Preparation method and application of SiC / SiC ceramic-based composite material with Si-based Hf-doped coating

Abstract

The invention relates to the technical field of coating preparation, and discloses a preparation method and application of a SiC / SiC ceramic-based composite material with a Si-based Hf-doped coating. The bonding layer is prepared on the surface of the SiC / SiC composite material by adopting a double-layer glow plasma surface metallurgy process and consists of an outer Si-Hf deposition layer and an inner mutual diffusion layer, and the contents of Si, Hf and C in the diffusion layer are changed in a gradient manner, so that the failure caused by component mutation and property difference is relieved. The high-temperature water oxygen corrosion resistance of the Si-based doped Hf coating is improved, meanwhile, the service environment temperature of an engine is increased, the service life of the engine is prolonged, and the Si-Hf coating prepared through the method has wide application prospects in the aerospace field.

Description

Technical Field

[0001] The present invention relates to the technical field of coating preparation, and particularly relates to a preparation method and application of a SiC / SiC ceramic matrix composite material with a Si-based doped Hf coating. Background Art

[0002] Due to the development of aeroengines that requires continuous improvement of its thrust-to-weight ratio, the gas temperature in front of the turbine is getting higher and higher. Therefore, the requirements for the high-temperature strength, corrosion resistance, oxidation resistance, etc. of the materials for its hot-end components are also getting higher and higher. SiC ceramic matrix composites have the advantages of low density, excellent mechanical properties, oxidation resistance, etc., and are potential alternative materials for superalloys used in the hot-end components of high-thrust-to-weight-ratio aeroengines, such as combustion chamber flame tubes, guide vane blades, outer ring blocks, working blades, the flow-through part of the turbine frame, as well as regulating vanes, sealing sheets, etc. When an aeroengine is operating, the interaction of multiple factors such as high-temperature and high-speed gas erosion, complex stress environment, and the presence of pores in the composite material itself causes the surface stability of the continuous SiC fiber-reinforced SiC ceramic matrix composite to deteriorate rapidly, which is one of the main factors restricting its application in the hot-end components of aeroengines. In the high-temperature and high-speed gas of an aeroengine, there is oxygen and water vapor with a volume fraction of 5% - 10%. When the aeroengine is operating, the oxygen therein will react with SiC to form a dense SiO2 film, and then SiO2 will react with high-temperature water vapor to form a volatile product Si(OH)4, which will cause corrosion degradation of the material, namely high-temperature water-oxygen corrosion.

[0003] Finding effective methods to resist high-temperature water-oxygen corrosion is a key requirement for expanding the application fields of SiC / SiC ceramic matrix composites. To improve the corrosion resistance of SiC / SiC ceramic matrix composites in a high-temperature water-oxygen environment, the mainstream coating technologies include:

[0004] 1. SiC / Si3N4 coatings: Prepared by CVD, PVD or slurry sintering, with good thermal matching but prone to failure due to the formation of volatile Si(OH)4 by water-oxygen; 2. Noble metal coatings (Pt, Ir): Prepared by electroplating or magnetron sputtering, with strong corrosion resistance but high cost and poor adhesion; 3. Rare earth silicate coatings (Y2SiO5, etc.): Prepared by sol-gel or plasma spraying, with excellent water-oxygen resistance but high brittleness; 4. Multilayer composite coatings (such as SiC / mullite / YSZ): The gradient structure alleviates thermal stress, but the process is complex and prone to interface defects; 5. MAX phase coatings (such as Ti3SiC2): Having both toughness and oxidation resistance, but with insufficient long-term stability. The insufficient bonding strength between the coating and the matrix and the growth of the TGO oxide layer greatly limit the safety and service life of the coating. Summary of the Invention

[0005] At present, when SiC / SiC ceramic matrix composites are used as hot-end components of aeroengines, when facing high-temperature water-oxygen corrosion, the reaction products are prone to sublimation, generating cracks, resulting in a decrease in the strength of the parts, causing failure, and affecting the service life. The present invention aims to solve problems such as weak bonding strength between the coating and the matrix, insufficient service temperature of the coating, and coating failure in a high-temperature water-oxygen environment, and provides a preparation method and application of a SiC / SiC ceramic matrix composite with a Si-based doped Hf coating. This coating has a high bonding strength with the ceramic matrix and strong resistance to high-temperature water-oxygen corrosion, so as to improve the safety and service life of the SiC / SiC ceramic matrix composite.

[0006] To solve the problems of the prior art, the technical solution adopted by the present invention is:

[0007] A preparation method of a SiC / SiC ceramic matrix composite with a Si-based doped Hf coating is prepared by a double-glow plasma surface metallurgy process. The specific steps are as follows:

[0008] Step 1, surface treatment and cleaning of the substrate. Sand the substrate with 1000# sandpaper and ultrasonically clean it for 10 - 15 minutes, using ethanol as the cleaning medium.

[0009] Step 2, use the double-glow plasma surface metallurgy process to prepare a coating on the surface of the substrate. The targets are Si and Hf grid-shaped targets.

[0010] Step 3, vacuum diffusion annealing to promote element diffusion.

[0011] As an improvement, the substrate in Step 1 is a SiC / SiC ceramic matrix composite.

[0012] As an improvement, the purity of the Si target and the Hf target in Step 2 is 99.95%, and the protective atmosphere of the double-glow plasma surface metallurgy process is argon.

[0013] As an improvement, the process parameters adopted in Step 2 are: the working furnace pressure is 35 Pa, the workpiece voltage is 350 V, and the source electrode voltage is 750 V; the process temperature is 900 - 1100 °C, the electrode spacing is 18 mm, and the working time is 8 h; the vacuum diffusion annealing temperature is 600 - 1200 °C.

[0014] The SiC / SiC ceramic matrix composite with a Si-based doped Hf coating prepared by the above preparation method. The surface layer of the Si-based doped Hf coating is a Si-Hf deposition layer, and the inner layer is a diffusion layer connected to the SiC / SiC ceramic matrix composite. Interdiffusion occurs between the diffusion layer and the matrix; the thickness of the Si-based doped Hf coating is 20 - 40 μm; the working temperature exceeds 1250 °C.

[0015] Application of the above SiC / SiC ceramic matrix composite with Si-based doped Hf coating on the protective layer of working equipment in a high-temperature water-oxygen environment.

[0016] Beneficial effects:

[0017] During service, SiC / SiC ceramic matrix composites are subject to continuous high-temperature oxidation, high-temperature water-oxygen corrosion, and thermal shock. The conventional SiC / SiC ceramic matrix composites produce SiO2 due to continuous high-temperature oxidation. The phase change caused by the generation of oxides leads to volume changes, thereby generating internal stress. At the same time, the reaction with high-temperature water vapor produces volatile Si(OH)4, accelerating the spalling failure of the coating. In order to increase the service temperature of SiC / SiC ceramic matrix composites, their high-temperature oxidation resistance, high-temperature water-oxygen corrosion resistance, and extend their service life, the present invention uses a Si-Hf coating. Hf can improve the stability and denseness of the SiO2 layer, enhancing its ability to resist spalling and crack propagation. The high melting point (2758 °C) of HfO2 generated by high-temperature oxidation can increase the service temperature of the coating. Si-O-Hf will form a chemical bond, reacting to form HfSiO4 with a low oxygen diffusion rate and good phase stability, which can not only weaken the accumulation of thermal stress caused by phase change, but also effectively prevent the internal cracks of the coating from connecting with each other during the growth process of the dispersed HfSiO4 / HfO2 particles, making the ceramic coating have good high-temperature water-oxygen corrosion resistance.

[0018] In addition, the double glow plasma surface metallurgy process used in the present invention has the function of metal and non-metal unit or multi-element composite plating, and can prepare a dense and uniform plating layer, which makes the prepared coating have good bonding strength with the substrate, greatly reducing the stress concentration during mechanical stress or thermal cycling, and improving safety and service life.

[0019] Specific advantages are as follows:

[0020] (1) Adding a certain amount of active metal element Hf to the coating. On the one hand, Hf can improve the stability and denseness of the SiO2 layer, enhancing its ability to resist spalling and crack propagation, and further improving the protection effect. On the other hand, using the double glow plasma surface metallurgy process for preparation can improve the bonding strength between the coating and the substrate;

[0021] (2) HfSiO4 formed in a high-temperature oxidation environment has excellent high-temperature water-oxygen corrosion resistance, can significantly increase the working temperature of the coating, inhibit phase change, reduce stress concentration, and has a certain crack self-healing ability; at the same time, the doping of Hf can reduce the difference in thermal expansion coefficients between the coating and the substrate.

[0022] (3) Compared with traditional processes (such as thermal spraying and cold spraying), the double glow plasma surface metallurgy process has the function of metal and non-metal unit or multi-element composite infiltration plating, and can prepare a dense and uniform infiltration coating with a continuous gradient structure. This makes the prepared coating have good bonding strength with the substrate, greatly reduces the stress concentration during mechanical stress or thermal cycling, significantly reduces the influence of phase volume change caused by the coefficient of thermal expansion, and greatly improves the service environment and service life of the coating substrate. At the same time, the doped Hf helps to improve the high-temperature water and oxygen corrosion resistance of the coating and reduce the oxidation rate, showing broad application prospects in the aerospace field. Description of the Drawings

[0023] Figure 1 Schematic diagram of the structure of the coating with a gradient structure prepared in Example 1 of the present invention;

[0024] Figure 2 Schematic diagram of the cross-sectional morphology of the coating prepared in Example 1 of the present invention;

[0025] Figure 3 Schematic diagram of the cross-sectional element distribution of the coating (a) prepared in Example 1 of the present invention and the coating (b) of Comparative Example 1 after high-temperature water and oxygen corrosion;

[0026] Figure 4 Surface morphology of the coating prepared in Example 1 of the present invention at 25 h (a), 50 h (b), 75 h (c), and 100 h (d) of high-temperature water and oxygen corrosion. Detailed Description of the Invention

[0027] The specific embodiments of the present invention will be described in detail below with reference to the specific drawings. It should be noted that the technical features described in the following embodiments or the combination of technical features should not be considered isolated, and they can be combined with each other to achieve better technical effects.

[0028] Example 1

[0029] A preparation method of a SiC / SiC ceramic matrix composite material with a Si-based doped Hf coating, comprising the following steps:

[0030] Step 1, pretreatment of the substrate material:

[0031] Prepare a SiC / SiC ceramic matrix composite material, and polish it step by step on metallographic sandpaper in the order of 180# to 1000#, and then polish it to a mirror surface without scratches. After ultrasonic cleaning in alcohol, dry it for standby;

[0032] Step 2, cleaning and placing the workpiece:

[0033] Use fine sandpaper to polish the interior of the double glow furnace body, the thermal insulation cover, and the target. After polishing, clean them with alcohol. During the preparation process, the SiC / SiC ceramic matrix composite material serves as the cathode, and the Hf and Si targets serve as the source electrodes. The target is a grid target, specifically a hafnium target and a silicon target, and the purity of the target is 99.95%.

[0034] Step 3, evacuate the vacuum:

[0035] Turn on the mechanical pump and evacuate the air pressure in the double glow furnace to below 0.1 Pa. Then, introduce argon for ten minutes for gas cleaning to remove gas impurities in the furnace and avoid contamination of the coating sample by impurity gases during the preparation process. As the working gas, argon will be continuously introduced during the preparation process.

[0036] Step 4, initiate glow discharge:

[0037] Start the bias power supply cabinet and gradually adjust the workpiece voltage to 500 V and then keep it warm for 15 minutes to bombard the workpiece surface with argon ions to remove impurities on the workpiece surface. At the same time, provide high temperature and defect concentration on the workpiece surface to create conditions for diffusion;

[0038] Step 5, prepare the Si-Hf coating by double glow plasma metallurgy technology:

[0039] The distance between the lower surface of the Hf and Ta targets and the upper surface of the SiC / SiC ceramic matrix composite material is 18 mm. The air pressure in the furnace is controlled at 35 Pa, the source electrode voltage is set at 750 V, and the workpiece voltage is set at 350 V. Prepare the Si and Hf coatings for 8 h under pure argon conditions;

[0040] Step 6, shut down the equipment:

[0041] When the heat preservation is completed, slowly reduce the workpiece voltage and the source electrode voltage to 300 V and 400 V respectively. After keeping it warm for 30 minutes, shut down the equipment;

[0042] Step 7, vacuum annealing:

[0043] Put the prepared semi-finished product into a vacuum tube furnace, heat it to 800 °C at a rate of 10 °C / min and then keep it warm for 6 h for vacuum diffusion annealing. Then, cool it to room temperature at a rate of 10 °C / min and take out the sample.

[0044] Conduct high-temperature water and oxygen corrosion experiments on the prepared Si-Hf coating, observe the surface morphology after high-temperature water and oxygen corrosion, and study the high-temperature water and oxygen corrosion behavior of the Si-Hf coating using a high-temperature water and oxygen tube furnace.

[0045] The specific operations are as follows: Measure and record the weight of the sample, place the sample in a crucible, then put the crucible into a tube furnace, gradually increase the temperature of the tube furnace to 1350 °C at a rate of 5 °C / min, then introduce steam and oxygen according to the ratio of 90% H2O - 10% O2, keep the temperature for 100 h, and then gradually cool the temperature of the tube furnace to 25 °C at a rate of 5 °C / min. After taking out the sample, measure and record the weight of the sample. Calculate the coating weight gain rate to be 3.5×10 -2 mg / (cm 2 ·h).

[0046] Comparative Example 1

[0047] Compared with Example 1, instead of preparing a coating on the substrate surface, a high-temperature water-oxygen corrosion experiment is directly carried out, the surface morphology after high-temperature water-oxygen corrosion is observed, and the high-temperature water-oxygen corrosion behavior of SiC / SiC ceramic matrix composites is studied using a high-temperature water-oxygen tube furnace.

[0048] The specific operations are as follows: Measure and record the weight of the sample, place the sample in a crucible and then put the crucible into a tube furnace, gradually increase the temperature of the tube furnace to 1350 °C at a rate of 5 °C / min, then introduce steam and oxygen according to the ratio of 90% H2O - 10% O2, keep the temperature for 100 h, and then gradually cool the temperature of the tube furnace to 25 °C at a rate of 5 °C / min. After taking out the sample, measure and record the weight of the sample. Calculate the weight gain rate of the SiC / SiC ceramic matrix composite sample to be 1.25×10 -1 mg / (cm 2 ·h).

[0049] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a SiC / SiC ceramic matrix composite with an Si-based doped Hf coating, characterized in that, It is prepared by using the double glow plasma surface metallurgy process, and the specific steps are as follows: Step 1, surface treatment and cleaning of the substrate. Sand the substrate with 1000# sandpaper, and ultrasonically clean it for 10 - 15 minutes with ethanol as the cleaning medium; Step 2, use the double glow plasma surface metallurgy process to prepare a coating on the substrate surface. The target materials are Si and Hf grid-shaped target materials; Step 3, vacuum diffusion annealing to promote element diffusion.

2. The preparation method of a SiC / SiC ceramic matrix composite with a Si-based doped Hf coating according to claim 1, characterized in that, The substrate described in Step 1 is a SiC / SiC ceramic matrix composite.

3. The preparation method of a SiC / SiC ceramic matrix composite with a Si-based doped Hf coating according to claim 1, characterized in that, The purity of the Si target and the Hf target described in Step 2 is 99.95%, and the protective atmosphere of the double glow plasma surface metallurgy process is argon.

4. The preparation method of a SiC / SiC ceramic matrix composite with a Si-based doped Hf coating according to claim 1, characterized in that, The process parameters used in Step 2 are: the working furnace pressure is 35 Pa, the workpiece voltage is 350 V, and the source voltage is 750 V; the process temperature is 900 - 1100 °C, the electrode spacing is 18 mm, and the working time is 8 h; the vacuum diffusion annealing temperature is 600 - 1200 °C.

5. A SiC / SiC ceramic matrix composite with a Si-based doped Hf coating prepared by the preparation method according to any one of claims 1-4, characterized in that The surface layer with the Si-based doped Hf coating is a Si-Hf deposition layer, and the inner layer is a diffusion layer connected to the SiC / SiC ceramic matrix composite. Interdiffusion occurs between the diffusion layer and the substrate; the thickness of the Si-based doped Hf coating is 20 - 40 μm; the working temperature exceeds 1250 °C.

6. Application of the SiC / SiC ceramic matrix composite with a Si-based doped Hf coating according to claim 5 on the protective layer of a working device in a high-temperature water-oxygen environment.

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