Daigo Setoyama

In Situ Three-Dimensional Orientation Mapping in Plastically-Deformed Polycrystalline Iron by Three-Dimensional X-Ray Diffraction

In situ three-dimensional crystallographic orientation mapping in plastically-deformed polycrystalline iron is demonstrated using a modified three-dimensional x-ray diffraction method. This voxel-by-voxel measurement method enables the observation of intragranular orientation distribution. The experiment is performed using coarse-grained ferrite with a mean grain size of ~ 60 μm and an incident x-ray beam with a beam size of 20 μm × 20 μm. Grains averagely rotate approximately toward the <110> preferred orientation of body-centered cubic uniaxial tensile texture. Intragranular orientation distributions are spread as the tensile strain increases to 10.7 %. Furthermore, intragranular multidirectional rotations are observed in grains near the <100> and <111> corners in the inverse pole figure.

Crystal Plasticity Finite Element Analysis Based on Crystal Orientation Mapping with Three-Dimensional X-Ray Diffraction Microscopy

In other study we examined the plastic behavior for polycrystalline iron by three-dimensional x-ray diffraction (3DXRD) experiment. In this study we analyze the behavior by crystal plasticity finite element (CPFE) analysis, to confirm the validity of application to the deformation analysis of engineering steels of a couple of constitutive models. In the CPFE analysis, the observed microstructure and its crystal orientation are modeled with finite elements to take the inter-granular and intra-granular interactions into consideration. The plastic deformation state of the finite element model was computed by means of CPFE analysis based on the {110}<111> slip system in body centered cubic (BCC) crystal. The experiment showed that the most of the grains rotated toward the preferred orientation <110> along the tensile axis and that intra-granular orientation spread and multi-directionally rotated as the tensile strain increased. These results are reproduced by the CPFE analysis, in which the influence of interaction between neighboring grains is taken into consideration.

Scanning Three-Dimensional X-Ray Diffraction Microscopy with a High-Energy Microbeam at SPring-8

The grain-resolved residual stress (type II) in commercial-quality low carbon steel was observed using scanning three-dimensional X-ray diffraction (3DXRD) microscopy. In this method, grain orientations and lattice parameters are mapped using a monochromatic high-energy X-ray microbeam and 3DXRD-based polycrystalline indexing. Defining the reference lattice parameter a0 as the average value in the entire field of view, grain orientations and lattice parameters are converted into stress tensors, yielding a grain-resolved stress tensor map. The effectiveness of the scanning 3DXRD method was demonstrated by evaluating the residual stress in a cold-rolled low carbon steel sheet using a 50 keV microbeam at SPring-8. The area of the cross-sectional sample was 1×1 mm2, which was sufficiently larger than the grain size of about 20 μm. To produce a two-dimensional map of a circular region with a diameter of 160 μm at a pixel size of 1×1 μm2, the measurement time was about 1 h. From the stress tensor map, differences in residual stress of about 150–200 MPa between some neighboring grains were observed.

Maximization of Strengthening Effect of Microscopic Morphology in Duplex Steels

An inverse analysis method based on nonlinear finite element analysis is developed to find an optimized morphology of periodic microstructure for improving the macroscopic mechanical properties in duplex elastoplastic solids. Here a gradient-based computational optimization method and two types of homogenization methods are employed. In this study, the optimization problem is defined as the maximization of the sum of macroscopic external works for several macroscopic deformation modes, enabling us to obtain a high strength material. The morphologic strengthening effect is discussed through a comparison with experiments and classical theories.