Flame tube heat-resistant coating with gas film holes and preparation method of flame tube heat-resistant coating

Abstract

The invention belongs to the technical field of aero-engine hot end part protective coatings, and particularly relates to a flame tube heat-resistant coating with gas film holes and a preparation method of the flame tube heat-resistant coating. The coating is composed of an oxide mixture bonding bottom layer, a diffusion barrier middle layer and a high-reflectivity surface layer, the total thickness of the coating is smaller than or equal to 30 microns, and the coating is prepared by combining an air spraying process with an atmospheric sintering method and has the advantages that construction is convenient, the thickness does not affect the aperture size of an air film hole, and the heat insulation effect is good.

Description

Technical Field

[0001] The invention belongs to the technical field of protective coatings for hot end components of aviation engines, and in particular relates to a heat-resistant coating for a flame tube with air film holes and a preparation method thereof. Background Art

[0002] As one of the important components of the main combustion chamber of an aircraft engine, the flame tube is an important place for organizing the mixing of fuel and air and burning. It is subjected to high-speed erosion of high-temperature and high-pressure gas, high-temperature radiation and high thermal stress during service, and is one of the parts of the engine that bears the highest thermal load. In order to improve the heat resistance of the flame tube, on the one hand, the base material of the part adopts a high-temperature alloy material with higher temperature bearing capacity; on the other hand, a large number of holes with a small diameter (about 0.7-0.8mm) with a complex inclination angle are punched on the wall of the flame tube to form a continuous "air film blanket". The cold side airflow boundary layer is sucked through the small hole intake to enhance the heat exchange on the cold side, the densely distributed multi-inclined holes increase the heat exchange area, and the air film protection is formed on the hot side after the cold air flows out, etc., to achieve the purpose of efficient cooling.

[0003] In order to further improve the temperature bearing capacity of the flame tube, a thermal barrier coating is further coated on its surface. The thickness of this type of coating is generally 0.25 mm to 0.35 mm. The low thermal conductivity of the thermal barrier coating blocks the heat transfer from the high-temperature gas to the high-temperature alloy substrate, thereby reducing the temperature of the high-temperature alloy substrate. As we all know, there are three ways of heat transfer: heat conduction, convection and heat radiation. The low emissivity ceramic layer of the current thermal barrier coating is mainly 7~8w.t% Y 2 O 3 Partially stabilized ZrO 2 (YSZ), the infrared transmittance in the wavelength range of 1-5μm is 70%, that is, the thermal barrier coating is transparent or translucent in the high temperature environment of the engine, and part of the heat is transferred to the metal substrate through the phonon heat transfer of the ceramic material, while the other part is directly transferred to the metal substrate through the coating as infrared radiation. The coupling effect of high-temperature radiation and conduction changes the thermal conductivity mechanism of the low thermal conductivity ceramic coating, greatly reducing the thermal insulation performance of the coating, so that it cannot block the heating effect of thermal radiation on the substrate, resulting in its limited thermal insulation capacity. In addition, due to the thick thickness of the thermal barrier coating (0.25 mm ~ 0.35 mm), the aperture of the air film hole is inevitably reduced and the air flow direction is changed during the coating process, which significantly affects the air film cooling effect. Even if the method of coating the coating first and then punching is used to solve the problem of air film hole blocking, it is easy to cause the coating interface separation, peeling failure, poor repairability of parts and other consequences, affecting the long life and high reliability service of the parts.

[0004] In summary, it can be seen that the surface of the flame tube with air film holes needs to be coated with a heat-resistant coating, but the existing thermal barrier coatings have limited thermal insulation capacity and affect the air film cooling effect of parts during the coating process, and cannot meet the needs of engineering applications. There is an urgent need to apply a thin coating with good thermal insulation properties and a preparation method that is easy to construct. Summary of the invention

[0005] In response to the problems in the prior art, the present invention provides a heat-resistant coating for a flame tube with air film holes and a preparation method thereof. The coating is prepared by an air spraying process combined with an atmospheric sintering method, and has the characteristics of convenient construction, thickness that does not affect the aperture size of the air film holes, and good thermal insulation effect.

[0006] The technical solution of the present invention is: A heat-resistant coating for a flame tube with air film holes, the coating consisting of an oxide mixture bonding bottom layer, a diffusion barrier middle layer and a high reflectivity surface layer, with a total coating thickness of ≤30 μm; the oxide mixture bonding bottom layer takes into account the thermal matching principle with a high-temperature alloy substrate, high-temperature oxidation resistance and high-temperature flow film-forming performance, the diffusion barrier middle layer effectively prevents the mutual diffusion between the high-reflectivity surface layer and the high-temperature alloy substrate, and the high-reflectivity surface layer reduces the heating of the flame tube by high-temperature and high-speed fuel gas radiation.

[0007] Furthermore, in the above-mentioned heat-resistant coating of the flame tube with air film holes, the composition of the oxide mixture bonding bottom layer is SiO 2 -15~20 wt%(Al 2 O 3 +B 2 O 3 )- 3~6 wt%(K 2 O+Na 2 O)-10~15 wt% (CaO+SrO)-8~15w.t.% (Cr 2 O 3 +ZrO 2 ), and this component is recorded as A.

[0008] Among them, SrO acts as a solvent component in the oxide to ensure high density and chemical bonding between the interface between the bonding layer and the alloy matrix; SiO 2 As a network forming agent component, its content exceeds 50%, ensuring high thermal stability and anti-oxidation performance of the bonding layer; K 2 O+Na 2 O is used as a monovalent solvent component to match the divalent solvent oxides CaO+SrO to regulate the fluidity of the oxide mixture, ensure the sintering density of the bonding layer, and form a mutually interlocking interface transition structure with the diffusion barrier layer to enhance the interface bonding strength.

[0009] Furthermore, the above-mentioned heat-resistant coating of the flame tube with air film holes, the diffusion barrier intermediate layer is composed of Al 2 O 3 Cr 2 O 3 The co-strengthening oxide mixture is composed of A-10~15 wt% Al 2 O 3 -2~5 wt% Cr 2 O 3 , and this component is recorded as B.

[0010] Furthermore, in the above-mentioned heat-resistant coating of the flame tube with air film holes, the composition of the high reflectivity surface layer is Pt-55~85w.t.%Ag+10 wt%A, and this composition is recorded as C.

[0011] The above-mentioned method for preparing a heat-resistant coating of a flame tube with air film holes comprises the following steps: Step (1), protecting the non-coated area of ​​the part; Step (2), dry sandblasting the area of ​​the part to be sprayed with coating using 36-80 mesh white corundum sand; Step (3), prepare powder A, whose composition is SiO 2 -15~20 wt%(Al 2 O 3 +B 2 O 3 )- 3~6 wt%(K 2 O+Na 2 O)-10~15 wt% (CaO+SrO)-8~15 wt% (Cr 2 O 3 +ZrO 2 ); prepare B powder, whose composition is A-10~15w.t.% Al 2 O 3 -2~5 wt% Cr 2 O 3 , prepare C powder, whose composition is Pt-55~85w.t.%Ag+10 wt%A; Step (4), according to the configuration of 1g A powder in 20ml alcohol, 1g B powder in 20ml alcohol, and 1g C powder in 30ml alcohol, mix A, B, and C powders into alcohol, and place them in an ultrasonic cleaner for shaking and stirring until there is no powder or precipitation, to obtain mixed solution A, mixed solution B, and mixed solution C for use; Step (5), according to the configuration of 0.5-0.55 ml of mixed solution A per cm2 of part surface, 0.25-0.3 ml of mixed solution B per cm2 of part surface, and 2 ml-3 ml of mixed solution C per cm2 of part surface, the oxide mixture bonding bottom layer, the diffusion barrier middle layer and the high reflectivity surface layer are sprayed on the part surface in sequence by compressed air spraying, the spraying pressure is 0.1-0.2 MPa, the spraying distance is 100-200 mm, and the spray gun is perpendicular to the surface to be sprayed during the spraying process; Step (6), after each layer is sprayed, it is dried and cured at room temperature for 1-2 hours, then placed in a vacuum furnace for sintering, and removed from the furnace after cooling; Step (7), use 800# diamond sandpaper to polish the coating to reveal its silvery white metallic luster, with a surface roughness of ≤3µm. Monitor the coating thickness during the polishing process to prevent over-polishing of the coating. Finally, the heat-resistant coating thickness is 25~30µm. Then wipe the sample surface with alcohol to clean the surface of the part.

[0012] Furthermore, in the above-mentioned method for preparing a heat-resistant coating of a flame tube with air film holes, the specific conditions of the sand blasting treatment in step (2) are: wind pressure of 0.2-0.4 MPa, sand blasting distance of 120-150 mm, and sand blasting angle of 60°-75°.

[0013] Furthermore, in the above-mentioned method for preparing a heat-resistant coating of a flame tube with air film holes, the particle sizes of the A, B, and C powders are all less than 10 μm.

[0014] Furthermore, in the above-mentioned method for preparing a heat-resistant coating of a flame tube with air film holes, the sintering system of step (6) is: when the vacuum degree of the heat treatment furnace is ≤0.013Pa, start heating, heat to 800℃ at (15±5)℃ / min, keep warm for (2~5)min, reduce the partial pressure to (100±20)Pa, then heat to 950℃~1050℃ at (15±5)℃ / min and keep warm for 20min~30min, then fill with argon and cool to (650±28)℃ within 6min, and then cool to below 80℃ before taking out of the furnace.

[0015] Advantages and beneficial effects of the present invention: 1. The total thickness of the coating of the present invention is 25-30µm, and the size of the air film holes of the parts will not be affected after spraying; 2. The coating of the present invention has the characteristic of high reflectivity and can significantly reduce the surface temperature of parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a cross-sectional morphology diagram of the coating of the present invention; Figure 2 The figure is a diagram showing the change in the pore size of the air film before and after coating the coating of the present invention. DETAILED DESCRIPTION

[0017] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention but cannot be used to limit the scope of the present invention. Example 1

[0018] This embodiment is a heat-resistant coating of a flame tube with air film holes, such as Figure 1 As shown, it is composed of an oxide mixture bonding bottom layer, a diffusion barrier middle layer and a high reflectivity surface layer, the coating thickness is 25 μm, the coating interface is well bonded, and the preparation method thereof includes the following steps: Step 1: Protect the non-coating area of ​​the parts; Step 2: Use 80 mesh white corundum sand to perform dry sandblasting on the coating area of ​​the parts, with an air pressure of 0.3 MPa, a sandblasting distance of 150 mm, and a sandblasting angle of 60°; Step 3: Prepare A powder, SiO 2 、Al 2 O 3 , B 2 O 3 , K 2 O、Na 2 O, CaO, SrO, Cr 2 O 3 、ZrO 2 The weight ratio is 51:10:5:3:3:5:10:6:7; Prepare B powder, mix A powder, Al 2 O 3 Cr 2 O 3 Configured in a weight ratio of 80:15:5; Prepare C powder, Pt powder, Ag powder and A powder in a weight ratio of 35:55:10; The diameter of the above powders is 5 μm.

[0019] Step 4: Mix the powder prepared in step 3 with alcohol, according to the configuration of 1g A powder in 20ml alcohol, 1g B powder in 20ml alcohol, and 1g C powder in 30ml alcohol, and place in an ultrasonic cleaner for vibration and stirring until there is no powder and no precipitation, to obtain mixed solution A, mixed solution B, and mixed solution C for standby use; Step 5. Prepare three spray guns, clean and dry the spray guns before each processing, and increase the air pressure of the spray guns to 0.2MPa; Step 6: Pour the mixed solution A into the spray gun and spray 0.5 ml of the mixed solution per cm² of the sample surface. At this time, the alloy matrix is ​​covered with powder and is invisible to the naked eye. The spraying distance is 100 mm, and the spray gun is perpendicular to the surface to be sprayed during the spraying process. Step 7, pour the mixed solution B into the second spray gun, and spray it at 0.25 ml of the mixed solution per cm² of the sample surface. At this time, the mixed oxide powder has been covered by the mixed powder, and the green mixed oxide powder is no longer visible to the naked eye; the spraying distance is 100 mm, and the spray gun is perpendicular to the surface to be sprayed during the spraying process; Step 8. Pour the mixed liquid C into the last spray gun and spray 3 ml of the mixed liquid per cm² of the sample surface. At this time, the mixed powder is completely covered by the alloy and the surface is dark gray-black. The spraying distance is 200 mm, and the spray gun is perpendicular to the surface to be sprayed during the spraying process. Step 9, the sprayed workpiece is dried in air at room temperature for 2 hours; Step 10, placing the workpiece in a vacuum sintering furnace, starting to heat up when the vacuum degree of the heat treatment furnace is 0.009Pa, heating to 800℃ at 10℃ / min, keeping warm for 5min, reducing the partial pressure to 100Pa, then heating to 1050℃ at 10℃ / min, sintering at a constant temperature for 20min, then cooling to 650℃ within 6min after filling with argon, cooling to 80℃ with the furnace, and then cooling to room temperature in the air; Step 11: Use 800# sandpaper to polish the workpiece surface until the silver-white metallic luster is completely exposed, and the final coating thickness is 25µm; Step 12: Use diamond grinding paste with Ra=1.5μm on the wool felt to polish the surface of the workpiece until there are no obvious scratches. The average surface roughness of the sample is Ra1.6μm.

[0020] The changes in the pore size of the air film before and after coating are as follows: Figure 2 As shown, it can be observed from the figure that the coating does not affect the pore size of the air film.

Claims

1. A heat-resistant coating for a flame tube with air film holes, characterized in that: The coating is composed of an oxide mixture bonding bottom layer, a diffusion barrier middle layer and a high reflectivity surface layer, and the total thickness of the coating is ≤30 μm; The oxide mixture bonding bottom layer composition takes into account the thermal matching principle with the high-temperature alloy substrate, high-temperature oxidation resistance and high-temperature flow film-forming performance. The diffusion barrier intermediate layer effectively prevents the mutual diffusion between the high-reflectivity surface layer and the high-temperature alloy substrate. The high-reflectivity surface layer reduces the heating of the flame tube by high-temperature and high-speed fuel gas radiation.

2. The heat-resistant coating of the flame tube with air film holes according to claim 1 is characterized in that: The composition of the oxide mixture bonding bottom layer is SiO2-15~20 wt% (Al2O3+B2O3)- 3~6 wt% (K2O+Na2O)-10~15 wt% (CaO+SrO)-8~15 wt% (Cr2O3+ZrO2), which is recorded as A.

3. The heat-resistant coating of the flame tube with air film holes according to claim 2 is characterized in that: Ensure that the SiO2 content exceeds 50%.

4. The heat-resistant coating of the flame tube with air film holes according to claim 2 is characterized in that: The diffusion barrier intermediate layer is composed of an oxide mixture co-strengthened by Al2O3 and Cr2O3, and its composition is A-10~15 wt% Al2O3 -2~5 wt%Cr2O3, and this composition is recorded as B.

5. The heat-resistant coating of the flame tube with air film holes according to claim 2 is characterized in that: The composition of the high reflectivity surface layer is Pt-55~85w.t.%Ag+10 wt%A, which is recorded as C.

6. The method for preparing a heat-resistant coating of a flame tube with air film holes according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step (1), protecting the non-coated area of ​​the part; Step (2) dry sandblasting the area of ​​the part to be sprayed with coating using 36-80 mesh white corundum sand, with an air pressure of 0.2-0.4 MPa, a sandblasting distance of 120-150 mm, and a sandblasting angle of 60°-75°; Step (3), prepare powder A, whose composition is SiO2-15~20 wt% (Al2O3+B2O3)- 3~6 wt% (K2O+Na2O)-10~15 wt% (CaO+SrO)-8~15 wt% (Cr2O3+ZrO2); prepare powder B, whose composition is A-10~15 wt%Al2O3 -2~5 wt% Cr2O3, prepare powder C, whose composition is Pt-55~85w.t.%Ag+10 wt%A; Step (4), according to the configuration of 1g A powder in 20ml alcohol, 1g B powder in 20ml alcohol, and 1g C powder in 30ml alcohol, mix A, B, and C powders into alcohol, and place them in an ultrasonic cleaner for shaking and stirring until there is no powder or precipitation, to obtain mixed solution A, mixed solution B, and mixed solution C for use; Step (5), according to the configuration of 0.5-0.55 ml of mixed liquid A per cm2 of part surface, 0.25-0.3 ml of mixed liquid B per cm2 of part surface, and 2 ml-3 ml of mixed liquid C per cm2 of part surface, the oxide mixture bonding bottom layer, the diffusion barrier middle layer and the high reflectivity surface layer are sprayed on the part surface in sequence by compressed air spraying, the spraying pressure is 0.1-0.2 MPa, the spraying distance is 100-200 mm, and the spray gun is perpendicular to the surface to be sprayed during the spraying process; Step (6), after each layer is sprayed, it is dried and cured at room temperature for 1-2 hours, then placed in a vacuum furnace for sintering, and removed from the furnace after cooling; Step (7), use 800# diamond sandpaper to polish the coating to reveal its silvery white metallic luster, with a surface roughness of ≤3µm. Monitor the coating thickness during the polishing process to prevent over-polishing of the coating. The final coating thickness is 25~30µm. Then wipe the sample surface with alcohol to clean the surface of the part.

7. The method for preparing a heat-resistant coating of a flame tube with air film holes according to claim 6, characterized in that: The specific conditions of the sand blasting treatment in step (2) are: wind pressure of 0.2-0.4 MPa, sand blasting distance of 120-150 mm, and sand blasting angle of 60°-75°.

8. The method for preparing a heat-resistant coating of a flame tube with air film holes according to claim 7, characterized in that: The particle sizes of A, B and C powders are all less than 10 μm.

9. The method for preparing a heat-resistant coating of a flame tube with air film holes according to claim 8, characterized in that: The sintering system of step (6) is as follows: when the vacuum degree of the heat treatment furnace is ≤0.013Pa, the temperature is increased to 800°C at a rate of (15±5)°C / min, kept at this temperature for (2~5)min, the partial pressure is reduced to (100±20)Pa, and then the temperature is increased to 950°C~1050°C at a rate of (15±5)°C / min, kept at this temperature for 20min~30min, and then cooled to (650±28)°C within 6min after being filled with argon gas, and then cooled to below 80°C before being taken out of the furnace.

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