Wavelength-resolved neutron transmission analyses of textured materials

Abstract

Wavelength-resolved neutron imaging for diffraction contrast often referred to as Bragg edge imaging is a neutron-based technique that has gained attention in recent years due to its promising ability to characterize the microstructure of polycrystalline materials with spatial resolution. This method relies on spatially resolved analyses of diffraction induced features in transmission spectra within the thermal neutron range. Assessable characteristics are e.g. phase fractions, lattice strains, and crystallographic texture. For the latter forward modelling of transmission spectra from known orientation distribution functions (ODFs) has been demonstrated for various materials. However, solving the inverse problem—retrieving crystallographic texture from transmission spectra—presents a more complex challenge. In recent years, the authors have developed two theoretical approaches to model the relationship between transmission spectra and texture, either by decomposing the ODF into individual orientation fractions or by expanding it into a Fourier series. Both approaches have shown excellent predictive capability for materials with different crystal symmetries, including hexagonal, FCC, and BCC structures. Here we present the comparison between the proposed models, highlighting the advantages and disadvantages of the direct method based on different approaches for the analysis of wavelength-resolved neutron transmission experiments of textured materials. Finally, we present the future trends in the inversion method, i.e., the estimation of the ODFs from transmission spectra in tomography experiments.