High-entropy ceramic material resistant to cmas corrosion and method of making same

Abstract

The application discloses a high-entropy ceramic material resistant to CMAS corrosion and a preparation method thereof. 2(1‑x) Yb 2x Zr2O7, wherein 0<=x<1, and the preparation method comprises the following steps: according to the chemical composition of the high-entropy ceramic material, raw oxide materials are prepared, the raw oxide materials are subjected to first ball milling to obtain mixed powder, the mixed powder is subjected to pre-sintering to obtain pre-sintered powder, the pre-sintered powder is subjected to second ball milling to obtain pre-sintered ball-milled powder, the pre-sintered ball-milled powder is granulated to obtain granulated powder, the granulated powder is subjected to compression molding to obtain a green body, and the green body is subjected to sintering to obtain the high-entropy ceramic material. The high-entropy ceramic material has excellent high-temperature stability and CMAS corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of thermal barrier coatings, and particularly relates to a high-entropy ceramic material resistant to CMAS corrosion and a preparation method thereof. BACKGROUND

[0002] Thermal barrier coatings (TBCs) are a key technology for improving the reliability and service life of turbine blades of an aero-engine. The currently widely used thermal barrier coating material 7-8YSZ ceramic material has the advantages of high melting point, low thermal conductivity, and similar thermal expansion coefficient to the alloy substrate, but with the development of aero-engines and the increase of service temperature, YSZ also has many problems that are difficult to solve. At about 1170℃ and 2370℃, ZrO2 will undergo phase transition from monoclinic phase (m-ZrO2) to tetragonal phase (t-ZrO2) and cubic phase (c-ZrO2), and in the cooling process after the temperature drops, t-ZrO2 in YSZ will also undergo reverse phase transition to m-ZrO2. The volume change caused by the phase transition is about 4%, and due to the volume change in the thermal cycle process, the ceramic layer fails, and eventually leads to the peeling of the coating. In addition, the YSZ coating will also be subjected to molten CMAS corrosion in a high-temperature environment. After the CMAS is melted at high temperature, it is deposited on the engine blade, penetrates into the interior of the coating on the surface of the blade through pores and cracks, and reacts with YSZ, which promotes the gradual transformation of the metastable phase (t'-ZrO2) in YSZ into t-ZrO2 phase and c-ZrO2 phase. The phase transition leads to volume expansion, and after the CMAS penetrates into the gap of the columnar structure of the YSZ coating, the strain tolerance of the coating is reduced, which leads to the reduction of the service life of the coating and the acceleration of the peeling speed. Therefore, it is necessary to develop a new type of thermal barrier coating material with high-temperature structural stability and high-temperature corrosion resistance. SUMMARY

[0003] In view of the deficiencies in the prior art, a first object of the present application is to provide a high-entropy ceramic material resistant to CMAS corrosion. The high-entropy ceramic material provided by the present application has excellent high-temperature stability and CMAS corrosion resistance.

[0004] A second object of the present application is to provide a preparation method of a high-entropy ceramic material resistant to CMAS corrosion.

[0005] In order to achieve the above object, the present application provides the following technical solutions:

[0006] The present application provides a high-entropy ceramic material resistant to CMAS corrosion, and the chemical formula of the high-entropy ceramic material is (YGdErDy) 2(1-x) Yb 2x Zr2O7, wherein 0≤x<1, preferably 0.2≤x<0.8, and further preferably 0.4≤x<0.8.

[0007] The high-entropy ceramic material provided by the application contains a plurality of rare earth ions with different radii after being corroded by CMAS, which react with Ca and Si elements to generate needle-shaped apatite, and zirconate decomposes to generate ZrO2. The element with smaller rare earth ion radius is easy to form larger size spherical ZrO2, and the element with larger rare earth ion radius is more likely to form needle-shaped apatite. With the extension of corrosion time, the two products form a dense reaction layer to block the further corrosion of CMAS. Yb2O3 has smaller ion radius and good compatibility, which is beneficial to phase stability. With the increase of Yb2O3 content and the extension of corrosion time, Yb 3+ ions enter ZrO2 to form more and larger spherical ZrO2, and the contact is more close, so that the reaction layer is more dense to block the further corrosion of CMAS.

[0008] In a preferred embodiment, the high-entropy ceramic material resistant to CMAS corrosion is a single-phase fluorite structure. The high-entropy ceramic material formed by the chemical formula of the application is a single-phase fluorite structure, which is stable in structure and will not change phase when corroded. Therefore, compared with the YSZ ceramic double-phase structure, which will change phase when corroded, the high-entropy ceramic material has more excellent CMAS corrosion resistance.

[0009] The application also provides a preparation method of the high-entropy ceramic material resistant to CMAS corrosion. The raw oxide materials are weighed according to the chemical composition of the high-entropy ceramic material, and the raw oxide materials are first ball milled to obtain a mixed powder. The mixed powder is pre-sintered to obtain a pre-sintered powder, and the pre-sintered powder is secondly ball milled to obtain a pre-sintered ball milled powder. The pre-sintered ball milled powder is granulated to obtain a granulated powder, and the granulated powder is pressed to obtain a green body. After sintering, the high-entropy ceramic material is obtained.

[0010] The technical scheme of the application is simple and controllable, low in cost, and can obtain the high-entropy ceramic material resistant to CMAS corrosion by traditional solid-phase method through one pre-sintering and one sintering.

[0011] In a preferred embodiment, the raw oxide materials are calcined at 700-800 DEG C for 2-3 h. In actual operation, the raw oxide materials are placed in different zirconia crucibles and calcined to remove water and organic impurities in the raw materials.

[0012] In a preferred embodiment, the Y2O3 powder, the Gd2O3 powder, the Er2O3 powder, the Dy2O3 powder, the Yb2O3 powder and the ZrO2 powder are weighed according to the chemical composition of the high-entropy ceramic material. The particle sizes of the Y2O3 powder, the Gd2O3 powder, the Er2O3 powder, the Dy2O3 powder, the Yb2O3 powder and the ZrO2 powder are all 50-100 nm, and the purity of each of the powders is greater than or equal to 99.9%.

[0013] The particle size of each raw material powder is controlled in the above range, the final obtained high-entropy ceramic material has the best density and the most uniform composition, the structural defects generated in the preparation process are more in the particle size range, the sintering activity is high, and the sintering and densification are promoted.

[0014] In a preferred embodiment, the rotation speed of the first ball milling is 300-350 rpm, and the time of the first ball milling is 10-12 h.

[0015] In a preferred embodiment, the first ball milling is wet ball milling, and the ball milling medium is anhydrous ethanol.

[0016] In a preferred embodiment, after the first ball milling is completed, drying is performed, and then grinding is performed to obtain a mixed powder, the drying temperature is 70-90°C, and the time is 6-10 h.

[0017] In a preferred embodiment, the pre-sintering temperature is 1500-1550°C, and the time is 6-10 h. Through pre-sintering, the raw materials react to form the target product, but the pre-sintering temperature cannot be too high, and if the temperature is too high and the holding time is too long, the activity of the sintered powder is worse, which is not conducive to subsequent sintering, and if the pre-sintering temperature is too low, the reaction is not sufficient.

[0018] In a preferred embodiment, the rotation speed of the second ball milling is 450-500 rpm, and the time of the second ball milling is 10-12 h. In the present application, the rotation speed of the second ball milling greatly affects the density of the final ceramic material, if the rotation speed is too low, the grinding is insufficient, the powder particle size is large, which is not conducive to subsequent sintering, and the ceramic density decreases, and if the ball milling rotation speed is too large, the powder will be contaminated.

[0019] In a preferred embodiment, the second ball milling is wet ball milling, and the ball milling medium is anhydrous ethanol.

[0020] In a preferred embodiment, after the second ball milling is completed, drying is performed to obtain pre-sintering ball milling powder, the drying temperature is 70-90°C, and the time is 6-10 h.

[0021] In a preferred embodiment, the granulation process is as follows: after polyvinyl alcohol (PVA) is added to the pre-sintering ball milling powder, grinding is performed, and then the mixture is passed through a 300-500 mesh sieve to obtain the granulated product, and the addition amount of the PVA is 6-8% of the mass of the pre-sintering ball milling powder.

[0022] In the granulation process, the addition amount of the PVA is controlled in the above range, which can fully grind the pre-sintering ball milling powder uniformly and can be well formed, if the addition amount of the PVA is too small, the adhesion is not enough, which affects the briquetting forming, and if the addition amount of the PVA is too large, the grinding is not uniform.

[0023] Preferably, the granulated powder is preformed by moulding, and then green compact is obtained by cold isostatic pressing, the preforming pressure is 10-20 MPa, the preforming pressure maintaining time is 5-7 min, the cold isostatic pressing pressure is 200-220 MPa, and the cold isostatic pressing pressure maintaining time is 5-7 min.

[0024] In actual operation, the powder is preformed by tabletting machine under 20 MPa for 5-7 min to obtain green compacts of different shapes, and then the preformed green compacts are pressed by cold isostatic pressing under 200-220 MPa for 5-7 min to obtain the final compacts required by the experiment.

[0025] Preferably, the sintering temperature is 1550-1700 DEG C, and the sintering time is 10-20 h.

[0026] Further preferably, the sintering process is as follows: the temperature is raised to 600-700 DEG C at a rate of 5-10 DEG C / min, and then maintained for 2-3 h, then the temperature is raised to 1550-1700 DEG C at a rate of 5-10 DEG C / min, and then maintained for 10-20 h, then the temperature is lowered to 700-800 DEG C at a rate of 1-2 DEG C / min, and then the furnace is cooled down.

[0027] In the further preferred sintering process, the temperature is first raised from room temperature to 600-700 DEG C, in this stage, the shape of the particles is basically unchanged, the whole sintering body does not shrink, and the density increases little. The temperature is maintained at 600-700 DEG C for 2-3 h to remove PVA. Then the temperature is raised to 1550-1700 DEG C, and maintained for 10-20 h, the grains grow, the substances on the grain boundary diffuse and fill the pores, and the sintering body is gradually densified. After the temperature maintaining, the temperature is lowered to 700-800 DEG C at a rate of 1-2 DEG C / min to avoid the large thermal stress caused by the large temperature difference between the inside and outside of the ceramic due to the rapid temperature drop, which may cause the ceramic to crack. In the whole sintering process, the sintering temperature needs to be effectively controlled, if the sintering temperature is too high, the grains will grow rapidly and coarsely, which is not conducive to the removal of pores, and will result in a large number of residual pores, which limits the density of the material. And the excessive growth of the grains will cause the mechanical properties of the ceramic to decrease.

[0028] Beneficial effects:

[0029] The present application is a new thermal barrier coating material, by high-entropy rare earth zirconate, design (YGdErDy) 2(1-x) Yb 2xZr2O7 high-entropy ceramic material. The material is single-phase fluorite structure after high-temperature sintering, has higher structural stability than YSZ, is suitable for higher temperature service conditions, and is beneficial to improve the service life of thermal barrier coatings. At the same time, the reaction layer of the material is far smaller than YSZ under CMAS corrosion at 1300℃, and the reaction layer is dense, which is beneficial to block the further corrosion of CMAS. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 XRD diffraction patterns of ceramic samples obtained in four examples;

[0031] Figure 2 Morphology diagrams of ceramic samples obtained in four examples: (a) Example 1; (b) Example 2; (c) Example 3; (d) Example 4;

[0032] Figure 3 Cross-sectional schematic diagrams of the examples and the comparative example after CMAS corrosion at 1300℃: (a) Example 1 corroded for 1h; (b) Example 2 corroded for 1h; (c) Example 3 corroded for 1h; (d) Example 4 corroded for 1h; (e) Comparative Example 1 corroded for 1h;

[0033] Figure 4 Cross-sectional schematic diagrams of the examples and the comparative example after CMAS corrosion at 1300℃: (a) Example 1 corroded for 50h; (b) Example 2 corroded for 50h; (c) Example 3 corroded for 50h; (d) Example 4 corroded for 50h; (e) Comparative Example 1 corroded for 50h. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application will be further described in detail below in combination with examples and comparative examples. The specific examples described herein are only used to explain the present application and do not limit the present application.

[0035] Some test methods used in each example and comparative example are as follows:

[0036] CMAS resistance performance test:

[0037] CaO, MgO, Al2O3, SiO2 powders were ball-milled and uniformly mixed according to the molar percentage of 33:9:13:45, placed in a 1300℃ box-type resistance furnace for constant temperature heating for 8 hours, and then cooled with the furnace. The formed glassy CMAS was ground and sieved to a particle size of about 30μm powder. The CMAS was placed in a 20mg / cm2 2The coating amount of the coating solution is uniformly coated on the surface of the prepared ceramic bulk with different components, and then placed in a resistance furnace for corrosion at 1300°C for different time, and then cooled with the furnace. The cross section of the corroded sample is made into a metallographic sample, and the corrosion area of the bulk by CMAS is characterized by scanning electron microscope (SEM) with energy dispersive spectrometer (EDS), and the penetration depth of CMAS in the ceramic is compared.

[0038] Example 1

[0039] (Y 0.25 Gd 0.25 Er 0.25 Dy 0.25 Preparation of Y2Zr2O7ceramic (x=0)

[0040] (1) Put various oxide raw materials in different zirconia crucibles, and calcine at 700-800°C for 2 hours to remove water and organic impurities in the raw materials.

[0041] (2) The powders are weighed according to the molar ratio of Y2O3, Gd2O3, Er2O3, Dy2O3, Yb2O3, and ZrO2 as 1:1:1:1:0:8, and then poured into a zirconia ball mill jar in turn, and an appropriate amount of zirconia balls and anhydrous ethanol is added. Then, the first ball milling is carried out at a speed of 300 rpm for 10 hours.

[0042] (3) Put the mixed slurry into a drying box and dry at 80°C for 10 hours. After drying, grind to obtain a mixed powder. The mixed powder is pre-sintered at a temperature of 1550°C for 10 hours to obtain a pre-sintered powder.

[0043] (4) Mix the pre-sintered powder with anhydrous ethanol for the second ball milling at a speed of 500 rpm for 10 hours. Then, dry at 80°C for 10 hours, and then pass through a 300 mesh sieve. Then, add 8% PVA and grind to granulate.

[0044] (5) Use a tablet press to pre-form the powder at 20 MPa for 5-7 min to obtain green bodies of different shapes. Then, cold isostatic press the pre-formed green bodies at 200-220 MPa for 5-7 min to obtain the final green bodies required for the experiment.

[0045] (6) Finally, the second sintering is carried out at a temperature of 1550°C for 20 hours. The sintering process includes: increasing the temperature to 700°C at a rate of 10°C / min, and keeping it for 2 hours to remove PVA. Then, increase the temperature to 1550°C at a rate of 5°C / min, and keep it for 20 hours. After keeping, decrease the temperature to 800°C at a rate of 1°C / min to prevent the sample from cracking due to rapid cooling. Then, cool with the furnace. Finally, the ceramic bulk is obtained.

[0046] CMAS powder was weighed at a dosage of 20 mg / cm 2 The obtained ceramic bulk was placed in a high-temperature resistance furnace for corrosion experiment at a corrosion temperature of 1300°C.

[0047] The (Y 0.25 Gd 0.25 Er 0.25 Dy 0.25 )2Zr2O7 ceramic prepared by the above method has a single-phase fluorite structure, a density of 98.1%, a reaction layer depth of 22.4 μm after corrosion for 1 h, and a reaction layer depth of 60.2 μm after corrosion for 50 h.

[0048] Example 2

[0049] The (Y 0.2 Gd 0.2 Er 0.2 Dy 0.2 Yb 0.2 )2Zr2O7 ceramic (x = 0.2) was prepared

[0050] An appropriate amount of powder was weighed according to the molar ratio of Y2O3, Gd2O3, Er2O3, Dy2O3, Yb2O3 and ZrO2 being 1:1:1:1:1:10, and the ceramic was prepared by using the preparation method described in Example 1.

[0051] CMAS powder was weighed at a dosage of 20 mg / cm 2 The obtained ceramic bulk was placed in a high-temperature resistance furnace for corrosion experiment at a corrosion temperature of 1300°C.

[0052] The (Y 0.2 Gd 0.2 Er 0.2 Dy 0.2 Yb 0.2 )2Zr2O7 ceramic prepared by the above method has a single-phase fluorite structure, a density of 98.3%, a reaction layer depth of 20 μm after corrosion for 1 h, and a reaction layer depth of 54.7 μm after corrosion for 50 h.

[0053] Example 3

[0054] The (Y 0.15 Gd 0.15 Er 0.15 Dy 0.15 Yb 0.4 )2Zr2O7 ceramic (x = 0.4) was prepared

[0055] Weigh appropriate amounts of powder according to the molar ratio of Y2O3, Gd2O3, Er2O3, Dy2O3, Yb2O3, and ZrO2 of 3:3:3:3:8:40, and prepare ceramics using the preparation method described in Example 1.

[0056] At 20mg / cm 2 Weigh out the amount of CMAS powder, coat it evenly onto the surface of the obtained ceramic block, and then place it in a high-temperature resistance furnace for corrosion testing at a corrosion temperature of 1300℃.

[0057] The (Y) prepared by the above method 0.15 Gd 0.15 Er 0.15 Dy 0.15 Yb 0.4 The ceramic phase structure of 2Zr2O7 is a single-phase fluorite structure with a density of 97.8%. The reaction layer depth is 18.2 μm after 1 hour of corrosion and 41.9 μm after 50 hours of corrosion.

[0058] Example 4

[0059] (Y 0.05 Gd 0.05 Er 0.05 Dy 0.05 Yb 0.8 Preparation of Zr₂O₇ ceramics (x = 0.8)

[0060] Weigh appropriate amounts of powder according to the molar ratio of Y2O3, Gd2O3, Er2O3, Dy2O3, Yb2O3, and ZrO2 of 1:1:1:1:16:40, and prepare ceramics using the preparation method described in Example 1.

[0061] At 20mg / cm 2 Weigh out the amount of CMAS powder, coat it evenly onto the surface of the obtained ceramic block, and then place it in a high-temperature resistance furnace for corrosion testing at a corrosion temperature of 1300℃.

[0062] The (Y) prepared by the above method 0.05 Gd 0.05 Er 0.05 Dy 0.05 Yb 0.8 The ceramic phase structure of 2Zr2O7 is a single-phase fluorite structure with a density of 97.9%. The reaction layer depth is 16.7 μm after 1 hour of corrosion and 30.1 μm after 50 hours of corrosion.

[0063] Comparative Example 1

[0064] Weigh appropriate amounts of powder from Y2O3 and ZrO2 in a mass ratio of 7%:93%, and prepare ceramic YSZ using the preparation method described in Example 1.

[0065] The CMAS powder was weighed at 20 mg / cm 2 The surface of the obtained ceramic block was uniformly coated with the CMAS powder, and then placed in a high-temperature resistance furnace for corrosion experiments at a corrosion temperature of 1300°C.

[0066] The YSZ ceramic prepared by the above method has a two-phase structure, a density of 92.3%, a reaction layer depth of 714.2 μm after 1 h of corrosion, and a reaction layer depth of 922.1 μm after 50 h of corrosion.

[0067] Comparative Example 2

[0068] Only the second ball milling speed was changed to 300 rpm, and the other conditions were consistent with Example 1. The color of the sintered ceramic was inconsistent, the composition was uneven, and cracks appeared on the surface.

[0069] Comparative Example 3

[0070] Only the cooling rate during sintering was changed, and the ceramic was directly cooled with the furnace after holding. The other conditions were consistent with Example 1. The sintered ceramic cracked when touched.

[0071] Performance Test Analysis

[0072] It can be seen from Figure 1 that the prepared ceramic material is a single-phase fluorite structure, is stable at 1550°C, and has good structural stability.

[0073] It can be seen from Figure 2 that the ceramic material provided by the example has a dense surface and fewer pores.

[0074] It can be seen from Figure 3 and Figure 4 that the reaction layer of the ceramic material is much smaller than that of YSZ. After the high-entropy ceramic is corroded by CMAS, the rare earth ions in it react with Ca and Si elements to form needle-shaped apatite, and zirconate decomposes to produce ZrO2. With the increase of Yb2O3 content and the extension of corrosion time, more spherical ZrO2 is generated, making the reaction layer more dense and blocking the further corrosion of CMAS. Therefore, the ceramic material has stronger resistance to CMAS corrosion than YSZ.

Claims

1. A method for preparing a high-entropy ceramic material resistant to CMAS corrosion, characterized in that: According to the chemical composition of high-entropy ceramic materials, each oxide raw material is prepared, the oxide raw material is ball-milled for the first time to obtain mixed powder, the mixed powder is pre-fired to obtain pre-fired powder, the pre-fired powder is ball-milled for the second time to obtain pre-fired ball-milled powder, the pre-fired ball-milled powder is granulated to obtain granulated powder, the granulated powder is pressed into shape to obtain green body, and the green body is sintered to obtain high-entropy ceramic material. Y2O3 powder, Gd2O3 powder, Er2O3 powder, Dy2O3 powder, Yb2O3 powder, and ZrO2 powder are prepared according to the chemical composition of high-entropy ceramic materials. The particle size of the Y2O3 powder, Gd2O3 powder, Er2O3 powder, Dy2O3 powder, Yb2O3 powder, and ZrO2 powder is 50-100 nm. The first ball milling speed is 300-350 rpm, and the first ball milling time is 10-12 hours; After the first ball milling is completed, the mixture is dried, and then ground to obtain a mixed powder. The drying temperature is 70-90℃ and the time is 6-10 hours. The second ball milling speed is 450-500 rpm, and the second ball milling time is 10-12 hours; After the second ball milling, the powder is dried to obtain pre-calcined ball mill powder. The drying temperature is 70-90℃ and the time is 6-10h. The granulated powder pressing process is as follows: first, pre-forming is carried out by molding, and then green body is obtained by cold isostatic pressing. The pressure of pre-forming is 10-20MPa, and the holding time of pre-forming is 5-7min. The pressure of cold isostatic pressing is 200-220MPa, and the holding time of cold isostatic pressing is 5-7min. The chemical formula of the high-entropy ceramic material is (YGdErDy). 2(1-x) Yb 2x Zr₂O₇, where 0 ≤ x < 1.

2. The method for preparing a high-entropy ceramic material resistant to CMAS corrosion according to claim 1, characterized in that: Each oxide raw material is first calcined at 700-800℃ for 2-3 hours; The particle size of the Y2O3 powder, Gd2O3 powder, Er2O3 powder, Dy2O3 powder, Yb2O3 powder, and ZrO2 powder is 50-100 nm, and the purity is ≥99.9%.

3. The method for preparing a high-entropy ceramic material resistant to CMAS corrosion according to claim 1, characterized in that: The pre-firing temperature is 1500-1550℃, and the time is 6-10h.

4. The method for preparing a high-entropy ceramic material resistant to CMAS corrosion according to claim 1, characterized in that: The granulation process is as follows: PVA is added to the pre-calcined ball mill powder, and then the powder is ground and passed through a 300-500 mesh sieve to obtain the granulation powder. The amount of PVA added is 6-8% of the mass of the pre-calcined ball mill powder.

5. The method for preparing a high-entropy ceramic material resistant to CMAS corrosion according to claim 1, characterized in that: The sintering temperature is 1550-1700℃, and the sintering time is 10-20h.

6. The method for preparing a high-entropy ceramic material resistant to CMAS corrosion according to claim 1: characterized in that: The sintering process is as follows: the temperature is increased to 600-700℃ at a heating rate of 5-10℃ / min, held for 2-3 hours, then increased to 1550-1700℃ at a heating rate of 5-10℃ / min, held for 10-20 hours, and then decreased to 700-800℃ at a cooling rate of 1-2℃ / min, followed by furnace cooling.

7. The high-entropy ceramic material resistant to CMAS corrosion according to claim 1, characterized in that: The high-entropy ceramic material resistant to CMAS corrosion has a single-phase fluorite structure.

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