Coating removal method

Abstract

Provided herein are compositions and methods for removing a coating (e.g., an environmental barrier coating, EBC) from a substrate. The method of removing a coating from a substrate includes contacting the coating with a salt, the salt being a solid, by some method. The method also involves heating the coating and the salt to a temperature equal to or greater than the melting point of the salt, converting the coating to a dissolvable reaction product by fusion of the coating with the salt. Upon formation of the dissolvable reaction product, at least a portion of the coating is then removed from the substrate using an acid to dissolve the product.

Description

Technical Field

[0001] This disclosure generally relates to compositions and methods for removing coatings from a substrate. Background Technology

[0002] Gas turbine engines may operate at high temperatures. Components exposed to these high temperatures typically contain protective coatings. For example, turbine blades and turbine vanes may contain one or more layers of coating to protect the components and improve their durability under harsh operating conditions. Environmental barrier coatings (EBCs) are a type of protective coating that can be applied to components subjected to high temperatures. EBCs protect components from reactive substances such as hot water vapor.

[0003] When using an Environmental Barrier Coating (EBC) as part of component maintenance, it may be necessary to remove and replace the EBC from the component. For example, if a layer of the EBC is damaged during engine operation, it may be necessary to remove and replace the EBC. Additionally, it may be necessary to remove the EBC from the component during the component manufacturing process, for example, to address coating defects or damage. Therefore, methods for removing environmental barrier coatings may be essential. Summary of the Invention

[0004] In one aspect, this disclosure provides a method for removing a coating from a substrate, wherein the method includes: contacting the coating with a salt, the salt being solid; heating the coating and the salt to a temperature equal to or above the melting point of the salt, thereby converting the coating into a soluble reaction product through fusion of the coating and the salt; and using an acid to dissolve the soluble reaction product, thereby removing at least a portion of the coating from the substrate.

[0005] In another aspect, this disclosure provides a method for removing an environmental barrier coating from a substrate, wherein the method includes: fusing the environmental barrier coating with a solid salt to convert at least a portion of the environmental barrier coating into a soluble reaction product; and immersing the soluble reaction product in an acid bath to dissolve the soluble reaction product. Attached Figure Description

[0006] The compositions and methods for removing coatings described in the following detailed embodiments, especially when studied in conjunction with the accompanying drawings, can at least partially meet various needs. This specification is intended for those skilled in the art, and provides a complete and implementable disclosure of various aspects of this disclosure, including its preferred embodiments, with reference to the accompanying drawings, in which:

[0007] Figure 1 A flowchart of a method for removing a coating from a substrate;

[0008] Figure 2 A table including the composition of the experimental specimens;

[0009] Figure 3A , 3B Image of a specimen (Specimen A) with an air plasma spraying (APS) environmental barrier coating (EBC) and no substrate, and 3C.

[0010] Figure 4 This is a table that includes the experimental results described in Example 1;

[0011] Figure 5 This is a table that includes the experimental results described in Example 1;

[0012] Figure 6A and 6B Image of a specimen (Specimen A) with an air plasma spraying (APS) environmental barrier coating (EBC) and no substrate;

[0013] Figure 7 A table including the experimental results described in Example 2; and

[0014] Figure 8 This is a table that includes the experimental results described in Example 2.

[0015] The elements in the accompanying drawings are not necessarily drawn to scale for the sake of simplicity and clarity. For example, to aid in a better understanding of the various embodiments of this disclosure, the size and / or relative position of some elements may be exaggerated relative to other elements. Furthermore, for clarity in understanding the various embodiments of this disclosure, common but well-known elements that are useful or necessary in commercially feasible implementations are generally omitted. Certain operations and / or steps may be described or depicted in a specific order, but those skilled in the art will understand that such a specific order is not practically necessary. Detailed Implementation

[0016] The compositions and methods described herein for removing coatings can be used to remove environmental barrier coatings (EBCs) from a substrate. The methods described herein involve the reaction or fusion of the coating with a molten salt. The salt can be a pyrosulfate or tetraborate, which converts oxides present in the EBC into sulfates or other soluble reaction products. After the coating has been converted into soluble reaction products through the fusion reaction between the coating and the molten salt, an acid can be used to digest or dissolve the soluble reaction products, thereby peeling the coating off the substrate. The compositions and methods for removing coatings can be used to peel coatings off EBC substrates, for example, before recoating or repairing the substrate.

[0017] The compositions and methods for removing coatings described herein can be used with a variety of coatings, one set of exemplary coatings being EBCs. EBCs can consist of a single layer or multiple layers of materials. Each layer can consist of one or more chemical compositions. EBC materials include, but are not limited to: rare earth (RE) disilicates; rare earth (RE) monosilicates; alkaline earth (AE) aluminosilicates (… ); aluminum silicate or mullite ( Zirconium silicate ( ) ); Hafnium silicate ( );Mode Compounds; formula Compounds; silicon nitride ( ); Silicon carbide (SiC); Ceramics based on silicon, aluminum, oxygen, and nitrogen (SiAlON); Formula Compounds; oxide composites; non-oxide composites. Rare earth elements include cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y). Alkaline earth elements include strontium (Sr), barium (Ba), and radium (Ra). Examples of alkaline earth aluminosilicates are... (BSAS). In the above formula, M is a rare earth element, hafnium (Hf), titanium (Ti), or tantalum (Ta). In some examples, the EBC mentioned herein does not include zirconium oxide-based ceramic coatings.

[0018] The compositions and methods for removing coatings described herein can be used to remove coatings from a variety of substrates. In some examples, the substrate is a ceramic matrix composite (CMC). In some examples, the CMC may be a silicon carbide (SiC) material. CMCs may include, but are not limited to: CMCs having a silicon carbide matrix and silicon carbide fibers (when prepared by silicon melt infiltration, this matrix will contain residual free silicon); silicon carbide / silicon matrix mixtures and silicon carbide fibers; silicon carbide fiber-reinforced silicon carbide (SiC / SiC); oxide-oxide CMCs may consist of a matrix and reinforcing fibers, the reinforcing fibers comprising an oxide-based material, such as silicon dioxide (SiC). ), aluminosilicates and their mixtures; carbon fiber reinforced carbon (C / C); carbon fiber reinforced silicon carbide (C / SiC).

[0019] Furthermore, the substrate on which the coating is applied can take many forms. In some methods, the substrate can be a component or part of a component. In some embodiments, the component is a component subjected to harsh operating conditions (e.g., high temperature, supersonic speed, high stress, or severe oxidation). In some embodiments, the component is a component incorporated into at least one of turbine, aero-engine, aerospace, hypersonic, or space applications. For example, the component can be a turbine component (e.g., blades, guide vanes, shrouds) or an aero-engine component (e.g., stator guide vanes, rotor blades, bushings, combustion chambers, nozzles, etc.). Aerospace applications include, but are not limited to, applications related to aircraft, spacecraft, propulsion systems, satellites, etc. Hypersonic applications include, but are not limited to, applications related to hypersonic vehicles, propulsion systems, etc. Space applications include, but are not limited to, applications related to launchable vehicles and propulsion systems. It is conceivable that the component can be any engine component or structural component in aerospace, hypersonic, or space applications.

[0020] Traditional methods for removing EBC coatings from substrates include mechanical methods, such as sandblasting. These mechanical methods can cause mechanical damage to the underlying substrate. When the underlying substrate (e.g., a component) is damaged during coating removal, subsequent repair and / or replacement of the substrate may be necessary, increasing costs. Furthermore, mechanical methods (e.g., sandblasting) are typically labor-intensive and require skilled operators, further increasing the time and cost associated with coating repair.

[0021] Advantageously, the compositions and methods described herein for removing coatings can be used for the chemical removal of coatings from a substrate (e.g., EBC). Therefore, coating removal can be performed without exposing the part to a corrosive mechanical medium, thus helping to prevent or reduce damage to the substrate beneath the coating. Chemical methods typically involve a fusion reaction with a salt to convert the coating into a soluble reaction product. The soluble reaction product can then be exposed to an acid to dissolve it. These chemical methods are less labor-intensive because the process is more automated and involves immersing or coating the part with salt and / or acid.

[0022] Furthermore, the compositions and methods for removing coatings described herein can be used in conjunction with mechanical polishing. Using the methods described herein, the coating can be weakened prior to mechanical polishing, allowing for mechanical removal using less aggressive media. Mechanical removal using less aggressive media reduces damage to the underlying substrate during the coating removal process.

[0023] Composition

[0024] The composition for removing a coating includes: a salt that contacts the coating to form a soluble reaction product by reaction or fusion, and an acid for dissolving the soluble reaction product.

[0025] The salt can be any suitable salt. In some methods, the salt is a solid. For example, the salt can be a granular solid. The composition of the salt may depend on the specific coating that needs to be removed. In some examples, the salt can be a pyrosulfate or a tetraborate. In some examples, the salt includes at least one of the following: sodium pyrosulfate (… ), potassium pyrosulfate ( Sodium bisulfate ( ), potassium bisulfate ( Sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate ( ), potassium carbonate ( Sodium peroxide ), boric acid ( Sodium tetraborate () Lithium tetraborate () Lithium metaborate () ), ammonium bifluoride ( Sodium fluoride (NaF), potassium fluoride (KF), or potassium hydrogen fluoride ( In some examples, when the coating is EBC, the salt includes at least one of the following: sodium pyrosulfate (…). ), potassium pyrosulfate ( Sodium bisulfate ( ), potassium bisulfate ( Sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate ( ), potassium carbonate ( Sodium tetraborate () Lithium tetraborate () Lithium metaborate () ), ammonium bifluoride ( Sodium fluoride (NaF), potassium fluoride (KF), or potassium hydrogen fluoride ( In some examples, the salt includes at least one of the following: potassium bisulfate (and ) and lithium tetraborate ( In other examples, the salt is selected from potassium bisulfate ( ). Lithium tetraborate () ) and mixtures thereof. In some embodiments, when the coating is TBC, the salt includes at least one of the following: sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate ( ) or potassium carbonate ( ).

[0026] In some respects, the salt can be selected based on the composition of the substrate beneath the coating to be removed. For example, salts such as pyrosulfates or tetraborates may be suitable for targeting coatings on CMC substrates because such salts do not form a melt with silica and / or silicates.

[0027] In some respects, the melting point of the salt causes the coating (e.g., the target coating to be removed) to dissolve in the salt at its melting point or to be soluble in the salt. In some respects, the melting point of the salt is lower than that of the substrate. In some respects, the melting point of the salt can be about 100°C to about 1650°C, about 100°C to about 1350°C, or about 100°C to about 1200°C.

[0028] The acid can be any acid suitable for dissolving or digesting the reaction products of the salt and the coating. In some methods, the acid is a strong acid. In some methods, the acid is at least one of nitric acid or hydrochloric acid.

[0029] The pH of the acid is less than or equal to 7, less than or equal to about 3, and in some methods, the pH is less than or equal to about 1.

[0030] The acid can be an aqueous solution. In some methods, the acid is an aqueous solution with an acid concentration (by weight) of about 5% to about 70%, about 20% to about 70%, about 5% to about 50%, about 5% to about 30%, or about 5% to about 20%.

[0031] method

[0032] The coating removal methods described herein can use one or more of the compositions described herein. In particular, these methods can use the compositions described herein to remove coatings such as EBCs or thermal barrier coatings (TBCs) from a substrate. The substrate can be a component. In some embodiments, the component is a component subjected to harsh operating conditions (e.g., high temperature, supersonic speed, high stress, or severe oxidation). In some embodiments, the component is a component incorporated into at least one of turbine, aero-engine, aerospace, hypersonic, or space applications. For example, the component can be a turbine component (e.g., blades, guide vanes, shrouds) or an aero-engine component (e.g., stator guide vanes, rotor blades, bushings, combustion chambers, nozzles, etc.). Aerospace applications include, but are not limited to, applications related to aircraft, spacecraft, propulsion systems, satellites, etc. Hypersonic applications include, but are not limited to, applications related to hypersonic vehicles, propulsion systems, etc. Space applications include, but are not limited to, applications related to launchable vehicles and propulsion systems. It is conceivable that the component can be any engine component or structural component in aerospace, hypersonic, or space applications. In some aspects, the substrate contains CMCs.

[0033] Figure 1An exemplary method for removing a coating from a substrate is shown. At box 110, the method includes contacting the coating with salt. In some methods, the salt is a solid. In some methods, the salt is a particulate solid. Using a particulate solid increases the surface area of ​​the salt, thereby exposing more salt to the coating and increasing the reaction rate.

[0034] In some methods, the weight ratio of salt to coating can be about 6:1 to about 20:1, about 6:1 to about 12:1, about 8:1 to about 12:1, or in some respects about 10:1.

[0035] The coating can be an environmental barrier coating (EBC). The EBC can be manufactured using any suitable method. In some embodiments, the EBC is manufactured using a thermal spraying method. In other embodiments, the EBC is manufactured using a slurry-based process. In other embodiments, the EBC is manufactured using physical vapor deposition processes, including but not limited to electron beam physical vapor deposition (EBPVD) and plasma spray physical vapor deposition (PSPVD). In other embodiments, the EBC is manufactured using sputtering techniques, including but not limited to magnetron sputtering, RF sputtering, diode sputtering, or reactive sputtering. Thermal spraying methods that can be used to manufacture the EBC include, but are not limited to, air plasma spraying (APS), ultra-low pressure plasma spraying (VLPPS), suspension plasma spraying (SPS), high-velocity oxygen fuel (HVOF) spraying, solution precursor plasma spraying (SPPS), and high-velocity air fuel (HVAF) spraying. APS involves generating a high-temperature plasma jet to melt and accelerate fine powder particles ejected onto a substrate. VLPPS involves spraying materials at low chamber pressures, which allows for the formation of fine molten droplets or vapor deposition. SPS involves injecting a liquid suspension containing fine powder particles into a plasma jet, where the liquid rapidly evaporates and the particles melt before deposition onto a substrate. HVOF spraying involves burning a mixture of fuel and oxygen to generate a high-pressure jet that propels powder toward a substrate at supersonic speeds. SPPS involves injecting a liquid precursor solution containing dissolved compounds into a high-temperature plasma jet. When the solution enters the plasma, it rapidly evaporates and undergoes thermal decomposition, forming fine oxide particles or droplets that are sprayed toward the substrate. HVAF spraying involves using compressed air to burn fuel, generating a high-speed hot gas jet that propels powder particles toward a substrate at high speed. These thermal spraying methods are merely examples, and EBC preparation methods are not limited to the methods or thermal spraying techniques listed. In some examples, the EBC may be at least one of air plasma spraying (APS) or slurry-based EBC.

[0036] EBCs can also be prepared using one or more sintering aids. For example, one or more sintering aids can be used in any of the above-described preparation techniques (e.g., thermal spraying, slurry-based processes, physical vapor deposition, or sputtering).

[0037] In some methods, the coating is an EBC comprising rare earth silicates and / or rare earth oxides. In other methods, the coating may be an EBC comprising refractory metals (e.g., hafnium (Hf), zirconium (Zr), etc.). In still other methods, the coating is a TBC, such as a yttrium oxide-stabilized coating (e.g., yttrium oxide-stabilized zirconium oxide).

[0038] In some examples, a salt-coated layer may be used to form a coating, and the coating may be heated to a temperature equal to or above the melting point of the salt. For example, as described in box 120, granular solid salt may be spread onto the coating to cover it before heating the salt and coating. In some examples, the salt may be in the form of a strip, wherein the salt is disposed on one side of the strip so that it adheres to the coating.

[0039] At box 120, the coating and salt are heated to a temperature equal to or above the salt's melting point, transforming the coating into a soluble reaction product through fusion with the salt. For example, a furnace, oil bath, burner, or hot plate can be used to heat the coating and salt. In some cases, the coating and salt are placed in a crucible, which is then placed in a furnace. At such temperatures, the salt becomes molten, and the coating reacts with the molten salt through a fusion reaction to form a soluble reaction product.

[0040] In some methods, the coating and salt are heated to a temperature of about 100°C to about 1650°C, about 100°C to about 1350°C, or about 100°C to about 1200°C.

[0041] In some methods, the coating and salt are heated to a temperature equal to or above the salt's melting point for approximately 0.5 to approximately 4 hours. Heating within this timeframe provides sufficient time for the fusion reaction to complete. The time can depend, for example, on the amount of salt and the amount of coating available for the reaction. The salt can be a limiting agent, so additional time does not equate to additional coating removal once the salt has completely reacted or been depleted.

[0042] The composition of the soluble reaction products depends on the composition of the salt and the coating. In some examples, when the salt is a pyrosulfate or tetraborate, the soluble reaction products are sulfates.

[0043] At box 130, after the coating is converted into a soluble reaction product, the soluble reaction product is dissolved using acid. To dissolve the soluble reaction product, it is brought into contact with acid. For example, acid can be poured into a crucible containing the coating, sprayed onto the coating surface, or the coating can be immersed in an acid bath. Dissolving the soluble reaction product with acid removes it. During the conversion of the coating into a soluble reaction product, part or all of the coating fuses with salt to form a glassy fusion product. The fusion product (i.e., the soluble reaction product) is dissolved and detached from the component by acid.

[0044] In some methods, acids can be used to weaken soluble reaction products, which may prevent the coating from being completely removed from the part. In such cases, mechanical grinding can be used to remove the weakened soluble reaction products from the part.

[0045] In some methods, the acid is maintained at a higher temperature to accelerate the dissolution rate. While lower temperatures can be used, this may result in a longer exposure time required to dissolve the soluble reaction products. In some examples, the acid is maintained at a temperature from about 25 °C to about 100 °C.

[0046] In some methods, the exposure time of the soluble reaction product to the acid is about 0.5 hours to about 15 hours, about 0.5 hours to about 10 hours, about 0.5 hours to about 5 hours, or about 0.5 hours to about 3 hours. The exposure time required to dissolve the soluble reaction product may depend on a variety of factors, such as the volume of the coating being removed, the volume of the acid, the concentration of the acid, and / or the temperature of the acid.

[0047] In some examples, at box 130, a substrate containing the soluble reaction product is immersed in an acid bath, allowing the soluble reaction product to come into contact with the acid and dissolve. The acid bath may be stirred to accelerate the dissolution rate.

[0048] In some embodiments, after at least a portion of the soluble reaction products have come into contact with the acid, a portion of the coating can also be removed by mechanical polishing. For example, converting the coating into soluble reaction products and dissolving them with acid can weaken the coating, making it removable by mechanical polishing. Any suitable mechanical polishing method can be used. Suitable mechanical polishing methods include, but are not limited to, sandblasting, ice blasting, or water jetting. It is conceivable that, using such methods, less aggressive forms of mechanical abrasion (e.g., sandblasting with a walnut shell as a medium) can be used to remove EBC from the substrate compared to the mechanical abrasion used in conventional EBC removal methods.

[0049] In one embodiment, after the coating is removed or peeled off from the substrate, the substrate can be recoated with at least one of an adhesive coating or other coatings. Once the substrate is exposed, recoating can be performed with only minimal surface treatment. Conventional mechanical coating removal methods (e.g., sandblasting) may damage or erode the surface of the component (e.g., the coated substrate); the chemical methods described herein can remove the coating while leaving the underlying substrate substantially undamaged and in a recoatable state. In some embodiments, the recoated surface may include coating the substrate with an adhesive coating or a new coating.

[0050] To further illustrate this disclosure, the following embodiments are provided. It should be understood that these embodiments are for illustrative purposes only and should not be construed as limiting the scope of this disclosure.

[0051] Example

[0052] Example 1

[0053] A fusion-based coating removal process is employed, using a salt flux—specifically potassium bisulfate ( — The coating was removed from the three test pieces.

[0054] Figure 2 The composition of three specimens (Specimen A, Specimen B, and Specimen C) is shown. These specimens are essentially tile-shaped and roughly square. Specimen A is made of air plasma spraying (APS) environmental barrier coating (EBC). In Specimen A, the EBC coating is free-standing and not applied to the substrate. Specimen B is made of EBC coated on a ceramic matrix composite (CMC) substrate. One side of Specimen B is coated with EBC. Specimen C is made of EBC coated on a CMC substrate. One side of Specimen C is coated with EBC. Calcium magnesium aluminum silicate (CMAS) is fused onto the EBC of Specimen C.

[0055] Each specimen underwent the same coating removal process. The coating removal process began by contacting the specimen with a potassium bisulfate flux. The specimen was then subjected to a digestion treatment, which included heating in a furnace and exposure to acid.

[0056] The sample and potassium bisulfate flux were heated to 600 °C and held for 1 hour to form a soluble reaction product.

[0057] After heating the sample with potassium bisulfate flux, the sample was dissolved using a 10% (by weight) hydrochloric acid (HCl) aqueous solution. The HCl aqueous solution was maintained at 120 °C for 1 hour.

[0058] In Example 1, the dissolution step was performed twice, with the same operation each time: heating for 1 hour followed by exposure to an aqueous HCl solution for 1 hour. After completing the heating and dissolution steps, the sample was dried.

[0059] For sample A, the mass ratio of salt flux to EBC is 0.76.

[0060] For specimens B and C, the mass ratio of salt flux to EBC was approximately 3.6.

[0061] Figure 3A , 3B Images of 3C are from the coating removal process in Example 1. Figure 3A The initial state of sample A is shown before treatment with a salt flux and / or an acid (e.g., an aqueous HCl solution). Figure 3B The image shows sample A after the first complete digestion process (e.g., 60 minutes in the oven + 60 minutes of acid exposure). Figure 3CThe image shows sample A after a second complete digestion process (e.g., a total of 120 minutes in the furnace + a total of 120 minutes of acid exposure). Figures 3A-3C As shown, in the coating removal process of Example 1, the initial appearance of sample A may be similar to the appearance after the first complete digestion treatment and the second complete digestion treatment.

[0062] Figure 4 and Figure 5 The experimental results of the coating removal process in Example 1 are included.

[0063] During the coating removal process, sample A lost approximately 2.9% of its initial weight. Since sample A contains substrate-free EBC, this weight loss is attributed to the loss of the EBC. During the 2-hour processing time, approximately 33% of the EBC was lost.

[0064] During the coating removal process, sample B lost approximately 4.7% of its initial weight.

[0065] During the coating removal process, specimen C lost approximately 4.2% of its initial weight. This thickness loss is believed to be attributed to the loss of the EBC, as visual inspection of the specimen revealed no significant damage to the underlying CMC substrate.

[0066] The experimental coating removal process in Example 1 demonstrates that a fusion-based coating removal process provides an option for at least partial decomposition of the EBC. The coating removal process can then be completed by EBC weakening (e.g., through mechanical polishing).

[0067] Furthermore, sample A is composed of an EBC different from that of samples B and C. Therefore, Example 1 demonstrates that the process is applicable to different EBC coatings, but the removal rates differ.

[0068] Example 2

[0069] Use a salt, specifically lithium tetraborate ( The coating was removed from three samples using a fusion-based coating removal process.

[0070] Figure 5 The composition of three specimens (Specimen A, Specimen B, and Specimen C) is shown. Specimen A is made of air plasma spraying (APS) environmental barrier coating (EBC). In Specimen A, the EBC coating is self-supporting and not applied to the substrate. Specimen B is made of EBC coated on a ceramic matrix composite (CMC) substrate. Specimen C is made of EBC coated on a CMC substrate. Calcium magnesium aluminum silicate (CMAS) is deposited on the EBC of Specimen C.

[0071] Each sample underwent the same coating removal process. The coating removal process began by contacting the sample with a lithium tetraborate flux. The sample and the lithium tetraborate flux were heated at 1100 °C for 4 hours to form a soluble reaction product.

[0072] After heating the sample with lithium tetraborate flux, use 20% (by weight) nitric acid ( The test piece was dissolved in an aqueous solution. The aqueous solution was kept at 90 °C for approximately 5 hours. After the dissolution step, the sample was dried.

[0073] For sample A, the mass ratio of salt flux to EBC is 0.70.

[0074] For specimens B and C, the mass ratio of salt flux to EBC was approximately 3.6.

[0075] Figure 7 and Figure 8 The experimental results of the coating removal process in Example 2 are included.

[0076] During the coating removal process, sample A lost approximately 76% of its initial weight. Since sample A contained only EBC without a substrate, this weight loss was attributed to the loss of the EBC. The EBC was not completely dissolved.

[0077] Figure 6A and 6B The image shown is of specimen A during the coating removal process. Figure 6A The image shows the initial state of specimen A before the salt flux was applied and the specimen was exposed to an aqueous HCl solution. Figure 6B The image shown is of specimen A at the end of the coating removal process.

[0078] During the coating removal process, sample B lost approximately 34% of its initial weight.

[0079] During the coating removal process, sample C lost approximately 32% of its initial weight.

[0080] It is noteworthy that, for specimens B and C, complete dissolution of the EBC was observed in Example 2. In Example 2, damage to the CMC substrate was observed by visual inspection; therefore, some weight loss in specimens B and C can be attributed to the loss of the CMC substrate.

[0081] Example 3

[0082] Boric acid was coated onto a ceramic matrix composite component with TBC, and the boric acid-coated component was heated to 350 °C for 3 hours to initiate a fusion reaction. The fusion reaction product was dissolved in a 10% (by weight) aqueous hydrochloric acid solution at 90 °C for 2 hours. The experimental coating process in Example 3 demonstrates that a fusion-based coating removal process provides an option for achieving at least partial decomposition of TBC using boric acid.

[0083] Example 4

[0084] Potassium hydroxide (KOH) was coated onto a ceramic matrix composite component with EBC (Extra-Body-Containing Cell). The component coated with potassium hydroxide was heated to 600 °C for 0.5 hours to initiate a fusion reaction. The fusion reaction product was then treated with 15% (by weight) nitric acid. The aqueous solution was dissolved at 85°C for 1.5 hours. The experimental coating process in Example 4 shows that the fusion-based coating removal process provides an option for achieving at least partial decomposition of EBC using potassium hydroxide (KOH).

[0085] Example 5

[0086] Sodium peroxide ( Sodium peroxide was coated onto a ceramic matrix composite component with TBC. The component covered with sodium peroxide was heated to 700 °C for 2 hours to initiate a fusion reaction. The fusion reaction product was dissolved in a 10% (by weight) hydrochloric acid (HCl) aqueous solution at 90 °C for 2 hours. The experimental coating process in Example 5 shows that the coating removal process based on fusion is achieved using sodium peroxide (… Implementing at least a partial breakdown of TBC provides one option.

[0087] The terms and expressions used herein have the ordinary technical meanings that would be given to such terms and expressions by those skilled in the art, unless otherwise specified herein. Unless otherwise expressly stated, the word "or" as used herein shall be interpreted as a selection relationship rather than a parallel relationship. Unless otherwise specified herein, the terms "coupled," "fixed," "connected to," etc., refer to both direct coupling, fixing, or connection, and indirect coupling, fixing, or connection through one or more intermediate components or features.

[0088] Unless the context clearly indicates otherwise, the singular forms “a,” “a,” and “the” include plural references.

[0089] Approximate language, as used throughout this specification and claims, is used to modify any quantitative expression that may vary without altering its essential function. Therefore, values ​​modified by words such as “about,” “approximately,” and “essentially” should not be limited to the specified precise value. In at least some cases, an approximate expression may correspond to the precision of the instrument measuring the value, or to the precision of the method or machine used to construct or manufacture the component and / or system. For example, an approximate expression may refer to a value within a 10% error range.

[0090] Further aspects of this disclosure are provided by the subject matter of the following provisions:

[0091] A method for removing a coating from a substrate, the method comprising: contacting the coating with a salt, the salt being solid; heating the coating and the salt to a temperature equal to or above the melting point of the salt, thereby converting the coating into a soluble reaction product through fusion of the coating and the salt; and dissolving the soluble reaction product using an acid to remove at least a portion of the coating from the substrate.

[0092] The method according to any one of the foregoing clauses, wherein the coating is an environmental barrier coating (EBC).

[0093] The method according to any one of the foregoing clauses, wherein the environmental barrier coating comprises rare earth oxides.

[0094] The method according to any one of the foregoing clauses, wherein the substrate is a ceramic matrix composite material.

[0095] The method according to any one of the foregoing clauses, wherein the salt comprises at least one of the following: sodium pyrosulfate ( ), potassium pyrosulfate ( Sodium bisulfate ( Potassium bisulfate ( Sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate ( ), potassium carbonate ( Sodium peroxide ), boric acid ( Sodium tetraborate () Lithium tetraborate () Lithium metaborate () ), ammonium bifluoride ( Sodium fluoride (NaF), potassium fluoride (KF), or potassium hydrogen fluoride ( ).

[0096] The method according to any one of the foregoing clauses, wherein the acid comprises at least one of nitric acid or hydrochloric acid.

[0097] The method according to any one of the foregoing clauses, wherein the substrate is a component incorporated into at least one of turbines, aero-engines, aerospace applications, hypersonic applications, or space applications.

[0098] The method according to any one of the foregoing clauses, wherein the salt is a particulate solid.

[0099] The method according to any one of the foregoing clauses, wherein the ratio of salt to coating by weight is about 6:1 to about 20:1.

[0100] The method according to any one of the foregoing clauses, wherein the coating is a thermal barrier coating.

[0101] The method according to any one of the foregoing clauses, wherein the acid is an aqueous solution with an acid concentration of about 5% to about 70%.

[0102] The method according to any one of the foregoing clauses, wherein contacting the coating with salt comprises contacting the coating with salt at a temperature of about 100 °C to about 1650 °C.

[0103] The method according to any one of the foregoing clauses, wherein the coating and salt are heated to a temperature equal to or above the melting point of the salt to form a molten salt fused with the coating.

[0104] The method according to any one of the foregoing clauses, wherein the salt forms a molten salt, and the contact between the coating and the molten salt causes the coating to fuse with the molten salt.

[0105] The method according to any one of the foregoing clauses further includes: recoating the surface of the substrate with at least one of an adhesive coating or a new coating.

[0106] The method according to any one of the foregoing clauses further includes: removing at least a portion of the coating by mechanical grinding after dissolving the soluble reaction product.

[0107] A method for removing an environmental barrier coating from a substrate, wherein the method comprises: fusing the environmental barrier coating with a solid salt to convert at least a portion of the environmental barrier coating into a soluble reaction product; and immersing the soluble reaction product in an acid bath to dissolve the soluble reaction product.

[0108] The method according to any one of the foregoing clauses, wherein the acid bath is maintained at a temperature of about 25 °C to about 100 °C.

[0109] The method according to any one of the foregoing clauses, wherein the acid bath comprises at least one of nitric acid or hydrochloric acid.

[0110] According to any one of the preceding clauses, the method of fusing the environmental barrier coating with the solid salt comprises: covering the environmental barrier coating with the solid salt to form a coated environmental barrier coating, and heating the coated environmental barrier coating to a temperature equal to or higher than the melting point of the solid salt.

Claims

1. A method for removing a coating from a substrate, wherein, The method includes: The coating is brought into contact with a solid salt. Heating the coating and salt to a temperature equal to or above the melting point of the salt, thereby converting the coating into a soluble reaction product through fusion of the coating and salt; and Acid dissolution can be used to dissolve the reaction products and remove at least a portion of the coating from the substrate.

2. The method according to claim 1, wherein, The coating is an environmental barrier coating (EBC).

3. The method according to claim 2, wherein, The environmental barrier coating contains rare earth oxides.

4. The method according to claim 1, wherein, The substrate is a ceramic matrix composite material.

5. The method according to claim 1, wherein, The salt includes at least one of the following: sodium pyrosulfate ( ), potassium pyrosulfate ( Sodium bisulfate ( ), potassium bisulfate ( Sodium hydroxide (NaOH), potassium hydroxide (KOH), sodium carbonate ( ), potassium carbonate ( Sodium peroxide ), boric acid ( Sodium tetraborate () Lithium tetraborate () Lithium metaborate () ), ammonium bifluoride ( Sodium fluoride (NaF), potassium fluoride (KF), or potassium hydrogen fluoride ( ).

6. The method according to claim 1, wherein, The acid includes at least one of nitric acid or hydrochloric acid.

7. The method according to claim 1, wherein, The substrate is a component incorporated into at least one of turbines, aero-engines, aerospace applications, hypersonic applications, or space applications.

8. The method according to claim 1, wherein, The salt is a granular solid.

9. The method according to claim 1, wherein, The ratio of salt to coating by weight is approximately 6:1 to approximately 20:

1.

10. A method for removing an environmental barrier coating from a substrate, wherein, The method includes: fusing an environmental barrier coating with a solid salt to convert at least a portion of the environmental barrier coating into a soluble reaction product; and immersing the soluble reaction product in an acid bath to dissolve the soluble reaction product.

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