Precipitation strengthening high-temperature alloy metallographic corrosion method and metallographic corrosive agent thereof

Abstract

The invention discloses a precipitation strengthening high-temperature alloy metallographic corrosion method and a metallographic corrosive agent thereof, and belongs to the technical field of high-temperature alloy materials. The metallographic corrosion method comprises the steps that a high-temperature alloy sample subjected to mechanical polishing treatment is corroded through metallographic corrosion liquid till a black corrosion layer is formed on the surface of the sample, and then the sample is washed through clear water and ethyl alcohol and dried; and wiping the surface of the treated high-temperature alloy sample by using a cotton swab soaked in the metallographic corrosive liquid to remove the black corrosion layer, then washing by using clear water and alcohol, and drying. According to the method, two times of chemical corrosion are adopted, gamma'phase particles in different types of high-temperature alloys for the ultra-supercritical unit are displayed through a simple chemical corrosion method under the condition that a corrosive agent formula and test parameters are not changed, and meanwhile the morphology of crystal grains and crystal boundaries and carbides in the crystal grains are displayed.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy materials technology, specifically relating to a precipitation-strengthened high-temperature alloy metallographic corrosion method and its metallographic etchant. Background Technology

[0002] To address global climate change and improve energy efficiency, developing high-parameter, large-capacity ultra-supercritical power generation technology is the core direction for the future of coal-fired power. The high temperature (>600℃), high pressure (>25MPa), and harsh steam environment of high-parameter ultra-supercritical thermal power generating units pose extremely severe challenges to key structural materials. Precipitation-strengthened iron-based superalloys, nickel-iron-based superalloys, nickel-based superalloys, and nickel-cobalt-based superalloys, due to their excellent high-temperature strength, creep resistance, corrosion resistance, and oxidation resistance, have become irreplaceable materials for manufacturing key components of high-parameter ultra-supercritical units (such as boiler superheaters / reheaters).

[0003] The microstructure of precipitation-strengthened high-temperature alloys in high-parameter ultra-supercritical units mainly consists of a matrix γ phase, a strengthening γ′ phase, and grain boundary carbides. The high-temperature mechanical properties of these alloys are closely related not only to the size, morphology, volume fraction, and spatial distribution of the γ′ phase, but also to the microstructural characteristics of the grain boundary carbides. Therefore, in-depth research is urgently needed on the precipitation behavior and evolution of the strengthening phase in these alloys.

[0004] Currently, the main metallographic preparation methods for high-temperature alloys are chemical etching and electrolytic etching. With chemical etching, the γ′ phase particles are severely eroded after etching using existing techniques, leaving only the γ matrix and carbides in the alloy metallographic sample, preventing the γ′ phase particles from being visible. With electrolytic etching, the γ matrix in the alloy metallographic sample is dissolved, revealing the γ′ phase particles; however, the carbides in the alloy are also severely corroded, making their characteristics undetectable. Furthermore, this method requires specialized electrolytic polishing / etching equipment, making the process complex and difficult to operate. During electrolytic etching, the current density is concentrated at the sample edges and sharp corners, resulting in over-etching in these areas while the central area is under-etched, leading to uneven corrosion on the sample surface. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for metallographic corrosion of precipitation-strengthened high-temperature alloys and its metallographic etchant, which can effectively protect the γ′ strengthening phase and carbide precipitate phase while corroding the γ matrix, thereby achieving simultaneous, clear and complete display of the microstructural features of the γ′ phase, carbides, grain boundaries and matrix in high-temperature alloys.

[0006] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for metallographic corrosion of precipitation-strengthened high-temperature alloys, comprising the following steps: Step 1: After mechanical polishing, the high-temperature alloy sample is etched with a metallographic etchant until a black etched layer is formed on the sample surface. Then, it is rinsed with water and alcohol and dried. Step 2: Wipe the surface of the high-temperature alloy sample treated in Step 1 with a cotton swab soaked in the metallographic etchant to remove the black corrosion layer, then rinse with water and alcohol and dry.

[0007] A further improvement of the present invention is that, before step 1, the high-temperature alloy sample is subjected to coarse grinding, fine grinding and mechanical polishing to the metallographic level, then ultrasonically cleaned in an alcohol solution for 1-4 minutes and dried for later use.

[0008] A further improvement of the present invention is that, in step 1, the corrosion time is 5-25 seconds.

[0009] A further improvement of the present invention is that the high-temperature alloy sample processed by the method can display γ′ phase particles, and simultaneously display the morphology of grains and grain boundaries, as well as other precipitated phases distributed within the grains and grain boundaries.

[0010] Secondly, the present invention also provides a metallographic etchant for the above-mentioned metallographic etching method, comprising an acid and an organic corrosion inhibitor, wherein the volume ratio of the acid to the organic corrosion inhibitor is 20.2-40.5:12-21.

[0011] A further improvement of the present invention is that the acidic substances include hydrochloric acid, nitric acid and molybdic acid, wherein the ratio of hydrochloric acid, nitric acid and molybdic acid is 10mL-20mL: 10mL-20mL: 0.2g-0.5g.

[0012] A further improvement of the present invention is that the mass concentration of the hydrochloric acid is 36%-38%, the mass concentration of the nitric acid is 65%-68%, and the molybdic acid is an analytical grade reagent.

[0013] A further improvement of the present invention is that the organic corrosion inhibitor comprises deionized water, ethylene glycol and methanol, wherein the volume ratio of deionized water, ethylene glycol and methanol is 1:(0.8-1.2):(0.8-1.2).

[0014] A further improvement of the present invention is that its preparation method includes: first adding molybdenum acid to hydrochloric acid and stirring until the molybdenum acid is completely dissolved to form a mixed acid solution; then adding nitric acid and an organic corrosion inhibitor to the mixed acid solution, mixing evenly, and letting it stand for 3-5 minutes to obtain the solution.

[0015] A further improvement of the present invention is that the metallographic etchant is suitable for iron-based high-temperature alloys, nickel-iron-based high-temperature alloys, nickel-based high-temperature alloys, or nickel-cobalt-based high-temperature alloys used in γ′ phase-strengthened ultra-supercritical units.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a precipitation-strengthened high-temperature alloy metallographic etching method. This two-step etching process enables clear and accurate visualization of the γ′ phase in various types of high-temperature alloys, including iron-based, nickel-iron, nickel-based, and nickel-cobalt-based high-temperature alloys used in ultra-supercritical power units. First, a pre-etching stage forms a loose corrosion protective layer on the sample surface, reducing the etching rate and preventing the dissolution of γ′ phase particles, thus significantly improving the contrast and imaging effect of the γ′ phase. Second, the black corrosion layer formed during pre-etching is removed by wiping with a cotton swab soaked in metallographic etchant, avoiding over-etching and thus clearly and accurately revealing the microstructure details of the high-temperature alloy. This method, without changing the metallographic etchant formulation and experimental parameters, can use ordinary chemical etching methods to etch and reveal the γ′ phase in various types of ultra-supercritical high-temperature alloys used in units. At the same time, it obtains the outline and morphology of precipitated phases such as grain boundaries, grain boundary carbides, and intragranular carbides, which facilitates the observation and analysis of grain size, etc. Nickel-based and nickel-iron-based high-temperature alloys treated by this method can also simultaneously reveal the morphology of grains and grain boundaries, as well as the carbides inside the grains.

[0017] This invention also provides a metallographic etchant that achieves a fine balance between corrosivity and inhibition by compounding an acidic substance with an organic corrosion inhibitor in a specific volume ratio. Specifically, the acidic substance provides the necessary corrosion kinetics to erode the γ matrix, while the organic corrosion inhibitor forms a protective film on the surface of key phases such as the γ′ phase and carbides to significantly slow down their dissolution rate, ultimately achieving an optimal dynamic balance between the two. Simultaneously, this formulation effectively avoids localized corrosion phenomena such as pitting corrosion, ensuring uniform corrosion across the entire observation surface of the sample, without over- or under-corrosion areas, significantly improving the reliability and reproducibility of metallographic observation. Furthermore, this volume ratio design reduces reliance on operator experience and allows for wide application in the microstructure analysis of various types of high-temperature alloys used in γ′ phase-strengthened ultra-supercritical units, including iron-based, nickel-iron-based, nickel-based, and nickel-cobalt-based alloys, demonstrating high technical and practical value.

[0018] Furthermore, the organic corrosion inhibitors in this corrosion agent formulation, such as ethylene glycol and methanol, can significantly slow down the corrosion rate of acidic substances such as hydrochloric acid and nitric acid on the alloy matrix, preventing the dissolution of γ′ phase particles or local over-corrosion caused by excessively rapid reaction, thereby ensuring the uniformity and controllability of the corrosion process and obtaining a high-contrast γ′ phase morphology. Attached Figure Description

[0019] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way. Furthermore, the shapes and proportions of the components in the drawings are merely illustrative to aid in understanding the invention and do not specifically limit the shapes and proportions of the components of the invention.

[0020] Figure 1 The image shows a scanning electron microscope image of the γ / γ′ microstructure in a deformed nickel-iron-based high-temperature alloy obtained by corrosion treatment using the method of this invention. Figure 2 These are scanning electron microscope images of the internal grains and grain boundary carbides of deformed nickel-iron nickel-based superalloys obtained by corrosion treatment using the method of this invention. Figure 3 These are scanning electron microscope images of the γ / γ′ microstructure in deformed iron-based superalloys after aging heat treatment using the etchant of this invention. Figure 4 These are scanning electron microscope images of the γ / γ′ microstructure of Haynes 282 alloy, a deformed nickel-based superalloy obtained by aging heat treatment using the etchant of this invention. Figure 5 This is a scanning electron microscope image of the γ / γ′ microstructure in the Inconel 617B alloy, a deformed nickel-cobalt-based superalloy obtained by the present invention. Figure 6 Scanning electron microscope images of the microstructure of the deformed nickel-iron-based superalloy obtained by corrosion treatment using the chemical reagents and methods of Comparative Example 1. Figure 7 Scanning electron microscope images of the microstructure of the deformed iron-based superalloy obtained by corrosion treatment using the chemical reagents and methods of Comparative Example 2. Figure 8 Scanning electron microscope images of the microstructure of the deformed nickel-based superalloy Haynes 282 obtained by treatment with the chemical reagents and methods of Comparative Example 3. Figure 9 Scanning electron microscope (SEM) images of the microstructure of the deformed nickel-cobalt-based superalloy Inconel 617B obtained by treatment with the chemical reagents and methods of Comparative Example 3. Detailed Implementation

[0021] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0022] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0023] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0024] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0025] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0026] This invention provides a method for metallographic corrosion of precipitation-strengthened high-temperature alloys, comprising the following steps: Step 1, Pretreatment: The high-temperature alloy sample is subjected to coarse grinding, fine grinding and mechanical polishing to the metallographic level, then ultrasonically cleaned in alcohol solution for 1-4 minutes, and dried for later use. Step 2, Pre-etching: The high-temperature alloy sample after mechanical polishing is etched with a metallographic etchant for 10-25 seconds until a black etched layer is formed on the sample surface. Then it is rinsed with water and alcohol and dried. Step 3, metallographic wiping and etching: Wipe the surface of the high-temperature alloy sample treated in Step 1 with a cotton swab soaked in the metallographic etchant to remove the black corrosion layer. Then rinse with water and alcohol. After etching, the sample surface is bright white and there is no obvious corrosion gradation phenomenon observed by the naked eye. The surface corrosion color is uniform and there are no obvious pits. The γ′ phase in the microstructure can then be observed and analyzed by scanning electron microscopy.

[0027] The present invention also provides a metallographic etchant for the above-mentioned metallographic etching method, the metallographic etchant comprising an acid and an organic corrosion inhibitor, wherein the volume ratio of the acid to the organic corrosion inhibitor is 20.2-40.5:12-21.

[0028] As a preferred embodiment, the acidic substances include hydrochloric acid, nitric acid, and molybdic acid, wherein the hydrochloric acid has a mass concentration of 36%-38%, the nitric acid has a mass concentration of 65%-68%, and the molybdic acid is an analytical grade reagent. Organic corrosion inhibitors include deionized water, ethylene glycol, and methanol.

[0029] Preferably, the metallographic etchant is prepared from 10-20 ml of nitric acid, 10-20 ml of hydrochloric acid, 0.2-0.5 g of molybdic acid, 4-7 ml of deionized water, 4-7 ml of ethylene glycol, and 4-7 ml of methanol. All chemical reagents used are analytical grade standards and are used to visualize the γ′ phase in high-temperature alloys used in ultra-supercritical power units.

[0030] The preparation method includes: first, adding molybdenum acid to hydrochloric acid and stirring until the molybdenum acid is completely dissolved to form a mixed acid solution; then, adding a measured amount of nitric acid and an organic corrosion inhibitor to the mixed acid solution, mixing evenly, and letting it stand for 3-5 minutes to obtain the solution.

[0031] The method of using the metallographic etchant is as follows: place the mechanically polished γ′ phase-strengthened ultra-supercritical unit iron-based high-temperature alloy, nickel-iron-based high-temperature alloy, nickel-based high-temperature alloy and nickel-cobalt-based high-temperature alloy in the metallographic etchant and perform chemical etching according to the above etching method. Then, the high-temperature alloy after chemical etching can show γ′ phase particles, and at the same time show the morphology of grains and grain boundaries, as well as other precipitated phases distributed in the grains and grain boundaries.

[0032] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0033] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0034] Example 1 In this embodiment, the nickel-iron-chromium-based high-temperature alloy in the patent application No. 201210513438.0 entitled "A High-Strength Corrosion-Resistant Nickel-Iron-Chromium-Based High-Temperature Alloy and Its Preparation Method" is used for chemical corrosion.

[0035] Before the alloy is etched, it is first ground and cleaned. The sample to be observed is polished to metallographic level through multiple passes before etching. Then the sample surface is immersed in an alcohol solution and ultrasonically cleaned for 2 minutes. Finally, the surface is dried.

[0036] The chemical etching of the sample is carried out in two steps, specifically including: Step 1, Pre-etching: Place the sample in a metallographic etchant prepared by 0.4g molybdic acid + 15ml hydrochloric acid + 6ml deionized water + 7ml ethylene glycol + 6ml methanol + 15ml nitric acid and let it stand for 5 seconds. After a black etching layer forms on the polished surface of the sample, clean it with water and alcohol and dry it. Step 2, metallographic wiping and etching: Use cotton swabs soaked in a metallographic etchant prepared by 0.4g molybdic acid + 15ml hydrochloric acid + 6ml deionized water + 7ml ethylene glycol + 6ml methanol + 15ml nitric acid to remove the black corrosion layer on the surface of the high-temperature alloy after pre-etching treatment. Then rinse with water and alcohol and dry.

[0037] Scanning electron microscopy allows for clear observation of the distributed γ′ phase within the grains and the carbides at the grain boundaries, such as... Figure 1 and Figure 2 As shown.

[0038] Example 2 In this embodiment, the iron-nickel-based superalloy used in the application with application number 201911296733.3, entitled "A High-Strength, High-Toughness, and Oxidation-Resistant Iron-Nickel-Based Superalloy and Its Preparation Method", is subjected to chemical corrosion.

[0039] Before the alloy is etched, it is first ground and cleaned. The sample to be observed is polished to metallographic level through multiple passes before etching. Then the sample surface is immersed in an alcohol solution and ultrasonically cleaned for 3 minutes. Finally, the surface is dried.

[0040] The chemical etching of the sample is carried out in two steps, specifically including: Step 1, Pre-etching: Place the sample in a metallographic etchant prepared by 0.3g molybdic acid + 10ml hydrochloric acid + 5ml deionized water + 4ml ethylene glycol + 4ml methanol + 12.5ml nitric acid and let it stand for 10 seconds. After a black etching layer forms on the polished surface of the sample, clean it with water and alcohol and dry it. Step 2, metallographic wiping and etching: Use cotton swabs soaked in a metallographic etchant prepared by 0.3g molybdic acid + 10ml hydrochloric acid + 5ml deionized water + 4ml ethylene glycol + 4ml methanol + 12.5ml nitric acid to remove the black corrosion layer on the surface of the high-temperature alloy after pre-etching treatment. Then rinse with water and alcohol and dry.

[0041] The γ′ phase distributed within the grains can be clearly observed using a scanning electron microscope, such as... Figure 3 As shown.

[0042] Example 3 In this embodiment, a chemical etching method using Haynes 282, a nickel-based high-temperature alloy for commercial ultra-supercritical units, is employed.

[0043] Before the alloy is etched, it is first ground and cleaned. The sample to be observed is polished to metallographic level through multiple passes before etching. Then the sample surface is immersed in alcohol solution and ultrasonically cleaned for 4 minutes. Finally, the surface is dried.

[0044] The chemical etching of the sample is carried out in two steps, specifically including: Step 1, Pre-etching: Place the sample in a metallographic etchant prepared by 0.5g molybdic acid + 18ml hydrochloric acid + 5ml deionized water + 5ml ethylene glycol + 5ml methanol + 20ml nitric acid and let it stand for 15 seconds. After a black etching layer forms on the polished surface of the sample, clean it with water and alcohol and dry it. Step 2, metallographic wiping and etching: Use cotton swabs soaked in a metallographic etchant prepared by 0.5g molybdic acid + 18ml hydrochloric acid + 5ml deionized water + 5ml ethylene glycol + 5ml methanol + 20ml nitric acid to remove the black corrosion layer on the surface of the high-temperature alloy after pre-etching treatment. Then rinse with water and alcohol and dry.

[0045] Scanning electron microscopy allows for clear observation of the distributed γ′ phase compounds within the grains, such as... Figure 4 As shown.

[0046] Example 4 In this embodiment, a method for chemical etching of Inconel 617B using a nickel-cobalt-based high-temperature alloy for commercial ultra-supercritical units is employed.

[0047] Before the alloy is etched, it is first ground and cleaned. The sample to be observed is polished to metallographic level through multiple passes before etching. Then the sample surface is immersed in alcohol solution and ultrasonically cleaned for 4 minutes. Finally, the surface is dried.

[0048] The chemical etching of the sample is carried out in two steps, specifically including: Step 1, Pre-etching: Place the sample in a metallographic etchant prepared by 0.4g molybdic acid + 10ml hydrochloric acid + 7ml deionized water + 7ml ethylene glycol + 7ml methanol + 15ml nitric acid and let it stand for 25 seconds. After a black etching layer forms on the polished surface of the sample, clean it with water and alcohol and dry it. Step 2, metallographic wiping and etching: Use cotton swabs soaked in a metallographic etchant prepared by 0.4g molybdic acid + 10ml hydrochloric acid + 7ml deionized water + 7ml ethylene glycol + 7ml methanol + 15ml nitric acid to remove the black corrosion layer on the surface of the high-temperature alloy after pre-etching treatment. Then rinse with water and alcohol and dry.

[0049] Scanning electron microscopy allows for clear observation of the distributed γ′ phase compounds within the grains, such as... Figure 5 As shown.

[0050] Comparative Example 1 A etchant prepared from 0.4g molybdic acid + 15ml hydrochloric acid + 6ml deionized water + 6ml ethylene glycol + 6ml methanol + 15ml nitric acid was used to chemically etch the nickel-iron-chromium-based superalloy in application number 201210513438.0, entitled "A High-Strength Corrosion-Resistant Nickel-Iron-Chromium-Based Superalloy and Its Preparation Method Thereof," using a conventional method. This etchant completely dissolved the γ′ phase, making it impossible to accurately display the morphology and distribution of the γ′ phase. Figure 6 As shown.

[0051] Comparative Example 2 A mixture of 20g copper sulfate, 100mL hydrochloric acid, 5mL sulfuric acid, and 80mL water was used to chemically corrode the iron-nickel-based superalloy described in application number 201911296733.3, entitled "A High-Strength, High-Toughness, and Oxidation-Resistant Iron-Nickel-Based Superalloy and Its Preparation Method Thereof." Figure 7 As shown. Comparison Figure 3 It is evident that the etchant simultaneously corroded both the matrix and the γ′ phase. Consequently, the γ′ phase particles could not be visualized.

[0052] Comparative Example 3 A conventional chemical etching process was performed on Haynes 282, a nickel-based high-temperature alloy used in commercial ultra-supercritical power units, using a mixture of 0.5g molybdic acid, 18ml hydrochloric acid, 5ml deionized water, 5ml ethylene glycol, 5ml methanol, and 20ml nitric acid. The resulting microstructure resembled the following: Figure 8 As shown. Comparison Figure 4 It can be seen that the etchant cannot clearly show the γ′ phase particles in the alloy, and the etchant often strongly corrodes the matrix, leaving large corrosion pits, which greatly interferes with the accurate measurement of the γ′ phase particle size.

[0053] Comparative Example 4 A conventional chemical etching process was performed on Inconel 617B, a nickel-based high-temperature alloy used in commercial ultra-supercritical power units, using a mixture of 20g copper sulfate, 100mL hydrochloric acid, 5mL sulfuric acid, and 80mL water. The morphology of its microstructure resembled that of... Figure 9 As shown. Comparison Figure 5It can be seen that the etchant cannot clearly show the γ′ phase particles in the alloy, and the etchant often strongly corrodes the matrix, leaving large corrosion pits, which greatly interferes with the accurate measurement of the γ′ phase particle size.

[0054] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for metallographic corrosion of precipitation-strengthened high-temperature alloys, characterized in that, Includes the following steps: Step 1: After mechanical polishing, the high-temperature alloy sample is etched with a metallographic etchant until a black etched layer is formed on the sample surface. Then, it is rinsed with water and alcohol and dried. Step 2: Wipe the surface of the high-temperature alloy sample treated in Step 1 with a cotton swab soaked in the metallographic etchant to remove the black corrosion layer, then rinse with water and alcohol and dry.

2. The method for precipitation-strengthened high-temperature alloy metallographic corrosion according to claim 1, characterized in that, Before step 1, the high-temperature alloy sample is subjected to coarse grinding, fine grinding and mechanical polishing to the metallographic level, then ultrasonically cleaned in an alcohol solution for 1-4 minutes and dried for later use.

3. The method for precipitation-strengthened high-temperature alloy metallographic corrosion according to claim 1, characterized in that, In step 1, the corrosion time is 5-25 seconds.

4. The method for precipitation-strengthened high-temperature alloy metallographic corrosion according to claim 1, characterized in that, The high-temperature alloy sample processed by the method can display γ′ phase particles, as well as the morphology of grains and grain boundaries, and other precipitates distributed within and at the grain boundaries.

5. A metallographic etchant for use in the metallographic etching method as described in claim 1, characterized in that, It includes acidic substances and organic corrosion inhibitors, wherein the volume ratio of the acidic substances to the organic corrosion inhibitors is 20.2-40.5:12-21.

6. The metallographic etchant according to claim 5, characterized in that, The acidic substances include hydrochloric acid, nitric acid, and molybdic acid, wherein the ratio of hydrochloric acid, nitric acid, and molybdic acid is 10mL-20mL: 10mL-20mL: 0.2g-0.5g.

7. The metallographic etchant according to claim 6, characterized in that, The hydrochloric acid has a mass concentration of 36%-38%, the nitric acid has a mass concentration of 65%-68%, and the molybdic acid is an analytical grade reagent.

8. The metallographic etchant according to claim 5, characterized in that, The organic corrosion inhibitor comprises deionized water, ethylene glycol, and methanol, wherein the volume ratio of deionized water, ethylene glycol, and methanol is 1:(0.8-1.2):(0.8-1.2).

9. The metallographic etchant according to claim 5, characterized in that, The preparation method includes: first, adding molybdenum acid to hydrochloric acid and stirring until the molybdenum acid is completely dissolved to form a mixed acid solution; then, adding nitric acid and an organic corrosion inhibitor to the mixed acid solution, mixing evenly, and letting it stand for 3-5 minutes to obtain the solution.

10. A metallographic etchant according to claim 5, characterized in that, The metallographic etchant is suitable for iron-based superalloys, nickel-iron-based superalloys, nickel-based superalloys, or nickel-cobalt-based superalloys used in γ′ phase-strengthened ultra-supercritical units.

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