In-situ three-dimensional surface reconstruction method based on scanning electron microscope

Abstract

The invention provides an in-situ three-dimensional surface reconstruction method based on a scanning electron microscope, and relates to the technical field of material microscopic characterization analysis, and the method comprises the following steps: preparing a metal sample suitable for an in-situ mechanical test, fixing the metal sample on an in-situ test bed, and fixing the whole metal sample in a scanning electron microscope chamber; carrying out an in-situ mechanical test, and continuously collecting symmetrical four-region images of the surface of the sample at different deformation stages by using a four-region back scattering electron detector; extracting direction gradient information through a gradient calculation formula, and calculating a surface X / Y direction gradient matrix; and solving a three-dimensional height field sequence by adopting a regularization method to realize three-dimensional surface reconstruction in a dynamic deformation process. The invention innovatively provides a three-dimensional surface reconstruction algorithm based on multi-detector image fusion, solves the problem that the high-precision three-dimensional shape of any deformation area cannot be obtained in real time in an in-situ scanning electron microscope test, and supports cross-scale characterization. And the analysis capability of a surface microscopic deformation mechanism of the metal material under complex stress conditions such as stretching and fatigue is obviously improved.

Description

Technical Field

[0001] The present invention relates to the technical field of microscopic characterization and analysis of materials, and particularly to an in-situ three-dimensional surface reconstruction method based on a scanning electron microscope. Background Art

[0002] In the research of materials science, understanding the surface topography changes of metal materials during the stress process is crucial for revealing their mechanical properties and deformation mechanisms. Traditional material characterization methods often have difficulty in obtaining high-precision and high-resolution three-dimensional surface information during in-situ testing. As a powerful microscopic characterization tool, a scanning electron microscope (SEM) can provide high-resolution images of the material surface, but applying it to the three-dimensional reconstruction of in-situ testing of metal materials faces many challenges.

[0003] Most of the existing three-dimensional reconstruction methods are based on optical microscopes or other non-in-situ technologies, and these methods have limitations in resolution and capturing the true surface state of the material. Combining the SEM with an in-situ testing device can observe the microscopic changes of the material during deformation, but how to accurately extract and reconstruct the three-dimensional surface height information from the SEM images, especially for precise analysis of any region at different deformation stages, is still an urgent problem to be solved. Currently, there is a lack of an effective algorithm and method to achieve this goal during in-situ SEM testing, which limits the in-depth understanding of the surface micro-behavior of metal materials under complex stress conditions. Summary of the Invention

[0004] The present invention provides an in-situ three-dimensional surface reconstruction method based on a scanning electron microscope to solve the problem of the lack of accurate three-dimensional surface height information for any region at different deformation stages during the existing in-situ SEM testing, and can effectively strengthen the in-depth understanding of the surface micro-deformation behavior of metal materials under complex stress conditions.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] An in-situ three-dimensional surface reconstruction method based on a scanning electron microscope, the steps are as follows:

[0007] S1. Mechanically grind and polish the original metal sample, a gauge section area is set in the middle area of the metal sample to obtain an in-situ experimental specimen; horizontally fix the in-situ experimental specimen on an in-situ test bench, and then fix the in-situ test bench in the scanning electron microscope chamber for in-situ mechanical testing along the X direction;

[0008] S2. During the in-situ mechanical testing, use a four-region backscattered electron detector containing four independent regions A, B, C, and D to capture four-region images I with different electron intensity distributions of the surface microstructure of the in-situ experimental specimen at different deformation stages. A , I B , I C , I D , where I A , I B and I C , I D are centrosymmetric about the center point of the detector respectively;

[0009] S3. Based on the four-region images I A , I B , I C , I D at different deformation stages, calculate the surface X-direction and Y-direction gradient matrices G x , G y of the captured area of the image;

[0010] S4. Based on the X-direction and Y-direction gradient matrices G x , G y , use the regularization three-dimensional reconstruction method to reconstruct the three-dimensional height field sequence Z of the captured area at different deformation stages, and complete the in-situ surface three-dimensional reconstruction.

[0011] Further, the in-situ test bench includes an in-situ tensile test bench, an in-situ fatigue test bench, and an in-situ creep test bench, corresponding to in-situ tensile testing, in-situ fatigue testing, and in-situ creep testing.

[0012] Further, in step S2, the center of the four-region backscattered electron detector coincides with the center of the scanning electron microscope electron beam. The amplification coefficients of the hardware amplifiers connected behind the four-region backscattered electron detector should be calibrated in advance to be consistent. During the acquisition process, the field of view of the scanning electron microscope remains fixed, and the working distance WD of the scanning electron microscope electron beam ≤ 18 mm to obtain excellent imaging quality. The process of capturing the surface microstructure morphology of the specimen can include any magnification factor to achieve cross-scale characterization.

[0013] Further, in step S3, the gradient calculation formulas for the A and B directions are: The gradient calculation formulas for the C and D directions are: where k is the first-order term proportionality coefficient, b is the third-order term proportionality coefficient and b < 0, ε is a very small constant, and the third-order term is used to eliminate the shadow effect caused by high-slope planes;

[0014] Subsequently, based on the obtained gradients G in the A and B directionsAB With the gradients G in the C and D directions CD Calculate the gradient matrices Gx and Gy in the X and Y directions y , and the calculation formula is:

[0015]

[0016] where θ 1 , θ 2 is the included angle of the detector distribution, which is related to the detector installation angle and can be directly measured.

[0017] Furthermore, in step S4, the gradient matrices G x , G y in the X and Y directions are respectively reconstructed into column vectors along the column direction, and then spliced into a column vector G. The least squares method combined with the regularization method is used to solve the three-dimensional height field The solution formula is:

[0018]

[0019] where P is the forward difference operator, L is the regularization matrix using the central difference operator, and λ is the regularization coefficient; the three-dimensional height fields under different deformation stages are respectively calculated to form a sequence Z, completing the in-situ surface three-dimensional reconstruction.

[0020] Advantages of the present invention:

[0021] The present invention overcomes the problem that in in-situ SEM testing, it is impossible to provide accurate three-dimensional surface height information for any region at different deformation stages, thereby significantly improving the in-depth understanding of the surface micro-deformation behavior of metal materials under complex stress states. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below.

[0023] Figure 1 is a flow chart of the in-situ three-dimensional surface reconstruction method based on a scanning electron microscope provided by the present invention.

[0024] Figure 2 is a schematic diagram of an in-situ mechanical test bench and scanning electron microscope imaging.

[0025] Figure 3 is the force-displacement curve of in-situ tension of 5B70 aluminum alloy.

[0026] Figure 4 is the surface gradient of the gauge section center indentation in the initial state of 5B70 aluminum alloy.

[0027] Figure 5It is the three-dimensional height field of the indentation at the center of the gauge section in the initial state of 5B70 aluminum alloy.

[0028] Figure 6 It is the three-dimensional height field of the indentation at the center of the gauge section of 5B70 aluminum alloy at different tensile displacements. Specific implementation manners

[0029] In order to enable those skilled in the art to better understand the solutions of the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention; obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0030] The object of the present invention is to provide an in-situ three-dimensional surface reconstruction method based on a scanning electron microscope, which solves the problem of the lack of accurate three-dimensional surface height information for any region in different deformation stages in existing in-situ SEM tests, and effectively promotes a deeper understanding of the surface micro-deformation behavior of metal materials under complex stress environments.

[0031] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0032] Embodiment:

[0033] In this embodiment, based on the CIQTEK SEM 5000Pro scanning electron microscope equipped with a four-region backscattered electron detector, a uniaxial in-situ tensile test is performed on an aluminum alloy sample of grade 5B70, and four-region images of the indentation at the center of the gauge section are obtained and three-dimensionally reconstructed at different deformation stages during the test, overcoming the problem that in in-situ SEM tests, it is impossible to provide accurate three-dimensional surface height information for any region in different deformation stages.

[0034] As Figure 1 shown, the in-situ three-dimensional surface reconstruction method based on a scanning electron microscope provided in this embodiment is as follows:

[0035] S1. Prepare 5B70 aluminum alloy samples suitable for in-situ tensile experiments. The samples are in the shape of dog bones, 50 mm in length, and contain an observation gauge section with a length of 1.5 mm and a width of 1.35 mm. Mechanically polish the original tensile specimens successively with 400-mesh, 600-mesh, 800-mesh, and 1200-mesh sandpapers, and then rough-polish and fine-polish the polished samples successively using a vibratory polisher. Test and leave a cross indentation at the center of the gauge section using a hardness tester. Horizontally fix the sample on the in-situ tensile test bench, and then fix the in-situ tensile test bench in the scanning electron microscope chamber for in-situ mechanical testing along the X direction, as Figure 2 shown;

[0036] S2. During the in-situ tensile test, use a four-region backscattered electron detector containing four independent regions A, B, C, and D, where A, C, B, and D are arranged counterclockwise in sequence. At every 100-μm displacement along the tensile direction, take four-region images with different electron intensity distributions in the indentation region at the center of the gauge section of the sample at different deformation stages. The center of the four-region backscattered electron detector coincides with the center of the scanning electron microscope electron beam. The current amplification factor of the hardware amplifier connected to the four-region backscattered electron detector should be calibrated in advance to be consistent. During the acquisition process, the scanning electron microscope field of view remains fixed, and the center of the indentation is always used as the center of the field of view. The working distance of the scanning electron microscope electron beam is maintained at about 15 mm. After the experiment, output the force-displacement curve, as Figure 3 shown.

[0037] S3. Based on the four-region images I A , I B , I C , I D at different deformation stages, calculate the gradients along the A, B directions and C, D directions in the region photographed by this image through the formulas and . In this example, k = 1.6, b = -0.2, ε = 10 -6 ;

[0038] Furthermore, through the formula:

[0039]

[0040] calculate the surface gradient matrices G x , G y in the X and Y directions. In this example, θ 1 = 40°, θ 2 = -50°. The surface gradient of the indentation at the center of the gauge section of the sample is as Figure 4 shown.

[0041] S4. The gradient matrices G x , G y, they are respectively reconstructed along the column direction into column vectors, and then spliced into column vector G. The least squares method combined with the regularization method is used to solve the three-dimensional height field. The solution formula is:

[0042]

[0043] where P is the forward difference operator, L is the regularization matrix, the central difference operator is adopted, and λ is the regularization coefficient; in this example, the image size is 1536×1024 pixels, the image width W is 1536 pixels, the image height H is 1024 pixels, and the horizontal field of view width HFW is 260 μm. P is the forward difference matrix for sparse representation, with a size of [2×H×W, H×W]. Among them, the first [H×W, H×W] is the horizontal difference part, generating a total of H×W - H rows. In each row, the position on the diagonal is the negative effective value, and the position H away from the right side of the diagonal is the positive effective value; the latter [H×W, H×W] is the vertical difference part, generating a total of W×(H - 1) rows. The horizontal adjacent nodes are processed in blocks, with each block step size of H. In the first H - 1 rows, the position on the diagonal is the negative effective value, and the position 1 away from the right side of the diagonal is the positive effective value. The size of the effective value is the image width W divided by the horizontal field of view width HFW, which is used to represent the actual distance occupied by each pixel. L is the central difference regularization matrix for sparse representation, with a size of [2×H×W, H×W]. Among them, the first [H×W, H×W] is the horizontal difference part, generating a total of H×(W - 2) rows. In each row, the position on the diagonal is the positive effective value, the position 2H away from the right side of the diagonal is twice the negative effective value, and the position 2H away from the right side of the diagonal is the positive effective value; the latter [H×W, H×W] is the vertical difference part, generating a total of W×(H - 2) rows. The horizontal adjacent nodes are processed in blocks, with each block step size of H. In the first H - 2 rows, the position on the diagonal is the positive effective value, the position 1 away from the right side of the diagonal is twice the negative effective value, and the position 2 away from the right side of the diagonal is the positive effective value. The size of the effective value is the same as that in P. The value of λ is 0.05. The three-dimensional height fields at different deformation stages are calculated respectively to form a sequence Z, completing the in-situ surface three-dimensional reconstruction, as Figure 5 , Figure 6 shown.

[0044] The results show that after obtaining the three-dimensional height field of the microstructure morphology on the sample surface during the in-situ mechanical test using three-dimensional reconstruction, the three-dimensional surface height information of the metal material at different deformation stages can be effectively supplemented, and the in-depth understanding of the surface micro-deformation behavior of the material under complex stress conditions can be effectively strengthened.

[0045] It can be seen that the in-situ three-dimensional surface reconstruction method based on a scanning electron microscope provided by the present invention realizes the restoration of high-height information on the microstructural evolution of materials at different deformation stages during the in-situ process through an in-situ mechanical test bench combined with four-region backscattered electron detector imaging.

[0046] The structure, features and effects of the present invention have been described in detail based on the illustrated embodiments above. The above are only the preferred embodiments of the present invention, but the present invention is not limited to the scope of implementation shown in the drawings. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified into equivalent changes, should still be within the protection scope of the present invention as long as they do not exceed the spirit covered by the description and the drawings.

Claims

1. An in-situ three-dimensional surface reconstruction method based on scanning electron microscopy, characterized in that: include: S1. Mechanically grinding and polishing the original metal sample, wherein the middle area of ​​the metal sample is provided with a gauge length section area, to obtain an in-situ experimental sample; horizontally fixing the in-situ experimental sample on an in-situ test bench, and then fixing the in-situ test bench in a scanning electron microscope chamber to perform an in-situ mechanical test along the X direction; S2. During the in-situ mechanical test, a four-region backscattered electron detector including four independent regions A, B, C, and D is used to capture four-region images I with different electron intensity distributions of the surface microstructure of the in-situ experimental sample at different deformation stages. A ,I B ,I C ,I D , where I A ,I B and I C ,I D They are respectively symmetrical about the center point of the detector; S3, based on the four-region image I at different deformation stages A ,I B ,I C ,I D , calculate and obtain the surface gradient matrix G in the X and Y directions of the image area at different deformation stages x ,G y ; S4, based on the X-direction and Y-direction gradient matrix G x ,G y , the regularized 3D reconstruction method is used to reconstruct the 3D height field sequence Z of the photographed area at different deformation stages, and the in-situ surface 3D reconstruction is completed.

2. The in-situ surface three-dimensional reconstruction method based on scanning electron microscopy according to claim 1, characterized in that: The in-situ test bench includes an in-situ tensile test bench, an in-situ fatigue test bench, and an in-situ creep test bench, corresponding to in-situ tensile test, in-situ fatigue test, and in-situ creep test.

3. The in-situ surface three-dimensional reconstruction method based on scanning electron microscopy according to claim 1, characterized in that: In step S2, the center of the four-region backscattered electron detector coincides with the center of the electron beam of the scanning electron microscope. The amplification factor of the hardware amplifier connected to the four-region backscattered electron detector should be calibrated in advance to be consistent. During the acquisition process, the field of view of the scanning electron microscope remains fixed, and the working distance WD of the electron beam of the scanning electron microscope is ≤18mm to obtain excellent imaging quality.

4. The in-situ surface three-dimensional reconstruction method based on scanning electron microscopy according to claim 1, characterized in that: In step S3, the gradient calculation formula in the A and B directions is: The gradient calculation formula in the C and D directions is: Where k is the linear term proportionality coefficient, b is the cubic term proportionality coefficient and b<0, ε ​​is a very small constant, and the cubic term is used to eliminate the shadow effect caused by the high slope plane; Then based on the obtained A, B direction gradient G AB With C, D direction gradient G CD Calculate the X-direction and Y-direction gradient matrices Gx,G y , the calculation formula is: Among them, θ1 and θ2 are the detector distribution angles, which are related to the detector installation angle and can be directly measured.

5. The in-situ surface three-dimensional reconstruction method based on scanning electron microscopy according to claim 1, characterized in that: In step S4, the X-direction and Y-direction gradient matrices G x ,G y Reconstruct them into column vectors along the column direction, and then splice them into column vector G. Use the least squares method combined with the regularization method to solve the three-dimensional height field The solution formula is: Wherein P is a forward difference operator, L is a regularization matrix using a central difference operator, and λ is a regularization coefficient; the three-dimensional height fields at the different deformation stages are calculated respectively to form a sequence Z, and the in-situ surface three-dimensional reconstruction is completed.

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