A Rietveld-Type Analysis Code for Pulsed Neutron Bragg-Edge Transmission Imaging and Quantitative Evaluation of Texture and Microstructure of a Welded α-Iron Plate

摘要

Bragg-edge transmission imaging using a pulsed neutron source is expected to be a new method to investigate the crystallographic and metallographic structure of a material. This method has attracted the attention in the research field of material characterization for materials development and industrial applications because it non-destructively provides the images on the texture and the microstructure inside a material such as a thick steel bulk over the wide area of the material. For deducing such information from the Bragg-edge transmission spectrum, a data analysis code like a Rietveld analysis code for powder diffractometry is indispensable. So far, only the information on the crystallographic anisotropy has been deduced. However, this information is incomplete since both the preferred orientation and the crystallite size affect the Bragg-edge transmission spectrum. Therefore, we have developed a Rietveld-type analysis code, RITS, that allows us to obtain the information on preferred orientation and crystallite size at the same time. To examine the feasibility and the usefulness of the RITS code, we have analyzed the Bragg-edge transmission spectra of rolled and welded a-iron plates, and we have successfully obtained the preferred orientation data and the crystallite size data over the wide area of the bulk specimens.