Thermal barrier coating removing method based on plasma electrolysis technology

Abstract

A thermal barrier coating removing method based on a plasma electrolysis technology belongs to the technical field of material surface treatment and comprises the following steps: constructing a specific plasma electrolysis system, preparing a solution containing specific ions, and controlling key parameters such as voltage, solution temperature and treatment time; by means of high temperature, high pressure, strong electric field and other physical and chemical environments generated by plasma, a series of physical and chemical changes of the YSZ coating are promoted, and therefore efficient removal of the coating is achieved. According to the method, the YSZ coating can be rapidly and selectively stripped, only part of the bonding layer between the substrate and the coating is left, compared with a traditional coating removal method, the plasma electrolysis technology shows remarkable advantages, and the method has the advantages of being high in removal efficiency, environmentally friendly, high in adaptability to parts with complex shapes and the like, and has good application prospects. And an innovative and practical solution is expected to be provided for repairing and reusing a thermal barrier coating of a GH4169 high-temperature alloy part in the fields of aerospace and the like.

Description

Technical Field

[0001] This invention belongs to the field of material surface treatment technology, specifically relating to a method for removing thermal barrier coatings based on plasma electrolysis technology. Background Technology

[0002] GH4169 high-temperature alloy, due to its excellent high-temperature strength, corrosion resistance, and machinability, is widely used in critical load-bearing components such as turbine blades for aerospace engines and hot-end components of gas turbines in the energy sector. To further enhance its high-temperature service performance, a YSZ thermal barrier coating is typically applied to the alloy surface. This coating effectively blocks the thermal shock of high-temperature combustion gases to the substrate, reducing the substrate temperature by 50°C to 150°C and significantly extending the service life of the components. However, under extreme service environments such as long-term high temperature, high pressure, and high-speed airflow erosion, the YSZ coating is prone to failure phenomena such as peeling and cracking, requiring repair or removal and recoating.

[0003] In the overhaul and maintenance of aero-engines and gas turbines, efficient removal of failed coatings is a crucial step in achieving component remanufacturing. Currently, traditional YSZ coating removal methods mainly include mechanical peeling, chemical etching, and laser removal. Mechanical peeling methods, such as sandblasting and grinding, while relatively simple to operate, easily cause mechanical damage to the alloy substrate, forming microcracks and affecting the substrate's mechanical properties. This is especially true for complex-shaped aero-engine components, where uniform removal is difficult to achieve. Chemical etching utilizes highly corrosive solutions to react with the YSZ coating. While it can remove the coating to some extent, this method is not only inefficient and time-consuming but also generates large amounts of waste liquid containing heavy metal ions and corrosive substances, causing serious environmental pollution. Laser removal, while offering high removal precision, suffers from high equipment costs, complex process parameter control, and is prone to changes in the alloy substrate structure due to localized overheating, resulting in thermal stress deformation.

[0004] In recent years, plasma electrolysis technology has been widely used in micro-arc oxidation, cathodic plasma electrolytic deposition, plasma electroporation, and plasma electropolishing due to the synergistic effect of electrochemical corrosion and plasma thermochemical effects. Plasma electrolytic removal technology originates from plasma electropolishing technology. This technology applies a high voltage to the electrolyte to induce micro-arc discharge on the workpiece surface, with localized instantaneous temperatures reaching over 1000°C, thereby destroying the coating structure. Simultaneously, the chemical action of the electrolyte accelerates coating dissolution, demonstrating potential in the field of coating removal. However, existing research has largely focused on plasma electropolishing of stainless steel or titanium alloys, and systematic research on GH4169 high-temperature alloys and YSZ coating systems remains lacking.

[0005] Therefore, it is necessary to develop an efficient, environmentally friendly, non-destructive coating removal technology suitable for complex-shaped components. Plasma electrolysis technology, based on the high temperature and high pressure characteristics of plasma and the effect of electric field, can induce unique physicochemical processes on the material surface, providing a new approach and direction for solving the aforementioned problems. Summary of the Invention

[0006] To address the shortcomings of existing technologies and to solve the problems of low efficiency, environmental unfriendliness, or easy damage to the substrate caused by existing methods for removing thermal barrier coatings from the surface of GH4169 high-temperature alloy, this invention proposes a thermal barrier coating removal method based on plasma electrolysis technology.

[0007] A method for removing thermal barrier coatings based on plasma electrolysis technology specifically includes the following steps:

[0008] (1) The GH4169 high-temperature alloy workpiece to be treated is ultrasonically cleaned in deionized water and alcohol until the surface of the workpiece is clean.

[0009] (2) The cleaned workpiece is used as the anode and the graphite rod is used as the cathode. The workpiece is immersed in a neutral salt solution or ammonium sulfate solution composed of ammonium fluoride solution and potassium fluoride solution. The thermal barrier coating is removed by applying voltage in a voltage stabilization mode.

[0010] (3) After removing the coating, the workpiece is ultrasonically cleaned in deionized water and alcohol in sequence, then dried and placed in a container with a buffer material for later use to maintain the material properties.

[0011] in:

[0012] In step (2), the mass concentration of ammonium fluoride solution is 3%~4%, the mass concentration of potassium fluoride solution is 3%~4%, and the mass ratio of ammonium fluoride solution to potassium fluoride solution is 1:3.

[0013] In step (2), the mass concentration of both ammonium fluoride solution and potassium fluoride solution is 3.5%, and the mass ratio of ammonium fluoride solution to potassium fluoride solution is 1:(2~5).

[0014] In step (2), the mass concentration of the ammonium sulfate solution is 1% to 5%.

[0015] In step (2), the voltage is 220V~280V.

[0016] The key technical point of this invention is:

[0017] This invention utilizes plasma electrolysis technology to remove thermal barrier coatings. A vapor-gas envelope layer is excited on the surface of the anode workpiece. Due to the extremely high resistance between the gas layers, a significant pressure drop occurs between the workpiece surface and the solution, causing the gas layer to break down and generating plasma. The high-energy particles of the plasma bombard the YSZ coating surface, causing electrochemical dissolution, mechanical peeling, and thermal stress-induced interfacial peeling. Because the electrochemical potentials of the GH4169 high-temperature alloy and the YSZ coating differ, the potential difference at the interface accelerates the redox reaction at the coating-substrate interface during electrolysis, weakening the adhesion between the two and making the coating easier to peel off. During discharge, gases (such as H2 and O2) generated on the electrode surface form bubbles. These bubbles burst under high pressure, generating shock waves that exert mechanical impact on the coating surface. Furthermore, due to the difference in thermal expansion coefficients between the GH4169 high-temperature alloy and the YSZ coating, the periodic thermal shocks from the plasma discharge accumulate thermal stress at the interface, causing the coating to peel off from the substrate surface. Ultimately, efficient coating removal is achieved through the synergistic effect of electrochemical corrosion, physical impact, and thermal stress.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The method provided by this invention does not require expensive special equipment or rare materials, and the electrolyte and related consumables used are inexpensive and readily available. Energy consumption is low throughout the entire processing, significantly reducing energy costs compared to traditional processing technologies.

[0020] 2. This invention utilizes the high-energy characteristics of plasma, which can react rapidly with the material surface during processing, greatly improving the efficiency of coating removal.

[0021] 3. The processing of this invention generates very few harmful pollutants. The electrolytes used are mostly environmentally friendly formulations, free of heavy metals or other substances that are seriously harmful to the environment. After processing, the electrolyte is easy to handle and recycle, and will not pollute soil, water bodies, or other environmental elements. Furthermore, this technology does not require highly polluting chemical treatment steps, reducing negative environmental impacts from the source and aligning with the concept of green and environmentally friendly development.

[0022] 4. This invention breaks through the limitation of traditional electrolysis technology, which can only process conductive materials. Through a unique plasma discharge mechanism, it can induce chemical reactions or physical changes on the surface of non-conductive coatings, thus expanding the scope of material processing and providing new technical means for the application and development of non-conductive materials. Attached Figure Description

[0023] Figure 1 A schematic diagram of the mechanism for plasma electrolysis removal of thermal barrier coatings according to the present invention;

[0024] Figure 2Comparison of thermal barrier coating removal effects in Examples 1-5 of the present invention; wherein, (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, and (e) is Example 5;

[0025] Figure 3 Comparison of thermal barrier coating removal effects in Examples 6-10 of the present invention; wherein, (f) is Example 6, (g) is Example 7, (h) is Example 8, (i) is Example 9, and (j) is Example 10;

[0026] Figure 4 Comparison of thermal barrier coating removal effects in Examples 8 and 11-14 of this invention; where (h) is Example 8, (k) is Example 11, (l) is Example 12, (m) is Example 13, and (n) is Example 14;

[0027] Figure 5 EDS spectrum of typical region A in Example 1 of the present invention, showing the effect of thermal barrier coating removal;

[0028] Figure 6 EDS spectrum of typical region B of thermal barrier coating removal effect diagram in Embodiment 1 of the present invention;

[0029] Figure 7 EDS spectrum of a typical area of ​​the thermal barrier coating removal effect diagram in Embodiment 3 of the present invention;

[0030] Figure 8 EDS spectrum of typical region A in Example 12 of the present invention for the effect of thermal barrier coating removal;

[0031] Figure 9 EDS spectrum of typical region B of thermal barrier coating removal effect diagram in Embodiment 12 of the present invention;

[0032] Figure 10 The thermal barrier coating removal effect diagram and EDS spectrum of Embodiment 8 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] A method for removing thermal barrier coatings based on plasma electrolysis technology. The reaction mechanism diagram of this method is shown below. Figure 1 As shown, the specific steps include:

[0035] (1) The GH4169 high-temperature alloy workpiece to be treated was ultrasonically cleaned in deionized water and alcohol until the workpiece surface was clean; the thickness of the YSZ coating was measured using a TT230 eddy current thickness gauge; the types and contents of elements on the surface of the YSZ coating were detected using a field emission scanning electron microscope, and the surface morphology of the YSZ coating was photographed.

[0036] (2) The cleaned workpiece is used as the anode and the graphite rod is used as the cathode. The workpiece is immersed in a neutral salt solution consisting of 3wt.%~4wt.% ammonium fluoride solution and 3wt.%~4wt.% potassium fluoride solution in a mass ratio of 1:3, or an ammonium sulfate solution with a mass concentration of 1%~5%. The thermal barrier coating is removed by applying a voltage of 220V~280V in a voltage stabilization mode.

[0037] When the mass concentration of both the ammonium fluoride solution and the potassium fluoride solution is 3.5%, the mass ratio of the ammonium fluoride solution to the potassium fluoride solution is 1:(2~5).

[0038] (3) After removing the coating, the workpiece was ultrasonically cleaned in deionized water and alcohol in sequence, and then dried. The surface micromorphology of the sample was observed by field emission scanning electron microscopy (FET), and the amount of coating removed was calculated. The types and contents of elements on the sample surface were detected by FET. The surface roughness Ra of the sample was measured using a KathMatic KC series laser spectroscopic confocal microscope. The surface roughness of each sample surface was measured five times at equal intervals, and the average value was calculated as the surface roughness characterization value. Then, it was placed in a container with cushioning material for later use to maintain the material properties.

[0039] Example 1

[0040] A solution for plasma electrolytic removal of thermal barrier coatings, specifically comprising 1 wt.% ammonium sulfate solution.

[0041] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0042] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 220V.

[0043] Example 1 Thermal barrier coating removal effect diagram. Typical region A EDS spectrum is shown below. Figure 5 As shown, the EDS spectrum of typical region B is as follows: Figure 6 As shown.

[0044] Example 2

[0045] A solution for plasma electrolytic removal of thermal barrier coatings, specifically comprising 2 wt.% ammonium sulfate solution.

[0046] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0047] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 235V.

[0048] Example 3

[0049] A solution for plasma electrolytic removal of thermal barrier coatings, specifically comprising 3 wt.% ammonium sulfate solution.

[0050] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0051] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 250V.

[0052] Example 3 Thermal barrier coating removal effect diagram: EDS spectrum of a typical area is shown below. Figure 7 As shown.

[0053] Example 4

[0054] A solution for plasma electrolytic removal of thermal barrier coatings, specifically comprising 4 wt.% ammonium sulfate solution.

[0055] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0056] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 265V.

[0057] Example 5

[0058] A solution for plasma electrolytic removal of thermal barrier coatings, specifically comprising 5 wt.% ammonium sulfate solution.

[0059] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0060] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 280V.

[0061] The thermal barrier coatings removed using the solutions from Examples 1-5 showed the following effects: Figure 2 As shown in the figures, (a) is Example 1, (b) is Example 2, (c) is Example 3, (d) is Example 4, and (e) is Example 5. The figures show that a 3 wt.% ammonium sulfate solution is effective in removing the YSZ coating from the surface of GH4169 high-temperature alloy using plasma electrolysis.

[0062] Example 6

[0063] A solution for plasma electrolytic removal of thermal barrier coatings, wherein the solution composition is a mixture of 3 wt.% ammonium fluoride solution and 3 wt.% potassium fluoride solution in a mass ratio of 1:3.

[0064] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0065] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 220V.

[0066] Example 7

[0067] A solution for plasma electrolytic removal of thermal barrier coatings, wherein the solution composition is specifically a mixture of 3.3 wt.% ammonium fluoride solution and 3.3 wt.% potassium fluoride solution in a mass ratio of 1:3.

[0068] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0069] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 235V.

[0070] Example 8

[0071] A solution for plasma electrolytic removal of thermal barrier coatings, wherein the solution composition is specifically a mixture of 3.5 wt.% ammonium fluoride solution and 3.5 wt.% potassium fluoride solution in a mass ratio of 1:3.

[0072] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0073] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 250V.

[0074] Example 8 shows the thermal barrier coating removal effect diagram and EDS spectrum. Figure 10 As shown.

[0075] Example 9

[0076] A solution for plasma electrolytic removal of thermal barrier coatings, wherein the solution composition is specifically a mixture of 3.7 wt.% ammonium fluoride solution and 3.7 wt.% potassium fluoride solution in a mass ratio of 1:3.

[0077] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0078] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 265V.

[0079] Example 10

[0080] A solution for plasma electrolytic removal of thermal barrier coatings, wherein the solution components are specifically a mixture of 4 wt.% ammonium fluoride solution and 4 wt.% potassium fluoride solution in a mass ratio of 1:3.

[0081] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0082] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 280V.

[0083] The thermal barrier coatings removed using the solutions from Examples 6-10 showed the following effects: Figure 3 As shown, (f) is Example 6, (g) is Example 7, (h) is Example 8, (i) is Example 9, and (j) is Example 10.

[0084] Example 11

[0085] A solution for plasma electrolytic removal of thermal barrier coatings, wherein the solution composition is specifically a mixture of 3.5 wt.% ammonium fluoride solution and 3.5 wt.% potassium fluoride solution in a mass ratio of 1:2.

[0086] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0087] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 220V.

[0088] Example 12

[0089] A solution for plasma electrolytic removal of thermal barrier coatings, specifically comprising a mixture of 3.5 wt.% ammonium fluoride solution and 3.5 wt.% potassium fluoride solution in a mass ratio of 1:2.8.

[0090] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0091] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 235V.

[0092] Example 12 Thermal barrier coating removal effect diagram. Typical region A EDS spectrum is shown below. Figure 8 As shown, the EDS spectrum of typical region B is as follows: Figure 9 As shown.

[0093] Example 13

[0094] A solution for plasma electrolytic removal of thermal barrier coatings, wherein the solution composition is specifically a mixture of 3.5 wt.% ammonium fluoride solution and 3.5 wt.% potassium fluoride solution in a mass ratio of 1:4.

[0095] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0096] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 265V.

[0097] Example 14

[0098] A solution for plasma electrolytic removal of thermal barrier coatings, wherein the solution composition is specifically a mixture of 3.5 wt.% ammonium fluoride solution and 3.5 wt.% potassium fluoride solution in a mass ratio of 1:5.

[0099] The application of the above solution in plasma electrolytic removal of thermal barrier coatings specifically includes the following steps:

[0100] A GH4169 high-temperature alloy sample (20mm×10mm×1mm) coated with a thermal barrier coating was used as the anode, and a graphite rod was used as the cathode. The sample was immersed in a prepared solution, and the thermal barrier coating was removed after applying a voltage of 280V.

[0101] The thermal barrier coatings removed using the solutions from Examples 8 and 11-14 showed the following effects: Figure 4 As shown, (h) is Example 8, (k) is Example 11, (l) is Example 12, (m) is Example 13, and (n) is Example 14.

[0102] The figure shows that using a 3wt.% ammonium sulfate solution or a mixture of 3.5wt.% ammonium fluoride solution and 3.5wt.% potassium fluoride solution in a mass ratio of 1:3 is more effective in removing the YSZ coating from the surface of GH4169 high-temperature alloy by plasma electrolysis, exhibiting higher removal efficiency, less surface residue, and a more controllable reaction process.

[0103] The scope of protection of this invention is not limited to the embodiments described above. Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its scope and spirit. If these modifications and variations fall within the scope of this invention and its equivalents, then the intent of this invention also includes these modifications and variations.

Claims

1. A method for removing thermal barrier coatings based on plasma electrolysis technology, characterized in that, Specifically, the following steps are included: (1) The GH4169 high-temperature alloy workpiece to be treated is ultrasonically cleaned in deionized water and alcohol until the surface of the workpiece is clean. (2) The cleaned workpiece is used as the anode and the graphite rod is used as the cathode. The workpiece is immersed in a neutral salt solution or ammonium sulfate solution composed of ammonium fluoride solution and potassium fluoride solution. The thermal barrier coating is removed by applying voltage in a voltage stabilization mode. (3) After removing the coating, the workpiece is ultrasonically cleaned in deionized water and alcohol in sequence, then dried and placed in a container with a buffer material for later use to maintain the material properties.

2. The method for removing thermal barrier coatings based on plasma electrolysis technology according to claim 1, characterized in that, In step (2), the mass concentration of ammonium fluoride solution is 3%~4%, the mass concentration of potassium fluoride solution is 3%~4%, and the mass ratio of ammonium fluoride solution to potassium fluoride solution is 1:

3.

3. The method for removing thermal barrier coatings based on plasma electrolysis technology according to claim 1, characterized in that, In step (2), the mass concentration of both ammonium fluoride solution and potassium fluoride solution is 3.5%, and the mass ratio of ammonium fluoride solution to potassium fluoride solution is 1:(2~5).

4. The method for removing thermal barrier coatings based on plasma electrolysis technology according to claim 1, characterized in that, In step (2), the mass concentration of the ammonium sulfate solution is 1% to 5%.

5. The method for removing thermal barrier coatings based on plasma electrolysis technology according to claim 1, characterized in that, In step (2), the voltage is 220V~280V.

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