IMS: Development of Orientation Quantification for Single Crystal and Textured Polycrystals from Neutron Transmission Data

The correlation between material properties and microstructure is well known, which motivates development of methods to quantify the latter. Bulk averaged texture can be determined from x-ray diffraction methods, and techniques for mapping of grains and their orientation include scanning electron microscopy with electron backscatter diffraction (SEM-EBSD), and X-ray diffraction (XRD) imaging. Both techniques are limited by the penetration depth of the radiation sub-micrometers (SEM-EBSD), and micrometers (XRD imaging). Neutrons generally have a higher penetration depth than both electrons or X-rays, and this expanded penetration depth provides new opportunities for studying bulk samples.

Time-of-Flight (TOF) neutron transmission spectra of single crystal or multi-grain samples are characterized by dips at wavelengths where Bragg’s law is being fulfilled for unique crystal orientations, which can be used to resolve the mosaicity and orientation of the crystals, while TOF neutron transmission spectra through ideally random textured polycrystalline samples are characterized by sudden well-defined step increase in intensity (Bragg-edges) at neutron wavelength locations that exceed the Bragg condition for coherent scattering at that corresponding interplanar spacing. For samples in which the grains orientations are not random (i.e., nearly all manufactured materials), the preferred crystallographic orientation results in TOF neutron transmission spectra characterized by “deformed” Bragg-edges at the location of these “non-random oriented” planes.

In this presentation, I will discuss efforts to recover the orientation matrix of a single crystal using neutron transmission measurements. The map of the recovered orientation matrix is validated using Sinpol, which is a collection of routines for calculation of the total cross section that determines the attenuation of neutron beam by crystalline specimen. A similar effort to determine the preferred crystallographic orientation in textured polycrystalline samples is explored.

This research used resources at the Spallation Neutron Source, a DOE Office Science User Facility operated by the Oak Ridge National Laboratory.