CN114538964B - SiC-Si coated carbon/carbon composite material surface rich in MoSi2 high temperature anti-oxidation coating and preparation method - Google Patents

Abstract

The invention relates to a SiC-Si coated carbon/carbon composite material with rich MoSi on the surface ₂ The preparation method comprises the steps of firstly preparing an Mo original coating on the surface of a sample by adopting a slurry brushing method and taking absolute ethyl alcohol, polyvinyl alcohol (PVA) binder and Mo powder as raw materials, and secondly obtaining Mo through heat treatment ₅ Si ₃ Porous layer, finally filling the pores with liquid silicon at high temperature and with Mo ₅ Si ₃ Reaction to prepare the product rich in MoSi ₂ The multiphase damascene coating of (1). The method has simple process and low cost, can adjust the thickness of the coating by brushing times, indirectly regulate and control the phase composition of the final coating by changing the proportion of Mo powder added into slurry, or promote the Mo layer to be converted into Mo by properly increasing the heat treatment temperature and prolonging the time ₅ Si ₃ The efficiency of the porous layer is adjusted, and the pore size of the porous layer is adjusted, so that the MoSi in the coating is optimized ₂ And Si phase distribution. Finally, the design MoSi is adopted ₂ The base anti-oxidation coating system and the method for improving the anti-oxidation performance of the base anti-oxidation coating system provide a simple and effective method.

Description

SiC-Si coated carbon/carbon composite material surface is rich in MoSi2 high temperature anti-oxidation coating and Preparation

technical field

The invention belongs to the surface of a carbon/carbon (C/C) composite material, and relates to a high-temperature anti-oxidation coating and a preparation method thereof, in particular to a SiC-Si coated carbon/carbon composite material surface rich in MoSi2 for high _- temperature oxidation resistance Coating and preparation method.

Background technique

Carbon fiber reinforced carbon matrix (C/C) composites have a series of excellent properties such as low density, high specific strength, high specific modulus, low thermal expansion coefficient, thermal shock resistance, and wear resistance. Above) advanced composite materials that can still maintain their mechanical properties at room temperature in a non-oxidizing atmosphere. The use of C/C composites as hot-end parts of aero-engines (such as turbine disks, combustion chambers, guide vanes, etc.) that are used at high temperatures for a long time has very broad application prospects. However, C/C composites are easily oxidized in a high-temperature oxidizing atmosphere, and the oxidation rate increases rapidly with the increase of temperature. Without protective measures, long-term use of C/C composites in a high-temperature oxidizing environment will inevitably cause disastrous consequences.

Therefore, anti-oxidation becomes the key to the practical application of C/C composites. At present, the high-temperature and long-term anti-oxidation of C/C composite materials mainly adopts coating technology, that is, high-temperature anti-oxidation coatings are prepared on the surface of C/C composite materials to isolate the direct contact between oxygen and C/C composite materials. It is a very effective method to improve the oxidation resistance of C/C composites. Among them, MoSi2 ceramics are materials with excellent high _- temperature oxidation resistance, so MoSi2 _- based coatings are currently one of the most in-depth research and most mature anti-oxidation coating systems. On the one hand, the _SiO2 produced by the oxidation reaction in an aerobic environment has an extremely low oxygen diffusion coefficient at high temperature, which can provide effective oxidation protection for C/C composites; in addition, as the oxidation temperature increases, SiO The viscosity of ₂ is reduced, which can fill cracks and other defects in the coating at high temperature, and act as a sealing substance to block the intrusion of oxygen. So far, the commonly used methods for preparing _MoSi2 ceramic coatings mainly include embedding and solidification method, electrophoretic deposition method, plasma spraying method and so on. Among these preparation methods, due to the high preparation temperature (1900-2100°C) of the embedding and solidification method, it is easy to cause silicide damage to the C/C matrix, and it is difficult to form MoSi due to the influence of the precipitation of MoSi ₂ ceramics in molten silicon. ₂ Coatings with large ceramic content and uniform distribution; the MoSi ₂ coatings prepared by the latter two methods are usually formed only by particle accumulation, resulting in poor bonding and compactness of the substrate. In the end, it is impossible to meet the requirement that the prepared coated C/C composite can be used at high temperature for a long time.

Document 1 "Oxidation-protective and mechanical properties of SiC nanowire-toughened Si–Mo–Cr composite coating for C/C composites, Chu Yan-Hui, Li He-Jun, Fu Qian-Gang, Shi Xiao-Hong, Qi Le- Hua, Wei Bing-Bo.Corrosion Science 58(2012) 315–320”reported the preparation of Si–Mo–Cr multiphase composite coating on the surface of C/C composite materials by embedding and solidification technology, and also used SiC nanowires The coating is toughened. In the method, firstly, a reticular SiC nanowire layer is prepared on the surface of the C/C composite material by CVD method; secondly, MoSi ₂ particles are introduced into the coating layer through the infiltration reaction of molten silicon by embedding method. Although this technology is easy to operate and the cycle is short; however, during the process of embedding and solidification, due to the relatively large molecular weight of MoSi ₂ compared with SiC and Si, physical precipitation easily occurs in molten silicon, and finally the coating "upper and lower "The phase distribution of MoSi ₂ is very different and uneven, so that the MoSi ₂ in the coating cannot fully and uniformly exert its excellent high-temperature oxidation resistance characteristics.

Literature 2 "Influence of iodine concentration on microstructure and oxidation resistance of SiB ₆ –MoSi ₂ coating deposited by pulse arc discharge deposition, Huang Jian-Feng, Zhang Yong-Liang, Zhu Kong-Jun, Cao Li-Yun, Li Cui-Yan, Zhou Lei, Ouyang Hai-Bo, Zhang Bo-Ye, Hao Wei. Journal of Alloys and Compounds 633(2015) 317–322” discloses a novel pulsed arc discharge method on the surface of C/C composites coated with SiC coating To deposit SiB ₆ -MoSi ₂ coating, first prepare a MoSi ₂ suspended charged solution, then place the sample on the cathode in the solution and place it in a hydrothermal reactor, and finally complete the coating deposition process by arc discharge . The results show that the structure of the SiB ₆ – MoSi ₂ coating prepared by this method is relatively loose, and the weight loss of the sample has reached 1.98% after isothermal oxidation protection in the air environment at 1500 ° C for 168 hours, and the SiC inner layer has resisted most of the oxidation protection. Partial oxygen attack.

Document 3 "Oxidation and erosion resistant property of SiC/Si–Mo–Cr/MoSi ₂ multi-layer coated C/C composites,Fu Qian-Gang,Shan Yu-Cai,Cao Cui-Wei,Li He-Jun,Li Ke -Zhi. Ceramics International 41(2015)4101–4107” reported the preparation of MoSi ₂ outer coating on the surface of C/C composite coated with SiC/Si–Mo–Cr double-layer coating by supersonic plasma spraying technology, In this method, the MoSi ₂ powder is first granulated, and then the molten MoSi ₂ is sprayed onto the surface of the sample through the ultra-high temperature plasma flow, and the MoSi ₂ coating is prepared after cooling. Although this technology is easy to operate and has high efficiency, due to the high spraying temperature and short cooling time, it is easy to cause stress concentration and crack the coating; in addition, the coating is composed of particles stacked and there will be a large number of pores, and the particles only rely on Mechanical extrusion bonding, the bonding force is also poor. Therefore, the high temperature oxidation protection performance of the coating is poor.

Contents of the invention

technical problem to be solved

In order to avoid the deficiencies of the prior art, the present invention proposes a SiC-Si coated carbon/carbon composite material surface rich in MoSi ₂ high-temperature anti-oxidation coating and its preparation method, so as to better realize that the coating can protect the C/C composite The long-term service of the material in a high-temperature aerobic environment, and at the same time solve the problems existing in the existing preparation method of MoSi ₂ coating.

Technical solutions

A SiC-Si-coated carbon/carbon composite material surface is rich in MoSi ₂ high-temperature anti-oxidation coating, which is characterized in that: the inner layer is SiC-Si, the outer layer is MoSi ₂ , and the coating is filled with molten silicon; the inner layer The surface connecting SiC-Si and the outer layer has a rough structure, which makes the inner layer of SiC-Si and the outer layer of MoSi ₂ form a mechanically interlocked interface, and the inner and outer layers form a tightly integrated overall structure.

A method for preparing the surface of the SiC-Si coated carbon/carbon composite material rich in MoSi ₂ high temperature oxidation resistant coating, characterized in that the steps are as follows:

Step 1: Ultrasonic cleaning and drying of the C/C composite coated with SiC-Si coating;

Step 2: Apply the slurry solution on the SiC-Si coating and dry it;

The slurry solution is a mixed solution of 54-59.5% by mass percent of absolute ethanol, 0.5% of polyvinyl alcohol PVA and 40-45% of Mo powder;

Step 3: Put it into the corundum crucible again, and place it in a high-temperature tube furnace for heat treatment under a protective atmosphere. During heat treatment, raise the furnace temperature to 1500-1600°C at a heating rate of 5°C/min, and keep it warm for 3-4 hours ; After the heat preservation is completed, the tube furnace is lowered to room temperature at a cooling rate of 10°C/min;

Step 4: Lay the bottom of the graphite crucible with the mixed powder, then put the heat-treated material in step 3 into the graphite crucible, and use the mixed powder to bury it;

The mixed powder is as follows: according to the mass ratio of 15-20:1, the silicon carbon powder is weighed for ball milling, the mixed powder is sieved and dried;

Step 5: Put the graphite crucible in the tube furnace, and repeat the heat treatment step in step 4, wherein the holding temperature is set to 1450-1500°C, the holding time is set to 1-1.5h, and the heating and cooling rates are kept consistent, and finally the rich Multiphase mosaic coating with _MoSi2 .

In the step 3, after the corundum crucible is put into the high-temperature tube furnace, the tube furnace is locked and sealed, vacuumized and kept vacuum for a period of time, and after checking that the airtightness of the equipment is good, the argon gas is slowly ventilated to normal pressure.

In step 3, the tube furnace is lowered to room temperature at a cooling rate of 10° C./min, and finally the argon gas is turned off and the locking valve is disassembled to take out the crucible to obtain materials therefrom.

Beneficial effect

A kind of SiC-Si coated carbon/carbon composite material surface that the present invention proposes is rich in MoSi ₂ High-temperature anti-oxidation coating and preparation method thereof, this method first adopts slurry brushing method to use dehydrated alcohol, polyvinyl alcohol (PVA) Binder and Mo powder were used as raw materials to prepare Mo original coating on the surface of the sample, followed by heat treatment to obtain Mo ₅ Si ₃ porous layer, and finally using liquid silicon to fill the pores at high temperature and react with Mo ₅ Si ₃ to prepare MoSi-rich ₂ for multiphase mosaic coatings. The method is simple in process and low in cost. The thickness of the coating can be adjusted by the number of times of coating, the phase composition of the final coating can be indirectly adjusted by changing the proportion of Mo powder added to the slurry, or by appropriately increasing the heat treatment temperature and prolonging the time. To promote the efficiency of the transformation of the Mo layer into the Mo ₅ Si ₃ porous layer, and at the same time adjust the pore size of the porous layer, thereby optimizing the distribution of the MoSi ₂ and Si phases in the coating. Finally, a simple and effective method is provided for designing MoSi2 _- based anti-oxidation coating system and improving its anti-oxidation performance.

The beneficial effects of the present invention are: the method of applying slurry combined with heat treatment effectively sinters the Mo powder sufficiently; secondly, the free silicon in the inner layer of SiC-Si enters the Mo layer during high-temperature heat treatment and generates The reaction finally generates Mo ₅ Si ₃ ; in addition, the rough structure of the inner layer of SiC-Si can form a mechanically interlocked interface with the Mo ₅ Si ₃ porous layer, ensuring a stable interfacial combination between the two; finally, after being filled with molten silicon, The inner and outer layers form a dense overall structure. Furthermore, compared with methods for preparing _MoSi2 coatings such as embedding and solidification, electrophoretic deposition, and plasma spraying, the preparation method adopted in the present invention has simple procedures and low cost, and the obtained coating has a compact structure, _MoSi2 content and coating Layer thickness is controllable.

Description of drawings

Fig. 1 is an XRD pattern and a scanning electron microscope photo of a Mo ₅ Si ₃ porous layer prepared in an embodiment of the present invention.

Fig. 2 is an XRD pattern and a scanning electron micrograph of a MoSi2 _- rich multi-phase mosaic coating prepared in an embodiment of the present invention.

Fig. 3 is an isothermal oxidation curve of a coating sample prepared in an embodiment of the present invention in air at 1700°C.

Fig. 4 is a scanning electron micrograph of the coating prepared in Counter Example 1 of the embodiment of the present invention.

Fig. 5 is a scanning electron micrograph of the coating prepared in counter example 2 of the embodiment of the present invention.

Fig. 6 is a scanning electron micrograph of the coating prepared in Counter Example 3 of the embodiment of the present invention.

Detailed ways

Now in conjunction with embodiment, accompanying drawing, the present invention will be further described:

Example 1:

1. The coated SiC-Si coated C/C composite material with a size of 10mm×10mm×10mm was ultrasonically cleaned with anhydrous ethanol for 2 hours (the power was set to 100W), and then dried in an oven for later use.

2. Weigh anhydrous ethanol, PVA and Mo powder according to the mass percentages of 54.5%, 0.5% and 45% respectively to prepare a slurry solution. Then use a stirrer to stir the slurry solution for 12h for later use.

3. Apply the SiC-Si coating-coated C/C composite sample prepared in 1 to the surface of the sample evenly with the slurry solution prepared in 2, and then dry it in an oven for later use.

4. Put the sample that has been painted and dried in step 3 into a high-temperature tube furnace for heat treatment in a protective atmosphere. The specific process is as follows:

(1) Put the dried coated Mo layer sample in the corundum crucible, and then put the corundum crucible into the tube furnace;

(2) Carry out locking and sealing treatment on the tube furnace, vacuumize and keep the vacuum for a period of time, check and confirm that the airtightness of the equipment is good, and slowly pass argon to normal pressure;

(3) Raise the furnace temperature to 1500°C at a heating rate of 5°C/min, and keep it warm for 4 hours;

(4) After the heat preservation is completed, the tube furnace is lowered to room temperature at a cooling rate of 10°C/min, and finally the argon gas is turned off and the locking valve is disassembled to take out the crucible, and samples are obtained from it for later use.

5. To prepare the infiltration powder, weigh a certain amount of silicon carbon powder according to the mass ratio of 20:1, carry out ball milling to make it fully mixed, and sieve out the mixed powder and dry it for later use.

6. Pave the bottom of the graphite crucible with the powder mixed in step 5, then put the sample obtained after heat treatment in step 4 into the graphite crucible, and then bury the sample with the powder mixed in step 5.

7. Put the graphite crucible in 6 in the tube furnace, and repeat the heat treatment step in 4, wherein the holding temperature is changed to 1450°C, the holding time is changed to 1.5h, and the heating and cooling rate is kept consistent, and finally the rich _MoSi2 heterogeneous mosaic coating specimen.

From the XRD pattern shown in Figure 1a, it can be determined that the main composition phase of the prepared coating is Mo ₅ Si ₃ . It can be seen from Figure 1b that the Mo ₅ Si ₃ porous layer prepared in this example on the surface of the C/C composite sample coated with SiC-Si coating has a pore size of 1-10 μm and a thickness of the porous layer of ~155 μm. It forms a mechanical interlock interface with the inner layer, which is beneficial to improve the interfacial bonding of the inner and outer coatings.

Example 2:

1. Clean the coated SiC-Si coated C/C composite material with a size of 10mm×10mm×10mm ultrasonically for 2 hours with absolute ethanol (the power is set to 100W), and dry it in an oven for later use.

2. Weigh anhydrous ethanol, PVA and Mo powder according to the mass percentages of 59.5%, 0.5% and 40% respectively to prepare a slurry solution. Then use a stirrer to stir the slurry solution for 12h for later use.

3. Apply the SiC-Si coating-coated C/C composite sample prepared in 1 to the surface of the sample evenly with the slurry solution prepared in 2, and then dry it in an oven for later use.

4. Put the sample that has been painted and dried in step 3 into a high-temperature tube furnace for heat treatment in a protective atmosphere. The specific process is as follows:

(1) Put the dried coated Mo layer sample in the corundum crucible, and then put the corundum crucible into the tube furnace;

(2) Carry out locking and sealing treatment on the tube furnace, vacuumize and keep the vacuum for a period of time, check and confirm that the airtightness of the equipment is good, and slowly pass argon to normal pressure;

(3) Raise the furnace temperature to 1600°C at a heating rate of 5°C/min, and keep it warm for 3 hours;

(4) After the heat preservation is completed, the tube furnace is lowered to room temperature at a cooling rate of 10°C/min, and finally the argon gas is turned off and the locking valve is disassembled to take out the crucible, and samples are obtained from it for later use.

5. To prepare the infiltration powder, weigh a certain amount of silicon carbon powder according to the mass ratio of 15:1, perform ball milling to make it fully mixed, and sieve out the mixed powder and dry it for later use.

6. Pave the bottom of the graphite crucible with the powder mixed in step 5, then put the sample obtained after heat treatment in step 4 into the graphite crucible, and then bury the sample with the powder mixed in step 5.

7. Put the graphite crucible in 6 in the tube furnace, and then repeat the heat treatment step in 4, wherein the holding temperature is changed to 1500°C, the holding time is changed to 1h, and the heating and cooling rate is kept consistent, and finally MoSi-rich ₂ for heterogeneous mosaic coating samples.

From the XRD pattern shown in Figure 2a, it can be determined that the main composition phases of the prepared coating are MoSi ₂ and Si. It can be seen from Figure 2b that the MoSi ₂ -rich multi-phase mosaic coating prepared on the surface of the C/C composite sample coated with SiC-Si coating in this embodiment, and the coating thickness is ~160 μm. After the infiltration of liquid silicon, the inner and outer layers have been integrated into a whole, and no obvious interface was observed. In addition, Figure 3 is the isothermal oxidation mass change curve of the coating sample in air at 1700 °C, and the results show that the coating can protect the C/C composite material in air at 1700 °C for more than 200 h.

Implement counterexample 1:

1. Clean the coated SiC-Si coated C/C composite material with a size of 10mm×10mm×10mm ultrasonically for 2 hours with absolute ethanol (the power is set to 100W), and dry it in an oven for later use.

2. Weigh anhydrous ethanol, PVA and Mo powder according to the mass percentages of 59.5%, 0.5% and 40% respectively to prepare a slurry solution. Then use a stirrer to stir the slurry solution for 12h for later use.

3. Apply the SiC-Si coating-coated C/C composite sample prepared in 1 to the surface of the sample evenly with the slurry solution prepared in 2, and then dry it in an oven for later use.

4. Put the sample that has been painted and dried in step 3 into a high-temperature tube furnace for heat treatment in a protective atmosphere. The specific process is as follows:

(1) Put the dried coated Mo layer sample in the corundum crucible, and then put the corundum crucible into the tube furnace;

(2) Carry out locking and sealing treatment on the tube furnace, vacuumize and keep the vacuum for a period of time, check and confirm that the airtightness of the equipment is good, and slowly pass argon to normal pressure;

(3) Raise the furnace temperature to 1600°C at a heating rate of 5°C/min, and keep it warm for 3 hours;

(4) After the heat preservation is completed, the tube furnace is lowered to room temperature at a cooling rate of 10°C/min, and finally the argon gas is turned off and the locking valve is disassembled to take out the crucible, and samples are obtained from it for later use.

5. To prepare the infiltration powder, weigh a certain amount of silicon carbon powder according to the mass ratio of 10:1, carry out ball milling to make it fully mixed, sieve out the mixed powder and dry it for later use.

6. Pave the bottom of the graphite crucible with the powder mixed in step 5, then put the sample obtained after heat treatment in step 4 into the graphite crucible, and then bury the sample with the powder mixed in step 5.

7. Put the graphite crucible in 6 in the tube furnace, and then repeat the heat treatment step in 4, wherein the holding temperature is changed to 1500°C, the holding time is changed to 1h, and the heating and cooling rate is kept consistent, and finally the coating test is obtained. perform characterization observations.

It can be found from the scanning electron microscope photo of the coating prepared on the surface of the C/C composite material sample coated with SiC-Si coating in the negative example of this embodiment in Fig. 4 that there are some holes in the coating, which is due to the silicon powder in the infiltration powder. A decrease in the content will affect the filling effect of molten silicon on the pores in the Mo ₅ Si ₃ porous layer. In addition, if the pure silicon powder is infiltrated and filled, the sample will be completely bonded in the solidified block of liquid silicon, and the sampling cannot be completed smoothly. Therefore, it is more important to maintain an appropriate proportion of silicon powder in the infiltration mixed powder.

Implement Counter-Example 2:

1. Clean the coated SiC-Si coated C/C composite material with a size of 10mm×10mm×10mm ultrasonically for 2 hours with absolute ethanol (the power is set to 100W), and dry it in an oven for later use.

2. Weigh anhydrous ethanol, PVA and Mo powder according to the mass percentages of 59.5%, 0.5% and 40% respectively to prepare a slurry solution. Then use a stirrer to stir the slurry solution for 12h for later use.

3. Apply the SiC-Si coating-coated C/C composite sample prepared in 1 to the surface of the sample evenly with the slurry solution prepared in 2, and then dry it in an oven for later use.

4. Put the sample that has been painted and dried in step 3 into a high-temperature tube furnace for heat treatment in a protective atmosphere. The specific process is as follows:

(1) Put the dried coated Mo layer sample in the corundum crucible, and then put the corundum crucible into the tube furnace;

(2) Carry out locking and sealing treatment on the tube furnace, vacuumize and keep the vacuum for a period of time, check and confirm that the airtightness of the equipment is good, and slowly pass argon to normal pressure;

(3) Raise the furnace temperature to 1600°C at a heating rate of 5°C/min, and keep it warm for 3 hours;

(4) After the heat preservation is completed, the tube furnace is lowered to room temperature at a cooling rate of 10°C/min, and finally the argon gas is turned off and the locking valve is disassembled to take out the crucible, and samples are obtained from it for later use.

5. To prepare the infiltration powder, weigh a certain mass of NH ₃ F, Al ₂ O ₃ and Si powder according to the mass ratio of 15:55:30, and ball mill them in a dry environment to make them fully mixed for later use.

6. Pave the bottom of the graphite crucible with the powder mixed in step 5, then put the sample obtained after heat treatment in step 4 into the graphite crucible, and then bury the sample with the powder mixed in step 5.

7. Put the graphite crucible in 6 in the tube furnace, and then repeat the heat treatment step in 4, wherein the holding temperature is changed to 1250°C, the holding time is changed to 5h, and the heating and cooling rate remains the same. This step is based on the reported halide-assisted siliconizing method to try to prepare MoSi ₂ coating.

From the scanning electron microscope photo observation of the coating prepared on the surface of the C/C composite material sample coated with SiC-Si coating in the negative example of this embodiment in Figure 5, it is found that the coating is still porous, so the halide-assisted siliconizing method cannot be used. The Mo ₅ Si ₃ porous layer is effectively sealed.

Implement counterexample 3:

1. Clean the coated SiC-Si coated C/C composite material with a size of 10mm×10mm×10mm ultrasonically for 2 hours with absolute ethanol (the power is set to 100W), and dry it in an oven for later use.

2. Weigh anhydrous ethanol, PVA and Mo powder according to the mass percentages of 59.5%, 0.5% and 40% respectively to prepare a slurry solution. Then use a stirrer to stir the slurry solution for 12h for later use.

3. Apply the SiC-Si coating-coated C/C composite sample prepared in 1 to the surface of the sample evenly with the slurry solution prepared in 2, and then dry it in an oven for later use.

4. Put the sample that has been painted and dried in step 3 into a high-temperature tube furnace for heat treatment in a protective atmosphere. The specific process is as follows:

(1) Put the dried coated Mo layer sample in the corundum crucible, and then put the corundum crucible into the tube furnace;

(2) Carry out locking and sealing treatment on the tube furnace, vacuumize and keep the vacuum for a period of time, check and confirm that the airtightness of the equipment is good, and slowly pass argon to normal pressure;

(3) Raise the furnace temperature to 1600°C at a heating rate of 5°C/min, and keep it warm for 3 hours;

(4) After the heat preservation is completed, the tube furnace is lowered to room temperature at a cooling rate of 10°C/min, and finally the argon gas is turned off and the locking valve is disassembled to take out the crucible, and samples are obtained from it for later use.

5. To prepare the infiltrating powder, weigh a certain amount of Si, C and Al ₂ O ₃ powder according to the mass ratio of 5:1:0.5, carry out ball milling to make them fully mixed, sieve out the mixed powder and dry it for later use.

6. Pave the bottom of the graphite crucible with the powder mixed in step 5, then put the sample obtained after heat treatment in step 4 into the graphite crucible, and then bury the sample with the powder mixed in step 5.

7. Put the graphite crucible in 6 in the tube furnace, and then repeat the heat treatment step in 4, wherein the holding temperature is changed to 2100°C, the holding time is changed to 2h, and the heating and cooling rate remains the same. In this step, the Mo ₅ Si ₃ porous layer is sealed by using the reported embedding method.

It can be found from the scanning electron microscope photo of the coating prepared on the surface of the C/C composite material sample coated with SiC-Si coating in the negative example of this embodiment in Fig. 6 that although the coating structure is compact, the content of MoSi ₂ phase (white area) accounts for Therefore, the high-temperature embedding method cannot be used to prepare MoSi ₂ -rich multi-phase mosaic coatings.

In all embodiments, described dehydrated alcohol is analytically pure (mass percentage composition≥99.8%), and the purity of Si powder is 99.5%, and particle size is 500 orders, and the purity of C powder is 99.5%, and particle size is 500 orders, The Al ₂ O ₃ powder has a purity of 99.5% and a particle size of 500 meshes, and the Mo powder has a purity of 99.5% and a particle size of 1-5 μm.

Claims (3)

1. A method for preparing a SiC-Si coated carbon/carbon composite surface rich in MoSi ₂ high-temperature oxidation-resistant coating, characterized in that: the inner layer is SiC-Si, the outer layer is MoSi ₂ , and the coating is filled with Fused silicon; the surface where the inner layer SiC-Si and the outer layer connect is a rough structure, which makes the SiC-Si inner layer and the MoSi ₂ outer layer form a mechanically interlocked interface, and the inner and outer layers form a tightly integrated overall structure; the prepared The steps of the coating are as follows: Step 1: Ultrasonic cleaning and drying of the C/C composite coated with SiC-Si coating; Step 2: Apply the slurry solution on the SiC-Si coating and dry it; Described slurry solution is the mixed solution of the dehydrated alcohol of mass percent 54～59.5%, the polyvinyl alcohol PVA of 0.5% and the Mo powder of 40～45%; Step 3: Put it into the corundum crucible again, and place it in a high-temperature tube furnace for heat treatment under a protective atmosphere. During heat treatment, raise the furnace temperature to 1500~1600℃ at a heating rate of 5℃/min, and keep it warm for 3~4h ; After the heat preservation is completed, the tube furnace is lowered to room temperature at a cooling rate of 10°C/min; Step 4: Lay the bottom of the graphite crucible with the mixed powder, then put the heat-treated material in step 3 into the graphite crucible, and use the mixed powder to bury it; The mixed powder is as follows: according to the mass ratio of 15-20:1, the silicon carbon powder is weighed for ball milling, the mixed powder is sieved and dried; Step 5: Put the graphite crucible in the tube furnace, and then repeat the heat treatment step in step 4, wherein the holding temperature is set to 1450~1500°C, the holding time is set to 1~1.5h, and the heating and cooling rates are kept consistent, and finally the rich Multiphase mosaic coating with _MoSi2 . 2. The method according to claim 1, characterized in that: in step 3, after the corundum crucible is put into the high-temperature tube furnace, the tube furnace is locked and sealed, vacuumed and vacuumed for a period of time, and then checked and determined After the airtightness of the equipment is good, the argon gas is slowly ventilated to normal pressure. 3. The method according to claim 1, characterized in that in step 3, the tube furnace is lowered to room temperature at a cooling rate of 10°C/min, and finally the argon gas is turned off and the locking valve is disassembled to take out the crucible, from which Material.

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