GB/T 40307-2021Non-destructive testing - Test method for texture by neutron diffraction (English PDF)

1 Scope

China's national method for measuring crystallographic texture by neutron diffraction. It specifies the terms and definitions, the principle and the apparatus. Texture is the tendency of the grains in a polycrystalline metal to share an orientation rather than being random, and it is produced by every forming operation - rolling, drawing, extrusion. It matters because a textured material is anisotropic: its strength, its formability and its magnetic and elastic properties differ with direction, sometimes by a great deal. X-ray diffraction measures texture at the surface, in a layer tens of microns thick, and for a rolled sheet the surface texture differs from the interior. Neutrons penetrate centimetres of steel, so they measure the bulk - the average through the whole thickness of a plate or through the wall of a tube, non-destructively. That is the measurement this method provides, and it is why it needs a reactor or a spallation source.

This Document specifies the method for detecting the texture of materials on the reactor by neutron diffraction technology. This Document is applicable to the detection of texture of polycrystalline materials.

2 Normative References

The following documents are essential to the application of this Document. For the dated documents, only the versions with the dates indicated are applicable to this Document; for the undated documents, only the latest version (including all the amendments) is applicable to this Document.

GB/T 12604.8 Terminology for Non-Destructive Testing - Neutron Testing

GB/T 26140 Non-Destructive Testing - Standards Test Method for Determining Residual Stresses by Neutron Diffraction

3 Terms and Definitions

For the purposes of this Document, the terms and definitions given in GB/T 12604.8 and GB/T 26140 and the following apply.

3.1 Texture The crystal grains in the polycrystalline sample are arranged in different directions with different orientation characteristics, which is manifested as the preferred orientation structure of the sample. NOTE: The neutron detection method can obtain pole figures of multiple crystal planes, obtain accurate orientation directions, and obtain quantitative data of texture intensity.

3.2 Neutron diffractometer for texture measurement Neutron radiation detection device for measuring texture of materials.

3.3 Pole figure The projection map of the orientation distribution of the selected crystal plane of each crystal grain in the material in the sample coordinate system. NOTE: The sample coordinate system refers to the rectangular orthogonal coordinate system established according to the sample shape, which is the basic expression form of texture intensity.

3.4 Inverse pole figure The projection map of the orientation distribution of the selected crystal plane of each crystal grain in the material in the crystal coordinate system. NOTE: The crystal coordinate system refers to the rectangular coordinate system established in accordance with the crystal orientation, which is the basic expression form of texture intensity.

3.5 Pole density Polycrystalline materials are projected to the polar equator, and the weighted density distribution of the crystal grain volume represented by each point on the sphere.

3.6 Orientation distribution function An optimized azimuth expression form of the three-dimensional spatial distribution of crystal elements.

4 Principle

After being irradiated by neutron rays, a polycrystalline sample with regularly arranged atoms shall produce coherent scattering at a specific angle. This process is called Bragg diffraction, and the process is given by Formula (1): Where: d - interplanar spacing, in nm; theta - 1/2 diffraction angle, in °; lambda - neutron wavelength, in nm. The texture shall cause the Bragg diffraction peaks of the sample in the three- dimensional space and cause the changes in intensity. The texture intensity of the material is obtained by collecting the diffraction peaks of different spatial angles in the three-dimensional space and analysing the diffraction peaks. The monochromator is a device that uses crystals to select and reflect rays. The monochromator is mainly composed of single crystal, focusing device, adjustment table and other components. The energy range of the neutron beam selected by the monochromator should be 5meV~25meV; and the corresponding neutron wavelength range is 0.1nm~0.3nm. The monochromator should have vertical focusing or horizontal and vertical double focusing capabilities to increase the neutron fluence rate at the sample. The monochromators commonly used in neutron diffractometer for texture measurement include: silicon monocrystalline monochromator, pyrolytic graphite monocrystalline monochromator, monocrystalline germanium monochromator, and so on.

5.2.3 Euler ring The Euler ring is used to realize the assembly and positioning of the sample, and to provide the rotation of the sample in the three-dimensional space coordinate. The Euler ring shall realize the sample rotation azimuth phi and the Euler ring rotation azimuth chi according to the set pace and ensure the angular accuracy. Among them, the phi angle should be in the range of 0°~360°, the chiangle should be in the range of 0°~360°, and the angular accuracy should be better than 0.1°.

5.2.4 Detector The detector is a device for capturing and recording neutron signals. The detector can detect neutron energy in the range of 5meV~25meV. Commonly used detectors on neutron diffractometer for texture measurement include 3He counter tube detectors, 3He gas multifilament position sensitive detectors, and so on.

8 Data Processing and Analysis...