A sample surface positioning method for short wavelength characteristic X-ray diffraction near-surface residual stress testing
By fitting the diffraction intensity variation curve or using thin-film positioning, the problem of complex sample surface positioning in short-wavelength X-ray diffraction technology has been solved, realizing high-precision and simple near-surface residual stress testing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTHWEST TECHNICAL ENGINEERING RESEARCH INSTITUTE OF CHINA SOUTH IND GROUP
- Filing Date
- 2023-10-19
- Publication Date
- 2026-07-21
Smart Images
Figure CN117405711B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of short-wavelength characteristic X-ray diffraction nondestructive testing technology, specifically to a sample surface positioning method for near-surface residual stress by short-wavelength characteristic X-ray diffraction. Background Technology
[0002] Short-wavelength characteristic X-ray diffraction technology uses an X-ray tube as a radiation source to non-destructively detect residual stress, texture, and phases inside materials / workpieces. Its implementation scheme can be found in the literature ZL2004100688802 / US7583788B2 / EP2541238.
[0003] Short-wavelength characteristic X-ray diffraction (SWD) technology uses highly penetrating characteristic X-rays (such as WKα, AuKα, AgKα, UKα, WKβ, etc.) emitted from a heavy metal target X-ray tube. It utilizes a parallel optical path formed by an incident collimator and a receiving collimator (the intersection of the incident and diffracted rays is the spatial location of the sample test point, i.e., the center of the short-wavelength X-ray diffractometer circle; the collimator divergence is less than 0.2°) to non-destructively measure the diffraction pattern of the material at the center of the diffractometer circle. Precise sample positioning is crucial for obtaining the diffraction pattern of a specific location on the sample.
[0004] Based on existing short-wavelength X-ray diffraction measurement devices and methods (ZL2004100688802), for a considerable period of time, the positioning of the tested sample was almost always done by locating the intermediate thickness coordinates of the sample and coordinate conversion. However, obtaining the surface coordinates of the sample is difficult in practice, the specific process is relatively complex, and it requires a high level of technical knowledge and experience from the technicians, making it difficult to meet the positioning requirements of near-surface residual stress testing. Summary of the Invention
[0005] In order to solve at least the technical problems mentioned in the background art, the present invention aims to provide a sample surface positioning method based on near-surface residual stress testing using short-wavelength characteristic X-ray diffraction.
[0006] The present invention adopts the following technical solution.
[0007] A sample surface positioning method for near-surface residual stress testing using short-wavelength characteristic X-ray diffraction is characterized by the following: when the texture of the sample along its thickness is uniform and its influence on the diffraction intensity along its thickness is negligible, the precise positioning of the sample surface is achieved by fitting a curve showing the change in diffraction intensity as the diffraction volume is gradually filled by the sample; or, when the texture of the sample along its thickness is non-uniform, the precise positioning of the sample surface is achieved by using a thin sheet tightly attached to the sample surface.
[0008] In this invention, after fixing the detector angle, the X-ray intensity is acquired within the same time interval as the diffraction volume is gradually filled by the sample; or, after obtaining the diffraction spectrum as the diffraction volume is gradually filled by the sample by scanning with the detector, the maximum value of the diffraction intensity in the diffraction spectrum is taken as the X-ray intensity; or, after obtaining the diffraction spectrum as the diffraction volume is gradually filled by the sample by scanning with the detector, the integrated intensity of the diffraction spectrum is taken as the X-ray intensity. As one of the preferred options, when determining the sample surface coordinates by fitting the diffraction intensity distribution curve as the diffraction volume is gradually filled by the sample, the sample thickness should not be less than 6 mm, so as to ensure that a plateau region with little or no change in diffraction intensity is formed near the highest point of the thickness distribution curve.
[0009] As a second preferred option, when the sample thickness is less than 6 mm and the diffraction volume is gradually filled by the sample, and there is no plateau region with small or no intensity change near the highest point of the diffraction intensity distribution curve, a thin sheet needs to be installed on the sample surface for positioning.
[0010] Furthermore, the sample surface coordinates are determined as follows: the sample diffraction intensity is corrected for absorption, and the fitting range of the diffraction intensity distribution curve when the diffraction volume is gradually filled by the sample is between the minimum and maximum values on one side. The X-coordinate value corresponding to the middle intensity of the diffraction intensity along the thickness distribution curve is the sample surface position.
[0011] Furthermore, when fitting the curve, R 2 The value is greater than 0.999.
[0012] In order to enable faster and more accurate sample surface positioning, the thickness of the sheet is no more than 0.5 mm, and its diffraction angle is significantly different from that of the sample being tested.
[0013] In this scheme, the center coordinates of the thin film are determined by fitting the distribution of diffraction intensity along the thickness direction of the thin film, and the surface coordinates of the sample under test are calculated based on the center coordinates and thickness of the thin film.
[0014] In this scheme, when the texture of the thin sheet is basically uniform along the thickness distribution, the diffraction intensity along the thickness distribution of the thin sheet exhibits parabolic or Gaussian distribution characteristics. The thickness center coordinates of the thin sheet are determined by using the parabolic or Gaussian peak (the center layer represents a surface, and what is actually measured is the coordinates of a certain point. Is it appropriate to use the center layer here?). Then, the surface coordinates of the sample are determined according to the geometric relationship between the sample and the thin sheet.
[0015] In this invention, the thin sheet has a strong preferred orientation in the diffraction vector direction, such as a plate texture or a filament texture, and still has a high diffraction intensity even when the tested sample is relatively thick, so as to obtain high-precision positioning coordinates. In this invention, (A) When the texture of the sample is uniform along the thickness distribution and its influence on the diffraction intensity along the thickness distribution is negligible, proceed with steps 11 to 13: Step 11: Obtain the diffraction intensity distribution curve as the diffraction volume is gradually filled by the sample by fixing the detector angle or scanning the diffraction peaks. Step 12: Perform X-ray absorption correction on the diffraction intensity distribution curve as the diffraction volume is gradually filled by the sample to obtain the corrected curve; Step 13: Fit the corrected curve, with the fitting range between the minimum and maximum values on one side, to obtain the sample surface coordinates; or, (B) When the texture of the sample is not uniform along the thickness distribution, proceed with steps 21 to 24: Step 21: Tightly attach a thin film of a different material from the sample being tested and whose diffraction peaks do not overlap to the surface of the sample being tested; Step 22: Scan to obtain the diffraction intensity distribution curve along the thickness direction. Step 23: Determine the center position of the thickness direction of the thin slice by parabolic or Gaussian fitting. Step 24: Based on the coordinates of the center position of the thickness direction of the obtained thin sheet, determine the surface coordinates of the sample under test according to the geometric relationship between the sample under test and the thin sheet.
[0016] Beneficial effects: The solution provided by this invention not only has the advantages of high positioning accuracy, simple positioning operation and low operation difficulty, but also can quickly achieve precise surface positioning during the near-surface residual stress test of materials / workpieces. It is especially suitable for materials / workpieces with uneven texture distribution along the thickness, and solves the problem of difficult surface positioning of materials with uneven internal texture distribution along the thickness. Attached Figure Description
[0017] Figure 1 This is a schematic diagram showing the fitting of the diffraction volume as the sample gradually fills the diffraction volume with the corresponding diffraction intensity. Figure 2 A schematic diagram of absorption correction for the diffraction intensity distribution curve as the diffraction volume is gradually filled by the sample. Figure 3 A schematic diagram illustrating the fitting of sample surface position and corresponding diffraction intensity using the central layer position of a thin film; Figure 4 This is an example of surface positioning based on the diffraction intensity distribution as the diffraction volume is gradually filled by the sample. The number 8 in the figure indicates a thickness of 8 mm. Figure 5 This is a schematic diagram showing the abrupt change in diffraction intensity along the thickness direction of a sample with uneven texture. Figure 6This is an example of surface localization of a sample with uneven texture based on a thin sheet. In the figure, the numbers 14.8 and 10.8 represent the thickness of the corresponding parts of the sample. Detailed Implementation
[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0019] The equipment used in this invention is described in reference ZL2004100688802. The cost and maintenance expenses of this type of instrument are lower than those of neutron diffraction and hard X-ray diffraction of high-energy synchrotron radiation. It can non-destructively detect the stress of commonly used materials and workpieces with centimeter-level thickness.
[0020] A sample surface positioning method for near-surface residual stress testing using short-wavelength characteristic X-ray diffraction is divided into two cases, A and B, as follows.
[0021] (A) When the texture of the sample is uniform along the thickness distribution and its influence on the diffraction intensity along the thickness distribution is negligible, proceed with steps 11 to 13: Step 11: By fixing the detector angle or scanning the diffraction peaks, obtain the diffraction intensity distribution curve as the diffraction volume is gradually filled by the sample, such as... Figure 1 As shown; During the process, as the sample moves along its thickness direction, the diffraction intensity gradually increases, exhibiting a pattern of "increasing slowly at first, then increasing rapidly, and then increasing slowly again (until a plateau region with little or no change is formed)". When the center line of the diffraction volume is just flush with the sample surface, the diffraction intensity is located at the position with the largest increase on the fitted curve, and then the increase gradually decreases. When the diffraction volume is completely inside the sample, the diffraction intensity hardly changes. Step 12: Perform X-ray absorption correction on the diffraction intensity distribution curve as the diffraction volume is gradually filled by the sample to obtain the corrected curve, as shown below. Figure 2 As shown; Step 13: Fit the corrected curve, with the fitting range between the minimum and maximum values on one side, to obtain the sample surface coordinates, such as... Figure 2 The depth coordinates corresponding to the test data shown are the sample surface locations.
[0022] (B) When the texture of the sample is not uniform along the thickness distribution, proceed with steps 21 to 24: Step 21: Tightly attach a thin film of a different material from the sample being tested and whose diffraction peaks do not overlap to the surface of the sample being tested; Step 22: Scan to obtain the diffraction intensity distribution curve along the thickness, as shown below. Figure 6 As shown, During the process, if a thin section is not used, the diffraction intensity will exhibit a "random increase and decrease" as the sample moves along its thickness direction, resulting in the following... Figure 5 As shown in the curve, in this case, it is impossible to locate the sample based on the changes in its own diffraction intensity. Step 23: Determine the center position of the thickness direction of the thin slice by parabolic or Gaussian fitting. Step 24: Combine the coordinates of the center position of the obtained thin sheet in the thickness direction, and determine the surface coordinates of the sample under test according to the geometric relationship between the sample under test and the thin sheet. Example 1
[0023] Surface positioning of 7075 aluminum alloy sheet is achieved by utilizing the diffraction intensity distribution along the thickness of the aluminum alloy sheet. The specific steps are as follows: (1) Mount the aluminum alloy plate on the sample stage of the short-wavelength X-ray diffraction measuring device; (2) Fix the detector at a specific diffraction angle, such as 5.12° of Al(111); (3) Set the X-ray voltage to 200kV and the current to 1mA, and step the Z-axis with a step size of 0.3mm to make the sample gradually pass through the diffraction volume of the instrument along the thickness direction to obtain the distribution of diffraction intensity along the Z-axis. (4) When the diffraction intensity does not change abruptly along the thickness, it indicates that the texture of the sample is uniformly distributed along the thickness. (5) Select the data from the lowest to the highest point of the diffraction intensity on one side of the surface to be positioned, such as... Figure 4 As shown; (6) Use the Boltzmann function to fit the data, and the midpoint coordinates obtained by fitting are the sample surface coordinates. Example 2
[0024] Surface positioning of 7075 aluminum alloy stepped sample plate: The surface positioning of the aluminum alloy stepped sample is carried out by utilizing the diffraction intensity distribution along the thickness. The specific steps are as follows: (1) Mount the stepped aluminum alloy sample on the sample stage of the short-wavelength X-ray diffraction measuring device; (2) Fix the detector at a specific diffraction angle, such as 5.12° of Al(111); (3) Step the Z-axis with a step size of 0.3 mm to make the sample gradually pass through the diffraction volume of the instrument along the thickness direction. Set the X-ray tube voltage to 200 kV and the tube current to 1 mA to obtain the distribution of diffraction intensity along the thickness direction of the sample. (4) The results show that the diffraction intensity of the sample undergoes a sudden change along the thickness direction, such as Figure 5As shown, the texture of the sample is unevenly distributed along the thickness, requiring the use of a thin sheet for positioning. Continue with the following steps. (5) A thin metal sheet, 0.2 mm thick, is pasted onto an aluminum alloy stepped plate; (6) Set the X-ray voltage to 200kV and the current to 1mA. Set the diffraction angle to the theoretical diffraction angles of Cu(111) 2θ=5.737° and θ=2.088°. Step the Z-axis with a step size of 0.3mm to make the copper foil gradually pass through the diffraction volume of the instrument along the thickness direction and obtain the distribution of diffraction intensity along the thickness direction of the sample. (7) By fitting the distribution function of the diffraction intensity along the thickness direction of the thin film using a Gaussian or parabolic function, the center coordinates of the thin film in the thickness direction can be obtained, such as... Figure 6 As shown; (8) Based on the geometric relationship between the aluminum alloy stepped plate and the thin sheet, the surface coordinates of the aluminum alloy stepped plate are calculated. The surface coordinates = the coordinates of the scanning center layer - the thickness of the thin sheet / 2.
Claims
1. A sample surface positioning method for near-surface residual stress testing using short-wavelength characteristic X-ray diffraction, characterized in that: When the texture of the sample along the thickness is uniform and its influence on the diffraction intensity along the thickness is negligible, the precise positioning of the sample surface can be achieved by fitting the curve of the diffraction intensity change as the diffraction volume is gradually filled by the sample; or, when the texture of the sample along the thickness is non-uniform, the precise positioning of the sample surface can be achieved by using a thin sheet that is tightly attached to the sample surface. (A) When the texture of the sample is uniform along the thickness distribution and its influence on the diffraction intensity along the thickness distribution is negligible, proceed with steps 11 to 13: Step 11: Obtain the diffraction intensity distribution curve as the diffraction volume is gradually filled by the sample by fixing the detector angle or scanning the diffraction peaks. Step 12: Perform X-ray absorption correction on the diffraction intensity distribution curve as the diffraction volume is gradually filled by the sample to obtain the corrected curve; Step 13: Fit the corrected curve, with the fitting range between the minimum and maximum values on one side, to obtain the sample surface coordinates; or, (B) When the texture of the sample is not uniform along the thickness distribution, proceed with steps 21 to 24: Step 21: Tightly attach a thin film of a different material from the sample being tested and whose diffraction peaks do not overlap to the surface of the sample being tested; Step 22: Scan to obtain the diffraction intensity distribution curve along the thickness direction. Step 23: Determine the center position of the thickness direction of the thin slice by parabolic or Gaussian fitting. Step 24: Based on the coordinates of the center position of the thickness direction of the obtained thin sheet, determine the surface coordinates of the sample under test according to the geometric relationship between the sample under test and the thin sheet.
2. The sample surface positioning method as described in claim 1, characterized in that: After fixing the detector angle, the X-ray intensity is collected at the same time interval as the diffraction volume is gradually filled by the sample; or, after obtaining the diffraction spectrum as the diffraction volume is gradually filled by the sample by scanning with the detector, the maximum value of the diffraction intensity in the diffraction spectrum is taken as the X-ray intensity; or, after obtaining the diffraction spectrum as the diffraction volume is gradually filled by the sample by scanning with the detector, the integrated intensity of the diffraction spectrum is taken as the X-ray intensity.
3. The sample surface positioning method as described in claim 1, characterized in that: When determining the sample surface coordinates by fitting the diffraction intensity distribution curve as the diffraction volume is gradually filled by the sample, the sample thickness should not be less than 6 mm to ensure that a plateau region with little or no change in diffraction intensity is formed near the highest point of the thickness distribution curve.
4. The sample surface positioning method as described in claim 1, characterized in that: When the sample thickness is less than 6 mm and the diffraction volume is gradually filled by the sample, and there is no plateau region with small or no intensity change near the highest point of the diffraction intensity distribution curve, a thin sheet needs to be installed on the sample surface for positioning.
5. The sample surface positioning method as described in claim 1, characterized in that, The sample surface coordinates are determined as follows: Absorption correction is applied to the diffraction intensity as the diffraction volume is gradually filled with the sample. The fitting range of the diffraction intensity distribution curve as the diffraction volume is gradually filled with the sample is between the minimum and maximum values on one side. The X-coordinate corresponding to the intermediate intensity along the thickness distribution curve is the sample surface position. When fitting the curve, R... 2 The value is greater than 0.
999.
6. The sample surface positioning method according to any one of claims 1-5, characterized in that: The thickness of the thin sheet is no more than 0.5 mm, and its diffraction angle is significantly different from that of the sample being tested.
7. The sample surface localization method for near-surface diffraction analysis using short-wavelength characteristic X-ray diffraction as described in claim 6, characterized in that: The center coordinates of the thin film are determined by fitting the distribution of diffraction intensity along the thickness direction of the thin film, and the surface coordinates of the sample under test are calculated based on the center coordinates and thickness of the thin film.
8. The sample surface positioning method as described in claim 7, characterized in that: When the texture of the thin sheet is basically uniform along the thickness distribution, the diffraction intensity along the thickness distribution of the thin sheet exhibits parabolic or Gaussian distribution characteristics. The center thickness coordinates of the thin sheet are determined by using the parabolic or Gaussian peak, and then the surface coordinates of the sample are determined according to the geometric relationship between the sample and the thin sheet.
9. The sample surface positioning method as described in claim 7, characterized in that: The thin sheet has a strong preferred orientation in the diffraction vector direction, such as a plate texture or a filament texture, and its diffraction intensity is high.