Preparation method of graded porous functional coating

Abstract

The invention discloses a preparation method of a graded porous functional coating, and belongs to the technical field of high-temperature alloy surface strengthening. The method comprises the following steps: firstly, preparing NiAlMo multi-component alloy powder, grading and screening the NiAlMo multi-component alloy powder into alloy powder A (1t: 10 microns), B (10-40 microns) and C (40-70 microns) with different particle sizes, and mixing spherical aluminum powder with specific particle sizes into the B and the C; and then the high-temperature alloy matrix is subjected to sand blasting coarsening, and then the three layers of powder are sequentially sprayed through the plasma spraying technology. And finally, graded alkali liquor activation is conducted, specifically, initial micropores are formed through mild reaction with low-concentration alkali liquor, then the aluminum pore-forming agent is deeply dissolved out with high-concentration alkali liquor, and therefore a gradient type multi-scale porous structure with the pore diameter gradually increasing from inside to outside is formed in the coating. The bonding strength and the specific surface area of the coating and the matrix and the stability under high-temperature service are remarkably improved, and the method is suitable for surface strengthening and functionalization of high-temperature alloy parts under extreme working conditions.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy surface strengthening and functional coating technology, specifically a method for preparing a hierarchical porous functional coating. Background Technology

[0002] High-temperature alloys are widely used in aerospace, energy, and petrochemical industries. Their surface properties directly affect the service life and operating efficiency of equipment under extreme conditions such as high temperature, high pressure, and strong corrosion. Currently, thermal spraying, electroplating, and chemical vapor deposition are commonly used surface treatment technologies. Among them, thermal spraying is flexible and produces coatings with good performance, making it one of the mainstream technologies. However, traditional thermal spray coatings still suffer from problems such as low porosity, small specific surface area, and insufficient surface properties, making it difficult to meet the application requirements under extreme conditions. Summary of the Invention

[0003] To address the problems of simple pore structure, low bonding strength, and insufficient specific surface area in existing coatings, this invention provides a method for preparing a graded porous functional coating. Through graded mixing, graded spraying, and graded activation processes, a gradient multi-scale porous structure is constructed on the surface of a high-temperature alloy to improve the bonding strength between the coating and the substrate, increase the specific surface area, and enhance its service stability and surface performance under extreme environments.

[0004] Technical solution

[0005] The method for preparing the hierarchical porous functional coating of the present invention includes the following steps:

[0006] S1. Preparation of multi-component alloy powder: NiAlMo or NiMoAl-based multi-component alloy powder was prepared and graded by sieving to obtain three alloy powders with different particle sizes:

[0007] - Alloy powder A: Particle size < 10 μm;

[0008] - Alloy powder B: Particle size 10–40 μm;

[0009] - Alloy powder C: Particle size 40–70 μm.

[0010] S2. Sandblasting: Sandblasting pretreatment is performed on the surface of the high-temperature alloy substrate to enhance surface roughness and activity.

[0011] S3. Graded Spraying: Using plasma spraying equipment, alloy powder A, alloy powder B, and alloy powder C are sequentially sprayed onto the sandblasted substrate surface, wherein:

[0012] - Alloy powder A is used as the base layer with a thickness of 5–15 μm;

[0013] - Alloy powder B is the main layer, with a thickness of 30–50 μm;

[0014] - Alloy powder C is the surface layer, with a thickness of 50–70 μm.

[0015] S4. Graded activation pore formation:

[0016] a) First activation: Use 3–10 wt% KOH or NaOH solution and treat at 30–50℃ for 60–80 min to form initial micropores through a gentle reaction;

[0017] b) Second activation: Use 20–30 wt% KOH or NaOH solution and treat at 60–80℃ for 18–20 h to accelerate the dissolution of aluminum components, expand pores and optimize pore size distribution, and finally form a gradient porous structure.

[0018] Furthermore, spherical Al powder with particle sizes of 30–40 μm and 50–60 μm are respectively mixed into alloy powder B and alloy powder C to improve the pore-forming effect and structural stability.

[0019] Furthermore, the plasma spraying process parameters are: input power 65–96KW, powder feeding gas is argon, pressure 0.35–0.65MPa, and powder feeding rate 1–18r / min.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] Stable structure: The sequence of spraying followed by activation, combined with graded particle size design, ensures interfacial adhesion and avoids damage to the coating structure during the activation process.

[0022] Pore ​​gradient: By designing pore size to increase layer by layer from the inside out, a gradient porous structure is formed, which is beneficial to material transport and surface performance improvement;

[0023] Large specific surface area: graded activation significantly improves the porosity and specific surface area of ​​the coating, enhancing the surface properties and service stability of high-temperature alloys under extreme conditions. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the preparation method of the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of the hierarchical porous coating obtained in this invention. Detailed Implementation

[0026] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0027] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] Example 1

[0029] 1. Prepare NiAlMo alloy powder and sieve it (using a vibrating sieve with corresponding mesh sizes):

[0030] - Alloy powder A: Passed through a 1500-mesh sieve, particle size <10μm;

[0031] - Alloy powder B: Passed through a 400–1500 mesh sieve, with a particle size of 10–40 μm;

[0032] - Alloy powder C: Passed through a 200–400 mesh sieve, with a particle size of 40–70 μm.

[0033] 2. Spherical Al powder with a particle size of 30–40 μm is mixed into alloy powder B at a mass ratio of 34:1; spherical Al powder with a particle size of 50–60 μm is mixed into alloy powder C at a mass ratio of 10:1.

[0034] Mixing process: A high-energy ball mill (stainless steel tank) is used, with a ball-to-material ratio of 5:1, a rotation speed of 800 rpm, and a mixing time of 4 hours. Argon gas is continuously introduced during the ball milling process to prevent oxidation.

[0035] 3. After sandblasting the high-temperature alloy substrate, spray the following: the input power of the spraying equipment is 90KW, the main gas pressure is argon 0.55Mba, and the powder feeding rate is 1~18r / min.

[0036] - Alloy powder A: Thickness 10μm;

[0037] - Alloy powder B: Thickness 40μm;

[0038] - Alloy powder C: Thickness 60μm.

[0039] 4. Graded activation:

[0040] 1) First activation (gentle pore formation):

[0041] - Activation solution: 5wt% NaOH;

[0042] -Temperature: 40℃;

[0043] -Time: 70min;

[0044] - The reaction vessel is a polytetrafluoroethylene tank with continuous gentle stirring.

[0045] 2) Second activation (deep hole expansion):

[0046] - Activation solution: 25wt% NaOH;

[0047] -Temperature: 70℃;

[0048] -Time: 20 hours;

[0049] -During the process, you can see continuous and gentle bubble generation (hydrogen release).

[0050] 5. Clean and dry with deionized water to obtain a gradient porous coating.

[0051] Example 2

[0052] It is basically the same as Example 1, except that:

[0053] The mass ratio of alloy powder B to Al powder is 29:1;

[0054] The mass ratio of C powder to Al powder in the alloy is 9:1.

[0055] Compared to Example 1, the average porosity was 30.73%. In Example 2, the Al content in the inner and outer coatings was further increased, and the measured average porosity was 34.61%.

[0056] Example 3

[0057] It is basically the same as Example 1, except that:

[0058] The mass ratio of alloy powder B to Al powder is 19:1;

[0059] The mass ratio of C powder to Al powder in the alloy is 8:1.

[0060] Compared to Implementation Case 2, the Al content in the middle and outer coatings is further increased, with an average porosity of 45.50%. This can effectively further increase the specific surface area of ​​the high-temperature alloy coating.

[0061] In this invention, the high-temperature alloy substrate is first pretreated by sandblasting to enhance its surface activity. Then, ultrafine alloy powder A is sprayed onto the surface of the high-temperature alloy as a base layer, which increases the bonding force between the coating and the high-temperature alloy. Next, alloy powder B is sprayed, which mainly serves to construct a main coating with a certain thickness and porosity, providing a larger specific surface area and good surface properties. Then, alloy powder C is sprayed, which has a larger particle size. By spraying alloy powder and aluminum powder with larger particle size, a balance between a larger specific surface area and stability is established. After activation, a structure is formed in which the pores of the coating become larger from the inside out, which is beneficial for material transport and surface performance improvement. Finally, the high-temperature alloys coated with alloy powders A, B, and C undergo a secondary activation treatment: the first activation uses a low-concentration alkaline solution for a gentle reaction to avoid generating excessive hydrogen gas in a short time, which could damage the surface coating structure of the high-temperature alloy. At the same time, it initially dissolves the aluminum pore-forming agent in the surface coating, forming micropores. The second activation uses a high-concentration alkaline solution to accelerate the dissolution of aluminum, increase porosity, and optimize pore size distribution, ultimately forming a gradient multi-scale porous structure on the surface of the high-temperature alloy and increasing its specific surface area.

[0062] This invention forms a gradient multi-scale porous structure on the surface of a high-temperature alloy substrate coating through graded spraying and graded activation. This results in a high-temperature alloy substrate coating with higher bonding strength between the catalytic coating and the substrate, increased gradual porosity after activation, and a larger specific surface area. It solves the problems of low porosity, low stability, and low activation performance of mass-produced single alloy powder or mixed powder spraying, further improving the subsequent service stability of the high-temperature alloy substrate coating and effectively improving its hydrogen production catalytic efficiency.

[0063] This invention forms a gradient multi-scale porous structure on the surface of a high-temperature alloy through graded spraying and graded activation, resulting in a high-temperature alloy coating with higher bonding strength between the functional coating and the substrate, increased gradual porosity after activation, and larger specific surface area. This solves the problems of low porosity, low stability, and low surface performance of mass-produced single alloy powder or mixed powder spraying, further improving the subsequent service stability of the high-temperature alloy coating and effectively enhancing its surface performance.

[0064] More stable structure: This invention first sprays and then activates. After all functional coatings are sprayed, multi-stage activation treatment is carried out to ensure the bonding force of the spray interface, reduce damage to the pore-forming structure, and make the structure more stable. The surface performance after activation and pore-forming is also better.

[0065] Multi-stage spraying, through the design of gradually increasing alloy particle size in the high-temperature alloy functional coating from the inside out, enables the high-temperature alloy surface to form a gradient-like pore structure from the inside out after activation, resulting in a high-temperature alloy coating with a more stable structure, higher specific surface area, and better surface performance, which is beneficial to improving the service performance of high-temperature alloys under extreme working conditions.

[0066] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a hierarchical porous functional coating, characterized in that, Includes the following steps: S1. Preparation of multi-component alloy powder: NiAlMo or NiMoAl-based multi-component alloy powder was prepared and graded by sieving to obtain three alloy powders with different particle sizes: - Alloy powder A: Particle size < 10 μm; - Alloy powder B: Particle size 10–40 μm; - Alloy powder C: Particle size 40–70 μm. S2. Sandblasting: Sandblasting pretreatment is performed on the surface of the high-temperature alloy substrate to enhance surface roughness and activity. S3. Graded Spraying: Using plasma spraying equipment, alloy powder A, alloy powder B, and alloy powder C are sequentially sprayed onto the sandblasted substrate surface, wherein: - Alloy powder A is used as the base layer with a thickness of 5–15 μm; - Alloy powder B is the main layer, with a thickness of 30–50 μm; - Alloy powder C is the surface layer, with a thickness of 50–70 μm. S4. Graded activation pore formation: a) First activation: Use 3–10 wt% KOH or NaOH solution and treat at 30–50℃ for 60–80 min to form initial micropores through a gentle reaction; b) Second activation: Use 20–30 wt% KOH or NaOH solution and treat at 60–80℃ for 18–20 h to accelerate the dissolution of aluminum components, expand pores and optimize pore size distribution, and finally form a gradient porous structure.

2. The method for preparing a hierarchical porous functional coating according to claim 1, characterized in that: The alloy powders A, B, and C are NiAlMo or NiMoAl alloys.

3. The method for preparing a hierarchical porous functional coating according to claim 2, characterized in that: The alloy powders B and C also contain Al powder.

4. The method for preparing a hierarchical porous functional coating according to claim 3, characterized in that: The Al powder and alloy powders A, B, and C are all spherical powders.

5. The method for preparing a hierarchical porous functional coating according to claim 3, characterized in that: The particle size of Al powder in alloy powder B is 30–40 μm; The particle size of Al powder in alloy powder C is 50–60 μm.

6. The method for preparing a hierarchical porous functional coating according to claim 3, characterized in that: The composition of alloy powder A is: Ni 85%, Al 10%, Mo 5%; The composition of alloy powder B is: Ni 80.75–83.3%, Al 11.8–14.5%, Mo 4.75–4.9%; The composition of alloy powder C is: Ni 72.25–80.75%, Al 14.5–23.5%, Mo 4.25–4.75%.

7. The method for preparing a hierarchical porous functional coating according to claim 1, characterized in that: The thickness of the alloy powder A sprayed is 5–15 μm; Alloy powder B has a coating thickness of 30–50 μm; The thickness of alloy powder C spray coating is 50–70 μm.

8. The method for preparing a hierarchical porous functional coating according to claim 1, characterized in that: The conditions for the first activation are: temperature 30–50℃, time 60–80 min; The conditions for the second activation were: temperature 60–80℃, time 18–20h.

9. The method according to any one of claims 1–8, characterized in that: The plasma spraying parameters are: input power 65–96KW, argon powder feeding, pressure 0.35–0.65MPa, and powder feeding rate 1–18r / min.

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