A thermal shock resistant gradient composite coating on the surface of a silicon carbide-based composite material and its preparation method

Abstract

This invention discloses a thermal shock resistant gradient composite coating on the surface of a silicon carbide-based composite material and its preparation method, relating to the field of high-temperature protective coating technology. The method includes sequentially preparing n layers of silicon-doped tantalate aSi-b(DTa) on a fiber-reinforced silicon carbide-based composite material matrix. 1‑x Si 2x O4 forms a thermal shock resistant gradient composite coating system, wherein a = 1–0, b = 0–1, and x = 0.01–0.09; the thickness of each silicon-doped tantalate layer increases sequentially from the inside out, while the porosity decreases sequentially. Due to the intrinsic properties of the coating material and the gradient coating structure design, the gradient composite coating of this invention possesses stronger fracture toughness, higher bonding strength, lower thermal diffusion rate, and a more suitable coefficient of thermal expansion, giving it superior thermal shock resistance and significantly improving the service life of silicon carbide-based composite materials. It is an extremely advanced high-temperature protective coating for silicon carbide-based composite material surfaces.

Description

Technical Field

[0001] This invention relates to the field of high-temperature protective coating technology, and in particular to a thermal shock resistant gradient composite coating on the surface of a silicon carbide-based composite material and its preparation method. Background Technology

[0002] Silicon carbide ceramics play a vital role in manufacturing due to their excellent properties such as high specific strength, high specific modulus, corrosion resistance, wear resistance, and oxidation resistance. However, the material failure caused by the low toughness of silicon carbide ceramics in service environments greatly limits their application range. Silicon carbide-based composite materials prepared by particle fiber reinforcement technology can compensate for the material's high-temperature toughness deficiency while retaining the original excellent properties, enabling them to be widely used in chemical energy, shipbuilding machinery, and aerospace fields.

[0003] However, silicon carbide-based composite materials often operate in environments with high temperatures, water, oxygen, and corrosive media. The SiO2 passivation layer on the surface and the internal carbon fibers are difficult to maintain for extended periods. Oxidation causes rapid loss of matrix elements, leading to damage to the surface structure and degradation of internal properties, ultimately resulting in composite material failure. The preparation of high-temperature protective coatings for silicon carbide-based composite materials is one of the optimal methods to address this problem. Therefore, research is needed on coating material preparation methods that offer advantages such as low preparation cost, simple preparation methods, and no damage to the matrix structure and properties, prompting the rapid development of this technology. However, the limitations of the intrinsic properties of traditional coating materials and the simplistic design of coating structures make it difficult to achieve a balance between bonding strength, thermal diffusion rate, fracture toughness, and suitable coefficient of thermal expansion in silicon carbide-based composite surface protective coating systems. The coatings often exhibit relatively poor thermal shock resistance, significantly reducing the service life of hot-end components in service environments. In view of the above, it is urgent to develop high-temperature and thermal shock resistant protective coating systems with excellent coating material performance and reasonable coating structure design for silicon carbide-based composite materials. Summary of the Invention

[0004] The main objective of this invention is to provide a thermal shock resistant gradient composite coating for the surface of silicon carbide-based composite materials and its preparation method. By optimizing the screening of coating powder materials and the design of coating structure, and by adopting an optimal preparation scheme, the invention comprehensively considers the coupling results of the performance of each functional layer, thereby solving the problems of low bonding strength, high thermal diffusivity, high thermal expansion coefficient, and low fracture toughness of traditional protective coatings for silicon carbide-based composite materials.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A thermal shock resistant gradient composite coating on the surface of a silicon carbide-based composite material, wherein the silicon carbide-based composite material is a fiber-reinforced silicon carbide-based composite material, and the thermal shock resistant gradient composite coating on the surface of the silicon carbide-based composite material uses the fiber-reinforced silicon carbide-based composite material as a matrix, and n layers of silicon-doped tantalate aSi-b(DTa) are sequentially prepared on the fiber-reinforced silicon carbide-based composite material matrix. 1-x Si 2x O4 forms a thermal shock resistant gradient composite coating system, where n = 5, a = 1 to 0, b = 0 to 1, and x = 0.01 to 0.09; the thickness of each silicon-doped tantalate layer increases sequentially from the inside to the outside, and the porosity decreases sequentially.

[0007] This thermal shock resistant gradient composite coating exhibits stable high-temperature performance, high bonding strength, low thermal diffusivity, high fracture toughness, and high thermal adaptability unique to gradient coatings. It demonstrates exceptional performance in thermal shock tests, significantly extending the service life of silicon carbide-based composite materials.

[0008] The second reinforcing phase of the fiber-reinforced silicon carbide-based composite material is one of carbon fiber, silicon carbide fiber, boron fiber, alumina fiber, aluminum silicate fiber, alumina whiskers, silicon carbide whiskers, and other dispersed reinforcing phases.

[0009] Preferably, the silicon-doped tantalate aSi-b(DTa) 1-x Si 2x In O4, D stands for Al.

[0010] Preferably, the thermal shock resistant gradient composite coating system consists of a Si layer, a...

[0011] 0.75Si-0.25(AlTa) 1-x Si 2x O4 layer, 0.5Si-0.5(AlTa) 1-x Si 2x O4 layer

[0012] 0.25Si-0.75(AlTa) 1-x Si 2x O4 layer, (AlTa) 1-x Si 2x O4 layer.

[0013] Preferably, the thicknesses of each silicon-doped tantalate layer are 20–30 μm, 30–40 μm, 40–50 μm, 50–60 μm, and 60–70 μm, respectively, and the total thickness of the coating system is 200–250 μm; the system has a higher internal stress tolerance and can better resist external impact stress.

[0014] Preferably, the porosity of each silicon-doped tantalate layer is 97-99%, 95-97%, 93-95%, 91-93%, and 89-91%, respectively, which provides a sufficient silicon source while having a higher thermal insulation gradient.

[0015] A method for preparing a thermal shock resistant gradient composite coating on the surface of a silicon carbide-based composite material includes the following steps:

[0016] (1) Powders in the thermal shock gradient composite coating system were prepared by spray granulation, and powders with uniform particle size were screened and the flowability of the powders was measured.

[0017] (2) The surface of the fiber-reinforced silicon carbide matrix composite material is pretreated to remove oil stains and roughen the matrix surface.

[0018] (3) A gradient composite coating system with thermal shock resistant gradient composite coating is prepared by vacuum plasma spraying on the surface of a pretreated fiber-reinforced silicon carbide matrix.

[0019] (4) Heat treatment was performed on the sprayed thermal shock resistant gradient composite coating system sample to remove residual stress inside the coating system.

[0020] Preferably, in step (1), the sprayed powder of the Si layer in the thermal shock resistant gradient composite coating system has a flowability of 25–40 s / 50 g and a particle size distribution of 18–25 μm; 0.75Si-0.25(AlTa) 1-x Si 2x O4 layer, 0.5Si-0.5(AlTa) 1- x Si 2x O4 layer, 0.25Si-0.75(AlTa) 1-x Si 2x The O4 layer mixed two-phase spray powder has a flowability of 30–45 s / 50 g and a particle size distribution of 23–58 μm; (AlTa) 1-x Si 2x The O4 layer has a powder flowability of 40–55 s / 50 g and a particle size distribution of 38–74 μm.

[0021] The powder screening adopts ultrasonic vibration sieving, with a vibration frequency of 30-45kHz, an excitation force of 450-500N, and a motor power of 0.75-1kw.

[0022] By adopting the above technical solution, the screening of powder for gradient composite coating is achieved, ensuring the uniformity and flowability of the powder during the spraying process.

[0023] Preferably, the pretreatment in step (2) is as follows: the surface of the fiber-reinforced silicon carbide matrix is ​​impacted with 70-80 mesh fine white corundum at 0.3 MPa and a 30° angle; the fiber-reinforced silicon carbide matrix is ​​then placed in acetone or anhydrous ethanol and ultrasonically cleaned for 10-15 minutes; and then dried in a vacuum oven at 80-110°C for 2-4 hours to obtain a degreased and destained fiber-reinforced silicon carbide matrix; the degreased and destained fiber-reinforced silicon carbide matrix is ​​then sandblasted with gravel, the gravel being 20-40 mesh coarse brown corundum, the sandblasting pressure being 0.5-0.75 MPa, the sandblasting distance being 50-150 mm, and the sandblasting angle being 70-90°.

[0024] By employing the above technical solution, the surface pretreatment of silicon carbide-based composite materials is completed, achieving surface cleanliness and roughness.

[0025] Preferably, the temperature of the vacuum plasma sprayed fiber-reinforced silicon carbide matrix in step (3) is maintained at 90–160°C.

[0026] The specific parameters of the vacuum plasma spraying gradient composite coating Si layer in step (3) are as follows: power supply 48-66kW, working current 480-550A, working voltage 100-120V, argon flow rate 2300-2700L / h, hydrogen flow rate 600-750L / h, powder feeding rate 250-400L / h, rotation speed 1.0-1.7r / s, and cooling temperature 50-70℃.

[0027] The 0.75Si-0.25(AlTa) gradient composite coating applied in step (3) by vacuum plasma spraying 1-x Si 2x O4 layer, 0.5Si-0.5(AlTa) 1-x Si 2x O4 layer, 0.25Si-0.75(AlTa) 1-x Si 2x The specific parameters for the O4 layer two-phase coating are as follows: power supply 28-66kW, operating current 350-550A, operating voltage 80-120V, argon flow rate 1800-2700L / h, hydrogen flow rate 450-750L / h, powder feeding rate 200-400L / h, rotation speed 0.8-1.7r / s, and cooling temperature 50-70℃.

[0028] The Si-(AlTa) gradient composite coating applied in step (3) by vacuum plasma spraying 1-x Si 2xThe specific parameters for the O4 coating are as follows: power supply 28-40kW, working current 350-450A, working voltage 80-90V, argon flow rate 1800-2100L / h, hydrogen flow rate 450-600L / h, powder feeding rate 200-250L / h, rotation speed 0.8-1.2r / s, and cooling temperature 50-70℃.

[0029] By employing the above technical solution, a gradient coating is applied to the surface of a pretreated substrate using vacuum plasma spraying, thereby suppressing the formation of oxides and precipitated phases during the spraying process.

[0030] Preferably, the vacuum degree during heat treatment in step (4) is 3.0 to 5.6 × 10⁻⁶. -3 The treatment time is 3-5 hours, with a pressure of 700-900℃.

[0031] By employing the above technical solution, heat treatment of the sprayed gradient composite coating is achieved, thereby removing residual stress within the coating system.

[0032] The beneficial effects of this invention are as follows:

[0033] 1. The Si-layered metallized silicon spraying powder of this invention possesses physicochemical properties and structure similar to silicon carbide-based composite materials. During thermal spraying, the interdiffusion of elements between this material and the substrate, along with excellent mechanical bonding, results in higher coating bonding strength. The Si layer, as a bonding layer for the silicon carbide-based composite matrix, is an excellent bonding material. Si layer, 0.75Si-0.25(AlTa) 1-x Si 2x O4 layer, 0.5Si-0.5(AlTa) 1-x Si 2x O4 layer, 0.25Si-0.75(AlTa) 1- x Si 2x O4 layer, (AlTa) 1-x Si 2x In the thermal shock resistant gradient composite coating system formed by the O4 layer, the material content of each functional layer changes in a gradient, and the composition of adjacent coatings is similar, with no obvious discontinuity in physicochemical properties. This is different from the weak bonding strength between traditional adhesive layers and ceramic layers. Therefore, there are no obvious weak bonding areas in the thermal shock resistant gradient composite coating system formed in this way.

[0034] 2. The tantalate ceramic powder of the present invention is selected from aluminum tantalate ceramic with a low coefficient of thermal expansion, and its high-temperature performance is further optimized by SiO2 doping to give it a lower thermal diffusion rate. At the same time, in order to meet the small compositional differences between layers, the coating system structure is designed with up to 5 functional layers. The interface structure is weakened by heating the substrate and heat treatment. However, the irregular lamellar structure, coating interface and dual-phase ceramic grain boundary formed by vacuum atmospheric plasma spraying used in the present invention still provide strong interface scattering, providing a large thermal insulation gradient for the substrate.

[0035] 3. The tantalate ceramic powder of the present invention has a slightly higher content than that of silicon carbide-based composite materials (4.5-5.5 W·kJ). -1 ·m -1 The coefficient of thermal expansion is reduced, and with the doping of Si, an element with a small ionic radius, the interatomic spacing is reduced, the interatomic interaction is improved, and the coefficient of thermal expansion is reduced. Furthermore, the gradient coating structure design allows the coefficient of thermal expansion of the coating system to transition slowly from the Si layer to the tantalate layer without obvious abrupt changes, and the coating system has excellent thermal compatibility with the substrate.

[0036] 4. The Si-(AlTa) of the present invention 1-x Si 2x O4 two-phase powder, with its optimized second-phase toughening and dispersion strengthening mechanism, exhibits lower SiO2 activity, higher fracture toughness, and higher hardness compared to traditional silicon carbide-based ceramic surface protective coating materials such as mullite and BSAS, and can provide a more stable internal environment for the matrix. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of the thermal shock resistant gradient composite coating of the present invention;

[0038] Figure 2 These are examples and comparative stress-strain curves of the thermal shock resistant gradient composite coating of the present invention, as well as cross-sectional views of the coating specimens used for bonding strength testing.

[0039] Figure 3 These are the thermal conductivity curves of the thermal shock resistant gradient composite coating embodiments and comparative examples of the present invention;

[0040] Figure 4 These are the fracture toughness curves of the thermal shock resistant gradient composite coating embodiments and comparative examples of the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0042] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0043] Example 1:

[0044] Si-(AlTa) was prepared on the surface of silicon carbide fiber-reinforced silicon carbide matrix composites. 0.99 Si 0.02 The O4 gradient composite coating was prepared according to the following steps:

[0045] (1) The powder obtained by spray granulation is placed in an ultrasonic vibrating sieve. The vibration frequency is set to 30kHz, the excitation force to 450N, the motor power to 0.75kw, and the four sieves are 180 mesh, 300 mesh, 400 mesh, and 500 mesh respectively. The particle size distribution of the Si sprayed powder is 18-25μm, and the Si-(AlTa) powder is... 0.99 Si 0.02 The O4 mixed spray powder has a particle size distribution of 23-58 μm, (AlTa) 0.99 Si 0.02 O4 ceramic spraying powder has a particle size distribution of 38-74μm;

[0046] (2) Weigh out Si powder and 0.75Si-0.25(AlTa) respectively. 0.99 Si 0.02 O4 powder, 0.5Si-0.5(AlTa) 0.99 Si 0.02 O4 powder, 0.25Si-0.75(AlTa) 0.99 Si 0.02 O4 powder, (AlTa) 0.99 Si 0.02 50g of O4 powder was poured into a calibrated Hall effect flow meter, and the time it took for the powder to flow was measured. The flowability of Si powder was 25s / 50g, and the flowability was 0.75Si-0.25(AlTa). 0.99 Si 0.02O4 powder flowability 30s / 50g, 0.5Si-0.5(AlTa) 0.99 Si 0.02 O4 powder flowability 33s / 50g, 0.25Si-0.75(AlTa) 0.99 Si 0.02 O4 powder flowability 37s / 50g, (AlTa) 0.99 Si 0.02 O4 powder flowability 40s / 50g.

[0047] (3) The surface of the silicon carbide-reinforced silicon carbide-based composite material was impacted with 70-mesh fine white corundum at 0.3 MPa and a 30° angle to reduce surface undulations and remove particulate debris. The matrix material was then placed in acetone and ultrasonically cleaned for 10 minutes, and then dried in a vacuum oven at 80°C for 2 hours. The cleaned matrix was then placed in a sandblasting device, using 20-mesh medium-coarse brown corundum as the sand for sandblasting, with a sandblasting pressure of 0.5 MPa, a sandblasting distance of 50 mm, and a sandblasting angle of 70°.

[0048] (4) The pretreated substrate is mounted on a spraying fixture, and the substrate temperature is maintained at 90-110℃ by heating equipment. Si-(AlTa) is then prepared by vacuum atmospheric plasma spraying. 0.99 Si 0.02 The O4 gradient composite coating, wherein the specific parameters of the Si layer are: power supply 48kW, operating current 480A, operating voltage 100V, argon flow rate 2300L / h, hydrogen flow rate 600L / h, powder feeding rate 250L / h, rotation speed 1.0r / s, cooling temperature 50℃; Si-(AlTa) 0.99 Si 0.02 The specific parameters for the O4 two-phase coating are as follows: power supply 28-48kW, operating current 350-480A, operating voltage 80-100V, argon flow rate 1800-2300L / h, hydrogen flow rate 450-600L / h, powder feeding rate 200-250L / h, rotation speed 0.8-1.0r / s, and cooling temperature 50℃; (AlTa) 0.99 Si 0.02 The specific parameters for the O4 coating are as follows: power supply 28kW, working current 350A, working voltage 80V, argon flow rate 1800L / h, hydrogen flow rate 450L / h, powder feeding rate 200L / h, rotation speed 0.8r / s, and cooling temperature 50℃.

[0049] (5) Spray-coated Si-(AlTa) 0.99 Si 0.02 The O4 gradient composite coating sample was placed in a vacuum oven for heat treatment. The specific heat treatment parameters were: vacuum degree 3.0*10. -3 Pa, heat treatment temperature 700℃, heat treatment time 3h.

[0050] The prepared gradient composite coating structure is as follows Figure 1 As shown.

[0051] Example 2:

[0052] The preparation process and coating parameters of this embodiment are the same as those of Example 1, except that the matrix material is a carbon fiber reinforced silicon carbide matrix composite material.

[0053] Example 3:

[0054] Si-(AlTa) was prepared on the surface of silicon carbide fiber-reinforced silicon carbide matrix composites. 0.98 Si 0.04 The O4 gradient composite coating is prepared according to the following steps:

[0055] (1) The powder obtained by spray granulation is placed in an ultrasonic vibrating sieve. The vibration frequency is set to 40kHz, the excitation force to 470N, the motor power to 0.8kw, and the four sieves are 180 mesh, 300 mesh, 400 mesh, and 500 mesh respectively. The particle size distribution of the Si sprayed powder is 18-25μm, and the Si-(AlTa) powder is... 0.98 Si 0.04 The O4 mixed spray powder has a particle size distribution of 23-58 μm, (AlTa) 0.98 Si 0.04 O4 ceramic spraying powder has a particle size distribution of 38-74μm.

[0056] (2) Weigh out Si powder and 0.75Si-0.25(AlTa) respectively. 0.98 Si 0.04 O4 powder, 0.5Si-0.5(AlTa) 0.98 Si 0.04 O4 powder, 0.25Si-0.75(AlTa) 0.98 Si 0.04 O4 powder, (AlTa) 0.98 Si 0.04 50g of O4 powder was poured into a calibrated Hall effect flow meter, and the time it took for the powder to flow was measured. The flowability of Si powder was 25s / 50g, and the flowability was 0.75Si-0.25(AlTa). 0.98 Si 0.04 O4 powder flowability 32s / 50g, 0.5Si-0.5(AlTa) 0.98 Si 0.04 O4 powder flowability 35s / 50g, 0.25Si-0.75(AlTa) 0.98 Si 0.04 O4 powder flowability 40s / 50g, (AlTa) 0.98 Si 0.04O4 powder flowability 45s / 50g.

[0057] (3) The surface of the silicon carbide-reinforced silicon carbide-based composite material was impacted with 70-mesh fine white corundum at 0.3 MPa and a 30° angle to reduce surface undulations and remove particulate debris. The matrix material was then placed in acetone and ultrasonically cleaned for 12 minutes, and then dried in a vacuum oven at 85°C for 3 hours. The cleaned matrix was then placed in a sandblasting device, using 30-mesh medium-coarse brown corundum as the sand for sandblasting, with a sandblasting pressure of 0.6 MPa, a sandblasting distance of 70 mm, and a sandblasting angle of 80°.

[0058] (4) The pretreated substrate is mounted on a spraying fixture, and the substrate temperature is maintained at 90-110℃ by heating equipment. Si-(AlTa) is then prepared by vacuum atmospheric plasma spraying. 0.98 Si 0.04 The O4 gradient composite coating, wherein the specific parameters of the Si layer are: power supply 55kW, operating current 500A, operating voltage 110V, argon flow rate 2400L / h, hydrogen flow rate 620L / h, powder feeding rate 300L / h, rotation speed 1.2r / s, cooling temperature 60℃; Si-(AlTa) 0.98 Si 0.04 The specific parameters for the O4 two-phase coating are as follows: power supply 34-55kW, operating current 400-500A, operating voltage 85-110V, argon flow rate 1900-2400L / h, hydrogen flow rate 550-620L / h, powder feeding rate 220-300L / h, rotation speed 1.0-1.2r / s, and cooling temperature 60℃; (AlTa) 0.98 Si 0.04 The specific parameters for the O4 coating are as follows: power supply 34kW, operating current 400A, operating voltage 85V, argon flow rate 1900L / h, hydrogen flow rate 550L / h, powder feeding rate 220L / h, rotation speed 1.0r / s, and cooling temperature 60℃.

[0059] (5) Spray-coated Si-(AlTa) 0.98 Si 0.04 The O4 gradient composite coating sample was placed in a vacuum oven for heat treatment. The specific heat treatment parameters were: vacuum degree 3.0*10. -3 Pa, heat treatment temperature 750℃, heat treatment time 4h.

[0060] Example 4:

[0061] The preparation process and coating parameters of this embodiment are the same as those of Example 3, except that the matrix material is a boron fiber reinforced silicon carbide matrix composite material.

[0062] Example 5:

[0063] Si-(AlTa) was prepared on the surface of silicon carbide fiber-reinforced silicon carbide matrix composites. 0.94 Si 0.12 The O4 gradient composite coating is prepared according to the following steps:

[0064] (1) The powder obtained by spray granulation is placed in an ultrasonic vibrating sieve. The vibration frequency is set to 40kHz, the excitation force to 470N, the motor power to 1kW, and the four sieves to be 180 mesh, 300 mesh, 400 mesh, and 500 mesh respectively. The particle size distribution of the Si sprayed powder is 18-25μm, and the Si-(AlTa) powder is... 0.94 Si 0.12 The O4 mixed spray powder has a particle size distribution of 23-58 μm, (AlTa) 0.94 Si 0.12 O4 ceramic spraying powder has a particle size distribution of 38-74μm.

[0065] (2) Weigh out Si powder and 0.75Si-0.25(AlTa) respectively. 0.94 Si 0.12 O4 powder, 0.5Si-0.5(AlTa) 0.94 Si 0.12 O4 powder, 0.25Si-0.75(AlTa) 0.94 Si 0.12 O4 powder, (AlTa) 0.94 Si 0.12 50g of O4 powder was poured into a calibrated Hall effect flow meter, and the time it took for the powder to flow was measured. The flowability of Si powder was 30s / 50g, 0.75Si-0.25(AlTa). 0.94 Si 0.12 O4 powder flowability 35s / 50g, 0.5Si-0.5(AlTa) 0.94 Si 0.12 O4 powder flowability 40s / 50g, 0.25Si-0.75(AlTa) 0.94 Si 0.12 O4 powder flowability 456s / 50g, (AlTa) 0.94 Si 0.12 O4 powder flowability 51s / 50g.

[0066] (3) The surface of the silicon carbide-reinforced silicon carbide-based composite material was impacted with 70-mesh fine white corundum at 0.3 MPa and a 30° angle to reduce surface undulations and remove particulate debris. The matrix material was then placed in anhydrous ethanol and ultrasonically cleaned for 15 minutes, and then dried in a vacuum oven at 100°C for 4 hours. The cleaned matrix was then placed in a sandblasting device, and medium-coarse brown corundum of 40 mesh was selected as the sandblasting gravel. The sandblasting pressure was 0.75 MPa, the sandblasting distance was 125 mm, and the sandblasting angle was 90°.

[0067] (4) The pretreated substrate is mounted on a spraying fixture, and the substrate temperature is maintained at 90-130℃ by heating equipment. Si-(AlTa) is then prepared by vacuum atmospheric plasma spraying. 0.94 Si 0.12 The O4 gradient composite coating, wherein the specific parameters of the Si layer are: power supply 66kW, operating current 550A, operating voltage 120V, argon flow rate 2700L / h, hydrogen flow rate 750L / h, powder feeding rate 400L / h, rotation speed 1.7r / s, cooling temperature 70℃; Si-(AlTa) 0.94 Si 0.12 The specific parameters for the O4 two-phase coating are as follows: power supply 40-66kW, operating current 450-550A, operating voltage 90-120V, argon flow rate 2100-2700L / h, hydrogen flow rate 600-750L / h, powder feeding rate 250-400L / h, rotation speed 1.2-1.7r / s, and cooling temperature 70℃; (AlTa) 0.94 Si 0.12 The specific parameters for the O4 coating are as follows: power supply 40kW, operating current 450A, operating voltage 90V, argon flow rate 2100L / h, hydrogen flow rate 600L / h, powder feeding rate 250L / h, rotation speed 1.2r / s, and cooling temperature 70℃.

[0068] (5) Spray-coated Si-(AlTa) 0.94 Si 0.12 The O4 gradient composite coating sample was placed in a vacuum oven for heat treatment. The specific heat treatment parameters were: vacuum degree 3.0*10. -3 Pa, heat treatment temperature 750℃, heat treatment time 4h.

[0069] Example 6:

[0070] The preparation process and coating parameters of this embodiment are the same as those of Embodiment 5, except that the matrix material is a boron fiber reinforced silicon carbide matrix composite material.

[0071] The coating structure density of Examples 1-6 is shown in Table 1.

[0072] Table 1

[0073]

[0074] The coating thicknesses of Examples 1-6 are shown in Table 2.

[0075] Table 2

[0076]

[0077] Comparative Example 1:

[0078] It has the same matrix material and preparation parameters as Example 1, the difference being that only the Si binder layer and (AlTa) are prepared. 0.99 Si 0.02 The O4 ceramic layer does not have a two-phase gradient composition or gradient structure.

[0079] Comparative Example 2:

[0080] It has the same substrate and coating powder as in Example 1, except that the gradient coating is prepared by atmospheric plasma spraying.

[0081] Comparative Example 3:

[0082] It has the same preparation process as Example 1, the difference being in the gradient coating material (AlTa). 0.99 Si 0.02 The O4 ceramic was replaced with 8YSZ ceramic.

[0083] Comparative Example 4:

[0084] It has the same matrix material and preparation parameters as Example 3, except that the sprayed coating sample did not undergo high-temperature heat treatment.

[0085] Comparative Example 5:

[0086] It has the same preparation process as Example 2, except that the overall thickness of the coating system reaches 500 μm.

[0087] Experiment Example 1 Performance Testing

[0088] (1) Combined strength test

[0089] Vertical tensile tests were conducted on 25mm diameter circular coated samples using a Model E45 universal testing machine. The tensile adhesive used was FM1000 thermosetting adhesive, which was preheated in an oven at low temperature and then heated to 200℃ for cross-linking and curing. Threaded pull heads were installed on both sides, and a level was used to calibrate the machine. The samples were clamped vertically in the universal testing machine fixtures, and the initial value was zeroed before the bond strength test was performed. The bond strength test results of the coatings obtained in Examples 1, 3, and 5, and Comparative Examples 1 and 2 are as follows: Figure 2 As shown.

[0090] Depend on Figure 2 It can be seen that the gradient coating prepared by the method described in this invention has excellent bonding strength (greater than 22 MPa); while Comparative Example 1 only prepared a Si bonding layer and (AlTa). 0.99 Si 0.02The O4 ceramic layer lacks a two-phase gradient composition and gradient structure, with significant abrupt changes in composition between layers, low interdiffusion of elements, and weak mechanical bonding, making it difficult to maintain high bonding strength. The gradient coating in Comparative Example 2 was prepared solely by atmospheric plasma spraying. Due to the low power and the large amount of oxygen involved in the preparation process, thermally grown oxides with high mechanical properties appeared between the Si components in the coating structure, resulting in excessively low coating bonding strength, which is difficult to meet service requirements.

[0091] (2) Thermal conductivity testing

[0092] The thermal conductivity of the prepared gradient coatings in Example 1 and Comparative Example 3 was measured using the flash method, and the results are as follows: Figure 3 As shown.

[0093] Depend on Figure 3 It can be seen that in Comparative Example 3, the gradient coating material (AlTa) 0.99 Si 0.02 Replacing O4 ceramic with 8YSZ ceramic resulted in a significantly higher coating thermal conductivity, while Si-(AlTa) was prepared on the surface of silicon carbide fiber-reinforced silicon carbide-based composite materials. 0.99 Si 0.02 The O4 gradient composite coating has a thermal conductivity of only 0.8 W·k at high temperatures. -1 ·m -1 The extremely low thermal conductivity can provide a higher thermal insulation gradient for the matrix, greatly improving the service life of silicon carbide-based composite materials.

[0094] (3) Fracture toughness testing

[0095] The hardness values ​​of the coatings in Examples 1, 2, and 3, and Comparative Examples 2, 3, and 4 were measured using the indentation method and a Vickers hardness tester. Each sample was tested five times, and the average value was taken. The fracture toughness of the coating was calculated using the following formula:

[0096]

[0097] In the formula:

[0098] Z—Empirical constant for square indentation, 0.018

[0099] HV – Vickers hardness

[0100] P — Load 2.942N

[0101] C—Average crack length

[0102] Test results are as follows Figure 4 As shown. By Figure 4It can be seen that Embodiments 1, 2, and 3 of the present invention have high fracture toughness, which is beneficial for the coating to resist greater stress. However, the fracture toughness of Comparative Examples 2, 3, and 4 is relatively low due to the growth of TGO structure, the intrinsic properties of coating materials, and the lack of heat treatment to remove internal stress, and only meets the performance range of traditional coatings.

[0103] (4) Thermal shock performance testing

[0104] Si-(AlTa) on the surface of silicon carbide-based composite materials 1-x Si 2x Examples 1-6 and Comparative Examples 1-5 of the O4 thermal shock resistant gradient composite coating were placed in a fully automatic thermal cycling device for cyclic heating at 1350°C and then quenched and cooled to room temperature. The number of thermal shocks that caused the coating failure was recorded, and the results are shown in Table 3.

[0105] Table 3

[0106]

[0107]

[0108] Comparing the test results, the surface of the silicon carbide-based composite material of the present invention exhibits Si-(AlTa) content. 1-x Si 2x The O4 thermal shock resistant gradient composite coating exhibits excellent thermal shock resistance. However, in the thermal shock test at 1350℃, the coating life of Comparative Examples 1-5 was only 30 cycles at most. This is because Comparative Example 4 has a preferred coating material and gradient structure, but the sprayed coating did not undergo heat treatment to transform the sprayed metastable phase and remove the stress concentration caused by rapid cooling. The other comparative examples all have defects in coating structure, coating material, and coating preparation method. The thermal shock test results also prove the necessity and irreplaceability of each step in the coating preparation method described in this invention.

[0109] In summary, the present invention provides a silicon carbide-based composite material with a Si-(AlTa) surface. 1-x Si 2x O4 thermal shock resistant gradient composite coating and its preparation method: The coating has stable high-temperature performance, high bonding strength, low thermal diffusivity, high fracture toughness, and high thermal adaptability unique to gradient coatings. It has excellent performance in thermal shock tests, overcomes the shortcomings of existing technologies, stably isolates silicon oxide-based composite ceramics from high-temperature oxygen-containing service environments, and greatly extends the service life of silicon carbide-based composite materials.

[0110] The specific embodiments of the invention have been described in detail above, but these are merely examples, and the invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications or substitutions to the invention are also within the scope of this invention. Therefore, all equivalent transformations, modifications, and improvements made without departing from the spirit and principles of this invention should be included within the scope of this invention.

Claims

1. A thermal shock resistant gradient composite coating on the surface of a silicon carbide-based composite material, wherein the silicon carbide-based composite material is a fiber-reinforced silicon carbide-based composite material, and the thermal shock resistant gradient composite coating on the surface of the silicon carbide-based composite material uses the fiber-reinforced silicon carbide-based composite material as a matrix, characterized in that: n layers of silicon-doped tantalate aSi-b(DTa) were sequentially prepared on a fiber-reinforced silicon carbide matrix using vacuum plasma spraying. 1-x Si 2x O4 forms a thermal shock resistant gradient composite coating system, and the sprayed thermal shock resistant gradient composite coating system sample is heat treated; where a=1~0, b=0~1, x=0.01~0.09; the thickness of each silicon doped tantalate layer increases sequentially from the inside to the outside, and the porosity decreases sequentially. The silicon-doped tantalate aSi-b(DTa) 1-x Si 2x In O4, D stands for Al; The thermal shock resistant gradient composite coating system consists of a Si layer, followed by a 0.75Si-0.25(AlTa) layer from the inside out. 1-x Si 2x O4 layer, 0.5Si-0.5(AlTa) 1-x Si 2x O4 layer, 0.25Si-0.75(AlTa) 1-x Si 2x O4 layer, (AlTa) 1-x Si 2x O4 layer.

2. The thermal shock resistant gradient composite coating on the surface of the silicon carbide-based composite material as described in claim 1, characterized in that, The thicknesses of each silicon-doped tantalate layer are 20–30 μm, 30–40 μm, 40–50 μm, 50–60 μm, and 60–70 μm, respectively, and the total thickness of the coating system is 200–250 μm.

3. The thermal shock resistant gradient composite coating on the surface of the silicon carbide-based composite material as described in claim 2, characterized in that, The porosities of the silicon-doped tantalate layers are 97–99%, 95–97%, 93–95%, 91–93%, and 89–91%, respectively.

4. A method for preparing a thermal shock resistant gradient composite coating on the surface of a silicon carbide-based composite material, wherein the thermal shock resistant gradient composite coating on the surface of the silicon carbide-based composite material as described in any one of claims 1-3 is characterized in that, Includes the following steps: (1) Powders in the thermal shock gradient composite coating system were prepared by spray granulation, and powders with uniform particle size distribution were screened and the flowability of the powders was measured. (2) Pre-treat the surface of the fiber-reinforced silicon carbide matrix to remove oil and stains and roughen the matrix surface; (3) A gradient composite coating system with thermal shock resistant is formed by preparing a gradient composite coating on the surface of a pretreated fiber-reinforced silicon carbide matrix using vacuum plasma spraying. (4) Heat treatment is performed on the sprayed thermal shock resistant gradient composite coating system sample to remove residual stress inside the coating system.

5. The method for preparing the thermal shock resistant gradient composite coating on the surface of the silicon carbide-based composite material as described in claim 4, characterized in that, In step (1), the sprayed powder of the Si layer in the thermal shock resistant gradient composite coating system has a flowability of 25–40 s / 50 g and a particle size distribution of 18–25 μm; 0.75Si-0.25(AlTa) 1-x Si 2x O4 layer, 0.5Si-0.5(AlTa) 1-x Si 2x O4 layer, 0.25Si-0.75(AlTa) 1-x Si 2x The O4 layer mixed two-phase spray powder has a flowability of 30–45 s / 50g and a particle size distribution of 23–58 μm; (AlTa) 1-x Si 2x The O4 layer has a powder flowability of 40–55 s / 50g and a particle size distribution of 38–74 μm.

6. The method for preparing the thermal shock resistant gradient composite coating on the surface of the silicon carbide-based composite material as described in claim 4, characterized in that, The pretreatment in step (2) is as follows: the surface of the fiber-reinforced silicon carbide matrix is ​​impacted with 70-80 mesh fine white corundum at 0.3 MPa and a 30° angle. The fiber-reinforced silicon carbide matrix is ​​then placed in acetone or anhydrous ethanol and ultrasonically cleaned for 10-15 minutes. It is then placed in a vacuum oven at 80-110°C and dried for 2-4 hours to obtain a degreased and destained fiber-reinforced silicon carbide matrix. The degreased and destained fiber-reinforced silicon carbide matrix is ​​then sandblasted with 20-40 mesh coarse brown corundum. The sandblasting pressure is 0.5-0.75 MPa, the sandblasting distance is 50-150 mm, and the sandblasting angle is 70-90°.

7. The method for preparing the thermal shock resistant gradient composite coating on the surface of the silicon carbide-based composite material as described in claim 4, characterized in that, The vacuum degree during heat treatment in step (4) is 3.0 to 5.6 × 10⁻⁶. -3 The treatment time is 3-5 hours, with a pressure of 700-900℃.

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