An efficient nanospeck preparation method for in-situ SEM-HR DIC and EBSD synchronization analysis

Abstract

The application belongs to the field of material characterization and mechanical testing, and proposes a high-efficiency nano-speck preparation method for in-situ SEM-HRDIC and EBSD synchronous analysis. A sample substrate with a smooth surface, no residual strain and clear grain boundaries is obtained through mechanical polishing, electrolytic polishing and light polishing of silicon oxide; then, a ultra-thin Au precursor film is deposited on the surface of the high-temperature pre-oxidized sample substrate by low-energy physical vapor deposition, and under the condition of wet steam assisted annealing, the precursor film is self-assembled into nano-Au specks with uniform particle size and dense distribution under the driving of surface energy and diffusion. The obtained specks have high contrast in SEM imaging and do not affect the EBSD diffraction signal. The preparation cycle of the method is short and the repeatability is high, which solves the contradiction that it is difficult to obtain high-quality EBSD signal for mechanically polished samples and it is difficult to form uniform nano-specks for electrolytically polished samples, realizes in-situ synchronous acquisition of micro-strain field and crystallographic information in the same area, and significantly improves the precision and efficiency of micro-mechanical characterization.

Description

Technical Field

[0001] This invention belongs to the field of materials characterization and micro / nano-scale mechanical testing technology. Specifically, it relates to an efficient metal sample preparation process and method for simultaneous analysis of high-resolution digital image correlation (HRDIC) and electron backscatter diffraction (EBSD) under in-situ scanning electron microscopy (SEM) conditions. It is particularly suitable for strain measurement at the microscale and research on intragranular deformation mechanisms of metallic materials. Background Technology

[0002] High-resolution digital image correlation (HRDIC) relies on surface nanoscale speckle to obtain high spatial resolution displacement / strain fields, making it a key characterization technique for studying the deformation mechanisms at the grain scale of metals. Electron backscatter diffraction (EBSD) provides crystallographic orientation, grain boundary distribution, and substructure information. The coupling of these two techniques can establish a direct correspondence between strain and crystallographic features at the microscale, possessing significant scientific value and promising engineering applications. However, existing techniques suffer from the following key contradictions and shortcomings in achieving in-situ simultaneous characterization using HRDIC and EBSD.

[0003] Process-Signal Discrepancy: Traditional speckle pattern preparation typically involves mechanical mirror polishing followed by deposition of noble metal precursors and controlled heat treatment (such as steam or atmosphere annealing) to induce nanoparticle formation. While this process can produce high-contrast speckles suitable for HRDIC, the plastic deformation layer and residual stress introduced by mechanical polishing alter the surface microstructure, severely weakening or destroying the recognition capability of EBSD diffraction signals, leading to a significant decrease in grain recognition rate or even complete inability to resolve them.

[0004] Characterization and localization contradictions: For samples that have only undergone mirror polishing without etching and development, grain boundaries and microstructure features cannot be significantly displayed in SEM imaging (i.e., insufficient imaging contrast). Therefore, it is impossible to accurately locate specific morphological grains or target microstructure regions in the field of view before in-situ loading. Traditional operations often involve in-situ loading over a large field of view and subsequent retrospective selection of regions, resulting in low experimental efficiency and a lack of crystallographic basis for region selection, affecting the representativeness and reliability of HRDIC-EBSD coupled analysis.

[0005] Surface roughness-adhesion contradiction: High-quality EBSD data usually rely on low-stress, high-gloss mirror surfaces obtained by electropolishing; however, due to unfavorable wettability and nucleation conditions, mirror surfaces are difficult to form uniform, dense and size-controllable nanospecks, thus failing to simultaneously meet HRDIC's requirements for speckle quality and EBSD's requirements for surface stress and smoothness.

[0006] In summary, there is currently a lack of a repeatable process that can simultaneously achieve the formation of nanospecks and high contrast, high recognition rate and low residual stress on the same sample surface, and enable pre-crystall localization and simultaneous acquisition of HRDIC and EBSD data under in-situ SEM.

[0007] In studies that extensively utilize HRDIC, surface treatment prior to speckle preparation almost invariably employs high-grade mechanical polishing, colloidal polishing, or plasma polishing, while electrolytic polishing is rarely used. Although electrolytically polished sample surfaces are "smooth," they are not "facilitating adhesion." Therefore, efforts should be focused on preparing metallographic sample surfaces that are "nanoscale clean, slightly rough, and have adhesion."

[0008] Through long-term experimental accumulation and exploration, the applicant of this invention has proposed a solution to the incompatibility problem between HRDIC and EBSD technologies in the testing of the same sample. This method not only realizes multiple characterization methods through in-situ deformation experiments, but is also low-cost and easy to operate. Most existing speckle pattern preparation techniques are overly complex, costly, and have long experimental cycles, or are incompatible with EBSD technology. In summary, the key issue lies in the preparation of speckles and the integration of multiple characterization techniques.

[0009] Purpose of the invention To overcome the above contradictions, this invention aims to provide a processable, repeatable, efficient and compatible method for preparing nanospeck patterns, which can form nanoAu speckles that meet HRDIC requirements on the same sample surface while maintaining the high resolution of EBSD data. This enables in-situ SEM observation and crystallographic orientation acquisition of the micro-region during loading, thereby improving the accuracy and efficiency of micro-deformation coupled characterization.

[0010] The technical solution adopted in this invention is as follows: A highly efficient method for preparing nanospeckled patterns for simultaneous in-situ SEM-HRDIC and EBSD analysis includes the following steps: (1) Surface pretreatment: The metal sample is subjected to mechanical grinding, electrolytic polishing and light polishing with nano silica suspension in stages to obtain a mirror substrate with low surface roughness, stress layer elimination and grain boundary development characteristics. Then it is placed on a heating table for pre-oxidation treatment in air atmosphere. (2) Precursor thin film deposition: a discontinuous nanoscale Au precursor ultrathin film is deposited on the surface of the substrate using a low-energy physical vapor deposition process. By controlling the deposition power, time and vacuum degree, the film can be made into an island-like or discontinuous structure. (3) Steam-assisted annealing: The deposited sample is placed in a dual-field coupling environment where a heating stage and distilled water vapor work together for steam-assisted annealing. Under the action of surface energy driving and interface energy regulation, the Au precursor ultrafilm undergoes granular reconstruction to form spherical nano Au particles evenly distributed on the sample surface. (4) Finishing treatment: The formed nano Au speckle sample is subjected to plasma cleaning to remove weakly bound particles and surface residual impurities, thereby obtaining a sample with both high contrast speckle and high resolution EBSD signal.

[0011] Furthermore, the metal sample is Z6CND17.12 nuclear power steel, or other austenitic stainless steel, or an alloy material that requires micro-strain-crystal coupling characterization.

[0012] Furthermore, the progressive mechanical grinding uses 600#, 1000#, 1500#, 2000#, 3000#, and 5000# sandpaper in sequence to gradually remove the surface work-hardened layer and provide a uniform surface base for subsequent fine surface treatment.

[0013] Furthermore, the electropolishing includes: electrolyzing in a 10% perchloric acid-anhydrous ethanol solution at 25 V voltage and -10℃ to -15℃ for 40~50 s to obtain a low-stress mirror sample; and electrolyzing in a 10% oxalic acid aqueous solution at 2.5~3 V voltage and room temperature for about 60 s to selectively develop grain boundaries, thereby facilitating precise grain boundary-assisted localization of the study area under SEM visualization (grain boundaries, as feature points, help in the localization of the study area).

[0014] Furthermore, after the electropolishing, a mixture of nano-silica suspension (OPS) and deionized water (volume ratio 1:20~30, pH≈7) is used for light polishing at a low speed of 100~150 r / min for 12~20 min to release residual stress and further improve surface uniformity.

[0015] Furthermore, the pre-oxidation treatment is carried out in an air atmosphere at 230~260℃ for 20~30 min, preferably at about 260℃ for 30 min, so as to form a uniform and stable ultrathin oxide layer in situ on the sample surface, which is used to regulate the nucleation behavior and interface bonding state in the subsequent Au deposition process.

[0016] Furthermore, the low-energy physical vapor deposition is performed using a gold sputtering apparatus, with a power of 8-10 W and a vacuum of 5 Pa for 20-30 s to obtain a discontinuous Au precursor film with an average thickness of less than 30 nm.

[0017] Furthermore, during the steam-assisted annealing process, one side of the sample is in contact with the heating stage to provide a stable thermal field, while the other side is exposed to distilled water vapor to regulate the interfacial energy, thereby promoting Au atom migration and particle self-assembly under the dual-field coupling effect of the heating stage and steam.

[0018] Furthermore, the steam-assisted annealing involves heating to 260~300 ℃ and holding for 6~8 h.

[0019] Furthermore, the plasma cleaning is performed under an argon atmosphere with a processing power of 15-40 W, a vacuum degree of approximately 10 Pa, and a time of 180-240 s, in order to remove weakly bound particles and air deposits on the surface while maintaining the stability of the nanospeckled pattern.

[0020] A method for simultaneous in-situ SEM-HRDIC and EBSD analysis is proposed. The specimen prepared by the above method can achieve high-resolution DIC displacement / strain field measurement and high-resolution EBSD crystallographic characterization in the same area during in-situ SEM tensile testing, thereby avoiding the spatial and temporal deviations caused by traditional ex-situ methods.

[0021] Compared with the prior art, the present invention has the following significant advantages and technical effects: 1) Good compatibility between speckle and EBSD: The prepared sample surface has both good speckle image quality, which is suitable for HRDIC analysis and testing, and high EBSD resolution, which meets the requirements for the acquisition of grain-level microstructure information, truly realizing the in-situ and efficient combination of DIC technology and EBSD technology. 2) High preparation efficiency and simple operation: The method of this invention can quickly prepare a smooth, flat, scratch-free and stress-free metal sample mirror surface within 1.5 hours, which is much shorter than the 3-5 hours required by traditional vibration polishing or mechanical polishing methods, making it suitable for rapid sample preparation in the laboratory. 3) Controllable speckle particle size and uniform distribution: Nanoscale Au particles are self-assembled through distillation-induced method. The particle size is concentrated below 80nm, with stable morphology and high image contrast, which is suitable for nanoscale strain measurement. 4) Non-destructive and highly repeatable: The combination of electropolishing and OPS light polishing technology produces a metal sample mirror surface that is both stress-free and has high adhesion, ensuring the stability of nano-spots under multiple loading conditions. 5) Wide range of applications: This method is not only applicable to Z6CND17.12 nuclear power steel, but can also be extended to austenitic stainless steels such as 316L and 304, as well as other metallic materials that require in-situ synchronous structure-mechanical coupling testing. Attached Figure Description

[0022] Figure 1This is a comparison of the SEM microstructure of speckled gold nanoparticles on the mirror surface of Z6CND17.12 austenitic stainless steel samples with and without pre-oxidation treatment in Example 1. (a) is the sample without pre-oxidation treatment, and (b) is the sample with pre-oxidation treatment.

[0023] Figure 2 The images show the surface and speckle SEM morphology of the in-situ tensile specimen prepared by SEM-HRDIC in Example 1 (ε=0). Among them, (a) is a partial SEM morphology of a certain grain after the speckle preparation of the tensile specimen, (b) is a high-magnification magnified image (35K×) of the grain in (a), and (c) is a statistical diagram of speckle grain size.

[0024] Figure 3 This is the IPF image of the Z6CND17.12 austenitic stainless steel tensile specimen with nano-gold particle speckles on the surface in Example 1.

[0025] Figure 4 The results are from the SEM-HRDIC analysis of the tensile specimen in Example 2. Figure 4 (a) shows the tissue under low magnification SEM. Figure 4 (b) is Figure 2 (a) SEM image after binarization. Figure 4 (c) is Figure 4 Strain contour plots were analyzed using VIC-2D software after the strain in region (b) increased by 3%. Figure 4 (d) is Figure 2 (b) SEM image after binarization. Figure 4 (e) is Figure 4 Strain contour plots were analyzed using VIC-2D software after the strain in the middle (d) region was 3%.

[0026] Figure 5 The dimensions are those of the in-situ SEM-HRDIC sample.

[0027] Figure 6 The diagram shows a distillation apparatus, where (a) is the front view of the speckled distillation apparatus and (b) shows the sample placement position. Detailed Implementation

[0028] The technical solution of the present invention will now be described in detail and completely with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] The technical solution of this invention can be summarized as follows: After performing a mechanical-electrolytic polishing combined surface pretreatment on the Z6CND17.12 nuclear power steel sample to simultaneously obtain a surface morphology with developable grain boundaries and a low residual stress substrate, a nanoscale gold (Au) precursor ultrathin film (discontinuous film structure) is deposited on the sample surface using low-energy physical vapor deposition (PVD). Subsequently, under controlled steam-assisted annealing conditions, "steam-heating stage dual-field coupling" annealing is performed, causing the Au precursor film to undergo island formation and self-assembly granulation under the action of surface energy driving, interface energy regulation, and enhanced diffusion kinetics, ultimately forming nanoscale Au speckles with uniform particle size and dense distribution on the sample surface. This process takes into account both the grayscale contrast of the speckles and the transmittance / identifiability of EBSD, and supports pre-crystallographic localization under in-situ SEM and simultaneous HRDIC / EBSD acquisition.

[0030] Key innovations in this technical solution include: combining mechanical polishing with directional electropolishing to simultaneously achieve grain boundary development and release of residual surface stress; pre-oxidation can significantly improve the nucleation and deposition behavior of gold particles on the surface; using low-energy PVD to prepare discontinuous Au precursor films and precisely control the precursor morphology; introducing steam-assisted annealing and utilizing the dual-field coupling between the sample and the heating stage to regulate interfacial energy and diffusion kinetics, promoting controlled island self-assembly, and forming size-controllable and firmly attached nanospeckles.

[0031] Example 1: This embodiment provides a highly efficient method for preparing nanospeckled patterns for simultaneous in-situ HRDIC and EBSD analysis, comprising the following steps: S1: The Z6CND17.12 nuclear power steel sample was successively polished on 600#, 1000#, 1500#, 2000#, 3000#, and 5000# sandpaper. By gradually removing the surface processing layer, scratches, and oxide layer with abrasives from coarse to fine, the sample surface gradually obtained a substrate with low roughness and high flatness.

[0032] S2: The mechanically polished sample is placed in a 10% perchloric acid-anhydrous ethanol solution and electropolished at -10°C (liquid nitrogen cooling) under a voltage of 25 V for 50 seconds. After completion, the sample is immediately transferred to a beaker containing anhydrous ethanol for ultrasonic cleaning and then dried with cold air at room temperature to obtain a smooth and scratch-free mirror-finish sample.

[0033] S3: After mirror polishing, the sample is placed in a 10% oxalic acid aqueous solution and electropolished at a low voltage of 2.5V at room temperature for approximately 60 seconds. Immediately after electrolysis, the sample is ultrasonically cleaned in anhydrous ethanol and dried at room temperature to prevent secondary surface oxidation. In this step, oxalic acid, as a mild electrolytic medium, preferentially acts on the grain boundary region under a controlled low voltage, creating a difference in dissolution rate between the grain boundary and intragranular regions, thus revealing a clear grain boundary profile. Figure 4 As shown in (a), after a series of surface treatments, the grain boundaries of the HRDIC tensile specimens in the SEM field of view are clearly visible, thus achieving grain boundary development, which facilitates the screening and positioning of the study area in the later stage. Compared with traditional chemical etching, this method avoids the surface roughening problem caused by strong etchants and can obtain significant grain boundary contrast while maintaining surface smoothness.

[0034] S4: After completing the grain boundary development and electropolishing, the sample is placed on a clean velvet polishing cloth for light mechanical polishing. No pressure should be applied to the sample during this process; it must be operated gently with the polishing disc speed controlled at 100 r / min. The polishing solution is a mixture of imported silica suspension (OPS) and deionized water at a volume ratio of 1:30, with a solution pH ≈ 7. The average particle size of the silica nanoparticles used is approximately 25 nm, and the polishing time is 15 min. During this process, the nano-SiO2 particles in the OPS solution can gently grind and chemically-mechanically interact with the sample surface under low speed and low pressure conditions, thereby further removing the weak surface layer remaining from the electropolishing process, reducing microscopic surface stress, and improving the overall smoothness and uniformity.

[0035] S5: Place the OPS-polished sample in anhydrous ethanol and ultrasonically clean it at 150 W for about 5 minutes to remove residual particles and polishing solution from the surface. Then dry it with cold air and place it on a clean polishing cloth for light mechanical polishing for 3 minutes, adding distilled water during the process to aid cleaning. Finally, ultrasonically clean it again with alcohol and dry it to ensure that the sample surface appears smooth, clean, and free of residual contaminants under a metallographic microscope.

[0036] S6: Place the polished surface of the sample upwards in a plasma cleaning device, using an argon ion source, and treat for 240 s at a power of 40 W and a vacuum of 10 Pa. This process removes residual organic matter from the surface through physical sputtering and simultaneously activates the surface.

[0037] S7: Place the plasma-cleaned sample on a heating stage and perform controlled oxidation treatment (i.e., pre-oxidation treatment) in an air environment. The heating temperature is 240℃ and the heating time is 30 min.

[0038] S8: Using a 108 sputtering apparatus, a gold (Au) precursor film was deposited on the sample surface under conditions of 8W power and 5 Pa vacuum, with a deposition time of 25s. This process ensures that the gold film is a discontinuous nanoscale ultrathin film, rather than a thick film coverage.

[0039] S9: The gold-sprayed sample is placed in a distilled water vapor environment and heated to 300 ℃ on a heating stage for 6 hours. During this time, one side of the sample is continuously subjected to the thermal field of the heating stage, while the other side is exposed to the water vapor environment, forming a "heating stage-vapor" dual-field coupling condition. Under this action, the precursor gold film undergoes surface energy-driven islanding and diffusion aggregation, eventually self-assembling into uniformly distributed, controllable-size (below 80 nm) speckled nano-Au particles. Figure 6 This is a schematic diagram of a distillation apparatus.

[0040] S10: Place the distilled sample back into the plasma cleaning equipment and treat it with 15 W power and 10 Pa vacuum for 240 s.

[0041] S11: The prepared specimen is mounted in a scanning electron microscope equipped with an in-situ tensile stage, and an in-situ tensile test is performed under the set loading conditions. At each strain amplitude, high-resolution SEM images (for DIC analysis) and high-quality EBSD data can be acquired simultaneously for the same area.

[0042] One of the innovative aspects of this invention is the pre-oxidation treatment of the sample mirror surface before speckle preparation. Figure 1 As shown in (a), the nucleation and distribution of gold particles on the matrix surface are significantly uneven, and the speckle pattern exhibits local aggregation characteristics. The particles are mainly concentrated in a few areas, while the speckle density in other areas is low, resulting in insufficient overall coverage. The speckle size distribution is discrete, with large particles or intergrowth structures in some local areas, which is not conducive to the formation of a continuous and uniform random speckle field. Figure 1 (b) shows the sample that underwent pre-oxidation treatment. After pre-oxidation, the gold particles achieved a high-density and uniform distribution on the surface, and the speckle distribution exhibited good randomness and continuity. The particle size was generally consistent, the interparticle spacing was significantly reduced, the surface coverage was significantly improved, and there were almost no obvious large-scale agglomerations or blank areas. A fine and clearly contrasting nanoscale speckle structure was formed on the surface.

[0043] Figure 2 Images (a) and (b) show the speckle morphology of nano-Au particles on the surface of Z6CND17.12 nuclear power steel. These speckle particles exhibit a high-density, uniform, and randomly distributed speckle morphology, with particle sizes at the nanoscale and clear grayscale contrast. The speckle coverage is continuous, without obvious agglomeration or blank areas, and the overall isotropy is good. This speckle morphology meets the spatial resolution and stability requirements of high-resolution HRDIC.

[0044] Figure 3 The image shows the IPF (Intensity Performance Factor) of a Z6CND17.12 austenitic stainless steel tensile test with speckled gold nanoparticles on the surface. Even with speckled particles distributed on the sample surface, the EBSD test still achieved a high resolution of 94.6%, indicating that the speckled gold particles on the sample surface have little impact on the EBSD resolution. This lays the foundation for subsequent acquisition and analysis of SEM-HRDIC and EBSD data.

[0045] Example 2: This embodiment provides a method for characterizing local micro-strain on the surface of Z6CND17.12 nuclear power steel, including the following steps: S1: Gold speckle particles were prepared on the surface of Z6CND17.12 nuclear power steel sample using the HRDIC speckle preparation method described in Example 1 above.

[0046] S2: The surface of the speckled Z6CND17.12 nuclear power steel sample prepared in step S1 was photographed using the secondary electron imaging mode of a scanning electron microscope (SEM). Undeformed morphological SEM images were obtained, see [link to SEM image]. Figure 2 (a) and (b) are shown in the image, and the region is photographed using backscattered electron diffraction mode to obtain an undistorted EBSD image of the region.

[0047] S3: The Z6CND17.12 nuclear power steel sample was deformed. After the sample was deformed, the deformed sample was photographed using the secondary electron imaging mode of a scanning electron microscope to obtain the deformed SEM image.

[0048] S4: The SEM images of the undeformed specimen from step S2 and the deformed specimen from step S3 were compared and analyzed using the computer software VIC-2D to obtain displacement and local strain information, and the local strain of the Z6CND17.12 nuclear power steel specimen was characterized.

[0049] Furthermore, the deformation in step S3 is a tensile test. Figure 5 The dimensions of the in-situ tensile specimen obtained by SEM are shown.

[0050] Further, step S4 specifically involves: using EBSD data to obtain the grain boundary distribution map of the Z6CND17.12 nuclear power steel sample material, and then obtaining the local strain distribution of the sample based on the speckle pattern on the undeformed SEM image and the deformed SEM image; and overlaying the grain boundary distribution map with the local strain distribution to obtain a cloud map that simultaneously contains grain boundary information and strain distribution.

[0051] The SEM-HRDIC analysis results of the tensile specimen in this embodiment are as follows: Figure 4As shown, (b) and (c) mainly characterize the micro-deformation within the grains and grain boundaries of the sample, as well as the high strain at the grain boundaries between the two grains; (d) and (e) are SEM morphologies under high magnification, which are mainly used to analyze the micro-strain and micro-deformation such as slip bands within the grains.

[0052] The above-mentioned method for characterizing the local strain of micro-regions on the surface of Z6CND17.12 nuclear power steel is applied to the evaluation of the plastic deformation mechanism and damage failure of austenitic stainless steel, the optimization of processing technology, and the prediction of the service life of nuclear power steel in nuclear power plants.

[0053] The main innovative points of this invention include: 1) Efficient sample polishing method (efficient combination of mechanical polishing and electrolytic polishing). This invention combines mechanical polishing and electrolytic polishing to quickly prepare metallographic samples with no or low stress and suitable surface roughness, which facilitates the formation of nanospecks. It solves the problems that pure mechanical polishing introduces stress during sample preparation, making EBSD testing impossible, and electrolytic polishing makes it difficult to form nanospecks due to excessively smooth surfaces.

[0054] 2) Pre-oxidation treatment of the sample before gold coating. The sample is pre-oxidized (at a temperature lower than the distillation temperature) before the gold film is deposited in the vapor phase. This forms an oxide film of tens of nanometers on the sample surface, which improves the formability of the nano-spherical gold particles.

[0055] 3) Grain Boundary-Assisted Localization. This invention employs a novel electropolishing process to achieve grain boundary development, facilitating precise localization in HRDIC studies. Common in-situ EBSD+HRDIC studies use microhardness indentation to locate the region. This approach can be considered blind selection, as the microstructure of the indented area may not be representative, increasing the probability of experimental failure. However, after grain boundary development treatment on the smooth surface of the metal sample, the region of interest can be directly selected under dynamic SEM visualization during subsequent EBSD+HRDIC testing. Microstructure regions relevant to the research objective can be selected based on grain morphology and other information, significantly improving experimental efficiency and success rate. This method of locating micro-regions using grain boundaries is non-destructive to the sample. Existing microhardness indentation techniques cause permanent damage to the sample surface, and the indentation deformation zone may affect the micro-deformation mode and mechanism of local sample areas, introducing external factors into the experiment.

[0056] 4) Enables the combined use of EBSD and HRDIC, and speckle does not affect the EBSD signal quality.

[0057] The specific embodiments of the present invention disclosed above are intended to help understand the content of the present invention and to implement it accordingly. Those skilled in the art will understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention. The present invention should not be limited to the content disclosed in the embodiments of this specification; the scope of protection of the present invention is defined by the claims.

Claims

1. A method for preparing highly efficient nanospeckled patterns for simultaneous in-situ SEM-HRDIC and EBSD analysis, characterized in that, Includes the following steps: The metal sample was subjected to progressive mechanical grinding, electrolytic polishing and light polishing with nano-silica suspension to obtain a mirror substrate with low surface roughness, stress layer elimination and grain boundary development characteristics. Then it was placed on a heating stage for pre-oxidation treatment in an air atmosphere. Discontinuous nanoscale Au precursor ultrathin films were deposited on the surface of the substrate using a low-energy physical vapor deposition process. By controlling the deposition power, time, and vacuum level, the films were made to have an island-like or discontinuous structure. The deposited sample was placed in a dual-field coupled environment of heating stage and distilled water vapor for steam-assisted annealing. Under the action of surface energy driving and interface energy regulation, the Au precursor ultrafilm underwent granular reconstruction, forming spherical nano Au particle speckles uniformly distributed on the sample surface. The formed nano-Au speckle sample was subjected to plasma cleaning to remove weakly bound particles and surface residual impurities, thereby obtaining a sample with both high-contrast speckle and high-resolution EBSD signal.

2. The method according to claim 1, characterized in that, The metal sample is Z6CND17.12 nuclear power steel, or other austenitic stainless steel, or an alloy material that requires micro-strain-crystal coupling characterization.

3. The method according to claim 1, characterized in that, The progressive mechanical grinding process uses 600#, 1000#, 1500#, 2000#, 3000#, and 5000# sandpaper in sequence to gradually remove the surface work-hardened layer and provide a uniform surface base for subsequent fine electrolytic polishing.

4. The method according to claim 1, characterized in that, The electropolishing process includes: electropolishing in a 10% perchloric acid-anhydrous ethanol solution at 25 V voltage and -10 ℃ to -15 ℃ for 40~50 s to obtain a low-stress mirror-like sample; followed by electropolishing in a 10% oxalic acid aqueous solution at 2.5~3 V voltage and room temperature for about 60 s to selectively develop grain boundaries, thereby facilitating precise grain boundary localization in the study area under SEM visualization.

5. The method according to claim 1, characterized in that, After electropolishing, a mixture of nano-silica suspension and deionized water is used for light polishing at a low speed of 100-150 r / min for 12-20 min. This avoids introducing micro-strain and micro-stress while moderately increasing the surface roughness of the sample to facilitate the adhesion of Au particles. The volume ratio of nano-silica suspension to deionized water in the mixture is 1:20-30, and the pH is approximately 7.

6. The method according to claim 1, characterized in that, The pre-oxidation treatment is carried out in air at 230~260℃ for 20~30 min to form a uniform and stable ultrathin oxide layer on the sample surface in situ.

7. The method according to claim 1, characterized in that, The low-energy physical vapor deposition was performed using a gold sputtering apparatus, with a power of 8-10 W and a vacuum of 5 Pa for 20-30 s to obtain a discontinuous Au precursor film with an average thickness of less than 30 nm.

8. The method according to claim 1, characterized in that, During the steam-assisted annealing process, one side of the sample is in contact with the heating stage to provide a stable thermal field, while the other side is exposed to distilled water vapor to regulate the interfacial energy. This promotes Au atom migration and particle self-assembly under the dual-field coupling effect of the heating stage and steam. The steam-assisted annealing involves heating to 260~300 ℃ and holding for 6~8 h.

9. The method according to claim 1, characterized in that, The plasma cleaning is performed under an argon atmosphere with a processing power of 15-40 W, a vacuum degree of approximately 10 Pa, and a time of 180-240 s, in order to remove weakly bound particles while maintaining the stability of the nanospeckled pattern.

10. A method for simultaneous in-situ SEM-HRDIC and EBSD analysis, characterized in that, The specimens prepared by the method described in any one of claims 1 to 9 can achieve simultaneous acquisition of high-resolution DIC displacement field / strain field measurement and high-resolution EBSD crystallographic characterization in the same area during in-situ SEM tensile testing, thereby avoiding the spatial and temporal deviations caused by traditional quasi-in-situ or ex-situ methods.

Images