Methods for assessing the degree of irradiation damage to materials

Abstract

This invention belongs to the field of material defect characterization and provides a method for evaluating the degree of irradiation damage to materials, comprising the following steps: (1) providing an irradiated sample; (2) using EBSD to obtain the grain orientation information of the irradiated sample, and selecting target grains according to the grain orientation, adjusting the electron gun accelerating voltage value and the position of the irradiated sample to perform ECCI characterization on the target grains; (3) comparing whether the total surface density ρ1 of the defects in the irradiated sample in the S / TEM characterization results and the total surface density ρ2 of the defects in the irradiated sample in the ECCI characterization results satisfy |ρ 1‑ ρ2|≤1×10 17 pcs / m 2 If not, proceed to step (4); (4) adjust the electron gun accelerating voltage to perform ECCI characterization on the target grain; (5) repeat steps (3)-(4) until ρ1 and ρ2 satisfy |ρ 1‑ ρ2|≤1×10 17 pcs / m 2 Therefore, this method can conveniently assess the degree of irradiation damage to bulk materials and rapidly screen materials irradiated with ions.

Description

Technical Field

[0001] This invention relates to the field of material defect characterization, and more specifically, to a method for assessing the degree of irradiation damage to materials. Background Technology

[0002] High-dose irradiation at high temperatures can degrade the properties of materials. This irradiation-induced degradation can be attributed to the generation and continuous evolution of point defects (excessive gaps and vacancies). Observing and statistically analyzing irradiation defects is key to understanding macroscopic irradiation effects and designing radiation-resistant materials from a microscopic perspective.

[0003] Currently, the design and selection of structural materials for nuclear reactors involves numerous material samples and varying irradiation parameters. This necessitates extensive experimental testing of different materials to observe and statistically analyze irradiation defects before designing radiation-resistant materials. At present, S / TEM (scanning / transmission electron microscopy) is primarily used for defect observation. However, this method is labor-intensive, requires highly precise sample preparation, and has a limited observation area, resulting in high characterization costs, long experimental cycles, and significant analytical challenges for material irradiation defects.

[0004] Therefore, it is particularly important to develop a rapid and convenient method for assessing the degree of irradiation damage to materials. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the related art.

[0006] This invention proposes a method for assessing the degree of irradiation damage to materials, comprising the following steps:

[0007] (1) Provide irradiated samples;

[0008] (2) Use EBSD to obtain the grain orientation information of the irradiated sample, and select target grains according to the grain orientation, adjust the electron gun acceleration voltage and the position of the irradiated sample, so as to perform ECCI characterization on the target grains;

[0009] (3) Compare the total surface density ρ1 of the irradiated sample defects in the S / TEM characterization results with the total surface density ρ2 of the irradiated sample defects in the ECCI characterization results to see if they satisfy |ρ 1- ρ2|≤1×10 17 pcs / m 2 If not, proceed to step (4);

[0010] (4) Adjust the electron acceleration voltage to perform ECCI characterization on the target grain;

[0011] (5) Repeat steps (3)-(4) until ρ1 and ρ2 satisfy |ρ 1- ρ2|≤1×10 17 pcs / m 2 .

[0012] The method of this invention uses ECCI (electron channel imaging) to characterize irradiated materials. By comparing the total areal density ρ1 of the irradiated material's S / TEM characterization results with the total areal density ρ2 of the irradiated sample defects in the ECCI characterization results, the electron gun accelerating voltage value suitable for ECCI characterization of this type of material can be quickly selected. At this electron gun accelerating voltage value, ECCI is used to rapidly characterize the material's irradiation defects. Specifically, by comparing the ECCI characterization results and S / TEM observation results of irradiated samples at different electron gun accelerating voltages, the operating condition parameters of ECCI characterization that are closest to the S / TEM results can be found. This allows for the determination of the most suitable electron gun accelerating voltage for this type of material when using ECCI to assess ion irradiation damage, and thus enables rapid assessment of the damage degree of large batches of ion-irradiated samples.

[0013] According to an embodiment of the present invention, the comparison includes the following steps:

[0014] (3-1) Based on the irradiated sample, a three-dimensional coordinate system is defined. The length direction of the irradiated sample is defined as the X-axis, and the length of the irradiated sample is H. The longitudinal direction of the irradiated sample is defined as the Y-axis, and the irradiation depth H1 of the irradiated sample is located in the Y-axis direction. The normal of the irradiated sample is defined as the Z-axis. In the Y-axis direction, the irradiated sample is divided into n layers of observation regions with a thickness of H2. S / TEM characterization is performed on the YZ surface of each of the n observation regions. The surface density ρ of the defects in the i-th observation region is calculated. 3i H2 and H1 satisfy H1=nH2, where n is a positive integer greater than 1, and i takes values ​​from 1 to n;

[0015] (3-2) The defect surface density ρ of the YZ surface of the i-th observation region 3i Transformed into the volume density ρ of the YZ surface of the i-th observation region 4i Then the volume density ρ 4i Converted into the defect surface density ρ of the i-th observation region XZ surface 5i ;

[0016] (3-3) Using the principle of layer-by-layer superposition, the defect surface density ρ of n XZ surfaces is... 5i Add them together to obtain the total surface density ρ1 of the defects in the irradiated sample, i.e. Therefore, a relationship can be established between the TEM characterization results and the ECCI characterization results of irradiated samples to compare the accuracy of the ECCI characterization results.

[0017] According to an embodiment of the present invention, in step (3-2), the defect surface density ρ of the YZ surface of the region to be observed is... 3i With respect to the volume density ρ of the region to be observed 4i Satisfying the relation: ρ 4i =ρ 3i / H.

[0018] According to an embodiment of the present invention, in step (3-2), the volume density ρ4 of the region to be observed and the defect density ρ of the XZ plane of the region to be observed are... 5i Satisfying the relation: ρ 5i =ρ 4i ×H2.

[0019] According to an embodiment of the present invention, the H2 is 50-150 nm. This facilitates obtaining accurate test results.

[0020] According to an embodiment of the present invention, H1 is obtained by calculation using the simulation software SRIM.

[0021] According to an embodiment of the present invention, n is 10-15.

[0022] According to an embodiment of the present invention, the target grain refers to an on-axis grain.

[0023] According to an embodiment of the present invention, ECCI characterization of the target grain includes selecting the target grain, tilting the irradiated sample, and performing ECCI characterization on the target grain.

[0024] Optionally, the tilt angle θ of the irradiated sample is 0 < θ ≤ 4°.

[0025] According to an embodiment of the present invention, the accelerating voltage is 10-30kV.

[0026] According to an embodiment of the present invention, the irradiated sample comprises an irradiated FeCrNiCo high-entropy alloy.

[0027] Optionally, the irradiation includes at least one of ion irradiation, neutron irradiation, and proton irradiation;

[0028] Optionally, the ion irradiation includes one of He irradiation and Fe ion irradiation, and the energy of the ion irradiation is 10 keV-10 MeV. Attached Figure Description

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0030] Figure 1This is a STEM-BF image of the irradiated FeCoNiCr high-entropy alloy from Example 1;

[0031] Figure 2 This is a TEM-BF image of He bubbles in the irradiated FeCoNiCr high-entropy alloy of Example 1;

[0032] Figure 3 These are the SE and ECCI images of the irradiated FeCoNiCr high-entropy alloy from Example 1;

[0033] Figure 4 This is the ECCI diagram of the irradiated FeCoNiCr high-entropy alloy from Example 1;

[0034] Figure 5 This is a comparison of the TEM and ECCI characterization results of the irradiated FeCoNiCr high-entropy alloy in Example 1. Detailed Implementation

[0035] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0036] Currently, S / TEM is widely used to observe defects in irradiated materials. To obtain clear contrast of irradiated defects, several unique and stringent imaging conditions are required. Common methods for characterizing irradiation-induced dislocation loops include bright-field (BF) imaging under kinematic two-beam conditions, Rel-Rod dark-field (DF) imaging, dark-field imaging under weak-beam conditions, and regional S / TEM-BF imaging. The S / TEM imaging process also requires complex sample tilting to select and determine the diffraction vector g. Furthermore, S / TEM demands high sample quality, and the observed area is typically less than 100 μm. 2 The area is significantly smaller than the actual irradiated area, leading to inaccurate defect statistics. Electron channel contrast imaging (ECCI) based on backscattered electrons can be used to assess defects in irradiated materials, but key evidence is still lacking, such as data on the effect of electron beam energy on defects, and methods for assessing the consistency between the data and S / TEM observations.

[0037] Therefore, the present invention proposes a method for assessing the degree of damage to irradiated materials, comprising the following steps:

[0038] (1) Provide irradiated samples;

[0039] (2) Use EBSD to obtain the grain orientation information of the irradiated sample, and select target grains according to the grain orientation, adjust the electron gun acceleration voltage value and the position of the irradiated sample, so as to perform ECCI characterization on the target grains;

[0040] (3) Compare the total surface density ρ1 of the irradiated sample defects in the S / TEM characterization results with the total surface density ρ2 of the irradiated sample defects in the ECCI characterization results to see if they satisfy |ρ 1- ρ2|≤1×10 17 pcs / m 2 If not, proceed to step (4);

[0041] (4) Adjust the electron acceleration voltage to perform ECCI characterization on the target grain;

[0042] (5) Repeat steps (3)-(4) until ρ1 and ρ2 satisfy |ρ 1- ρ2|≤1×10 17 pcs / m 2 .

[0043] The method of this invention uses ECCI to characterize irradiated materials. By comparing the total areal density ρ1 of the irradiated material's S / TEM characterization results with the total areal density ρ2 of the defects in the irradiated sample from the ECCI characterization results, the electron gun accelerating voltage value for this type of irradiated material can be quickly screened. At this electron gun accelerating voltage value, the defects of the irradiated material can be rapidly characterized using ECCI. Specifically, by comparing the ECCI characterization results and S / TEM observation results of irradiated samples at different electron gun accelerating voltages, the operating condition parameters of ECCI characterization that are closest to the S / TEM results can be found. This allows for the determination of the most suitable electron gun accelerating voltage for this type of material when using ECCI to assess ion irradiation damage, thereby enabling rapid assessment of the damage degree of a large batch of ion-irradiated samples.

[0044] Understandably, the ECCI characterization operating conditions parameters that are closest to the S / TEM characterization results can be either using the same ECCI characterization conditions for this type of material, or fine-tuning the operating conditions to quickly screen the damage level of this type of material using ECCI. This type of material refers to metallic materials with face-centered cubic (FCC), body-centered cubic (BCC), hexagonal close-packed (HCP), and other crystal structures.

[0045] According to the present invention, in step (1), an irradiated sample is provided.

[0046] In some embodiments, the process further includes polishing the sample to obtain a smooth, scratch-free, and stress-free surface, followed by irradiation treatment of the smooth sample. Specifically, the surface polishing techniques for the material include electropolishing and vibratory polishing.

[0047] In some embodiments, the irradiated sample is a material with a specific crystal structure. Optionally, the irradiated sample includes a metal material with an irradiated face-centered cubic structure, a metal material with an irradiated body-centered cubic structure, or a metal material with an irradiated close-packed cubic structure.

[0048] In some implementations, the irradiation experiment includes ion irradiation, neutron irradiation, or proton irradiation.

[0049] Optionally, the energy of the ion irradiation is 30 keV to 10 MeV.

[0050] Optionally, the neutron irradiation energy is 50 keV-10 MeV.

[0051] Optionally, the energy of the proton irradiation is 10 keV-10 MeV.

[0052] As some specific embodiments, the irradiated sample is a FeCrNiCo high-entropy alloy with a face-centered cubic structure;

[0053] Optionally, the ion irradiation is one of He irradiation and Fe ion irradiation, and the energy of the ion irradiation is 10 keV-3 MeV.

[0054] According to the present invention, in step (2), the irradiated material is characterized by ECCI.

[0055] In some implementations, in step (2), the target grain refers to an on-axis grain, which means that the grain is located at or near the low index band axis.

[0056] Alternatively, the low-index band axis of the face-centered cubic metallic material refers to the

[001] axis,

[011] axis, and

[111] axis.

[0057] As an example, the irradiated sample is an irradiated FeCrNiCo high-entropy alloy with an equiatomic body-centered cubic structure, and the low-index band axis of the irradiated equiatomic FeCrNiCo high-entropy alloy is the

[001] axis.

[0058] In some embodiments, step (2), performing electron channel shaping (ECCI) characterization on the target grain includes selecting the target grain, tilting the irradiated sample, and performing ECCI characterization on the target grain using electron backscattering diffraction. Optionally, the tilt angle θ of the irradiated sample is 0 < θ ≤ 4°.

[0059] In some implementations, in step (2), the electron gun accelerating voltage is 10-30kV.

[0060] According to the present invention, in step (3), the total surface density ρ1 of the irradiated sample defects in the S / TEM characterization results and the total surface density ρ2 of the irradiated sample defects in the ECCI characterization results are compared to see if they satisfy |ρ 1- ρ2|≤1×10 17 pcs / m 2 .

[0061] In some embodiments, step (3) further includes: preparing the irradiated sample to be characterized by S / TEM using FIB technology. Generally, the cross-sectional sample H prepared by focused ion beam is 30-100 nm.

[0062] In some implementations, step (3) includes the following steps:

[0063] (3-1) Based on the irradiated sample, a three-dimensional coordinate system is defined. The length direction of the irradiated sample is defined as the X-axis, and the sample length is H. The longitudinal direction of the irradiated sample is defined as the Y-axis, and the irradiation depth H1 of the irradiated sample is located in the Y-axis direction. The normal of the irradiated sample is defined as the Z-axis. In the Y-axis direction, the irradiated sample is divided into n layers of observation regions with a thickness of H2. S / TEM characterization is performed on the YZ surface of each of the n observation regions. The surface density ρ of the defects in the i-th observation region is calculated. 3i H2 and H1 satisfy H1=nH2, where n is a positive integer greater than 1, and i takes values ​​from 1 to n;

[0064] (3-2) The defect surface density ρ of the YZ surface of the i-th observation region 3i Transformed into the volume density ρ of the YZ surface of the i-th observation region 4i Then the volume density ρ 4i Converted into the defect surface density ρ of the i-th observation region XZ surface 5i ;

[0065] (3-3) Using the principle of layer-by-layer superposition, the defect surface density ρ of n XZ surfaces is... 5i Add them together to obtain the total surface density ρ1 of the defects in the irradiated sample, i.e. .

[0066] In some implementations, in step (3), H2 is the thickness of the region to be observed in each layer of the S / TEM sample. The selected thickness H2 for each layer is related to the accuracy of the defect observation structure, and a smaller H2 indicates better defect observation results. Optionally, H2 is 50-150 nm.

[0067] In some implementations, in step (3), H1 is the material irradiation intensity, calculated by the simulation software SRIM (Stopping and Range of Ions in Matter).

[0068] In some implementations, in step (3-2), the defect surface density ρ of the YZ surface of the region to be observed... 3i With respect to the volume density ρ of the region to be observed 4i Satisfying the relation: ρ 4i =ρ 3i / H.

[0069] In some implementations, in step (3-2), the volume density ρ4 of the region to be observed and the defect density ρ of the XZ plane of the region to be observed are... 5i Satisfying the relation: ρ 5i =ρ 4i ×H2.

[0070] As an example, at an irradiation temperature of 450°C and a vacuum degree of 10... -5 Under the Pa condition, the initial energy utilized is 400 keV and the flux is 3 × 10⁻⁶. 16 -6×10 16 cm -2 The polished FeCrNiCo high-entropy alloy was irradiated with a He ion beam, and then irradiated with an energy of 3 MeV and an irradiation dose rate of 2 × 10⁻⁶. -4 -5×10 -4 A FeCrNiCo high-entropy alloy was irradiated with a Fe ion beam at dpa / s, resulting in an irradiation damage depth H1 of 1500-2000 nm. The irradiated FeCrNiCo alloy was then cleaned with ethanol and dried. Subsequently, a focused ion beam (FIB) was used to prepare an S / TEM sample for testing. The irradiation depth H1 of the sample was defined as the Y-direction, and the surface perpendicular to this irradiation depth was defined as the XZ-plane. n layers of observation regions with a thickness of 100-150 nm were formed. S / TEM characterization was performed on the XZ-plane of each observation region, and the average size and areal density ρ of defects in each layer of the observation region were statistically analyzed. 3i .

[0071] According to the present invention, in step (4), the electron acceleration voltage is adjusted to perform electron channel integration (ECCI) characterization on the target grain. In this step, by adjusting the electron acceleration voltage, the difference in ECCI imaging quality under different electron gun acceleration voltages can be obtained, thereby selecting the electron gun acceleration voltage value of the most suitable ECCI characterization condition parameter for this type of sample, and then quickly screening the damage degree of this type of sample under the modified electron gun acceleration voltage value.

[0072] According to the present invention, in step (5), steps (3) and (4) are repeated until ρ1 and ρ2 satisfy |ρ 1- ρ2|≤1×10 17 pcs / m 2 .

[0073] The present invention will be described below through specific embodiments. It should be noted that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention.

[0074] S / TEM characterization was performed using a Thermo Fisher Titan-G2-300 scanning transmission electron microscope.

[0075] SEM characterization was performed using a Zeiss Gimi360 scanning electron microscope (SEM).

[0076] Example 1

[0077] (1) Provide irradiated samples

[0078] Equiatomic FeCrNiCo high-entropy alloys were prepared by arc melting. Before the ingot was drawn into the copper mold, it was repeatedly melted five times. The ingot inside the copper mold was then subjected to a solution treatment at 1180℃ for 24 hours to obtain the FeCrNiCo high-entropy alloy. The FeCrNiCo high-entropy alloy was cut into thin slices and polished smooth with 800#, 1000#, 3000#, and 7000# metallographic sandpaper, respectively. The samples were then polished to a mirror finish using 2.5μm and 0.5μm diamond polishing paste, respectively.

[0079] The polished sample was placed in a special electrolytic polishing solution (an ethanol solution with a perchloric acid content of 10%) and electrolytically polished at an electrode voltage of 5V, a current of 1A, and a temperature of -10℃ to obtain a smooth sample with no scratches and no stress. The sample dimensions were 5×5×1mm. 3 .

[0080] Then, under an irradiation temperature of 450℃ and a vacuum degree of 10... -5 Under Pa conditions, first utilize energy of 400 keV and flux of 5 × 10⁻⁶ Pa. 16 cm -2 The sample, polished by He ion beam irradiation, was then subjected to irradiation at an energy of 3 MeV and a dose rate of 3.5 × 10⁻⁶. -4 The sample was irradiated with an Fe ion beam of dpa / s to obtain an irradiated FeCoNiCr high-entropy alloy.

[0081] (2) ECCI characterization of the irradiated FeCoNiCr high-entropy alloy

[0082] The irradiated FeCoNiCr high-entropy alloy was immersed in acetone for 3 minutes and then dried with cold air.

[0083] Place the sample in the SEM, adjust the focal length and working distance so that the surface morphology of its XZ plane can be clearly seen in SE mode.

[0084] The grain orientation of the surface was obtained using EBSD technology, and the target grain was selected. The target grain was selected as the low index band axis

[001] . Then the sample stage was tilted so that it was completely on the axis. Subsequently, the BSE probe equipped with SEM was inserted, and ECCI characterization of the irradiated FeCrNiCo high-entropy alloy was performed using BSE mode imaging under the condition of electron acceleration voltage of 20kV.

[0085] (3) Compare the total density ρ1 of the irradiated sample in the S / TEM characterization results with the total density ρ2 of the irradiated sample in the ECCI characterization results.

[0086] The ion implantation direction (irradiation depth) of the irradiated sample is defined as the Y direction, the irradiation depth is 1800 nm, and the surface perpendicular to the irradiation depth direction Y is defined as the XZ surface. The irradiated sample is prepared into n layers of observation region with a thickness of 150 nm using a focused ion beam. The XZ surface of the observation region is characterized by S / TEM, and the average size and areal density ρ3 of the defects in the observation region are statistically analyzed. The thickness of the observation region of 150 nm and the irradiation depth of 1800 nm satisfy 1800 = 12 × 150, and n is 12.

[0087] The defect surface density ρ3 on the YZ surface of the region to be observed is converted into the volume density ρ4 of the region to be observed. 4i =ρ 3i / H, H=60nm), then convert the volume density ρ4 of the region to be observed into the defect density ρ5 of the XZ plane of the region to be observed (ρ 5i =ρ 4i ×150);

[0088] Using the principle of layer-by-layer superposition, the defect densities ρ5 of the 12 XZ planes are added together to obtain the total defect density ρ1 of the irradiated sample. ).

[0089] Compare whether ρ1 and ρ2 satisfy |ρ 1- ρ2|≤1×10 17 pcs / m 2 If not, continue adjusting the electron accelerating voltage and repeat step (3) until the total density ρ1 of the irradiated sample defects in the S / TEM characterization results and the total density ρ2 of the irradiated sample defects in the ECCI characterization results satisfy |ρ1-ρ2|≤1×10 17 pcs / m 2.

[0090] The S / TEM and ECCI characterization results of Example 1 above were analyzed.

[0091] Figure 1 (a)-(c) show He + and Fe 2+ STEM-BF images of

[001] grains of FeCoNiCr high-entropy alloy irradiated with light. Figure (c) shows the corresponding FEF pattern, and Figure (d) shows the STEM-HAADF image of dislocation loops. Figure 1 (e1)-(e4) and 1(f) are EDS elemental distribution diagrams of the high-entropy alloy. The irradiated region and the pristine region can be clearly distinguished based on the defect distribution. It can be found that the irradiation-induced defects in this study mainly include dislocation loops and black spot defects widely distributed throughout the irradiated region, as well as He bubbles concentrated near a depth of 800 nm. Figure 1 (c) is the corresponding FEF pattern. Figure 1 (d) shows a magnified STEM-HAADF image, with line scans of HAADF intensity and the percentage of atoms of a single element corresponding to the arrows. Dislocation loops of b=1 / 2

[110] are concentrated at a depth of ~900 nm. These dislocation loops are believed to have evolved from excess interstitial sites introduced by irradiation. Pre-irradiation of He will greatly limit the recombination of interstitial sites and vacancies (by increasing the vacancy migration energy), allowing more interstitial atoms to participate in the formation and evolution of dislocation loops. Figure 1 Elemental analysis was performed at the EDS line in (d), see Figure 1 (e1)-(e4) and 1(f), EDS spectra and line profiles show that no segregation was detected near the dislocation loops, and all high-entropy alloying elements fluctuated in the atomic percentage range of 20%-30%.

[0092] Figure 2 (a)-(c) are bright-field TEM images obtained under in-focus, overfocus, and underfocus conditions in the peak damage region of the FeCoNiCr high-entropy alloy under He ion irradiation. The images show that the contrast of the high-density dislocation loops makes it difficult to clearly identify and count He bubbles in the TEM-BF images. Specifically, the bubbles are not visible in the in-focus images, appear as dark contrast in the overfocus images, and appear as bright contrast in the underfocus images. Figure 2(d) and (e) show magnified bubble images in under-focus TEM-BF and STEM-HAADF imaging modes, respectively. It can be seen that the bubble appears approximately spherical under both imaging conditions. Figure 2 (f) shows the bubble diameter distribution within the depth range of 650-950 nm in 2(a). It can be seen that the bubble diameter exhibits an approximately Gaussian distribution, with approximately 75% of the bubbles having a diameter between 2 and 3.5 nm. The average diameter of all bubbles is 2.55 nm. Furthermore, the bubble number density is 4.74 × 10⁻⁶. 21 / m 2 .

[0093] Figure 3 (a) and (b) show a conventional secondary electron (SE) image and a BSE-based ECCI image of the same region of the FeCoNiCr high-entropy alloy, respectively. Unlike the SE image, which only shows the bright contrast of surface contamination, the ECCI image is filled with many bright circular, linear, and dotted bright contrasts against a dark background. Among these, the bright circular lines and diagonal lines in the ECCI image are b=1 / 2. <110> dislocation loop and b=1 / 3 <111> A typical contrast of partial dislocation loops is shown, with some dot-like bright contrasts arising from tiny He bubbles with an average diameter of 2.55 nm, irradiation-induced interstitial clusters, and surface defects resulting from electropolishing. Surface contamination is visible in the SE image, but irradiation defects are not observable. Figure 3 (c) shows a comparison of ECCI images of grains parallel to electrons along the

[001] axis of the FeCoNiCr high-entropy alloy and adjacent random grains. This result indicates that grain orientation has a significant impact on ECCI images. Obvious contrast of irradiated defects can be observed in grains with orientation Z=

[001] , while random grains show excessively bright contrast, making it difficult to highlight the defect contrast. Figure 3 (d)-(f) show ECCI images at different magnifications. The largest (Mag=200kX) and smallest (Mag=50kX) identifiable defects are a dislocation loop with a size of about 20nm and a point bubble contrast with a diameter of about 2nm, respectively. This indicates that ECCI can resolve irradiation-induced defects with a scale of about 2nm.

[0094] Figure 4(a)-(c) show ECCI images of irradiated samples obtained at different electron accelerating voltages (EHT = 10 kV, 20 kV, 30 kV), where (a) is SE imaging and (b) is ECCI based on BSE imaging. (c) compares ECCI images of tilted grains (Z =

[001] ) with those of random grains. The figures show that the defect contrast is best at 20 kV, especially since the smallest observable defect size at 20 kV is 1.6 nm, significantly smaller than 4.8 nm at 10 kV and 2.3 nm at 30 kV. Figure 4 As shown in (d), the lowest defect density can be observed at 10 kV, the lowest defect density can be observed at 20 kV with a significant increase, and the defect density observed at 30 kV is similar to that at 20 kV, but the defect contrast is significantly weaker than that at 20 kV.

[0095] Figure 5 (a) ECCI image of irradiation defects in an irradiated FeCoNiCr high-entropy alloy with

[001] as the target grain; (b) STEM-BF cross-sectional image of the irradiation defects; (c) Schematic diagram of SRIM simulation results and the layered method used in this study to estimate the area density; (d) Relationship between the estimated area density of visible defects (XZ plane) and the radiation damage depth (Y direction). The surface of the irradiated FeCoNiCr high-entropy alloy sample is defined as the XZ plane (X represents the thickness of the cross-sectional STEM sample, which is approximately 60 nm as measured by EELS). Therefore, the irradiated area can be continuously divided into countless thin layers of the XZ plane from the irradiation damage depth (Y direction), and it is assumed that the defects in each layer are uniformly distributed. Then, based on the defect area density ρ in the YZ plane of the STEM characterization image, the surface density of the defects is calculated. 3i Transformed into the volume density ρ of the YZ surface of the i-th observation region 4i Then the volume density ρ 4i Converted into the defect surface density ρ of the i-th observation region XZ surface 5i Finally, by summing the defect area densities on the XZ plane of each layer, the relationship between the total density ρ1 of the irradiated sample defects described in the TEM characterization results and the total density ρ2 of the irradiated sample defects described in the ECCI characterization results can be estimated. To simplify the calculation, this study uses a layer width of 150 nm for H2 to collect the projected defect density on the XZ plane from the sample surface to the irradiation damage depth of 1800 nm (H1=1800 nm, 12 layers in total). Figure 5 (d) shows the areal density of rings (>2 nm) and bubbles (>2 nm) on the XZ plane of each TEM-characterized sample of the same irradiated sample. The number density of rings and bubbles peaks at a depth of 900 nm and decreases rapidly after reaching a depth of 1200 nm. This phenomenon is consistent with... Figure 5The results shown in (c) are consistent with the SRIM simulation. Regarding dislocation loops, at an electron accelerating voltage of 20 kV, the dislocation density statistically observed from the ECCI image is 3 × 10⁻⁶. 18 pcs / m 2 This is close to the sum of the areal densities on the XZ plane of the first 12 layers at 1050nm, as statistically observed from the STEM image (29.37 × 10⁻⁶). 17 pcs / m 2 Therefore, it can be inferred that the contrast in the ECCI image is mainly caused by irradiation-induced defects ranging from the surface to a depth of about 1 μm.

[0096] In conclusion, Figure 4 and Figure 5 Irradiation-induced dislocation loops and He bubbles in FeCoNiCr high-entropy alloys were observed using STEM and ECCI, and the feasibility of using ECCI as an effective characterization strategy for studying micro-irradiation defects was evaluated. The results show that for ion irradiation with a damage depth of approximately 1 μm, ECCI image quality is optimal at 20 kV EHT, with a visible defect resolution limit of approximately 2 nm. Furthermore, the ECCI imaging contrast for dislocation loops is significantly better than that for bubbles, due to the smaller average diameter and lower lattice distortion (BSE yield) of bubbles. Finally, when the dislocation loop size is generally greater than 2 nm, the number density statistically obtained from ECCI images can correspond to the statistical data of TEM images through layer-by-layer accumulation. Therefore, ECCI can be used to rapidly and qualitatively assess irradiation damage in materials, and the observation area is generally greater than 1 mm. 2 .

[0097] and Figure 1 The STEM-based characterization strategy can only observe cross-sectional areas of 4 μm. 2 The tiny region, significantly smaller than the observation area during ECCI characterization, makes it difficult to obtain comprehensive information about the material after this irradiation.

[0098] In the description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0099] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for assessing the degree of irradiation damage to materials, characterized in that, Includes the following steps: (1) Provide irradiated samples; (2) Use EBSD to obtain the grain orientation information of the irradiated sample, and select the target grain according to the grain orientation, adjust the electron gun acceleration voltage and the position of the irradiated sample, so as to perform ECCI characterization on the target grain. (3) Compare the total surface density ρ1 of the irradiated sample defects in the S / TEM characterization results with the total surface density ρ2 of the irradiated sample defects in the ECCI characterization results to see if they satisfy |ρ 1- ρ2|≤1×10 17 pcs / m 2 If not, proceed to step (4); (4) Adjust the electron gun accelerating voltage to perform ECCI characterization on the target grain; (5) Repeat steps (3)-(4) until ρ1 and ρ2 satisfy |ρ 1- ρ2|≤1×10 17 pcs / m 2 To determine the electron gun accelerating voltage value suitable for ECCI characterization of the irradiated sample; In step (3), the comparison includes the following steps: (3-1) Based on the irradiated sample, a three-dimensional coordinate system is defined. The length direction of the irradiated sample is defined as the X-axis, and the thickness of the irradiated sample is H. The longitudinal direction of the irradiated sample is defined as the Y-axis, and the irradiation depth H1 of the irradiated sample is located in the Y-axis direction. The normal of the irradiated sample is defined as the Z-axis. In the Y-axis direction, the irradiated sample is divided into n layers of observation regions with a thickness of H2. S / TEM characterization is performed on the YZ surface of each of the n observation regions. The surface density ρ of the defects in the i-th observation region is calculated. 3i H2 and H1 satisfy H1=nH2, where n is a positive integer greater than 1, and i takes values ​​from 1 to n; (3-2) The defect surface density ρ of the YZ surface of the i-th observation region 3i Transformed into the volume density ρ of the YZ surface of the i-th observation region 4i Then the volume density ρ 4i Converted into the defect surface density ρ of the i-th observation region XZ surface 5i ; (3-3) Using the principle of layer-by-layer superposition, the defect surface density ρ of n XZ surfaces is... 5i Add them together to obtain the total surface density ρ1 of the defects in the irradiated sample, i.e. ; The calculation method for ρ1 is as described in (3-1) to (3-3).

2. The method according to claim 1, characterized in that, In step (3-2), the defect surface density ρ of the YZ surface of the region to be observed 3i With respect to the volume density ρ of the region to be observed 4i Satisfying the relation: ρ 4i =ρ 3i / H; And, the volume density ρ4 of the region to be observed and the defect density ρ of the XZ plane of the region to be observed. 5i Satisfying the relation: ρ 5i =ρ 4i ×H2.

3. The method according to claim 1, characterized in that, H1 was obtained through calculation using the simulation software SRIM.

4. The method according to claim 1, characterized in that, The H2 is 50-150nm.

5. The method according to claim 3 or 4, characterized in that, The value of n is 10-15.

6. The method according to claim 1, characterized in that, In step (2), the target grain refers to the on-axis grain.

7. The method according to claim 1, characterized in that, ECCI characterization of the target grain includes: after selecting the target grain, tilting the irradiated sample at a target angle, and performing ECCI characterization on the target grain.

8. The method according to claim 1, characterized in that, The irradiated sample is tilted at a target angle θ of 0 < θ ≤ 4°.

9. The method according to claim 1, characterized in that, The accelerating voltage is 10-30kV.

10. The method according to claim 1, characterized in that, The irradiated samples included irradiated FeCrNiCo high-entropy alloys.

11. The method according to claim 10, characterized in that, The irradiation includes at least one of ion irradiation, neutron irradiation, and proton irradiation.

12. The method according to claim 11, characterized in that, The ion irradiation includes one of He irradiation and Fe ion irradiation, and the energy of the ion irradiation is 10 keV-10 MeV.

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