Thermal barrier coating powder and method for producing the same, thermal barrier coating

Abstract

The present disclosure provides a thermal barrier coating powder and a preparation method thereof, and a thermal barrier coating, and relates to the technical field of high-temperature protective coating materials. The method comprises: performing mechanical-chemical grinding and surface hydroxylation treatment on a MAX phase powder; dispersing an activated MAX phase core in a liquid phase, uniformly coating a YSZ precursor on the surface of the core through double titration co-precipitation to obtain a core-shell structure precursor slurry; performing microwave hydrothermal treatment to in-situ crystallize the YSZ precursor to form a YSZ shell layer on the surface of the MAX phase core, thereby obtaining a core-shell structure unit; the core-shell structure unit has a core-shell structure composed of a MAX phase core and a YSZ shell; performing post-treatment and spray drying on the core-shell structure unit to obtain a thermal barrier coating powder; and the powder is obtained by agglomeration of multiple core-shell structure units. The interface between the core and the shell of the powder obtained by the method is firmly combined, can provide oxidation protection for the inner core of the MAX phase in coating preparation processes such as thermal spraying, and significantly improves the fracture toughness and thermal shock resistance of the thermal barrier coating.

Description

Technical Field

[0001] This disclosure relates to the field of high-temperature protective coating materials technology, specifically to a method for preparing thermal barrier coating powder, thermal barrier coating powder, and thermal barrier coating. Background Technology

[0002] As aero-engines and gas turbines advance towards higher efficiency, the operating temperatures of their hot-end components are increasing, placing more stringent demands on the overall performance of thermal barrier coatings. Yttria-stabilized zirconia (YSZ) remains the preferred top-layer material for thermal barrier coatings due to its low thermal conductivity and relatively high coefficient of thermal expansion. However, YSZ has inherently low fracture toughness and is prone to crack initiation and spalling failure under thermal cycling stress and impact from foreign objects.

[0003] To overcome this limitation, a second-phase toughening material can be introduced to construct a multiphase ceramic system. Among them, the MAX phase ceramic can effectively toughen brittle ceramic matrices. However, when YSZ and MAX phase powders are simply physically mixed and then thermally sprayed, the MAX phase rapidly undergoes oxidative decomposition, resulting in the complete loss of its toughening effect. It is difficult to provide effective protection for the MAX phase at the microscale, and the uniform distribution of the two phases cannot be guaranteed.

[0004] Based on this, the MAX phase can be protected by a core-shell structure. However, existing thermal barrier coating powders mostly use cerate, zirconate, or calcium silicate as shell materials, and their preparation processes often employ conventional chemical methods combined with high-temperature calcination. This results in problems such as poor coating uniformity, physical bonding at the core-shell interface, and limited bonding strength. Therefore, there is an urgent need to develop a thermal barrier coating powder and its preparation method that can effectively protect the MAX phase core, achieve uniform and dense coating, and utilize a mild process. Summary of the Invention

[0005] The purpose of this disclosure is to provide a method for preparing thermal barrier coating powder, thermal barrier coating powder, and thermal barrier coating, thereby overcoming, to at least a certain extent, the technical problems of easy oxidation and inability to provide effective protection of the MAX phase during thermal spraying due to the limitations and defects of related technologies.

[0006] According to one aspect of this disclosure, a method for preparing a thermal barrier coating powder is provided, comprising: The MAX phase powder was subjected to mechanical and chemical grinding and surface hydroxylation treatment to obtain activated MAX phase nuclei; The activated MAX phase nuclei were dispersed in a liquid phase containing a dispersant, and the YSZ precursor was uniformly coated on the nucleus surface by double titration co-precipitation to obtain a core-shell structured precursor slurry. Microwave hydrothermal treatment was performed on the core-shell structure precursor slurry to allow the YSZ precursor to crystallize in situ and form a YSZ shell on the surface of the MAX phase core, thus obtaining a core-shell structure unit; the core-shell structure unit has a core-shell structure with the MAX phase as the core and YSZ as the shell. The core-shell structural units are post-processed and spray-dried to obtain thermal barrier coating powder; the thermal barrier coating powder is obtained by agglomeration of multiple core-shell structural units.

[0007] In one exemplary embodiment of this disclosure, the average particle size of the activated MAX phase nuclei is 0.5~5 μm.

[0008] In one exemplary embodiment of this disclosure, the MAX phase is a phase having the general formula M n+1 AX n Ceramic materials; wherein M is a transition metal element, A is a main group element, X is C or N, and n=1, 2 or 3; or, the MAX phase is a phase with the general formula M n+1 AX n The high-entropy MAX phase, wherein the M site contains at least three different transition metal elements.

[0009] In one exemplary embodiment of this disclosure, the ball-to-powder ratio of MAX phase powder to grinding balls during the mechanochemical grinding process is 5:1 to 10:1, the rotation speed of the mechanochemical grinding is 300 to 500 rpm, and the mechanochemical grinding time is 10 to 30 min. The surface hydroxylation treatment is as follows: the mechanically and chemically ground powder is placed in a 1-3 mol / L nitric acid solution or sodium hydroxide solution and stirred at 70-90℃ for 1-2 h.

[0010] In one exemplary embodiment of this disclosure, the dual titration coprecipitation includes: converting the YSZ precursor and the precipitant into aerosols using ultrasonic atomization and simultaneously spraying them into the reaction system; conducting the reaction at a constant pH of 9.5-11 and a temperature of 65-80°C; and the ultrasonic atomization spraying time is 2-3 h; after the ultrasonic atomization spraying is completed, the mixture is kept warm and stirred at the same temperature for 0.5-2 h.

[0011] In one exemplary embodiment of this disclosure, the YSZ precursor is a mixed solution containing a zirconium source and a yttrium source, or the YSZ precursor is a mixed solution containing a zirconium source, a yttrium source and a rare earth dopant. The rare earth dopant is gadolinium nitrate or ytterbium nitrate, wherein the doping amount of Gd2O3 or Yb2O3 accounts for 1~2 mol of the total molar amount of zirconium source and rare earth source.

[0012] In one exemplary embodiment of this disclosure, the dispersant is polyethylene glycol, and the amount of dispersant added is 0.1% to 1% of the total mass of the reaction system.

[0013] In one exemplary embodiment of this disclosure, the temperature of the microwave hydrothermal treatment is 180~200°C, the power of the microwave hydrothermal treatment is 150~180 W, and the time of the microwave hydrothermal treatment is 1~2 h. Post-processing includes multiple centrifugal washing and microwave drying; the microwave drying power is 500~800 W, the microwave drying temperature is 60~80℃, and the microwave drying time is 0.5~2 h; the inlet temperature of the spray dryer is 220~260℃, and the atomizer frequency is 180~240 Hz.

[0014] According to one aspect of this disclosure, a thermal barrier coating powder is provided, which is prepared by the above method; the thermal barrier coating powder is a micron-sized spherical agglomerate, which is composed of nano- to submicron-sized core-shell structural units, wherein the core-shell structural units have a MAX phase as the core and a YSZ phase as the shell.

[0015] According to one aspect of this disclosure, a thermal barrier coating is provided, which is prepared from the aforementioned thermal barrier coating powder.

[0016] In the technical solution provided by the embodiments of this disclosure, on the one hand, by mechanically and chemically grinding and activating the MAX phase powder and performing surface hydroxylation treatment, the YSZ precursor is uniformly coated on the surface of the MAX phase core through a double titration co-precipitation method under the action of a dispersant. Then, the YSZ is crystallized in situ and the core-shell interface is strengthened through microwave hydrothermal treatment to form a dense YSZ shell layer. This shell layer can provide antioxidant protection for the MAX phase core in the thermal spraying process, solving the problem of easy oxidation of MAX phase materials during thermal spraying. It can provide effective protection for the MAX phase at the microscale and ensure the uniform distribution of the two phases. Compared with the existing ordinary chemical method and high-temperature calcination process, the microwave hydrothermal low-temperature crystallization can avoid the oxidation of the MAX phase core. At the same time, the uniform coating is achieved by ultrasonic atomization double titration, which solves the technical problem in related technologies that cannot take into account both the density of the shell layer and the activity of the core phase, and improves the bonding strength of the core-shell interface. On the other hand, by ensuring the uniform distribution of the two phases, the toughening ability of the MAX phase core is fully preserved in the final thermal barrier coating, improving the fracture toughness and thermal shock resistance of the thermal barrier coating. This integrates the thermal barrier properties of YSZ with the unique high toughness of the MAX phase, achieving a synergistic multiplication of material properties. Furthermore, the preparation method of the thermal barrier coating powder has good scalability, increasing its application prospects and versatility. Attached Figure Description

[0017] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0018] Figure 1 The flowchart illustrates a method for preparing a thermal barrier coating powder according to an embodiment of the present disclosure.

[0019] Figure 2 This is a schematic transmission electron microscope (TEM) image of the core-shell structure unit prepared according to Example 1.

[0020] Figure 3 This is a schematic scanning electron microscope image of the thermal barrier coating powder prepared according to Example 1. Detailed Implementation

[0021] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the example embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of the specific details omitted, or other methods, components, apparatus, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0022] The terms “a,” “an,” “the,” and “the” are used in this specification to indicate the presence of one or more elements / components, etc.; the terms “including” and “having” are used to indicate an open-ended inclusion and to mean that there may be other elements / components, etc., in addition to those listed; the terms “first” and “second” are used only as markings and are not a limitation on the number of objects.

[0023] In related technologies, in order to overcome the inherently low fracture toughness of YSZ (typically about 2.5~3.0 MPa·m) 1 / 2The limitations imposed by the coating on premature spalling failure due to crack initiation under thermal cycling stress and foreign impact can be addressed by introducing second-phase toughening materials to construct multiphase ceramic systems. Among them, MAX phase ceramics (such as Ti2AlC and Cr2AlC) possess excellent properties of both metals and ceramics due to their unique nanolayered crystal structure, especially their excellent damage tolerance, high fracture toughness, and machinability, making them an ideal way to improve the toughness of YSZ coatings. Theoretical simulations and bulk material studies have shown that MAX phases have the potential to effectively toughen brittle ceramic matrices through mechanisms such as crack deflection, bridging, and lamellar pull-out.

[0024] However, when this theoretical concept is put into practice using thermal spraying, the most commonly used coating preparation method, it faces severe and unresolved technical obstacles: the MAX phase has extremely poor thermodynamic stability in the high temperatures (often exceeding 3000℃) and oxygen-rich flames generated by thermal spraying, and will rapidly undergo oxidative decomposition, generating brittle oxides such as TiO2 and Al2O3, resulting in the complete loss of its toughening effect. This process not only completely negates the expected toughening effect, but the volume changes and formation of brittle phases caused by oxidation can also become microcrack initiations, severely deteriorating the coating's bonding strength and overall performance. Simply mixing YSZ and MAX phase powders and then spraying them is insufficient to provide effective protection for the MAX phase at the microscale, and cannot guarantee the uniform distribution of the two phases. This prevents the excellent performance of the MAX phase from being realized in the final coating, and may even have the opposite effect.

[0025] To overcome the defects of the aforementioned physical mixing, the MAX phase can be coated and protected using a core-shell structure. However, most existing thermal barrier coating powders use cerates, zircons, or calcium silicates as shell materials, and there are no reports of core-shell structures with the MAX phase as the core and YSZ as the shell. The preparation processes of cerates, zircons, or calcium silicates as shell materials mostly employ ordinary co-precipitation combined with high-temperature calcination, which has problems such as poor coating uniformity, physical bonding at the core-shell interface, and limited bonding strength. Furthermore, high-temperature calcination easily leads to oxidative decomposition and particle agglomeration of the core phase, making it difficult to balance the density of the shell with the activity of the core phase.

[0026] Based on this, the present disclosure provides a method for preparing thermal barrier coating powder, solving the technical problem that the MAX phase cannot exert its excellent toughening effect in YSZ coatings due to easy oxidation during thermal spraying. (Reference) Figure 1 As shown, the preparation method of the thermal barrier coating powder mainly includes the following steps: In step S110, the MAX phase powder is subjected to mechanical and chemical grinding and surface hydroxylation treatment to obtain activated MAX phase nuclei; In step S120, the activated MAX phase nucleus is dispersed in a liquid phase containing a dispersant, and the YSZ precursor is uniformly coated on the nucleus surface by double titration co-precipitation to obtain a core-shell structure precursor slurry. In step S130, the core-shell structure precursor slurry is subjected to microwave hydrothermal treatment to allow the YSZ precursor to crystallize in situ to form a YSZ shell on the surface of the MAX phase core, thereby obtaining a core-shell structure unit; the core-shell structure unit has a core-shell structure with the MAX phase as the core and YSZ as the shell. In step S140, the core-shell structural units are post-processed and spray-dried to obtain thermal barrier coating powder; the thermal barrier coating powder is obtained by agglomeration of multiple core-shell structural units.

[0027] Next, the preparation method of the thermal barrier coating powder in the embodiments of this disclosure will be described in detail.

[0028] In step S110, the MAX phase powder is subjected to mechanical and chemical grinding and surface hydroxylation treatment to obtain activated MAX phase nuclei.

[0029] In this embodiment of the disclosure, the MAX phase is a phase with M n+1 AX n A ceramic material with a general structure, where M is a transition metal element, A is a main group element, X is carbon or nitrogen, and n = 1, 2, or 3. For example, M is a transition metal element, such as Ti, V, Nb, etc.; A is a main group element, such as Al, etc. This material exhibits excellent comprehensive properties and is suitable as a toughening phase. For example, the MAX phase can be one or more of Ti₂AlC, V₂AlC, and Nb₂AlC.

[0030] In other embodiments, the MAX phase can also be of the general formula M. n+1 AX n The high-entropy MAX phase contains at least three different transition metal elements at site M. In some embodiments, the type of transition metal element can be determined based on its formation energy. Transition metal elements are selected, for example, from Ti, V, Nb, Ta, Hf, Zr, Cr, Mo, etc. A is an element such as Al, X is C or N, and n = 1, 2, or 3. Exemplarily, the high-entropy MAX phase can be (Ti,V,Nb,Mo)₂AlC, (Ti,V,Nb,Mo,Ta)₂AlC, etc.

[0031] The grinding balls used in mechanochemical grinding can be zirconia grinding balls to achieve particle refinement and surface activation. For example, MAX phase powder (such as Ti2AlC, high-entropy MAX phase, etc.) and zirconia grinding balls are placed in a planetary ball mill at a ball-to-powder ratio of 5:1 to 10:1 and ground at 300 to 500 rpm for 10 to 30 minutes. By adjusting the above parameters, the average particle size of the mechanochemically ground powder can be controlled within the range of 0.5 to 5 μm. Simultaneously, the mechanochemical effect generates a large number of lattice defects and activation sites on the particle surface, significantly increasing its surface energy.

[0032] After mechanically and chemically grinding the MAX phase powder to obtain mechanically ground powder, the surface of the mechanically ground powder can be hydroxylated to obtain activated MAX phase nuclei. Surface hydroxylation treatment refers to placing the mechanically ground powder in a nitric acid solution or a sodium hydroxide solution for acid or alkali treatment. Specifically, the mechanically ground powder can be placed in a nitric acid solution or a sodium hydroxide solution and stirred at 70-90°C for 1-2 h. Both acid and alkali treatments can effectively introduce hydroxyl (-OH) functional groups onto the surface of MAX phase particles. Acid treatment forms M-OH at M sites (such as Ti), while alkali treatment may involve slight etching of A sites (such as Al) and the formation of corresponding hydroxylates. Both provide active sites for subsequent heterogeneous nucleation of YSZ. The concentration of the nitric acid solution or sodium hydroxide solution can be 1-3 mol / L.

[0033] Surface hydroxylation treatment was performed on the mechanochemically ground powder to obtain activated MAX phase nuclei. The surface hydroxylation treatment involved placing the mechanochemically ground powder in a 1–3 mol / L nitric acid solution or sodium hydroxide solution and stirring at 70–90 °C for 1–2 h. This surface hydroxylation treatment grafted abundant -OH functional groups onto the surface of the MAX phase particles, which greatly improved their dispersibility and wettability in aqueous systems and provided the necessary chemically active sites for subsequent heterogeneous nucleation of YSZ. Activated MAX phase nuclei were obtained through mechanochemical grinding and surface hydroxylation treatment. The activated MAX phase nuclei were powders that had undergone mechanochemical activation and surface hydroxylation pretreatment, with an average particle size of 0.5–5 μm. The surface of the activated MAX phase nuclei was rich in hydroxyl active sites.

[0034] In step S120, the activated MAX phase nucleus is dispersed in a liquid phase containing a dispersant, and the YSZ precursor is uniformly coated on the core surface by double titration co-precipitation to obtain a core-shell structured precursor slurry.

[0035] In this embodiment, the liquid phase is deionized water. First, the activated MAX phase nuclei are dispersed in deionized water to prepare a 5-10 wt% suspension. Further, a dispersant can be added to the suspension to enhance stability, resulting in a suspension with added dispersant as the dispersant-containing liquid phase. The dispersant can be polyethylene glycol, and the amount added is 0.1%-1% of the total mass of the reaction system. For example, the dispersant can be 0.1%-1% PEG-400, and the suspension with added dispersant can be placed in a reaction apparatus equipped with mechanical stirring, a constant-temperature water bath circulation system, and an online pH monitor.

[0036] The suspension containing the dispersant was placed in a reaction apparatus equipped with mechanical stirring, a constant-temperature water bath circulation system, and an online pH monitor. The YSZ precursor and precipitant were simultaneously and uniformly sprayed into the suspension containing the dispersant via double titration co-precipitation. The pH of the reaction system was controlled to remain stable at a constant pH. After ultrasonic atomization, stirring and maintaining the temperature were continued under the same conditions. Specifically, the YSZ precursor and precipitant were converted into aerosols by ultrasonic atomization and simultaneously sprayed into the reaction system. The reaction was carried out at a constant pH of 9.5–11 and a temperature of 65–80°C for 2–3 hours. After ultrasonic atomization, stirring and maintaining the temperature were continued for 0.5–2 hours. The average particle size of the aerosol droplets produced by ultrasonic atomization was less than 50 μm.

[0037] The dual-titermination coprecipitation step employs an ultrasonic atomizing jet injection device. Specifically, the prepared YSZ precursor solution and precipitant are separately delivered to the ultrasonic atomizer via independent peristaltic pumps. Under ultrasonic action, the liquid is broken into fine droplets with an average particle size of less than 50 μm. The two aerosol streams are guided to the central region of the reactor's stirred vortex, ensuring full and instantaneous contact with the highly dispersed activated MAX phase nuclei. This process utilizes a closed-loop feedback system with an online pH meter and an automatic control system to dynamically adjust the injection rate, ensuring the pH of the reaction system remains stable within the range of 9.5–11. Converting the YSZ precursor and precipitant into separate aerosols before injection increases the contact area between the two phases, achieving instantaneous and uniform mixing at the molecular level. This atomized coprecipitation enhances coating uniformity and efficiency, achieving uniform coating on the surface of the MAX phase nuclei.

[0038] The YSZ precursor refers to the yttrium oxide-stabilized zirconia precursor, which can be a mixed solution containing a zirconium source and a yttrium source, or a mixed solution containing a zirconium source, a yttrium source, and a rare earth dopant. When the YSZ precursor is a mixed solution containing a zirconium source and a yttrium source, the zirconium source can be zirconium oxychloride (ZrOCl2·8H2O), and the yttrium source can be yttrium nitrate (Y(NO3)3·6H2O). The proportion of yttrium oxide in the yttrium oxide-stabilized zirconia, i.e., the molar percentage of Y2O3, is 4-7%, for example, 5.5%. When the YSZ precursor is a mixed solution containing a zirconium source, a yttrium source, and a rare earth dopant, the zirconium source can be zirconium oxychloride (ZrOCl2·8H2O), and the yttrium source can be yttrium nitrate (Y(NO3)3·6H2O). The proportion of yttrium oxide in the yttrium-stabilized zirconium oxide, i.e., the molar percentage of Y2O3, is 4-7%, for example, 4%, 5.5%, 7%, etc. The rare earth dopant can be gadolinium nitrate (Gd(NO3)3) or ytterbium nitrate (Yb(NO3)3), and the doping amount of the rare earth dopant accounts for 1-2 mol% of the total molar percentage of the zirconium source and the rare earth source, for example, 1 mol%, 1.5 mol%, or 2 mol%.

[0039] Ammonia can be used as the precipitant. The double titration co-precipitation is carried out at a constant pH of 9.5–11 and a temperature of 65–80°C. Uniform heterogeneous nucleation is achieved by controlling the reaction supersaturation, and the ultrasonic atomization spraying time is 2–3 hours. Controlling the pH value within the range of 9.5–11 is beneficial for the formation of Zr / Y hydroxide precipitate and inhibits colloid formation; controlling the temperature at 65–80°C ensures a sufficient reaction rate while avoiding excessively rapid precursor precipitation and aggregation due to excessively high temperatures.

[0040] For example, under constant stirring and at 65-80℃, a dual-titer co-precipitation method was used. A mixed solution containing zirconium source (ZrOCl2·8H2O), yttrium source (Y(NO3)3·6H2O, Y2O3 molar percentage 4-7%), and rare earth dopant (such as Gd(NO3)3 or Yb(NO3)3, doping amount 1-2 mol%) was used as the YSZ precursor. This solution was converted into an aerosol with the precipitant ammonia and simultaneously and uniformly sprayed into a suspension containing a dispersant. The ultrasonic atomization spraying process was strictly controlled for 2-3 hours, and the pH of the reaction system was maintained constant at 9.5-11.0. The dual-titer co-precipitation method effectively suppressed the autonomous homogeneous nucleation of YSZ through the dispersing effect of the dispersant PEG and the precise control of supersaturation and pH. This allowed the YSZ precursor to undergo heterogeneous nucleation and uniform deposition on the surface of the MAX phase nucleus, achieving complete and uniform coating, resulting in a core-shell structured precursor slurry.

[0041] In step S130, the core-shell structure precursor slurry is subjected to microwave hydrothermal treatment to allow the YSZ precursor to crystallize in situ to form a YSZ shell on the surface of the MAX phase core, thereby obtaining a core-shell structure unit; the core-shell structure unit has a core-shell structure with the MAX phase as the core and YSZ as the shell.

[0042] In this embodiment, the core-shell structure precursor slurry is transferred to a polytetrafluoroethylene-lined microwave hydrothermal reactor. After sealing, the reactor is placed in a microwave hydrothermal synthesizer to perform a reaction, thereby achieving microwave hydrothermal treatment. The microwave hydrothermal treatment temperature is 180~200℃, the microwave hydrothermal treatment power is 150~180 W, and the microwave hydrothermal treatment time is 1~2 hours. The microwave hydrothermal treatment temperature can be, for example, 180℃, 190℃, or 200℃. The microwave hydrothermal treatment power can be, for example, 150 W, 160 W, 170 W, or 180 W.

[0043] This step utilizes the bulk heating and non-thermal effects of microwaves to induce the transformation of amorphous YSZ precursors into cubic YSZ nanocrystals. Simultaneously, the high temperature and pressure conditions under hydrothermal conditions promote atomic interdiffusion and chemical reactions between the MAX phase core surface and the YSZ precursor, resulting in strong chemical bonds at the interface. This allows the YSZ precursor to crystallize in situ on the MAX phase core surface and strengthens the core-shell interface bonding, forming a YSZ shell chemically bonded to the MAX phase core. Ultimately, a stable and tightly bonded core-shell structural unit is obtained as the microwave hydrothermal product. The microwave hydrothermal product refers to the untreated core-shell structural unit, i.e., core-shell structured nanoparticles. Microwave hydrothermal treatment causes the YSZ precursor to hydrothermally crystallize at a low temperature of 180–200°C, forming a dense YSZ shell chemically bonded to the active sites on the MAX phase core surface, thus obtaining core-shell structural units with nanometer to submicron dimensions.

[0044] During microwave hydrothermal treatment, under a relatively low temperature and high pressure hydrothermal environment of 180~200℃, microwave energy directly acts on polar molecules such as water and precursors, promoting the rapid hydrolysis, condensation, and low-temperature in-situ crystallization of the YSZ precursor, directly generating nano / submicron-sized YSZ crystals. Simultaneously, it strengthens the interfacial chemical bonds between YSZ grains and between the YSZ shell and the MAX phase, forming a stable core-shell structure. This not only achieves the goal of shell crystallization but also improves the interfacial bonding quality and maintains the nanostructure.

[0045] After post-processing, microwave hydrothermal products can be converted into core-shell structured unit powders. These powders possess a core-shell structure with a MAX phase core and a YSZ shell, exhibiting strong interfacial bonding between the core and shell. Here, the core-shell structure refers to a three-dimensional core-shell encapsulation structure. The YSZ shell layer has a thickness of 50–300 nm, and the YSZ shell layer is firmly bonded to the MAX phase core through interfacial chemical bonding.

[0046] In step S140, the core-shell structural units are post-processed and spray-dried to obtain thermal barrier coating powder; the thermal barrier coating powder is obtained by agglomeration of multiple core-shell structural units.

[0047] In this embodiment, the post-processing may include multiple centrifugal washing and microwave drying. Post-processing the core-shell structural unit represented by the microwave hydrothermal product yields a dried core-shell structural unit. The dried core-shell structural unit can be a nanoparticle / submicron-sized powder with a MAX phase core and a YSZ shell, specifically determined by the size of the MAX phase. Specifically, the core-shell structural unit is subjected to multiple centrifugal washings to remove impurity ions, resulting in cleaned nano / submicron-sized core-shell structural units. The cleaned nano / submicron-sized core-shell structural units are then subjected to microwave drying to achieve rapid and uniform drying, preventing nanoparticle agglomeration, thus obtaining a dried core-shell structural unit. The microwave drying power is 500~800W, the microwave drying temperature is 60~80℃, and the microwave drying time is 0.5~2 h.

[0048] The dried core-shell structural units were mixed with deionized water at a mass ratio of 1:5 to 1:3 to form a slurry, and an organic binder, either polyvinyl alcohol (PVA) or polyethylene glycol (PEG), was added. The organic binder accounted for 0.5% to 1.0% of the slurry mass. After the prepared slurry was thoroughly mixed, it was placed in a spray dryer for spray drying. The inlet temperature of the spray dryer was controlled at 220 to 260°C, and the atomizer frequency was 180 to 240 Hz. The resulting thermal barrier coating powder was obtained by agglomerating multiple core-shell structural units, each with a core-shell structure consisting of a MAX phase core and a YSZ phase shell. The prepared core-shell thermal barrier coating powder was a micron-sized spherical agglomerate obtained by spray drying, exhibiting good flowability. Specifically, the flowability of the thermal barrier coating powder was <45 s / 50g.

[0049] It should be noted that adjustments to the type and particle size of the MAX phase, the specific parameters of the mechanochemical grinding, the concentration and type of reagents used in the surface hydroxylation treatment, the pH value and temperature range of the double titration coprecipitation reaction, the power and time of the microwave hydrothermal process, and the process conditions of the spray drying should all be considered to fall within the scope of protection of this disclosure.

[0050] In this embodiment, a core-shell structure based on the MAX phase as the core and YSZ as the shell is constructed. Through interface activation and microwave hydrothermal crystallization, a complete, dense, and chemically bonded YSZ shell layer is formed on the surface of the MAX phase. This shell layer effectively blocks oxygen diffusion during thermal spraying, achieving in-situ retention of the MAX toughening phase. The resulting powder exhibits excellent sphericity and flowability, with a strong interfacial bond between the core and shell, meeting the requirements of high-end thermal spraying. It can provide antioxidant protection for the MAX phase core in coating preparation processes such as thermal spraying, significantly improving the fracture toughness and thermal shock resistance of thermal barrier coatings. Moreover, the process is controllable, low-cost, and suitable for mass production. It can be used for long-term high-temperature protection of hot-end components such as aero-engines and gas turbines.

[0051] Next, the preparation method of the thermal barrier coating powder provided in this disclosure will be described in detail with reference to the embodiments.

[0052] Example 1

[0053] This embodiment illustrates a method for preparing a thermal barrier coating powder with Ti2AlC as the core and yttrium oxide-stabilized zirconia (YSZ) as the shell.

[0054] Step 1: Take 100 g of Ti₂AlC powder with an average particle size of 0.5~2 μm, place it in a planetary mill, add zirconia grinding balls at a ball-to-particle ratio of 5:1, and grind at 300 rpm for 20 min to obtain mechanochemically ground powder. Then, place the mechanochemically ground powder in a 1 mol / L nitric acid solution and stir at 80℃ for 1.5 h to complete the surface hydroxylation treatment. After washing with deionized water until neutral, dry in a microwave drying apparatus for 1 h to obtain activated MAX phase nuclei. The microwave drying apparatus has a power of 600 W and a drying temperature of 70℃.

[0055] Step 2: Disperse the activated MAX phase nuclei in deionized water to prepare a suspension with a solid content of 8 wt%. Maintain the system temperature at 65℃ and the stirring speed at 400 rpm. Co-precipitate by double titration over 2 h. A mixed solution containing zirconium oxychloride and yttrium nitrate (Y₂O₃ molar percentage 5.5%) is used as the YSZ precursor and ammonia as the precipitant, both converted into aerosols. These aerosols are simultaneously and uniformly sprayed onto the suspension containing the dispersant. The pH of the reaction system is maintained at 10, and the temperature is maintained at 65℃ to achieve double titration co-precipitation. Before ultrasonic atomization of the YSZ precursor and precipitant, add 0.1% (by mass) of PEG-400 dispersant to the suspension. After ultrasonic atomization, continue stirring and maintaining the temperature for 1 h under the same conditions to uniformly coat the YSZ precursor onto the surface of the MAX phase nuclei, obtaining a core-shell structured precursor slurry.

[0056] Step 3: The core-shell structure precursor slurry obtained by double titration co-precipitation is transferred to a microwave hydrothermal reactor for microwave hydrothermal treatment to obtain core-shell structure units at the nanometer to submicron scale. The microwave hydrothermal treatment is carried out at 180℃ and 150 W microwave power for 2 h.

[0057] Step 4: Centrifuge, wash, and microwave dry the core-shell structure units at the nanometer to submicrometer scale to obtain dried core-shell structure units.

[0058] Step 5: Mix the dried core-shell structural units with deionized water at a mass ratio of 1:5 to form a slurry, and add 0.5 wt% PVA binder. Perform spray drying using a spray dryer with an inlet temperature of 220℃ and an atomization frequency of 180 Hz to obtain micron-sized spherical core-shell composite powder as a thermal barrier coating powder. Micron-sized spherical core-shell composite powder refers to powder obtained by the agglomeration of multiple core-shell structural units. The thermal barrier coating powder in Example 1 can be a core-shell composite powder with a YSZ outer shell encapsulating a Ti2AlC core, specifically represented as Ti2AlC@YSZ core-shell composite powder.

[0059] refer to Figure 2 and Figure 3 As shown, transmission electron microscopy (TEM) reveals that the core-shell structure of the thermal barrier coating powder obtained in Example 1 exhibits a complete core-shell structure, with a uniform YSZ shell thickness of approximately 100–200 nm. Scanning electron microscopy (SEM) shows that the thermal barrier coating powder after spray drying exhibits good sphericity, uniform particle size distribution, and a flowability of 44 s / 50 g.

[0060] Example 2

[0061] Example 2 illustrates a method for preparing Gd rare earth-doped thermal barrier coating powder, which mainly includes the following steps: Step 1: Take 100 g of Ti₂AlC powder with an average particle size of 0.5~3 μm and place it in a planetary mill. Add zirconia grinding balls at a ball-to-particle ratio of 10:1 and grind at 450 rpm for 15 min to obtain mechanochemically ground powder. Subsequently, place the mechanochemically ground powder in a 3 mol / L nitric acid solution and stir at 90℃ for 1 h to complete the surface hydroxylation treatment. After washing with deionized water until neutral, dry in a microwave drying device for 1 h to obtain activated MAX phase nuclei. The microwave drying device has a power of 600 W and a drying temperature of 70℃.

[0062] Step 2: Disperse the activated MAX phase cores in deionized water to prepare a suspension with a solid content of 8 wt%. Maintain the system temperature at 75℃ and the stirring speed at 450 rpm. Using a dual titration system, convert a mixed solution containing zirconium oxychloride, yttrium nitrate (Y₂O₃ molar percentage 5.5%), and gadolinium nitrate (Gd₂O₃ doping amount 1.5 mol%) into aerosols as the YSZ precursor and the precipitant ammonia water within 2.5 h. Simultaneously and uniformly spray these aerosols into the suspension containing the dispersant, controlling the pH of the reaction system to be stable at 10.5 and the temperature at 75℃. Before ultrasonic atomization spraying of the YSZ precursor and precipitant, add 0.5% (by mass) of the dispersant PEG-400 to the suspension. After ultrasonic atomization spraying is completed, continue stirring at the same conditions for 1 h to obtain a core-shell structured precursor slurry.

[0063] In Example 2, gadolinium nitrate (Gd(NO3)3·6H2O) was added as a rare earth dopant to the reaction solution of the double titration coprecipitation method in step two. The doping amount of Gd2O3 was controlled to be 1.5% of the total molar amount of zirconium source and rare earth source to prepare a rare earth-doped modified shell. The zirconium source refers to zirconium oxychloride, and the rare earth source refers to the added gadolinium nitrate.

[0064] Step 3: The core-shell structure precursor slurry obtained after double titration co-precipitation is transferred to a microwave hydrothermal reactor for microwave hydrothermal treatment to obtain core-shell structure units at the nanometer to submicron scale. The microwave hydrothermal treatment is carried out at 200℃ and 180 W for 1 h.

[0065] Step 4: Centrifuge, wash, and microwave dry the core-shell structure units at the nanometer to submicrometer scale to obtain dried core-shell structure units.

[0066] Step 5: Mix the dried core-shell structural units with deionized water at a mass ratio of 1:5 to form a slurry, and add 0.5 wt% PVA binder. Perform spray drying using a spray dryer with an inlet temperature of 260℃ and an atomization frequency of 220 Hz to obtain micron-sized spherical core-shell composite powder as the thermal barrier coating powder. The thermal barrier coating powder in Example 2 can be a composite powder obtained by agglomerating multiple Gd-YSZ-coated Ti2AlC core-shell structural units, specifically, a Ti2AlC@Gd-YSZ core-shell composite powder.

[0067] The thermal barrier coating powder prepared in Example 2 also has good sphericity and flowability, with a flowability of 40s / 50g.

[0068] Example 3

[0069] Example 3 illustrates a method for preparing thermal barrier coating powder with a high-entropy MAX phase, mainly including the following steps: Step 1: Take 100 g of high-entropy MAX phase powder with an average particle size of 1-5 μm and place it in a planetary mill. The chemical formula of the high-entropy MAX phase can be (Ti,V,Nb,Mo)₂AlC. Add zirconia grinding balls at a ball-to-powder ratio of 8:1 and grind at 400 rpm for 25 min to obtain mechanochemically ground powder. Subsequently, place the mechanochemically ground powder in a 2 mol / L sodium hydroxide solution and stir at 75℃ for 2 h to complete the surface hydroxylation treatment. After washing with deionized water until neutral, dry in a microwave drying device for 1 h to obtain activated high-entropy MAX phase nuclei. The power of the microwave drying device is 600 W and the drying temperature is 70℃.

[0070] Step 2: Disperse the activated high-entropy MAX phase nuclei in deionized water to prepare a suspension with a solid content of 8 wt%. Maintain the system temperature at 80℃ and the stirring speed at 400 rpm. Using a dual titration system, simultaneously and uniformly spray a mixed solution containing zirconium oxychloride and yttrium nitrate (Y₂O₃ molar percentage 5.5%) and the precipitant ammonia water into the suspension to construct the reaction system within 3 h. Control the pH value of the reaction system to be stable at 11 and the temperature at 80℃. Before ultrasonic atomization spraying of the YSZ precursor and precipitant, add 1% (by mass) of PEG-400 dispersant to the suspension. After ultrasonic atomization spraying is completed, continue stirring at the same conditions for 1 h to uniformly coat the YSZ precursor on the surface of the high-entropy MAX phase nuclei to obtain a core-shell structured precursor slurry.

[0071] Step 3: The core-shell structure precursor slurry obtained by double titration co-precipitation is transferred to a microwave hydrothermal reactor for microwave hydrothermal treatment to obtain core-shell structure units at the nanometer to submicron scale. The microwave hydrothermal treatment is carried out at 190℃ and 170 W for 1.5 h.

[0072] Step 4: Centrifuge, wash, and microwave dry the core-shell structure units at the nanometer to submicrometer scale to obtain dried core-shell structure units.

[0073] Step 5: Mix the dried core-shell structure units with deionized water at a mass ratio of 1:5 to form a slurry, and add 0.5 wt% PVA binder. Perform spray drying using a spray dryer with an inlet temperature of 240℃ and an atomization frequency of 200 Hz to obtain micron-sized spherical core-shell composite powder as a thermal barrier coating powder.

[0074] The thermal barrier coating powder in Example 3 can be a composite powder obtained by agglomeration of YSZ core-shell structure units coated with high-entropy MAX, and can be represented as high-entropy MAX@YSZ powder. This thermal barrier coating powder has good sphericity and a flowability of 42s / 50g.

[0075] Comparative Example 1

[0076] Comparative Example 1 uses a physical mixing method to prepare composite powder of MAX phase YSZ.

[0077] YSZ powder and Ti2AlC powder were physically mixed at a mass ratio of 85:15 to obtain a physically mixed powder. The physical mixing was carried out by mixing in a V-type mixer for 2 hours. The particle size of the YSZ powder was similar to that of the final powder in Example 1, and the particle size of the Ti2AlC powder was similar to that of the MAX phase raw material used in Example 1. Subsequently, the physically mixed powder was mixed with deionized water at a mass ratio of 1:5 to form a slurry, and 0.5 wt% PVA binder was added. Granulation was carried out under the same spray drying conditions as in Example 1, i.e., spray drying was performed using a spray dryer with an inlet temperature of 240°C and an atomization frequency of 200 Hz. The final physically mixed powder was obtained, which was a physically mixed spherical powder with a flowability of approximately 40 s / 50g.

[0078] Furthermore, thermal barrier coatings were prepared using the thermal barrier coating powders prepared in Examples 1-3 and the physically mixed spherical powders prepared in Comparative Example 1, under the same atmospheric plasma spraying (APS) process. The main gas in the atmospheric plasma spraying (APS) process was Ar, and the auxiliary gas was H2. The spraying parameters included: main gas flow rate 50 SLPM, auxiliary gas flow rate 12 SLPM, powder feed gas (Ar) flow rate 5 SLPM, arc current 550 A, spraying distance 100 mm, and powder feed rate 30 g / min.

[0079] The prepared thermal barrier coating was subjected to a water-quenched thermal shock test. The number of cycles required to achieve 20% surface area spalling was recorded to evaluate the toughness and thermal shock resistance of the prepared thermal barrier coating powder when used as a thermal barrier coating. The water-quenched thermal shock test temperature ranged from room temperature to 1100℃. The comparison results of the thermal shock resistance of the thermal barrier coating powders prepared in Examples 1-3 and Comparative Example 1 are shown in Table 1: Table 1 Comparison of thermal shock performance of thermal barrier coating powders

[0080] The experimental results are shown in Table 1. In this disclosure, the thermal barrier coating powders prepared according to Examples 1-3 exhibit significantly better thermal shock resistance lifetimes than the physically mixed powder prepared in Comparative Example 1, with a lifetime increase of approximately 2.5 times. Therefore, this disclosure achieves a synergistic multiplication of the performance of the YSZ and MAX phases. The above data indicates that the thermal barrier coating powders prepared by the preparation method of this disclosure effectively protect the toughening core of the MAX phase through a complete YSZ shell. In Comparative Example 1, the physically mixed powder suffered severe oxidation of the MAX phase during thermal spraying, leading to the loss of its toughening effect and thus a lower lifetime. Examples 1-3, due to their complete core-shell structure, achieved a significant improvement in lifetime. Examples 2 and 3, through shell doping and core phase adjustment, further improved the lifetime by approximately 10% based on the core-shell structure.

[0081] In this embodiment, the technical problem of easy oxidation of MAX phase materials during thermal spraying is solved by designing a microstructure of thermal barrier coating powder with "MAX phase as core and YSZ as shell". This structure is not a simple physical encapsulation, but rather a combination of several precise and controllable processes, including mechanochemical activation, surface hydroxylation treatment, dual titration co-precipitation, and microwave hydrothermal crystallization strengthening. First, the MAX phase core is pretreated with mechanochemical activation and surface hydroxylation to provide a highly active surface. Then, the YSZ precursor is uniformly and completely coated on the core surface using dual titration co-precipitation ultrasonic atomization spraying technology. Microwave hydrothermal treatment is used instead of traditional high-temperature calcination to simultaneously achieve low-temperature crystallization of the YSZ shell and chemical bonding strengthening of the core-shell interface under mild conditions, achieving uniform coating and interfacial chemical bonding of the YSZ shell on the MAX phase core surface. The YSZ shell acts as an efficient oxygen diffusion barrier during thermal spraying, ensuring that the toughening ability of the MAX phase core is completely retained in the final coating. Experimental data demonstrates that, compared to the physically mixed powder prepared in Comparative Example 1, the thermal barrier coating prepared from the thermal barrier coating powder obtained by the preparation method in this disclosure exhibits approximately 2.5 times improved thermal shock resistance life. This proves that this disclosure integrates the excellent thermal barrier properties of YSZ with the unique high toughness of the MAX phase, achieving a synergistic multiplication of material properties. Furthermore, the process route provided in the preparation method of this disclosure possesses good universality and scalability; its core process is applicable to materials with M... n+ 1AX n The family of general-structure MAX phase ceramic materials (such as conventional Ti2AlC and cutting-edge high-entropy MAX phases) is also compatible with rare-earth doping modification of the YSZ shell (such as Gd, Yb, etc.), providing a powerful material platform for the design of high-performance thermal barrier coatings. This increases application prospects and versatility, and has high scalability.

[0082] In this embodiment of the disclosure, a thermal barrier coating powder is also provided, which can be prepared according to the preparation method of thermal barrier coating powder in steps S110 to S140.

[0083] Based on this, this disclosure also provides a thermal barrier coating, which is prepared from the aforementioned thermal barrier coating powder through a thermal spraying process. The thermal barrier coating can be used for long-term protection of hot-end components such as aero-engines and gas turbines, and can also be used in other equipment, without specific limitations. The prepared thermal barrier coating provides intrinsic, long-term antioxidant protection to the MAX phase core through the YSZ shell in the thermal barrier coating powder, fundamentally improving the fracture toughness, thermal shock resistance, and overall reliability of the coating. It solves the problem of easy oxidation of MAX phase materials during thermal spraying, ensuring that the toughening ability of the MAX phase core is completely preserved in the final thermal barrier coating, improving the fracture toughness and thermal shock resistance of the thermal barrier coating, and enhancing its reliability. This allows the thermal barrier coating to be used for long-term high-temperature protection of various hot-end components.

[0084] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of this disclosure and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0085] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

[0086] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for preparing a thermal barrier coating powder, characterized in that, include: The MAX phase powder was subjected to mechanical and chemical grinding and surface hydroxylation treatment to obtain activated MAX phase nuclei; The activated MAX phase nucleus is dispersed in a liquid phase containing a dispersant, and the YSZ precursor is uniformly coated on the core surface by double titration co-precipitation to obtain a core-shell structured precursor slurry. The core-shell structure precursor slurry is subjected to microwave hydrothermal treatment to allow the YSZ precursor to crystallize in situ to form a YSZ shell on the surface of the MAX phase nucleus, thereby obtaining a core-shell structure unit. The core-shell structure unit has a core-shell structure with the MAX phase as the core and the YSZ phase as the shell; The core-shell structural unit is post-processed and spray-dried to obtain thermal barrier coating powder. The thermal barrier coating powder is obtained by agglomeration of multiple core-shell structural units.

2. The method for preparing thermal barrier coating powder according to claim 1, characterized in that, The average particle size of the activated MAX phase nuclei is 0.5~5 μm.

3. The method for preparing thermal barrier coating powder according to claim 1, characterized in that, The MAX phase has the general formula M n+1 AX n Ceramic materials; wherein M is a transition metal element, A is a main group element, X is C or N, and n = 1, 2 or 3; or, the MAX phase is a phase with the general formula M n+1 AX n The high-entropy MAX phase, wherein the M site contains at least three different transition metal elements.

4. The method for preparing thermal barrier coating powder according to claim 1, characterized in that, The ratio of MAX phase powder to grinding balls in the mechanochemical grinding process is 5:1 to 10:1, the rotation speed of the mechanochemical grinding is 300 to 500 rpm, and the grinding time is 10 to 30 min. The surface hydroxylation treatment is as follows: the mechanically and chemically ground powder is placed in a 1-3 mol / L nitric acid solution or sodium hydroxide solution and stirred at 70-90℃ for 1-2 h.

5. The method for preparing thermal barrier coating powder according to claim 1, characterized in that, The dual titration coprecipitation includes: using ultrasonic atomization to convert the YSZ precursor and precipitant into aerosols and simultaneously spraying them into the reaction system; carrying out the dual titration coprecipitation reaction at a constant pH of 9.5-11 and a temperature of 65-80℃; the ultrasonic atomization spraying time is 2-3 h; after the ultrasonic atomization spraying is completed, the mixture is kept warm and stirred at the same temperature for 0.5-2 h.

6. The method for preparing thermal barrier coating powder according to claim 1, characterized in that, The YSZ precursor is a mixed solution containing a zirconium source and a yttrium source, or the YSZ precursor is a mixed solution containing a zirconium source, a yttrium source and a rare earth dopant. The rare earth dopant is gadolinium nitrate or ytterbium nitrate, wherein the doping amount of Gd2O3 or Yb2O3 accounts for 1 to 2 mol of the total molar number of zirconium source and rare earth source.

7. The method for preparing thermal barrier coating powder according to claim 1, characterized in that, The dispersant is polyethylene glycol, and the amount of the dispersant added is 0.1% to 1% of the total mass of the reaction system.

8. The method for preparing thermal barrier coating powder according to claim 1, characterized in that, The microwave hydrothermal treatment temperature is 180~200℃, the microwave hydrothermal treatment power is 150~180 W, and the microwave hydrothermal treatment time is 1~2 hours; The post-processing includes multiple centrifugal washing and microwave drying. The microwave drying power is 500~800 W, the microwave drying temperature is 60~80℃, and the microwave drying time is 0.5~2 h. The inlet temperature of the spray dryer is 220~260℃, and the atomizer frequency is 180~240 Hz.

9. A thermal barrier coating powder, characterized in that, The thermal barrier coating powder is prepared by the method described in any one of claims 1-8; the thermal barrier coating powder is a micron-sized spherical agglomerate, which is composed of nano- to submicron-sized core-shell structural units, wherein the core-shell structural units have a MAX phase as the core and a YSZ phase as the shell.

10. A thermal barrier coating, characterized in that, The thermal barrier coating is prepared from the thermal barrier coating powder according to claim 9.

Images