CN104446670B - C/SiC composite material surface coating system and preparation method thereof - Google Patents

Abstract

The invention discloses a C/SiC composite material surface coating system and a preparation method thereof. The surface coating system is arranged on the surface of the C/SiC composite material substrate, including mullite coating and yttrium silicate coating arranged sequentially from bottom to top. The preparation method includes (1) preparation of Al ₂ O ₃ ‑SiO ₂ composite sol; (2) preparation of slurry raw material for yttrium silicate coating; (3) preparation of mullite coating; (4) preparation of yttrium silicate single-layer coating layer or yttrium silicate multilayer coating. The surface coating system of the C/SiC composite material of the present invention has the characteristics of high density and high temperature resistance, and its preparation method has universal engineering application.

Description

C/SiC composite material surface coating system and its preparation method

technical field

The invention belongs to the field of high-temperature-resistant fiber-reinforced ceramic-based composite materials, and relates to a C/SiC composite material surface coating system and a preparation method thereof, in particular to a novel double-layer high-temperature-resistant and Oxidized coatings and methods for their preparation.

Background technique

Carbon fiber reinforced silicon carbide (C/SiC) composites have excellent properties such as high specific strength and specific modulus, high temperature resistance, high damage tolerance, corrosion resistance, etc., and are considered as a strategic thermal structural material. , energy, chemical and other fields have broad application prospects. As a thermal structural material, C/SiC composites face the problem of high-temperature oxidation failure during application. The main reason is that carbon fibers will be severely oxidized above 400 °C and there are a large number of pores and cracks in the composite.

The preparation of high-temperature and anti-oxidation coatings on the surface of composite materials is the most effective anti-oxidation method at present, and the composition and structure of the coating are the key factors affecting the anti-oxidation effect. Yttrium silicate has three crystal phase structures: Y ₂ SiO ₅ , Y ₂ Si ₂ O ₇ , and Y ₄ Si ₃ O ₁₂ , among which the former two are the most common, with melting points of 1980°C and 1775°C respectively. In addition to high melting point, yttrium silicate also has the characteristics of low thermal expansion coefficient, low high-temperature oxygen permeability, low modulus, low high-temperature volatility, low thermal conductivity, good chemical and thermal stability, etc., making it a high-temperature anti-oxidation coating one of the best candidate materials. As an anti-oxidation coating for C/C and C/SiC composites, yttrium silicate has attracted widespread attention and has been studied a lot.

The most common way to prepare yttrium silicate coating on the surface of C/SiC composite material is to first prepare SiC inner coating by chemical vapor deposition, in order to alleviate the thermal mismatch between the composite material substrate and the yttrium silicate coating Degree to improve the bonding strength, and then use the hot isostatic pressing method, mud brushing and sintering method, electrophoretic deposition method, plasma spraying method, sol-gel method, etc. to prepare the yttrium silicate outer coating. The shortcomings of these solutions are: (1) The density of the yttrium silicate coating itself is not enough, and the diffusion coefficient of oxygen in Y ₂ O ₃ and SiO ₂ is very low, but if the coating itself is not dense enough, this Much advantage is lost. Blindly increasing the sintering temperature may not achieve the effect, but will cause damage to the composite material substrate. Although the density can be improved by adding the outermost layer of the glass phase, the temperature resistance of the glass phase is limited, and the performance in a corrosive atmosphere is not ideal; (2) As time goes on, the SiC inner coating will gradually oxidize to SiO _2. When the gaseous by-products diffuse outward, the yttrium silicate coating will crack or fall off, thus affecting the long-term anti-oxidation effect of the coating; (3) Some preparation methods such as hot isostatic pressing and chemical vapor deposition , electrophoretic deposition methods, etc. are difficult to apply to the preparation of surface coatings for components with complex shapes.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art, provide a high-density, high-temperature-resistant C/SiC composite surface coating system, and provide the preparation of the surface coating system with engineering application universality method.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A C/SiC composite material surface coating system, the surface coating system is arranged on the surface of the C/SiC composite material substrate, and the surface coating system includes mullite (chemical formula 3Al ₂ O ₃ · 2SiO ₂ ) coating and yttrium silicate coating.

In the above-mentioned C/SiC composite surface coating system, preferably, the yttrium silicate coating is a single-layer coating of yttrium silicate or a multi-layer coating of yttrium silicate; the single-layer coating of yttrium silicate is It is composed of a mixed coating of Y ₂ Si ₂ O ₇ and Y ₂ SiO ₅ , a single-phase coating of Y ₂ SiO ₅ and a single-phase coating of Y ₂ Si ₂ O ₇ ; the multilayer coating of yttrium silicate The layer is a mixed coating of Y ₂ Si ₂ O ₇ and Y ₂ SiO ₅ , a Y ₂ SiO ₅ single-phase coating, and a multi-layer (two or more layers) in a Y ₂ Si ₂ O ₇ single-phase coating constitute.

In the above-mentioned C/SiC composite material surface coating system, preferably, the thickness of the mullite coating is 10 μm to 30 μm; the thickness of the yttrium silicate monolayer coating is 30 μm to 100 μm, and the silicic acid The thickness of a single layer of the yttrium multilayer coating is 30 μm to 100 μm.

As a general technical concept, the present invention also provides a method for preparing the above-mentioned C/SiC composite material surface coating system, comprising the following steps:

(1) Prepare Al ₂ O ₃ -SiO ₂ composite sol: mix Al ₂ O ₃ sol and SiO ₂ sol to obtain Al ₂ O ₃ -SiO ₂ composite sol;

(2) Prepare the slurry raw material for yttrium silicate coating: add silicone resin and Y ₂ O ₃ powder into an organic solvent, and the silicon yttrium atomic ratio is 1:1~2 to obtain the slurry material for yttrium silicate coating;

(3) Preparation of mullite coating: immerse the C/SiC composite substrate in the Al ₂ O ₃ -SiO ₂ composite sol prepared in step (1), and prepare the mullite coating on the surface of the C/SiC composite substrate by dipping and pulling method. Mullite coating to obtain a C/SiC composite substrate with mullite coating;

(4) Preparation of yttrium silicate coating: The C/SiC composite substrate with mullite coating is immersed in the slurry raw material of yttrium silicate coating prepared in step (2), and the mullite A yttrium silicate coating is prepared on the surface of the stone coating, and the yttrium silicate coating is a monolayer coating of yttrium silicate to obtain a C/SiC composite material surface coating system.

As a general technical concept, the present invention also provides a method for preparing the above-mentioned C/SiC composite material surface coating system, comprising the following steps:

(1) Prepare Al ₂ O ₃ -SiO ₂ composite sol: mix Al ₂ O ₃ sol and SiO ₂ sol to obtain Al ₂ O ₃ -SiO ₂ composite sol;

(2) Preparation of slurry raw materials for yttrium silicate coating: Add _two or more silicone resins and _Y2O3 powders with different silicon yttrium atomic ratios to organic solvents to prepare different silicon yttrium atomic ratios. Mud raw materials, in each mud raw material, the atomic ratio of silicon and yttrium is in the range of 1:1-2;

(3) Preparation of mullite coating: immerse the C/SiC composite substrate in the Al ₂ O ₃ -SiO ₂ composite sol prepared in step (1), and prepare the mullite coating on the surface of the C/SiC composite substrate by dipping and pulling method. Mullite coating to obtain a C/SiC composite substrate with mullite coating;

(4) Preparation of yttrium silicate single-layer coating: the C/SiC composite substrate with mullite coating is immersed in one of the mud raw materials prepared in step (2), and the mullite A monolayer coating of yttrium silicate is prepared on the coating surface;

(5) Preparation of yttrium silicate coating: repeat the operation method of step (4), and prepare yttrium silicate with different silicon yttrium atomic ratios from bottom to top on the yttrium silicate monolayer coating prepared in step (4) A single-layer coating forms a yttrium silicate coating, and the yttrium silicate coating is a multi-layer coating of yttrium silicate to finally obtain a C/SiC composite material surface coating system.

In the above preparation method, preferably, in the step (1), the mass ratio of Al ₂ O ₃ to SiO ₂ in the Al ₂ O ₃ -SiO ₂ composite sol is 1-2:1, and the Al ₂ The solid content of the O ₃ -SiO ₂ composite sol is 20wt%-40wt%; in the step (2), the organic solvent is ethanol (more preferably absolute ethanol).

In the above preparation method, preferably, the specific process of preparing the mullite coating by dipping and pulling method is: (a) immersing the C/SiC composite material substrate into the Al ₂ O ₃ -SiO ₂ composite sol And keep it, take it out to form a film, place it, and then dry it; (b) Repeat the step (a) of dipping, pulling, placing and drying (it can increase the thickness and density of the coating), and then raise the temperature to 1200 in vacuum or inert atmosphere ℃～1400℃ for heat preservation (that is, calcination); (c) take step (a) and step (b) as a cycle, repeat the cycle process, make the mullite coating reach the preset thickness and densify, and obtain a Mullite-coated C/SiC composite substrate.

In the above preparation method, preferably, the specific parameters for the preparation of the mullite coating by dipping and pulling method are: in the step (a), the C/SiC composite substrate is immersed in Al ₂ O ₃ - The holding time in the SiO ₂ composite sol is 2min to 20min, the pulling speed is 5cm/min to 20cm/min, the standing time is 10min to 120min, and the drying temperature is 60°C to 200°C , the drying time is 0.5h to 4h; in the step (b), the number of repetitions of the dipping, lifting and drying process is 4 to 10 times, and the heating rate is 2°C/min to 10°C /min, the time of the heat preservation is 1h-4h; in the step (c), the number of repetitions of the cycle process is 4-8 times.

In the above preparation method, preferably, the specific process of preparing the yttrium silicate single-layer coating by dipping and pulling method is: (a) the C/SiC composite substrate with mullite coating Immerse in the yttrium silicate-coated mud raw material and keep it, pull it to form a film, take it out and place it; (b) repeat the dipping and pulling process of step (a) (it can increase the thickness and density of the coating), and then the obtained The sample is cross-linked in the air at 200°C-300°C; (c) repeat the process of step (b), and then crack in the air at 600°C-1000°C to convert the silicone resin into SiO ₂ , and then Raise the temperature to 1200 ℃ ~ 1400 ℃ in vacuum or inert atmosphere and keep it warm (calcination); (d) take steps (a), (b) and (c) as a cycle, repeat the cycle process, so that the coating reaches the preset thick and densified to obtain a monolayer coating of yttrium silicate.

In the above preparation method, preferably, the specific parameters for preparing the yttrium silicate single-layer coating by dipping and pulling method are: in the step (a), the C/ The SiC composite material substrate is immersed in the yttrium silicate-coated slurry raw material for 2 minutes to 20 minutes, the pulling speed is 5 cm/min to 20 cm/min, and the standing time is 10 minutes to 120 minutes; In step (b), the number of repetitions of the dipping, lifting and placement process is 4 to 10 times, and the time for crosslinking is 1h to 4h; in the step (c), the number of repetitions of step (b) is 4 ~8 times, the cracking time is 1h~4h, the heating rate is 2°C/min~10°C/min, and the holding time is 1h~4h; in the step (d), the The number of repetitions of the cyclic process is 4 to 8 times.

The technical scheme of the present invention is based on the C/SiC composite material as the substrate. First, the high solid content Al ₂ O ₃ -SiO ₂ composite sol is used as the raw material of the mullite coating, and a dense mullite coating is prepared on the surface of the substrate by the dipping and pulling method. Mullite coating, and then use the slurry prepared by silicone resin + Y ₂ O ₃ powder in ethanol as raw material, and prepare a dense yttrium silicate coating on the surface of the mullite coating by dipping and pulling. Among them, by changing the _ratio of _{silicone resin} and _{Y 2 O 3 powder , yttrium silicate single} Layer coatings can also be prepared as yttrium silicate multi-layer coatings, such as gradient yttrium silicate coatings from inner Y ₂ Si ₂ O ₇ to outer Y ₂ SiO ₅ .

The performance parameters of the double-layer anti-oxidation coating system on the surface of the C/SiC composite material of the present invention can be determined by the following method: the C/SiC composite material with double-layer coating is placed in an air environment of 1400 ° C to 1600 ° C (Ma Furnace) for 0.5h to 1h oxidation, and then measure the weight change rate and strength retention rate before and after oxidation.

In the preparation method of the present invention, when preparing the Al ₂ O ₃ -SiO ₂ composite sol, a method that can be preferably adopted is: mix the purchased Al ₂ O ₃ sol and SiO ₂ sol in the required ratio, and mix the One sol is slowly poured into the other with stirring.

In the preparation method of the present invention, when the C/SiC composite material substrate with mullite coating is immersed in the mud raw material of yttrium silicate coating, in order to ensure the stability and uniformity of the mud raw material, the mud raw material is carried out before use. Stir and sonicate to avoid sedimentation of Y ₂ O ₃ powder.

In the preparation method of the present invention, the average particle diameter of the Y ₂ O ₃ powder may preferably be 2 μm˜10 μm.

In the preparation method of the present invention, when preparing the slurry raw material for yttrium silicate coating, it is preferable to blend the silicone resin and _Y2O3 powder according to the silicon-yttrium atomic ratio of 1:1~ ₂ , and use ethanol (preferably absolute ethanol) For the medium, carry out ball milling dispersion mixing. The silicon yttrium atomic ratio of 1:2 corresponds to the Y ₂ SiO ₅ phase, and the silicon yttrium atomic ratio of 1:1 corresponds to the Y ₂ Si ₂ O ₇ phase, and a mixture of Y ₂ SiO ₅ + Y ₂ Si ₂ O ₇ can be obtained between the two Mutually.

Compared with the prior art, the present invention has the advantages of:

(1) The surface coating system of the C/SiC composite material of the present invention includes mullite coating and yttrium silicate coating. The thermal expansion coefficient of mullite is almost the same as that of SiC in C/SiC composite materials, and the chemical compatibility is also very good. It has good oxidation resistance and no further oxidation reaction, thus avoiding the SiC Oxidative volatilization of the inner coating leads to cracking or peeling off of the yttrium silicate outer coating. Since both mullite and yttrium silicate are oxides, both have SiO ₂ in the composition, which is conducive to the formation of a strong bond between the two, thereby improving the oxidation resistance and erosion resistance of the coating.

(2) In the preparation method of the present invention, the synthesis of mullite by high solid phase content Al ₂ O ₃ -SiO ₂ composite sol avoids the shortcoming of low efficiency of the route starting from the solution containing Al and Si containing compounds, and maintains The advantage of sol-gel synthesis of mullite at low temperature is realized. While silicone resin is used as SiO ₂ raw material, it also has good cohesiveness, so the "silicone resin + Y ₂ O ₃ powder" slurry is not only easy to form a film on the surface of the composite material, but also avoids the need to remove the external binder. Detrimental effects of cleaning on coating preparation and performance. By changing the ratio of silicone resin and Y ₂ O ₃ powder, Y ₂ SiO ₅ , Y ₂ Si ₂ O ₇ single-phase coatings or Y ₂ SiO ₅ +Y ₂ Si ₂ O ₇ mixed coatings were prepared.

(3) In the preparation method of the present invention, the SiO _{2 obtained by converting the SiO 2 in} the composite sol and the silicone resin in the mud raw material has very high activity, and can be compared with Al ₂ O ₃ and Y ₂ O ₃ at a lower Mullite or yttrium silicate is formed by reaction at a temperature (≤1400°C), and SiO ₂ has good viscous flow characteristics at 1000°C, which can promote the low-temperature densification of the coating, thereby avoiding the impact of high-temperature sintering on the composite material. coming adverse effects.

(4) In the preparation method of the present invention, the synthesis of mullite and yttrium silicate is based on liquid phase raw materials, and the coating can be prepared by dipping and pulling. The process of this method is simple and easy to control, and has low requirements on equipment. It is not only suitable for large-sized and complex-shaped components, but also for components with inner cavity structures, and has good universality in engineering applications.

(5) The surface anti-oxidation coating system prepared by the present invention can also effectively enhance the mechanical properties of the C/SiC composite material itself, and the related raw materials used are widely, stable and inexpensive.

Description of drawings

FIG. 1 is a schematic structural view of a C/SiC composite material surface coating system in an embodiment of the present invention.

Fig. 2 is the XRD pattern of mullite formed when the C/SiC composite material surface coating system in Examples 1-3 of the present invention is calcined at 1200°C, 1400°C, and 1300°C respectively.

Fig. 3 is the XRD pattern of yttrium silicate formed when the C/SiC composite material surface coating system in Examples 1-3 of the present invention was calcined at 1300°C and 1400°C respectively.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

All materials and instruments used in the following examples are commercially available.

Example 1 :

A kind of C/SiC composite material surface coating system of the present invention, as shown in Figure 1, this surface coating system is arranged on the C/SiC composite material substrate surface, and this surface coating system comprises Molai Stone (3Al ₂ O ₃ 2SiO ₂ ) coating and yttrium silicate coating.

In this embodiment, the yttrium silicate coating is a Y ₂ Si ₂ O ₇ single-phase coating, and the thickness of the single layer is 30 μm. The thickness of the mullite coating is 15 μm.

A preparation method of the C/SiC composite material surface coating system of the above-mentioned present embodiment, comprising the following steps:

(1) Mix Al ₂ O ₃ sol and SiO ₂ sol (the two are commercially available), the mass ratio of Al ₂ O ₃ and SiO ₂ is 1:1, and prepare Al with a high solid content of 22wt% ₂ O ₃ -SiO ₂ composite sol as raw material for mullite coating.

(2) Preparation of slurry raw materials for yttrium silicate coating: blend silicone resin and Y ₂ O ₃ powder (average particle size 3 μm) according to silicon yttrium atomic ratio 1:1, and use absolute ethanol as the medium for ball milling dispersion mixing , to obtain slurry raw materials for the preparation of yttrium silicate coatings (Y ₂ Si ₂ O ₇ single-phase coatings).

(3) Preparation of mullite coating: (a) Using the Al ₂ O ₃ -SiO ₂ composite sol in step (1) as the raw material, immerse the C/SiC composite material substrate into the composite sol, and after 2 min Pull out at a speed of 1/min, place for 10min and then dry in the air at 100°C for 0.5h; (b) Repeat the dipping, pulling, placing and drying process 6 times to form a composite sol coating on the surface of the substrate, and then apply the composite sol coating Place the substrate in an inert atmosphere (either nitrogen or argon, the same below), and heat it at 5°C/min to 1200°C (calcination) for 1h; (c) Take steps (a) and (b) as one Cycle, repeat this cycle 4 times, prepare a dense mullite coating with a thickness of 15 μm, and obtain a C/SiC composite material substrate with a mullite coating.

(4) Preparation of yttrium silicate coating: (a) Immerse the C/SiC composite substrate with mullite coating obtained in step (3) into the mud raw material prepared in step (2) (in order to ensure stability and uniformity properties, the mud should be stirred and ultrasonically oscillated before use to avoid the sedimentation of Y ₂ O ₃ powder), held for 2 minutes, then pulled out at a speed of 15cm/min and left for 10 minutes; (b) Repeat the dipping and pulling process for 8 secondly, form a slurry raw material coating on the surface of the mullite coating, and then cross-link the substrate with the mud raw material coating at 300 ° C in air for 1 h; (c) repeat the process of step (b) 4 times, in the air Crack at 800°C for 1 hour to convert the silicone resin into SiO ₂ , then raise the temperature to 1300°C at 5°C/min in an inert atmosphere for 1 hour (calcination); (d) follow steps (a), (b) and (c) ) as one cycle, repeating this cycle 4 times to prepare a dense yttrium silicate coating (Y ₂ Si ₂ O ₇ single-phase coating) with a single layer thickness of 30 μm to obtain a C/SiC composite surface coating system. The XRD patterns of the mullite coating formed at 1200°C and the yttrium silicate coating formed at 1300°C in the C/SiC composite surface coating system are shown in Figure 2 and Figure 3, respectively.

The C/SiC composite material with the surface coating system of this example was oxidized in air at 1500°C (muffle furnace, the same below) for 0.5h, the weight loss was only 0.69%, and the strength retention rate of the composite material reached 144.3%. That is, the strength increases after oxidation. This is due to the high phase stability of the Y ₂ Si ₂ O ₇ single-phase coating and the good chemical compatibility with the substrate, further sintering and densification will occur during the oxidation process, and the bonding with the substrate will also be strengthened, resulting in The composite material has almost no oxidation weight loss, but its mechanical properties have increased.

Example 2 :

A kind of C/SiC composite material surface coating system of the present invention, as shown in Figure 1, this surface coating system is arranged on the C/SiC composite material substrate surface, and this surface coating system comprises Molai stone coating and yttrium silicate coating.

In this embodiment, the yttrium silicate coating is a mixed coating of 30wt% Y ₂ SiO ₅ and 70wt% Y ₂ Si ₂ O ₇ , and the thickness of a single layer is 75 μm. The thickness of the mullite coating is 25 μm.

A preparation method of the C/SiC composite material surface coating system of the above-mentioned present embodiment, comprising the following steps:

(1) Mix Al ₂ O ₃ sol and SiO ₂ sol, the mass ratio of Al ₂ O ₃ and SiO ₂ is 2:1, prepare Al ₂ O ₃ -SiO ₂ composite with high solid phase content of 25wt% solid content Sol, as a raw material for mullite coating.

(2) Preparation of slurry materials for yttrium silicate coating: blend silicone resin and Y ₂ O ₃ powder (average particle size 5 μm) according to silicon yttrium atomic ratio 1:1.2, and use absolute ethanol as medium for ball milling to disperse and mix , to obtain the slurry raw material for the preparation of yttrium silicate coating (that is, a mixed coating of 30wt% Y ₂ SiO ₅ and 70wt% Y ₂ Si ₂ O ₇ ).

(3) Preparation of mullite coating: (a) Using the Al ₂ O ₃ -SiO ₂ composite sol in step (1) as the raw material, immerse the C/SiC composite material substrate in the sol, dip coating for 5 minutes, and then use 10cm Pull out at a speed of 1/min, place for 30min and then dry in the air at 100°C for 1h; (b) repeat the process of dipping and pulling for 8 times to form a composite sol coating on the surface of the substrate, and then apply the composite sol coating The substrate is placed in an inert atmosphere, and the temperature is raised to 1400 °C at 5 °C/min for 1 h; (c) Step (a) and step (b) are used as a cycle, and this cycle is repeated 5 times to prepare dense mullite with a thickness of 25 μm coating to obtain a C/SiC composite substrate with a mullite coating.

(4) Preparation of yttrium silicate coating: (a) Immerse the C/SiC composite substrate with mullite coating obtained in step (3) into the mud raw material prepared in step (2) (in order to ensure stability and uniformity In order to avoid the sedimentation of Y ₂ O ₃ powder, stir and ultrasonically oscillate the mud before use), pull out at a speed of 10 cm/min after immersion for 10 minutes and leave it for 30 minutes; (b) repeat the process of immersion, pulling and placing for 10 The first step is to form a slurry raw material coating on the surface of the mullite coating, and then cross-link the substrate with the mud raw material coating at 300 °C in the air for 2 h; (c) After repeating the process of step (b) 6 times, the Crack at 800°C for 1 hour to convert the silicone resin into SiO ₂ , then raise the temperature to 1400°C for 1 hour at 5°C/min in an inert atmosphere; (d) Take steps (a), (b) and (c) as a cycle , repeat this cycle 5 times to prepare a dense yttrium silicate coating with a single layer thickness of 75 μm, that is, a mixed coating of 30wt% Y ₂ SiO ₅ and 70wt% Y ₂ Si ₂ O ₇ , and obtain a C/SiC composite surface coating system. The XRD patterns of the mullite coating and the yttrium silicate coating formed at 1400°C in the C/SiC composite surface coating system are shown in Figure 2 and Figure 3, respectively.

The C/SiC composite material with the surface coating system of this example was oxidized in air at 1600°C for 0.5h, the weight loss was only 1.07%, and the strength retention rate of the composite material reached 131.2%, that is, the strength increased after oxidation. This is due to the high phase stability of the mixed coating of 30wt% Y ₂ SiO ₅ and 70wt% Y ₂ Si ₂ O ₇ and good chemical compatibility with the substrate, further sintering and densification will occur during the oxidation process, and the The combination of the composite material will also be strengthened, resulting in a small oxidation weight loss of the composite material, and the mechanical properties will increase instead.

Example 3 :

A kind of C/SiC composite material surface coating system of the present invention, as shown in Figure 1, this surface coating system is arranged on the C/SiC composite material substrate surface, and this surface coating system comprises Molai stone coating and yttrium silicate coating.

In this example, the yttrium silicate coating from bottom to top (also from inside to outside) is a mixed coating of 30wt% Y ₂ SiO ₅ and 70wt% Y ₂ Si ₂ O ₇ , 70wt% Y ₂ SiO ₅ and 30wt% Y ₂ Si ₂ O ₇ mixed coating, Y ₂ SiO ₅ single-phase coating, the thickness of each single layer is 35 μm, and the total thickness of the yttrium silicate coating is 105 μm. The thickness of the mullite coating is 21 μm.

A preparation method of the C/SiC composite material surface coating system of the above-mentioned present embodiment, comprising the following steps:

(1) Mix Al ₂ O ₃ sol and SiO ₂ sol, the mass ratio of Al ₂ O ₃ and SiO ₂ is 1.8:1, and prepare Al ₂ O ₃ -SiO ₂ with a solid content of 22.6wt% and a high solid phase content Composite sol, as raw material for mullite coating.

(2) Preparation of slurry materials for yttrium silicate coating: blend silicone resin and Y ₂ O ₃ powder (average particle size 2 μm) according to the silicon yttrium atomic ratio of 1:1.2, 1:1.6, and 1:2, respectively, to Anhydrous ethanol was used as the medium for ball milling to disperse and mix to obtain three kinds of slurry raw materials, which were used to prepare yttrium silicate coatings with different phase compositions, which were mixed coatings of 30wt% Y ₂ SiO ₅ and 70wt% Y ₂ Si ₂ O ₇ , 70wt% Y ₂ SiO ₅ and 30wt% Y ₂ Si ₂ O ₇ mixed coating, Y ₂ SiO ₅ single-phase coating.

(3) Preparation of mullite coating: (a) Using the Al ₂ O ₃ -SiO ₂ composite sol in step (1) as a raw material, immerse the C/SiC composite substrate in the sol, and after immersion for 10 minutes, use 13cm/ min at a speed of 60 min, and then dried in the air at 100°C for 2 h after standing for 60 min; (b) Repeat the dipping, pulling and drying process 4 times to form a composite sol coating on the surface of the substrate, and then place the substrate with the composite sol coating Place in an inert atmosphere, heat at 5°C/min to 1300°C for 2h; (c) take step (a) and step (b) as a cycle, repeat this cycle 6 times, and prepare a dense mullite coating with a thickness of 21 μm layer to obtain a C/SiC composite substrate with a mullite coating.

(4) Preparation of yttrium silicate monolayer coating: immerse the C/SiC composite substrate with mullite coating obtained in step (3) into the 1:1.2 mud raw material prepared in step (2) (to ensure Stability and uniformity, the mud should be stirred and ultrasonically oscillated before use to avoid the sedimentation of Y ₂ O ₃ powder), after immersion for 8 minutes, it was pulled out at a speed of 15cm/min and left for 60 minutes; (b) Repeated immersion and pulling Place the process 6 times, and then cross-link in the air at 300°C for 4h; (c) After repeating the process of step (b) 5 times, crack in the air at 800°C for 1.5h to convert the silicone resin into SiO ₂ , then in an inert atmosphere In the process, the temperature was raised to 1400°C at 5°C/min for 2h; (d) Steps (a), (b) and (c) were used as a cycle, and this cycle was repeated 4 times to prepare dense yttrium silicate with a single layer thickness of 35 μm A single-layer coating, the yttrium silicate single-layer coating is a mixed coating of 30wt% Y ₂ SiO ₅ and 70wt% Y ₂ Si ₂ O ₇ .

(5) Preparation of yttrium silicate coating: First, use 1:1.6 mud raw material, repeat the operation method of step (4), and prepare dense 70wt% Y ₂ SiO ₅ and 30wt% Y ₂ Si ₂ O with a single layer thickness of 35 μm ₇ ; then use 1:2 mud raw material, repeat the operation method of step (4) to prepare a dense Y ₂ SiO ₅ single-phase coating with a single layer thickness of 35 μm, and obtain an yttrium silicate multilayer coating ( That is, the yttrium silicate coating in this embodiment), the total thickness is 105 μm, and finally a C/SiC composite material surface coating system is obtained. The XRD patterns of the mullite coating formed at 1300°C and the yttrium silicate coating formed at 1400°C in the C/SiC composite surface coating system are shown in Figure 2 and Figure 3, respectively.

The C/SiC composite material with the surface coating system of this embodiment was oxidized in air at 1400°C for 1 hour, and the weight loss rate was 0%, that is, no weight change was detected, and the strength retention rate of the composite material reached 143.4%, that is, The strength increased after oxidation. This is due to the high phase stability of the yttrium silicate coating itself with different phase compositions and good chemical compatibility with the substrate, further sintering and densification will occur during the oxidation process, and the bonding with the substrate will also be strengthened, resulting in The composite material did not lose weight by oxidation, but its mechanical properties increased.

In summary, it can be seen from Figure 2 that in the surface coating systems of Examples 1 to 3 of the present invention, the mullite coating has undergone obvious mullite reaction since 1200°C, and the mullite reaction has basically occurred at 1300°C. Completely, a well-crystallized mullite phase is obtained at 1400 °C. It can be seen from Figure 3 that in the surface coating systems of Examples 1 to 3 of the present invention, the yttrium silicate coating is obviously yttrium-silicate at 1300°C (yttrium-silicate reaction occurs from 1200°C) , The reaction is complete at 1400°C, and a well-crystallized yttrium silicate phase is formed.

The above descriptions are only preferred implementations of the present invention, and the scope of protection of the present invention is not limited to the above examples. All technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims (9)

1. a C/SiC composite material surface coating system, it is characterised in that described lacquer systems is located at C/SiC composite substrate surface, described lacquer systems includes mullite coating and the iridium silicate coating layer laid the most successively；In described mullite coating, Al₂O₃With SiO₂Mass ratio be 1～2: 1, the thickness of described mullite coating is 10 μm～30 μm.

C/SiC composite material surface coating system the most according to claim 1, it is characterised in that described iridium silicate coating layer is yttrium silicate signal layer coating or yttrium silicate laminated coating；Described yttrium silicate signal layer coating is by Y₂Si₂O₇And Y₂SiO₅Mixed coating, Y₂SiO₅Single-phase coating, Y₂Si₂O₇One layer of composition in single-phase coating；Described yttrium silicate laminated coating is by Y₂Si₂O₇And Y₂SiO₅Mixed coating, Y₂SiO₅Single-phase coating, Y₂Si₂O₇Multilamellar in single-phase coating is constituted.

C/SiC composite material surface coating system the most according to claim 2, it is characterised in that the thickness of described yttrium silicate signal layer coating is 30 μm～100 μm, the thickness in monolayer of described yttrium silicate laminated coating is 30 μm～100 μm.

4. a preparation method for the C/SiC composite material surface coating system as according to any one of claims 1 to 3, comprises the following steps:

(1) preparation Al₂O₃-SiO₂Complex sol: by Al₂O₃Colloidal sol and SiO₂Colloidal sol mixes, and obtains Al₂O₃-SiO₂Complex sol；

(2) the mud raw material of iridium silicate coating layer is prepared: by silicones and Y₂O₃Powder adds to organic solvent, and silicon yttrium atom ratio is 1: 1～2, obtains the mud raw material of iridium silicate coating layer；

(3) mullite coating is prepared: C/SiC composite substrate is immersed the Al that step (1) is prepared₂O₃-SiO₂In complex sol, prepare mullite coating by dip-coating method on C/SiC composite substrate surface, obtain the C/SiC composite substrate with mullite coating；

(4) iridium silicate coating layer is prepared: immersed by the C/SiC composite substrate with mullite coating in the mud raw material of the iridium silicate coating layer that step (2) is prepared, iridium silicate coating layer is prepared on mullite coating surface by dip-coating method, this iridium silicate coating layer is yttrium silicate signal layer coating, obtains C/SiC composite material surface coating system；

In described step (1), described Al₂O₃-SiO₂Al in complex sol₂O₃With SiO₂Mass ratio be 1～2: 1；Described Al₂O₃-SiO₂The solid content of complex sol is 20wt%～40wt%；

The detailed process that described mullite coating is prepared by dip-coating method is: C/SiC composite substrate is immersed in Al by (a)₂O₃-SiO₂In complex sol and keep, pulling film forming is placed after taking out, and is then dried；B () is repeated the Best-Effort request of step (a) and is placed dry run, be then warming up to 1200 DEG C～1400 DEG C in vacuum or inert atmosphere and be incubated；C () is a circulation with step (a) and step (b), repeat this cyclic process, make mullite coating reach preset thickness densification, obtain the C/SiC composite substrate with mullite coating.

5. a preparation method for the C/SiC composite material surface coating system as according to any one of claims 1 to 3, comprises the following steps:

(1) preparation Al₂O₃-SiO₂Complex sol: by Al₂O₃Colloidal sol and SiO₂Colloidal sol mixes, and obtains Al₂O₃-SiO₂Complex sol；

(2) the mud raw material of iridium silicate coating layer is prepared: by silicones and the Y of two or more different silicon yttrium atom ratios₂O₃Powder is added separately in organic solvent, is prepared as the mud raw material with different silicon yttrium atom ratio, and in each mud raw material, silicon yttrium atom ratio is all in the range of 1: 1～2；

(3) mullite coating is prepared: C/SiC composite substrate is immersed the Al that step (1) is prepared₂O₃-SiO₂In complex sol, prepare mullite coating by dip-coating method on C/SiC composite substrate surface, obtain the C/SiC composite substrate with mullite coating；

(4) yttrium silicate signal layer coating is prepared: immersed in the one of which mud raw material that step (2) is prepared by the C/SiC composite substrate with mullite coating, prepare yttrium silicate signal layer coating by dip-coating method on mullite coating surface；

(5) iridium silicate coating layer is prepared: repeat the operational approach of step (4), the yttrium silicate signal layer coating that step (4) prepares is sequentially prepared the yttrium silicate signal layer coating with different silicon yttrium atom ratios from the bottom to top, form iridium silicate coating layer, this iridium silicate coating layer is yttrium silicate laminated coating, finally gives C/SiC composite material surface coating system；

In described step (1), described Al₂O₃-SiO₂Al in complex sol₂O₃With SiO₂Mass ratio be 1～2: 1；Described Al₂O₃-SiO₂The solid content of complex sol is 20wt%～40wt%；

The detailed process that described mullite coating is prepared by dip-coating method is: C/SiC composite substrate is immersed in Al by (a)₂O₃-SiO₂In complex sol and keep, pulling film forming is placed after taking out, and is then dried；B () is repeated the Best-Effort request of step (a) and is placed dry run, be then warming up to 1200 DEG C～1400 DEG C in vacuum or inert atmosphere and be incubated；C () is a circulation with step (a) and step (b), repeat this cyclic process, make mullite coating reach preset thickness densification, obtain the C/SiC composite substrate with mullite coating.

6., according to the preparation method described in claim 4 or 5, it is characterised in that in described step (2), described organic solvent is ethanol.

7. according to the preparation method described in claim 4 or 5, it is characterised in that the design parameter that described mullite coating is prepared by dip-coating method is: in described step (a), and described C/SiC composite substrate is immersed in Al₂O₃-SiO₂The time kept in complex sol is 2min～20min, and the speed of described lifting is 5cm/min～20cm/min, and the time of described placement is 10min～120min, and described dry temperature is 60 DEG C～200 DEG C, and the described dry time is 0.5h～4h；In described step (b), it is 4～10 times that described Best-Effort request places the number of repetition of dry run, and the speed of described intensification is 2 DEG C/min～10 DEG C/min, and the time of described insulation is 1h～4h；In described step (c), the number of repetition of described cyclic process is 4～8 times.

8. according to the preparation method described in claim 4 or 5, it is characterized in that, the detailed process that described yttrium silicate signal layer coating is prepared by dip-coating method is: the described C/SiC composite substrate with mullite coating is immersed in the mud raw material of iridium silicate coating layer and keeps by (a), and pulling film forming is placed after taking out；B () repeats the Best-Effort request placement process of step (a), then cross-linked at 200 DEG C～300 DEG C in atmosphere by gained sample；C () repeats the process of step (b), crack the most in atmosphere, make silicones change into SiO at 600 DEG C～1000 DEG C₂, then in vacuum or inert atmosphere, it is warming up to 1200 DEG C～1400 DEG C insulations；D () is a circulation with step (a) and (b) and (c), repeat this cyclic process, make coating reach preset thickness densification, obtain yttrium silicate signal layer coating.

Preparation method the most according to claim 8, it is characterized in that, the design parameter that described yttrium silicate signal layer coating is prepared by dip-coating method is: in described step (a), the described C/SiC composite substrate with mullite coating be immersed in the mud raw material of iridium silicate coating layer keep time be 2min～20min, the speed of described lifting is 5cm/min～20cm/min, and the time of described placement is 10min～120min；In described step (b), the number of repetition of described Best-Effort request placement process is 4～10 times, and the time of described crosslinking is 1h～4h；In described step (c), the number of times repeating step (b) is 4～8 times, and the time of described cracking is 1h～4h, and the speed of described intensification is 2 DEG C/min～10 DEG C/min, and the time of described insulation is 1h～4h；In described step (d), the number of repetition of described cyclic process is 4～8 times.