A medium-entropy rare earth tantalate ceramic, a preparation method and application thereof

Abstract

This invention discloses a medium-entropy rare-earth tantalate ceramic, its preparation method, and its application. The chemical formula of the medium-entropy rare-earth tantalate ceramic is Y0. 1‑x / 2 Ta 1‑x / 2 M x O4; where 0 < X ​​< 0.8, M represents Ti, Hf, and Zr, and the molar content of each element in M ​​is equal. The preparation method involves weighing the corresponding Y2O3 powder, Ta2O5 powder, HfO2 powder, TiO2 powder, and ZrO2 powder, adding a solvent to mix, ball milling using a planetary ball mill, sieving, compacting in a mold, and then sintering to obtain the final product. The medium-entropy rare-earth tantalate ceramic raw material provided by this invention has a simple composition and low thermal conductivity at high temperatures, exhibiting good thermal insulation performance. Simultaneously, its high coefficient of thermal expansion at high temperatures reduces the expansion stress between the powder and the substrate material (or adhesive layer) when used as a thermal barrier coating, thus reducing cracking. Furthermore, its excellent fracture toughness allows it to effectively resist external impacts during service, showing broad application prospects in surface coatings for hot-end components of aero-engines.

Description

Technical Field

[0001] This invention belongs to the field of ceramic coating technology, specifically relating to a medium-entropy rare earth tantalate ceramic, its preparation method, and its application. Background Technology

[0002] With the further development of the aerospace industry, the development direction of aero-engines is gradually moving towards higher flow ratios, higher thrust-to-weight ratios, and higher inlet temperatures. It has been reported that the inlet temperature of the most advanced aero-engines currently exceeds 1700℃, and future temperatures are expected to exceed 2000℃. However, the effective operating temperature of aero-engine turbine blades is far lower than the actual operating temperature of the combustion chamber, greatly limiting the development of aero-engines. Thermal barrier coatings play an irreplaceable role in the development of temperature resistance. Using thermal barrier coatings can significantly increase the upper temperature limit of aero-engines, with an improvement comparable to that achieved by the development of high-temperature alloys over the past few decades.

[0003] YSZ, RE2Zr2O7, and RE3TaO7 are widely used thermal barrier coating materials. However, YSZ undergoes a phase transition above 1200℃, resulting in a lower operating temperature (≤1200℃), and YSZ also has relatively high thermal conductivity. RE3TaO7 and RE2Zr2O7 suffer from low coefficients of thermal expansion and low fracture toughness. While performance can be improved by doping the RE and Ta sites, the requirements remain unmet. This necessitates the development of new materials to replace these ceramic thermal barrier coatings. Rare earth tantalates (YTaO4) have attracted attention due to their low thermal conductivity, ferroelastic phase transition, and high-temperature stability. However, research on YTaO4 has primarily focused on theoretical calculations of its crystal structure and luminescence properties. In recent years, extensive research and experimental findings have provided a theoretical basis for the application of YTaO4 in thermal barrier coatings.

[0004] To better apply YTaO4 in the field of thermal barrier coatings, it is necessary to further reduce its thermal conductivity and improve its thermophysical and mechanical properties, such as coefficient of thermal expansion, hardness, and fracture toughness. Summary of the Invention

[0005] The first objective of this invention is to provide a medium-entropy rare-earth tantalate ceramic, and the second objective of this invention is to provide a method for preparing the medium-entropy rare-earth tantalate ceramic.

[0006] The first objective of this invention is achieved by providing a medium-entropy rare-earth tantalate ceramic with the chemical formula Y. 1-x / 2Ta 1-x / 2 M x O4; where 0 < X ​​< 0.8, M is Ti, Hf, Zr, and the molar content of each element in M ​​is equal.

[0007] The second objective of this invention is achieved by the method for preparing the medium-entropy rare-earth tantalate ceramic, which is carried out according to the following steps:

[0008] 1) Weigh the raw materials according to the formula: Y2O3 powder, Ta2O5 powder, HfO2 powder, TiO2 powder and ZrO2 powder, add solvent and ball mill using a planetary ball mill for 24~36h, ball mill speed is 600~1000r / min; the solvent is ethanol or distilled water;

[0009] 2) After drying the powder obtained from ball milling in step 1), pass it through a 100-200 mesh sieve, pre-calcine it in a muffle furnace at 1000-1200℃ for 5-10 hours, and then pass it through a 300-600 mesh sieve.

[0010] 3) Place the sieved powder from step 2) into a mold, compact it, and sinter it at 1500-1700℃ for 5-7 hours to obtain the target tantalate ceramic.

[0011] The medium-entropy rare-earth tantalate ceramics are used in the surface coating of hot-end components of aero engines.

[0012] The entropy rare earth tantalate ceramics in this invention include those with the chemical formula Y 1-x / 2 Ta 1-x / 2 M x The substance is O4; where 0 < X ​​< 0.8 (when X > 0.8, a large amount of second phase is generated, which accumulates at the grain boundaries, causing the prepared tantalate material to become embrittled at the grain boundaries, thus reducing its performance). M is a mixture of three metal cations: Ti, Hf, and Zr, with different metal cations having the same molar content. Since the sum of the radii of the three metal cations Ti, Hf, and Zr is approximately twice the sum of the radii of a Y ion and a Ta ion, to maintain the electroneutrality of the compound, the three metal cations Ti, Hf, and Zr simultaneously replace Y and Ta ions and enter the tantalate lattice. By controlling the content of the three metal cations Ti, Hf, and Zr entering the tantalate lattice, the lattice configuration entropy and lattice parameters a, b, and c can be further controlled, thereby changing the phase structure of the tantalate and thus giving the tantalate material superior performance.

[0013] The beneficial effects of this invention are as follows: The medium-entropy rare-earth tantalate ceramic raw material provided by this invention has a simple composition and low thermal conductivity at high temperatures, exhibiting good thermal insulation performance. Simultaneously, its high coefficient of thermal expansion at high temperatures reduces the expansion stress between the powder and the substrate material (or adhesive layer) when used as a thermal barrier coating, thus reducing cracking. Furthermore, its excellent fracture toughness enables it to effectively resist external impacts during service, showing broad application prospects in surface coatings for hot-end components of aero-engines. Attached Figure Description

[0014] Figure 1 The XRD patterns are of the tantalate ceramics prepared in Examples 1-4 of this invention.

[0015] Figure 2 This is a SEM image of the tantalate ceramic prepared in Example 4 of the present invention;

[0016] Figure 3 The thermal conductivity diagrams are for the tantalate ceramics prepared in Examples 1-4 and Comparative Example 1 of this invention.

[0017] Figure 4 The thermal expansion coefficient diagrams are shown for the tantalate ceramics prepared in Examples 1-4 and Comparative Example 1 of this invention. Detailed Implementation

[0018] The present invention will be further described below, but this is not intended to limit the invention in any way. Any modifications made based on the present invention are within the scope of protection of the present invention.

[0019] This invention relates to a medium-entropy rare-earth tantalate ceramic with the chemical formula Y. 1-x / 2 Ta 1-x / 2 M x O4; where 0 < X ​​< 0.8, M is Ti, Hf, Zr, and the molar content of each element in M ​​is equal.

[0020] The medium-entropy rare-earth tantalate ceramic has a thermal conductivity of 1.23-1.42 W·m at 900℃. -1 ·K -1 The coefficient of thermal expansion at 1400℃ is 9.8-10.4 × 10⁻⁶. -6 K -1 Its fracture toughness is 4.7-5.2 MPa. 0.5 .

[0021] This invention also provides a method for preparing the aforementioned medium-entropy rare-earth tantalate ceramic, which is implemented according to the following steps:

[0022] 1) Weigh the raw materials according to the formula: Y2O3 powder, Ta2O5 powder, HfO2 powder, TiO2 powder and ZrO2 powder, add solvent and ball mill using a planetary ball mill for 24~36h, ball mill speed is 600~1000r / min; the solvent is ethanol or distilled water;

[0023] 2) After drying the powder obtained from ball milling in step 1), pass it through a 100-200 mesh sieve, pre-calcine it in a muffle furnace at 1000-1200℃ for 5-10 hours, and then pass it through a 300-600 mesh sieve.

[0024] 3) Place the sieved powder from step 2) into a mold, compact it, and sinter it at 1500-1700℃ for 5-7 hours to obtain the target tantalate ceramic.

[0025] In step 1), the molar ratio of raw material to solvent is 2-6:1.

[0026] In step 1), the purity of Y2O3 powder, Ta2O5 powder, HfO2 powder, TiO2 powder and ZrO2 powder is not less than 99.9%.

[0027] In step 2), the drying temperature is 100~150℃ and the drying time is 24~36h.

[0028] In step 3), the holding pressure is 200~300MPa and the holding time is 2~4min.

[0029] The present invention further provides the application of the medium-entropy rare earth tantalate ceramic, specifically its application in the surface coating of hot-end components of aero-engines.

[0030] Examples 1-6

[0031] Examples 1-6 illustrate the preparation of medium-entropy rare-earth tantalate ceramics according to the following steps, with specific parameters shown in Table 1:

[0032] 1) Weigh out yttrium oxide (Y₂O₃) powder, tantalum oxide (Ta₂O₅) powder, hafnium oxide (HfO₂) powder, titanium oxide (TiO₂) powder, and zirconium oxide (ZrO₂) powder according to the specified proportions, and mix them with solvent ethanol or distilled water. The molar ratio of the five powders (Y₂O₃, Ta₂O₅, HfO₂, TiO₂, and ZrO₂) to the solvent is (2:1) to (6:1). Ball mill the mixture using a planetary ball mill to obtain powder A. The ball milling time is 24–36 hours, the ball mill speed is 600–1000 r / min, and the purity of the raw materials (Y₂O₃, Ta₂O₅, HfO₂, TiO₂, and ZrO₂) powders is not less than 99.9%.

[0033] 2) After drying the powder A obtained in step (1), the powder B is obtained by first sieving. The drying temperature is 100~150℃, the drying time is 24~36h, and the sieve mesh for the first sieving is 100~200 mesh.

[0034] 3) After pre-firing the powder B obtained in step (2) in a muffle furnace, perform a second sieve to obtain powder C. The pre-firing temperature is 1000~1200℃, the pre-firing time is 5~10 hours, and the sieve mesh for the second sieve is 300~600 mesh.

[0035] 4) Place the powder C obtained in step (3) into the mold and compact it to form block C. The holding pressure is 200~300MPa and the holding time is 2~4min.

[0036] 5) Sinter the block C from step (4) to obtain tantalate material. The sintering temperature is 1500-1700℃ and the sintering time is 5-7h.

[0037] Tantalate ceramics with low thermal conductivity, high thermal expansion, and high fracture toughness were prepared using the above method. To fully illustrate the low thermal conductivity, high thermal expansion, and high fracture toughness tantalate ceramics prepared by the above method, six examples are selected for explanation.

[0038] Table 1. Preparation parameters of entropy rare earth tantalate ceramics in Examples 1-6 of this invention

[0039]

[0040] Comparative Example 1

[0041] The difference between this comparative example and Example 1 is that only yttrium oxide (Y2O3) powder and tantalum oxide (Ta2O5) powder are added to the raw material powder, that is, the content of hafnium oxide (HfO2) powder, titanium oxide (TiO2) powder and zirconium oxide (ZrO2) powder is 0%mol, and the chemical formula of the prepared tantalate ceramic is YTaO4.

[0042] Comparative Example 2

[0043] The difference between this comparative example and Example 1 is that only yttrium oxide (Y₂O₃), tantalum oxide (Ta₂O₅), and titanium oxide (TiO₂) powders were added to the raw material powder, i.e., the content of hafnium oxide (HfO₂) powder and zirconium oxide (ZrO₂) powder was 0%mol. The chemical formula of the prepared tantalate ceramic is Y. 0.98 Ta 0.98 Ti 0.04 O4.

[0044] Comparative Example 3

[0045] The difference between this comparative example and Example 1 is that only yttrium oxide (Y₂O₃) powder, tantalum oxide (Ta₂O₅) powder, and zirconium oxide (ZrO₂) powder were added to the raw material powder. Specifically, the content of titanium oxide (TiO₂) powder and hafnium oxide (HfO₂) powder was 0%mol. The resulting tantalate ceramic has the chemical formula Y. 0.98 Ta 0.98 Zr 0.04 O4.

[0046] Comparative Example 4

[0047] The difference between this comparative example and Example 1 is that only yttrium oxide (Y₂O₃) powder, tantalum oxide (Ta₂O₅) powder, and hafnium oxide (HfO₂) powder were added to the raw material powder, i.e., the content of titanium oxide (TiO₂) powder and zirconium oxide (ZrO₂) powder was 0%mol. The chemical formula of the prepared tantalate ceramic is Y. 0.98 Ta 0.98 Hf 0.04 O4.

[0048] Comparative Example 5

[0049] The difference between this comparative example and Example 1 is that x = 0.8, and the chemical formula is: Y 0.6 Ta 0.6 M 0.8 O4.

[0050] Test results of the structure and properties of tantalate ceramics prepared in Examples 1-6

[0051] 1. XRD characterization

[0052] The tantalate ceramics prepared in Examples 1-4 were tested using X-ray diffraction.

[0053] like Figure 1 As shown, the XRD diffraction peaks of Examples 1-3 correspond one-to-one with the standard peaks of their standard PDF card #24-1415. The absence of second-phase diffraction peaks indicates that the prepared ceramics are single-phase ceramics, and that HfO2, TiO2, and ZrO2 have entered the YTaO4 lattice, resulting in a monoclinic crystal structure. The main phase of the ceramic prepared in Example 4 is the same as that in Examples 1-3, but a few second-phase diffraction peaks appear, indicating that the phase structure of the tantalate has been altered by equal doping with Ti, Zr, and Hf. The lattice parameters a, b, c and α, γ, β of Examples 1-4 are shown in Table 2. Comparison of the XRD diffraction peaks reveals no significant shift, proving that Ti, Hf, and Zr atoms simultaneously replace Y and Ta atoms, thus maintaining the electroneutrality of the crystal structure. This is because the sum of the ionic radii of Ti, Hf, and Zr ions is approximately twice the sum of the ionic radii of a single Y and a single Ta ion.

[0054] Table 2. Lattice parameters of tantalate ceramics prepared in Examples 1-4

[0055]

[0056] 2. SEM characterization

[0057] from Figure 2It can be seen that the tantalate ceramic prepared in Example 4 has a pore-free crystal structure, uniform grain distribution, clear grain boundaries, and good bonding between grains. The second phase exists in the grains (those with black spots are the second phase), which can enhance the toughness of the ceramic.

[0058] The tantalate ceramics prepared in Comparative Examples 1-4 all exhibit numerous small pores in their crystal structures, located at grain boundaries, resulting in a non-dense bulk, blurred grain boundaries, and frequent grain boundary fractures. In Comparative Example 5, the presence of a large amount of second phase at grain boundaries leads to grain boundary embrittlement and compromises the ceramic's properties.

[0059] 3. Thermal conductivity testing

[0060] The tantalate ceramic blocks obtained in Examples 1-4 and Comparative Example 1 were polished into φ6×2mm circular thin sheets, and their thermal conductivity was measured using a laser thermal conductivity meter.

[0061] Result: As Figure 3 As shown, the thermal conductivity of the ceramic blocks prepared in Examples 1-4 and Comparative Example 1 decreased sharply as the temperature continued to rise. The thermal conductivity of the ceramic blocks prepared in Examples 1-4 was excellent at high temperatures, but the thermal conductivity of the tantalate ceramics prepared in Examples 1-4 was significantly lower than that of Comparative Example 1 at high temperatures.

[0062] 4. Thermal expansion test

[0063] The ceramic blocks obtained in Examples 1-4 and Comparative Example 1 were polished into cuboids of 10×3×1.5mm, and their coefficient of thermal expansion at 100~1400℃ was measured using a thermal expansion analyzer (TMA 402 F3).

[0064] Result: From Figure 4 It can be seen that the tantalate ceramics obtained in Examples 1-4 and Comparative Example 1 all have a better coefficient of thermal expansion, which results in less thermal stress during use.

[0065] 5. Fracture toughness testing

[0066] The ceramic blocks obtained in Examples 1-6 and Comparative Examples 1-5 were polished, and the fracture toughness of the tantalate ceramics was calculated using the indentation method. Specifically, the polished ceramic blocks were indented with a Vickers hardness tester under a certain load (F) to obtain the hardness (H), with each sample subjected to 10 indentations. Then, the diagonal length of the indentation (a) and the crack length (c) along the diagonal were obtained from the scanning electron microscope images. The fracture toughness was then calculated using the formula... E is Young's modulus, used to calculate fracture toughness (average of 10 measurements for each sample). The calculation results are shown in Table 3.

[0067] Results: As shown in Table 3, the fracture toughness of the tantalate ceramics prepared in Examples 1-6 of this invention is significantly higher than that of Comparative Examples 1-5, with the average fracture toughness of the tantalate ceramic prepared in Example 4 reaching as high as 5.18 MPa. 0.5 In contrast, the tantalate ceramic prepared in Comparative Example 5 exhibits a large amount of second phase aggregation at grain boundaries due to x=0.8, resulting in a decrease in fracture toughness.

[0068] Table 3. Fracture toughness of tantalate ceramics prepared in Examples 1-6 and Comparative Examples 1-5

[0069]

[0070] In summary, the tantalate ceramics prepared in Examples 1-6 of this invention exhibit distinct grains, clear grain boundaries, and good intergranular bonding within their crystal structure. They also demonstrate low thermal conductivity at high temperatures, exhibiting excellent thermal insulation properties. Furthermore, their high coefficient of thermal expansion at high temperatures reduces the expansion stress between the powder and the substrate material (or adhesive layer) when used as a thermal barrier coating, thus minimizing cracking. Additionally, their excellent fracture toughness enables them to effectively resist external impacts during service.

Claims

1. A medium-entropy rare-earth tantalate ceramic, characterized in that, The chemical formula of the medium-entropy rare earth tantalate ceramic is Y. 1-x / 2Ta 1-x / 2 M x O4; where 0 < X ​​< 0.8, M is Ti, Hf, Zr, and the molar content of each element in M ​​is equal.

2. The medium-entropy rare-earth tantalate ceramic according to claim 1, characterized in that, The medium-entropy rare-earth tantalate ceramic has a thermal conductivity of 1.23-1.42 W·m at 900℃. -1 ·K -1 The coefficient of thermal expansion at 1400℃ is 9.8-10.4 × 10⁻⁶. -6 K -1 Its fracture toughness is 4.7-5.2 MPa. 0.5 .

3. The method for preparing the medium-entropy rare-earth tantalate ceramic according to claim 1, characterized in that, Follow these steps to achieve the following: 1) Weigh the raw materials according to the formula: Y2O3 powder, Ta2O5 powder, HfO2 powder, TiO2 powder and ZrO2 powder, add solvent and ball mill using a planetary ball mill for 24~36h, ball mill speed is 600~1000r / min; the solvent is ethanol or distilled water; 2) After drying the powder obtained from ball milling in step 1), pass it through a 100-200 mesh sieve, pre-calcine it in a muffle furnace at 1000-1200℃ for 5-10 hours, and then pass it through a 300-600 mesh sieve. 3) Place the sieved powder from step 2) into a mold, compact it, and sinter it at 1500-1700℃ for 5-7 hours to obtain the target tantalate ceramic.

4. The method for preparing medium-entropy rare-earth tantalate ceramics according to claim 3, characterized in that, In step 1), the molar ratio of raw material to solvent is 2-6:

1.

5. The method for preparing medium-entropy rare-earth tantalate ceramics according to claim 3, characterized in that, In step 1), the purity of Y2O3 powder, Ta2O5 powder, HfO2 powder, TiO2 powder and ZrO2 powder is not less than 99.9%.

6. The method for preparing medium-entropy rare-earth tantalate ceramics according to claim 3, characterized in that, In step 2), the drying temperature is 100~150℃ and the drying time is 24~36h.

7. The method for preparing medium-entropy rare-earth tantalate ceramics according to claim 3, characterized in that, In step 3), the pressure during compaction is 200~300MPa and the holding time is 2~4min.

8. The application of the medium-entropy rare-earth tantalate ceramic of claim 1 in the surface coating of hot-end components of aero-engines.

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