Preparation method of silicon carbide coating based on CVD (Chemical Vapor Deposition)

Abstract

The invention provides a preparation method of a silicon carbide coating based on CVD, and belongs to the technical field of silicon carbide coatings. According to the preparation method, a matrix is remodeled through pulse water vapor hydroxylation and a reaction of bis (diethylamino) silane, a uniform and high-activity organic silicon anchoring interface layer is constructed, and an amorphous silicon carbide isolation layer is grown on the organic silicon anchoring interface layer through low-temperature circulating chemical vapor deposition; the problems of low adhesive force caused by heterogeneity of a substrate and interface pollution caused by atom migration in a traditional process are solved; on the basis, the main coating grows in a gradient manner: firstly, a nanocrystalline / amorphous composite flexible cushion layer is deposited to relieve thermal mismatch stress, and then a high-hardness columnar crystal functional surface layer is transitionally deposited to provide excellent wear resistance; and the coating with high bonding strength, interface purity, high toughness and high hardness is obtained.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide coating technology, and relates to a method for preparing silicon carbide coatings based on CVD. Background Technology

[0002] Special ceramic components such as ceramic valves and ceramic cylinder valve plates operate under conditions involving particulate media, chlorine / sulfur-containing fluids, and frequent start-stop cycles, requiring surfaces that balance wear resistance, erosion resistance, and chemical corrosion resistance. To improve service reliability, silicon carbide coatings are often used for surface strengthening.

[0003] Traditional chemical vapor deposition (CVD) for silicon carbide deposition on ceramic substrates faces the problem of uncontrolled interfacial chemistry. First, the surface of the ceramic substrate is not homogeneous at the atomic scale; the random distribution of its chemically active sites leads to selective adsorption and island nucleation of the silicon carbide precursor. This creates numerous nanopores and weak bonding regions at the interface, the root cause of insufficient coating adhesion. Second, under the high-temperature environment required for CVD, this discontinuous initial structure provides pathways for the outward migration of lattice atoms from the substrate itself. These lattice atoms react with the deposit, forming a contamination layer with poor mechanical properties at the interface. Finally, corrosive byproducts generated during the process preferentially attack these structurally weak island boundaries and contaminated areas, amplifying initial nanodefects into micron-level fatal cracks. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a method for preparing a silicon carbide coating based on CVD. This application first hydroxylates the substrate using pulsed water vapor, then introduces bis(diethylamino)silane to reshape the substrate, constructing a uniform and highly active organosilicon anchoring interface layer, thus solving the problem of low adhesion caused by substrate heterogeneity. Based on this, an amorphous silicon carbide isolation layer is grown in situ at a low temperature of 400-500℃ using a cyclic chemical vapor deposition mode. This layer inhibits the outward migration of substrate atoms during subsequent high-temperature deposition, reducing the probability of weak interface phase formation. Finally, the main coating is grown in a gradient manner: first, a flexible nanocrystalline / amorphous composite pad is deposited at 850-950℃ to alleviate and absorb thermal mismatch stress; then, the temperature is slowly increased to 1050-1200℃ to transition and deposit a high-hardness columnar crystalline functional surface layer, providing excellent wear resistance. A coating with high bonding strength, interface purity, high toughness, and high hardness is obtained.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing a CVD-based silicon carbide coating, the method comprising:

[0007] S1: After cleaning and drying the silicon nitride ceramic substrate, place it in a chemical vapor deposition furnace, evacuate it, heat it to the first temperature, and pulse deionized water vapor into the reaction chamber to carry out the reaction.

[0008] S2: Maintain the reaction chamber temperature at the first temperature, and pulse bis(diethylamino)silane into the reaction chamber to carry out the reaction;

[0009] S3: Raise the reaction chamber temperature to the second temperature, and perform cyclic chemical vapor deposition using bis(diethylamino)silane as the silicon source and acetylene as the carbon source in alternating pulses;

[0010] S4: The temperature of the reaction chamber is increased to the third temperature at the first heating rate, and hydrogen is continuously introduced as a carrier gas. Methyltrichlorosilane is introduced for the first stage of deposition. Then the temperature of the reaction chamber is increased to the fourth temperature at the second heating rate for the second stage of deposition.

[0011] S5: After deposition, the temperature is programmed to decrease at a decreasing rate under an argon atmosphere.

[0012] As a preferred technical solution of the present invention, in step S1, the first temperature is 200-300℃, for example, it can be 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃ or 300℃, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0013] In some alternative embodiments, the temperature of the deionized water vapor is 30-50°C, for example, it can be 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C, 44°C, 46°C, 48°C or 50°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0014] In some optional embodiments, the single-pass time for pulsed introduction of deionized water vapor into the reaction chamber is 0.5-1.5 s, for example, 0.5 s, 0.6 s, 0.7 s, 0.8 s, 0.9 s, 1.0 s, 1.1 s, 1.2 s, 1.3 s, 1.4 s or 1.5 s, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0015] In some optional embodiments, after the deionized water vapor is pulsedly introduced into the reaction chamber, nitrogen purging is performed. The single purging time of nitrogen is 15-25s, for example, 15s, 16s, 17s, 18s, 19s, 20s, 21s, 22s, 23s, 24s or 25s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] In some optional embodiments, the total number of cycles in S1 is 30-50 times, for example, 30 times, 32 times, 34 times, 36 times, 38 times, 40 times, 42 times, 44 times, 46 times, 48 ​​times or 50 times, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] As a preferred technical solution of the present invention, in step S2, the temperature of the bis(diethylamino)silane pulsed in is 30-50°C, for example, it can be 30°C, 32°C, 34°C, 36°C, 38°C, 40°C, 42°C, 44°C, 46°C, 48°C or 50°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] In some optional embodiments, the single-pass time for pulsed introduction of bis(diethylamino)silane into the reaction chamber is 0.8-2 s, for example, it can be 0.80 s, 0.92 s, 1.04 s, 1.16 s, 1.28 s, 1.40 s, 1.52 s, 1.64 s, 1.76 s, 1.88 s or 2.00 s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0019] In some optional embodiments, after the bis(diethylamino)silane is pulsedly introduced into the reaction chamber, nitrogen purging is performed. The single purging time is 20-30 s, for example, 20 s, 21 s, 22 s, 23 s, 24 s, 25 s, 26 s, 27 s, 28 s, 29 s or 30 s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] In some optional embodiments, the number of cycles in S2 is 3-5 times, for example, 3 times, 4 times or 5 times, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] As a preferred technical solution of the present invention, in step S3, the second temperature is 400-500℃, for example, it can be 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃ or 500℃, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0022] In some optional embodiments, the single-pass time of bis(diethylamino)silane in the cyclic chemical vapor deposition is 0.8-2.0 s, for example, 0.80 s, 0.92 s, 1.04 s, 1.16 s, 1.28 s, 1.40 s, 1.52 s, 1.64 s, 1.76 s, 1.88 s or 2.00 s, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0023] In some optional embodiments, the cyclic chemical vapor deposition is followed by nitrogen purging after the introduction of bis(diethylamino)silane. The single purging time of nitrogen is 25-40 s, for example, 25.0 s, 26.5 s, 28.0 s, 29.5 s, 31.0 s, 32.5 s, 34.0 s, 35.5 s, 37.0 s, 38.5 s, or 40.0 s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] In some optional embodiments, the single-pass time of acetylene in the cyclic chemical vapor deposition is 1-2.5 s, for example, it can be 1.00 s, 1.15 s, 1.30 s, 1.45 s, 1.60 s, 1.75 s, 1.90 s, 2.05 s, 2.20 s, 2.35 s or 2.50 s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0025] In some optional embodiments, the cyclic chemical vapor deposition is followed by nitrogen purging after the introduction of acetylene. The single purging time of nitrogen is 25-40 s, for example, it can be 25.0 s, 26.5 s, 28.0 s, 29.5 s, 31.0 s, 32.5 s, 34.0 s, 35.5 s, 37.0 s, 38.5 s or 40.0 s, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] In some optional embodiments, the number of cycles of the cyclic chemical vapor deposition is 80-120, for example, 80, 84, 88, 92, 96, 100, 104, 108, 112, 116 or 120, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0027] As a preferred technical solution of the present invention, in step S4, the first heating rate is 80-120℃ / min, for example, it can be 80℃ / min, 84℃ / min, 88℃ / min, 92℃ / min, 96℃ / min, 100℃ / min, 104℃ / min, 108℃ / min, 112℃ / min, 116℃ / min or 120℃ / min, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0028] In some optional embodiments, the third temperature is 850-950°C, for example, it can be 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, 940°C or 950°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0029] In some optional embodiments, the flow rate of hydrogen gas continuously introduced as a carrier gas at the third temperature is 200-500 sccm, for example, it can be 200 sccm, 230 sccm, 260 sccm, 290 sccm, 320 sccm, 350 sccm, 380 sccm, 410 sccm, 440 sccm, 470 sccm or 500 sccm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0030] In some alternative embodiments, the temperature of the methyltrichlorosilane is 25-40°C, for example, 25.0°C, 26.5°C, 28.0°C, 29.5°C, 31.0°C, 32.5°C, 34.0°C, 35.5°C, 37.0°C, 38.5°C, or 40.0°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the deposition time of the first stage is 30-60 min, for example, it can be 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0032] In some optional embodiments, the molar flow ratio of hydrogen to methyltrichlorosilane is (10-20):1, for example, it can be 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] In some optional embodiments, the single-pass time of methyltrichlorosilane in the pulse timing of the first stage deposition is 5-10 s, for example, it can be 5.0 s, 5.5 s, 6.0 s, 6.5 s, 7.0 s, 7.5 s, 8.0 s, 8.5 s, 9.0 s, 9.5 s or 10.0 s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the interval after the introduction of methyltrichlorosilane in the pulse timing of the first stage deposition is 15-30 s, for example, it can be 15.0 s, 16.5 s, 18.0 s, 19.5 s, 21.0 s, 22.5 s, 24.0 s, 25.5 s, 27.0 s, 28.5 s or 30.0 s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0035] In some alternative embodiments, the second heating rate is 2-5 °C / min, for example, it can be 2.0 °C / min, 2.3 °C / min, 2.6 °C / min, 2.9 °C / min, 3.2 °C / min, 3.5 °C / min, 3.8 °C / min, 4.1 °C / min, 4.4 °C / min, 4.7 °C / min or 5.0 °C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0036] In some optional embodiments, the fourth temperature is 1050-1200°C, for example, it can be 1050°C, 1065°C, 1080°C, 1095°C, 1110°C, 1125°C, 1140°C, 1155°C, 1170°C, 1185°C or 1200°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0037] In some optional embodiments, the deposition time of the second stage is 80-120 min, for example, it can be 80 min, 84 min, 88 min, 92 min, 96 min, 100 min, 104 min, 108 min, 112 min, 116 min or 120 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0038] In some optional embodiments, the single-pass time of methyltrichlorosilane in the pulse timing of the second stage deposition is 10-15 s, for example, it can be 10.0 s, 10.5 s, 11.0 s, 11.5 s, 12.0 s, 12.5 s, 13.0 s, 13.5 s, 14.0 s, 14.5 s or 15.0 s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0039] In some optional embodiments, the interval after the introduction of methyltrichlorosilane in the pulse timing of the second stage deposition is 10-20 s, for example, it can be 10 s, 11 s, 12 s, 13 s, 14 s, 15 s, 16 s, 17 s, 18 s, 19 s or 20 s, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0040] As a preferred technical solution of the present invention, in step S5, the flow rate of the argon atmosphere is 100-300 sccm, for example, it can be 100 sccm, 120 sccm, 140 sccm, 160 sccm, 180 sccm, 200 sccm, 220 sccm, 240 sccm, 260 sccm, 280 sccm or 300 sccm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] In some alternative embodiments, the cooling rate is 10-20℃ / min, for example, it can be 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min or 20℃ / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0042] The purpose of step S1 in this application is to modify the chemically complex and heterogeneously active surface of a raw silicon nitride ceramic into a chemically homogeneous active surface. First, this application uses pulsed water vapor to modify the entire substrate surface into a homogeneous active surface. Second, through chemical grafting, an anchoring layer is constructed on the homogeneous surface of the ceramic substrate, providing a high-density nucleation site for subsequent silicon carbide growth. In step S2, bis(diethylamino)silane, a special precursor, is used. The silicon-nitrogen bonds in its molecules exhibit reactivity and selectivity towards hydroxyl groups. Through pulsed injection, bis(diethylamino)silane reacts with the hydroxyl groups on the substrate surface. Once the surface hydroxyl groups are reacted away, subsequent bis(diethylamino)silane molecules cannot find reaction sites and are swept away by nitrogen gas. This process is equivalent to forming an anchoring layer in situ on the substrate surface. Through this process, a chemically complex heterogeneous surface is transformed into a chemically homogeneous functionalized surface, providing a good reaction basis for subsequent coatings.

[0043] Step S3 of this application, based on S2, grows a dense amorphous silicon carbide isolation layer on the anchoring layer of the ceramic substrate, thereby avoiding interface contamination problems in the subsequent high-temperature chemical vapor deposition environment. Under cyclic chemical vapor deposition conditions, alternating pulses of bis(diethylamino)silane and acetylene, utilizing a pulse-purge-pulse quasi-atomic layer deposition mode, suppress gas-phase reactions and promote surface-controlled layer-by-layer growth. Simultaneously, the reaction temperature of 400-500℃ is sufficient to drive the surface reaction, but lower than the temperature for substrate atomic migration. In this way, an amorphous silicon carbide thin film can be constructed. This film physically isolates the substrate from the reaction environment in the subsequent high-temperature chemical vapor deposition stage, suppressing nitrogen atom migration and reducing the formation of interface contaminant phases.

[0044] In the gradient growth stage of S4, instead of growing a single-structure silicon carbide, a composite structure is constructed. The first stage is carried out at a relatively low temperature (850-950℃) with a high hydrogen ratio. Under these conditions, the reaction kinetics favor nucleation rather than grain growth, resulting in the deposition of a composite structure composed of nanocrystalline and amorphous materials. This structure exhibits good toughness and moderate hardness, effectively alleviating the significant interfacial stress caused by the mismatch in thermal expansion coefficients between the silicon carbide and silicon nitride substrates, thus acting as a flexible pad. Simultaneously, pulsed operation suppresses the self-etching of hydrogen chloride byproducts and provides time for atomic surface migration relaxation, which is beneficial for obtaining a denser nanostructure. Subsequently, through a slow temperature program at a rate of 2-5℃ / min, the crystallinity and grain growth rate of SiC gradually increase with rising temperature, and the coating transitions from nanocrystalline to micron-sized columnar crystals. Finally, stable deposition occurs in the high-temperature region of 1050-1200℃. High temperature promotes the preferential growth of silicon carbide grains along specific directions, forming a columnar crystal structure. Its highly ordered and dense arrangement endows the coating surface with high hardness, wear resistance and high-temperature oxidation resistance.

[0045] Ultimately, during the programmed cooling process, the slow and controlled cooling allows the coating and substrate ample time to shrink uniformly, keeping the final residual thermal stress within the material's tolerance range. The process is carried out under an inert atmosphere to prevent oxidation of the silicon carbide surface by residual gases at high temperatures.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] This application constructs a uniform, highly active organosilicon anchoring interface layer by chemically modifying the substrate surface at the atomic scale. This anchoring layer provides a nucleation template for subsequent coatings, tending random island-like nucleation into uniform layered initiation growth, thereby forming a tightly integrated interface. For ceramic valves / cylinder valve plates that experience frequent start-stop cycles and particulate erosion, the above-mentioned nucleation and interface state is beneficial to improving adhesion consistency and reducing the probability of early microcrack initiation and edge peeling.

[0048] This application achieves an amorphous silicon carbide isolation layer by first growing it at a low temperature of 400-500℃ using a cyclic chemical vapor deposition mode before high-temperature chemical vapor deposition. This isolation layer inhibits the migration of substrate atoms in the subsequent high-temperature stage, ensuring that the silicon carbide main coating is grown on a pure silicon carbide substrate, thereby obtaining an ideal interface that is pollution-free and highly stable.

[0049] This application constructs a composite structure coating. Its base is a nanocrystalline / amorphous composite flexible pad layer deposited at a lower temperature. This layer possesses excellent toughness and can effectively absorb and alleviate interfacial stress caused by thermal expansion mismatch, improving the coating's crack resistance. Its surface layer consists of coarse columnar crystals grown at high temperatures, endowing the coating with excellent wear resistance and oxidation resistance. This transitional structure allows the coating to achieve both high adhesion and high hardness on the valve plate-seat friction pair, extending the valve's maintenance cycle and service life. Detailed Implementation

[0050] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that employ any obvious substitutions and modifications made to the embodiments described herein.

[0051] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone further purification or processing.

[0052] Example 1

[0053] This embodiment provides a method for preparing a CVD-based silicon carbide coating, which specifically includes the following steps:

[0054] S1: The silicon nitride ceramic substrate is cleaned, dried and placed in a chemical vapor deposition furnace. After vacuuming, it is heated to the first temperature of 250°C. Deionized water vapor at 45°C is pulsed into the reaction chamber to carry out the reaction. One cycle consists of 1.0s of water vapor introduction and 20s of nitrogen purging. A total of 40 cycles are performed.

[0055] S2: Maintain the reaction chamber temperature at the first temperature, and pulse 38°C bis(diethylamino)silane into the reaction chamber to carry out the reaction. The reaction is carried out by 1.5s of bis(diethylamino)silane and 28s of nitrogen purging. This constitutes one cycle, and a total of 4 cycles are performed.

[0056] S3: Raise the reaction chamber temperature to the second temperature of 450℃, and perform cyclic chemical vapor deposition with alternating pulses using bis(diethylamino)silane as the silicon source and acetylene as the carbon source. One cycle consists of introducing bis(diethylamino)silane for 1.8s, followed by nitrogen purging for 30s, then introducing acetylene for 2.0s, followed by nitrogen purging for 38s. A total of 100 cycles are performed.

[0057] S4: The reaction chamber temperature is increased to a third temperature of 900℃ at a first heating rate of 100℃ / min. Hydrogen gas is continuously introduced at a flow rate of 300 sccm as a carrier gas, and methyltrichlorosilane at 30℃ is introduced for the first stage deposition for 45 min. The molar flow ratio of hydrogen to methyltrichlorosilane is 15:1. The pulse sequence of the first stage deposition is 8 s of methyltrichlorosilane introduction followed by a 20 s interval. Subsequently, the reaction chamber temperature is increased to a fourth temperature of 1100℃ at a second heating rate of 3℃ / min for the second stage deposition for 100 min. During this process, the methyltrichlorosilane introduction time is 12 s and the interval time is 15 s.

[0058] S5: After deposition, the temperature is programmed to decrease at a rate of 15°C / min under an argon atmosphere with a flow rate of 250 sccm.

[0059] Example 2

[0060] This embodiment provides a method for preparing a CVD-based silicon carbide coating, which specifically includes the following steps:

[0061] S1: After cleaning and drying the silicon nitride ceramic substrate, place it in a chemical vapor deposition furnace, evacuate it, and heat it to the first temperature of 300°C. Then, pulse 30°C deionized water vapor is introduced into the reaction chamber to carry out the reaction. One cycle consists of 1.5 seconds of water vapor introduction and 15 seconds of nitrogen purging. A total of 50 cycles are performed.

[0062] S2: Maintain the reaction chamber temperature at the first temperature, and pulse 50°C bis(diethylamino)silane into the reaction chamber to carry out the reaction. The reaction is carried out by 0.8s of bis(diethylamino)silane and 20s of nitrogen purging. A total of 5 cycles are performed.

[0063] S3: Raise the reaction chamber temperature to the second temperature of 500℃, and perform cyclic chemical vapor deposition with alternating pulses using bis(diethylamino)silane as the silicon source and acetylene as the carbon source. One cycle consists of introducing bis(diethylamino)silane for 0.8s, followed by nitrogen purging for 40s, then introducing acetylene for 1s, followed by nitrogen purging for 25s. A total of 80 cycles are performed.

[0064] S4: The reaction chamber temperature is increased to a third temperature of 850°C at a first heating rate of 120°C / min. Hydrogen gas is continuously introduced at a flow rate of 500 sccm as a carrier gas, and methyltrichlorosilane at 40°C is introduced for the first stage deposition for 30 min. The molar flow ratio of hydrogen to methyltrichlorosilane is 20:1. The pulse sequence of the first stage deposition is 5 s of methyltrichlorosilane introduction followed by a 30 s interval. Subsequently, the reaction chamber temperature is increased to a fourth temperature of 1200°C at a second heating rate of 5°C / min for the second stage deposition for 80 min. During this process, the methyltrichlorosilane introduction time is 15 s and the interval time is 10 s.

[0065] S5: After deposition, the temperature is programmed to decrease at a rate of 10°C / min under an argon atmosphere with a flow rate of 100 sccm.

[0066] Example 3

[0067] This embodiment provides a method for preparing a CVD-based silicon carbide coating, which specifically includes the following steps:

[0068] S1: The silicon nitride ceramic substrate is cleaned, dried, and placed in a chemical vapor deposition furnace. After vacuuming, it is heated to the first temperature of 220°C. 35°C deionized water vapor is pulsed into the reaction chamber to carry out the reaction. The water vapor is introduced for 0.8s and nitrogen is purged for 22s as one cycle. A total of 35 cycles are carried out.

[0069] S2: Maintain the reaction chamber temperature at the first temperature, and pulse 42°C bis(diethylamino)silane into the reaction chamber to carry out the reaction. The reaction is carried out by 1.2s of bis(diethylamino)silane introduction followed by 22s of nitrogen purging. This constitutes one cycle, and a total of 3 cycles are performed.

[0070] S3: Raise the reaction chamber temperature to the second temperature of 420℃, and perform cyclic chemical vapor deposition with alternating pulses using bis(diethylamino)silane as the silicon source and acetylene as the carbon source. One cycle consists of introducing bis(diethylamino)silane for 1.0s, followed by nitrogen purging for 35s, then introducing acetylene for 1.5s, followed by nitrogen purging for 30s. A total of 110 cycles are performed.

[0071] S4: The reaction chamber temperature is increased to a third temperature of 920°C at a first heating rate of 90°C / min. Hydrogen gas is continuously introduced at a flow rate of 400 sccm as a carrier gas, and methyltrichlorosilane at 35°C is introduced for the first stage deposition for 50 min. The molar flow ratio of hydrogen to methyltrichlorosilane is 12:1. The pulse sequence of the first stage deposition is 6 s of methyltrichlorosilane introduction followed by a 25 s interval. Subsequently, the reaction chamber temperature is increased to a fourth temperature of 1150°C at a second heating rate of 4°C / min for the second stage deposition for 115 min. During this process, the methyltrichlorosilane introduction time is 10 s and the interval time is 20 s.

[0072] S5: After deposition, the temperature is programmed to decrease at a rate of 18°C / min under an argon atmosphere with a flow rate of 150 sccm.

[0073] Example 4

[0074] This embodiment provides a method for preparing a CVD-based silicon carbide coating, which specifically includes the following steps:

[0075] S1: After cleaning and drying the silicon nitride ceramic substrate, place it in a chemical vapor deposition furnace, evacuate it, and heat it to the first temperature of 200°C. Then, pulse 50°C deionized water vapor into the reaction chamber to carry out the reaction. The water vapor is introduced for 0.5 seconds and nitrogen is purged for 25 seconds as one cycle. A total of 30 cycles are performed.

[0076] S2: Maintain the reaction chamber temperature at the first temperature, and pulse 30°C bis(diethylamino)silane into the reaction chamber to carry out the reaction. The reaction is carried out by 2.0s of bis(diethylamino)silane and 30s of nitrogen purging. This constitutes one cycle, and a total of 4 cycles are performed.

[0077] S3: Raise the reaction chamber temperature to the second temperature of 400℃, and perform cyclic chemical vapor deposition with alternating pulses using bis(diethylamino)silane as the silicon source and acetylene as the carbon source. One cycle consists of 2.0s of bis(diethylamino)silane followed by 25s of nitrogen purging, followed by 2.5s of acetylene followed by 40s of nitrogen purging. A total of 120 cycles are performed.

[0078] S4: The reaction chamber temperature is increased to a third temperature of 950°C at a first heating rate of 80°C / min. Hydrogen gas is continuously introduced at a flow rate of 200 sccm as a carrier gas, and methyltrichlorosilane at 25°C is introduced for the first stage deposition for 60 min. The molar flow ratio of hydrogen to methyltrichlorosilane is 10:1. The pulse sequence of the first stage deposition is methyltrichlorosilane introduction for 10 s followed by an interval of 15 s. Subsequently, the reaction chamber temperature is increased to a fourth temperature of 1050°C at a second heating rate of 2°C / min for the second stage deposition for 120 min. During this process, the methyltrichlorosilane introduction time is 11 s and the interval time is 18 s.

[0079] S5: After deposition, the temperature is programmed to decrease at a rate of 20°C / min under an argon atmosphere with a flow rate of 300 sccm.

[0080] Comparative Example 1

[0081] This comparative example provides a method for preparing a silicon carbide coating based on CVD. The difference from Example 1 is that the first-stage deposition steps S1, S2, S3 and S4 are omitted, and a one-step high-temperature chemical vapor deposition process is directly adopted.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing a silicon carbide coating based on CVD. The difference from Example 1 is that step S2 is omitted, while other operation steps and process parameters are exactly the same as in Example 1.

[0084] Comparative Example 3

[0085] This comparative example provides a method for preparing a silicon carbide coating based on CVD. The difference from Example 1 is that step S3 is omitted, while other operation steps and process parameters are exactly the same as in Example 1.

[0086] Comparative Example 4

[0087] This comparative example provides a method for preparing a silicon carbide coating based on CVD. The difference from Example 1 is that the first stage of deposition in step S4 is omitted, and the temperature is directly raised to the fourth temperature for deposition. Other operation steps and process parameters are exactly the same as in Example 1.

[0088] The performance of the silicon nitride ceramic substrates with silicon carbide coatings in Examples 1-4 and Comparative Examples 1-4 was tested, and the specific process is as follows:

[0089] The adhesion of ceramic coatings was tested according to ISO 20502:2016.

[0090] The hardness of the ceramic coating was tested according to ISO 14577-1:2015.

[0091] The sample was held in a muffle furnace at 800℃ for 15 minutes, and then quickly quenched in deionized water at room temperature. After the sample dried, the cycle was repeated, and visual inspections were performed periodically. The first visible macroscopic cracking or peeling of the coating was used as the failure criterion, and the total number of cycles that the sample could withstand before failure was recorded.

[0092] The test results are shown in Table 1.

[0093] Table 1 Test results of Examples 1-4 and Comparative Examples 1-3

[0094]

[0095] As can be seen from the test results of Example 1 and Comparative Example 1 in Table 1, omitting the first-stage deposition of S1, S2, S3 and S4 and directly adopting a single-step high-temperature deposition process leads to a decrease in coating performance: Since silicon carbide is directly deposited on the ceramic surface without any chemical modification, the two rely on weak van der Waals forces for physical adsorption, resulting in extremely low adhesion; although the high temperature of 1100℃ is sufficient to grow high-hardness SiC crystals, due to the lack of interfacial bonding and stress management mechanisms, the coating has many microcracks caused by thermal stress and lacks load-bearing capacity. This fragile interfacial bonding and huge internal stress determine that the coating cannot withstand thermal stress cycles, and its maximum thermal cycle tolerance decreases.

[0096] As shown in Table 1, the test results of Example 1 and Comparative Example 2 reveal that omitting step S2 leads to a decrease in coating performance. Although the hydroxylation treatment in S1 provides certain active sites for deposition, the lack of a step to build chemical bridges between the hydroxyl groups and the subsequent silicon carbide layer reduces the interfacial bonding strength from primarily chemical bonding to a weaker physicochemical interaction, thus decreasing adhesion. The omitted step has no effect on the growth process and final structure of the main coating in S4, therefore the hardness remains essentially the same as in Example 1. Ultimately, this weak interfacial bonding will easily break down at the interface under repeated thermal stress, resulting in a decrease in its maximum thermal cycle tolerance.

[0097] As shown in Table 1, the test results of Example 1 and Comparative Example 3 indicate that omitting step S3 leads to coating performance degradation. Although the anchoring layer in S2 successfully establishes the initial chemical bond, during the subsequent heating to 900-1100℃ in S4, nitrogen atoms in the matrix penetrate this extremely thin organosilicon anchoring interface layer and migrate outward, reacting with the growing silicon carbide to form a brittle amorphous contamination layer in situ at the interface. This contamination layer acts like a brittle interlayer inserted into a robust chemically bonded interface, compromising the integrity and strength of the interface, thus reducing adhesion. Since this defect is also concentrated at the interface and does not affect the main coating structure, its hardness does not change significantly. Ultimately, this brittle interface contamination layer becomes the preferred cracking point under thermal stress, causing the coating to peel off at the interface after a certain number of thermal cycles, resulting in a decrease in its maximum thermal cycle tolerance.

[0098] As shown in Table 1, the test results of Example 1 and Comparative Example 4 reveal that by omitting the low-temperature gradient growth in the first stage (S4) and directly performing high-temperature deposition, while retaining the preceding interface engineering (S1-S3), the initial adhesion did not change significantly. However, since the entire coating consists of hard columnar crystals grown at 1100℃, its overall hardness is even higher than that of Example 1. This high-hardness, rigid overall structure lacks an effective stress buffering mechanism. During thermal cycling, the enormous thermal mismatch stress cannot be effectively absorbed and alleviated by the bottom flexible layer, but instead acts directly on the entire hard coating, causing the coating itself to undergo extensive brittle cracking (cohesive failure) due to its inability to withstand the enormous tensile stress, thus reducing its maximum thermal cycle tolerance.

[0099] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a silicon carbide coating based on CVD, characterized in that, The preparation method includes: S1: After cleaning and drying the silicon nitride ceramic substrate, place it in a chemical vapor deposition furnace, evacuate it, heat it to the first temperature, and pulse deionized water vapor into the reaction chamber to carry out the reaction. S2: Maintain the reaction chamber temperature at the first temperature, and pulse bis(diethylamino)silane into the reaction chamber to carry out the reaction; S3: Raise the reaction chamber temperature to the second temperature, and perform cyclic chemical vapor deposition using bis(diethylamino)silane as the silicon source and acetylene as the carbon source in alternating pulses; S4: The temperature of the reaction chamber is increased to the third temperature at the first heating rate, and hydrogen is continuously introduced as a carrier gas. Methyltrichlorosilane is introduced for the first stage of deposition. Then the temperature of the reaction chamber is increased to the fourth temperature at the second heating rate for the second stage of deposition. S5: After deposition, the temperature is programmed to decrease at a decreasing rate under an argon atmosphere.

2. The method for preparing a CVD-based silicon carbide coating according to claim 1, characterized in that, In S1: The single-pass time for pulsed introduction of deionized water vapor into the reaction chamber is 0.5-1.5s.

3. The method for preparing a CVD-based silicon carbide coating according to claim 1, characterized in that, In S1: After deionized water vapor is pulsedly introduced into the reaction chamber, nitrogen purging is performed, with each nitrogen purging session lasting 15-25 seconds.

4. The method for preparing a CVD-based silicon carbide coating according to claim 1, characterized in that, In S2: The single-pass time for pulsed introduction of bis(diethylamino)silane into the reaction chamber is 0.8-2 s.

5. The method for preparing a CVD-based silicon carbide coating according to claim 1, characterized in that, In S2: After bis(diethylamino)silane is pulsed into the reaction chamber, nitrogen purging is performed, with each purging session lasting 20-30 seconds.

6. The method for preparing a CVD-based silicon carbide coating according to claim 1, characterized in that, In S3: The single-pass time for bis(diethylamino)silane in the cyclic chemical vapor deposition is 0.8-2.0 s; In the cyclic chemical vapor deposition process, bis(diethylamino)silane is introduced followed by nitrogen purging, with each nitrogen purging cycle lasting 25-40 seconds.

7. The method for preparing a CVD-based silicon carbide coating according to claim 1, characterized in that, In S3: The acetylene introduction time in the cyclic chemical vapor deposition is 1-2.5 s; In the cyclic chemical vapor deposition process, acetylene is introduced followed by nitrogen purging, with each nitrogen purging cycle lasting 25-40 seconds.

8. The method for preparing a CVD-based silicon carbide coating according to claim 1, characterized in that, In S4: The flow rate of hydrogen gas continuously introduced as a carrier gas at the third temperature is 200-500 sccm; The molar flow ratio of hydrogen to methyltrichlorosilane is (10-20):

1.

9. The method for preparing a CVD-based silicon carbide coating according to claim 1, characterized in that, In S4: The introduction time of methyltrichlorosilane in the pulse timing of the first stage deposition is 5-10 s; The interval between the introduction of methyltrichlorosilane in the pulse timing of the first stage deposition is 15-30 s.

10. The method for preparing a CVD-based silicon carbide coating according to claim 1, characterized in that, In S4: The methyltrichlorosilane induction time in the second stage deposition pulse timing is 10-15 s; The interval between the introduction of methyltrichlorosilane in the pulse timing of the second stage deposition is 10-20 s.

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