A dual-phase high-entropy ceramic material for high-temperature thermal barrier coatings and a method of making the same

Abstract

The application relates to a dual-phase high-entropy ceramic material for high-temperature thermal barrier coatings and a preparation method thereof, in particular to a dual-phase high-entropy ceramic (La 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 )2Zr2O7 with low thermal conductivity and high thermal expansion coefficient, which is mainly used for thermal isolation, thermal barrier coatings and other applications in high-temperature environments. The application is prepared by adopting a solid-phase reaction sintering process through accurate design of the combination of rare earth elements, forms a stable dual-phase structure, effectively inhibits grain growth through grain boundary pinning, and thus maintains a nanoscale grain structure. Meanwhile, the material can efficiently block heat transfer at high temperatures through optimization of phase proportion, and the thermal expansion characteristics are matched with a metal base layer, effectively avoiding the falling risk caused by the difference in thermal expansion of the two, and thus greatly improving the service life and reliability of the material in a high-temperature environment. The high-entropy ceramic material of the application can be widely applied to fields with high demand for high-temperature thermal isolation in aerospace, aviation, automobile industry and the like, is especially suitable for thermal barrier coatings, high-temperature thermal insulation materials and other high-temperature thermal insulation applications, and has important engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of functional ceramics technology, specifically relating to a dual-phase high-entropy ceramic material for high-temperature thermal barrier coatings and its preparation method. Background Technology

[0002] With the continuous development of high-temperature technology applications, especially in aerospace, aviation, energy, and automotive industries, the performance requirements for thermal barrier materials in high-temperature environments are becoming increasingly stringent. As a key material, thermal barrier coatings play an irreplaceable role in reducing heat loss in equipment and protecting substrate materials from high-temperature damage. Thermal barrier coating materials need to simultaneously meet the requirements of high thermal insulation performance (low thermal conductivity) and a well-matched coefficient of thermal expansion with the substrate metal. Low thermal conductivity helps reduce heat conduction, thereby improving the material's thermal insulation performance, while a matching coefficient of thermal expansion can effectively prevent cracks and failures caused by thermal stress between the coating and the substrate metal. In high-temperature environments, differences in the coefficients of thermal expansion of materials can lead to thermal stress accumulation, affecting the stability and durability of the coating. Therefore, designing thermal barrier coating materials that possess both low thermal conductivity and optimized coefficients of thermal expansion is crucial for improving their performance and extending their service life. However, the coordination between thermal conductivity, coefficient of thermal expansion, and thermal stability of existing thermal barrier coating materials under high-temperature conditions still faces many challenges.

[0003] Currently, traditional thermal barrier coating materials such as yttrium-stabilized zirconia (YSZ), while exhibiting good thermal insulation properties, show some shortcomings under ultra-high temperature conditions (>1200°C). For example, YSZ is prone to phase transformation at high temperatures, leading to increased thermal conductivity and material volume instability. Furthermore, YSZ has weak resistance to CMAS (calcium magnesium aluminum silicate) corrosion, limiting its long-term use in harsh environments. Although researchers have attempted to reduce the thermal conductivity of materials through rare-earth doping, nanostructure design, and multilayer composites, these methods typically come with problems such as reduced material strength, increased processing complexity, or increased costs.

[0004] In recent years, high-entropy ceramics have attracted widespread attention due to their unique high-entropy effect. High-entropy ceramics, through the introduction of various metals or rare earth elements, form chemically complex solid solution structures, exhibiting excellent thermal stability, low thermal conductivity, high coefficient of thermal expansion, and good oxidation resistance. Rare earth zirconate high-entropy ceramics possess two types of lattice structures: an ordered pyrochlore phase and a disordered fluorite phase. However, the fluorite phase typically exhibits low thermal conductivity and a low coefficient of thermal expansion, while the pyrochlore phase possesses a high coefficient of thermal expansion and high thermal conductivity. Since it is difficult to simultaneously obtain materials with low thermal conductivity and a high coefficient of thermal expansion using a single phase, the design of two-phase materials has become an effective solution. By rationally proportioning these two phases with different thermal properties, two-phase ceramic structures can effectively coordinate the matching of thermal conductivity and coefficient of thermal expansion, significantly improving the overall performance of the material in high-temperature environments. Studies have shown that the design of two-phase structures can not only achieve a balance between low thermal conductivity and a good coefficient of thermal expansion, but also enhance thermal shock resistance through the interfacial effect between the two phases, thereby further extending the service life of the material.

[0005] In summary, with the increasing demands for high-temperature thermal management, developing dual-phase high-entropy ceramic materials with low thermal conductivity, high coefficient of thermal expansion, and excellent high-temperature stability has become one of the important directions in the research field of thermal barrier coatings. This research will not only help overcome the performance bottlenecks of traditional materials, but will also provide important support for technological advancements in aerospace, aviation, and high-temperature energy fields. Summary of the Invention

[0006] This invention relates to a dual-phase high-entropy ceramic material for high-temperature thermal barrier coatings and its preparation method, belonging to the field of high-performance functional ceramics. The invention aims to address the problems of high thermal conductivity, poor matching of thermal expansion coefficients, and insufficient high-temperature stability in existing thermal barrier coating materials under high-temperature conditions, and proposes an innovative material and its preparation process that combines dual-phase structure design and high-entropy effect.

[0007] The dual-phase high-entropy ceramic material of this invention is prepared by mixing rare earth oxides (La₂O₃, Nd₂O₃, Gd₂O₃, Y₂O₃, Ho₂O₃) with ZrO₂ in a stoichiometric ratio, through scientific formulation and process optimization. Its chemical composition is (R₁, R₂, R₃, R₄, R₅)₂Zr₂O₇, where R₁, R₂, R₃, R₄, and R₅ are rare earth elements, selected from at least two of La, Nd, Gd, Y, and Ho. By rationally controlling the molar ratio of the rare earth oxides, this material exhibits excellent thermophysical properties, including low thermal conductivity (0.5–1.7 W / m·K) and high coefficient of thermal expansion (10⁻¹² × 10⁻¹⁰). -6 K -1 This significantly improves its overall performance as a thermal barrier coating material in high-temperature environments.

[0008] To achieve the above objectives, this invention provides a method for preparing a two-phase high-entropy ceramic material with low thermal conductivity and high coefficient of thermal expansion, specifically comprising the following steps:

[0009] Preparation of high-entropy zirconate ceramic powder:

[0010] First, rare earth oxides (such as La2O3, Nd2O3, etc.) and ZrO2 are weighed according to a predetermined stoichiometric ratio.

[0011] The weighed oxide is mixed with deionized water or anhydrous ethanol to prepare a slurry.

[0012] The slurry was ball-milled using a planetary or horizontal ball mill, with zirconia grinding balls added as the milling medium. To improve the uniformity of the ball milling, a mixture of large and small zirconia balls (8–12 mm and 2–6 mm, respectively) was used. The milling speed was 100–400 rpm, and the milling time was 3–36 hours.

[0013] The ball-milled slurry is dried and sieved to obtain a uniform powder. The sieve mesh size is 40–250 mesh.

[0014] Finally, the obtained powder is placed in a muffle furnace for pre-firing at a temperature controlled between 1100℃ and 1450℃ for 0.5 to 5 hours to obtain uniform high-entropy zirconate ceramic powder. The purpose of pre-firing is to further improve the chemical homogeneity and thermal stability of the powder.

[0015] Preparation of high-entropy zirconate ceramic bulk:

[0016] Depending on whether the powder has been pre-calcined, different processing routes can be adopted:

[0017] For pre-calcined powder: secondary ball milling is performed, and after ball milling and drying, polyvinyl alcohol solution (concentration of 8% to 12%) is added as a binder for granulation. Uniform particles are obtained by sieving, and then the granulated powder is molded.

[0018] For unpre-calcined powder: directly add binder for granulation, skipping the secondary ball milling step, and then sieve and mold after granulation.

[0019] The prepared ceramic green body is wrapped in high-entropy zirconate ceramic powder with the same composition as the powder, and then sintered in a high-temperature muffle furnace at a temperature of 1500℃~1650℃ for 1~15 hours to finally obtain a high-entropy zirconate ceramic block.

[0020] Protective measures during sintering: To avoid contamination by impurities during sintering, the green body should be encapsulated in high-entropy zirconate ceramic powder with a particle size of 1–20 µm. The encapsulation method can be loose filling or light compaction to ensure compositional purity and performance stability during sintering.

[0021] The dual-phase high-entropy ceramic materials prepared by the above method have the following technical advantages.

[0022] Low thermal conductivity: Thermal conductivity is significantly reduced to 0.5–1.7 W / m·K, effectively reducing heat transfer.

[0023] High coefficient of thermal expansion: reaching 10 to 12 × 10 -6 K -1 It has good compatibility with common metal matrix materials (such as Ni-based alloys), significantly reducing the risk of cracks and peeling caused by thermal stress.

[0024] High temperature stability: The material remains stable at temperatures above 1400°C, making it suitable for ultra-high temperature applications.

[0025] Thermal shock resistance: The dual-phase structure design effectively enhances the material's thermal shock resistance, making it suitable for complex thermal environments.

[0026] Corrosion resistance: It exhibits excellent resistance to CMAS (calcium magnesium aluminum silicate) corrosion, significantly extending the coating life.

[0027] The dual-phase high-entropy ceramic material of this invention is suitable for thermal barrier coatings, aerospace, and high-temperature insulation. Its stability and reliability in high-temperature environments make it an ideal choice for gas turbine blades, aero-engine turbine components, and other ultra-high-temperature equipment. Attached Figure Description

[0028] Figure 1 The (La) prepared in Example 1 of this invention 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 XRD pattern of Zr2O7 ceramic

[0029] Figure 2 The (La) prepared in Example 1 of this invention 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 SEM image of Zr2O7 ceramics

[0030] Figure 3 The (La) prepared in Example 1 of this invention 0.2 Nd 0.2Gd 0.2 Y 0.2 Ho 0.2 Surface scan EDS image of Zr2O7 ceramics

[0031] Figure 4 The (La) prepared in Example 1 of this invention 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 Spot scan EDS image of Zr2O7 ceramics

[0032] Figure 5 The (La) prepared in Example 1 of this invention 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 XRD pattern of Zr2O7 ceramic after annealing at 1400℃ for 130 hours.

[0033] Figure 6 The (La) prepared in Example 1 of this invention 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 Thermal conductivity curve of Zr2O7 ceramic

[0034] Figure 7 The (La) prepared in Example 1 of this invention 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 Thermal expansion coefficient curve of Zr2O7 ceramic

[0035] Figure 8 The (La) prepared in Example 1 of this invention 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 Comparison of thermal conductivity and coefficient of thermal expansion properties of Zr₂O₇ ceramics with other oxide ceramics Detailed Implementation

[0036] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of the invention.

[0037] The above description of the invention is not intended to describe every disclosed embodiment or implementation of the invention. Instead, the following description provides more specific examples of exemplary embodiments. Throughout this application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0038] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. All reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing. Similarly, the instruments used in the embodiments are commercially available.

[0039] Example 1

[0040] Step 1: First, six oxides—La₂O₃, Nd₂O₃, Gd₂O₃, Y₂O₃, Ho₂O₃, and ZrO₂—were mixed in deionized water at a molar ratio of 1:1:1:1:1:5 and then ball-milled to form a relatively uniform slurry. The ball milling equipment used was a planetary ball mill, and the dispersion media were deionized water and zirconia balls, including large and small zirconia balls. The large zirconia balls had a diameter of 8 mm, and the small zirconia balls had a diameter of 4 mm. The volume ratio of oxide powder:zirconia balls:deionized water was 1:10:1.5. The ball milling was performed at a mechanical speed of 300 rpm for 24 hours, thus obtaining the desired ceramic slurry.

[0041] Step 2: Place the ceramic slurry in an oven for drying at 120°C for 8 hours until it reaches a constant weight. Then grind the slurry and pass it through a standard sieve with a mesh size of 200 to obtain the desired ceramic powder.

[0042] Step 3: Add ceramic powder to polyvinyl alcohol (PVA) for granulation. The concentration of PVA is 8%. Then, sieve the granulated powder through a sieve with a mesh size of 80 to ensure the uniformity of the powder particles, and obtain the required granulated powder.

[0043] Step 4: Place the granulated powder into a mold and press it on a press to obtain the desired ceramic green block. The mold is a circle with a diameter of 20mm, the pressure is 225MPa, and the holding time is 1.5min.

[0044] Step 5: Place the ceramic green body into a high-temperature muffle furnace for sintering at a temperature of 1600℃ for 10 hours. The powder used as a pad in the crucible is the prepared high-entropy zirconate ceramic powder.

[0045] Figure 1 The high-entropy ceramic bulk material (La) obtained in Example 1 is given. 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 The XRD pattern of 2Zr2O7 shows that the diffraction peaks in the magnified range of 28°-30° are asymmetrical, which may indicate the presence of a two-phase structure, namely a defective fluorite structure and an ordered pyrochlore structure.

[0046] Figure 2 The high-entropy ceramic bulk material (La) obtained in Example 1 is given. 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 The SEM image of 2Zr2O7 shows that the grain boundaries of the high-entropy ceramic bulk are clear, indicating good sintering. The average grain size is 0.96 μm, which effectively demonstrates that the presence of the two phases can effectively inhibit grain growth through grain boundary pinning.

[0047] Figure 3 The high-entropy ceramic bulk material (La) obtained in Example 1 is given. 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 The EDS diagram of 2Zr2O7 shows that the Nd, Gd, and Y elements in the high-entropy ceramic block are uniformly distributed without enrichment or segregation, while La and Ho show some segregation. This suggests that the high-entropy ceramic block may have a two-phase structure of pyrochlore and fluorite.

[0048] Figure 4 The composition corresponding to different morphological grains is shown in the scanning electron microscope images. It can be seen that the composition corresponding to large grains tends to be a disordered fluorite structure, while the composition corresponding to small grains is an ordered pyrochlore structure.

[0049] Figure 5 The high-entropy ceramic bulk material (La) obtained in Example 1 is given. 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2The XRD pattern of 2Zr2O7 after annealing at 1400℃ for 130 hours shows that the sample did not undergo phase transformation or oxide coefficient, indicating excellent thermal stability.

[0050] Figure 6 The high-entropy ceramic bulk material (La) obtained in Example 1 is given. 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 The experimental thermal conductivity graph of 2Zr2O7 shows that its thermal conductivity ranges from 1.511 to 1.672 W·m. –1 ·K –1 (25~800℃). A comparison of its thermal conductivity with other oxide ceramics reveals that its thermal conductivity is lower than that of YSZ and other high-entropy oxide ceramics.

[0051] Figure 7 The high-entropy ceramic bulk material (La) obtained in Example 1 is given. 0.2 Nd 0.2 Gd 0.2 Y 0.2 Ho 0.2 The thermal expansion curve of 2Zr2O7 shows that its coefficient of thermal expansion is 11.52 × 10⁻⁶. -6 K -1 (1200℃), higher than the reported La2Zr2O7 (9.1 × 10⁻⁶). -6 K -1 ,1200℃), 8YSZ (10.7×10 -6 K -1 ,1200℃), (Y 0.25 Yb 0.25 Er 0.25 Lu 0.25 )2(Zr 0.5 Hf 0.5 )2O7(8.97 × 10 -6 K -1 (1200℃) and (Sm 0.2 Eu 0.2 Tb 0.2 Dy 0.2 Lu 0.2 )2Zr2O7(11 × 10 -6 K -1 (1200℃), the enhanced TEC helps reduce thermal expansion mismatch between the ceramic coating and the adhesive coating.

[0052] Figure 8 The high-entropy ceramic bulk material (La) obtained in Example 1 was compared with that obtained in Example 1. 0.2 Nd0.2 Gd 0.2 Y 0.2 Ho 0.2 The thermal conductivity and coefficient of thermal expansion of Zr2O7 compared with those of other oxide ceramics show that it outperforms YSZ and other high-entropy oxide ceramics, especially since it combines low thermal conductivity with a high coefficient of thermal expansion.

[0053] The dual-phase high-entropy ceramic material prepared by this invention possesses high-temperature stability, good thermal expansion, and low thermal conductivity, making it particularly suitable for aerospace, high-temperature insulation, and thermal barrier coatings. Through rational process design and composition optimization, the reliability and durability of the material under high-temperature environments are significantly improved, demonstrating broad engineering application prospects.

[0054] Example 2

[0055] Step 1: First, six oxides—La₂O₃, Nd₂O₃, Gd₂O₃, Y₂O₃, Ho₂O₃, and ZrO₂—were mixed in deionized water at a molar ratio of 1:1:1:1:1:5 and then ball-milled to form a relatively uniform slurry. A planetary ball mill was used, employing deionized water and zirconia balls as the dispersion media. These included large and small zirconia balls; the large zirconia balls had a diameter of 8 mm, and the small zirconia balls had a diameter of 4 mm. The volume ratio of oxide powder to zirconia balls to deionized water was 1:10:1.5. The ball milling was performed at a speed of 300 rpm for 12 hours, yielding the desired ceramic slurry.

[0056] Step 2: Place the ceramic slurry in an oven for drying at 120°C for 8 hours until it reaches a constant weight. Then grind the slurry and pass it through a standard sieve with a mesh size of 200 to obtain the desired ceramic powder.

[0057] Step 3: The sieved powder is placed in a muffle furnace for pre-firing to further improve chemical homogeneity and powder stability. The pre-firing temperature is set at 1200℃, and the sintering time is 2 hours, which improves the thermal stability and homogeneity of the powder. After pre-firing, the powder is cooled to obtain high-entropy zirconate ceramic powder.

[0058] Step 4: Place the pre-fired high-entropy ceramic powder into a secondary ball mill for ball milling at a speed of 300 rpm for 12 hours. After ball milling, place the pre-fired ceramic slurry into an oven for drying at 120℃ for 8 hours until constant weight is achieved. Then, grind the slurry and pass it through a standard sieve (200 mesh) to obtain the desired pre-fired ceramic powder.

[0059] Step 5: Add polyvinyl alcohol (PVA) to the pre-fired ceramic powder for granulation. The concentration of PVA is 8%. Then, sieve the granulated powder through a sieve with a mesh size of 80 to ensure the uniformity of the powder particles, and obtain the required granulated powder.

[0060] Step 6: Place the granulated powder into a mold and press it on a press to obtain the desired ceramic green body. The mold is a circle with a diameter of 20mm, the pressure is 225MPa, and the holding time is 1.5min.

[0061] Step 7: Place the ceramic green body into a high-temperature muffle furnace for sintering at a temperature of 1600℃ for 10 hours. The powder used as a pad in the crucible is the prepared high-entropy zirconate ceramic powder.

Claims

1. A dual-phase high-entropy ceramic material for high-temperature thermal barrier coatings and its preparation method, characterized in that, Includes the following steps: Step A: Preparation of high-entropy zirconate ceramic powder (1) Weigh rare earth oxides and ZrO2 according to the stoichiometric ratio, add deionized water or anhydrous ethanol and mix to obtain a slurry; (2) The slurry is further mixed by ball milling, and zirconia balls are added as the ball milling medium during the ball milling process; (3) Dry the slurry obtained after ball milling; (4) The dried powder is passed through a standard sieve to obtain a uniform powder; (5) The sieved powder is placed in a muffle furnace for pre-firing to obtain high-entropy zirconate ceramic powder; (6) The powder can be selectively pre-calcined to further improve chemical homogeneity and powder stability; Step B: Preparation of high-entropy zirconate ceramic bulk (1) When the powder is pre-calcined: A second ball milling process is performed, followed by drying and the addition of a binder for granulation. The granulated powder is loaded into a mold and a ceramic green body is made by powder pressing process. (2) When the powder has not been pre-calcined: The dried and sieved powder is directly mixed with the binder and granulated, eliminating the secondary ball milling step; The granulated powder is loaded into a mold and pressed to form a ceramic green body. (3) The obtained green body is wrapped in high-entropy zirconate ceramic powder and sintered in a high-temperature muffle furnace to obtain high-entropy zirconate ceramic block.

2. A dual-phase high-entropy ceramic material for high-temperature thermal barrier coatings according to claim 1, characterized in that, Its main chemical composition is (R1,R2,R3,R4,R5)2Zr2O7, wherein R1, R2, R3, R4, and R5 are rare earth elements selected from at least two of La, Nd, Gd, Y, and Ho.

3. The dual-phase high-entropy ceramic material for high-temperature thermal barrier coating according to claim 2, characterized in that, When the total molar ratio of rare earth components is 1, the molar ratio of its rare earth oxides is: La2O3: 0~0.5, Nd2O3: 0~0.5, Gd2O3: 0~0.5, Y2O3: 0~0.5, Ho2O3: 0~0.5, forming a high-entropy zirconate ceramic material with ZrO2.

4. The preparation method according to claim 1, characterized in that, In step A, the ball milling equipment is a planetary or horizontal ball mill, and the media balls are zirconium balls, including large zirconium balls and small zirconium balls. The diameter of the large zirconium balls is 8-12 mm, and the diameter of the small zirconium balls is 2-6 mm. The ball milling speed is 100-400 rpm, the ball milling time is 3-36 hours, and the standard sieve mesh size is 40-250 mesh. The powder pre-calcination temperature is 1100℃-1450℃, and the time is 0.5-5 hours.

5. The preparation method according to claim 1, characterized in that, In step B, an 8% to 12% polyvinyl alcohol solution is used as a binder. After granulation, the granulated powder is obtained by sieving through a 60-250 mesh screen. The powder is pressed at a pressure range of 50-400 MPa for 0.5-3 minutes. The sintering temperature is 1500℃-1650℃ for 1-15 hours.

6. The preparation method according to claim 1, characterized in that, In step B, the powder surrounding the ceramic green body is a high-entropy zirconate ceramic powder with the same composition as the green body, to avoid impurity phase contamination during sintering. The particle size of this powder ranges from 1 to 20 µm. The coating method can be loose filling or light compaction to avoid impurity phase contamination during sintering.

7. The preparation method according to claim 1, characterized in that, The thermal conductivity of the prepared high-entropy zirconate ceramic bulk is 0.5–1.7 W / m·K (test temperature range: room temperature to 1200°C), and the coefficient of thermal expansion is 9–12 × 10⁻⁶. -6 K -1 (Test temperature range: room temperature to 1200°C), average grain size 0.8-1.0 μm (sintered at 1600°C for 10 hours).

8. A dual-phase high-entropy ceramic material for high-temperature thermal barrier coatings according to claim 1, characterized in that, This material is suitable for thermal barrier coatings, aerospace, and high-temperature thermal insulation applications, and has the following performance advantages: Excellent high-temperature stability, can be used for a long time at temperatures above 1400°C; Lower thermal conductivity significantly reduces heat transfer; A coefficient of thermal expansion that matches the metal prevents the coating from peeling off due to thermal stress at high temperatures. Excellent thermal shock resistance, suitable for complex thermal environments; The material is highly corrosion resistant and can withstand CMAS (calcium magnesium aluminum silicate) erosion.

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