Integrally-formed environmental barrier coating with high bonding strength and preparation method thereof

Abstract

The invention discloses an integrally-formed environmental barrier coating with high bonding strength and a preparation method thereof.The preparation method comprises the steps that firstly, a fiber prefabricated part is subjected to interface phase preparation, a certain amount of carbon-rich ceramic matrix is introduced, the carbon-rich ceramic matrix is controlled to have certain density and porosity, then ytterbium silicate and the like are used as environmental barrier coating materials, and the carbon-rich ceramic matrix is prepared. A coating with a certain thickness is prepared on the treated surface of the composite material by adopting a plasma spraying method, and finally, the coating and the composite material are subjected to siliconizing together to introduce a silicon carbide ceramic matrix, so that the density of the composite material is further increased, and finally, an integrally formed composite material / environmental barrier coating finished product is obtained. The environmental barrier coating prepared through the method is high in bonding strength and good in thermal shock resistance, the preparation procedure of a bonding layer is omitted, and the environmental barrier coating higher in reliability, higher in service temperature and longer in service life can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of high-performance environmental barrier coatings, and particularly to an integrated formed environmental barrier coating with high bonding strength and a preparation method thereof applied to the corrosion protection field of silicon-based non-oxide ceramic matrix composites such as SiC f / SiC. Technical Background

[0002] With the increasing urgency of the demand for developing high-performance aero-engines in various countries, the key performance indicators such as the thrust, thrust-to-weight ratio, and fuel efficiency of the engines are continuously improved, which all require the working temperature of the aero-engines to be continuously increased. And the increase in the working temperature brings higher requirements for the temperature resistance performance of materials. The materials of traditional engine hot-end components mostly use various superalloys, supplemented by complex cooling air duct designs and thermal barrier coatings with heat insulation functions. However, after decades of development, the temperature resistance performance of the alloy materials themselves has approached the design limit, becoming the most important factor restricting the turbine inlet temperature of aero-engines.

[0003] Novel high-temperature ceramic matrix composites represented by continuous silicon carbide fiber-reinforced silicon carbide ceramic matrix composites (SiC f / SiC) have much better high-temperature resistance performance than alloys and are recognized as transformative new materials that can replace traditional alloy materials and lead the development of the next generation of high-performance aero-engines and gas turbines. In addition to the high-temperature resistance ability exceeding 1200 °C, SiC f / SiC also has significant advantages such as low density, oxidation resistance, corrosion resistance, high strength, high modulus, and creep resistance. However, silicon carbide ceramics have the problem of water-oxygen corrosion in the high-temperature water vapor environment of aero-engine gas, and silicon carbide will be continuously corroded to generate volatile Si(OH) 4 etc., resulting in material loss, performance degradation, and even component failure. The existence of water-oxygen corrosion causes the service life of SiC f / SiC to be much lower than expected, becoming the key problem restricting the application of SiC f / SiC.

[0004] An effective measure to solve the water-oxygen corrosion problem is the environmental barrier coating technology. The environmental barrier coating is a layer or multiple layers of high-temperature resistant coatings with a protective effect formed on the surface of the composite material by means of spraying, chemical vapor deposition, etc. The environmental barrier coating can form a physical barrier between the gas environment rich in water vapor and the composite material, thereby effectively blocking the erosion and damage of the external corrosion medium to the composite material substrate. Therefore, the selection of the material of the environmental barrier coating is the key to achieving the above goal. Since the end of the last century, materials such as mullite, yttria-stabilized zirconia (YSZ), and calcium magnesium aluminum silicate composite ceramics (BSAS) have been successively used for environmental coatings. At present, ytterbium pyrosilicate (Yb 2 Si2 O 7 ) represented rare earth silicate materials have become the most advantageous environmental barrier coating materials due to their excellent high-temperature stability and good thermal physical property matching.

[0005] Along with the development of environmental barrier coating materials, the development of the bond coat has also occurred. Generally speaking, ceramic matrix composites and environmental barrier coatings are two phases with different physical and chemical properties. Even if their thermal physical properties are close, the wettability of the ceramic coating on the surface of the composite material is usually not good and the bonding force is weak. To solve this problem, the bond coat is introduced. As the transition region between the ceramic top coat and the composite substrate, the bond coat plays an important role in effectively bonding the two. Therefore, the basic structure of the current environmental barrier coating is actually a structure of composite material / bond coat / ceramic top coat, with clear interfaces between the layers, and the bond coat has become an important part of the environmental barrier coating system. The bond coat material paired with rare earth silicate materials is mainly silicon (Si). Silicon has good affinity with rare earth silicate and SiC f / SiC, so it has become the most commonly used bond coat material at present. Like the ceramic top coat, there are also many preparation methods for the bond coat. However, no matter which specific preparation technology is adopted, the preparation of the current environmental barrier coating follows the order of composite material - bond coat - ceramic top coat to be prepared and formed in sequence.

[0006] The bond coat solves the problem of insufficient bonding force between the coating and the substrate. However, the use of the bond coat has also brought new problems. On the one hand, the melting point of silicon is much lower than that of rare earth silicate and silicon carbide. Limited by this, the actual service temperature of the comprehensive system composed of the entire composite material and the environmental barrier coating is restricted, and the advantage of high-temperature resistance cannot be fully exerted. On the other hand, even at the current service temperature, the stability of silicon is poor, and there are relatively serious phase change problems in the thermally grown silica formed by the oxidation of silicon during thermal cycling, resulting in cracks easily occurring between the bond coat and the top coat, thereby reducing the coating stability and providing a channel for the entry of corrosive media. A large number of studies have shown that the spalling and failure of environmental barrier coatings are many due to the first failure of the bond coat, resulting in the loss of stable support of the ceramic top coat and failure. Summary of the Invention

[0007] To solve the technical problems that the existing environmental barrier coating system has limited bonding strength with the composite substrate and is prone to premature failure due to bond coat damage, the present invention provides an integrally formed environmental barrier coating with high bonding strength and its preparation method. The environmental barrier coating provided by the present invention removes the traditional silicon bond coat in the structural design, breaks through the inherent mode of step-by-step preparation and forming of the conventional environmental barrier coating, realizes the integrally formed of the composite material and its coating, and at the same time the prepared coating has higher bonding strength with the composite substrate.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A preparation method of an integrated environmental barrier coating with high bonding strength, comprising the following steps:

[0010] Step 1: Prepare an interfacial phase for the fiber preform and introduce a silicon carbide ceramic matrix to obtain a semi-dense composite material; the density of the obtained semi-dense composite material is 1.82 - 2.10 g / cm 3 , and the porosity is 20.5 - 24.4%;

[0011] Step 2: Ball mill, granulate, and screen the raw materials for preparing the environmental barrier coating to obtain sprayable powder; wherein, a binder with a mass fraction of 2.5 - 5% is added during the granulation process;

[0012] Step 3: Prepare an environmental barrier coating on the surface of the semi-dense composite material obtained in Step 1 with the sprayable powder obtained in Step 2 to obtain a semi-dense composite material with a coating;

[0013] Step 4: Integrally introduce a silicon carbide matrix into the semi-dense composite material with a coating obtained in Step 3, namely, the described integrated environmental barrier coating with high bonding strength is prepared, and the overall density of the composite material at the end of the preparation is 2.45 - 2.75 g / cm 3 .

[0014] Further, the specific methods for preparing the interfacial phase for the fiber preform and introducing the silicon carbide ceramic matrix in Step 1, and for integrally introducing the silicon carbide matrix in Step 4 are all chemical vapor infiltration method (CVI), precursor infiltration and pyrolysis method (PIP), or reaction melt infiltration method (RMI).

[0015] Further, in Step 1 or Step 4, if the chemical vapor infiltration method is used, the reaction temperature is 1000 - 1150 °C, the carrier gas flow rate is 200 - 350 mL / min, the reaction zone pressure is 0.85 - 1.25 MPa, and the reaction duration is 35 - 50 h;

[0016] If the precursor infiltration and pyrolysis method is used, the precursor curing temperature is 150 - 200 °C, the curing holding time is 4 - 6 h, the precursor pyrolysis temperature is 1050 - 1250 °C, the pyrolysis holding time is 2 - 3.5 h, and the number of cycles is 3 - 5 times;

[0017] If the reaction melt infiltration method is used, the reaction temperature is 1550 - 1700 °C, and the holding time is 1 - 2.5 h.

[0018] Further, in Step 2, the raw materials for preparing the environmental barrier coating are ytterbium pyrosilicate and / or ytterbium monosilicate powder.

[0019] Further, in step two, the binder is polyvinyl alcohol or gum arabic.

[0020] Further, in step two, the method for granulating the pulverized powder after ball milling is centrifugal spray granulation, and the particle size of the granulated pulverized powder is 15 - 65 μm.

[0021] Further, before step three, it also includes surface treatment of the semi - dense composite material obtained in step one, specifically: surface cleaning, degreasing, and sandblasting.

[0022] Further, in step three, the sprayable pulverized powder obtained in step two is used to prepare an environmental barrier coating on the surface of the semi - dense composite material obtained in step one. The methods used are atmospheric plasma spraying, chemical vapor deposition, sol - gel method, or plasma spraying - physical vapor deposition method. In particular, when using the atmospheric plasma spraying method, the main gas flow rate is 25 - 38 L / min, the secondary gas flow rate is 3.2 - 5.1 L / min, the working current is 350 - 450 A, and the spraying distance is 85 - 130 mm.

[0023] Further, in step three, the open porosity of the obtained coating is 7.5 - 15%; the coating thickness is 200 - 300 μm.

[0024] The present invention also provides an integrally formed environmental barrier coating with high bonding strength, which is prepared by the above - mentioned preparation method.

[0025] The beneficial effects of the present invention are as follows:

[0026] When preparing environmental barrier coatings using traditional methods, the preparation of the bond coat is an important step, ensuring a firm bond between the coating and the composite material. However, the currently mainstream silicon bond coat has problems such as low melting point, easy formation of TGO, and high intrinsic brittleness, which often become the weak part leading to premature spalling or even failure of the environmental barrier coating, and also restrict the performance of the coating and the composite material itself. The present invention changes the traditional mode of independent molding of the composite material and its coating in sequence during the preparation of the environmental barrier coating. By utilizing the characteristics of gradual densification and molding of the composite material, the preparation processes of the composite material and the environmental barrier coating are overlapped, realizing the integrated molding of the two, that is, the composite material and its environmental barrier coating are prepared simultaneously. The greatest advantage of using this integrated molding lies in that there is not only mechanical bonding but also partial chemical bonding between the surface of the coating and the composite material during the preparation process, resulting in a very high bonding strength between the finally prepared coating and the composite material and good thermal shock resistance. In addition, the environmental barrier coating prepared by the method provided by the present invention eliminates the preparation of the bond coat, shortens the coating preparation process, reduces the heterogeneous interfaces in the system, avoids problems such as TGO generated by the bond coat, and reduces the potential hazards during the service of the coating. The bonding strength between the plasma spray coating prepared by this method and the surface of the composite material exceeds 20 MPa, and it can withstand more than 600 thermal shock cycles without cracking or spalling between room temperature and 1300 °C.

[0027] Specifically, in the traditional process of preparing environmental barrier coatings, the composite material - bond coat - top coat are formed in sequence, which results in obvious heterogeneous interfaces between different parts. The materials on both sides of the interface have significant differences in physical and chemical properties. Therefore, under the extreme service conditions of thermal - mechanical - oxygen coupling faced by environmental barrier coatings, these heterogeneous interfaces, as the discontinuities of structure and performance, are natural weak parts and often the source of coating damage or even failure. In addition, although the bond coat plays an adhesive role between the top coat and the composite material, the bonding of these heterogeneous interfaces still mostly relies on physical bonding and mechanical bonding of van der Waals forces, and there are a large number of unbonded voids, which leads to the still limited bonding strength of the coating. The coating prepared by the method of the present invention is carried out before the composite material is completely formed. Then, the coating and the semi - finished composite material are subjected to silicon infiltration together. Silicon reacts with the carbon - rich matrix in the composite material to obtain a denser silicon carbide matrix, which grows continuously and finally is tightly connected to the coating to achieve integral forming. Therefore, the bonding between the coating of the present invention and the substrate is not only achieved instantaneously by thermal spraying, but also accompanied throughout the entire time domain of the growth process of the silicon carbide matrix in the composite material. The voids between the coating prepared in this way and the composite material are greatly reduced, and the bond coat is omitted. The interface between the coating and the composite material is no longer a continuous heterogeneous interface, but a discontinuous, interpenetrating structure where you are in me and I am in you, with a strong mechanical interlocking and pinning effect. On the other hand, during the process of silicon infiltration reacting chemically with the carbon - rich matrix and growing, a metallurgical bond and a chemical bond can be further formed between the coating and the matrix, further enhancing the bonding strength between the coating and the matrix. The characteristics of high bonding strength and few heterogeneous interfaces enable the coating to maintain excellent stability during thermal shock cycling.

[0028] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The following will refer to the accompanying drawings to further elaborate on the present invention in detail. Brief Description of the Drawings

[0029] From the following detailed description of the embodiments of the present invention in conjunction with the accompanying drawings, these and / or other aspects and advantages of the present invention will become clearer and easier to understand, where:

[0030] Figure 1 is the macroscopic morphology of the integrally formed environmental barrier coating prepared in Example 1 of the present invention during thermal shock;

[0031] Figure 2 is the electron microscope image of the integrally formed environmental barrier coating prepared in Example 1 of the present invention, where Figure 2 (a) is the overall cross - sectional morphology of the integrally formed coating prepared with a SiC f / SiC composite material as the substrate; (b) is the detailed morphology of the interface bonding region between the integrally formed coating and the composite material;

[0032] Figure 3 Weight change curve of the integrally formed environmental barrier coating prepared in Example 1 of the present invention during thermal shock;

[0033] Figure 4 Bond strength test data of the integrally formed environmental barrier coating prepared in Example 1 of the present invention;

[0034] Figure 5 XRD pattern of the integrally formed environmental barrier coating prepared in Comparative Example 1 of the present invention. Detailed implementation manners

[0035] In order to enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners. However, the content of the present invention is not limited to the following examples. For those not specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0036] The present invention provides a method for preparing an integrally formed environmental barrier coating with high bond strength, which specifically includes the following steps:

[0037] S1. Semi-densification of the composite material: Prepare a certain amount of silicon carbide ceramic matrix in the fiber preform woven according to the required size and shape to obtain a semi-dense composite material with a lower density and a higher porosity;

[0038] S2. Surface treatment of the composite material: Perform surface cleaning, degreasing, and sandblasting on the semi-dense composite material component obtained in S1;

[0039] S3. Preparation of coating raw materials: Ball mill, granulate, and screen the raw material powder used to prepare the environmental barrier coating to obtain a sprayable powder with a particle size distribution within a certain range;

[0040] S4. Preparation of the environmental barrier coating: Use the powder obtained in S3 to prepare an environmental barrier coating on the surface of the composite material obtained in S2 to obtain a semi-dense composite material with a coating;

[0041] S5. Integral forming: Integrally introduce a silicon carbide matrix into the semi-dense composite material component with a coating obtained in S4, further increase the density, reduce the porosity, and densify it until it meets the use requirements, that is, the integrally formed environmental barrier coating with high bond strength described in the present invention is prepared.

[0042] Further, the specific methods for preparing the interface phase and introducing the silicon carbide ceramic matrix to the fiber preform in step S1, and for integrally introducing the silicon carbide matrix in step S4 can both be chemical vapor infiltration (CVI), precursor infiltration and pyrolysis (PIP), or reaction melt infiltration (RMI).

[0043] Further, in step S1 and step S4, if the CVI method is used, the optional reaction temperature is 1000 - 1150 °C, the carrier gas flow rate is 200 - 350 mL / min, the reaction zone pressure is 0.85 - 1.25 MPa, and the reaction duration is 35 - 50 h.

[0044] If the PIP method is used, the precursor curing temperature is 150 - 200 °C, the curing holding time is 4 - 6 h, the precursor pyrolysis temperature is 1050 - 1250 °C, the pyrolysis holding time is 2 - 3.5 h, and the number of cycles is 3 - 5 times.

[0045] If the RMI method is used, the reaction temperature is 1550 - 1700 °C, and the holding time is 1 - 2.5 h.

[0046] Further, the density of the semi-dense composite material obtained in step S1 is generally 1.82 - 2.10 g / cm 3 , and the porosity is 20.5 - 24.4%. The methods for obtaining the above density and porosity are the Archimedes drainage method.

[0047] Further, for the surface sandblasting treatment of the semi-dense composite material in step S2, corundum sand or silicon carbide sand can be used, and the sandblasting pressure is 0.4 - 0.8 MPa.

[0048] Further, the environmental barrier coating material used in step S3 is ytterbium pyrosilicate (Yb 2 Si 2 O 7) , ytterbium monosilicate (Yb 2 SiO 5 ), or a mixture of ytterbium pyrosilicate / ytterbium monosilicate powders; the above raw materials can be directly purchased as commercial powder products or synthesized independently.

[0049] Further, the granulation method for the ball-milled powder in step S3 is centrifugal spray granulation, and the particle size of the granulated powder is 40 ± 25 μm.

[0050] Further, when granulating the powder in step S3, a binder with a mass fraction of 2.5 - 5% needs to be added. Optionally, the binder can be polyvinyl alcohol or gum arabic.

[0051] Further, the environmental barrier coating in step S4 can be prepared by atmospheric plasma spraying, chemical vapor deposition, sol-gel method, plasma spraying-physical vapor deposition, etc. When using the atmospheric plasma spraying method, the main gas flow rate is 25-38 L / min, the secondary gas flow rate is 3.2-5.1 L / min, the working current is 350-450 A, and the spraying distance is 85-130 mm.

[0052] Further, the open porosity of the coating prepared in step S4 is 7.5-15%; the coating thickness is 200-300 μm.

[0053] The present invention will be explained and described below in conjunction with specific embodiments.

[0054] Example 1

[0055] This example provides a preparation method for an integrated environmental barrier coating with high bonding strength, including the following steps:

[0056] S1. Use the CVI method to prepare a silicon carbide ceramic matrix in a silicon carbide fiber preform woven into a certain shape and size, where the reaction temperature is 1100 °C, the carrier gas flow rate is 300 mL / min, the reaction zone pressure is 1.00 MPa, and the reaction duration is 40 h to obtain a semi-dense composite material with a density of 1.91 g / cm 3 , and the porosity is 21.2%;

[0057] S2. After cleaning and degreasing the surface of the semi-dense composite material obtained in S1 that needs to be coated, use corundum sand to perform sandblasting roughening under a pressure of 0.6 MPa;

[0058] S3. Ball-mill the purchased commercial ytterbium pyrosilicate powder at a rotation speed of 400 rpm for 10 h to obtain a fine powder with a powder particle size of 1-6 μm; use a centrifugal spray dryer to granulate the fine powder, and at the same time add a polyvinyl alcohol binder with a mass ratio of 3.5%, and pass the prepared powder through a 200-mesh sieve to obtain granulated powder; the granulated powder particle size is 30-46 μm;

[0059] S4. Use the atmospheric plasma spraying method to prepare a coating on the surface of the semi-dense composite material obtained in S2. Feed the granulated powder obtained in S3 into the spraying equipment, control the main gas flow rate during spraying to be 30 L / min, the secondary gas flow rate to be 4.5 L / min, the working current to be 400 A, and the spraying distance to be 120 mm; the prepared coating thickness is 250 μm, and the open porosity is 10.5% to obtain a semi-dense composite material with a coating;

[0060] S5. Introduce a silicon carbide ceramic matrix into the coated semi-dense composite material obtained in S4 by the RMI method for integral densification, where the reaction temperature is 1600 °C and the holding time is 2 h, and finally obtain a finished composite material component of an integrally formed environmental barrier coating with a density of about 2.60 g / cm 3 ³.

[0061] For the integrally formed coating sample in this example, the coating bonding strength is tested by the tensile method according to the HB5476-1991 standard. The sample is subjected to thermal shock testing between room temperature and 1300 °C. Each thermal shock cycle includes holding at 1300 °C for 10 min and air cooling to room temperature for 5 min.

[0062] The macroscopic and microscopic morphologies of the integrally formed environmental barrier coating obtained by the above method are as shown in Figure 1 and Figure 2 . It can be seen from Figure 1 and Figure 2 that the coating and the matrix are well bonded. After the sample undergoes 690 thermal shock cycles, there are no cracks or spalling on the surface layer of the environmental barrier coating, and there is no obvious change in the composite material matrix. It can be seen from Figure 3 that during the thermal shock process of the above sample, the mass is stable and the change range is very small. After the sample undergoes 690 thermal shock cycles, the weight gain rate or weight loss rate is less than 0.5%. It can be seen from Figure 4 that the environmental barrier coating prepared in this example has a very high bonding strength with the composite material, all of which are above 20 MPa, and the average value exceeds 25 MPa. It can be seen from Figure 5 that the coating phase of this example is ytterbium pyrosilicate and silica formed by the oxidation of silicon carbide, and the stability is good.

[0063] Example 2

[0064] This example provides a preparation method for an integrally formed environmental barrier coating with high bonding strength, including the following steps:

[0065] S1. Prepare a ceramic matrix in a silicon carbide fiber preform woven into a certain shape and size by the PIP method, where the precursor curing temperature is 150 °C and the curing holding time is 5 h; the precursor pyrolysis temperature is 1200 °C and the pyrolysis holding time is 3 h, and a total of 4 cycles are carried out. Obtain a semi-dense composite material sample with a density of 1.82 g / cm 3 ³ and a porosity of 24.4%;

[0066] S2. Clean and degrease the surface of the semi-dense composite material sample obtained in S1 that needs to be coated, and then carry out sandblasting roughening with silicon carbide sand under a pressure of 0.5 MPa;

[0067] S3. Ball mill the purchased commercial ytterbium pyrosilicate powder at a rotational speed of 300 rpm for 12 h to obtain fine powder with a particle size of 1 - 8 μm; granulate the fine powder by centrifugal spray method, and simultaneously add polyvinyl alcohol with a mass ratio of 2.5% as a binder; sieve the prepared powder through a 200-mesh sieve to obtain granulated powder with a particle size of 25 - 57 μm;

[0068] S4. Prepare a coating on the surface of the semi-dense composite material obtained in S2 by atmospheric plasma spraying. Feed the granulated powder obtained in S3 into the spraying equipment, control the main gas flow rate during spraying to be 25 L / min, the secondary gas flow rate to be 3.2 L / min, the working current to be 350 A, and the spraying distance to be 85 mm; the thickness of the prepared coating is 200 μm, and the open porosity is 8.8%, obtaining a semi-dense composite material with a coating;

[0069] S5. Introduce and integrally densify the silicon carbide ceramic matrix into the semi-dense composite material with a coating obtained in S4 by the PIP method (the process parameters are the same as those in S1), conduct 6 cycles, and take out to obtain a finished composite material of an integrally formed environmental barrier coating with an overall density of 2.45 g / cm 3 ³.

[0070] The average bonding strength of the integrally formed environmental barrier coating obtained in this example is 24.3 MPa by tensile testing, and the coating shows no damage after 650 thermal shock cycles under the same conditions.

[0071] Example 3

[0072] This example provides a preparation method for an integrally formed environmental barrier coating with high bonding strength, including the following steps:

[0073] S1. Use the RMI method to prepare a ceramic matrix in a silicon carbide fiber preform woven into a certain shape and size, where the reaction temperature is 1650 °C and the heat preservation time is 2 h to obtain a semi-dense composite material sample with a density of 2.10 g / cm 3 ³ and a porosity of 20.5%;

[0074] S2. Clean and degrease the surface of the semi-dense composite material obtained in S1 that needs to be coated, and then perform sandblasting roughening with silicon carbide sand under a pressure of 0.4 MPa;

[0075] S3. Ball mill the purchased commercial ytterbium pyrosilicate powder at a rotational speed of 450 rpm for 8 h to obtain fine powder with a particle size range of 3 - 9 μm; granulate the fine powder by centrifugal spray method, and simultaneously add polyvinyl alcohol with a mass ratio of 5% as a binder; sieve the prepared powder through a 200-mesh sieve to obtain granulated powder with a particle size of 32 - 58 μm;

[0076] S4. Prepare a coating on the surface of the semi-dense composite material obtained in S2 by using the atmospheric plasma spraying method. Feed the granulated powder obtained in S3 into the spraying equipment, and control the main gas flow rate during spraying to be 35 L / min, the secondary gas flow rate to be 5.1 L / min, the working current to be 450 A, and the spraying distance to be 130 mm; prepare a coating with a thickness of 300 μm and an open porosity of 14.2% to obtain a semi-dense composite material with a coating.

[0077] S5. Adopt the RMI method, control the reaction temperature to be 1650 °C, and the holding time to be 2.5 h. Introduce a silicon carbide ceramic matrix into the semi-dense composite material with a coating obtained in S4 for integral densification, and take out to obtain a finished composite material of an integrated forming environmental barrier coating with a bulk density of 2.75 g / cm 3 .

[0078] The average bonding strength of the integrated forming environmental barrier coating obtained in this example is 23.6 MPa after testing, and the coating is undamaged after 600 thermal shock cycles under the same conditions.

[0079] Comparative Example 1

[0080] This comparative example is an environmental barrier coating system containing a silicon bonding layer prepared by using a traditional method. The basic steps are as follows. Unless otherwise specified, the conditions are the same as those in Example 1:

[0081] S1. Adopt the PIP method, control the precursor curing temperature to be 200 °C, the curing holding time to be 6 h, the precursor pyrolysis temperature to be 1200 °C, and the pyrolysis holding time to be 3.5 h, and conduct 8 cycles; prepare a SiC 3 / SiC composite material with a density of 2.45 g / cm f , and roughen the surface where the coating needs to be prepared with corundum sandblasting.

[0082] S2. Use the plasma spraying method to first prepare a silicon bonding layer on the surface of the composite material obtained in S1. The parameters for preparing the silicon bonding layer are: the main gas flow rate is 35 L / min, the secondary gas flow rate is 5.0 L / min, the working current is 500 A, and the spraying distance is 120 mm; the thickness of the prepared bonding layer is 45 μm.

[0083] S3. Adopt the atmospheric plasma spraying method, and use ytterbium metasilicate granulated powder to prepare an environmental barrier coating surface layer on the surface of the composite material with a bonding layer prepared in S2.

[0084] The environmental barrier coating sample obtained in this example was tested, and its bonding strength was only 7.8 - 11.6 MPa. After 355 thermal shock cycles under the same conditions, peeling and warping failures occurred on the coating. In this example, the environmental barrier coating was prepared by sequentially forming a traditional composite material - bonding layer - surface layer. In S1, a substrate that had undergone a complete densification process was obtained. Therefore, there was no integrated densification process like step S5 in Example 1 after the coating was prepared. As a result, the final coatings had only weak physical bonding, with many heterogeneous interfaces and interface voids, leading to limited coating bonding strength. Moreover, the oxides formed by the oxidation of the bonding layer were prone to phase changes during the thermal cycling process, which further caused the poor thermal shock resistance of the coatings in this example.

[0085] Comparative Example 2

[0086] In this comparative example, except that in S1, the CVI method was used with a reaction temperature of 1200 °C, a carrier gas flow rate of 400 mL / min, a reaction zone pressure of 1.3 MPa, and a reaction duration of 80 h, resulting in a semi-dense composite material density of 2.32 g / cm 3 , and the porosity was approximately 14.2%, all other conditions were the same as in Example 1.

[0087] The environmental barrier coating obtained in this example was tested, and its average bonding strength was 12.2 MPa. In this comparative example, due to the use of a larger flow rate, pressure, and longer reaction time in S1, the composite material had a relatively high density when the coating was prepared by plasma spraying later. As a result, during the integrated forming process in S5, the growth of both silicon infiltration and silicon carbide matrix was greatly restricted, and the matrix and the coating could not be fully combined, and the voids between them were not completely filled, resulting in a low final coating bonding strength.

[0088] Comparative Example 3

[0089] In this comparative example, except that in S5, the RMI method was used with a reaction temperature of 1500 °C and a holding time of 1 h, resulting in a finished composite material density of 2.35 g / cm 3 otherwise, all other conditions were the same as in Example 1.

[0090] The environmental barrier coating obtained in this example was tested, and its average bonding strength was 14.3 MPa. In this comparative example, the RMI reaction temperature in step S5 was too low, resulting in an insufficient integrated densification process. While the overall density of the sample was low, the silicon carbide matrix did not grow sufficiently to form a tight and firm bond with the coating, resulting in a coating bonding strength lower than expected.

[0091] In summary, compared with the environmentally-barrier coatings prepared by traditional step-by-step methods, the integrally formed environmentally-barrier coating with high bonding strength proposed in this application eliminates the bonding layer that would bring weaknesses. At the same time, the coating still has a very high bonding strength, and the stability and thermal shock resistance of the coating are greatly improved, which is conducive to solving the problems of short lifespan and low service temperature of environmentally-barrier coatings. In addition, compared with traditional methods, the coating preparation method proposed in this application is more compact, the time cost and economic cost are both reduced, and the feasibility is high.

[0092] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the technical content disclosed above, or modify it into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing an integrated environmental barrier coating with high bonding strength, characterized in that: The following steps are involved: Step 1: Prepare the interface phase of the fiber preform and introduce the silicon carbide ceramic matrix to obtain a semi-dense composite material; the density of the obtained semi-dense composite material is 1.82-2.10 g / cm 3 , porosity is 20.5~24.4%; Step 2: ball milling, granulating and sieving the raw materials for preparing the environmental barrier coating to obtain a sprayable powder; wherein a binder with a mass fraction of 2.5 to 5% is added during the granulation process; Step 3: using the sprayable powder obtained in step 2 to prepare an environmental barrier coating on the surface of the semi-dense composite material obtained in step 1, so as to obtain a semi-dense composite material with a coating; Step 4: The semi-dense composite material with coating obtained in step 3 is integrated into a silicon carbide matrix to obtain the aforementioned high bonding strength integrated molding environmental barrier coating. When the preparation is completed, the overall density of the composite material is 2.45-2.75 g / cm 3 .

2. The method for preparing a high bonding strength integrated environmental barrier coating according to claim 1, characterized in that: The specific methods of preparing the interface phase of the fiber preform and introducing the silicon carbide ceramic matrix in step one and integrally introducing the silicon carbide matrix in step four are both chemical vapor infiltration, precursor impregnation and cracking method or reactive melt infiltration method.

3. The method for preparing a high bonding strength integrated environmental barrier coating according to claim 2, characterized in that: In step 1 or step 4, if chemical vapor infiltration is used, the reaction temperature is 1000-1150° C., the carrier gas flow rate is 200-350 mL / min, the pressure in the reaction zone is 0.85-1.25 MPa, and the reaction time is 35-50 h; If the precursor impregnation pyrolysis method is used, the precursor curing temperature is 150-200°C, the curing holding time is 4-6 hours, the precursor pyrolysis temperature is 1050-1250°C, the pyrolysis holding time is 2-3.5 hours, and the number of cycles is 3-5 times; If the reaction infiltration method is used, the reaction temperature is 1550-1700°C and the holding time is 1-2.5h.

4. The method for preparing a high bonding strength integrated environmental barrier coating according to claim 1, characterized in that: In step 2, the raw material used to prepare the environmental barrier coating is ytterbium disilicate and / or ytterbium monosilicate powder.

5. The method for preparing a high bonding strength integrated environmental barrier coating according to claim 1, characterized in that: In step 2, the binder is polyvinyl alcohol or gum arabic.

6. The method for preparing a high bonding strength integrated environmental barrier coating according to claim 1, characterized in that: In step 2, the powder after ball milling is granulated by centrifugal spraying, and the particle size of the powder after granulation is 15 to 65 μm.

7. The method for preparing a high bonding strength integrated environmental barrier coating according to claim 1, characterized in that: Before step three, the method further includes performing surface treatment on the semi-dense composite material obtained in step one, specifically: surface cleaning, degreasing, and sandblasting.

8. The method for preparing a high bonding strength integrated environmental barrier coating according to claim 1, characterized in that: In step three, the sprayable powder obtained in step two is used to prepare an environmental barrier coating on the surface of the semi-dense composite material obtained in step one, and the method used is atmospheric plasma spraying, chemical vapor deposition, sol-gel method, or plasma spray-physical vapor deposition method.

9. The method for preparing a high bonding strength integrated environmental barrier coating according to claim 1, characterized in that: In step 3, the open porosity of the obtained coating is 7.5-15%; the thickness of the coating is 200-300 μm.

10. An integrated environmental barrier coating with high bonding strength, characterized in that: The method is prepared by the preparation method described in any one of claims 1 to 9.

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