Method for eliminating black spots induced by EBSD metal sample electrolytic polishing preparation
By combining wire cutting, ultrasonic cleaning, multi-stage sandpaper grinding, and specific electropolishing parameters, the problem of black spots during the electropolishing process of EBSD samples was solved, and high-quality EBSD samples were prepared, which are applicable to a variety of metal materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- YANGZHOU UNIV
- Filing Date
- 2025-12-15
- Publication Date
- 2026-05-05
AI Technical Summary
During EBSD sample preparation, black spots often appear after the electropolishing step, affecting the observation and analysis of microstructures, and existing technologies have not been able to effectively solve this problem.
Electropolishing is performed using wire cutting, ultrasonic cleaning, multi-stage sandpaper grinding, diamond polishing paste, and a specially formulated electrolyte. Electropolishing parameters such as voltage and current are controlled to ensure that the sample surface is free of black spots.
High-quality, black-spot-free EBSD samples were prepared, suitable for different metallic materials, with clear microstructure observation and wide applicability.
Smart Images
Figure CN121978144A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of EBSD sample preparation technology, specifically to a method for eliminating black spots induced during the electropolishing preparation of EBSD metal samples. Background Technology
[0002] The core function of EBSD (Electron Backscatter Diffraction) technology is to perform qualitative and quantitative analysis of the microstructure of crystalline materials. By detecting and analyzing diffraction patterns in a scanning electron microscope, it rapidly acquires crystallographic information of micro-regions on the material surface, enabling precise characterization of grain orientation, size, distribution, and phase composition. It can also identify grain boundary types, analyze deformation and recrystallization degrees, making it a powerful tool for studying material texture, phase transformation, deformation mechanisms, and failure analysis. As is well known, the EBSD sample preparation steps are as follows: sampling → cleaning → rough grinding → fine grinding → rough polishing → fine polishing → electropolishing → observation. However, in routine EBSD sample preparation, especially after the electropolishing step, black spots often appear on the surface due to the current, severely affecting normal microstructural observation, detection, and analysis. This has become a pressing sample preparation problem in scientific research. Preliminary investigations have not yet found a convenient and rapid solution to this problem. Summary of the Invention
[0003] The purpose of this invention is to provide a method for eliminating black spots induced during the electropolishing of EBSD metal samples, so as to solve the technical problems mentioned in the background art.
[0004] To achieve the above objectives, the present invention provides the following technical solution: S1. Cutting and cleaning the sample: Cut the sample with a wire EDM machine, clean it in an ultrasonic cleaner and then blow it dry. S2. Coarse grinding: Use sandpaper on a metallographic grinding machine to remove the hardened layer produced by wire cutting; S3. Fine grinding: Use sandpaper with different grits to wet grind the sample in order of increasing grit. Each grinding session should ensure that the sample is rotated 90° and the scratches from the next grinding session cover those from the previous one. S4. Rough polishing: Lay the polishing cloth flat on the polishing machine, apply the first diamond polishing paste evenly, and polish until only shallow scratches remain on the sample surface. Add a small amount of distilled water during the rough polishing process. S5. Fine polishing: Apply the second diamond polishing paste evenly and continuously add distilled water to the surface of the polishing sample until it becomes mirror-like, then rinse and blow dry; S6. Prepare the electrolyte: Prepare a mixed solution by adding anhydrous ethanol and perchloric acid in the order of addition. After preparation, let it stand until the reaction is complete and then cool to room temperature. S7. Electrolytic polishing: Set the parameters of the electrolytic polishing machine to 25V voltage, 1.45A~1.55A current, and 12s time. Clamp the anode of the electrolytic polishing machine onto the sample. After the electrolysis starts, immerse the observation surface of the sample in the electrolyte. After the electrolysis is completed, rinse and dry immediately.
[0005] Furthermore, in step S3, if the fine grinding process cannot remove the scratches from the previous mesh size at a high mesh size, then it returns to the previous mesh size for re-grinding, and the force applied to the sample decreases as the mesh size increases.
[0006] Furthermore, the ultrasonic cleaning process in step S1 specifically involves adding 75% anhydrous ethanol, controlling the temperature at 40°C, and cleaning for ten minutes.
[0007] Furthermore, in step S2, coarse grinding uses 80-grit sandpaper, and in step S3, fine grinding uses sandpaper with grits ranging from low to high: 100, 200, 500, 800, and 1000. Distilled water is used for wet grinding during the fine grinding process.
[0008] Furthermore, in step S4, the first diamond polishing paste uses a W2.5 particle size, and in step S5, the second diamond polishing paste uses a W0.5 particle size.
[0009] Furthermore, in step S6, the electrolyte is prepared as follows: the volume ratio of perchloric acid to anhydrous ethanol is 1:9; the concentration of perchloric acid is 50%; and the concentration of anhydrous ethanol in the electrolyte is 100%.
[0010] Furthermore, in step S5, the rinsing process uses 75% anhydrous ethanol; in step S7, the rinsing process uses 99.7% anhydrous ethanol.
[0011] Beneficial effects: This invention is simple and safe, can prepare high-quality EBSD samples without black spots, and has a wide range of applications, applicable to the preparation of EBSD samples of different metal materials. Attached Figure Description
[0012] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0013] Figure 1 This is an optical microscope observation of GCr15 after polishing using the method of Example 1 of the present invention; Figure 2 This is an optical microscope observation of GCr15 after polishing using the method of Comparative Example 1. Figure 3This is an optical microscope observation of GCr15 after polishing using the method of Comparative Example 2. Figure 4 This is an optical microscope observation of GCr15 after polishing using the method of Comparative Example 3. Figure 5 This is an optical microscope observation of GCr15 after polishing using the method of Comparative Example 4. Figure 6 This is an optical microscope observation of GCr15 after polishing using the method of Comparative Example 5. Figure 7 This is an optical microscopic observation of GCr15 after polishing using the method of Comparative Example 6. Figure 8 This is an optical microscopic observation of GCr15 after polishing using the method of Comparative Example 7. Figure 9 EBSD metal sample of steel grade 18CrNiMo7-6 prepared using the method in Example 1 is observed under an optical microscope. Figure 10 An EBSD metal sample of steel grade GCr15 was observed under an optical microscope. Detailed Implementation
[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0015] GCr15 steel is a high-carbon, high-chromium cold work die steel with high hardness and suitable toughness, making it a high-performance alloy bearing steel. Its chemical composition is: C: 1.01±0.02%, Cr: 1.41±0.05%, Mo: 0.05±0.003%, Si: 0.21±0.01%, Mn: 0.35±0.03%. This steel was used as an EBSD sample.
[0016] like Figures 1-10 As shown, the present invention provides a method for eliminating black spots induced by electropolishing of EBSD metal samples, the specific steps of which are as follows: Example
[0017] S1. Use a wire EDM machine to cut the sample into 1cm×1cm dimensions; Ultrasonic cleaning: Place the sample in an ultrasonic cleaner, add 75% anhydrous ethanol, control the temperature at 40℃, clean for ten minutes, and then dry the sample with a hair dryer. S2. Rough grinding: Use 80-grit sandpaper on a metallographic grinding machine to remove the hardened layer produced by wire cutting; S3. Fine grinding: The sample is wet-ground with 100, 200, 500, 800 and 1000 grit sandpaper in sequence. Each time the sample is ground, it is necessary to rotate the sample by 90°. The scratches of the next grinding should cover the scratches of the previous grinding. It is important to note that distilled water is used for wet grinding during the fine grinding process. S4. Rough polishing: Lay the polishing cloth flat on the polishing machine, apply W2.5 diamond polishing paste evenly, and polish until only shallow scratches remain on the sample surface. During the rough polishing process, only a small amount of distilled water needs to be added, and keep your hands steady. S5. Fine polishing: Apply W0.5 diamond polishing paste evenly and continuously add distilled water to the surface of the polishing sample until it becomes mirror-like. Then rinse with 75% anhydrous ethanol and dry with a hair dryer. S6. Prepare the electrolyte: Prepare perchloric acid and anhydrous ethanol at a volume ratio of 1:9, wherein the concentration of perchloric acid is 50% and the concentration of anhydrous ethanol is 100%. In this embodiment, take 10 ml of perchloric acid solution and 40 ml of anhydrous ethanol solution, and use a dropper with a guide rod. The key point of this step is the order of solution preparation. Anhydrous ethanol should be added to the beaker first, followed by the perchloric acid solution. After preparation, let it stand until the solution reaction is complete and cool to room temperature. S7. Electrolytic Polishing: Set the electrolytic polishing machine parameters to 25V, 1.5A, and 12s. First, hold the sample with tweezers, then clamp the anode of the electrolytic polishing machine onto it. After clicking start, immerse the observation surface of the sample in the electrolyte. Immediately after electrolysis, rinse with 99.7% anhydrous ethanol, then dry with a hair dryer. Figure 1 As shown, the sample has no black spots, a bright surface, and a uniform distribution. During the electrolytic polishing process, it is necessary to ensure that the sample surface is immersed in the electrolyte and that the sample surface is parallel to the negative electrode patch of the electrolytic device. During the electrolysis process, the sample should be kept stable. After the electrolysis is completed, the sample surface should be cleaned with anhydrous ethanol immediately.
[0018] The difference between Examples 2 and 3 and Example 1 lies in the parameters of the electropolishing machine in step S7: Example
[0019] The parameters of the electropolishing machine were set to 25V voltage, 1.45A current, and 12s time. Example
[0020] The parameters of the electropolishing machine were set to 25V voltage, 1.55A current, and 12s time.
[0021] The following Comparative Examples 1-7 adopt steps S1-S6 of Example 1, and the electropolishing machine parameters in step S7 are as follows: Comparative Example 1 The parameters for the electrolytic polishing machine are: voltage 25V, current 0.8A, time 15s. Figure 2 As shown, numerous black spots appeared on the surface of the sample; Comparative Example 2 The parameters for the electrolytic polishing machine are: voltage 25V, current 0.4A, time 15s. Figure 3 As shown, the black spots on the sample only decreased but did not disappear; Comparative Example 3 The parameters for the electrolytic polishing machine are: voltage 25V, current 1.2A, time 15s. Figure 4 As shown, the large black spots have disappeared, but small black spots remain; Comparative Example 4 The parameters for the electrolytic polishing machine are: voltage 25V, current 1.4A, time 15s. Figure 5 As shown, the number of dark spots has decreased, but there are still some light spots. Comparative Example 5 The parameters for the electrolytic polishing machine are: voltage 25V, current 1.6A, time 15s. Figure 6 As shown, the number of light-colored black spots has decreased, but some areas are still excessively corroded. Comparative Example 6 The parameters for the electrolytic polishing machine are: voltage 25V, current 1.5A, time 15s. Figure 7 As shown, the light-colored black spots have been further reduced, but they have clearly not reached the optimal state. Comparative Example 7 The parameters for the electrolytic polishing machine are: voltage 25V, current 1.5A, time 10s. Figure 8 As shown, the corrosion is slightly lighter and the black spots have increased slightly.
[0022] As shown in the table below, under the conditions of 25V voltage and 15s time: Voltage Current time Corresponding diagram Comparative Example 1 25V 0.8A 15s Figure 2 Comparative Example 2 25V 0.4A 15s Figure 3 Comparative Example 3 25V 1.2A 15s Figure 4 Comparative Example 4 25V 1.4A 15s Figure 5 Comparative Example 5 25V 1.6A 15s Figure 6 Comparative Example 6 25V 1.5A 15s Figure 7 As the current decreases, the black spots on the sample only decrease but do not disappear. However, when the current increases, large black spots on the sample disappear, but small black spots still remain. As the current increases, the black spots become lighter, but there are also cases where some areas are corroded too deeply. Therefore, under the same time, a small change in current cannot effectively eliminate black spots, but can only change the size of the black spots.
[0023] At a voltage of 25V and a current of 1.5A: Voltage Current time Corresponding diagram Comparative Example 6 25V 1.5A 15s Figure 7 Comparative Example 7 25V 1.5A 10s Figure 8 Example 1 25V 1.5A 12s Figure 1 The above comparison shows that the polishing parameters given in Example 1 are superior to those of other comparative examples, which have no black spots, a bright surface, and a uniform distribution.
[0024] EBSD metal samples were prepared using steel grades 18CrNiMo7-6 and GCr15 according to this invention. Please refer to... Figure 9 and Figure 10 The prepared samples have the following characteristics: High resolution and integrity: The low noise (unlabeled black dots) in the image indicates high quality of Kikuchi flower pattern and extremely high calibration success rate, indicating excellent sample surface preparation quality and no residual stress layer interference.
[0025] Clear grain boundaries: The boundaries between grains with different orientations are smooth and continuous, the lath boundaries are clearly distinguishable, and there is no obvious orientation ambiguity.
[0026] Rich in structural detail: The ability to clearly distinguish extremely fine lath bundles and blocks in this lath-like microstructure indicates that the spatial resolution is sufficient to resolve complex internal structures.
[0027] Therefore, this method can be used to prepare high-quality EBSD metal samples.
[0028] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.
[0029] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.
Claims
1. A method for eliminating black spots induced during electropolishing of EBSD metal samples, characterized in that, Includes the following steps: S1. Cutting and cleaning the sample: Cut the sample with a wire EDM machine, clean it in an ultrasonic cleaner and then blow it dry. S2. Coarse grinding: Use sandpaper on a metallographic grinding machine to remove the hardened layer produced by wire cutting; S3. Fine grinding: Use sandpaper with different grits to wet grind the sample in order of increasing grit. Each grinding session should ensure that the sample is rotated 90° and the scratches from the next grinding session cover those from the previous one. S4. Rough polishing: Lay the polishing cloth flat on the polishing machine, apply the first diamond polishing paste evenly, and polish until only shallow scratches remain on the sample surface. Add a small amount of distilled water during the rough polishing process. S5. Fine polishing: Apply the second diamond polishing paste evenly and continuously add distilled water to the surface of the polishing sample until it becomes mirror-like, then rinse and blow dry; S6. Prepare the electrolyte: Prepare a mixed solution by adding anhydrous ethanol and perchloric acid in the order they are added. After preparation, let it stand until the reaction is complete and then cool to room temperature. S7. Electrolytic polishing: Set the parameters of the electrolytic polishing machine to 25V voltage, 1.45A~1.55A current, and 12s time. Clamp the anode of the electrolytic polishing machine onto the sample. After the electrolysis starts, immerse the observation surface of the sample in the electrolyte. After the electrolysis is completed, rinse and dry immediately.
2. The method for eliminating black spots induced during electropolishing of EBSD metal samples according to claim 1, characterized in that, If the fine grinding process in step S3 fails to remove the scratches from the previous mesh size at a high mesh size, then the process returns to the previous mesh size for re-grinding, and the force applied to the sample decreases as the mesh size increases.
3. The method for eliminating black spots induced by electropolishing of EBSD metal samples according to claim 1, characterized in that: The ultrasonic cleaning process in step S1 involves adding 75% anhydrous ethanol, controlling the temperature at 40°C, and cleaning for ten minutes.
4. The method for eliminating black spots induced by electropolishing of EBSD metal samples according to claim 1, characterized in that: In step S2, coarse grinding uses 80-grit sandpaper, and in step S3, fine grinding uses sandpaper with grits ranging from low to high: 100, 200, 500, 800, and 1000. Distilled water is used for wet grinding during the fine grinding process.
5. The method for eliminating black spots induced by electropolishing of EBSD metal samples according to claim 1, characterized in that: In step S4, the first diamond polishing paste used for coarse polishing has a W2.5 grit size, and in step S5, the second diamond polishing paste used for fine polishing has a W0.5 grit size.
6. The method for eliminating black spots induced by electropolishing of EBSD metal samples according to claim 1, characterized in that: The electrolyte preparation in step S6 is as follows: the volume ratio of perchloric acid to anhydrous ethanol is 1:9; the concentration of perchloric acid is 50%; and the concentration of anhydrous ethanol in the electrolyte preparation is 100%.
7. The method for eliminating black spots induced by electropolishing of EBSD metal samples according to claim 1, characterized in that: In step S5, the rinsing process uses 75% anhydrous ethanol; in step S7, the rinsing process uses 99.7% anhydrous ethanol.