Etching agent for displaying alloy grain boundary as well as preparation method and application thereof

Abstract

The invention discloses an aggressive agent for displaying an alloy grain boundary as well as a preparation method and application thereof. The invention belongs to the technical field of metallographic structure display. The invention solves the problems of unclear grain boundary, blackening of phase in the grain boundary and the like caused by corrosion of the grain boundary by an aggressive agent in the prior art. The aggressive agent is formed by mixing copper sulfate, perchloric acid, ethyl alcohol and distilled water, the prepared aggressive agent is low in acid component content, free of strong corrosivity, capable of displaying a clear deep-color grain boundary and accurately measuring the grain size, low in cost, capable of being stored in a sealed mode, capable of being repeatedly used and suitable for industrial production. The invention further provides an electroerosion method, and the method is simple in device, easy to operate and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of metallographic structure display, and particularly relates to an etchant for displaying alloy grain boundaries and a preparation method and application thereof. Background Art

[0002] Since the working environment of thermal power units is characterized by high temperature, certain pressure and easy oxidation and corrosion, high requirements are placed on the performance of working parts. Precipitated iron-nickel high-temperature alloy is a low-cost heat-resistant steel with excellent properties such as high strength and high-temperature oxidation resistance, which is suitable for the working environment of thermal power units.

[0003] Grain boundaries are very narrow areas that separate adjacent grains. Grain boundary strengthening is an important strengthening mechanism for metal materials. The smaller the metal grain size, the more obvious the strengthening effect. At the same time, the grain size also affects the metal hardness, tensile strength, plasticity and toughness and other material properties. Therefore, the evaluation of the material grain size is very important. There are three methods for measuring grain size: area method, intercept method and comparison method. These methods all require etching clear grain boundaries to determine the number, diameter and area of ​​grains, and then calculate the grain size.

[0004] At present, the commonly used etchants for precipitated iron-nickel high-temperature alloys are copper sulfate, hydrochloric acid and water. The etchants in the prior art require a high content of acid components, which will corrode the phases within the grain boundaries while corroding the grain boundaries, causing the grain boundaries and the detached phases to turn black, making it difficult to distinguish clear grain boundaries. Summary of the invention

[0005] The purpose of the present invention is to solve the problems in the prior art that the corrosive agent corrodes the grain boundary, causing the grain boundary to be unclear and the phase change in the grain boundary to be black. The present invention provides an corrosive agent for displaying alloy grain boundaries, and a preparation method and application thereof.

[0006] The technical solution of the present invention is as follows:

[0007] One of the purposes of the present invention is to provide an etchant for revealing alloy grain boundaries, wherein the etchant is a mixture of copper sulfate, perchloric acid, ethanol and distilled water.

[0008] It is further defined that the ratio of copper sulfate, perchloric acid, ethanol and distilled water is 2-8 g:2-10 mL:8-100 mL:10-35 mL.

[0009] A second object of the present invention is to provide a method for preparing an etchant, wherein:

[0010] Copper sulfate is dissolved in distilled water to obtain a copper sulfate solution, perchloric acid is added to ethanol to obtain a perchloric acid solution, and the copper sulfate solution and the perchloric acid solution are mixed to obtain an etchant.

[0011] The third object of the present invention is to provide an application of the above-mentioned etchant in showing the grain boundaries of precipitation-strengthened iron-nickel-based high-temperature alloys.

[0012] A fourth object of the present invention is to provide a method for etching grain boundaries of a precipitation-strengthened iron-nickel-based high-temperature alloy, wherein:

[0013] S1: Mechanical grinding and mechanical polishing of the test surface of the iron-nickel-based high-temperature alloy sample;

[0014] S2: The test surface of the iron-nickel-based high-temperature alloy sample ground and polished by S1 is used as the anode and the nickel plate is used as the cathode. They are immersed in the above-mentioned etchant for electrolytic etching.

[0015] It is further defined that in S1, the inspection surface of the iron-nickel-based high-temperature alloy sample is mechanically ground with sandpaper, and the inspection surface of the iron-nickel-based high-temperature alloy sample is mechanically polished with nylon and gold velvet polishing cloth.

[0016] Further limit, the sandpaper is selected to be 80-7000 mesh.

[0017] It is further defined that the electrolysis voltage in S2 is 15 to 25 V, and the electrolysis current is 0.5 to 2.3 A.

[0018] It is further defined that the electrolysis time in S2 is 15 to 48 s.

[0019] A fifth object of the present invention is to provide an application of the above-mentioned etching method in displaying precipitation-strengthened iron-nickel-based high-temperature alloy grain boundaries.

[0020] The beneficial effects of the present invention are as follows:

[0021] (1) The etchant for displaying alloy grain boundaries prepared by the present invention has a low acid component content, is not highly corrosive, can display clear dark grain boundaries, can measure grain size more accurately, is low in cost, can be sealed and stored, and can be reused.

[0022] (2) The method for etching the grain boundaries of precipitation-strengthened iron-nickel-based high-temperature alloy provided by the present invention has a simple device, is easy to operate, and has low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of electrolytic corrosion device, 1 is anode sample, 2 is cathode nickel plate, 3 is etching agent, 4 is DC power supply;

[0024] Figure 2 a is a microscope picture of the HT700 precipitation-strengthened iron-nickel-based high-temperature alloy in Example 1 after electrolytic etching, magnified 100 times, Figure 2 b is a microscope picture of the HT700 precipitation-strengthened iron-nickel-based high-temperature alloy of Example 1 after electrolytic etching, magnified 200 times;

[0025] Figure 3 a is a microscope picture of comparative example 1HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 100 times, Figure 3 b is a microscope picture of comparative example 1HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 200 times;

[0026] Figure 4 a is a microscope picture of comparative example 2HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 100 times, Figure 4 b is a microscope picture of comparative example 2HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 200 times;

[0027] Figure 5 a is a microscope picture of the comparative example 3HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 100 times, Figure 5 b is a microscope picture of the comparative example 3HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 200 times. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] The terms "comprising," "including," "having," "containing," or any other variations thereof, as used in the following examples, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus comprising the listed elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0030] When equivalent, concentration or other value or parameter is represented by the range limited by range, preferred range or a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether the scope is disclosed separately. For example, when disclosing range "1 to 5", described range should be interpreted as including range "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the scope is intended to include its end value and all integers and fractions within the scope. In the present application specification and claims, range limitation can be combined and / or interchanged, if these ranges are not otherwise stated, include all sub-ranges contained therein.

[0031] The indefinite articles "a" and "an" before the elements or components of the present invention have no limitation on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the quantity obviously refers to the singular form only.

[0032] The "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure or characteristic that can be included in at least one implementation of the present invention. The "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0033] The endpoints and any values ​​of the ranges disclosed in the invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this article.

[0034] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0035] Embodiment 1:

[0036] Prepare the etchant:

[0037] 5 g of copper sulfate was dissolved in 30 mL of distilled water, 5 mL of perchloric acid was added into 100 mL of ethanol to form a perchloric acid solution, and the two solutions were mixed to obtain an etching agent.

[0038] Shows the erosion method of grain boundaries of precipitation-strengthened Fe-Ni-based superalloys:

[0039] The inspection surface of the HT700 precipitation-strengthened iron-nickel-based high-temperature alloy sample was mechanically ground with 80-mesh, 600-mesh, 1000-mesh, 3000-mesh and 7000-mesh sandpapers in turn, and then polished with a nylon polishing cloth and a 1.0 μm diamond polishing agent, and then polished with a gold velvet polishing cloth and a 0.5 μm diamond polishing agent. The polished sample was used as the anode and the nickel plate as the cathode. The sample was electrolytically eroded at a voltage of 20 V and a current of 1.0 A for 30 s. The sample was taken out, rinsed and dried with water and ethanol in turn, and the sample surface was observed using a metallographic microscope.

[0040] Comparative Example 1:

[0041] Prepare the etchant:

[0042] 20 g of copper sulfate was dissolved in 80 mL of distilled water as an etchant.

[0043] Shows the erosion method of grain boundaries of precipitation-strengthened Fe-Ni-based superalloys:

[0044] The inspection surface of the HT700 precipitation-strengthened iron-nickel-based high-temperature alloy specimen was mechanically ground with 80-mesh, 600-mesh, 1000-mesh, 3000-mesh and 7000-mesh sandpapers in sequence, and then polished with a nylon polishing cloth and a 1.0 μm diamond polishing agent, and then polished with a gold velvet polishing cloth and a 0.5 μm diamond polishing agent. The etchant was dipped in an absorbent cotton ball and wiped the surface of the specimen for 5 seconds, and then rinsed and dried with water and ethanol in sequence, and the surface of the specimen was observed using a metallographic microscope.

[0045] Comparative Example 2:

[0046] Prepare the etchant:

[0047] The etching agent was prepared by adding 12.5 mL of hydrochloric acid, 2.5 mL of nitric acid and 15 mL of nitroglycerin to 50 mL of distilled water.

[0048] Shows the erosion method of grain boundaries of precipitation-strengthened Fe-Ni-based superalloys:

[0049] The inspection surface of the HT700 precipitation-strengthened iron-nickel-based high-temperature alloy specimen was mechanically ground with 80-mesh, 600-mesh, 1000-mesh, 3000-mesh and 7000-mesh sandpapers in sequence, and then polished with a nylon polishing cloth and a 1.0 μm diamond polishing agent, and then polished with a gold velvet polishing cloth and a 0.5 μm diamond polishing agent. The etchant was dipped in an absorbent cotton ball and wiped the surface of the specimen for 5 seconds, and then rinsed and dried with water and ethanol in sequence, and the surface of the specimen was observed using a metallographic microscope.

[0050] Comparative Example 3:

[0051] Prepare the etchant:

[0052] 10 mL of oxalic acid was added to 100 mL of distilled water as an etching agent.

[0053] Shows the erosion method of grain boundaries of precipitation-strengthened Fe-Ni-based superalloys:

[0054] The inspection surface of the HT700 precipitation-strengthened iron-nickel-based high-temperature alloy sample was mechanically ground with 80-mesh, 600-mesh, 1000-mesh, 3000-mesh and 7000-mesh sandpapers in turn, and then polished with a nylon polishing cloth and a 1.0 μm diamond polishing agent, and then polished with a gold velvet polishing cloth and a 0.5 μm diamond polishing agent. The polished sample was used as the anode and the nickel plate as the cathode. The sample was electrolytically eroded at a voltage of 25 V and a current of 0.5 A for 30 s. The sample was taken out, rinsed and dried with water and ethanol in turn, and the sample surface was observed using a metallographic microscope.

[0055] Figure 2 a is a microscope picture of the HT700 precipitation-strengthened iron-nickel-based high-temperature alloy in Example 1 after electrolytic etching, magnified 100 times, Figure 2 b is a microscope picture of the HT700 precipitation-strengthened iron-nickel-based high-temperature alloy in Example 1 after electrolytic etching, magnified 200 times. From the picture, we can see that the grain boundary obtained by electrolytic etching in Example 1 is dark black, and the linear phase is light brown in metallographic morphology. Clear grain boundaries can be obtained, and the grain size can be accurately measured, so as to effectively evaluate the structure and performance of metal materials.

[0056] Figure 3 a is a microscope picture of comparative example 1HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 100 times, Figure 3 b is a microscope picture of comparative example 1HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 200 times, Figure 4 a is a microscope picture of comparative example 2HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 100 times, Figure 4 b is a microscope picture of the comparative example 2HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 200 times. Figure 3 a. Figure 3 b. Figure 4 a and Figure 4 In b, we can see that the grain boundary is corroded and dark, and at the same time, the phase falls off to form dark line-like objects. The two are mixed, and it is impossible to obtain a clear grain boundary and accurately measure the grain size. This is because the copper sulfate and hydrochloric acid components in Comparative Examples 1 and 2 have high contents and are more corrosive, so it is impossible to obtain a clear grain boundary.

[0057] Figure 5 a is a microscope picture of the comparative example 3HT700 precipitation-strengthened iron-nickel-based high-temperature alloy after electrolytic etching, magnified 100 times, Figure 5b is a microscope picture of comparative example 3 HT700 precipitation-strengthened iron-nickel-based superalloy after electrolytic etching at a magnification of 200 times. From the picture, we can see that the grain boundaries of comparative example 3 are unevenly dyed and cannot show complete grain boundaries, because comparative example 3 only uses oxalic acid aqueous solution as an etching agent, which is weak in acidity and has a poor etching effect.

[0058] The above are only preferred specific embodiments of the present invention, which are all different implementations based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. An etchant for revealing alloy grain boundaries, characterized in that: The etching agent is prepared by mixing copper sulfate, perchloric acid, ethanol and distilled water.

2. The etching agent according to claim 1, characterized in that The ratio of copper sulfate, perchloric acid, ethanol and distilled water is 2-8g:2-10mL:8-100mL:10-35mL.

3. The method for preparing the etching agent according to claim 1, characterized in that: The method: Copper sulfate is dissolved in distilled water to obtain a copper sulfate solution, perchloric acid is added to ethanol to obtain a perchloric acid solution, and the copper sulfate solution and the perchloric acid solution are mixed to obtain an etchant.

4. Use of the etchant according to claim 1 or 2 in showing the grain boundaries of precipitation-strengthened iron-nickel-based high-temperature alloys.

5. A method for etching grain boundaries of a precipitation-strengthened iron-nickel-based high-temperature alloy, characterized in that: The method: S1: Mechanical grinding and mechanical polishing of the test surface of the iron-nickel-based high-temperature alloy sample; S2: The test surface of the iron-nickel-based high-temperature alloy sample ground and polished by S1 is used as the anode and the nickel plate is used as the cathode, and is immersed in the etchant described in claim 1 or 2 for electrolytic etching.

6. The etching method according to claim 5, characterized in that: In S1, the inspection surface of the iron-nickel-based high-temperature alloy sample is mechanically ground with sandpaper, and the inspection surface of the iron-nickel-based high-temperature alloy sample is mechanically polished with nylon and gold velvet polishing cloth.

7. The etching method according to claim 6, characterized in that: Choose sandpaper with mesh size of 80 to 7000.

8. The etching method according to claim 5, characterized in that: The electrolysis voltage in S2 is 15-25V, and the electrolysis current is 0.5-2.3A.

9. The etching method according to claim 5, characterized in that: The electrolysis time in S2 is 15 to 48 seconds.

10. Use of the etching method according to any one of claims 5 to 9 in displaying the grain boundaries of precipitation-strengthened iron-nickel-based high-temperature alloys.

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