Bonding layer of low-cracking SiC / SiC composite material and preparation method of bonding layer

Abstract

The invention discloses a bonding layer of a low-cracking SiC / SiC composite material and a preparation method of the bonding layer. A plurality of Si-HfO2 bonding layers with different HfO2 contents are prepared on the surface of a ceramic-based composite (SiC / SiC) substrate by adopting a vacuum plasma spraying technology, so that thermal stress mismatch caused by mismatching of coefficient of thermal expansion (CTE) can be effectively reduced, and stripping between the bonding layers and the SiC / SiC composite substrate is avoided; the Si-HfO2 bonding layer with high HfO2 content reacts at a high temperature to generate HfSiO4 which can hinder crack growth and prevent oxygen from permeating into the SiC / SiC composite material matrix to be oxidized and corroded, so that the SiC / SiC composite material matrix can stably serve in a high-temperature environment. The bonding layer disclosed by the invention can bear a 1300 DEG C water oxygen corrosion test, and has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of material preparation, and relates to a bonding layer of a low-cracking SiC / SiC composite material and a preparation method thereof. Background Art

[0002] Due to its advantages such as high strength, high specific modulus, high temperature resistance and good toughness, SiC / SiC composite material has become a new type of material for high-temperature components of aeroengines. However, in an extreme high-temperature environment, SiC / SiC composite material is extremely prone to high-temperature oxidation failure, so a coating needs to be added to its surface for protection. Thermal / environmental barrier coating (T / EBC), as a protective material with excellent high-temperature oxidation resistance and molten salt corrosion resistance, has been gradually applied to SiC / SiC composite material to improve its high-temperature oxidation resistance and molten salt corrosion resistance. However, due to the difference in thermal expansion coefficient between the thermal / environmental barrier coating (T / EBC) and the SiC / SiC composite material, a bonding layer between the two is required to achieve good bonding. The pure Si bonding layer has good adhesion with the SiC / SiC matrix and is widely used in the coating system of SiC / SiC composite material. However, the melting point of Si is only 1410 °C and it is also easy to oxidize and phase change at high temperature, resulting in a thermal mismatch phenomenon. In recent years, the National Aeronautics and Space Administration (NASA) of the United States has proposed to incorporate HfO2 into pure Si to increase its melting point, and at the same time, the obtained Si-HfO2 composite bonding layer reduces the thermal mismatch between the thermal / environmental barrier coating and the SiC / SiC matrix; on the other hand, the Si-HfO2 bonding layer can hinder the infiltration of oxygen and prevent the SiC / SiC matrix from being oxidized at high temperature.

[0003] Vacuum plasma spraying technology is a technology that heats powdery or granular materials to a molten or semi-molten state and then sprays them onto the surface of a substrate through a high-speed gas flow to form a coating. Since vacuum plasma spraying coatings usually have strong adhesion, wear resistance, corrosion resistance, high temperature resistance and good thermal insulation, they are widely used in the fields of aerospace, automotive, machinery, metallurgy, energy, etc. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a bonding layer of a low-cracking SiC / SiC composite material and a preparation method thereof. Preparing a thermal / environmental barrier coating on the SiC / SiC composite material can effectively improve its corrosion resistance and high-temperature oxidation resistance. The Si-HfO2 gradient bonding layer, as a thermal expansion coefficient transition layer, alleviates the thermal mismatch stress between the surface coating and the matrix, which causes the coating to fall off. And HfSiO4 generated by the oxidation reaction of Si and HfO2 at high temperature can pin the growth of cracks and hinder the crack propagation of the coating.

[0005] To solve the problems of the prior art, the technical solution adopted by the present invention is as follows:

[0006] A low-cracking SiC / SiC composite material, wherein the bonding layer is a Si-HfO2 bonding layer with a gradient structure and is located above the SiC / SiC base layer. The thickness of the Si-HfO2 bonding layer is 60-80 μm, and it sequentially includes a Si-HfO2 layer one, a Si-HfO2 layer two, and a Si-HfO2 layer three prepared from Si-HfO2 composite powders with HfO2 incorporation amounts of 5% mol, 15% mol, and 25% mol respectively, and the thickness of each layer is 20-30 μm.

[0007] The preparation method of the bonding layer of the above low-cracking SiC / SiC composite material includes the following steps:

[0008] Step S1: Weigh Si powder and HfO2 powder according to the molar ratios of 95:5, 85:15, and 75:25 respectively into a ball milling tank and conduct ball milling in a planetary ball mill.

[0009] Step S2: Put the ball-milled powder into an oven for drying, and then spray granulate to obtain spherical powder for use in spraying.

[0010] Step S3: Prepare a SiC / SiC substrate and pre-treat the SiC / SiC substrate.

[0011] Step S4: Before spraying, preheat the pre-treated SiC / SiC substrate, set the parameters of the vacuum plasma spraying equipment, and sequentially spray a Si-HfO2 layer one, a Si-HfO2 layer two, and a Si-HfO2 layer three with HfO2 incorporation amounts of 5% mol, 15% mol, and 25% mol on the pre-treated SiC / SiC substrate. After spraying, cool it to room temperature in a vacuum environment, then introduce air, and open the vacuum chamber to take out the sample.

[0012] As an improvement, the purity of the pure Si powder is 99.99%, the particle size is 1-3 μm, the purity of the pure HfO2 powder is 99.99%, and the particle size is 3-5 μm.

[0013] As an improvement, the ball milling speed in step S1 is 460-500 rpm, and the time is 12-15 hours.

[0014] As an improvement, the oven temperature in step S2 is 80-90 °C, the ventilation drying time is 5-8 hours, and the particle size of the spherical powder obtained by spray granulation is 10-20 μm.

[0015] As an improvement, in step S3, the size of the SiC / SiC substrate is 20 mm × 20 mm × 5 mm, and the pretreatment method is as follows: Corundum sand (Al2O3) with a particle size between 120 and 240 meshes is used, the sandblasting pressure is 0.4 - 0.8 MPa, the distance between the nozzle and the substrate is 10 - 20 cm, the angle between the nozzle and the substrate surface is 45 - 90°, and sandblasting is carried out at a constant speed; the sandblasting duration is 60 - 90 S to make the roughness of the substrate reach Ra = 5 - 10 μm.

[0016] As an improvement, in step S4, the vacuum degree reaches 10 -3 -10 -5 mbar to prevent the reaction of Si powder with O2 to form SiO2. The voltage of the plasma spraying equipment is 50 - 60 V, the current is 400 - 500 A, and the power range is 20 - 30 kW; the spraying distance is 80 - 120 mm, the powder feeding gas is argon (Ar), the flow rate is 5 - 10 L / min, and the powder feeding speed is 5 - 10 g / min.

[0017] As an improvement, the preheating temperature is 150 - 300 °C to prevent the substrate from deforming or the coating from cracking due to thermal shock during spraying.

[0018] Beneficial effects:

[0019] For the bonding layer of the low-cracking SiC / SiC composite material and its preparation method of the present invention, the incorporation of HfO2 improves the high-temperature resistance of the bonding layer, alleviates the thermal mismatch stress between the composite coating and the SiC / SiC substrate, reduces the tendency of the bonding layer to crack at high temperatures, hinders the infiltration of oxygen along the cracks, and improves the service life of the entire coating system. Description of the drawings

[0020] Figure 1 It is a schematic structural diagram of the SiC / SiC composite material with a surface coating and a bonding layer prepared in Example 1 of the present invention;

[0021] Figure 2 It is the thermal expansion coefficients of each layer of the Si-HfO2 gradient bonding layer, the SiC / SiC substrate, and the surface coating in the low-cracking SiC / SiC composite material prepared in Example 1 of the present invention;

[0022] Figure 3 It is the SEM image of the surface morphology of the low-cracking SiC / SiC composite material prepared in Example 1 after 100 hours of water-oxygen corrosion experiment at 1300 °C;

[0023] Figure 4 It is the SEM image of the surface morphology of the sample obtained in Example 2 after 100 hours of water-oxygen corrosion experiment at 1300 °C. Specific implementation manners

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] The experimental methods in the embodiments of the present invention are all normal operations in the laboratory. The test materials used in the embodiments of the present invention are all available in conventional reagent stores.

[0026] Example 1

[0027] An adhesive layer of a low-cracking SiC / SiC composite material, the adhesive layer is a Si-HfO2 adhesive layer with a gradient structure, and is located on the SiC / SiC substrate layer. The thickness of the Si-HfO2 adhesive layer is 60 μm, and successively includes a Si-HfO2 layer, a Si-HfO2 layer and a Si-HfO2 layer prepared from Si-HfO2 composite powders with HfO2 incorporation amounts of 5% mol, 15% mol, and 25% mol respectively, and the thickness of each layer is 20 μm.

[0028] The preparation method of the adhesive layer of the above-mentioned low-cracking SiC / SiC composite material includes the following steps:

[0029] Step S1: Weigh Si powder and HfO2 powder in a ball milling tank according to the molar ratios of 95:5, 85:15, and 75:25 respectively, and perform ball milling in a planetary ball mill at a speed of 500 rpm for 12 hours. Among them, the purity of the pure Si powder is 99.99%, the particle size is 1 μm, the purity of the pure HfO2 powder is 99.99%, and the particle size is 3 μm;

[0030] Step S2: Put the ball-milled powder into an oven and dry it at 80 °C for 5 hours, and then spray granulate to obtain spherical powder with a particle size of 10 μm for spraying standby;

[0031] Step S3: Prepare a SiC / SiC substrate and pre-treat the SiC / SiC substrate. Among them, the size of the SiC / SiC substrate is 20 mm × 20 mm × 5 mm, and the pre-treatment method is: use corundum sand (Al2O3) with a particle size between 120 meshes, the sandblasting pressure is 0.5 MPa, the distance between the nozzle and the substrate is 15 cm, the angle between the nozzle and the substrate surface is 45°, and perform sandblasting treatment at a constant speed; the sandblasting duration is 60 S, so that the roughness of the substrate is Ra = 5 μm;

[0032] Step S4: The SiC / SiC substrate needs to be preheated to 250°C before spraying to prevent substrate deformation or coating cracking caused by thermal shock during spraying. Set the parameters of the vacuum plasma spraying equipment, and successively spray Si-HfO2 layer one, Si-HfO2 layer two, and Si-HfO2 layer three with an HfO2 incorporation amount of 5% mol, 15% mol, and 25% mol on the SiC / SiC substrate. After spraying, cool it to room temperature in a vacuum environment, then introduce air and open the vacuum chamber to take out the sample. Among them, the vacuum degree reaches 10 - 5 mbar to prevent the reaction of Si powder with O2 to form SiO2. The voltage of the plasma spraying equipment is 50V, the current is 400A, and the power range is 20kW; the spraying distance is 100mm, the powder feeding gas is argon (Ar), the flow rate is 5L / min, and the powder feeding speed is 5g / min.

[0033] Comparative Example 1

[0034] A pure Si bonding layer is prepared by vacuum plasma spraying Si powder, and the coating thickness is 60μm.

[0035] The preparation method of the above pure Si coating includes the following steps:

[0036] Step S1: Take pure Si powder (purity is 99.99%, powder particle size is 1μm), and perform spray granulation to obtain spherical powder with a particle size of 10μm;

[0037] Step S2: Take a SiC / SiC substrate with a size of 20mm×20mm×5mm, select corundum sand (Al2O3) as the sandblasting medium, and set the particle size range to 120 mesh. To ensure the uniformity of the sandblasting effect and the required roughness of the substrate surface, set the sandblasting pressure range to 0.5MPa during sandblasting; the distance between the nozzle and the substrate surface needs to be kept within 15cm, and the nozzle forms a 45° angle with the substrate surface for sandblasting; during sandblasting, the sandblasting duration is controlled within 60 seconds to make the surface roughness Ra of the SiC / SiC substrate reach 5μm. To ensure that the surface quality meets the requirements, a uniform operation needs to be maintained during sandblasting; after sandblasting, use high-pressure air flow or ultrasonic cleaning method to ensure that there are no any residues on the surface;

[0038] Step S3: Set the parameters of the vacuum plasma spraying equipment and perform spraying work on the SiC / SiC substrate; first, run the vacuum equipment to pump vacuum, and use a molecular pump and a mechanical pump to pump gas jointly to make the initial vacuum degree reach 10 -5mbar to prevent the reaction of Si powder with O2 to form SiO2 at high temperatures; then set the process parameters of the plasma spraying equipment, including a voltage of 50V, a current of 400A, and a power range of 20kW; the spraying distance is 100mm, the powder feeding gas is argon (Ar) with a flow rate of 5L / min and a powder feeding speed of 5g / min; the substrate needs to be preheated before spraying, with a preheating temperature of 250°C, to prevent substrate deformation or coating cracking caused by thermal shock during spraying; after the sample is cooled to room temperature in a vacuum environment at the end of spraying, air is introduced, and the vacuum chamber is opened to take out the sample.

[0039] As Figure 1 shown, the thickness of the bonding layer with three different HfO2 doping amounts is 20 - 30μm, and the coating substrate is a SiC / SiC substrate.

[0040] As Figure 2 shown, the coefficient of thermal expansion (CTE) of pure Si and Si - HfO2 bonding layers with different amounts of HfO2 doping varying with temperature increases with the increase of HfO2 doping amount. The coefficient of thermal expansion of the SiC / SiC material is between 4.5 - 5.5×10 -6 K -1 , and the coefficient of thermal expansion of single / double ytterbium silicate is 6.5 - 7.5×10 -6 K -1 . The coefficient of thermal expansion of pure Si is very close to that of the SiC / SiC substrate, but there is a large gap with the coefficient of thermal expansion of the single / double ytterbium silicate on the coating surface layer. With the increase of HfO2 doping amount, the gap between the coefficient of thermal expansion of the Si - HfO2 bonding layer and that of the single / double ytterbium silicate on the coating surface layer is narrowing. The gap between the coefficient of thermal expansion of the Si - HfO2 bonding layer with 25%mol HfO2 doping amount and that of the single / double ytterbium silicate is the smallest. The thermal mismatch stress between the Si - HfO2 gradient bonding layer and the surface layer in a high - temperature environment is much smaller than that between the pure Si bonding layer and the surface layer. The Si - HfO2 bonding layer with a gradient structure can reduce the risk of coating spalling and improve the service life of the coating system.

[0041] Perform corrosion experiments on the materials prepared in Example 1 and Example 2. The test method is to simultaneously introduce water vapor and oxygen into a high - temperature tube furnace, with the ratio of water vapor to oxygen being 9:1. Deionized water is heated to generate water vapor at 130°C at a rate of 80μL / min through a water vapor generator. The temperature of the tube furnace is set at 1300°C and maintained for 100 hours, with a heating and cooling rate of 4°C / min.

[0042] As Figure 3As shown, after 100 hours of water-oxygen corrosion experiment at 1300 °C, there are no cracks and pores on the surface of the Si-HfO2 bonding layer with a gradient structure, indicating that the Si-HfO2 bonding layer with a gradient structure can effectively prevent oxygen from penetrating into the matrix of the ceramic matrix composite (SiC / SiC) in a high-temperature environment.

[0043] As Figure 4 shown, there are very obvious cracks on the surface of the pure Si bonding layer after 100 hours of water-oxygen corrosion experiment at 1300 °C. In a high-temperature environment, oxygen can penetrate from the cracks of the pure Si bonding layer to oxidize and corrode the matrix of the ceramic matrix composite (SiC / SiC), which is not conducive to improving the service life of the entire coating system.

[0044] In summary, for the Si-HfO2 bonding layer with a gradient structure in the present invention, the difference in the coefficient of thermal expansion from that of the SiC / SiC matrix and the single / double ytterbium silicate on the surface layer of the coating is very small, which can reduce the thermal mismatch stress between different positions of the coating system and lower the risk of coating spalling. Moreover, the Si-HfO2 bonding layer with a gradient structure performs excellently in the water-oxygen environment test experiment, with no cracks or pores on the surface, and can effectively prevent oxygen from penetrating to oxidize and corrode the ceramic matrix composite matrix at high temperature, thereby improving the service life of the coating system and the ceramic matrix composite.

Claims

1. A bond coat for a low-cracking SiC / SiC composite material, characterized in that, The bonding layer is a Si-HfO2 bonding layer with a gradient structure and is located on the SiC / SiC substrate layer. The thickness of the Si-HfO2 bonding layer is 60-80 μm, and successively includes a Si-HfO2 layer 1, a Si-HfO2 layer 2, and a Si-HfO2 layer 3 prepared from Si-HfO2 composite powders with HfO2 doping amounts of 5% mol, 15% mol, and 25% mol respectively, and the thickness of each layer is 20-30 μm.

2. The preparation method of the bonding layer of the low-cracking SiC / SiC composite material according to claim 1, characterized in that, It includes the following steps: Step S1: Weigh Si powder and HfO2 powder in a ball milling tank according to the molar ratios of 95:5, 85:15, and 75:25 respectively, and carry out ball milling in a planetary ball mill. Step S2: Put the ball-milled powder into an oven for drying, and then spray granulate to obtain spherical powder for spraying standby. Step S3: Prepare a SiC / SiC substrate and perform pretreatment on the SiC / SiC substrate. Step S4: Before spraying, the pretreated SiC / SiC substrate needs to be preheated. Set the parameters of the vacuum plasma spraying equipment, and successively spray the Si-HfO2 layer 1, the Si-HfO2 layer 2, and the Si-HfO2 layer 3 with HfO2 doping amounts of 5% mol, 15% mol, and 25% mol on the pretreated SiC / SiC substrate. After spraying, cool it to room temperature in a vacuum environment, then introduce air, and open the vacuum chamber to take out the sample.

3. The preparation method of the bonding layer of the low-cracking SiC / SiC composite material according to claim 2, characterized in that, In step S1, the purity of the pure Si powder is 99.99%, the particle size is 1-3 μm, the purity of the pure HfO2 powder is 99.99%, and the particle size is 3-5 μm.

4. The preparation method of the bonding layer of the low-cracking SiC / SiC composite material according to claim 2, characterized in that, In step S1, the ball milling speed is 460-500 rpm, and the time is 12-15 hours.

5. The preparation method of the bonding layer of the low-cracking SiC / SiC composite material according to claim 2, wherein, In step S2, the particle size of the spherical powder obtained by spray granulation is 10-20 μm.

6. The preparation method of the bonding layer of the low-cracking SiC / SiC composite material according to claim 2, characterized in that In step S3, the size of the SiC / SiC substrate is 20 mm × 20 mm × 5 mm, and the pretreatment method is as follows: Use corundum sand with a particle size between 120-240 mesh, the sandblasting pressure is 0.4-0.8 MPa, the distance between the nozzle and the substrate is 10-20 cm, the angle between the nozzle and the substrate surface is 45-90°, the sandblasting duration is 60-90 s, and perform sandblasting treatment at a constant speed; make the surface roughness of the substrate reach Ra = 5-10 μm.

7. The preparation method of the bonding layer of the low-cracking SiC / SiC composite material according to claim 2, characterized in that, In step S4, the vacuum reaches 10 -3 -10 -5 mbar, the voltage of the plasma spraying equipment is 50 - 60V, the current is 400 - 500A, and the power range is 20 - 30kW; the spraying distance is 80 - 120mm, the powder feeding gas is argon, the flow rate is 5 - 10L / min, and the powder feeding speed is 5 - 10g / min.

8. The preparation method of the bonding layer of the low-cracking SiC / SiC composite material according to claim 2, wherein, In step S4, the preheating temperature is 150-300 °C.

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