Electrolytic Corrosion Solution for Metallographic Structure of Cobalt and Cobalt-Based Alloys and Metallographic Corrosion Method Thereof

Abstract

The present invention relates to the technical field of metallographic corrosion, and specifically relates to an electrolytic corrosion solution for the metallographic structure of cobalt and cobalt-based alloys and a metallographic corrosion method thereof. The electrolytic corrosion solution for the metallographic structure of cobalt and cobalt-based alloys includes perchloric acid, benzotriazole, and absolute ethanol; the volume ratio of the perchloric acid solution, the saturated benzotriazole ethanol solution, and absolute ethanol is (20-30):(0.2-0.5):(69.5-79.8), and the concentration of the perchloric acid solution is 70-72%, realizing efficient and precise electrolytic corrosion of the metallographic structure of cobalt and cobalt-based alloy materials. This corrosion solution can not only clearly show the microscopic structure characteristics of the material, but also effectively avoid the phenomena of over-corrosion or under-corrosion, thus greatly improving the observation quality and accuracy of the metallographic structure. The corrosion effect of this corrosion solution is less affected by temperature, and good corrosion effects can be achieved at 0-60°C.

Description

Technical Field

[0001] The present invention relates to the technical field of metallographic corrosion, and particularly relates to an electrolytic corrosion solution for the metallographic structure of cobalt and cobalt-based alloys and a metallographic corrosion method thereof. Background Art

[0002] Cobalt and its alloys play an irreplaceable role in many high-tech fields such as aerospace, electronic communication, and mechanical manufacturing due to their excellent ferromagnetic properties, electrical conductivity, and corrosion resistance. With the rapid development of technology, the requirements for material properties in these fields are increasing day by day, prompting researchers to conduct more in-depth and detailed studies on the microstructure of cobalt and its alloys. The observation and analysis of the metallographic structure, as an important means to explore material properties, its accuracy and reliability are decisive for the progress of materials science.

[0003] However, traditional metallographic display methods face many challenges when dealing with cobalt and its alloys, especially high-purity cobalt and its alloys with complex compositions or fine grains. The patent document with the application number CN201210441849.3 discloses a metallographic erosion method for displaying the structure of cobalt-chromium alloys, and aqua regia is used as the corrosion solution in this method. The patent document with the application number CN201110396245.7 discloses a metallographic structure electrolyte, a corrosion method of cobalt, and a metallographic structure display method, and a mixed solution of ethanol, n-butanol, water, nitric acid, and hydrofluoric acid is used as the corrosion solution in this method. In actual operation, when directly using aqua regia or a mixed corrosion solution such as ethanol, n-butanol, nitric acid, and hydrofluoric acid to treat cobalt or cobalt-based alloys, the corrosion rate is relatively fast, the operation difficulty is relatively large, and it often leads to problems such as over-corrosion of the material structure or unclear display. Especially when dealing with cobalt-based alloys with fine grains or complex compositions, the phenomenon of incomplete grain display or over-corrosion often occurs, seriously affecting the observation and analysis accuracy of the metallographic structure. At the same time, the corrosion effect of the above corrosion solutions is significantly affected by the external temperature, and it is difficult to guarantee the corrosion success rate.

[0004] In addition, the components of traditional corrosion solutions are complex and contain harmful substances such as strong acids, which pose a potential threat to the experimental environment and the safety of operators. During the experiment, operators need to contact and handle these harmful substances, increasing the health risk, and the discharge and treatment of the corrosion solution also cause a burden on the environment. Summary of the Invention

[0005] Aiming at the problems of fast corrosion rate and obvious influence of corrosion effect by temperature existing in the above-mentioned prior art, the present invention provides an electrolytic corrosion solution for the metallographic structure of cobalt and cobalt-based alloys and a metallographic corrosion method thereof, using perchloric acid, benzotriazole, and absolute ethanol as the electrolytic corrosion solution, and using the strong oxidizing and strong corrosive properties of perchloric acid to corrode the metal, and using benzotriazole as a corrosion inhibitor to slow down the corrosion process.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] An electrolytic etching solution for the metallographic structure of cobalt and cobalt-based alloys, comprising perchloric acid, benzotriazole, and absolute ethanol; the volume ratio of the perchloric acid solution, saturated benzotriazole ethanol solution, and absolute ethanol is (20 - 30):(0.2 - 0.5):(69.5 - 79.8), and the concentration of the perchloric acid solution is 70 - 72%.

[0008] Further, the purity of the absolute ethanol ≥ 99%.

[0009] The present invention also includes the following technical solution:

[0010] A metallographic etching method using the above electrolytic etching solution for the metallographic structure of cobalt and cobalt-based alloys, comprising the following steps:

[0011] (1) Cut a cobalt or cobalt-based alloy sample of appropriate size to be observed, gradually polish the sample with silicon carbide sandpaper, and then polish the sample with diamond polishing agent.

[0012] (2) Add the electrolytic etching solution for the metallographic structure of cobalt and cobalt-based alloys to the electrolytic cell, place the polished sample into the electrolytic etching solution, stir, connect a DC power supply for electrolytic etching, the voltage of the electrolytic etching is 12 - 14 V, the etching time is 20 - 30 s, and the temperature is 0 - 60°C.

[0013] (3) Rinse the etched sample clean, dry it with cold air or in an oven, and observe it with a metallographic microscope.

[0014] Further, in step (1), gradually polish with 600, 1000, and 2000 - mesh silicon carbide sandpaper in sequence.

[0015] Further, in step (1), polish the sample with diamond polishing agent with a thickness of 1 - 1.5 μm, the polishing time is 5 - 10 min, and the polishing speed is 200 - 300 r / min.

[0016] Further, in step (2), the stirring speed is 2 - 5 r / s.

[0017] The reaction mechanism involved in the present invention is as follows:

[0018] Perchloric acid has strong oxidizing and corrosive properties. It can effectively remove oxides and impurities on the metal surface and corrode the metal. As a corrosion inhibitor, benzotriazole can form a protective film on the metal surface, effectively slowing down the corrosion process, protecting the material surface, preventing excessive corrosion, and its corrosion inhibition effect is more significant at high temperatures. The corrosion inhibition mechanism of benzotriazole is as follows: Benzotriazole is a nitrogen-containing organic heterocyclic compound, and it exhibits excellent reactivity and stability due to the unique nitrogen heterocycle in its molecular structure. The nitrogen atom in the benzotriazole molecule carries a lone pair of electrons, which can interact with metal ions on the metal surface, thereby forming a dense protective film on the metal surface and effectively inhibiting the corrosion process. At the same time, the nitrogen heterocyclic structure of benzotriazole gives it high thermal stability, enabling it to maintain the integrity of the molecular structure in a high-temperature environment, maintaining the uniform corrosion of the electrolyte on the material surface, effectively preventing tissue deformation caused by excessive erosion, and having significant advantages in corrosion protection applications in high-temperature environments.

[0019] The beneficial effects of the present invention compared with the prior art are as follows:

[0020] The present invention provides an electrolytic corrosion solution for the metallographic structure of cobalt and cobalt-based alloys and its metallographic corrosion method. By precisely proportioning perchloric acid solution, saturated benzotriazole ethanol solution and absolute ethanol, efficient and precise electrolytic corrosion of the metallographic structure of cobalt and cobalt-based alloy materials is achieved. This corrosion solution can not only clearly display the microscopic structure characteristics of the material, but also effectively avoid the phenomena of over-corrosion or insufficient corrosion, thereby greatly improving the observation quality and accuracy of the metallographic structure. Using perchloric acid with a concentration of 70 - 72% ensures that the corrosion solution has strong oxidation ability and stability, and can corrode the sample surface quickly and evenly. Using benzotriazole as an inhibitor can effectively control the corrosion rate, prevent the sample from being over-corroded, and improve the controllability and safety of the corrosion process; at the same time, benzotriazole has good thermal stability, so that the corrosion effect of this corrosion solution is less affected by temperature, and good corrosion effects can be achieved at 0 - 60°C. Absolute ethanol as a solvent not only helps the components to be evenly mixed, but also improves the stability and environmental friendliness of the corrosion solution. The metallographic corrosion method provided by the present invention has simple and clear steps and is easy to operate. During the electrolytic corrosion process, by controlling parameters such as voltage, time and temperature, precise control of the corrosion process can be achieved, so as to obtain an ideal metallographic structure observation effect. Description of the Drawings

[0021] The following further describes the embodiments of the present invention with reference to the accompanying drawings, where:

[0022] Figure 1 Shows the metallographic structure diagram of Example 1;

[0023] Figure 2Shows the metallographic structure diagram of Comparative Example 1;

[0024] Figure 3 Shows the metallographic structure diagram of Example 2;

[0025] Figure 4 Shows the metallographic structure diagram of Comparative Example 2;

[0026] Figure 5 Shows the metallographic structure diagram of Example 3;

[0027] Figure 6 Shows the metallographic structure diagram of Comparative Example 3. Detailed implementation manners

[0028] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below through specific examples in conjunction with the accompanying drawings. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention. Example 1

[0029] Cut a high-purity cobalt target sample of appropriate size to be observed, and successively polish the sample with silicon carbide sandpapers of 600, 1000, and 2000 meshes. Use water as a wetting agent during polishing. After polishing, rinse the sample surface clean. Then polish the sample with a 1.5 μm diamond polishing agent for 5 min at a rotational speed of 300 r / min. Add the metallographic electrolytic etching solution for cobalt and cobalt-based alloys to the electrolytic cell, put the polished sample into the electrolytic etching solution, stir at a stirring speed of 5 r / s; connect the DC power supply for electrolytic etching, the voltage of electrolytic etching is 14 V, the etching time is 30 s, and the temperature is 0°C. Rinse the etched sample clean, dry it with cold air or in an oven, and observe it with a metallographic microscope. The metallographic structure diagram is as shown in the appendix Figure 1 Shown.

[0030] In this example, the electrolytic etching solution includes perchloric acid, benzotriazole, and absolute ethanol. The volume ratio of the perchloric acid solution, saturated benzotriazole ethanol solution, and absolute ethanol is 30:0.2:69.8, and the concentration of the perchloric acid solution is 70%. Example 2

[0031] Cut a sample of high-purity cobalt target of appropriate size for observation, and successively polish the sample with silicon carbide sandpapers of 600, 1000, and 2000 meshes. Use water as a wetting agent during polishing. After polishing, rinse the surface of the sample clean. Then polish the sample with a 1.5 μm diamond polishing agent for 5 minutes at a rotational speed of 300 r / min. Add the metallographic electrolytic etching solution for cobalt and cobalt-based alloys to the electrolytic cell, put the polished sample into the electrolytic etching solution, stir at a stirring speed of 5 r / s; connect the DC power supply for electrolytic etching, with the electrolytic etching voltage of 14 V, the etching time of 30 s, and the temperature of 25°C. Rinse the etched sample clean, dry it with cold air or in an oven, and observe it with a metallographic microscope. The metallographic structure diagram is as attached Figure 3 as shown.

[0032] In this example, the electrolytic etching solution includes perchloric acid, benzotriazole, and absolute ethanol. The volume ratio of perchloric acid solution, saturated benzotriazole ethanol solution, and absolute ethanol is 30:0.2:69.8, and the concentration of the perchloric acid solution is 71%. Example 3

[0033] Cut a sample of high-purity cobalt target of appropriate size for observation, and successively polish the sample with silicon carbide sandpapers of 600, 1000, and 2000 meshes. Use water as a wetting agent during polishing. After polishing, rinse the surface of the sample clean. Then polish the sample with a 1 μm diamond polishing agent for 10 minutes at a rotational speed of 200 r / min. Add the metallographic electrolytic etching solution for cobalt and cobalt-based alloys to the electrolytic cell, put the polished sample into the electrolytic etching solution, stir at a stirring speed of 2 r / s; connect the DC power supply for electrolytic etching, with the electrolytic etching voltage of 12 V, the etching time of 20 s, and the temperature of 60°C. Rinse the etched sample clean, dry it with cold air or in an oven, and observe it with a metallographic microscope. The metallographic structure diagram is as attached Figure 5 as shown.

[0034] In this example, the electrolytic etching solution includes perchloric acid, benzotriazole, and absolute ethanol. The volume ratio of perchloric acid solution, saturated benzotriazole ethanol solution, and absolute ethanol is 20:0.5:79.5, and the concentration of the perchloric acid solution is 72%.

[0035] Comparative Example 1

[0036] The difference between this comparative example and Example 1 is that the electrolytic etching solution includes ethanol, n-butanol, water, nitric acid, and hydrofluoric acid. The volume ratio of ethanol, n-butanol, water, nitric acid, and hydrofluoric acid is 66:11:33:15:15. The electrolysis time is 20 s, and the electrolysis voltage is 35 V. The metallographic structure diagram is as attached Figure 2 as shown.

[0037] Comparative Example 2

[0038] The difference between this comparative example and Example 2 is that the electrolytic etching solution includes ethanol, n-butanol, water, nitric acid and hydrofluoric acid, and the volume ratio of ethanol, n-butanol, water, nitric acid and hydrofluoric acid is 66:11:33:15:15. The electrolysis time is 20 s and the electrolysis voltage is 35 V. The metallographic structure diagram is as attached Figure 4 shown

[0039] Comparative Example 3

[0040] The difference between this comparative example and Example 3 is that the electrolytic etching solution includes ethanol, n-butanol, water, nitric acid and hydrofluoric acid, and the volume ratio of ethanol, n-butanol, water, nitric acid and hydrofluoric acid is 66:11:33:15:15. The electrolysis time is 20 s and the electrolysis voltage is 35 V. The metallographic structure diagram is as attached Figure 6 shown

[0041] The present invention provides an electrolytic etching solution for the metallographic structure of cobalt and cobalt-based alloys and a metallographic etching method. By precisely proportioning perchloric acid solution, saturated benzotriazole ethanol solution and absolute ethanol, efficient and precise electrolytic etching of the metallographic structure of cobalt and cobalt-based alloy materials is achieved. This etching solution can not only clearly display the microscopic structure characteristics of the material, but also effectively avoid the phenomena of over-etching or insufficient etching, thus greatly improving the observation quality and accuracy of the metallographic structure. Using perchloric acid with a concentration of 70-72% ensures that the etching solution has strong oxidation ability and stability, and can quickly and evenly etch the surface of the sample. Using benzotriazole as an inhibitor can effectively control the etching rate, prevent over-etching of the sample, and improve the controllability and safety of the etching process; at the same time, benzotriazole has good thermal stability, so that the etching effect of this etching solution is less affected by temperature, and good etching effects can be achieved at 0-60°C. Absolute ethanol as a solvent not only helps the uniform mixing of each component, but also improves the stability and environmental friendliness of the etching solution. The metallographic etching method provided by the present invention has simple and clear steps and is easy to operate. During the electrolytic etching process, by controlling parameters such as voltage, time and temperature, precise control of the etching process can be achieved, so as to obtain an ideal metallographic structure observation effect

[0042] Some exemplary embodiments of the present invention have been described above. It can be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention. The features in these embodiments can be recombined in a suitable manner, and the solutions obtained thereby are still within the protection scope required by the present invention. Based on the above embodiments, all other embodiments obtained by those skilled in the art without creative efforts, that is, all modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this application, fall within the protection scope required by the present invention.

Claims

1. A metallographic electrolytic etching solution for cobalt and cobalt-based alloys, characterized in that: The invention comprises perchloric acid, benzotriazole and anhydrous ethanol; the volume ratio of the perchloric acid solution, the saturated benzotriazole ethanol solution and the anhydrous ethanol is (20-30): (0.2-0.5): (69.5-79.8), and the concentration of the perchloric acid solution is 70-72%.

2. The electrolytic etching solution for metallographic structure of cobalt and cobalt-based alloys according to claim 1, characterized in that: The purity of the anhydrous ethanol is ≥99%.

3. A metallographic etching method using the metallographic structure electrolytic etching solution of cobalt and cobalt-based alloys according to any one of claims 1-2, characterized in that: The following steps are involved: (1) Cut a cobalt or cobalt-based alloy sample of appropriate size to be observed, grind the sample step by step using silicon carbide sandpaper, and then polish the sample using diamond polishing agent; (2) Adding a metallographic electrolytic corrosion solution of cobalt and cobalt-based alloy into an electrolytic cell, placing the polished sample into the electrolytic corrosion solution, stirring, and connecting a DC power supply for electrolytic corrosion. The voltage of the electrolytic corrosion is 12-14 V, the corrosion time is 20-30 s, and the temperature is 0-60°C; (3) Rinse the corroded sample, blow dry with cold air or dry in an oven, and observe it using a metallographic microscope.

4. The metallographic corrosion method of cobalt and cobalt-based alloy according to claim 3, characterized in that: In step (1), 600, 1000, and 2000 mesh silicon carbide sandpapers are used for step-by-step grinding.

5. The metallographic corrosion method of cobalt and cobalt-based alloy according to claim 3, characterized in that: In step (1), the sample is polished using a diamond polishing agent with a coarseness of 1-1.5 μm, the polishing time is 5-10 min, and the polishing speed is 200-300 r / min.

6. The metallographic corrosion method of cobalt and cobalt-based alloy according to claim 3, characterized in that: In step (2), the stirring speed is 2-5 r / s.

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