Silicon-coated silicon nitride coating material as well as preparation method and application thereof

Abstract

The invention provides a silicon-coated silicon nitride coating material as well as a preparation method and application thereof, and relates to the technical field of thermal spraying surface engineering. Silicon nitride is a high-quality ceramic material with high temperature resistance and good toughness, but the silicon nitride cannot be sprayed at normal temperature and normal pressure to form a coating, so that the silicon-coated silicon nitride coating material provided by the invention is of a core-shell structure and comprises 3.0-20.0 wt.% of a silicon shell and the balance of a silicon nitride core; the particle size of the silicon-coated silicon nitride coating material is 30-50 [mu] m, the sphericity degree is 99%-100%, and the thickness of the silicon coating layer is 3-10 [mu] m. The silicon-coated silicon nitride core-shell structure coating material is constructed, the bonding strength of the coating is remarkably improved, a silicon shell serves as a bonding phase, the problems of bonding and thermal expansion mismatch between the coating and a matrix, insufficient high-temperature stability and the like are effectively solved, and the service life of the silicon-coated silicon nitride core-shell structure coating material is prolonged. Meanwhile, the wettability and the bonding strength of the composite particles and a matrix are improved due to the good ductility of silicon. And other non-silicon and non-nitrogen element impurity components are not introduced into the system, so that the high-purity silicon nitride coating is obtained.

Description

Technical Field

[0001] This invention relates to the field of thermal spraying surface engineering technology, and in particular to a silicon-coated silicon nitride coating material, its preparation method, and its application. Background Technology

[0002] Silicon nitride (Si3N4) is a new type of ceramic material with high hardness, high melting point, excellent high temperature oxidation resistance, corrosion resistance and low coefficient of thermal expansion. It is widely regarded as an ideal coating material for ultra-high temperature components in aerospace, energy, chemical and other fields.

[0003] For example, aero-engine combustion chamber components need to operate in high-temperature gas environments exceeding 1500°C for extended periods, while also withstanding gas corrosion and thermal shock. Silicon nitride coatings can effectively protect the substrate from damage. However, traditional silicon nitride coatings face the problem of low bonding strength in practical applications. Silicon nitride ceramics are brittle, and their coefficient of thermal expansion differs significantly from that of the substrate. Directly sprayed silicon nitride coatings are prone to cracking and peeling during thermal cycling due to thermal stress concentration. The bonding strength between the coating and the substrate is typically below 20 MPa, limiting the service life of silicon nitride coatings under high-temperature thermal shock conditions.

[0004] In addition, the insufficient high-temperature stability of traditional silicon nitride coatings is also a key problem that urgently needs to be solved. When the coating is used for a long time at temperatures above 1400°C, the silicon nitride particles are prone to sintering and densification, which leads to changes in the microstructure of the coating, increased porosity, and a gradually looser coating structure. This results in a significant decrease in oxidation resistance and mechanical properties, making it impossible to meet the stringent requirements of ultra-high temperature components such as aero-engine combustion chambers that operate continuously at temperatures above 1500°C.

[0005] From a manufacturing process perspective, existing silicon nitride coatings mostly employ chemical vapor deposition (CVD) or physical vapor deposition (PVD) methods. While these methods can produce dense coatings, they suffer from drawbacks such as coating thickness below 100 μm, susceptibility to wear and peeling, high equipment investment costs, low production efficiency, and complex processes. The manufacturing cycle for a single product can be as long as several hours or even tens of hours, making it difficult to achieve large-scale production and industrial application, which greatly limits the promotion of silicon nitride coating technology.

[0006] To improve the bonding strength between silicon nitride coatings and the substrate, traditional coating preparation techniques often employ the addition of metallic binders such as cobalt (Co) and nickel (Ni). However, the introduction of these metallic binders introduces new problems: on the one hand, the melting points of metals are relatively low (e.g., Co's melting point is approximately 1495℃), which may cause softening or even melting within the operating temperature range of the silicon nitride coating, leading to a sharp decline in the coating's high-temperature mechanical properties; on the other hand, the addition of metallic binders inevitably introduces impurity elements, affecting the purity of the coating and preventing its application in high-end fields such as semiconductor equipment where extremely high material purity is required.

[0007] Therefore, developing a silicon nitride coating material with high bonding strength, excellent high-temperature stability, simple and efficient preparation process, and low impurity content, and its preparation method, is one of the technical problems that urgently need to be solved in this field. Summary of the Invention

[0008] In view of this, the present invention provides a silicon-coated silicon nitride coating material, its preparation method, and its application. By constructing a silicon-coated silicon nitride core-shell structure coating material, the present invention achieves a significant improvement in coating bonding strength. The silicon shell acts as a binder phase, effectively solving the problem of thermal expansion mismatch between the coating and the substrate. Simultaneously, the good ductility of silicon improves the wettability and bonding strength between the composite particles and the substrate.

[0009] The first aspect of this invention is to provide a silicon-encapsulated silicon nitride coating material, which has a core-shell structure and comprises: The silicon outer shell is 3.0 wt.%-20.0 wt.%, with the balance being a silicon nitride core; The silicon nitride core serves as the functional phase of the coating, providing properties such as high bonding strength, high temperature resistance, high hardness, and corrosion resistance. The silicon shell acts as a binder phase, improving the bonding strength between the composite particles and the matrix. At the same time, it generates a silicon dioxide (SiO2) protective film at high temperature, preventing the silicon nitride core from sintering and densifying.

[0010] The silicon-coated silicon nitride coating material has a particle size of 30-50 μm to meet the powder feeding requirements of plasma spraying, a sphericity of 99%-100% to improve particle flowability and spraying uniformity, and a silicon coating thickness of 3-10 μm to ensure adhesion and protection.

[0011] A second aspect of the present invention is to provide a method for preparing the above-mentioned silicon-coated silicon nitride coating material, comprising the following steps: S1. Silane gas cracking: Silicon nitride seed crystals are added to a rotating fluidized bed, silane gas (SiH4) is introduced, and the temperature is raised to the cracking temperature to crack the silane gas (H2) and silicon atoms (reaction formula: SiH4→Si+2H2). S2, Silicon Atom Deposition: Hydrogen gas is used to blow up the silicon nitride seed crystal, making the seed crystal fluidized, so that silicon atoms are uniformly deposited on the surface of the silicon nitride particles to form a silicon coating shell, thus obtaining composite particles. S3. Collection and Cooling: Cool and collect the composite particles of S2 to obtain silicon-coated silicon nitride coating material.

[0012] Preferably, in step S1, the silicon nitride seed crystal has a particle size of 10-15 μm and a purity of 99.999% or higher, and the pyrolysis temperature is 550℃-650℃.

[0013] Preferably, in step S2, the hydrogen pressure is 0.1 MPa, the silicon atom deposition temperature is 500℃-600℃, and the deposition time is 1-2 h to ensure that the coating thickness reaches the target thickness.

[0014] Preferably, in step S3, the cooling temperature is ≤100℃.

[0015] A third aspect of this invention provides a method for preparing a composite coating with high bonding strength, high temperature resistance, high hardness, and corrosion resistance using the above-mentioned silicon-encapsulated silicon nitride coating material, comprising the following steps: After the silicon-encapsulated silicon nitride coating material is dried, it is sprayed onto the pretreated substrate and nitrided to obtain a composite coating with high bonding strength, high temperature resistance, high hardness, and corrosion resistance.

[0016] Preferably, the drying temperature is 70℃-90℃ and the drying time is 0.5-1.5 h. Drying can remove moisture from the silicon-coated silicon nitride coating material and prevent pores from forming during spraying.

[0017] Preferably, the substrate pretreatment method is as follows: The substrate workpiece is roughened by sandblasting with silicon nitride particles to improve the mechanical adhesion between the coating and the substrate. Subsequently, the substrate surface is cleaned with alcohol or acetone to remove oil and impurities. After drying, the coating is installed onto the workpiece to be coated. The silicon nitride particles have a particle size of 20-40 μm, the sandblasting gas pressure is 0.4-0.7 MPa, and the substrate roughness R after sandblasting is [value missing]. a The thickness is 3.0-6.0 μm, the drying temperature is 80℃-100℃, the drying time is 0.5 h, and the substrate is a metal substrate or a ceramic substrate.

[0018] Preferably, the spraying is plasma spraying, more preferably supersonic plasma thermal spraying; the spraying is carried out in an inert atmosphere to form an inert environment to prevent particle oxidation, more preferably nitrogen; the spraying parameters are: power 25-35kW, cooling gas flow rate 70-100 lpm, spraying distance 70-120 mm, powder feeding rate 25-45 g / min, coating thickness 200-350 μm, the cooling gas is an inert gas, more preferably argon; during the spraying process, the substrate temperature is controlled below 150℃ to prevent substrate deformation.

[0019] Preferably, the nitriding treatment method is as follows: the coated substrate workpiece is placed in a nitriding furnace and nitrided at 1000-1200℃ for 180-360 min, so that the silicon in the coating reacts with nitrogen to generate silicon nitride (reaction formula: 3Si+2N2→Si3N4), forming a mixed phase of silicon nitride, silicon, and silicon nitride, which further improves the high-temperature stability and bonding strength of the coating.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows: This invention significantly improves coating bonding strength by constructing a silicon-encased silicon nitride core-shell structure coating material. The silicon shell, acting as a binder phase, has a thermal expansion coefficient between that of the silicon nitride core and the substrate, effectively solving the thermal expansion mismatch problem between the coating and the substrate. It also acts as a stress buffer during temperature changes, reducing thermal stress concentration. Simultaneously, silicon's excellent ductility and wettability increase the contact area and mechanical interlocking force between the composite particles and the substrate surface, forming a stronger bond at the coating-substrate interface. This core-shell structure fundamentally solves the problems of low bonding strength and easy peeling caused by thermal expansion mismatch in traditional silicon nitride coatings, significantly improving the coating's anti-peeling performance and service reliability.

[0021] The silicon coating of this invention reacts with oxygen at high temperatures to form a dense silicon dioxide protective film. This protective film has an extremely high melting point and excellent chemical stability, effectively preventing the diffusion and penetration of oxygen and other corrosive gases into the silicon nitride core. The formation of the silicon dioxide protective film not only enhances the coating's oxidation resistance but also effectively inhibits the sintering and densification process of silicon nitride particles at high temperatures, maintaining the stability of the coating's microstructure. This in-situ generated protective mechanism enables the coating to operate stably for extended periods at higher temperatures and exhibits stronger resistance to cracking and peeling when subjected to repeated high-temperature heating and rapid cooling thermal shock cycles, significantly extending the coating's service life under extreme thermal cycling conditions.

[0022] This invention utilizes a rotating fluidized bed combined with silane gas pyrolysis deposition technology to prepare silicon-coated silicon nitride composite particles. The process is simple, convenient, and highly automated, enabling large-scale powder preparation in a single batch. The unique structural design of the rotating fluidized bed allows the silicon nitride seed crystals to boil under the influence of the gas flow, ensuring uniform deposition of silicon atoms on the particle surface and guaranteeing consistent coating thickness and integrity. Subsequent coating preparation employs mature plasma spraying technology. The entire process is easily scalable and allows for continuous manufacturing, with production efficiency far exceeding traditional chemical vapor deposition or physical vapor deposition methods. Compared to traditional methods, this invention significantly reduces equipment investment and operating costs.

[0023] This invention utilizes high-purity silicon nitride seed crystals and high-purity silane gas as raw materials, combined with strict process control and inert atmosphere protection, to prepare silicon-coated silicon nitride composite particles that maintain extremely high purity. This avoids the impurity contamination problems introduced by adding metal binders in traditional technologies. By replacing metal binders with silicon, this invention achieves both enhanced adhesion and maintains the high purity of the coating. This makes the coating suitable not only for conventional high-temperature applications such as aero-engines, but also for fields with high material purity requirements, such as high-temperature components in semiconductor equipment, thus expanding the application range of silicon nitride coatings.

[0024] The coating prepared by this invention retains the inherent high hardness of silicon nitride, effectively resisting wear and scratches; its excellent corrosion resistance enables it to operate stably for a long time in harsh chemical environments such as strong acids and alkalis; and its low coefficient of friction endows the coating with good friction-reducing and wear-resistant properties. The introduction of the silicon encapsulation layer significantly improves the coating's bonding strength and high-temperature stability without sacrificing these inherent properties. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Unless otherwise specified, all experiments were repeated three times, and the results are expressed as averages.

[0027] Example 1: Preparation of silicon-coated silicon nitride coating material, the method is as follows: The silicon-encapsulated silicon nitride coating material prepared in this embodiment has a core-shell structure, with a silicon shell content of 12.0 wt.% and the remainder being a silicon nitride core. The coating material has a particle size of 30-45 μm, a sphericity of 99.5%, a silicon encapsulation layer thickness of 6.5 ± 0.5 μm, and a purity of 99.9992%.

[0028] The preparation method of the silicon-encapsulated silicon nitride coating material is as follows: Silicon nitride seed crystals (particle size 10-15 μm, purity 99.999%), silane gas (purity 99.999%), and hydrogen gas (purity 99.999%) were selected. Rotary fluidized bed settings: Adjust the rotation speed of the rotary fluidized bed to 500 rpm, and set the pyrolysis temperature to 600℃ and the deposition temperature to 550℃; Silane gas cracking: 10 kg of silicon nitride seed crystals were added to a rotating fluidized bed, and silane gas (flow rate 500 mL / min) was introduced. The gas was cracked at 600℃ for 30 min to obtain hydrogen gas and silicon atoms. Silicon atom deposition: Hydrogen gas at a pressure of 0.1 MPa (flow rate 1000 mL / min) is introduced to blow up the silicon nitride seed crystal, making the seed crystal fluidized, so that silicon atoms are uniformly deposited on the surface of the silicon nitride particles. After deposition for 1 h, a silicon encapsulation layer shell is formed, resulting in composite particles with silicon nitride as the core and silicon as the shell. Collection and cooling: The composite particles settle to the bottom under the centrifugal force of the rotating fluidized bed, and are collected after cooling (80℃) to obtain silicon-coated silicon nitride coating material.

[0029] Example 2 The difference from Example 1 is that the particle size of the coating material is 35-50 μm and the deposition time is 2 h.

[0030] Example 3 Silicon-encapsulated silicon nitride coating The composite coating was prepared using the silicon-encapsulated silicon nitride coating material prepared in Example 1, and the method is as follows: Material drying: The silicon-coated silicon nitride coating material prepared in Example 1 was dried at 80°C for 1 h to remove moisture and prevent pores from forming during spraying; Matrix pretreatment: The ceramic matrix workpiece is roughened by sandblasting with high-purity silicon nitride particles (30μm in diameter) to achieve a matrix roughness R. a =4 μm, to improve the mechanical adhesion between the coating and the substrate; then clean the substrate surface with alcohol to remove oil and impurities, dry at 100°C for 0.5 h, and then install it onto the sprayed workpiece; Plasma spraying: The pretreated substrate is placed in the spraying chamber and evacuated to 25±5 mbar, then backfilled with argon to 45±5 mbar; a supersonic plasma thermal spraying method is adopted, and the spraying parameters are set as follows: power 30 kW, cooling gas (argon) flow rate 90 lpm, spraying distance 100 mm, powder feeding rate 35 g / min, and coating thickness 250 μm; during the spraying process, the substrate temperature is controlled below 150℃ to prevent substrate deformation, resulting in a composite coating with high bonding strength, high temperature resistance, high hardness, and corrosion resistance.

[0031] Nitriding treatment: The coated substrate workpiece is placed in a nitrogen furnace and nitrided at 1100℃ for 240 min. The silicon in the coating reacts with nitrogen to generate silicon nitride, forming a mixed phase of silicon nitride, silicon, and silicon nitride, which further improves the high-temperature stability and bonding strength of the coating.

[0032] Performance testing: The coating porosity is 4.5% (tested according to GB / T34887-2017); the bonding strength with the substrate is 32 MPa (tested according to GB / T1720-2020 nano-scratch method); the thermal shock resistance test at 1600℃ (air cooling to room temperature) is 260 cycles; the hardness (HV0.5) is 1800 MPa (tested according to GB / T4340.3-2012).

[0033] Example 4 The difference from Example 3 is that the silicon-encapsulated silicon nitride coating material of Example 2 is used, and the spraying parameters are set as follows: power 28 kW, cooling gas (argon) flow rate 80 lpm, spraying distance 100 mm, powder feeding rate 40 g / min, and coating thickness 300 μm.

[0034] Performance testing: In the thermal shock test at 1600℃, the coating obtained in this embodiment resisted more than 240 thermal shock cycles, and the bonding strength with the substrate was 31±6 MPa.

[0035] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A silicon over silicon nitride coating material, characterized by, The material has a core-shell structure and is composed as follows: The silicon outer shell is 3.0 wt.%-20.0 wt.%, with the balance being a silicon nitride core; The silicon-coated silicon nitride coating material has a particle size of 30-50 μm, a sphericity of 99%-100%, and a silicon coating thickness of 3-10 μm.

2. The method for preparing a silicon-coated silicon nitride coating material according to claim 1, characterized in that, Includes the following steps: S1. Silane gas cracking: Silicon nitride seed crystals are added to a rotating fluidized bed, silane gas is introduced, and the temperature is raised to the cracking temperature to crack the gas and obtain hydrogen and silicon atoms. S2, Silicon Atom Deposition: Hydrogen gas is used to blow up the silicon nitride seed crystal, making the seed crystal fluidized, so that silicon atoms are uniformly deposited on the surface of the silicon nitride particles to form a silicon coating shell, thus obtaining composite particles. S3. Collection and Cooling: Cool and collect the composite particles of S2 to obtain silicon-coated silicon nitride coating material.

3. The method for preparing a composite coating with high bonding strength, high temperature resistance, high hardness, and corrosion resistance using the silicon-coated silicon nitride coating material as described in claim 1, characterized in that... The steps are as follows: After the silicon-encapsulated silicon nitride coating material is dried, it is sprayed onto the pretreated substrate and nitrided to obtain a composite coating with high bonding strength, high temperature resistance, high hardness, and corrosion resistance.

4. The method for preparing the composite coating according to claim 3, characterized in that, The substrate pretreatment method is as follows: the substrate workpiece is roughened by sandblasting with silicon nitride particles, and then the substrate surface is cleaned with alcohol or acetone to remove oil, dust and impurities, and then dried.

5. The method for preparing a composite coating according to claim 4, characterized in that, The air pressure of the sandblasting gas is 0.4-0.7 MPa, and the roughness R a of the substrate after sandblasting is 3.0-6.0 μm.

6. The method for preparing a composite coating according to claim 4, characterized in that, The spraying is plasma spraying.

7. The method for preparing a composite coating according to claim 6, characterized in that, The plasma spraying is carried out in an inert atmosphere; the spraying parameters are: power 25-35 kW, cooling gas flow rate 70-100 lpm, spraying distance 70-120 mm, powder feeding rate 25-45 g / min, coating thickness 200-350 μm, and the cooling gas is an inert gas.

8. The method for preparing a composite coating according to claim 4, characterized in that, During the spraying process, the substrate temperature is controlled below 150℃.

9. The method for preparing a composite coating according to claim 4, characterized in that, The nitriding treatment method is as follows: the sprayed workpiece is heated and nitrided in nitrogen gas to form a mixed phase coating of silicon nitride, silicon, and silicon nitride.

10. The method for preparing a composite coating according to claim 9, characterized in that, The heating nitriding temperature is 1000℃-1200℃, and the heating nitriding time is 180-360 min.