Search

In the V-bending of sheet metals using a pair of plastic punch and die manufactured by a 3D printer, the effects of two different dimensions designed with the same tool geometry on the deformation behaviors of the punch, die, and sheet were evaluated. The deformation behavior and strain distribution of the punch, die, and sheet were analyzed using a digital image correlation method. Sheets from pure aluminum to ultra-high-strength steel were bent using the two tools with different spans; one was designed on the assumption of tool steel material, and the other was designed on the assumption of plastic material. In both tools, the large compressive strain appeared around the center of the punch tip and on the corners of the die. The tools with a long span for the plastic material gave a lower bending force and small deformation of the plastic tools. The angle difference between a bent sheet at the bottom dead center and a tool was smaller for the tools with the long span, although the springback in the bent sheet appeared. It was found that the design method on the assumption of the plastic material is effective for the V-bending plastic tools. [ABSTRACT FROM AUTHOR]

Understanding the deformation mechanism of cementite such as on a slip plane is important with regard to revealing and improving the mechanical property of steels. However, the deformation behavior of cementite has not been well investigated because of the difficulty of sample preparation given the single phase structure of cementite. In this study, by fabricating bulk single phase cementite samples using the method developed by the authors, the deformation texture formed by uniaxial compression was investigated using both electron back scatter diffraction and neutron diffraction. The fabricated sample had a random texture before the compression. After applying a compressive strain of 0.5 at 833 K, (010) fiber texture was formed along the compressive axis. It has been suggested from this trend that the primary slip plane of cementite is (010). [ABSTRACT FROM AUTHOR]

We revealed that hydrogen (H) in pure Fe promotes grain refinement during plastic deformation, which is caused by the increase in dislocation density by the shielding effect and the presence of vacancy-H clusters. The promotion effect of H was dependent on the temperature and the strain rate, which is considered to result from a change in the number density of vacancy-H clusters and the magnitude of shielding effect by H. [ABSTRACT FROM AUTHOR]

As a new method for evaluating single crystals and oligocrystals, pulsed neutron Bragg-dip transmission analysis/imaging method is being developed. In this study, a single Bragg-dip profile-fitting analysis method was newly developed, and applied for analyzing detailed inner information in a crystalline grain position-dependently. In the method, the spectrum profile of a single Bragg-dip is analyzed at each position over a grain. As a result, it is expected that changes in crystal orientation, mosaic spread angle and thickness of a perfect crystal can be evaluated from the wavelength, the width and the integrated intensity of the Bragg-dip, respectively. For confirming this effectiveness, the method was applied to experimental data of position-dependent Bragg-dip transmission spectra of a Si-steel plate consisting of oligocrystals. As a result, inner information of multiple crystalline grains could be visualized and evaluated. The small change in crystal orientation in a grain, about 0.4°, could be observed by imaging the Bragg-dip wavelengths. By imaging the Bragg-dip widths, both another grain and mosaic block in a grain were detected. Furthermore, imaging results of the integrated intensities of Bragg-dips were consistent with the results of Bragg-dip width imaging. These small crystallographic changes have not been observed and visualized by previous Bragg-dip analysis methods. [ABSTRACT FROM AUTHOR]

By employing mechanical rejuvenation, we demonstrated that the viscoelastic deformation become visible in macroscopic tensile test. The clear tensile strain rate dependence of yield stress was observed only in the rejuvenated sample, showing that the macroscopic elongation is governed by the thermally activated process. Activation volumes estimated from the mechanical responses during the macroscopic tensile test and microscopic nanoindentation test showed consistent values. The rejuvenated sample having tensile ductility showed larger STZ volume comparing with the relaxed samples. These results indicate that the fraction and connectivity of liquid-like regions in BMG can be controlled by appropriate use of mechanical rejuvenation. [ABSTRACT FROM AUTHOR]

A new mapping procedure for polycrystals using neutron Bragg-dip transmission is presented. This is expected to be useful as a new materials characterization tool which can simultaneously map the crystallographic direction of grains parallel to the incident beam. The method potentially has a higher spatial resolution than neutron diffraction imaging. As a demonstration, a Bragg-dip neutron transmission experiment was conducted at J-PARC on beamline MLF BL10 NOBORU. A large-grained Si-steel plate was used. Since this specimen included multiple grains along the neutron beam transmission path, it was a challenging task for existing methods to analyse the direction of the crystal lattice of each grain. A new data-analysis method for Bragg-dip transmission measurements was developed based on database matching. As a result, the number of grains and their crystallographic direction along the neutron transmission path have been determined. [ABSTRACT FROM AUTHOR]

Pulsed neutron sources enable the simultaneous measurement of small-angle neutron scattering (SANS) and Bragg edge transmission. This simultaneous measurement is useful for microstructural characterization in steel. Since most steels are ferromagnetic, magnetic scattering contributions should be considered in both SANS and Bragg edge transmission analyses. An expression for the magnetic scattering contribution to Bragg edge transmission analysis has been derived. The analysis using this expression was applied to Cu steel. The ferrite crystallite size estimated from this Bragg edge transmission analysis with the magnetic scattering contribution was larger than that estimated using conventional expressions. This result indicates that magnetic scattering has to be taken into account for quantitative Bragg edge transmission analysis. In the SANS analysis, the ratio of magnetic to nuclear scattering contributions revealed that the precipitates consist of body-centered cubic Cu0.7Fe0.3 and pure Cu, which probably has 9R structure including elastic strain and vacancies. These results show that effective use of the magnetic scattering contribution allows detailed analyses of steel microstructure. [ABSTRACT FROM AUTHOR]

High-pressure torsion (HPT) process is the only method which can obtain a 100 vol% of high-pressure ω-phase sample at ambient condition in pure Ti. In this paper, the mechanism of ω-phase stabilization by the HPT process is discussed on the basis of the reverse phase transformation kinetics of ω-phase in pure titanium formed by the HPT process and then measured using electrical resistivity and calorimetric experiments. The single ω-phase sample showed much higher electrical resistivity of 0.95 μΩ m at 350 K compared with that of the single α-phase sample (0.62 μΩ m). The ω-to-α reverse transformation behavior was clearly observed through both electrical resistivity and calorimetric measurements. The activation energy for ω-to-α reverse transformation, derived from the kinetics, showed a value close to that for the self-diffusion of Ti. The ω-phase obtained after the HPT process has an equiaxed submicron microstructure. The microstructure of reverse transformed α-phase showed no evidence of the occurrence of martensitic transformation. These results suggest that the mechanism governing ω-to-α phase transformation changed from diffusionless martensitic transformation to diffusion-controlled transformation after severe plastic deformation using the HPT process. [ABSTRACT FROM AUTHOR]