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

MATERIALS TRANSACTIONS Vol. 59 (2018), No. 5

  • Preparation and Compressive Performance of an A356 Matrix Syntactic Foam

    pp. 699-705

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    DOI:10.2320/matertrans.M2018003

    The uniformity of the cell size of aluminum foams prepared by traditional melt foaming and gas injection methods is difficult to control. In order to improve the controllability of cell size and mechanical performance of aluminum foam, an A356 matrix syntactic foam was prepared by the improved stir casting process. Moreover, the compressive property of the syntactic foam was studied and compared with other metal foams. Al2O3 hollow spheres with the diameters of 3–5 mm were added in the molten A356 alloy, then the syntactic foam can be obtained after stirring and compaction. The hollow spheres in the syntactic foam are random loose packed. The volume fraction of 3–3.5 mm hollow spheres in the syntactic foam could reach to 56%. The total densities of the syntactic foams are around 1.79 g/cm3. Through the analysis both in macroscopic and microscopic, the interfacial bonding between aluminum matrix and hollow spheres was proved to be good even after mechanical cutting. The quasi-static compression result showed that the plateau stress of the syntactic foam with 3–3.5 mm hollow spheres could reach up to 46 MPa, and the corresponding densification strain energy is 20 MJ/m3. Moreover, the plateau region is flat, long and relatively high. The syntactic foam with the hollow spheres of 3–4 mm diameter has the highest overall porosity and the best compressive performance. Compared with other traditional aluminum foams, this syntactic foam has advantages in energy absorption performance and the adjustability of cell size.
  • Molecular Dynamics Investigation of the Effect of Lanthanum on the Diffusivity of Niobium in Austenite

    pp. 706-711

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    DOI:10.2320/matertrans.M2018013

    By employing the force-matching method, an embedded-atom-method potential for Fe–Nb–La dilute solid solution has been constructed by fitting to a set of density-functional theory (DFT) data of reference structures. The developed potential reproduces the properties of the reference structures in good agreement. Using the developed potential, molecular dynamics simulations were performed to investigate the diffusion coefficients of Nb in Fe–Nb and Fe–Nb–La systems, respectively. The results indicate that the addition of La suppresses the diffusion of Nb in fcc Fe, the activation energy of Nb was determined to be 47551 J/mol in the absence of La while 82672 J/mol in the presence of La, and consequently leads to the longer incubation time of NbC precipitation in the La micro-alloyed austenite.
  • Martensitic Transformation of Retained Austenite in Ferrite Matrix for Low Alloy Steel

    pp. 712-716

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    DOI:10.2320/matertrans.M2017330

    Martensitic transformation behavior in low-alloy transformation-induced plasticity steels has been studied at 293 K and 193 K. The as-received austenite precipitated in the ferrite matrix satisfied the Kurdjumov–Sachs orientation relationship with the ferrite matrix. The transformed martensite in the ferrite matrix was detected and it commonly exhibited the same orientation as the ferrite matrix. The martensitic transformation was independent of the selection of variant by stress accommodation. Thus, the transformed martensite variant was chosen predominantly to reduce interfacial energy. The transformed martensite may contribute to work-hardening in the ferrite matrix as a harder phase. Further, the transformed martensite at ferrite grain boundaries was due to stress accommodation. The variant achieving the highest Schmid factor in individual austenite was predominantly chosen to introduce slip deformation.
  • Effect of Ag Addition to Zn22 mass%Al–2 mass%Cu Alloy on the Four-Phase Reaction η + ε → α + τ′

    pp. 717-723

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    DOI:10.2320/matertrans.M2017353

    The effect of Ag additions to the four-phase, η + ε → α + τ′, was studied experimental and thermodynamically using Zn–22 mass%Al–2 mass%Cu base alloys with four Ag contents from 0 to about 4 mass% Ag. SEM and XRD results indicated the presence of the τ′ phase decreased as the Ag content increased for the aged alloys which can be attributed to the stabilization of the ε phase because of its increase in Ag content which is in agreement with Thermo-Calc results. The Ag addition also promoted a slowest decrease in hardness in the aging curves at 200°C which can be attributed to the slowest diffusion process for the quaternary alloy.
  • Microstructures and Properties of Al–27%Si Composites: Influence of Rolling and Annealing

    pp. 724-729

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    DOI:10.2320/matertrans.M2017369

    Al/Si composites with 27 mass % Si were prepared by powder metallurgy, and then were multi-pass hot-rolled and, the deformation reduction was 8%–15% for each pass. An intermediate annealing treatment with the holding time of 30 min was prepared for the next rolling process until the rolling reduction was 70%. At last specimens were annealed at 400°C for 6 h followed by air cooling. Microstructures and properties of the composites were investigated. The results show that the prepared composites consist of Al and Si phases, and Si particles distribute uniformly in Al matrix. During the rolling process, the deformation behavior of the composites is sustained by Al matrix, while Si particles are not deformed. The coefficient of thermal expansion (CTE), the thermal conductivity (TC) and the mechanical strength of the composites are also improved by the rolling process. The TC are improved and the mechanical strength are reduced due to the decrease of residual stress after annealing treatment. The annealed composite with the rolling reduction of 70% shows comprehensive properties with the CTE of 17.61 × 10−6/K (25–200°C), the TC of 169 W/(m·K), the tensile strength of 137 MPa and the bending strength of 228 MPa.
  • Age Heat Treatment of the CoCrFeNiTi0.3 High-Entropy Alloy

    pp. 730-733

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    DOI:10.2320/matertrans.M2017418

    The hardness and microstructure of an as-cast CoCrFeNiTi0.3 high-entropy alloy after age heat treatment 24–144 h at 500–1000°C are investigated. The as-cast alloy has a dendritic structure in which the dendrite is a Ti-lean face-centered cubic solid solution phase (FCC1) and the interdendrite consists of a Ti-rich face-centered cubic solid solution phase (FCC2), a mixture of (Cr, Fe)-rich σ phase and (Ni, Ti)-rich η phase. After a 144 h of age heat treatment, age hardening is observed at temperatures of 600–800°C because the amount of σ phase increases in the interdendrite. The optimum hardness is obtained at an aging temperature of 700°C, which makes the hardness increase from HV366 to HV508. However, age softening occurs at 900–1000°C. The vanishing σ phase at 1000°C brings the alloy hardness to the minimum, HV223.
  • Effect of Heat Treatment within Alpha/Beta Dual-Phase Field on the Structure and Tensile Properties of Binary Ti–Mo Alloys

    pp. 734-740

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    DOI:10.2320/matertrans.M2017371

    The present study investigated the effect of heat treatment within the alpha (α)/beta (β) dual-phase field on the structure and tensile properties of Ti–(1.5–9.5) mass% Mo alloys. The alloys were prepared using an arc-melting vacuum-pressure type casting system. The cast alloys were heat-treated at 700, 750 and 800°C in vacuum for 30 minutes followed by quenching in ice water. The X-ray diffraction (XRD) results indicated that beta (β) phase intensities increased while α/alpha prime (α′) intensities decreased with increased heat treatment temperature (HTT) and Mo concentration. The β phase was observed to dominate the 800°C-treated Ti–9.5Mo alloy, while the highest alpha double prime (α′′) phase content was observed in the 800°C-treated Ti–7.5Mo alloy. Both optical and scanning electron microscopy indicated that a relatively coarse α platelet was always observed in Ti–1.5Mo. A fine, uniformly-distributed acicular microstructure was observed in Ti–7.5Mo, while an equi-axed β granular microstructure was clearly seen in Ti–9.5Mo. The tensile properties were found sensitive to the HTT and Mo concentration. When heat-treated at 700°C, the yield strength (YS) and ultimate tensile strength (UTS) increased while the elongation generally decreased with Mo concentration. The highest YS and UTS were found in Ti–7.5Mo and Ti–9.5Mo. When heat-treated at 750°C, the strength of Ti–5.5Mo was improved without reducing elongation. With Mo concentration increased to 7.5% or higher, the elongation further increased while the strength maintained a similar level. When treated at 800°C, the YS of Ti–3.5Mo, Ti–5.5Mo and Ti–7.5Mo maintained a lower level than Ti–1.5Mo and Ti–9.5Mo. A fully satisfactory interpretation for the tensile properties and their relationships to the complicated microstructures might not be a simple task due to several different factors simultaneously involved, yet practically it is interesting to note that selected alloys heat-treated within the dual-phase field demonstrated quite promising overall mechanical properties.
  • New Mg–V–Cr BCC Alloys Synthesized by High-Pressure Torsion and Ball Milling

    pp. 741-746

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    DOI:10.2320/matertrans.M2018001

    Mg–V–Cr alloys can be considered as alternatives to the Ti–V–Cr BCC (body-centered cubic) alloys for hydrogen storage at room temperature, but their synthesis has not been successful so far because Mg is immiscible in V and Cr. In this study, the first Mg–V–Cr BCC alloys were synthesized from elemental powders by severe plastic deformation via the high-pressure torsion (HPT) method as well as by high-energy ball milling. Structural homogeneity, thermal stability and hydrogen storage at room temperature were dependent on the composition and the best performances were achieved for the MgVCr composition with the maximum configurational entropy.
  • Modeling of Complete Stress-Strain Curves and Time-Dependent Behaviors of Rocks under Uniaxial Tension

    pp. 747-753

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    DOI:10.2320/matertrans.M-M2018808

    Tensile stresses likely occur in the rock masses around large or intricately shaped caverns. Hydraulic fracturing for oil, gas, or geothermal development requires a deep understanding of crack extensions under tensile stress. Computer simulation is helpful for the estimation of such deformation and failure of in-situ rocks and requires a mechanical model representing complex rock behaviors under tension. The authors’ research group previously proposed the variable-compliance-type (VC) model for rocks and examined the model under compression. In this study, the applicability of the VC model was investigated under uniaxial tension. The close relation between the VC model and the microscopic failure mechanisms of crack extensions under uniaxial tension was clarified using the linear elastic fracture mechanics and the damage mechanics. Based on the relation, the VC model was modified to reproduce the deformation and failure under uniaxial tension. Then the model was validated by comparing the simulated and experimental results of complete stress-strain curves in both dry and wet conditions, loading-rate dependence, and creep deformation of various rocks under uniaxial tension. In addition, the applicability of the model to numerical simulation programs and the future subjects were discussed.
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  • Lifetime in Steel Cord Wire Drawing Dies of WC–Co Cemented Carbide Containing TaNbC or Cr3C2

    pp. 754-759

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    DOI:10.2320/matertrans.Y-M2018811

    Wire-drawing dies and specimens of WC–Co cemented carbides containing TaNbC or Cr3C2 were fabricated by hot isostatic pressing (HIP) at 1633 K in 40 MPa Ar and by annealing at 1593 K in vacuum. The lifetimes of steel cord wire-drawing dies were evaluated and their mechanical properties such as hardness, transverse rupture strength, and fracture toughness were examined. The lifetime of the drawing die was noted to have remarkably improved by annealing for WC–Co cemented carbides containing both TaNbC and Cr3C2. The alloys containing TaNbC had longer lifetimes than those containing Cr3C2. The lifetime of a drawing die was weakly related to its hardness but appeared to have no correlation with its strength or toughness. The remarkable improvement in the drawing die lifetime resulting from annealing treatment after HIP and the longer lifetime of TaNbC-containing alloys can be understood in terms of the adhesion strength between the WC and Co phases being affected by the alloy content and heat treatment of cemented carbides. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 64 (2017) 17–22.
  • Strength and Microstructure of Copper Tube in Cross-Roll Straightening

    pp. 760-763

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    DOI:10.2320/matertrans.M2017396

    The diameter and wall thickness of copper tubes used for heat transfer in heat exchangers have been decreased in order to improve performance and save resources. One of the problems related to the reduction in tube wall thickness and diameter is ensuring the workability of the products. Copper tubes used in heat exchangers are subjected to various types of processing, such as hairpin bending, expansion, and flaring. Since the necessary stiffness cannot be achieved in copper tubes with thin walls, defects such as buckling may occur. Copper tube manufacturers deal with such problems by fine control of the mechanical properties of the materials. This paper focuses on straightening used in tube manufacture as a potential machining method for providing precise control of mechanical properties. The strength and microstructure of a work-hardened copper tube before and after straightening was investigated.A decrease in tensile strength after straightening was observed regardless of the drawing conditions. The decrease in tensile strength was larger when the tubes were drawn to higher reduction ratios of cross-sectional area; the largest decrease in tensile strength was observed when the reduction ratio of the cross-sectional area was 98%. In this case, the tensile strength before straightening was 450 MPa, and after straightening, decreased by 21 MPa to 429 MPa. Vickers hardness testing showed that the surface layer of the copper tube decreased in hardness. Crystal structure analysis showed that this corresponded with a change in balance of the orientation density of Cu and Goss orientations developed during drawing. Straightener rolls rotate crystal grains in the surface layer of the copper tube, changing the Cu orientation to the Goss orientation. The study confirmed that the mechanical properties of copper tubes could be altered by changing the texture of the material, even using processing operations such as straightening, without significant alteration of the cross-sectional area.
  • Effects of Doping Nano-La2O3 on the Microstructure and Mechanical Properties of Mo–9Si–18B Alloys

    pp. 764-770

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    DOI:10.2320/matertrans.M2017309

    The refractory Mo–9Si–18B (at%) alloy doped with different mass fractions of nano-La2O3 were prepared by combining arc-melting, mechanical alloying and vacuum hot-pressing sintering techniques. The microstructures and mechanical properties of the alloys were systematically investigated. The results showed that the doped alloys presented finer grains than that of the non-doped alloys. Interestingly, most of the La2O3 particles dispersed in the grains interior rather than gathered in the grain boundaries by this combining process. This optimal microstructure had led to corresponding improvement in the compression strength (both at room temperature and 1200°C) and room temperature fracture toughness of the Mo–9Si–18B alloys. Among these alloys, the 0.6 mass% La2O3 doped alloys exhibited the best mechanical properties. The predominant strengthening mechanisms are particles dispersion strengthening and fine-grain strengthening. And the toughening mechanism mainly involves particle toughening.
  • Deformation Microstructure Developed by Nanoindentation of a MAX Phase Ti2AlC

    pp. 771-778

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    DOI:10.2320/matertrans.MBW201703

    Deformation microstructure that developed during nanoindentation of a MAX phase Ti2AlC was characterized by the scanning probe microscopy and the transmission electron microscopy. To investigate the plastic anisotropy, nanoindentation measurements were made on grains with the normal parallel to ‹3362›, ‹0001›, and ‹1120›. The basal slip, {0001} ‹1120›, was found to be predominant as the deformation mechanism for all the indentation directions. It was also indicated that, upon nanoindentation along ‹0001› and ‹1120›, non-basal slips occurred underneath the indenter. The slip system of the non-basal dislocations was identified to be (1216)[1211] by analyzing the dislocations. Furthermore, fine-scaled kink-bands were found to form underneath the residual impression. The formation of the kink-band was accompanied by delamination, i.e., micro-cracking along the basal plane, suggesting that the delamination plays an important role for kink-band formation in Ti2AlC.
  • Corrosion Behavior of Sn-Bearing Steel under Wet/Dry Cyclic Environments Containing Cl

    pp. 779-786

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    DOI:10.2320/matertrans.M2017417

    The corrosion potential and corrosion rate of steel under wet/dry transitions were investigated using the Kelvin probe/pressure difference measurement system in order to elucidate the effect of Sn on the corrosion of steel covered by a thin electrolyte film in wet/dry environments containing chloride ions (Cl). The corrosion rate in the case of an electrolyte containing Cl during the drying stage was higher than that in the case of an electrolyte containing sulfate ions (SO42−). Cl accelerate the hydrolysis of Fe3+ and lead to the acidification of the anode site in the thin electrolyte film, while also contributing to corrosion during the drying stage. The Sn-bearing steel showed a lower corrosion rate during the drying stage than that of the mild steel. This was because the Sn ions from the steel can exist stably in the acidic thin electrolyte film and inhibit the anodic reaction during the drying stage. Thus, the superior corrosion resistance of the Sn-bearing steel under atmospheric conditions is attributable to the retardation of the anodic reaction during drying by Sn ions.
  • Selective Leaching and Surface Properties of Cu–Al–Ni Shape Memory Alloys

    pp. 787-792

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    DOI:10.2320/matertrans.M2017287

    This study investigated the selective leaching, chemical compositions, and electrochemical properties of Cu–XAl–4Ni (X = 12.5, 13.0, and 13.5) shape memory alloys (SMAs). The selective leaching results showed that the Cu–XAl–4Ni SMAs released approximately 200 ppb of Cu ions, 200 ppb of Al ions, and 600 ppb of Ni ions after immersion in Ringer’s solution for 90 days. The low concentrations of Cu and Al ions stem from the oxidation of Cu and Al atoms near the surface of the Cu–XAl–4Ni SMAs to form Cu2O and Al2O3 films. The selective leaching properties of the Cu–XAl–4Ni SMAs were inferior to that of the TiNi SMA, which possessed a highly passive TiO2 film on the surface, but were much better than those of the TiNiCu and TiNiFe SMAs, whose TiO2 films were deteriorated by the formation of NiO, Cu2O, and Fe2O3 oxides. Cu–XAl–4Ni SMAs are potential candidates to serve as biomaterials, owing to their acceptable surface and selective leaching properties, high martensitic transformation temperatures, low cost, good machinability, and excellent electric and thermal conductivities.
  • Preparation of Copper-Based Superhydrophobic Surfaces by Jet-Electrodeposition

    pp. 793-798

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    DOI:10.2320/matertrans.M2017361

    The surface state of metallic materials significantly affect their physical, chemical, and corrosion behavior. In the present study, superhydrophobic coating with copper deposits fabricated using a jet-electrodeposition device on the pure copper substrates for reducing the corrosion rate of the copper substrates was studied. The effect of the micro-nano structured superhydrophobic coating on the improvement of corrosion resistance was investigated. Factors including the microstructures and wetting properties of coating were comprehensively analyzed using a scanning electron microscope, a Fourier transformed infrared and a surface contact angle meter. Results showed that the superhydrophobic coatings demonstrated a micro-nanostructure on the copper substrates. After modifying the copper deposits with stearic acid, a superhydrophobic surface was consequently obtained. The static contact angle (CA) and the sliding angle of the copper-based superhydrophobic surface were 151.6° and 5.7°, respectively. The samples covered with superhydrophobic coating exhibited relatively higher corrosion potential and lower corrosion current than the bared pure copper samples, indicating a notable enhancement of corrosion resistance characterized using polarization tests by an electrochemical workstation.
  • Evaluation of Wrinkling States Using In-Process Ultrasonic Examination during Sheet Metal Forming

    pp. 799-804

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    DOI:10.2320/matertrans.P-M2018807

    In press forming, sampling inspection has been performed during production. However, in sampling inspection, there is the possibility that defective products will proceed to the next process despite inspection. In this paper, we investigated a method for detecting wrinkle defects occurring during deep drawing in order to prevent the outflow of defective products. Deep-drawing tests were performed using a drawing die incorporating an ultrasonic transducer. During deep drawing, ultrasonic waves were irradiated to the interface between the die and the workpiece, and the occurrence of wrinkles was examined on the basis of ultrasonic reflection characteristics. The ultrasonic reflection intensity was changed by the occurrence of the wrinkles. The influence of wrinkle height and wrinkle wavelength on relative reflection intensity was shown. It was demonstrated that ultrasonic measurement is an effective method of detecting wrinkles during press forming. This Paper was Originally Published in Japanese in J. JSTP 58 (2017) 393–397.
  • Effect of Shape Memory Heat Treatment on Microstructures and Mechanical Properties of Powder Metallurgy TiNi Shape Memory Alloy

    pp. 805-810

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    DOI:10.2320/matertrans.Y-M2018810

    The shape memory heat treatment effects on the microstructures and mechanical properties of TiNi shape memory alloys fabricated by powder metallurgy (PM) process were investigated in this study. Through the optimization of the shape memory heat treatment conditions, PM TiNi alloy showed a high plateau stress of 454 MPa and good shape recovery of 96.4% in 8% tensile strain applied via the heat treatment at 773 K for 10 min. A longtime heat treatment applied to PM TiNi alloys caused an increase of the amount of Ti3Ni4 precipitates in the TiNi matrix, and resulted in the relative decrease of Ni solid solution in the matrix which caused the decrease of the plateau stress. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 65 (2018) 85–90.
  • Comparison of the Photocatalytic Efficience for Cu and N Co-Doped TiO2 by Sol-Gel and Xerogel-Hydrothermal Methods

    pp. 811-815

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    DOI:10.2320/matertrans.M2018031

    In this study, mesoporous Cu and N doped TiO2 crystals were synthesized with Cu and N doped titania by xerogel-hydrothermal treatment and sol-gel treatment. The characteristics of Cu and N doped TiO2 were investigated with XRD, UV-vis, XPS and N2 sorption analysis. The photocatalytic activity of samples was evaluated by the photocatalytic oxidation of acetone under ultraviolet light. The photocatalytic activity of the xerogel-hydrothermal modified Cu and N doped TiO2 was considerably higher than that of the sol-gel modified Cu and N doped TiO2. This enhanced photoactivity is related to the smaller particle sizes, bicrystalline, the smaller pores and the larger specific area.
  • A Novel Directional Solidification of TiAl-Based Alloys by Electromagnetic Cold Crucible Zone Melting Technology with Y2O3 Moulds

    pp. 816-821

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    DOI:10.2320/matertrans.M2018018

    In order to decrease mould contamination, a novel directional solidification process was developed for TiAl-based alloys, where an Y2O3 mould was incorporated into electromagnetic cold crucible (EMCC) zone melting technology. To determine the characteristics of this process, the macro/microstructures and mechanical properties of directionally solidified (DS) Ti–45Al–2Cr–2Nb ingots prepared by two kinds of directional solidification techniques, namely traditional graphite heating (control group) and EMCC heating, were extensively investigated using electromagnetic field and temperature field. Compared with the control group, this new technique can induce bigger electromagnetic force in the tangential direction, generate a more rapid heating and higher temperature gradient, and decrease the interaction between the mould and melt; however the heat transfer is altered to inclining outward owe to the lateral heat transfer. The DS sample prepared by this method can achieve finer columnar crystals growing toward the axis, α2/γ lamellae, and lower levels of contamination with regard to Y2O3 particles and oxygen. These are beneficial to improve room temperature fracture toughness and tensile properties.
  • Grain Boundary Segregation and Precipitation during the Plastic Deformation of 30Cr2Ni4MoV Steel

    pp. 822-828

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    DOI:10.2320/matertrans.M2017363

    The carefully controlled forging of as-cast 30Cr2Ni4MoV steel was investigated as a mean to refine its coarse grain structure and crush the dendrites that cause segregation. This found that a fine-grained (∼50 um) structure could be achieved by deformation at 1000°C as a result of DRX. Grain boundary segregation of Mo caused a significant precipitation of MoC that could effectively pinned grain boundaries and suppressed the grain growth. In contrast, forging at temperatures above 1000°C led to a significant increase in grain size. Furthermore, the grain boundary segregation of sulfur resulted in the formation of low melting point sulfides near the grain boundaries that provided additional initiation points for intergranular cracking, thereby reducing the mechanical properties of the alloy. The results of this study therefore provide a basis for optimizing the forging process so as to improve the microstructure of heavy forgings, and sheds new light on the mechanism of grain refinement and crack initiation for 30Cr2Ni4MoV steel.
  • Fabrication and Mechanical Properties of Textured Ti3SiC2 Systems Using Commercial Powder

    pp. 829-834

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    DOI:10.2320/matertrans.Y-M2018812

    Ti3SiC2 is a typical Mn+1AXn (MAX) phase ceramic and exhibits both metal-like and ceramic-like properties. To improve these properties, texturing and Al2O3 addition were performed. The commercial Ti3SiC2 powder used contained approximately 10 mass% TiC phase. Textured Ti3SiC2 was prepared by slip casting in a strong magnetic field (MF) followed by spark plasma sintering (SPS) at 1623 K under a pressure of 40 MPa for 5 min. The Lotgering orientation factor of the (00l) peaks of Ti3SiC2 prepared under an MF was 0.96, and the relative density of samples exceeded 99%. The bending strength and fracture toughness of Ti3SiC2 were improved by texturing. The textured Ti3SiC2 exhibited an excellent bending strength of 978 MPa, but Al2O3 addition, reduced the bending strength and fracture toughness. The textured Ti3SiC2 showed the plastic deformation at a temperature of approximately 1173 K. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy, 64 (10) (2017) 552–557.
  • Heat-Conduction-Type and Keyhole-Type Laser Welding of Ti–Ni Shape-Memory Alloys Processed by Spark-Plasma Sintering

    pp. 835-842

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    DOI:10.2320/matertrans.M2017387

    High-brightness and high-power laser welding with different welding speeds and laser powers was applied to join Ti–51 at%Ni shape-memory alloy, which was fabricated from the elemental pure Ti and pure Ni powders by spark-plasma sintering. Dendritic microstructures were observed in all the welds except the heat-conduction-type weld with the minimum welding parameters. In addition, the weld seam consisted of equiaxial grains surrounded by a narrow dendritic region. Based on the micro-X-ray diffraction pattern, in the keyhole-type welding, the martensite phase declined on increasing laser power and welding speed. Abnormal peak intensities were detected for (211) in the heat-conduction weld and (200) in the keyhole weld. Differential scanning calorimetry results revealed that phase transformation peaks of the conduction-type weld seam were similar to the base metal of Ti–51 at%Ni SMA, whereas the corresponding peaks of the phase transformation in the other weld seams shifted towards lower temperatures due to Ni depletion in the matrix, grain coarsening and residual stress. Therefore, the findings suggest that heat-conduction-type can be a promising method for surface treatment of Ti–Ni SMAs with minimum effect on the microstructure and shape memory properties.
  • Scorodite Synthesis in As(V)-Containing Fe(II) Solution in the Presence of Hematite as a Fe(III) Source

    pp. 843-849

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    DOI:10.2320/matertrans.M-M2018809

    Stabilization of arsenic by precipitation of large crystalline scorodite (FeAsO4·2H2O) particles is considered to be a promising option for treating As(V) contained in industrial by-products. In this study, scorodite synthesis by direct addition of hematite particles as a Fe(III) source to Fe(II) solution containing As(V) was investigated with different initial Fe(II) concentrations. During scorodite formation, the Fe(II) concentration and pH of the reaction solution are almost constant, and the residual arsenic concentration in the solution is low. The initial Fe(II) concentration strongly affects scorodite formation, and larger faceted crystalline scorodite particles are obtained with higher initial Fe(II) concentration. The observed scorodite particle size is larger than that formed by the conventional DMSP method. Coarse faceted scorodite can also be obtained by direct addition of hematite powder to FeSO4 solution with As(V). From the results of environmental leaching tests, O2 gas blowing for a short time to convert the remaining unstable gel-like precursor to crystalline scorodite is very effective to prevent arsenic leaching. Furthermore, for the gel-like precursor formed in the initial stage of the scorodite synthesis process, chemical state analysis by X-ray absorption spectroscopy in the range of the X-ray absorption near-edge structure at the Fe K absorption edge for iron reveals that the precursor contains Fe(II) as well as Fe(III). This indicates that scorodite does not directly form from Fe(III) ions from hematite and arsenate ions from solution, but a gel-like precursor initially forms from Fe(II) ions in solution and is then converted to crystalline scorodite.
  • The Use of Methyl Ethyl Ketone in Nitric Acid Leaching Processes for Enhancement of Ag Recovery from Used X-ray Films

    pp. 850-854

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    DOI:10.2320/matertrans.M2017278

    A feasibility study was carried out to improve conventional recycling processes of used X-ray film, where silver was recovered mainly by concentrated nitric acid leaching. In the X-ray film, an emulsion layer containing silver is attached to polyester film base, and the enhancement of Ag leaching was expected by separating the emulsion layer from the polyester film base using methyl ethyl ketone (MEK), because the separation could increase the contact surface between nitric acid and Ag in the emulsion layer. First, the separation behaviors using MEK were investigated and the separation efficiencies of the emulsion layer increased with increasing temperature but decreasing film size and pulp density. The separation efficiency increased to 100% in MEK solution within 3 min under the following conditions; temperature 50°C; setting agitation speed 400 rpm; pulp density 50 g/L; film size 1 × 1 cm. In the followed nitric acid leaching test, the leaching result using the separated emulsion layer showed higher leaching efficiency than that using the unseparated X-ray film. Second, the effect of adding MEK to nitric acid leaching on the leaching efficiency of Ag was investigated by considering the amount of MEK added and temperature as experiment factors. The leaching efficiency of Ag increased with increasing the amount of MEK to 5%, but further addition of MEK to 7% rather reduce the leaching efficiency. With 5% of MEK addition, the leaching efficiency of Ag increased up to 95.9% in 120 min at 50°C whereas it increased and then decreased to 2.7% in the test at 70°C due to the formation of AgCl. These results indicate that the leaching efficiency of Ag could be enhanced using MEK in the nitric acid process for the recovery of Ag from the used X-ray film.
  • Hydrogen Desorption Isobar Properties of Ti1.1CrMn at High Temperatures and Pressures

    pp. 855-857

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    DOI:10.2320/matertrans.M2018012

    In this study, we developed a thermochemical technique to compress hydrogen gas up to more than 80 MPa. The results showed that Ti1.1CrMn alloys can generate a hydrogen pressure of 82 MPa upon being heated to ∼200°C. In order to evaluate the hydrogen absorption and desorption properties of the Ti1.1CrMn alloy at elevated temperatures, its pressure-composition (PC) isotherms were measured at 100, 140, and 180°C. To examine the durability of the alloy, hydrogen compression cycle tests were performed at pressures ranging from 14 to 80 MPa by heating the alloy from 35 to 200°C. In order to determine the temperature required for achieving the dissociation pressure of 82 MPa, we generated an isobar plot based on the PC isothermal measurements.
  • Low Young’s Modulus Ti–Nb–O with High Strength and Good Plasticity

    pp. 858-860

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    DOI:10.2320/matertrans.M2018021

    Oxygen was added to Ti–38Nb (mass%) alloys to improve their mechanical properties. Ti–38Nb–xO (x = 0.13, 0.24, 0.46, mass%) alloys were prepared by arc melting, and subsequently subjected to homogenization, hot rolling, and solution treatment. It was found that adding oxygen suppresses the martensite transformation and exhibits strong solution strengthening effect. Single β phase is obtained in Ti–38Nb–0.24O, whereas Ti–38Nb–0.13O is composed of both α′′ and β phases. Both alloys exhibit double yielding phenomena during tension, indicating a stress-induced martensitic transformation. Ti–38Nb–0.46O exhibits a non-linear deformation, a low Young’s modulus of 62 GPa, high tensile strength up to 780 MPa, and elongation around 23%, which are promising characteristics for biomedical applications.

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