MATERIALS TRANSACTIONS
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ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678

MATERIALS TRANSACTIONS Vol. 54 (2013), No. 5

  • PREFACE

    pp. 631-631

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    DOI:10.2320/matertrans.MPR2013902

  • Microstructures of Long-Period Stacking Ordered Phase of Mg–Zn–Y Alloy

    pp. 632-635

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    DOI:10.2320/matertrans.MI201219

    The microstructures of α-Mg, long-period stacking ordered (LPSO) phases, and kink bands in a Mg–Y–Zn alloy were observed by transmission electron microscopy (TEM). The results showed that extruded Mg97Zn1Y2 alloy included different kinds of phases: 2H-Mg, 2H-Mg with many stacking faults, 14H and 18R. Kink bands tended to occur in areas where there were many intermetallic compounds. The element distribution of Zn/Y/Mg in the LPSO phase including kink boundaries was also analyzed by scanning TEM energy dispersive X-ray spectroscopy. The results showed that the concentrations of atomic Zn/Y decreased, while the concentration of atomic Mg increased at kink boundaries. This can be understood in terms of the dislocation structure of kink boundaries where extended a-dislocations lying on sequential stacking faults in the LPSO phase cause the annihilation of Zn/Y-rich stacking faults between two partial dislocations.
  • Thermodynamic Analysis of the Mg–RE–Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method

    pp. 636-640

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    DOI:10.2320/matertrans.MI201222

    In this study, thermodynamic properties of the Mg–RE–Zn (RE = Y, La) ternary hcp phase at finite temperature have been investigated by means of first-principles calculations combined with the cluster variation method (CVM). Free energy calculation, including the configurational entropy, shows that the Mg–Y–Zn ternary hcp phase has a tendency to phase separation. Conversely, the Mg–La–Zn ternary system does not exhibit such behavior even around room temperature. Furthermore, the calculated spinodal region extends to a broader composition range and the maximal spinodal temperature reaches above 1000 K for the Mg–Y–Zn system. Conversely, the spinodal region for the Mg–La–Zn system is a limited narrow region near the Mg-rich side, and the maximal spinodal temperature is 300 K. Formation enthalpies calculated on the basis of recent information from structure analyses do not show a definite difference in these two ternary systems. Therefore, we propose that the dominant factors in the formation of a novel long period stacking ordered structure include spinodal decomposition as well as structure transformation from 2H to other structures having periodic stacking faults.
  • Experimental Study on Phase Equilibria in the Vicinity of X, W and H Phases in the Mg–Zn–Y Ternary System

    pp. 641-646

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    DOI:10.2320/matertrans.MI201209

    Three Mg–Zn–Y ternary alloys in the vicinity of X, W and H phases were prepared and were isothermally heat treated at 833, 793, 723 and 673 K to attain thermodynamic equilibrium. The microstructure was observed using electron probe microanalysis and transmission electron microscopy, and the chemical compositions of the equilibrium phases were analyzed using wavelength dispersive X-ray spectroscopy. The crystal structure of the W and H phases were analyzed using X-ray diffraction, electron back scattering diffraction and electron diffraction pattern obtained by transmission electron microscopy. The Mg–Zn–Y ternary phase diagrams of the isothermal section were also calculated using the Thermo-Calc to compare with the experimental results. The X phase was found to be solidified in high-Mg alloys not in a manner of eutectic reaction as reported previously but in a manner of peritectic reaction. The W phase has a Heusler (L21) type crystal structure with a stoichiometric composition of Mg1Zn2Y1, and fine mesh texture composed of α (Mg) and W phases was occasionally observed in non-equilibrium solidified parts, implying that the transient W phase has potential to be utilized as an additional strengthening phase. The equilibrium chemical composition of the H phase with a hexagonal crystal structure (P63/mmc) was found to be different from that of the previous reports.
  • Thermodynamic Analysis of Phase Equilibria in the Mg–Al–Ho Ternary System

    pp. 647-655

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    DOI:10.2320/matertrans.MI201226

    A thermodynamic analysis of phase equilibria in the Mg–Al–Ho ternary system has been carried out with special emphasis on the metastable phase separation of the hexagonal close-packed (hcp) phase. In this study, the Gibbs free energy of mixing of the hcp phase was evaluated using first-principles calculations combined with the cluster variation method (CVM), and the obtained results as well as the available experimental data were introduced into the analysis. The calculated results enabled the reproduction of experimental results on both the phase equilibria and the thermodynamic properties obtained from the first-principles calculations and the CVM. In addition, the calculations indicated a tendency for metastable two-phase separation in the hcp phase between the Mg-rich corner and the Al–Ho binary side, which was similar to the Mg–Y–Zn ternary system shown in our previous work.
  • First Principles Calculations of Solute Ordering in Mg–Zn–Y Alloys

    pp. 656-660

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    DOI:10.2320/matertrans.MI201207

    The formation mechanism of the LPSO structures of Mg–Zn–Y alloys has been investigated by the energetic assessments with the first principles calculations. For the key players of the LPSO structures, the stacking faults and the solute elements of Zn and Y, two scenarios are proposed; one is the stacking fault control and the other is the solute atom pair control. Both of them were declined through the detailed investigations of the energetic assessments. The enrichment of solute atoms induced by the stacking fault is suggested.
  • Phase-Field Simulation of Spinodal Decomposition on Metastable Hexagonal Close-Packed Phase in Magnesium–Yttrium–Zinc Alloy

    pp. 661-667

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    DOI:10.2320/matertrans.MI201212

    It has been proposed that a long-period stacking ordered (LPSO) structure is responsible for the excellent mechanical properties of lightweight alloys of Mg–Zn–RE (RE: rare earth elements) system. The phase separation of the metastable hexagonal close-packed (hcp) phase in the Mg–Y–Zn alloy was simulated by means of the phase-field method to discuss the mechanism of formation of the LPSO structure. Near the Mg-corner of the Mg–Y–Zn ternary system, metastable spinodal decomposition occurs before conventional spinodal decomposition, i.e., the supersaturated solid solution of Mg–7 at% Y–7 at% Zn alloy separates into two phases: Mg–12 at% Y and Mg–17 at% Zn. The resulting microstructure has a lamellar morphology, elongated along the [0001] direction of the hcp phase, with a wavelength of ∼7 nm. The calculated orientation of the lamellar is completely different from that of the LPSO structure. Therefore, it is difficult to explain the formation of the LPSO structure directly in terms of a spinodal decomposition of the hcp phase in the Mg–Y–Zn ternary system.
  • Structural and Compositional Modulation in Transformation of LPSO Structure in Mg97Zn1Y2 Cast Alloys

    pp. 668-674

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    DOI:10.2320/matertrans.MI201221

    This study investigated modulation of the long period stacking order (LPSO) structure in aged Mg97Zn1Y2 alloys using conventional transmission electron microscopy (TEM) and aberration-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The irregular stacking sequence of a fragment of 24R-type LPSO acts as a catalyst for the transformation from 18R- to 14H-type LPSO. The elementary step of the transformation from 18R- to 24R-type takes place by the ledge-pair movement on different (0001)Mg planes with Shockley partial dislocations. Each ledge has a transition region in front of it. The transition regions are HCP-type stacking sequence with lower Zn and Y concentrations than those of the FCC-type enrichment layer. The solute elements migrate easily in the region, where solute elements produce a kind of diffusion field. Therefore, structural modulation occurs by a mechanism resembling diffusional–displacive transformation. Local strain analysis using HAADF-STEM images has elucidated that lattice spacing of (0001)Mg in the FCC-type enrichment layer is shorter than that in the HCP-type transition region. These structural and compositional irregularities are an elementary step in the transformation of LPSO in Mg97Zn1Y2 alloys. A diffusional–displacive type transformation mechanism in LPSO has been proposed.
  • Discussion on Strain Accommodation Associated with Formation of LPSO Structure

    pp. 675-679

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    DOI:10.2320/matertrans.MI201224

    Plate-shaped precipitates accompanying change of chemical composition/order exhibit characteristics of displacive transformation when stacking sequence changes. One of intrinsic nature of long-period stacking ordered (LPSO) structures is, regular arrangements of stacking faults should cause significant change in local elastic strain field. This study intends to discuss problems of elastic strain in associated with LPSO structure and plastic accommodation processes by diffusion. It is indicated that required time for strain accommodation through boundary diffusion is negligibly small whereas that for volume diffusion is comparable to aging time where LPSO structure are formed via precipitation from the supersaturated Mg matrix. However, high degree of coherency between the fcc-base structural unit in the LPSO structure and Mg matrix, high-speed diffusion path for diffusional accommodation cannot be provided and thus, the volume diffusion controlled process or self-accommodation by combination of structural units with alternative shears should be dominant. The observation of 14H or 10H-type LPSO structure by aging clearly indicates such strain accommodation during sequence of precipitation.
  • Activation Free Energy of Nucleation of a Dislocation Pair in Magnesium

    pp. 680-685

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    DOI:10.2320/matertrans.MI201213

    Kink deformation is one of the possible principal deformation modes of alloys with a long-period stacking ordered structure under compression parallel to the basal plane. In this deformation, dislocation pairs are massively nucleated, and these dislocations align in a line to form kink bands. In this study, we investigated the nucleation of a dislocation pair in a pure magnesium single crystal by molecular dynamics simulations. We also evaluated the activation free energy of nucleation of a dislocation pair and investigated the dependence of the activation free energy on the applied shear stress and temperature.
  • Molecular Dynamics Analyses of Deformation Behavior of Long-Period-Stacking-Ordered Structures

    pp. 686-692

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    DOI:10.2320/matertrans.MI201211

    Magnesium alloys containing long-period-stacking ordered (LPSO) phases have attracted considerable attention because they have been reported to exhibit excellent mechanical properties, including high strength and reasonable ductility. It is thought that the LPSO phase plays a critical role in producing these favorable mechanical properties. We analyze the deformation behavior of the LPSO phases with different stacking sequences using molecular dynamics simulations. To highlight the specific deformation behavior of the LPSO phases, we also perform deformation analyses of hexagonal-close-packed and face-centered-cubic (FCC) structures. We focus on the influence of the stacking order rather than the segregated atoms around the FCC-structured layers, and we model an LPSO structure by single element composition where the interatomic interaction is described by a smoothed Lennard-Jones potential. Our simulations indicate that an LPSO structure with a shorter stacking sequence tends to exhibit a higher compressive flow stress, because FCC-structured layers inhibit twinning deformations and non-basal slips. Kinking deformation is observed for an LPSO structure when both compression and shear deformation are present. It is shown that the first-order pyramidal-< c + a> dislocation disarranges the stacking of an LPSO structure and leaves behind many lattice defects. In addition, those lattice defects activate numerous basal slips. Finally, basal dislocations arrange in a line and generate a misorientation angle. Furthermore, this angle originates the compressive deformation. We also observed some prismatic-< a> dislocations and cross slips to the basal plane. These results suggest the importance of non-basal slips for kinking deformation.
  • Non-Basal Slip Systems Operative in Mg12ZnY Long-Period Stacking Ordered (LPSO) Phase with 18R and 14H Structures

    pp. 693-697

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    DOI:10.2320/matertrans.MI201208

    Non-basal slip systems in the Mg12ZnY long-period stacking ordered (LPSO) phase, the operational frequency of which is increased at high-temperatures and affects the mechanical properties, were clarified. The {1\bar{1}00}<11\bar{2}0> prism slip was identified in both 18R and 14H LPSO phases, even though they have the different lattice systems. This behavior is different from that observed in a Ni-based LPSO phase. The peculiar chemical modulation in the Mg12ZnY LPSO phase may affect the selection of operative slip systems.
  • Micro-Kinking of the Long-Period Stacking/Order (LPSO) Phase in a Hot-Extruded Mg97Zn1Y2 Alloy

    pp. 698-702

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    DOI:10.2320/matertrans.MI201216

    Microstructures of a hot-extruded Mg97Zn1Y2 alloy containing the long-period stacking/order (LPSO) phase have been investigated by transmission electron microscopy (TEM), particularly focusing on kink-deformed LPSO crystals. It is found that kink-deformation in the LPSO phase grains are mostly characterized by singular straight interfaces across which the host crystals are sharply bended, as being similar to those reported previously. In addition to these common LPSO phase kink-bands, we occasionally find unique microscopic traces at the kink-boundaries, which are composed of multiply segmented kink-interfaces that are sequentially rotated with small angles in a same direction, accomplishing a macroscopic large crystalline bend; i.e., a micro-kinking feature. Occurrence of such micro-kinking may hardly be explained by generation of dipole-pair dislocations in the early stage of kinking, which have been successfully used for phenomenological understanding of kink deformation.
  • Effect of LPSO Phase-Stimulated Texture Evolution on Creep Resistance of Extruded Mg–Zn–Gd Alloys

    pp. 703-712

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    DOI:10.2320/matertrans.MI201218

    The creep behavior and microstructures of extruded Mg97Zn1Gd2 alloys with long period stacking ordered (LPSO) phase have been investigated. Creep properties of extruded alloys depend on pre-extrusion aging temperature; the optimum aging temperature to obtain excellent creep resistance is between 623 and 723 K. In this temperature range, a multimodal microstructure develops during subsequent extrusion at 623 K. The α-Mg matrix are bimodally grained; that is, it consists of fine DRXed grains and <10\bar{1}0>//ED fiber-textured coarse grains. The LPSO phase grains also develop the <10\bar{1}0>//ED fiber texture. Coarse block-shaped LPSO phase promotes dynamic recrystallization in α-Mg matrix via particle stimulated nucleation, while both fine plate-shaped LPSO phase and solute-segregated stacking faults (SFs) stimulate <10\bar{1}0>//ED fiber texture evolution in the α-Mg matrix. The creep strength increases with increasing area fraction of the <10\bar{1}0>//ED fiber textured region (coarse α-Mg grains and LPSO phase grains). Formation of plate-shaped LPSO phase and/or solute-segregated SFs before extrusion is most desirable for enhancing the creep properties of extruded Mg97Zn1Gd2 alloys, due to LPSO phase-stimulated texture evolution.
  • Dissolution Behavior of La2O3, Pr2O3, Nd2O3, CaO and Al2O3 in Sulfuric Acid Solutions and Study of Cerium Recovery from Rare Earth Polishing Powder Waste via Two-Stage Sulfuric Acid Leaching

    pp. 713-719

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    DOI:10.2320/matertrans.M-M2013802

    This study describes a hydrometallurgical process to investigate the cerium recovery from rare earth polishing powder waste (REPPW) containing main elements such as cerium, lanthanum, praseodymium, neodymium, calcium and aluminum. First, dissolution experiments on La2O3, Pr2O3, Nd2O3, CaO and Al2O3 with 5 µm particle size in sulfuric acid solutions were carried out using a batch reactor with various acid concentrations (1–15 mol/dm3) at different temperatures (30–180°C). The effects of these two parameters on the dissolution reaction were studied. The obtained results showed that two sequential leaching steps were needed to separate cerium from the mixture of CeO2, La2O3, Pr2O3, Nd2O3, CaO and Al2O3. The total process for cerium recovery from REPPW via two-stage acid leaching was then developed through the collection of experimental results. Moreover, the dissolution rate of Al2O3 was expressed by a shrinking core kinetics model. The variation of the dissolution rate constant with temperature obeyed the Arrhenius equation with activation energy of 130 kJ·mol−1 and reaction rate constant as a function of the acid concentration of C0.41. On the basis of the above data, a k-T (reaction rate constant-reaction temperature) diagram for a CeO2–Al2O3–H2SO4–H2O system that permits rational extraction of CeO2 and Al2O3 was devised.
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  • The Structure of an Al–Co–Ni Decagonal Quasicrystal in an Al72Co8Ni20 Alloy Studied by Cs-Corrected Scanning Transmission Electron Microscopy

    pp. 720-724

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    DOI:10.2320/matertrans.M2012333

    The structure of an Al–Co–Ni decagonal quasicrystal in an Al72Co8Ni20 alloy has been examined by Cs-corrected high-angle annular detector dark-field (HAADF)- and annular bright-field (ABF)-scanning transmission electron microscopy (STEM) observations with the incident beam parallel to the periodic axis. Observed ABF- and HAADF-STEM images clearly show the existence of large columnar clusters of a decagonal section with an about 3.2 nm in diameter and their arrangement with bond-orientational order (BOO) of a bond-length of 3.2 nm. Individual transition-metal (TM) atoms and mixed sites (MSs) of Al and TM atoms are represented as separated bright dots in observed HAADF-STEM images, and consequently arrangements of TM atoms and MSs on two quasiperiodic planes can be directly determined. The TM atoms and MSs are located at lattice points of a Penrose lattice with an edge-length of 0.25 nm, and so they are arranged with BOO on the two quasiperiodic planes. An atomic arrangement including Al atoms in the 3.2 nm cluster is speculated from observed HAADF- and ABF-STEM images.
  • Effects of 4 GPa Pressure Heat Treatment on Mechanical Properties and Electrical Conductivity of CuCrNiAl Alloy

    pp. 725-728

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    DOI:10.2320/matertrans.M2012360

    The hardness, compressive yield strength and electrical conductivity of CuCrNiAl alloy before and after 4 GPa pressure treatment were measured, and the microstructure of the CuCrNiAl alloy before and after 4 GPa pressure treatment were analyzed by metallurgical microscope, transmission electron microscopy and scanning electron microscope. Based on the experimental results, the effects of 4 GPa pressure heat treatment on the mechanical properties and electrical conductivity of CuCrNiAl alloy were discussed. The results showed that 4 GPa pressure treatment can increase the hardness and compressive yield strength of the CuCrNiAl alloy, and reduce its electrical conductivity. After 4 GPa pressure treatment and aged at 500°C for 1 h, higher mechanical properties and electrical conductivity of CuCrNiAl alloy could be obtained.
  • In-Situ TEM Study of Hydrogen-Induced Cracking in Carbide-Free Bainitic Steel

    pp. 729-731

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    DOI:10.2320/matertrans.M2012263

    Carbide-free bainitic steel is a typical high-strength steel and it is very sensitive to hydrogen embrittlement. Studies have shown that the hydrogen embrittlement in bainitic steels was decreased by the addition of aluminium. However, hydrogen embrittlement still exists in these steels. The in-situ tension in transmission electron microscope (TEM) was used to observe and analyse the effect of hydrogen on the dynamic process of dislocation motion and crack nucleation in carbide-free bainitic steel. A special self-made constant deflection device was used to install the specimen in TEM. Before and after hydrogen charging, the movement of dislocations and microcracks can be clearly observed. The results showed that hydrogen can facilitate the emission, multiplication and motion of dislocations. It also demonstrated that hydrogen can enhance the microcrack nucleation, growth and connection of carbide-free bainitic steel.
  • Effect of Hybrid Surface Treatment Composed of Plasma Nitriding and DLC Coating on Friction Coefficient and Fatigue Strength of Stainless Steel

    pp. 732-737

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    DOI:10.2320/matertrans.M2012426

    This study was conducted to investigate the effect of hybrid surface treatment composed of plasma nitriding and DLC (diamond-like carbon) coating on the friction coefficient and fatigue strength of stainless steel JIS SUS316. The obtained results were compared with the results of the previous study which investigated the effect of hybrid surface treatment composed of plasma carburizing and DLC coating. Plasma nitriding as a pretreatment was more effective to decrease the friction coefficient of DLC-coated stainless steel than plasma carburizing because the hardened layer with greater hardness supported the DLC layer. The mechanical properties were unaffected by both hybrid surface treatments. Plasma nitriding improved the fatigue strength of stainless steel more than plasma carburizing. DLC coating slightly improved the fatigue strength of the plasma-nitrided material; however, its effect was more significant on the plasma-carburized material.
  • Effect of Cold-Rolling on Damping Characteristics of Multi-Component Al–12%Si Alloy Measured by Dynamic Mechanical Analyzer

    pp. 738-744

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    DOI:10.2320/matertrans.M2012418

    Compared to pure Al, a multi-component Al–12%Si alloy deteriorates the low-frequency damping capacity in the temperature regions of an athermal damping background and a high-temperature damping background (HTDB) because the dislocation motions during damping are impeded by the abundant silicon particles in Al–12%Si alloy. However, Al–12%Si alloy improves the creep resistance in the HTDB temperature region because of an increase in the activation energy of the HTDB. Severely cold-rolled Al–12%Si alloy significantly increases the damping capacity and hardness, and a conspicuous internal friction peak appears at approximately 270°C which corresponds to the occurrence of grain recrystallization. The effect of cold-rolling becomes insignificant after recrystallization occurs.
  • Role of Lanthanum in Grain Refinement and Tensile Properties of Cast Mg–La–Zr Alloys

    pp. 745-754

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    DOI:10.2320/matertrans.M2012424

    In a previous investigation, a combined addition of zirconium and lanthanum was found to confer more marked grain refining than zirconium alone. The present experimental study confirmed this result. However, in this study, the microstructure was examined with more attention to the form of the zirconium-rich coring in the grain refined structures. It was concluded that although the average apparent grain size decreases with an addition of lanthanum, this is in part because grain growth takes place in the Mg–Zr alloy, while the suppression of grain growth occurs with an addition of lanthanum as small as 0.5%.
  • Accelerated Corrosion Tests of Nuclear Reactor Pressure Vessel Materials in NaCl–H3BO3 Solutions

    pp. 755-764

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    DOI:10.2320/matertrans.M2012405

    Following the 2011 accident at the Fukushima Daiichi nuclear power station, sea water for cooling and boric acid for maintaining a non-critical condition, both corrosive liquids, were injected into nuclear pressure vessels. In order to estimate corrosive characteristics of the pressure vessels an experimental study was undertaken to provide an accelerated corrosion test on SA533B low alloy steel and Inconel 600, materials used in the construction of the pressure vessels. In a typical experiment, samples of these materials were immersed in saturated NaCl and concentrated H3BO3 aqueous solutions at a temperature of 423 K. SA533B suffered little or no corrosion in saturated NaCl solution, significant corrosion in concentrated H3BO3 solution and substantial corrosion in the binary saturated NaCl-concentrated H3BO3 solution. Galvanic corrosion of SA533B was accelerated when Inconel 600 was also immersed in the same solution and the two samples were electrically connected either externally by a wire lead or internally by a screw made of SA533B or both. Corrosion rate in the initial stage was 0.07 mm per hour. The corrosion product on SA533B was porous and easily detachable, indicating corrosion to be progressive without producing a stable protective corrosion layer. The validity of the extreme experimental condition for accelerated corrosion tests is discussed and experimental programs for further investigation are proposed.
  • Effect of Temperature and Extrusion Pass on the Consolidation of Magnesium Powders Using Equal Channel Angular Extrusion

    pp. 765-768

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    DOI:10.2320/matertrans.M2013006

    The microstructure and characteristics of bulk magnesium consolidated from Mg powder by equal channel angular extrusion (ECAE) were investigated. Cu cans filled with Mg powder, of about 74 µm in diameter, were ECAE processed for one, two and four passes via the Bc route at 473, 523 and 573 K. The microstructure of ECAE-processed samples was observed by OM and SEM. The density of each sample was determined using Archimedes’ principle. Microhardness and compression tests were conducted to investigate the mechanical properties of each ECAE-processed sample. The best consolidated condition between powders was achieved after four passes of ECAE at 573 K. Density at 98.4% of the ideal density of bulk Mg was achieved, microhardness was about 49 Hv, and compressive yield stress was about 100 MPa.
  • Crystal Plasticity Finite Element Analysis of Texture Evolution during Rolling of fcc Polycrystalline Metal

    pp. 769-775

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    DOI:10.2320/matertrans.M2012346

    Localized strain and crystallographic orientation distribution during rolling process have a significant effect on anisotropic flow behavior in sheet forming of aluminum alloy, resulting in local thinning. In this study, crystal plasticity finite element method (CPFEM), which incorporates a crystal plasticity constitutive law into the three-dimensional finite element method, was used to investigate strain localization and textural evolution during the flat rolling process of the face-centered-cubic material. A rate-dependent polycrystalline theory based on the Taylor model was fully implemented into an in-house program, CAMProll3D. The through-thickness texture evolution depending on the degree of draught was predicted by using the developed CPFEM program and compared well with the experimental data available in the literature. The orientation distributions not only in the thickness direction but also in the width direction of the flat rolled sheet were investigated depending on the amount of reduction during the multi-pass flat rolling in terms of pole figure, orientation distribution function and flow potential surface in the π-plane. Finally, the effect of friction condition between the rolls and the material on rotation about the transverse direction was found to be important to determine the texture evolution at the surface of the rolled sheet.
  • Al0.5TiZrPdCuNi High-Entropy (H-E) Alloy Developed through Ti20Zr20Pd20Cu20Ni20 H-E Glassy Alloy Comprising Inter-Transition Metals

    pp. 776-782

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    DOI:10.2320/matertrans.M2012370

    An Al0.5TiZrPdCuNi high-entropy (H-E) alloy with a bcc single phase was found through a Ti20Zr20Pd20Cu20Ni20 H-E glassy alloy designed based on equi-atomicity inherent to H-E alloys. The constituent elements and the composition of the Ti20Zr20Pd20Cu20Ni20 alloy were determined by regarding a binary Cu64Zr36 bulk metallic glass as Cu60Zr40 alloy and subsequent replacements of the Cu and Zr atoms with other late- and early-transition metals, respectively. The Ti20Zr20Pd20Cu20Ni20 alloy in a ribbon shape forms into a glassy single phase. The addition of 0.5Al to the Ti20Zr20Pd20Cu20Ni20 H-E glassy alloy resulted in forming a bcc single phase for a rod specimen with a diameter of 1.5 mm. The analysis revealed that the Al0.5TiZrPdCuNi H-E alloy is characterized by mixing enthalpy of −46.7 kJ·mol−1 and Delta parameter of 8.8, which are considerably larger and negative for the former and larger for the latter against the conventional H-E alloys.
  • Relationship between Microstructures and Mechanical Properties in Ti–4.5Al–2Mo–1.6V–0.5Fe–0.3Si–0.03C for Next-Generation Aircraft Applications

    pp. 783-790

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    DOI:10.2320/matertrans.L-M2013803

    The effects of various heat treatments on the microstructure and mechanical properties of an (α + β)-type titanium alloy, Ti–4.5Al–2Mo–1.6V–0.5Fe–0.3Si–0.03C (KS Ti-9), were investigated systematically for possible use in next-generation aircraft applications.
    The as-received KS Ti-9 shows strong anisotropy of mechanical strength derived from the intense texture (T-texture) of the primary α phase. This anisotropy continues to be observed in KS Ti-9 annealed at a temperature below β transus followed by air cooling, but the anisotropy drastically decreases in KS Ti-9 when subjected to a duplex heat treatment, that is, when the as-received material of KS Ti-9 is sequentially heated to a temperature slightly below β transus followed by water quenching and then annealed followed by air cooling. It is considered that the reduction in the anisotropy in KS Ti-9 subjected to this duplex heat treatment is associated with the difference in the orientation of the precipitated acicular α phase.
  • Synthesis and Characterization of Mesoporous SiO2–CaO–P2O5 Bioactive Glass by Sol–Gel Process

    pp. 791-795

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    DOI:10.2320/matertrans.M2012417

    Ordered mesoporous SiO2–CaO–P2O5 bioactive glass with a highly specific surface area has been synthesized through a sol–gel process in the presence of a nonionic triblock copolymer acting as a template. The amorphous silicate can be detected on the mesoporous SiO2–CaO–P2O5 bioactive glass. The mesoporous SiO2–CaO–P2O5 bioactive glass exhibits the type IV isotherm curve with average pore size of 5.3 nm and high specific surface area of 317.24 m2/g for calcination at 600°C. Owing to the high specific surface area and pore volume, the mesoporous SiO2–CaO–P2O5 had a significantly enhanced bone-forming bioactivity compared with the conventional bioactive glass. After soaking the mesoporous SiO2–CaO–P2O5 in simulated body fluid (SBF) for 10 h, it can be observed that the formation of apatite nanocrystals occurs on the surface of the bioactive glass. It is anticipated that mesoporous SiO2–CaO–P2O5 with a controlled mesostructure may be potentially useful as novel tissue-engineering scaffolds in bone regeneration.
  • Effect of Addition of Small Amount of Zinc on Microstructural Evolution and Thermal Shock Behavior in Low-Ag Sn–Ag–Cu Solder Joints during Thermal Cycling

    pp. 796-805

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    DOI:10.2320/matertrans.MBW201206

    The effects of adding small amounts of Zn on the microstructural evolution of low-Ag Sn–Ag–Cu solders and thermal shock behavior during thermal cycling between −40 and 125°C were investigated. Observation of the visual appearance of the solder joints revealed that the probability of solder deformation and crack initiation in the solder fillets after thermal cycling was lower in Sn–1Ag–0.3Cu–1Zn than in Sn–3Ag–0.5Cu. Microstructural observation of the interface of the solder joints revealed that the addition of Zn to a low-Ag Sn–Ag–Cu solder inhibited the growth of the intermetallic compound layer between the solder and the Cu pad in printed circuit boards. The addition of small amounts of Zn improved the thermal shock behavior of the low-Ag Sn–Ag–Cu solder.
  • Effect of Starting Materials on the Morphological and Optical Properties of Er Doped BaTiO3 Nanocrystalline Films

    pp. 806-810

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    DOI:10.2320/matertrans.M2012313

    Erbium (5%mol) doped BaTiO3 films were prepared using different metallic precursors: barium acetate, titanium butoxide and isopropoxide with different molar ratios. Three different experimental methodologies (A, B and C) were proposed in order to obtain optical quality thick films incorporating polyvinylpyrrolidone (PVP) as a rheological agent at the sol stage. In all cases, Er doped BaTiO3 films were deposited in silica quartz substrates. The morphology was controlled by means of the incorporation of the chelating agent and water molar ratios. Through the three different synthesis routes, Er:BaTiO3 films presented mainly the cubic phase, as observed by X-ray diffraction. The films presented a homogeneous and crack-free surface of cross-linked particles. Photoluminescent results show that the highest intensity emission of the Er3+ (4S3/24I15/2) was obtained from Er:BaTiO3 film prepared using C methodology, which could be associated with the film’s thicknesses.
  • Effect of Autoclave and Hot Water Treatments on Surface Structure and In Vitro Apatite-Forming Ability of NaOH- and Heat-Treated Bioactive Titanium Metal

    pp. 811-816

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    DOI:10.2320/matertrans.M2013021

    Sodium hydroxide (NaOH)-, heat- and autoclave-treated Ti metal did not form apatite in simulated body fluid (SBF) within 604.8 ks, although some Na remained on the Ti metal surface after the autoclave treatment. When hot water treatment was applied between NaOH and heat treatments, the Ti metal formed apatite within 604.8 ks in SBF. While anatase TiO2 was partially precipitated by the NaOH and heat treatments, it disappeared after subsequent autoclave treatment. By adding hot water treatment between the NaOH and heat treatments, a considerable amount of anatase TiO2 was formed, which remained after the autoclave treatment; the zeta potential of Ti metal was almost zero in SBF. These results indicate that with intermediate hot water treatment, Ti metal can form apatite in SBF even after autoclave treatment. Anatase TiO2, rather than the amount of Na or the zeta potential in SBF, might play an important role in apatite formation.
  • Direct and Rapid Quantification of Calcium Phosphate Precipitate on Titanium by X-Ray Fluorescence Analysis Using Fundamental Parameter Method

    pp. 817-824

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    DOI:10.2320/matertrans.M2013020

    In the present study, we propose a characterization technique to determine the amount of calcium phosphate (CP) precipitate formed on a titanium (Ti) substrate. The quantitative analysis of the CP precipitate on a metallic substrate is significant for researchers of metallic biomaterials because CP that spontaneously precipitates in a simulated-body fluid gives information on the bioactivity of the metallic biomaterials. We focused on X-ray fluorescence (XRF) analysis and adopted the thin-film fundamental parameter method (thin-film FP method) because it allows direct (non-pretreatment) and rapid quantitative analysis without any reference materials. We show that XRF analysis using the thin-film FP method can be adequately applied to the quantitative analysis of the CP precipitate in the simulated-body fluid immersion test. We also show that the density of the CP-precipitate layer can be estimated by combining the XRF results with images of cross-sectional scanning electron microscopy (SEM).
    Consequently, XRF analysis combined with the thin-film FP method can provide a convenient means to evaluate the CP precipitate on a Ti substrate, which improves the accuracy and accessibility of the simulated-body fluid immersion test.
  • The Influence of Microstructure and Grain Boundary on the Electrical Properties of Scandia Stabilized Zirconia

    pp. 825-832

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    DOI:10.2320/matertrans.M2012385

    Nanocrystalline Sc2O3 (different doping content) stabilized ZrO2 (ScSZ) powders are prepared by the hydrothermal method. Dense ScSZ ceramic pellets are fabricated by isostatically pressing then sintering at 1350°C for 2 h. 8 mol% Sc2O3 doped Zirconia possesses the highest conductivity of all the samples measured by impedance spectroscopy. Different grain size of 8ScSZ samples which are observed by scanning electron microscopy (SEM) are prepared by sintering with different temperature and different hours. The correlation between grain size and electrical properties is analyzed by impedance spectroscopy fitting and calculating with brick-layer model and Mott–Shottky model: the total grain boundary conductivity decreases but the specific grain boundary conductivity increases with the decrease in grain size of 8ScSZ; the grain boundary space charge potential decreases and the concentration of oxygen vacancies in the space charge regions increases with decreasing grain size.
  • Corrosion Resistance of ASSAB Stavax ESR Stainless Steel by Heat and Cold Treatment

    pp. 833-838

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    DOI:10.2320/matertrans.M2012377

    This study compared cryogenic treatment, ultra-cryogenic treatment, and high-low temperature tempering treatment using ASSAB Stavax ESR, and conducted the following analyses of the prepared specimens: (1) analysis the structure by X-ray diffraction, (3) analysis of the texture of the processed specimens by optical microscopy, (2) using a hardness tester to analyze the changes in hardness of specimens processed by cryogenic and heat treatment, (3) analyzing the hydrophilicity and hydrophobicity by the water contact angle test, and (4) analyzing corrosion resistance by the corrosion resistance test. The experimental results showed that cryogenic temperature affects the amount and shape of the carbides, which are significantly reduced in cases of high-temperature tempering. The water contact angle test analysis showed that the coating film’s water contact angle performance is the best, followed by specimens of ultra-cryogenic treatment, specimens of cryogenic treatment, and specimens of traditional heat treatment. It was found that cryogenic treatment can increase polishability, and empower the specimens with good mold release performance. The coating-film corrosion resistance test showed that ultra-cryogenic treatment and cryogenic treatment can improve corrosion resistance; however, the performances of specimens by traditional heat treatment were the worst.
  • Effect of Precipitated Phases on the Pitting Corrosion of Z3CN20.09M Cast Duplex Stainless Steel

    pp. 839-843

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    DOI:10.2320/matertrans.M2012410

    The effect of precipitated phases on the pitting corrosion of a Z3CN20.09M cast duplex stainless steel (CDSS) which has been widely used in primary coolant pipes of nuclear power plants was investigated by using isothermal aging treatment and potentiodynamic anodic polarization methods. It was found that M23C6 carbide and σ phase precipitated at the ferrite/austenite boundaries and in ferrite of the aged steel. The pitting potentials of the specimens aged at 700°C decreased with increasing of the precipitates content. The experimental results indicated that even a few percent of precipitates (about 1.0 vol%) in this steel could also worsen its pitting resistance. The pitting of the aged Z3CN20.09M specimens developed at the ferrite/austenite phase boundaries where precipitates formed often. These effects could be directly attributed to the presence of secondary austenite at the ferrite/austenite phase boundaries, which was found to be poor in Cr by energy dispersive X-ray (EDX).
  • Production of Chemical Manganese Dioxide from Lithium Ion Battery Ternary Cathodic Material by Selective Oxidative Precipitation of Manganese

    pp. 844-849

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    DOI:10.2320/matertrans.M2012379

    We have conducted studies to produce chemical manganese dioxides (CMDs) from ternary cathodic materials by oxidative precipitation. In this study, a cathodic material was concentrated by pretreatment and leached with sulfuric acid to recover 1 L of a leachate containing 22.0 g/dm3 of Co, 21.6 g/dm3 of Mn, 24.2 g/dm3 of Ni, 9.5 g/dm3 of Li and 8 mg/dm3 of Al as valuable metals. For selective oxidative precipitation of Mn (II), the leachate was reacted with 1 equivalent of Na2S2O8 based on the Mn concentration with stirring at 500 rpm at a temperature of 363 K for 18000 s. As a result of the reaction, it was confirmed that the majority of Mn was precipitated from the solution. XRD, PSA, TG–DTA, LECO and ICP analyses were performed to characterize the precipitate. The analytical results revealed the production of a chemical manganese dioxide (CMD) having a chemical composition of 84.60% MnO, 1.40% Co3O4, 0.11% Li2O, 0.25% NiO, 0.02% Al2O3, 0.06% S and 0.52% Na2O, an average particle diameter of 10.7 µm, a crystal form of γ-MnO2, and a purity of at least 98%.
  • Relationship between Amount of Residual NaCl and Compressive Properties of Porous Al/NaCl Composites Fabricated by Sintering and Dissolution Process

    pp. 850-853

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    DOI:10.2320/matertrans.M2013023

    In this study, a porous Al/NaCl composite was fabricated by a sintering and dissolution process, and the possibility of controlling the mechanical properties of porous Al by varying the amount and distribution of residual NaCl was investigated. It was shown that the range of the plateau region decreased and the stress–strain curves became similar to those of dense materials as the amount of residual NaCl increased. The deformation started from the layers where NaCl was removed, then the layers where NaCl remained started to deform. This indicates that the strength of each region can be controlled by varying the amount and distribution of residual NaCl.
  • Development of Novel Optical Fiber System for Cathodoluminescence Detection in High Voltage Transmission Electron Microscope

    pp. 854-856

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    DOI:10.2320/matertrans.M2013025

    We have installed a new system to observe cathodoluminescence (CL) in a high voltage transmission electron microscope (HVTEM). The system is constructed of a ball lens for collection of CL, an optical fiber and a multi-channel optical detector. The system can be operated without any disturbance of TEM observation. The system was proved to be very useful to observe CL in HVTEM and will be a powerful tool to investigate production mechanisms of luminescence centers by observing CL changes with incident electron energy and flux (displacement damage effect), and temperature, together with simultaneous TEM observations of microstructure changes.
  • Erratum

    pp. 857-857

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    DOI:10.2320/matertrans.ERM201301

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