Transmission electron microscope sample preparation method of high-temperature bearing steel containing large-size carbide

Abstract

The invention discloses a transmission electron microscope sample preparation method of high-temperature bearing steel containing large-size carbides, and belongs to the technical field of microstructure characterization of metal materials. In order to solve the problem of high-temperature bearing steel transmission electron microscope sample preparation, the invention provides a transmission electron microscope sample preparation method for high-temperature bearing steel containing large-size carbides, which comprises the following steps: cutting the high-temperature bearing steel, grinding and thinning step by step to prepare a wafer with the thickness of 40-55 microns and the diameter of 3 + / -0.1 mm; ethyl alcohol, perchloric acid and ethylene glycol monobutyl ether serve as electrolyte, the electrolysis temperature and the electrolysis current are controlled, electrolysis double-spraying thinning is conducted at the stepped flow speed, finally, cleaning and airing are conducted, and the thin film is obtained. The high-temperature bearing steel TEM sample containing the large-size carbide is successfully prepared by adopting step-by-step grinding and thinning, electrolyte optimization, double-spraying condition adjustment, electrolysis temperature and electrolysis current control and step flow rate control.

Description

Technical Field

[0001] This invention belongs to the field of microstructure characterization technology of metallic materials, specifically relating to a transmission electron microscope sample preparation method for high-temperature bearing steel containing large-sized carbides. Background Technology

[0002] High-temperature bearing steel is a typical molybdenum-based high-speed steel with a carbon content greater than 0.7 wt% and the addition of elements such as Cr, Mo, and V. After quenching and multiple tempering treatments, the resulting martensitic matrix contains a large number of alloy carbides (including MC, M2C, M...). 23 High-temperature bearing steels (such as C6 and M6C) possess excellent high-temperature hardness, dimensional stability, and wear resistance. In the mid-1980s, high-temperature bearing steels began to be used in the manufacture of main shaft bearings for aero-engines and are currently the most widely used aero-engine bearing materials.

[0003] High-temperature bearing steel uses carbides as the strengthening phase, and its fatigue performance is affected by factors such as the size, quantity, and distribution of carbides. During the solidification process of high-temperature bearing steel, due to the segregation of alloying elements, ultra-large primary carbides are easily formed with irregular shapes. These carbides act as initiation sources of fatigue cracks during service, leading to fatigue failure of the bearing. Therefore, the study of the morphology, distribution, and structure of carbides in high-temperature bearing steel is of great significance. Identifying and characterizing the material structure, composition, and distribution at small scales has made transmission electron microscopy (TEM) the primary tool for microstructural analysis of steel.

[0004] In existing technologies, common methods for preparing metallic TEM samples include ion thinning, focused ion beam (FIB), and electrolytic double-jet techniques, each with its own characteristics and applicable conditions. Compared to electrolytic double-jet TEM sample preparation, ion thinning is slower and less efficient (sample preparation typically takes several hours), and the initial sample preparation is more difficult (sample thickness generally needs to be less than 25 μm, requiring the use of a pitting apparatus). Focused ion beam TEM sample preparation is extremely costly and slow, making it unsuitable for large-scale sample processing. Furthermore, both ion thinning and focused ion beam techniques are prone to forming amorphous damage layers during processing.

[0005] Electrolytic dual-jet thinning is a simple, fast, and low-cost method applicable to TEM sample preparation of various metallic materials. Electrolytic dual-jet preparation involves simultaneously thinning both sides of the sample using two nozzles. The infrared detection system rapidly terminates the thinning reaction the instant the sample is perforated, ensuring the integrity of the thinned area. During electrolytic dual-jet preparation, the sample is connected to the anode of the electrolysis unit, and the electrolyte is connected to the cathode. A pump sprays the electrolyte from the cathode onto both sides of the sample. Applying voltage causes electrolytic polishing of the sample. Figure 1However, the electrolytic double-jet method has many shortcomings for preparing steel samples with large-sized carbides. For example, due to the large difference in composition between the carbides and the matrix phases, one phase is prone to preferential reaction, forming a hollow network structure; unsuitable electrolyte composition can cause the sample surface to become dull, forming oxide adhesion, resulting in poor quality of the thin area and affecting the observation and analysis of the internal structure; or unsuitable electrolytic double-jet conditions can lead to the absence of a thin area in the sample, resulting in a low sample preparation success rate. Therefore, for high-temperature bearing steel containing large-sized carbides, ion thinning and focused ion beam (FIB) sample preparation are often used, but this results in extremely high sample preparation costs and low efficiency.

[0006] CN109406556A discloses a method for preparing GH4169 high-temperature alloy transmission electron microscopy samples, comprising: reducing the thickness of the GH4169 high-temperature alloy sample to 70-80 μm and then using an electrolytic double-jet method for thinning; the electrolytic double-jet method includes: placing the 70-80 μm sample in an electrolytic double-jet device for electrochemical thinning, the electrolyte being composed of 10-15% perchloric acid and 85-90% anhydrous ethanol by volume; the electrolytic voltage for electrochemical thinning being 30-35V; the electrolyte temperature being controlled at -15 to -10℃ during the electrochemical thinning process; and the GH4169 high-temperature alloy sample being mechanically thinned to 70-80 μm before the electrolytic double-jet method, and then subjected to double-sided cutting. However, this method requires mechanical thinning of a relatively thick layer and double-sided polishing. Furthermore, its design of electrolyte composition and electrolysis parameters (voltage, temperature) based on GH4169 high-temperature alloy steel is not suitable for high-temperature bearing steel containing large-sized carbides.

[0007] CN114486959A discloses a method for preparing eutectic high-entropy alloy TEM samples, comprising: cutting and polishing the eutectic high-entropy alloy sample to obtain a eutectic high-entropy alloy sample sheet with a thickness ranging from 40 to 60 μm; performing electrolytic double-jet thinning on the eutectic high-entropy alloy sample sheet to obtain the eutectic high-entropy alloy TEM sample; wherein, in the electrolytic double-jet thinning process, the electrolyte used is composed of perchloric acid with a volume fraction of 5-10% and ethanol of 90-95%; the electrolysis voltage is 10-30V; the electrolysis current is 4-8mA; the electrolysis temperature corresponding to the electrolyte is controlled at -40 to -25℃; and the diameter of the liquid surface formed after the electrolyte sprayed from the two nozzles of the electrolytic double-jet apparatus comes into contact is 3-5 mm. However, the eutectic high-entropy alloy samples in this method are fundamentally different from high-temperature bearing steel in terms of composition and microstructure. The two-phase or multi-phase in eutectic high-entropy alloys are generally distributed relatively uniformly according to certain rules, while the distribution of carbides in high-temperature bearing steel is random. The size and shape of carbides are irregular, and they are more distributed at grain boundaries. Therefore, this method is not suitable for high-temperature bearing steel containing large-sized carbides.

[0008] CN118190559A discloses a method for preparing transmission electron microscopy (TEM) samples of hot-dip galvanized steel coatings using electrolytic double-jet printing, comprising: Step 1, mechanically thinning the original hot-dip galvanized steel block sample to a thickness of 40±5μm, and punching holes in the mechanically thinned sample; Step 2, using an electrolytic double-jet thinning instrument to perform double-jet thinning on the punched sample, wherein the electrolytic double-jet thinning instrument is equipped with an electrolytic cell containing a 9±2% perchloric acid-alcohol solution, and the temperature of the electrolytic cell is -20±5℃, below a preset temperature below zero; the punched sample is inserted into the electrolytic cell, and the coating surface is protected by a protective structure until the double-jet thinning is completed; Step 3, starting the electrolytic double-jet thinning instrument, adjusting the double-jet voltage to 30±2V, setting the transmittance of the electrolytic double-jet thinning instrument, i.e., the photosensitivity stop value, to 150~300, and stopping the electrolytic double-jet thinning instrument after perforating the punched sample to the preset transmittance. The sample is removed, cleaned, and dried to obtain the final transmission electron microscope (TEM) sample. However, this method is based on hot-dip galvanized steel and involves designing the electrolyte composition and electrolysis parameters (current, temperature, etc.), and is not suitable for high-temperature bearing steel containing large-sized carbides.

[0009] Therefore, for high-temperature bearing steel containing large-sized carbides, there is an urgent need to develop a new transmission electron microscopy (TEM) sample preparation method to overcome the problems of existing processes. Summary of the Invention

[0010] The technical problem this invention aims to solve is that existing transmission electron microscopy (TEM) sample preparation methods are not suitable for high-temperature bearing steel containing large-sized carbides, resulting in issues such as hollowed-out thin areas in the sample, dull surface, absence of thin areas, high sample preparation costs, and low efficiency.

[0011] To address the aforementioned technical problems, this invention provides a method for preparing high-temperature bearing steel containing large-sized carbides for transmission electron microscopy, comprising the following steps: A. Preparation of electrolytic double-spray discs: The high-temperature bearing steel sample is cut into thin slices, and the slices are gradually thinned by grinding to a thickness of 40-55 μm. Then, a disc with a diameter of 3±0.1 mm is punched out. In step A, the stepwise sanding and thinning process specifically involves: under the rinsing of flowing water, first using 200# to 400# wet sandpaper to sand the sheet to a thickness of 250 to 300 μm, then using 500# to 600# wet sandpaper to sand the sheet to a thickness of 120 to 150 μm, then using 800# to 1200# wet sandpaper to sand the sheet to a thickness of 70 to 100 μm, and finally using 1500# to 2000# wet sandpaper to sand the sheet to a thickness of 40 to 55 μm; B. Electrolytic dual-jet thinning: B1. The solvent of the electrolyte is anhydrous ethanol, and the solutes are perchloric acid and ethylene glycol monobutyl ether, with a volume fraction of 7-13% for perchloric acid and 0.5-10% for ethylene glycol monobutyl ether. B2. Control the electrolysis temperature to -35 to -25℃; B3. When -35℃≤electrolysis temperature<-30℃, control the electrolysis current to be 30mA≤electrolysis current<40mA; when -30℃≤electrolysis temperature≤-25℃, control the electrolysis current to be 40mA≤electrolysis current≤50mA. B4. Scan the anodic polarization curve to determine the electrolysis voltage; B5. When starting dual spraying, use a fast flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is 2mm < diameter ≤ 3mm; after dual spraying for 15 to 35 seconds, reduce the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is 1mm ≤ diameter ≤ 2mm. B6. Electrolytically thin the sample disc until it is perforated by double spraying, then stop the electrolytic reaction; C. Cleaning: After the sample disc is thinned by electrolytic double spraying, it is cleaned and dried to obtain the transmission electron microscope sample.

[0012] In the above-mentioned transmission electron microscopy sample preparation method, in step A, the thickness of the thin slice is 0.5 to 1 mm.

[0013] In the above-mentioned transmission electron microscope sample preparation method, step A involves punching out a hole using a dedicated transmission electron microscope punch.

[0014] In the above-mentioned transmission electron microscopy sample preparation method, in step B1, the electrolyte is prepared by first mixing anhydrous ethanol and ethylene glycol monobutyl ether evenly, then slowly adding perchloric acid and stirring evenly.

[0015] In the above-mentioned transmission electron microscopy sample preparation method, in step B2, liquid nitrogen is added to the electrolyte to control the electrolysis temperature to -35 to -25°C.

[0016] In the above-mentioned transmission electron microscopy sample preparation method, in step B4, the electrolysis voltage is 18-45V.

[0017] In the above-mentioned transmission electron microscopy sample preparation method, step C involves cleaning with anhydrous ethanol.

[0018] In the above transmission electron microscopy sample preparation method, in step C, the width of the thin region of the obtained transmission electron microscopy sample is 8-15 μm.

[0019] The beneficial effects of this invention are: This invention employs a stepwise grinding process to thin mechanically cut samples to a thickness of 40–55 μm, improving grinding efficiency while ensuring sample quality. By determining a suitable electrolyte, adding an appropriate ratio of ethylene glycol monobutyl ether, and adjusting the dual-spray conditions, controlling the electrolysis current and temperature, and using stepped flow rate control to shorten the dual-spray time, the risk of sample surface oxidation and corrosion is reduced. This ensures that the thin region area of ​​the sample is large enough and that the edges do not curl, thus successfully preparing a high-temperature bearing steel TEM sample containing large-sized carbides. The thin region thickness is less than 100 nm, the thin region width is more than 8 μm, the thin region edge thickness is less than 20 nm, and most of the carbide precipitates are retained, meeting the characterization requirements for the morphology, distribution, and structure of high-temperature bearing steel and carbides in the steel.

[0020] The method of this invention is simple, fast and low-cost in sample preparation. It can be completed using existing equipment and can be extended to TEM sample preparation of steel materials with precipitates. It provides strong support for scientific innovation, technological improvement and theoretical research in related fields and has broad application value.

[0021] Currently, ion thinning sample preparation costs approximately 1000 yuan per sample, while focused ion beam sample preparation costs approximately 2000-3000 yuan per sample. Compared to the costs of ion thinning and focused ion beam sample preparation, the cost of electrolytic dual-jet sample preparation in this invention is negligible, resulting in significant economic benefits. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the electrolytic dual-jet thinning method of the present invention.

[0023] Figure 2 This is a bright-field characterization map of a random region of a TEM sample obtained in Example 1.

[0024] Figure 3 This is a bright-field characterization map of a random region of a TEM sample obtained in Example 1.

[0025] Figure 4 The STEM bright-field and EDS energy dispersive spectra of the TEM sample prepared in Example 2 are shown.

[0026] Figure 5 The image shows the bright-field characterization of the TEM sample prepared in Example 2. Detailed Implementation

[0027] Specifically, a transmission electron microscopy (TEM) sample preparation method for high-temperature bearing steel containing large-sized carbides includes the following steps: A. Preparation of electrolytic double-spray discs: The high-temperature bearing steel sample is cut into thin slices, and the slices are gradually thinned by grinding to a thickness of 40-55 μm. Then, a disc with a diameter of 3±0.1 mm is punched out. In step A, the stepwise sanding and thinning process specifically involves: under the rinsing of flowing water, first using 200# to 400# wet sandpaper to sand the sheet to a thickness of 250 to 300 μm, then using 500# to 600# wet sandpaper to sand the sheet to a thickness of 120 to 150 μm, then using 800# to 1200# wet sandpaper to sand the sheet to a thickness of 70 to 100 μm, and finally using 1500# to 2000# wet sandpaper to sand the sheet to a thickness of 40 to 55 μm; B. Electrolytic dual-jet thinning: B1. The solvent of the electrolyte is anhydrous ethanol, and the solutes are perchloric acid and ethylene glycol monobutyl ether, with a volume fraction of 7-13% for perchloric acid and 0.5-10% for ethylene glycol monobutyl ether. B2. Control the electrolysis temperature to -35 to -25℃; B3. When -35℃≤electrolysis temperature<-30℃, control the electrolysis current to be 30mA≤electrolysis current<40mA; when -30℃≤electrolysis temperature≤-25℃, control the electrolysis current to be 40mA≤electrolysis current≤50mA. B4. Scan the anodic polarization curve to determine the electrolysis voltage; B5. When starting dual spraying, use a fast flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is 2mm < diameter ≤ 3mm; after dual spraying for 15 to 35 seconds, reduce the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is 1mm ≤ diameter ≤ 2mm. B6. Electrolytically thin the sample disc until it is perforated by double spraying, then stop the electrolytic reaction; C. Cleaning: After the sample disc is thinned by electrolytic double spraying, it is cleaned and dried to obtain the transmission electron microscope sample.

[0028] In this invention, before electrolytic double-spraying, the sample needs to be prepared into a circular sheet with a thickness of 40-55 μm and a diameter of 3±0.1 mm. The quality of the electrolytic double-spraying disc directly affects the success rate of sample preparation. If the sample is too thick, the electrolysis process will be longer, which may cause the precipitated phase to be hollowed out. In step A, wire cutting tools are generally used to cut out thin sample sheets with a thickness of 0.5-1 mm. The size should not be too large, and the thickness of the sample sheet must be uniform during the grinding process.

[0029] In step A of this invention, the sample sheet is progressively thinned by using wet sandpaper of different grit sizes under the scouring of flowing water, reducing its thickness to 40–55 μm. The sample thickness must be uniform. Since deep scratches on the sample surface may cause perforation during the electrolytic double-jet process, leading to the cessation of the double-jet process and affecting the final thin area of ​​the sample, this invention correlates the required thinning thickness with the grit size of the wet sandpaper used in the progressive thinning process. This maximizes the grinding efficiency while ensuring sample preparation quality. After progressive thinning using this method, the sample does not require polishing.

[0030] In step A of this invention, the sample, after being progressively thinned by grinding, is punched into a circular disc with a diameter of 3±0.1 mm using a TEM-specific punch. The disc must be burr-free and flat. Burrs or unevenness at the sample edges may lead to poor contact between the sample and the anode clamp of the electrolytic double-jet apparatus, causing sample corrosion and affecting sample quality.

[0031] In step B1 of this invention, the electrolyte is prepared as follows: first, anhydrous ethanol and ethylene glycol monobutyl ether are mixed evenly, then perchloric acid is slowly added and stirred evenly to obtain the electrolyte. The perchloric acid, ethylene glycol monobutyl ether, and anhydrous ethanol are of analytical grade or higher purity, and the electrolyte is prepared fresh for each use. Ethylene glycol monobutyl ether acts as a cleaning agent in the double-spraying process, removing oil and oxides from the sample surface, inhibiting the adhesion and deposition of oxides on the sample surface that may occur during the double-spraying process, and improving the surface smoothness of the sample.

[0032] In steps B2-B4 of this invention, the method requires accurate control of the current density during electrolysis. A suitable current density is crucial for the size of the thin region of the sample and whether carbides within it detach. Too low a current density can easily cause sample etching and surface darkening; too high a current density, due to the large difference in composition between the precipitated phase and the matrix phase, can easily cause one phase to react preferentially, forming a hollow, mesh-like thin region. With the same electrolysis dual-spray equipment and sample, lowering the temperature reduces the electrolysis current because lower temperatures reduce the electrolysis reaction rate. For high-temperature bearing steel, when the electrolysis temperature is between -35 and -30°C (excluding -30°C), the electrolysis current should be between 30 and 40 mA (excluding 40 mA); when the electrolysis temperature is between -30 and -25°C, the electrolysis current should be between 40 and 50 mA. Because the distance between the cathode metal and the sample varies among different models of electrolytic double sprayers, the electrolyte resistance varies greatly. Therefore, the electrolysis voltage corresponding to the same electrolysis current varies greatly. The electrolysis voltage needs to be determined based on the anodic polarization curve. That is, before the sample is electrolyzed and sprayed, the anodic polarization curve (voltage-current curve) is measured first, and then the electrolysis voltage is determined based on the selected electrolysis current. The voltage is usually between 18 and 45V.

[0033] In step B2 of this invention, liquid nitrogen is added to the electrolyte to control the electrolysis temperature to -35 to -25°C (i.e., electrolyte temperature -35 to -25°C). At this temperature, the electrolysis reaction rate can be reduced, the current density of the sample during the electrolysis process can be controlled, and the stability of the liquid flow can be improved.

[0034] In step B5 of this invention, a relatively fast flow rate is used at the beginning of the dual spraying: the diameter of the liquid surface formed after the electrolyte phases from the two nozzles come into contact is 2-3 mm (excluding 2 mm); after 15-35 seconds of dual spraying, the flow rate is reduced, and the diameter of the liquid surface formed after the electrolyte phases from the two nozzles come into contact is approximately 1-2 mm. This invention uses a stepped flow rate control for the electrolyte flow rate in dual spraying: using a relatively fast flow rate at the beginning of dual spraying can shorten the dual spraying time and reduce the risk of oxidation and corrosion on the sample surface; reducing the electrolyte flow rate after a certain time can ensure that the thin area of ​​the sample is large enough and that the edges do not curl.

[0035] In step C of this invention, the cleaning is done with anhydrous ethanol. The cleaning and drying process is as follows: the sample is moved up and down in a beaker containing anhydrous ethanol to clean the electrolyte remaining on the sample. The anhydrous ethanol is replaced, and the sample is washed up and down again in anhydrous ethanol. The sample is then removed, immersed in anhydrous ethanol, removed, and placed on lint-free paper to dry, thus obtaining the TEM sample.

[0036] In step C of this invention, the thickness of the thin region of the obtained transmission electron microscope sample is less than 100 nm, the width of the thin region is 8 μm or more (generally 8 to 15 μm), the thickness of the thin region edge is less than 20 nm, and most of the carbide precipitates are retained, which meets the characterization requirements for the morphology, distribution and structure of high-temperature bearing steel and carbides in steel.

[0037] The present invention will be further described in detail below through embodiments, but the scope of protection of the present invention is not limited to the embodiments described herein.

[0038] Example 1: TEM sample preparation of high-temperature bearing steel.

[0039] 1. The sample was fabricated into a circular disc with a thickness of 45μm and a diameter of 3mm, as detailed below: (1) Using wire cutting, high-temperature bearing steel was cut into thin sample pieces to obtain circular pieces with a thickness of 0.6 mm and a diameter of 15 mm; (2) The sample was gradually thinned by grinding under the flushing of flowing water: first, the sample was ground to 280μm using 200# wet sandpaper, then the sample was ground to 145μm using 600# wet sandpaper, then the sample was ground to 75μm using 1000# wet sandpaper, and finally the sample was ground to 45μm using 2000# wet sandpaper. (3) Use a punch to punch out a circular sample with a diameter of 3mm. The edge is free of burrs and the sample is flat.

[0040] 2. Electrolytic double-jet thinning: Sample preparation was performed using a Struers TenuPol 5 electrolytic double-jet apparatus, as detailed below: (1) Prepare electrolyte: Add 880ml of anhydrous ethanol and 20ml of ethylene glycol monobutyl ether to the electrolyte tank, mix well, and then slowly add 100ml of perchloric acid. The reagent purity is analytical grade. Stir well. (2) Slowly add liquid nitrogen to the electrolyte tank until the temperature reaches -32℃; (3) Place the disc sample into the fixture, scan the anodic polarization curve, and select an electrolysis current of 33mA and an electrolysis voltage of 24V; (4) Adjust the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is about 2.5 mm; after spraying for 30 seconds, reduce the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is about 1.5 mm. (5) The sample is electrolyzed until it is thinned to the point of perforation, and the double spraying stops automatically.

[0041] 3. Sample cleaning: Remove the sample clamp and move it up and down in a beaker containing anhydrous ethanol to clean the electrolyte remaining on the sample. Replace with anhydrous ethanol and put the sample back into the clamp to clean it up and down again. Take out the sample and soak it in anhydrous ethanol for 10 seconds. Take out the sample and place it on a lint-free paper to dry to obtain the TEM sample.

[0042] 4. Check the sample preparation effect: Place this sample under a transmission electron microscope for observation. The thin region of this sample is about 11 μm wide, the thin region is flat, and most of the carbides are retained on the thin region, which can meet the TEM characterization requirements of the sample matrix and carbides. Figure 2 (Scale 200nm) Figure 3 (Scale 500 nm) TEM bright-field characterization of two randomly selected regions of this sample, where the elliptical particles are carbides in steel.

[0043] Example 2: TEM sample preparation of high-temperature bearing steel.

[0044] 1. The sample was fabricated into a circular disc with a thickness of 54μm and a diameter of 3mm, as detailed below: (1) Using wire cutting, high-temperature bearing steel was cut into thin sample pieces to obtain circular pieces with a thickness of 0.6 mm and a diameter of 15 mm; (2) The sample was gradually thinned by grinding under the flushing of flowing water: first, the sample was ground to 260μm using 400# wet sandpaper, then the sample was ground to 140μm using 600# wet sandpaper, then the sample was ground to 80μm using 1200# wet sandpaper, and finally the sample was ground to 54μm using 1500# wet sandpaper. (3) Use a punch to punch out a circular sample with a diameter of 3mm. The edge is free of burrs and the sample is flat.

[0045] 2. Electrolytic double-jet thinning: Sample preparation was performed using a Struers TenuPol 5 electrolytic double-jet apparatus, as detailed below: (1) Prepare electrolyte: Add 840ml of anhydrous ethanol and 50ml of ethylene glycol monobutyl ether to the electrolyte tank, mix well, and then slowly add 110ml of perchloric acid. The reagent purity is analytical grade. Stir well. (2) Slowly add liquid nitrogen to the electrolyte tank until the temperature reaches -28℃; (3) Place the disc sample into the fixture, scan the anodic polarization curve, and select an electrolysis current of 45mA and an electrolysis voltage of 35V; (4) Adjust the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is about 3 mm; after spraying for 15 seconds, reduce the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is about 2 mm. (5) The sample is electrolyzed until it is thinned to the point of perforation, and the double spraying stops automatically.

[0046] 3. Sample cleaning: Remove the sample clamp and move it up and down in a beaker containing anhydrous ethanol to clean the electrolyte remaining on the sample. Replace with anhydrous ethanol and put the sample back into the clamp to clean it up and down again. Take out the sample and soak it in anhydrous ethanol for 10 seconds. Take out the sample and place it on a lint-free paper to dry to obtain the TEM sample.

[0047] 4. Check the sample preparation effect: Place this sample in the TEM for observation. The thin region of this sample is about 9 μm wide, the thin region is flat, and most of the carbides are retained on the thin region, which can meet the TEM characterization requirements of the sample matrix and carbides. Figure 4 For this sample, STEM bright-field and EDS energy dispersive spectroscopy analyses were performed. The particles were found to be carbides, and the energy dispersive spectroscopy analysis showed that these carbides were enriched with molybdenum and vanadium.

[0048] Experimental Example 1 (existing electrolyte, i.e., without the addition of ethylene glycol monobutyl ether): TEM sample preparation of high-temperature bearing steel 1. The sample was fabricated into a circular disc with a thickness of 45μm and a diameter of 3mm, as detailed below: (1) Using wire cutting, high-temperature bearing steel was cut into thin sample pieces to obtain circular pieces with a thickness of 0.6 mm and a diameter of 15 mm; (2) The sample was gradually thinned by grinding under the flushing of flowing water: first, the sample was ground to 300μm using 200# wet sandpaper, then the sample was ground to 150μm using 600# wet sandpaper, then the sample was ground to 75μm using 1000# wet sandpaper, and finally the sample was ground to 45μm using 2000# wet sandpaper.

[0049] (3) Use a punch to punch out a circular sample with a diameter of 3mm. The edge is free of burrs and the sample is flat.

[0050] 2. Electrolytic double-jet thinning: Sample preparation was performed using a Struers TenuPol 5 electrolytic double-jet apparatus, as detailed below: (1) Prepare electrolyte: Add 900ml of anhydrous ethanol to the electrolyte tank, then slowly add 100ml of perchloric acid. The reagent purity is analytical grade. Stir well. (2) Slowly add liquid nitrogen to the electrolyte tank until the temperature reaches -31℃; (3) Place the disc sample into the fixture, scan the anodic polarization curve, and select an electrolysis current of 35mA and an electrolysis voltage of 26V; (4) Adjust the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is about 3 mm; after spraying for 15 seconds, reduce the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is about 2 mm. (5) The sample is electrolyzed until it is thinned to the point of perforation, and the double spraying stops automatically.

[0051] 3. Sample cleaning: Remove the sample clamp and move it up and down in a beaker containing anhydrous ethanol to clean the electrolyte remaining on the sample. Replace with anhydrous ethanol and put the sample back into the clamp to clean it up and down again. Take out the sample and soak it in anhydrous ethanol for 10 seconds. Take out the sample and place it on a lint-free paper to dry to obtain the TEM sample.

[0052] 4. Check the sample preparation effect: Place this sample in the TEM for observation. The width of the thin region is about 6μm. The area of ​​the thin region is small and the thickness is uneven.

[0053] Experimental Example 2 (Current density and voltage cannot be matched with electrolyte): TEM sample preparation of high-temperature bearing steel.

[0054] 1. The sample was fabricated into a circular disc with a thickness of 49 μm and a diameter of 3 mm, as detailed below: (1) Using wire cutting, high-temperature bearing steel was cut into thin sample pieces to obtain circular pieces with a thickness of 0.6 mm and a diameter of 15 mm; (2) The sample was gradually thinned by grinding under the flushing of flowing water: first, the sample was ground to 280μm using 200# wet sandpaper, then the sample was ground to 140μm using 600# wet sandpaper, then the sample was ground to 85μm using 1000# wet sandpaper, and finally the sample was ground to 49μm using 2000# wet sandpaper. (3) Use a punch to punch out a circular sample with a diameter of 3mm. The edge is free of burrs and the sample is flat.

[0055] 2. Electrolytic double-jet thinning: Sample preparation was performed using a Struers TenuPol 5 electrolytic double-jet apparatus, as detailed below: (1) Prepare electrolyte: Add 850ml of anhydrous ethanol and 50ml of ethylene glycol monobutyl ether to the electrolyte tank, mix well, and then slowly add 100ml of perchloric acid. The reagent purity is analytical grade. Stir well. (2) Slowly add liquid nitrogen to the electrolyte tank until the temperature reaches -28℃; (3) Place the disc sample into the fixture, scan the anodic polarization curve, and select an electrolysis current of 60mA and an electrolysis voltage of 46V; (4) Adjust the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is about 3 mm; after spraying for 25 seconds, reduce the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is about 2 mm. (5) The sample is electrolyzed until it is thinned to the point of perforation, and the double spraying stops automatically.

[0056] 3. Sample cleaning: Remove the sample clamp and move it up and down in a beaker containing anhydrous ethanol to clean the electrolyte remaining on the sample. Replace with anhydrous ethanol and put the sample back into the clamp to clean it up and down again. Take out the sample and soak it in anhydrous ethanol for 10 seconds. Take out the sample and place it on a lint-free paper to dry to obtain the TEM sample.

[0057] 4. Observe the sample preparation effect: Place this sample in a TEM for observation. The width of the thin area is about 10 μm, but most of the carbides have preferentially reacted and detached, leaving hollow holes in the thin area. Figure 5 (Scale 1μm~200nm).

[0058] Experimental Example 3 (using constant flow rate): TEM sample preparation of high-temperature bearing steel.

[0059] 1. The sample was fabricated into a circular disc with a thickness of 52μm and a diameter of 3mm, as detailed below: (1) Using wire cutting, high-temperature bearing steel was cut into thin sample pieces to obtain circular pieces with a thickness of 0.6 mm and a diameter of 15 mm; (2) The sample was gradually thinned by grinding under the flushing of flowing water: first, the sample was ground to 260μm using 200# wet sandpaper, then the sample was ground to 130μm using 600# wet sandpaper, then the sample was ground to 85μm using 1000# wet sandpaper, and finally the sample was ground to 53μm using 2000# wet sandpaper. (3) Use a punch to punch out a circular sample with a diameter of 3mm. The edge is free of burrs and the sample is flat.

[0060] 2. Electrolytic double-jet thinning: Sample preparation was performed using a Struers TenuPol 5 electrolytic double-jet apparatus, as detailed below: (1) Prepare electrolyte: Add 865ml of anhydrous ethanol and 50ml of ethylene glycol monobutyl ether to the electrolyte tank, mix well, and then slowly add 85ml of perchloric acid. The reagent purity is analytical grade. Stir well. (2) Slowly add liquid nitrogen to the electrolyte tank until the temperature reaches -34℃; (3) Place the disc sample into the fixture, scan the anodic polarization curve, and determine that the electrolysis current is 35mA and the electrolysis voltage is 28V; (4) Use a constant fast flow rate and adjust the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is 4 mm; (5) The sample is electrolyzed until it is thinned to the point of perforation, and the double spraying stops automatically.

[0061] 3. Sample cleaning: Remove the sample clamp and move it up and down in a beaker containing anhydrous ethanol to clean the electrolyte remaining on the sample. Replace with anhydrous ethanol and put the sample back into the clamp to clean it up and down again. Take out the sample and soak it in anhydrous ethanol for 10 seconds. Take out the sample and place it on a lint-free paper to dry to obtain the TEM sample.

[0062] 4. Check the sample preparation effect: Place this sample in the TEM for observation. The width of the thin area is about 10 μm, but some thin areas are uneven, with bending and edge curling. In addition, some carbides at the edge of the thin area have fallen off.

Claims

1. A method for preparing high-temperature bearing steel containing large-sized carbides for transmission electron microscopy, characterized in that: Includes the following steps: A. Preparation of electrolytic double-spray discs: The high-temperature bearing steel sample is cut into thin slices, and the slices are gradually thinned by grinding to a thickness of 40-55 μm. Then, a disc with a diameter of 3±0.1 mm is punched out. In step A, the stepwise sanding and thinning process specifically involves: under the rinsing of flowing water, first using 200# to 400# wet sandpaper to sand the sheet to a thickness of 250 to 300 μm, then using 500# to 600# wet sandpaper to sand the sheet to a thickness of 120 to 150 μm, then using 800# to 1200# wet sandpaper to sand the sheet to a thickness of 70 to 100 μm, and finally using 1500# to 2000# wet sandpaper to sand the sheet to a thickness of 40 to 55 μm; B. Electrolytic dual-jet thinning: B1. The solvent of the electrolyte is anhydrous ethanol, and the solutes are perchloric acid and ethylene glycol monobutyl ether, with a volume fraction of 7-13% for perchloric acid and 0.5-10% for ethylene glycol monobutyl ether. B2. Control the electrolysis temperature to -35 to -25℃; B3. When -35℃≤electrolysis temperature<-30℃, control the electrolysis current to be 30mA≤electrolysis current<40mA; when -30℃≤electrolysis temperature≤-25℃, control the electrolysis current to be 40mA≤electrolysis current≤50mA. B4. Scan the anodic polarization curve to determine the electrolysis voltage; B5. When starting dual spraying, use a fast flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is 2mm < diameter ≤ 3mm; after dual spraying for 15 to 35 seconds, reduce the flow rate so that the diameter of the liquid surface formed after the electrolyte phases sprayed from the two nozzles come into contact is 1mm ≤ diameter ≤ 2mm. B6. Electrolytically thin the sample disc until it is perforated by double spraying, then stop the electrolytic reaction; C. Cleaning: After the sample disc is thinned by electrolytic double spraying, it is cleaned and dried to obtain the transmission electron microscope sample.

2. The method for preparing high-temperature bearing steel containing large-size carbides for transmission electron microscopy according to claim 1, characterized in that: In step A, the thickness of the sheet is 0.5 to 1 mm.

3. The method for preparing high-temperature bearing steel containing large-size carbides for transmission electron microscopy according to claim 1, characterized in that: In step A, the punching is performed using a special punch for transmission electron microscopy.

4. The method for preparing high-temperature bearing steel containing large-size carbides for transmission electron microscopy according to claim 1, characterized in that: In step B1, the electrolyte is prepared by first mixing anhydrous ethanol and ethylene glycol monobutyl ether evenly, then slowly adding perchloric acid and stirring evenly.

5. The method for preparing high-temperature bearing steel containing large-size carbides for transmission electron microscopy according to claim 1, characterized in that: In step B2, liquid nitrogen is added to the electrolyte to control the electrolysis temperature to -35 to -25°C.

6. The method for preparing high-temperature bearing steel containing large-size carbides for transmission electron microscopy according to claim 1, characterized in that: In step B4, the electrolysis voltage is 18–45V.

7. The method for preparing high-temperature bearing steel containing large-size carbides for transmission electron microscopy according to claim 1, characterized in that: In step C, the cleaning process uses anhydrous ethanol.

8. The method for preparing high-temperature bearing steel containing large-size carbides for transmission electron microscopy according to any one of claims 1 to 7, characterized in that: In step C, the width of the thin region of the obtained transmission electron microscope sample is 8–15 μm.

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