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

MATERIALS TRANSACTIONS Vol. 57 (2016), No. 4

  • Ab-Initio Study of Electronic Structure of Martensitic Twin Boundary in Ni2MnGa Alloy

    pp. 477-480

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    DOI:10.2320/matertrans.M2015471

    The electronic structure of (110) and (011) martensitic twin boundary in Ni2MnGa alloys has been calculated by using ab initio method within the density-functional theory (DFT) and the supercell implementation. The calculated results show that the energy for the (110) twin boundary is larger than that for another twin due to their difference in the chemical decomposition and crystal structure. The atomic relaxation lowers the interface energies for both (110) and (011) twins and this kind of energy is still positive after relaxation. The structural stability and the magnetic properties of the twining interface are investigated and compared with each other from the total and spin density of states under atom-relaxation and -unrelaxation. The atoms such as Ni and Mn have different magnetic moments in the two kinds of twin boundaries. The total charge density on the plane passing through the twin plane gives the direct explanations of the bonding between atoms.
  • Lattice Statistics and Dynamics within Cluster Variation Method

    pp. 481-487

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    DOI:10.2320/matertrans.MBW201504

    The conventional Cluster Variation Method (CVM) does not explicitly consider both lattice vibration and local lattice relaxation effects. As discussed in the previous studies, these deficiencies result in overestimation of order-disorder transformation temperatures for the Cu-Au phase diagram. In the present paper, we propose modified CVM which explicitly takes both the effects mentioned above into account. By employing the present modified CVM, we evaluated both lattice vibration and local lattice relaxation effects, and estimated free energy of mixing for Cu-Au disordered phase at a finite temperature.
  • Formation of Nano-Microstructured Aluminum Alloy Film Using Thermal Spray Gun with Ultra Rapid Cooling

    pp. 488-493

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    DOI:10.2320/matertrans.M2015392

    A new thermal spray gun for nitrogen gas cooling and mist cooling has been developed. Aluminum-magnesium alloy films prepared by nitrogen gas cooling using the thermal spray gun had a partial nano microstructure because residual strains induced by rapid cooling acted as solid nuclei and a small amount of the amorphous phase became crystalline as a result of the heat of the thermal spray. Furthermore, the nano-microstructured aluminum magnesium films exhibited high corrosion resistance. Moreover, aluminum-magnesium alloy films containing a small amount of titanium prepared by mist gas cooling exhibited higher corrosion resistance than those without titanium. We consider that the aluminum -titanium compound acted as solid nuclei during ultra rapid solidification and that a strong passive layer was formed by mist gas cooling.
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    1. A Metallurgical Tool for Rapid Determination of Micro Inclusion Characteristics in Bearing Steel Production ISIJ International Vol.37(1997), No.6
  • A Comparative Study on the Effect of Electrode on Microstructure and Mechanical Properties of Dissimilar Welds of 2205 Austeno-Ferritic and 316L Austenitic Stainless Steel

    pp. 494-500

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    DOI:10.2320/matertrans.M2015321

    In the present study, the weldability, microstructures and mechanical properties of dissimilar welds (2205 austeno-ferritic and 316L austenitic stainless steel) was investigated by using shielded metal arc welding (SMAW) with the help of two different electrodes namely duplex (E2209) and austenitic (E309L). After welding, the microstructure of the different zones of joints was evaluated by using optical microscopy and scanning electron microscopy (SEM), while, the localized chemical information was obtained by energy dispersive spectrometer (EDS) attached to the SEM. In E2209 weld metal, the solidification was observed as the primary ferrite mode. While, 309L weld metal was observed as the primary ferrite with austenitic matrix. Optimum ferrite content was observed in both the electrode. Finally, it was concluded that for the joints between the 2205 austeno-ferritic and 316L austenitic stainless steel, the E2209 electrode was dominant property wise.
  • Limit Load Analysis of Pressure Structures Containing Pitting Defects Subjected to High Temperature Creep

    pp. 501-506

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    DOI:10.2320/matertrans.M2015393

    High-temperature technologies are widely used in many industries and the high temperature components are usually designed for long term operation. Creep damages are inevitable in service, which may lead to the loss of material strength. Volumetric defects such as pits may occur during the manufacturing process and during service. These defects may cause severe reduction of the limit load of structures. The existing assessment procedures do not take into account the effect of plasticity-damage due to creep, which may lead to inaccurate assessment results. This paper aims to investigate the limit load of pressurized components with volumetric defect subjected to high temperature creep. An elasto-plastic constitutive model with coupled plasticity-damage due to creep effects is proposed. The limit load of high temperature structures with volumetric defects is systematically studied using finite element method. Safety assessment approach for structures considering plasticity-damage due to creep effect is subsequently proposed based on the principle of “fitness for service”.
  • Log Angles: Characteristic Angles of Crystal Orientation Given by the Logarithm of Rotation Matrix

    pp. 507-512

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    DOI:10.2320/matertrans.M2015454

    A rotation matrix R with respect to a reference frame is used to describe certain crystal orientation. The logarithm of R, ln R is a skew symmetric tensor with three independent elements of real numbers. The goniometer-stage model in the present study shows that the three independent elements of ln R are the characteristic angles of R representing the rotation angles around coordinate axes. Different from various kinds of the Euler angles, the characteristic angles called the log angles are uniquely determined for certain R.
  • Adhesive Force Improvement of Lamination with 18-8 Stainless Steel and CFRP Separately Irradiated by Electron Beam Prior to Assembly and Hot-Pressing

    pp. 513-518

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    DOI:10.2320/matertrans.MBW201511

    Adhesive 2-layer lamination joints of 18mass%Cr-8mass%Ni austenite stainless steel and carbon fiber reinforced polymer (18-8/CFRP) were prepared using a new adhesion method consisting of applying low dose of 0.13 MGy of homogeneous low energy electron beam irradiation (HLEBI) to connecting surfaces of the 18-8 and CFRP prior to assembly and hot-pressing in vacuum under atmospheric pressure of about 1 Pa for 2 h at 401±0.5 K. Although untreated 18-8/CFRP joint exhibited decent adhesion by hot-pressing, application of 0.13 MGy HLEBI dose apparently improved the adhesive force of peeling resistance (oFp) of the 18-8/CFRP joint 145% at median accumulative peeling probability (Pp=0.50) from 18.9 to 27.4 Nm−1. In addition, the statistically lowest oFp for safety design (Fs at Pp=0) iterated by the 3-parameter Weibull equation was raised from zero for the untreated to 5.2 Nm−1 for the 0.13 MGy samples indicating increased reliability by the HLEBI. The higher adhesive strength induced by HLEBI was explained by results of XPS (X-Ray Photoelectron Spectroscopy) observations of the peeled surface of 18-8 side of lamination with and without 0.13 MGy-HLEBI. 0.13 MGy-HLEBI slightly increased the number of C=C bonds instead of slightly decreasing the numbers of C-C, C-H and O=C-O bonds near 18-8/CFRP interface. In addition, both increasing oxygen atoms and decreasing hydrogen atoms strongly attributed to bonding force at interface of epoxy of 18-8/CFRP. Since the experimental data showed the optimum HLEBI dose was about 0.13 MGy, above which at 0.13 MGy the oFp began to drop, carefulness in optimization was highly recommended when applying in industry to insure safety.
  • Formation of Nano-Structured Oxide Layers Formed on Ti-Fe Alloys by Anodization

    pp. 519-524

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    DOI:10.2320/matertrans.M2015460

    The present work reports the anodization of Ti-Fe alloys in a fluoride-containing ethylene glycol electrolyte and the morphology of resulting anodic oxide layers. The current density generated during the anodization at voltages ranged from 10 V to 50 V significantly decreases in the early stage, then increases once and finally exhibits gradual decrease with time although the magnitude of the current depends on the alloy composition. On pure Ti and Ti-10 at% Fe alloy, anodic oxide layers show a nanotubular structure at all applied voltages. On the other hand, at lower voltages, nanotubular oxide layers are also formed on Ti-50 at% Fe and Ti-70 at% Fe alloys, but at higher voltages the morphology of anodic oxide layers changes to an irregular-shaped porous structure. These results indicate that the morphology of anodic oxide layers is affected not only by the alloy composition but also by applied voltage.
  • Experimental and Numerical Analyses on the Deposition Behavior of Spherical Aluminum Particles in the Cold-Spray-Emulated High-Velocity Impact Process

    pp. 525-532

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    DOI:10.2320/matertrans.T-M2016803

    Understanding the deposition mechanism of fine solid particles is essential for the effective use of the cold spray (CS) technique, which is used to synthesize dense and thick metallic coatings. As such, in this study, the deposition behaviors of spherical pure aluminum particles were investigated in detail in order to understand the deposition mechanism; these particles had a diameter of 1 mm and were deposited on five metallic substrate materials, during the CS-emulated high-velocity impact process. A single particle impact testing system, which is a modified single-stage light gas gun, was used to evaluate the deposition process. This evaluation confirmed that the critical velocities of Al particles vary significantly with the substrate material. In order to identify the dominant factors, the bonding energies, rebound velocities, plastic deformation experienced by the particles and substrates, and removability of the natural oxide films were evaluated. The results revealed that the critical velocities increased significantly with increasing Ar sputtering time required for complete removal of the natural oxide film; this time represents the removability of the film. This result confirms that, of the factors considered, the removability of the natural oxide film exerts the most influence on Al particle deposition on metallic substrates.
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    1. Characteration of Laser Cladded Fe-Mn-Cr Alloy Coatings Modified by Plasma Nitriding MATERIALS TRANSACTIONS Vol.57(2016), No.4
  • Real Hydrostatic Pressure in High-Pressure Torsion Measured by Bismuth Phase Transformations and FEM Simulations

    pp. 533-538

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    DOI:10.2320/matertrans.M2015374

    Hydrostatic pressure is a significant parameter influencing the evolution of microstructure and phase transformations in the high-pressure torsion (HPT) process. Currently, there are significant arguments relating to the magnitude of the real hydrostatic pressure during the process. In this study, phase transformations in bismuth, copper and titanium combined with the finite element method (FEM) were employed to determine the real pressure in processing disc samples by HPT. Any break in the variation of steady-state hardness (monitored experimentally by in-situ torque and temperature rise measurements) versus pressure was considered as a phase transition. FEM simulations show that the hydrostatic pressure is reasonably isotropic but decreases with increasing distance from the disc center and remains unchanged across the disc thickness. Both experiments and simulations indicate that the mean hydrostatic pressure during HPT processing closely corresponds to the compressive load over the disc area plus the contact area between the anvils.
  • Characteration of Laser Cladded Fe-Mn-Cr Alloy Coatings Modified by Plasma Nitriding

    pp. 539-543

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    DOI:10.2320/matertrans.M2015396

    With the use of the high-performance precision mould, the requirements on the high speed, high reliable mould parts become more and more stringent. In order to further improve the surface wear resistance of moulds, Fe-Mn-Cr alloy coatings was prepared by a duplex treatment consisting of laser cladding followed by plasma nitriding. A dense structure coating with no cracks, pores or other defects were obtained after the duplex treatment, presenting a good metallurgical bonding to the substrate. After the duplex treatment, a nitride-layer of ξ-Fe2N+Cr2N and α-Fe with nitrogen were formed on the coating surface. The influence of the duplex treatment on the hardness and wear resistance of the cladding layer were investigated. The hardness of the coating significantly increased, with an average microhardness of 1788 HV, which ensured the wear resistance of the coating. Comparing with laser cladded coating, the samples with duplex treated coating dropped about 41% in wear rate, and performed a better wear resistance. The main wear mechanism of the samples with duplex treated coating was abrasive wear.
  • System and Experiment on Fast Testing Vermicular Graphite Percent in Cast Iron Based on Ultrasonic Longitudinal Wave

    pp. 544-548

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    DOI:10.2320/matertrans.M2015439

    Vermicular graphite percent is an important index of evaluating the vermiculation of graphite in cast iron. Quantitative metallographic method is commonly used to test the vermicular graphite percent, but it can only detect certain parts of the cast iron specimen. Therefore, an ultrasonic system was designed to detect the degree of the vermiculation in cast iron according to the relationship between the ultrasonic propagation velocity and the vermicular graphite percent, and it is composed of the sink filled with ultrasonic coupling agent, ultrasonic emitting probe, ultrasonic receiving probe, high-frequency signal generator, ultrasonic signal acquisition unit and computer. Without measuring the length of the cast iron specimen, the propagation velocity can be calculated by three different kinds of propagation time. A specific relation between the vermicular graphite percent η and the propagation velocity ν was got by experiments. When the propagation velocity is below 5700 m・s−1, they have an approximate exponential relationship, namely η = 0.6·exp(26800/ν). When the propagation velocity exceeds 5700 m・s−1, they have a linear relationship, namely η = −ν/1.53 + 5800/1.53. The comparative experiments showed that the coefficient of variation and the error were below 0.3% and 4%, respectively, which indicated the repeatability and accuracy of the system are very good.
  • Fabrication and All Solid-State Battery Performance of TiS2/Li10GeP2S12 Composite Electrodes

    pp. 549-552

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    DOI:10.2320/matertrans.Y-M2016804

    TiS2/Li10GeP2S12 composite electrodes were fabricated using a mill pot rotator, and their electrochemical properties were investigated in all solid-state batteries of TiS2 cathode/Li10GeP2S12 solid-electrolyte/In-Li anode. The batteries compressed under a pressure of 19 MPa demonstrated poor cycle stability and rate capability because of the deterioration of physical contact between the TiS2 and the Li10GeP2S12. The battery performance was considerably improved by applying a pressure of 228 MPa throughout the electrochemical cycling while maintaining the contact area. The battery delivered the reversible a capacity of over 160 mAh・g−1 under 1 C operation with high capacity retention.
  • Application and Compositional Optimization of Zn Alloys for High Temperature Solders

    pp. 553-557

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    DOI:10.2320/matertrans.MBW201514

    The effectiveness of the electronic parameter on the predicting the mechanical properties of Zn system alloys for high temperature applications was evaluated in order to satisfy both the tensile strength of 200 MPa and elongation of 5%. The electronic parameter was used s-orbital energy level (ΔMk) in this study. Promising composition of alloys were Zn-4Al-7Sn, Zn-10Al-0.5Sn, Zn-10Al-2Sn and Zn-5.1Al-0.5Sn in mass%, and their ΔMk values were 0.079, 0.080, 0.089 and 0.045, respectively. The experimental results of tensile test for designed alloys showed that the tensile strength of 195–225 MPa depend on the increment of ΔMk values, and elongation are 4.5–5.1%. Optimization of composition on Zn system alloys was found to be speedy and precisely achieved using the ΔMk parameter. The wetting contact angles between Cu plate and the designed alloys of Zn-4Al-7Sn, Zn-10Al-0.5Sn, Zn-10Al-2Sn and Zn-5.1Al-0.5Sn at 973 K in the Ar stream are 33.8°, 43.3°, 50.1° and 44.3°, respectively, suggesting that the designed alloys can be practically applied at high temperature. Moreover, the thermal conductivity, tensile test of designed alloys at high temperature were also evaluated.

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