CN102432345B - Carbon/carbon composite material silicon-based composite coating capable of resisting high-temperature oxidation for long time, and its preparation method and use - Google Patents

Abstract

The invention discloses a carbon/carbon composite material silicon-based composite coating capable of resisting high-temperature oxidation for a long time, and its preparation method and use. The carbon/carbon composite material silicon-based composite coating capable of resisting high-temperature oxidation for a long time is characterized in that composite coatings of a SiC connection layer combined with a carbon/carbon composite material matrix and a MoSi2-Si2N2O-CrSi2 ceramic layer are coated on a carbon/carbon composite material surface inside and out, wherein the SiC connection layer has a function of connecting the carbon/carbon composite material matrix and the MoSi2-Si2N2O-CrSi2 ceramic layer has a function of sealing and oxygen blocking. The carbon/carbon composite material silicon-based composite coating capable of resisting high-temperature oxidation for a long time can firmly combine with the carbon/carbon composite material matrix, does not produce penetrating cracks, can resist high-temperature oxidation for a long time, and can be completely utilized for preparation of an aeroengine afterburner material.

Description

A carbon/carbon composite material long-term high-temperature anti-oxidation silicon-based composite coating and its preparation and application method

technical field

The present invention relates to a surface treatment of a carbon/carbon composite material, in particular to a new type of aero-engine afterburner to replace a superalloy carbon/carbon composite material on the surface of a long-time high-temperature anti-oxidation silicon-based composite coating and its preparation and application method.

Background technique

Carbon/carbon composite material is a new type of high-temperature material with carbon fiber reinforced carbon matrix. The material has a light specific gravity and a theoretical density of 2.2g/cm ³ . It is an ideal high-temperature structure and ablation-resistant material, and is widely used in the aerospace field. At present, countries all over the world use anti-oxidation carbon/carbon composite materials as the preferred material for the nose cone and wing leading edge of the space shuttle. Carbon/carbon composite materials have the characteristics of light weight and heat resistance, so they are also important substitute materials for alloy materials of the hot end parts of aero-engines with a thrust-to-weight ratio greater than 10.

However, carbon/carbon composites are easily oxidized when used in a high-temperature aerobic environment. Under aerobic conditions, the initial oxidation temperature of carbon/carbon composites is 370°C; when it is higher than 500°C, the carbon/carbon composites will be rapidly oxidized and destructively damaged. Combustion chambers of traditional aero-engines mostly use alloy materials, and the outlet temperature of the combustion chambers reaches 1000°C-1500°C. If carbon/carbon composite materials can be used instead of alloy materials, the weight of the engine will be greatly reduced, thereby increasing the thrust-to-weight ratio of the aircraft. Therefore, it is of great significance to develop a new type of long-term high-temperature oxidation-resistant coated carbon/carbon composite material to replace the superalloy material so that it can be applied to the afterburner of the aircraft engine.

Coating anti-oxidation composite ceramic coating on the surface of carbon/carbon composite material is an effective measure. At the same time, in order to continuously improve or improve the protective performance of the anti-oxidation coating, the structural design of the coating has gradually developed from a single coating system to a composite coating system. Silicon-based ceramic coatings are currently the most intensively studied anti-oxidation coating systems. Among silicon-based ceramics, the thermal expansion coefficient of SiC is close to that of carbon matrix, and it has good chemical compatibility. The preparation of the SiC inner layer by the embedding method has the advantages of good bonding between the coating and the substrate and low cost. The MoSi ₂ in the outer layer has the high-temperature toughness of metal and excellent high-temperature oxidation resistance. Above 800 ℃, a dense, continuous and self-healing SiO ₂ film can be formed on the surface of MoSi ₂ , which can prevent the entry of oxygen. Cr reacts with Si to generate CrSi ₂ reacts with oxygen to generate SiO ₂ and Cr ₂ O ₃ with extremely low oxygen permeability, and the generated Cr ₂ O ₃ can improve the high temperature stability of SiO ₂ glass, this composite glass layer It can effectively prevent the intrusion of oxygen and has good high temperature stability. In addition, at 1100-1500°C, the oxidation rate of Si ₃ N ₄ is 2-3 orders of magnitude lower than that of SiC, mainly because Si ₃ N ₄ forms Si ₂ N which has a lower oxygen diffusivity than SiO ₂ during oxidation. ₂ O, compared with SiO ₂ film, Si ₂ N ₂ O film has a tighter network coating, so it plays an important role in anti-oxidation.

purpose of invention

The purpose of the present invention is to design and prepare a brand-new SiC/MoSi ₂ that is firmly bonded to the substrate and has no through cracks for the situation that the ceramic coating on the surface of the carbon/carbon composite material is prone to defects such as cracks due to physical and chemical mismatches. -Si ₂ N ₂ O-CrSi ₂ (from inside to outside) silicon-based ceramic composite coating resistant to high temperature oxidation for a long time, and its preparation and application method.

The purpose of the present invention is achieved in the following manner:

A method for preparing a carbon/carbon composite material for long-term high-temperature oxidation-resistant silicon-based composite coating,

The connecting layer and the ceramic coating are sequentially prepared on the surface of the carbon/carbon composite material from the inside to the outside; the connecting layer is a SiC layer prepared by an embedding method, and the ceramic coating is a brush coating method and a gas phase reaction method Prepared ceramic layer of MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ .

The embedding method to prepare the connection layer is to use Si powder, Al ₂ O ₃ powder, C powder, and SiC powder as raw materials. After ball milling and mixing, the carbon/carbon composite material is embedded and calcined at high temperature. The obtained connection layer The layer thickness is about 100 μm-200 μm.

Specific steps are as follows:

According to the mass ratio: Si 40-75%, Al ₂ O ₃ 2-13%, C 8-20%, SiC 10-38%, weigh Si powder, Al ₂ O ₃ powder, C powder, SiC powder, add Dispersant, ball milled and mixed thoroughly, taken out and dried before use; finally, put the carbon/carbon composite material in a graphite crucible, and completely bury it with the mixed powder, and then put the crucible into a high-temperature furnace, at 1700 Keep warm at ℃-2000℃ for 1.5-3h.

The Si powder, SiC powder, C powder, and Al ₂ O ₃ powder are all preferably over 325 mesh.

The preparation of the MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ ceramic layer by the brush coating method and the gas phase reaction method is to first weigh MoSi ₂ powder, Cr powder, Si powder, C powder and the sintering accelerator Al ₂ O ₃ and mix them. Use deionized water as the solvent and polyvinyl alcohol as the binder to prepare a slurry, brush the prepared slurry on the cleaned and dried carbon/carbon composite material with a SiC connection layer, dry, repeat The brushing and drying process is at least 3 times. Finally, the sample after brushing and drying is sintered at high temperature under nitrogen atmosphere. During the sintering process, N ₂ and SiO are introduced, and Si ₂ N ₂ O is prepared by gas phase reaction method. The resulting ceramic layer has a thickness of about 100 μm to 150 μm.

Specific steps are as follows:

MoSi _{2 :} Cr: Si: C: Al ₂ O ₃ = 20-50: 6-20: 30-50: 3-11: 2-10 mixed in weight ratio, deionized water is selected as solvent, polyvinyl alcohol is Binder, the ratio of solid phase mixed powder and binder is 1-3g: 20-30ml; the mass concentration of polyvinyl alcohol is 2-5%; prepare the slurry, brush the prepared slurry on the clean and dry On the dried carbon/carbon composite material with SiC connection layer, dry, repeat brushing and drying 3-4 times, and finally put the sample after brushing and drying into a vacuum carbon tube sintering furnace, in nitrogen Under the atmosphere, heat preservation at 1200°C-1600°C for 15-80min; N ₂ and SiO are introduced during the sintering process, and Si ₂ N ₂ O is prepared by gas phase reaction.

The MoSi ₂ powder, Cr powder, Si powder, and C powder are all preferably over 325 mesh.

The specific configuration process of the slurry is as follows: use an ultrasonic cleaner to clean the beaker in absolute ethanol, and use a magnetic stirrer for standby; dry the beaker and solid raw materials; weigh various raw material powders according to the set ratio and pour them into the beaker , stir on a magnetic stirrer for at least 4 h until the powder is evenly mixed.

The silicon-based composite coating of the invention is applied to the preparation of aeroengine afterburner materials.

The method of the invention can prepare the anti-oxidation functional composite coating of the C/C composite material prepared by the chemical vapor phase infiltration and/or liquid phase impregnation process.

Advantages and positive effects of the invention

Compared with prior art, advantage and positive effect of the present invention are embodied in:

(1) The role of SiC connection layer prepared by embedding method. Oxide ceramic coatings have high thermal expansion coefficients and poor chemical compatibility with carbon substrates, which easily lead to rapid failure of protective coatings. The thermal expansion coefficient of SiC and carbon matrix is relatively close and the chemical compatibility is better. Using SiC as the inner layer can effectively alleviate the thermal expansion mismatch between the outer coating and the substrate. In addition, using the embedding method to prepare the connecting layer has the advantages of simple process and cost saving. The most important thing is that this method can prepare a C-SiC coating with a certain concentration gradient, which can greatly alleviate the CTE mismatch between the coating and the carbon/carbon composite material, so that the coating sample has excellent thermal shock resistance. performance.

(2) The effect of brush coating method and gas phase reaction method on preparing MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ ceramic coatings. The advantages of the brush coating method are that the method is simple, convenient, fast and low in cost, and the pre-designed coating systems MoSi ₂ and CrSi ₂ can be easily prepared. The pre-designed Si ₂ N ₂ O composition of the coating can be easily obtained by the gas phase reaction method. These components have good chemical and physical compatibility with the SiC layer, and their oxides have excellent oxygen barrier function.

(3) Utilizing the main advantages of the above three methods to prepare a solid bond with the matrix, no penetrating cracks and interlayer cracks, and excellent thermal shock resistance, it can meet the long-term durability of carbon/carbon composite materials in an oxidizing environment. use. Moreover, the above method is easy to be extended and applied to the surface treatment of large-scale carbon/carbon composite materials.

Description of drawings

Fig. 1 is the cross-section, surface morphology and EDS line scanning result of the composite coating of the present invention, (a) is the cross-sectional view of the composite coating, respectively MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ ceramic layer from left to right, Embedded SiC connection layer, carbon/carbon composite material matrix; (b) is the corresponding energy spectrum line scanning results, in which the outer coating is the MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ ceramic layer; (c) is Surface micromorphology of MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ layer;

Figure 2 is the microscopic morphology of the MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ ceramic layer after oxidation at 1500°C;

Fig. 3 is the isothermal oxidation curve of the coating sample of the present invention at 1500° C., and the weight loss rate of the coating sample at 1500° C. is 1.37% after 108 hours.

Detailed ways

The following examples are intended to further illustrate the present invention, rather than limit the present invention.

Example 1

First, cut the C/C composite material into a block sample of 20×20×5mm, grind the chamfer with 400# sandpaper, then finely grind it with 800# sandpaper, clean it with alcohol, and bake it at 120°C for 1-2 hours before use. ;

Next is the embedding process to prepare the SiC connection layer:

The mixed powder for embedding was prepared from Si powder, SiC powder, C powder and Al ₂ O ₃ powder. The mass ratio of the powder is: 50% Si-12% Al ₂ O ₃ -18% C-20% SiC. Weigh Si powder (pass 325 mesh), Al ₂ O ₃ powder (pass 325 mesh), C powder (pass 325 mesh), SiC powder (pass 325 mesh) and use ethanol as dispersant in the above ratio, and place them on planetary Mix well in a ball mill, take out and dry before use. Finally, put the C/C composite material in a graphite crucible and bury it completely with the mixed powder, then put the crucible into a high-temperature furnace, from room temperature to 1100°C, it takes 50min; from 1100°C to 1800°C, it takes 50min 1.5h; heat preservation at 1800°C for 2.5h, protected by argon. This is followed by cooling, which takes 1 hour from 1800°C to 1200°C. Finally cool down with the furnace.

After the SiC bonding layer is prepared, the powder adhering to the coating is cleaned with alcohol in an ultrasonic cleaner, and the sample is placed in an oven at 100°C to fully dry.

Next, the outer layer of MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ is prepared by brush coating method and gas phase reaction method

First weigh MoSi ₂ powder (over 325 mesh), Cr powder (over 325 mesh), Si powder (over 325 mesh), C powder (over 325 mesh) and a small amount of sintering promoter (Al ₂ O ₃ ) to prepare mixed powder, Its weight ratio is MoSi ₂ :Cr:Si:C:Al ₂ O ₃ =25:6:50:11:8. Deionized water is selected as a solvent and polyvinyl alcohol (PVA) is used as a binder, wherein the concentration of the binder is 2-3%. When preparing the slurry, the ratio of the solid-phase mixed powder to the binder is 1g: 20ml. The specific configuration process of the slurry is as follows: 1. Clean the beaker, magnetic stirrer and other experimental related supplies in absolute ethanol with an ultrasonic cleaner; 2. Dry the experimental supplies and solid raw materials required for the experiment; 3. Follow the set recipe Pour various powders into glass cups and stir on a magnetic stirrer for more than 4 hours until the powders are evenly mixed. Next is the coating of pre-coating. Brush the prepared slurry on the cleaned and dried carbon/carbon composite material with SiC inner coating, and put it in an oven with a temperature of 80°C to dry or naturally dry. In order to obtain a certain coating thickness, repeat this process 3-4 times, and then put the coated pre-coated sample in a drying oven at 80°C for 12 hours. Finally, the sample after brushing and drying was put into a vacuum carbon tube sintering furnace, and kept at 1450° C. for 45 minutes under a nitrogen atmosphere. N ₂ and SiO were introduced during the sintering process, and Si ₂ N ₂ O was prepared by gas phase reaction. SiO is produced by the reaction of the mixed powder of Si powder and SiO ₂ powder placed in the sintering furnace, and the mass ratio of the two is Si:SiO ₂ =1:1. The specific heating process is: from room temperature to 1450°C, it takes 140 minutes, argon protection during the heating process, _N2 gas is introduced during the heat preservation process, and the furnace is cooled after the heat preservation.

The last is the anti-oxidation test. After 108 hours, the composite coating sample was subjected to the anti-oxidation test at 1500°C in the air. The coating remained intact without falling off or falling off. The oxidation weight loss rate was only 1.37%.

Example 2

Use 45% Si-10% Al ₂ O ₃ -10% C-35% SiC embedding material to prepare SiC connection layer; use MoSi ₂ : Cr: Si: C: _{Al 2} O ₃ =46:16:30:5: 3 The powder ratio is used to prepare the ceramic outer coating, and the rest of the steps are the same as above. The prepared coating sample was subjected to the oxidation resistance test in air at 1500°C for 108 hours, and the coating remained intact without falling off, and its oxidation weight loss rate was only 1.05%.

Example 3

Use 70% Si-4% Al ₂ O ₃ -12% C-14% SiC embedding material to prepare SiC connection layer; use MoSi ₂ : Cr: Si: C: _{Al 2} O ₃ =35:10:45:6: 4 The powder ratio is used to prepare the ceramic outer coating, and the rest of the steps are the same as above. The prepared coating sample was subjected to the oxidation resistance test in air at 1500°C for 108 hours, and the coating remained intact without falling off, and its oxidation weight loss rate was only 2.15%.

Claims (5)

1. A method for preparing a carbon/carbon composite material for a long time high-temperature oxidation-resistant silicon-based composite coating, characterized in that, The connecting layer and the ceramic coating are sequentially prepared on the surface of the carbon/carbon composite material from the inside to the outside; the connecting layer is a SiC layer prepared by an embedding method, and the ceramic coating is a brush coating method and a gas phase reaction method The prepared ceramic layer of MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ ; The specific steps of preparing the connection layer by the embedding method are as follows: According to the mass ratio: Si40-75%, _Al2O32-13 %, _C8-20 %, SiC10-38%, _weigh Si powder, _Al2O3 powder, C powder, SiC powder, add dispersant, After the ball mill is fully mixed, take it out and dry it for use; finally, put the carbon/carbon composite material in a graphite crucible, and completely bury it with the mixed powder, and then put the crucible into a high-temperature furnace, at 1700°C-2000°C Keep warm at ℃ for 1.5-3h; The specific steps for preparing the MoSi ₂ -Si ₂ N ₂ O-CrSi ₂ ceramic layer by the brush coating method and the gas phase reaction method are as follows: MoSi ₂ : Cr: Si: C: Al ₂ O ₃ = 20-50: 6-20: 30-50: 3-11: 2-10 mixed in weight ratio, using deionized water as solvent, polyvinyl alcohol as Binder, the ratio of solid phase mixed powder to binder is 1-3g:20-30mL; the mass concentration of polyvinyl alcohol is 2~5%; prepare the slurry, brush the prepared slurry on the clean and dry On the dried carbon/carbon composite material with SiC connection layer, dry, repeat brushing and drying 3-4 times, and finally put the sample after brushing and drying into a vacuum carbon tube sintering furnace, in nitrogen Under the atmosphere, keep warm at 1200°C-1600°C for 15-80min; introduce N ₂ and SiO during the sintering process, and prepare Si ₂ N ₂ O by gas phase reaction method; The specific configuration process of the slurry is as follows: use an ultrasonic cleaner to clean the beaker in absolute ethanol, and use a magnetic stirrer for standby; dry the beaker and solid raw materials; weigh various raw material powders according to the set ratio and pour them into the beaker , stir on a magnetic stirrer for at least 4 h until the powder is evenly mixed. the 2. The preparation method according to claim 1, characterized in that, the Si powder, SiC powder, C powder, and _Al2O3 powder all pass through ₃₂₅ mesh. 3. the preparation method according to claim 1 is characterized in that, described MoSi ₂ powder, Cr powder, Si powder, C powder all pass 325 orders. 4. A carbon/carbon composite material long-term high-temperature oxidation-resistant silicon-based composite coating, characterized in that it is a silicon-based composite coating prepared by the method described in any one of claims 1-3. the 5. The application method of the silicon-based composite coating according to claim 4, characterized in that it is applied to the preparation of aero-engine afterburner materials. the

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