Time-of-Flight Three Dimensional Neutron Diffraction in Transmission Mode for Mapping Crystal Grain Structures

Alberto Cereser,Stephen A Hall,Srinivasan Iyengar,Søren Schmidt,Anton S Tremsin,Τakayasu Hanashima ,Т Niendorf ,Erik Bergbäck Knudsen ,Poul Scheel Larsen ,Morten Sales,Ryoji Kiyanagi,A Steuwer ,Markus Ströbl ,T Shinohara ,Peter Kjær Willendrup ,Peter M Kadletz,Alice Bastos Da Silva Fanta,Taketo Moyoshi,Philipp Krooß ,Wolfgang W Schmahl

doi:10.1038/s41598-017-09717-w

Abstract

The physical properties of polycrystalline materials depend on their microstructure, which is the nano- to centimeter scale arrangement of phases and defects in their interior. Such microstructure depends on the shape, crystallographic phase and orientation, and interfacing of the grains constituting the material. This article presents a new non-destructive 3D technique to study centimeter-sized bulk samples with a spatial resolution of hundred micrometers: time-of-flight three-dimensional neutron diffraction (ToF 3DND). Compared to existing analogous X-ray diffraction techniques, ToF 3DND enables studies of samples that can be both larger in size and made of heavier elements. Moreover, ToF 3DND facilitates the use of complicated sample environments. The basic ToF 3DND setup, utilizing an imaging detector with high spatial and temporal resolution, can easily be implemented at a time-of-flight neutron beamline. The technique was developed and tested with data collected at the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Complex (J-PARC) for an iron sample. We successfully reconstructed the shape of 108 grains and developed an indexing procedure. The reconstruction algorithms have been validated by reconstructing two stacked Co-Ni-Ga single crystals, and by comparison with a grain map obtained by post-mortem electron backscatter diffraction (EBSD).

Highlights

Standard tools in metallography, such as optical and electron micrography, return information limited to the microstructure of a sample surface, which may not be representative of the bulk material[2, 3]
The number and size of the grains that can be reconstructed using neutron diffraction contrast tomography (nDCT) is limited by diffraction spots overlapping and blurring, which set a minimum grain size of 1 mm for a mosaicity of 0.1–0.2°9
ToF 3DND has advantages over another recent neutron-diffraction based imaging approach, namely nDCT, in that it has less limitations in terms of the number and size of the grains[9]

Summary

Introduction

Standard tools in metallography, such as optical and electron micrography, return information limited to the microstructure of a sample surface, which may not be representative of the bulk material[2, 3] These techniques require extensive sample preparation and can return 3D sample reconstructions only by repeatedly removing a layer of material and characterizing the surface beneath[4, 5]. ToF 3DND utilizes a conventional imaging geometry in time-of-flight mode, providing intrinsic neutron energy resolution that enables the reconstruction of the 3D shape and orientation of the grains composing polycrystalline materials. This approach is a generalization of the X-ray based direct-beam DCT technique (DCT-I) developed by Ludwig et al.[7]. The simultaneously available diffraction data may add significant information about individual grain strain states, mosaicity or twinning

Methods

Results

Conclusion