A method for preparing and testing a powder diffraction standard for determining internal residual stress

Abstract

This invention provides a method for preparing and testing powder diffraction standards for determining internal residual stress, belonging to the field of residual stress detection. The powder standards prepared by this invention possess shape retention capabilities, meeting the requirements of the transmission diffraction optical path in non-destructive diffraction determination of internal residual stress. The powder, after being bonded with an adhesive, forms a blocky solid form, and standards of different sizes can be prepared according to the penetration depth of different diffraction sources on different substrate materials. Furthermore, the ratio of powder to adhesive can be adjusted to obtain different diffraction volume ratios. By testing the uniformity of diffraction peak intensity distribution in translational and rotational degrees of freedom, the uniformity of the internal lattice distribution and orientation of the standard sample can be determined, thereby testing and judging the uniformity of the standard sample.

Description

Technical Field

[0001] This invention relates to a method for preparing and testing powder diffraction standards for determining internal residual stress, belonging to the field of residual stress detection. Background Technology

[0002] Residual stress is widely present in the processing and manufacturing of various core and critical components. Accurately assessing the distribution of residual stress in components is of significant scientific and engineering value for structural integrity evaluation and equipment operation monitoring. The residual stress inside an actual workpiece is a comprehensive result of lattice distortion caused by numerous factors. Diffraction methods characterize residual stress by non-destructively testing the lattice strain of the workpiece, offering advantages such as high accuracy and the ability to reflect process characteristics. These methods include conventional X-ray diffraction, neutron diffraction, high-energy synchrotron radiation diffraction, and short-wavelength characteristic X-ray diffraction. Conventional X-ray diffraction can only detect residual stress on the workpiece surface. With the increasing demands for non-destructive analysis of residual stress in precision manufacturing, simply testing the surface is insufficient; greater attention is being paid to the distribution of internal residual stress, necessitating corresponding stress-free powder diffraction standards.

[0003] Conventional X-ray diffraction phase analysis and stress detection also involve the preparation of powder standards, but their structure is suitable for testing surface reflection optical paths. However, when using neutron diffraction, high-energy synchrotron X-ray diffraction, or short-wavelength characteristic X-ray diffraction for internal residual stress testing, a transmission optical path is required. Such standards would obstruct the optical path (as shown in the attached image). Figure 1 (As shown). Therefore, a new method for preparing powder diffraction standards is needed to enable the powder standards to have a certain structural self-sustaining ability without obstructing the transmission diffraction optical path; in addition, in order to be used as stress-free reference standards, residual stress must not be introduced during the standard preparation process. Summary of the Invention

[0004] To address the shortcomings and deficiencies of the existing technology, and considering the characteristics of the transmission optical path in diffraction testing of internal residual stress, this invention provides a method for preparing and testing powder diffraction standards for determining internal residual stress, employing the following technical solution:

[0005] A method for preparing a powder diffraction standard for determining internal residual stress includes the following steps:

[0006] S1: Screening and pretreatment of powder;

[0007] S2: Mix the powder and binder in a certain proportion in the mold;

[0008] S3: Eliminates air bubbles during material mixing, and allows for curing and demolding;

[0009] S4: Shape and cut the standard sample, polish and stress-relieve the surface, and then package and store it.

[0010] Further, the screening in step S1 is that the powder for preparing the powder standard sample for measuring internal residual stress by diffraction method should satisfy that the grain size is not less than 25 μm, the particle diameter is 20-60 μm, and the powder shape is spherical; the pre-treatment is that the powder is subjected to sufficient stress relief annealing, and after holding for 3-5 hours, slowly cooled to room temperature, and for the powder which reacts with air, the annealing should be carried out in vacuum environment or protective atmosphere.

[0011] Further, the mass ratio of the powder to the adhesive in step S2 is 0.1:1-10:1, and the adhesive is epoxy resin and curing agent.

[0012] Further, the material mixing in step S3 should be put into a negative pressure device for 15-30 minutes, and placed in a dry environment for curing.

[0013] Further, the surface roughness Ra of the standard sample after the shaping, cutting and polishing in step S4 is not greater than 10 μm, and the stress relief treatment method of the polished surface is chemical etching or electrochemical etching method.

[0014] The method for measuring the internal residual stress of the standard sample prepared according to the above method is characterized in that the test method is diffraction method, and comprises the following steps:

[0015] (1) performing internal diffraction test to determine the internal diffraction angle 2θ and the interplanar spacing d of the sample;

[0016] (2) determining the uniformity in the three translational and two rotational freedom directions of the sample;

[0017] (3) performing internal residual stress test.

[0018] Further, the determination of the internal diffraction angle 2θ and the interplanar spacing d of the sample in step (1) is that the internal diffraction test adopts a non-destructive test method, and for X-ray, γ-ray or neutron diffraction method with shorter wavelength and certain penetration ability; the internal diffraction angle 2θ of the sample is measured, and the interplanar spacing d is calculated according to the Bragg equation 2dsinθ = λ (in which d is the interplanar spacing, θ is 1 / 2 of the diffraction angle, and λ is the wavelength of the ray), compared with the interplanar spacing of the standard powder diffraction, and calibrated according to the diffraction angle test result.

[0019] Further, the determination of the uniformity in the three translational and two rotational freedom directions inside the sample in step (2) is that at least 5 test points are randomly taken in each translational freedom direction inside the sample for diffraction spectrum test, the diffraction spectrum refers to the diffraction intensity I-diffraction angle 2θ distribution curve, and the sample is reciprocated in the three freedom directions during the test, and the relative deviation of the peak diffraction intensity is within ±7.5%, so that the sample is determined to be uniform; meanwhile, at the two rotational freedom directions of the 5 test points, the distribution test of the peak diffraction intensity with the rotation angle is performed, and the relative deviation of the peak diffraction intensity is within ±7.5%, so that the sample is determined to be uniform.

[0020] Further, the internal residual stress test in step (3) is that at least 5 test points are randomly taken inside the standard sample for non-destructive internal residual stress test, the average value of the results is taken as the stress value, and the sample standard deviation of the results is taken as the test error of the residual stress.

[0021] The beneficial effects of the present application are:

[0022] 1. A new diffraction powder standard sample preparation method with shape retention ability is obtained, which meets the needs of transmission diffraction light path when the internal residual stress is non-destructively measured by diffraction method.

[0023] 2. The powder is bonded into a block solid after being bonded by the adhesive, and different sizes of standard samples can be prepared according to the penetration depth of different diffraction ray sources to different measured matrix materials.

[0024] 3. The uniformity of the lattice distribution and orientation inside the standard sample can be determined by the test of the diffraction peak intensity distribution uniformity in the translational and rotational freedom directions, so that the standard sample is calibrated. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings, in which:

[0026] Figure 1 It is a schematic diagram of the standard sample suitable for different diffraction light paths according to the background technology of the present application;

[0027] Figure 2 It is a schematic diagram of the three translational and rotational freedom directions of the sample according to the embodiment of the present application, in which X, Y and Z are three translational axes, and K and θ are two rotational axes;

[0028] Figure 3 It is the distribution of the peak diffraction intensity inside the aluminum powder standard sample with K angle according to the embodiment of the present application;

[0029] Figure 4 It is the distribution of the peak diffraction intensity inside the copper powder standard sample with K angle according to the embodiment of the present application;

[0030] Figure 5 The distribution of peak diffraction intensity as a function of K angle within a silicon powder standard sample according to an embodiment of the present invention. Detailed Implementation

[0031] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] The powder used was 20 μm aluminum powder, with a mass ratio of aluminum powder to epoxy resin of 0.5:1. After uniform mixing, the mixture was vacuumed at 0.02 MPa for 15 min and then allowed to cure. The cured aluminum powder standard was cut into 7.9 mm thick sheets. Short-wavelength characteristic X-ray diffraction was used to test the aluminum powder standard, with Kα1 characteristic X-rays from a W target as the radiation source. The test crystal plane is Al(111) crystal plane, and the distribution of the peak diffraction intensity inside the aluminum powder standard sample with respect to the K angle is shown in the attached figure. Figure 3 As shown.

[0034] Example 2

[0035] The powder used was copper powder with a particle size of 40 μm. The mass ratio of copper powder to epoxy resin was 2:1. After uniform mixing, the mixture was evacuated at 0.02°C for 15 minutes and allowed to cure. The cured copper powder standard was cut into 2.0 mm thick sheets. Short-wavelength characteristic X-ray diffraction was used to test the copper powder standard, with Kα1 characteristic X-rays from a W target as the X-ray source. The test crystal plane is Cu(111) crystal plane, and the distribution of the peak diffraction intensity inside the copper powder standard sample with respect to the K angle is shown in the attached figure. Figure 4 As shown.

[0036] Example 3

[0037] The powder used was 50μm silicon powder, with a silicon powder to epoxy resin mass ratio of 0.5:1. After uniform mixing, the mixture was vacuumed at 0.01MPa for 5 min + 0.02MPa for 5 min, repeated three times, and then allowed to cure. The cured silicon powder sample was cut into 4.0mm thick sheets. Short-wavelength characteristic X-ray diffraction was used to test the silicon powder sample, with Kα1 characteristic X-rays from a W target as the X-ray source, and the wavelength... The test crystal plane is Si(111) crystal plane, and the distribution of the peak diffraction intensity inside the silicon powder standard sample with respect to the K angle is shown in the attached figure. Figure 5 As shown.

Claims

1. A method for preparing a powder diffraction standard for determining internal residual stress, characterized in that, Includes the following steps: S1: Screening and pretreatment of powder; S2: Mix the powder and binder in a certain proportion in the mold; S3: Eliminates air bubbles during material mixing, and allows for curing and demolding; S4: Shape and cut the standard sample, grind and stress-relieve the surface, and then package and store it. The screening described in step S1 is as follows: the powder used to prepare the powder standard for determining the internal residual stress by diffraction should meet the following requirements: the grain size should be not less than 25 μm, the particle diameter should be 20~60 μm, and the powder morphology should be spherical; the pretreatment is as follows: the powder is subjected to sufficient stress-relief annealing, held at the temperature for 3~5 hours, and then slowly cooled to room temperature. For powders that react with air, annealing should be performed in a vacuum environment or under a protective atmosphere. The surface roughness Ra of the standard sample after shaping, cutting and grinding in step S4 is no greater than 10 μm, and the stress relief treatment method for the ground surface is chemical etching or electrochemical etching.

2. The method for preparing powder diffraction standards for determining internal residual stress according to claim 1, characterized in that, The mass ratio of powder to adhesive in step S2 is 0.1:1 to 10:1, and the adhesive is epoxy resin and curing agent.

3. The method for preparing powder diffraction standards for determining internal residual stress according to claim 1, characterized in that, The process of eliminating air bubbles during material mixing, as described in step S3, involves placing the material in a negative pressure device for 15-30 minutes and then placing it in a dry environment for curing.

4. A method for determining the internal residual stress of a standard sample prepared according to the method of claim 1, characterized in that, The test method uses diffraction and includes the following steps: (1) Perform internal diffraction tests to determine the internal diffraction angle 2θ and interplanar spacing d of the sample; (2) Determine the uniformity of the sample in the three translational and two rotational degrees of freedom directions; (3) Conduct tests on internal residual stress.

5. The method for determining the internal residual stress of a standard sample according to claim 4, characterized in that, Step (1) involves determining the internal diffraction angle 2θ and interplanar spacing d of the sample. The internal diffraction test employs a non-destructive testing method. The internal diffraction angle 2θ of the sample is measured and determined according to the Bragg equation. In the formula, d is the interplanar spacing, θ is half of the diffraction angle, and λ is the wavelength of the X-ray. The interplanar spacing d is calculated and compared with the interplanar spacing of standard powder diffraction. The diffraction angle test results are then calibrated based on this.

6. The method for determining the internal residual stress of a standard sample according to claim 4, characterized in that, In step (2), the uniformity of the sample in the three translational and two rotational degrees of freedom is determined by randomly selecting at least 5 test points in each translational degree of freedom direction to perform diffraction spectrum tests. The diffraction spectrum refers to the distribution curve of diffraction intensity I-diffraction angle 2θ. During the test, the sample reciprocates in the three translational degrees of freedom directions. If the relative deviation of the peak diffraction intensity is within ±7.5%, the sample can be judged to be uniform. At the same time, the distribution test of the peak diffraction intensity with the rotation angle is performed in the three rotational degrees of freedom directions of these 5 test points. If the relative deviation of the peak diffraction intensity is within ±7.5%, the sample can be judged to be uniform.

7. The method for determining the internal residual stress of a standard sample according to claim 4, characterized in that, In step (3), the internal residual stress test is carried out by randomly selecting at least 5 test points inside the standard sample to perform non-destructive testing of internal residual stress, taking the average value of the results as the stress value, and taking the sample standard deviation of the results as the test error of residual stress.

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