A high-temperature alloy ultrafine wire metallographic etchant, a preparation method and application thereof

Abstract

This application relates to a metallographic etchant for ultra-fine high-temperature alloy wires, its preparation method, and its application, belonging to the field of materials analysis and testing technology. The raw materials for preparing the metallographic etchant, by mass parts, include: copper sulfate pentahydrate: 10-60 parts, hydrochloric acid: 90-150 parts, and sulfuric acid: 9-20 parts; the copper sulfate pentahydrate, hydrochloric acid, and sulfuric acid are all analytical grade reagents. The three components work synergistically within a specific ratio range, solving the technical problems of existing etchants causing excessively rapid and uncontrollable corrosion rates in the micro-areas of ultra-fine wires, as well as the easy formation of corrosion pits and blurred grain boundaries. This metallographic etchant is simple to prepare, uses readily available raw materials, is inexpensive, has a moderate and highly controllable corrosion rate, and exhibits good corrosion uniformity. It is suitable for metallographic microstructure detection and grain size assessment in the quality control, process optimization, and failure analysis of ultra-fine high-temperature alloy wires.

Description

Technical Field

[0001] This application relates to the field of materials analysis and testing technology, and in particular to a metallographic etchant for ultrafine high-temperature alloy wires, its preparation method, and its application. Background Technology

[0002] High-temperature alloys are increasingly used in extreme environments such as aerospace and energy chemical industries. Ultrafine high-temperature alloy wires (such as nickel-based and cobalt-based ultrafine high-temperature alloy wires) are key materials for manufacturing precision filters for aero-engines, high-temperature sensors, special braided fabrics, and micro-welding wires for additive manufacturing. The final performance of ultrafine high-temperature alloy wires strongly depends on their microstructure, including grain size and the morphology and distribution of second phases (such as γ′ strengthening phases, carbides, and borides). Therefore, accurately revealing the true metallographic structure of ultrafine high-temperature alloy wires is crucial for quality control, process optimization, and failure analysis.

[0003] Metallographic sample preparation of ultrafine high-temperature alloy wires is a highly challenging operation in materials analysis. These wires typically have a diameter of less than 0.5 mm and a tiny cross-sectional area, requiring extremely high selectivity, uniformity, and controllability of the etchant. Even slight over-etching can lead to excessively wide grain boundaries, blurred details, or even sample rejection.

[0004] In view of this, it is necessary to design a metallographic etchant for ultrafine high-temperature alloy wires, its preparation method and application, in order to solve the above problems. Summary of the Invention

[0005] This application provides a metallographic etchant for ultrafine high-temperature alloy wires, its preparation method, and its application, in order to solve the technical problem that current etchants cannot clearly and stably display the grain structure in ultrafine high-temperature alloy wires. In a first aspect, embodiments of this application provide a metallographic etchant for ultra-fine high-temperature alloy wires. The raw materials for preparing the metallographic etchant, by mass parts, include: copper sulfate pentahydrate: 10 to 60 parts, hydrochloric acid: 90 to 150 parts, and sulfuric acid: 9 to 20 parts; wherein the copper sulfate pentahydrate, the hydrochloric acid, and the sulfuric acid are all analytical grade reagents.

[0006] Optionally, the raw materials for preparing the metallographic etchant, by weight, include: copper sulfate pentahydrate: 35 parts, hydrochloric acid: 115 to 120 parts, and sulfuric acid: 12 to 13 parts.

[0007] Secondly, embodiments of this application provide a method for preparing the metallographic etchant described in the first aspect, comprising the following steps: The copper sulfate pentahydrate is mixed with the hydrochloric acid to obtain a first mixture; The mixture was stirred until the copper sulfate pentahydrate was completely dissolved to obtain a copper sulfate pentahydrate-hydrochloric acid solution. The sulfuric acid was added to the copper sulfate pentahydrate-hydrochloric acid solution to obtain a second mixture; The second mixture is stirred to obtain the metallographic etchant.

[0008] Thirdly, embodiments of this application provide the application of the metallographic etchant described in the first aspect, wherein the metallographic etchant is applied to the metallographic etching of ultrafine wires of high-temperature alloys.

[0009] Optionally, the diameter of the high-temperature alloy ultrafine wire is ≤0.5mm.

[0010] Optionally, the high-temperature alloy ultrafine wire includes either nickel-based high-temperature alloy ultrafine wire or cobalt-based high-temperature alloy ultrafine wire.

[0011] Optional, the following steps may be included: The metallographic etchant is heated to obtain a thermal metallographic etchant; The high-temperature alloy ultrafine wire metallographic sample that has undergone mounting treatment is immersed in the hot metallographic etchant for etching to obtain an etched metallographic sample. The corroded metallographic sample was cleaned and dried sequentially to obtain the metallographic sample to be observed.

[0012] Optionally, the heating temperature is 40℃~70℃.

[0013] Optionally, the heating temperature is 50℃~60℃.

[0014] Optionally, the corrosion time is 3s to 10s.

[0015] Optionally, the corrosion time is 5s to 6s.

[0016] The technical solutions provided in this application have the following advantages compared with the prior art: 1. This application provides a metallographic etchant for ultra-fine high-temperature alloy wires. By weight, the metallographic etchant is composed of the following raw materials: copper sulfate pentahydrate: 10-60 parts, hydrochloric acid: 90-150 parts, and sulfuric acid: 9-20 parts; all copper sulfate pentahydrate, hydrochloric acid, and sulfuric acid are analytical grade reagents. This metallographic etchant consists of only three analytical grade reagents, with few types of raw materials, wide availability, low price, no special storage conditions required, and a simple and quick preparation process. Copper ions dissociated from copper sulfate pentahydrate in hydrochloric acid systems have higher electrode potentials than the matrix elements of high-temperature alloys. Copper ions preferentially undergo displacement reactions in regions with irregular atomic arrangements and high energy, such as grain boundaries and phase boundaries, forming a microcouple effect. This causes the corrosion selectivity to begin at grain and phase boundaries rather than indiscriminately corroding the entire surface. At the same time, the copper elemental product of the displacement reaction is deposited on the sample surface, which acts as a buffer to inhibit over-corrosion. The chloride ions provided by hydrochloric acid effectively penetrate and destroy the dense oxide film on the surface of the high-temperature alloy, exposing the matrix to the corrosive environment. The hydrogen ions provided by hydrochloric acid maintain the acidic environment to ensure the continuous progress of the corrosion reaction. The additional hydrogen ions provided by sulfuric acid enhance the overall acidity of the solution to promote the activation of the alloy surface. At the same time, the sulfate ions moderately inhibit the over-aggressive copper ion displacement reaction through their oxidizing properties, making the corrosion process stable and controllable. The three components, within the ratio range of 10-60 parts of copper sulfate pentahydrate, 90-150 parts of hydrochloric acid, and 9-20 parts of sulfuric acid, achieve the best balance between the driving force of copper ion selective corrosion, the ability of chloride ion passivation film destruction, and the regulation of sulfate reaction stability, realizing a clear and stable display of the ultra-fine filamentary grain structure of the high-temperature alloy.

[0017] 2. This application provides a method for preparing a metallographic etchant for high-temperature alloy ultrafine wires. First, copper sulfate pentahydrate is mixed with hydrochloric acid and stirred until the copper sulfate pentahydrate is completely dissolved. This allows copper ions to be fully released and uniformly dispersed in the hydrochloric acid system, preventing local overheating and sudden acidity changes caused by premature addition of sulfuric acid, which could reduce the dissolution rate of copper sulfate pentahydrate or cause crystallization. Then, sulfuric acid is slowly added to the resulting copper sulfate pentahydrate-hydrochloric acid solution and stirred until homogeneous. This allows the dilution heat generated during the addition of sulfuric acid to be promptly dispersed and absorbed by the solution, preventing sudden temperature increases that could lead to solution splashing and copper salt precipitation. Simultaneously, the sulfate ions are uniformly distributed in the solution under stirring, ensuring that the oxidizing and acidity-regulating effects of sulfuric acid on the etchant are uniform and effective throughout the entire solution system. The prepared metallographic etchant has uniformly distributed copper ions, fully dispersed sulfate ions, and stable and consistent corrosion activity, and can be directly used for etching operations. The preparation method is simple and quick, and all raw materials used are analytical grade reagents. No special storage conditions are required, which ensures the consistency and repeatability of the performance between different batches of etchants, and provides a stable and reliable corrosion medium for metallographic corrosion of ultrafine wires of high-temperature alloys.

[0018] 3. This application provides an application of a metallographic etchant for ultrafine high-temperature alloy wires. By heating the metallographic etchant and then briefly immersing the mounted ultrafine high-temperature alloy wire metallographic sample in it, the synergistic effect of temperature on the exponential driving effect of the corrosion reaction rate and time on the precise control of the corrosion depth is utilized. This allows the corrosion depth to stop precisely at the critical point where the grain boundaries are fully exposed due to preferential erosion, while the intragranular structure remains intact due to less erosion. This achieves clear, stable, and repeatable metallographic corrosion effects on both nickel-based and cobalt-based ultrafine high-temperature alloy wires, various grades, and different heat treatment states. The operation is simple and quick, and has broad industrial application value. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a metallographic corrosion effect image provided in Example 1 of this application, with a magnification of 200×; Figure 2 This is a metallographic corrosion effect image provided in Embodiment 2 of this application, with a magnification of 200×; Figure 3 The image shown is a metallographic corrosion effect diagram provided in Comparative Example 1 of this application, with a magnification of 500×. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the content, amount added, etc., mentioned herein are based on mass; for example, an addition amount of 1% means that the additive accounts for 1% of the total mass of the system; a content of 10% means that the component has a mass fraction of 10% in the composition. Unless otherwise specified, the terms "comprising," "including," etc., used herein mean "including but not limited to"; relational terms such as "first," "second," etc., are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist alone or simultaneously; expressions such as "at least one," "multiple," "at least one," etc., refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned in this article, such as mass ratio and molar ratio, should be understood as the correspondence between the antecedent and consequent of a proportional equation, according to the order in which they are described. All raw materials, reagents, instruments, and equipment used in this article can be purchased commercially or prepared using existing methods.

[0024] In a first aspect, embodiments of this application provide a metallographic etchant for ultra-fine high-temperature alloy wires. The raw materials for preparing the metallographic etchant, by mass parts, include: copper sulfate pentahydrate: 10 to 60 parts, hydrochloric acid: 90 to 150 parts, and sulfuric acid: 9 to 20 parts; wherein the copper sulfate pentahydrate, the hydrochloric acid, and the sulfuric acid are all analytical grade reagents.

[0025] In this embodiment, the high-temperature alloy ultrafine wire refers to a filamentous material with a diameter of less than or equal to 0.5 mm, made of nickel-based or cobalt-based high-temperature alloys. Due to the extremely small diameter of the high-temperature alloy ultrafine wire, the cross-sectional area of ​​the metallographic sample of the high-temperature alloy ultrafine wire is much smaller than that of a conventional blocky high-temperature alloy sample. Therefore, the requirements for the corrosion rate, corrosion uniformity, and controllability of the etchant for the high-temperature alloy ultrafine wire are much higher than those for conventional metallographic corrosion scenarios.

[0026] Metallographic etchants are chemical reagent compositions used in the preparation of metallographic samples to reveal the microstructure of metallic materials through chemical etching. The performance of the metallographic etchant directly determines the clarity and accuracy of the metallographic structure display.

[0027] Copper sulfate pentahydrate, with the chemical formula CuSO4·5H2O and a molecular weight of 249.68, is a blue, transparent crystal and a commonly used copper salt reagent in analytical chemistry experiments. Its core role in the metallographic etchant of this application is to provide copper ions, which promote selective corrosion during the metallographic etching process. Specifically, in a hydrochloric acid system, copper sulfate pentahydrate dissociates into copper ions, which have a higher electrode potential than the matrix elements of high-temperature alloys, including nickel, cobalt, and chromium. When the metallographic sample is immersed in the etchant, the copper ions undergo a displacement reaction with the surface of the high-temperature alloy's ultrafine wire, forming a micro-couple effect at grain boundaries and phase boundaries. Grain boundaries and phase boundaries are regions with irregular atomic arrangements and high energy; the micro-couple effect causes corrosion to preferentially occur at these boundaries, thus selectively highlighting them rather than indiscriminately corroding the entire surface of the metallographic sample.

[0028] Furthermore, the substitution reaction product of copper ions is elemental copper, which deposits on the surface of the metallographic sample, further acting as a buffer to inhibit over-corrosion. The substitution reaction of copper ions and the buffering effect of elemental copper constitute a dual mechanism, making copper sulfate pentahydrate a key component for achieving selective and controlled corrosion.

[0029] The proportion of copper sulfate pentahydrate determines the concentration of copper ions in the metallographic etchant, which in turn determines the driving force of selective corrosion. When the proportion of copper sulfate pentahydrate is less than 10 parts, the copper ion concentration in the metallographic etchant is insufficient, the electrochemical driving force is weak, the displacement reaction rate is too slow, and the metallographic etchant is unable to effectively reveal grain boundaries on the tiny cross-sections of the ultrafine cross-sections of high-temperature alloy wires. When the proportion of copper sulfate pentahydrate is greater than 60 parts, the metallographic etchant approaches or reaches saturation, and crystallization easily occurs, reducing the stability of the metallographic etchant. Simultaneously, an excessively high copper ion concentration can lead to an overly vigorous displacement reaction, which can easily create corrosion pits on the surface of the ultrafine high-temperature alloy wire.

[0030] Hydrochloric acid is an aqueous solution of hydrogen chloride gas, the chemical formula of which is HCl. Analytical purity hydrochloric acid typically has a mass fraction of 36%–38% and a density of 1.18 g / mL–1.19 g / mL. In this application, hydrochloric acid plays a crucial role as the primary corrosive medium, providing chloride and hydrogen ions. Specifically, a dense oxide film naturally forms on the surface of high-temperature alloys in the air, primarily composed of Cr₂O₃. This oxide film possesses extremely strong corrosion resistance and is a significant source of the high-temperature alloy's corrosion resistance. Chloride ions have a strong ability to penetrate and destroy the passivation film on metal surfaces, effectively damaging the oxide film on the surface of high-temperature alloys and exposing the alloy substrate to a corrosive environment. Hydrogen ions provide an acidic environment, sustaining the corrosion reaction.

[0031] The amount of hydrochloric acid determines the ability of the metallographic etchant to destroy the passivation film on the surface of high-temperature alloys and the overall corrosion rate. When the amount of hydrochloric acid is less than 90 parts, the chloride ion concentration is insufficient, and the chloride ions cannot effectively penetrate the oxide film on the surface of the high-temperature alloy, resulting in insufficient corrosion ability and making it difficult for the metallographic etchant to initiate an effective corrosion reaction. When the amount of hydrochloric acid is greater than 150 parts, the acid mist is too large and the corrosion rate is too fast. For micro-section samples such as ultra-fine wires of high-temperature alloys, an excessively fast corrosion rate can easily lead to over-corrosion in a short period of time, resulting in widened grain boundaries and loss of grain detail.

[0032] Sulfuric acid has the chemical formula H₂SO₄. Analytical purity sulfuric acid typically has a mass fraction of 95%–98% and a density of 1.83 g / mL–1.84 g / mL. The core role of sulfuric acid in the metallographic etchant of this application is to regulate its oxidizing properties and acidity, acting as a buffer and regulator for the corrosion reaction. Specifically, sulfuric acid provides additional hydrogen ions, which enhance the overall acidity of the metallographic etchant, promoting the activation of the high-temperature alloy surface. Sulfate ions possess a certain degree of oxidizing property, which can moderately inhibit the excessive occurrence of the copper ion replacement reaction, making the corrosion process more stable and controllable. The addition of sulfuric acid allows the metallographic etchant to maintain sufficient corrosive power while avoiding over-corrosion and pitting problems caused by excessively rapid reactions.

[0033] The amount of sulfuric acid determines the degree of adjustment of the oxidizing power and acidity of the metallographic etchant. When the amount of sulfuric acid is less than 9 parts, the adjustment effect is not obvious, and the metallographic etchant may still cause uneven corrosion due to excessive copper ion replacement reaction. When the amount of sulfuric acid is more than 20 parts, the oxidizing power is too strong, the corrosion ability of the metallographic etchant is excessively inhibited, or the excessive oxidizing power leads to local pitting corrosion.

[0034] The combination of three numerical ranges—10-60 parts copper sulfate pentahydrate, 90-150 parts hydrochloric acid, and 9-20 parts sulfuric acid—ensures that the proportions of the three components are within a range that can produce a synergistic effect. Copper ions provide the selective corrosion driving force, chloride ions provide the ability to destroy the passivation film, and sulfate ions provide reaction stability regulation. Within this numerical range, copper ions, chloride ions, and sulfate ions work together to achieve the technical effect of moderate corrosion rate, good corrosion uniformity, and clear grain boundary display.

[0035] The advantage of using analytical grade reagents instead of industrial grade or chemical grade reagents in this application embodiment is that analytical grade reagents have extremely low impurity content and stable concentrations of effective components in each component.

[0036] In some embodiments, preferably, the raw materials for preparing the metallographic etchant include, by weight, 35 parts of copper sulfate pentahydrate, 115 to 120 parts of hydrochloric acid, and 12 to 13 parts of sulfuric acid.

[0037] Secondly, embodiments of this application provide a method for preparing the metallographic etchant described in the first aspect, comprising the following steps: The copper sulfate pentahydrate is mixed with the hydrochloric acid to obtain a first mixture; The mixture was stirred until the copper sulfate pentahydrate was completely dissolved to obtain a copper sulfate pentahydrate-hydrochloric acid solution. The sulfuric acid was added to the copper sulfate pentahydrate-hydrochloric acid solution to obtain a second mixture; The second mixture is stirred to obtain the metallographic etchant.

[0038] After copper sulfate pentahydrate is completely dissolved in hydrochloric acid, a copper sulfate pentahydrate-hydrochloric acid solution is obtained. Sulfuric acid is added to the copper sulfate pentahydrate-hydrochloric acid solution, and the mixture is stirred continuously. The sulfuric acid is added slowly, meaning it is introduced into the copper sulfate pentahydrate-hydrochloric acid solution in batches, either as a thin stream or dropwise, rather than being poured all at once.

[0039] Thirdly, embodiments of this application provide the application of the metallographic etchant described in the first aspect, wherein the metallographic etchant is applied to the metallographic etching of ultrafine wires of high-temperature alloys.

[0040] In some embodiments, the diameter of the high-temperature alloy ultrafine wire is ≤0.5mm.

[0041] In some embodiments, the high-temperature alloy ultrafine wire includes either nickel-based high-temperature alloy ultrafine wire or cobalt-based high-temperature alloy ultrafine wire.

[0042] Nickel-based superalloys typically contain 50% or more nickel by mass and include one or more alloying elements such as chromium, cobalt, molybdenum, aluminum, titanium, tungsten, and niobium. Typical nickel-based superalloys include, but are not limited to, grades GH141, GH4169, and GH4738. Cobalt-based superalloys typically contain 50% or more cobalt by mass and include one or more alloying elements such as nickel, chromium, tungsten, molybdenum, and carbon. Typical cobalt-based superalloys include, but are not limited to, grades GH5188 and GH5605.

[0043] In some implementations, the following steps are included: The metallographic etchant is heated to obtain a thermal metallographic etchant; The high-temperature alloy ultrafine wire metallographic sample that has undergone mounting treatment is immersed in the hot metallographic etchant for etching to obtain an etched metallographic sample. The corroded metallographic sample was cleaned and dried sequentially to obtain the metallographic sample to be observed.

[0044] In some embodiments, the heating temperature is 40°C to 70°C.

[0045] Heating the metallographic etchant to 40℃~70℃ is to provide a precise and controllable temperature environment for the subsequent corrosion reaction.

[0046] In some embodiments, preferably, the heating temperature is 50°C to 60°C.

[0047] In some embodiments, the corrosion time is 3s to 10s.

[0048] A corrosion time range of 3 to 10 seconds ensures that the corrosion depth reaches a critical state where grain boundaries are clearly visible while the intragranular structure remains intact. Within this time range, the corrosion reaction terminates at an equilibrium point where grain boundaries are sufficiently eroded but the intragranular structure is not significantly damaged. The operator can fine-tune this range based on changes in the sample surface color and the visibility of the microstructure under a microscope to address minor differences in the surface condition of different batches of samples.

[0049] In some embodiments, preferably, the corrosion time is 5s to 6s.

[0050] The best corrosion effect can be obtained by combining a corrosion time range of 5 to 6 seconds with a heating temperature of 50℃ to 60℃.

[0051] In some embodiments, the mounted high-temperature alloy ultrafine wire metallographic specimen is prepared by the following steps: High-temperature alloy ultrafine wires with a diameter of 0.1 mm to 0.5 mm are inlaid to fix the high-temperature alloy ultrafine wires in the inlay material, thereby obtaining an inlaid sample. The inlaid sample is ground step by step using multiple passes of sandpaper to make the inspection surface of the inlaid sample flat and the surface scratches gradually refined, thus obtaining the ground sample. The ground sample was polished with a polishing agent to obtain the high-temperature alloy ultrafine wire metallographic sample after mounting.

[0052] Inlay processing refers to the process of embedding ultrafine high-temperature alloy wires in solid inlay material. The purpose of this inlay processing is to fix the spatial position and orientation of the ultrafine high-temperature alloy wires, protect them from displacement, deformation or detachment during subsequent grinding and polishing, and provide a regular shape for easy handling or clamping in subsequent operations.

[0053] The placement orientation of the high-temperature alloy ultrafine wire in the mounting mold depends on the requirements of metallographic observation. When observing the cross-sectional microstructure of the high-temperature alloy ultrafine wire, it is placed vertically in the mounting mold, with its axis perpendicular to the bottom surface of the mold. When observing the longitudinal microstructure of the high-temperature alloy ultrafine wire, it is placed horizontally in the mounting mold, with its axis parallel to the bottom surface of the mold. Mounting can be performed using either cold mounting or hot mounting.

[0054] Gradual grinding refers to the process of using multiple passes of sandpaper, with the grit increasing sequentially, to grind the inspection surface of a mounted specimen. This gradual grinding process removes the scratches left by the previous pass of sandpaper by progressively increasing the grit, thus gradually reducing the surface roughness of the inspection surface. Each time a pass of sandpaper is changed, the mounted specimen is rotated 90 degrees around the normal direction of the inspection surface, so that the grinding direction of the current pass is perpendicular to the direction of the scratches left by the previous pass.

[0055] Polishing compound refers to an abrasive medium used to polish the inspection surface of a ground sample. This polishing compound contains fine abrasive particles and a corresponding carrier, which remove residual fine abrasions from the inspection surface of the ground sample through mechanical abrasion, achieving a mirror-like finish. Polishing continues until the inspection surface is mirror-like, bright, smooth, and free of pitting, scratches, trailing, and stains.

[0056] In some embodiments, the progressive grinding includes at least four sandpaper grinding processes with progressively increasing grit. The polishing agent is a diamond polishing agent with a particle size of 1.5 μm.

[0057] The sandpaper grit sequence for the four sandpaper grinding processes can be 180 grit, 400 grit, 800 grit, and 1200 grit.

[0058] Diamond polishing compound is a polishing medium that uses diamond microparticles as abrasive particles. Diamond is the hardest known material in nature, with a Mohs hardness of 10, far exceeding the hardness of all phases in high-temperature alloys. Polishing with diamond polishing compound simultaneously removes all phases in the high-temperature alloy, resulting in a smooth surface on the inspection surface with no height difference between the matrix, γ' reinforcing phase, and carbide particles, eliminating any relief effect. This smooth surface ensures uniform contact between all areas and the heated metallographic etchant during subsequent etching, resulting in consistent etching effects. The particle size of the diamond polishing compound is 1.5μm, which is neither too coarse, leaving visible scratches on the inspection surface after polishing, nor too fine, leading to excessively low polishing efficiency.

[0059] In some embodiments, the corroded metallographic sample is sequentially cleaned and dried, including: The corroded metallographic sample was rinsed with running water for at least 10 seconds to obtain the water-washed metallographic sample. The metallographic sample after water washing was rinsed with anhydrous ethanol to obtain the metallographic sample after alcohol washing. The metallographic sample after being washed with alcohol is wiped or blown dry to obtain the metallographic sample to be observed.

[0060] The residues on the surface of the etched metallographic sample include residual etchant liquid adhering to the inspection surface, metal salts produced by the corrosion reaction, and possibly deposited elemental copper. Cleaning and drying yield the metallographic sample to be observed. The purpose of cleaning and drying is to remove residual etchant and reaction products from the surface of the etched metallographic sample, ensuring the inspection surface is clean and dry in preparation for metallographic microscopy observation.

[0061] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0062] Example 1 This embodiment utilizes a metallographic etchant to perform metallographic etching on an ultrafine GH5188 high-temperature alloy wire. The GH5188 high-temperature alloy ultrafine wire has a diameter of 0.15 mm and is in a solution-treated state at 1000℃.

[0063] Take an appropriate amount of GH5188 high-temperature alloy ultrafine wire for inlay processing. Place the high-temperature alloy ultrafine wire vertically in the inlay mold, inject inlay material into the inlay mold, and obtain an inlay sample.

[0064] The mounted specimen was wet-ground sequentially using 180-grit, 400-grit, 800-grit, and 1200-grit silicon carbide sandpaper. Each time the sandpaper was changed, the mounted specimen was rotated 90° around the normal to its test surface, ensuring the current grinding direction was perpendicular to the grinding mark of the previous sandpaper. After grinding, the test surface of the specimen was polished with diamond polishing compound until it achieved a mirror-like, bright, and smooth surface, free from pitting, scratches, trailing, and stains. This yielded a high-temperature alloy ultrafine wire metallographic specimen after mounting.

[0065] By mass fraction, 118 parts of hydrochloric acid (analytical grade, 36% by mass) were added to 35 parts of copper sulfate pentahydrate (analytical grade), and stirred until the copper sulfate pentahydrate was completely dissolved to obtain a copper sulfate pentahydrate-hydrochloric acid solution. 12.9 parts of sulfuric acid (analytical grade, 95% by mass) were slowly added to the above copper sulfate pentahydrate-hydrochloric acid solution, and stirred until homogeneous to obtain a metallographic etchant.

[0066] The prepared metallographic etchant was placed on a heating furnace and heated, with the temperature monitored using a thermometer. When the temperature of the metallographic etchant reached 55°C, the high-temperature alloy ultrafine wire metallographic sample, which had been mounted, was immersed in the heated metallographic etchant for etching for 5 seconds.

[0067] Immediately rinse the corroded metallographic sample with running water for at least 10 seconds, then rinse with anhydrous ethanol, and finally gently wipe it dry with degreased cotton to obtain the metallographic sample to be observed.

[0068] The metallographic specimen to be observed is placed under a metallographic microscope for tissue observation and image acquisition. For example... Figure 1 As shown, under 200x magnification, the grain morphology, grain boundaries and twins of the GH5188 high-temperature alloy ultrafine wire can be clearly observed. The grain boundaries are clear and well-defined, with no over-corrosion or under-corrosion. This can be used to evaluate the grain size.

[0069] Example 2 This embodiment utilizes a metallographic etchant to perform metallographic etching on an ultrafine GH141 high-temperature alloy wire. The GH141 high-temperature alloy ultrafine wire has a diameter of 0.12 mm and is in a solution-treated state.

[0070] The GH141 high-temperature alloy ultrafine wire was inlaid, ground, and polished using the same method as in Example 1 to obtain a metallographic sample of the inlaid high-temperature alloy ultrafine wire. The preparation steps of the metallographic etchant were basically the same as in Example 1, except for the amount of sulfuric acid used. In Example 2, the amount of sulfuric acid used was 14.7 parts, while the amounts of the other components remained unchanged. The etching operation steps were the same as in Example 1.

[0071] After etching the GH141 high-temperature alloy ultrafine wire using the metallographic etchant and etching method of this embodiment, the metallographic structure image is as follows. Figure 2 As shown. By Figure 2 As can be seen, under 200x magnification, the grain boundary outlines of the GH141 high-temperature alloy ultrafine filaments are distinct, the second phase is clearly identifiable, and the microstructure is uniform and consistent, which meets the requirements for grain size evaluation.

[0072] Example 3 This embodiment utilizes a metallographic etchant to perform metallographic etching on an Inconel 600 high-temperature alloy ultrafine wire. The Inconel 600 high-temperature alloy ultrafine wire has a diameter of 0.16 mm and is in a solution-treated state.

[0073] The Inconel 600 high-temperature alloy ultrafine wire was inlaid, ground, and polished using the same method as in Example 1 to obtain a metallographic sample of the inlaid high-temperature alloy ultrafine wire. The preparation steps of the metallographic etchant were basically the same as in Example 1, except for the amount of sulfuric acid used. In Example 3, the amount of sulfuric acid used was 11.04 parts, and the amounts of the other components remained unchanged. The etching operation steps were the same as in Example 1.

[0074] After etching the Inconel 600 high-temperature alloy ultrafine wire using the metallographic etchant and etching method of this embodiment, under appropriate magnification conditions, the grain boundary outline of the Inconel 600 high-temperature alloy ultrafine wire is distinct, the second phase is clearly distinguishable, and the microstructure is uniform and consistent, which can meet the requirements of grain size evaluation.

[0075] Comparative Example 1 This comparative example uses hydrochloric acid-hydrogen peroxide etchant, a technique already in use, to perform metallographic etching on GH5188 high-temperature alloy ultrafine wires. The GH5188 high-temperature alloy ultrafine wires have a diameter of 0.15 mm and are in a solution-treated state at 1000℃.

[0076] The GH5188 high-temperature alloy ultrafine wire was inlaid, ground, and polished using the same method as in Example 1 to obtain a metallographic sample of the inlaid high-temperature alloy ultrafine wire. The metallographic etchant was prepared as follows: hydrochloric acid (analytical grade, 36% by mass) and hydrogen peroxide (analytical grade, 30% by mass) were mixed at a volume ratio of 1:1 and stirred until homogeneous to obtain the hydrochloric acid-hydrogen peroxide etchant. The etching process was as follows: the inlaid high-temperature alloy ultrafine wire metallographic sample was immersed in the above hydrochloric acid-hydrogen peroxide etchant and etched at room temperature for 13 seconds. The etched metallographic sample was rinsed with water and dried. The microstructure was observed as follows. Figure 3 As shown, under 500x magnification, the corrosion is uneven, and the degree of corrosion varies significantly in different areas of the test surface. Some areas are over-corroded while others are under-corroded. The grain boundaries are blurred and discontinuous, making it impossible to accurately assess the grain size.

[0077] Example 4 Example 4 provides a metallographic etchant that differs from Example 1 in the amount of anhydrous copper sulfate used. In Example 4, the amount of anhydrous copper sulfate used is 60 parts.

[0078] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0079] The above-mentioned metallographic etchant was used to perform metallographic etching on the ultrafine wire of GH5188 high-temperature alloy. The results showed that the grain boundaries were clearly distinguishable and there were no obvious corrosion pits on the surface, which met the requirements for grain size evaluation.

[0080] Comparative Example 2 Comparative Example 2 provides a metallographic etchant that differs from Example 1 in the amount of anhydrous copper sulfate used. In Comparative Example 2, the amount of anhydrous copper sulfate used is 5 parts.

[0081] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0082] Metallographic etching of GH5188 high-temperature alloy ultrafine wire with the above metallographic etchant was performed. The results showed that the grain boundaries were not fully revealed, the inspection surface was under-etched, and the microstructure contrast in the metallographic image was insufficient.

[0083] Comparative Example 3 Comparative Example 3 provides a metallographic etchant that differs from Example 1 in the amount of anhydrous copper sulfate used. The amount of anhydrous copper sulfate in Comparative Example 3 is 70 parts.

[0084] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0085] Metallographic etching of GH5188 high-temperature alloy ultrafine wires with the above-mentioned metallographic etchant was performed. The results showed that the grain boundaries were widened and the details were lost due to over-etching.

[0086] Example 5 Example 5 provides an application of a metallographic etchant, which differs from Example 1 in that the temperature at which the metallographic etchant is heated is different. In Example 5, the metallographic etchant is heated to 70°C, and the etching time is shortened to 3 seconds.

[0087] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0088] The above-mentioned metallographic etchant was used to perform metallographic etching on the ultrafine wire of GH5188 high-temperature alloy. The results showed that the grain boundaries were clearly distinguishable and could meet the requirements for grain size evaluation. However, the etching rate was relatively fast and precise timing was required.

[0089] Comparative Example 4 Comparative Example 4 provides an application of a metallographic etchant, which differs from Example 1 in that the temperature at which the metallographic etchant is heated is different. In Comparative Example 4, the metallographic etchant is heated to 25°C, and the etching time is 15 seconds.

[0090] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0091] The above-mentioned metallographic etchant was used to perform metallographic etching on the ultrafine wire of GH5188 high-temperature alloy. The results showed that the etching time was too long, the sample surface was under-etched, and the grain boundaries were not clear.

[0092] Comparative Example 5 Comparative Example 5 provides an application of a metallographic etchant, which differs from Example 1 in that the metallographic etchant is heated at a different temperature. In Comparative Example 5, the metallographic etchant is heated to 80°C.

[0093] The remaining steps and parameters are the same as in Example 1, and will not be repeated here.

[0094] The above-mentioned metallographic etchant was used to perform metallographic etching on the ultrafine wire of GH5188 high-temperature alloy. The results showed that the etching was severe, and the sample surface turned black due to over-etching, making it impossible to observe the microstructure.

[0095] Comparing Examples 1, 4, and 2-3, it can be seen that the content of anhydrous copper sulfate must be controlled within the range of 10 to 60 parts. If it is below this range, the corrosion driving force is insufficient, and if it is above this range, the solution is unstable and prone to over-corrosion, and a clear metallographic structure cannot be obtained.

[0096] Comparing Examples 1, 5, and 4-5, it can be seen that when the metallographic etchant is applied, the corrosion reaction rate is moderate when the heating temperature of the metallographic etchant is controlled within the range of 40℃ to 70℃. If the temperature is lower than this range, the corrosion rate is too slow, resulting in unevenness; if the temperature is higher than this range, the reaction is too intense, resulting in over-corrosion.

[0097] In summary, this application provides a metallographic etchant specifically for ultra-fine high-temperature alloy wires with a diameter ≤0.5mm, its preparation method, and its application. By using 10-60 parts of copper sulfate pentahydrate to provide selective corrosion driving force, 90-150 parts of hydrochloric acid to provide passivation film destruction ability, and 9-20 parts of sulfuric acid to regulate reaction stability, these three analytically pure reagents achieve synergistic chemical action within a specific ratio range. This solves the technical problems of existing etchants causing excessively rapid and uncontrollable corrosion rates in the micro-areas of ultra-fine wires, poor corrosion uniformity leading to corrosion pits, and blurred grain boundary displays.

[0098] Furthermore, one or more technical solutions in the embodiments of this application have at least the following technical effects or advantages: The metallographic etchant in this embodiment consists of only three analytically pure reagents: copper sulfate pentahydrate, hydrochloric acid, and sulfuric acid. All raw materials used are commonly used reagents in metallographic laboratories, which are widely available, inexpensive, require no special storage conditions, and are simple to prepare.

[0099] The embodiments of this application are highly adaptable to the grades and states of high-temperature alloys. They are applicable to both cobalt-based and nickel-based high-temperature alloys. Furthermore, they are widely adaptable to different heat treatment states, suitable for metallographic preparation in various states such as high-temperature solution state above 900℃ and aged state.

[0100] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A metallographic etchant for ultrafine high-temperature alloy wires, characterized in that, The raw materials for preparing the metallographic etchant, by mass parts, include: copper sulfate pentahydrate: 10 to 60 parts, hydrochloric acid: 90 to 150 parts, and sulfuric acid: 9 to 20 parts; wherein the copper sulfate pentahydrate, the hydrochloric acid, and the sulfuric acid are all analytical grade reagents.

2. The metallographic etchant according to claim 1, characterized in that, The raw materials for preparing the metallographic etchant, by mass, include: copper sulfate pentahydrate: 35 parts, hydrochloric acid: 115-120 parts, and sulfuric acid: 12-13 parts.

3. A method for preparing a metallographic etchant according to claim 1 or 2, characterized in that, Includes the following steps: The copper sulfate pentahydrate is mixed with the hydrochloric acid to obtain a first mixture; The mixture was stirred until the copper sulfate pentahydrate was completely dissolved to obtain a copper sulfate pentahydrate-hydrochloric acid solution. The sulfuric acid was added to the copper sulfate pentahydrate-hydrochloric acid solution to obtain a second mixture; The second mixture is stirred to obtain the metallographic etchant.

4. An application of the metallographic etchant according to claim 1 or 2, characterized in that, The metallographic etchant is used in the metallographic etching of ultrafine wires of high-temperature alloys.

5. The application according to claim 4, characterized in that, The diameter of the high-temperature alloy ultrafine wire is ≤0.5mm.

6. The application according to claim 4, characterized in that, The high-temperature alloy ultrafine wire includes either nickel-based high-temperature alloy ultrafine wire or cobalt-based high-temperature alloy ultrafine wire.

7. The application according to claim 4, characterized in that, Includes the following steps: The metallographic etchant is heated to obtain a thermal metallographic etchant; The high-temperature alloy ultrafine wire metallographic sample that has undergone mounting treatment is immersed in the hot metallographic etchant for etching to obtain an etched metallographic sample. The corroded metallographic sample was cleaned and dried sequentially to obtain the metallographic sample to be observed.

8. The application according to claim 7, characterized in that, The heating temperature is 40℃~70℃; or, The heating temperature is 50℃~60℃.

9. The application according to claim 7, characterized in that, The corrosion time is 3s to 10s; or, The corrosion time is 5s to 6s.

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