Cold neutron diffraction contrast tomography of polycrystalline material

Abstract

Traditional neutron imaging is based on the attenuation of a neutron beam through scattering and absorption upon traversing a sample of interest. It offers insight into the sample's material distribution at high spatial resolution in a non-destructive way. In this work, it is expanded to include the diffracted neutrons that were ignored so far and obtain a crystallographic distribution (grain mapping). Samples are rotated in a cold neutron beam of limited wavelength band. Projections of the crystallites formed by the neutrons they diffract are captured on a two dimensional imaging detector. Their positions on the detector reveal their orientation whereas the projections themselves are used to reconstruct the shape of the grains. Indebted to established synchrotron diffraction contrast tomography, this 'cold neutron diffraction contrast tomography' is performed on recrystallized aluminium for experimental comparison between both. Differences between set-up and method are discussed, followed by the application range in terms of sample properties (crystallite size and number, mosaicity and typical materials). Neutron diffraction contrast tomography allows to study large grains in bulky metallic structures.

Laue three dimensional neutron diffraction

“…It is important to underline the fact that this 3D grain mapping method is several times more efficient than previous neutron methods 6,8 . Since this method does not require to select the energy of the incoming neutrons, the necessary neutron instrumentation is required and the effective neutron flux on the sample is increased between one and two orders of magnitude in comparison with other methods.…”

“…In both metallurgy and solid-state physics, neutrons are better suited than X-rays for in-situ testing with bulkier sample environments. A first approach and proof-of-principle experiment with neutrons (nDCT) was reported recently 6 , using full sample illumination and a neutron beam with a narrow energy spectrum. The result was a grain boundary topological 3D reconstruction of 13 grains from an aluminum sample, measured with cold neutrons at the ICON beamline 7 of Paul Scherrer Institut (PSI).…”

Deriving Quantitative Crystallographic Information from the Wavelength-Resolved Neutron Transmission Analysis Performed in Imaging Mode

“…Although detailed crystallographic characterization of a single-crystal material can be performed by whole pattern fitting analysis toward Bragg-dip transmission spectrum [29,30], the author considered that the Bragg-dip neutron transmission method also becomes a useful method for grain orientation imaging as well as neutron diffraction imaging techniques [31,32]. Since a fast determination method of the number of grains and their crystal orientations from a Bragg-dip pattern is developed for this aim, the data analysis procedure is briefly presented in this section; the details are reported in [28].…”

Exploiting diffraction in neutron imaging to reveal spatial variation in crystal properties

“…The crystallites are color coded by their orientation based on the inverse pole fi gure color map for a top view on the sample (taken from[9]). The crystallites are color coded by their orientation based on the inverse pole fi gure color map for a top view on the sample (taken from[9]).…”