High flowability ceramic powder, ceramic composite coating and method of making

Abstract

The application relates to the technical field of advanced ceramic materials, and specifically discloses a high-fluidity ceramic powder, a ceramic composite coating and a preparation method. The raw material system is modified by introducing a nano metal degassing agent and a rare earth dopant, and a sol-gel / freeze-drying technology is used to reconstruct the microstructure of the precursor; meanwhile, the pre-sintering process is creatively optimized into two-stage gradient sintering, and direct current plasma is upgraded into radio frequency plasma. Through the above component design and process cooperation, the technical problems that bubbles are difficult to remove and liquid droplets are not fully spheroidized in the melting process are effectively solved, and the compactness, sphericity and fluidity of the ceramic powder are significantly improved.

Description

Technical Field

[0001] This invention relates to the technical field of advanced ceramic materials, and in particular to a high-flowability ceramic powder, a ceramic composite coating, and a preparation method thereof. Background Technology

[0002] With the rapid development of modern aerospace technology, the requirements for the service temperature of thermal barrier coatings (TBCs) are becoming increasingly stringent. Magnesium-based lanthanum hexaaluminate (LaMgAl) is considered an ideal next-generation TBC material due to its excellent high-temperature phase stability, low thermal conductivity, and good anti-sintering properties. Yttrium-stabilized zirconia (6-8YSZ) is currently the most widely used TBC material, but it undergoes a series of phase transformations above 1200℃, causing changes in coating volume and a volume mismatch with the binder and substrate materials, leading to a sharp degradation in coating performance. Therefore, it is necessary to develop TBC materials that can stably operate at higher temperatures. 11 O 19 It has a magnetite-like structure, is plate-like, and possesses many advantages such as low thermal conductivity, high melting point, and good resistance to sintering. The performance of the coating largely depends on the characteristics of the ceramic powder used. Ideal ceramic powders for plasma spraying or supersonic flame spraying should have characteristics such as high sphericity, high density, and uniform particle size distribution.

[0003] Currently, spray drying is widely used in industrial production to prepare thermal barrier coated ceramic powders. However, this method has some inherent drawbacks. For example, the original particles obtained by spray drying are porous agglomerates. Although high-temperature sintering can improve the strength, it is difficult to completely eliminate the internal pores, resulting in low effective powder density. In order to achieve high density, sintering treatment is required, which easily leads to many problems such as reduced sphericity, decreased fluidity, excessive grain growth, interparticle adhesion, and reduced yield.

[0004] Therefore, developing a preparation method that can simultaneously achieve high powder density, high sphericity, and ultra-high flowability is a key challenge currently facing this field. Summary of the Invention

[0005] To improve the density, sphericity, and flowability of ceramic powder, this application provides a high-flowability ceramic powder, a ceramic composite coating, and a preparation method thereof.

[0006] Firstly, this application provides a method for preparing highly fluid ceramic powder, which adopts the following technical solution: A method for preparing a highly fluid ceramic powder includes the following steps: S1, according to LaMgAl 11 O 19The compounds containing lanthanum, magnesium, and aluminum sources were weighed according to the stoichiometric ratio, added to deionized water, mixed evenly, and then nano-metal degassing agent and rare earth dopant were added. The mixture was then wet-milled to obtain a stable sol with a solid content of 20-40 wt.%. S2. The stabilized sol is frozen into ice crystals at a low temperature of -20℃ to -80℃, and the ice crystals are sublimated to obtain a porous precursor blank with a three-dimensional through-pore structure. S3. Place the porous precursor blank in air or an inert atmosphere, heat it to 1650-1700℃ at a rate of 5-10℃ / min, hold it for 5-30min, and then cool it to 1350-1450℃ at a rate of ≥20℃ / min, and hold it for 12-24 hours to obtain pre-sintered powder. S4. The pre-sintered powder is fed into an RF plasma stream, melted and spheroidized in an inert working gas atmosphere, and then subjected to a ≥10 6 Rapidly solidify at a rate of K / s, collect the solidified powder, and sieve to obtain highly fluid ceramic powder.

[0007] In one specific implementation, the nano-metal degassing agent is nano-aluminum powder or nano-magnesium powder.

[0008] In one specific implementation, the amount of the nano-metal degassing agent is 0.1-0.5 wt. of the total weight of the compound containing lanthanum, magnesium, and aluminum sources.

[0009] In one specific implementation, the rare earth dopant is yttrium oxide or cerium oxide.

[0010] In one specific implementation, the amount of the rare earth dopant is 0.05-0.2 wt.% of the total weight of the compound containing lanthanum, magnesium, and aluminum sources.

[0011] In one specific implementation, in step S4, the inert working gas is an argon-helium mixture with a volume percentage of 20-40% helium.

[0012] In one specific implementation scheme, in step S4, the radio frequency power of the radio frequency plasma flame is 40-120kW, the center temperature of the plasma flame is ≥10000℃, and the residence time of the pre-sintered powder in the isothermal zone is 10-30 milliseconds.

[0013] In one specific feasible implementation, the particle size of the high-flowability ceramic powder is 45-150 μm.

[0014] Secondly, the high-flowability ceramic powder provided in this application is prepared by the above-mentioned method for preparing high-flowability ceramic powder.

[0015] Thirdly, the ceramic composite coating provided in this application is prepared by plasma spraying or supersonic flame spraying of the aforementioned high-flowability ceramic powder.

[0016] In summary, this application has the following beneficial effects: 1. This application eliminates surface porosity by using nano-metal degassing agents and rare-earth dopants, combined with an ultra-smooth surface and ultra-high sphericity obtained through radio frequency plasma. This resolves the contradiction between densification and sphericity in traditional methods, while simultaneously improving the relative density, average sphericity, and Hall flow rate of the ceramic powder, thus enhancing its compactness, sphericity, and flowability. Using the high-flowability powder of this application enables stable powder feeding and efficient deposition, resulting in a final ceramic composite coating with lower porosity and higher bonding strength, significantly extending the service life of hot-end components.

[0017] 2. The method in this application uses a sol-gel method combined with freeze-drying technology to replace traditional spray drying, resulting in superior porosity and a more uniform pore size distribution. Two-stage gradient pre-sintering imparts sufficient mechanical strength to the powder, and residual porosity is slowly eliminated through grain boundary diffusion, achieving near-full densification in a fine-grained state. Radio frequency plasma melting and rapid solidification are employed to obtain an optically smooth surface.

[0018] 3. The present application uses a stable sol with a solid content of 20-40 wt.%, which can further improve the density, sphericity and flowability of ceramic powder. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope (SEM) image of the ceramic powder prepared in Comparative Example 4; Figure 2 Here are scanning electron microscope (SEM) images of the ceramic powder prepared in Example 1; Figure 3 The images show the surface microstructure of the thermal barrier coating prepared from ceramic powder in Comparative Example 4 after 100 thermal shock cycles. Figure 4 These are images showing the surface microstructure of the thermal barrier coating prepared from ceramic powder in Example 1 after 100 thermal shocks. Detailed Implementation

[0020] Unless otherwise specified, all raw materials used in this application were commercially available. La(NO3)3·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O were all AR grade. Nano-aluminum powder had an aluminum content ≥99.9% and a particle size of 5000 mesh. Yttrium oxide had an effective content of 99.99% and a particle size of 30-50 nm. Nano-magnesium powder had a magnesium content ≥99.9% and a particle size of 5000 mesh. Cerium oxide had an effective content of 99.99% and a particle size of 30-50 nm.

[0021] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0022] Example Example 1

[0023] This embodiment provides a method for preparing highly fluid ceramic powder, including the following steps: S1, according to LaMgAl 11 O 19 La(NO3)3·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O were weighed according to their stoichiometric ratios, added to deionized water, and stirred until homogeneous. Nano-aluminum powder and yttrium oxide were then added, and the mixture was wet-milled for 8 hours to obtain a stable sol with a solid content of 30 wt.%. The amount of nano-aluminum powder used was 0.3 wt.% of the total weight of La(NO3)3·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O. The amount of yttrium oxide was 0.12 wt.% of the total weight of La(NO3)3·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O.

[0024] S2. Pour the stabilized sol into a mold and freeze it in a refrigerator at -50°C to form columnar ice crystals. Transfer the columnar ice crystals to a freeze dryer and freeze dry them at -80°C and 10Pa for 48 hours. The columnar ice crystals will sublimate to obtain a porous precursor blank with a three-dimensional through-pore structure.

[0025] S3. Place the porous precursor blank in a muffle furnace, heat it to 1680℃ at 8℃ / min in an air atmosphere, hold it for 15min, cool it to 1400℃ at a rate of 20℃ / min, and hold it for 18 hours to obtain pre-sintered powder.

[0026] S4. Using an RF plasma spheroidization system, the working gas is an argon-helium mixture with a helium volume ratio of 30%. The RF power of the RF plasma stream is 80kW, and the center temperature of the plasma stream is ≥10000℃. The pre-sintered powder is fed into the RF plasma stream, and the residence time of the pre-sintered powder in the isothermal region is 20 milliseconds. The pre-sintered powder melts and spheroidizes, and then... 6 Rapidly solidify the powder at a rate of K / s, collect the solidified powder, and sieve it to obtain a highly fluid ceramic powder with a particle size between 45-150 μm.

[0027] Example 2

[0028] The only difference between this embodiment and Embodiment 1 is that, in step S1, the amount of deionized water is adjusted to obtain a stable sol with a solid content of 10 wt.%.

[0029] Example 3

[0030] The only difference between this embodiment and Embodiment 1 is that, in step S1, the amount of deionized water is adjusted to obtain a stable sol with a solid content of 20 wt.%.

[0031] Example 4

[0032] The only difference between this embodiment and Embodiment 1 is that, in step S1, the amount of deionized water is adjusted to obtain a stable sol with a solid content of 40 wt.%.

[0033] Example 5

[0034] The only difference between this embodiment and Embodiment 1 is that, in step S1, the amount of deionized water is adjusted to obtain a stable sol with a solid content of 50 wt.%.

[0035] Example 6

[0036] The only difference between this embodiment and Embodiment 1 is that, in step S2, the stabilized sol is poured into a mold and frozen in a refrigerator at -20°C into columnar ice crystals.

[0037] Example 7

[0038] The only difference between this embodiment and Embodiment 1 is that, in step S2, the stabilized sol is poured into a mold and frozen in a refrigerator at -80°C into columnar ice crystals.

[0039] Example 8

[0040] The only difference between this embodiment and Embodiment 1 is that in step S3, the temperature is increased to 1650°C at a rate of 5°C / min, held for 5 min, and then decreased to 1350°C at a rate of 25°C / min, held for 12 hours to obtain pre-sintered powder.

[0041] Example 9

[0042] The only difference between this embodiment and Embodiment 1 is that in step S3, the temperature is increased to 1700°C at a rate of 10°C / min, held for 30 min, and then decreased to 1450°C at a rate of 30°C / min, held for 24 hours to obtain pre-sintered powder.

[0043] Example 10

[0044] The only difference between this embodiment and Embodiment 1 is that, in step S4, at 10 7 Rapidly cool and solidify at a rate of K / s, and collect the solidified powder.

[0045] Example 11

[0046] The only difference between this embodiment and Embodiment 1 is that, in step S4, at 10 8 Rapidly cool and solidify at a rate of K / s, and collect the solidified powder.

[0047] Example 12

[0048] The only difference between this embodiment and Embodiment 1 is that, in step S1, an equal amount of nano-magnesium powder is used to replace nano-aluminum powder.

[0049] Example 13

[0050] The only difference between this embodiment and Embodiment 1 is that, in step S1, yttrium oxide is replaced with an equal amount of cerium oxide.

[0051] Example 14

[0052] The only difference between this embodiment and Embodiment 1 is that, in step S4, the working gas is an argon-helium mixture with a helium volume percentage of 20%.

[0053] Example 15

[0054] The only difference between this embodiment and Embodiment 1 is that, in step S4, the working gas is an argon-helium mixture with a volume ratio of 40% helium.

[0055] Example 16

[0056] The only difference between this embodiment and embodiment 1 is that in step S4, the radio frequency power of the radio frequency plasma flame is 40kW, the center temperature of the plasma flame is ≥10000℃, the pre-sintered powder is fed into the radio frequency plasma flame, and the residence time of the pre-sintered powder in the isothermal zone is 10 milliseconds.

[0057] Example 17

[0058] The only difference between this embodiment and embodiment 1 is that in step S4, the radio frequency power of the radio frequency plasma flame is 120kW, the center temperature of the plasma flame is ≥10000℃, the pre-sintered powder is fed into the radio frequency plasma flame, and the residence time of the pre-sintered powder in the isothermal zone is 30 milliseconds.

[0059] Example 18

[0060] The only difference between this embodiment and Example 1 is that, in step S1, the amount of nano-aluminum powder used is 0.1 wt.% of the total weight of La(NO3)3·6H2O, Mg(NO3)2·6H2O and Al(NO3)3·9H2O.

[0061] Example 19

[0062] The only difference between this embodiment and Example 1 is that, in step S1, the amount of nano-aluminum powder used is 0.5 wt.% of the total weight of La(NO3)3·6H2O, Mg(NO3)2·6H2O and Al(NO3)3·9H2O.

[0063] Example 20

[0064] The only difference between this embodiment and Example 1 is that, in step S1, yttrium oxide is 0.05 wt.% of the total weight of La(NO3)3·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O.

[0065] Example 21

[0066] The only difference between this embodiment and Example 1 is that, in step S1, yttrium oxide is 0.2 wt.% of the total weight of La(NO3)3·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O.

[0067] Example 22

[0068] The only difference between this embodiment and Embodiment 1 is that in step S4, the solidified powder is collected, sieved, and high-flowability ceramic powder with a particle size between 10-40 μm is obtained.

[0069] Example 23

[0070] The only difference between this embodiment and Embodiment 1 is that in step S4, the solidified powder is collected, sieved, and high-flowability ceramic powder with a particle size between 155-180 μm is obtained.

[0071] Comparative Example Comparative Example 1 The only difference between this comparative example and Example 1 is that nano-aluminum powder is not added in step S1.

[0072] Comparative Example 2 The only difference between this comparative example and Example 1 is that yttrium oxide is not added in step S1.

[0073] Comparative Example 3 The only difference between this comparative example and Example 1 is that nano-aluminum powder and yttrium oxide are not added in step S1.

[0074] Comparative Example 4 The only difference between this comparative example and Example 1 is that this comparative example provides a method for preparing ceramic powder, including the following steps: S1, according to LaMgAl 11 O 19La(NO3)3·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O were weighed according to their stoichiometric ratios, added to deionized water, and stirred until homogeneous. Nano-aluminum powder and yttrium oxide were then added, and the mixture was wet-milled for 8 hours to obtain a stable sol with a solid content of 30 wt.%. The amount of nano-aluminum powder used was 0.3 wt.% of the total weight of La(NO3)3·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O. The amount of yttrium oxide was 0.12 wt.% of the total weight of La(NO3)3·6H2O, Mg(NO3)2·6H2O, and Al(NO3)3·9H2O.

[0075] S2. The stabilized sol is granulated by passing it through a spray drying tower, with the inlet temperature controlled at 200-250℃ and the outlet temperature at 90-120℃, to obtain spherical porous precursor powder with a particle size distribution of D50=55μm.

[0076] S3. Place the spherical porous precursor powder in a muffle furnace, heat it to 1680℃ at 8℃ / min in an air atmosphere, hold it for 15min, then cool it to 1400℃ at a rate of 20℃ / min and hold it for 18 hours to obtain the pre-sintered powder.

[0077] S4. Using an RF plasma spheroidization system, the working gas is an argon-helium mixture with a helium volume ratio of 30%. The RF power of the RF plasma stream is 80kW, and the center temperature of the plasma stream is ≥10000℃. The pre-sintered powder is fed into the RF plasma stream, and the residence time of the pre-sintered powder in the isothermal region is 20 milliseconds. The pre-sintered powder melts and spheroidizes, and then... 6 Rapidly solidify the powder at a rate of K / s, collect the solidified powder, and sieve it to obtain ceramic powder with a particle size between 45-150 μm.

[0078] Performance testing The following performance tests were conducted on Examples 1-23 and Comparative Examples 1-4: Density test: The relative density of the prepared ceramic powder was tested according to GB / T25995 "Test Method for Density and Apparent Porosity of Fine Ceramics".

[0079] Sphericity test: The average sphericity of the prepared ceramic powder is tested according to ISO 9276-6.

[0080] Flowability test: The Hall flow rate of the prepared ceramic powder was tested according to GB / T1482 "Standard funnel method for determination of flowability of metal powder".

[0081] The prepared ceramic powder was used to prepare thermal barrier coating samples on a nickel-based superalloy substrate by atmospheric plasma spraying (APS). The coating thickness was 300 μm and the porosity was 1.5%. The thermal barrier coating sample was placed in a furnace preheated to 1100℃ and held for 20 minutes. The sample was then removed and subjected to forced air cooling at room temperature for 10 minutes until the surface temperature was ≤100℃, completing one full thermal shock cycle. After every 20 cycles, the surface macromorphology of the thermal barrier coating sample was observed with a digital camera to check for cracks, edge lifting, or local peeling. When the peeling area reached 5% of the total surface area of ​​the sample, the current cycle number was recorded as Nf1. The failure cycle numbers Nf1 to Nf5 were recorded for 5 parallel samples, and the arithmetic mean was taken as the average thermal shock lifetime of the batch of coatings. After 100 thermal shock cycles, the thermal barrier coating samples prepared from the ceramic powder of Example 1 and Comparative Example 4 were observed using a scanning electron microscope to examine the surface micromorphology that was invisible to the naked eye.

[0082] The test results are shown in Table 1.

[0083] The ceramic powders prepared in Example 1 and Comparative Example 4 were subjected to scanning and X-ray diffraction. Figure 1 This is a scanning electron microscope (SEM) image of the ceramic powder prepared in Comparative Example 4. Figure 2 This is a scanning electron microscope (SEM) image of the ceramic powder prepared in Example 1. Figure 3 The images show the surface microstructure of the thermal barrier coating prepared from ceramic powder in Comparative Example 4 after 100 thermal shocks. Figure 4 These are images showing the surface microstructure of the thermal barrier coating prepared from ceramic powder in Example 1 after 100 thermal shocks.

[0084] Table 1

[0085] from Figure 1-4 It can be seen that the powder prepared in Example 1 has a smoother surface and higher sphericity. Moreover, the thermal barrier coating prepared from the ceramic powder in Example 1 still has relatively narrow, invisible cracks in its surface microstructure after 100 thermal shocks, while the thermal barrier coating prepared from the ceramic powder in Comparative Example 4 has wider, invisible cracks in its surface microstructure after 100 thermal shocks.

[0086] As can be seen from Example 1 and Comparative Examples 1-4 and Table 1, compared with Example 1, the relative density, average sphericity, Hall flow rate and average thermal shock lifetime of Comparative Examples 1-4 are significantly reduced. This shows that the raw material ratio and preparation method of Example 1 can simultaneously improve the density, sphericity and flowability of ceramic powder. The thermal barrier coating made of the ceramic powder prepared in Example 1 has a longer thermal shock lifetime.

[0087] This is likely because the vaporization and expansion of nano-aluminum powder at high temperatures effectively breaks down the oxide film on the surface of molten droplets and generates microjets, providing channels for gas escape and thus reducing surface defects. Yttrium oxide effectively pins grain boundaries, refines grains, and reduces melt viscosity, contributing to the formation of a smooth surface. The use of a sol-gel method combined with freeze-drying technology instead of traditional spray drying results in superior porosity and a more uniform pore size distribution, laying the microstructural foundation for subsequent complete densification. Two-stage gradient pre-sintering first utilizes high temperature to rapidly drive interparticle necking, giving the powder sufficient mechanical strength to withstand subsequent powder feeding impacts while strictly suppressing grain growth. Then, a lower grain boundary migration rate is used to slowly eliminate residual porosity through grain boundary diffusion, achieving near-complete densification in a fine-grained state. Radio frequency plasma melting and rapid solidification are employed. Radio frequency plasma features no electrode contamination, a large isothermal region (diameter exceeding 100 mm), and a uniform temperature field, ensuring completely homogeneous melting of particles of all sizes. The molten droplets rapidly contracted into perfect spheres under the influence of surface tension, and then entered the water-cooled copper wall cooling chamber at >10 6 Rapid solidification at an ultra-high cooling rate of K / s effectively suppresses grain growth and segregation, resulting in an optically smooth surface. Therefore, it can simultaneously improve the density, sphericity, and flowability of ceramic powder. The stable powder feeding and efficient deposition brought about by the high flowability of the powder result in a final ceramic composite coating with lower porosity and higher bonding strength, significantly extending the service life of hot-end components.

[0088] As can be seen from Examples 1-23 and Table 1, the ceramic powders prepared in Examples 1-23 all exhibit high relative density, average sphericity, Hall flow rate, and average thermal shock lifetime. This indicates that the raw material ratios and preparation methods within the range of Examples 1-23 can simultaneously improve the density, sphericity, and flowability of ceramic powders.

[0089] By comparing the test data of various embodiments, it can be seen that using a stable sol with a solid content of 20-40 wt.% can further improve the compactness, sphericity and flowability of ceramic powder.

[0090] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing a highly fluid ceramic powder, characterized in that, Includes the following steps: S1, according to LaMgAl 11 O 19 The compounds containing lanthanum, magnesium, and aluminum sources are weighed according to the stoichiometric ratio, added to deionized water, mixed evenly, and then a nano-metal degassing agent and rare earth dopant are added. The mixture is then wet-milled to obtain a stable sol with a solid content of 20-40 wt.%. The nano-metal degassing agent is nano-aluminum powder or nano-magnesium powder. S2. The stabilized sol is frozen into ice crystals at a low temperature of -20℃ to -80℃, and the ice crystals are sublimated to obtain a porous precursor blank with a three-dimensional through-pore structure. S3. Place the porous precursor blank in air or an inert atmosphere, heat it to 1650-1700℃ at a rate of 5-10℃ / min, hold it for 5-30min, and then cool it to 1350-1450℃ at a rate of ≥20℃ / min, and hold it for 12-24 hours to obtain pre-sintered powder. S4. The pre-sintered powder is fed into an RF plasma stream, melted and spheroidized in an inert working gas atmosphere, and then subjected to a ≥10 6 Rapidly solidify at a rate of K / s, collect the solidified powder, and sieve to obtain highly fluid ceramic powder.

2. The method for preparing high-flowability ceramic powder according to claim 1, characterized in that: The amount of the nano-metal degassing agent is 0.1-0.5 wt. of the total weight of the compound containing lanthanum, magnesium and aluminum sources.

3. The method for preparing high-flowability ceramic powder according to claim 1, characterized in that: The rare earth dopant is yttrium oxide or cerium oxide.

4. The method for preparing high-flowability ceramic powder according to claim 3, characterized in that: The amount of the rare earth dopant is 0.05-0.2 wt. of the total weight of the compound containing lanthanum, magnesium and aluminum sources.

5. The method for preparing high-flowability ceramic powder according to claim 1, characterized in that: In step S4, the inert working gas is an argon-helium mixture with a volume percentage of 20-40% helium.

6. The method for preparing high-flowability ceramic powder according to claim 5, characterized in that: In step S4, the radio frequency power of the radio frequency plasma flame is 40-120kW, the center temperature of the plasma flame is ≥10000℃, and the residence time of the pre-sintered powder in the isothermal zone is 10-30 milliseconds.

7. The method for preparing high-flowability ceramic powder according to claim 1, characterized in that: The particle size of the high-flowability ceramic powder is 45-150 μm.

8. A high-flowability ceramic powder, characterized in that: The high-flowability ceramic powder was prepared using the method described in any one of claims 1-7.

9. A ceramic composite coating, characterized in that: The high-flowability ceramic powder described in claim 8 is prepared by plasma spraying or supersonic flame spraying.

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