A dense, thermoshock-resistant gradient ceramic coating and method of making same

Abstract

The application belongs to the technical field of ceramic coating materials, and particularly relates to a dense thermal shock resistant gradient ceramic coating and a preparation method thereof. The dense thermal shock resistant gradient ceramic coating is composed of a porous silicon-based ceramic substrate and a dense ceramic coating coated on the surface of the substrate. The dense ceramic coating is a multilayer structure, and the difference between the thermal expansion coefficients of each layer of the dense ceramic coating from the bottom to the surface of the dense ceramic coating is less than 10%, and the Young's modulus decreases layer by layer to form the gradient ceramic coating. The obtained coating is a multilayer ceramic coating structure with the modulus increasing from the surface to the inside, and the unstable expansion of cracks caused by thermal shock in the coating is inhibited to improve the structural stability of the coating.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic coating materials, in particular to a dense thermal shock resistant gradient ceramic coating and a preparation method thereof. BACKGROUND

[0002] The wave-transparent material for radome / window is a structure-function integrated material for preventing the adverse effects of high temperature, aerodynamic load and high-speed particle impact on the normal operation of its radar system. The flight speed of existing aircraft is getting faster and faster, and the strong aerodynamic heating causes the extreme service environment of high speed, high temperature and high pressure. Porous ceramics have excellent comprehensive performance, and their light weight, high temperature resistance, thermal shock resistance and easy processing performance characteristics enable them to meet the requirements of stable use of high Mach number aircraft in severe service environment, and have the potential to be used as high-temperature wave-transparent materials. Among them, silicon-based ceramics such as porous Si3N4 ceramic materials and porous Sialon ceramic materials are the current research hotspots. However, the pore structure of porous ceramics is easy to adsorb water vapor in the environment, which leads to unstable dielectric properties of the material, seriously endangering the functionality of the wave-transparent component, therefore, a dense coating needs to be prepared on its surface. To ensure the safe and reliable operation of the radome / window, the surface coating is required to meet the following requirements: ① high density to isolate high-temperature water vapor; ② high temperature resistance to ensure the stability of its structure and performance in a thermal shock environment.

[0003] Inorganic materials have excellent high-temperature chemical stability and are the preferred material for the surface coating of wave-transparent porous ceramics. However, traditional ceramic and glass inorganic coatings have poor toughness, and the micro-cracks caused by thermal shock will quickly destabilize and expand, leading to coating failure. This problem seriously restricts the development of surface coatings for aerospace wave-transparent materials, is a common problem of existing inorganic coatings, and is a bottleneck problem that needs to be broken through in technology.

[0004] As is known to all, the inevitable thermal physical property mismatch between the coating and the substrate is the root cause of thermal shock damage. Traditional single-layer coatings have a large difference in thermal expansion coefficient with the substrate material, and the thermal expansion mismatch will cause a large thermal stress, which will produce micro-cracks at the coating / substrate interface, and the further expansion of the cracks will lead to coating cracking and even peeling.

[0005] For ceramic surface multilayer coating, the commonly used coating materials at present mainly include the following: (1) silicate, alumina coating prepared by plasma spraying. The phase composition of this kind of coating is controllable, and the density is good, but in the spraying process, high-speed high-temperature particles will quickly cool and solidify when encountering low-temperature substrate, resulting in cracks and pores in the coating, and the coating contains a large amount of amorphous phase, when the coating is used at high temperature for a long time, the existing amorphous phase will begin to crystallize, and the volume change will produce internal stress, which can easily cause the coating to crack, that is, the coating prepared by this method has poor thermal stability. (2) Nitride (including Si3N4 and BN), carbide (including SiC and B4C) coating prepared by chemical vapor deposition (CVD) method. The structure of this kind of coating is dense, but the deposition efficiency is low, the cost is high, and cracks are easy to form on the surface of the substrate with large size and complex shape, which is not conducive to industrial application. At the same time, the coating is usually amorphous, so the coating has low high-temperature stability and low thermal shock resistance.

[0006] In summary, the coatings prepared by these technologies all have obvious shortcomings, and the existing multilayer coatings are mostly prepared layer by layer. The surface passivation between layers inevitably exists, which makes the coating have a large interfacial energy and interfacial thermal stress, which is not conducive to the bonding of the coating material and the substrate material, leading to easy failure under thermal shock conditions, and the coating loses its waterproof ability. Therefore, there is an urgent need for a method to improve the bonding effect between the layers in the coating and ensure the structural stability of the coating under thermal shock conditions. SUMMARY

[0007] In order to ensure the structural stability of the coating under thermal shock conditions, the present application provides a dense thermal shock resistant gradient ceramic coating and a preparation method thereof.

[0008] A dense thermal shock resistant gradient ceramic coating, the gradient ceramic coating is composed of a porous silicon-based ceramic substrate and a dense ceramic coating coated on the surface thereof.

[0009] The dense ceramic coating is a multilayer structure, and the difference between the thermal expansion coefficients of each layer of the dense ceramic coating from the innermost layer to the surface of the dense ceramic coating is less than 10%, and the Young's modulus decreases layer by layer to form the gradient ceramic coating.

[0010] A preparation method of a dense thermal shock resistant gradient ceramic coating, characterized in that it comprises the following steps:

[0011] (1) Polishing treatment of the porous ceramic substrate: grinding the surface to be flat, then ultrasonic cleaning with anhydrous ethanol solvent and drying;

[0012] (2) Preparation of the spraying slurry: micron RE2Si2O7 powder is mixed with anhydrous ethanol, with the solid phase accounting for 20-30% of the total mass, and ball-milling for 24-30 hours to prepare a RE2Si2O7 / ethanol suspension slurry; wherein RE is any of Y, Yb, Er, Lu, Sm, and Sc;

[0013] The mixture of SiO2, Al2O3, and RE2O3 powder is mixed with anhydrous ethanol, with the solid phase accounting for 20-30% of the total mass, and ball-milling for 24-30 hours to prepare a RE2O3 / SiO2 / Al2O3 / ethanol suspension slurry;

[0014] (3) Spraying of the slurry: the RE2Si2O7 / ethanol slurry prepared in step (2) with the highest Young's modulus is sprayed on the surface of the porous ceramic substrate, and the anhydrous ethanol solvent is volatilized during the spraying process, and the RE2Si2O7 solid phase powder is deposited on the surface of the substrate; the step is repeated, and the remaining RE2Si2O7 solid phase powders are deposited in order of decreasing Young's modulus;

[0015] The RE2O3 / SiO2 / Al2O3 / ethanol slurry prepared in step (2) is sprayed on the surface of the outer RE2Si2O7 solid phase powder layer to form the outermost RE2O3 / SiO2 / Al2O3 mixture;

[0016] (4) Sintering of the coating: after the spraying is completed, the residual anhydrous ethanol solvent is removed by drying, and the dried coating is sintered at 1300-1500°C and 0.25 MPa in a N2 atmosphere for 15-60 minutes.

[0017] Preferably, the porosity of the porous ceramic substrate is 20-60%.

[0018] Preferably, in step (1), 400-mesh, 800-mesh, 1000-mesh, 1200-mesh, and 1500-mesh sandpaper is used for grinding, and the surface is ground to be flat in sequence, and the dried product is dried in an air atmosphere at 60-80°C for more than 24 hours.

[0019] Preferably, in step (2), RE is any three of Y, Yb, Er, Lu, Sm, and Sc.

[0020] Preferably, in step (2), agate balls are used for ball-milling, and the volume ratio of agate balls to RE2Si2O7 powder is 1-3:1, and the volume ratio of agate balls to the mixture powder is 1-3:1.

[0021] Preferably, in step (2), the molar ratio of RE2O3:SiO2:Al2O3 in the mixture powder is 1-2:5-10:3-5.

[0022] Preferably, in step (3), an air pressure atomizing spray gun is used, the air pressure atomizing spray gun uses a gravity type spray gun, the nozzle diameter is 0.5 cm, the air pressure during spraying is 0.7 MPa, the spray gun moving speed is 15-25 cm / s, the spray gun is vertically perpendicular to the sample surface, and the spraying distance is 15-25 cm.

[0023] Preferably, in step (4), the heating rate of sintering is 10 ℃ / min below 1000 ℃, and the heating and cooling rates are both 5 ℃ / min above 1000 ℃.

[0024] Compared with the prior art, the present application has the beneficial effects that:

[0025] The coating obtained by the present application has a multilayer ceramic coating structure with increasing modulus from the surface to the inside, and can inhibit the crack instability expansion in the coating caused by thermal shock, so as to improve the structural stability of the coating.

[0026] The coating obtained by the present application has a typical multilayer structure, and each dense layer is obtained by using a powder slurry spraying method, layer-by-layer deposition on the surface of a porous substrate, and then liquid phase assisted sintering at high temperature by using the outermost oxide mixture powder. The obtained coating body is at least three layers, and from the substrate to the surface of the coating, each layer is made of a rare earth silicate with similar thermal expansion coefficient and decreasing elastic modulus. With the infiltration of high-temperature liquid phase, each layer of powder is co-sintered to form a dense gradient coating. The excess high-temperature liquid phase continues to infiltrate into the porous substrate to form a transition layer, effectively pinning the gradient coating and the substrate, and ensuring the coating / substrate interface bonding. Such a structure design can effectively reduce the thermal stress during thermal shock, ensure the structural stability, and ensure good waterproof ability of the coating before and after thermal shock.

[0027] The present application designs a layer-by-layer matching thermal physical property distribution, constructs a gradient coating with similar thermal expansion coefficient and increasing Young's modulus on the surface of a porous ceramic, reduces the thermal stress during thermal shock, prevents crack initiation and expansion, and thus significantly improves the high-temperature structural stability of the coating. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A schematic diagram of the method for preparing the gradient ceramic coating of the present application is shown in the figure.

[0029] Figure 2 The macroscopic morphology of the gradient ceramic coating of Example 1 is shown in the figure.

[0030] Figure 3 The micro-morphology of the gradient ceramic coating of Example 1 is shown in the figure, wherein (a) is the micro-morphology of the coating surface, (b) is the micro-morphology of the coating cross section, and (c) is the element line scanning EDS result.

[0031] Figure 4 Micrographs of the gradient ceramic coating of Example 1 after thermal shock of 1200°C→room temperature, wherein (a) is the surface micrograph of the coating after thermal shock, (b) is the cross-section micrograph of the coating after thermal shock;

[0032] Figure 5 Micrographs of the coating of Comparative Example 1 after thermal shock, wherein (a) is the surface micrograph, (b) is the cross-section micrograph;

[0033] Figure 6 Micrographs of the coating of Comparative Example 2 after thermal shock, wherein (a) is the surface micrograph, (b) is the cross-section micrograph;

[0034] Figure 7 Micrographs of the coating of Comparative Example 3 after thermal shock, wherein (a) is the surface micrograph, (b) is the cross-section micrograph. DETAILED DESCRIPTION

[0035] The specific embodiments of the present application are described in detail below, but it should be understood that the scope of the present application is not limited to the specific embodiments. Based on the examples in the present application, all other examples obtained by those skilled in the art without making creative efforts are within the scope of the present application. The experimental methods described in the embodiments of the present application are conventional methods unless otherwise specified.

[0036] The micrometer level refers to a particle size range of 1-5 μm, and 1.2 μm is selected in the following examples.

[0037] Example 1

[0038] The gradient ceramic coating is composed of a porous Si3N4 ceramic substrate and a Y2Si2O7 / Yb2Si2O7 / Lu2Si2O7 coating on the surface thereof.

[0039] The Y2Si2O7 / Yb2Si2O7 / Lu2Si2O7 gradient coating on the surface of the porous Si3N4 ceramic substrate comprises the following steps:

[0040] (1) Substrate pretreatment: Select a porous Si3N4 ceramic substrate with a porosity of 50%, and use 400 mesh, 800 mesh, 1000 mesh, 1200 mesh, and 1500 mesh sandpaper to grind the surface successively until it is flat. Then use anhydrous ethanol solvent to ultrasonically clean for half an hour, and place it in an oven to dry at 60°C in an air atmosphere for 24 hours;

[0041] (2) Configuration of spraying slurry: micron-sized Lu2Si2O7 powder, Yb2Si2O7 powder, Y2Si2O7 powder are selected as raw materials for building multi-layer ceramic coating, which are mixed with anhydrous ethanol respectively, with solid phase mass ratio of 20%. Use agate balls to mix in agate ball mill for 24h, rotation speed of 300r / min.

[0042] Mix Y2O3, SiO2, Al2O3 powder in a molar ratio of 2:5:3, then suspend in anhydrous ethanol solvent, solid phase mass ratio of 20%, use agate balls to mix in agate ball mill for 24h, rotation speed of 300r / min.

[0043] (3) Slurry spraying: Lu2Si2O7 / ethanol slurry, Yb2Si2O7 / ethanol slurry, Y2Si2O7 / ethanol slurry prepared are respectively loaded into air pressure atomizing spray gun with nozzle diameter of 0.5cm, air pressure of 0.7MPa is maintained during spraying, spray gun moving rate is 20cm / s, spray gun is vertically opposite to sample surface, spraying distance is 20cm, each kind of slurry is sprayed on the surface of the substrate for 4 times.

[0044] After the anhydrous ethanol solvent volatilizes, the prepared Y2O3 / SiO2 / Al2O3 / ethanol slurry is vertically sprayed on the sample surface with the same process parameters.

[0045] (4) Coating sintering: the sample after spraying is placed in a 40℃ air oven for drying for 24h to remove residual anhydrous ethanol solvent. The dried sample is placed in a gas pressure sintering furnace, and is kept at 1400℃, 0.25MPa N2 atmosphere for 60min. The specific heating / cooling process is as follows: the heating rate below 1000℃ is 10℃ / min, the heating / cooling rate between 1000℃ and 1400℃ is 5℃ / min, the cooling rate between 1000℃ and 800℃ is 10℃ / min, and the cooling rate below 800℃ is along with the furnace.

[0046] It is determined that the Y2Si2O7 / Yb2Si2O7 / Lu2Si2O7 gradient coating prepared in this embodiment reduces the water absorption rate of the material by 95.0%, and the high temperature resistance grade reaches 1200℃, can withstand 1200℃→room temperature thermal shock impact, and no peeling, cracking, etc. is observed on the coating, and the coating is firmly combined with the substrate.

[0047] Example 2

[0048] The gradient ceramic coating is composed of a porous Si3N4 ceramic substrate and a Y2Si2O7 / Yb2Si2O7 / Sm2Si2O7 coating coated on the surface thereof.

[0049] Preparation of Y2Si2O7 / Yb2Si2O7 / Sm2Si2O7 gradient coating on the surface of porous Si3N4 ceramic substrate, comprising the following steps:

[0050] (1) Pretreatment of the substrate: select a porous Si3N4 ceramic substrate with a porosity of 50%, use 400 mesh, 800 mesh, 1000 mesh, 1200 mesh, 1500 mesh sandpaper to grind the surface successively until it is flat, then use anhydrous ethanol solvent to ultrasonic clean for half an hour, and place it in an oven to dry at 60℃ in air atmosphere for 24h;

[0051] (2) Configure the spraying slurry: select micron-sized Sm2Si2O7 powder, Yb2Si2O7 powder, and Y2Si2O7 powder as the raw materials for constructing the multi-layer ceramic coating, mix them with anhydrous ethanol respectively, with a solid phase mass ratio of 30%. Use agate balls to ball mill the mixture in an agate ball mill tank for 24h at a rotation speed of 300r / min.

[0052] Mix Y2O3, SiO2, and Al2O3 powders in a molar ratio of 1:6:3, then suspend them in anhydrous ethanol solvent with a solid phase mass ratio of 20%, and use agate balls to ball mill the mixture in an agate ball mill tank for 24h at a rotation speed of 300r / min.

[0053] (3) Slurry spraying: load the prepared Sm2Si2O7 / ethanol slurry, Yb2Si2O7 / ethanol slurry, and Y2Si2O7 / ethanol slurry into an air pressure atomization spray gun with a nozzle diameter of 0.5cm respectively, maintain the air pressure during spraying at 0.7MPa, the spray gun moving speed at 20cm / s, the spray gun perpendicular to the sample surface, and the spraying distance at 20cm, and move and spray each kind of slurry on the substrate surface for 4 times in turn.

[0054] After the anhydrous ethanol solvent evaporates, spray the prepared Y2O3 / SiO2 / Al2O3 / ethanol slurry on the sample surface with the same process parameters.

[0055] (4) Coating sintering: place the sample after spraying in a 40℃ air oven to dry for 24h to remove residual anhydrous ethanol solvent. Place the dried sample in a gas pressure sintering furnace, heat it at 1400℃ in a N2 atmosphere at 0.25MPa for 60min. The specific heating / cooling process is as follows: the heating rate below 1000℃ is 10℃ / min, the heating / cooling rate between 1000℃ and 1400℃ is 5℃ / min, the cooling rate between 1000℃ and 800℃ is 10℃ / min, and the cooling rate below 800℃ is random.

[0056] The Y2Si2O7 / Yb2Si2O7 / Sm2Si2O7 gradient coating prepared in the embodiment reduces the water absorption of the material by 93.7%, and the high-temperature resistance grade reaches 1200°C, can withstand thermal shock impact of 1200°C→room temperature, and no peeling or cracking is observed on the coating, and the coating is firmly combined with the substrate.

[0057] Example 3

[0058] The gradient ceramic coating is composed of a porous Si3N4 ceramic substrate and a Y2Si2O7 / Yb2Si2O7 / Sc2Si2O7 coating coated on the surface of the substrate.

[0059] The Y2Si2O7 / Yb2Si2O7 / Sc2Si2O7 gradient coating is prepared on the surface of the porous Si3N4 ceramic substrate, including the following steps:

[0060] (1) substrate pretreatment: select a porous Si3N4 ceramic substrate with a porosity of 55%, use 400 mesh, 800 mesh, 1000 mesh, 1200 mesh, and 1500 mesh sandpaper to grind the surface successively until it is flat, then use anhydrous ethanol solvent for ultrasonic cleaning for half an hour, and place it in an oven for drying at 60°C in an air atmosphere for 24 hours;

[0061] (2) configuration of spraying slurry: select micron-sized Sc2Si2O7 powder, Yb2Si2O7 powder, and Y2Si2O7 powder as raw materials for constructing the multi-layer ceramic coating, mix them with anhydrous ethanol respectively, and the solid phase mass ratio is 25%. Use agate balls to ball mill in an agate ball mill tank for 24 hours at a speed of 300 revolutions / min.

[0062] Mix Yb2O3, SiO2, and Al2O3 powders in a molar ratio of 2:5:3, then suspend them in anhydrous ethanol solvent, and the solid phase mass ratio is 25%. Use agate balls to ball mill in an agate ball mill tank for 24 hours at a speed of 300 revolutions / min.

[0063] (3) slurry spraying: load the prepared Sc2Si2O7 / ethanol slurry, Yb2Si2O7 / ethanol slurry, and Y2Si2O7 / ethanol slurry into an air pressure atomization spray gun with a nozzle diameter of 0.5 cm in sequence, maintain the air pressure during spraying at 0.7 MPa, the spray gun moves at a speed of 15-25 cm / s, the spray gun is perpendicular to the surface of the sample, the spraying distance is 20 cm, and each kind of slurry is sprayed on the surface of the substrate for 4 passes.

[0064] After the anhydrous ethanol solvent evaporates, the prepared Yb2O3 / SiO2 / Al2O3 / ethanol slurry is vertically sprayed on the surface of the sample with the same process parameters.

[0065] (4) Coating sintering: After the spraying is completed, the sample is placed in a 40°C air oven for drying for 24h to remove the residual anhydrous ethanol solvent. The dried sample is placed in a gas pressure sintering furnace, and is kept at 1350°C in a N2 atmosphere of 0.25MPa for 60min. The specific temperature rising / rising process is as follows: the temperature rising rate is 10°C / min below 1000°C, the temperature rising / rising rate is 5°C / min from 1000°C to 1350°C, the temperature rising rate is 10°C / min from 1000°C to 800°C, and the furnace is cooled below 800°C.

[0066] It is determined that the Y2Si2O7 / Yb2Si2O7 / Sc2Si2O7 gradient coating prepared in the embodiment reduces the water absorption of the material by 96.0%, and the high temperature resistance grade reaches 1200°C, can withstand thermal shock impact of 1200°C→room temperature, and no peeling, cracking, etc. is observed on the coating, and the coating is firmly combined with the substrate.

[0067] Example 4

[0068] The gradient ceramic coating is composed of a porous Sialon ceramic substrate and a Y2Si2O7 / Yb2Si2O7 / Er2Si2O7 coating coated on the surface thereof.

[0069] The Y2Si2O7 / Yb2Si2O7 / Er2Si2O7 gradient coating is prepared on the surface of the porous Sialon ceramic substrate, including the following steps:

[0070] (1) Substrate pretreatment: a porous Sialon ceramic substrate with a porosity of 30% is selected, the surface thereof is sequentially polished to be flat by using 400-mesh, 800-mesh, 1000-mesh, 1200-mesh and 1500-mesh sandpaper, and then the substrate is ultrasonically cleaned for half an hour using anhydrous ethanol solvent and is dried in an oven at 60°C in an air atmosphere for 24h;

[0071] (2) Preparation of spraying slurry: micron-sized Er2Si2O7 powder, Yb2Si2O7 powder and Y2Si2O7 powder are selected as raw materials for constructing the multilayer ceramic coating, and are mixed with anhydrous ethanol at a solid phase mass ratio of 20%. The mixture is ball-milled in a corundum ball mill tank using corundum balls at a rotation speed of 300r / min for 24h.

[0072] Y2O3, SiO2 and Al2O3 powders are mixed at a molar ratio of 1.5:6:4, and then are suspended in anhydrous ethanol solvent at a solid phase mass ratio of 20%. The mixture is ball-milled in a corundum ball mill tank using corundum balls at a rotation speed of 300r / min for 24h.

[0073] (3) slurry spraying: the prepared Er2Si2O7 / ethanol slurry, Yb2Si2O7 / ethanol slurry, and Y2Si2O7 / ethanol slurry were sequentially loaded into an air pressure atomization spray gun with a nozzle diameter of 0.5 cm, the air pressure during spraying was maintained at 0.7 MPa, the spray gun moved at a rate of 20 cm / s, the spray gun was vertically and directly opposite to the sample surface, the spraying distance was 20 cm, and each slurry was sequentially sprayed on the surface of the substrate for 4 passes.

[0074] After the anhydrous ethanol solvent volatilized, the prepared Y2O3 / SiO2 / Al2O3 / ethanol slurry was vertically and directly sprayed on the surface of the sample using the same process parameters.

[0075] (4) coating sintering: the sample after spraying was placed in a 40°C air oven for drying for 24 h to remove residual anhydrous ethanol solvent. The dried sample was placed in a gas pressure sintering furnace, and was kept at 1400°C under a N2 atmosphere of 0.25 MPa for 30 min. The specific temperature rising / rising process was as follows: the temperature rising rate below 1000°C was 10°C / min, the temperature rising / rising rate from 1000°C to 1400°C was 5°C / min, the temperature rising rate from 1000°C to 800°C was 10°C / min, and the temperature was cooled below 800°C with the furnace.

[0076] It was determined that the Y2Si2O7 / Yb2Si2O7 / Er2Si2O7 gradient coating prepared in this embodiment reduced the water absorption rate of the material by 97.1%, and the high temperature resistance grade reached 1200°C, and could withstand thermal shock impact of 1200°C→room temperature, and no peeling, cracking, etc. was observed on the coating, and the coating was firmly combined with the substrate.

[0077] Example 5

[0078] The gradient ceramic coating was composed of a porous Sialon ceramic substrate and a Y2Si2O7 / Yb2Si2O7 / Lu2Si2O7 coating coated on the surface of the substrate.

[0079] The Y2Si2O7 / Yb2Si2O7 / Lu2Si2O7 gradient coating was prepared on the surface of the porous Sialon ceramic substrate, including the following steps:

[0080] (1) substrate pretreatment: a porous Sialon ceramic substrate with a porosity of 40% was selected, the surface thereof was sequentially polished to be flat using 400 mesh, 800 mesh, 1000 mesh, 1200 mesh, and 1500 mesh sandpaper, and then the substrate was ultrasonically cleaned for half an hour using anhydrous ethanol solvent and was placed in an oven for drying for 24 h under a 60°C air atmosphere;

[0081] (2) Configuration of spraying slurry: micron-sized Lu2Si2O7 powder, Yb2Si2O7 powder, Y2Si2O7 powder are selected as raw materials for building multi-layer ceramic coating, which are mixed with anhydrous ethanol respectively, with solid phase mass ratio of 25%. Use agate balls to mix in agate ball mill for 24h, rotation speed of 300r / min.

[0082] Mix Y2O3, SiO2, Al2O3 powder in a molar ratio of 1.5:6:4, then suspend in anhydrous ethanol solvent, solid phase mass ratio of 20%, use agate balls to mix in agate ball mill for 24h, rotation speed of 300r / min.

[0083] (3) Slurry spraying: Lu2Si2O7 / ethanol slurry, Yb2Si2O7 / ethanol slurry, Y2Si2O7 / ethanol slurry prepared are respectively loaded into air pressure atomization spray gun with nozzle diameter of 0.5cm, air pressure of 0.7MPa is maintained during spraying, spray gun moving rate is 20cm / s, spray gun is vertically opposite to sample surface, spraying distance is 20cm, each kind of slurry is sprayed on the surface of the substrate for 4 times.

[0084] After the anhydrous ethanol solvent volatilizes, the prepared Y2O3 / SiO2 / Al2O3 / ethanol slurry is vertically sprayed on the sample surface with the same process parameters.

[0085] (4) Coating sintering: the sample after spraying is placed in a 40℃ air oven for drying for 24h to remove residual anhydrous ethanol solvent. The dried sample is placed in a gas pressure sintering furnace, and is kept at 1300℃ in N2 atmosphere of 0.25MPa for 30min. The specific heating / cooling process is as follows: the heating rate below 1000℃ is 10℃ / min, the heating / cooling rate between 1000℃ and 1300℃ is 5℃ / min, the cooling rate between 1000℃ and 800℃ is 10℃ / min, and the cooling rate below 800℃ is random.

[0086] It is determined that the Y2Si2O7 / Yb2Si2O7 / Lu2Si2O7 gradient coating prepared in this embodiment reduces the water absorption rate of the material by 94.5%, and the high temperature resistance grade reaches 1200℃, can withstand 1200℃→room temperature thermal shock impact, and no peeling, cracking, etc. is observed on the coating, and the coating is firmly combined with the substrate.

[0087] Comparative Example 1

[0088] The difference between Comparative Example 1 and Example 1 is that the ceramic coating is composed of a porous Si3N4 ceramic substrate and a Y2Si2O7 layer coated on the surface thereof, and in step (4), the temperature is kept at 1350℃ in N2 atmosphere for 30min, and the rest of the steps and conditions are the same as those of Example 1.

[0089] The Y2Si2O7 coating prepared by Comparative Example 1 (1350℃ for 30 min) reduces the water absorption of the material by about 93.0%, but the high-temperature resistance grade is poor, and after experiencing a thermal shock of 1200℃→room temperature, micro-cracks are detected in the coating, the water absorption of the coating rapidly increases by 6 times, and the waterproof performance of the coating deteriorates sharply.

[0090] Comparative Example 2

[0091] Comparative Example 2 differs from Example 1 in that the ceramic coating is composed of a porous Si3N4 ceramic substrate and a Y2Si2O7 layer coated on the surface thereof, and in step (4), the temperature is 1400℃ in a N2 atmosphere for 30 min, and the remaining steps and conditions are the same as in Example 1.

[0092] The Y2Si2O7 coating prepared by Comparative Example 2 (1400℃ for 30 min) reduces the water absorption of the material by about 93.3%, but the high-temperature resistance grade is poor, and after experiencing a thermal shock of 1200℃→room temperature, micro-cracks are detected in the coating, the water absorption of the coating rapidly increases by 7 times, and the waterproof performance of the coating deteriorates sharply.

[0093] Comparative Example 3

[0094] Comparative Example 1 differs from Example 1 in that the ceramic coating is composed of a porous Si3N4 ceramic substrate and a Y2Si2O7 layer coated on the surface thereof, and in step (4), the temperature is 1450℃ in a N2 atmosphere for 30 min, and the remaining steps and conditions are the same as in Example 1.

[0095] The Y2Si2O7 coating prepared by Comparative Example 3 (1450℃ for 30 min) reduces the water absorption of the material by about 94.0%, but the high-temperature resistance grade is poor, and after experiencing a thermal shock of 1200℃→room temperature, micro-cracks are detected in the coating, the water absorption of the coating rapidly increases by 8 times, and the waterproof performance of the coating deteriorates sharply.

[0096] The gradient ceramic coating prepared in Example 1 is uniform and dense, with a thickness of about 50-200μm, and can withstand a thermal shock of 1200℃→room temperature, and no significant change in micro-morphology is detected before and after the thermal shock. The relevant test results are as follows:

[0097] Figure 2 The macro-morphology of the gradient ceramic coating of Example 1 shows that water droplets can stay on the surface of the coating material without penetrating, indicating good waterproof performance. After testing, the water absorption of the material after the coating is prepared is only 2.7%;

[0098] Figure 3 The micro-morphology of the gradient ceramic coating of Example 1 shows that the prepared multi-layer gradient coating has no micro-cracks or other defects on the surface and cross-section, and the structure is complete.

[0099] Figure 4 The micro-morphology of the gradient ceramic coating of Example 1 after thermal shock of 1200°C→room temperature can be seen from the figures, the coating surface and cross-section have no micro-cracks and other defects, the microstructure of the coating after one thermal shock is complete, and the water absorption of the coating after thermal shock is about 4.1%.

[0100] The coatings prepared in Comparative Examples 1, 2 and 3 cannot withstand thermal shock of 1200°C→room temperature, and obvious cracks are detected after thermal shock. The relevant test results are as follows:

[0101] Figure 5 The micro-morphology of the ceramic coating of Comparative Example 1 after thermal shock of 1200°C→room temperature.

[0102] Figure 6 The micro-morphology of the ceramic coating of Comparative Example 2 after thermal shock of 1200°C→room temperature.

[0103] Figure 7 The micro-morphology of the ceramic coating of Comparative Example 3 after thermal shock of 1200°C→room temperature. As can be seen from Comparative Examples 1-3, when the coating is prepared using only one silicate, i.e. Y2Si2O7, the thermal shock resistance of the coating is poor, and the coating cracks after one thermal shock, the water absorption sharply increases, and the coating fails.

[0104] It should be noted that when the present application claims involve numerical ranges, both endpoints of each numerical range and any number between the two endpoints can be selected. In order to prevent repetition, the present application describes preferred embodiments.

[0105] Although preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to these embodiments once they know the basic inventive concept. Therefore, the appended claims are intended to include the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0106] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A dense, thermoshock-resistant gradient ceramic coating, characterized in that, The gradient ceramic coating is composed of a porous silicon-based ceramic substrate and a dense ceramic coating coated on the surface of the substrate; The dense ceramic coating is a multilayer structure, and the difference between the thermal expansion coefficients of each layer of the dense ceramic coating from the innermost layer to the surface of the dense ceramic coating is less than 10%, and the Young's modulus decreases layer by layer to form the gradient ceramic coating; The preparation method of the dense thermal shock-resistant gradient ceramic coating comprises the following steps: (1) Polishing treatment of the porous ceramic substrate: grinding the surface to be flat, then cleaning with anhydrous ethanol solvent and drying; (2) Preparation of the spraying slurry: micron-sized RE2Si2O7 powder is mixed with anhydrous ethanol, the solid phase accounts for 20-30% of the total mass, ball milling for 24-30 hours to prepare RE2Si2O7 / ethanol slurry; wherein RE is any three of Y, Yb, Er, Lu, Sm and Sc; The mixture powder of SiO2, Al2O3 and RE2O3 is mixed with anhydrous ethanol, the solid phase accounts for 20-30% of the total mass, ball milling for 24-30 hours to prepare RE2O3 / SiO2 / Al2O3 / ethanol suspension slurry; (3) Spraying of the slurry: the RE2Si2O7 / ethanol slurry prepared in step (2) with the highest Young's modulus is sprayed on the surface of the porous ceramic substrate, and the anhydrous ethanol solvent volatilizes during the spraying process, and the RE2Si2O7 solid phase powder is deposited on the surface of the substrate; repeat the step, and deposit the remaining RE2Si2O7 solid phase powder in the order of decreasing Young's modulus; The RE2O3 / SiO2 / Al2O3 / ethanol slurry prepared in step (2) is sprayed on the surface of the outer layer of RE2Si2O7 solid phase powder layer to form the outermost layer of RE2O3 / SiO2 / Al2O3 mixture; (4) Sintering of the coating: after the spraying is completed, the residual anhydrous ethanol solvent is removed by drying, and then the dried coating is sintered at 1300-1500℃ and 0.25MPa in N2 atmosphere for 15-60min.

2. The dense, thermoshock-resistant gradient ceramic coating of claim 1, wherein, The porosity of the porous ceramic substrate is 20-60%.

3. The dense, thermoshock-resistant gradient ceramic coating of claim 1, wherein, In step (1), 400 mesh, 800 mesh, 1000 mesh, 1200 mesh and 1500 mesh sandpaper is used for grinding the surface to be flat, and the drying is performed at 60-80℃ in air atmosphere for more than 24h.

4. The dense, thermoshock-resistant gradient ceramic coating of claim 1, wherein, In step (2), RE is any three of Y, Yb, Er, Lu, Sm and Sc.

5. The dense, thermoshock-resistant gradient ceramic coating of claim 1, wherein, In step (2), the volume ratio of agate grinding balls to RE2Si2O7 powder is 1-3:1, and the volume ratio of agate grinding balls to mixture powder is 1-3:

1.

6. The dense, thermoshock-resistant gradient ceramic coating of claim 1, wherein, In step (2), the molar ratio of RE2O3:SiO2:Al2O3 in the mixture powder is 1-2:5-10:3-5.

7. The dense, thermoshock-resistant gradient ceramic coating of claim 1, wherein, In step (3), an air pressure atomization spray gun is used for spraying, the air pressure atomization spray gun uses a gravity type spray gun, the nozzle diameter is 0.5cm, the air pressure during spraying is 0.7MPa, the spray gun moving speed is 15-25cm / s, the spray gun is perpendicular to the surface of the sample, and the spraying distance is 15-25cm.

8. The dense, thermoshock-resistant gradient ceramic coating of claim 1, wherein, The heating rate of sintering in step (4) is 10°C / min below 1000°C and 5°C / min above 1000°C. The heating rate of sintering in step (4) is 10°C / min below 1000°C and 5°C / min above 1000°C.

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