A method for etching and displaying the grain of nickel-chromium alloy

Abstract

The application provides a nickel-chromium alloy etchant and a grain corrosion display method of a nickel-chromium alloy. The nickel-chromium alloy etchant comprises a mixed solution of hydrofluoric acid, nitric acid and water, and the volume ratio of hydrofluoric acid:nitric acid:water is 1:(9-11):(18-22). The nickel-chromium alloy etchant is used for chemical corrosion, the grain display is clear, the metallographic display range is wide, product analysis is more accurate, the process is stable and simple and can be reused, the detection time is short, the result can be obtained quickly, and the production of unqualified products is effectively avoided.

Description

Technical Field

[0001] This invention relates to the field of material corrosion technology, specifically to a method for displaying grain corrosion of nickel-chromium alloys using a nickel-chromium alloy etching agent. Background Technology

[0002] The internal microstructure of metallic materials is directly and closely related to their properties such as hardness, strength, and ductility. Metallographic observation is the most direct and effective method for studying the internal microstructure of metallic materials. Metallography refers to the chemical composition of a metal or alloy, as well as the physical and chemical states of these components within the alloy. In the field of metallic materials, quantitative metallography is generally used to determine the three-dimensional morphology of the metallographic structure. Based on this three-dimensional morphology, a quantitative relationship is established between the constituent components, microstructure, and properties, thereby obtaining information about the characteristic properties of the metallic material. The principle of quantitative metallography is to measure and calculate the metallographic microstructure of the ground surface or thin film of a metallographic sample to determine its three-dimensional morphology.

[0003] To conduct metallographic observation, the metal grains must first be visualized, and then the metallographic structure is observed using a metallographic microscope. Even small metallic materials contain many small crystals. Because these small crystals, with essentially the same lattice phase, have irregular shapes and are granular, they are called "grains." The size and shape of the grains significantly affect the material's properties. Generally, the finer and more uniform the grains, the better the material's overall performance. Grain boundaries in metallographic structures are the interfaces between crystals with the same structure but different orientations. At grain boundaries, atomic arrangement transitions from one orientation to another; therefore, the atomic arrangement at grain boundaries is in a transitional state. Metallic grain boundaries are generally revealed using etching methods, which are extremely important for studying the internal structure of materials.

[0004] With the development of science and technology, the demand for alloy metals in industrial production is increasing. New methods for studying the metallographic structure of novel alloy materials are needed. Nickel-chromium alloys are highly corrosion-resistant alloy materials. To fully reveal the metallographic structure of nickel-chromium alloys, suitable etching agents and display methods are required. Corrosion data for nickel-chromium alloy metallographic samples is very limited, and existing methods for preparing nickel-chromium alloy metallographic solutions and using various etching agent ratios have many shortcomings. Etching nickel-chromium alloy metallographic samples with etching agents prepared in a certain proportion of nitric acid and water, or nitric acid, hydrochloric acid, and water, results in two problems: first, the corrosion time is long; second, the corrosion effect is not obvious, and a clear metallographic structure cannot be observed, with unclear grain boundaries. Increasing the nitric acid or the ratio of nitric acid to hydrochloric acid leads to over-corrosion, causing both grain boundaries and grains to turn black, making it impossible to observe a clear metallographic structure. Therefore, the preparation of the etching agent is extremely crucial to observing a clear metallographic structure with distinct boundaries and contrast between different phases.

[0005] CN 104513985 A discloses a metallographic etching solution and etching method for nickel-chromium alloys. The etching solution is a mixed solution of concentrated nitric acid, concentrated hydrochloric acid, glacial acetic acid, and water, with a volume ratio of 1:1:1:1. The etching method includes: dripping the etching solution onto the etching surface of a nickel-chromium alloy metallographic sample that has been ground and polished, with the etching solution immersing the sample to a depth of 1-2 mm and the etching time being 10 s-10 min; rinsing the sample surface with distilled water for at least 2 minutes; rinsing the sample surface with alcohol, and then wiping the sample surface with degreased cotton soaked in alcohol.

[0006] CN 106501058 A discloses a method for displaying the metallographic structure of a nickel-chromium alloy using an etchant. The etchant comprises a mixed solution of nitric acid and hydrochloric acid; the volume ratio of nitric acid to hydrochloric acid is 1:1, the concentration of nitric acid is 65 wt%, and the concentration of hydrochloric acid is 36 wt%. The metallographic structure display method includes the following steps: grinding the nickel-chromium alloy; mechanically polishing the ground nickel-chromium alloy; immersing the polished nickel-chromium alloy in the etchant for etching; and drying.

[0007] However, for high-precision grinding of nickel-chromium alloys, the grinding surface must be scratch-free, and during immersion, part of the product must be exposed to air while the other part is immersed. Metallographic features should be visible at the interface between the two surfaces when taking images, but not clearly visible in other areas. Therefore, a novel nickel-chromium alloy etchant and a method for revealing the grain corrosion of nickel-chromium alloys are still needed. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides a method for displaying the grain corrosion of nickel-chromium alloys using a nickel-chromium alloy etchant. The nickel-chromium alloy etchant comprises a mixed solution of hydrofluoric acid, nitric acid, and water, and the volume ratio of hydrofluoric acid:nitric acid:water is 1:(9-11):(18-22). Using the aforementioned nickel-chromium alloy etchant for chemical etching results in clear grain display, a wide metallographic display range, more accurate product analysis, a stable and simple process that can be reused, short testing time, and quick results, effectively avoiding the generation of defective products.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] One of the objectives of this invention is to provide a nickel-chromium alloy etching agent comprising a mixed solution of hydrofluoric acid, nitric acid and water, wherein the volume ratio of hydrofluoric acid:nitric acid:water is 1:(9-11):(18-22).

[0011] In this invention, the volume ratio of hydrofluoric acid:nitric acid:water is 1:(9-11):(18-22), for example, 1:9:18, 1:9:20, 1:9:22, 1:10:18, 1:10:20, 1:10:22, 1:11:18, 1:11:20 or 1:11:22, etc.

[0012] Nickel-chromium alloys are corrosion-resistant alloys. If the corrosiveness of the etchant is too low, the metallographic structure of the nickel-chromium alloy cannot be fully displayed; if the corrosiveness of the etchant is too high, the metallographic structure of the nickel-chromium alloy will be over-etched, which will also affect the display effect of the metallographic structure of the nickel-chromium alloy. Therefore, the nickel-chromium alloy etching agent of the present invention includes a mixed solution of hydrofluoric acid, nitric acid and water, and strictly limits the concentration and volume ratio of hydrofluoric acid, nitric acid and water. It can moderately etch the surface of nickel-chromium alloy, thereby fully displaying the metallographic structure of the nickel-chromium alloy.

[0013] As a preferred embodiment of the present invention, the concentration of the hydrofluoric acid is 35-45 wt%, such as 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, or 45 wt%, etc., and the concentration of the nitric acid is 65-68 wt%, such as 65 wt%, 66 wt%, 67 wt%, or 68 wt%, etc.

[0014] It should be noted that tap water can be used to prepare the nickel-chromium alloy etching agent.

[0015] A second objective of this invention is to provide a method for displaying grain corrosion of a nickel-chromium alloy using the nickel-chromium alloy etchant described in the first objective, the method comprising the following steps:

[0016] The nickel-chromium alloy is subjected to grinding, electrolytic polishing, primary cleaning, chemical etching, secondary cleaning, and drying in sequence; wherein, the chemical etching is performed using the nickel-chromium alloy etching agent.

[0017] In this invention, images can be taken from all areas after electropolishing, resulting in a large image area, more accurate product analysis, and relatively lower requirements for grinding.

[0018] As a preferred technical solution of the present invention, the polishing includes: polishing the nickel-chromium alloy sequentially on 240# water-based sandpaper and 1000# water-based sandpaper, using water as a wetting agent.

[0019] As a preferred technical solution of the present invention, the polishing time is 5-10 minutes, such as 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes.

[0020] As a preferred embodiment of the present invention, the electrolyte used in the electropolishing comprises a mixed solution of ethanol, 2-butoxyethanol and perchloric acid, and the volume ratio of ethanol:2-butoxyethanol:perchloric acid is x:y:z=(0.65-0.75):(0.05-0.15):(0.15-0.25), x+y+z=1; wherein the concentration of ethanol is 95wt% and the concentration of perchloric acid is 30wt%.

[0021] In this invention, the volume ratio of ethanol:2-butoxyethanol:perchloric acid is x:y:z=(0.65-0.75):(0.05-0.15):(0.15-0.25), x+y+z=1, for example 0.65:0.15:0.2, 0.65:0.1:0.25, 0.7:0.1:0.2, 0.7:0.15:0.15, 0.75:0.05:0.2 or 0.75:0.1:0.15, etc.

[0022] As a preferred technical solution of the present invention, the voltage of the electropolishing is 35-40V, such as 35V, 36V, 37V, 38V, 39V or 40V.

[0023] As a preferred technical solution of the present invention, the electropolishing time is 50-100s, such as 50s, 60s, 70s, 80s, 90s or 100s.

[0024] As a preferred technical solution of the present invention, the chemical etching includes: using the nickel-chromium alloy etching agent, dripping it onto the electrolytic polishing area of ​​the nickel-chromium alloy, and leaving it for 60-90 seconds, such as 60 seconds, 65 seconds, 70 seconds, 75 seconds, 80 seconds, 85 seconds, or 90 seconds.

[0025] As a preferred technical solution of the present invention, the grain etching display method includes the following steps:

[0026] The nickel-chromium alloy is subjected to grinding, electrolytic polishing, primary cleaning, chemical etching, secondary cleaning, and drying in sequence.

[0027] The polishing process includes: sequentially polishing the nickel-chromium alloy with 240# and 1000# water-based sandpaper, using water as a wetting agent, for 5-10 minutes; the electropolishing process uses an electrolyte comprising a mixture of ethanol, 2-butoxyethanol, and perchloric acid, with a volume ratio of ethanol:2-butoxyethanol:perchloric acid of x:y:z = (0.65-0.75):(0.05-0.15):(0.15-0.25), x+y+z = 1; the concentration of ethanol is 95wt%, and the concentration of perchloric acid is 30wt%; the voltage for electropolishing is 35-40V, and the time is 50-100s; the chemical etching process uses the nickel-chromium alloy etchant; the chemical etching process includes: applying the nickel-chromium alloy etchant to the electropolished area of ​​the nickel-chromium alloy and leaving it for 60-90 seconds.

[0028] Compared with existing technical solutions, the present invention has at least the following beneficial effects:

[0029] This invention provides a method for displaying the grain corrosion of nickel-chromium alloys using a nickel-chromium alloy etchant. The nickel-chromium alloy etchant comprises a mixed solution of hydrofluoric acid, nitric acid, and water, with a volume ratio of hydrofluoric acid:nitric acid:water of 1:(9-11):(18-22). Using this nickel-chromium alloy etchant for chemical etching results in clear grain display, a wide metallographic display range, more accurate product analysis, a stable and simple process that can be reused, short testing time, and rapid results, effectively preventing the generation of defective products. Attached Figure Description

[0030] Figure 1 These are metallographic microscope images observed in Embodiment 1 of the present invention;

[0031] Figure 2 These are metallographic microscope images observed in Embodiment 2 of the present invention;

[0032] Figure 3 These are metallographic microscope images observed in Embodiment 3 of the present invention;

[0033] Figure 4 These are metallographic microscope images observed in Example 4 of the present invention;

[0034] Figure 5 These are metallographic microscope images observed in Embodiment 5 of the present invention;

[0035] Figure 6 These are metallographic microscope images observed in Embodiment 6 of the present invention;

[0036] Figure 7 These are metallographic microscope images observed in Embodiment 7 of the present invention;

[0037] Figure 8These are metallographic microscope images observed in Example 8 of the present invention;

[0038] Figure 9 These are metallographic microscope images observed in Example 9 of the present invention;

[0039] Figure 10 These are metallographic micrographs observed in Comparative Example 1 of this invention;

[0040] Figure 11 This is a metallographic micrograph observed in Comparative Example 2 of this invention. Detailed Implementation

[0041] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0042] To better illustrate the present invention and facilitate understanding of its technical solutions, typical but non-limiting embodiments of the present invention are as follows:

[0043] Example 1

[0044] This embodiment provides a method for revealing grain corrosion in nickel-chromium alloys, comprising the sequential processes of grinding, electrolytic polishing, primary cleaning, chemical etching, secondary cleaning, and drying. The chemical etching uses a nickel-chromium alloy etching agent formulation of: 40wt% hydrofluoric acid, 65wt% nitric acid, and water in a volume ratio of 1:10:20. The electrolytic polishing uses an electrolyte formulation of: 95wt% ethanol, 2-butoxyethanol, and 30wt% perchloric acid in a volume ratio of 7:1:2.

[0045] The method for revealing grain corrosion of nickel-chromium alloys includes the following steps:

[0046] (1) First, polish the nickel-chromium alloy on 240# and 1000# water-based sandpaper in turn for 8 minutes. Use water as a wetting agent and polish until the surface is bright.

[0047] (2) Place the polished nickel-chromium alloy into an electrolytic polishing machine, use the homemade electrolyte, electrolytic polish at 36V for 50 seconds, then take it out and wash it with clean water.

[0048] (3) Use a self-made nickel-chromium alloy etching agent, drop it onto the electrolytic polishing area of ​​the nickel-chromium alloy, leave it for 70 seconds, and then rinse it with clean water;

[0049] (4) After drying the nickel-chromium alloy, observe the metallographic structure in a metallographic microscope and take pictures for analysis.

[0050] The metallographic micrographs observed in this embodiment are as follows: Figure 1As shown, the metallographic structure of the nickel-chromium alloy in this embodiment has a good display effect, while the black spots are product defects and not due to excessive corrosion of the metallographic structure.

[0051] Example 2

[0052] This embodiment provides a method for revealing grain corrosion in nickel-chromium alloys, comprising the sequential processes of grinding, electrolytic polishing, primary cleaning, chemical etching, secondary cleaning, and drying. The chemical etching uses a nickel-chromium alloy etching agent formulation of 40wt% hydrofluoric acid, 65wt% nitric acid, and water in a volume ratio of 1:9:18. The electrolytic polishing uses an electrolyte formulation of 95wt% ethanol, 2-butoxyethanol, and 30wt% perchloric acid in a volume ratio of 7:1:2.

[0053] The method for revealing grain corrosion of nickel-chromium alloys includes the following steps:

[0054] (1) First, polish the nickel-chromium alloy on 240# and 1000# water-based sandpaper in turn for 5 minutes. Use water as a wetting agent and polish until the surface is bright.

[0055] (2) Place the polished nickel-chromium alloy into an electrolytic polishing machine, use the homemade electrolyte, electrolytic polish at 36V for 50 seconds, then take it out and wash it with clean water.

[0056] (3) Use a self-made nickel-chromium alloy etching agent, drop it onto the electrolytic polishing area of ​​the nickel-chromium alloy, leave it for 60 seconds, and then rinse it with clean water.

[0057] (4) After drying the nickel-chromium alloy, observe the metallographic structure in a metallographic microscope and take pictures for analysis.

[0058] The metallographic micrographs observed in this embodiment are as follows: Figure 2 As shown, the metallographic structure of the nickel-chromium alloy in this embodiment has a good display effect.

[0059] Example 3

[0060] This embodiment provides a method for revealing grain corrosion in nickel-chromium alloys, comprising the sequential processes of grinding, electrolytic polishing, primary cleaning, chemical etching, secondary cleaning, and drying. The chemical etching uses a nickel-chromium alloy etching agent formulation of 40 wt% hydrofluoric acid, 65 wt% nitric acid, and water in a volume ratio of 1:11:22. The electrolytic polishing uses an electrolyte formulation of 95 wt% ethanol, 2-butoxyethanol, and 30 wt% perchloric acid in a volume ratio of 7:1:2.

[0061] The method for revealing grain corrosion of nickel-chromium alloys includes the following steps:

[0062] (1) First, polish the nickel-chromium alloy on 240# and 1000# water-based sandpaper in turn for 10 minutes. Use water as a wetting agent and polish until the surface is bright.

[0063] (2) Place the polished nickel-chromium alloy into an electrolytic polishing machine, use the homemade electrolyte, electrolytic polish at 36V for 50 seconds, then take it out and wash it with clean water.

[0064] (3) Use a self-made nickel-chromium alloy etching agent, drop it onto the electrolytic polishing area of ​​the nickel-chromium alloy, leave it for 90 seconds, and then rinse it with clean water.

[0065] (4) After drying the nickel-chromium alloy, observe the metallographic structure in a metallographic microscope and take pictures for analysis.

[0066] The metallographic micrographs observed in this embodiment are as follows: Figure 3 As shown, the metallographic structure of the nickel-chromium alloy in this embodiment has a good display effect.

[0067] Example 4

[0068] This embodiment provides a method for displaying grain corrosion of nickel-chromium alloys. Compared with embodiment 1, the only difference is that the electrolytic polishing in step (2) is replaced by mechanical polishing. Specifically, the nickel-chromium alloy after being polished with 1000# water-based sandpaper is further polished with 1500# water-based sandpaper for 10 minutes. Water is used as a wetting agent and the surface is polished until it is bright.

[0069] The metallographic micrographs observed in this embodiment are as follows: Figure 4 As shown, there are no visible grains and the entire surface is covered with polished scratches.

[0070] Example 5

[0071] This embodiment provides a method for revealing grain corrosion in nickel-chromium alloys. Compared with Embodiment 1, the only difference is that the electrolyte formulation used in electropolishing is adjusted, with the volume ratio of 95wt% ethanol: 2-butoxyethanol: 30wt% perchloric acid being 6:2:2.

[0072] The metallographic micrographs observed in this embodiment are as follows: Figure 5 As shown, the electrolyte can polish the product, but the grain size is poor.

[0073] Example 6

[0074] This embodiment provides a method for displaying grain corrosion of nickel-chromium alloys. Compared with embodiment 1, the only difference is that in step (2), after electropolishing at 30V for 100s, the alloy is taken out and washed with clean water.

[0075] The metallographic micrographs observed in this embodiment are as follows: Figure 6 As shown, it can be seen that the product can be polished under the voltage and time of this electropolishing, but the grain size is poor.

[0076] Example 7

[0077] This embodiment provides a method for displaying grain corrosion of nickel-chromium alloys. Compared with embodiment 1, the only difference is that in step (2), after electrolytic polishing at 45V for 40s, the alloy is taken out and washed with clean water.

[0078] The metallographic micrographs observed in this embodiment are as follows: Figure 7 As shown, it can be seen that the product can be polished under the voltage and time of this electropolishing, but the grain size is poor.

[0079] Example 8

[0080] This embodiment provides a method for grain corrosion display of nickel-chromium alloys. Compared with Embodiment 1, the only difference is that in step (3), the dwell time is reduced to 50s.

[0081] The metallographic micrographs observed in this embodiment are as follows: Figure 8 As shown, the short etching time in the nickel-chromium alloy etchant results in the complete absence of grain boundaries in the metallographic structure of the nickel-chromium alloy, leading to a poor metallographic structure display effect in this embodiment.

[0082] Example 9

[0083] This embodiment provides a method for grain corrosion display of nickel-chromium alloys. Compared with Embodiment 1, the only difference is that in step (3), the dwell time is increased to 100s.

[0084] The metallographic micrographs observed in this embodiment are as follows: Figure 9 As shown, the corrosion time in the etchant for nickel-chromium alloy is relatively long, which leads to excessive corrosion of the metallographic structure of the nickel-chromium alloy and corrosion of some grain boundaries. The metallographic structure of the nickel-chromium alloy in this comparative example is poor.

[0085] Comparative Example 1

[0086] This comparative example provides a method for displaying grain corrosion of nickel-chromium alloys. Compared with Example 1, the only difference is that the formulation of the nickel-chromium alloy etchant used in chemical corrosion is adjusted, with a volume ratio of 40wt% hydrofluoric acid, 65wt% nitric acid, and water of 1:10:16, that is, the acid concentration in the nickel-chromium alloy etchant is increased.

[0087] The metallurgical microscope images observed in this comparative example are as follows: Figure 10As shown, it can be seen that an increase in acid concentration in the nickel-chromium alloy etchant leads to excessive corrosion of the metallographic structure of the nickel-chromium alloy, with some grain boundaries being corroded. The metallographic structure of the nickel-chromium alloy in this comparative example is poorly displayed.

[0088] Comparative Example 2

[0089] This comparative example provides a method for displaying grain corrosion of nickel-chromium alloys. Compared with Example 1, the only difference is that the formulation of the nickel-chromium alloy etchant used in chemical corrosion is adjusted, with a volume ratio of 40wt% hydrofluoric acid, 65wt% nitric acid, and water of 1:10:24, that is, the acid concentration in the nickel-chromium alloy etchant is reduced.

[0090] The metallurgical microscope images observed in this comparative example are as follows: Figure 11 As shown, it can be seen that a decrease in acid concentration in the nickel-chromium alloy etching agent will result in the complete absence of grain boundaries in the metallographic structure of the nickel-chromium alloy, and the metallographic structure display effect of the nickel-chromium alloy in this comparative example is poor.

[0091] In summary, this invention provides a method for displaying the grain corrosion of nickel-chromium alloys using a nickel-chromium alloy etchant. The nickel-chromium alloy etchant comprises a mixed solution of hydrofluoric acid, nitric acid, and water, with a volume ratio of hydrofluoric acid:nitric acid:water of 1:(9-11):(18-22). Using this nickel-chromium alloy etchant for chemical etching results in clear grain display, a wide metallographic display range, more accurate product analysis, a stable and simple process that can be reused, short testing time, and quick results, effectively avoiding the generation of defective products. In particular, the display methods of Examples 1-3 provide clearer grain display than other formulations.

[0092] The present invention has been illustrated with the above embodiments to illustrate its detailed structural features. However, the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0093] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0094] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable way without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0095] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A nickel-chromium alloy etchant, characterized by, The nickel-chromium alloy etchant includes a mixed solution of hydrofluoric acid, nitric acid and water, and the volume ratio of hydrofluoric acid:nitric acid:water is 1:(9-11):(18-22); the concentration of the hydrofluoric acid is 35-45wt%, and the concentration of the nitric acid is 65-68wt%.

2. A grain etching display method for a nickel-chromium alloy using the nickel-chromium alloy etchant according to claim 1, characterized by The grain etching display method includes the following steps: The nickel-chromium alloy is sequentially subjected to polishing, electrolytic polishing, primary cleaning, chemical etching, secondary cleaning and drying; wherein the chemical etching uses the nickel-chromium alloy etchant.

3. The grain corrosion display method according to claim 2, characterized by, The polishing includes sequentially polishing the nickel-chromium alloy on 240# aqueous sandpaper and 1000# aqueous sandpaper, and using water as a wetting agent.

4. The grain corrosion display method according to claim 2, characterized by, The polishing time is 5-10min.

5. The grain corrosion display method according to claim 2, characterized by, The electrolytic polishing uses an electrolyte including a mixed solution of ethanol, 2-butoxyethanol and perchloric acid, and the volume ratio of ethanol:2-butoxyethanol:perchloric acid is x:y:z=(0.65-0.75):(0.05-0.15):(0.15-0.25), and x+y+z=1.

6. The grain corrosion display method according to claim 2, characterized by The electrolytic polishing voltage is 35-40V.

7. The grain corrosion display method according to claim 2, characterized by The electrolytic polishing time is 50-100s.

8. The grain corrosion display method according to claim 2, characterized by The chemical etching includes dropping the nickel-chromium alloy etchant on the electrolytic polishing area of the nickel-chromium alloy and staying for 60-90s.

9. The grain corrosion display method according to claim 2, characterized by, The grain etching display method includes the following steps: The nickel-chromium alloy is sequentially subjected to polishing, electrolytic polishing, primary cleaning, chemical etching, secondary cleaning and drying; The polishing includes sequentially polishing the nickel-chromium alloy on 240# aqueous sandpaper and 1000# aqueous sandpaper, and using water as a wetting agent, and the polishing time is 5-10min; the electrolytic polishing uses an electrolyte including a mixed solution of ethanol, 2-butoxyethanol and perchloric acid, and the volume ratio of ethanol:2-butoxyethanol:perchloric acid is x:y:z=(0.65-0.75):(0.05-0.15):(0.15-0.25), and x+y+z=1; the concentration of the ethanol is 95wt%, and the concentration of the perchloric acid is 30wt%; the electrolytic polishing voltage is 35-40V, and the time is 50-100s; the chemical etching uses the nickel-chromium alloy etchant; and the chemical etching includes dropping the nickel-chromium alloy etchant on the electrolytic polishing area of the nickel-chromium alloy and staying for 60-90s.

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