A method for in-situ characterization of nano-phase hydrogen trapping behavior based on SKPFM-TEM combined technology

Abstract

This invention provides a method for in-situ characterization of hydrogen capture behavior in nanophases based on SKPFM-TEM combined technology, belonging to the field of material microstructure characterization and hydrogen-induced failure analysis technology. The method includes: preparing metallic material samples for SKPFM experimental characterization; identifying the hydrogen capture behavior at the interface between the precipitated phase and the matrix by in-situ monitoring of the sample surface potential change before and after hydrogen charging using SKPFM; extracting specific precipitated phase regions using FIB to prepare TEM samples; analyzing the phase composition, interface structure, chemical characteristics, and strain state of the nanoprecipitated phase using TEM; and correlating SKPFM potential data with TEM characterization results to reveal the hydrogen capture behavior and mechanism at the interface between the nanoprecipitated phase and the matrix. This invention provides a feasible method for directly exploring the characteristic hydrogen capture behavior and mechanism at the nanoscale, opening a new avenue for the study of the atomic mechanism of hydrogen-induced fracture.

Description

Technical Field

[0001] This invention relates to the field of material microstructure characterization and hydrogen-induced failure analysis technology, specifically to a method for in-situ characterization of hydrogen capture behavior in nanophases based on SKPFM-TEM combined technology. Background Technology

[0002] To achieve the dual carbon goals of "carbon peaking" and "carbon neutrality," green hydrogen energy will become an important energy source. However, hydrogen embrittlement is a problem encountered in the production, transportation, storage, and use of hydrogen. Hydrogen adsorption and diffusion into metallic materials reduces their ductility, leading to hydrogen embrittlement. Generally, the higher the strength of a material, the stronger its susceptibility to hydrogen embrittlement, and the more prone it is to intergranular cracking, which is caused by hydrogen segregation at grain boundaries. To prevent and mitigate hydrogen embrittlement, carbide precipitates are introduced into materials. These are widely used for strengthening and toughening materials, and can also act as hydrogen traps to capture hydrogen, hindering its diffusion and accumulation, thereby reducing the material's susceptibility to hydrogen embrittlement.

[0003] Numerous studies have shown that hydrogen can be captured within coherent or semi-coherent carbide precipitates and at the interface between the precipitate and the matrix. The microscopic mechanisms of hydrogen capture include vacancies, specific interfacial structures, strain, and mismatched dislocations. However, the question of whether incoherent carbide precipitates, which are ubiquitous in steel, can capture hydrogen remains controversial due to a lack of effective computational methods and direct experimental evidence. Given that hydrogen capture behavior depends on structural and chemical characteristics, and the incoherent interface structure between carbides and the matrix is ​​complex and diverse, it is speculated that their hydrogen capture behavior may be varied. Methods such as TDS, which characterize the overall average hydrogen concentration within a sample, are insufficient to reveal the hydrogen capture behavior and mechanism of individual nanoprecipitates. Furthermore, although APT can directly image the spatial distribution of hydrogen in nanoprecipitates, it requires sample destruction during testing, hindering further microstructural characterization of hydrogen capture sites. SKPFM alone can monitor the correlation between surface potential and hydrogen concentration in situ, but it cannot reveal the influence of the microstructure of the nano-precipitated phase interface on hydrogen capture behavior; TEM alone can achieve atomic-level structural analysis, but requires offline sample preparation and cannot dynamically monitor the interaction process between hydrogen and the precipitated phase.

[0004] In summary, existing methods all have certain limitations in characterizing the hydrogen capture behavior of nano-precipitated phases. Therefore, it is necessary to propose an in-situ coupled technique that combines the dynamic monitoring advantages of SKPFM with the microstructural analysis capabilities of TEM. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a method for in-situ characterization of hydrogen capture behavior in nanophases based on a combined SKPFM-TEM technique. Employing a combined scanning Kelvin probe microscopy (SKPFM) and transmission electron microscopy (TEM) technique, the hydrogen capture behavior at the interface between a single incoherent nanophase and the matrix in metallic materials, as well as the atomic-scale structure and chemical characteristics of hydrogen capture sites, are visualized. This method overcomes the previous limitation that macroscopic hydrogen capture behavior could not be correlated with specific microstructures, providing a feasible approach for directly exploring the characteristics and mechanisms of hydrogen capture at the nanoscale, and opening up new avenues for studying the atomic mechanisms of hydrogen-induced fracture.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for in-situ characterization of hydrogen capture behavior in nanophases based on SKPFM-TEM combined technology, characterized by comprising:

[0008] (1) Preparation of metallic material samples for SKPFM experimental characterization;

[0009] (2) The surface potential change of the sample before and after hydrogen charging was monitored in situ using SKPFM technology to identify the hydrogen capture behavior at the interface between the precipitated phase and the matrix.

[0010] (3) Use focused ion beam (FIB) to extract specific precipitated phase regions and prepare samples for transmission electron microscopy (TEM);

[0011] (4) The chemical composition, crystal structure, chemical characteristics and interfacial strain of the precipitated phase were characterized by scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS).

[0012] (5) By correlating the SKPFM potential change data with the TEM characterization results, the hydrogen capture or hydrogen repulsion behavior of the interface between the nano-precipitated phase and the matrix can be determined.

[0013] Further, in step (1), the sheet-like metal material sample is first mechanically polished on a velvet cloth using SiO2 suspension particles with a diameter of 40 nm, and then argon ion etching is performed for 27-33 minutes to remove surface oxides and contaminants.

[0014] Furthermore, in step (2), the SKPFM experiment uses the same probe tip with a platinum-iridium (PtIr) coating throughout, with a cantilever elastic coefficient of 2.8 N / m, a frequency of 60-100 kHz, a radius of curvature of <25 nm, and a set lift height of 55-65 nm. The experiment is conducted at room temperature and in air with a relative humidity of 38±1%. The potential is calibrated with highly oriented pyrolytic graphite (HOPG) before and after the experiment to ensure the accuracy of the potential measurement.

[0015] Furthermore, in step (2), highly oriented pyrolytic graphite (HOPG) is used before and after the SKPFM experiment; the hydrogen charging is performed on one side of the sample; after hydrogen charging, the sample is immediately transferred to the SKPFM instrument for potential characterization.

[0016] Furthermore, in step (3), during the FIB sample preparation process, a carbon layer and a platinum layer need to be pre-deposited on the sample surface to protect the microstructure of the nano-precipitated phase and avoid FIB etching damage to the precipitated phase; a thin film containing the target precipitated phase is extracted by FIB cutting and thinned to 40-60 nm to meet the requirements of TEM observation.

[0017] Furthermore, in step (4), based on the image from a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), the chemical composition of the precipitated phase is determined by energy-dispersive X-ray spectroscopy (EDS), and the orientation relationship between the precipitated phase and the surrounding matrix is ​​determined by selected area electron diffraction (SAED).

[0018] Furthermore, in step (4), the existence of vacancy defects is analyzed by analyzing the valence state changes of specific elements at the interface through electron energy loss spectroscopy (EELS).

[0019] Further, in step (4), the interface strain analysis is performed using CalAtom software. Based on the atomic resolution HAADF-STEM image, the matrix position 140-180 nm away from the precipitated phase interface is selected as the unstrained reference area. The atomic strain map is generated by comparing the nearest neighbor distance between atoms in a specific crystal orientation with its reference value, and the lattice strain field near the interface between the precipitated phase and the matrix is ​​calculated.

[0020] Furthermore, the definitions of hydrogen capture and hydrogen repulsion in step (5) are analyzed in conjunction with SKPFM and TEM data. If the potential of the precipitated phase interface with the matrix is ​​lower than that of the matrix in the SKPFM test, and the TEM shows that there are vacancies at the interface and tensile strain in the matrix near the interface, it is hydrogen capture. If a "bright ring" appears at the interface of the precipitated phase with the matrix in the SKPFM test, that is, the potential is higher than that of the matrix, and the TEM shows that there are no obvious vacancies at the interface and compressive strain in the matrix near the interface, it is hydrogen repulsion.

[0021] The beneficial effects of the technical solutions provided by the embodiments of the present invention include:

[0022] 1. This invention combines SKPFM with TEM to achieve in-situ monitoring of hydrogen capture behavior with atomic-scale structural and chemical characterization of hydrogen capture sites, thus overcoming the limitations of single technologies.

[0023] 2. The method provided by this invention can monitor the potential change of the incoherent interface between the precipitated phase and the matrix in situ during hydrogen charging. Combined with high-resolution structural analysis, it can directly correlate hydrogen capture behavior with microstructure, providing a reliable basis for the study of hydrogen embrittlement mechanism.

[0024] 3. The solution provided by this invention has wide applicability and can be used to characterize the hydrogen capture behavior of nanoscale microstructures (such as grain boundaries, inclusions and other defects) in various metallic materials. It opens up new avenues for the study of the atomic mechanism of hydrogen-induced cracking and has important guiding significance for material design and performance optimization. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0026] Figure 1 The following is a schematic diagram of the in-situ SKPFM experiment provided in the embodiment of the present invention: a) initial SKPFM potential scan of the uncharged sample; b) single-sided hydrogen charging on the back side of the sample; c) SKPFM potential scan of the sample after hydrogen charging.

[0027] Figure 2 The in-situ SKPFM test potential diagrams provided in this embodiment of the invention are as follows: ad is the SKPFM potential diagram of phase 1# without hydrogen charging and at 160 minutes, 1320 minutes, and 4940 minutes after hydrogen charging; e is the potential distribution along the yellow dashed line in diagrams a and d; fi is the SKPFM potential diagram of phase 3# without hydrogen charging and at 360 minutes, 1200 minutes, and 4860 minutes after hydrogen charging; j is the potential distribution along the yellow dashed line in diagrams f and i.

[0028] Figure 3 This is a schematic diagram of TEM-FIB sample preparation provided in an embodiment of the present invention. a) is identifying the precipitated phase, b) is extracting the precipitated phase, and c) is performing FIB thinning on the extracted sample.

[0029] Figure 4The STEM-HAADF image and EDS result image provided in the embodiment of the present invention are shown in Figures a and b, respectively, which are STEM images of precipitates #2 and #3, respectively; c and d are the EDS results of the boxed areas in Figures a and b, respectively; e and f are the EDS line data along the yellow lines in Figures c and d, respectively, which characterize the elemental composition of the interface between the precipitate and the matrix.

[0030] Figure 5 The HRTEM image of the precipitated phase and the SEAD image of the interface between the precipitated phase and the matrix provided in the embodiments of the present invention are shown in the figures. a is the HRTEM image of precipitated phase #2, b is the SEAD image of the interface between precipitated phase #2 and the matrix, c is the HRTEM image of precipitated phase #3, and d is the SEAD image of the interface between precipitated phase #3 and the matrix.

[0031] Figure 6 The diagram shows the Ti valence state change at the interface provided in this embodiment of the invention. a is the EELS spectrum of the interior and interface of precipitate #2, and b is the EELS spectrum of the interior and interface of precipitate #3. The dashed lines in the diagram represent the peak positions of L2 and L3.

[0032] Figure 7 The above are atomic-level strain distribution maps of the matrix near the precipitate interface provided in this embodiment of the invention. a and b are filtered HAADF-STEM images of the matrix within 3 nm of the precipitate interface #2, and corresponding... and Atomic-level strain distribution maps for two crystal orientations; c and d are filtered HAADF-STEM images of the matrix within 3 nm near the precipitate interface #3, and the corresponding... and Atomic-level strain distribution diagrams for two crystal orientations, where e is a box plot of the strain measurement statistics for precipitates #2 and #3. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] This invention provides a method for in-situ characterization of hydrogen capture behavior in nanophases based on SKPFM-TEM coupled technology, comprising:

[0035] 1. SKPFM Sample Preparation

[0036] A high-strength low-alloy steel sample with a thickness of 0.49 mm (containing Ti2CS precipitates) was selected and mechanically polished on a cloth with a SiO2 suspension with a diameter of 40 nm. Then, argon ion etching was performed for 30 minutes to remove the surface oxides.

[0037] 2. In-situ SKPFM experiment

[0038] The sample was characterized using a Nanoscope V (Veeco Instruments) in tapping mode. The probe was a platinum-iridium (PtIr) coated tip with a cantilever elastic modulus of 2.8 N / m, a frequency range of 60-100 kHz, a radius of curvature <25 nm, and a set lift height of 60 nm. Testing was conducted at room temperature and in air with a relative humidity of 38 ± 1%. The potential was calibrated with highly oriented pyrolytic graphite (HOPG) before and after the experiment to ensure the accuracy of the potential measurement.

[0039] The in-situ SKPFM experimental procedure is as follows: Figure 1 As shown, the uncharged sample underwent an initial SKPFM potential scan, and was then transferred to a hydrogen charging device for single-sided hydrogen charging on the back side for 25 minutes. The electrochemical hydrogen charging solution consisted of 0.2 mol / L NaOH + 0.22 g / L thiourea, with a current density of 12 mA / cm². 2 After being charged with hydrogen, the sample was immediately transferred back to the SKPFM instrument for potential characterization.

[0040] In-situ SKPFM potential scan, such as Figure 2 As shown, the potential of the region containing the precipitated phase was scanned before hydrogen charging, and the potential of the same region was monitored in situ after hydrogen charging. The potential at the interface between the 1# nano-precipitated phase and the matrix was lower than that inside the precipitated phase and the matrix; the potential at the interface between the 3# precipitated phase and the matrix was significantly higher than that inside the matrix and the precipitated phase, showing a "bright ring" feature in the SKPFM potential diagram.

[0041] 3. TEM-FIB Sample Preparation

[0042] TEM samples were prepared using a Thermo Fisher Helios focused ion beam (FIB) system, such as... Figure 3 As shown, FIB extracts samples containing precipitates #2 (consistent with the behavior of #1) and #3, and the surface is protected by carbon and platinum layers.

[0043] 4. TEM characterization

[0044] The procedure was performed on a Thermo Fisher Themis Z TEM. Based on images from a high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM), the chemical composition of the precipitated phase was determined using EDS images, such as... Figure 4 As shown; SAED analysis was used to determine the orientation relationship between the precipitated phase and the surrounding matrix, such as... Figure 5 As shown.

[0045] By analyzing the Ti-L precipitate inside and at the interface of the precipitated phase 2,3 EELS analysis of the peaks was performed to determine whether carbon or sulfur vacancies existed at the interface between the precipitated phase and the matrix, such as... Figure 6 As shown.

[0046] The strain state was analyzed by directly resolving the atomic column positions in the HAADF-STEM images at atomic resolution near the interface. CalAtom software was used to determine the precise position of each atomic column, which was then compared with the martensitic matrix region approximately 140-180 nm from the interface. HRTEM images and corresponding atomic-level strain maps of the martensitic matrix within 3 nm of the interface were generated, and all strain values ​​within the selected region were statistically analyzed. Figure 7 As shown.

[0047] 5. Joint analysis of SKPFM-TEM data

[0048] The presence of vacancies and tensile strain of atoms near the interface at the precipitated phase-matrix interface results in a low hydrogen dissolution energy, which manifests as hydrogen capture, consistent with the SKPFM potential results. Conversely, the absence of significant vacancies and compressive strain of atoms near the interface at the precipitated phase-matrix interface results in a high hydrogen dissolution energy, which manifests as hydrogen repulsion, matching the "bright ring" characteristic of SKPFM.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for in-situ characterization of hydrogen capture behavior in nanophases based on SKPFM-TEM coupled technology, characterized in that, include: (1) Preparation of metallic material samples for SKPFM experimental characterization; (2) The surface potential change of the sample before and after hydrogen charging was monitored in situ using SKPFM technology to identify the hydrogen capture behavior at the interface between the precipitated phase and the matrix. (3) Use focused ion beam (FIB) to extract specific precipitated phase regions and prepare samples for transmission electron microscopy (TEM); (4) The chemical composition, crystal structure, chemical characteristics and interfacial strain of the precipitated phase were characterized by scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS). (5) By correlating the SKPFM potential change data with the TEM characterization results, the hydrogen capture or hydrogen repulsion behavior of the interface between the nano-precipitated phase and the matrix can be determined.

2. The method according to claim 1, characterized in that, In step (1), the thin sheet metal sample is first mechanically polished on a velvet cloth using SiO2 suspension particles with a diameter of 40 nm, and then argon ion etching is performed for 27-33 minutes to remove surface oxides and contaminants.

3. The method according to claim 1, characterized in that, In step (2), the SKPFM experiment uses the same probe tip with a platinum-iridium (PtIr) coating throughout. The cantilever elasticity coefficient is 2.8 N / m, the frequency is 60-100 kHz, the radius of curvature is <25 nm, and the set lift height is 55-65 nm. The experiment is conducted at room temperature and relative humidity of 38±1% in the air. The potential is calibrated with highly oriented pyrolytic graphite (HOPG) before and after the experiment to ensure the accuracy of the potential measurement.

4. The method according to claim 1 or 3, characterized in that, In step (2), highly oriented pyrolytic graphite (HOPG) is used before and after the SKPFM experiment; hydrogen charging is performed on one side of the sample; after hydrogen charging, the sample is immediately transferred to the SKPFM instrument for potential characterization.

5. The method according to claim 1, characterized in that, In step (3), during the FIB sample preparation process, a carbon layer and a platinum layer need to be pre-deposited on the sample surface to protect the microstructure of the nano-precipitated phase and avoid FIB etching damage to the precipitated phase; the thin film containing the target precipitated phase is extracted by FIB cutting and thinned to 40-60 nm to meet the requirements of TEM observation.

6. The method according to claim 1, characterized in that, In step (3), a sample is prepared for transmission electron microscopy (TEM).

7. The method according to claim 1, characterized in that, In step (4), the chemical composition of the precipitated phase is determined by energy dispersive X-ray spectroscopy (EDS) based on the image of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and the orientation relationship between the precipitated phase and the surrounding matrix is ​​determined by selected area electron diffraction (SAED).

8. The method according to claim 1, characterized in that, In step (4), the presence of vacancy defects is detected by analyzing the valence state changes of specific elements at the interface using electron energy loss spectroscopy (EELS).

9. The method according to claim 1, characterized in that, In step (4), the interface strain analysis is performed using CalAtom software. Based on the atomic resolution HAADF-STEM image, the matrix position 140-180 nm away from the precipitated phase interface is selected as the unstrained reference area. The atomic strain map is generated by comparing the nearest neighbor distance between atoms in a specific crystal orientation with its reference value, and the lattice strain field near the interface between the precipitated phase and the matrix is ​​calculated.

10. The method according to claim 1, characterized in that, The definitions of hydrogen capture and hydrogen repulsion in step (5) are analyzed in conjunction with SKPFM and TEM data. If the potential of the precipitated phase interface with the matrix is ​​lower than that of the matrix in the SKPFM test, and the TEM shows that there are vacancies at the interface and tensile strain in the matrix near the interface, it is hydrogen capture. If a "bright ring" appears at the interface of the precipitated phase with the matrix in the SKPFM test, that is, the potential is higher than that of the matrix, and the TEM shows that there are no obvious vacancies at the interface and compressive strain in the matrix near the interface, it is hydrogen repulsion.

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