A characterization method for directly obtaining the orientation of the cleavage plane of the fracture surface using EBSD technology

Abstract

The present application relates to the field of material science and fracture mechanics, in particular to a technical method for characterizing fracture microstructure. Specifically, the present application provides a characterization method for directly obtaining the orientation of cleavage surface of fracture by EBSD technology, which can be used for orientation analysis of smooth cleavage surface or quasi-cleavage surface on the fracture of tensile, fatigue or impact samples. The method realizes direct characterization of cleavage surface by EBSD (electron backscatter diffraction) technology combined with three-dimensional orientation characterization method of fracture, thereby improving the characterization accuracy of micro features of fracture surface, greatly reducing the characterization cost, and realizing visual characterization of the spatial orientation information of the facet by crystallographic calculation.

Description

Technical Field

[0001] The present invention relates to the technical field of material fracture behavior analysis, and in particular to a characterization method for directly obtaining the orientation of a fracture cleavage plane by utilizing EBSD technology. Background Art

[0002] Fracture analysis is an important tool for understanding the fracture behavior of metallic materials. By observing and analyzing the microscopic features of a fracture surface, we can gain a deeper understanding of the fracture mechanism of the material. For fracture surfaces with cleavage characteristics, such as cleavage and quasi-cleavage planes in tensile, fatigue, or impact specimens, accurately determining their spatial orientation is a crucial foundation for studying fracture behavior.

[0003] At present, EBSD technology has been widely used in the microstructure and orientation analysis of materials. However, due to the complex geometric morphology of the fracture surface, there are certain limitations in directly performing EBSD orientation analysis on the surface grains. In particular, the sample surface needs to be additionally processed or the sample itself needs to be destroyed in order to obtain and analyze EBSD data. For example, one of the common characterization methods is to use FIB technology or laser processing to cut a plane of a certain area from the target characterization grain on the fracture, and further perform orientation characterization on this plane. However, while obtaining the crystal orientation information, the fracture itself is destroyed. Therefore, the existing method is not only time-consuming, but also easy to damage the sample, causing the sample to be destroyed and unable to be subsequently characterized, which increases the complexity and error cost of the characterization and consumes a lot of manpower and material resources. Therefore, developing a method that can directly characterize the spatial orientation of the cleavage plane of the fracture without additional processing is of great significance for the study of fracture behavior. Summary of the Invention

[0004] In response to the above technical problems, the present invention proposes a characterization method for directly obtaining the orientation of the cleavage plane of the fracture surface using EBSD technology. By combining the three-dimensional orientation calculation of the fracture surface, the spatial orientation of the cleavage plane or quasi-cleavage plane of the material fracture surface is accurately analyzed. Without destroying the fracture surface, the orientation analysis of the cleavage plane or quasi-cleavage plane on the fracture surface of the tensile, fatigue, or impact specimen is directly performed.

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

[0006] The present invention provides a characterization method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology, comprising the following steps:

[0007] S1. Cut the fracture surface of the sample after mechanical test along the direction perpendicular to the stress axis to prepare the sample for SEM experiment;

[0008] S2. Place the sample with the fracture on the sample stage of the scanning electron microscope and fix it in the microscope chamber. Select a relatively smooth and flat facet as the characterization site of the fracture.

[0009] S3. By adjusting the angle of the sample stage and using the fracture three-dimensional orientation calculation method, calculate the spatial orientation (normal space vector) before the facet angle correction. i +b j +c k ;

[0010] S4, determining a rotation angle and a tilt angle of the sample stage according to the spatial orientation before correction, and rotating and tilting the sample stage to correct the facet normal to be parallel to the electron beam direction;

[0011] S5. Repeat the fracture three-dimensional orientation calculation method to calculate the spatial orientation a' after the facet angle is corrected i +b' j +c' k ;

[0012] S6. Tilt the sample stage 70° around the X-axis of the electron microscope system coordinate system so that the angle between the facet normal and the electron beam is 70°, and perform EBSD characterization on the target characterization site;

[0013] S7. If there is any obstruction, repeat steps 3-5 to prevent the diffraction beam and the electron beam from being obstructed;

[0014] S8. Based on crystallographic calculations and combined with EBSD data, the relationship between facet spatial orientation and crystallographic orientation is established.

[0015] As a further illustration of the present invention, in step S1, a fracture with a height of about 10 mm can be cut along a direction perpendicular to the stress axis by wire cutting to prepare a sample.

[0016] As a further illustration of the present invention, the sample preparation process in step S1 requires careful attention to the protection of the fracture surface. A protective layer, such as a special coating or film, can be applied to the material surface to prevent oxidation or damage to the fracture surface during the wire cutting process. After cutting, the fracture surface must be cleaned and dried to prevent rust.

[0017] As a further explanation of the present invention, in step S2, the selection of the characterization site must ensure that the facet is relatively smooth and flat, and is not within holes or pits, and there is no obvious obstruction around it. Only under this condition can the analysis effect of the faceted grains be achieved. The larger the range of surface smoothness and the less obstruction, the better the analysis effect.

[0018] As a further illustration of the present invention, in step S2, after the sample is fixed on the SEM sample stage, it is placed in the electron microscope chamber and not taken out again. Only the sample stage is rotated and the SEM and EBSD imaging modes are switched.

[0019] As a further illustration of the present invention, based on the principles of EBSD characterization technology, describing the spatial orientation of facets requires the use of two coordinate systems: the sample coordinate system and the electron microscope system coordinate system. The sample coordinate system is defined as (X1-Y1-Z1), and the electron microscope system coordinate system is defined as (XYZ). The sample is rotated about the Z-axis of the electron microscope system coordinate system (i.e., the rotation angle is the rotation angle about the Z-axis of the electron microscope system coordinate system), and the sample is tilted about the X-axis of the electron microscope system coordinate system (i.e., the tilt angle is the rotation angle about the X-axis of the electron microscope system coordinate system). Subsequent rotation and tilting processes will cause the sample coordinate system to change, but the electron microscope system coordinate system remains unique. Therefore, the calculation processes in steps S1 through S6 are based on the electron microscope system coordinate system.

[0020] As a further illustration of the present invention, the fracture 3D orientation calculation method is an analytical method for determining the spatial orientation of the fracture facets of a material. This method is based on two sets of tissue photographs taken at different inclinations. The method locates four nonlinearly distributed feature points in each set of photographs and calculates the 3D spatial coordinates of the feature points based on their 2D coordinates. This further determines the normal vector of the face where the feature points are located. The rotation angle and tilt angle of the sample stage required to correct the facet angle are determined according to the normal vector of the facet, and the sample stage is rotated along the X-axis and Z-axis respectively so that the normal direction of the facet coincides with the Z-axis in the electron microscope system coordinate system (XYZ).

[0021] As a further illustration of the present invention, the rotation and tilting process will cause the sample coordinate system to change, and the facet spatial orientation a calculated in step S3 i +b j +c k The sample coordinate system is the sample coordinate system X1-Y1-Z1 before facet angle correction, and the facet spatial orientation a' calculated in step S5 is i +b' j +c' k The sample coordinate system is the new sample coordinate system X1*-Y1*-Z1* after the facet angle is corrected.

[0022] As a further illustration of the present invention, step S3 is specifically as follows: quantitatively tilting the fracture surface by adjusting the angle of the sample stage, thereby obtaining two facet morphology photos of the fracture surface at different tilt angles before facet angle correction under the same magnification, selecting four nonlinearly distributed feature points X, A, B, C on each of the obtained morphology photos, and calculating the spatial orientation a before facet angle correction using the three-dimensional orientation of the fracture surface. i +b j +c k .

[0023] As a further illustration of the present invention, the resolution of the topographic photograph obtained in step S3 is greater than 1024*768. The tilt angle used in this characterization method is generally selected within a range of 10° to 45°, resulting in an error of 0° to 5° in the calculated results. The four feature points selected on the facet of the target characterization site must be non-collinear to reduce calculation errors.

[0024] As a further illustration of the present invention, in step S6, when performing EBSD characterization on the target characterization site, it is necessary to switch to EBSD imaging mode, and then perform EBSD characterization on the facet area, subtract the background and obtain a clear and stable Kikuchi pattern, and then start characterization.

[0025] As a further illustration of the present invention, when subtracting the background in the EBSD imaging mode, since a good background pattern cannot be obtained on the fracture surface, the same smooth material needs to be used for background collection.

[0026] As a further illustration of the present invention, when obtaining a stable pattern in EBSD imaging mode, a stable, clear, high-resolution Kikuchi pattern is obtained by adjusting the distance to the phosphor screen or appropriately correcting the tilt angle (-5° to +5°).

[0027] As a further explanation of the present invention, step S8 is specifically: deriving the Euler angle information of the faceted grain through EBSD data, drawing the inverse pole figure of the grain along the spatial orientation direction based on the Euler angle information, and confirming the relationship between the facet spatial orientation and the crystal orientation based on the pole position.

[0028] As a further illustration of the present invention, the method provided by the present invention is applicable to fractures with smooth cleavage facet characteristics such as low-cycle, high-cycle, load-holding, impact, creep, and tensile fractures, but is not applicable to samples with excessive fluctuations in fracture micromorphology.

[0029] The above-mentioned method provided by the present invention, combined with the characterization methods of SEM and EBSD, can realize non-destructive analysis of the fracture surface and internal grain spatial orientation obtained after mechanical testing. Specifically, the method first calculates the three-dimensional spatial orientation of the fracture facets, and determines their accurate orientation in the three-dimensional space of the electron microscope cabin by analyzing the morphological characteristics of the cleavage facets or quasi-cleavage facets on the fracture. This spatial orientation information is then used to correct the angle of the facets during the EBSD characterization process, and the EBSD technology is used to directly realize the precise orientation characterization of the fracture cleavage facets or quasi-cleavage facets.

[0030] Compared with the prior art, the present invention has the following beneficial technical effects:

[0031] 1. The present invention mainly uses SEM and EBSD analysis and characterization methods to directly obtain the orientation information of faceted grains on the fracture surface with complex geometric morphology. The spatial orientation of the faceted grains is obtained through the three-dimensional orientation calculation of the fracture. The sample stage in the scanning electron microscope chamber is rotated to correct the facet normal to be parallel to the electron beam direction, thereby achieving direct characterization of the faceted grains. Compared with other characterization methods, this method does not require destruction or additional processing of the fracture surface, greatly reducing experimental costs, sample damage and errors in the characterization process, significantly improving experimental efficiency and characterization accuracy, helping to reveal the fracture mechanism of the material, and providing a reference basis for optimizing the design and manufacturing process of the material.

[0032] 2. The characterization result of the present invention is that the spatial orientation of the cleavage plane or quasi-cleavage plane can be represented on its orientation IPF inverse pole figure through crystallographic calculation, thereby realizing a visual characterization of the microscopic orientation of the fracture surface.

[0033] Other features and advantages of this technical solution will be described in the subsequent description, and in part will become apparent from the description, or understood by practicing this technical solution. The objectives and other advantages of this technical solution can be achieved and obtained through the structures specifically pointed out in the written description and the accompanying drawings.

[0034] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the present technical solution and constitute a part of the specification. Together with the embodiments of the present technical solution, they are used to explain the present technical solution and do not constitute a limitation of the present technical solution. In the accompanying drawings:

[0036] Figure 1 This is a flow chart of the characterization method provided by the present invention for directly obtaining the orientation of the fracture cleavage plane or quasi-cleavage plane by using the EBSD technology combined with the fracture three-dimensional orientation characterization method.

[0037] Figure 2 The high-resolution SEM / SE photos of the facet before and after tilting and the selected feature point positions at the same magnification before the facet angle correction in Example 1 are as follows: (a) tilt angle θ 1 = 0°; (b) tilt angle θ 2=20°.

[0038] Figure 3 The three-dimensional spatial orientation of the facets in the SEM chamber under different conditions: (a) before facet angle correction; (b) after facet angle correction; (c) in EBSD imaging mode, after the sample stage is tilted 70° around the X-axis of the SEM system coordinate system; (d) a real-time photo of the EBSD characterization process in the SEM chamber.

[0039] Figure 4 Schematic diagram of the Kikuchi pattern obtained on the facet after angle correction in the EBSD imaging mode in Example 1: (a) and (b) are the Kikuchi patterns obtained on the facets with and without obstruction on the surface, respectively.

[0040] Figure 5 The high-resolution SEM / SE images of the facet before and after tilting and the selected feature point positions at two identical magnifications after the facet angle correction in Example 1: (a) tilt angle θ 1 = 0°; (b) tilt angle θ 2=20°.

[0041] Figure 6 The good analytical effect of the facet in Example 1 without obstruction in EBSD imaging mode: (a) is the selected scanning area; (b) is the corresponding EBSD image (IPF / / Z1*) of the facet in the area.

[0042] Figure 7 This is the triangular inverse pole figure obtained by crystallographic calculation in Example 1, which represents the relationship between the facet spatial orientation and the crystal orientation distribution. DETAILED DESCRIPTION

[0043] The preferred embodiments of the present technical solution are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present technical solution and are not used to limit the present technical solution.

[0044] The materials used in the following examples are rod-shaped fracture specimens of Ti150 alloy obtained by forging after load-maintained fatigue failure. The specimens have no anisotropy in other directions except the stress direction, and no additional surface treatment. The microstructure is bimodal, consisting of an equiaxed primary α phase and a lamellar secondary α phase. The average size of the primary α grains is about 30 μm, and the average length of the secondary α lamellae is about 100 μm. Example 1

[0045] Step 1: Apply a layer of acrylic varnish to the fracture surface of the Ti150 alloy rod specimen after load-holding fatigue failure. Use wire cutting to cut a fracture with a height of about 10 mm along the direction perpendicular to the stress axis. Immerse it in acetone for ultrasonic cleaning. Finally, remove the paint with isopropyl alcohol and dry it to obtain a specimen of appropriate size that can be placed in the scanning electron microscope cabin.

[0046] Step 2: Fix the cut fracture surface on the SEM sample stage with conductive glue, place it in the SEM electron microscope chamber, observe the faceted grains near the crack source area on the sample surface, and select the facet with a relatively smooth and flat surface that is closer to the crack source grain as the characterization site of the fracture surface, and try to avoid surrounding obstructions.

[0047] Step 3: Adjust the angle of the sample stage to quantitatively tilt the fatigue fracture surface under load, so as to obtain two images with the same magnification and different tilt angles before facet angle correction. θ The fracture surface facet morphology photos were taken. Four nonlinearly distributed characteristic points X, A, B, C were selected on each of the two high-resolution fracture crack source SEM photos. The position coordinates are shown in Table 1. The spatial orientation (normal space vector) before facet angle correction was calculated using the three-dimensional orientation of the fracture. i -0.03 j +0.99 k .

[0048] Table 1 Position coordinates and measurement results of the selected feature points before and after facet angle correction and quantitative tilt

[0049]

[0050] Step 4: Based on the spatial orientation of the facet, the rotation angle of the sample stage is determined to be 13.02° counterclockwise, and the tilt angle is determined to be 7.81° counterclockwise. Based on this result, the sample stage is rotated and tilted to correct the normal direction of the facet to be parallel to the electron beam direction.

[0051] Step 5: As the sample stage rotates, the normal vector of the face changes at this moment. Repeat the fracture three-dimensional orientation calculation method to obtain the spatial orientation 0.14 after the facet angle correction. i +0 j -0.99 k , the feature point coordinates and calculation results are shown in Table 2.

[0052] Table 2 Position coordinates and measurement results of the selected feature points before and after quantitative tilting after facet angle correction

[0053]

[0054] Step 6: After correcting the facet angle, tilt the sample stage 70° around the X-axis of the electron microscope system coordinate system, that is, the angle between the facet normal and the electron beam is 70°, switch to EBSD imaging mode, perform EBSD characterization on the facet area, subtract the background and obtain a clear and stable Kikuchi pattern, as shown in the figure. Figure 5 (b) and then start characterization. The characterization results are shown as Figure 6 As shown, most of the smooth areas of the facets have good resolution.

[0055] Step 7: When performing EBSD characterization on the facet area, first set a larger step size and perform a rough scan to observe the resolution effect of the facet. If the surrounding obstruction causes poor resolution of a large area, repeat steps 3 to 5, adjust the angle or change the characterization site, and then perform precise characterization.

[0056] Step 8: The Euler angle information of the faceted grain can be derived from the EBSD data. Based on the Euler angle information, the grain is drawn along the spatial orientation direction 0.14 i +0 j -0.99 k The inverse pole figure of . The connection between facet space orientation and crystal orientation can be confirmed based on the pole position. In this example, the facet space normal is at an angle of approximately 20° with the

[0001] direction, meaning that the facets are formed on a plane that is at an angle of 20° with (0001).

[0057] Figure 1 This is a flow chart of the characterization method for directly obtaining the orientation of the fracture cleavage plane or quasi-cleavage plane using the EBSD technology combined with the fracture three-dimensional orientation calculation method in this embodiment.

[0058] Figure 2 The following are high-resolution SEM / SE images of the Ti150 alloy fatigue fracture surface before and after quantitative tilting, as well as the locations of the selected feature points, taken at the same magnification before facet angle correction for the load-maintained fracture in this example. The crack source facet location and its propagation path are visible. The surface in this area is relatively flat, and there are no significant obstructions around it, ensuring that the four selected morphological feature points are not collinear and have unique characteristics that are difficult to confuse. X1 and X2, A1 and A2, B1 and B2, and C1 and C2 correspond to the same morphological feature points in the two scanned facet images.

[0059] Figure 3 is the three-dimensional spatial orientation of the facets in the SEM chamber under different states in this embodiment, Figure 3 (a) It can be seen that before the facet angle is corrected, there is a certain angle between the facet normal and the stress direction, but after the facet angle is corrected, that is, Figure 3 (b) It can be seen that the normal direction of the facet is parallel to the stress direction. After switching to EBSD imaging mode, the sample stage is tilted 70° around the X-axis of the electron microscope system coordinate system, as shown in Figure 3 (c) shows that its actual position in the SEM chamber can be seen from Figure 3 (d) can be seen.

[0060] Figure 4 This is a schematic diagram of the Kikuchi pattern obtained on the facet after angle correction under the EBSD imaging mode in this embodiment. It can be seen from the figure that if there is any obstruction, the Kikuchi pattern will not be recognized. The obtained Kikuchi pattern is as follows: Figure 4 By rotating the sample and repeating step 3, the sample position is readjusted to avoid blocking of the diffraction beam and electron beam, thus obtaining a clear and stable Kikuchi pattern similar to that on the facet of this example, as shown in (a). Figure 4 (b)

[0061] Figure 5 These are high-resolution SEM / SE photos of the facets before and after quantitative tilting and the positions of the selected characteristic points of the Ti150 alloy under load-maintained fatigue fracture in this embodiment after the facet angle is corrected at two identical magnifications.

[0062] Figure 6 In this example, the Ti150 alloy fatigue fracture facet under EBSD imaging mode shows good unobstructed analysis. The characterized area and identifiable sites are marked on the left image. The analysis results are shown in the right image, which are sufficiently representative to explain the orientation of this area.

[0063] Figure 7 This is the IPF diagram obtained by crystallographic calculation in Example 1, which shows the relationship between facet spatial orientation and crystal orientation.

[0064] It can be seen from the experimental results of Example 1 that the present invention achieves non-destructive direct characterization of the orientation of some key areas on the fracture surface without additional processing of the fracture, providing a more convenient, fast and accurate technical means for studying the fracture mechanics behavior of materials and revealing the relationship between the material microstructure and the fracture mechanism.

[0065] Obviously, those skilled in the art may make various changes and modifications to this technical solution without departing from the spirit and scope of this technical solution. Thus, if these modifications and variations of this technical solution fall within the scope of the claims of this technical solution and their equivalents, this technical solution is intended to include these modifications and variations.

Claims

1. A characterization method for directly obtaining the orientation of the cleavage plane of a fracture using EBSD technology, characterized in that: The steps include: S1. Cut the fracture surface of the sample after mechanical test along the direction perpendicular to the stress axis to prepare the sample for SEM experiment; S2. Place the sample with the fracture on the sample stage of the scanning electron microscope and fix it in the microscope chamber. Select a relatively smooth and flat facet as the characterization site of the fracture. S3. By adjusting the angle of the sample stage, the spatial orientation a before facet angle correction is calculated using the fracture three-dimensional orientation calculation method. i +b j +c k ; S4, determining a rotation angle and a tilt angle of the sample stage according to the spatial orientation before correction, and rotating and tilting the sample stage to correct the facet normal to be parallel to the electron beam direction; S5. Repeat the fracture three-dimensional orientation calculation method to calculate the spatial orientation a' after the facet angle is corrected i +b' j +c' k ; S6. Tilt the sample stage 70° around the X-axis of the electron microscope coordinate system so that the angle between the facet normal and the electron beam is 70°, and perform EBSD characterization on the target characterization site; S7. If there is any obstruction, repeat steps 3-5 to prevent the diffraction beam and the electron beam from being obstructed; S8. Based on crystallographic calculations and combined with EBSD data, the relationship between facet spatial orientation and crystallographic orientation is established.

2. The method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology according to claim 1, wherein: In step S2, the selection of the characterization site must ensure that the facet is relatively smooth and flat, and is not within a hole or pit, and has no obvious obstruction around it.

3. The method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology according to claim 1, wherein: The coordinate systems on which the calculation processes of steps S1 to S6 are based are all the electron microscope system coordinate systems.

4. The method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology according to claim 1, wherein: The facet spatial orientation a calculated in step S3 i +b j +c k The sample coordinate system is the sample coordinate system X1-Y1-Z1 before facet angle correction, and the facet spatial orientation a' calculated in step S5 is i +b' j +c' k The sample coordinate system is the new sample coordinate system X1*-Y1*-Z1* after the facet angle is corrected.

5. The method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology according to claim 1, wherein: Step S3 is specifically as follows: By adjusting the angle of the sample stage to quantitatively tilt the fracture, two facet morphology photos of the fracture surface with different tilt angles before facet angle correction under the same magnification are obtained. Four nonlinearly distributed feature points X, A, B, C are selected on each of the obtained morphology photos, and the spatial orientation a before facet angle correction is calculated using the three-dimensional orientation of the fracture. i +b j +c k .

6. The method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology according to claim 5, wherein: The resolution of the topography photograph obtained in step S3 is greater than 1024*768.

7. The characterization method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology according to claim 1, characterized in that: In step S6, when performing EBSD characterization on the target characterization site, it is necessary to switch to the EBSD imaging mode, and then perform EBSD characterization on the facet area, subtract the background and obtain a clear and stable Kikuchi pattern, and then start characterization.

8. The method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology according to claim 7, wherein: When subtracting the background in EBSD imaging mode, the same smooth material needs to be used for background acquisition.

9. The method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology according to claim 7, wherein: When acquiring stable patterns in EBSD imaging mode, stable, clear, and high-resolution Kikuchi patterns can be obtained by adjusting the distance to the phosphor screen or appropriately correcting the tilt angle.

10. The method for directly obtaining the orientation of the cleavage plane of a fracture surface using EBSD technology according to claim 1, wherein: Step S8 is specifically as follows: The Euler angle information of the faceted grain is derived from the EBSD data, and the inverse pole figure of the grain along the spatial orientation direction is drawn based on the Euler angle information. The relationship between the facet spatial orientation and the crystal orientation is confirmed based on the pole position.

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