A seal coat and a method of making the same

Abstract

The present application relates to the field of abradable seal coating technology and spraying technology, and particularly relates to a seal coating and a preparation method thereof. The seal coating comprises a dense layer of a surface layer and a porous layer inside; the porosity of the dense layer is less than 1%, and the surface roughness Ra is less than 3 microns; the porosity of the porous layer is 5% to 40%. The seal coating has the characteristics of a dense surface layer and a porous inside, the surface roughness of the coating is less than 3 microns (which can be as low as 1.6 microns) to minimize aerodynamic loss, the internal porosity is 5% to 40% to minimize the damage of the pair rubbing, the highest use temperature of the coating is 650 DEG C, and the coating can be used with various pairs such as titanium alloy, high-temperature alloy and the like, and meets the use requirements of various axial flow compression equipment such as turboshaft engines, turbofan engines and industrial compressors.

Description

Technical Field

[0001] This invention relates to the field of abrasive sealing coating technology and spraying technology, and in particular to a sealing coating and its preparation method. Background Technology

[0002] In axial flow compressors, sealing coatings are key components for reducing gap leakage and improving equipment efficiency. Their performance directly affects the aerodynamic losses, service life of mating components, and overall operational reliability. Current axial flow compressors are evolving towards higher speeds, higher compression ratios, and lighter weights, with increasingly demanding operating conditions. Coatings must simultaneously meet multiple requirements, including high surface finish and low abrasion damage, driving continuous iteration and upgrading of sealing coating technology. Currently, mainstream coating systems cover metal-based, ceramic-based, and metal-ceramic composite systems, with plasma spraying and cold spraying as the main preparation processes. Development is moving towards precise control of coating microstructure and improved composition design adaptability. However, in practical applications, coatings still face technical challenges such as the difficulty of balancing surface finish and abrasion resistance at high temperatures, becoming a core area for further improvement in compressor performance.

[0003] Currently, existing sealing coatings suffer from the following problems: they cannot achieve a balance between high surface finish and low abrasion damage, resulting in significant shortcomings in core performance. Existing coatings cannot simultaneously achieve a precise gradient structure of "dense surface and porous interior," leading to unreasonable structural design: if a monolithic dense structure is used, the lack of internal porous buffering means that impact forces cannot be absorbed during abrasion with mating parts such as titanium alloys and high-temperature alloys, easily causing scratches, wear, and even coating cracking; if a monolithic porous structure is used, insufficient surface density results in a surface roughness that cannot meet the high surface finish requirement of Ra < 1.6 μm, leading to high airflow resistance, significant aerodynamic losses, and severely reduced operating efficiency of axial flow compressors. Furthermore, the preparation methods for existing sealing coatings are vague, resulting in poor coating performance stability and batch-to-batch consistency. Existing preparation methods suffer from unreasonable pore-forming agent selection, inefficient removal methods, poor compatibility with coating powders, and a lack of clear content control standards. The process parameters for thermal and cold spraying lack clear standards and are not specifically optimized for the structural differences between dense and porous layers, resulting in uneven transitions and weak bonding between the coating surface and internal structure, leading to delamination and peeling. Furthermore, unreasonable surface finishing parameters fail to control surface roughness to Ra < 1.6 μm without damaging the internal porous structure, and the coating performance fluctuates greatly after processing, hindering large-scale production and engineering applications. Therefore, developing a high-gloss sealing coating and its stable and controllable preparation method has become a core technical challenge urgently needing breakthroughs in this field. Summary of the Invention

[0004] Based on the above, this invention provides a sealing coating and its preparation method. This invention employs a process route of "layered spraying - pore-forming agent removal - surface finishing" to achieve a gradient structure of dense surface and porous interior, as well as a highly glossy surface.

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is a sealing coating, comprising a dense surface layer and an internal porous layer; the porosity of the dense layer is less than 1%, and the surface roughness Ra is less than 3 μm; the porosity of the porous layer is 5% to 40%.

[0006] In a preferred embodiment of the present invention, the pore size of the porous layer is 20μm to 80μm.

[0007] The porous layer has a uniform or gradient distribution of pores.

[0008] In a preferred embodiment of the present invention, the thickness of the dense layer is 20 μm to 30 μm, and the thickness of the porous layer is 0.5 mm to 3.0 mm.

[0009] In a preferred embodiment of the present invention, the total thickness of the sealing coating is 0.6 mm to 3.1 mm.

[0010] In a preferred embodiment of the present invention, the sealing coating is a pure metal coating or an alloy coating; the pure metal coating is a gold, silver, lead, aluminum or copper coating; the alloy coating is a copper-aluminum alloy coating, an aluminum-silicon alloy coating or an MCrAlY coating.

[0011] In a preferred embodiment of the present invention, the copper-aluminum alloy coating comprises, by mass percentage: 8 wt.% to 10 wt.% Al, with the balance being Cu; or the aluminum-silicon alloy coating comprises: 10 wt.% to 15 wt.% Si, with the balance being Al.

[0012] The second technical solution of the present invention is a method for preparing the above-mentioned sealing coating, comprising the following steps: Step 1, Substrate pretreatment: The substrate surface is successively ground, degreased and sandblasted; Step 2, Preparation of spray powder: Metal powder and pore-forming agent are mechanically mixed at a mass ratio of (65~85):(15~35) to obtain porous layer spray powder; Metal powder and pore-forming agent are mechanically mixed at a mass ratio of (98.5~99.9):(0.1~1.5) to obtain a dense layer spraying powder; Step 3, Layered spraying: A porous layer is sprayed onto the pretreated substrate surface using a thermal spraying process; a dense layer is sprayed onto the porous layer surface using a cold spraying process. Step 4, Remove the pore-forming agent: Remove the pore-forming agent by ablation, chemical method, or a combination thereof; Step 5, Post-processing: The coating after removing the pore-forming agent is subjected to surface finishing to obtain a sealing coating with a surface roughness Ra of less than 3μm; Steps 1 and 2 are not in any particular order.

[0013] In a preferred embodiment of the present invention, in step 1, white corundum sand is used for sandblasting, with a particle size of 80~120 mesh, a sandblasting pressure of 0.3~0.5MPa, a sandblasting distance of 80~120mm, and the surface roughness of the substrate after sandblasting is controlled at Ra1.0~2.0μm. Spraying is carried out within 30 minutes after pretreatment.

[0014] In a preferred embodiment of the present invention, the metal powder is gold, silver, lead, aluminum, copper, copper-aluminum alloy, aluminum-silicon alloy, or MCrAlY powder; the particle size of the metal powder is 10μm~100μm; the flowability of the metal powder is ≥15s / 50g, and the loose packing density is 1.2~2.5g / cm³. 3 .

[0015] The pore-forming agent is at least one of polyphenylene ester, polyurethane, and sodium salt; the particle size of the pore-forming agent is 20μm~80μm; the mechanical mixing speed is 350r / min~450r / min, and the mixing time is 2.5h~3.5h.

[0016] The purpose of ensuring that the pore-forming agent content in the dense layer spray powder does not exceed 1.5 wt.% is to eliminate the micropores generated during the spraying process and ensure the density of the dense layer.

[0017] In a preferred embodiment of the present invention, in step 3, the thermal spraying process is atmospheric plasma spraying; the process parameters for atmospheric plasma spraying are: argon flow rate 50L / min~70L / min, hydrogen flow rate 5L / min~7L / min, current 400A~500A, power 25kW~35kW, spraying distance 80mm~150mm, and agitator gas flow rate 3~5L / min; the process parameters for cold spraying are: nitrogen pressure 40bar~50bar, nitrogen flow rate 80m³ / min. 3 / h~120m 3 / h, working gas temperature 300℃~500℃, carrier gas flow rate 10m³ / h 3 / h~20m 3 / h, spray gun moving speed 10mm / s~30mm / s, powder feeder speed 3rpm~7rpm.

[0018] In step 4, the ablation method is used: the sprayed sample is placed in a heat treatment furnace and ablated using a segmented heating method. The specific steps are as follows: the temperature is raised from room temperature to 200°C and held for 1-2 hours to remove moisture from the coating; then the temperature is raised to 300-500°C and held for 2-4 hours to allow the pore-forming agent to fully decompose and volatilize; finally, the temperature is cooled to room temperature with the furnace, and the heating rate is controlled at 5-10°C / min to avoid cracking of the coating due to excessive heating. Chemical method: Immerse the sprayed sample in a chemical solution. Sodium salt pore-forming agent is immersed in deionized water at a temperature of 25-50℃ for 4-8 hours, with stirring every hour to ensure complete dissolution of the sodium salt. Organic pore-forming agent residue is immersed in a 5%-10% (mass fraction) sodium hydroxide solution at a temperature of 40-60℃ for 2-4 hours. After immersion, rinse thoroughly with deionized water and then dry in a drying oven at 100-120℃ for 2-3 hours to remove surface moisture.

[0019] In a preferred embodiment of the present invention, in step 5, the surface finishing process is grinding or turning. The grinding process includes a rough grinding stage and a fine grinding stage: the rough grinding stage uses an 80-150 grit diamond grinding wheel, a wheel linear speed of 18-22 m / s, a feed rate of 80-120 mm / min, and a grinding depth of 0.01 mm-0.03 mm; the fine grinding stage uses a 600-1000 grit diamond grinding wheel, a wheel linear speed of 12-15 m / s, a feed rate of 40-60 mm / min, and a grinding depth of 0.005-0.01 mm; oil cooling is used during the grinding process to control the grinding temperature and ensure that the surface roughness of the coating can reach an optimal 1.6 μm.

[0020] The turning process includes roughing and finishing stages: the roughing stage has a cutting speed of 30-40 m / min, a feed rate of 0.1-0.2 mm / r, and a depth of cut of 0.05-0.2 mm; the finishing stage has a cutting speed of 40-60 m / min, a feed rate of 0.03-0.06 mm / r, and a depth of cut of 0.02-0.05 mm. A diamond cutting tool is used, and emulsion cooling is employed during the cutting process to prevent burrs and burns on the coating surface, ensuring that the coating surface roughness Ra can reach an optimal of 1.6 μm.

[0021] The sealing coating prepared by the method of the present invention has a double-layer structure with dense surface and porous interior and high surface smoothness. Its maximum working temperature can reach 650℃, and the bonding strength can reach more than 27MPa. After long-term service at 650℃ for ≥1000h, there is no peeling or cracking. It effectively improves aerodynamic loss and minimizes the impact damage to mating parts.

[0022] The sealing coating of this invention has a dense surface and a porous interior. The surface roughness of the coating is as low as 1.6 μm to minimize aerodynamic losses, and the internal porosity is 5% to 40% to minimize wear damage to mating parts. The coating has a maximum operating temperature of 650°C and can be used with various mating parts such as titanium alloys and high-temperature alloys to meet the requirements of various axial flow compression equipment such as turboshaft engines, turbofan engines, and industrial compressors.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. The sealing coating provided by this invention adopts a gradient structure with a dense surface and porous interior, which cleverly balances the core requirements of high gloss and low impact damage: the dense surface (porosity <1%) and high gloss after surface finishing (Ra as low as 1.6μm) minimize the aerodynamic loss of axial flow compressor equipment and improve equipment operating efficiency; the porous interior (porosity 5%~40%) can effectively buffer the impact between the coating and the mating parts, minimize damage to the mating parts, and extend the service life of the mating parts.

[0024] 2. The sealing coating provided by this invention can operate at a temperature of up to 650℃, making it suitable for medium and high temperature conditions. The coating composition can be flexibly selected and can be matched with various mating parts such as titanium alloys and high temperature alloys. It has a wide range of applications and can meet the usage requirements of various axial flow compression equipment such as turboshaft engines, turbofan engines, and industrial compressors.

[0025] 3. The preparation method provided by this invention has a clear process and well-defined parameters. The pore-forming agent is selected reasonably and removed efficiently and thoroughly. The spraying process and finishing process are well matched. It can effectively control the porosity, surface roughness and thickness of the coating, ensuring stable coating performance and good batch consistency, and can realize large-scale production and engineering application.

[0026] 4. The preparation method provided by this invention does not require complex equipment, has strong process controllability and good repeatability, and the pore-forming agent and spraying material are widely available and moderately priced. Compared with the existing preparation process, it significantly reduces production costs and production difficulty, and has significant economic practicality. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a scanning electron microscope image of the surface microstructure of the dense layer of the sealing coating prepared in Example 1 of the present invention; Figure 2 This is a scanning electron microscope image of the surface microstructure of the porous layer of the sealing coating prepared in Example 1 of the present invention; Figure 3 This is a schematic diagram of the cross-sectional structure of the sealing coating of the present invention; in the figure, 1-substrate, 2-porous layer, 3-dense layer, 4-pores of the porous layer. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] Unless otherwise specified, the methods and equipment used in the embodiments are conventional methods and equipment in the art, and the raw materials used are all conventional commercially available raw materials.

[0035] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1 This embodiment provides a sealing coating consisting of a dense surface layer and an internal porous layer, suitable for medium- and high-temperature operating conditions (temperature range 400~800℃) and used in auxiliary parts of turbofan engines. The sealing coating has a thickness of 0.62 mm, with a dense layer extending 20 μm from the surface to the interior. It has a porosity of 0.9 vol.% and a surface roughness Ra = 1.6 μm. The surface microstructure is as follows: Figure 1 As shown. The internal porous layer has a porosity of 30 vol.%, a thickness of 0.6 mm, a pore size of 60–80 μm, and uniform pore distribution. The surface microstructure of the porous layer is shown in the figure. Figure 2 As shown, the cross-sectional structure of the sealing coating is as follows: Figure 3 As shown.

[0037] The sealing coating is a CuAl coating, with the following elemental composition by mass percentage: 9 wt.% Al, and the balance being Cu. The sealing coating is prepared using CuAl composite powder, with a particle size of 10~80 μm; the CuAl composite powder composition by mass percentage is: 9 wt.% Al, and the balance being Cu.

[0038] The preparation method of the above sealing coating includes the following steps: Step 1, Matrix Pretreatment The high-temperature titanium alloy substrate was sequentially subjected to grinding, ethanol degreasing, and sandblasting. Sandblasting was performed using 120-mesh white corundum abrasive at a pressure of 0.5 MPa and a distance of 120 mm. The surface roughness of the substrate after sandblasting was Ra = 1.8 μm. Spraying was carried out within 15 minutes of the pretreatment. Compressed air was used to blow away any residual dust from the substrate surface.

[0039] Step 2, Preparation of spray powder (1) Preparation of porous layer spraying powder: Copper-aluminum alloy powder (particle size 30~50μm) and polystyrene pore-forming agent (particle size 60~80μm) are mechanically mixed at a mass ratio of 75:25 (i.e., polystyrene mass fraction is 25wt.%), the mixing speed is 450r / min, and the mixing time is 3.5h to obtain porous layer spraying powder; (2) Preparation of dense layer spray powder: Copper-aluminum alloy powder (particle size 30~50μm) and polyphenylene pore-forming agent (particle size 60~80μm) are mechanically mixed at a mass ratio of 99:1 (i.e., the mass fraction of polyphenylene is 1wt.%), the mixing speed is 450r / min, and the mixing time is 3.5h to obtain dense layer spray powder.

[0040] Step 3, Coating Preparation (1) Preparation of porous layer: A porous layer was sprayed onto the pretreated titanium alloy substrate using atmospheric plasma spraying. The spraying material was porous layer spraying powder, and the spraying thickness was 0.6 mm. The process parameters were: argon flow rate 70 L / min, hydrogen flow rate 5 L / min, current 410 A, power 28 kW, spraying distance 100 mm, and stirrer gas flow rate 3.5 L / min. (2) Preparation of dense layer: A dense layer was sprayed onto the surface of the porous layer using a cold spraying process. The spraying material was dense layer spraying powder, and the spraying thickness was 20 μm. The process parameters were: nitrogen pressure 40 bar, nitrogen flow rate 100 m³ / h. 3 / h, working gas temperature 500℃, carrier gas flow rate 12m³ / h 3 / h, spray gun moving speed 30mm / s, powder feeder rotation speed 3rpm.

[0041] Step 4, Remove the pore-forming agent The pore-forming agent was removed by a combination of ablation and chemical methods. First, ablation was performed: the temperature was raised from room temperature to 200℃ and held for 2 hours, then raised to 450℃ and held for 3.5 hours, with a heating rate of 7℃ / min, and cooled with the furnace. Then, the solution was soaked in 8% sodium hydroxide solution for 3 hours (soaking temperature 50℃). After soaking, the solution was rinsed with deionized water and dried at 120℃ for 3 hours.

[0042] Step 5, Post-processing The coating after removing the pore-forming agent was ground. The rough grinding stage used a 150-grit diamond wheel with a wheel speed of 20 m / s, a feed rate of 90 mm / min, and a grinding depth of 0.01–0.03 mm. The fine grinding stage used an 800-grit diamond wheel with a wheel speed of 14 m / s, a feed rate of 50 mm / min, and a grinding depth of 0.005–0.01 mm. Oil cooling was used during the grinding process. The resulting sealing coating had a surface roughness Ra of 1.6 μm and a high surface finish.

[0043] Comparative Example 1 This comparative example uses the method described in Example 1 of CN 116219351 A to prepare a double-layer sealing coating.

[0044] Comparative Example 2 (Increasing the porosity of the dense surface layer) The only difference from Example 1 is that in step 2, the dense layer spraying powder is prepared by mechanically mixing copper-aluminum alloy powder (particle size 30~50μm) and polystyrene pore-forming agent (particle size 60~80μm) at a mass ratio of 85:15 (i.e., polystyrene mass fraction is 15wt.%), with a mixing speed of 450r / min and a mixing time of 3.5h to obtain the dense layer spraying powder; the remaining steps and parameters are the same as in Example 1.

[0045] As a result, the sealing coating prepared in this comparative example consists of a dense layer on the surface and a porous layer inside. The dense layer has a porosity of 17.6 vol.% from the surface to a depth of 20 μm, while the porous layer has a porosity of 30 vol.%.

[0046] Comparative Example 3 (the method of preparing the dense layer was changed from cold spraying to hot spraying) The only difference from Example 1 is that in step 3, the dense layer is prepared by spraying a dense layer onto the surface of the porous layer using an atmospheric plasma spraying process. The spraying material is dense layer spraying powder, and the spraying thickness is 20 μm. The process parameters are: argon flow rate 70 L / min, hydrogen flow rate 5 L / min, current 410 A, power 28 kW, spraying distance 100 mm, and stirrer gas flow rate 3.5 L / min.

[0047] The sealing coatings prepared in Example 1 and Comparative Examples 1-3 were subjected to performance testing. The strength test was conducted in accordance with GB / T8642-2002, the thermal shock resistance test was conducted in accordance with Q / BK 910-2014, the abrasion resistance test was conducted in accordance with Q / BK 908-2014, and the surface roughness test was conducted in accordance with GB / T 37421-2019. The results are shown in Table 1.

[0048] Comparative Example 4 The only difference from Example 1 is that the pore-forming agent in the dense layer spraying powder is omitted, that is, the dense layer spraying powder is a copper-aluminum alloy powder with a particle size of 30~50μm; the other steps and parameters are the same as in Example 1.

[0049] Table 1

[0050] As shown in Table 1, the bonding strength of the high-gloss sealing coating prepared by this invention reaches over 27 MPa, indicating good interfacial bonding. The sealing coating of this invention has a uniform pore distribution, excellent thermal shock resistance and abrasion resistance, and a surface finish of up to 1.6 μm. It minimizes aerodynamic losses and can be used with various mating parts such as titanium alloys and high-temperature alloys, meeting the requirements of various axial-flow compression equipment such as turboshaft engines, turbofan engines, and industrial compressors.

[0051] Example 2 This embodiment provides a sealing coating consisting of a dense surface layer and an internal porous layer, suitable for medium and low temperature operating conditions (temperature range: room temperature to 400℃), and used for sealing parts of industrial compressors. The sealing coating has a thickness of 0.82 mm, with a dense layer extending 20 μm from the surface to the interior, a porosity of 0.6 vol.%, and a surface roughness Ra=1.6 μm. The internal porous layer has a porosity of 25 vol.%, a thickness of 0.8 mm, a pore size of 20~40 μm, and a pore gradient distribution (porosity increases from 10 vol.% to 25 vol.% from the surface to the interior).

[0052] The sealing coating is an AlSi coating, with the following elemental composition by mass percentage: 12 wt.% Si, with the balance being Al. The sealing coating is prepared using AlSi composite powder, with a particle size of 10–80 μm; the AlSi composite powder composition by mass percentage is: 12 wt.% Si, with the balance being Al.

[0053] The preparation method of the above sealing coating includes the following steps: Step 1, Matrix Pretreatment The titanium alloy substrate was sequentially subjected to grinding, ethanol degreasing, and sandblasting. Sandblasting used 80-mesh white corundum abrasive at a pressure of 0.3 MPa and a distance of 80 mm. The surface roughness of the substrate after sandblasting was Ra = 1.2 μm. Spraying was performed within 25 minutes of the pretreatment. Compressed air was used to blow away any residual dust from the substrate surface.

[0054] Step 2, Preparation of spray powder (1) Preparation of porous layer spraying powder: Aluminum-silicon alloy powder (particle size 10~30μm) and polyphenylene pore-forming agent (particle size 30~50μm) are mechanically mixed at a mass ratio of 70:30 (i.e., polyphenylene mass fraction is 30wt.%), the mixing speed is 350r / min, and the mixing time is 2.5h to obtain porous layer spraying powder; (2) Preparation of dense layer spray powder: Aluminum-silicon alloy powder (particle size 10~30μm) and polyphenylene pore-forming agent (particle size 30~50μm) are mechanically mixed at a mass ratio of 99:1 (i.e., the mass fraction of polyphenylene is 1wt.%), the mixing speed is 350r / min, and the mixing time is 2.5h to obtain dense layer spray powder.

[0055] Step 3, Coating Preparation (1) Preparation of porous layer: A porous layer was sprayed onto the pretreated titanium alloy substrate using atmospheric plasma spraying. The spraying material was porous layer spraying powder, and the spraying thickness was 0.8 mm. The process parameters were: argon flow rate 60 L / min, hydrogen flow rate 7 L / min, current 400 A, power 28 kW, spraying distance 90 mm, and stirrer gas flow rate 4.0 L / min. (2) Preparation of dense layer: A dense layer was sprayed onto the surface of the porous layer using a cold spraying process. The spraying material was dense layer spraying powder, and the spraying thickness was 20 μm. The process parameters were: nitrogen pressure 40 bar, nitrogen flow rate 100 m³ / h. 3 / h, working gas temperature 450℃, carrier gas flow rate 12m³ / h 3 / h, spray gun moving speed 10mm / s, powder feeder rotation speed 7rpm.

[0056] Step 4, Remove the pore-forming agent The pore-forming agent was removed by ablation: the temperature was raised from room temperature to 200℃ and held for 2 hours, then raised to 450℃ and held for 3.5 hours, with a heating rate of 7℃ / min, and then cooled with the furnace.

[0057] Step 5, Post-processing The coating after removing the pore-forming agent was turned. During the rough turning stage, the cutting speed was 35 m / min, the feed rate was 0.1 mm / r, and the depth of cut was 0.1 mm. During the finish turning stage, the cutting speed was 40~60 m / min, the feed rate was 0.04 mm / r, and the depth of cut was 0.02 mm. A diamond turning tool was used, and emulsion cooling was applied. After turning, a sealing coating with a surface roughness Ra of 1.6 μm was obtained, with high surface finish.

[0058] The sealing coating prepared in Example 2 was subjected to the same tests as in Example 1. The results showed that the sealing coating prepared in Example 2 had a bonding strength of 27.71 MPa, did not peel off after 25 cycles of water cooling thermal shock at 600℃, had a wearable feed depth ratio of 11.38%, and a surface roughness of 1.6 μm.

[0059] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A sealing coating, characterized in that, It includes a dense surface layer and an internal porous layer; the porosity of the dense layer is less than 1%, and the surface roughness Ra is less than 3 μm; the porosity of the porous layer is 5% to 40%.

2. The sealing coating according to claim 1, characterized in that, The pore size of the porous layer is 20μm~80μm.

3. The sealing coating according to claim 1, characterized in that, The thickness of the dense layer is 20μm~30μm, and the thickness of the porous layer is 0.5mm~3.0mm.

4. The sealing coating according to claim 1, characterized in that, The total thickness of the sealing coating is 0.6 mm to 3.1 mm.

5. The sealing coating according to claim 1, characterized in that, The sealing coating is a pure metal coating or an alloy coating; the pure metal coating is a gold, silver, lead, aluminum or copper coating; the alloy coating is a copper-aluminum alloy coating, an aluminum-silicon alloy coating or an MCrAlY coating.

6. The sealing coating according to claim 5, characterized in that, The copper-aluminum alloy coating comprises, by weight percentage: 8 wt.% to 10 wt.% Al, with the balance being Cu; or the aluminum-silicon alloy coating comprises: 10 wt.% to 15 wt.% Si, with the balance being Al.

7. A method for preparing the sealing coating according to any one of claims 1 to 6, characterized in that, Includes the following steps: Step 1, Substrate pretreatment: The substrate surface is successively ground, degreased and sandblasted; Step 2, Preparation of spray powder: Metal powder and pore-forming agent are mechanically mixed at a mass ratio of (65~85):(15~35) to obtain porous layer spray powder; Metal powder and pore-forming agent are mechanically mixed at a mass ratio of (98.5~99.9):(0.1~1.5) to obtain a dense layer spraying powder; Step 3, Layered spraying: A porous layer is sprayed onto the pretreated substrate surface using a thermal spraying process; a dense layer is sprayed onto the porous layer surface using a cold spraying process. Step 4, Remove the pore-forming agent: Remove the pore-forming agent by ablation, chemical method, or a combination thereof; Step 5, Post-processing: The coating after removing the pore-forming agent is subjected to surface finishing to obtain a sealing coating with a surface roughness Ra of less than 3μm; Steps 1 and 2 are not in any particular order.

8. The preparation method according to claim 7, characterized in that, The metal powder is gold, silver, lead, aluminum, copper, copper-aluminum alloy, aluminum-silicon alloy, or MCrAlY powder; the particle size of the metal powder is 10μm~100μm; The pore-forming agent is at least one of polyphenylene ester, polyurethane, and sodium salt; the particle size of the pore-forming agent is 20μm~80μm; the mechanical mixing speed is 350r / min~450r / min, and the mixing time is 2.5h~3.5h.

9. The preparation method according to claim 7, characterized in that, In step 3, the thermal spraying process is atmospheric plasma spraying; the process parameters for atmospheric plasma spraying are: argon flow rate 50L / min~70L / min, hydrogen flow rate 5L / min~7L / min, current 400A~500A, power 25kW~35kW, spraying distance 80mm~150mm, and agitator gas flow rate 3~5L / min. The process parameters for the cold spraying are: nitrogen pressure 40 bar to 50 bar, nitrogen flow rate 80 m³ / h. 3 / h~120m 3 / h, working gas temperature 300℃~500℃, carrier gas flow rate 10m³ / h 3 / h~20m 3 / h, spray gun moving speed 10mm / s~30mm / s, powder feeder speed 3rpm~7rpm.

10. The preparation method according to claim 7, characterized in that, In step 5, the surface finishing process is either grinding or turning. The grinding process includes a rough grinding stage and a fine grinding stage: the rough grinding stage uses an 80-150 grit diamond grinding wheel, a wheel linear speed of 18-22 m / s, a feed rate of 80-120 mm / min, and a grinding depth of 0.01 mm-0.03 mm; the fine grinding stage uses a 600-1000 grit diamond grinding wheel, a wheel linear speed of 12-15 m / s, a feed rate of 40-60 mm / min, and a grinding depth of 0.005-0.01 mm. The turning process includes a roughing stage and a finishing stage: the roughing stage has a cutting speed of 30~40m / min, a feed rate of 0.1~0.2mm / r, and a depth of cut of 0.05~0.2mm; the finishing stage has a cutting speed of 40m / min~60m / min, a feed rate of 0.03~0.06mm / r, and a depth of cut of 0.02~0.05mm.

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