All issues
Volume 79, Issue 5
Displaying 1-8 of 8 articles from this issue
- |<
- <
- 1
- >
- >|
Overview
-
Yasukazu Murakami2015 Volume 79 Issue 5 Pages 233-242
Published: 2015
Released on J-STAGE: May 02, 2015
JOURNAL FREE ACCESSThis overview article reports on the electron holography studies about the magnetism of interface regions in metallic alloys. Recent progress of electron holography enabled pin-point analysis of the magnetic flux density from nanometer-scale interface regions; e.g., antiphase boundaries (APBs) produced in ordered alloys, and the amorphous grain-boundary phase in sintered magnets. The observations have demonstrated magnetism that is amplified by structural disorder within APBs produced in Fe70Al30, which appears in contrast to the traditional understating. With respect to the ultrathin grain-boundary phase in a Nd-Fe-B magnet, the electron holography study determined the magnetic flux density at 1.0 T (±0.1 T). The result provided useful information for deeper understanding of the coercivity mechanism in the Nd-Fe-B sintered magnet.
View full abstractDownload PDF (7694K)
Regular Article
-
Hiroaki Nakano, Shingo Arakawa, Satoshi Oue, Shigeo Kobayashi2015 Volume 79 Issue 5 Pages 243-248
Published: 2015
Released on J-STAGE: May 02, 2015
JOURNAL FREE ACCESSElectrodeposition behavior of Zn-Fe alloys was investigated at current densities of 10-500 A•m−2 and a charge of 5×104 C•m−2 in an unagitated zincate solution containing triethanolamine, which forms a stable complex with Fe2+ ions at 308 K. The content of Fe in deposit changed significantly depending on the current density. At lower current densities than 20 A•m−2, the content of Fe was approximately 90 mass%, that is, the Zn-Fe alloy exhibited normal codeposition, wherein electrochemically more noble Fe deposited preferentially, while at higher current densities than 100 A•m−2, it exhibited anomalous codeposition, wherein less noble Zn deposited preferentially. The current density, at which the content of Fe in deposit changed significantly, corresponded to the one, at which the cathode potential in total polarization curve abruptly shifted to the less noble region than the equilibrium potential for Zn deposition. Iron deposition and H2 evolution were significantly suppressed in the region of anomalous codeposition at higher current densities, showing the formation of an inhibitor for deposition, which results from Zn2+ ions in the cathode layer. The current efficiency for alloy deposition was not close to zero even in the region of normal codeposition, and the content of Fe in the region of anomalous codeposition was close to the composition reference line, which shows the different deposition behavior from the sulfate solutions. In the region of normal codeposition at lower current densities, the underpotential deposition of Zn occurred with Fe. TEM analysis revealed that Zn-Fe alloys deposited at lower current densities were composed of a stable intermetallic compound of Fe5Zn21. The activity coefficient of Zn in the deposit appears to decrease remarkably because of the formation of a stable Fe5Zn21.
View full abstractDownload PDF (3360K) -
Yoichi Tobiyama, Masahiko Tada, Sakae Fujita, Masao Takeyama2015 Volume 79 Issue 5 Pages 249-256
Published: 2015
Released on J-STAGE: May 02, 2015
JOURNAL FREE ACCESSThe effect of accelerated oxidation prior to annealing on the galvanizability of 1.4 mass%Si-bearing steel was investigated. Oxidation process accelerated by ammonium sulfate improved the galvanizability of the steel under the oxidation condition where the steel without ammonium sulfate showed poor galvanizability: iron oxides containing more than 0.42 g•m−2 oxygen were found to improve the galvanizability. Iron oxides produced during accelerated oxidation prior to annealing improved the galvanizability because a continuous pure reduced iron layer formed on the surface of the steel was free of the surface segregation of silicon and manganese during annealing. This is because silicon and manganese were internally oxidized beneath the reduced iron layer as silica and complex oxides of silicon and manganese by oxygen in iron oxides. It is proposed that the amount of iron oxides required for the improvement of galvanizability is that of iron oxides which can supply that of oxygen required for capturing silicon and manganese as the internal oxides during annealing.
View full abstractDownload PDF (6245K) -
Kouji Sakaki, Hyunjeong Kim, Hirotoshi Enoki, Minako Hosono, Shin-ichi ...2015 Volume 79 Issue 5 Pages 257-264
Published: 2015
Released on J-STAGE: May 02, 2015
JOURNAL FREE ACCESSThe effect of substitution elements on hysteresis and flatness of the equilibrium pressure plateau in ZrxTi1−xMn0.8V0.2Ni1.0 was investigated. For a metal hydride (MH) actuator in rehabilitation devices, the suitable hydrogen storage alloys were developed. The equilibrium pressure decreased with increasing Zr/Ti ratio. By Al substitution, the hysteresis factor became smaller, while Fe and Cu substitution did not change the hydrogenation properties. It was confirmed that ferrovanadium is available in these alloys to reduce not only the material cost but also the hysteresis factor leading to better properties for the MH actuator. The developed Zr0.5Ti0.5Mn0.8V0.2Ni0.9Al0.1 showed no significant reduction of hydrogen capacity and no significant change in the shape of the pressure-composition (P-C) isotherms even after 1000 cycles.
View full abstractDownload PDF (5678K) -
Yasuhiro Tanaka, Yuichi Ikeshita2015 Volume 79 Issue 5 Pages 265-272
Published: 2015
Released on J-STAGE: May 02, 2015
JOURNAL FREE ACCESSDental casting Au-Ag-Pd alloys exhibit a singular phenomenon that they get hardened after softening solution treatment when the temperature is higher than 800℃. The purpose of this study is to clarify the hardening mechanism in terms of the concentration distribution of the constituent elements. Two types of commercial dental alloys with different Ag/Cu ratios were subjected. Samples were solution-treated using a vertical furnace and dropped into ice water to quench the specimens. During the solution treatment, the specimens were kept in a vacuumed silica tube or in Ar-gas flow. The cooling rate was slightly different between both situations and the cooling rate in the former was slightly slower than in the latter one. The samples stayed soft after solution treatment below 750℃. At 800℃, only the vacuumed samples got hardened. Elemental maps using SEM-EDX were not able to find distinguished difference in the microstructure between the softened and hardened specimens, even the difference based on the composition of the commercial dental alloys was detected. Higher-Ag-containing alloy revealed two-phase structure in which one is α phase of fcc matrix and the other is rod-like β phase of B2 type ordered CuPd. Higher-Cu-containing alloy did three-phase structure in which the fcc matrix was separated into a fine eutectic structure composed of Ag-rich α1 and Cu-rich α2 phases. Coherent precipitation of β′ phase with L10 type ordered structure was detected in the α or α1 fcc matrix from the hardened specimens. STEM-EDX results revealed rapid evolution of concentration fluctuation between Ag and Cu that occurred during quenching. The rapid evolution of the concentration fluctuation was considered to spontaneously proceed from spinodal decomposition between Ag and Cu in the α or α1 fcc matrix. The spinodal decomposition caused the concentration modulation, and the Cu-concentrated part immediately formed the coherent β′ precipitation by coupling with Pd.
View full abstractDownload PDF (13280K) -
Ryutaro Akiyoshi, Ken-ichi Ikeda, Satoshi Hata, Hideharu Nakashima, Ta ...2015 Volume 79 Issue 5 Pages 273-279
Published: 2015
Released on J-STAGE: May 02, 2015
JOURNAL FREE ACCESSTensile tests and microstructural observations were carried out to investigate the influence of aging products on tensile deformation behavior of Al-0.62 mass%Mg-0.32 mass%Si alloy. Solution-treated alloys were aged to form needle-like β″ precipitates or Mg-Si clusters. The aged alloy with β″ precipitates showed higher yield stress than that with Mg-Si clusters. Transmission electron microscopy observations revealed that the β″ precipitates pinned dislocations. It was suggested that the strengthening types of the alloy with β″ precipitates were both Orowan and cutting mechanism, by estimating the Orowan stress and considering crystal structure of β″ precipitates. In contrast, the aged alloys with Mg-Si clusters showed excellent performance of uniform elongation due to large work hardening compared to those of the alloy with β″ precipitates. Dislocations in the alloy with Mg-Si clusters were wavy in morphology. The yield stress of the alloy with Mg-Si clusters was higher than that of the solution-treated alloy and much lower than the estimated Orowan stress. This result indicated that the cutting mechanism was the main strengthening type of the aged alloy with Mg-Si clusters, and this strengthening mechanism gave a good balance of strength and elongation.
View full abstractDownload PDF (4537K) -
Yasuhiro Nagatomo, Hisao Esaka, Kei Shinozuka2015 Volume 79 Issue 5 Pages 280-286
Published: 2015
Released on J-STAGE: May 02, 2015
JOURNAL FREE ACCESSThe volume fraction of primary β-Sn (fβ-Sn) is larger than the equilibrium value when hypoeutectic Sn-X alloys solidify in a crucible. However, fβ-Sn decreases with time when the alloy sample is held in the mushy state after observing recalescence. This study investigated the effect of the holding temperature on the change in fβ-Sn, using Sn-25.7 mass% Pb alloy. The volume fraction of primary β-Sn was characterized as a function of holding temperature and time. Primary β-Sn formed after recalescence (primary I) ripened during isothermal holding, and its volume fraction decreased. In addition, dendritic primary β-Sn (primary II) formed during cooling after isothermal holding. The volume fraction of primary I decreased rapidly as the holding temperature increased. Reaction rate analysis revealed that the rate-determining step may be diffusion in the solid. The grains of primary I increased in size in accordance with the Ostwald ripening effect even though the volume fraction decreased, and the grains floated upward in the crucible. Since a large quantity of primary II solidified, the total volume fraction of β-Sn was larger than the equilibrium value.
View full abstractDownload PDF (5943K) -
Hiroshi Masuda, Satoshi Taniguchi, Eiichi Sato, Yoshito Sugino, Shigeh ...2015 Volume 79 Issue 5 Pages 287-294
Published: 2015
Released on J-STAGE: May 02, 2015
JOURNAL FREE ACCESSHigh-temperature tensile deformation was performed using ODS ferritic steel, which has grain structure largely elongated and aligned in one direction, in the direction perpendicular to the grain axis. In the superplastic region II, two-dimensional grain boundary sliding (GBS) was achieved, in which the material did not shrink in the grain-axis direction and grain-boundary steps appeared only in the surface perpendicular to the grain axis. In this condition, a classical grain switching event was observed. Using kernel average misorientation maps drawn with SEM/EBSD, dominant deformation mechanisms and accommodation processes for GBS were examined in the different regions. Cooperative grain boundary sliding, in which only some of grain boundaries slide, was also observed.
View full abstractDownload PDF (11994K)
- |<
- <
- 1
- >
- >|