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

MATERIALS TRANSACTIONS Vol. 43 (2002), No. 9

  • HVEM/AFM Observation of Hinge-Type Plastic Zones Associated with Cracks in Silicon Crystals

    pp. 2169-2172

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    DOI:10.2320/matertrans.43.2169

    Dislocation structures developed in hinge-type plastic zones associated with cracks in silicon crystals have been studied using a high voltage electron microscope (HVEM). Fine slip bands due to those dislocations have been also examined by an atomic force microscope (AFM). {100} and {110} cracks were introduced into {110} silicon wafers at room temperature by Vickers indentation method. The temperature of the wafer chips indented was raised to higher than 823 K to activate dislocations around crack tips under a residual stress due to the indentation. In specimens with the heat-treatment, prominent dislocation arrays corresponding to the hinge-type plastic zone were observed not only near the crack tip but also in the crack wake. AFM observations showed that very fine slip bands with the step height of a few nano-meters were formed with the regular spacing of a few microns. Based on the analyses of those dislocations and slip bands, it has been revealed that those dislocations were shielding-type increasing the fracture toughness.
  • Oxidation Mechanism of Copper at 623-1073 K

    pp. 2173-2176

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    DOI:10.2320/matertrans.43.2173

    In reviewing the results reported for copper oxidation at intermediate temperatures from 573 to 1173 K, the oxidation mechanism at the lower part of this temperature range and the reason for the change in activation energy with decreasing the temperature remain unclear. To make it clear, copper oxidation is studied at 623–1073 K under 0.1 MPa O2 using a commercial 99.9999% pure copper. The oxidation kinetics is essentially parabolic, and the activation energy decreases from 111 kJ/mol at 873–1073 K to 40 kJ/mol at 623–773 K . The growth of Cu2O is predominant and it obeys the parabolic law at 623–773 K, as well as the case at 873–1073 K . In addition to grain boundary diffusion of copper along the fine and thin columnar Cu2O grains, the non-protective CuO whisker layer, which cannot keep the oxygen potential constant at the Cu2O/CuO interface, should be responsible for the decrease in the activation energy at 623–773 K.
  • TEM Observation of Interfaces between Particles in Al-Mg Alloy Powder Compacts Prepared by Pulse Electric Current Sintering

    pp. 2177-2180

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    DOI:10.2320/matertrans.43.2177

    Aluminum–Magnesium (Al–Mg) alloys powders with various amounts of Mg addition were sintered using the pulse electric current sintering (PECS) process. The behavior of Mg in the surface oxide film and the effect of Mg amounts on characters of the interfaces between Al–Mg alloys powder particles were investigated using transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The results showed that there were interfaces of direct metal/metal bonding and metal/oxide layer/metal bonding for all Al–Mg alloys powders compacts. In pure Al powder compacts, the oxide layer in the interface was amorphous alumina. And precipitates were observed in the bonding interface for the alloys powders compacts with Mg addition. The amounts of the precipitates increased, and the compositions of the precipitates changed with an increase in Mg amount in the alloys powders: MgAl2O4 for Al–0.3Mg, MgAl2O4+MgO for Al–1.0Mg, and MgO for Al–2.5, 10Mg alloys powders compacts.
  • Magnetic Properties of Ni-Mn Alloys with Dispersed Ferromagnetic Nanoparticles

    pp. 2181-2184

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    DOI:10.2320/matertrans.43.2181

    We investigated the magnetic properties of Ni1−xMnx (x=0.20–0.30) alloys with dispersed nanoparticles having a ferromagnetic Ni3Mn ordered phase, which is caused by suitable heat treatment. Magnetic analysis shows that for 0.3≥x>0.25 alloys interaction between 4–10 nm particles through Mn-rich matrix is antiferromagnetic. The Néel temperature increases with both Mn concentration and long-range-order parameter. On the contrary, for 0.25>x≥0.20 alloys, interaction between ∼ 4 nm particles through Ni-rich matrix is ferromagnetic. These alloys exhibit soft magnetic properties and have permeability of 400–600 for 1–500 kHz high frequency.
  • Continuous Displacement Cluster Variation Method in Fourier Space

    pp. 2185-2188

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    DOI:10.2320/matertrans.43.2185

    The diffuse scattering spectra originated from both short range order and local atomic displacements for a binary alloy in a two dimensional square lattice are calculated within the realm of Continuous Displacement Cluster Variation Method (CDCVM). The key ingredient of the present scheme is to regard a displaced atom as a distinguished species and to reduce the displacement spectrum to the Short Range Order Diffuse Intensity (SROI) for a multicomponent alloy. The peak of the diffuse intensity appears at the wave vector (1/2, 1/2). By comparing with the SROI calculated by the conventional Cluster Variation Method (CVM), it is realized that the majority of the intensity originates from the contribution of short range order configurational fluctuation. The topology of the intensity distribution of the present result is similar to that derived by the conventional CVM, however the magnitude of the peak intensity differs. This is due to the fact that the directionalily of the atomic displacement is averaged out and is renormalized in the present calculation.
  • Theoretical Investigation of Coarsening Process of L10-Ordered Domain Based on Phase Field Method and Cluster Variation Method

    pp. 2189-2192

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    DOI:10.2320/matertrans.43.2189

    A hybridized calculation of Phase Field Method and Cluster Variation Method is applied to investigate the relaxation process of Long-Range-Order parameter (LRO) originating from competitive growth of ordered domains. It is shown that the coarsening process proceeds by both the curvature-driven growth and coalescence among in-phase ordered domains. In the early annealing period, an average radius of ordered domains increases proportional to t1⁄2 as predicted by the curvature-driven growth. In the later period, however, a deviation from this relation is manifested by coalescence process. The LRO relaxation kinetics largely depends on the frequency of coalescence event.
  • Microstructure and Mechanical Properties of Ti-B-N Cast Alloys Prepared by Reactive Arc-Melting

    pp. 2193-2196

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    DOI:10.2320/matertrans.43.2193

    Ti–B–N cast alloys were prepared by a reactive arc-melting technique using elemental titanium and boron nitride powders. The alloys obtained were composites of titanium matrix containing nitrogen of 3 mol% or less and a small amount of TiB reinforcement. The microstructure of the matrix was a cellular structure consisting of elongated dislocation cells with 1–2 \\micron in width and 5–10 \\micron in length, for Ti–1B–1N alloy. The TiB particles were rod-like in shape with size of less than 0.5 \\micron in diameter and agglomerated to form clusters along the grain boundary. The mechanical properties were mainly dependent on the content of nitrogen and the influence of TiB on the mechanical properties was relatively small. The Ti–B–N cast alloys containing suitable concentration of nitrogen, Ti–0.5B–0.5N alloys, had a high strength of 920 MPa with adequate ductility of more than 5%.
  • Material Analysis Methods Applied to the Study of Ancient Monuments, Works of Art and Artefacts

    pp. 2197-2200

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    DOI:10.2320/matertrans.43.2197

    Cultural heritage resources are often subject to the singular or combined action of different weathering phenomena. To study these deleterious processes conservation scientists can rely on a whole variety of analysis techniques, which provide both bulk and localised (micrometer scale) chemical information. In this presentation an overview is given of the analytical approaches that are at present most commonly applied to solve cultural heritage related problems. The use of some of these techniques is illustrated with a case study on the weathering of two historically important Belgian building stone types. Future cultural heritage related research at the IMR (Tohoku University) is briefly discussed.
  • Mechanical Properties of Nb-18Si-5Mo-5Hf-2C In-Situ Composite Prepared by Arc-Casting Method

    pp. 2201-2204

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    DOI:10.2320/matertrans.43.2201

    Niobium-base in-situ composite, Nb–18Si–5Mo–5Hf–2C (in mol%), was fabricated by arc-casting method and heat-treated at 2070 K for 20 h in vacuum. The microstructure is composed of Nb solid solution (NbSS) matrix phase and secondary phase of Nb5Si3. The Nb5Si3 was found to have two kinds of structure: one is the α phase reported in the Nb–Si binary phase diagram and the other is a hexagonal phase with Mn5Si3-type structure. To evaluate the mechanical properties of the composite, nano-indentation hardness tests and tensile tests were conducted. The hardness and elastic modulus at ambient temperature were evaluated using nano-indentation hardness tester and the tensile properties were examined by an Instron-type materials testing machine at temperatures of 300, 1470, 1570, 1670 and 1770 K, and at an initial strain rate of 1×10−4 s−1. The hardness and elastic modulus of the NbSS phase are 480 GPa and 170 GPa and those of the silicide are 1480 GPa and 380 GPa. The composite exhibited the excellent ultimate tensile strength of 450 MPa at 1470 K, and the brittle to ductile transition temperature is between 1470 and 1570 K . The fracture behavior of the in-situ composite is complex, however, involving cleavage of the Nb5Si3, NbSS/Nb5Si3 interface separation, ductile rupture of the NbSS and correlations of these.
  • Comparison of the Characteristics of Nanocrystalline Ferrite in Fe-0.89C Steels with Pearlite and Spheroidite Structure Produced by Ball Milling

    pp. 2205-2212

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    DOI:10.2320/matertrans.43.2205

    Nanocrystalline ferrite formation by ball milling in Fe–0.89C steels with initial pearlite and spheroidite microstructures and their annealing behaviors have been studied through microstructural observation and microhardness measurement. It was found that nanocrystalline ferrite first forms near the surface of powders due to localized severe deformation. The microhardness of nanocrystalline ferrite regions is much higher than that of work-hardening regions. The dissolution of cementite was observed together with the nanocrystallization of ferrite. The nanocrystallization rate of pearlite powder is faster than that of spheroidite powder due to higher work-hardening rate and smaller cementite size. After long time ball milling, the equiaxed nanocrystalline ferrite with less than 10 nm grain size forms in the whole powders of both pearlite and spheroidite structures, and the cementite dissolves completely. By annealing the milled pearlite and spheroidite powders, recrystallization was observed in the work-hardening regions, while continuous grain growth was observed in the nanocrystalline ferrite region. After annealing, microhardness of the former nanocrystalline ferrite region is always higher than that of the former work-hardening region when compared at the same annealing condition. The grain growth rate of nanocrystalline ferrite produced from pearlite structure is lower than that of spheroidite structure due to the finer grains.
  • Effect of Morphology of Copper Precipitation Particles on Hydrogen Embrittlement Behavior in Cu-Added Ultra Low Carbon Steel

    pp. 2213-2218

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    DOI:10.2320/matertrans.43.2213

    Changes in fracture and hydrogen evolution behaviors in Cu-added ultra low carbon steels due to hydrogen charging were examined by small punch (SP) tests and thermal desorption spectroscopic (TDS) analyses, respectively, to understand effect of morphology of copper precipitation particles on susceptibility to hydrogen embrittlement. The SP tests and TDS analyses were applied to the hydrogen-charged steels, which had been thermally aged at 500°C for duration ranging from 2×103 to 5×106 s and provided with various kinds of fine particles. Experimental results revealed that the higher strength steel has a larger reduction in strength due to hydrogen charging. This degradation of the strength due to hydrogen charging was strongly dependent on the morphology of copper precipitation particles although, basically, the degradation had a tendency to be more pronounced with increasing hydrogen content. More hydrogen can be allowed in the steel in which the ε-copper exists. The grown copper particles, such as an ε-copper, are preferable to the copper clusters and/or the twinned 9R structures as trapping site for hydrogen and contribute the suppression of the reduction in strength caused by hydrogen.
  • Phase Equilibrium between Ni-S Melt and FeOX-SiO2 or FeOX-CaO Based Slag under Controlled Partial Pressures

    pp. 2219-2227

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    DOI:10.2320/matertrans.43.2219

    To provide thermodynamic data for converting the nickel matte to liquid nickel, an experimental study was conducted in the phase equilibrium between the Ni–S alloy and the FeOX–SiO2 or FeOX–CaO based slag in a magnesia crucible at 1773 K under controlled pSO2 of 10.1 kPa and pO2 in a range between 5.1×10−3 and 1.6 Pa by using CO–CO2–SO2 gas mixtures. The solubility of nickel in these slags at pO2 of 1.6 Pa, above which precipitation of a FeOX–NiO solid solution was anticipated, was found to be 10.1 and 20.3 mass% for the FeOX–SiO2 and FeOX–CaO based slags, respectively. The contents of iron, sulfur and oxygen in the nickel melt equilibrated with these slags were 2, 3 and 0.5 mass% for the FeOX–SiO2 based slag and 1, 3 and 0.5 mass% for the FeOX–CaO based slag, respectively. The dissolutions of nickel and sulfur in the slags were discussed on the basis of distribution ratio and sulfide capacity, respectively.
  • Investigation of the Mechanism of Alloy Dendrite Deflection due to Flowing Melt by Phase-Field Simulation

    pp. 2228-2234

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    DOI:10.2320/matertrans.43.2228

    Phase-field simulation of the dendrite growth of an Fe–0.15 mass%C binary alloy with fluid flow was carried out, and the mechanism of deflection of dendrites in the alloy system was examined. In the simulation, the primary arms growing in a flowing melt inclined toward the upstream direction, and the deflection angle increased with increase in flow velocity. Decrease in deflection angle with increase in growth velocity of the dendrite tip and accelerated growth of side branches were also observed in the simulation. These results of simulation were in good agreement with experimental results. The simulation showed that the change in the thermal field has little effect on the deflection and that the change in the solutal field is the main factor responsible for the deflection of a dendrite in an alloy system. The maximum deflection angle of a single dendrite in the simulation was less than 15°. The large deflection angles of grains (more than 20°–30°) in the experiments were thought to have been caused by nucleation in front of the dendrites and the subsequent competitive growth.
  • Ionic Conductivity in Liquid Sn-Se, Sb-Se and Bi-Se Alloys

    pp. 2235-2242

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    DOI:10.2320/matertrans.43.2235

    Simultaneous measurements of ionic and electronic conductivities around the stoichiometric composition have been carried out on liquid Sn–Se, Sb–Se and Bi–Se alloys by applying the residual potential theory. The ionic conductivity, σi, in liquid Sn–Se and Sb–Se alloys increases with increasing temperature, while, in liquid Bi–Se alloys, it decreases with increasing temperature. The isothermal σi in liquid Sn–Se and Sb–Se alloys at higher temperatures exhibits a minimum at the stoichiometric composition of SnSe and Sb2Se3, respectively, and, on the other hand, it shows a maximum at Bi2Se3 in liquid Bi–Se alloys. Values of σi at SnSe, Sb2Se3 and Bi2Se3 near the melting temperature are 7.40 Sm−1 at 1173 K, 0.448 Sm−1 at 893 K and 45.3 Sm−1 at 993 K, respectively, which are about two orders of magnitude smaller than the corresponding electronic conductivities, σe. The value of σi of liquid Bi2Se3, which is the largest among three liquids, is roughly comparable to that for ionic liquid alloys such as Ag and Tl-chalcogenides. In contrast, liquid Sb2Se3 indicates the smallest σi due to the strong covalent bonding between unlike atoms. The minimum of the σi-isotherm at SnSe and Sb2Se3 in liquid Sn–Se and Sb–Se alloys also reflect the covalent nature in these liquids.
  • Microstructure Evolution of Polycrystalline Pure Nickel during Static Recrystallization

    pp. 2243-2248

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    DOI:10.2320/matertrans.43.2243

    The difference in mechanisms of microstructure formation between static and dynamic recrystallization in pure nickel was studied on the basis of texture and EBSP analyses. Uniaxial compression was conducted at room temperature, followed by annealing at 905 K from 10 s to 28.8 ks. The process of static, primary recrystallization was traced by optical microscopy and the measurement of micro-Vickers hardness. Fraction of statically recrystallized region was 30% and 80% at annealing for 10 s and 60 s, respectively. Annealing longer than 60 s results in a 100% recrystallized state. The value of maximum pole density of texture was 4.6 after the uniaxial compression up to the true strain of −0.66. During static recrystallization, the texture became weak and finally the maximum pole density fell off in 2.0. The position of maximum pole density, however, did not change from (011) (compression plane). At the early stage of static recrystallization, new grains nucleated with random orientation in the vicinity of grain boundaries, inhomogeneously deformed regions. On the other hand, at the later stage of static recrystallization, new grains formed from the regions suffered from relatively homogeneous deformation. At this stage, the main component of the texture was (011) though the texture itself was weak. In dynamic recrystallization, new grains nucleated with random orientation during the deformation giving high values of Zener-Hollomon parameter. It was concluded that, during dynamic recrystallization, the deformation proceeded and hence inhomogeneously deformed regions continuously formed in the vicinity of grain boundaries, resulting the preferential formation of new grains.
  • Distinction between Thermal and Stress-Induced Martensitic Transformations and Inhomogeneity in Internal Stress

    pp. 2249-2255

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    DOI:10.2320/matertrans.43.2249

    A concept of inhomogeneous internal stress called shape change stress (SCS) was introduced in martensitic transformations (MTs). The SCS was considered to be required because martensite plates formed on cooling must deform the surrounding untransformed parent. The concept enabled successful elucidation of the reason for the progress of thermally induced MTs (TIMTs) with changing temperature and for that of stress-induced MTs (SIMTs) under constant stress on the basis of the Gibbs phase rule. Decreasing SCS with decreasing specimen size (mass) explained the downward shifts of experimental equilibrium temperatures To=(Ms+Af)⁄2 with decreasing specimen mass m so far observed in the TIMTs of some shape memory alloys. Furthermore, the concept that no SCS is generated either in SIMTs or at the ultimate end of m=0 in TIMTs rationalized the following observation on a monocrystalline Cu–13.4Al–4.2Ni (mass%) alloy. That is, the variations of Ms and Mf with m converged at the extrapolation to m=0, and those of As and Af also did; Ms#=Mf# and As#=Af# (the superscript # indicates the transformation temperatures at the ultimate end of m=0). The former coincided with TL(0) where the dependence of transformation stress σL on temperature was extrapolated to stress zero, and the latter coincided with TU(0) where a similar extrapolation in the case of reverse transformation stress σU was performed.
  • Interface Temperature under Dry Sliding Conditions

    pp. 2256-2261

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    DOI:10.2320/matertrans.43.2256

    In present paper, the influence of sliding speed, contact load, sliding time and microstructure on interface temperature during the sliding of eutectic Al–Si alloy (LM13) and hypereutectic Al–Si alloy (LM28) has been investigated. Sliding test was conducted under dry sliding conditions against hardened steel En-32 counter surface over a range of sliding speed from 0.2 to 5.0 m/s and contact load from 10 N to 30 N . It was observed that the interface temperature is a function of contact load, sliding speed, microstructure and thermal softening characteristics of sliding metal. Heat treatment of LM28 alloy decreases frictional heating and hence interface-temperature, however that of LM13 alloy does not affect the interface temperature especially under severe sliding conditions. Wear of aluminium alloys has close relationship with interface temperature. There is a critical temperature for each alloy corresponding to transition from mild to severe wear. LM28 alloy shows higher value of the critical temperature than the LM13 alloy under identical alloy conditions.
  • Magnetoimpedance Effect in Amorphous Nd4Fe77.5B18.5 As Cast Ribbon

    pp. 2262-2266

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    DOI:10.2320/matertrans.43.2262

    In the present work, the magnetoimpedance effect is reported in as cast Nd4Fe77.5B18.5 amorphous ribbon. The magnetoimpedance (Z(0)−Z(H))⁄Z(0) is about 16% under H=2.08×104 A·m−1 at 5.1 MHz. The magnetoreactance (X(0)−X(H))⁄X(0) can reach 43.71% under H=2.08×104 A·m−1 at 121 kHz. With increasing ac frequency, the magnetoimpedance (Z(0)−Z(H))⁄Z(0) increases at first, undergoes a peak and finally drops again. The magnetoimpedance (Z(0)−Z(H))⁄Z(0), magnetoresistance (R(0)−R(H))⁄R(0) and magnetoreactance (X(0)−X(H))⁄X(0) intersect at a frequency. Under a lower field H=4.22×103 A·m−1, the peak frequency fZ is larger than the intersecting frequency fi. Under higher fields H≥6.92×103 A·m−1, the peak frequency fZ coincides with the intersecting frequency fi. Both peak frequency fZ and intersecting frequency fi increase with increasing dc field.
  • Effect of Rh and V Additions on Plastic Deformation Behaviour in Ni3Nb Single Crystals with D0a Structure

    pp. 2267-2274

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    DOI:10.2320/matertrans.43.2267

    The effect of Rh and V additions on phase stability and plastic deformation behaviour in Ni3Nb single crystals with the D0a structure was investigated, focusing on the slip behaviour of (010)[100], (010)[001] and (001)[100] systems in a wide temperature range between room temperature and 1200°C. The V addition induces no significant change in the critical resolved shear stress (CRSS) for (010)[100] slip at low temperatures, while the Rh addition is effective in increasing the CRSS at temperatures below 500°C and above 800°C, resulting in significant improvement of high-temperature strength. The increment of high-temperature strength is closely related to suppression of the climb motion of edge dislocations. The Rh addition also effectively increases the CRSS for (010)[001] and (001)[100] slip. The V addition was expected to enhance activation of the (010)[001] slip by reducing the SISF energy between the superpartials, but that was not achieved.
  • Calculations of Crystallization Temperature of Multicomponent Metallic Glasses

    pp. 2275-2284

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    DOI:10.2320/matertrans.43.2275

    A model for calculating crystallization temperature (Tx) of multicomponent metallic glasses is proposed by modifying the Miedema’s model which is used for calculating Tx of binary systems. The calculations were carried out for nearly 900 metallic glasses including 470 binary and 398 ternary alloys. In the present model, the cavity formation energy (ΔHcavityfor) for multicomponent metallic glasses was theoretically derived on the basis of the Miedema’s model. The equation for expressing the relation between experimental Tx and theoretical ΔHcavityfor was statistically analyzed by the least-squares method, yielding Tx=4.16×ΔHcavityfor+318. The binary and ternary systems tend to show different equations between Tx and ΔHcavityfor. The inherent equation in each system was analyzed as simultaneous achievement of the increase in stability of metallic glasses and decrease in ΔHcavityfor due to multicomponent alloying. Furthermore, the glass-forming ability was predicted by reduced crystallization temperature instead of reduced glass transition temperature. As a result, it was found that reduced crystallization temperature can be calculated close to reduced glass transition temperature except for Pt-, Pd- and La-based systems. It is of great importance that Tx can be calculated for multicomponent metallic glasses by semi-empirical method.
  • Continuous Rheocasting for Aluminum-Copper Alloys

    pp. 2285-2291

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    DOI:10.2320/matertrans.43.2285

    An experimental study was performed on the homogeneous refinement of microstructures and the improvement of mechanical properties in Al–5 mass%Cu and Al–10 mass%Cu alloys using a novel continuous rheocasting process. The crystal grain size in an Al–10 mass%Cu alloy sheet was 6.9±1.8 \\micron in the continuous rheocasting process, which was much finer than the typical grain sizes on the order of 100 \\micron for the conventional rheocasting process and the grain size of 72±26 \\micron in Al–10 mass%Cu alloy for the batch-type rheocasting by Ichikawa et al. The ultimate tensile strength in the Al–10%Cu alloy sheet was 248 MPa at room temperature, which was higher as compared to the tensile strength of 192 MPa in a die-cast Al–10 mass%Cu alloy. The tensile elongation in the Al–10 mass%Cu alloy sheet was 297% at 773 K, which was resulted from superplasticity. It is considered that the crystal grain size in the Al–10%Cu alloy is determined by the “big-bang” nucleation and the multiplication of crystal grains in the numerous spattered droplets made by a rotating screw-shaped stirrer in the continuous rheocasting process.
  • X-ray Spectroscopic Analysis of Solid State Reaction during Mechanical Alloying of Molybdenum and Graphite Powder Mixture

    pp. 2292-2296

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    DOI:10.2320/matertrans.43.2292

    Molybdenum and graphite powders were mechanically alloyed. Carbon K X-ray emission spectra of the mechanically alloyed powders were measured using electron probe microanalyzer (EPMA) in order to investigate the solid state reaction process. In the early stage of the mechanical alloying (∼ 36 ks), graphite did not react with molybdenum, but particle size of graphite became smaller. In the next stage of mechanical alloying (36∼144 ks), graphite react with molybdenum gradually as the time increases. Molybdenum carbides were formed on mechanical alloying for 288 ks. The mechanically alloyed powders for 288 ks were heat-treated in a vacuum. Mo–33 at%C system heat-treated at 1273 K was a mixture of Mo2C and molybdenum, while Mo–50 at%C system heat-treated was a mixture of Mo2C, mechanically ground graphite and graphite.
  • Influence of P on Microstructure and Thermoelectric Property of Sintered (Bi0.2Sb0.8)2Te3 Alloy

    pp. 2297-2302

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    DOI:10.2320/matertrans.43.2297

    A combination of mechanical alloying and pulse discharge sintering (MA-PDS) was employed to synthesize the bulk (Bi0.2Sb0.8)2Te3 alloys with the P addition up to 2.0 mass%. The effect of P on the microstructure and thermoelectric performance of the compacts were investigated. The added P exists in the alloyed powders and compacts in the form of second phase particles. The dispersed P particles were found to decrease the size of (Bi, Sb)2Te3 crystallites and inhibit the densification of the alloyed powders. When the P content ≥1.0 mass%, (Bi0.2Sb0.8)2Te3/P nanocomposites were developed by the MA-PDS process. Inclusion of a small fraction of P (≤0.1 mass%) is harmless to the thermoelectric performance of the p-type (Bi0.2Sb0.8)2Te3 alloy. In the samples with high P contents, in particular, ≥1.0 mass%, however, the increase in the electrical resistivity is much greater than the decrease in the thermal conductivity, finally giving rise to degradation of the room-temperature figure of merit.
  • Surface Layer Formed by Selective Oxidation in High-Purity Copper-Titanium Binary Alloys

    pp. 2303-2308

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    DOI:10.2320/matertrans.43.2303

    X-ray photoelectron spectroscopy (XPS) and secondary mass ion spectrometry (SIMS) have been used for studying surface layers formed by selective oxidation of titanium in high-purity copper-titanium alloys. Sheets of copper-0.5, 1.0, 1.5, 2.0 and 3.4 mass% titanium alloys were annealed at 873 K under a low partial pressure of oxygen. XPS results indicate titanium enrichment on the surface side of a sample to form titanium oxides. With increasing bulk concentration of titanium, the amount of titanium oxides formed on the sample surface increased, while the amount of metallic copper decreased. SIMS depth profiles of these samples showed that titanium oxides are formed in a surface layer less than one micrometer thick, and a titanium-depleted zone is formed beneath the surface layer containing titanium oxides. A concentration profile of titanium formed beneath the titanium-depleted zone was found to be described by outward diffusion of titanium in the matrix, indicating that the oxidation process is mainly controlled by diffusion of titanium in copper.
  • Characterization of Directionally Solidified B4C-SiC Composites Prepared by a Floating Zone Method

    pp. 2309-2315

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    DOI:10.2320/matertrans.43.2309

    Directionally solidified B4C–SiC composites were prepared by a Floating Zone method. The lamellar texture was observed at 53 mol%SiC . The c-axis of B4C phase was tilted 20° to the growth direction. The (102) plane and [\\bar1\\bar21] direction of the B4C phase were parallel to the (311) plane and [12\\bar1] direction of the SiC phase, respectively. The thermal conductivity of the composite parallel to the growth direction (κ||) was about twice as great as that of monolithic B4C . The anisotropy of electrical conductivity and thermal conductivity were explained by a mixing law using the values of B4C and SiC . The mass gain due to oxidation was about 1/3 to 1/5 less than that of monolithic B4C at 1023 K . The surface perpendicular to the growth direction showed slightly better oxidation resistance than that parallel to the growth direction. The microhardness of the composite was almost the same as that of B4C.
  • Pseudo Float Melting State in Ladle Arc-Melt-Type Furnace for Preparing Crystalline Inclusion-Free Bulk Amorphous Alloy

    pp. 2316-2319

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    DOI:10.2320/matertrans.43.2316

    A homogeneous melting state without any crystalline inclusions was achieved in an arc melt furnace by using a ladle arc-melting-type furnace. Molten alloy for pouring can be melted completely by arc heating just above the mold in a pseudo float melting (PFM) state. We combined a ladle arc-melt-type furnace and the squeeze cast method to produce bulk amorphous alloy sheet with a single amorphous phase structure, thereby successfully producing crystalline inclusion-free Zr50Cu30Ni10Al10 bulk amorphous alloy sheets. The tensile strengths of the Zr50Cu30Ni10Al10 bulk amorphous alloys exceeded 1800 MPa, and the bending deflection of the alloys was improved by a factor of 10 using the PFM process.
  • Microstructures and Mechanical Properties of Ultra Low Carbon IF Steel Processed by Accumulative Roll Bonding Process

    pp. 2320-2325

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    DOI:10.2320/matertrans.43.2320

    An ultra low carbon IF steel was severely strained by accumulative roll-bonding (ARB) process and subsequently annealed for 0.5 h at various temperatures ranging from 673 to 1073 K for strengthening by grain refinement. The ARB process was carried out up to 5 cycles (an apparent equivalent strain of 4.0) at ambient temperature without lubrication. The as-ARBed specimen exhibited a dislocation cell structure with relatively high dislocation density, rather than a well-defined ultrafine grained structure. However, the subsequent annealing at 673 or 773 K resulted in the formation of ultrafine grains in the structure. This indicates that the heating (recovery) is necessary for the formation of ultrafine grains in the present IF steel severely deformed by ARB process. The tensile strength of the as-ARB processed IF steel increased with strain, reached a maximum of 813 MPa, which is about 3 times higher than the initial value. The elongation dropped largely from 60 to below 10% at the 1st cycle, but it hardly changed from the 2nd cycle even if the ARB cycle increased. The strength decreased gradually and the elongation increased with annealing temperature. Changes in the mechanical properties with the annealing temperatures corresponded well with the changes in the microstructures.
  • Friction and Elongation of Al Electrodes due to Micro-Sliding between the Inner Mo Electrode and the Al Electrodes in High-Power Devices

    pp. 2326-2330

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    DOI:10.2320/matertrans.43.2326

    The high friction coefficients between the inner Mo electrode and the cathodes Al electrodes in large-area, high-power devices causes Al to stick to Mo or causes short circuiting due to the large elongation of the Al electrodes. Equipment which can reproduce these friction behaviors has developed. The friction coefficients and the Al elongation were evaluated for various combination systems. It was found that friction coefficients and Al elongation were much smaller for Mo/Cd||Al and Mo||Mo foil||Al systems than those for the conventional Mo||Al system. The reliability of large-area, high power devices using Mo foil was satisfactory.
  • The Characterization of Reinforced TiAl Intermetallic with Dispersed Cr Particles Consolidated by HIP

    pp. 2331-2336

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    DOI:10.2320/matertrans.43.2331

    A Chromium (Cr) containing TiAl intermetallic has been consolidated by Hot Isostatic Pressing (HIP) process using high purity TiAl pre-alloyed powder as original material. Cr has been selected as an element which improves high temperature mechanical properties of HIPed TiAl intermetallic compound. Cr additions in TiAl powder were changed systematically and microstructure and mechanical properties at elevated temperatures were examined. This study determined the densification behavior of Cr containing TiAl intermetallic powder during HIP process conducted at 1273 K under the pressure of 200 MPa. Microstructure of consolidated TiAl+xCr as well as high temperature mechanical properties are presented. Improvement of high temperature tensile strength of as-HIPed TiAl compound was achieved by the effect of Cr particles dispersion and reactive zone formation between Cr particles and TiAl matrix. From these results, it was concluded that tensile strength of HIPed TiAl–5Cr becomes 1.2–1.5 times high than that of HIPed and MIMed TiAl and machinability of TiAl at R.T. also was improved by high elongation of HIPing and Cr addition.
  • Soft Magnetic Properties of Nanocystalline Fe-Si-B-Nb-Cu Rod Alloys Obtained by Crystallization of Cast Amorphous Phase

    pp. 2337-2341

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    DOI:10.2320/matertrans.43.2337

    An amorphous alloy rod of 0.5 mm in diameter was produced for an Fe72.5Si10B12.5Nb4Cu1 alloy by copper mold casting, though the maximum diameter of 1.5 mm for (Fe0.75Si0.1B0.15)96Nb4 alloy decreased by the addition of 1 at%Cu and the decrease in B content. The amorphous alloy rod crystallizes through multi-stage exothermic reactions. The first exothermic peak is due to the precipitation of nanoscale bcc-Fe phase and the following exothermic peaks result from the transition of bcc-Fe+amorphous→bcc-Fe+Fe23B6+Fe2B+Fe3Si+Fe2Nb. The bcc-Fe phase has a particle size of about 10 nm and its volume fraction is approximately 70% after annealing for 300 s at 883 K . The alloy rod consisting of bcc-Fe and amorphous phases exhibits good soft magnetic properties, i.e., high saturated magnetic flux density of 1.21 T, low coercive force of 1.8 A/m and high initial permeability of 32000. The good soft magnetic properties for the nanocrystalline Fe72.5Si10B12.5Nb4Cu1 alloy in a rod form of 0.5 mm in diameter are encouraging for future development as a new type of nanocrystalline soft magnetic bulk material.
  • Effects of Ti on the Thermal Stability and Glass-Forming Ability of Ni-Nb Glassy Alloy

    pp. 2342-2345

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    DOI:10.2320/matertrans.43.2342

    The thermal stability, glass-forming ability (GFA) and mechanical properties of the Ni60Nb40−xTix (x=0 to 40) glassy alloys have been investigated. As the Ti content increases, the supercooled liquid region ΔTx (= TxTg) and reduced glass transition temperature (TgTl) increase, the maximum ΔTx of 54 K and TgTl of 0.622 are obtained at 22.5%Ti and 15%Ti, respectively, and then the ΔTx and the TgTl gradually decrease. The Ni60Nb25Ti15 glassy alloy was formed in a rod form with a diameter up to 1.5 mm. The Tg and Tx of the bulk glassy alloy were 859 K and 906 K, respectively. The Vicker’s hardness (Hv), Young’s modulus (E), compressive fracture strength (σc,f) and compressive plastic elongation (εc,p) were 833, 167 GPa, 3085 MPa and 1.8%, respectively, for the bulk alloy. There is a tendency for fracture strength to increase with increasing glass transition temperature (Tg). It is therefore interpreted that the high strength is due to strong bonding nature among the constituent elements.
  • Formation and Mechanical Properties of Ti-Zr-Ni-Cu Amorphous Alloy Containing Icosahedral Nanoscale Quasicrystalline Phase

    pp. 2346-2349

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    DOI:10.2320/matertrans.43.2346

    Amorphous Ti60Zr15Ni15Cu10 alloy ribbons containing an icosahedral quasicrystalline phase were prepared by melt-spinning. The microstructure of this alloy strongly depends on cooling rate, which controlled by the circumferential velocity of copper roll. At a low velocity of 10 m/s, stable α-Ti/Zr, Ti2Ni and Ti2Cu crystalline phases are formed. At the velocities of 15 and 20 m/s, an icosahedral quasicrystal phase (I-phase) is formed directly. At the velocities of 25, 30 and 35 m/s, a mixed structure consisting of I- and amorphous phases is formed and the size of I-phase is in the range of 5–50 nm. At the high velocity of 40 m/s, a single amorphous phase is formed. The DSC traces of these melt-spun alloys obtained during continuous heating from room temperature to 1000 K at a heating rate of 0.67 K/s show distinct exothermic peaks. The amount of the first exothermic heat decreases with a decrease of cooling rate, indicating an increase of the precipitated I-phase in these melt-spun ribbons. For the single amorphous phase ribbon, the Vickers microhardness (Hv), tensile fracture strength (σf) and distinct plastic elongation (ε) are 460, 1480 and 1.42% respectively. For the nano-scale I-phase bearing amorphous composite ribbons, the σf, Hv and ε depend on the volume fraction (Vf) of the I-phase. The maximum σf (1650 MPa) and ε (1.52%) was obtained at about Vf=28% with particle size of 5–20 nm.
  • Formation and Soft Magnetic Properties of Fe-B-Si-Zr Bulk Glassy Alloys with High Saturation Magnetization above 1.5 T

    pp. 2350-2353

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    DOI:10.2320/matertrans.43.2350

    A new Fe-based bulk glassy alloy with good soft magnetic properties and high saturation magnetization (Is) above 1.5 T was formed at the composition of (Fe0.75B0.15Si0.1)99Zr1. The addition of 1 at%Zr to Fe75B15Si10 caused the appearance of glass transition (Tg) at 815 K, followed by a supercooled liquid region (ΔTx (= TxTg)) of 52 K, in addition to a decrease of Curie temperature (Tc) from 714 to 688 K and an increase of crystallization temperature (Tx) from 845 to 868 K . The reduced glass transition temperature (TgTl) was measured as 0.59. The increase in the supercooled liquid region enabled us to form bulk glassy alloy rods in the diameter range up to 0.75 mm by the copper mold casting method. The Tc, Tg, ΔTx and crystallization peak behavior for the bulk glassy alloy rods are nearly the same as those for the corresponding ribbon sample. The bulk glassy alloy rods exhibit high Is of 1.53 T and low coercive force (Hc) of 2.8 A/m which are comparable to commercial Fe-based amorphous alloy ribbons. The good combination of the new Fe-based alloy composition, high glass-forming ability and good soft magnetic properties indicates that the new bulk glassy alloy may be used as a new type of soft magnetic material.
  • Rapid Synthesis of Yttria-Partially-Stabilized Zirconia Films by Metal-Organic Chemical Vapor Deposition

    pp. 2354-2356

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    DOI:10.2320/matertrans.43.2354

    Yttria-partially-stabilized zirconia (YPSZ) films were synthesized on Hastelloy-XR as thermal barrier coatings (TBC) at a high deposition rate of 100 \\micron h−1 (2.8×10−8 ms−1) by metal-organic chemical vapor deposition (MOCVD) using Zr(dpm)4 and Y(dpm)3 precursors. The deposition rate of 100 \\micron h−1 was the highest among the reported values for YPSZ films by CVD . The YPSZ films were columnar morphology and (200) oriented with a tetragonal structure.
  • Fabrication of Bulk Glassy Hf50Cu30Ni10Al10 Alloy by Copper Mold Casting

    pp. 2357-2359

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    DOI:10.2320/matertrans.43.2357

    The glass-forming ability of the Hf50Cu30Ni10Al10 alloy was examined by melt-spinning and copper mold casting methods. A new Hf50Cu30Ni10Al10 bulk glassy rod of 3 mm in diameter was formed by copper mold casting. The crystallization temperature (Tx), glass transition temperature (Tg) and TgTl of the glassy alloy rod were 780 K, 860 K and 0.61, respectively. The Hf50Cu30Ni10Al10 bulk glassy alloy exhibits density of 11.0×103 kg/m3, Vickers hardness of 590, Young’s modulus of 118 GPa and compressive fracture strength of 2420 MPa. The synthesis of the Hf-based bulk glassy alloy with high TgTl, high fracture strength and high density is encouraging for future application of bulk glassy alloys.
  • Magnetic and Martensitic Phase Transformations in a Ni54Ga27Fe19 Alloy

    pp. 2360-2362

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    DOI:10.2320/matertrans.43.2360

    The martensitic and magnetic transitions of Ni54Ga27Fe19 alloy were investigated by differential scanning calorimetry and X-ray powder diffraction and with a vibrating sample magnetometer. The alloy is martensitically transformed from a L21 to a martensite phase with a 14M (7R) structure. The ferromagnetic transition is also accompanied by the martensitic transformation from a paramagnetic parent phase to a ferromagnetic martensite phase in the temperature interval between Ms (= 293 K) and Mf (= 274 K). The Ni–Ga–Fe system is promising as a ferromagnetic shape memory alloy.

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