Reconstructing intragranular strain fields in polycrystalline materials from scanning 3DXRD data.

N Axel Henningsson,Stephen A Hall,Johan Hektor,Jonathan P Wright

doi:10.1107/s1600576720001016

Abstract

Two methods for reconstructing intragranular strain fields are developed for scanning three-dimensional X-ray diffraction (3DXRD). The methods are compared with a third approach where voxels are reconstructed independently of their neighbours [Hayashi, Setoyama & Seno (2017). Mater. Sci. Forum, 905, 157-164]. The 3D strain field of a tin grain, located within a sample of approximately 70 grains, is analysed and compared across reconstruction methods. Implicit assumptions of sub-problem independence, made in the independent voxel reconstruction method, are demonstrated to introduce bias and reduce reconstruction accuracy. It is verified that the two proposed methods remedy these problems by taking the spatial properties of the inverse problem into account. Improvements in reconstruction quality achieved by the two proposed methods are further supported by reconstructions using synthetic diffraction data.

Highlights

Modern synchrotrons provide X-ray beams of sufficiently high brilliance to enable the study of granular and inter-granular phenomena in dense polycrystalline materials
The strain state of a columnar tin (Sn) grain was reconstructed with the presented methods: Single-crystal refinement (SCR), Polycrystal refinement (PCR) and Algebraic strain refinement (ASR)
Turning first to the E33 strain, we find that ASR and PCR are in agreement while the reconstruction of SCR deviates

Summary

Introduction

Modern synchrotrons provide X-ray beams of sufficiently high brilliance to enable the study of granular and inter-granular phenomena in dense polycrystalline materials. Relying on the use of parallel and monochromatic X-rays, Poulsen (2004) and co-workers developed three-dimensional X-ray diffraction (3DXRD). The 3DXRD technique provides a nondestructive way of studying polycrystalline materials on a grain-by-grain basis. The method has been refined and adopted in several synchrotron facilities across the globe. In 3DXRD, to avoid diffraction spot overlap, the beam cross section can be reduced, limiting the number of simultaneously illuminated grains. If the beam cross section is small enough, diffraction originating from subparts of grains is measured. This opens up the possibility to reconstruct intragranular variations in the crystal structure

Methods

Results

Discussion

Conclusion