Example 1 of this invention.
[0040] Figure 4 The images show TEM bright-field images and EDS surface scan results of the high-entropy rare-earth hafnium salt ceramics prepared in Example 1 of this invention. Detailed Implementation
[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0042] The following combination Figure 1 This describes the method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting in each of these embodiments.
[0043] Example 1
[0044] 1. The target chemical formula is defined as a non-equimolar ratio (Dy 0.24 Ho 0.22 Er 0.20 Yb0.18 Lu 0.16 )2Hf2O7. The rare earth ion radius at the A site is based on the Shannon octagonal coordination ion radius, Hf 4+ Shannon's six-coordinate ionic radius was used as the design criterion for the pyrochlore / defect fluorite structure in the A2B2O7 system. Based on Shannon's ionic radius data (under 8 coordination), Dy 3+ =1.027Å,Ho 3+ =1.015Å, Er 3+ =1.004Å, Yb 3+ =0.985Å, Lu 3+ =0.977Å; Hf under 6 coordination 4+ =0.710Å;), the A-site configuration parameter of this component is calculated as follows:
[0045] ① A-site configuration entropy It satisfies the high entropy criterion of ≥ 1.55R;
[0046] ②Standardized entropy at position A ;
[0047] ③Average ionic radius at site A A / B ionic radius ratio It is within the radius ratio range that is conducive to suppressing the long-range order of pyrochlore and promoting the formation of defective fluorite;
[0048] ④ Disorder of A-position dimensions To characterize the degree of lattice distortion.
[0049] Powders of Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2 with a purity ≥99.9% were selected. Approximately 50g of powder was prepared each time, with a nominal composition of (Dy... 0.24 Ho 0.22 Er 0.20 Yb 0.18 Lu 0.16The target ingot of 2Hf₂O₇ was prepared for batching. High-purity hafnium foil was planned to be used as the arc initiator, providing 2.0 mol% of the total hafnium required for the target chemical formula, corresponding to a hafnium foil mass of 0.444 g. The remaining 98.0 mol% of hafnium was provided by HfO₂, and during batching, the amount of hafnium corresponding to the hafnium foil was proportionally deducted from the theoretical amount of HfO₂ to be added. Specifically, the sample weighing consisted of: Dy₂O₃ 5.562 g, Ho₂O₃ 5.165 g, Er₂O₃ 4.753 g, Yb₂O₃ 4.407 g, Lu₂O₃ 3.956 g, and HfO₂ 25.633 g, plus 0.444 g of high-purity hafnium foil to ensure that the final product after reoxidation annealing fully conformed to the nominal stoichiometry.
[0050] 2. The mixed powder weighed according to the above ratio was placed in a ball mill jar and wet-milled at 350 rpm for 12 h using anhydrous ethanol as the medium and zirconia balls as the grinding media (ball-to-powder ratio 10:1). After drying and sieving, the uniformly mixed powder was pressed into a green body with a diameter of 20 mm and a thickness of 4 mm under a pressure of 20 MPa. The green body was heated to 1500℃ in air at a rate of 5℃ / min, held for 3 h, and then cooled in the furnace. This step, through solid-phase pre-reaction, allows the raw material powder to initially form a high-entropy phase and establish a ceramic neck connection with a certain strength. The relative density of the pre-fired skeleton was measured to be approximately 68%, with a large number of interconnected open pores remaining inside. This porous skeleton can effectively discharge residual gases generated during subsequent melting and prevent powder splashing caused by direct arc impact.
[0051] 3. Place the porous skeleton in the center of the water-cooled copper crucible in the vacuum arc melting furnace, and cover the upper surface of the skeleton with pre-cut high-purity hafnium foil, ensuring good contact between the foil and the top surface of the skeleton. After closing the furnace chamber, first evacuate to 4.5 × 10⁻⁶ mm. -3The pressure was increased to 0.05 MPa by backfilling with high-purity argon gas to establish a stable inert protective environment. The arc ignition current was set to 240 A. After arc ignition, the arc first acted on the metal hafnium foil, causing it to melt rapidly and form a conductive wetting zone on the surface of the skeleton. With the combined effects of arc radiation heating, particle bombardment, surface melting heat transfer, and local molten pool convection, the molten area gradually expanded into the skeleton. Under the conditions of this embodiment, a continuous liquid phase molten pool could be formed in the skeleton body within about 80 seconds. The temperature was maintained for another 90 seconds to further homogenize the components inside the molten pool. Then the arc was extinguished, and rapid solidification was achieved using a water-cooled copper crucible. After the sample cooled, the resulting ingot was flipped over and the above melting process was repeated, for a total of 4 ingot flipping and remelting operations. The hafnium foil is added only once during the initial arc initiation, and no further additions are made during subsequent ingot remelting processes. If the arc initiation stability is insufficient after a later ingot flip, auxiliary hafnium arc-initiating plates can be added, but the total amount of hafnium added in all rounds should be equal to the molar amount of hafnium deducted from the theoretical amount of HfO2 added in the previous stages. Through multiple remelting processes, the risk of local unmelted areas and micro-segregation of components can be further reduced, improving the overall homogeneity and densification of the sample. Finally, a dense, button-shaped high-entropy rare-earth hafnium salt ingot is obtained.
[0052] 4. Place the arc-remelted ingot in an air atmosphere furnace and heat it to 1300℃ at a rate of 5℃ / min. Hold it at this temperature for 3 hours, then cool it with the furnace. This step is used to compensate for any oxygen deficiency that may occur during the melting process and to ensure that the metallic hafnium introduced into the system during the arc ignition process is converted into Hf, which is required for the crystal lattice, under oxygen-containing conditions. 4+ This improves the stoichiometric stability of the oxide in the final product.
[0053] Example 2
[0054] 1. The target chemical formula is defined as a non-equimolar ratio (Dy 0.22 Ho 0.21 Er 0.20 Yb 0.19 Lu 0.18 )2Hf2O7. The rare earth ion radius at the A site is based on the Shannon octagonal coordination ion radius, Hf 4+ Shannon's six-coordinate ionic radius was used as the design criterion for the pyrochlore / defect fluorite structure in the A2B2O7 system. Based on Shannon's ionic radius data (under 8 coordination), Dy 3+ =1.027Å,Ho 3+ =1.015Å, Er 3+ =1.004Å, Yb 3+ =0.985Å, Lu 3+ =0.977Å; Hf under 6 coordination 4+=0.710Å;), the A-site configuration parameter of this component is calculated as follows:
[0055] ① A-site configuration entropy It satisfies the high entropy criterion of ≥ 1.55R;
[0056] ②Standardized entropy at position A ;
[0057] ③Average ionic radius at site A A / B ionic radius ratio It is within the radius ratio range that is conducive to suppressing the long-range order of pyrochlore and promoting the formation of defective fluorite;
[0058] ④ Disorder of A-position dimensions To characterize the degree of lattice distortion.
[0059] Compared to Example 1, this example appropriately increases the proportion of smaller radius heavy rare earth ions, thereby further reducing the average ionic radius while maintaining a high normalized entropy and size disorder. This composition helps to further weaken the tendency of the system to form a long-range ordered structure.
[0060] Powders of Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2 with a purity ≥99.9% were selected. Approximately 50g of powder with a nominal composition of (Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2) were prepared each time. 0.22 Ho 0.21 Er 0.20 Yb 0.19 Lu 0.18 The target ingot of 2Hf₂O₇ was prepared for batching. High-purity hafnium foil was planned to be used as the arc initiator, providing 3.0% of the total hafnium molar amount required for the target chemical formula, corresponding to a hafnium foil mass of 0.665 g. The remaining 97.0% of the hafnium was provided by HfO₂, and during batching, the amount of hafnium corresponding to the hafnium foil was deducted proportionally from the theoretical amount of HfO₂ to be added. Specifically, the sample weighing consisted of: Dy₂O₃ 5.094 g, Ho₂O₃ 4.926 g, Er₂O₃ 4.749 g, Yb₂O₃ 4.648 g, Lu₂O₃ 4.447 g, and HfO₂ 25.351 g, plus 0.665 g of high-purity hafnium foil to ensure that the final product after reoxidation annealing fully conformed to the nominal stoichiometry.
[0061] 2. The various oxide raw material powders were added to a zirconia ball mill jar in proportion, using anhydrous ethanol as the medium and zirconia balls as the grinding media, with a ball-to-material ratio controlled at 12:1. The ball milling conditions were set at 400 rpm for 10 hours. Higher ball milling intensity allowed for more thorough crushing and mixing of the components, resulting in a finer-grained and better-dispersed mixed powder. The ball-milled slurry was dried at 80°C and then passed through a 200-mesh sieve. The sieved powder was placed in a mold and pressed into a circular blank with a diameter of 30 mm and a thickness of 5 mm under a pressure of 40 MPa. Compared to Example 1, this example increased the pressing pressure to improve the initial packing density of the blank and the mechanical integrity of the subsequent pre-fired skeleton. The blank was heated to 1550°C in air at a rate of 5°C / min, held for 4 hours, and then cooled in the furnace. After pre-firing under these conditions, a more complete solid-phase sintering bond was formed between the powder particles, resulting in a porous skeleton with a relative density of approximately 75%. Although the porosity of this skeleton is lower than that of Example 1, it still retains a certain amount of interconnected pores, which can meet the requirements of mechanical strength and exhaust channels.
[0062] 3. Place the pre-fired high-strength porous skeleton in a water-cooled copper crucible within a vacuum arc melting furnace, and place a high-purity hafnium metal sheet flat on the center of the skeleton's top surface. Evacuate the furnace chamber to 4.5 × 10⁻⁶ mm. -3 After Pa, high-purity argon gas was backfilled to 0.08 MPa. The arc-starting current was set to 220 A. After arc ignition, the arc first coupled to the surface of the metal hafnium sheet and melted it, forming a stable conductive molten zone. Subsequently, under the action of high-temperature radiation from the arc, heat transfer from the surface liquid phase, and the flow of the molten pool, the melting range gradually expanded from the surface to the interior. Due to the relatively high density and low porosity of the skeleton in this embodiment, in order to ensure that the main body of the sample melts fully, the single continuous heating time was extended to about 110 s, and the temperature was held for another 120 s after the formation of a continuous molten pool. After the arc was cut off, rapid solidification was carried out by water-cooling a copper crucible. After the ingot cooled, it was flipped and remelted, and a total of 6 flipping and remelting were performed. By increasing the number of flipping, the problem of local melting inhomogeneity that may be caused by the high density of the skeleton can be further reduced, thereby improving the overall uniformity of the sample structure.
[0063] 4. The ingot after arc remelting is placed in an air atmosphere furnace and heated to 1400℃ at a heating rate of 5℃ / min. After holding at this temperature for 2 hours, it is cooled with the furnace. This reoxidation treatment compensates for the oxygen depletion that may occur during the high-temperature stage of the arc and promotes the stable existence of the metallic hafnium introduced during the arc ignition stage in the final ceramic lattice in an oxidized state.
[0064] Example 3
[0065] 1. The target chemical formula is defined as a non-equimolar ratio (Dy 0.26 Ho 0.22 Er 0.18 Yb 0.18 Lu0.16 )2Hf2O7. The rare earth ion radius at the A site is based on the Shannon octagonal coordination ion radius, Hf 4+ Shannon's six-coordinate ionic radius was used as the design criterion for the pyrochlore / defect fluorite structure in the A2B2O7 system. Based on Shannon's ionic radius data (under 8 coordination), Dy 3+ =1.027Å,Ho 3+ =1.015Å, Er 3+ =1.004Å, Yb 3+ =0.985Å, Lu 3+ =0.977Å; Hf under 6 coordination 4+ =0.710Å;), the A-site configuration parameter of this component is calculated as follows:
[0066] ① A-site configuration entropy It satisfies the high entropy criterion of ≥ 1.55R;
[0067] ②Standardized entropy at position A ;
[0068] ③Average ionic radius at site A A / B ionic radius ratio It is within the radius ratio range that is conducive to suppressing the long-range order of pyrochlore and promoting the formation of defective fluorite;
[0069] ④ Disorder of A-position dimensions To characterize the degree of lattice distortion.
[0070] Powders of Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2 with a purity ≥99.9% were selected. Approximately 50g of powder was prepared each time, with a nominal composition of (Dy... 0.26 Ho 0.22 Er 0.18 Yb 0.18 Lu 0.16The target ingot of 2Hf₂O₇ was prepared for batching. High-purity hafnium foil was planned to be used as the arc initiator, providing 3.0% of the total hafnium molar amount required for the target chemical formula, corresponding to a hafnium foil mass of 0.665 g. The remaining 97.0% of the hafnium was provided by HfO₂, and during batching, the amount of hafnium corresponding to the hafnium foil was proportionally deducted from the theoretical amount of HfO₂ to be added. Specifically, the sample weighing consisted of: Dy₂O₃ 5.560 g, Ho₂O₃ 4.928 g, Er₂O₃ 4.514 g, Yb₂O₃ 4.650 g, Lu₂O₃ 4.202 g, and HfO₂ 25.362 g, plus 0.665 g of high-purity hafnium foil to ensure that the final product after reoxidation annealing fully conformed to the nominal stoichiometry.
[0071] 2. The weighed oxide powders were added to a ball mill jar, using anhydrous ethanol as the dispersion medium and zirconia balls as the grinding media, with a ball-to-powder ratio controlled at 15:1. A planetary ball mill was used for wet ball milling at 300 rpm for 20 hours to improve the mixing uniformity of the components at the microscale and minimize the risk of local component fluctuations under subsequent non-compression molding conditions. After ball milling, the slurry was dried at 90°C. The dried powder was then lightly ground and passed through a 100-mesh sieve to obtain a loosely aggregated powder with good flowability. Unlike Examples 1 and 2, this example does not involve compression molding. Instead, the mixed powder was directly loaded into a high-purity corundum crucible and gently compacted to form a natural accumulation state. The loaded corundum crucible was placed in an air atmosphere furnace and heated to 1580°C at 8°C / min, held for 6 hours, and then cooled with the furnace. After high-temperature pre-sintering, the loose powder particles form a certain degree of sintering connection, resulting in a sintered mineral-like porous framework. The measured relative density of this framework is approximately 58%, and it retains a large number of open and interconnected pores. This high porosity structure facilitates gas expulsion, surface liquid phase expansion, and heat transfer to the interior of the framework during subsequent arc heating.
[0072] 3. Place the sintered porous ore framework into a water-cooled copper crucible in a vacuum arc melting furnace, and cover the top of the framework with high-purity hafnium foil. After closing the furnace chamber, first evacuate to 5×10⁻⁶ ppm. -3Pa, then backfill with high-purity argon gas to 0.03 MPa. The arc-starting current is set to 300 A. After arc ignition, the metal hafnium foil melts first and forms a surface conductive zone. Under higher current conditions, the effects of arc radiation, particle bombardment, and localized melting heat transfer are more significant. Due to the high porosity of the skeleton itself, heat is more easily extended inward along the pore network and the surface melting zone. Under the conditions of this embodiment, the sample body can form a continuous liquid phase molten pool within about 60 s, and continue to be held at temperature for another 60 s to promote the homogenization of the molten pool. Subsequently, the arc is extinguished and rapid solidification is carried out using a water-cooled copper crucible. After the sample cools, the resulting ingot is flipped over and remelted repeatedly, for a total of 3 ingot flipping and remelting.
[0073] 4. The ingot obtained from arc remelting is placed in an oxygen-containing atmosphere furnace and heated to 1200℃ at a rate of 5℃ / min. It is then held at this temperature for 5 hours under an oxygen partial pressure of approximately 0.21 atm before being cooled in the furnace. This step helps improve the stoichiometry of the oxides in the sample and enhances its structural stability.
[0074] Comparative Example 1
[0075] 1. In this comparative example, the target chemical formula is set as (Dy 0.28 Ho 0.24 Er 0.20 Yb 0.16 Lu 0.12 )2Hf2O7.
[0076] Based on Shannon's ionic radius data (under 8 coordination, Dy 3+ =1.027Å, Ho 3+ =1.015Å, Er 3+ =1.004Å, Yb 3+ =0.985Å, Lu 3+ =0.977Å; Hf under 6 coordination 4+ =0.710Å;), the A-site configuration parameter of this component is calculated as follows:
[0077] ① A-site configuration entropy ;
[0078] ②Standardized entropy at position A ;
[0079] ③Average ionic radius at site A A / B ionic radius ratio ;
[0080] ④ Disorder of A-position dimensions .
[0081] The raw materials selected are Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2 powders with a purity of not less than 99.9%. Approximately 50 g of powder with a nominal composition of (Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2) is prepared each time. 0.28 Ho 0.24 Er 0.20 Yb 0.16 Lu 0.12 The target ingot of 2Hf2O7 was prepared. High-purity hafnium foil was planned to be used as the arc igniter, providing 2.0 mol% of the total hafnium required for the target chemical formula, corresponding to a hafnium foil mass of 0.444 g. The remaining 98.0 mol% of hafnium was provided by HfO2, and during weighing, the amount of hafnium corresponding to the hafnium foil was proportionally deducted from the theoretical amount of HfO2 to be added. Specifically, the sample weighing consisted of: Dy2O3 6.500 g, Ho2O3 5.644 g, Er2O3 4.761 g, Yb2O3 3.924 g, Lu2O3 2.972 g, HfO2 25.675 g, and 0.444 g of high-purity hafnium foil, to maintain the arc ignition conditions and stoichiometric control method as consistent as possible with Example 1.
[0082] 2. The weighed oxide powders according to the above proportions were added to a ball mill jar. Anhydrous ethanol was used as the dispersion medium, and zirconia balls were used as the grinding media, with a ball-to-powder ratio controlled at 10:1. A planetary ball mill was used for wet ball milling at 350 rpm for 12 hours to promote uniform mixing of different component powders at the microscale and reduce particle agglomeration. After ball milling, the resulting slurry was dried in an 80℃ oven to remove the ethanol. The dried mixed powder was then lightly ground and passed through a 200-mesh sieve to obtain a more uniform mixed powder. The mixed powder was then placed in a steel mold and pressed into circular blanks with a diameter of 20 mm and a thickness of 4 mm under a pressure of 20 MPa. The blanks were heated to 1500℃ in air at a heating rate of 5℃ / min, held for 3 hours, and then cooled in the furnace. After this step, a porous framework with basic mechanical integrity was obtained. The measured relative density of the pre-fired framework was approximately 67%–69%.
[0083] 3. Place the porous skeleton in the center of the water-cooled copper crucible of the vacuum arc melting furnace, and cover the upper surface of the skeleton with pre-cut high-purity hafnium foil, ensuring good contact between the foil and the top surface. After closing the furnace chamber, first evacuate to 4.5 × 10⁻³ Pa, then backfill with high-purity argon gas to 0.05 MPa to establish a stable inert protective environment. Set the arc ignition current to 240 A. After arc ignition, the arc first acts on the hafnium foil, causing it to melt rapidly and form a conductive wetting zone on the skeleton surface. Subsequently, under the combined action of arc radiation heating, particle bombardment, surface melting heat transfer, and molten pool flow, the molten area gradually expands into the skeleton. Under the conditions of this comparative example, the skeleton body can also form a continuous liquid phase molten pool. Continue holding for 90 s to promote further homogenization of the components within the molten pool. Then, extinguish the arc and achieve rapid solidification using the water-cooled copper crucible.
[0084] After the sample cools, the resulting ingot is flipped over and the above melting process is repeated. A total of 4 ingot flipping and remelting are carried out to finally obtain a button-shaped high-entropy rare earth hafnium salt ingot.
[0085] 4. Place the arc-remelted ingot in an air atmosphere furnace and heat it to 1300℃ at a rate of 5℃ / min. Hold it at this temperature for 3 hours and then cool it with the furnace. This is to compensate for any oxygen loss that may occur during the melting process and to ensure that the metallic hafnium introduced into the system during the arc ignition process is converted into Hf, which is required for the crystal lattice, under oxygen-containing conditions. 4+ state.
[0086] Comparative Example 2
[0087] 1. In this comparative example, the target chemical formula is set as (Dy 0.24 Ho 0.22 Er 0.20 Yb 0.18 Lu 0.16 )2Hf2O7, which is completely consistent with Example 1.
[0088] The raw materials selected are Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2 powders with a purity of not less than 99.9%. Approximately 50 g of powder with a nominal composition of (Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2) is prepared each time. 0.24 Ho 0.22 Er 0.20 Yb 0.18 Lu 0.16The target sample of HfO2 was prepared. Since this comparative example does not employ arc ignition and remelting processes, no hafnium foil was introduced, and there is no need to deduct the theoretical amount of HfO2. The specific sample weights were: Dy2O3 5.562 g, Ho2O3 5.165 g, Er2O3 4.753 g, Yb2O3 4.407 g, Lu2O3 3.956 g, and HfO2 26.156 g.
[0089] 2. The weighed oxide powders according to the above proportions were added to a ball mill jar. Anhydrous ethanol was used as the dispersion medium, and zirconia balls were used as the grinding media, with a ball-to-powder ratio controlled at 10:1. A planetary ball mill was used for wet ball milling at 350 rpm for 12 hours to ensure thorough mixing of the powder components. After ball milling, the resulting slurry was dried in an 80°C oven. The dried mixed powder was then lightly ground and passed through a 200-mesh sieve to improve the density of subsequent molding. The mixed powder was then pre-pressed in a steel mold and cold-pressed at 200 MPa to obtain a circular blank with a diameter of 20 mm and a thickness of 4 mm. To improve the initial density of the blank, the molding pressure in this comparative example was significantly higher than that in Example 1.
[0090] 3. Place the green blank in a high-purity corundum crucible and heat it to 1500℃ at a heating rate of 5℃ / min under air atmosphere, holding it at this temperature for 3 hours for pre-reaction treatment. Then, remove the pre-fired sample, slightly crush it, and re-grind it before pressing it again to maximize mixing uniformity. Place the re-pressed blank in a high-temperature box furnace and heat it to 1650℃ at a heating rate of 5℃ / min under air atmosphere, holding it at this temperature for 20 hours before cooling it in the furnace.
[0091] The above steps represent the solid-phase reaction-high-temperature heat preservation densification route commonly used in the field, which mainly relies on solid-state diffusion to achieve component reaction and porosity elimination, without introducing a liquid-phase remelting step.
[0092] Comparative Example 3
[0093] 1. In this comparative example, the target chemical formula is set as (Dy 0.24 Ho 0.22 Er 0.20 Yb 0.18 Lu 0.16 )2Hf2O7, which is completely consistent with Example 1.
[0094] The raw materials selected are Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2 powders with a purity of not less than 99.9%. Approximately 50 g of powder with a nominal composition of (Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2) is prepared each time. 0.24 Ho 0.22 Er 0.20 Yb0.18 Lu 0.16 The target ingot of 2Hf₂O₇ was prepared for batching. To maintain variable control, high-purity hafnium foil was still used as the arc igniter in this comparative example. The molar amount of hafnium provided by it accounted for 2.0% of the total molar amount of hafnium required for the target chemical formula, corresponding to a hafnium foil mass of 0.444 g. The remaining 98.0% of the hafnium was provided by HfO₂, and during the weighing and batching, the molar amount of hafnium corresponding to the hafnium foil was deducted equally from the theoretical amount of HfO₂ to be added. The specific sample weighing was as follows: Dy₂O₃ 5.562 g, Ho₂O₃ 5.165 g, Er₂O₃ 4.753 g, Yb₂O₃ 4.407 g, Lu₂O₃ 3.956 g, HfO₂ 25.633 g, and 0.444 g of high-purity hafnium foil.
[0095] 2. The weighed oxide powders according to the above proportions are added to a ball mill jar. Anhydrous ethanol is used as the dispersion medium, and zirconia balls are used as the grinding media, with a ball-to-powder ratio controlled at 10:1. A planetary ball mill is used for wet ball milling at 350 rpm for 12 hours to promote uniform mixing of different component powders at the microscale and reduce particle agglomeration. After ball milling, the resulting slurry is dried in an 80°C oven to remove ethanol. The dried mixed powder is then lightly ground and passed through a 200-mesh sieve to obtain a mixed powder with a relatively uniform particle size. Unlike Example 1, this comparative example does not involve pressing and pre-firing the skeleton. Instead, the mixed powder is directly placed in a water-cooled copper crucible in a vacuum arc melting furnace to form a loose powder layer with a thickness of approximately 3-4 mm. Subsequently, a pre-cut high-purity hafnium foil is placed on top of the powder layer, ensuring contact between the foil and the powder surface.
[0096] 3. After closing the furnace chamber, first evacuate to 4.5 × 10⁻³ Pa, then backfill with high-purity argon to 0.05 MPa to establish a stable inert protective environment. Set the arc ignition current to 240 A, and keep other arc parameters as consistent as possible with Example 1. After arc ignition, the arc first acts on the metal hafnium foil, causing it to melt rapidly and form a locally conductive wetting zone. However, due to the loosely packed mixed powder below, lacking the overall support and interconnected pore network provided by the pre-burned skeleton, the powder surface is prone to local scattering and collapse in the early stage of arc action. As the molten area expands inward, some areas can form a locally continuous liquid phase, but the molten pool boundary and liquid surface morphology are not as stable as in Example 1. To promote overall melting as much as possible, this comparative example still maintains a continuous heating time of about 80 s, and holds for 90 s after the continuous molten pool appears; then the arc is cut off, and rapid solidification is achieved with the help of a water-cooled copper crucible. After the sample cools, the resulting ingot is flipped over and the above melting process is repeated, for a total of 4 ingot flipping and remelting. Although repeated remelting can improve sample integrity to some extent, the morphological stability and repeatability of the resulting samples are lower than those of Example 1 due to significant powder migration and local material loss in the initial stage.
[0097] 4. Place the arc-melted ingot in an air atmosphere furnace and heat it to 1300℃ at a heating rate of 5℃ / min. Hold it at this temperature for 3 hours and then cool it with the furnace to compensate for the oxygen loss that may occur during the melting process and to restore the stoichiometric state of the oxides in the sample as much as possible.
[0098] Comparative Example 4
[0099] 1. In this comparative example, the target chemical formula is set as (Dy 0.2 Ho 0.2 Er 0.2 Yb 0.2 Lu 0.2 )2Hf2O7. According to Shannon's ionic radius data (under 8 coordination, Dy 3+ =1.027Å, Ho 3+ =1.015Å, Er 3+ =1.004Å, Yb 3+ =0.985Å,Lu 3+ =0.977Å; Hf under 6 coordination 4+ =0.710Å;), the A-site configuration parameter of this component is calculated as follows:
[0100] ① A-site configuration entropy ;
[0101] ②Standardized entropy at position A ;
[0102] ③Average ionic radius at site A A / B ionic radius ratio ;
[0103] ④ Disorder of A-position dimensions .
[0104] The raw materials selected are Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2 powders with a purity of not less than 99.9%. Approximately 50 g of powder with a nominal composition of (Dy2O3, Ho2O3, Er2O3, Yb2O3, Lu2O3, and HfO2) is prepared each time. 0.2 Ho 0.2 Er 0.2 Yb 0.2 Lu 0.2 The target ingot of 2Hf₂O₇ was prepared for batching. High-purity hafnium foil was planned to be used as the arc initiator, providing 2.0% of the total hafnium molar amount required for the target chemical formula, corresponding to a hafnium foil mass of 0.443 g. The remaining 98.0% of the hafnium was provided by HfO₂, and during batching, the amount of hafnium corresponding to the hafnium foil was deducted from the theoretical amount of HfO₂ to be added. Specifically, the sample weighing consisted of: Dy₂O₃ 4.627 g, Ho₂O₃ 4.688 g, Er₂O₃ 4.746 g, Yb₂O₃ 4.889 g, Lu₂O₃ 4.937 g, and HfO₂ 25.591 g, with an additional 0.443 g of high-purity hafnium foil to ensure that the final product after reoxidation annealing returned to the nominal stoichiometric ratio.
[0105] 2. Weigh the oxide powders according to the above proportions and add them to a ball mill jar. Use anhydrous ethanol as the dispersion medium and zirconia balls as the grinding media, with a ball-to-powder ratio controlled at 10:1. Use a planetary ball mill and wet ball mill at 350 rpm for 12 hours to promote uniform mixing of different powder components at the microscale and reduce particle agglomeration.
[0106] After ball milling, the resulting slurry was dried in an 80°C oven to remove ethanol. The dried mixed powder was then lightly ground and passed through a 200-mesh sieve to obtain a mixed powder with a relatively uniform particle size. Subsequently, the mixed powder was placed in a steel mold and pressed into a circular blank with a diameter of 20 mm and a thickness of 4 mm under a pressure of 20 MPa.
[0107] The green blank was placed in a high-purity corundum crucible and heated to 1500°C at a heating rate of 5°C / min in air atmosphere. After holding at this temperature for 3 hours, it was cooled with the furnace. The measured relative density of the pre-fired skeleton was approximately 68%, which is basically consistent with that of Example 1, in order to ensure the comparability of this reference comparative example with Example 1 in terms of the precursor state as much as possible.
[0108] 3. Place the porous framework in the center of the water-cooled copper crucible of the vacuum arc melting furnace, and cover the upper surface of the framework with pre-cut high-purity hafnium foil, ensuring good contact between the foil and the top surface of the framework. After closing the furnace chamber, first evacuate to 4.5 × 10⁻³ Pa, then backfill with high-purity argon gas to 0.05 MPa to establish a stable inert protective environment. Set the arc ignition current to 240 A.
[0109] After arc ignition, the electric arc first acts on the metal hafnium foil, causing it to melt rapidly and form a conductive wetting zone on the skeleton surface. With the combined effects of arc radiation heating, particle bombardment, surface melting heat transfer, and localized molten pool convection, the molten zone gradually expands into the skeleton. Under the conditions of this comparative reference, a continuous liquid-phase molten pool can also be formed in the skeleton body. The temperature is maintained for another 90 seconds to further homogenize the components within the molten pool. The arc is then extinguished, and rapid solidification is achieved using a water-cooled copper crucible.
[0110] After the sample cooled, the resulting ingot was flipped over and the above melting process was repeated, for a total of 4 ingot flipping and remelting. Finally, a dense, button-shaped high-entropy rare earth hafnium salt ingot was obtained.
[0111] 4. Place the arc-remelted ingot in an air atmosphere furnace and heat it to 1300℃ at a rate of 5℃ / min. Hold it at this temperature for 3 hours and then cool it with the furnace. This is to compensate for any oxygen loss that may occur during the melting process and to ensure that the metallic hafnium introduced into the system during the arc ignition process is converted into Hf, which is required for the crystal lattice, under oxygen-containing conditions. 4+ state.
[0112] The materials prepared in the above embodiments and comparative examples were subjected to structural characterization, microstructure, mechanical property testing, and high-temperature stability testing.
[0113] 1. Structural Characterization: The phase composition of the material was determined using X-ray diffraction (XRD). The testing conditions were: Cu Kα radiation, tube voltage 40 kV, tube current 40 mA, scanning range 2θ = 10°–90°, step size 0.02°. The phase composition, lattice constant, and structural stability of the defective fluorite were analyzed based on the diffraction peak positions and shapes. The Rietveld full-spectrum refinement method was used to fit the diffraction data, with the defective fluorite main phase as the master phase. Based on the presence of distinguishable ordered pyrochlore or other impurity phase diffraction peaks in the diffraction pattern, corresponding candidate second phases were introduced for multiphase refinement. The mass fraction of each crystalline phase was obtained through refinement and converted to volume fraction using the theoretical density of each phase, thereby determining the total amount of the second phase.
[0114] 2. Microscopic tissue characterization
[0115] (1) The micromorphology of the material was observed by scanning electron microscopy (SEM) to characterize the cross-sectional compactness, pore distribution and grain size.
[0116] (2) The uniformity of the distribution of each element in the material was detected by transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) surface scanning method. The distribution of Dy, Ho, Er, Yb, Lu and Hf elements in the micro-area was analyzed to evaluate the compositional uniformity of the sample.
[0117] (3) The relative density of the material was determined by Archimedes' displacement method.
[0118] 3. Mechanical property testing
[0119] (1) The Vickers hardness of the material was tested using a micro Vickers hardness tester with a load of 9.8 N and a holding time of 15 s.
[0120] (2) The compressive strength of the material was tested using an electronic universal testing machine at room temperature to evaluate the load-bearing capacity of the sample under compressive load.
[0121] (3) The impact performance of the material was tested using the pendulum bending impact test method. The impact performance of the ceramic core sample was tested at room temperature using a pendulum impact tester.
[0122] 4. High-Temperature Stability Test: The material was placed in an air atmosphere furnace and held at 1400℃ for 20 h, followed by furnace cooling. After high-temperature heat treatment, the samples were examined again using an X-ray diffractometer. By comparing the changes in the position, peak width, and local characteristic peaks of the main diffraction peaks before and after heat treatment, the high-temperature ordering tendency and the ability to retain the defective fluorite structure of different samples were analyzed.
[0123] 5. Remelting Mass Loss Test: The remelting mass loss is determined by weighing. Record the total mass m0 of the pre-fired skeleton and the metal hafnium igniter before melting, and the mass m1 of the ingot obtained after all ingots have been remelted and cooled before reoxidation annealing. Calculate the remelting mass loss using the following formula:
[0124] Remelting mass loss (%) = (m0- m1) / m0×100%.
[0125] Table 1. Location of the main peak in the room temperature XRD of Example 1 and different comparative samples.
[0126]
[0127] refer to Figure 2As shown in Table 1, XRD tests revealed that the samples from Example 1 all exhibited typical defective fluorite structural characteristics. The main peaks were located at approximately 29.8°, 34.6°, 49.7°, 59.1°, 62.0°, and 73.0°, corresponding to the (111), (200), (220), (311), (222), and (400) crystal planes, respectively, indicating that they all formed stable cubic defective fluorite structures. At the same time, the peak shapes were generally symmetrical, and no obvious second phase peaks were observed within the detection range, indicating that the non-equimolar component design combined with the arc remelting process described in this invention can stably obtain high-phase-purity samples.
[0128] Compared to the examples, Comparative Example 1, although still dominated by defective fluorite structure, exhibits slightly poorer peak symmetry, and weak superstructure peaks of ordered pyrochlore phases such as (111) and (311) can be observed within certain angular ranges, indicating that the system is more prone to local ordering when the non-equimolar composition deviates from the parameter constraints required by the present invention. Comparative Example 2 also features a defective fluorite phase, but the diffraction peaks are significantly broadened, and the background at the peak base is high, indicating insufficient crystal integrity and microscopic uniformity under conventional solid-state sintering conditions. The main peak position of Comparative Example 3 is close to that of the examples, but the background fluctuations are larger, and the peak reproducibility is poor, indicating that direct arc melting under framework-less conditions is more likely to introduce local solidification defects and compositional fluctuations. Comparative Example 4 shows that equimolar composition can also form a single-phase defective fluorite structure under the process conditions of the present invention, but its peak shape is sharper than that of the examples, indicating that its local disorder and lattice distortion retention is lower than that of the non-equimolar composition optimized by the present invention.
[0129] Table 2. Densification behavior and mechanical properties of different embodiments and comparative samples
[0130]
[0131] The densification behavior and mechanical properties of Examples 1-3 and different comparative samples are shown in Table 2. From Table 2, Figure 3 and Figure 4It can be seen that the surface bonding of the sample in the examples is good, and there are no obvious pores or defects under visual inspection and SEM observation. EDS results show that the elements inside the sample are uniformly distributed and there is no segregation. In summary, the sample in the examples exhibits higher relative density, compressive strength, and Vickers hardness, indicating that the non-equimolar component design combined with the porous skeleton-assisted arc remelting process described in this invention can effectively improve the densification and mechanical integrity of high-entropy rare earth hafnium oxide ceramics. The relative density and hardness of Comparative Example 1 are close to those of the sample in the examples, but its compressive strength and impact toughness are lower than those of the examples. This indicates that when the non-equimolar component deviates from the parameter constraints required by this invention, although a relatively dense sample can still be obtained, its microstructure uniformity and structural stability are not as good as those of the examples of this invention. Comparative Example 2 uses a conventional solid-state sintering process, and its relative density is only 93.6%. Its Vickers hardness, compressive strength, and impact toughness are all the lowest. This indicates that under the condition of lacking liquid-phase remelting homogenization, the sample has more residual pores inside, making it difficult to obtain mechanical properties comparable to those of the examples of this invention. Comparative Example 3, which was directly smelted without a skeleton, showed a remelting mass loss of up to 9.2%, and a significant decrease in compressive strength and impact toughness. This indicates that the prefabrication of a porous skeleton plays an important role in stabilizing arc initiation, reducing scattering, and improving densification quality.
[0132] Table 3. Thermophysical properties and high-temperature stability of different embodiments and comparative samples
[0133]
[0134] The thermophysical properties and high-temperature stability test results of Examples 1-3 and different comparative samples are shown in Table 3. As can be seen from Table 3, the samples of the present invention exhibit low thermal diffusivity and thermal conductivity at both room temperature and high temperature. The thermal transport parameters of Examples 2 and 3 are further reduced, indicating that the present invention, through a non-equimolar composition design that satisfies specific parameter constraints, introduces stronger dimensional disorder, mass fluctuations, and local lattice mismatches. These disordered characteristics are effectively retained in the lattice during rapid arc cooling, thereby enhancing phonon scattering and reducing the material's thermal transport capacity. Meanwhile, the average linear expansion coefficients of Examples 1-3 remain within a narrow range, indicating that the material of the present invention still possesses good thermal dimensional stability over a wide temperature range.
[0135] Furthermore, after being treated at 1400℃ for 20 h, the total amount of the second phase in samples 1 to 3 was all less than 1 vol.%, indicating that the samples obtained in the embodiments of the present invention can maintain the single-phase defect fluorite structure well under high temperature conditions. Among them, the total amount of the second phase in Example 2 was the lowest, which comprehensively indicates that its high-temperature structural stability was the best; Example 3 shows that the obtained sample still has good high-temperature stability under conditions of higher current and fewer ingot turnings. In contrast, Comparative Example 1 showed a significant increase in the total amount of the second phase after high-temperature treatment, indicating that the system is more prone to local order reconstruction when the non-equimolar components deviate from the parameter constraints defined in this invention. The comparative example also showed a higher thermal conductivity, indicating that conventional solid-state sintering processes are inferior to this invention in reducing heat transport and maintaining high-temperature disordered structures. The results of Comparative Example 3 show that omitting the porous framework prefabrication step leads to an increase in local solidification defects and micro-region compositional fluctuations, which is detrimental to improving the stability of the high-temperature structure. Comparative Example 4 shows that equimolar components can also form a single-phase defect fluorite structure under the process conditions of this invention, but its thermal conductivity and the total amount of the second phase after high-temperature treatment are slightly higher, indicating that its ability to retain local disorder and lattice distortion is weaker than that of the non-equimolar component system optimized in this invention.
[0136] Figure 4 The images show TEM bright-field images and EDS surface scan results of the high-entropy rare-earth hafnium salt ceramics prepared in Example 1. As can be seen from the figures,
[0137] The high-density, single-phase stable defect fluorite-structured high-entropy rare-earth hafnium salt ceramics prepared by this invention, due to their low porosity and second-phase content, can reduce thermal stress concentration and crack initiation, thereby improving the mechanical integrity and high-temperature service reliability of the material. Simultaneously, the single-phase stable defect fluorite structure helps avoid thermal mismatch induced by multiphase interfaces and radiation-induced local instability, thus enhancing the structural stability of the material under high-temperature and radiation environments. Furthermore, the size disorder, mass fluctuations, and local lattice mismatches introduced by the non-equimolar design and retained by rapid arc cooling can enhance phonon scattering, reduce lattice thermal transport capacity, and improve the material's ability to accommodate and mitigate radiation defects. Based on these advantages, the material of this invention can be applied to nuclear reactor control materials, radiation-resistant functional ceramics in advanced nuclear energy systems, high-temperature insulation and thermal barrier ceramics, thermal protection structural ceramics for extreme environments, and other components and scenarios requiring high-temperature stability, low thermal conductivity, and radiation resistance.
[0138] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting, characterized in that, Includes the following steps: S1, according to the target chemical formula (Dy) a Ho b Er c Yb d Lu e The raw materials are prepared using 2Hf₂O₇, where a+b+c+d+e=1, 0.22≤a≤0.26, 0.20≤b≤0.24, 0.18≤c≤0.22, 0.16≤d≤0.20, and 0.14≤e≤0.
18. The raw material powders include Dy₂O₃, Ho₂O₃, Er₂O₃, Yb₂O₃, Lu₂O₃, and HfO₂, wherein the molar amount of HfO₂ is 96.0%–98.0% of the total molar amount of hafnium required for the target chemical formula. S2. After mixing the raw material powders, pre-sinter them to obtain a porous skeleton; S3. Place the porous framework in a water-cooled crucible of a vacuum arc melting furnace. Use metallic hafnium as an arc igniter to contact the porous framework. After evacuating the furnace cavity, introduce a protective gas. After igniting the arc, melt the metallic hafnium first, and then continue arc heating until the porous framework melts to obtain a liquid melt. Hold the melt at this temperature for 60–180 s, then extinguish the arc and cool to obtain an ingot. Turn the ingot over and repeat the melting process to obtain a remelted ingot. The sum of the molar amounts of metallic hafnium and HfO2 added is equal to the total molar amount of hafnium required for the target chemical formula. S4. The remelted ingots are re-oxidized and annealed in an oxygen-containing atmosphere at 1100–1450 °C for 1–6 h to obtain high-density, high-entropy rare-earth hafnium salt ceramics.
2. The method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting according to claim 1, characterized in that: Dy, Ho, Er, Yb, and Lu are A-site components, and the proportions of the A-site components satisfy the following conditions: (1) A-site configuration entropy ; (2) Standardized entropy of position A ; (3) Disorder of A-position size And it is within the range of inhibiting long-range ordered reconstruction; (4) Average ionic radius at site A , ; Where, x i r represents the mole fraction of each rare earth element at position A. i R represents the ionic radius of the corresponding rare earth element under 8 coordination, and R is the ideal gas constant.
3. The method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting according to claim 1, characterized in that: The relative density of the porous skeleton is 55% to 78%.
4. The method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting according to claim 1, characterized in that: In step S2, the raw material powder is wet ball milled and mixed, and dried to obtain a mixed powder. The mixed powder is pre-sintered in air atmosphere at a temperature of 1480-1580℃ for 2-8 hours.
5. The method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting according to claim 1, characterized in that: In step S3, the furnace cavity is evacuated to a vacuum level not exceeding 5 × 10⁻⁶. -3 Pa, then backfill with argon gas to 0.03-0.08 MPa.
6. The method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting according to claim 1, characterized in that: In step S3, the arc-starting current is 180–320 A, the time to completely melt and obtain the liquid phase melt is 20–120 s, and the number of times the ingot is flipped and remelted is 3–6.
7. The method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting according to claim 1, characterized in that: The hafnium metal is made of sheet material with a thickness of 50–150 μm.
8. The method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting according to claim 1, characterized in that: In step S4, the oxygen partial pressure of the oxygen-containing atmosphere is 10. -3 ~0.21 atm.
9. A high-density, high-entropy rare-earth hafnium salt ceramic, characterized in that: The ceramic is prepared by the method for preparing high-density, high-entropy rare-earth hafnium salt ceramics by arc remelting according to any one of claims 1 to 8; the ceramic has a single-phase defect fluorite structure, the total amount of the second phase is not higher than 1 vol.%, and the relative density is not lower than 97.5%.