Inverse pole figure mapping of bulk crystalline grains in a polycrystalline steel plate by pulsed neutron Bragg-dip transmission imaging

Abstract

A new mapping procedure for polycrystals using neutron Bragg-dip transmission is presented. This is expected to be useful as a new materials characterization tool which can simultaneously map the crystallographic direction of grains parallel to the incident beam. The method potentially has a higher spatial resolution than neutron diffraction imaging. As a demonstration, a Bragg-dip neutron transmission experiment was conducted at J-PARC on beamline MLF BL10 NOBORU. A large-grained Si-steel plate was used. Since this specimen included multiple grains along the neutron beam transmission path, it was a challenging task for existing methods to analyse the direction of the crystal lattice of each grain. A new data-analysis method for Bragg-dip transmission measurements was developed based on database matching. As a result, the number of grains and their crystallographic direction along the neutron transmission path have been determined.

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

“…The crystal-lattice direction parallel to the neutron beam direction [UVW] was estimated as [100 30 8] for Grain Orientation 1 and was estimated as [100 38 0] for Grain Orientation 2, respectively. Note that evaluated crystal orientations are reasonable according to SEM-EBSD [28]. …”

“…Hereafter, a grain orientation analysis/imaging method using the Bragg-dip neutron transmission spectrum [28] is presented. 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].…”

“…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]. …”

“…Finally, the wavelength where (hkl) Bragg-dip appears is calculated from Equations (1) Figure 3 shows two examples of Bragg-dip transmission data and the database matching result (cross × marks) with the information of indexing (hkl) [28]. The single-crystal sample was 3.4wt% Sisteel plate of 5 mm thickness and was measured at a pulsed cold-neutron beam-line, BL10 "NOBORU" [33] of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC).…”

“…The size of the VAMAS sample is 5 cm in diameter and 5 cm in height. The macro-strain distribution is axial symmetric which can be described by Equation (28). For this sample, projection data of d-spacing of Al {111} were measured by a Bragg-edge transmission imaging experiment and then macro-strain tomographic images of εθθ and εrr were reconstructed by the ML-EM based tensor CT method and Equation (2).…”