Preparation method of NiCrAl-NiC composite coating

Abstract

The invention discloses a preparation method of a NiCrAl-NiC composite coating, which belongs to the technical field of preparation of NiCrAl-NiC coatings and comprises the steps of part inspection, preparation before spraying, determination of process parameters, cleaning, protection before sand blowing, sand blowing, spraying and cleaning. The coating raw material is prepared from NiCrAl and NiC mixed powder through a thermal spraying process, the content of NiCrAl is 10%-30%, and a staged spraying mode is adopted in the spraying process. When the first 1 / 2 thickness is sprayed, the oxygen flow is 19-25 L / min, the acetylene pressure flow is 13-18 L / min, the distance of a spray gun is 130-160 mm, the powder feeding rate is 35-44 g / min, spraying powder is fully melted, and a coating obtained after spraying has compactness and hardness; and when the second 1 / 2 thickness is sprayed, the oxygen flow is 24-28 L / min, the acetylene pressure flow is 18-22 L / min, the distance of the spray gun is 170-200 mm, and the powder feeding rate is 45-55 g / min, so that the sprayed powder is not completely melted, and a loose structure is obtained, and good abradability is obtained. The hardness of the coating can be controlled within the range of (45-65) HR15Y, the working temperature of the part is increased to 650 DEG C from 450 DEG C, and the bonding strength of the coating is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of NiCrAl-NiC coating preparation, and in particular relates to a method for preparing a NiCrAl-NiC composite coating based on a thermal spraying technology. Background Art

[0002] With the increasing development of aviation technology and the continuous improvement of sealing coating technology, abradable sealing coatings are increasingly being used on aircraft engine components. As a sealing coating, the NiC coating prepared using NiC composite powder generally has a service temperature of 200℃ to 400℃. With the rapid development of high-temperature technology, people's requirements for the high-temperature resistance of NiC coatings are getting higher and higher. Studies have shown that adding different NiCrAl contents to NiC can significantly improve the high-temperature resistance of NiC coatings (up to 650℃ or more), but the coating prepared using conventional thermal spraying technology has a low bonding strength, and the preparation process of coatings with high bonding strength is not mature. Summary of the invention

[0003] In view of the shortcomings of the prior art, the present invention provides a method for preparing a NiCrAl-NiC composite coating. The method is an improvement on the thermal spraying process of the NiC composite coating, and NiCrAl is added to NiC to prepare a NiCrAl-NiC (nickel-chromium-aluminum-nickel-graphite) composite coating, which can significantly improve the high temperature resistance of the NiC coating, and the service temperature can reach above 650°C, while having high bonding strength and abradability.

[0004] In order to obtain higher bonding strength without sacrificing its abradability, the present invention flame sprays NiCrAl-NiC composite coating on the high temperature resistant alloy substrate (GH4169) based on the original NiC flame spraying process to achieve the purpose of high temperature resistance; at the same time, the process method with different powder feeding rates is adopted in stages to make the coating close to the substrate side more dense and have higher bonding force; the coating away from the substrate side is looser, ensuring that it has better abradability. Finally, the performance of the parts after spraying is tested to ensure that it meets the acceptance requirements. The specific steps include: parts inspection → preparation before spraying → determination of process parameters → cleaning → protection before sand blasting → sand blasting → spraying → cleaning.

[0005] The NiCrAl-NiC composite coating of the present invention is prepared by thermal spraying mixed powder of nickel-chromium-aluminum (NiCrAl) and nickel-graphite (NiC), wherein the content of NiCrAl is 10% to 30%.

[0006] The specific spraying process includes: using a staged spraying method;

[0007] When spraying the first 1 / 2 thickness, the oxygen flow rate is 19-25L / min, the acetylene pressure flow rate is 13-18L / min, the spray gun distance is 130-160mm, and the powder feeding rate is 35-44g / min, so that the spraying powder is fully melted, and the coating obtained after spraying has higher density and hardness, that is, the coating bonding strength is improved; when spraying the second 1 / 2 thickness, the oxygen flow rate is 24-28L / min, the acetylene pressure flow rate is 18-22L / min, the spray gun distance is 170-200mm, and the powder feeding rate is 45-55g / min, so that the spraying powder is not completely melted, thereby obtaining a relatively loose structure to obtain better abradability.

[0008] After spraying, there is no obvious difference in appearance between NiC coating and NiCrAl-NiC composite coating with different NiCrAl contents, and the performance of NiCrAl-NiC composite coating specimens prepared by different powder feeding rates in stages meets the acceptance requirements of HB 20035, that is, tensile bonding strength ≥5MPa; surface Rockwell hardness is within the range of (45-65)HR15Y; under the conditions of temperature 650℃, water cooling, and cycle number not less than 30 times, the coating has no peeling and delamination phenomenon, and the peeling of the coating along the four sides of the specimen and within 2mm of the edge of the process hole is not counted (thermal shock performance); after 500h of heat preservation at 650℃, the surface Rockwell hardness of the coating is within the range of (45-70)HR15Y (thermal stability). In addition, the coating has good wear resistance.

[0009] Beneficial effects of the present invention:

[0010] The hardness of the coating after spraying can be controlled within the range of (45-65)HR15Y, and the working temperature of the parts is increased from 450°C to 650°C, and the bonding strength of the coating is improved (that is, the service life is extended).

[0011] The method of the present invention is used to spray parts, and the effect is as follows: Figure 1 As shown, (a) is the effect diagram of threaded parts after spraying. After spraying, not only the thread groove coating is guaranteed to have sufficient thickness, but also the thickness of the thread teeth can be guaranteed; (b) is a multi-stage flat part, and it can be seen that its coating thickness can be well guaranteed; (c) is a ring part, which has good turning performance; (d) after turning (abrasion resistance), its surface is smooth, and due to its good hardness and bonding performance, the edge of the coating can form a right-angle edge that meets the process.

[0012] The process of the present invention has been used on site and has been used for parts spraying for different manufacturers that need to spray NiC coatings. According to preliminary calculations, the annual acceptance task is 50 units, with a profit of 2,000 yuan per unit and an annual profit of 100,000 yuan. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1Effects of parts after spraying; (a) threaded parts, (b) multi-stage parts, (c) ring parts, (d) the state of ring parts after coating and machining;

[0014] Figure 2 The performance of the NiCrAl-NiC composite coating test piece in Example 1 was tested;

[0015] Figure 3 The NiC coating test piece in Example 1 tested performance;

[0016] Figure 4 The performance of the NiCrAl-NiC composite coating test piece in Example 2;

[0017] Figure 5 The performance of the NiCrAl-NiC composite coating test piece in Example 3 was tested. DETAILED DESCRIPTION

[0018] Example 1

[0019] A preparation method of a NiCrAl-NiC composite coating comprises the following specific steps: parts inspection→preparation before spraying→determining process parameters→cleaning→protection before sand blasting→sand blasting→spraying→cleaning.

[0020] The raw material for preparing the NiCrAl-NiC composite coating in this embodiment 1 is a mixture of 10% nickel-chromium-aluminum (NiCrAl) and 90% nickel-graphite (NiC) powder.

[0021] Thermal spraying process parameters:

[0022] When spraying the first 1 / 2 thickness, the oxygen flow rate is 19L / min, the acetylene pressure flow rate is 13L / min, the spray gun distance is 160mm, and the powder feeding rate is 44g / min, so that the spray powder is fully melted; when spraying the second 1 / 2 thickness, the oxygen flow rate is 24L / min, the acetylene pressure flow rate is 18L / min, the spray gun distance is 200mm, and the powder feeding rate is 55g / min, so that the spray powder is not completely melted. Ensure that the coating has good bonding strength and good abradability. The average bonding strength of the test piece is 16.5MPa, and the thermal shock resistance test is more than 60 times. Figure 2 shown.

[0023] When the NiC coating is sprayed by conventional spraying method, the average bonding strength of the test piece is 9.2MPa. When the thermal shock test exceeds 40 times, the coating peels off. Figure 3 shown.

[0024] Example 2

[0025] A preparation method of a NiCrAl-NiC composite coating comprises the following specific steps: parts inspection→preparation before spraying→determining process parameters→cleaning→protection before sand blasting→sand blasting→spraying→cleaning.

[0026] The raw material for preparing the NiCrAl-NiC composite coating in this embodiment 2 is a mixture of 20% nickel-chromium-aluminum (NiCrAl) and 80% nickel-graphite (NiC) powder.

[0027] Thermal spraying process parameters:

[0028] When spraying the first 1 / 2 thickness, the oxygen flow rate is 22L / min, the acetylene pressure flow rate is 16L / min, the spray gun distance is 150mm, and the powder feeding rate is 40g / min, so that the spray powder is fully melted; when spraying the second 1 / 2 thickness, the oxygen flow rate is 26L / min, the acetylene pressure flow rate is 20L / min, the spray gun distance is 180mm, and the powder feeding rate is 50g / min, so that the spray powder is not completely melted. Ensure that the coating has good bonding strength and good abradability. The test piece is used to detect its bonding strength of 22.7MPa, and the thermal shock resistance test is more than 60 times. Figure 4 shown.

[0029] When the NiC coating is sprayed by conventional spraying method, the bonding strength of the test piece is 9.2MPa. When the thermal shock test exceeds 40 times, the coating peels off. Figure 3 shown.

[0030] Example 3

[0031] A preparation method of a NiCrAl-NiC composite coating comprises the following specific steps: parts inspection→preparation before spraying→determining process parameters→cleaning→protection before sand blasting→sand blasting→spraying→cleaning.

[0032] The raw material for preparing the NiCrAl-NiC composite coating in this embodiment 3 is a mixture of 30% nickel-chromium-aluminum (NiCrAl) and 70% nickel-graphite (NiC) powder.

[0033] Thermal spraying process parameters:

[0034] When spraying the first 1 / 2 thickness, the oxygen flow rate is 23L / min, the acetylene pressure flow rate is 17L / min, the spray gun distance is 130mm, and the powder feeding rate is 35g / min, so that the spray powder is fully melted; when spraying the second 1 / 2 thickness, the oxygen flow rate is 28L / min, the acetylene pressure flow rate is 22L / min, the spray gun distance is 170mm, and the powder feeding rate is 45g / min, so that the spray powder is not completely melted. Ensure that the coating has good bonding strength and good abradability. The test piece is used to detect its bonding strength of 17.8MPa, and the thermal shock resistance test is more than 60 times. Figure 5shown.

[0035] When the NiC coating is sprayed by conventional spraying method, the bonding strength of the test piece is 9.2MPa. When the thermal shock test exceeds 40 times, the coating peels off. Figure 3 shown.

Claims

1. A method for preparing a NiCrAl-NiC composite coating, characterized in that: The process includes the following steps: parts inspection, preparation before spraying, determination of process parameters, cleaning, protection before sand blasting, sand blasting, spraying, and cleaning.

2. The method for preparing a NiCrAl-NiC composite coating according to claim 1, characterized in that: The NiCrAl-NiC composite coating is prepared from mixed powder of NiCrAl and NiC by thermal spraying process, wherein the content of NiCrAl is 10% to 30%.

3. The method for preparing a NiCrAl-NiC composite coating according to claim 2, characterized in that: The spraying process adopts a staged spraying method.

4. The method for preparing a NiCrAl-NiC composite coating according to claim 3, characterized in that: When spraying the first 1 / 2 thickness, the oxygen flow rate is 19-25L / min, the acetylene pressure flow rate is 13-18L / min, the spray gun distance is 130-160mm, and the powder feeding rate is 35-44g / min, so that the spraying powder can be fully melted and the coating obtained after spraying has density and hardness.

5. The method for preparing a NiCrAl-NiC composite coating according to claim 3, characterized in that: When spraying the second 1 / 2 thickness, the oxygen flow rate is 24-28L / min, the acetylene pressure flow rate is 18-22L / min, the spray gun distance is 170-200mm, and the powder feeding rate is 45-55g / min, so that the spraying powder is not completely melted, thereby obtaining a loose structure to obtain good abradability.

6. The method for preparing a NiCrAl-NiC composite coating according to claim 3, characterized in that: The performance of the prepared NiCrAl-NiC composite coating specimens meets the acceptance requirements of HB 20035, with a tensile bonding strength of ≥5MPa; the surface Rockwell hardness is within the range of (45-65)HR15Y; under the conditions of a temperature of 650°C, water cooling, and a cycle number of not less than 30 times, the coating has no peeling or delamination phenomenon, and the peeling of the coating along the periphery of the specimen and within 2mm of the edge of the process hole is not counted; After being kept at 650℃ for 500h, the Rockwell hardness of the coating surface is in the range of (45~70)HR15Y.

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