Thermal shock resistant composite coating on inner wall of cylindrical graphite base and preparation method of thermal shock resistant composite coating

Abstract

The invention discloses a thermal shock resistant composite coating on the inner wall of a cylindrical graphite base and a preparation method thereof.The thermal shock resistant composite coating is arranged on the inner wall of the cylindrical graphite base, and a nanocarbon / TiC composite transition layer, a Ta transition layer and a TaC protection layer are sequentially arranged on the inner side of the cylindrical graphite base from outside to inside; and the linear expansion coefficients of the nanocarbon / TiC composite transition layer, the Ta transition layer and the TaC protection layer are gradually reduced from outside to inside. The preparation method comprises the following steps: pretreating the inner surface of the cylindrical graphite matrix; generating a nanocarbon / TiC composite transition layer on the inner wall of the pretreated cylindrical graphite matrix through CVD co-deposition; a Ta transition layer is deposited on the inner wall of the nanocarbon / TiC composite transition layer through a double glow method; and preparing a TaC protective layer on the surface of the Ta transition layer by using a plasma spraying method. The obtained coating is stable in adhesive force under the action of thermal stress, free of layering and cracking, good in oxidation resistance, high in film-substrate binding force and good in thermal shock resistance.

Description

Technical Field

[0001] This invention pertains to coatings and their preparation methods, specifically a thermal shock resistant composite coating for the inner wall of a cylindrical graphite substrate and its preparation method. Background Technology

[0002] With the rapid development of the semiconductor industry, MOCVD equipment, as a key piece of equipment in the semiconductor field, plays an increasingly important role. MOCVD epitaxial growth processes use graphite as a support component; the graphite substrate serves as the carrier and heat source for the substrate, directly determining the uniformity and purity of the thin film material. Graphite, as an excellent substrate material, plays a crucial role in the semiconductor industry. Under this premise, higher and more stringent requirements are placed on the performance, applicable environment, and lifespan of graphite substrates. However, graphite is prone to oxidation in oxygen-containing high-temperature environments; oxidation occurs above 400℃, and the oxidation rate increases with increasing temperature. This may lead to a loose surface structure and flaking of the graphite. Therefore, improving the surface properties of graphite substrates has become one of the problems to be solved in the semiconductor field.

[0003] Surface modification methods for graphite materials can be divided into three types: matrix modification, solution impregnation, and surface coating. Among these, surface coating is the most direct and effective way to solve surface problems of graphite substrates. This is because surface coating can improve various properties such as oxidation resistance, corrosion resistance, and wear resistance. Ceramic coatings are widely used because they are easier to form, have better thickness control, and provide a tighter bond in terms of electrical and thermal conductivity. As a type of ultra-high temperature ceramic, TaC has excellent oxidation resistance, thermal stability, and good chemical compatibility with carbon-based materials. It can be used as a protective coating for graphite substrates.

[0004] Although TaC coating can improve the oxidation problem on the graphite substrate surface, tantalum carbide has weak plasticity, is sensitive to stress and cracks, and has poor thermal shock resistance. Furthermore, the thermal expansion coefficients and mechanical properties of graphite and tantalum carbide differ significantly. This increased performance mismatch leads to the occurrence of thermal stress and dislocations. Under the action of thermal stress, the adhesion of the coating begins to decrease, and it is very easy to delamination, cracking, or even peeling. Summary of the Invention

[0005] Purpose of the invention: In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a thermal shock resistant composite coating for the inner wall of a cylindrical graphite substrate with good anti-oxidation properties, strong inter-film-substrate bonding, and good thermal shock resistance. Another purpose of this invention is to provide a method for preparing a thermal shock resistant composite coating for the inner wall of a cylindrical graphite substrate with a shorter preparation time, higher uniformity, and greater thickness.

[0006] Technical solution: The present invention provides a thermal shock resistant composite coating for the inner wall of a cylindrical graphite substrate, wherein a nano-carbon / TiC composite transition layer, a Ta transition layer, and a TaC protective layer are sequentially arranged from the outside to the inside of the cylindrical graphite substrate; the coefficient of linear expansion of the nano-carbon / TiC composite transition layer, the Ta transition layer, and the TaC protective layer gradually decreases from the outside to the inside.

[0007] Furthermore, the thickness of the nano-carbon / TiC composite transition layer is 1~2μm, the thickness of the Ta transition layer is 4~8μm, and the thickness of the TaC protective layer is 20~25μm.

[0008] Furthermore, the mass percentage of TiC in the nano-carbon / TiC composite transition layer is 25~35wt%.

[0009] The method for preparing the thermal shock resistant composite coating on the inner wall of the above-mentioned cylindrical graphite substrate includes the following steps:

[0010] Step 1: Plasma activation pretreatment of the inner surface of the cylindrical graphite matrix;

[0011] Step 2: A nano-carbon / TiC composite transition layer is generated on the inner wall of the pretreated cylindrical graphite matrix by CVD co-deposition.

[0012] Step 3: Deposit a Ta transition layer on the inner wall of the nano-carbon / TiC composite transition layer using a dual-glow plasma surface metallization method;

[0013] Step 4: Prepare a TaC protective layer on the surface of the Ta transition layer using plasma spraying.

[0014] Furthermore, in step one, the plasma activation pretreatment involves introducing argon gas with a purity greater than 99.99%, at a power of 100~200W, a pressure of 10~20Pa, and a time of 10~20min.

[0015] Furthermore, in step two, the raw materials for CVD co-deposition are carbon source, titanium source, and H2 in a volume ratio of 1:0.2~0.4:10, the catalyst is Ni nanoparticles, the reaction temperature is 700~900℃, the gas pressure is 1~5kPa, and the deposition time is 10~30min.

[0016] Furthermore, in step two, the carbon source is C2H2 with a purity greater than 99.99%, and the titanium source is TiCl4 with a purity greater than 99.99%.

[0017] Further, step three specifically involves loading the cylindrical graphite substrate and rod-shaped Ta target, which have already undergone nano-carbon / TiC composite transition layer deposition, into a dual-glow plasma surface metallurgy infiltration furnace. The vacuum level is 0.1~0.2 Pa, argon gas is introduced and maintained at 35~40 Pa, the workpiece cathode voltage is 460~500 V, the source voltage is 650~750 V, the temperature is 600~800 °C, and the holding time is 2~3 h.

[0018] Furthermore, in step four, the plasma spraying method uses a radial powder feeding spray gun specifically designed for the inner wall, with the spraying angle perpendicular to the inner wall of the cylindrical graphite matrix.

[0019] Furthermore, in step four, the powder used in the plasma spraying method is TaC powder, the plasma gas is Ar, the power is 40~50kW, the spraying distance is 80~120mm, the powder feeding rate is 20~30g / min, and the spray gun moving speed is 300~500mm / s.

[0020] Principle of Preparation: The design of a thermal shock resistant coating for the inner wall of a cylindrical graphite substrate must first address the problem of delamination and cracking caused by the significant difference in thermal expansion coefficients and mechanical properties between graphite and tantalum carbide. A transition layer is needed to alleviate this issue. Previous work revealed that Ta / TaC gradient coatings exhibit a gradient distribution from the inside out in terms of composition, mechanical properties, and thermal expansion coefficient. This continuous transition effectively mitigates the performance mismatch between the coating and the substrate. To further improve the performance matching between the substrate and the tantalum layer, a nano-carbon / TiC composite transition layer was designed. This layer achieves a clever transition in thermal expansion coefficients and mechanical properties between the substrate and the tantalum layer, with its thermal expansion coefficient and mechanical properties falling between those of the substrate and the tantalum layer. This improves the wettability of subsequent metal layers and forms a Ta-Ti-C solid solution in the Ta layer, creating a chemical bond network that enhances interfacial bonding energy.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0022] 1. The resulting coating has stable adhesion under thermal stress and will not delaminate or crack. It has good oxidation resistance, strong inter-film-substrate bonding, and good thermal shock resistance.

[0023] 2. The presence of nano-carbon / TiC composite transition layer can improve the wettability of subsequent metal layers. The introduction of TiC can inhibit the direct reaction between Ta and graphite to form brittle phase Ta2C, embed it into the amorphous carbon matrix to form a pinning effect, and form a Ta-Ti-C solid solution with the Ta layer, forming a chemical bond network to enhance the interfacial bonding energy.

[0024] 3. The presence of the Ta transition layer prevents a direct hard abrupt change at the interface between the substrate and the hard ceramic coating, thus playing a mechanical buffering role. This makes the surface hardness closer to the original high hardness value of TaC, thereby improving the hardness of the coating.

[0025] 4. Gradient coatings exhibit a gradient distribution in composition, mechanical properties, and coefficient of thermal expansion. This continuous variation can effectively alleviate the performance mismatch between the substrate and the coating, resulting in the TaC protective layer experiencing less tensile stress during thermal shock.

[0026] 5. The Ta transition layer can absorb some of the thermal shock energy and release thermal stress between the membrane and the substrate. This can alleviate the stress concentration between the membrane and the substrate and achieve the effect of stress relaxation, so that the TaC protective layer is subjected to less impact energy and stress, and resists interlayer cracking and peeling caused by performance mismatch between the membrane and the substrate.

[0027] 6. When the composite coating reaches the impact limit and cracks, due to the superposition of the composite coating, the cracks of each layer are almost not on the same axis, but are distributed in an interlaced manner. This can effectively reduce the rapid pathway for the formation of oxygen atoms, inhibit oxygen atoms from directly contacting the graphite substrate and forming an oxide film on the substrate surface, which would lead to cracking between the film and the substrate, thus improving the coating's ability to resist thermal shock. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the present invention;

[0029] Figure 2 This is a SEM image of the surface of the composite coating prepared in Example 1 of the present invention. Detailed Implementation

[0030] In the following embodiments, all materials and reagents used, unless otherwise specified, are commercially available. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions or as recommended by the manufacturer. The experimental materials used include 99.99% high-purity Ta target, TaC powder with a purity greater than 99%, C2H2 with a purity greater than 99.99%, H2 with a purity greater than 99.99%, TiCl4 with a purity greater than 99.99%, Ar gas, and a special high-purity isostatic graphite cylinder. The dimensions of the special high-purity isostatic graphite cylinder are: inner diameter 44 mm, outer diameter 54 mm, and height 58 mm.

[0031] Example 1

[0032] A method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite substrate 1 includes the following steps:

[0033] (1) The surfaces of the cylindrical graphite substrate 1 and the rod-shaped Ta target are sanded, ultrasonically cleaned with selected ethanol cleaning agent, dried, and the TaC powder is placed in a drying oven.

[0034] (2) The surface of the cylindrical graphite substrate 1 was pretreated by plasma activation using a plasma cleaner. Ar with a purity greater than 99.99% was introduced, the power was 100W, the pressure was 10Pa, and the time was 10min.

[0035] (3) A nano carbon / TiC composite transition layer 2 was generated on the inner wall surface of the cylindrical graphite substrate 1 by CVD co-deposition. The carbon source was C2H2, the titanium source was TiCl4, the dilution gas was H2, the volume ratio of C2H2 to TiCl4 to H2 was 1:0.3:10, the reaction temperature was 700℃, the gas pressure was 1kPa, the deposition time was 10min, and the catalyst was Ni nanoparticles.

[0036] (4) The Ta transition layer 3 was prepared by the double glow plasma surface metallurgy method. The cylindrical graphite substrate 1 and the rod-shaped Ta target with the nano carbon / TiC composite transition layer 2 deposited were loaded into the double glow plasma surface metallurgy furnace. The substrate was the workpiece electrode and the target material was the source electrode. The electrode spacing was 15 mm. The mechanical pump was turned on to evacuate to a vacuum of 0.1 Pa. Argon gas was introduced and the argon gas pressure was kept at 38 Pa during operation. The two-electrode power supply was turned on and the workpiece cathode voltage was set to 480 V, the source electrode voltage to 700 V, the temperature to 700 °C, and the holding time to 2.5 h.

[0037] (5) The TaC protective layer 4 was prepared by plasma spraying. The cylindrical graphite substrate 1 with the Ta transition layer 3 already deposited was placed in Ar and preheated to 300°C. The plasma spraying was carried out using a radial powder feeding spray gun with a special inner wall, and the spraying angle was perpendicular to the inner wall of the graphite cylinder. The plasma gas was Ar, the power was 45kW, the spraying distance was 100mm, the powder feeding rate was 25g / min, and the spray gun moving speed was 400mm / s.

[0038] like Figure 1 As shown, the thickness of the nano-carbon / TiC composite transition layer 2 obtained in this embodiment is 1 μm, the thickness of the Ta transition layer 3 is 7 μm, the thickness of the TaC protective layer 4 is 22 μm, and the total thickness is 30 μm. The mass percentage of TiC in the nano-carbon / TiC composite transition layer 2 is 30 wt%.

[0039] like Figure 2 As shown, the coating surface is relatively smooth, with high density and no cracks or impurities. It has few pores, and the coating only has a very small number of micropores caused by incomplete growth of island clusters and incomplete adhesion between islands.

[0040] The thermal shock resistant coating obtained in this embodiment was tested for hardness, and the surface hardness of the coating was 1003.27 HV.

[0041] The bonding performance of the thermal shock coating obtained in this embodiment was further investigated using the scratch method. The critical load during separation between the film and the substrate was used to characterize the bonding force between the film and the substrate. The critical load in this embodiment was 0.18 N.

[0042] The thermal shock resistance test in this embodiment was conducted in a muffle furnace (KSL-1100X-S). Specifically, the coated sample was cut and placed in a square crucible, then placed in the muffle furnace at 650°C. After holding at this temperature for 15 minutes, it was quickly removed and cooled in air for 15 minutes to complete one thermal shock cycle. This cycle was repeated 40 times. The coating obtained in this embodiment exhibited good thermal shock resistance after these 40 thermal shock cycles; no cracking or peeling occurred. The average oxygen content on the surface after 40 thermal shock cycles was 23.22%.

[0043] Example 2

[0044] A method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite substrate 1 includes the following steps:

[0045] (1) The surfaces of the cylindrical graphite substrate 1 and the rod-shaped Ta target are sanded, ultrasonically cleaned with selected ethanol cleaning agent, dried, and the TaC powder is placed in a drying oven.

[0046] (2) The surface of the cylindrical graphite substrate 1 was pretreated by plasma activation using a plasma cleaner. Ar with a purity greater than 99.99% was introduced, the power was 150W, the pressure was 15Pa, and the time was 15min.

[0047] (3) A nano carbon / TiC composite transition layer 2 was generated on the inner wall surface of the cylindrical graphite substrate 1 by CVD co-deposition. The carbon source was C2H2, the titanium source was TiCl4, the dilution gas was H2, the volume ratio of C2H2 to TiCl4 to H2 was 1:0.2:10, the reaction temperature was 800℃, the gas pressure was 3kPa, the deposition time was 15min, and the catalyst was Ni nanoparticles.

[0048] (4) The Ta transition layer 3 was prepared by the double glow plasma surface metallurgy method. The cylindrical graphite substrate 1 and the rod-shaped Ta target with the nano carbon / TiC composite transition layer 2 deposited were loaded into the double glow plasma surface metallurgy furnace. The substrate was the workpiece electrode and the target material was the source electrode. The electrode spacing was 15 mm. The mechanical pump was turned on to evacuate to a vacuum of 0.15 Pa. Argon gas was introduced and the argon gas pressure was kept at 35 Pa during operation. The two-electrode power supply was turned on and the workpiece cathode voltage was set to 460 V, the source electrode voltage to 650 V, the temperature to 600 °C, and the holding time to 2 h.

[0049] (5) The TaC protective layer 4 was prepared by plasma spraying. The cylindrical graphite substrate 1 with the Ta transition layer 3 already deposited was placed in Ar and preheated to 300°C. The plasma spraying was carried out using a radial powder feeding spray gun with a special inner wall. The spraying angle was perpendicular to the inner wall of the graphite cylinder. The plasma gas was Ar, the power was 40kW, the spraying distance was 80mm, the powder feeding rate was 20g / min, and the spray gun moving speed was 300mm / s.

[0050] The thickness of the nano-carbon / TiC composite transition layer 2 obtained in this embodiment is 1.5 μm, the thickness of the Ta transition layer 3 is 4.5 μm, the thickness of the TaC protective layer 4 is 21 μm, and the total thickness is 27 μm. The mass percentage of TiC in the nano-carbon / TiC composite transition layer 2 is 25 wt%.

[0051] The thermal shock resistant coating obtained in this embodiment was subjected to a hardness test, and the surface hardness of the coating was 967.54 HV.

[0052] The bonding performance of the thermal shock coating obtained in this embodiment was further investigated using the scratch method. The critical load during separation between the film and the substrate was used to characterize the bonding force between the film and the substrate. The critical load in this embodiment was 0.17 N.

[0053] The thermal shock resistance test in this embodiment was conducted in a muffle furnace (KSL-1100X-S). Specifically, the coated sample was cut and placed in a square crucible, then placed in the muffle furnace at 650°C. After holding at this temperature for 15 minutes, it was quickly removed and cooled in air for 15 minutes to complete one thermal shock cycle. This cycle was repeated 40 times. The coating obtained in this embodiment exhibited good thermal shock resistance after these 40 thermal shock cycles; no cracking or peeling occurred. The average oxygen content on the surface after 40 thermal shock cycles was 25.27%.

[0054] Example 3

[0055] A method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite substrate 1 includes the following steps:

[0056] (1) The surfaces of the cylindrical graphite substrate 1 and the rod-shaped Ta target are sanded, ultrasonically cleaned with selected ethanol cleaning agent, dried, and the TaC powder is placed in a drying oven.

[0057] (2) The surface of the cylindrical graphite substrate 1 was pretreated by plasma activation using a plasma cleaner. Ar with a purity greater than 99.99% was introduced, the power was 200W, the pressure was 20Pa, and the time was 20min.

[0058] (3) A nano carbon / TiC composite transition layer 2 was generated on the inner wall surface of the cylindrical graphite substrate 1 by CVD co-deposition. The carbon source was C2H2, the titanium source was TiCl4, the dilution gas was H2, the volume ratio of C2H2 to TiCl4 to H2 was 1:0.4:10, the reaction temperature was 900℃, the gas pressure was 5kPa, the deposition time was 20min, and the catalyst was Ni nanoparticles.

[0059] (4) The Ta transition layer 3 was prepared by the double glow plasma surface metallurgy method. The cylindrical graphite substrate 1 and the rod-shaped Ta target with the nano carbon / TiC composite transition layer 2 deposited were loaded into the double glow plasma surface metallurgy furnace. The substrate was the workpiece electrode and the target material was the source electrode. The electrode spacing was 15 mm. The mechanical pump was turned on to evacuate to a vacuum of 0.2 Pa. Argon gas was introduced and the argon gas pressure was kept at 40 Pa during operation. The two-electrode power supply was turned on and the workpiece cathode voltage was set to 500 V, the source electrode voltage to 750 V, the temperature to 800 °C, and the holding time to 3 h.

[0060] (5) The TaC protective layer 4 was prepared by plasma spraying. The cylindrical graphite substrate 1 with the Ta transition layer 3 already deposited was placed in Ar and preheated to 300°C. The plasma spraying was carried out using a radial powder feeding spray gun with a special inner wall, and the spraying angle was perpendicular to the inner wall of the graphite cylinder. The plasma gas was Ar, the power was 50kW, the spraying distance was 120mm, the powder feeding rate was 30g / min, and the spray gun moving speed was 500mm / s.

[0061] In this embodiment, the thickness of the nano-carbon / TiC composite transition layer 2 is 2 μm, the thickness of the Ta transition layer 3 is 8 μm, the thickness of the TaC protective layer 4 is 24 μm, and the total thickness is 34 μm. The mass percentage of TiC in the nano-carbon / TiC composite transition layer 2 is 35 wt%.

[0062] The thermal shock resistant coating obtained in this embodiment was tested for hardness, and the surface hardness of the coating was 1107.84 HV.

[0063] The bonding performance of the thermal shock coating obtained in this embodiment was further investigated using the scratch method. The critical load during separation between the film and the substrate was used to characterize the bonding force between the film and the substrate. The critical load in this embodiment was 0.19 N.

[0064] The thermal shock resistance test in this embodiment was conducted in a muffle furnace (KSL-1100X-S). Specifically, the coated sample was cut and placed in a square crucible, then placed in the muffle furnace at 650°C. After holding at this temperature for 15 minutes, it was quickly removed and cooled in air for 15 minutes to complete one thermal shock cycle. This cycle was repeated 40 times. The coating obtained in this embodiment exhibited good thermal shock resistance after these 40 thermal shock cycles; no cracking or peeling occurred. The average oxygen content on the surface after 40 thermal shock cycles was 20.93%.

[0065] Comparative Example 1

[0066] The method for preparing a pure Ta coating includes the following steps:

[0067] (1) The cylindrical graphite base 1, the rod-shaped Ta target and the surface are sanded and ultrasonically cleaned with ethanol cleaning agent and then dried.

[0068] (2) The cylindrical graphite base 1 is activated by plasma and the surface of the base is pretreated. The equipment is a plasma cleaner, Ar with a purity greater than 99.99% is introduced, the power is 100W, the pressure is 10Pa, and the time is 10min.

[0069] (3) The Ta transition layer 3 was prepared by the double glow plasma surface metallurgy method. The cylindrical graphite base 1 and the rod-shaped Ta target were loaded into the double glow plasma surface metallurgy furnace. The substrate was the workpiece electrode and the target material was the source electrode. The electrode spacing was 15 mm. The mechanical pump was turned on to evacuate to a vacuum of 0.1 Pa. Argon gas was introduced and the argon gas pressure was kept at 38 Pa during operation. The two-electrode power supply was turned on and the workpiece cathode voltage was set to 480 V, the source electrode voltage to 700 V, and the temperature to 700 °C. The temperature was kept for 2.5 h.

[0070] The Ta transition layer obtained in this comparative example has a thickness of 7 μm.

[0071] The hardness of the thermal shock resistant coating obtained in Comparative Example 1 was tested, and the surface hardness of the coating was 437.98 HV.

[0072] The bonding performance of the thermal shock coating obtained in Comparative Example 1 was further investigated using the scratch method. The bonding force between the film and the substrate was characterized by the critical load when the film and substrate separated. The critical load of Comparative Example 1 was 0.8 N.

[0073] The thermal shock resistance test of Comparative Example 1 was conducted in a muffle furnace (KSL-1100X-S). Specifically, the coated sample was cut and placed in a square crucible, then placed in the muffle furnace at 650°C. After holding at this temperature for 15 minutes, the sample was quickly removed and cooled in air for 15 minutes to complete one thermal shock cycle. This cycle was repeated 40 times. After undergoing these 40 thermal shock cycles, the coating obtained in Comparative Example 1 showed numerous network-like voids and pores on its surface due to severe oxidation. The average oxygen content on the surface after 40 thermal shock cycles was 37.89%.

[0074] Comparative Example 2

[0075] The method for preparing a pure TaC coating includes the following steps:

[0076] (1) The surface of the cylindrical graphite base 1 is sanded and ultrasonically cleaned with ethanol cleaning agent, dried, and the TaC powder is placed in a drying oven.

[0077] (2) The cylindrical graphite base 1 is activated by plasma and the surface of the base is pretreated. The equipment is a plasma cleaner, Ar with a purity greater than 99.99% is introduced, the power is 100W, the pressure is 10Pa, and the time is 10min.

[0078] (3) The TaC protective layer 4 was prepared by plasma spraying. The plasma spraying used a radial powder feeding spray gun with a special inner wall, and the spraying angle was perpendicular to the inner wall of the cylindrical graphite base 1. The cylindrical graphite base 1 was placed in Ar and preheated to 300°C. The plasma gas was Ar, the power was 45kW, the spraying distance was 100mm, the powder feeding rate was 25g / min, and the spray gun moving speed was 400mm / s.

[0079] The TaC protective layer obtained in this comparative example has a thickness of 19 μm.

[0080] The thermal shock resistant coating obtained in Comparative Example 2 was subjected to a hardness test, and the surface hardness of the coating was 889.05 HV.

[0081] The bonding performance of the thermal shock coating obtained in Comparative Example 2 was further investigated using the scratch method. The bonding force between the film and the substrate was characterized by the critical load when the film and substrate separated. The critical load of Comparative Example 2 was 0.08 N.

[0082] The thermal shock resistance test of Comparative Example 2 was conducted in a muffle furnace (KSL-1100X-S). The specific procedure involved cutting the coating sample and placing it in a square crucible, then immersing it in the muffle furnace at 650°C for 15 minutes. After holding at this temperature for 15 minutes, the sample was quickly removed and cooled in air for 15 minutes to complete one thermal shock cycle. This cycle was repeated 40 times. After 10 thermal shock cycles, the coating obtained in Comparative Example 2 exhibited earlier cracking, primarily starting from the coating edges. After 40 thermal shock cycles, the average oxygen content on the surface was 32.85%.

[0083] In summary, the optimal embodiment is Embodiment 1.

Claims

1. A thermal shock resistant composite coating for the inner wall of a cylindrical graphite substrate, wherein the coating is disposed on the inner wall of a cylindrical graphite substrate (1), characterized in that: The inner side of the cylindrical graphite matrix (1) is provided with a nano carbon / TiC composite transition layer (2), a Ta transition layer (3) and a TaC protective layer (4) from the outside to the inside; the linear expansion coefficients of the nano carbon / TiC composite transition layer (2), the Ta transition layer (3) and the TaC protective layer (4) gradually decrease from the outside to the inside.

2. The thermal shock resistant composite coating for the inner wall of a cylindrical graphite base according to claim 1, characterized in that: The thickness of the nano-carbon / TiC composite transition layer (2) is 1~2μm, the thickness of the Ta transition layer (3) is 4~8μm, and the thickness of the TaC protective layer (4) is 20~25μm.

3. The thermal shock resistant composite coating for the inner wall of a cylindrical graphite base according to claim 1, characterized in that: The mass percentage of TiC in the nano-carbon / TiC composite transition layer (2) is 25~35wt%.

4. The method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite substrate according to claim 1, characterized in that, Includes the following steps: Step 1: Plasma activation pretreatment of the inner surface of the cylindrical graphite matrix (1); Step 2: A nano-carbon / TiC composite transition layer (2) is generated on the inner wall of the pretreated cylindrical graphite substrate (1) by CVD co-deposition. Step 3: Deposit a Ta transition layer (3) on the inner wall of the nano-carbon / TiC composite transition layer (2) using the dual-glow plasma surface metal infiltration method. Step 4: Prepare a TaC protective layer (4) on the surface of the Ta transition layer (3) using plasma spraying.

5. The method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite substrate according to claim 4, characterized in that: In step one, the plasma activation pretreatment involves introducing argon gas with a purity greater than 99.99%, at a power of 100-200W, a pressure of 10-20Pa, and a time of 10-20min.

6. The method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite base according to claim 4, characterized in that: In step two, the raw materials for CVD co-deposition are carbon source, titanium source and H2 in a volume ratio of 1:0.2~0.4:10, the catalyst is Ni nanoparticles, the reaction temperature is 700~900℃, the gas pressure is 1~5kPa, and the deposition time is 10~30min.

7. The method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite base according to claim 6, characterized in that: In step two, the carbon source is C2H2 with a purity greater than 99.99%, and the titanium source is TiCl4 with a purity greater than 99.99%.

8. The method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite base according to claim 4, characterized in that: The third step specifically involves loading the cylindrical graphite substrate (1) and the rod-shaped Ta target material, which have already undergone nano-carbon / TiC composite transition layer (2) deposition, into a dual-glow plasma surface metallurgy infiltration furnace. The vacuum degree is 0.1~0.2 Pa, argon gas is introduced and maintained at 35~40 Pa, the cathode voltage of the workpiece is 460~500 V, the source voltage is 650~750 V, the temperature is 600~800 °C, and the holding time is 2~3 h.

9. The method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite base according to claim 4, characterized in that: In step four, the plasma spraying method uses a radial powder feeding spray gun specifically for the inner wall, and the spraying angle is perpendicular to the inner wall of the cylindrical graphite substrate (1).

10. The method for preparing a thermal shock resistant composite coating on the inner wall of a cylindrical graphite substrate according to claim 4, characterized in that: In step four, the powder used in the plasma spraying method is TaC powder, the plasma gas is Ar, the power is 40~50kW, the spraying distance is 80~120mm, the powder feeding rate is 20~30g / min, and the spray gun moving speed is 300~500mm / s.

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