Microcosmic residual stress detection method based on FIB-DIC technology

Abstract

The invention discloses a microcosmic residual stress detection method based on an FIB-DIC technology, and belongs to the field of material mechanical property testing. Platinum mark points are deposited on a to-be-detected area of a sample, and a first image of the to-be-detected area is obtained; and carrying out successive ring core FIB milling on the outer side of the platinum layer, and recording a second image of the to-be-detected area in situ in the ring core FIB milling process. Performing grid division on the first image to obtain a sub-region corresponding to the first image and a first position of the sub-region on the first image; searching a region with the maximum correlation coefficient with the sub-region in the second image to obtain a second position of the sub-region on the second image; and determining the dependent variable of the platinum mark point based on the difference between the first position and the second position. And according to the dependent variable, calculating the residual stress of the to-be-measured area in each ring core FIB milling process. According to the invention, the problem of low detection precision of residual stress in the prior art is solved.

Description

Technical Field

[0001] The present application relates to the field of material mechanical property testing, and in particular to a microscopic residual stress detection method based on FIB-DIC technology. Background Art

[0002] Residual stress refers to the self-balanced internal stress that remains in the material after the external force or uneven temperature field is eliminated. Residual stress at the microscopic level of the material is commonly found in various machined parts, which dominates the deformation, dimensional tolerance and surface accuracy of machined parts, so it is necessary to develop residual stress measurement technology for machined parts.

[0003] However, in current research, the measurement of residual stress of machined parts comes from macroscopic millimeter-level evaluation methods, such as the ring core method, which processes an annular groove on the surface of the sample to release the residual stress inside the sample, and calculates the residual stress by measuring the deformation around the groove through strain gauges. This method can only evaluate the residual stress at the millimeter level, and the accuracy is low. There is still a lack of microscopic measurement methods for residual stress on the surface of machined parts. Therefore, it is urgent to develop a high-resolution microscopic residual stress detection method to solve the problem of low residual stress detection accuracy in the existing technology. Summary of the invention

[0004] The present application provides a method for detecting microscopic residual stress based on FIB-DIC technology, which can detect the residual stress of machined parts at the micron and submicron scale.

[0005] To achieve the above objectives, the embodiments of the present application adopt the following technical solutions:

[0006] In a first aspect, an embodiment of the present application provides a method for detecting microscopic residual stress based on FIB-DIC technology, the method comprising:

[0007] Depositing platinum marking points on the area to be tested of the sample, and depositing a platinum layer around the area to be tested; acquiring a first image of the area to be tested; performing successive ring-core FIB milling on the outer side of the platinum layer, and in-situ recording a second image of the area to be tested during each ring-core FIB milling process;

[0008] Dividing the first image into grids by using DIC to obtain a sub-region corresponding to the first image and a first position of the sub-region on the first image; searching for a region with a maximum correlation coefficient with the sub-region in the second image to obtain a second position of the sub-region on the second image; and determining the strain of the platinum marking point based on a difference between the first position and the second position;

[0009] According to the strain amount, the residual stress of the area to be measured during each ring core FIB milling process is calculated.

[0010] In combination with the first aspect, in a possible design manner, searching in the second image for a region with a maximum correlation coefficient with the subregion to obtain a second position of the subregion on the second image includes:

[0011] Calculating the sum of squares of pixel values ​​between the sub-region and each region in the second image to obtain a correlation coefficient between the sub-region and each region;

[0012] A region having a maximum correlation coefficient with the sub-region is searched in the second image to obtain a second position of the sub-region on the second image.

[0013] In combination with the first aspect, in a possible design manner, the expression of the correlation coefficient is as follows:

[0014]

[0015] In the formula, C is the correlation coefficient, f(x i ,y j ) is the first image on (x i ,y j ), g(x i ′ ,y j ′ ) is the second image on (x i ′ ,y j ′ ) pixel value, f m is the average pixel value of the reference subset, and g m is the average pixel value of the target subset.

[0016] In combination with the first aspect, in a possible design, depositing a plurality of platinum marking points on the area to be tested of the sample includes:

[0017] placing the sample under a scanning electron microscope for observation, and selecting a region to be tested under the scanning electron microscope;

[0018] A plurality of platinum marking points are deposited on the surface of the test area by using FIB, and the plurality of platinum marking points are arranged in a dot matrix.

[0019] In combination with the first aspect, in a possible design, the residual stress of the area to be measured during each ring core FIB milling process is calculated according to the strain, including:

[0020] Using Expression The residual stress of the measured area during each ring core FIB milling process is calculated, where E is Young's modulus, v is Poisson's ratio, σ is the residual stress, and -Δε is the strain.

[0021] In combination with the first aspect, in a possible design, the shape of the area to be tested is circular, the diameter of the circle is in the range of 10 μm to 15 μm, and the shape of the platinum layer is ring-shaped.

[0022] In combination with the first aspect, in a possible design, the diameter of the platinum marking point is 80nm to 120nm, and the distance between two adjacent platinum marking points is 180nm to 400nm.

[0023] In combination with the first aspect, in a possible design, the inner diameter of the ring core FIB milling is 10 μm to 15 μm, and the outer diameter is 15 μm to 20 μm, and the outer diameter is 5 μm larger than the inner diameter.

[0024] In combination with the first aspect, in a possible design, the machining depth of each ring core FIB milling is 0.5 μm to 1.0 μm.

[0025] In a second aspect, an embodiment of the present application provides a microscopic residual stress detection device based on FIB-DIC technology, the device comprising:

[0026] The FIB module is used to deposit platinum marking points on the area to be tested of the sample and deposit a platinum layer around the area to be tested; obtain a first image of the area to be tested; perform successive ring-core FIB milling on the outer side of the platinum layer, and in-situ record a second image of the area to be tested during each ring-core FIB milling process;

[0027] A DIC module is used to divide the first image into grids to obtain a sub-region corresponding to the first image and a first position of the sub-region on the first image; to find a region with a maximum correlation coefficient with the sub-region in the second image to obtain a second position of the sub-region on the second image; and to determine the strain of the platinum marking point based on a difference between the first position and the second position;

[0028] The residual stress calculation module is used to calculate the residual stress of the area to be measured during each ring core FIB milling process according to the strain.

[0029] Compared with the prior art, the present invention provides a microscopic residual stress detection method based on FIB-DIC technology, which deposits platinum marking points on the area to be tested of the sample and deposits a platinum layer around the area to be tested. A first image of the area to be tested is obtained; the outer side of the platinum layer is subjected to successive ring core FIB milling, and a second image of the area to be tested during each ring core FIB milling process is recorded in situ. The first image is gridded using DIC to obtain a sub-area corresponding to the first image and a first position of the sub-area on the first image. In the second image, the area with the largest correlation coefficient with the sub-area is found to obtain the second position of the sub-area on the second image; based on the difference between the first position and the second position, the strain of the platinum marking point is determined. According to the strain, the residual stress of the area to be tested during each ring core FIB milling process is calculated. The method uses DIC technology to obtain the graphic displacement of the platinum marking point during the ring core FIB milling process. Because the spatial resolution of the image can reach micrometers and submicrometers, the strain of the platinum marking point determined based on the image displacement can reach micrometers and submicrometers, and the residual stress calculated based on the strain has high detection accuracy. And by recording the second image in situ, the dynamic changes of the sample during the FIB milling process can be observed in real time, achieving the effect of dynamic detection.

[0030] Details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0032] Figure 1 A hardware structure block diagram of a computer device provided in an embodiment of the present application is shown;

[0033] Figure 2 A flow chart of a microscopic residual stress detection method based on FIB-DIC technology provided in an embodiment of the present application is shown;

[0034] Figure 3 A flow chart of a correlation coefficient calculation method provided in an embodiment of the present application is shown;

[0035] Figure 4 shows an overall view of the Pt marking points deposited using FIB in Example 1;

[0036] Figure 5 A partial enlarged view of the Pt marking point deposited by FIB in Example 1 is shown;

[0037] Figures 6 to 9A schematic diagram of in-situ SEM recording of FIB ring core processing in Example 1 is shown, wherein: Figure 6 Schematic diagram of the initial unprocessed in-situ SEM recording. Figure 7 Schematic diagram of in situ SEM recording after milling to a depth of 0.5 μm. Figure 8 Schematic diagram of in situ SEM recording after milling to a depth of 5 μm. Fig. 9 Schematic diagram of in situ SEM recording after milling to a depth of 10 μm;

[0038] Figures 10 to 13 FIG. 1 is a schematic diagram showing the distribution law of the displacement of a pattern obtained by using DIC in Example 1, wherein: Fig.10 is the distribution diagram under the initial no-displacement state, Fig.11 This is the distribution diagram of the displacement after milling to a depth of 0.5 μm. Fig.12 This is the distribution diagram of displacement after milling to a depth of 5 μm. Fig.13 The distribution diagram of displacement after milling 10μm depth;

[0039] Figure 14 to Figure 15 The statistical diagram of the distribution law of the displacement of the pattern obtained by using DIC in Example 1 is shown, wherein: Fig.14 For overall strain, Fig.15 is the microscopic strain between two adjacent Pt marking points;

[0040] Fig.16 The microscopic residual stress values ​​calculated based on FIB technology and DIC in Example 1 are shown;

[0041] Fig.17 The microscopic residual stress values ​​calculated based on FIB technology and DIC in Example 2 are shown;

[0042] Fig.18 The microscopic residual stress values ​​calculated based on FIB technology and DIC in Example 3 are shown;

[0043] Fig.19 A structural block diagram of a microscopic residual stress detection device based on FIB-DIC technology provided in an embodiment of the present application is shown. DETAILED DESCRIPTION

[0044] In order to more clearly understand the purpose, technical solutions and advantages of the present application, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments.

[0045] Unless otherwise defined, the technical terms or scientific terms involved in this application shall have the general meaning understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a", "the", "these" and the like in this application do not indicate quantitative restrictions, and they can be singular or plural. The terms "include", "comprise", "have" and any variants thereof involved in this application are intended to cover non-exclusive inclusions; for example, a process, method and apparatus, product or equipment comprising a series of steps or modules (units) is not limited to the listed steps or modules (units), but may include unlisted steps or modules (units), or may include other steps or modules (units) inherent to these processes, methods, products or equipment. The words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but may include electrical connections, whether directly or indirectly. The "multiple" involved in this application refers to two or more. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, "A and / or B" can mean: A exists alone, A and B exist at the same time, and B exists alone. Usually, the character " / " indicates that the objects associated with each other are in an "or" relationship. The terms "first", "second", "third", etc. involved in this application are only used to distinguish similar objects and do not represent a specific ordering of the objects.

[0046] At the millimeter scale, the measurement methods of residual stress mainly include:

[0047] Mechanical testing methods: drilling method, ring core method, cutting method, etc.

[0048] Non-destructive testing methods: X-ray diffraction, neutron diffraction, ultrasonic method, magnetic method, etc.

[0049] The following is an introduction to the ring core method. The ring core method processes an annular groove on the surface of the sample to release the residual stress inside the sample, and measures the deformation around the groove with a strain gauge to calculate the residual stress. This method can only evaluate the residual stress at millimeter-level accuracy, and the accuracy is low.

[0050] The embodiment of the present application provides a microscopic residual stress detection method based on FIB-DIC technology, which combines focused ion beam (FIB) technology and digital image correlation (DIC) to achieve the purpose of detecting residual stress at the microscopic level. Specifically, the method combines a scanning electron microscope (SEM) to obtain images of the sample test area before and after deformation. SEM is a microscope that uses an electron beam to scan the surface of a sample. It can provide a higher resolution than an optical microscope, allowing users to observe nanometer-level details in the image. Then the strain of the platinum marking point can reach the micron and submicron scale, and the detection accuracy of the residual stress calculated based on the strain is higher.

[0051] The method can be executed in a terminal, a computer or a similar computing system. For example, running on a computer device, Figure 1 FIG. 1 shows a hardware structure block diagram of a computer device provided in an embodiment of the present application. Figure 1 As shown, the computer device may include one or more ( Figure 1 Only one is shown in the figure) processor 102, and memory 104 for storing data.

[0052] The processor 102 may include but is not limited to a processing device such as a microprocessor MCU or a programmable logic device FPGA. The above-mentioned computer device may also include a transmission device 106 and an input and output device 108 for communication functions. It can be understood by those skilled in the art that Figure 1 The structure shown is only for illustration and does not limit the structure of the above-mentioned computer device. Figure 1 More or fewer components as shown, or with Figure 1 Different configurations are shown.

[0053] The memory 104 can be used to store computer programs, for example, software programs and modules of application software. The processor 102 executes various functional applications and data processing by running the computer programs stored in the memory 104, that is, to implement the above method. The memory 104 can be used to store data. The memory 104 may include a high-speed random access memory, and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some examples, the memory 104 may further include a memory remotely arranged relative to the processor 102, and these remote memories may be connected to the computer device via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0054] The transmission device 106 is used to receive or send data via a network. The specific example of the above network may include a wireless network provided by a communication provider of the computer device. In one example, the transmission device 106 includes a network adapter (Network Interface Controller, referred to as NIC), which can be connected to other network devices through a base station so as to communicate with the Internet. In one example, the transmission device 106 can be a radio frequency (RF) module, which is used to communicate with the Internet wirelessly.

[0055] Figure 2 FIG. 4 is a flowchart of a method for detecting microscopic residual stress based on FIB-DIC technology provided in an embodiment of the present application. Figure 2 As shown, the method includes steps S201 to S207.

[0056] Step S201: deposit platinum marking points on the area to be tested of the sample, and deposit a platinum layer around the area to be tested.

[0057] Among them, the sample refers to the machined parts, including processed Cu alloys, Al alloys, Ti alloys, etc. FIB is used to deposit platinum (Pt) marking points on the surface of the sample, and the side length of the deposition area ranges from 10μm to 15μm. Determine the area to be tested of the sample. The shape of the area to be tested can be circular, rectangular, etc. Taking the shape of the area to be tested as a circle as an example, the diameter range of the circle is 10μm to 15μm, such as the diameter range of the circle is 10μm, 12μm, 15μm, etc. The diameter of the platinum marking point is 80nm to 120nm, such as the diameter is 80nm, 100nm, 120nm, etc. The distance between two adjacent platinum marking points is 180nm to 400nm, such as the distance is 180nm, 300nm, 400nm, etc.

[0058] In this step, the platinum marking point will be used as a deformation carrier of the sample surface to test the release of residual strain. At the same time, the FIB is used to deposit a platinum layer around the outside of the test area, so that during the FIB milling of the outer arc, the complete shape of the edge can be guaranteed to prevent the platinum marking point of the test area from being damaged. The shape of the platinum layer can be annular.

[0059] In one embodiment, platinum marking points are deposited on the area to be tested of the sample, including: placing the sample under a scanning electron microscope for observation, and selecting the area to be tested under the scanning electron microscope; using FIB to deposit multiple platinum marking points on the surface of the area to be tested, and the multiple platinum marking points are arranged in a lattice. Among them, the multiple platinum marking points can present an irregular randomly distributed lattice, or can be arranged into an orderly lattice according to a specific rule. For example and not limitation, the distance between each adjacent two platinum marking points is between 180nm and 400nm, and each distance can be equal, presenting an orderly arrangement; the distance can also be unequal, presenting a disordered arrangement.

[0060] In this embodiment, the small dot matrix will be used as a deformation carrier of the sample surface to test the release of residual strain, and the platinum layer is deposited around the area to be tested to prevent the small dot matrix from being damaged.

[0061] Step S202: Acquire a first image of the area to be tested.

[0062] The first image refers to the image before deformation. The first image is obtained by scanning the area to be tested with an electron beam, and the platinum marking points on the surface of the area to be tested interact with the electron beam to excite secondary electrons. The secondary electrons emitted in all directions are collected by the secondary electron collector, and then accelerated to the scintillator by the accelerating electrode, converted into a light signal, and then passed through the light guide to the photomultiplier tube, so that the light signal is converted into an electrical signal. This electrical signal is amplified by the video amplifier and transmitted to the gate of the cathode ray tube to modulate the brightness of the cathode ray tube. Finally, a first image with different brightness levels reflecting the surface morphology of the sample is presented on the fluorescent screen.

[0063] Step S203, performing ring core FIB milling on the outer side of the platinum layer one by one, and in-situ recording a second image of the area to be measured during each ring core FIB milling process.

[0064] In this step, the processing depth of each ring core FIB milling is 0.5μm to 1.0μm, the inner diameter of the ring core FIB milling is 10μm to 15μm, the outer diameter is 15μm to 20μm, and the outer diameter is 5μm larger than the inner diameter. For example, the processing depth each time can be 0.5μm, 0.7μm, 1.0μm, etc. The inner diameter is 10μm, 12μm, 15μm, etc. When the inner diameter is 10μm, the outer diameter is 15μm; when the inner diameter is 12μm, the outer diameter is 17μm; when the inner diameter is 15μm, the outer diameter is 20μm.

[0065] In this embodiment, an electron beam is used to scan the area to be tested. During each ring core FIB milling process, the platinum marking points on the surface of the area to be tested interact with the electron beam to excite secondary electrons. The second image is obtained by collecting and processing the secondary electrons. The second image refers to the deformed image.

[0066] After step S203, the strain of the platinum marking point is obtained using the DIC technique, with specific reference to steps S204 to S206 below.

[0067] Step S204: divide the first image into grids to obtain a sub-region corresponding to the first image and a first position of the sub-region on the first image.

[0068] In this step, the first image corresponds to a plurality of sub-regions, and a first position of each sub-region on the first image is determined. For any sub-region, the following step S205 is executed.

[0069] Step S205: searching the second image for a region having the largest correlation coefficient with the sub-region, and obtaining a second position of the sub-region on the second image.

[0070] In this step, it is assumed that each sub-region moves rigidly, and the position of the sub-region movement is determined by finding the region with the largest correlation coefficient with the sub-region, so as to achieve image registration before and after deformation. The correlation coefficient can be the similarity of pixel values, the matching degree of image features, etc. As an example, the pixel value can be a grayscale value.

[0071] In some embodiments, step S205 further includes: Figure 3 Step S301 and step S302 are shown.

[0072] Step S301: Calculate the sum of square errors between the pixel values ​​of the sub-region and each region in the second image to obtain the correlation coefficient between the sub-region and each region.

[0073] Step S302: searching the second image for a region having the largest correlation coefficient with the sub-region, and obtaining a second position of the sub-region on the second image.

[0074] The error sum of squares is continuous and differentiable, which makes it easier to apply optimization algorithms such as gradient descent during the optimization process. The objective function of the error sum of squares is smooth and monotonically decreasing, which can effectively help the algorithm find the best solution for image registration. In this embodiment, the error sum of squares measures the similarity of two images at the pixel level. Specifically, the higher the similarity of pixel values, the more related the two images are.

[0075] As an example, the expression of the correlation coefficient is as follows:

[0076]

[0077] In the formula, C is the correlation coefficient, f(x i ,y j ) is the first image on (x i ,y j ), g(x i′ ,y j ′ ) is the second image on (x i ′ ,y j ′ ) pixel value, f m is the average pixel value of the reference subset, and g m is the average pixel value of the target subset.

[0078] Step S206: determining the strain amount of the platinum marking point based on the difference between the first position and the second position.

[0079] It should be noted that, in order to achieve registration, the first image and the second image are in the same coordinate system.

[0080] In some embodiments, the first position and the second position are represented by coordinate points, and the coordinate difference between the coordinate point of the first position and the coordinate point of the second position is determined as the strain. Alternatively, the coordinate difference between the coordinate point of the second position and the coordinate point of the first position is determined as the strain.

[0081] For each sub-region, step S205 is used to achieve position matching to obtain the new position of the sub-region after deformation, and then obtain the deformation information of the area to be measured, that is, the strain of the sample.

[0082] Step S207: Calculate the residual stress of the area to be measured during each ring core FIB milling process according to the strain.

[0083] This step allows the calculation of residual stresses using Hooke's law.

[0084] Specifically, referring to the Cartesian coordinate system, the sample surface is the χ1 and X2 axes, the sample normal is the X3 axis, the out-of-plane normal stress σ3=0, and assuming that the residual stress state is an equibiaxial state, then σ1=σ2=σ, and the strain between the original residual stress state and the strain relief state is expressed as Δε. According to Hooke's law, the strain -Δε is caused by the equibiaxial residual stress σ, as follows:

[0085]

[0086] Transforming this formula, we get the expression In the expression, E is Young's modulus, v is Poisson's ratio, σ is residual stress, and -Δε is strain. According to the above expression, the residual stress in the micron range and submicron range can be calculated.

[0087] Through the above steps S201 to S207, this embodiment provides a microscopic residual stress detection method based on FIB-DIC technology. The method combines FIB technology and DIC technology to achieve the purpose of detecting residual stress at the microscopic level. Specifically, the method uses DIC technology to obtain the graphic displacement of the platinum marker point during the FIB milling process of the ring core. Because the spatial resolution of the image can reach microns and submicrons, the strain of the platinum marker point determined based on the image displacement can reach microns and submicrons. The residual stress calculated based on the strain has high detection accuracy. In addition, by recording the second image in situ, the dynamic changes of the sample during the FIB milling process can be observed in real time, achieving the effect of dynamic detection.

[0088] The method provided in the embodiments of the present application is further illustrated below with some specific examples.

[0089] Example 1

[0090] Taking the processed Cu alloy as an example, the microscopic residual stress detection method based on FIB technology and DIC includes the following steps 1.1 to 1.4.

[0091] Step 1.1: Use FIB to deposit Pt markers on the sample surface. The side length of the deposition area is 10μm, the diameter of the marker is 100nm, and the distance between two adjacent Pt markers is 180nm to 400nm. These small dot matrices will be used as deformation carriers on the sample surface to test the release of residual strain. At the same time, a circular Pt ring with a diameter of 10μm is deposited on the surface, so that during the FIB milling of the outer arc, the complete shape of the edge can be guaranteed to prevent the small dot matrix in the central area from being destroyed.

[0092] Step 1.2: Use FIB to perform ring core FIB milling on the outside of the Pt ring. The inner and outer diameters of the grooves are set to 10μm and 15μm respectively. The initial processing depth of each pass is 0.5μm, repeated 10 times, and the later processing depth of each pass is 1μm, repeated 5 times, and the cumulative processing depth is 10μm. During the ring core processing process, high-resolution images with graphic features are recorded in situ by electron beam.

[0093] Step 1.3: Use DIC to calculate the graphic displacement of the Pt marking point during the FIB milling of the ring core to obtain the microscopic strain.

[0094] Step 1.4: According to Hooke's law, the Young's modulus of the Cu alloy is known to be 110 GPa and the Poisson's ratio is 0.34. Substituting the micro deformation into the value, the micro residual stress value of the Cu alloy can be calculated.

[0095] Figure 4 The overall picture of the Pt marking point deposited by FIB in Example 1 is shown. Figure 4It can be seen that the image accuracy can reach 2μm. Figure 5 A partial enlarged view of the Pt marking point deposited by FIB in Example 1 is shown. Figure 5 In the process, the spatial resolution of the image reaches sub-micron level, so the dynamic changes of the sample obtained by the image can reach sub-micron level.

[0096] Figures 6 to 9 A schematic diagram of in-situ SEM recording of FIB ring core processing in Example 1 is shown, wherein: Figure 6 Schematic diagram of the initial unprocessed in-situ SEM recording. Figure 7 Schematic diagram of in situ SEM recording after milling to a depth of 0.5 μm. Figure 8 Schematic diagram of in situ SEM recording after milling to a depth of 5 μm. Fig. 9 Schematic diagram of in situ SEM recording after milling to a depth of 10 μm.

[0097] Figures 7 to 9 and Figure 6 By comparison, it can be seen that the circular Pt ring prevents the Pt marking points from being destroyed during the milling process, ensuring the complete shape of the small dot matrix and the integrity of the edges of the small dot matrix.

[0098] Figures 10 to 13 FIG. 1 is a schematic diagram showing the distribution law of the displacement of a pattern obtained by using DIC in Example 1, wherein: Fig.10 is the distribution diagram under the initial no-displacement state, Fig.11 This is the distribution diagram of the displacement after milling to a depth of 0.5 μm. Fig.12 This is the distribution diagram of displacement after milling to a depth of 5 μm. Fig.13 The displacement distribution after milling to a depth of 10 μm. Figures 10 to 13 It can be seen that with the increase of machining depth, the residual stress is gradually released and the displacement of the Pt marking point gradually increases.

[0099] Figure 14 to Figure 15 The statistical diagram of the distribution law of the displacement of the pattern obtained by using DIC in Example 1 is shown, wherein: Fig.14 For overall strain, Fig.15 is the microscopic strain between two adjacent Pt marking points. Fig.14 As the cutting depth increases, the residual stress is gradually released, and the overall microstrain gradually increases. When the cutting depth reaches 7 μm, the overall microstrain reaches a stable value, and the residual stress is basically released completely. By arbitrarily selecting two adjacent Pt marking points, the local microstrain of the material can be obtained, such as Fig.15 As shown in the figure, by comparing the microstrain of two Pt marking points separated by 290nm, it is found that the microstrain at marking point 2 is greater than that at marking point 1, indicating that the residual stress at marking point 2 is higher. Figure 14 to Figure 15It can be seen that the spatial resolution of micro-scale stress analysis of residual stress can reach below 300nm, indicating high detection accuracy.

[0100] Fig.16 The microscopic residual stress values ​​calculated based on FIB technology and DIC in Example 1 are shown. The surface of the processed Cu alloy presents compressive stress, the action depth of the microscopic residual stress is 7 μm, and the residual stress value is about 300 MPa.

[0101] Example 2

[0102] Taking the processed Al alloy as an example, the microscopic residual stress detection method based on FIB technology and DIC includes the following steps 2.1 to 2.4.

[0103] Step 2.1: Use FIB to deposit Pt markers on the sample surface. The side length of the deposition area is 15μm, the diameter of the marker is 120nm, and the distance between two adjacent Pt markers is 300nm. These small dot matrices will be used as deformation carriers on the sample surface to test the release of residual strain. At the same time, a circular Pt ring with a diameter of 15μm is deposited on the surface, so that during the FIB milling of the outer arc, the complete shape of the edge can be guaranteed to prevent the small dot matrix in the central area from being destroyed.

[0104] Step 2.2: Use FIB to perform ring core FIB milling on the outside of the Pt ring. The inner and outer diameters of the grooves are set to 15μm and 20μm respectively. The initial processing depth of each pass is 0.5μm, repeated 10 times, and the later processing depth of each pass is 1μm, repeated 5 times, and the cumulative processing depth is 10μm. During the ring core processing process, high-resolution images with graphic features are recorded in situ by electron beam.

[0105] Step 2.3: Use DIC to calculate the graphic displacement of the Pt marking point during the FIB milling of the ring core to obtain the microscopic strain.

[0106] Step 2.4: According to Hooke's law, the Young's modulus of Al alloy is known to be 80 GPa and the Poisson's ratio is 0.3. Substituting the micro deformation into the value, the micro residual stress value of Al alloy can be calculated.

[0107] Fig.17 The microscopic residual stress values ​​calculated based on FIB technology and DIC in Example 2 are shown. The surface of the processed Al alloy presents compressive stress, the action depth of the microscopic residual stress is 4 μm, and the residual stress value is about 170 MPa.

[0108] Example 3

[0109] Taking the processed Ti alloy as an example, the microscopic residual stress detection method based on FIB technology and DIC includes the following steps 3.1 to 3.4.

[0110] Step 3.1: Use FIB to deposit Pt markers on the sample surface. The side length of the deposition area is 12μm, the diameter of the marker is 110nm, and the distance between two adjacent Pt markers is 320nm. These small dot matrices will be used as deformation carriers on the sample surface to test the release of residual strain. At the same time, a circular Pt ring with a diameter of 12μm is deposited on the surface, so that during FIB milling of the outer arc, the complete shape of the edge can be guaranteed to prevent the small dot matrix in the central area from being destroyed.

[0111] Step 3.2: Use FIB to perform ring core FIB milling on the outside of the Pt ring. The inner and outer diameters of the grooves are set to 12μm and 17μm respectively. The initial processing depth of each pass is 0.5μm, repeated 10 times, and the later processing depth of each pass is 1μm, repeated 5 times, and the cumulative processing depth is 10μm. During the ring core processing process, high-resolution images with graphic features are recorded in situ by electron beam.

[0112] Step 3.3: Use DIC to calculate the graphic displacement of the Pt marking point during the FIB milling of the ring core to obtain the microscopic strain.

[0113] Step 3.4: According to Hooke's law, the Young's modulus of the Ti alloy is known to be 120 GPa and the Poisson's ratio is 0.33. Substituting the micro deformation into the value, the micro residual stress value of the Ti alloy can be calculated.

[0114] Fig.18 The microscopic residual stress values ​​calculated based on FIB technology and DIC in Example 3 are shown. The surface of the processed Ti alloy presents compressive stress, the action depth of the microscopic residual stress is 8 μm, and the residual stress value is about 360 MPa.

[0115] In summary, the method provided in the embodiment of the present application combines FIB technology and DIC technology to record images in situ during the FIB milling process of the ring core, and uses the displacement of the graphics of the Pt marking points in different images to determine the strain. Since the image is obtained by SEM scanning, the user can observe nano-level details in the image, so the strain of the platinum marking point can reach the micron and submicron scale, and the detection accuracy of the residual stress calculated based on the strain is higher. The problem of low detection accuracy of residual stress in the prior art is solved.

[0116] Fig.19 FIG. 4 shows a structural block diagram of a microscopic residual stress detection device based on FIB-DIC technology provided in an embodiment of the present application. Fig.19 As shown, the device comprises:

[0117] The FIB module 191 is used to deposit platinum marking points on the area to be tested of the sample and deposit a platinum layer around the area to be tested. A first image of the area to be tested is obtained; the outer side of the platinum layer is subjected to successive ring core FIB milling, and a second image of the area to be tested is recorded in situ during each ring core FIB milling process.

[0118] The DIC module 192 is used to divide the first image into grids to obtain a sub-region corresponding to the first image and a first position of the sub-region on the first image; to find a region with a maximum correlation coefficient with the sub-region in the second image to obtain a second position of the sub-region on the second image; and to determine the strain amount of the platinum marking point based on the difference between the first position and the second position.

[0119] The residual stress calculation module 193 is used to calculate the residual stress of the area to be measured during each ring core FIB milling process according to the strain.

[0120] In some of the embodiments, the DIC module 192 is further used to calculate the sum of square errors between the pixel values ​​of the sub-region and each region in the second image to obtain the correlation coefficient between the sub-region and each region; and to search for the region with the largest correlation coefficient with the sub-region in the second image to obtain the second position of the sub-region on the second image.

[0121] In some embodiments, the DIC module 192 is further configured to calculate the correlation coefficient using the following expression:

[0122]

[0123] In the formula, C is the correlation coefficient, f(x i ,y j ) is the first image on (x i ,y j ), g(x i ′ ,y j ′ ) is the second image on (x i ′ ,y j ′ ) pixel value, f m is the average pixel value of the reference subset, and g m is the average pixel value of the target subset.

[0124] In some of the embodiments, the FIB module 191 is also used to deposit a plurality of platinum marking points on the surface of the sample; the sample is placed under a scanning electron microscope for observation, and an area to be tested is selected under the scanning electron microscope; and a plurality of platinum marking points are deposited on the surface of the area to be tested using FIB, and the plurality of platinum marking points are arranged in a dot matrix.

[0125] In some embodiments, the residual stress calculation module 193 is also used to use the expression Calculate the residual stress in the measured area during each ring core FIB milling process. In the expression, E is Young's modulus, v is Poisson's ratio, σ is the residual stress, and -Δε is the strain.

[0126] It should be noted that the above modules can be functional modules or program modules, and can be implemented by software or hardware. For modules implemented by hardware, the above modules can be located in the same processor; or the above modules can be located in different processors in any combination.

[0127] It should be noted that the specific examples in this embodiment can refer to the examples described in the above embodiments and optional implementation modes, and will not be repeated in this embodiment.

[0128] In addition, in combination with the method provided in the above embodiment, a storage medium can also be provided in this embodiment to implement the method. The storage medium stores a computer program; when the computer program is executed by the processor, any one of the microscopic residual stress detection methods based on FIB-DIC technology in the above embodiment is implemented.

[0129] The embodiment of the present application also provides a computer program product. When the computer program product is run on a computer, the computer executes each function or step executed by the processor in the above method embodiment.

[0130] It should be understood that the specific embodiments described herein are only used to explain the application, rather than to limit it. Based on the embodiments provided in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of this application.

[0131] Obviously, the drawings are only some examples or embodiments of the present application. For ordinary technicians in the field, the present application can also be applied to other similar situations based on these drawings without creative work. In addition, it is understandable that although the work done in this development process may be complicated and lengthy, for ordinary technicians in the field, certain changes in design, manufacturing or production based on the technical content disclosed in this application are only conventional technical means and should not be regarded as insufficient content disclosed in this application.

[0132] The term "embodiment" in this application refers to a specific feature, structure or characteristic described in conjunction with the embodiment that can be included in at least one embodiment of the present application. The appearance of this phrase in various locations in the specification does not necessarily mean the same embodiment, nor does it mean that it is mutually exclusive with other embodiments and is independent or optional. It is clearly or implicitly understood by those of ordinary skill in the art that the embodiments described in this application can be combined with other embodiments without conflict.

[0133] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of patent protection. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the attached claims.

Claims

1. A microscopic residual stress detection method based on FIB-DIC technology, characterized in that: The method comprises: Depositing platinum marking points on the area to be tested of the sample, and depositing a platinum layer around the area to be tested; acquiring a first image of the area to be tested; performing successive ring-core FIB milling on the outer side of the platinum layer, and in-situ recording a second image of the area to be tested during each ring-core FIB milling process; Dividing the first image into grids by using DIC to obtain a sub-region corresponding to the first image and a first position of the sub-region on the first image; searching for a region with a maximum correlation coefficient with the sub-region in the second image to obtain a second position of the sub-region on the second image; and determining the strain of the platinum marking point based on a difference between the first position and the second position; According to the strain amount, the residual stress of the area to be measured during each ring core FIB milling process is calculated.

2. The microscopic residual stress detection method based on FIB-DIC technology according to claim 1 is characterized in that: The step of searching the second image for a region with a maximum correlation coefficient with the sub-region to obtain a second position of the sub-region on the second image includes: Calculating the sum of squares of pixel values ​​between the sub-region and each region in the second image to obtain a correlation coefficient between the sub-region and each region; A region having a maximum correlation coefficient with the sub-region is searched in the second image to obtain a second position of the sub-region on the second image.

3. The microscopic residual stress detection method based on FIB-DIC technology according to claim 1 or claim 2, characterized in that: The expression of the correlation coefficient is as follows: In the expression, C is the correlation coefficient, f(x i ,y j ) is the first image on (x i ,y j ), g(x i ′ ,y j ′ ) is the second image on (x i ′ ,y j ′ ) pixel value, f m is the average pixel value of the reference subset, and g m is the average pixel value of the target subset.

4. The microscopic residual stress detection method based on FIB-DIC technology according to claim 1 is characterized in that: The step of depositing a plurality of platinum marking points on the area to be tested of the sample comprises: placing the sample under a scanning electron microscope for observation, and determining a region to be tested under the scanning electron microscope; A plurality of platinum marking points are deposited on the surface of the test area by using FIB, and the plurality of platinum marking points are arranged in a dot matrix.

5. The microscopic residual stress detection method based on FIB-DIC technology according to claim 1 is characterized in that: The method of calculating the residual stress of the area to be measured during each ring core FIB milling process according to the strain amount includes: Using Expression The residual stress of the measured area during each ring core FIB milling process is calculated, where E is Young's modulus, v is Poisson's ratio, σ is the residual stress, and -Δε is the strain.

6. The microscopic residual stress detection method based on FIB-DIC technology according to claim 1 is characterized in that: The shape of the area to be tested is circular, the diameter of the circle ranges from 10 μm to 15 μm, and the shape of the platinum layer is ring-shaped.

7. The microscopic residual stress detection method based on FIB-DIC technology according to claim 1 is characterized in that: The diameter of the platinum marking point is 80nm to 120nm, and the distance between two adjacent platinum marking points is 180nm to 400nm.

8. The microscopic residual stress detection method based on FIB-DIC technology according to claim 1 is characterized in that: The inner diameter of the toroidal core FIB milling is 10 μm to 15 μm, and the outer diameter is 15 μm to 20 μm, and the outer diameter is 5 μm larger than the inner diameter.

9. The microscopic residual stress detection method based on FIB-DIC technology according to claim 1 is characterized in that: The machining depth of toroidal core FIB milling is 0.5μm to 1.0μm each time.

10. A microscopic residual stress detection device based on FIB-DIC technology, characterized in that: The device comprises: The FIB module is used to deposit platinum marking points on the area to be tested of the sample and deposit a platinum layer around the area to be tested; obtain a first image of the area to be tested; perform successive ring-core FIB milling on the outer side of the platinum layer, and in-situ record a second image of the area to be tested during each ring-core FIB milling process; A DIC module is used to divide the first image into grids to obtain a sub-region corresponding to the first image and a first position of the sub-region on the first image; to find a region with a maximum correlation coefficient with the sub-region in the second image to obtain a second position of the sub-region on the second image; and to determine the strain of the platinum marking point based on a difference between the first position and the second position; The residual stress calculation module is used to calculate the residual stress of the area to be measured during each ring core FIB milling process according to the strain.

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