Yusuke Onuki

Rapid measurement scheme for texture in cubic metallic materials using time‐of‐flight neutron diffraction at iMATERIA

A rapid texture measurement system has been developed on the time-of-flight neutron diffractometer iMATERIA (beamline BL20, MLF/J-PARC, Japan). Quantitative Rietveld texture analysis with a neutron beam exposure of several minutes without sample rotation was investigated using a duplex stainless steel, and the minimum number of diffraction spectra required for the analysis was determined experimentally. The rapid measurement scheme employs 132 spectra, and by this scheme the quantitative determination of volume fractions of texture components in ferrite and austenite cubic phases in a duplex stainless steel can be made in a short time. This quantitative and rapid measurement scheme is based on the salient features of iMATERIA as a powder diffractometer, i.e. a fairly high resolution in d spacing and numerous detectors covering a wide range of scattering angle.

Rapid Measurement of Texture of Metals by Time-of-Flight Neutron Diffraction at iMATERIA and its Applications

The authors have developed the texture measurement system at iMATERIA, which is the neutron diffractometers built in Materials and Life Science Experimental Facility (MLF) at J-PARC, Japan. The high flux of the incident beam and Time-Of-Flight method enabled the complete texture measurement within several minutes in case of steels. Since the neutron beam can transmit most of the materials, the measured texture represents the state of whole exposed volume. The multi-histogram analysis also enables to determine phase fractions in a multiphase material as well as the texture of each phase.

Angular dependence of hysteresis scaling and coercivity for anisotropically distributed ferromagnetic nanoparticles in paramagnetic matrix

We have investigated anisotropy behavior of coercivity and scaling law for nano-scale ferromagnetic phases embedded in a paramagnetic matrix of an austenitic stainless steel. Small ferromagnetic martensites are induced by uniaxial tensile deformation. A scaling-law relationship between the hysteresis loss and remanence, with a power law exponent of 1.47 ± 0.09, has been found, irrespective of stress, martensite volume fraction, and angle between the magnetization and tensile directions. A coefficient of the scaling law decreases with volume fraction, whereas it increases with increasing the angle and maximizes when the magnetization direction is perpendicular to that of the tensile. This trend is opposite to that of coercivity. The behavior of the coefficient and the coercivity was discussed from the viewpoint of morphology of martensite particles.

Evaluation of Tri-Axial Magnetostriction in Cube-Oriented Fe-Ga Single Crystal by Using X-Ray Diffraction Method

We carried out in situ tri-axial magnetostriction analysis for cube-oriented Fe-18%Ga single crystal by X-ray diffraction measurement under magnetic field. Periodic change in tri-axial magnetostriction with applied magnetic field direction was clearly observed. However, those values in [100] and [010] directions were not equivalent. Theoretical calculation of magnetostriction considering domain structure revealed this is caused by the non-equivalent volume fraction of initial magnetic domains.

Characterization of Microscopic Stresses in a Polycrystalline Fe-Ga Alloy with Large Elastic Anisotropy

Fe-Ga alloys show large magnetostriction, which strongly depends on crystal orientation. This phenomenon is associated to some degree with large elastic anisotropy. In this study, white X-ray diffraction with micro-beam synchrotron radiation was used to evaluate the microscopic stresses evolved in a polycrystalline Fe-Ga alloy under tensile loading. In the analysis, the large elastic anisotropy of the Fe-Ga alloy was focused. The stress distribution in the alloy microstructure under tensile loading was estimated using a finite element method (FEM) simulation that considered the dependence of the elasticity on the crystal orientation. The crystal orientation of grains in the polycrystalline Fe-Ga alloy was measured using electron backscatter diffraction. The FEM simulation showed that the stress distribution in the microstructure depended on the crystal orientation. The X-ray diffraction stress analysis indicated that under tensile loading, the stresses in the alloy depended on the crystal orientation. This finding is similar to the results obtained from the FEM simulation, although the absolute values of the stresses may have reflected the effects of heterogeneous deformation on the stress distribution.

Current status of iMATERIA and recent result of LIB research

Ibaraki prefecture, local government of Japan’s area where the J-PARC sites are located, has decided to build a versatile neutron diffractometer (IBARAKI Materials Design Diffractometer, iMATERIA [1]) to promote industrial applications for the neutron beam in J-PARC. iMATERIA is planned to be a high-throughput diffractometer that could be used by materials engineers and scientists in their materials development work like the chemical analytical instruments. It covers the d in range 0.18 < d (Å) < 5 with Δd/d = 0.16 % at high resolution bank, and 5 < d (Å) < 800 with the resolution changing gradually at three detector banks of 90 degree, low angle and small angle. So, this diffractometer covers very wide d-range (0.18 < d (Å) < 800). All of the four banks, include small-angle bank are user operational. It takes about 5 minutes (DF mode) to obtain a ‘Rietveldquality’ data in the high-resolution bank at 500 kW beam power for about 1 g of standard oxide samples. The automatic sample changer is the most important sample environment for high-throughput experiments. Our automatic sample changer [2] consists of sample storage, elevating system of two lines, two sets of pre-vacuum chambers and a sample sorting system. We can handle more than 600 samples continuously at room temperature without breaking the vacuum of the sample chamber. The main aim for this instrument is open for industrial users. Ibaraki prefecture is preparing many application systems, such as monthly apply system (a general proposal), mail in service, etc. for industrial users. Therefore, about 50 % of industrial users of MLF is iMATERIA users. Neutron diffraction technique can be determined the position of Li and O, precisely. The LIB materials are one of suitable materials for neutron diffraction study. Therefore, many experiments has been carried out by not only academic users but also industrial users. In this presentation, we will introduce some example of study for LIB materials.

Stress and Strain Analysis in an Fe-Ga Alloy Single Crystal

We carried out in situ x-ray diffraction measurements of magnetostriction in an Fe-18at%Ga alloy single crystal under magnetic fields. The sample studied here was a Goss-oriented square plate (dimensions: 10 mm × 10 mm × 1 mm height) cutting from as-grown single crystal ingot produced by the Czochralski method. In-plain magnetic fields were applied with various directions in this study. The influence of magnetic field direction on the stress/strain states was precisely analyzed by using our original x-ray single crystal stress/strain measurement method. As a result, applied field angle dependence of tri-axial magnetostriction states was successfully obtained. Thereby, we found that the singular anisotropic mechanical properties of this material play an important role for its magnetostriction properties.

Textures and Microstructures Formed in WE43 and AZ31 Magnesium Alloys during High Speed Rolling and Their Formation Mechanisms

High speed rolling is recognized as the process that can produce sheets of magnesium alloys having RD-split basal texture without or with minimum preheating. However, the mechanism of the texture formation during high speed rolling has not been fully clarified yet. In this study, conventional AZ31 and a rare earth - yttrium added alloy, WE43 were rolled with high rolling speed. The specimens having different textures were prepared by changing the cutting geometry to initially textured sheets. It is seen that the crack, microstructure and texture formations are strongly influenced by the initial textures in AZ31. These features are strongly related to the extension twinning, {10-12} . In the case of WE43, cracks are formed more often than in AZ31, despite of the weak initial textures. It is proposed that the activities of the contraction and double twinning systems give more chance of stress concentration, resulting in the narrow shear banding and subsequent cracking. In addition to the experimental analysis, results of the numerical simulation using VPSC model are also used to discuss the texture formation mechanism.

Depletion of Manganese in the Surface Layers of Fe-Mn-Si Shape Memory Alloys by Annealing

X-ray diffraction (XRD) and electron microprobe microanalysis (EPMA) were used for characterizing the structure and composition of surface layers formed on austenitic Fe-Mn-Si shape memory alloys under vacuum. The XRD results demonstrated that during annealing, face centered cubic austenite is transformed to hexagonal close packed martensite on the alloy surface. The EMPA results revealed that manganese in the surface layer was depleted during annealing. Further, this analysis determined that the thickness of the surface layer of the alloy annealed at 1173 K for 1 h was approximately 20 μm and that value is consistent with the depth detected by XRD. The compositional changes of the surface layers such as manganese depletion by annealing were discussed based on the ternary Fe-Mn-Si phase diagram. Although the formation of body centered cubic ferrite is detrimental to shape memory alloys, the amount of manganese was also observed to change during processing and strongly influence the stability of the shape memory alloys.