High-precision Texture Data Analysis And Experimental Strategy Research For Neutron Diffraction

Neutron diffraction is a non-destructive testing technology of material structure,measuring the strain and grain orientation of crystal materials.Compared with other beams for material characterization such as X-ray and electron,neutron has superior penetrating ability for metal materials.Therefore,neutron diffraction can obtain the statistical information of strain and orientation distribution in bulk metal materials,which is difficult for other characterization approaches.The texture is closely related to the macroscopic mechanical properties of materials.Neutron diffraction is a powerful tool for texture measurement of metal materials,especially for engineering metal materials.The texture characterization of neutron diffraction is of great significance to the basic scientific research of material microstructure and the detection of large engineering parts.With the development of reactor technology in recent years,the neutron fluence is increasing and the signal-to-noise ratio of neutron is improved.The current data processing software cannot meet the needs of high-precision and complex texture measurement.Besides,the experimental resources of neutron diffraction are very scarce,so it is of practical significance to improve the efficiency of data processing and experimental strategy.The fundamental data of this work come from three neutron diffraction experiments by different diffractometers.On the one hand,a new data-processing method,called ‘pixel projection method’,has been developed,calculating the texture information from the diffraction image with improved precision and efficiency.On the other hand,based on the inverse operation of the former,the diffraction patterns of textured samples have been simulated,guiding the detector placement and sample rotation to optimize the efficiency of texture measurement experiments.In terms of data processing,the development of ‘pixel projection method’is based on the geometric principle of neutron diffraction and related parameters of experimental equipment and adapted to the data structure of the area detector.The core algorithm of this method is to process the position and intensity information of each pixel individually and directly project it to the pole figure.In this work,the ‘pixel projection method’ has been tested on the original neutron diffraction data measured at CMRR and ANSTO.The results show that the new method can calculate the pole figures with higher resolution and higher accuracy than current software based on the same raw data.The new method can clearly reflect the details of complex texture and distinguish the adjacent texture peaks.Moreover,it can correct the error caused by the overlap or separation of the detected Debye ring areas.In this work,the ‘pixel projection method’ is integrated into a professional data-processing software HRTex for texture measurement of two-dimensional position-sensitive detector of monochromatic neutron diffraction spectrometer with improved precision,accuracy and efficiency.In the aspect of experimental strategy,the neutron diffraction image simulation system is developed to improve the efficiency of texture measurement by guiding the rotation of Eulerian cradle and the placement of detector.The system can simulate the signal position and intensity distribution of textured polycrystalline samples in neutron diffraction experiment,with the verification of experimental data and simulated data.Based on this system,the texture measurement efficiency of single-detector mode is optimized,and two efficient texture measurement strategies are proposed for the three-detector mode of the neutron spectrometer,‘HETU’,which is being jointly constructed by SJTU and CAEP.At the same time,the ‘pixel projection method’ was used to process the simulated image under different experimental strategies to test their reliability.In short,the ‘pixel projection method’ and image simulation of this work are independent but closely related.They are mutual verifications while solving different engineering problems.They constitute a closed-loop from diffraction image to texture information and to diffraction image,which can continuously update itself and improve the precision and efficiency of neutron diffraction texture measurement.It is of important guiding significance for both active spectrometers and spectrometers under construction.