A high-temperature resistant ceramic protective coating based on the cocktail effect and its construction method

Abstract

This invention belongs to the technical field of high-temperature oxidation and corrosion resistant protective coatings, specifically relating to a modified polysilazane coating based on the cocktail effect and its construction method. The coating is composed of modified polysilazane, coupling agent, diluent, glass powder, and modified MAX phase ceramic powder, wherein the MAX phase is one or more of modified Ti3SiC2, modified Cr2AlC, or modified Ti3AlC2. The synergistic effect of the cocktail effect of the components in the coating results in a coating with high density, low porosity, excellent interfacial adhesion, and wide-temperature-range self-healing ability. The added modified MAX phase oxidizes at high temperatures to form functional products, which slow down ion diffusion through defect regulation, significantly improving oxidation resistance, enhancing thermal insulation, and reducing crack propagation. The construction method of this coating is process-controllable and efficient, effectively extending the service life of metal substrates in high-temperature oxidation and corrosion environments, and is suitable for high-temperature furnace components, heat exchangers, and other applications.

Description

[0001] This invention belongs to the field of high-temperature resistant oxidation and corrosion protective coating technology, specifically relating to a modified polysilazane coating based on the "cocktail effect" and its construction method. Background Technology

[0002] Polysilazanes are a class of inorganic polymers whose main chain uses Si-N bonds as repeating units, and they have attracted widespread attention in the field of protective coatings in recent years. Polysilazanes combine the easy processability of polymer coatings with the high-temperature stability of ceramic materials. They can be coated to form films under mild conditions, or pyrolyzed at high temperatures to transform into dense SiCN, SiCNO, or SiO2 ceramic coatings. Compared with traditional ceramic coating preparation techniques, the polysilazane precursor method has significant advantages such as simple process, uniform film formation, applicability to complex-shaped substrates, and good adhesion to various substrates. However, existing polysilazane coating technologies still have the following shortcomings: First, during the pyrolysis conversion of polysilazane, small molecule gases such as ammonia and methane are released, leading to severe volume shrinkage of the coating and easy formation of microcracks, thus limiting the critical thickness of a single coating. Second, the high-temperature oxidation resistance of pure polysilazane converted into ceramic coatings still has room for improvement, especially in oxidizing environments above 1000℃, where the long-term stability of the coating is not ideal. Third, existing technologies mostly focus on single-component polysilazane or simple filler composite systems, and research on systematic enhancement strategies for high-temperature oxidation resistance is insufficient. Therefore, developing an optimized polysilazane high-temperature protective coating based on the "cocktail effect" that combines high density, high adhesion, excellent high-temperature oxidation resistance, and simple construction process has significant engineering application value. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a polysilazane coating modified based on the "cocktail effect". Another technical problem this invention aims to solve is to provide a method for constructing this coating.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] The high-temperature oxidation-resistant protective coating based on the "cocktail effect" is composed of five components: 32%–75% modified polysilazane, 0.1%–10% coupling agent, 5%–48% diluent, 1%–15% glass powder, and 2%–30% of one or more of modified Ti3SiC2, modified Cr2AlC, and modified Ti3AlC2.

[0006] The modified polysilazane is reinforced by composite fillers, wherein the fillers are any one or more oxides containing Yb, B, and Y.

[0007] The coupling agent is at least one of γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, or N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0008] The diluent is at least one of xylene, anisole, octane, methylcyclohexane, and dibutyl ether.

[0009] The glass powder is at least one of silicate glass powder or borate glass powder.

[0010] Component five is one or more of modified Ti3SiC2, modified Cr2AlC, and modified Ti3AlC2, wherein these materials are all modified MAX phases. The modified material refers to the solid solution doping element at the M or A position, specifically, doping the M position with one or more of the transition group elements Ta, W, Nb, Zr, etc.; and doping the A position with one or two of the elements Al or Sn. The modified material specifically refers to doping at the M or A position, or simultaneously at both positions. The atomic proportion of the modified element at the M position is 0.1% to 20%; the atomic proportion of the modified element at the A position is 0.5% to 50%. The doped modified MAX phase material can simultaneously improve the mechanical structural stability and high-temperature oxidation resistance of the material, and improve the stability and comprehensive high-temperature corrosion resistance of the coating.

[0011] The method for constructing the high-temperature resistant oxidation coating includes:

[0012] (1) Prepare a mixed slurry by mixing one or more of modified Ti3SiC2, modified Cr2AlC, and modified Ti3AlC2 with glass powder and alcohol, with a mixing ratio of powder to alcohol of 1:1; then ball mill in a ball mill jar for 24 hours at a speed greater than 200 rpm, and then air dry for later use.

[0013] (2) Mix the powder with modified polysilazane, diluent and coupling agent, and then stir in a magnetic stirrer for 1 hour at a speed greater than 700 rpm to form a composite sol;

[0014] (3) Apply the mixed solution to the substrate to be protected by brushing or spraying.

[0015] (4) The substrate to which the coating is applied is subjected to high-temperature heat treatment in air atmosphere, and a dense coating is obtained by heat preservation.

[0016] The heating process involves heating to 120℃~150℃ at a heating rate of 5℃ / min, holding at that temperature for half an hour, then heating to 600℃~800℃ at a heating rate of 3℃ / min, holding at that temperature for 30~60 minutes, and then naturally cooling to room temperature.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) This invention enhances interfacial bonding through a dual mechanism of chemical bonding and mechanical locking. First, the active groups (such as Si-H, Si-NH-Si) in the polysilazane precursor can undergo condensation reactions with the hydroxyl groups or oxide layer on the surface of the metal substrate to form covalent bonds. Second, the introduction of Yb2O3 or Y2O3 can undergo rare earth activation reactions with the native oxide film on the surface of the base metal (such as stainless steel, high-temperature alloy) to generate Yb-OM or YOM interfacial bonding layers (M is Fe, Cr, Ni, etc.). Third, the glass powder wets the substrate surface during sintering, further increasing the contact area. Scratch test results show that the critical load (Lc) of the coating of this invention is increased by more than 24% compared with the pure polysilazane coating, and the bonding strength retention rate after thermal shock is greater than 82%.

[0019] (2) This invention achieves ultra-low porosity through multi-component synergistic filling. During high-temperature sintering, the glass powder softens and flows, filling the submicron-level pores within the coating. The composite oxide system of Yb₂O₃, B₂O₃, and Y₂O₃ can react with the pyrolysis products of polysilazane, reducing interfacial pores. The layered structure of the modified MAX phase powder exhibits a self-compacting effect during coating formation. Under the combined effect of these three aspects, the porosity of the coating of this invention can be controlled below 3%, and almost no through-holes exist. This significantly improves the density compared to existing polysilazane coatings, effectively blocking the penetration paths of oxygen and corrosive media.

[0020] (3) This invention achieves excellent thermal insulation performance through multilayer thermal resistance design. The SiCN(O) amorphous phase generated by the cracking of polysilazane has low intrinsic thermal conductivity; the modified MAX phase powder has a unique layered crystal structure, with significant differences in thermal conductivity along the in-plane and out-of-plane (anisotropy), and the lattice of the oxidation products changes after doping, forming tortuous heat flow transport paths when randomly distributed in the coating, enhancing phonon scattering. Laser scintillation test shows that the equivalent thermal conductivity of the coating of this invention can be as low as 0.9 to 1.3 W / m·K, which is more than 28% lower than that of the unmodified polysilazane coating, and the temperature drop at 900℃ is increased by 50 to 80℃.

[0021] (4) This invention uses polysilazane as a precursor, which transforms into an amorphous SiCN(O) ceramic phase during high-temperature pyrolysis, possessing excellent thermal stability. Based on this, Yb2O3 or Y2O3 and modified MAX phase powder are further introduced. Yb2O3 and Y2O3, as rare earth oxide stabilizers, effectively inhibit the crystallization and decomposition of the SiCN(O) phase above 1200℃; the modified MAX phase (such as Ti3AlC2, Cr2AlC, etc.) generates dense doped oxide products (such as doped Al2O3, TiO2, Cr2O3) in situ under high-temperature oxidation conditions, further slowing down the diffusion rate of metal ions and oxygen ions. Compared to a pure polysilazane coating without the above components, the coating of this invention, after heat treatment in air at 1200℃ for 15 hours, exhibits a mass loss rate reduced by more than 60%, maintains an amorphous / nanocrystalline stable phase structure, and increases the high-temperature resistance limit by approximately 200℃.

[0022] (5) This invention constructs a multi-component synergistic self-healing system. B2O3 begins to soften and flow at approximately 500℃, serving as a low-temperature healing component to fill early microcracks; glass powder exhibits viscous flow in the 600–800℃ range, achieving mid-temperature healing; the oxidation products of Y2O3 and modified MAX phases (such as doped TiO2, Cr2O3, and Al2O3) can inhibit crack propagation at higher temperatures, deflecting it and preventing problems such as coating peeling caused by crack expansion. The three healing mechanisms cover a wide temperature range from 500℃ to 1200℃, forming a gradient self-healing response. Thermal cycling tests show that after 10 thermal shocks from room temperature to 1200℃, the surface microcrack density of the coating of this invention is reduced by more than 70% compared to the control coating without added healing components, and the crack width is controlled within 5μm. Attached Figure Description

[0023] To more clearly illustrate the embodiments of the present invention, the figures in the embodiments are briefly described. Obviously, the figures described below are merely some embodiments of the present invention, and those skilled in the art or researchers can obtain other figures based on these figures without creative effort.

[0024] Figure 1 The surface morphology of the coating obtained in Example 1 is shown.

[0025] Figure 2 The surface morphology of the coating prepared in Example 1 before oxidation after high-temperature treatment;

[0026] Figure 3 This is a surface view of the coating obtained in Example 1 after oxidation.

[0027] Figure 4The surface morphology of the coating prepared in Example 2 before oxidation after high-temperature treatment;

[0028] Figure 5 This is a surface view of the coating obtained in Example 2 after oxidation. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but this does not limit the present invention in any way.

[0030] The substrates used in the following examples are stainless steel sheets, including 304, 304L, 316, 316L, 321, 310, 310S, 314, and 446, etc., for medium and high temperature applications. The sheets can be polished before coating or sandblasted. Polishing involves progressively grinding with 150#, 400#, 600#, 800#, and 1000# metallographic sandpaper. After polishing, the samples are ultrasonically cleaned with acetone, alcohol, and deionized water for 15 minutes each, and then air-dried for later use. Sandblasting refers to large-scale sandblasting using a sandblasting machine to remove rust and dirt, and increase surface roughness.

[0031] Example 1

[0032] First, prepare 321 steel plate and cut it into 20*20*2mm pieces. 3 The cube sample was sandblasted. A coating was prepared using modified Ti3SiC2 powder doped with 10% W (10%), Ta (7.5%), and Al (35%), along with 40% Yb2O3-modified polysilazane, 7% borate glass powder, 3% γ-methacryloyloxypropyltrimethoxysilane, and 40% xylene. First, the W, Ta, and Al-modified Ti3SiC2 powder and borate glass powder were mixed with alcohol in a 1:1 ratio. Then, the mixture was ball-milled for 24 hours at 240 r / min. After mixing, the slurry was removed and dried. The dried powder mixture was then mixed with the modified polysilazane, diluent, and coupling agent according to the specified ratio, and stirred in a magnetic stirrer for 1 hour at 750 r / min to form a composite sol.

[0033] The composite solvent was sprayed onto the 321 substrate sample using a large-diameter pneumatic spray gun, such as... Figure 1 As shown. Then, high-temperature heat treatment was performed in air atmosphere, with the temperature increased to 150℃ at a rate of 5℃ / min and held for half an hour. Subsequently, the temperature was increased to 800℃ at a rate of 3℃ / min and held for 45 minutes, followed by natural cooling to room temperature. This yielded a smooth, flat surface with a porosity of approximately 1%, tightly bonded to the matrix (critical load 8.2 MPa), and a surface temperature of 900... oThe coating sample, with a bond strength retention rate of approximately 87% after 10 thermal shock cycles and a thermal conductivity of 1.2 W / m·K, exhibits the following surface morphology after heat treatment: Figure 2 As shown.

[0034] The sample was placed in a box furnace under an air atmosphere at 10°C. o Temperature increased to 1100 °C / min o C. Incubate at this temperature for 20 hours, then allow to cool naturally. After cooling, remove the coating sample. The coating should remain intact, without peeling or flaking. Figure 3 As shown, the oxidative weight gain is 6 mg / cm³. 2 No obvious cracks were observed on the surface.

[0035] Example 2

[0036] First, prepare a 446 steel plate and cut it into 20*20*2mm pieces. 3 The cube sample was polished. A coating was prepared using 11% Nb (7%) and Si (25%) modified Cr2AlC powder, 7% Nb (9%) and Si (10%) modified Ti3AlC2 powder, 35% Y2O3 modified polysilazane, 12% silicate glass powder, 5% γ-glycidyl etheroxypropyltrimethoxysilane, and 30% dibutyl ether. First, the Nb and Si modified Cr2AlC and Ti3AlC2 powders and silicate glass powder were mixed with alcohol in a 1:1 ratio. Then, the mixture was ball-milled for 24 hours at 260 r / min. After mixing, the slurry was removed and dried. The dried powder mixture was then mixed with modified polysilazane, diluent, and coupling agent according to the specified ratio, and stirred in a magnetic stirrer for 1 hour at 800 r / min to form a composite sol.

[0037] The composite solvent was sprayed onto the 446 substrate sample using a large-diameter pneumatic spray gun. Then, high-temperature heat treatment was performed in air atmosphere, with the temperature increased to 140℃ at a rate of 5℃ / min and held for half an hour. Subsequently, the temperature was increased to 750℃ at a rate of 3℃ / min and held for half an hour, followed by natural cooling to room temperature. This yielded a smooth, flat sample with a porosity of approximately 2.5%, tightly bonded to the substrate (critical load 8.4 MPa), and a 950℃ high-temperature coating. o The coating sample, which retained approximately 86% of its bond strength after 10 thermal shocks and had a thermal conductivity of 1.1 W / m•K, exhibited the following surface morphology: Figure 4 As shown.

[0038] The sample was placed in a box furnace in an air atmosphere at 10°C. o Temperature increased to 1200 °C / min oC. Incubate at this temperature for 15 hours, then allow to cool naturally. After cooling, remove the coating sample. The coating remains intact, without peeling or flaking. A white substance appears on the surface, such as... Figure 5 As shown, the oxidative weight gain was 13 mg / cm³. 2 No obvious cracks were found on the surface.

[0039] Example 3

[0040] First, prepare a 304 stainless steel plate and cut it into 20*20*2mm pieces. 3 The cube samples were sandblasted. A coating was prepared using Ti3AlC2 powder modified with 30% Zr (1%), Nb (3%), Si (25%), and Sn (15%), along with 40% B2O3-modified polysilazane, 2% silicate glass powder, 0.7% N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, and 27.3% methylcyclohexane. First, the Zr, Nb, Si, and Sn-modified Ti3AlC2 powder and silicate glass powder were mixed with alcohol in a 1:1 ratio. Then, the mixture was ball-milled for 24 hours at 270 r / min. After mixing, the slurry was removed and dried. The dried powder mixture was then mixed with the modified polysilazane, diluent, and coupling agent according to the specified ratio, and stirred in a magnetic stirrer for 1 hour at 780 r / min to form a composite sol.

[0041] The composite solvent was brush-coated onto the 304 substrate sample. Then, high-temperature heat treatment was performed in air atmosphere. The temperature was increased to 120°C at a rate of 5°C / min and held for half an hour. Subsequently, the temperature was increased to 650°C at a rate of 3°C / min and held for 1 hour. The sample was then naturally cooled to room temperature, resulting in a smooth, flat surface with a porosity of approximately 1.5%, strong adhesion to the substrate (critical load 8.1 MPa), and a 900... o The coating sample has a bond strength retention rate of approximately 89% and a thermal conductivity of 1.3 W / m•K after 10 thermal shocks.

[0042] The sample was placed in a box furnace in an air atmosphere at 10°C. o Temperature increased to 950 °C / min o C, heat-treated for 25 hours, then allowed to cool naturally. After cooling, the coating sample was removed, and the coating remained intact without peeling or flaking. The oxidative weight gain was 3.5 mg / cm³. 2 No obvious cracks were found on the surface.

[0043] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should be protected by the present invention.

Claims

1. A high-temperature oxidation-resistant protective coating based on the "cocktail effect," characterized in that: It is composed of five components: component one is modified polysilazane, component two is a coupling agent, component three is a diluent, component four is glass powder, and component five is one or more of modified Ti3SiC2, modified Cr2AlC, and modified Ti3AlC2. Among them, the weight percentage of component one is 32% to 75%; the weight percentage of component two is 0.1% to 10%; the weight percentage of component three is 5% to 48%; the weight percentage of component four is 1% to 15%; and the weight percentage of component five is 2% to 30%.

2. The high-temperature oxidation-resistant protective coating according to claim 1, characterized in that: The modified polysilazane is reinforced by composite fillers, wherein the fillers are any one or more oxides containing Yb, B, and Y.

3. The high-temperature oxidation-resistant protective coating according to claim 1, characterized in that: The coupling agent is at least one of γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, or N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

4. The high-temperature oxidation-resistant protective coating according to claim 1, characterized in that: The diluent is at least one of xylene, anisole, octane, methylcyclohexane, and dibutyl ether.

5. The high-temperature oxidation-resistant protective coating according to claim 1, characterized in that: The glass powder is at least one of silicate glass powder or borate glass powder.

6. The high-temperature oxidation-resistant protective coating according to claim 1, characterized in that: Component five is one or more of modified Ti3SiC2, modified Cr2AlC, and modified Ti3AlC2, wherein these materials are all modified MAX phases. The modified material refers to the solid solution doping element at the M or A position, specifically, the M position is doped with one or more of the transition group elements Ta, W, Nb, Zr, etc.; and the A position is doped with one or two of the elements Al or Sn. The modified material specifically refers to doping at the M or A position, or simultaneously at both positions. The atomic proportion of the modified element at the M position is 0.1% to 20%; and the atomic proportion of the modified element at the A position is 0.5% to 50%.

7. A method for preparing the high-temperature oxidative corrosion resistant coating as described in claim 1, characterized in that, Includes the following steps: Step S1: Prepare a slurry by mixing one or more of the modified Ti3SiC2, modified Cr2AlC, and modified Ti3AlC2 with glass powder and alcohol, with a powder to alcohol ratio of 1:1; then ball mill in a ball mill jar for 24 hours at a speed greater than 200 rpm, and then air dry for later use. Step S2: Mix the powder with modified polysilazane, diluent, and coupling agent, and then stir in a magnetic stirrer for 1 hour at a speed greater than 700 rpm to form a composite sol; Step S3: Apply the mixed solution to the substrate to be protected by brushing or spraying. Step S4: The substrate to be coated is subjected to high-temperature heat treatment in air atmosphere, and a dense coating is obtained by heat preservation.

8. The coating construction method according to claim 7, characterized in that, The heating process involves heating to 120℃~150℃ at a heating rate of 5℃ / min, holding at that temperature for half an hour, then heating to 600℃~800℃ at a heating rate of 3℃ / min, holding at that temperature for 30~60 minutes, and then naturally cooling to room temperature.

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