Ceramic surface layer chemical removal method without damaging metal bonding layer of thermal barrier coating

Abstract

The invention discloses a ceramic surface layer chemical removal method without damaging a metal bonding layer of a thermal barrier coating, and relates to the field of preparation and maintenance of thermal barrier coatings of engine turbine blades. The method comprises the following steps that S100, a ceramic surface layer removing agent is stored in a crucible in a heat preservation mode; s200, putting the sample into a crucible, and carrying out first cleaning; s300, putting the sample subjected to the first cleaning into an acid solution, and carrying out second cleaning; s400, the test subjected to second cleaning is subjected to water sand blowing cleaning, and drying is conducted after cleaning is completed; the ceramic surface layer remover is composed of potassium hydroxide, sodium carbonate and sodium nitrite; the acid liquor is composed of nitric acid and phosphoric acid; the purposes that a ceramic surface layer of the thermal barrier coating is removed, and a blade base body and a metal bonding layer are not damaged are achieved.

Description

Technical Field

[0001] The invention relates to the field of preparation and maintenance of thermal barrier coatings for engine turbine blades, in particular to a method for chemically removing a ceramic surface layer without damaging a metal bonding layer of the thermal barrier coating. Background Art

[0002] In the aviation industry, in order to ensure the stable operation of aircraft engine blades, thermal barrier coatings (TBC) for anti-oxidation, anti-corrosion, and heat insulation are required on their surfaces. The thermal barrier coatings commonly used on domestic and foreign aircraft engines are usually composed of a ceramic surface layer and a metal bonding layer. Among them, the ceramic surface layer generally has a low thermal conductivity, and common ones include aluminum oxide, hafnium oxide, zirconium oxide, yttrium oxide, etc. The most commonly used on active aircraft engines is yttrium oxide (7~8wt%) partially stabilized zirconium oxide (abbreviated as YSZ), which mainly plays the role of reducing the substrate temperature, preventing foreign body impact, and providing thermal corrosion resistance. The metal bonding layer is usually MCrAlY multi-metal solid solution, where M includes metals such as Ni, Co or NiCo. Its function is first to provide adhesion to the ceramic layer, and at the same time, it can also provide oxidation resistance and thermal corrosion resistance to the substrate.

[0003] On the one hand, during the operation of aircraft engines, the ceramic surface layer of thermal barrier coatings will peel off, delaminate, and fall off due to harsh working environments such as high temperature. During the overhaul of the engine, when there are no blade cracks or damage to the metal bonding layer, compared with the traditional repair of removing all thermal barrier coatings and then applying a new thermal barrier coating, only the ceramic surface layer of the thermal barrier coating can be repaired, and the surface layer can be applied after the ceramic surface layer is removed. On the other hand, the newly prepared thermal barrier coating on the surface of the blade needs to be reworked for secondary coating due to surface blistering and unqualified coating. When reworking and re-coating the thermal barrier coating, only the ceramic surface layer can be coated as appropriate. In the above two aspects of thermal barrier coating repair, only the ceramic surface layer repair has the advantage of saving time and money costs. At this time, it is necessary to ensure that the ceramic surface layer of the thermal barrier coating can be removed without damaging the metal bonding layer. The pre-treatment process of only removing the ceramic surface layer without affecting the metal bonding layer will directly affect the quality of the newly coated ceramic surface layer. Unqualified quality will directly affect the use of the blade. Therefore, exploring the ceramic surface layer removal process that does not damage the metal bonding layer can provide important technical guarantees for the repair of thermal barrier coatings. Summary of the invention

[0004] The object of the present invention is to provide a method for chemically removing a ceramic surface layer without damaging a metal bonding layer of a thermal barrier coating, so as to achieve the purpose of removing the ceramic surface layer of the thermal barrier coating without damaging a blade substrate and a metal bonding layer.

[0005] In order to achieve the above object, the present invention adopts the following technical means: A method for chemically removing a ceramic surface layer without damaging a metal bonding layer of a thermal barrier coating comprises the following steps: S100. The ceramic surface layer remover is stored in a crucible in a heat preservation state; S200. Place the sample in a crucible and perform a first cleaning; S300. Place the sample after the first cleaning into an acid solution for a second cleaning; S400. The second cleaning test is completed by water sandblasting cleaning, and then drying; The ceramic surface layer remover is composed of potassium hydroxide, sodium carbonate and sodium nitrite; The acid solution consists of nitric acid and phosphoric acid.

[0006] Preferably, in parts by weight, the potassium hydroxide is 400-600 parts, the sodium nitrite is 10-20 parts, and the sodium carbonate is 3-7 parts; the sodium nitrite and the sodium carbonate serve as corrosion inhibitors, and the potassium hydroxide is a solid base.

[0007] Furthermore, the step S100 includes: S110. Adding potassium hydroxide, sodium carbonate and sodium nitrite to a nickel-based crucible; S120. Place the nickel-based crucible with the material at 380-420°C and keep it warm for 1-3 hours.

[0008] Furthermore, the step S200 includes: S210. Place the sample in a nickel-based crucible and react for 50 to 70 minutes; S220. Take out the reacted sample and put it into a cold water tank for water quenching for 10 to 30 minutes; S230. Place the water-quenched material in an ultrasonic cleaning chamber for 20 to 60 minutes.

[0009] Furthermore, the step S230 includes: S231. First, the water-quenched material is placed in cold water for ultrasonic cleaning for 10 to 30 minutes; S232. Then place the material in hot water for ultrasonic cleaning for 10 to 30 minutes at a temperature of 60 to 80°C.

[0010] Furthermore, the step S300 includes: S310. The object after the first cleaning is placed in an acid solution for reaction for 1 to 3 hours; S320. Then place the object in a clean water tank for ultrasonic cleaning at room temperature for 10 to 30 minutes.

[0011] Furthermore, the acid solution is composed of 10-20wt% nitric acid and 60-80wt% phosphoric acid in a volume ratio of 1:0.5-2.

[0012] Furthermore, in step S400, the sand blowing pressure is 0.2-0.3 MPa, and the time is 10-20 seconds; the drying temperature is 190-10° C., and the time is 1-2 hours.

[0013] The present invention has the following beneficial effects during application: The process method of the invention can remove the ceramic surface layer without damaging the metal matrix and the bonding layer.

[0014] The process method of the invention is simple, the equipment is low-cost, and can be applied industrially.

[0015] The process method of the present invention can improve the preparation and repair efficiency of blade coatings and save costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the actual picture before removing the ceramic surface layer of the sample.

[0017] Figure 2 Metallographic image before removing the ceramic surface layer of the sample Figure 3 This is the actual picture after removing the ceramic surface layer of the sample.

[0018] Figure 4 This is the metallographic image after removing the ceramic surface layer of the sample. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0020] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0022] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0023] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use, or the positions or positional relationships commonly understood by those skilled in the art, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0024] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] A method for chemically removing a ceramic surface layer without damaging a metal bonding layer of a thermal barrier coating comprises the following steps: S100. The ceramic surface layer remover is stored in a crucible in an insulated state; Specifically, it includes S110. adding 400-600 parts of potassium hydroxide, 10-20 parts of sodium nitrite, and 3-7 parts of sodium carbonate in parts by weight into a nickel-based crucible; wherein the sodium nitrite and the sodium carbonate serve as corrosion inhibitors, and the potassium hydroxide is a solid base.

[0026] S120. Place the nickel-based crucible with the material at 380-420°C and keep it warm for 1-3 hours.

[0027] Then, S200. placing the sample into a crucible and performing a first cleaning; Wherein, step S200 includes: S210. Place the sample in a nickel-based crucible and react for 50 to 70 minutes; S220. Take out the reacted sample and put it into a cold water tank for water quenching for 10 to 30 minutes; S230. Place the water-quenched material in an ultrasonic cleaning chamber for 20 to 60 minutes.

[0028] Step S230 includes: S231. First, the water-quenched material is placed in cold water for ultrasonic cleaning for 10 to 30 minutes; S232. Then place the material in hot water for ultrasonic cleaning for 10 to 30 minutes at a temperature of 60 to 80°C.

[0029] Next, S300. placing the sample that has completed the first cleaning into an acid solution for a second cleaning; Wherein, step S300 includes: S310. The object after the first cleaning is placed in an acid solution for reaction for 1 to 3 hours; S320. Then place the object in a clean water tank for ultrasonic cleaning at room temperature for 10 to 30 minutes.

[0030] Furthermore, the acid solution is composed of 10-20wt% nitric acid and 60-80wt% phosphoric acid in a volume ratio of 1:0.5-2.

[0031] Finally, S400. The test that has completed the second cleaning is subjected to water sandblasting cleaning and then dried after completion; In S400, the sand blowing pressure is 0.2~0.3MPa, the time is 10~20s; the drying temperature is 190~10℃, the time is 1~2h.

[0032] The following is a detailed explanation in conjunction with specific practical operations.

[0033] Example 1 a. A nickel-based crucible containing 500 g of potassium hydroxide, 15 g of sodium nitrite and 5 g of sodium carbonate was placed in an oven; b. Place the nickel-based crucible containing the solid base and the corrosion inhibitor in an oven and heat at 400°C for 2h; c. After heating at 400°C for 2h, the sample with a ceramic layer on the surface was placed in a nickel-based crucible filled with molten alkali and reacted for 50min; d. After the reaction is completed, the sample is immediately taken out of the crucible and placed in a cold water tank for quenching for 20 minutes to peel off the remaining ceramic layer on the sample; e. The sample after water quenching cleaning was further subjected to cold water ultrasonic cleaning for 20 minutes to remove the reactants in the inner cavity and on the surface; f. The sample after cold water ultrasonic cleaning was further ultrasonically cleaned in 70℃ hot water for 20 minutes to remove the reactants in the cavity and on the surface g. Place the ultrasonically cleaned sample in a prepared acid (15wt.% nitric acid and 70wt.% phosphoric acid in a 1:1 volume ratio) for 2h to remove the residual alkali after the reaction; h. Place the pickled sample in a clean water tank and perform ultrasonic cleaning at room temperature for 20 minutes; i. Place the cleaned sample in an air heating furnace at 200°C for 2 hours for drying under a sand blowing pressure of 0.25 MPa and a sand blowing time of 15 seconds.

[0034] Figure 1 This is the actual picture of the sample without removing the ceramic surface layer. Figure 2 This is the metallographic image of the sample when the ceramic surface layer is not removed. Figure 3 This is a real picture of the sample after the ceramic layer is removed in this embodiment. Figure 3 It can be seen that the ceramic layer is completely removed without any ceramic layer residue. After removing the ceramic layer, the surface of the sample has a uniform color, and there are no defects such as metal layer peeling, peeling, and bubbling.

[0035] In order to verify the thinning of the metal bonding layer after the ceramic layer is removed, the sample after this implementation scheme is dissected to detect the coating thickness, such as Figure 4 The microstructure of the metal layer after the ceramic layer is removed is shown in Figure 2 The microstructure of the thermal barrier coating before the ceramic layer was removed was compared, and no cracking of the metal layer occurred. At the same time, the thickness of the metal layer was tested before and after the ceramic layer was removed. It can be seen that the thickness of the metal bonding layer did not change between the part where the ceramic layer was removed and the part where the ceramic layer existed, and the metal bonding layer was well preserved.

[0036] Example 2 a. A nickel-based crucible containing 550 g of potassium hydroxide, 16.5 g of sodium nitrite and 5.5 g of sodium carbonate was placed in an oven; b. Place the nickel-based crucible containing the solid base and the corrosion inhibitor in an oven and heat at 420°C for 2h; c. After heating at 420°C for 2 hours, the sample with a ceramic layer on the surface was placed in a nickel-based crucible filled with molten alkali and reacted for 40 minutes; d. After the reaction is completed, the sample is immediately taken out of the crucible and placed in a cold water tank for quenching for 20 minutes to peel off the remaining ceramic layer on the sample; e. The sample after water quenching cleaning was further subjected to cold water ultrasonic cleaning for 20 minutes to remove the reactants in the inner cavity and on the surface; f. The sample after cold water ultrasonic cleaning was further ultrasonically cleaned in 70°C hot water for 20 min to remove the reactants in the inner cavity and on the surface; g. Place the ultrasonically cleaned sample in a prepared acid (15wt.% nitric acid and 70wt.% phosphoric acid in a 1:1 volume ratio) for 2h to remove the residual alkali after the reaction; h. Place the pickled sample in a clean water tank and perform ultrasonic cleaning at room temperature for 20 minutes; i. Place the cleaned sample in an air heating furnace at 200°C for 2 hours for drying under a sand blowing pressure of 0.25 MPa and a sand blowing time of 15 seconds.

[0037] Example 3 a. A nickel-based crucible containing 600g potassium hydroxide, 20g sodium nitrite and 7g sodium carbonate was placed in an oven; b. Place the nickel-based crucible containing the solid base and the corrosion inhibitor in an oven and heat at 420°C for 3h; c. After heating at 420°C for 3 hours, the sample with a ceramic layer on the surface was placed in a nickel-based crucible filled with molten alkali and reacted for 50 minutes; d. After the reaction is completed, the sample is immediately taken out of the crucible and placed in a cold water tank for quenching for 30 minutes to peel off the remaining ceramic layer on the sample; e. The sample after water quenching cleaning was further subjected to cold water ultrasonic cleaning for 30 minutes to remove the reactants in the inner cavity and on the surface; f. The sample after cold water ultrasonic cleaning was further ultrasonically cleaned in 80°C hot water for 30 min to remove the reactants in the inner cavity and on the surface; g. Place the ultrasonically cleaned sample in a prepared acid (20wt.% nitric acid and 80wt.% phosphoric acid in a volume ratio of 1:2) for 3h to remove the residual alkali after the reaction; h. Place the pickled sample in a clean water tank and perform ultrasonic cleaning at room temperature for 30 minutes; i. Place the cleaned sample in an air heating furnace at 210°C and heat for 2 hours to dry it at a sand blowing pressure of 0.3MPa and a sand blowing time of 20s.

[0038] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for chemically removing a ceramic surface layer without damaging a metal bonding layer of a thermal barrier coating, characterized in that: The following steps are involved: S100. The ceramic surface layer remover is stored in a crucible in an insulated state; S200. Place the sample in a crucible and perform a first cleaning; S300. Place the sample after the first cleaning into an acid solution for a second cleaning; S400. The second cleaning test is completed by water sandblasting cleaning and drying after completion; The ceramic surface layer remover is composed of potassium hydroxide, sodium carbonate and sodium nitrite; The acid solution consists of nitric acid and phosphoric acid.

2. The method for chemically removing the ceramic surface layer without damaging the metal bonding layer of the thermal barrier coating according to claim 1, characterized in that: In parts by weight, the potassium hydroxide comprises 400 to 600 parts, the sodium nitrite comprises 10 to 20 parts, and the sodium carbonate comprises 3 to 7 parts; the sodium nitrite and the sodium carbonate serve as corrosion inhibitors, and the potassium hydroxide is a solid base.

3. The method for chemically removing the ceramic surface layer without damaging the metal bonding layer of the thermal barrier coating according to claim 1, characterized in that: The step S100 includes: S110. Adding potassium hydroxide, sodium carbonate and sodium nitrite to a nickel-based crucible; S120. Place the nickel-based crucible with the material at 380-420°C and keep it warm for 1-3 hours.

4. The method for chemically removing the ceramic surface layer without damaging the metal bonding layer of the thermal barrier coating according to claim 1, characterized in that: The step S200 includes: S210. Place the sample in a nickel-based crucible and react for 50 to 70 minutes; S220. Take out the reacted sample and put it into a cold water tank for water quenching for 10 to 30 minutes; S230. Place the water-quenched material in an ultrasonic cleaning chamber for 20 to 60 minutes.

5. The method for chemically removing the ceramic surface layer without damaging the metal bonding layer of the thermal barrier coating according to claim 4, characterized in that: The step S230 includes: S231. First, the water-quenched material is placed in cold water for ultrasonic cleaning for 10 to 30 minutes; S232. Then place the material in hot water for ultrasonic cleaning for 10 to 30 minutes at a temperature of 60 to 80°C.

6. The method for chemically removing the ceramic surface layer without damaging the metal bonding layer of the thermal barrier coating according to claim 1, characterized in that: The step S300 includes: S310. The object after the first cleaning is placed in an acid solution for reaction for 1 to 3 hours; S320. Then place the object in a clean water tank for ultrasonic cleaning at room temperature for 10 to 30 minutes.

7. The method for chemically removing the ceramic surface layer without damaging the metal bonding layer of the thermal barrier coating according to claim 1 or 6, characterized in that: The acid solution is composed of 10-20wt% nitric acid and 60-80wt% phosphoric acid in a volume ratio of 1:0.5-2.

8. The method for chemically removing the ceramic surface layer without damaging the metal bonding layer of the thermal barrier coating according to claim 1, characterized in that: In the step S400, the sand blowing pressure is 0.2-0.3 MPa, and the time is 10-20 seconds; the drying temperature is 190-10° C., and the time is 1-2 hours.

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