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

MATERIALS TRANSACTIONS Vol. 45 (2004), No. 2

  • Smart Materials Group at the National Institute of Applied Science Recent Data and Trends

    pp. 166-172

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    DOI:10.2320/matertrans.45.166

    During the last decade constant improvements have been made in materials and structures design and control. But now some performance objectives in particular in the field of the reliability cannot be achieved using classical technologies and require the use of the ‘smart materials concept’. Periodical maintenance NDT based inspections are today of a general acceptance for almost all complex technological structures. Nevertheless the idea that the integrated and continuous sensing techniques can optimize the operating conditions is now in progress. Different aspects of this evolution towards the desirable continuous health monitoring are discussed in relation with the smart materials concept through this non exhaustive review of some realisations or experiences. In the domain of sensitive materials, passive techniques such as Barkhausen effect, thermoelectric power, electrical impedance monitoring, acoustic emission, and active piezoelectric implant based methods, are briefly presented. Moreover, taking into account the growing demand in the field of actuators and artificial muscles for robotic and biomimetic devices, shape memory alloys and electroactive polymers are in progress. Finally the ‘self healing’ concept will be presented in the case of one ceramic-ceramic composite.
  • Combinatorial Investigation of Ferromagnetic Shape-Memory Alloys in the Ni-Mn-Al Ternary System Using a Composition Spread Technique

    pp. 173-177

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    DOI:10.2320/matertrans.45.173

    Using a thin-film composition spread technique, we have mapped the phase diagram of the Ni-Mn-Al ternary system in search of ferromagnetic shape-memory alloys (FMSA). A characterization technique that allows detection of martensitic transitions by visual inspection using micromachined cantilever arrays was combined with quantitative magnetization mapping using scanning superconducting quantum interference device (SQUID) microscopy. A large compositional region in the Al deficient part of the phase diagram was found to be ferromagnetic and reversibly martensitic at room temperature. In addition, in the Al rich region, a new compositional range that displays marked ferromagnetism was found.
  • Enhanced Piezoelectric Properties of Piezoelectric Single Crystals by Domain Engineering

    pp. 178-187

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    DOI:10.2320/matertrans.45.178

    Various engineered domain configurations were induced into barium titanate (BaTiO3) single crystals, and their piezoelectric properties were investigated as a function of (1) the crystal structure, (2) the crystallographic orientation and (3) the domain size. As a result, the orthorhombic mm2 BaTiO3 crystals showed the highest piezoelectric properties among three kinds of BaTiO3 crystals such as tetragonal 4mm, orthorhombic mm2 and rhombohedral 3m phases. On the other hand, the [001]c oriented BaTiO3 crystals always exhibited the larger piezoelectric properties than the [111]c oriented BaTiO3 crystals. Moreover, the domain size dependence on the piezoelectric properties was discussed, and this result revealed that the piezoelectric property was strongly dependent on the domain size, i.e., the piezoelectric properties significantly increased with decreasing domain size. On the basis of the above results, the most suitable engineered domain configuration was proposed for the high-strain high-coupling piezoelectric application.
  • Rearrangement of Martensite Variants in Iron-Based Ferromagnetic Shape Memory Alloys under Magnetic Field

    pp. 188-192

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    DOI:10.2320/matertrans.45.188

    We have investigated magnetic field-induced strain (MFIS) associated with rearrangement of martensite variants and its corresponding magnetization process in a disordered Fe-31.2Pd(at%) single crystal and an ordered Fe3Pt single crystal, exhibiting a cubic to tetragonal martensitic transformation at 230 K and 85 K, respectively. When magnetic field is applied along [001] direction to a specimen with a multivariant state, it expands along the field direction for Fe-31.2Pd and contracts for Fe3Pt, because the variants whose easy axis of magnetization (a axis for Fe-31.2Pd and c axis for Fe3Pt) lies along the field direction is selected to grow. The fraction of such variants reaches 100% for Fe-31.2Pd but does not for Fe3Pt. In the field removing process, a part of the MFIS recovers for Fe3Pt but does not for Fe-31.2Pd. From the magnetization curve, the energy dissipated due to the rearrangement of variants by magnetic field is obtained to be about 260 kJ/m3 for Fe-31.2Pd and about 180 kJ/m3 for Fe3Pt. Concerning Fe-31.2Pd, this value is roughly the same as that evaluated by stress-strain curves, suggesting that the rearrangement of variants by magnetic field takes essentially the same path as that by external stress. Based on these results and magnetocrystalline anisotropy constants of martensite phases, the mechanism of rearrangement of variants under magnetic field is discussed from a macroscopic point of view.
  • Microstructure and Magnetostriction of Rapid-Solidified Fe-15 at%Ga Alloy

    pp. 193-198

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    DOI:10.2320/matertrans.45.193

    Melt-spun, rapid solidified Fe-Ga ribbon sample exhibited large magnetostriction and good ductility as compared with conventional bulk sample. But the origin was not clear yet. In order to investigate the occurrence of large magnetostriction in Fe-Ga ribbon sample, the correlation between magnetostriction and the crystal grain morphology was inspected in detail by SEM/EBSP method for Fe-15 at%Ga alloy. In comparison with as-spun ribbon sample, short-time (0.5 h) heat treated ribbon had stronger [100] oriented texture and exhibited larger magnetostriction of 140 ppm (×10−6) at 800 kA/m. These phenomena suggest that such a large magnetostriction is caused by the release of considerable large internal stresses in as-spun ribbon as well as the remained strong textures after annealing.
  • Magnetostriction of Fe-Ga-B Alloys in Amorphous and Crystallized States

    pp. 199-203

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    DOI:10.2320/matertrans.45.199

    A ternary (Fe0.82Ga0.18)85B15 alloy was vitrified by melt spinning at wheel velocities of over 28.5 m/s. Two exothermic peaks were observed at onset temperatures of 692 K and 787 K. The melt-spun amorphous alloy ribbon exhibits saturation magnetostriction of +30 × 10−6 at the field of 80 kA/m. The magnetostriction increased by crystallization, i.e. precipitation of the bcc-Fe(Ga) phase, and reached a maximum value of +62 × 10−6 in conjunction with good response which is same as that for the as-spun amorphous sample. The maximum value is equivalent to that of the random orientated polycrystalline Fe82Ga18 alloy. In addition, the crystallized Fe-Ga-B alloy had better response as compared with the polycrystalline Fe82Ga18 alloy. The reason why the Fe-Ga-B alloy exhibits the high magnetostriction even in the coexistent state with C16-Fe2B and L12-Fe3Ga phases, seems to result from the precipitation of the supersaturated bcc-Fe(Ga) solid solution with high Ga concentrations as the crystallization -included phase.
  • Phase Transformation and Magnetic Property of Heusler Type Co2NiGa Alloys

    pp. 204-207

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    DOI:10.2320/matertrans.45.204

    We studied the phase transformation of a new Heusler type ferromagnetic shape memory alloy, Co2NiGa, by using an Acoustic Elastometer method. The alloy displays large magnetostriction, caused by the magnetic-field-induced rearrangement of martensite twin boundary. The ribbon samples produced by rapidly solidified melt-spinning method show large magnetostriction of about 100 × 10−6 at room temperature. While heating and cooling, the modulus defect, ΔM/M, and damping, Q−1, of the ribbon sample exhibits drastic changes at As and Mf, which differ slightly from the magnetic results.
  • Texture Analysis and Properties of Rapidly Solidified Ti52Ni38Cu10 Shape Memory Alloy

    pp. 208-213

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    DOI:10.2320/matertrans.45.208

    Texture of Ti52Ni38Cu10 rapidly solidified ribbons was investigated. Characterization of some of the properties such as transformation temperatures, deformation behavior, transformation strain, microstructure etc. was also carried out for the rapidly solidified ribbons in as-spun condition and after heat-treatment at 1073 K. The transformation temperatures of the ribbon specimens are found to be less than those of ingot specimens. As-spun ribbons were found to be slightly amorphous in nature, while after heat-treatment they became completely crystalline. Asspun and heat-treated ribbons show strong ‹200› fiber texture. From the thermomechanical studies it was observed that the hysteresis of the heat-treated ribbon specimen decreased whereas the transformation strain and the transformation temperatures showed an increase with increase in stress.
  • Texture and Microstructure of Ti-Ni Melt-Spun Shape Memory Alloy Ribbons

    pp. 214-218

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    DOI:10.2320/matertrans.45.214

    The shape memory behavior, texture and microstructure were studied for Ti-Ni ribbons fabricated by a melt-spinning method where the Ni contents were designed to be 49.0 at%, 50.0 at% and 51.0 at%. The texture of the parent B2 phase was determined by X-ray diffraction pole figures. A strong ‹100› fiber texture was found in both pole figures and orientation distribution functions (ODF). TEM observation revealed that all the ribbons are fully crystallized and that disk-type precipitates of about 10 nm in length locate on {100} of B2 phase uniformly. The thermal cyclic tests under various constant stresses showed shape recoverable strains exceeding 5% and critical stresses for plastic deformation being higher than 400 MPa for Ti-49.0 at%Ni and Ti-50.0 at%Ni as-spun ribbons. These excellent shape memory characteristics of the melt-spun ribbons are due to the formation of these disk-type precipitates. In addition, Ti2Ni precipitates of 25 nm in diameter appeared along grain boundaries of Ti-51.0 at%Ni as-spun ribbon. Since the Ni content of the matrix is condensed due to the formation of Ti2Ni precipitates, no shape memory effect was observed in Ti-51.0 at%Ni as-spun ribbon under the experimental conditions.
  • Influence of Heat Treatment on Phase Transformation of Ni-rich TiNi Foils Produced via Ultrafine Laminates

    pp. 219-224

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    DOI:10.2320/matertrans.45.219

    Using the ultrafine laminate method, thin foils (50 μm) of Ni-rich TiNi shape memory alloys were produced. Overall composition of the Ti/Ni laminate is Ti-50.7%Ni. TiNi (B2) phase was obtained after different diffusion treatments at 1073 K for 259.2 ks and 1173 K for 36 ks and 259.2 ks. Aging treatments at 773 K for 3.6, 18, 36, 72 and 144 ks were also performed. Multiple step martensitic transformation was observed for aged samples. The shape memory strain was 3.69 × 10−2 in the sample aged at 773 K for 18 ks.
  • Ar Ion Beam Irradiation Effects on Magnetostrictive Characteristics of Tb-Fe Thin Film

    pp. 225-228

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    DOI:10.2320/matertrans.45.225

    TbFe2 films prepared by a flash evaporation system onto Si(100) or polyimide substrate have been irradiated with different Ar ion doses at zero, 1.3 × 1017 and 2.7 × 1017 cm−2 and at 10 kV. Magnetostrictive properties, i.e., saturated magnetostriction and magnetostrictive susceptibility, of TbFe2 film with disordered structure were improved by Ar ion beam irradiation. This result was probably caused increasing of in-plane compressive stress corresponding to change of volume magnetostriction.
  • Electrical Nondestructive Determination of Collision Fatigue Limit for PZT

    pp. 229-232

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    DOI:10.2320/matertrans.45.229

    To determine the collision fatigue limit for piezoelectric ceramics, an electrical nondestructive method was suggested. The materials show large changes in electrical potential induced by pressure on the collision. Measurements on this type of material found a relationship between the maximum value of electrical potential (Vm) and supplied collision energy (Ecs) below the collision fatigue limit. It was expressed by the following simple equation.
    Vm = 9.5(Ecs)0.5
    Applying the critical differential electrical potential (Vc = 4 V), we confirmed that the collision fatigue limit was nondestructively determined for PZT materials.
  • Ferroelectric and Piezoelectric Properties of Disk Shape Lead Zirconate Titanate Thick Films

    pp. 233-235

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    DOI:10.2320/matertrans.45.233

    A combination of the preparation techniques for the ferroelectric films and the micro machining of Si is considered to be an effective way to fabricate microelectromechanical systems (MEMS), such as piezoelectric micro-transducer devices for the electrical and medical fields. In this study, disk shape lead zirconate titanate (PZT) thick films were successfully fabricated. 10-μm-thick PZT films were deposited onto Pt/Ti/SiO2/Si substrate using a chemical solution deposition (CSD) process. Pt top electrode and PZT layer were etched by reactive ion etching (RIE) process, and 100 to 500-μm-diameter PZT thick film disks were fabricated. The relative dielectric constant, dissipation factor, remnant polarization and coercive field were εr = 1130, tanδ = 0.02, Pr = 0.14 C/m2 and Ec = 2.5 MV/m, respectively. This means that the ferroelectric and dielectric properties of the PZT thick film disks were comparable with that of the bulk PZT ceramics. Moreover, the prepared PZT thick film disks showed the butterfly-shaped displacement curve, related with piezoelectric response, in the case of bipolar measurement. The PZT thick film disks could be poled with 80 V at room temperature, which is easier than the poling condition of bulk PZT. The piezoelectric constant of the poled PZT thick film disks was estimated to be AFM d33 = 221 pm/V. Therefore, the micro fabricated 10-μm-thick PZT disks is considered to be applicable for piezoelectric micro devices.
  • Estimating Noise Level in Dynamical Behavior for Detecting Mechanical Damage

    pp. 236-239

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    DOI:10.2320/matertrans.45.236

    The diagnostic algorithm introduced by Wayland et al. to test for degrees of visible determinism in complex dynamical behavior is applied to precise estimation of noise level for the gear-noise sound emanated from automobile automatic transmissions. It is shown that the method successfully captures such a small difference in acoustical characteristics indicating micro mechanical flaws on the gear surface that power spectral analysis fails to detect.
  • Ionic Conductivity Enhancement of YSZ Film Induced by Piezoelectric Vibration

    pp. 240-243

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    DOI:10.2320/matertrans.45.240

    To improve electric properties of oxide ion conducting yttria-stabilized zirconia (YSZ) films at low temperatures, a mechanical distortion was induced by a piezoelectric actuator. YSZ films containing 8 mol%Y2O3 were prepared by metalorganic chemical vapor deposition. The YSZ film was placed on a PZT (lead zirconate titanate) multilayer piezoelectric actuator. The effect of piezoelectric vibration on electric properties of the YSZ film was investigated. The resistivity of the YSZ film decreased with increasing amplitude of the piezoelectric vibration. Electrical conductivity of the YSZ film at 353 K vibrated by the actuator was 2 × 10−6 Sm−1, 103 times greater than that without vibration.
  • Magnetostrictive LC Circuit Sensors

    pp. 244-248

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    DOI:10.2320/matertrans.45.244

    Magnetostrictive thin films in electric resonant LC circuits are attractive as novel strain sensors. In order to achieve high resonance frequencies exchange coupled nanometer multilayers were used. LC circuits incorporating Fe50Co50/Co80B20 multilayers exhibited a gauge factor ((Δf/f)/Δε) of the order of 1000. This LC circuit sensor enables wireless interrogation, which is demonstrated in a torque measurement.
  • Properties of Ti-Aluminides-Reinforced Ti-Matrix Laminate Fabricated by Pulsed-Current Hot Pressing (PCHP)

    pp. 249-256

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    DOI:10.2320/matertrans.45.249

    Ti-aluminides-reinforced Ti-matrix composites were fabricated from 0.04 mm-thick Ti foils and 0.012 mm- and 0.024 mm-thick aluminum foils, in a process using a pulsed-current hot pressing (PCHP) equipment, and the effect of reaction temperature on properties of the composites was investigated. The composites were of laminated structure and composed of Ti and reacted layers containing Ti-aluminides. The composition of the reacted layers was dependent on the reaction temperature employed. Tensile testing at room temperature revealed that the reaction temperature was effective for the mechanical properties, including tensile strength, elongation and fracture mode, of the composites. The tensile strength and the elongation of composites fabricated at 1273 K from 0.04-mm-thick Ti and 0.012-mm-thick Al foils were 810 MPa and 3.64%, respectively, while they were 677 MPa and 3.44% for composites fabricated at 1173 K. Microstructure observations of fractured specimens showed that Ti layers of the composites fabricated at 1173 and 1273 K played a significant role in improving ductility by prohibiting the growth of numerous cracks emanating from Ti-aluminides.
  • Evaluation of Thermal Deformation Process of Nickel Based Active Composites by Laser AE Technique

    pp. 257-263

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    DOI:10.2320/matertrans.45.257

    A fiber reinforced nickel was developed base on the concept of active composites due to the thermal deformation, and its reproducibility at elevated temperature has been investigated. It was reported that curvature of the composite changed non-linearly during heating/cooling cycle. This hysterisis behavior may be involved with microfracture in the composites. Acoustic emission (AE) technique is very useful to monitor a dynamic microfracture. However, conventional AE technique has a limit in application at elevated temperature. We have investigated the non-contact laser AE technique using laser interferometer as a sensor. In this study, we tried to evaluate thermal deformation process of the active composite by this method. Specimens of pure nickel plate as matrix, SiC continuous fiber as reinforcement fiber and pure aluminum plate as insert layer were prepared by hot pressing. AE signals during heating and cooling processes were detected at the reverse of the specimen using a heterodyne type laser interferometer. Observation results showed that three failure modes such as cracking in matrix layer, debonding of matrix/fiber interface, and breakage of SiC fiber occurred during thermal deformation process. These failure modes were discussed based on AE source models. AE behavior of the composite showed thermal Keiser effect. This indicates thermal stresses in the composite cause microfracture during thermal deformation process. As a result of the test with the maximum temperature of 1073 K, AE event rate increased rapidly at 960 K and AE signals were detected even in cooling process. This temperature was identified to be the transition temperature of microfracture process in this composite. AE generation temperature was also in good agreement with the critical temperature of hysterisis of curvature.
  • A Study on the Fabrication of TiNi/Al6061 Shape Memory Composite Material by Hot-Press Method and its Mechanical Property

    pp. 264-271

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    DOI:10.2320/matertrans.45.264

    An attempt was made to fabricate composite material of an Al alloy matrix reinforced by TiNi shape memory fiber using a hot-press method and to investigate its microstructures and mechanical properties. The analysis of SEM and EDS showed that the composite material had good interface bonding. The stress-strain behavior of the composite material was evaluated at room temperature and 363 K as a function of pre-strain, and it showed that the yield stress at 363 K is higher than that at room temperature. It is also found that the yield stress of the composite material increased with increasing the amount of pre-strain and depended on the volume fraction of the fiber and heat treatment. The smartness of the composite could be given due to the shape memory effect of the TiNi fiber, which generated compressive residual stress in the matrix material when heated after being pre-strained. Microstructural observation revealed that interfacial reactions occurred between the matrix and fiber, creating two intermetallic layers.
  • Shape Memory Alloy Artificial Muscles for Treatments of Fecal Incontinence

    pp. 272-276

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    DOI:10.2320/matertrans.45.272

    Shape memory alloys (SMAs) have the features of large force-to-weight ratio and large deformation, are considered suitable for actuator uses. This paper describes the applications of an SMA material with two-way shape memory as artificial muscles for the treatment of fecal incontinences. Two designs of the proposed artificial sphincters are presented; one for a complete replacement of the anal sphincter and the other as an auxiliary sphincter to assist the puborectal muscles for maintaining fecal continence. Their functional evaluations have been conducted through fundamental experiments on the thermal responses and the mechanical deformation. The functionality of both was confirmed by in vitro experiments. The first design, the artificial anal sphincter was subjected to animal experiments for up to 4 weeks. Satisfactory results in respects of the biofunctionality of the SMA artificial sphincter imply its potential for practical uses.
  • Effect of pH on the Electrodeposition of ZnTe Film from a Citric Acid Solution

    pp. 277-280

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    DOI:10.2320/matertrans.45.277

    Potentiostatic cathodic electrodeposition of ZnTe was investigated from the viewpoint of the effect of pH on the deposits' composition and crystallinity using citric acidic electrolytic baths, in which Zn(II) and Te(IV) species were dissolved to form ZnH2Cit+, ZnHCit, ZnCit, Zn(Cit)24− and HTeO2+, HTeO3, respectively (Cit: citrate) at various pH. The complex equilibrium calculation was carried out to examine the most predominant complex ion for Zn-Cit system at different pH. Deposition of three kinds of deposits, i.e., polycrystalline ZnTe with closely stoichiometric composition, crystalline Te, and the mixed crystal due to Te and ZnTe, can be controlled by changing the pH and [Zn(II)]/[Te(IV)] concentration ratio of the baths. All the deposits obtained at pH 4.0 were well crystallized with a ZnTe cubic preferential orientation along the (111) plane without any post-treatment. The difference of the electrodeposition behavior at various pH was also discussed.
  • Anisotropic Behavior of Water Vapor Corrosion of Rutile TiO2 at High Temperature

    pp. 281-283

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    DOI:10.2320/matertrans.45.281

    Water vapor corrosion behavior of rutile TiO2 was examined at 1773 K in 30 mass% H2O environment. The corrosion rate for this sample was 2.2 × 10−4 kg·m−2·h under this experimental conditions. Anisotropic corrosion behavior was recognized in the planes that are parallel to c-axis. Many rectangular shaped etch-pits were generated at the grain surfaces. The corrosion proceeded from the side wall of the etch-pits and then, terrace fields were grown on the grain surface. Ridge-shaped microstructure was observed on the side wall of the terrace owing to the anisotropic corrosion.
  • Retraction:Effect of Carbon Nanotube Addition on the Compressive Fracture Characteristics of Zr-based Bulk Metallic Glass Composites

    pp. 284-287

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    DOI:10.2320/matertrans.45.284

    This article was retracted. See the Notification.
  • Microscopic Observations of Friction Stir Welded 6061 Aluminum Alloy

    pp. 288-291

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    DOI:10.2320/matertrans.45.288

    As the automotive industry trends towards increased use of aluminum, the friction stir welding process offers many potential benefits for joining of aluminum. In this study, the microstructure in friction stir welded 6061 aluminum alloy was observed by metallographic technique, electron backscatter diffraction pattern (EBSD) and optical microscopy. The microstructure in the heat affected zone (HAZ) was significantly different from that in a thermo-mechanically affected zone (TMAZ). EBSD indicated that many more low-angle grain boundaries in TMAZ, i.e., subgrains with a recovered granular structure, were observed than in HAZ. Friction heating and plastic flow during friction stir welding created fine recrystallized grains and recovered grains in the TMAZ. The friction stir welding process produced a softened region in the 6061 Al welded alloy. In the stir zone, equiaxed grains were created and the grain size was smallest in the bottom area.
  • Hydrogenation and Dehydrogenation Properties of RHNi5 (RH = Heavy Rare Earth) Binary Intermetallic Compounds

    pp. 292-295

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    DOI:10.2320/matertrans.45.292

    We systematically investigated the hydrogenation and dehydrogenation properties for heavy rare earth-based binary RHNi5 (RH = Gd, Tb and Dy) intermetallic compounds and evaluated the correlations between crystallographic and thermodynamic properties. XRD analysis shows that all RHNi5 compounds crystallize in the hexagonal CaCu5-type crystal structure. In analogy to the light rare earth-based RLNi5 (RL = La, Pr, Nd and Sm) compounds both lattice constants of RHNi5 compounds decrease with increasing the atomic number of RH element due to the lanthanide contraction. On the pressure-composition (P-C) isotherms, GdNi5-H2 system shows two well-separated pressure plateaux qualitatively similar to RLNi5-H2 systems. Looking over from Gd to Dy in the RHNi5 compounds, we find three specific dehydrogenation properties on the P-C isotherms: 1. The first plateau pressure (pP1) increases in this order (at around H/RHNi5 = 2.5) due to less stability of hydrogen in the unit cell by the lanthanide contraction. Linear correlations are also observed between log pP1 and the unit cell volume (V) which fall onto the same lines extrapolated from those observed in case of the RLNi5 compounds. 2. The second plateau (P2) tends to disappear because the P-C isotherm goes beyond the critical point of the phase transition. 3. Fairly flat first plateau separates into two parts in which a new plateau (PN) appears at low hydrogen content (H/RHNi5 ≤ 2) with hysteretic phase transition. So long as the first plateau of dehydrogenation is concerned, from LaNi5 to DyNi5 we can predict the first plateau pressure from the unit cell volume of compounds and temperature.
  • Interfacial Layer in Friction-Bonded Joint of Low Carbon Steel to Al-Mg Alloy (AA5083) and its Influence on Bond Strength

    pp. 296-299

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    DOI:10.2320/matertrans.45.296

    The metallographic factor controlling the strength of friction-bonded interface of low carbon steel (approximately 0.10 mass%C) to aluminum-magnesium (Al-Mg) alloy (equivalent to AA5083) has been investigated by TEM observations. The bond strength, estimated from the tensile strength of a specimen with a circumferential notch at the interface, rose rapidly with an increase in friction time, and then reduced. A maximum strength of 306 MPa was obtained at a friction time of 2 s (rotation speed = 20 s−1, friction pressure = 40 MPa, and forge pressure = 230 MPa). At a friction time of 1 s, an IMC layer about 100 nm wide that consisted of (Fe,Mn)Al6 and Mg2Si was formed at the interface, and an Al-oxide layer of a width less than 10 nm was observed between this IMC layer and low carbon steel substrate. In a joint showing the highest bond strength (friction time = 2 s), no Al-oxide layer could be detected between the low carbon steel substrate and IMC layer which consisted of (Fe,Mn)Al6, Fe4Al13, Fe2Al5, and Mg2Si. The width of the interfacial layer was increased to about 300 nm. At a friction time of 4 s, a layer of MgAl2O4 was observed in addition to intermetallic compounds of (Fe,Mn)Al6, Fe4Al13, Fe2Al5 and Mg2Si. The width of this layer was about 700 nm. Thus the phases formed in the interfacial layer as well as its width were altered depending on the friction time. The change in the bond strength with friction time was discussed in view of these differences in the interfacial microstructure.
  • Behavior of Superficial Oxide Film at Solid-State Diffusion-Bonded Interface of Tin

    pp. 300-302

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    DOI:10.2320/matertrans.45.300

    The microstructure of the solid-state diffusion-bonded interface of tin has been investigated by TEM observations in order to reveal the evolution of the superficial oxide film of tin with the progress in bonding. The diffusion bonding was carried out in a vacuum chamber at bonding temperatures Tj of 373—493 K and at bonding pressures Pj of 90—170 MPa (bonding time = 1.8 ks). The tensile strength of the joint was increased with bonding temperature and pressure; joints having tensile strength comparable with the base metal were obtained at Tj = 493 K at Pj = 130 MPa and at Tj = 443 K at Pj = 130 MPa. When the joint strength was much lower than the base-metal strength, an interfacial region ∼500 nm in width was observed where a number of very fine inclusions that could be regarded as tin oxide were distributed. As the joint strength increased with bonding temperature, these inclusions were coarsened, and their number density was decreased. The increase in the bonding pressure enhanced these changes in the inclusion. The rise in the joint strength with bonding temperature corresponded well with the observed change in the size and density of the inclusion.
  • Microstructure and High-Temperature Strength of Directionally Solidified Al2O3/YAG/ZrO2 Eutectic Composite

    pp. 303-306

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    DOI:10.2320/matertrans.45.303

    The microstructures of an A2O3/YAG/ZrO2 eutectic Melt-Growth-Composite (MGC) solidified unidirectionally by the modified-pulling-down method were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and electron backscattered pattern (EBSP) method. The anisotropy of strength was investigated by hardness tests and compression tests at various directions of the composite at elevated temperatures. The eutectic MGC has strong preferred growing orientation and the constituent phases hold the orientation relationship. The eutectic MGC shows excellent high-temperature strength and can deform plastically above about 1500 K. High-temperature strength above 1500 K depends on strain rate, temperature and orientation.
  • Effect of Heat Treatment on Microstructure and Mechanical Properties of Stoichiometric SiC/SiC Composites

    pp. 307-310

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    DOI:10.2320/matertrans.45.307

    Polymer impregnation and pyrolysis (PIP) is one of the most attractive fabrication processes for silicon carbide (SiC) composites due to the shape flexibility, mass production and relatively low cost. In particular, advanced PIP SiC/SiC composite with high-crystallinity and near-stoichiometric composition is expected to have superior thermo-mechanical properties including good oxidation resistance, due to the reduction of impurities and well-organized crystal structure. Additionally, by applying a thin carbon interphase by chemical vapor infiltration (CVI), control of the crack propagation and oxidation resistance are also achieved. In this study, a CVI + PIP hybrid process based on the recently developed stoichiometric PIP process was performed. Specifically, matrix crystallization was enhanced by heat treatment in Ar, and its effect on microstructures and mechanical properties were evaluated. Stoichiometric SiC/SiC composites exhibit superior flexural strength up to 1573 K in Ar and 1273 K in air. This is because the stoichiometric composition in PIP-SiC matrix reduces inner oxidation by impurities. Also, the thin pyrolytic carbon interphase tailored by CVI process effectively controls crack propagation at fiber and matrix interphase. In a similar manner, the microstructure of the stoichiometric PIP-SiC matrix, constructed by the mixture of amorphous SiC and highly crystalline SiC, was stable against the high-temperature heat exposure up to 1773 K in Ar. In particular, stoichiometric SiC/SiC composites heated at 1773 K in Ar provides superior stability of mechanical properties up to 1573 K even in air atmosphere, although extensive crystallization, in the case of heat treatment at 1973 K in Ar, caused brittle composite fracture.
  • Structural Transformation of MnAs1-xSbx under High Magnetic Fields

    pp. 311-314

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    DOI:10.2320/matertrans.45.311

    Structural transformation induced by magnetic fields on MnAs and MnAs0.9Sb0.1 was investigated by the X-ray diffraction measurements in high magnetic fields up to 5 T. The X-ray diffraction profiles at 319 K for MnAs showed a single phase of the orthorhombic MnP-type structure in zero field, and applying a magnetic field of 3 T caused an appearance of the hexagonal NiAs-type structure. On further increase of magnetic fields, the single phase with the hexagonal structure was confirmed above 3.5 T in a forced ferromagnetic state. The X-ray diffraction profiles at 295 K for MnAs0.9Sb0.1 showed the hexagonal NiAs-type structure. However, the coexistence of two kinds of the NiAs-type structure with different lattice parameters was confirmed in the magnetic field of 2.5 T. The two phase coexistence was also confirmed in the temperature variation measurements in zero magnetic field. The lattice volume of the ferromagnetic phase was 1.1% larger than that of the paramagnetic phase. These results imply that the transition at TC for MnAs0.9Sb0.1 is of the first-order.
  • Visualization of Hydrogen Distribution in Tensile-Deformed Al-5%Mg Alloy Investigated by means of Hydrogen Microprint Technique with EBSP Analysis

    pp. 315-318

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    DOI:10.2320/matertrans.45.315

    Hydrogen distribution in high-purity-based polycrystalline Al-5%Mg alloys prepared by changing the melting atmosphere was visualized by means of hydrogen microprint technique with electron backscattering pattern analysis after a tensile deformation at room temperature. The number of hydrogen atoms observed as silver particles on the slip lines was increased when the applied strain was increased. Hydrogen atom observed on the slip lines was totally increased when the melting atmosphere of the alloys was changed from argon to air. Hydrogen atom was observed at both slip lines and special grain boundaries when an air-melted specimen was deformed. It was shown that hydrogen atom accumulation at grain boundaries varied with the misorientation of grains and the angle to the tensile direction.
  • Fabrication of Dense Shoulder Components through Traveling Zone Sintering Assisted by a Multi-Way Loading System

    pp. 319-322

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    DOI:10.2320/matertrans.45.319

    Dense forming of shoulder components through the pulse discharge sintering process was examined. A new technique of multi-way loading system is proposed. This loading system is able to control the pressure in a powder compact body equally even if it has an irregular sectional profile. The traveling zone heating method combined with this loading system will allow the successful sintering of shoulder components through the PDS process, since no sinking due to pressure difference occurs in a powder compact. Based on this idea, the conventional sintering procedure with a perforated spacer was applied to production of a shoulder component. The spacer dictated the loading stroke on the thin side. The result was that an aluminum shoulder component with diameters of φ15 mm at the thin side and φ25 mm at the thick side was satisfactorily produced. The relative density of the component exceeded 99%. Some problems remain to be solved, but this procedure has potential for achieving high reproducibility by developing a precise load control system and stable contact between the electrode and the cylinder.
  • Eutectic Modification of Al-Si Alloys with Rare Earth Metals

    pp. 323-326

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    DOI:10.2320/matertrans.45.323

    The effects of different concentrations of individual additions of rare earth metals (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) on eutectic modification in Al-10 mass%Si has been studied by thermal analysis and optical microscopy. According to the twin-plane reentrant edge (TPRE) and impurity induced twinning mechanism, rare earth metals with atomic radii of about 1.65 times larger than that of silicon, are possible candidates for eutectic modification. All of the rare earth elements caused a depression of the eutectic growth temperature, but only Eu modified the eutectic silicon to a fibrous morphology. At best, the remaining elements resulted in only a small degree of refinement of the plate-like silicon. The samples were also quenched during the eutectic arrest to examine the eutectic solidification modes. Many of the rare-earth additions significantly altered the eutectic solidification mode from that of the unmodified alloy. It is concluded that the impurity induced twinning model of modification, based on atomic radius alone, is inadequate and other mechanisms are essential for the modification process. Furthermore, modification and the eutectic nucleation and growth modes are controlled independently of each other.
  • Effects of the Density on Compressive Properties in Cellular Aluminum Produced by the Sintering Method

    pp. 327-329

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    DOI:10.2320/matertrans.45.327

    The cellular aluminum materials with relative densities of 0.1∼0.25 were fabricated by the sintering method and effects of the density on mechanical properties of the cellular aluminum were investigated by compressive tests. The cellular aluminum exhibited a plateau region with a nearly constant flow stress. The stress in the plateau region increased with increasing relative density, on the other hand, the densification strain decreased with increasing relative density. Observation of the deformed cells revealed that the cell walls were bent. Besides, the stress in the plateau region was proportional to 1.9 power of the density. These suggest that plastic collapse is dominated by bending of the cell walls for the cellular aluminum produced by the sintering method.
  • The Effect of Additional Elements on Hydrogen Permeation Properties of Melt-Spun Ni-Nb-Zr Amorphous Alloys

    pp. 330-333

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    DOI:10.2320/matertrans.45.330

    The (Ni0.6Nb0.4)45Zr50X5 (X = Al, Co, Cu, P, Pd, Si, Sn, Ta or Ti) alloy ribbons were produced by the melt-spinning technique. All ribbon specimens were confirmed to have a single amorphous phase by XRD analysis. The crystallization temperatures of the melt-spun (Ni0.6Nb0.4)45Zr50X5 (X = Al, P, Pd, Si or Sn) amorphous alloys are higher than that of the (Ni0.6Nb0.4)50Zr50 amorphous alloy (727 K). Although the hydrogen permeability of the (Ni0.6Nb0.4)45Zr50X5 (X = Si, Sn, Ta or Ti) amorphous alloys could not be measured due to severe embrittlement during the permeation test, the (Ni0.6Nb0.4)45Zr50X5 (X = Al, Co, Cu, P or Pd) amorphous alloys had high ductility which was enough to measure the permeability. The hydrogen permeabilities of the (Ni0.6Nb0.4)45Zr50Co5 and the (Ni0.6Nb0.4)45Zr50Cu5 amorphous alloys were 2.46 × 10−8 and 2.34 × 10−8 [mol·m−1·s−1·Pa−1/2] at 673 K, respectively. The (Ni0.6Nb0.4)45Zr50P5 amorphous alloy possesses the lowest permeability of 1.36 × 10−8 [mol·m−1·s−1·Pa−1/2] at 673 K among the alloys where the permeability was measured. The reduction of the permeability in the (Ni0.6Nb0.4)45Zr50P5 amorphous alloy is thought to be due to a preferential development of Zr-P atomic pairs which may suppress hydrogen solubility and hydrogen diffusivity in the alloy, because the heat of mixing for Zr-P atomic paris is negatively larger than those of other pairs such as Ni-P and Nb-P. It is concluded that the Ni-Nb-Zr-X (X=Co or Cu) amorphous alloys have high potential to hydrogen permeable membranes.
  • Evaporation Behavior of SiO2 in N2-O2-H2O Atmospheres

    pp. 334-337

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    DOI:10.2320/matertrans.45.334

    In order to clarify the influence of water vapor on evaporation and crystallization of an amorphous SiO2 scale formed on SiO2-formers, fused silica was exposed for up to 49 h at 1373—1673 K in N2-O2-H2O atmospheres. The water vapor concentration was regulated to 19.6 and 46.7% (vol%). Under conditions of low water vapor concentration, the mass change in the fused silica was negligible. On the other hand, the mass linearly decreased with the duration of exposure under high water vapor concentration. From the temperature dependence of the evaporation rate, it was speculated that the main volatile species were Si(OH)4 and SiO(OH)2 in N2-H2O and N2-O2-H2O, respectively. Moreover, although crystallization of fused silica was observed in both atmospheres, air and N2-O2-H2O, the rate of crystallization in the N2-O2-H2O atmosphere was much higher than that in air. These results indicate that crystallization is accelerated by the presence of water vapor.
  • Factors Controlling Irradiation Hardening of Iron-Copper Model Alloy

    pp. 338-341

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    DOI:10.2320/matertrans.45.338

    The factors controlling irradiation hardening and their contributions to the hardening in electron irradiated pure-iron and Fe-0.15 mass%Cu alloy were determined by means of post-irradiation annealing experiments, such as hardness measurements, positron annihilation spectroscopy (PAS) measurements, transmission electron microscope (TEM) observations and three dimensional atom probe (3DAP) analyses. In pure-iron, almost complete recovering of the hardness was observed after the annealing to 773 K, which was accompanied by disappearing of the interstitial type dislocation loops (I-loops) that were observed in as-irradiated specimen. In contrast, the hardening of Fe-0.15 mass%Cu alloy recovered in a two-step mode; about a half of the hardening recovered by the 773 K annealing, and a complete recovery was observed after annealing to 973 K. Most of the I-loops observed in as-irradiated specimen again disappeared after the annealing to 773 K. These clearly show that the I-loops are one of the main factors controlling irradiation hardening in iron-copper alloy. The residual hardening in the Fe-0.15 mass%Cu alloy after the annealing to 773 K, which is about a half of the irradiation hardening, was attributed to the copper-rich precipitates (CRP) through the direct observation by 3DAP analysis. PAS measurements revealed the disagreement between the recovery behaviors of the hardness and lifetime parameters. Based on the quantitative data analysis, it was concluded that the factor controlling the irradiation hardening of pure-iron is the I-loops, and those in Fe-0.15 mass%Cu alloy are both the I-loops and CRP of which the contributions to the hardening are almost same.
  • High-Cycle Fatigue Properties at Cryogenic Temperatures in INCONEL 718 Nickel-based Superalloy

    pp. 342-345

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    DOI:10.2320/matertrans.45.342

    High-cycle fatigue properties at 4 K, 77 K and 293 K were investigated in forged-INCONEL 718 nickel-based superalloy with a mean gamma (γ) grain size of 25 μm. In the present material, plate-like delta phase precipitated at γ grain boundaries and niobium (Nb)-enriched MC type carbides precipitated coarsely throughout the specimens. The 0.2% proof stress and the ultimate tensile strength of this alloy increased with decreasing temperature, without decreasing elongation or reduction of area. High-cycle fatigue strengths also increased with decreasing temperature although the fatigue limit at each temperature didn't appear even around 107 cycles. Fatigue cracks initiated near the specimen surface and formed faceted structures around crack initiation sites. Fatigue cracks predominantly initiated from coarse Nb-enriched carbides and faceted structures mainly corresponded to these carbides. In lower stress amplitude tests, however, facets were formed through transgranular crack initiation and growth. These kinds of distinctive crack initiation behavior seem to lower the high-cycle fatigue strength below room temperature in the present material.
  • Oxidation Restriction of In-flight Particles upon GS-HVOF Spraying by Nitrogen Addition to Combustion Gas

    pp. 346-349

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    DOI:10.2320/matertrans.45.346

    In order to improve the environmental barrier property of coatings fabricated by the HVOF spray process with a gas shroud, their oxygen content of 0.19 mass% as the lowest conventional figure was still more reduced by changing the composition of combustion gas. Introduction of nitrogen gas to the combustion chamber lowered the temperature of the in-flight spray particles while maintaining their high velocity. This method could reduce the oxygen level of a HastelloyC coating to 0.063 mass% at the lowest present value, which is comparable to that of the feedstock with 0.042 mass%. Other coating with 0.14 mass% could be obtained along with the open porosity below 0.1 vol%. The latter coating exhibited the improved environmental barrier property in artificial seawater.
  • Effect of Cobalt Addition on Shape Memory Properties of Ferromagnetic Ni-Mn-Ga Sputtered Films

    pp. 350-352

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    DOI:10.2320/matertrans.45.350

    Effect of adding cobalt on the shape memory properties of Ni-Mn-Ga sputtered films was investigated. It was found that the films containing cobalt less than 5.1 mol% has a single phase and those with more than 6.8 mol%Co has two phases. The Curie temperature increased and the saturation magnetization decreased with increasing cobalt content. These films exhibited one way shape memory effect. The shape recovery start temperature increased and the temperature range of shape change broadened with increasing cobalt content.
  • Unidirectional Solidification of Aluminum-Indium Monotectic Alloys by Ohno Continuous Casting

    pp. 353-356

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    DOI:10.2320/matertrans.45.353

    The vertical Ohno Continuous Casting (OCC) process was used to examine the possibility of casting Al-In monotectic alloys with a homogeneous microstructure. Three compositions, Al-17.3 mass%In, Al-20 mass%In, and Al-25 mass%In were used in this study. Al-In alloy ingots with a diameter of 8 mm and a length of 400 mm could be continuously cast by controlling the temperature and solidification velocity of the melt regardless of the alloy compositions. The Al-In alloy ingots had a very beautiful surface and a unidirectional macrostructure. Furthermore, the Al-In alloys exhibited a good distribution of β-In particles throughout all sections without any segregation of β-In phase.
  • Precipitation of the Icosahedral Quasicrystalline Phase, R-phase and Laves Phase in Ferritic Alloys

    pp. 357-360

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    DOI:10.2320/matertrans.45.357

    Precipitation behavior of intermetallic phases in ferrite matrix is investigated by transmission electron microscopy (TEM) in Fe-10Cr-1.4W-4.5Co (at%) alloys with and without 0.3 at%Si. It is intended to provide basic information for the alloy design of ferritic heat resistant alloys strengthened by intermetallic compounds. In the alloy containing Si, icosahedral quasicrytalline phase (I-phase) is found to precipitate during aging at 873 K. It is confirmed that selected area diffraction (SAD) patterns of the precipitates exhibit two-, three- and five-fold symmetry and have diffraction spots in the positions related to the golden section. In the Si-free alloy, the R-phase precipitates instead of I-phase at 873 K, and the Laves phase precipitates in both alloys during aging at higher temperature, 973 K. The Laves phase formed at 973 K transforms to the I-phase in the alloy containing Si but to the R-phase in the Si-free alloy during subsequent aging at 873 K. It is found that the structures among icosahedral quasicrystalline and crystalline R- and Laves phases are closely similar by comparing the orientation relationship, precipitate morphology and stability of I-phase with those of R- and Laves phases.
  • Blow Forming of Mg Alloy Recycled by Solid-State Recycling

    pp. 361-364

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    DOI:10.2320/matertrans.45.361

    Blow forming characteristics of AZ31 Mg alloy recycled by solid-state recycling were investigated. Cylindrical scraps and machined chips were recycled by hot extrusion and hot rolling in air. Oxide layers were observed in the recycled specimens by oxygen mapping with EPMA (Electron Probe Micro Analyser). The interval of the oxygen layers for the specimen from machined chips was much shorter than that for the specimen from cylindrical scraps. As a result of tensile tests, the mechanical properties of the specimen from cylindrical scraps were found to be almost the same as those of a rolled specimen from a virgin ingot. On the other hand, at elevated temperatures, the elongation of the specimens from machined chips was low, compared with those of the rolled specimens from a virgin ingot. The large amount of oxide contamination is likely to be responsible for the lower elongation of the specimens from machined chips. In blow-forming tests, the specimen from cylindrical scraps exhibited excellent formability similar to the rolled specimen from a virgin ingot. However, the specimen from machined chips showed poor formability. Thus, oxide contamination adversely affected the formability of recycled Mg alloy.
  • Surface Oxidation of Fe-48 mol%Al Single Crystal under a High Vacuum

    pp. 365-368

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    DOI:10.2320/matertrans.45.365

    In order to investigate the effect of aging heat treatment and surface orientation on oxidation during the nanopore formation of B2-type FeAl, the surface of Fe-48 mol%Al single crystal was analyzed by Auger Electron Spectroscopy (AES). Electropolished and plasma-cleaned surfaces were aged for 18 ks at 723 K, in vacuum (about 5 × 10−4 Pa). A thin oxide layer was already formed on the non-aged surface. A thicker oxide layer was grown on the aged surface, but the difference in thickness of the oxide layers was slight. Further, the orientation dependence of the thickness of the oxide layers was even smaller. The thickness of the oxide layer on the FeAl single crystal is comparable to that of the passive film on the aluminum foil. Therefore, it is concluded that the influence of the aging heat treatment on oxidation during the nanopore formation of B2-type FeAl is negligible.
  • Microstructures and Magnetic Properties of Sm-Fe-N Thick Films Produced by the Aerosol Deposition Method

    pp. 369-372

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    DOI:10.2320/matertrans.45.369

    This paper describes magnetic properties and microstructures of Sm-Fe-N thick films prepared by the aerosol deposition (AD) method. The maximum thickness (d) of 77 μm was obtained in the AD conditions of gas flow rate (gfr) = 6 × 10−3 m3/min for 4 min. From this result, the deposition rate was estimated as 19 μm/min. The density (ρ) of Sm-Fe-N films were in the range of 4.9 × 103−5.9 × 103 kg/m3, which were 64—77% of the X-ray density of the Sm2Fe17N3 compound reported (7.67 × 103 kg/m3). However, they were higher than the density of the green compact of Sm-Fe-N host powders (3.86 × 103 kg/m3). The Sm-Fe-N AD films showed the remanences (Br) of 0.36—0.42 T, which were 58—68% of that of host powder (0.62 T). The coercivities (μ0HcJ) increased from 1.16 T to 1.69—1.86 T after the deposition because the average grain size decreased from 1.94 to 0.32 μm. XRD analysis revealed that the ratio of peak intensity of (006) to (033) in the Sm-Fe-N AD films was higher than that in the host powder. In addition, the remanence measured in perpendicular to the film plane was higher than that in parallel after the compensation of demagnetizing field. Therefore, it is considered that the c-axis in Sm-Fe-N AD films has a tendency to align in perpendicular to the film plane.
  • Synthesis and Consolidation of Ternary Compound Ti3SiC2 from Green Compact of Mixed Powders

    pp. 373-375

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    DOI:10.2320/matertrans.45.373

    Ternary compound Ti3SiC2 has been successfully synthesized and concurrently consolidated by sintering green compact of starting powder mixture. 3Ti/SiC/C powder mixture was compacted and heated in vacuum or in Ar atmosphere at temperatures from 1573 to 1773 K for a time period ranged from 2 to 6 hours. It has been found that either in vacuum or in Ar atmosphere the Ti3SiC2 content reached 100% in the surface layer. The growth of Ti3SiC2 in a layered manner on the surface of the sample was observed. It was also found that the sample sintered in Ar atmosphere is denser than those sintered in vacuum. After sintered in Ar atmosphere at 1773 K for 2 hours, the relative density of the compound reached 97%. Occurrence of liquid phase during sintering contributed to the densification of the compound.
  • Comparison of Nanocrystalline Surface Layer in Steels Formed by Air Blast and Ultrasonic Shot Peening

    pp. 376-379

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    DOI:10.2320/matertrans.45.376

    Surface nanocrystallization in various steels by shot peening (both air blast (ABSP) and ultrasonic (USSP)) was investigated. In all the shot-peened specimens, the equiaxed nanocrystals with grain size of several 10 nm were observed at the surface regions. The depth of nanocrystalline (NC) layers was several μm. The NC layers have extremely high hardness and were separated from the deformed structure regions just under the NC layers with sharp boundaries. By annealing, the NC layers show the substantially slow grain growth without recrystallization. These characteristics are similar to those observed in the specimens treated by ball milling, ball drop and particle impact deformation. Comparing ABSP and USSP at the similar peening condition, the produced volume of NC region in ABSP is larger than that in USSP.
  • Thermodynamic Study of the Phase Equilibria in the Sn-Ag-Bi-Cu Quaternary System

    pp. 380-383

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    DOI:10.2320/matertrans.45.380

    The phase equilibria in the Sn-Ag-Bi-Cu quaternary system have been studied experimentally and using thermodynamic calculations. The phase boundaries in some vertical sections of the Sn-Bi-Cu and Sn-Ag-Bi-Cu systems were determined using differential scanning calorimetry. The experimental values of the thermodynamic parameters were used in the calculations of the phase diagrams for the quaternary system. Thermodynamic evaluation of the Sn-Bi-Cu system was performed by considering a two-phase separation of the liquid phase. The phase diagram calculations showed that the Cu-Sn-based compounds form as the primary crystals, even for low Cu concentrations, and accordingly, the melting point of the alloys rises markedly. The microstructure of the solidified alloys was observed using a scanning electron microscope. We observed that coarsened Bi particles existed alongside the Cu-Sn-based primary crystals. Based on these results, a non-equilibrium solidification process using the Scheil model was simulated and compared with the observed structures. Our calculations reasonably explain the Bi-enrichment in the final solidification zone.
  • Grain Size Refinements of Mg Alloys (AZ61, AZ91, ZK60) by HDDR Treatment

    pp. 384-387

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    DOI:10.2320/matertrans.45.384

    The present paper describes the grain size refinements of Mg alloys (AZ61, AZ91, ZK60) by HDDR treatment. As a result of the HDDR treatment at 350°C under a hydrogen pressure of 7 MPa for 24 h, following by evacuation at 350°C for 3 h, the grain size of AZ61 alloys was reduced from 10∼20 μm to 100∼200 nm. At the hydrogenation stage for the AZ91 alloys, the disproportionation reaction occurred with forming MgH2, Mg2Al3 and Al phases. At the following desorption stage, the three phases were recombined and the Mg-Al-Zn solid-solution alloy was reformed. After the HDDR treatment, the grain size of AZ91 alloys was reduced to 100∼200 nm. For the ZK60 alloy without Al, the grain size was reduced from 2∼20 μm to about 300 nm by the HDDR treatment.
  • Growth Analysis of Banded Microstructure Formed during Directional Solidification of Peritectic Alloys

    pp. 388-391

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    DOI:10.2320/matertrans.45.388

    In this work, a growth analysis is made on the banded microstructure formation during directional solidification of peritectic alloys. The convection model, which has been proposed to explain the discrete banded microstructure formation, is extended in the part of the nucleation condition. Applying the nucleation and constitutional undercooling criterion, a new calculation was developed. Concentration profile calculated by the model was compared with experimentally obtained banded microstructure in Fe-Co and also with those of the convection and the diffusion models. Consistent agreement with experiments is shown. In comparison with the other models, interesting difference in predictions of concentration profile is obtained between them.
  • Effect of Refractory Elements (X: Mo, W, Re) on the Microstructure Evolution of Fe-8Cr-0.1C-X Martensitic Steels during Tempering

    pp. 392-395

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    DOI:10.2320/matertrans.45.392

    It is well known that the refractory elements (Mo, W, Re) play an important role in increasing the creep strength of heat resistant ferritic steels. However, the long-term creep strength of the ferritic steels depends on a number of factors, e.g., phase stability of the martensite, the diffusivity of alloying elements, the coarsening rate of precipitates in the steels, etc. Therefore, it is important for the future alloy design to make it clear the main factor influenced by the refractory elements. The purpose of this study is to examine the effect of the refractory elements only on the phase stability of martensite itself. For this purpose, the microstructure evolution was investigated using quaternary martensitic steels: Fe-Cr-C-X (X: Mo, W, Re). It was found that the microstructure evolution was retarded by the Re addition, since Re worked to increase the phase of the martensite and also to suppress the carbide (M23C6) agglomeration during tempering. On the other hand, it was suggested that W could suppress the recovery of defects such as dislocations in the martensite phase.
  • Thermal-Mechanical Fatigue Property of Ni-Base Single Crystal Superalloys TMS-82+ and TMS-75

    pp. 396-398

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    DOI:10.2320/matertrans.45.396

    The effect of hold time (th) on the thermal-mechanical fatigue property (TMF) of two nickel-base single crystal superalloys TMS-82+ and TMS-75, which are second- and third-generation single crystals, respectively, was investigated. Cycles to failure for both alloys decreased drastically with the increase in the hold time. The TMS-75 showed a longer life than the TMS-82+ at th=0. The TMS-82+ showed a longer life than the TMS-75 at th≠0, which could be attributed to the higher tensile strength at 400 °C and higher stress relaxation resistance at 900 °C in the TMS-82+. From microstructural studies, a slightly rafted γ/γ′ structure was observed in the TMS-82+ for TMF with a hold time. This work indicates that the TMS-82+ is appropriate to be served in gas turbine engines under specific conditions such as electric power generation.
  • Effect of Heat Treatment on Impact Toughness of Aluminum Silicon Eutectic Alloy Processed by Rotary-Die Equal-Channel Angular Pressing

    pp. 399-402

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    DOI:10.2320/matertrans.45.399

    A Rotary-die equal-channel angular pressing (RD-ECAP) process was applied to improve the impact toughness of Al-11 mass%Si eutectic alloy (AC8A). RD-ECAP was effective at improving impact toughness: the impact toughness increased as the number of pressings increased. In addition, the effects of heat treatments on impact toughness were investigated. When samples were heat-treated under the T6 condition before the RD-ECAP process, they exhibited a higher impact toughness than the samples without T6 treatments. The absorbed energy of the heat-treated samples followed by RD-ECAP 4 times was 4.32 J/cm2, which was much higher than that of the non-heat-treated samples, 2.89 J/cm2, and three times higher than the value of the heat-treated but non-processed samples, 1.08 J/cm2. The results show that the combination of the T6 treatment and the RD-ECAP process is more effective at improving the impact toughness, compared to applying the RD-ECAP process alone.
  • Refined Solidification Structure and Improved Formability of A356 Aluminum Alloy Plate Produced using a High-Speed Twin-Roll Strip Caster

    pp. 403-406

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    DOI:10.2320/matertrans.45.403

    An A356 aluminum alloy was cast into a 2 mm thick plate by a strip caster equipped with a pair of water-cooled rolls made of pure copper. The twin-roll cast plate exhibited fairly refined primary aluminum dendrite- and eutectic solidified structure. The estimated maximum cooling rate at the near-surface region of the plate is 4000 K/s. These values are significantly higher than the cooling rate for the permanent mold cast (2 K/s). The cast plate was cold-rolled and annealed into a 0.5 mm thick sheet. The resultant sheet was subjected to the 180° bending test. No cracking occurred in the twin-roll cast product. Improved formability is considered to be mainly due to the homogeneous distribution of fine Si particles.
  • Mechanical Properties and Microstructure of F82H Steel doped with Boron or Boron and Nitrogen as a Function of Heat Treatment

    pp. 407-410

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    DOI:10.2320/matertrans.45.407

    Effect of heat treatment on mechanical properties and microstructures of Fe-8Cr-2W-0.1C-0.2V-0.04Ta martensitic steel F82H doped with about 60 mass ppm B or both of 60 mass ppm B and 200 mass ppm N has been examined. The normalization was heated at temperatures from 950 to 1250°C for 1.8 ks, followed by air cooling or water quenching. After tempering treatment at 780°C or 750°C, the distributions of boron, boron nitride and oxygen were measured by a secondary ion mass spectrometry (SIMS). Optical microstructural observation and tensile and Charpy impact tests were performed also. In the boron doped F82H the tensile properties were similar to the non-doped F82H, but the ductile-brittle transition temperature (DBTT) shifted from −43°C to 15°C. SIMS images with high intensity of boron were observed in localized regions of the boron doped F82H. Water quenching reduced the DBTT shift, about 30°C, and the localized boron intensity was slightly decreased. In the boron and nitrogen doped tempered-F82H heat-treated by the water quenching from the normalizing temperature, the properties of tensile and Charpy impact were similar to the non doped F82H, and no pronounced localized boron image was observed in the SIMS image and no intensities of oxides and boron nitride were observed either.
  • Characteristic Depth Profiles of Surface Layers Formed in Cu-based Alloys by Annealing in Low Partial Pressure of Oxygen

    pp. 411-414

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    DOI:10.2320/matertrans.45.411

    Secondary ion mass spectrometry (SIMS) has been used for characterizing the depth distribution of alloying elements in three different copper-based dilute alloys, i.e. copper-chromium, copper-iron and copper-nickel-silicon alloys, which were annealed at high temperatures under low oxygen partial pressure. SIMS depth profiles showed that oxygen penetrated into the copper-based alloys, and chromium and silicon were enriched to the surface side so as to form oxides during annealing. Chromium and silicon were depleted beneath the enriched layer. On the other hand, depth profiles of iron and nickel were similar to that of copper. These phenomena were likely to be associated with the reactivity of alloying elements with oxygen. The formation kinetics of the depleted zones of chromium and silicon was discussed coupled with the selective oxidation of these alloying elements.
  • Relationship between Deformation and Recrystallization Structures in Fe-Si Single Crystal and Bicrystal Containing {111}‹112› Grain

    pp. 415-418

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    DOI:10.2320/matertrans.45.415

    To study the relationship between slip morphology and recrystallization of body centered cubic metals, an Fe-3%Si alloy single crystal sample of {111}‹112› orientation and a bicrystal sample having {111}‹112› and {001}‹110› component grains were deformed in tension and subsequently annealed. Both samples exhibited necking at the beginning of plastic deformation. The appearance of slip bands was totally different in the component grains of the bicrystal sample. Straight slip bands aligned along the traces of two {110} slip planes were observed in the {111}‹112› grain. On the other hand, wavy slip bands accompanied by high-step cross-slip were observed in the {001}‹110› grain. After annealing, the tensile-deformed single crystal sample did not recrystallize. In the bicrystal sample, recrystallized grains were formed only in the {111}‹112› grain. The difficulty in recrystallization of tensile-deformed samples is discussed in relation to the tendency to cross-slip.
  • Fatigue of Welded Magnesium Alloy Joints

    pp. 419-422

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    DOI:10.2320/matertrans.45.419

    Fatigue tests were carried out on welded joints of commercial AZ31 alloy and AZ61 alloy in air as welded surface condition. Alloys were extruded or rolled to a plate shape. Pairs of the same type of alloy plates were butt-welded by tungsten inert gas (TIG) welding or friction stir welding (FSW). All welded joints except FSW-ed AZ61 have joint efficiency of around 90% for static tensile strength. Extruded AZ31 alloy joints by TIG or FSW showed fatigue joint efficiency of about 80%. However, fatigue joint efficiencies for other joints were at around 60%. Fracture surfaces showed brittle fatigue crack propagation; moreover, the directions of crack propagation were influenced remarkably by the microstructures.
  • Effective Thermal Conductivity of Anisotropic Cu-Mo Composites

    pp. 423-426

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    DOI:10.2320/matertrans.45.423

    High thermal conductivity and small thermal expansion coefficient are property requirements for heat sink materials, and Cu−Mo composite is an attractive one. Owing to the thermal property of Cu−Mo composite which varies much when the microstructure is changing, the composition and microstructure should be carefully designed to achieve appropriate combination of properties. Consequently it is very important to quantitatively evaluate properties of the composite.
    In this research, a method that estimates the thermal conductivity of composites directly from their microstructure assisted with Finite Element Analysis (FEA) and Digital Image Based (DIB) technique was investigated. The effective thermal conductivities of rolled anisotropic Cu−Mo composite plates were evaluated parallel to and perpendicular to the rolling direction. The calculated thermal conductivities perpendicular to the rolling direction were compared with experimental data and found they are in good agreement. Hence, the FEA combined with DIB technique is a very helpful method for estimation of effective thermal conductivity of anisotropic composite materials.
  • Ferromagnetic Co-Ni-Al Shape Memory Alloys with β+γ Two-Phase Structure

    pp. 427-430

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    DOI:10.2320/matertrans.45.427

    The effects of the introduction of the γ (A1) phase into the β (B2) phase on the mechanical and shape memory properties in ferromagnetic Co-Ni-Al shape memory alloys with the β+γ two-phase structure were investigated by cold-rolling, tensile tests, and bending tests. The mechanical properties were found to be improved with an increase in the volume fraction of the γ phase, and Co-33 at%Ni-26 at%Al alloy with Vγ=36% exhibited excellent cold workability with a critical reduction ratio of 40%. Although the degree of shape recovery decreases with an increase in the volume fraction of the γ phase, it can be enhanced by training. Since two-phase β+γ Co-Ni-Al alloys have several advantages such as cost efficiency and workability, this alloy system is considered as being a new type of ferromagnetic shape memory alloys (FSMAs).
  • Microstructure Control of Al2O3/ZrO2 Composite by Fibrous Monolithic Process

    pp. 431-434

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    DOI:10.2320/matertrans.45.431

    Homogeneously tailored Al2O3-ZrO2 composites were fabricated using a fibrous monolithic process. The microstructure of the composites was varied depending on the area reduction ratio, and correlated well with calculated data. The sintered bodies presented a continuously fibrous monolithic microstructure and no swelling occurred during the binder burning-out. Microcracks were observed at the Al2O3-ZrO2 interfaces, due to the mismatch of thermal expansion coefficients between Al2O3 and ZrO2 phases. Most of the ZrO2 grains included twin defects to accommodate the stress field during the sintering process.
  • Characterization of Nanodome on GaN Nanowires Formed with Ga Ion Irradiation

    pp. 435-439

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    DOI:10.2320/matertrans.45.435

    Structure of nano-domes formed by Ga+ ion irradiation with a focused ion beam (FIB) apparatus onto GaN nanowires (NWs) was examined with conventional transmission electron microscopy (CTEM), electron energy-loss spectroscopy (EELS) and energy-filtering TEM (EF-TEM). The nano-dome consisted of metallic gallium, covered by a GaN layer, the structure of which is amorphous or liquid. It is considered that the dome structure is formed by preferential displacement of lighter element (N) and agglomeration of heavier one (Ga). 1 MeV electron irradiation onto the sample pre-irradiated by Ga+ ions at a dose below the threshold for the dome formation induced the N2 bubble formation without segregating Ga atoms, which suggests the radiation-enhanced diffusion (RED) of heavy atoms plays an important role in the nano-dome formation.
  • Characterization of Structure and Properties of As-cast AlCuMg Alloys

    pp. 440-446

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    DOI:10.2320/matertrans.45.440

    Early stages of transformation of a metastable AlCuMg alloy have been studied by DSC, X-ray powder diffraction method, quantitative microstructure analysis, hardness, compression strength and by scanning electron microscope. Differential scanning calorimetry has been done for samples: AlCu15Mg1 (0%Ti), AlCu15Mg1 (0.25%Ti), AlCu15Mg2 (0.25%Ti), AlCu15Mg3 (0%Ti), AlCu15Mg3 (0.25%Ti), AlCu15Mg4 (0.25%Ti), AlCu15Mg5 (0%Ti), AlCu15Mg5 (0.25%Ti). This method has produced DSC-curve, where endothermal effects are present, on the basis of which the heat of transition has been obtained. With increasing the magnesium and titanium content in the alloy, for the first and the second detectable endothermal effect, the value of heat of transition decreases. The formation of intermetallic compounds Al2Cu and Al2CuMg is monitored by X-ray powder diffraction. This method has shown that a tetragonal intermetallic compound Al2Cu and orthorhombic intermetallic compound Al2CuMg are formed for AlCuMg alloy. The effect of the magnesium and titanium content on the microstructure was monitored quantitatively. Using automatic image analysis we were able to measure the linear intercept grain size, the secondary dendrite arm spacing (DAS), the size of eutectic cells (Le), as well as the size distribution and volume fractions of the α-solid solution and the eutectic. In alloys containing high magnesium the average values of the DAS and grain size were found to be reduced.
  • Plastic Anisotropy of Strip-Cast Low-Carbon Steels

    pp. 447-456

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    DOI:10.2320/matertrans.45.447

    Two low-carbon steels with different impurity contents were prepared by strip casting to clarify the advantages of the process. The mechanical properties and the plastic anisotropy of the as-cast, the homogenized and the recrystallization annealed strips were investigated and compared. The as-cast strips showed a good strength-ductility balance and a superior plastic anisotropy to the other strips. The largest average ferrite grain oriented in the γ-fiber is concluded to be responsible for the highest normal anisotropy in the as-cast strips. Meanwhile, the orientation volume ratio between the γ-fiber and the α-fiber showed a roughly linear relationship with the normal anisotropy of the recrystallization annealed strips. The lower planar anisotropy in the as-cast and homogenized samples was related to the orientation distribution on the ‹114› ¦¦ ND orientation line.
  • Effects of Deformation and Thermal Cycling on Damping Capacity of Co-21 mass% Mn alloy

    pp. 457-460

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    DOI:10.2320/matertrans.45.457

    Effects of deformation and thermal cycling on damping capacity of Co-21 mass% Mn alloy have been studied. The thermal ε martensite produced during cooling improves the damping capacity of the alloy. However, the ε martensite formed by deformation or thermal cycling treatment deteriorates the damping capacity. The reason is that the dislocations introduced during the deformation or thermal cycling treatment interrupt the movement of damping sources such as stacking fault boundaries in ε martensite.
  • Analysis of Fatigue Crack Initiation and Propagation in Cold Forging Tools by Local Approach of Fracture

    pp. 461-468

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    DOI:10.2320/matertrans.45.461

    The local approach of fracture based on continuum damage mechanics (CDM) combined with the finite element method (FEM) was applied to establish a more precise method of estimation of service life of cold forging tools by simulating the initiation and growth of a fatigue crack. After a brief explanation on the local approach of fracture based on CDM combined with FEM, modeling of elastic-plastic-damage behavior of tool steel was conducted in the framework of thermodynamics. In the modeling, the salient unilateral property of the tool material is considered by introducing a modified stress tensor. The proposed constitutive equations can be found to describe the experimental behaviors under uniaxial tension and compression properly. Then, the initiation and propagation of a fatigue crack in the cold forward extrusion die was analyzed by the local approach of fracture. The initiation of the fatigue crack in the vicinity of the die radius was found to occur when the number of extrusion increased. Then, the crack propagated along the direction perpendicular to the surface of the die radius. Furthermore, the proposed approach was found to estimate the actual behavior of the fatigue crack growth in good agreement with the calculated change of the rate of crack propagation to the number of extrusion. The calculated crack propagation rate also tended to decrease due to a decrease in tensile principal stress at the crack tip as the crack propagates.
  • Nanofractal Analysis of Material Surfaces Using Atomic Force Microscopy

    pp. 469-478

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    DOI:10.2320/matertrans.45.469

    The surface structures of four materials (a pure aluminum sheet, an aluminum alloy sash, a thickness gauge and a magnetic tape) are observed on the nanometer scale by atomic force microscopy (AFM) and analyzed by one-dimensional fractal analyses. It is confirmed for all the surfaces that they have a self-affined fractal property under a resolution of 1 nm. The two-dimensional fast Fourier transformation (2D-FFT) analysis is also applied to these surfaces and their characteristics are clarified. The power spectrum model for surface simulation is proposed and its validity is confirmed by experimental results. A method for simulating the surface structure of any materials is presented, and its validity is shown on some materials whether in-plane isotropic or anisotropic. A computer-aided engineering (CAE) system composed of 2D-FFT and inverse FFT (IFFT) for quantitative estimation of surface nanostructures is advanced and applied to various surface problems. It enables the mass data of a material surface to compress into only three parameters. This compressed information includes all surface waviness, complexity, irregularity, roughness and in-plane anisotropic properties.
  • Effect of Nano-Scale Copper Sulfide Particles on the Yield Strength and Work Hardening Ability in Strip Casting Low Carbon Steel

    pp. 479-487

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    DOI:10.2320/matertrans.45.479

    Direct near net shape casting is an attractive process for the production of sheet metal because of its economical profit and the production of a new microstructure due to the fast solidification rate. To explore further advantages of direct near net shape casting, the differences in the mechanical properties between the as-cast and annealed strips of a steel with comparatively high contents of the impurities (Cu, P and S) were investigated in this paper with an emphasis on the microstructural effects. This process not only produced fine microstructures but also resulted in nano-scale copper sulfides. The as-cast strip has higher yield and tensile strengths and maintains high work hardening ability at higher stress levels than that of the annealed strip. Both the as-cast and annealed strips have a superior balance of strength and work hardening ability compared to the strips without the impurities. The nano-scale copper sulfide particles in the as-cast strip contributed most to the increase in the yield strength. The as-cast strip also could not produce the good work hardening ability without the nano-size particles. Further improvements in strength and work hardening ability can be attained by controlling the particles' size and the volume fraction in the strip.
  • Improvement of Mechanical Characteristics in Severely Plastic-deformed Mg Alloys

    pp. 488-492

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    DOI:10.2320/matertrans.45.488

    The commercial pure Mg, AZ31 and AZ61 alloys were severly plastic-deformed through equal channel angular pressing (ECAP). The grain size of pure Mg was decreased from 400 to 80 μm after ECAP and the 4 ECA pressed AZ31 alloy revealed the mixed microstructure of fine grains of less than 5 μm and coarser grains of approximately 5∼10 μm. Newly formed grains were attributed to dynamic recrystallization during ECAP at temperatures of higher than 1/2 Tm, where Tm is melting temperature. There was small increase of microhardness, yield stress and tensile strength in the ECA pressed pure Mg, while those of AZ31 and AZ61 alloys drastically increased after 1 pressing. The yield stress in the ECA pressed AZ31 and AZ61 alloys gradually decreased with increasing the number of pressings, but the tensile strength increased slightly. In particular, there was a typical tensile characteristic when compared with the other ECA pressed metals; a marked improvement in elongation was found concurrent with the pronounced strain hardening, without sacrificing the tensile strength, in the 4 ECA pressed AZ31 and AZ61 alloys. These tensile deformation characteristics were explained based on the observation of the deformed microstructure in the vicinity of fracture surface.
  • Effect of Alloy Chemistry on the High Temperature Strengths and Room Temperature Fracture Toughness of Advanced Nb-Based Alloys

    pp. 493-501

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    DOI:10.2320/matertrans.45.493

    High temperature strength and room temperature fracture toughness of Nb-based alloy system were investigated to explore a candidate material for gas turbine use at 1773 K as a function of chemical compositions. 0.2% proof stress at 1773 K and the fracture toughness were studied for the solid-solution hardening Nb-Mo-W alloys and the Nb5Si3-reinforcing Nb-Si-Mo-W-Hf alloys, and were found that the 0.2% proof stress linearly increases with increasing (Mo+1.5W) content and also increases with volume fraction of Nb5Si3, while the fracture toughness decreases with (MO+1.5W) content in solid-solution. The critical content for a ductile-to-brittle transition to occur is at (Mo+1.5W) content of 33.5 mol% together with molybdenum content of 15 mol%. Nb-16Si-5Mo-15W-5Hf alloy with a microstructure consisting of 50 vol% solid-solution and 50 vol% Nb5Si3, obtained by optimizing the alloy chemistry without a significant loss of high temperature capability and ductility, and by modifying with 5Hf-5C addition, was found to demonstrate an unprecedentedly excellent creep resistance and also a creep rupture strength exceeding the target strength of 150 MPa and above at 1773 K for 100 h.
  • Micromechanics Model Concerning Yield Behavior of Nanocrystalline Materials

    pp. 502-508

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    DOI:10.2320/matertrans.45.502

    This analysis was conducted to investigate the influence that dispersion in crystal grain sizes has upon the yield behavior of nanocrystalline materials. In the model proposed for this purpose, the distribution of crystal grains was expressed in a log-normal manner. It was assumed that the yield stress of each crystal grain was determined by the relationship between the grain size and the stress required for the generation of dislocations from a grain boundary. Furthermore, using the micromechanics of inclusions, we carefully considered the internal stresses in the crystal grains yielded at a different remote applied stress and in the matrix which is still elastic. The result of the analysis showed that the increase of compliance with the yielding of crystal grains from large to small can cause the macroscopic yielding of nanocrystalline materials. It was also inferred that the distribution of crystal grains was one of the important factors which affect the shape of the stress-strain curve and the macroscopic yield stress.
  • In-Plane Compression Response of Regularly Cell-Structured Materials

    pp. 509-515

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    DOI:10.2320/matertrans.45.509

    A quasi-static compression response of regularly cell-structured materials is studied by experimental and analytical procedures. A hexagonal close-packed cell-structure is fabricated by mechanical joining under compressive stress. The nominal stress-strain curve is typical to the cellular solids. It has three stages in deformation: linear elastic, plastic collapsing and densification regions. SEM-Servopulser is also used to describe the sequence of deformation images during uniaxial compressive test. Elasto-plastic model can predict quantitatively the compression behavior of copper cell-structured materials. Besides the relative density, the loading condition plays an important role on the deformation mode change and loading capacity. With increasing the contact radius ratio to cell wall thickness, the symmetric deformation changes itself to asymmetric deformation.
  • Using Nickel as a Catalyst in Ammonium Thiosulfate Leaching for Gold Extraction

    pp. 516-526

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    DOI:10.2320/matertrans.45.516

    The use of copper as a catalyst for gold leaching in ammonium thiosulfate solution might cause the high consumption of thiosulfate. Also, the high copper consumption is resulted in the zinc precipitation process for recovering the gold from the pregnant solution. In this investigation, nickel was used as a catalyst to minimize the reagent consumption. On a 100 mass%-75 μm of silicate type gold ore containing 16 g/t Au and 0.2 mass% of Fe and C, the nickel catalyzed ammonium thiosulfate solution could extract 95% of gold with the 1.2 kg/t-ore of ammonium thiosulfate consumption in 24 hours at the most favorable reagent combination of 0.0001 mol/dm3 NiSO4, 0.05 mol/dm3 (NH4)2S2O3 and 0.5 mol/dm3 NH4OH at pH9.5, while the standard cyanidation at 0.02 mol/dm3 (1.0 g/dm3) NaCN consumed around 1.5 kg/t-ore NaCN. In the concentration range of 0.0001∼0.005 mol/dm3 Ni2+, the ammonium thiosulfate consumption was 1∼5 kg/t-ore, while the ammonium thiosulfate consumption of copper catalyzed lixiviant was greatly increased from 3 kg/t-ore to 21 kg/t-ore as the increase of Cu2+ concentration from 0.0001 mol/dm3 to 0.001 mol/dm3. The feasibility of recycling barren solution was confirmed with zinc precipitation at nearly 100% of gold recovery. Nickel consumption on the cementation process was less than 50%. For extracting gold from the copper bearing sulfide ore, a higher ammonia and thiosulfate concentrations were required with 0.0001 mol/dm3 of Ni2+. The ammonium thiuosulfate consumption with nickel as catalyst on the copper bearing sulfide ore was about 1∼5 kg/t-ore less than that using copper as catalyst.
  • Diffusion Bonding of TiAl Alloy to Eutectoid Steel and its Interfacial Self-destruction Behavior

    pp. 527-531

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    DOI:10.2320/matertrans.45.527

    Interfacial microstructures and bonding strength of TiAl alloy/eutectoid steel joints have been investigated from the viewpoint of diffusion barrier effect of carbide layer formed at the interface. Diffusion bonding was performed at 1073 to 1273 K for 3.6 ks in a vacuum, and then several specimens were heated at 1073 to 1273 K for 10.8 to 86.4 ks in evacuated quartz tube to examine the growth behavior of reaction layer. The joint has essentially four kinds of the reaction layers. They are composed of two layers with Ti, Al and Fe elements, TiC layer containing Fe-Al compounds and ferrite layer. This indicates that the joint is difficult to have stable diffusion barrier layer consisting only of the TiC due to contribution of Al element to the interfacial reaction. Although the joint bonded at 1073 K shows high bonding strength of 160 MPa, the strength dramatically decreases with increasing bonding temperature. In addition, self-destruction phenomenon is recognized at the interface in the joints heat-treated at 1173 and 1273 K, and the origin is also discussed.
  • Cu-Based Bulk Glass Formation in the Cu-Zr-Ga Alloy System and Their Mechanical Properties

    pp. 532-535

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    DOI:10.2320/matertrans.45.532

    The thermal stability, glass-forming ability (GFA) and mechanical properties of a new Cu-based glassy alloy in Cu-Zr-Ga ternary system have been investigated. The supercooled liquid region ΔTx(= TxTg) exceeding 40 K and reduced glass transition temperature (Tg/Tl) above 0.59 are obtained simultaneously in the composition range from 2.5 to 7.5%Ga and 37.5 to 42.5%Zr, and the highest Tg/Tl is 0.62 for Cu52.5Zr42.5Ga5 and Cu55Zr40Ga5 alloys. The Cu-based Cu-Zr-Ga glassy alloys are formed in a rod form with a diameter up to 2.0 mm by the copper mold casting. The bulk glassy alloys exhibit good mechanical properties of 550-580 for Vicker's hardness (Hv), 105-111 GPa for Young's modulus (E), 1910-2130 MPa for compressive fracture strength (σc,f), and 0.2-0.5% for plastic elongation. The GFA of Cu-based Cu-Zr-Ga glassy alloys is more closely related to Tg/Tl values rather than ΔTx. The present new Cu-based bulk glassy alloys are expected to be developed as another type of bulk structural material with higher strength combined with good ductility.
  • Microstructure, Metal-Mold Reaction and Fluidity of Investment Cast-TiAl Alloys

    pp. 536-541

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    DOI:10.2320/matertrans.45.536

    The objective of this study is to investigate the effects of mold preheating temperature on microstrcutural evolution, metal-mold reaction and fluidity of TiAl alloys. A conventional induction melting furnace was used for melting and casting of TiAl alloys in the present investigation. The previous research showed that metal-mold reaction of titanium castings was inevitable during titanium casting. However, there is no metal-mold reaction of TiAl alloys castings regardless mold materials. These results were supported by the experimental results and thermodynamic calculations. However, the grain size of TiAl alloy castings is gradually reduced with mold preheating temperature due to heterogeneous nucleation near outside of mold and diffusion of metallic element from the mold and binder. A fused Al2O3 is promising mold for investment casting of TiAl alloys because of low cost, good strength and thermal stability. The fluidity length of TiAl alloys is increasing gradually with mold preheating temperature. However, it is difficult to predict the accurate applicable limit of preheating temperature of Al2O3 mold for investment casting of TiAl alloys due to the relationship between metal-mold reaction and fluidity. Therefore, mold material, binder and mold preheating temperature are the most important process parameter of TiAl alloys investment casting.
  • Microstructural Modeling and Thermal Property Simulation of Unidirectional Composite

    pp. 542-549

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    DOI:10.2320/matertrans.45.542

    The electrical, thermal and mechanical properties of functionally graded materials vary with microstructure and composition. Consequently it is very important to know quantitatively the properties of composites for the design of functionally graded materials. However, few methods of quantitative and theoretical evaluation for material properties on wide compositional range have been established. In this research, a method that estimates the material properties of composites directly from their microstructure assisted with finite element analysis was investigated. As an example of the estimation of material properties, the thermal conductivity of Mo fiber-Cu matrix composites has been evaluated. Calculated results of thermal conductivity are well in agreement with the experimental data measured by using a laser flash apparatus and the smallest deviation is 1.9%. The finite element analysis using a metallographic model is a very accurate method for estimation of composite properties.
  • Silicon Contamination Adsorbed on Pure Titanium Plate during Soaking Test in Hanks' Balanced Saline Solution

    pp. 550-553

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    DOI:10.2320/matertrans.45.550

    Silicon contamination adsorbed on pure Titanium plate during soaking test in Hanks' balanced saline solution (HBSS) and distilled water was investigated. Amounts of silicon eluted from various materials of vessels were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The amounts of silicon deposited on the surface of pure titanium plates after soaking were evaluated by XPS. The amounts of eluted silicon in the solutions were dependent on the materials of vessels and pH value of solutions. The surface concentration of silicon on titanium plates reflected the amounts of eluted silicon in solutions. It is possible to reduce the silicon contamination by choosing suitable vessels as containers for solutions. However, in spite of using a vessel with no silicon elution, surface concentration of silicon on titanium plates was detected because of the silicon impurity of solution itself.
  • Effect of Zirconium on Microstructure and Mechanical Properties of Cast Fine-Grain CM 247 LC Superalloy

    pp. 554-561

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    DOI:10.2320/matertrans.45.554

    This study investigates the effect of Zr minor additions, with Zr content from 0.015 to 0.15 mass%, on microstructure and mechanical properties of fine-grain (65 μm) CM 247 LC superalloy. Tensile test results indicate that minor addition of Zr to fine-grain CM 247 LC can dramatically improve the yield strength at 300 K as well as both the yield strength and the elongation at 1033 K. Under creep conditions of 1033 K/725 MPa or 1200 K/345 MPa, the Zr additions drastically increased the rupture life, creep rate and elongation. The AES observation reveal that Zr may enrich at grain-boundary and boride/matrix interface and dissolve in matrix, carbide of γ′ phase. Thus, Zr may change the primary MC carbide characteristics and inhibit the script-like MC carbide formation. Moreover, Zr is apparently to increase the effects of the cohesive energy of both the precipitated phase/matrix interface and the grain boundaries, also it is beneficial to stress accommodation and retards the crack initiation and propagation.
  • Characteristics and Mechanical Properties of Polycrystalline CM 247 LC Superalloy Casting

    pp. 562-568

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    DOI:10.2320/matertrans.45.562

    The CM 247 LC superalloy was remelted and cast to obtain the desired polycrystalline test bars by controlling casting parameters, followed by the investigation of precipitation morphology and mechanical properties. The experimental results show that by well-controlled casting parameters the CM 247 LC owns excellent castability to form a superalloy with fine grain structure, high strength as well as superior creep resistance.
  • Effect of Maximum Temperature on the Cyclic-Heating-Induced Embrittlement of High-Silicon Ferritic Spheroidal-Graphite Cast Iron

    pp. 569-576

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    DOI:10.2320/matertrans.45.569

    This study examines the effect of maximum temperature on cyclic-heating-induced embrittlement. Experimental results indicated a significant deterioration of tensile properties when the maximum heating temperature was 1023 K. Significant recrystallization of ferrite grains occurred when the heating temperature was raised to over 1073 K and this suppressed the embrittlement. Moreover, evidence of partial phase transformation was observed when the maximum heating temperature was raised to 1123 K. When a specimen was heated to 1023 K with a certain number of cycles, a distinct area fraction of intergranular fracture could be recognized from tensile fractography. The initiation site of these thermal cracks was at the prior-solidificational eutectic cell boundary of the ferrite matrix, which is related to magnesium-containing oxide inclusions. These oxide inclusions were analyzed and found to contain mainly magnesium, oxygen, phosphorus and cerium. It has been confirmed that the formation of magnesium-containing inclusions in the solidification process is mainly responsible for intergranular fracture, and consequently plastic deformation is promoted when the number of heating cycles is increased. From observation of the vicinity of crack initiation and propagation paths, significant slip evidence was found and was revealed using etch-pit techniques. In conclusion, the cyclic heating induced severe embrittlement at a specific maximum temperature of 1023 K. It is suggested that this resulted predominantly from periodic strain and stress accumulation of the inclusions which caused plastic deformation in the prior-solidification eutectic cell boundary region.
  • Effects of Eutectic Carbide Content on Erosion Behaviors in Ductile Cast Irons

    pp. 577-583

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    DOI:10.2320/matertrans.45.577

    During the casting process of thin-wall parts, due to fast cooling rate or chemical composition of the ductile iron, iron carbide (cementite) may exist in the microstructure that retards the mechanical properties of the iron greatly. In this study we discuss the effects of eutectic carbide contents in relation to the cooling parameters and the erosion behavior of the erosion incident angle on the casting specimens. Different content of eutectic carbide was produced by varying the cooling rate and silicon content. Solid particle erosion tests were performed using a shot-blasting machine with angular Al2O3 particles. The results show that, the largest amount of eutectic carbon (plate-like) exists in the faster cooling rate and lower silicon content. The amount of pearlite and nodules counts produced at lower cooling rates also decreased accordingly. Erosion rate also was found in the same trend that higher carbide content yielded better erosion resistance and lower erosion rates, but the amount of reduction is lower than the amount of increase on the hardness level. The maximum erosion rate occurred at the incident angle equaling to π/4.5, and the deepest erosion penetration occurred at an incident angle of π/3.6 for four comparison specimens. The impinged surface morphologies of four specimens exhibit cutting and plowed furrows at lower incident angles, but the overlapped chippings at higher incident angles. The erosion mechanisms, at medium and high incident angle erosion, show fatigue crack and subsurface lateral crack propagation in higher eutectic carbide specimen, but platelet peeling-off and internal crack and deformation in lower eutectic carbide specimen. The test also revealed that the failure mechanism of the casting thin plates tend to be ductile-brittle fracture.
  • Formation, Thermal Stability and Mechanical Properties of Cu-Zr and Cu-Hf Binary Glassy Alloy Rods

    pp. 584-587

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    DOI:10.2320/matertrans.45.584

    Glassy alloy rods with diameters up to 1.5 mm exhibiting a large supercooled liquid region before crystallization and high mechanical strength were formed in Cu-Zr and Cu-Hf binary alloy systems by the copper mold casting method. The large supercooled liquid region exceeding 40 K was obtained in the composition range of 30 to 70 at%Zr and 35 to 60 at%Hf. The largest value of the supercooled liquid region defined by the difference between glass transition temperature (Tg) and crystallization temperature (Tx), ΔTx (= TxTg), was 58 K for Cu60Zr40 and 59 K for Cu55Hf45. The reduced glass transition temperature (Tg/Tl) of the two alloys was 0.61 and 0.59, respectively. The alloys with large ΔTx above 50 K were formed into a bulk glassy alloy form with diameters up to 1.5 mm by copper mold casting. The Cu60Zr40, Cu45Zr55, Cu60Hf40 and Cu55Hf45 glassy alloy rods exhibited high fracture strength of 1920, 1880, 2245 and 2260 MPa, respectively, Young's modulus of 107, 102, 120 and 121 GPa, respectively, a nearly constant elastic elongation of about 1.9% and plastic elongation up to 2.2%. The formation of these binary glassy alloy rods can be interpreted in the framework of the concept of the formation of the unique glassy structure consisting mainly of icosahedral atomic configuration as similar to that for special multi-component alloys with the three component rules.
  • Wetting Properties of and Interfacial Reactions in Lead-free Sn-Zn Based Solders on Cu and Cu Plated with an Electroless Ni-P/Au Layer

    pp. 588-594

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    DOI:10.2320/matertrans.45.588

    The wetting time, wetting force, contact angle and interfacial reaction of Sn-8.55Zn-0.45Al-XAg (mass%) and Sn-9Zn (mass%) lead-free solders on Cu and Cu/Ni-P/Au substrates have been investigated. The Ag content, X, of the solders investigated was 0-3 mass%. The results indicate that the wettability of Sn-8.55Zn-0.45Al-XAg solders decreases with increasing Ag content. The Sn-8.55Zn-0.45Al-XAg solders containing low Ag content, less than 1mass%, exhibit better wettability than the eutectic Sn-9Zn solder. Furthermore, it was also found that the wettability of Sn-Zn based solders on Cu substrate is better than that on Cu/Ni-P/Au substrate. The when used on Cu and Cu/Ni-P/Au, Sn-9Zn solder forms Cu5Zn8 and AuZn3 respectively, while the Al-containing solders form Al4.2Cu3.2Zn0.7 and Al2(Au, Zn). Further addition of Ag gave rise to AgZn3 particles attached to the underlying intermetallic compound.
  • Ti-Based Bulk Metallic Glasses with High Specific Strength

    pp. 595-598

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    DOI:10.2320/matertrans.45.595

    The glass forming ability of melt-spun Ti65-xZrxBe18Cu9Ni8 (x = 0, 5, 10, 15) amorphous alloys have been investigated by differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). With increasing Zr contents, x from 0 to 15, ΔTx (= TxTg), Trg (= Tg/Tl) and γ (= Tx/(Tg + Tl)), where Tg = glass transition temperature, Tx = crystallization temperature and Tl = liquidus temperature, gradually increase from 35 to 40 K, from 0.558 to 0.621, and from 0.378 to 0.406, respectively. The Ti65-xZrxBe18Cu9Ni8 (x = 10, 15) BMG cylinders with the diameter up to 6 mm are successfully fabricated by the injection casting method, exhibiting high Vickers hardness (681-700) and yield strength (2.0-2.1 GPa). Ti-Zr-Be-Cu-Ni alloys with >50 at% Ti content have higher specific strength than any other Ti-based BMGs reported so far.
  • Microwave Plasma Nitriding of Hollow Tube Inner Wall

    pp. 599-601

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    DOI:10.2320/matertrans.45.599

    Microwave plasma nitriding at the internal wall surface of hollow tubes is