Atsushi Moriai

Current Status of Engineering Materials Diffractometer at J-PARC

The Engineering Materials Diffractometer “TAKUMI” is designed and has been constructed at Materials & Life Science Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC) to conduct various kinds of studies on materials science and engineering and to promote industrial applications, related with strain measurements. The commissioning of TAKUMI has been started from September 2008, and several user programs have been done. In the commissioning, a resolution Δd/d at high resolution mode (with incident beam collimation) of less than 0.2% was achieved in a diffraction experiment using 2 mm diameter thick annealed piano wire. The d-range measured by TAKUMI with single pulse frame, i.e. standard operation, was confirmed to be 0.05 nm to 0.27 nm, showing that the optimum range for materials research is covered by this machine. TAKUMI adopted an event mode data recording method. It was found that the recording method is very useful to manipulate data as we like, for instance, detector range, time of flight binning width and time resolved data, even after the experiment has been finished.

Design of Engineering Diffractometer at J-PARC

An engineering diffractometer designed to solve many problems in materials science and engineering including investigations of stresses and crystallographic structures within engineering components is now being developed at J-PARC project. This instrument views a decoupled-poisoned liquid H2 moderator providing neutrons with good symmetrical diffraction profiles in the acceptable wavelength range. The primary flight path and the secondary flight path are 40 m and 2.0 m, respectively, for 90 degree scattering detector banks. A curved supermirror neutron guide will be installed to avoid intensity loss due to the long flight path and to reduce backgrounds from fast neutrons and gamma rays. Therefore, stress measurements with sufficient accuracies in many engineering studies are quite promising. The optimization of this instrument has been performed with a Monte Carlo simulation, and an appropriate resolution of less than 0.2 % in d/d has been confirmed. A prototyped radial collimator to define a gauge width of 1 mm has been designed and manufactured. From performance tests conducted at the neutron diffractometer for residual stress analysis RESA in JRR-3 of Japan Atomic Energy Agency, the normal distribution with a full width at half maximum of 1 mm was obtained in a good agreement with the simulation.

Application Software Development for the Engineering Materials Diffractometer, TAKUMI

The Engineering Materials Diffractometer Application Kit called EMAKi has been developed to control the Engineering Materials Diffractometer, TAKUMI, and treat data obtained by it. It is expected that TAKUMI will be widely used by not only academic users but also industrial users. We have designed EMAKi to be user-friendly interface for novice users by graphical user interface (GUI). In addition, adopting Python programming language for its development has enabled advanced users to control the diffractometer flexibly and treat the data easily. During instrumentation commissioning and running user programs, the software has demonstrated useful.

Aspire to Become TAKUMI - TAKUMI Present Status and Research Topics -

The construction of The Engineering Materials Diffractometer, TAKUMI of J-PARC has been finished on March 2009, and the commissioning has been started from September 2008 being parallel with the final stage of the construction. In the commissioning, after checking the validity and the stability of the detectors and the data acquisition system, powder diffraction data of an austenitic steel alloy with 10 mm diameter without beam collimation (high intensity mode) was measured, and the resolution Δd/d of 0.4% was confirmed, as designed. Further commissioning was done also with 2 mm diameter of annealed piano wire with combination of beam collimation (high resolution mode), and the resolution Δd/d of less than 0.2% was confirmed to be achieved. TAKUMI adopted an event mode data recording method. It was found that the recording method is very useful to manipulate data as we like, for instance, detector range, time of flight binning width and time resolved data, even the experiment has been finished.

A Measurement Method of Residual Stress in Quenched Steel by Neutron Diffraction

An experimental methodology was developed for identification of residual stresses inside quenched steel by neutron diffraction considering gradient distribution of martensite phases. A hybrid method is used by which the residual stress in the quenched steel was measured with neutron diffraction integrated with numerical simulation results of microstructure and phase distribution. A coupled finite element analysis based on metallo-thermo-mechanical theory was carried out to predict the microstructure due to phase transformation during quenching process. The non-strain lattice spacing and elastic modulus were measured with rotating specimen method in tensile test. Then, residual stresses in the (110) plane are measured using the cylinder specimens of quenched S45C and SCr420 steel by the neutron diffraction method. Finally the measured results of XRD, neutron diffraction as well as the calculated values were compared and discussed. Introduction Mechanical parts often undergo surface-hardening treatments, such as quenching, carburizing, nitriding, shot-peening, etc., which generate compressive residual stresses in the surface layers and modify their chemical composition, microstructure, and mechanical properties in the bulk material. In the manufacturing process incorporating temperature history and microstructure variation, complex thermal mechanical behavior will lead to macro and micro residual stresses and distortion of phase transformation of mechanical parts. At present, there is a great need for experimental methods to determine the residual stress inside the surface-treated materials. Many measurement methods of residual stress have been developed in industry technology such as X-ray diffraction, rapid drilling and so on [1, 2]. These techniques have only capability to measure residual stresses near the surface of machine parts. Neutron diffraction has been an attractive technique recently as the capability of measuring residual stresses inside of materials. The neutron ray has an absorption coefficient as small as 1/hundreds to 1/thousands compared with that of X-ray on the same grade of wavelength. By using high penetration power of the neutron ray, it allows us to measure the residual stress inside of bulk materials by non-destruction to a centimeter order [3-6]. To determine the residual stress, it is necessary to know the non-strain lattice spacing d0 and elastic constant of the material. Powder diffraction method is a general way of determining the parameter d0. However, after thermal chemical process such as quenching, phase transformations near surface modifies the microstructure of the material, the d0 and elastic constant vary in depth as a gradient distribution. For engineering materials especially those involving large plastic deformations or phase transformations often have preferred crystallographic orientation or non-homogenous distribution of phase or composition, the measured d0 by powder diffraction method could not coincide with the true original lattice spacing of the material with variable phase and texture. Though we can fabricate small samples with a homogeneous cross section representative of those gradually distributed layers, it is very difficult to get each material point or Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 139-146 doi:10.4028/www.scientific.net/KEM.270-273.139

Tensile Deformation Behaviors of Metastable Austenitic Stainless Steels Studied by Neutron Diffraction

Tensile deformation behaviors of three austenitic stainless steels, JIS-SUS310S, 304 and 301L, were studied by static tensile tests and in situ neutron diffraction. In the mechanical properties obtained by the static tensile tests, the 304 and 301L steels showed better balance of tensile strength and uniform elongation than the 310S one because of TRIP effect. The angular dispersion neutron diffractions with a wavelength of 0.16 or 0.182 nm were performed during stepwise tensile testing by using a neutron diffractometer for residual stress analysis (RESA) at the Japan Atomic Energy Agency. The lattice plane strain, stress-induced martensite volume fraction, dislocation density and so on were estimated by the profile analysis as a function of applied stress. The change in lattice plane spacing for austenite indicated four deformation stages. In the comparison of lattice plane strain among the tested steels, a phase stress caused by the stress-induced martensite seems to overlap the intergranular stress of austenite phase. Judging from the results of profile analysis, the strain partitioning of austenite phase in metastable austenitic steels became larger with increasing of the volume fraction of stress-induced martensite during tensile deformation.

Neutron Diffraction Profile Analysis to Determine Dislocation Density and Grain Size for Drawn Steel Wires

Dislocation density and crystallite size of steel wires with various carbon concentrations and drawing strains were determined by profile analyses for neutron diffraction profiles. The density is found to increase while the size decreases with increasing of carbon concentration and/or drawing strain. Both of the Bailey-Hirsch relation and Hall-Petch relation hold for the present results to suggest that these two are not independent., i.e., indicating an identical strengthening mechanism from a different point of view.

Development of New Stress Measurement Method Using Neutron Diffraction

In this study, we proposed the high-versatility stress measurement method using neutron diffraction which can determine the residual stress states by measuring the lattice strains in two or three orthogonal directions even if the measured diffraction families were different in all three directions. In addition, we also proposed the stress measurement method without using the stress-free lattice spacing d0 which was measured using the powder sample or annealed sample. To verify this method, the residual stress distributions in a shrink-fit ring and plug specimen of aluminum alloy A7075 with texture were measured. The profile of the measured stress distributions almost agreed with the simulated stress distributions in the assumption of the plane stress condition. Our method which can determine the tri-axial stress states using observed lattice strains in two orthogonal directions was secondly applied to evaluate the stress states of A7075, high tensile strength steel HT1000, and Ni-base alloy NCF600 loaded in-situ. Measured stresses almost agreed with theoretical value with 10 MPa to 60 MPa error. On the other hand, the residual stress states of NCF600 were measured under the uni-axial loading condition by the stress measurement method without using the measured d0. Estimated lattice constant a was almost agreed with the lattice constant of its annealed sample, and changes in stress states evaluated using the proposed method coincided with the theoretical value.

Measurement of residual stress on a unidirectional solidified Al2O3/YAG eutectic composite using synchrotron and neutron diffraction

The residual stress in the pure YAG phase was measured on the surface of an Al2O3–Y3Al5O12 (YAG) eutectic composite (Al2O3/YAG–MGC) using low energy synchrotron X-rays. The residual stress in the plane stress condition was significantly different between top and side surfaces of the specimen. In addition, the internal residual stress of the melt growth composite (MGC) was also measured using a neutron diffraction. The residual stress in the YAG phase rose from compression in the solidification direction to tension in the perpendicular direction. The residual stress in the Al2O3 phase was anisotropic compression and there was no tension in any direction. This anisotropic residual stress could be explained by the crystallographic anisotropy of thermal expansion in the Al2O3 phase. However, both phase stresses were not balanced, so that it is expected that there would be a stress distribution in the MGC.

Dissolution of Cementite Plates by Drawing, Re-Precipitation with Annealing and Corresponding Changes in Tensile Behavior in a Pearlite Steel

The microstructural change with drawing and subsequent annealing for a patented pearlite steel was investigated by means of neutron diffraction. The dissolution of cementite plates with drawing and re-precipitation of spherical cementite particles with annealing after sever drawing were observed. In situ neutron diffraction during tensile loading was performed and it is revealed that the strengthening mechanism of the specimen without cementite differs from that for a ferrite-cementite steel where the load transfer is a main mechanism. The possible strengthening mechanism for the heavily drawn specimen is proposed.