A method for in-situ growth of thermal shock resistant tantalum carbide coating on a carbon-based substrate

Abstract

The present invention discloses a method for in-situ growth of a thermal shock-resistant tantalum carbide coating on a carbon-based substrate. The specific steps are as follows: 1) placing the substrate in a deposition chamber of a laser chemical vapor deposition device; 2) evacuating the deposition chamber to below the vacuum threshold, introducing H2, a carbon source, and a carrier gas containing a tantalum source, Ar, and adjusting the deposition pressure and stabilizing it for 1 to 5 minutes; 3) turning on the laser to irradiate the substrate, heating it to the deposition temperature for deposition, and then turning off the carrier gas Ar and the laser after deposition. When the substrate temperature reaches 150°C, turning off the H2 and carbon source, and then evacuating the substrate. Waiting for the substrate to cool to room temperature, a tantalum carbide coating material is obtained on the substrate surface. The bottom of the porous tantalum carbide coating material provided by the present invention, which contacts the substrate, has a porous structure that can buffer thermal shock stress. The surface is composed of dense tantalum carbide, which can provide good protection for the substrate, significantly alleviate the problem of thermal expansion coefficient mismatch between the coating and the substrate, and improve the thermal shock resistance of the coating.

Description

Technical Field

[0001] The invention belongs to the general field of plating technology of vacuum evaporation, sputtering, ion implantation or chemical vapor deposition, and particularly relates to a method for in-situ growth of a thermal shock resistant tantalum carbide coating on a carbon-based substrate. Background Art

[0002] Carbon materials, such as graphite, carbon fibers, and carbon / carbon composites, are considered one of the most promising thermostructural materials due to their excellent high-temperature mechanical properties, including low density, low thermal expansion coefficient, good thermal shock resistance, and good heat resistance. However, carbon materials are susceptible to oxidation and failure at temperatures above 370°C, which greatly limits their application in advanced aircraft and other fields.

[0003] Chemical vapor deposition (CVD) of tantalum carbide (TaC) coatings on carbon surfaces is an effective way to improve the ablation and oxidation resistance of carbon materials. Tantalum carbide, with its excellent oxidation resistance and mechanical properties, is widely considered a suitable candidate for thermal protection coatings on carbon materials. However, the mismatch in the coefficient of thermal expansion (CTE) between the tantalum carbide coating and the carbon material can generate significant thermal stresses, which can lead to cracking and debonding between the coating and the substrate under severe thermal shock conditions.

[0004] To improve the overall thermal shock resistance of coatings, there are currently two main approaches: one is to deposit a SiC coating between the substrate and the TaC coating as a buffer layer; the other is to deposit TaC and SiC simultaneously to produce a TaC-SiC multiphase coating. These methods can effectively reduce the CTE mismatch between the coating and the substrate, but they require the introduction of a second phase, making the deposition process more complex and significantly increasing production costs. Furthermore, the poor compatibility between the different coating components reduces the long-term service stability of the product. Therefore, developing a method for in-situ preparation of TaC coatings with excellent thermal shock resistance is of great significance and practical value. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art and provide a method for in-situ growth of a thermal shock-resistant tantalum carbide coating on a carbon-based substrate. A tantalum carbide coating with good thermal shock resistance is in-situ grown on the surface of a carbon-based substrate by laser chemical vapor deposition. No additional treatment of the carbon-based substrate is required. Only by adjusting the deposition temperature can a tantalum carbide coating with excellent thermal shock resistance be obtained, and the process is simple.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0007] A method for in-situ growth of a thermal shock resistant tantalum carbide coating on a carbon-based substrate is provided, comprising the following steps:

[0008] 1) Place the cleaned carbon-based substrate into the deposition chamber of the laser chemical vapor deposition equipment and adjust the position of the carbon-based substrate so that it is within the laser coverage range;

[0009] 2) The deposition chamber is evacuated to below the vacuum threshold, H2, carbon source, and Ar carrier gas containing a tantalum source are introduced, and the deposition pressure is adjusted and stabilized for 1 to 5 minutes;

[0010] 3) Turn on the laser to irradiate the carbon-based substrate, so that the surface of the carbon-based substrate is heated to the deposition temperature for deposition. After the deposition is completed, turn off TaCl5, carrier gas Ar and laser in sequence. When the temperature of the carbon-based substrate shows 150°C, turn off H2, and then vacuum, wait for the carbon-based substrate to cool to room temperature, and obtain tantalum carbide coating material on the surface of the carbon-based substrate.

[0011] According to the above scheme, the carbon-based substrate in step 1) is a carbon / carbon composite material or a graphite substrate.

[0012] According to the above scheme, the carbon source in step 2) is methane, propane or a mixture of the two, and the tantalum source is tantalum pentachloride vapor (obtained by heating and evaporating tantalum pentachloride).

[0013] According to the above scheme, in step 2), the H2 purity is above 99 vol%, the flow rate is 500-2000 sccm, the carbon source flow rate is 300-500 sccm, the Ar flow rate is 200-500 sccm, and the tantalum source flow rate is 0.3-0.5 g / min.

[0014] According to the above scheme, the deposition pressure in step 2) is 1 to 6 kPa.

[0015] According to the above scheme, the laser wavelength in step 3) is 700-1200 nm.

[0016] According to the above scheme, the deposition process conditions in step 3) are: first deposit at 1000-1200° C. for 5-10 minutes, then heat up to 1300-1400° C. and deposit for 10-15 minutes.

[0017] The present invention also includes a tantalum carbide coating with good thermal shock resistance obtained by the above method, wherein the thermal shock resistant tantalum carbide coating consists of a porous layer and a dense layer located above the porous layer, wherein the porous layer is obtained by dense growth of conical tantalum carbide crystals perpendicular to a carbon-based substrate, and the structure is dense at the bottom of the porous layer, and the remaining part of the porous layer forms connected or unconnected micropores between the tantalum carbide crystals.

[0018] According to the above solution, the thickness of the porous layer is 30 to 50 μm, and the thickness of the dense layer is 60 to 80 μm.

[0019] The present invention also includes the application of the above-mentioned tantalum carbide coating in aircraft anti-ablation coating.

[0020] The present invention adopts laser chemical vapor deposition to prepare tantalum carbide porous coating material with good thermal shock resistance. By adjusting the deposition process parameters, the nucleation and growth process of tantalum carbide grains are controlled. In the early stage of growth, a large number of tantalum carbide nanoparticles with no preferred orientation grow on the surface of the substrate to form a dense structure. By controlling the process conditions, the tantalum carbide porous coating material with good thermal shock resistance is prepared. <111> Oriented grains grow rapidly, forming a concave-convex structure on the substrate surface. As the growth continues, due to the shadow effect, the higher <111> The oriented tantalum carbide grains prevent the precursor from reaching the concave region, so the growth of the concave region stops and produces <111> The oriented side branches form a porous tantalum carbide coating, which can relieve thermal stress and improve thermal shock resistance. The process conditions are then adjusted to deposit a dense layer on the surface of the porous tantalum carbide coating. The dense tantalum carbide can effectively protect the substrate.

[0021] The beneficial effects of the present invention are as follows: 1. The bottom of the porous tantalum carbide coating material provided by the present invention, where it contacts the substrate, is porous, capable of buffering thermal shock stress. The surface, composed of dense tantalum carbide, provides excellent protection for the substrate, significantly alleviating the mismatch in thermal expansion coefficients between the coating and the substrate, and improving the coating's thermal shock resistance. 2. The preparation method of the present invention has simple process steps; a tantalum carbide coating with excellent thermal shock resistance can be obtained simply by adjusting the deposition process temperature, making it easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a field emission scanning electron microscope image of a sample having a tantalum carbide coating prepared in Example 1 of the present invention;

[0023] Figure 2 This is a field emission scanning electron microscope image of the sample prepared in Example 1 after the thermal shock test;

[0024] Figure 3 This is a field emission scanning imaging image of the tantalum carbide porous coating material prepared in Comparative Example 1;

[0025] Figure 4 This is a field emission electron scanning imaging image of the tantalum carbide coating material prepared in Comparative Example 2;

[0026] Figure 5 This is a field emission electron scanning microscope image of the sample prepared in Comparative Example 2 after thermal shock testing;

[0027] Figure 6 This is a transmission electron microscope image of the tantalum carbide coating material prepared in Comparative Example 2;

[0028] Figure 7 This is a field emission scanning microscope image of the tantalum carbide coating sample of Comparative Example 3;

[0029] Figure 8This is a field emission scanning microscope image of the sample of Comparative Example 3 after thermal shock testing;

[0030] Figure 9 The XRD patterns of the coatings prepared in Example 1 and Comparative Examples 1-3 are shown. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings.

[0032] Example 1

[0033] A thermal shock resistant tantalum carbide coating material, the preparation method of which has the following specific steps:

[0034] 1) A graphite sheet (2H graphite, 15 mm in diameter and 1 mm in thickness) was cleaned using ultrasonic cleaning. The graphite sheet was used as a substrate and placed in the deposition chamber of a laser chemical vapor deposition apparatus. The substrate was positioned so that it was within the laser coverage area.

[0035] 2) The deposition chamber was evacuated to below 20 Pa, and dilution gases H2 (99.999%), CH4 (99.999%), and a carrier gas Ar (99.999%) containing TaCl5 vapor (TaCl5 heated to 180°C) were introduced. The H2 flow rate was 500 sccm, the CH4 flow rate was 300 sccm, the Ar flow rate was 400 sccm, and the TaCl5 vapor flow rate was 0.4 g / min. The deposition pressure was adjusted to 2 kPa and stabilized for 5 minutes.

[0036] 3) Turn on the laser to irradiate the substrate, the laser irradiation output wavelength is 1000nm, and the substrate surface is heated to 1100℃ for deposition for 7 minutes, and then the deposition temperature is increased to 1300℃ for 10 minutes;

[0037] 4) After the deposition is completed, the carrier gas Ar and the laser are turned off in turn. When the substrate temperature shows 150°C, the H2 and CH4 are turned off, vacuum is applied, and the substrate is cooled to room temperature to obtain a tantalum carbide coating material with a porous lower layer and a dense upper layer on the substrate surface.

[0038] The field emission scanning electron microscope image of the sample with tantalum carbide coating prepared in this embodiment is as follows: Figure 1 As shown, Figure 1 (a) is the surface morphology of the coating. Figure 1(b) is a cross-sectional morphology of the sample. It can be seen that the coating deposited on the surface of the substrate has a double-layer structure. The lower layer is a porous layer of tantalum carbide obtained by dense growth of conical tantalum carbide crystals perpendicular to the substrate. The structure of the porous layer is dense where it contacts the substrate, and there are pores between the crystals in the direction of continued upward growth. The upper layer is a dense tantalum carbide surface layer. The thicknesses of the lower and upper layers are 33.65μm and 65.35μm, respectively. The deposition rate of the porous layer is 288.4μm / h, and the deposition rate of the dense layer is 653.5μm / h.

[0039] The samples of this embodiment were subjected to a thermal shock test. The specific test method is as follows: the sample is placed in the deposition chamber of a laser chemical vapor deposition device, argon and hydrogen are introduced into the deposition chamber, the argon flow rate is 400 sccm, and the hydrogen flow rate is 500 sccm. The sample is rapidly heated to 1400°C by a laser and maintained for 5 seconds. Then the laser is turned off, and the sample is rapidly cooled to room temperature under argon and hydrogen purge. This is considered one cycle. A thermal shock test includes 10 cycles. After the test is completed, the cracks in the coating and the bonding with the substrate are observed using a scanning electron microscope, and the thermal shock resistance of the coating is evaluated based on indicators such as the number and length of cracks.

[0040] The field emission scanning electron microscope image of the sample after the thermal shock test of this embodiment is as follows Figure 2 As shown, Figure 2 (a) is the surface morphology of the coating. Figure 2 (b) is the cross-sectional morphology of the sample. Microcracks can be observed on the coating surface and penetrating cracks can be observed from the cross section, but the number of cracks is relatively small. Figure 2 (b) Cracks can be observed initiating in the dense tantalum carbide coating on the upper layer and propagating downward, but the cracks stop propagating when they reach the porous buffer layer. This is because the porous tantalum carbide coating, acting as a buffer layer, effectively relieves the thermal stress between the dense tantalum carbide coating and the substrate. Furthermore, the numerous voids within the porous tantalum carbide coating prevent crack propagation, effectively improving the coating's overall thermal shock resistance.

[0041] Comparative Example 1

[0042] A tantalum carbide coating material, the preparation method of which is similar to that of Example 1, except that in step 3) the deposition temperature is 1000° C. and the deposition time is 10 min.

[0043] The field emission scanning imaging image of the tantalum carbide porous coating material prepared in this comparative example is as follows: Figure 3 As shown, Figure 3 (a) is the surface morphology of the coating. Figure 3(b) shows the cross-sectional morphology of the coating. The surface of the coating prepared in this comparative example is pyramidal. The cross-section reveals dense growth of conical tantalum carbide crystals perpendicular to the substrate. A dense layer forms at the bottom of the coating, while in the upper portion, numerous feather-like branches grow from the main tantalum carbide crystal trunks, forming a nanoporous structure between the crystals. The total coating thickness is approximately 70 μm, and the deposition rate is 700 μm / h.

[0044] Comparative Example 2

[0045] A tantalum carbide coating material, the preparation method of which is similar to that of Example 1, except that in step 3) the deposition temperature is 1100° C. and the deposition time is 30 min.

[0046] The field emission electron scanning imaging image of the tantalum carbide coating material prepared in this comparative example is as follows: Figure 4 As shown, the coating is tightly bonded to the substrate, with a pyramidal surface and a dendritic cross-section. Significant pores can be observed on both the surface and cross-section, indicating that the tantalum carbide coating prepared under these conditions is porous. The coating thickness is approximately 96 μm, and the deposition rate is 576 μm / h.

[0047] The tantalum carbide coating material sample prepared in this comparative example was subjected to a thermal shock test using the method of Example 1. The field emission electron scanning microscope image of the sample after the thermal shock test is as follows: Figure 5 As shown in the test results, no cracks were observed on the surface or cross-section of the coating material after the thermal shock test, demonstrating excellent thermal shock resistance. During the thermal shock process, the dense structure of tiny tantalum carbide nanoparticles at the bottom ensured a strong bond between the coating and the substrate, while the nanoporous structure within the coating helped to relieve thermal stress.

[0048] The transmission electron microscope image of the tantalum carbide coating material prepared in this comparative example is as follows: Figure 6 As shown, Figure 6 (a)-(c) are SEM and HRTEM images of the coating material. It can be observed that the tantalum carbide crystal structure consists of a trunk and branches. There are not only a large number of gaps of varying sizes between the trunks, but also a large number of gaps of varying sizes between the branches. Figure 6 (d) High-resolution transmission electron micrograph and diffraction pattern of the trunk area. The results show that the tantalum carbide crystals are along the <111> Direction growth.

[0049] Comparative Example 3

[0050] A tantalum carbide coating material, the preparation method of which is similar to that of Example 1, except that in step 3) the deposition temperature is 1300° C. and the deposition time is 10 min.

[0051] The field emission scanning microscope imaging of the tantalum carbide coating sample prepared in this comparative example is as follows: Figure 7As shown, Figure 7 (a) is the surface morphology of the coating, Figure 7 (b) is a cross-sectional morphology of the coating, the coating thickness is about 100 μm, and the deposition rate is 1000 μm / h. The results show that the coating obtained in this comparative example has a dense structure. The comparative example sample was subjected to a thermal shock test using the method of Example 1. The field emission scanning microscope image of the sample after the thermal shock test is shown in FIG. Figure 8 The test results show that microcracks can be observed on the coating surface, longitudinal cracks can be observed in the cross section, and a clear gap has been formed between the coating and the substrate, indicating that the coating has a tendency to fall off. The formation of microcracks is caused by thermal stress caused by the mismatch in thermal expansion coefficients between the tantalum carbide coating and the graphite substrate during the thermal shock test.

[0052] Figure 9 The XRD patterns of the coatings prepared in Example 1 and Comparative Examples 1-3 show that the tantalum carbide crystals on the coating surfaces of Example 1 and Comparative Example 3 are randomly oriented, while the tantalum carbide crystals in the coatings of Comparative Examples 1 and 2 are <111> Select the best orientation.

[0053] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention in detail. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for in-situ growth of a thermal shock resistant tantalum carbide coating on a carbon-based substrate, characterized in that: The specific steps are as follows: 1) Place the cleaned carbon-based substrate into the deposition chamber of the laser chemical vapor deposition equipment and adjust the position of the carbon-based substrate so that it is within the laser coverage range; 2) Evacuate the deposition chamber to below the vacuum threshold, introduce H2, carbon source, and Ar carrier gas containing tantalum source, adjust the deposition pressure, and stabilize it for 1-5 minutes; 3) Turn on the laser to irradiate the carbon-based substrate, so that the surface of the carbon-based substrate is heated to the deposition temperature for deposition. The deposition process conditions are: first deposit at 1000-1200°C for 5-10 minutes, then heat to 1300-1400°C and deposit for 10-15 minutes. After the deposition is completed, turn off the carrier gas Ar and the laser in sequence. When the temperature of the carbon-based substrate shows 150°C, turn off the H2 and carbon source, and then evacuate the carbon-based substrate and wait for the carbon-based substrate to cool to room temperature to obtain a tantalum carbide coating material on the surface of the carbon-based substrate.

2. The method for in-situ growth of a thermal shock resistant tantalum carbide coating on a carbon-based substrate according to claim 1, characterized in that: Step 1) The carbon-based substrate is a carbon / carbon composite material or a graphite substrate.

3. The method for in-situ growth of a thermal shock resistant tantalum carbide coating on a carbon-based substrate according to claim 1, wherein: Step 2) The carbon source is methane, propane or a mixture of the two, and the tantalum source is tantalum pentachloride vapor.

4. The method for in-situ growth of a thermal shock resistant tantalum carbide coating on a carbon-based substrate according to claim 1, wherein: Step 2) H2 purity is above 99 vol%, flow rate is 500~2000 sccm, carbon source flow rate is 300~500 sccm, Ar flow rate is 200~500 sccm, and tantalum source flow rate is 0.3~0.5 g / min.

5. The method for in-situ growth of a thermal shock resistant tantalum carbide coating on a carbon-based substrate according to claim 1, wherein: Step 2) The deposition pressure is 1~6KPa.

6. The method for in-situ growth of a thermal shock resistant tantalum carbide coating on a carbon-based substrate according to claim 1, wherein: Step 3) The laser wavelength is 700~1200nm.

7. A thermal shock resistant tantalum carbide coating obtained according to any one of claims 1 to 6, characterized in that: The thermal shock resistant tantalum carbide coating consists of a porous layer and a dense layer located above the porous layer, wherein the porous layer is obtained by dense growth of conical tantalum carbide crystals perpendicular to a carbon-based substrate, and the structure is dense at the bottom of the porous layer, and the rest of the porous layer forms connected or unconnected micropores between the tantalum carbide crystals.

8. The thermal shock resistant tantalum carbide coating according to claim 7, characterized in that: The thickness of the porous layer is 30-50 μm, and the thickness of the dense layer is 60-80 μm.

9. Use of the thermal shock resistant tantalum carbide coating according to claim 7 or 8 in aircraft anti-ablation coating.

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