A corrosion solution for CMSX-4 nickel-based single crystal superalloys and methods of preparation and use thereof

Abstract

The application relates to the technical field of alloy corrosion technology, and particularly discloses a corrosion solution for CMSX-4 nickel-based single-crystal high-temperature alloy and a preparation and use method thereof. The corrosion solution is composed of the following components: perchloric acid, concentrated nitric acid, distilled water and liquid soap. The ratio of the components is as follows: perchloric acid: nitric acid: distilled water: liquid soap is equal to 8-12 ml: 8-12 ml: 30 ml: 1 drop (0.04-0.06 ml) of liquid soap. The corrosion solution can not only quickly and efficiently corrode the metallographic structure of the CMSX-4 alloy, but also can obtain higher contrast by selectively corroding the gamma prime phase compared with the existing traditional corrosion solution. The microstructure resolution under a scanning electron microscope is much higher than that of other corrosion methods, and even reaches the level of a transmission electron microscope. The nanoscale secondary gamma prime phase and phase interface groove morphology can be clearly observed, which has important significance for the characterization and quantitative statistics of the nanoscale microstructure under a large field of view.

Description

Technical Field

[0001] This application belongs to the field of corrosion technology of nickel-based single crystal superalloys, specifically relating to a corrosion solution for CMSX-4 nickel-based single crystal superalloy and its preparation and application methods. Background Technology

[0002] High-temperature alloys are metallic materials based on iron, nickel, and cobalt, capable of long-term operation at temperatures above 600℃ and under certain stress. They possess excellent high-temperature strength, creep resistance, and structural stability. Single-crystal high-temperature alloys eliminate grain boundaries, reducing the use of grain boundary strengthening elements and significantly improving their overall performance. For the second-generation nickel-based single-crystal high-temperature alloy CMSX-4, 3% Re was added to enhance its high-temperature resistance. Its microstructure consists of γ and γ′ phases. After standard heat treatment, a large number of cubic γ′ phases are uniformly distributed in the continuous γ phase matrix, giving the alloy excellent high-temperature strength, making it a primary material for manufacturing turbine blades for aero engines and gas turbines.

[0003] Compared to traditional superalloys, single-crystal superalloys exhibit a uniform overall orientation, thus eliminating the need for grain boundary corrosion studies to investigate grain characteristics. Conversely, single-crystal superalloys contain a high proportion of γ′ strengthening phases (typically 60%–70%) in their matrix, significantly impacting their mechanical properties. Therefore, focusing on the morphology and interfacial evolution of the γ′ phase is crucial for understanding the alloy's deformation mechanism and improving its service performance. However, the γ′ phase is generally very small. After standard heat treatment, its size is typically 200–600 nm, and nanoscale grooves exist at the interface, making precise observation and characterization of the intrinsic features and interfacial evolution of the γ′ phase extremely difficult. Furthermore, extremely fine secondary γ′ phases, only tens of nanometers in size, precipitate within the matrix channels. Existing corrosion processes, such as those using aqua regia or Karin reagents, often lack sufficient contrast under a scanning electron microscope. Although transmission electron microscopy (TEM) can be used to observe nanoscale γ′ phase characteristics, its complex sample preparation process, high testing costs, and limitation to localized features within micro-regions make it difficult to observe the overall morphology, significantly increasing the difficulty of quantitative statistics. Therefore, there is an urgent need for a simple, efficient, and effective etchant and etching method with high microstructural contrast. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a fast, efficient, and better corrosion contrast etching solution for CMSX-4 nickel-based single-crystal superalloys.

[0005] Another objective of this invention is to provide a method for preparing and using CMSX-4 nickel-based single-crystal superalloy etching solution. This method can be extended to other nickel-based single-crystal superalloy fields.

[0006] Specifically, the first aspect of this application provides a corrosion solution for CMSX-4 nickel-based single crystal high-temperature alloy, the corrosion solution comprising the following components: perchloric acid, concentrated nitric acid, distilled water, and liquid soap, the ratio of these four components being: perchloric acid: nitric acid: distilled water: liquid soap equals: 8-12 ml: 8-12 ml: 30 ml: 1 drop (0.04-0.06 ml) of liquid soap.

[0007] As further clarification of this application, the ratio of perchloric acid: concentrated nitric acid: distilled water: liquid soap is 10 ml: 10 ml: 30 ml: 0.05 ml.

[0008] As a further explanation of this application, the concentration of the perchloric acid is 70-72%; the concentration of the concentrated nitric acid is 65-68%; and the pH value of the liquid soap is 8-9.

[0009] As a further explanation of this application, the etching solution is capable of selectively etching and adhering the γ′ phase of the CMSX-4 nickel-based single crystal superalloy.

[0010] As a further explanation of this application, the composition of the CMSX-4 nickel-based single crystal superalloy, by mass percentage, includes: Al: 5.45%~5.75%; Co: 9.3%-10.0%; Cr: 6.2%-6.6%; Hf: 0.07%-0.12%; Mo: 0.5%-0.7%; Re: 2.8%-3.2%; Ta: 6.3%-6.7%; Ti: 0.7%-1.2%; W: 6.2%-6.6%.

[0011] A second aspect of this application provides a method for preparing the etching solution of the above-mentioned CMSX-4 nickel-based single crystal superalloy, the method comprising the following steps:

[0012] Step 1: Use a graduated cylinder and dropper to measure distilled water and put it into a beaker;

[0013] Step 2: Slowly pour the perchloric acid along the wall of the container into the distilled water while stirring constantly to prevent splashing.

[0014] Step 3: Slowly pour in concentrated nitric acid and stir well;

[0015] Step 4: Add liquid soap and continue stirring. After stirring evenly, let it stand for at least 10 minutes.

[0016] A third aspect of this application provides a method for using the etching solution of the above-mentioned CMSX-4 nickel-based single crystal high-temperature alloy, the method comprising the following steps:

[0017] Step 1: Place the pretreated CMSX-4 nickel-based single crystal high-temperature alloy metallographic sample into the prepared CMSX-4 nickel-based single crystal high-temperature alloy etching solution, so that the etching solution completely submerges the surface of the metallographic sample, and etch for 120-180 seconds at room temperature.

[0018] Step 2: Clean and dry the etched metallographic sample for observation of its microstructure.

[0019] As a further explanation of this application, the preprocessing procedure in step 1 specifically includes:

[0020] CMSX-4 nickel-based single crystal superalloy, after directional solidification or heat treatment, was wire-cut to prepare metallographic specimens of suitable size.

[0021] Use low-grit sandpaper to polish the metallographic sample to remove the surface oxide scale;

[0022] Grinding with metallographic sandpaper of different grit sizes removes coarse scratches from the surface;

[0023] Polishing is performed sequentially using diamond polishing paste and water on a metallographic polishing machine to remove the surface stress layer and fine scratches.

[0024] Rinse the surface of the metallographic sample with water, then rinse it with alcohol, and finally dry it with a hair dryer.

[0025] As a further explanation of this application, the preferred size of the metallographic specimen obtained by the wire cutting is 10×10×8mm.

[0026] As a further explanation of this application, the grit size of the low-mesh sandpaper is 240 mesh;

[0027] The grinding process using metallographic sandpaper of different grit sizes specifically includes: first, using 400-mesh, 800-mesh, and 1000-mesh metallographic sandpaper to perform rapid metallographic grinding on the metallographic sample, and then using 1500-mesh and 2000-mesh metallographic sandpaper to perform slow metallographic grinding on the metallographic sample.

[0028] As a further explanation of this application, the polishing process using diamond polishing paste and water sequentially on a metallographic polishing machine specifically includes:

[0029] First, polish the metallographic sample on a metallographic polishing machine using 1.5-micron diamond polishing paste. When the surface of the metallographic sample is observed to be smooth and without obvious scratches, replace the polishing cloth with a clean one and then polish the metallographic sample with 0.25-micron diamond polishing paste. When the surface of the metallographic sample is observed to be smooth and without any scratches, replace the polishing cloth with a clean one and use distilled water as a lubricant for polishing for 100-120 seconds.

[0030] As a further explanation of this application, step 2 above involves cleaning and drying the corroded metallographic sample, specifically including:

[0031] The surface of the metallographic sample after corrosion was rinsed with distilled water and then rinsed with alcohol.

[0032] Dry the metallographic sample with a hair dryer, and then observe the microstructure using a scanning electron microscope.

[0033] This invention utilizes the difference in corrosion resistance between the γ′ phase and the γ matrix to selectively corrode and adhere the γ′ phase by preparing a specific corrosion solution, thereby greatly improving the morphological contrast of the alloy under a scanning electron microscope.

[0034] By comparing the microstructure of CMSX-4 alloy etched using a conventional etching solution (Kalin's reagent) under a scanning electron microscope... Figure 1 Microstructure of CMSX-4 alloy after etching with the etching solution of the present invention under a scanning electron microscope Figure 2 and Figure 3 As can be seen, after etching using traditional methods, the microstructure becomes blurred at magnification of 30,000 times, the γ′ phase interface outline is unclear, and it is difficult to distinguish the secondary γ′ phase in the matrix channels. However, after etching using the method of this invention, the image contrast is high, the microstructure is clearly visible, the γ′ phase interface outline is sharp, and the presence of phase interface grooves can be clearly characterized. Secondary γ′ phases of tens or even several nanometers can be observed in the matrix channels, and the image remains clear even at magnification of 100,000 times.

[0035] By comparing tissues under a transmission electron microscope Figure 4 Microstructure of CMSX-4 alloy after etching with the etching solution of the present invention under a scanning electron microscope Figure 2 and Figure 3 It can be seen that after etching using the method of this invention, the characterization effect of the alloy under a scanning electron microscope can reach or even exceed the level of transmission electron microscopy. Furthermore, compared to transmission electron microscopy, this method is simpler to prepare samples and allows for extensive observation and precise quantitative statistics of the microstructure under a large field of view, demonstrating significant advantages.

[0036] This invention utilizes the difference in corrosion resistance between the γ′ phase and the γ matrix to selectively corrode and adhere the γ′ phase by preparing a specific corrosion solution, thereby significantly improving the morphological contrast of the alloy under a scanning electron microscope. On one hand, the mixture of nitric acid and perchloric acid exhibits strong selective corrosivity towards the γ′ phase; on the other hand, the addition of liquid soap can regulate the etching rate, better control the degree of etching, and prevent damage to the original nanostructure due to the loss of the γ′ phase. Furthermore, the surfactants in the liquid soap can reduce the surface tension of the sample and improve the wettability of the corrosion reagent, thereby enhancing the morphological contrast and corrosion effect of the sample.

[0037] Compared with the prior art, this application has the following beneficial technical effects:

[0038] The CMSX-4 nickel-based single-crystal superalloy etching solution of this invention can easily and efficiently etch out the metallographic structure of CMSX-4 alloy, and the contrast of the alloy's microstructure is greatly improved. Under a scanning electron microscope, several nanometer-scale fine precipitates can be clearly distinguished, with high image clarity and sharp visible phase interfaces. The characterization effect can reach or even exceed the level of transmission electron microscopy, demonstrating significant advantages. In addition, the etching method proposed in this invention has a certain degree of universality and can be reasonably extended to other nickel-based single-crystal superalloy fields. For single-crystal superalloys, studying the evolution of microstructure is an important means to analyze its deformation mechanism and improve the service life of the alloy. This invention provides researchers and production and R&D enterprises with a brand-new solution for accurate and quantitative characterization of the microstructure of nickel-based single-crystal superalloys and product defect detection. The method is simple, convenient, and low-cost, with good application prospects and potential economic benefits. Attached Figure Description

[0039] Figure 1 This is a microstructure of CMSX-4 alloy after etching with conventional Carin reagent under a scanning electron microscope.

[0040] Figure 2 This is a microstructure diagram of the CMSX-4 alloy after corrosion in Example 1 of the present invention under a scanning electron microscope;

[0041] Figure 3 This is a microstructure diagram of the CMSX-4 alloy after corrosion under a scanning electron microscope in Example 2 of the present invention;

[0042] Figure 4 These are microstructure images of CMSX-4 alloy under a transmission electron microscope, where (a) is the bright field phase and (b) is the high-angle annular dark field image. Detailed Implementation

[0043] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] Example 1

[0045] The material used in this embodiment is CMSX-4, a second-generation nickel-based single-crystal high-temperature alloy produced by a certain company after standard heat treatment. According to the test, its actual composition by mass percentage is: Al: 5.7%; Co: 9.7%; Cr: 6.4%; Hf: 0.1%; Mo: 0.6%; Re: 3.0%; Ta: 6.4%; Ti: 0.9%; W: 6.4%.

[0046] The etching solution used in this embodiment is a CMSX-4 nickel-based single-crystal high-temperature alloy etching solution, which consists of the following components: 8 ml perchloric acid, 8 ml concentrated nitric acid, 30 ml distilled water, and 1 drop (0.04-0.06 ml) of liquid soap. The concentration of perchloric acid is 70%, the concentration of concentrated nitric acid is 65%, and the pH value of the liquid soap is 8.

[0047] When preparing the CMSX-4 nickel-based single crystal high-temperature alloy etching solution, first measure 30ml of distilled water into a beaker using a graduated cylinder and dropper; then slowly pour 8ml of perchloric acid into the distilled water along the wall of the container while stirring continuously to prevent splashing; subsequently, slowly pour in 8ml of concentrated nitric acid and stir evenly; finally, add 1 drop of liquid soap and continue stirring. After stirring evenly, let it stand for 15 minutes.

[0048] When using the CMSX-4 nickel-based single-crystal high-temperature alloy etching solution, first take a sample of the heat-treated CMSX-4 alloy and cut it into 10×10×8mm metallographic specimens by wire cutting. Then, polish the metallographic specimens with 240-grit sandpaper to remove the oxide scale on the surface. Use 400-grit, 800-grit, and 1000-grit metallographic sandpaper for rapid metallographic grinding, and then use 1500-grit and 2000-grit metallographic sandpaper for slow metallographic grinding to remove coarse scratches on the surface. Before changing to higher-grit sandpaper at each step, ensure that the scratches on the surface of the metallographic specimen are uniform. Then, polish the metallographic specimens on a polishing machine with 1.5-micron diamond polishing paste. When the surface of the metallographic specimen is observed to be bright and smooth without obvious scratches, change to a clean polishing cloth and polish the metallographic specimens with 0.25-micron diamond polishing paste. Once the surface of the metallographic sample is observed to be smooth and free of scratches, replace the polishing cloth with a clean one and polish for 2 minutes using distilled water as a lubricant. Then, rinse the surface of the metallographic sample with distilled water and then with alcohol, and dry the sample with a hairdryer. Place the metallographic sample in the prepared CMSX-4 nickel-based single-crystal high-temperature alloy etching solution at room temperature, ensuring the solution completely wets the sample surface. Use a stopwatch to time the etching process. After 150 seconds, remove the sample with clamps. Rinse the etched surface of the sample with distilled water for 2 minutes to remove any remaining etching solution. Then, wipe the surface with cotton wool soaked in alcohol, and rinse with alcohol. Finally, dry the sample with a hairdryer before using a scanning electron microscope for microscopic observation.

[0049] from Figure 2 As can be seen, the CMSX-4 nickel-based single crystal high-temperature alloy etching solution has a good etching effect, the alloy microstructure is clearly visible, the γ′ phase has high contrast, the interface morphology is clear and sharp, and the presence of nanoscale secondary γ′ phase can be observed in the matrix channel, which facilitates the analysis of microstructure characteristics.

[0050] Example 2

[0051] The material used in this embodiment is CMSX-4 alloy, a second-generation nickel-based single-crystal high-temperature alloy produced by a certain company after standard heat treatment. Its actual composition by mass percentage is as follows: Al: 5.7%; Co: 9.7%; Cr: 6.4%; Hf: 0.1%; Mo: 0.6%; Re: 3.0%; Ta: 6.4%; Ti: 0.9%; W: 6.4%. The concentration of perchloric acid is 70%, the concentration of concentrated nitric acid is 65%, and the pH value of the liquid soap is 8.

[0052] The etching solution used in this embodiment is a CMSX-4 nickel-based single crystal high-temperature alloy etching solution, which consists of the following components: 10 ml perchloric acid, 10 ml concentrated nitric acid, 30 ml distilled water, and 1 drop (0.04-0.06 ml) of liquid soap.

[0053] When preparing the CMSX-4 nickel-based single crystal high-temperature alloy etching solution, first measure 30ml of distilled water into a beaker using a graduated cylinder and dropper; then slowly pour 10ml of perchloric acid into the distilled water along the wall of the container while stirring continuously to prevent splashing; subsequently, slowly pour in 10ml of concentrated nitric acid and stir evenly; finally, add 1 drop of liquid soap and continue stirring. After stirring evenly, let it stand for 15 minutes.

[0054] When using the CMSX-4 nickel-based single-crystal high-temperature alloy etching solution, first take a sample of the heat-treated CMSX-4 alloy and cut it into 10×10×8mm metallographic specimens by wire cutting. Then, polish the metallographic specimens with 240-grit sandpaper to remove the oxide scale on the surface. Use 400-grit, 800-grit, and 1000-grit metallographic sandpaper for rapid metallographic grinding, and then use 1500-grit and 2000-grit metallographic sandpaper for slow metallographic grinding to remove coarse scratches on the surface. Before changing to higher-grit sandpaper at each step, ensure that the scratches on the surface of the metallographic specimen are uniform. Then, polish the metallographic specimens on a polishing machine with 1.5-micron diamond polishing paste. When the surface of the metallographic specimen is observed to be bright and smooth without obvious scratches, change to a clean polishing cloth and polish the metallographic specimens with 0.25-micron diamond polishing paste. Once the surface of the metallographic sample is observed to be smooth and free of scratches, replace the polishing cloth with a clean one and polish for 2 minutes using distilled water as a lubricant. Then, rinse the surface of the metallographic sample with distilled water and then with alcohol, and dry the sample with a hairdryer. Place the metallographic sample in the prepared CMSX-4 nickel-based single-crystal high-temperature alloy etching solution at room temperature, ensuring the solution completely wets the sample surface. Use a stopwatch to time the etching process. After 180 seconds, remove the sample with clamps. Rinse the etched surface of the sample with distilled water for 2 minutes to remove any remaining etching solution. Then, wipe the surface with cotton wool soaked in alcohol, and rinse with alcohol. Finally, dry the sample with a hairdryer before using a scanning electron microscope for microscopic observation.

[0055] from Figure 3 As can be seen, the CMSX-4 nickel-based single crystal high-temperature alloy etching solution has a good etching effect, the alloy microstructure is clearly visible, the γ′ phase has high contrast, the interface morphology is clear and sharp, and the presence of nanoscale secondary γ′ phase can be observed in the matrix channel, which facilitates the analysis of microstructure characteristics.

[0056] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0057] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A corrosion solution for CMSX-4 nickel-based single-crystal superalloy, characterized in that, The corrosive solution comprises the following components: perchloric acid, concentrated nitric acid, distilled water, and liquid soap. The ratio of these four components is: perchloric acid : concentrated nitric acid : distilled water : liquid soap = 8-12 ml : 8-12 ml : 30 ml : 0.04-0.06 ml liquid soap. The concentration of the perchloric acid is 70-72%. The concentration of the concentrated nitric acid is 65-68%. The pH value of the liquid soap is 8-9.

2. The etching solution for CMSX-4 nickel-based single-crystal superalloy as described in claim 1, characterized in that, Perchloric acid: concentrated nitric acid: distilled water: liquid soap equals: 10ml: 10ml: 30ml: 0.05ml.

3. The etching solution for the CMSX-4 nickel-based single-crystal superalloy as described in claim 1, characterized in that, The corrosion solution can selectively corrode and adhere the γ′ phase of the CMSX-4 nickel-based single crystal superalloy.

4. The etching solution for the CMSX-4 nickel-based single-crystal superalloy as described in claim 1, characterized in that, The composition of the CMSX-4 nickel-based single-crystal superalloy, by mass percentage, includes: Al: 5.45%~5.75%; Co: 9.3%-10.0%; Cr: 6.2%-6.6%; Hf: 0.07%-0.12%; Mo: 0.5%-0.7%; Re: 2.8%-3.2%; Ta: 6.3%-6.7%; Ti: 0.7%-1.2%; W: 6.2%-6.6%.

5. A method for preparing an etching solution for the CMSX-4 nickel-based single-crystal superalloy according to any one of claims 1-4, characterized in that, The method includes the following steps: Step 1: Use a graduated cylinder and dropper to measure distilled water and put it into a beaker; Step 2: Slowly pour the perchloric acid along the wall of the container into the distilled water while stirring constantly to prevent splashing. Step 3: Slowly pour in concentrated nitric acid and stir well; Step 4: Add liquid soap and continue stirring. After stirring evenly, let it stand for at least 10 minutes.

6. A method of using the etching solution for CMSX-4 nickel-based single-crystal superalloy according to any one of claims 1-4, characterized in that, The method includes the following steps: Step 1: Place the pretreated CMSX-4 nickel-based single crystal high-temperature alloy metallographic sample into the prepared CMSX-4 nickel-based single crystal high-temperature alloy etching solution, so that the etching solution completely submerges the surface of the metallographic sample, and etch for 120-180 seconds at room temperature. Step 2: Clean and dry the etched metallographic sample for observation of its microstructure.

7. The method of using the etching solution for CMSX-4 nickel-based single-crystal superalloy as described in claim 6, characterized in that, The preprocessing process in step 1 specifically includes: CMSX-4 nickel-based single crystal superalloy, after directional solidification or heat treatment, was wire-cut to prepare metallographic specimens of suitable size. Use low-grit sandpaper to polish the metallographic sample to remove the surface oxide scale; Grinding with metallographic sandpaper of different grit sizes removes coarse scratches from the surface; Polishing is performed sequentially using diamond polishing paste and water on a metallographic polishing machine to remove the surface stress layer and fine scratches. Rinse the surface of the metallographic sample with water, then rinse it with alcohol, and finally dry it with a hair dryer.

8. The method of using the etching solution for CMSX-4 nickel-based single-crystal superalloy as described in claim 7, characterized in that, The low-mesh sandpaper has a grit size of 240 mesh; The grinding process using metallographic sandpaper of different grit sizes specifically includes: first, using 400-mesh, 800-mesh, and 1000-mesh metallographic sandpaper to perform rapid metallographic grinding on the metallographic sample, and then using 1500-mesh and 2000-mesh metallographic sandpaper to perform slow metallographic grinding on the metallographic sample.

9. The method of using the etching solution for CMSX-4 nickel-based single-crystal superalloy as described in claim 7, characterized in that, The process of polishing with diamond polishing paste and water sequentially on a metallographic polishing machine specifically includes: First, polish the metallographic sample on a metallographic polishing machine using 1.5-micron diamond polishing paste. When the surface of the metallographic sample is observed to be smooth and without obvious scratches, replace the polishing cloth with a clean one and then polish the metallographic sample with 0.25-micron diamond polishing paste. When the surface of the metallographic sample is observed to be smooth and without any scratches, replace the polishing cloth with a clean one and use distilled water as a lubricant for polishing for 100-120 seconds.

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