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

MATERIALS TRANSACTIONS Vol. 57 (2016), No. 5

  • Corrosion of Ultrafine Grained Materials by Severe Plastic Deformation, an Overview

    pp. 559-572

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    DOI:10.2320/matertrans.M2015452

    Corrosion of ultrafine grain (UFG) materials by severe plastic deformation (SPD) is reviewed in light of the existing literature and microstructural change. Fortunately, by holistic survey of the literature, it seems likely that grain refinement by SPD, while enhancing mechanical properties, does not compromise the overall corrosion resistance, and in many case, improve it in comparison with coarse-grained counterparts, although there are some contradictory results within the same materials and same environment. The degree of impact of UFG formation on corrosion is highest in stainless steels followed by aluminum and magnesium alloys whereas it is relatively marginal in pure copper and titanium. The effect of UFG formation by SPD on corrosion is imparted by not only grain refinement, but also other microstructural change occurring commonly in SPD in general and unique to each specific SPD method. In this review, an attention is paid specifically to the former case, and this includes shuffling or redistribution of chemical inhomogeneity into a finer scale, deformation-induced grain boundaries and high internal stress stemming from these grain boundaries. The literature on stress corrosion cracking (SCC) of UFG materials are definitely insufficient to find the general trends, more studies are waited.
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    2. Friction Lap Joining of Thermoplastic Materials to Carbon Steel ISIJ International Vol.56(2016), No.7
  • High-Performance Ceramic-Lined Composite Pipes with ZrO2 Additive Prepared by Centrifugal-SHS Process

    pp. 573-581

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    DOI:10.2320/matertrans.MC201503

    High-performance ceramic-lined composite steel pipes (CLCSPs) were fabricated by self-propagating high-temperature synthesis and centrifugal casting technique. ZrO2 powders doped by 3 mol% Y2O3 were added into Al-Fe2O3 thermit to improve the mechanical properties of CLCSPs. The phase constituents and microstructural evolution of ceramic layers after addition of ZrO2 were analyzed by means of X-ray diffractometer, optical microscope, scanning electron microscope and energy dispersive X-ray spectrometer. The effects of ZrO2 on fracture toughness of ceramic layers, and crushing strength as well as mechanical shock of CLCSPs were investigated using Vickers indentation microfracture method, squeezing test and repetitive impacting method. The results show that addition of ZrO2 changes the morphology and preferential orientation of Al2O3 dendrites, and reduces the width of Al2O3 dendrites, leading to the microstructure of Al2O3 dendrites with fine t-ZrO2 phase particles distributed at boundaries. The hardness of ceramic layer decreases, while the crushing strength of CLCSP changes slightly after addition of ZrO2. The fracture toughness of ceramic layer is significantly enhanced; meanwhile the mechanical shock resistance of CLCSPs was also greatly improved by adding more than 2% ZrO2. The optimum adding amount of ZrO2 is 4%–6%.
  • Effect of the Interfacial Thermal Resistance on the Effective Thermal Conductivity of Aluminum Matrix Composites

    pp. 582-589

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    DOI:10.2320/matertrans.MC201505

    To investigate the degree of the effect of the interfacial thermal resistance between the matrix and the reinforcement, the effective thermal conductivity of aluminum matrix composites (Al/SiC, Al/TiB2, Al/Al2O3 and Al/SiO2) was calculated with the new simulation code which can take account of heat transfer at the interface. The critical element size was defined by a simple equation, Lcr = h/λ, where λ is the harmonic mean of thermal conductivities of the reinforcement and the matrix, and h is the coefficient of heat transfer between the reinforcement and the matrix. This critical element size is important value to design composites. If the size of the reinforcement is smaller than the critical element size, it is predicted that the effective thermal conductivity will decrease by the interfacial thermal resistance. On the other hand, if the size of the reinforcement is large enough, the effective thermal conductivity will not decrease. The validity of the critical element size for aluminum matrix composites was confirmed in this study.
  • Fabrication of Fe-Mn-Si-Cr Shape Memory Alloy Fiber/Aluminum Matrix Smart Composite by Casting

    pp. 590-599

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    DOI:10.2320/matertrans.MC201504

    If the composites are reinforced by the shape memory alloy (SMA) fiber that shrinks in the matrix, one can introduce an artificial compressive residual stress along the direction of the shrinkage. In our previous study, an SMA fiber/plaster smart composite, using Fe-Mn-Si-Cr alloy fibers, was fabricated and it was found that the bending strength of the composite was improved by the compressive stress due to the shape recovery force of the SMA fibers. However, the imperfect bonding at interface between SMA fiber and plaster matrix decreased the bending strength of fabricated composite. In this study, Al matrix smart composites containing Fe-Mn-Si-Cr SMA fibers are studied, since it is well known that Fe and its alloys react with Al. Straight Fe-28.2mass%Mn-6.03mass%Si-5.11mass%Cr SMA fibers were arranged on the fiber holder, they were immersed into a mold with molten Al. During this step, ferrous SMA reacted with Al at fiber/matrix interface, results in the good bonding strength at interface. After solidification, ferrous SMA fiber/Al matrix composite could be obtained. This composite was subjected to the rolling deformation to induce the martensitic transformation from γ austenite to ε martensite in SMA fibers. Then the composite was heated to induce the reverse transformation from ε martensite to γ austenite. The ferrous SMA fibers in the composite shrank during this reverse transformation, which could induce tensile stress in fibers and compressive stress in the matrix. This compressive stress in the matrix is a key factor that enhances the mechanical properties of such smart composite. Mechanical properties of fabricated smart composites were also studied.
  • Spark Sintering Behavior of Ubiquitously Fe-B and Fe Powders and Characterization of Their Hard Composites

    pp. 600-607

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    DOI:10.2320/matertrans.MC201506

    Spark sintering behaviors of 10 vol% Fe added FeB powders with 10 μm size (here after called FeB-10Fe) were investigated in spark sintering process for the development of alternative materials of WC-Co alloys. Spark sintering behaviors of FeB-10Fe in the temperature range of 600 to 1493 K were the same in the sintering curves although their maximum temperatures changed from 1493 to 1523 K. The densification rates, , of FeB-10Fe and pure Fe were also obtained experimentally, and the maximum point of was shown at the D of approximately 0.75. The plastic deformation and power law creep deformation of Fe binder phase in FeB-10Fe compacts occurred before and after reaching maximum point of , respectively. The sinterability was improved by 10 vol% Fe addition, and apparent relative density of FeB-10Fe compacts was increased with the increment of the sintering temperature of 1493 K to 1523 K. In contrast, the mean density of FeB-10Fe compacts was decreased with the increment of sintering temperature because of the poor wettability between liquid phase (Fe and Fe2B) and FeB phase in the liquid phase state at 1505 K and 1523 K. The values of Rockwell hardness of FeB-10Fe compacts were decreased with increment of sintering temperature because of the increment of porosities in FeB-10Fe compacts. In contrast, the values of micro hardness on the interfaces between grains were increased with increment of sintering temperature, because of the promotion of atomic diffusion between particles. There were maximum value of compressive-stress and -strain on compacts sintered at highest temperature, also because of promotion of the sintering in the interface between grains.
  • Detection of Cracks in Metallic Objects by Arbitrary Scanning Direction Using a Double U-Shaped Orthogonal ACFM Probe

    pp. 608-612

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    DOI:10.2320/matertrans.M2015384

    Alternating current field measurement (ACFM) technique is developed for sizing cracks on structures. According to the theory of ACFM, the induced current field should be perpendicular to the crack in metallic objects. So conventional ACFM probes should scan the crack in a particular direction. In this paper, a double u-shaped orthogonal ACFM probe is present for cracks detection at arbitrary scanning direction using induced rotating current field. The finite element method (FEM) model is employed to analyze the rotating current field induced by the double u-shaped orthogonal ACFM probe. The experiments are carried out to test the crack on specimen at arbitrary scanning direction. Results show that the crack can be detected effectively at arbitrary scanning direction using the double u-shaped orthogonal ACFM probe.
  • Substance Flow Analysis of Tantalum in Taiwan

    pp. 613-617

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    DOI:10.2320/matertrans.M2015420

    Substance Flow Analysis (SFA) is mainly used to quantify flows and stocks of a particular substance distributed in a finite ecosystem. It can also be used to help decision-makers select the best strategy to implement resource allocation and management. This study focused on tantalum flow in Taiwan in 2013, specifically as tantalum capacitors, powder, and waste products. Tantalum, a rare metal that has a lot of potential, especially in the electronics industry, is not locally produced in Taiwan; so an SFA is vital to monitor supply, demand, and accumulation. Best estimates were done in coordination with Taiwan companies and government agencies, namely: Ministry of Economic Affairs; Ministry of Finance; Customs Department; and Environmental Protection Administration. In 2013, Taiwan imported a total of 340,355 kg of tantalum; 84.5% of this remained in Taiwan either as electronic products or as raw materials, while the rest were exported.
  • Effects of Sr+Ce on Microstructure and Abrasive Resistance of In-Situ Mg2Si/Al-Si-Cu Composites

    pp. 618-623

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    DOI:10.2320/matertrans.M2015334

    In the present study, the modification effect of Sr+Ce in Mg2Si/Al-Si-Cu composites was investigated for controlling both the microstructure and mechanical properties. Furthermore, the hardness and the abrasive resistance after modification were also studied. The results show that when the composites were modified by 0.40 mass% Ce, the morphology of the primary Mg2Si phase changes to a polygonal morphology with a size of 15 μm. However, in those with a 0.40 mass% Ce and 0.05 mass% Sr addition, the morphology changes to an irregular and equiaxed shape, and the size increases to 50 μm. Furthermore, in the 0.40 mass% Ce and 0.10 mass% Sr addition, the primary Mg2Si morphology transforms to a rectangular trapezoid, or “T” shape, with sizes measuring 70 μm. Additionally, in the 1.00 mass% Ce and 0.05 mass% Sr, and the 1.00 mass% Ce and 0.10 mass% Sr addition, the primary Mg2Si morphologies become either polygonal or irregular shaped, respectively. The eutectic phases change shows that, with the addition of Ce or Sr, the eutectic phases exist in the form of the binary eutectic of Al+Mg2Si or the ternary eutectic of Al+Mg2Si+Si. The hardness test illustrates that the hardness of the 1.00 mass% Ce and 0.05 mass% Sr and the 0.40 mass% Ce and 0.05 mass% Sr, modified composites are higher than the unmodified composites. The abrasive resistance data shows that modified composites with the 1.00 mass% Ce and 0.05 mass% Sr are higher than that of the modified and unmodified composites with a 0.40 mass% Ce and 0.05 mass% Sr. The abrasive resistance agrees with the hardness test results, and this demonstrates that the Sr+Ce addition can change the microstructure and enhance the mechanical properties of the material.
  • Effect of Aging and Stress on Stability of β Phase in Au-Cd-Ag

    pp. 624-626

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    DOI:10.2320/matertrans.MB201514

    Au52.5-xCd47.5Agx has a single β phase in the composition range of x ≤ 41 and a wide temperature range extending to room temperature or below. Coexistence of the β and α phases has been observed for 41 < x < 47, and the coexistence of the β, α, and ζ phases has been observed for x ≥ 47, as thermal equilibrium states. We found that the α phase appears and coexists with the β phase for x ≤ 41 in the aged alloy at room temperature. The mole fraction and the stability of the α phase depend on the atomic order of the β phase. Moreover, it was found that the ζ phase is stress induced in the composition range of x ≤ 41. The ζ phase disappears with heat treatment to release strain, and so this ζ phase is not stable.
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  • Early Stage Clustering Behavior in Al-Mg-Si Alloys Observed via Time Dependent Magnetization

    pp. 627-630

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    DOI:10.2320/matertrans.M2015474

    Time dependent magnetization of Al-0.67 at.%Mg-0.73 at.%Si, Al-1.07 at.%Mg-0.33 at.%Si and Al-1.07 at.%Mg-0.53 at.%Si alloys are presented over a range of constant temperatures between 250 and 320 K. The magnetization vs. time curves for the samples show minima for temperatures near 290 K. The observed times at which the magnetization minima occur were found to depend on both the solute concentrations and the measurement temperatures. From these results the activation energies from the Si-rich clustering stage to the Mg-Si co-clustering stage were extracted. The deduced activation energies were found to be comparable to those from the positron annihilation measurements, depending on the solute concentrations.
  • Effect of Si Addition on Microstructure and Mechanical Properties of Dual Two-Phase Ni3Al and Ni3V Intermetallic Alloys

    pp. 631-638

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    DOI:10.2320/matertrans.M2015436

    The effects of Si addition on the microstructures and mechanical properties of dual two-phase Ni3Al and Ni3V intermetallic alloys with a composition of Ni75Al9V13Nb3 (expressed by at%) were investigated, focusing on the substitution manner of Si for Ni, Al or V. Solubility limit of Si in the present microstructure was less than 2 at% Si irrespective of the substitution manner of Si for Ni, Al or V. The eutectoid microstructure in the channel region was degenerated when Si was substituted for V. Third-phase dispersions containing Nb, i.e., Ni16Si7Nb6 (G phase: D8a) were present at grain boundaries of the alloys exceeding the solubility limit. In the alloy in which Si was substituted for Ni, unit cell volume of the constituent Ni3Al phase increased while that of the constituent Ni3V phase little changed. In the alloy in which Si was substituted for Al, unit cell volumes of both phases decreased. The alloys in which Si was substituted for Al or Ni hardened while the alloy in which Si was substituted for V softened. The hardening in the former alloys was attributed to solid solution hardening due to Si substituted for solvent atoms Ni, Al and/or V while the softening in the latter alloy was attributed to the degenerated eutectoid microstructure in the channel region. Also, it was shown that the third-phase dispersions little affected hardness as well as yield strength.
  • Effect of Deformation Temperature on Low-Cycle Fatigue Properties of Fe-28Mn-6Si-5Cr Shape Memory Alloy

    pp. 639-646

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    DOI:10.2320/matertrans.MBW201503

    Effect of deformation temperature on low-cycle fatigue properties of an Fe-28Mn-6Si-5Cr shape memory alloy was investigated. Cyclic push-pull loadings at a total strain range of 0.02 were applied to the alloy at various deformation temperatures ranging from 223 to 523 K. The microstructures and fracture surfaces in the fatigue tested samples were analyzed by means of X-ray diffraction, scanning electron microscopy and electron backscattering diffraction. The highest fatigue life of 22,400 cycles was obtained at 423 K. Increasing or decreasing the deformation temperature resulted in a decrease in fatigue life to several thousand cycles. The specimens deformed to fatigue fracture at temperatures below 298 K exhibited microstructures with ε-martensite and brittle characteristics of the fracture surface, while the specimens deformed above 473 K exhibited the single γ-phase and ductile characteristics of the fracture surface. The deformation at 423 K resulted in a moderate amount of the ε-martensite and a mixed brittle/ductile fracture surface patterns. It is suggested that the highest fatigue life can be obtained when the fatigue temperature lies between Msσ and Md.
  • Effect of Boron on the Hot Ductility of Low-Carbon Nb-Ti-Microalloyed Steel

    pp. 647-653

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    DOI:10.2320/matertrans.M2015388

    Hot tensile tests were performed to examine the effect of boron on the hot ductility of Nb-Ti-microalloyed steels. The equilibrium precipitation in the steel was predicted by Thermo-Calc calculation. The microstructure, fracture surface and precipitates in the deformed steel were examined. The results show that boron addition is favorable to improving the hot ductility of Nb-Ti-microalloyed steel. This beneficial effect is caused by the soluble boron instead of coarse BN in the steel. The hot ductility of the steel decreases less from 1000℃ with increasing boron addition. The hot ductility trough shifts toward lower temperatures because ferrite formation was restrained with increasing boron content of the steel. The formation of NbC, TiN and thin film-like ferrite along austenite grain boundaries lead to the decrease in the hot ductility of the steel. Boron addition has negligible influence on the precipitation temperature and amount of TiN and NbC precipitates in Nb-Ti-microalloyed steel. The amount of NbC precipitates is largest in the steel, followed by TiN and BN. The precipitation temperature of BN increases considerably with further increasing the boron content. The fracture mode of Nb-Ti-microalloyed steel tends to be more ductile with the increase in the boron content of the steel.
  • Effect of Lamination Constitution on Post-Buckling Behavior of Symmetrically Laminated Plates with Initial Deflections

    pp. 654-660

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    DOI:10.2320/matertrans.M2016015

    Advanced fiber-reinforced composite materials are being used as structural members in various fields because of their high strength and high stiffness-to-weight ratios. Hence, analysis of thin laminated structures is important. The post-buckling behaviors of thin laminated plates under uniaxial compression have been discussed by many researchers. However, little research has been performed on the secondary buckling phenomenon for thin laminated plates, which occurs with further increase of load. In this paper, the stability conditions of carbon–epoxy symmetrically laminated plates with initial deflections under uniaxial compression that are simply supported along four edges are determined using the second variation of total potential energy. The necessity of secondary buckling is proven analytically, and the effects of various factors, such as initial deflection, lamination constitution, and number of layers, are elucidated.
  • Investigation of Interfacial Friction and Inverse Flowing Behavior under the Adhesive State

    pp. 661-668

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    DOI:10.2320/matertrans.M2015434

    For improving the precision of numerical simulations in metal forming, it is critical to accurately evaluate the interfacial friction between die/specimen and material deformed behavior. However, there is a huge challenge to assess interfacial friction and material deformed behavior due to the complex mechanisms of tribology at the interfaces. In this study, a program of experimental work directed by ring upsetting has been carried out to evaluate interfacial friction and material deformed behavior on account of the specific adhesive friction state. The behavior of adhesive friction was qualitatively identified with characterized phenomenon and quantitatively identified with friction coefficient, which was obtained by taking advantage of Boltzmann distribution characteristics between the radial velocity field and the relative displacements relevant to metal particles on the meridian plane. Furthermore, simple mathematics methods were applied to analyze inverse flowing behavior under the condition of adhesive friction based on the transients displacement achieved by ring upsetting. And the driven mechanism of inverse flowing behavior was also revealed systematically. Finally, a new theory of bi-directionality theory was proposed to illustrate inverse flowing behavior, and the sustainability of adhesive friction was synthetically analyzed.
  • A Sensitive Zinc Ion Electrode Based on Electrochemically Deposited Ethylene Diamine Tetra Acetic onto Glassy Carbon Surface

    pp. 669-673

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    DOI:10.2320/matertrans.M2015253

    The current work was interested in the elaboration of a new electrochemical sensor based on modified glassy carbon electrode for zinc detection. For this 4-para nitrobenzene diazonium (P-NBD), 4-nitrophenyl (NP) and 4-aminophenyl (AP), and ethylene diamine tetra acetic (EDTA) were electrochemically deposited from aqueous solution on the surface of glassy carbon (GC) electrode by potential cycling in the range between 0.4 and −1.25 V. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Square wave voltammetry (SWV) were used to characterize the GC sensor. We show that the Zinc ion sensor based on modified CG electrode was characterized by low limit of detection (LOD) for about 3.74 10−11 g L−1, high sensitivity and wide linear detection range between 2.5 10−12 g L−1 and 2.0 10−07 g L−1. This proposed sensor gave satisfactory results in determination of zinc in water and can be successfully used in the detection of real water samples.
  • Acoustic Emission Monitoring of Laser Shock Peening by Detection of Underwater Acoustic Wave

    pp. 674-680

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    DOI:10.2320/matertrans.M2015401

    Acoustic Emission (AE) technique is one of the nondestructive methods to evaluate the size, location and generation time of deformation or damage of material in real times. Generally AE sensors are directly attached on the surface of the component to detect AE wave, however this method brings about inconvenient setting to many industrial processes. In the present study, an arrangement of AE sensors was investigated to monitor laser shock peening (LSP). Instead of direct attachment of the sensors on the target, several AE sensors were located in the water layer to detect acoustic wave propagating through the water. The results showed that the sensor arrangement has a good performance to monitor LSP. Impact pressures during LSP process were obtained from detected AE waveforms by deconvolution technique. In addition, with AE measurement, sample surface was observed by high speed camera and investigated phenomena during LSP process.
  • The Effect of Fe Addition on the Mechanical Properties of Ti–6Al–4V Alloys Produced by the Prealloyed Powder Method

    pp. 681-685

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    DOI:10.2320/matertrans.Y-M2016806

    The effect of Fe addition on the mechanical properties of Ti–6Al–4V alloys was investigated. Ti–6Al–4V prealloyed powders were prepared via a hydrogenation and dehydrogenation process using turning chips of Ti–6Al–4V alloys as the starting material. Mixed powders of Ti–6Al–4V powders and 3–4 mass% Fe powders were consolidated using a hot extrusion process and subsequently hot rolled. With increasing Fe content, the tensile strength and 0.2% proof stress of the Fe-containing alloys increased by 2%–30% compared to those of the Fe-free alloy in both as-hot-rolled and air-cooled specimens. The results also showed that the elongation in the 3% Fe-containing alloys was at least 10%, regardless of the treatment procedure. The balance between the generated martensitic phase and the β-phase ratio in (α+β)-dual-phase alloys appears to determine both the strength and elongation of the alloys. The Ti alloys obtained in this study have strong potential for application in automobiles and aircraft.
  • Investigation of Microstructure and Mechanical Properties of Friction Stir Lap-Jointed A6061/HT590 Alloys

    pp. 686-690

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    DOI:10.2320/matertrans.M2015413

    In this study, the mechanical properties of friction stir lap-jointed A6061/HT590 alloys were evaluated. Friction stir welding was conducted at a tool rotational speed of 500 rpm and a traveling speed of 300 mm/min, where Ar gas was introduced to prevent the materials from corroding during the welding process. Electron back-scattering diffraction was used to characterize the microstructural parameters such as the grain size, misorientation angle, and crystal orientation. The evolution of intermetallic compounds in A6061 during the process was examined in terms of the morphology, size, and aspect ratio in three distinct zones in the Al base material, the heat affected zone, and the stir zone, where transmission electron microscopy was used. It was revealed that friction stir welding gave rise to grain refinement as well as the growth of intermetallic compounds in A6061. The morphological changes in the intermetallic compounds influenced the mechanical properties, resulting in the occurrence of fracture in part of the base material instead of the jointed parts (heat affected zone and stir zone). This study systematically evaluated the microstructural evolution during the friction stir welding for joining A6061 with HT590 and its effect on the mechanical properties.
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    1. Corrosion of Ultrafine Grained Materials by Severe Plastic Deformation, an Overview MATERIALS TRANSACTIONS Vol.57(2016), No.5
  • Enhanced Mechanical Properties of Nanostructured 2.25CoAl-Al2O3 Composite Sintered by Pulsed Current Activated Heating

    pp. 691-694

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    DOI:10.2320/matertrans.M2015419

    The nanopowders of CoAl and Al2O3 were synthesized from Co3O4 and Al powders using high energy ball milling. The nanostructured 2.25CoAl-Al2O3 composite from the milled powder was consolidated within two min by the pulsed current activated sintering. The mechanical properties and microstucture of the nanostructured 2.25CoAl-Al2O3 was investigated from the view points of using Vickers hardness measurement, X-ray diffraction analysis and FE-SEM observation.
  • Anomalous Temperature Dependence of Hydrogen Permeability through Palladium–Silver Binary Alloy Membrane and Its Analysis Based on Hydrogen Chemical Potential

    pp. 695-702

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    DOI:10.2320/matertrans.M2016020

    The hydrogen permeability of Pd–Ag alloy membranes has been investigated over a wide temperature range between 100℃ and 500℃. The hydrogen permeation coefficient, Φ, for Pd–23mol%Ag decreases with decreasing temperature above 300℃, in good agreement with the previous literature. However, Φ starts to increases below 250℃, and a peak is observed at around 180℃. Considering the silver concentration and operating temperature, the α–α' phase transition never occurs in this condition. In other words, the α–α' phase transition is not the reason for the anomalous peak behavior of Pd–23mol%Ag alloy at low temperature. In addition, it is confirmed that the diffusion–limiting hydrogen permeation reaction takes place from room temperature up to 500℃. To understand the reason for the peak appearance, the hydrogen permeability has been analyzed in view of the new description of hydrogen permeation based on hydrogen chemical potential. As a result, it is found that the temperature dependence of the PCT factor, fPCT, is dominant for the peak appearance, meaning that the corresponding pressure–composition–isotherms (PCT curves) are essential for the understanding of hydrogen permeability of the alloy. Dependences of the pressure condition and silver concentration on the peak behavior have also been investigated. The peak temperature increases with increasing the hydrogen pressure at feed side. In addition, the peak appears at lower temperature and becomes remarkable with decreasing silver concentration of Pd–Ag alloy membrane. In other words, the composition of Pd–Ag alloy membranes must be designed based on the operating temperature or pressure condition. Thus, this study suggests new possibilities of alloy design for Pd–Ag alloy membranes.
  • Fabrication and Characterization of TiO2 Nanorod Array Based Visible-Blind Ultraviolet Photodetector by Hydrothermal Process

    pp. 703-708

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    DOI:10.2320/matertrans.M2015366

    In this study, a TiO2 nanorod array based TiO2/water solid-liquid heterojunction ultraviolet photodetector, fabricated via a low-cost hydrothermal process is reported. The device exhibits several excellent characteristics such as self-powered, visible-blind and fast response, high photosensitivity, and linear variations in photocurrent for incident UV-light intensities. In addition, suggestions are provided to further improve device performance and increase the growth density of TiO2 nanorod array in the initial growth stage of the hydrothermal process to avoid the FTO surface being directly exposed to the electrolyte (water) which is a key factor in the developing direction.
  • Relation of Critical Current and n-Value of Local Sections to Those of Sample in a Multi-Filamentary Bi2223 Superconducting Composite Tape with Applied Stress-Induced Cracks

    pp. 709-715

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    DOI:10.2320/matertrans.MBW201502

    Under the application of tensile stress to a multi-filamentary Bi2Sr2Ca2Cu3O10+x (Bi2223) composite tape sample composed of a series of sections, the relation of superconducting properties (voltage– current curve, critical current and n-value) of sections to those of the sample were studied experimentally and analytically. The voltage–current curve of the most extensively cracked section whose critical current was the lowest among the sections, was the nearest in position to the voltage–current curve of the sample and played a dominant role in determination of the critical current of the sample. On the other hand, the n-value of the sample was significantly affected not only by the voltage–current curve of the most extensively cracked section but also on the position in relation to the voltage– current curves between the most extensively cracked section and the other sections. The denser the voltage–current curve of the other sections in the neighborhood of the voltage–current curve of the most extensively cracked section, the higher the n-value of sample became. In analysis of the experimental results, an equivalent crack - current shunting model, in which multiple cracks existing inside were replaced by an equivalent crack, was employed. With this model, the measured critical current and n-value of both sections and sample, and the correlation between n-value and critical current both for sections and sample, were described satisfactorily.
  • Effect of Hygrothermal Treatment on Reliability of Thermo-Compression Bonded FPCB/RPCB Contact Joints

    pp. 716-720

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    DOI:10.2320/matertrans.M2016006

    In this study, electrodes on a flexible printed circuit board (FPCB) and rigid printed circuit board (RPCB) were bonded together by thermo-compression (TC) bonding, using a Sn-3.0Ag-0.5Cu solder as an interlayer. In order to investigate the hygrothermal reliability of the TC bonded FPCB/RPCB joints, a temperature-humidity (TH) test of 85℃/85% relative humidity, and a 90° peel test, were conducted. The relationships between the TH treatment, peel strength, and failure analysis result were discussed. The peel strength significantly decreased as TH time increased. In contrast, a significant variation in electrical resistance was not observed during TH testing. Thin and uniform (Ni,Cu)3Sn4 intermetallic compound (IMC) layers were formed at both FPCB/Sn-3.0Ag-0.5Cu/RPCB interfaces. After a TH test for 500 h, the thickness of the IMC layer was slightly increased. In the case of the joint without TH treatment, a fracture occurred at the polyimide of the FPCB. After the TH test, the degradation of the adhesion between the polyimide and Cu in the FPCB occurred, due to the hygrothermal treatment, resulting in a switch of failure mode, from a polyimide failure to a brittle polyimide/Cu interface failure. X-ray photoelectron spectroscopy (XPS) analyses showed that the decrease in C-O and C=O bond ratios caused a decrease in peel strength of the TC bonded FPCB-RPCB joints, after the TH test. When comparing the TH and HTS tests, the TH test significantly deteriorated the integrity of the TC bonded FPCB-RPCB joints.
  • Microstructure and Wear Resistance of a Novel Mo-Ni-Si System Intermetallic Composite with Ductile Mo Phase

    pp. 721-725

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    DOI:10.2320/matertrans.M2015449

    It has been a challenge to improve the toughness of intermetallic compound at low and medium temperatures for developing wear resistance materials. The refractory metals, with a high melting point, strong atomic bonds, high ductility and toughness, are ideal toughening phases for intermetallic composites. This paper presents a novel composite having the microstructure of ductile Mo primary dendrites, binary intermetallic compound NiMo and ternary metallic silicide Mo2Ni3Si. The composite exhibits outstanding wear resistance and pretty low wear-load coefficient at ambient temperature, which are attributed to the contribution of refractory metal Mo to toughness of intermetallic matrix, in addition to the high strength and hardness of binary NiMo and ternary Mo2Ni3Si intermetallic phases. The wear mechanism analyzed by examining the worn surface and debris morphologies is in terms of soft abrasive wear.
  • Synthesis of Pure Na–X and Na–P Zeolite from Acid-Extracting Residues of CFB Fly Ash by a Single-Step Hydrothermal Method

    pp. 726-731

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    DOI:10.2320/matertrans.M2015463

    Acid-extracting residue of circulating fluidized bed (CFB) fly ash is still underutilized leaving disposal problems. In fact, high silica content inside this material opens a possibility to become a potential zeolites precursor. In this study, fine particles of acid residues have been reused to prepare zeolite Na–X and Na–P with high purity and intensity. Acid residue was used to synthesize zeolite Na–X and Na–P using a single–step hydrothermal process. The effects of crystallization time, temperature and sodium hydroxide concentration on the end products were investigated. The results revealed that crystallization time and temperature determined whether or not zeolite Na–X or Na–P was formed. The zeolites were characterized in terms of their mineralogical composition, morphology, and fourier-transform infrared spectroscopy.
  • Investigation of the Characteristics of Submicron-Structured Powder-Fabricated Cr50Ni50 Alloys via Different Hot-Press Sintering Pressures

    pp. 732-737

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    DOI:10.2320/matertrans.M2015400

    In this study, two different compositions of submicron-structured chromium and nickel powders are mixed to fabricate Cr50Ni50 alloys by vacuum hot-press sintering. The research imposes various hot-press sintering pressures (12, 24, 36 and 48 MPa), while the temperature is maintained at 1275℃ for 1 h, respectively. The experimental results show the optimum parameters of the hot-press sintered Cr50Ni50 alloys to be 1275℃ at 48 MPa for 1 h. The relative density reaches 96.29%, and the hardness and electrical conductivity increase to 75.2 HRA and 2.01 × 104 Scm−1, respectively. Simultaneously, the transverse rupture strength (TRS) value increases to 1109 MPa. Moreover, the Cr50Ni50 alloys dramatically acquire a more homogeneous microstructure, and the mean grain size decreases to 3.48 μm. Consequently, it is shown that hot-press sintering has a positive influence on the sintering behavior and improves the performance of the refractory metals.
  • Effect of Microstructure on High Temperature Mechanical Properties of A319 Casting Alloy for Automotive Cylinder Heads

    pp. 738-747

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    DOI:10.2320/matertrans.M2015402

    A quantitative study has been conducted to evaluate the relationship between microstructural features such as secondary DAS (dendrite arm spacing), eutectic structures and the mechanical behaviors of A319 casting alloys. Depending on the cooling rate affecting the primary and eutectic microstructure, the storage elastic modulus measured by DMA (dynamic mechanical analysis) increased with decreasing DAS, with a concomitant increase in the tensile strength and elongation at RT and also high tempertures. Contrarily, the thermal expansion coefficient increased with increasing temperature, but did not vary with microstructural changes. The hardness of the eutectic phase increased with increasing DAS due to the enlarged size of the eutectic particles, whereas the hardness of the primary phase was similar regardless of DAS, owing to the precipitates that formed during heat treatment. The increase of both of LCF (low cycle fatigue) and HCF (high cycle fatigue) lives with decreasing DAS was observed, mainly due to homogeneous deformation owing to the fine size of eutectic silicon and Fe intermetallic particles. The results of fractography observation showed that finer α-Al and eutectic phases were effective to the resistance of fatigue crack initiation and propagation due to the shorter crack path along the secondary particles. The LCF lives increased with increasing test temperature according to the Coffin-Manson relation due to the larger elongation. On the other hand, an analysis of the fatigue lives with the hysteresis loop energy, which consists of both strength and elongation, showed that the fatigue lives were normalized with an alloy of the same strengthening mechanisms regardless of the test temperature. DMA analysis demonstrated that the mechanical properties of the Al2Cu precipitate hardened alloy were maintained at temperatures greater than 250℃, whereas degradation in the mechanical properties of the Mg-containing alloy occurred at 170℃ due to coarsening in the precipitation phase of Mg2Si.
  • Functionally Graded Al Foam Fabricated by Sintering and Dissolution Process with Remaining Spacers

    pp. 748-750

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    DOI:10.2320/matertrans.M2015404

    Functionally graded materials composed of Al foam and Al/spacer composites were fabricated by a sintering dissolution process, in which removal of the spacers was stopped during the dissolution process. The deformation of the material started in the low-strength Al foam layer then in the high-strength layer with the remaining spacers.
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  • Lattice Parameter Dependence of Kinematic Compatibility in Martensite Microstructure of Cubic-Orthorhombic Transformation

    pp. 751-754

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    DOI:10.2320/matertrans.M2015456

    The lattice deformation strain dependence of the invariant plane (IP) condition at the habit plane, and the kinematic compatibility (KC) condition at the interface between habit plane variants (HPVs), were numerically analyzed in the cubic-orthorhombic martensitic transformation. The IP condition can be satisfied in a limited region of the principal component space of the lattice deformation. The KC condition at the averaged junction plane between HPVs can be satisfied in only the six types of HPV pairs classified in our previous study, provided the IP condition at the habit plane is satisfied. Furthermore, three of the six types of HPV pairs can form a fully compatible junction plane as long as the IP condition is satisfied. The kinds of interfaces that can be kinematically compatible in the six morphologies are invariant against the lattice parameters when the IP condition at the habit plane is maintained.
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    1. Functionally Graded Al Foam Fabricated by Sintering and Dissolution Process with Remaining Spacers MATERIALS TRANSACTIONS Vol.57(2016), No.5
  • Electrochemical Performance of Titanium Hydride for Bulk-Type All-Solid-State Lithium-Ion Batteries

    pp. 755-757

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    DOI:10.2320/matertrans.M2016024

    TiH2 was utilized as a negative electrode material for lithium ion battery by using LiBH4 solid electrolyte. High reversibility of the TiH2 conversion reaction was successfully obtained in this work. The favorable electrochemical properties of TiH2 electrode such as robust cyclic and rate performances were reported for the first time, which are superior to the previous report by means of conventional organic liquid electrolyte system. It can be considered as a promising candidate as negative electrode for lithium-ion batteries.

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