Effect of ultrafine grain refinement on hydrogen embrittlement of metastable austenitic stainless steel

Micro-tensile tests were performed on high-pressure-torsion-processed specimens of type 304 steel with grain sizes in the range of 0.1–0.5 μm to clarify the effect of ultrafine grain refinement on the hydrogen embrittlement (HE) of metastable austenitic steel. The ultrafine-grained (UFG) specimens with average grain sizes < ～0.4 μm exhibited a limited uniform elongation followed by a steady-stress regime in the stress–strain curves, which was attributed to a martensitic transformation. A high yield stress and a moderate elongation to failure were attained for the UFG specimens with an average grain size of ～0.5 μm in the uncharged state. Hall–Petch relationships well hold between the yield stress and the average grain size for each uncharged and hydrogen-charged specimen. Hydrogen charging increased the friction stress by 40% but did not change the Hall–Petch coefficient. Hydrogen-induced ductility loss was mitigated by ultrafine grain refinement. Ductility loss due to hydrogen charging manifested in the local deformation after a martensitic transformation. This indicates that hydrogen does not significantly affect the martensitic transformation, but shortens the subsequent local deformation process.     

Classification of ground faults in distribution lines according to phase-plane trajectories of waveforms

Recently, a greater demand for stable supply of electric power has resulted from a higher standard of living. It becomes important that the causes and locations of ground faults in distribution lines be found early and defects be repaired as soon as possible. Therefore, a unit for recording the waveform I₀ of ground fault's current and the waveform V₀ of its voltage is installed in distribution substations. The establishment of a technology to distinguish fault causes automatically is being hastened. This paper presents a new classification method for ground fault waveforms, based on phase-plane trajectories for the current or voltage and their differential values. Examinations of ground fault waveforms based on real data show that the waveform of current I₀ is more suitable than that of voltage V₀ for the classification of waveforms at ground faults and that the trajectory of each of the three types of waveforms, such as sine waves, trapezoidal waves, and spikes, has all of the characteristics in its figure. It is also found from the distribution of 167 sampling points on the phase plane that any waveforms at a real ground fault may be classified into three characteristic point distributions, which gives the possibility of easy display for the classification of ground fault causes. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 8–16, 1998     

Microstructural characteristics of tungsten-base nanocomposites produced from micropowders by high-pressure torsion

Micropowder mixtures of W–50% Al, W–50% Ti and W–50% Ni were subjected to severe plastic deformation at 573 K using high-pressure torsion (HPT). The powder mixtures were consolidated and nanocomposites of W/Ti, W/Ti and W/Ni, with average grain sizes as small as ～9, ～15 and ～12 nm, respectively, were formed by imposing large shear strains. The nanocomposites exhibited Vickers microhardness as high as ～900 Hv, a level that has rarely been reported for metal–matrix composites. X-ray diffraction analyses together with high-resolution transmission electron microscopy showed that in addition to grain refinement, an increase in the fraction of grain boundaries up to 20%, the dissolution of elements in each other up to ～15 mol.%, an increase in the lattice strain up to 0.6%, and an increase in density of edge dislocations up to 10¹⁶ m^?2 occurred by HPT. The current study introduces the HPT process as an effective route for the production of ultrahigh-strength W-base nanocomposites, fabrication of which is not generally easy when processing at high temperatures because of interfacial reaction and formation of brittle intermetallics.     

Effect of High-Pressure Torsion Processing and Annealing on Hydrogen Embrittlement of Type 304 Metastable Austenitic Stainless Steel

The effect of high-pressure torsion (HPT) and annealing on hydrogen embrittlement (HE) of a type 304 stainless steel was studied by metallographic characterization and tensile test after hydrogen gas charging. A volume fraction of ~78 pct of the austenite transformed to α′ martensite by the HPT processing at an equivalent strain of ~30. Annealing the HPT-processed specimen at a temperature of 873 K (600 °C) for 0.5 hours decreased the α′ martensite to ~31 pct with the average grain size reduced to ~0.43 μm through the reverse austenitic transformation. Hydrogen charge into the HPT-processed and the HPT+annealed specimens in the hydrogen content of ~10 to 20 ppm led to no severe HE but appeared in the solution-treated specimen. Especially the 873 K (600 °C) annealed specimen had the ~1.4 GPa tensile strength and the ~50 pct reduction of area (RA) despite the hydrogenation.     

High-pressure torsion of TiFe intermetallics for activation of hydrogen storage at room temperature with heterogeneous nanostructure

TiFe is a potential candidate for the stationary hydrogen storage systems, but it requires initial activation to absorb hydrogen. This study shows that TiFe processed by high-pressure torsion (HPT) absorbs and desorbs 1.7 wt.% hydrogen at room temperature without activation. The absorption pressure decreases from 2 MPa in the first hydrogenation cycle to 0.7 MPa in the latter cycles. The HPT-processed TiFe exhibits heterogeneous microstructures composed of nanograins, coarse-grains, amorphous-like phases and disordered phases with a high hardness of ∼1050 Hv.     

Evaluating the influence of pressure and torsional strain on processing by high-pressure torsion

Tests were conducted on an Al-6061 alloy to evaluate the separate effects of the applied pressure and the torsional straining in processing by high-pressure torsion (HPT). The values of the Vickers microhardness were measured after processing and plotted both linearly across the diameters of the disks and as three-dimensional representations. The measurements show that the applied pressure increases the hardness in the absence of torsional straining. In the presence of a pressure and torsional straining, the hardness values are high at the edges of the disk but lower in the central region. There is a gradual evolution toward a hardness homogeneity with increasing numbers of HPT revolutions. The hardness values at the edges of the disks are reasonably independent of the applied pressure but the extent of this region of high hardness depends upon both the applied pressure and the numbers of turns in the HPT processing.     

Tiliroside, a glycosidic flavonoid, inhibits carbohydrate digestion and glucose absorption in the gastrointestinal tract

Scope Recent studies have reported that tiliroside, a glycosidic flavonoid, possesses anti‐diabetic activities. In the present study, we investigated the effects of tiliroside on carbohydrate digestion and absorption in the gastrointestinal tract. Methods and results This study showed that tiliroside inhibits pancreatic α‐amylase (IC₅₀ = 0.28 mM) in vitro. Tiliroside was found as a noncompetitive inhibitor of α‐amylase with K_i values of 84.2 μM. In male ICR mice, the increase in postprandial plasma glucose levels was significantly suppressed in the tiliroside‐administered group. Tiliroside treatment also suppressed hyperinsulinemia after starch administration. Tiliroside administration inhibited the increase of plasma glucose levels in an oral glucose tolerance test, but not in an intraperitoneal glucose tolerance test. In human intestinal Caco‐2 cells, the addition of tiliroside caused a significant dose‐dependent inhibition of glucose uptake. The inhibitory effects of both sodium‐dependent glucose transporter 1 (SGLT1) and glucose transporter 2 (GLUT2) inhibitors (phlorizin and phloretin, respectively) on glucose uptake were significantly inhibited in the presence of tiliroside, suggesting that tiliroside inhibited glucose uptake mediated by both SGLT1 and GLUT2. Conclusion These findings indicate that the anti‐diabetic effects of tiliroside are at least partially mediated through inhibitory effects on carbohydrate digestion and glucose uptake in the gastrointestinal tract.     

Analysis of metribuzin and its metabolites in livestock products and seafoods by liquid chromatography-tandem mass spectrometry

A method for simultaneous determination of metribuzin (MET) and three metribuzin metabolites in livestock products and seafoods by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. MET and its metabolites were extracted from a sample with acetonitrile, followed by InertSepC18 and BondElut SAX cartridge cleanup. The LC separation was performed on a C18 column using 0.01 mol/L ammonium formate-acetonitrile-methanol (70 :21 : 9) as the mobile phase and MS detection with both positive and negative ion electrospray ionization. The mean recoveries from 10 livestock products and seafoods were generally >60%, and the relative standard deviations were <20%     

Activation of TiFe for hydrogen storage by plastic deformation using groove rolling and high-pressure torsion: Similarities and differences

Intermetallics of TiFe were processed using three different routes: annealing, plastic deformation using groove rolling and severe plastic deformation using high-pressure torsion (HPT). Hydrogen absorption was less than 0.2 wt.% in the coarse-grained annealed sample because of difficult activation. The groove-rolled sample, with subgrain structure and high density of dislocations and cracks, absorbed 0.3, 1.0, 1.4 and 1.7 wt.% of hydrogen in the first, second, third and fourth hydrogenation cycles, respectively. The HPT-processed sample, containing nanograins, absorbed 1.7–2 wt.% of hydrogen in any hydrogenation cycles. Both samples activated by groove rolling and HPT were not deactivated by long time exposure to the air. No surface segregation was detected after groove rolling, while the HPT-processed sample exhibited surface segregation. The current study confirmed the significance of plastic deformation and formation of grain boundaries and cracks on activation for hydrogen storage.     

Enhancement of the crystalline quality of reactively sputtered yttria-stabilized zirconia by oxidation of the metallic target surface

Yttria-stabilized zirconia (YSZ) thin films were fabricated on glass substrates by direct current magnetron reactive sputtering. We found out that the crystalline quality of the YSZ film was improved by an oxidation process of the metallic target surface prior to the sputtering deposition process. It is speculated that, at the initial stage of the sputtering, the sputtered particles from the oxidized target surface form a layer with higher degree of crystallization on the substrate, compared with those particles from the metallic target surface. This crystallized layer can enhance the crystallization of the film deposited subsequently. Other sputtering conditions such as sputtering pressure, oxygen flow rate, substrate temperature, and Y₂O₃ content in the film were investigated, for optimization of the crystalline quality of the deposited YSZ film.