Preparation method of a graphite-based Yb2O3-TiB2-SiC ceramic coating material

Abstract

The present invention relates to the technical field of graphite-based ceramic coating materials, and particularly relates to a preparation method of a graphite-based Yb2O3-TiB2-SiC ceramic coating material. The method of the present invention mixes SiC powder, TiB2 powder and Yb2O3 powder evenly, coats them on a graphite substrate and sinter them. During the sintering process, pressure is applied, and the sintering pressure is controlled to be 30 MPa. After the sintering process is completed, the graphite-based Yb2O3-TiB2-SiC ceramic coating material can be obtained. The method of the present invention performs sintering under pressure, and there is no need to prepare a SiC bottom layer between the graphite substrate and the ceramic coating, thus solving the problem of unstable performance of the ceramic coating caused by the mismatch of thermal expansion coefficients between the graphite substrate and the ceramic coating. The obtained ceramic coating has good bonding with the substrate, the surface of the ceramic coating is flat, the composition distribution is uniform, there are no obvious defects, and the performance is stable; at the same time, the preparation method is simpler and more efficient, the coating thickness is controllable, and it has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of graphite-based ceramic coating materials, and particularly to a preparation method of a graphite-based Yb2O3-TiB2-SiC ceramic coating material. Background Art

[0002] Ceramic coatings are the general name for various inorganic protective layers, and have advantages such as wear resistance, corrosion resistance, high temperature resistance, high hardness, high strength, and good biocompatibility; ceramic coatings can provide special functional characteristics for the substrate to overcome the defects of the substrate material and improve the use efficiency of the material; therefore, ceramic coatings are widely used in the fields of aerospace, automotive manufacturing, energy, chemical industry, electronics, and biomedicine; in the face of the requirements of the industrial engineering field, it is urgent to prepare ceramic coatings with excellent performance.

[0003] Due to the difference in thermal expansion coefficients between the substrate material and the ceramic coating, in existing preparation methods, an inner coating is often prepared between the substrate material and the ceramic coating to ensure the stability of the ceramic coating; for example: Ren et al. (Xuanru Ren, et al., Preparation of oxidation protective Hf 0.2 Ta 0.8 B 2-x -SiC coating by in-situ reaction method on SiC-coated carbon / carbon composite, Journal of Alloys and Compounds, 2015, 618: 390-395.) prepared an outer coating of Hf0.2Ta0.8B2-x on the surface of a C / C substrate with an SiC inner coating by the in-situ reaction method; Chinese invention patent: "CN111960830A A SiC / HfB2-SiC-La2O3 / SiC anti-ultra-high temperature oxidation composite coating on a graphite substrate", prepared an SiC bottom layer between the graphite substrate and the ceramic coating, etc.

[0004] However, preparing an inner coating between the substrate material and the ceramic coating makes the preparation process more complex, takes longer time and has low efficiency on the one hand, and also increases the preparation cost, bringing inconvenience to practical applications on the other hand. Summary of the Invention

[0005] The object of the present invention is to provide a preparation method of a graphite-based Yb2O3-TiB2-SiC ceramic coating material, so as to solve the problem that the existing preparation methods all adopt the inner coating method to deal with the difference in thermal expansion coefficient between the matrix material and the ceramic coating, resulting in long material preparation time, low efficiency and high cost, which is not convenient for practical application.

[0006] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a graphite-based Yb2O3-TiB2-SiC ceramic coating material, comprising the following steps:

[0007] S1. Mix SiC powder, TiB2 powder and Yb2O3 powder according to a certain mass ratio to obtain a uniformly mixed raw material powder;

[0008] S2. Pretreat the graphite matrix;

[0009] S3. Coating the raw material powder obtained in S1 on the pretreated graphite matrix in S2, and performing high-temperature sintering under pressure to obtain the graphite-based Yb2O3-TiB2-SiC ceramic coating material.

[0010] Further, in the S1, the particle sizes of the SiC powder, TiB2 powder and Yb2O3 powder are all 4-8 μm; the purities of the SiC powder, TiB2 powder and Yb2O3 powder are ≥99.9%.

[0011] Further, in the S1, the mass ratio of the SiC powder, TiB2 powder and Yb2O3 powder is 2:3:0.4.

[0012] Further, in the S1, the mixed powder is uniformly mixed by wet ball milling to form a slurry, and the slurry is dried and sieved to obtain a uniformly mixed raw material powder.

[0013] Further, the mass ratio of the grinding balls to the raw material powder in the ball milling is 2:1, the grinding balls are composed of ZrO2, the diameter is 3 mm; the ball milling medium is anhydrous ethanol; the ball milling speed of the ball milling is 90 r / min, and the ball milling time is 24 h.

[0014] Further, in the sieving process, a 30-mesh stainless steel sieve is used to separate the grinding balls in the slurry, and the separated slurry is placed in an 80°C constant temperature drying oven for drying for 12 h, and a 200-mesh stainless steel sieve is used to sieve the dried powder to obtain a uniformly mixed raw material powder.

[0015] Further, in the S2, the method for pretreating the graphite matrix powder is: sandpaper is used to polish the surface of the graphite matrix, and after polishing, ultrasonic cleaning and drying operations are performed.

[0016] Further, the specification of the graphite substrate is a disc with a diameter of Φ18mm and a thickness of 3mm; the graphite substrate is polished with 200-mesh and 800-mesh sandpapers respectively, and the polishing time for both sandpapers on the graphite substrate is 2 minutes; the ultrasonic cleaning frequency is 40kHz, and the ultrasonic time is 5 minutes; drying is carried out in a constant-temperature drying oven, the drying temperature is 80°C, and the drying time is 2 hours.

[0017] Further, in the step S3, the temperature control program for the sintering process is as follows: the heating rate is 50°C / min below 1000°C; the heating rate is 30°C / min from 1000°C to the highest temperature; the holding time after heating to the highest temperature is 20 minutes; then it is cooled to 1000°C at a rate of 50°C / min, and then cooled to room temperature with the furnace; the highest temperature ≥ 1800°C.

[0018] Further, in the step S3, the pressure applied during the sintering process is 30Mpa.

[0019] Advantages of the present invention:

[0020] 1. The method of the present invention realizes the preparation of Yb2O3-TiB2-SiC single ceramic coating on the graphite substrate under pressurized conditions, and the preparation process is simpler and more efficient;

[0021] 2. The Yb2O3-TiB2-SiC ceramic coating obtained by the method of the present invention has a flat layer surface, uniform composition distribution, no obvious defects, good bonding with the substrate, solves the problem of unstable performance of the ceramic coating caused by the mismatch of thermal expansion coefficients between the graphite substrate and the ceramic coating, and ensures the stability of the ceramic coating;

[0022] 3. The Yb2O3-TiB2-SiC ceramic coating obtained by the method of the present invention has good oxidation resistance at high temperatures. In addition, the thickness of the coating can be adjusted to further improve the oxidation resistance of the material, and has broad application prospects. Description of the drawings

[0023] Figure 1 is the X-ray diffraction pattern of the Yb2O3-TiB2-SiC ceramic coating prepared in Example 1 of the present invention;

[0024] Figure 2 is the surface morphology photo (100μm) of the Yb2O3-TiB2-SiC ceramic coating prepared in Example 1 of the present invention;

[0025] Figure 3 is the surface morphology photo (1μm) of the Yb2O3-TiB2-SiC ceramic coating prepared in Example 1 of the present invention;

[0026] Figure 4 It is a cross-sectional morphology photo of the Yb2O3-TiB2-SiC ceramic coating prepared in Example 1 of the present invention;

[0027] Figure 5 It is a surface morphology photo of the Yb2O3-TiB2-SiC ceramic coating prepared in Comparative Example 1 of the present invention;

[0028] Figure 6 It is the surface morphology of the Yb2O3-TiB2-SiC ceramic coating prepared in Example 1 of the present invention after oxidation at 1300 °C for 24 h;

[0029] Figure 7 It is the cross-sectional morphology of the Yb2O3-TiB2-SiC ceramic coating prepared in Example 1 of the present invention after oxidation at 1300 °C for 24 h;

[0030] Figure 8 It is a macroscopic photo of the sample prepared in Comparative Example 2 of the present invention. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0032] Example 1

[0033] A method for preparing a ceramic coating includes the following steps:

[0034] S1. Using raw materials TiB2, SiC and Yb2O3, calculate and weigh according to a mass ratio of 2:3:0.4; wherein the particle sizes of TiB2 powder, SiC powder and Yb2O3 powder are all 4-8 μm, the purity is ≥99.9%, after weighing the powder, add the raw material powder, zirconia grinding balls with a diameter of 3 mm and absolute ethanol into the ball mill according to a mass ratio of 1:2:7, and perform roller ball milling for 24 h at a rotation speed of 90 r / min; the milled powder is separated from the grinding balls through a 30-mesh stainless steel sieve, and the sieved slurry is placed in an 80 °C constant temperature drying oven for drying for 12 h. After the dried powder is sieved through a 200-mesh stainless steel sieve, a uniformly mixed dried powder is obtained.

[0035] S2. Using a graphite wafer with a specification of Φ18 mm × 3 mm as the substrate; first, manually grind and polish the graphite wafer on 200-mesh SiC sandpaper for 2 min, rinse the residual particles on the graphite surface with clear water, then use 800-mesh SiC sandpaper to grind and polish for 2 min, after rinsing off the residual particles on the surface, perform ultrasonic cleaning at a frequency of 40 kHz for 5 min, remove impurities and then place it in an 80 °C constant temperature drying oven for drying for 12 h.

[0036] S3. Load the dried powder obtained in S1 and S2 and the treated graphite matrix into a special die for spark plasma sintering with a specification of Φ20mm. Separate the powder and the die with clean carbon paper. Weigh 1.5g of the powder to wrap the graphite matrix in the center, and flatten the surface of the powder after each step. After installing the die, perform spark plasma sintering with a set sintering pressure of 30MPa.

[0037] The temperature regime of the sintering program is as follows: During the heating process, the heating rate is 50°C / min below 1000°C; the heating rate is 30°C / min from 1000 to 1800°C. After holding at 1800°C for 20 min, cool down to 1000°C at a rate of 50°C / min, and finally cool down to room temperature with the furnace. After taking it out, perform grinding and polishing treatment with sandpaper to remove the carbon paper, and obtain the Yb2O3-TiB2-SiC ceramic coating sample.

[0038] As Figure 1 shown, the phase composition of the prepared Yb2O3-TiB2-SiC ceramic coating sample is Yb2O3, TiB2, and SiC, and there are no other impurity diffraction peaks, indicating that the coating has been successfully prepared.

[0039] Figure 2 , 3 and Figure 4 respectively show the surface and cross-sectional morphologies of the coating sample. The surface of the coating is flat, the composition distribution is uniform, there are no obvious defects, and the bonding with the matrix is good. In addition, during the coating preparation process, its composition and thickness are controllable.

[0040] Investigation on oxidation resistance experiment:

[0041] Take the material obtained in this example and oxidize it in a static air environment at 1300°C for 24h. The weight gain per unit area is 0.92mg / cm 2 , showing good oxidation resistance.

[0042] As Figure 6 shown, it can be seen from the surface morphology of the oxidized coating that a dense oxide layer is formed on the surface of the oxidized coating sample. TiO2 with light gray contrast and Yb2Si2O7 with bright white contrast are closely embedded in SiO2 with dark gray contrast, and they have a pinning effect on the oxide layer, which is beneficial to improving the high-temperature stability of the oxide layer.

[0043] As Figure 7 shown, it can be known from the cross-sectional morphology image of the oxidized coating sample that both the coating and the oxide layer are relatively complete, there are no obvious defects, and it shows good high-temperature stability; it should be noted that the coating thickness of the material of the present invention is controllable, and the high-temperature oxidation resistance of the material can be further improved by increasing the thickness.

[0044] Example 2

[0045] In S3, sintering is carried out at 1900 °C, and other conditions are the same as in Example 1.

[0046] The obtained coating was detected to be basically the same as that in Example 1, and the coating was successfully prepared.

[0047] Comparative Example 1

[0048] A method for preparing a ceramic coating, comprising the following steps:

[0049] S1. Using raw materials TiB2, SiC and Yb2O3, weighing according to the mass fraction ratio of 2:3:0.4; wherein the particle sizes of TiB2 powder, SiC powder and Yb2O3 powder are 4-8 μm, and the purity is ≥99.9%. After weighing the powders, the raw material powders, zirconia grinding balls with a diameter of 3 mm and absolute ethanol are added to the ball mill tank according to the mass ratio of 1:2:7, and ball milling is carried out for 24 h at a rotation speed of 90 r / min. The ball-milled powder is separated from the grinding balls through a 30-mesh stainless steel sieve, and the sieved slurry is placed in an 80 °C constant-temperature drying oven for drying for 5 h. After the dried powder is sieved through a 200-mesh stainless steel sieve, a uniformly mixed dried powder is obtained.

[0050] S2. Using a graphite wafer with a specification of Φ18 mm×3 mm as the substrate; first, the graphite wafer is ground and polished manually on 200-mesh SiC sandpaper for 2 min, and the residual particles on the graphite surface are washed away with clear water. Then, it is ground and polished with 800-mesh SiC sandpaper for 2 min. After washing away the residual particles on the surface, it is ultrasonically cleaned at a frequency of 40 kHz for 5 min. After removing impurities, it is placed in an 80 °C constant-temperature drying oven for drying for 2 h.

[0051] S3. The dried powder obtained in S1 and the treated graphite substrate are loaded into a special mold for spark plasma sintering with a specification of Φ20 mm, and a clean carbon paper is used to separate the powder and the mold; 1.5 g of powder is weighed to wrap the graphite substrate in the center, and the surface of the powder is flattened after each step to ensure the uniformity of the coating; after the mold is loaded, spark plasma sintering is carried out, and the set sintering pressure is 30 MPa.

[0052] The temperature program during the sintering process is as follows: during the heating process, 50 °C / min is used below 1000 °C; 30 °C / min is used from 1000 to 1700 °C; the holding time at 1700 °C is 20 min; during the cooling process, it is cooled to 1000 °C at a rate of 50 °C / min, and then the program ends, and it is cooled to room temperature in the furnace. After taking out, it is polished with sandpaper to remove the carbon paper, and a Yb2O3-TiB2-SiC ceramic coating sample is obtained.

[0053] By Figure 5As shown, the Yb2O3-TiB2-SiC ceramic coating sample prepared by spark plasma sintering at 1700℃ for 20min has a low density and many holes on the surface. When the carbon paper is removed, the coating is easily ground off over a large area to expose the graphite matrix, and the integrity of the coating is destroyed.

[0054] Combining Example 1, Example 2 and Comparative Example 1, it can be clearly seen that the ceramic coating of the present invention cannot be prepared when the temperature is low.

[0055] Comparative Example 2

[0056] No pressure is applied during the sintering process in S3, and other conditions are the same as in Example 1.

[0057] The experimental results are as follows Figure 8 As shown, the coating powder was only loosely attached to the graphite substrate, and the Yb2O3-TiB2-SiC ceramic coating was not successfully prepared.

[0058] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material, characterized in that: The following steps are involved: S1. Mix SiC powder, TiB2 powder and Yb2O3 powder in a certain mass ratio to obtain a uniformly mixed raw material powder; S2, pre-treating the graphite substrate; S3. The raw material powder obtained in S1 is coated on the pretreated graphite substrate in S2, and high-temperature discharge plasma sintering is performed under pressure to obtain a graphite-based Yb2O3-TiB2-SiC ceramic coating material.

2. The method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material according to claim 1, characterized in that: In the S1, the particle sizes of SiC powder, TiB2 powder and Yb2O3 powder are all 4-8 μm; the purity of SiC powder, TiB2 powder and Yb2O3 powder is ≥99.9%.

3. The method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material according to claim 1, characterized in that: In the S1, the mass ratio of SiC powder, TiB2 powder and Yb2O3 powder is 2:3:0.

4.

4. The method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material according to claim 1, characterized in that: In the above-mentioned S1, the mixed powders are mixed uniformly by wet ball milling to form slurry, and the slurry is dried and sieved to obtain uniformly mixed raw material powder.

5. The method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material according to claim 4, characterized in that: The mass ratio of the ball mill to the raw material powder is 2:1, the ball composition is ZrO2, and the diameter is 3mm; the ball milling medium is anhydrous ethanol; the ball milling speed is 90r / min, and the ball milling time is 24h.

6. The method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material according to claim 4, characterized in that: During the screening process, a 30-mesh stainless steel screen is used to separate the grinding balls in the slurry, and the separated slurry is placed in a constant temperature drying oven at 80° C. and dried for 12 hours. A 200-mesh stainless steel screen is used to screen the dried powder to obtain a uniformly mixed raw material powder.

7. The method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material according to claim 1, characterized in that: In the above-mentioned S2, the method for pre-treating the graphite substrate powder is: using sandpaper to polish the surface of the graphite substrate, and then performing ultrasonic cleaning and drying operations after polishing.

8. The method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material according to claim 7, characterized in that: The specification of the graphite substrate is a Φ18mm×3mm disc; the graphite substrate is polished using 200-mesh and 800-mesh sandpapers respectively, and the polishing time of the two types of sandpapers on the graphite substrate is 2 minutes; the frequency of ultrasonic cleaning is 40kHz, and the ultrasonic time is 5 minutes; drying is carried out in a constant temperature drying oven, the drying temperature is 80°C, and the drying time is 2 hours.

9. The method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material according to claim 1, characterized in that: In the S3, the temperature control program of the sintering process is: the heating rate below 1000°C is 50°C / min; the heating rate from 1000°C to the maximum temperature is 30°C / min; the holding time after heating to the maximum temperature is 20 minutes; then the temperature is reduced to 1000°C at a rate of 50°C / min, and then cooled to room temperature with the furnace; the maximum temperature is ≥1800°C.

10. The method for preparing a graphite-based Yb2O3-TiB2-SiC ceramic coating material according to claim 1, characterized in that: In the above-mentioned S3, the pressure applied during the sintering process is 30 MPa.

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