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

MATERIALS TRANSACTIONS Vol. 43 (2002), No. 3

  • Material Recycling in OECD Countries

    pp. 282-284

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    DOI:10.2320/matertrans.43.282

    Material recycling occurs naturally when there are market incentives. When the economics of recycling is only marginal, government and institutional incentives are required. Here a simple framework for graphically representing the “cost-quality” dynamics of recycling is presented. Examples of policy and technology approaches are outlined based upon a recent study of several OECD countries \\citerf1 In addition large scale trends for these countries show the complex effects of wealth (GNP per capita) on recycling.
  • Barrier-Free Processing of Materials for Environmentally Benign Life-Cycle Design

    pp. 285-291

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    DOI:10.2320/matertrans.43.285

    It is required to develop innovative materials technology for environmentally benign manufacturing toward dematerialization. Recently, some barrier-free processes in a variety of materials such as steels, light metals, polymers, woods have been studied from the viewpoint of recycling for scraps and materials selection for poison-free materials, and forming for high performance materials. The present paper reviews the contents of the barrier-free processing. The key technologies of the barrier-free processing are the synthesis of harmless materials from scraps by dispersion control and the simultaneity of forming and microstructural control by in-process control.
  • Suppression of Surface Hot Shortness due to Cu in Recycled Steels

    pp. 292-300

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    DOI:10.2320/matertrans.43.292

    The most serious problem in the recycling of steel is the occurrence of surface hot shortness during hot deformation due to the mixing of Cu from scrap into steels. Tin accelerates the effect of Cu. The surface hot shortness is caused by liquid embrittlement, that is, formation of the liquid Cu-enriched phase through preferential oxidation of Fe atoms at the steel/scale interface during heating for hot deformation and penetration of this Cu-enriched phase into the grain boundaries. Decrease in the amount of the liquid Cu-enriched phase penetrating into grain boundaries can suppress the surface hot shortness. The amount of the liquid Cu-enriched phase penetrating into the grain boundaries can be reduced by the suppression of oxidation, occlusion of the Cu-enriched phase into the scale, back-diffusion of Cu into the steel matrix and suppression of penetration of the liquid Cu-enriched phase. Therefore, the effects of various elements and conditions of heating and deformation on the surface hot shortness, oxidation, amount of the Cu-enriched phase at the interface and the penetration were examined by tensile tests at high temperatures, thermogravimetry and optical microscopy. The conclusion can be summarized as follows. Silicon, Mn, S (+Mn) and B reduce the susceptibility to the surface hot shortness through decreasing the amount of Cu-enriched phase at the steel/scale interface. The effect of Si is significant. Carbon reduces the oxidation rate in LNG combustion gas. Phosphorus, Si, B and C reduce the susceptibility to the surface hot shortness through restraining the penetration of the Cu-enriched phase into grain boundaries. Heating at higher temperatures reduces the susceptibility mainly through a reduction in the amount of the Cu-enriched phase at the steel/scale interface, although the loss of steels by oxidation increases. A large grain size accelerates the surface hot shortness. A small amount of H2O in air significantly accelerates the surface hot shortness. Effects of H2O in heating atmosphere depend on the steel composition and more detailed research on this is desired. Very slow deformation does not cause liquid embrittlement through dynamical re-crystallization, while at a fast deformation rate the embrittlement is suppressed by an increase in the critical stress for the liquid embrittlement. Multiple methods using physical metallurgy suggested by the present research for suppressing the surface hot shortness should be applied together with other methods through separation, smelting and design of fabrication in order to promote the recycling of steels.
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  • Deformation and Fracture Mechanism of Consolidated Fe-Cu Alloy from Rapidly Solidified Powder

    pp. 301-304

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    DOI:10.2320/matertrans.43.301

    Deformation and fracture mechanism during tensile testing is investigated for consolidated Fe–Cu alloy. Fe–Cu rapidly solidified powder in which copper is supersaturated is consolidated using groove rolling. Copper content, rolling temperature, and heat exposure condition are varied to obtain samples with various microstructures. The samples are subjected to tensile testing; some tests are suspended to observe the microstructure change during loading. The tensile behavior and the microstructure are correlated based on the obtained stress-strain curves and SEM observation. The difference of the stress-strain curve is explained from the morphology change of the microstructures and the following change of the microfracture behavior during loading.
  • Microstructure of Cast Strip in 0.1 mass%C Steels Containing Phosphorus

    pp. 305-310

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    DOI:10.2320/matertrans.43.305

    Cast strips of 0.1 mass%C steels with phosphorus contents ranging from 0.01 to 0.2 mass% have been produced by using a twin drum type continuous casting machine, and their microstructures have been characterized. Fine dendrite structure in the strips provides a fine dispersion of the segregated phosphorus regime. Phosphorus addition changes the α grain structure dramatically and decreases the γ grain size. The EPMA (Electron Probe Micro Analyzer) mapping and the diffusion analysis of phosphorus in the γ phase indicate the presence of a retained δ phase in the austenite temperature. The pinning effect of the δ-ferrite on the γ-grain growth must be kept in the temperature range of the rapid γ grain growth. The balance of strength and ductility for the cast strip is improved as the phosphorus content increases.
  • Aluminum-Alloyed Cast Iron as a Versatile Alloy

    pp. 311-314

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    DOI:10.2320/matertrans.43.311

    The feasibility of intelligent utilization of iron-aluminum scraps is explored in this work. Through adding aluminum which is contained in the scraps to cast iron, the changes in wear resistance, heat resistance and damping property of aluminum-alloyed cast irons were systematically investigated. Superior properties were obviously manifested in the cast irons with certain aluminum contents. Iron-aluminum mixed scraps are expected to be utilized as a raw material for high quality cast irons.
  • Solid State Recycling of Recyclable Aluminum Wastes with In-Process Microstructure Control

    pp. 315-321

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    DOI:10.2320/matertrans.43.315

    Aiming for actual dematerialization, mass flow must be optimized to make full use of the recyclable materials as input and to reduce total amount of wastes. Since the material efficiency is strongly dependent on their adaptivity to the design demand for recycled products, an effective recycling process must accompany the advanced materials processing and manufacturing to improve their original properties to the level above the demand. In the present paper, the light-mass non-ferrous metallic alloys such as aluminum alloys are targeted, to utilize their bulk wastes, which are often ejected from the electric parts or members, as an input material, and to aim for their reuse as an automotive part. Dense, high-strengthened aluminum alloy compact, or, green materials are handled in the present forming and manufacturing up to the final net-shape formation of products by sinter-forging. Selection of reused materials and in-process improvement of their properties are essential keys in this barrier-free processing. Possibility to replace the conventional processing with this barrier-free process lies in: (1) Reduction of in-process energy and mass consumption, (2) Flexibility to yield various kinds of products without any realignment of processes, and (3) Adaptive in-process material modification to design for products in practical use.
  • Solid-State Recycle Processing for Magnesium Alloy Waste via Direct Hot Forging

    pp. 322-325

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    DOI:10.2320/matertrans.43.322

    A solid-state recycle processing for magnesium alloy waste has been developed by combining cyclic plastic working and direct hot forging under the short thermal explosion. AZ91D machined chips, which were employed as wasted materials in this study, were consolidated to the green compact with fine microstructures via bulk mechanical alloying (BMA) process, where the compaction and forward extrusion in the closed die were repeated at room temperature. To keep fine microstructures after hot forging, that is, to prevent from the matrix softening due to the grain and/or intermetallic growth, the thermal damage on the green compact in pre-heating before forging was controlled by using the infrared gold image rapid heating furnace. The hot forged AZ91D alloy showed superior mechanical properties such as hardness and ultimate tensile strength (UTS) to the cast one used as input raw materials. The same effects were recognized in the case of wasted Al–Si alloys via this process. The developed solid-state recycle processing revealed a possibility to improve the mechanical properties of the consolidated light alloys even in employing their wasted materials.
  • New Heat-Resistant and Soluble Aramids Synthesized by Palladium-Catalyzed Carbonylation-Polycondensation

    pp. 326-331

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    DOI:10.2320/matertrans.43.326

    As a candidate for the alternate of conventional, insoluble thermosetting resins that are matrix components of fiber reinforced plastics (FRP), soluble and heat-resistant aramids (wholly aromatic polyamides) were synthesized. To obtain rigid biphenyl-containing aramid, one-step procedure from dihalobiphenyl and aromatic diamine by palladium-catalyzed carbonylation-polycondensation was successfully applied. Reaction parameters, such as base, solvent, palladium-phosphine catalyst and CO pressure in the reaction of 2,7-dibromo-9,10-dihydrophenanthrene (1) and 4,4-diaminodipheyl ether (2a), were very important for successful synthesis. They affected the molecular weight of resulting aramid significantly. Under optimum conditions, poly[amino-1,4-phenyleneoxy-1,4-phenyleneaminocarbonyl(9,10-dihydro-2,7-phenanthrenediyl)carbonyl] (3a) was obtained in 99% yield with high molecular weight (polystyrene equivalent Mw=128100). The procedure was applied to some other diamines. The aramid 3a was heat-resistant and soluble in polar organic solvent. On the basis of thermal analysis, 10% weight loss temperature (T10) of the aramid was 461°C. The tensile strength and tensile modulus were 48 MPa and 1.6 GPa, respectively; these properties are roughly in the same level as those of conventional unsaturated polyester resin. Judging from the data, aramid 3a is applicable for matrix of FRP. Some other aramids exhibited similar properties.
  • Present State of Wood Waste Recycling and a New Process for Converting Wood Waste into Reusable Wood Materials

    pp. 332-339

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    DOI:10.2320/matertrans.43.332

    The amounts of new wood used for housing construction and wood waste from demolished buildings was calculated using various scenarios of wood recycling. Diverse utilization of waste and increase in reuse rate was found to be effective to reduce the total amounts of final waste and the use of new wood materials. For recycling wood waste, the water vapor explosion (WVE) process was developed. In this process, wood materials were exploded from within by the force of water vapor generated by compression under high pressure and temperature and evaporation of the internal moisture, and they were separated into small wood elements. The WVE process was directly applied to the separation of Sugi (Cryptomeria Japonica) and Karamatsu (Laryx leptolepis) sawn timbers and slabs. The WVE of them produced small wood elements including fiber bundles, strands, and chips at certain experimental conditions (pressure, temperature, and compressing time). Fiber bundles were long, narrow and flexible elements, and it appeared that they could not be obtained by the conventional processes.
  • Corrosion Resistance and Adhesion Properties of the Chromium-Free Coating Using an Urethane-Base Resin for AZ91E Magnesium Alloy

    pp. 340-342

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    DOI:10.2320/matertrans.43.340

    Corrosion resistance and adhesion properties of a chromium–free (poison-free) coating using an urethane-base resin for AZ91E Magnesium alloy have been investigated by salt immersion tests and thermal and humid resistance tests. As a result of the salt immersion tests, the corrosion resistance of the chromium-free coated specimen was almost equal to that of the Chromium-based chemical conversion. Also, the thermal and humid resistance tests showed that no changes were found in the coating with an urethane resin base layer; however, exfoliation was observed in the coating with a phenolic resin base layer. In the coating with an urethane resin base layer, the boundaries between the base layer and the aluminum middle layer were relatively flat and there were no pores, though a lot of pores were observed between the base layer and the aluminum middle layer in the coating with a phenolic resin base layer. Therefore, it is suggested that the good adhesion properties of the chromium-free coating are related to the strong adhesion between the urethane resin base layer and the aluminum middle layer.
  • Superhigh Strength Metal Injection Molded Low Alloy Steels by In-Process Microstructural Control

    pp. 343-347

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    DOI:10.2320/matertrans.43.343

    Metal Injection molding (MIM) process is an advanced powder processing technique because of net shaping with shape complexity at low processing energy and 100% material utilization. This study has been performed to clarify and to optimize the relationship between the mechanical properties and the microstructures for the superhigh strengthening sintered low alloy steels (Fe–Ni system) by using MIM process. A 6 mass%Ni MIM steel showed excellent properties of 2000 MPa tensile strength, 5% elongation and 500 MPa fatigue strength. Instead of Fe–Ni, moreover, the Fe–Mn low alloy steel was investigated to obtain high performance properties, because Ni has a harmful influence upon the human body, for example, a Ni allergy.
  • Environmentally Benign Manufacturing of Automotive Parts via Powder Metallurgy

    pp. 348-351

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    DOI:10.2320/matertrans.43.348

    Automotive parts produced using a powder metallurgy (P/M) process are commonly used in automobiles because they can be produced without the use of machining and with a special alloy design. This paper describes how the P/M process can be applied to the production of environmentally friendly automotive parts. The paper begins with a discussion on how the utilization of P/M for net-shape manufacturing makes it possible to conserve both energy and materials due to the fact that machining is unnecessary. Evidence is then presented that shows that it is possible to produce warm-compacted automotive P/M parts with sufficient strength even without the use of special alloy elements and/or heat treatments. As a final example, magnet materials made using spark-plasma sintering are described. This spark-plasma sintering process makes it possible to create high-performance magnet parts that are highly energy efficient. Finally, taking into consideration the above-mentioned example, the ideal P/M process is discussed from an environmentally benign point of view.
  • Preparation of MoSi2-X(X=B, Al, Nb) Alloys by Mechanical Alloying and Pulse Discharge Sintering Process

    pp. 352-354

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    DOI:10.2320/matertrans.43.352

    Mechanical alloying and pulse discharge sintering (MA-PDS) process was employed to fabricate MoSi2 alloys with additions of Al, B or Nb alloy elements. Microstructure and mechanical properties of these alloys were investigated. An exothermic behavior was identified during milling. This process is related to the reaction of each element to synthesize intermetallic MoSi2. The MoSi2 alloys fabricated by MA-PDS process showed a very fine microstructure compared to that sintered from the commercial MoSi2 alloy powders. Significant hardness increase was found due to the refinement of the binary MoSi2 microstructure. Alloys made from powders milled in air show higher hardness compared to those in Ar gas. This was because of the oxides formed during milling process.
  • In Situ High-Temperature X-ray Observations of Crystallization of Zinctellurite Glass

    pp. 355-358

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    DOI:10.2320/matertrans.43.355

    A reliable fabrication process of non-silica glasses is required to suppress crystallization. The crystallization behavior of zinctellurite (ZnO–TeO2) glass at different rates of heating and cooling were studied by an in situ high-temperature X-ray diffractometer (a rapid measurement system) and differential thermal analysis (DTA). The DTA results compared with the X-ray diffraction data resulted in crystallization and phase relations, during heating and cooling, of the glass. During the heating process, α-TeO2 and ZnTeO3 were found to crystallize first, followed by the crystallization of Zn2Te3O8. While during the cooling process from melt, α-TeO2 was found to crystallize first, followed by the crystallization of Zn2Te3O8. The present study results in reliable data of the crystallization process and presents a possibility of an approach to make accurate T-T-T diagram which can show the crystallization tendency.
  • Environmentally Benign Manufacturing and Ecomaterials; Product Induced Material Flows

    pp. 359-363

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    DOI:10.2320/matertrans.43.359

    In this paper we examine the product induced material flows through the product manufacturing system. Research strategies to reduce materials related environmental loads based upon this examination are suggested.
  • Material Flow Challenges in Industrial Ecosystems

    pp. 364-367

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    DOI:10.2320/matertrans.43.364

    In Industrial Ecology the core idea is to find symbiotic relationships where waste material from one company is being used by other companies and industrial ecosystems are created. Although the idea is simple, fundamental challenges exist related to the quality of the material, stability of the system, etc. A core question is how to assess of the “goodness” of such a system. In this paper, it is shown how ecological input-output analysis metrics can be used to analyze flows.
  • Integrated Environment-Conscious Life-Cycle Design (Eco-Life-Cycle Design) of Building Structural Composite Materials, Components, and/or Systems -as a Basis of Establishment of Sustainable Eco-buildings and Eco-cities-

    pp. 368-375

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    DOI:10.2320/matertrans.43.368

    In order to develop effective environmentally benign manufacturing and materials processing (EBM) in architecture, concept and procedures of integrated environment-conscious life-cycle design (Eco-LCD) are proposed and reported, for building structural composite materials, and components such as steel reinforced concrete (RC), and continuous fiber reinforced concrete (FRPRC), and/or systems such as external thermal insulation ones (ETI) using short-cut fiber reinforced cement composites (FRC) including thermal insulations as exterior thermal insulation panels.
  • High Performance Materials for Long-Term Usage

    pp. 376-378

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    DOI:10.2320/matertrans.43.376

    Although high performance materials offer many advantages in reducing overall material usage and waste generation, there are limitations that must be addressed to their use. These include problems in materials design, testing and evaluation, manufacturing processing and recycling. These limitations will be discussed.
  • Exergy Analysis of Steel Production Processes

    pp. 379-385

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    DOI:10.2320/matertrans.43.379

    Continuous increase of the annual amount of steel scrap generated presents a problem to the sustainability of human society. The effective utilization of scrap is a serious problem to be solved in the near future, and the optimization of the global system of steel production should be considered from various viewpoints, particularly those of environmental load and material efficiency. For the consideration of a global system that contains many different kinds of flow, a criterion for evaluating the efficiency of the system is necessary for optimizing the utilization of materials in the system. The concept of exergy was adopted in this study and the application of exergy analysis to the evaluation of a complicated system was considered. A simulation model was developed for the steel industry in Japan and the exergy analysis of the Blast Furnace-LD converter (BF-LD) process and the Electric Arc Furnace (EF) process was conducted. The exergy loss was expressed as a function of parameters, such as the mixing rate of pig iron in the EF process and the total exergy loss in the system was calculated. The applicability of exergy as a criterion for the analysis of a production process and for evaluating material efficiency was discussed.
  • Graded Design of Carrier Concentration in Thermoelectric PbTe System by Heat-treatment

    pp. 385-389

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    DOI:10.2320/matertrans.43.385

    In order to develop a new process of forming a carrier concentration gradient in PbTe only by using heat-treatment, the effect of heat-treatment on a carrier concentration n of the p-type PbTe has been investigated, and the p-type PbTe has been heat-treated using a temperature gradient. The as-grown stoichiometric PbTe was p-type with an n of 1.0×1024 m−3. Vacuum thermal exposure with Te-rich PbTe at 900 K for 1 h increased the n of the stoichiometric PbTe to 5.1×1024 m−3, which indicates that hole formation was achieved by thermal exposure at this temperature and duration. The thermally exposed stoichiometric PbTe was heat-treated in the temperature range of 400 to 900 K for a period of 24 h. The n decreased with an increasing heat-treatment temperature of between 300 and 500 K, while the n increased with an increasing heat-treatment temperature of between 500 and 900 K. A minimum n was measured at 500 K, above which the formation energy of holes was determined to be 16.4 kJ/mol. On the basis of these results, a 19 mm long thermally exposed stoichiometric PbTe was heat-treated using a temperature gradient of 340–900 K for a period of 24 h. A continuous change in n was formed in the PbTe, and a minimum value of n was determined to be at a position corresponding to the heat-treatment temperature of 500 K. A continuous gradient of hole production was successfully achieved in the p-type PbTe only by heat-treatment using a temperature gradient.
  • Critical Issues in Promotion of Environmentally Benign Manufacturing and Materials Processing

    pp. 390-396

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    DOI:10.2320/matertrans.43.390

    Regional differences on the strategy against crisis to environment make a common frame invisible to promote the effective directions toward significant reduction of total mass requirement or dematerialization. This overview summarizes the intimate discussions, proposals and advisable comments at the first US-Japan Workshop on the Environmentally Benign Manufacturing and Materials Processing at Hawaii on the October 5th, 2001, in order to integrate the state-of-the-art research activities in both countries. In the discussion over the recyclable materials, value/cost-quality diagram is used to redefine the recycling process and to characterize various processes in the environmentally benign manufacturing. Influence of light-weight material selection on the dematerialization is discussed to find out a new direction. Importance of the trade-off-balancing on the high performance for long term use is reconsidered to search for a solution in the design of innovative manufacturing and materials processing. Mass flow analysis in the life cycle assessment is recognized as a tool to make eco-system design for industrial ecology. Several issues for further research are also argued to promote the related activities to the environmentally benign manufacturing and materials processing.
  • New Step of Ecomaterial to Break through the Barrier between Ecomaterial-Selection and Eco-Design

    pp. 397-405

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    DOI:10.2320/matertrans.43.397

    Based on the review of ten years progress of ecomaterials’ research and development, a barrier free processing is proposed as a next step of ecomaterials. In the first place, the development of ecomaterial is reviewed. The concept of ecomaterial has been widely spread in the design of materials as life-cycle thinking and has been realized in the various area as a form of consumer material, commodity material and energy-transmission material with the keyword of “hazardous substance free”, “green environmental profile”, “higher recyclability” and “higher materials efficiency”. The importance of the connection of the ecomaterial with DfE (design for the environment) is emphasized as the next step. The existence of the barrier in the material processing technology between ecomaterial-selection and DfE is pointed out. The barrier on the input-flow of the process makes it difficult to use of environmental friendly raw materials. The barrier on the output-flow of the process prevents it from the flexible formability to give the shape to realize DfE. In order to solve those problems, a new research project, named as “Study on the Barrier-Free Processing of Materials for Life-Cycle Design for Environment”, has been launched.
  • Magnetic Properties and Microwave Absorption Properties of Polymer-Protected Cobalt Nanoparticles

    pp. 406-409

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    DOI:10.2320/matertrans.43.406

    This paper describes magnetic properties and microwave absorption properties of polymer-protected cobalt nanoparticles. Cobalt nanoparticles were prepared using the thermal decomposition of dicobalt octacarbonyl in ethylene glycol. They were stabilized and dispersed by coexisting with poly(N-vinyl-2-pyrrolidone) (PVP), resulting in an average diameter of 45 nm. The X-ray diffraction (XRD) analysis revealed that the Co-PVP sample synthesized at 170°C for 3 h, with the mole ratio of cobalt:PVP=1:10 (mol : unit mole), consisted of two phases of hcp and fcc cobalt. Their saturation magnetization measured using a vibrating sample magnetometer (VSM) was 1.53×10−4 Wb·m·kg−1. The compacted sample, produced from the PVP-protected cobalt nanoparticles, showed a reflection loss (R.L.) less than −20 dB at the frequency (matching frequency: fm) of 0.54 and 0.64 GHz with the thickness (matching thickness: dm) of 6.16 and 5.04 mm, respectively. Therefore, it is concluded that polymer-protected cobalt nanoparticles have a possibility for the use as microwave absorption materials.
  • Effects of Compositions on Formation of 1, 2 Protorides in Ti-Cr-V Alloys

    pp. 410-413

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    DOI:10.2320/matertrans.43.410

    Ti–Cr–V alloys are known to absorb protium up to H/M=2. However, Ti–Cr–20 at%V alloys with more than 56 at%Cr content were found to absorb up to H/M=1. This paper aims to make clear the effects of compositions on formations of 1, 2 protorides in Ti–Cr–V alloys, and the structure of the mono-protorides. It was found that the mono-protorides with fcc and hcp structures exist. The mono-protoride with the fcc structure was different from the di-protoride with the FCC structure in the lattice constants. Some relationship between appearance of the mono-protorides and disappearance of the plateau regions in low hydrogen pressure regions was considered to exist. As a result, the appearance regions of 1, 2 protorides in Ti–Cr–V alloys were derived.
  • Characterization of Small Areas of Thin-Films by Grazing-Exit Electron Probe X-ray Microanalysis

    pp. 414-416

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    DOI:10.2320/matertrans.43.414

    Metallic thin films deposited on Si wafers were analyzed by EPMA under grazing-exit geometry. The experimental setup consisted of the conventional SEM and EDX. The exit angle was controlled by moving the EDX up and down. After the SEM observation, the electron beam fixed on the analyzed position. And then, the intensities of characteristic X-rays were measured as a function of exit angle. These angle dependences were analyzed by curve fitting of the simulated curves. As a result, the thickness and the density of thin films were evaluated. The difference of the density of chromium thin films prepared by different methods was found. The GE-EPMA measurement was performed for Au–Ag layers on the Si wafer. The thin-film characterization for each layer was independently performed at localized region on Ag and Au layers.
  • Hydrogen-Storage Properties and Structure Characterization of Melt-Spun and Annealed Mg-Ni-Nd Alloy

    pp. 417-420

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    DOI:10.2320/matertrans.43.417

    The hydriding/dehydriding characteristics of a Mg-rich Mg–Ni–Nd alloy produced by melt-spinning and subsequent annealing have been investigated. This alloy absorbs ∼ 4.7 mass% hydrogen (H⁄M∼ 1.5) quickly between 423 and 573 K and wholly desorbs it at moderate speeds above 453 K. Transmission electron microscope observations and selected-area electron diffraction analyses of this alloy before and after hydriding demonstrate that it consists of multiple phases of Mg2Ni and Nd-hydride precipitated uniformly in a nano-structured Mg matrix. The fast reaction kinetics is caused by an interplay between a catalytic action of the Nd-hydrides and the surrounding nano-sized Mg grains which quickly store or evolve hydrogen across the interfaces.
  • Hydrogen Absorption and Desorption Properties of Ti3Al-Ni Alloys

    pp. 421-423

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    DOI:10.2320/matertrans.43.421

    Structures of as-cast and homogenized Ti75−xAl25Nix alloys before and after hydrogenation, the hydrogen content and the hydrogen desorption temperature of the hydrogenated Ti75−xAl25Nix alloys were investigated by a powder X-ray diffractometer (XRD) and a hydrogen analyzer. The hydrogen content of these alloys decreased with increasing Ni content, and was almost independent of the hydrogenation temperature and the structure of the alloys, but 50% hydrogen desorption temperature, Td, varied widely with them. The formation of amorphous phases raised Td. On the contrary, a drop in Td was achieved by hydrogenation of a mixture alloy of the D019 and C14 Laves phases.
  • Anomalous Magnetic Moments of Mn13 and Mn19 Clusters

    pp. 424-427

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    DOI:10.2320/matertrans.43.424

    Recently, sharply reduced magnetic moments were measured in Mn13 and Mn19 clusters with values of about 0.5 \\microB/atom, while other clusters had moments of 1 to 1.4 \\microB/atom. It was postulated that this sharply reduced magnetic moment results from the icosahedral growth sequence. We confirm the stability of the icosahedral structures. The icosahedral Mn13 and Mn19 clusters have several nearly degenerate low energy states, each with a low magnetic moment. It is shown that the mixture of ferromagnetic and antiferromagnetic coupling is responsible for the low net magnetic moments.
  • Ternary Compound Ti3SiC2: Part I. Pulse Discharge Sintering Synthesis

    pp. 428-431

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    DOI:10.2320/matertrans.43.428

    Pulse discharge sintering (PDS) technique was employed to synthesize the ternary compound Ti3SiC2 from four starting powder mixtures. The experimental results demonstrated that when the starting material of 3Ti/Si/2C or 3Ti/SiC/C was used high content of the secondary phase, TiC, higher than 30 mass%, was found in the sintered material. When TiC powder as starting material was used (Ti/Si/2TiC) in the same stoichiometric composition, however, the final sintered product contained low TiC content of a few percent. Further adjusting the composition to the off-stoichiometric of 2Ti/2Si/3TiC, the content of the secondary phase TiC was further controlled to be around 1 mass%. In the materials sintered from Ti/Si/2TiC and 2Ti/2Si/3TiC an optimum sintering temperature exists at 1573 K, at which the highest Ti3SiC2 phase purity was achieved. When sintered at the optimum temperature a density of higher than 99% was obtained. At the optimum sintering temperature, both the phase purity and the density of the material sintered from 2Ti/2Si/3TiC showed very little dependence on the sintering time ranging from a few minutes to four hours, indicating the phase stability at this temperature.
  • Ternary Compound Ti3SiC2: Part II. Deformation and Fracture Behavior at Different Temperatures

    pp. 432-435

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    DOI:10.2320/matertrans.43.432

    Compressive tests were conducted in vacuum at temperatures up to 1203 K, on the Ti3SiC2 samples synthesized from 2Ti/2Si/3TiC powder mixture through pulse discharge sintering technique. The compressive strength of Ti3SiC2 compound showed a monotonic decrease with increasing testing temperature. The Ti3SiC2 samples displayed obvious brittle fracture behavior at temperatures below 1073 K. When the testing temperature was above 1123 K, obvious pseudo-plastic deformation behavior was observed in the stress-strain curves. At these temperatures, after an initial pseudo-strain-hardening, a decrease in stress follows with further increasing strain. The pseudo-plastic behavior of Ti3SiC2 at temperature above 1123 K could be attributed to the basal plane slip, kink-band formation, delamination of layers at local sites, and intergranular cracking. Further increase in strain causes the growth and linkage of microcracks, which gives rise to the reduction of the real area of the cross section of specimen and hence lead to the “strain-softening” phenomenon.
  • Crystal Distortion and Magnetic Structure of γ-MnPd Alloys

    pp. 436-438

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    DOI:10.2320/matertrans.43.436

    We have made X-ray and neutron diffraction experiments and magnetic susceptibility measurements for γ-MnPd alloys. The alloy containing 10.5 at%Pd shows a face center orthorhombic structure with a=0.3839, b=0.3780 and c=0.3717 nm and a non-collinear antiferromagntic structure with μa=0, μb=1.26 and μc=2.14 μB/Mn atom at 10 K. The crystal distortion occurs from the orthorhombic structure to a tetragonal structure with ca<1 at 320 K, and finally to a cubic structure at 430 K. Another alloy with 13 at%Pd shows a face centered tetragonal with a=0.3800 and b=0.3846 nm (ca=1.012) at 293 K, and transforms to a cubic structure at 350 K. More Pd rich alloy with 15 at% shows [c] structure down to 27 K. A phase diagram for γ-MnPd alloy system with 8–17 at%Pd is proposed.
  • Relationship between the Crystallographic Structure of Electrodeposited Fe-Cr Alloy Film and Its Thermal Equilibrium Diagram

    pp. 439-442

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    DOI:10.2320/matertrans.43.439

    The crystallographic structure and morphology of electrodeposited Fe–Cr films under different bath conditions were studied in detail by using XRD, HRTEM and SEM. The crystallographic structures of the Fe–Cr electrodeposits were also compared with the Fe–Cr thermal equilibrium diagram. The results indicated that the crystallographic structure of electrodeposited Fe–Cr alloy film gradually changed from microcrystalline to amorphous with increasing Cr content. The deposited film exists as α-Fe solid solution when the Cr compositions of deposited films are below 3.1 at%, whereas, it existed as a meta-stable crystal when the Cr compositions of deposited films are from 4.5 at% to 22.4 at%, which have not been reported up to now. The deposited films with various Cr compositions from 22.9 at% to 74.4 at% chromium exist as amorphous phase. Hence, the crystallographic structure of the electrodeposited Fe–Cr alloy film is closely related to its thermal equilibrium diagram, but does not always agree with it.
  • Microstructures and Mechanical Properties of Porous Titanium Compacts Prepared by Powder Sintering

    pp. 443-446

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    DOI:10.2320/matertrans.43.443

    Using pure Ti powder with particle sizes from 300 to 500 \\micron prepared by the plasma rotating electrode process (PREP), porous pure Ti compacts for biomedical applications were synthesized by powder sintering, and microstructures and mechanical properties of the compacts were investigated in this study. Porous compacts having porosity of 19–35 vol% are successfully fabricated by controlling sintering condition. It is found that Young’s modulus and compressive yield strength decrease linearly with increasing porosity, and porous Ti compacts having porosity of about 30–35 vol% exhibit identical Young’s modulus of human bone.
  • Microstructure and Mechanical Properties of L12-(Al, Cr)3Ti/Ti2AlC Composites Prepared by Combustion Synthesis

    pp. 447-450

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    DOI:10.2320/matertrans.43.447

    L12–(Al, Cr)3Ti/Ti2AlC composites have been prepared by the reactive arc-melting technique using elemental powders of Ti, Al, Cr, and C. Resulting composites have been reinforced using 4.5, 9, and 18 vol%Ti2AlC in a matrix of L12 trialuminide Ti–61 mol%Al–13 mol%Cr alloy. The Ti2AlC particles having a rod-like morphology of 1.5 \\micron width and 5–20 \\micron in length were homogeneously dispersed in the matrix. The matrix grain size was reduced through addition of Ti2AlC particles. These composite materials have revealed higher mechanical properties (bending strength and fracture toughness) than that of the monolithic alloy. This improvement is attributed to the Ti2AlC particles dispersion and to the fine grain of the matrix.
  • Observation of Tritium Distribution in V-4Cr-4Ti alloy by Tritium Radioluminography

    pp. 451-454

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    DOI:10.2320/matertrans.43.451

    Tritium distribution in V–4 mass%Cr–4 mass%Ti alloy has been observed by the tritium radioluminography, and the relation between the tritium distribution and the constituent elements of the alloy have been investigated. In the as-cast specimen, tritium concentration has been higher in the titanium enriched region, that is, the local tritium concentrations at the lower and higher titanium region are 156 and 202 mol ppb, respectively. The tritium distribution has shown a strong correlation with the titanium segregation in the interdendritic region. In the heat treated specimen, the tritium distribution has been rarely affected by the interdendritic titanium segregation. Tritium concentration at the central area and at the surrounding area in the specimen surface have been 209 and 147 mol ppb, respectively. It has been thought that this accumulation of tritium to the central area is caused by the Gorsky effect which generated due to the constraint condition of the stress field in the plate shaped specimen. In the heat treated specimen, the tritium distribution has been more strongly affected by the shape of the specimen than by the titanium segregation in it.
  • Adsorptive Properties of Mn-Substituted Goethite Particles for Aqueous Solutions of Lead, Copper, and Zinc

    pp. 455-458

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    DOI:10.2320/matertrans.43.455

    The substitution of Mn for Fe in the goethite (α-FeOOH) framework and the excess addition of Mn beyond the solid-solubility limit, approximately 1.5 mol%Mn, contribute to the change of adsorptive properties for metal ions, PbII, CuII, and ZnII, in aqueous solutions. Removal of PbII from the metal solution at pH 4 was enhanced by the excess addition of Mn in the synthetic process for Mn-substituted goethite. This enhancement was caused by the formation of a new composite adsorbent, α-(Fe, Mn)OOH particles with (Fe, Mn)3O4 precipitates on their surfaces.
  • A Thermodynamic Study of the HDDR Conditions in the Sm2Fe17Nx Compound

    pp. 459-461

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    DOI:10.2320/matertrans.43.459

    This paper describes the relationship between hydrogen pressure and temperature (P-T curve) in the HDDR treatment of the Sm2Fe17 compound. The P-T curve suggested that the HDDR condition of the Sm2Fe17 compound is more sensitive to temperature than that of the Nd2Fe14B compound. It was also found that the HDDR treatment of the Sm2Fe17 compound has to be controlled in the hydrogen pressure range of one order lower than that of the Nd2Fe14B compound, because of its lower optimum HDDR temperature. Using the P-T curve, new HDDR treatments named v-HD and s-DR, were carried out in order to induce anisotropic feature. However, the normalized remanence of the new HDDR treated powders was around 0.52, which suggested that the powders were almost magnetically isotropic.
  • Temperature Distributions and Thermoelectrical Performance of a Porous FeSi2 Element in a Steady State of Reciprocatory Flow Combustion

    pp. 462-465

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    DOI:10.2320/matertrans.43.462

    Temperature distributions and thermoelectrical performance of a porous FeSi2 in a steady state of reciprocatory flow combustion have been examined. The temperature gradient between the hot and the cold side of the elements reached about 200 K/cm, resulting in high output power per density of 226 Wh/m2. It has been also found that the incoming gases were preheated by the porous element to a temperature where combustion occurs and exhaust gases transferred the thermal energy to the element before leaving the element. This energy recirculation leads to an extension of the flammable limit for dilute fuel gases, equivalence ratio; φ=0.27. The low conversion efficiency of 0.033% would be attributed to the convective heat loss by the exhaust gases due to the small volumetric surface area inside the porous element.
  • The Effects of Static Strain on the Damping Capacity of High Damping Alloys

    pp. 466-469

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    DOI:10.2320/matertrans.43.466

    Influences of static strain on the damping capacity in Mn-based M2052 and Fe–6Al alloys were studied with the forced flexural oscillation method by using a dynamic mechanical analyzer (DMA). The static surface strain was applied on the 3-point bending specimens in the range of 1.0×10−5–2.0×10−4. The damping capacity of the M2052 alloy showed a continuous increase, but that of the Fe–6Al alloy showed a continuous decrease with increasing static strain in the range below 1.0×10−4. The variation of the damping capacity with increasing static strain was fitted with an exponential function, and the exponential index turned out to be 0.25 and −0.5 for the M2052 and Fe–6Al alloys, respectively. Static strains in the vicinity of 1.0×10−4 caused the formation of a damping peak, which accelerated the increase of the damping capacity in the M2052 alloy, but softened the decrease of the damping capacity in the Fe–6Al alloy. A significant reduction of the damping capacity appeared at static strains above 1.0×10−4 in both high damping alloys.
  • Crystal Structure and Protium Absorption Properties of Ti-Cr-X Alloys

    pp. 470-473

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    DOI:10.2320/matertrans.43.470

    This paper aims to develop the vanadium free Ti–Cr–X BCC solid solution alloys with high protium content. The effects of additional elements such as Mo, W, Nb and Ta to the phase formation on the Ti–Cr alloys were studied. It was found that Mo-added heat-treated alloys had the flattened plateau regions with the capacity of more than 2.2 mass% protium with maximum of 3.6 mass% protium content, which is equal to that of Ti–Cr–V alloys. It was found that the Ti–Cr–Mo alloys with BCC structure transformed to protide phase with BCC or FCC structure. The plateau pressure of the Ti–Cr–Mo alloys increased with increasing Mo content, but the lattice parameters decreased. The H/M ratio of the alloy with less than 10 at%Mo was 1.8 at 10 MPa hydrogen pressure and was almost unchanged with Mo content.
  • Precise Evaluation of Charging Effect on SiO2 Particles by Simulation of Holograms

    pp. 474-477

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    DOI:10.2320/matertrans.43.474

    The charging effect due to the electron irradiation in spherical SiO2 particles of 250 nm in diameter has been analyzed by electron holography. Electron holograms of a charged SiO2 particle on the side surface of the carbon film were simulated taking into account the electric shielding effect due to the carbon film. In order to compare the observed hologram and the simulated holograms quantitatively, the residual index between the observed and simulated images was evaluated. Through the quantitative analysis taking into account the shielding effect with the limited side surface area of the carbon film, the amount of the charge was evaluated to be 3.38×10−17 C for the current density of incident electron beam at 0.24 A/m2 without an objective aperture.
  • Improvement of Ta Barrier Film Properties in Cu Interconnection by Using a Non-mass Separated Ion Beam Deposition Method

    pp. 478-481

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    DOI:10.2320/matertrans.43.478

    Ta/Si (100) and Cu/Ta/Si (100) film structures were fabricated by using ion beam deposition with a modified RF sputter-type ion source, in which a strong RF discharge was introduced in order to enhance the plasma density. For Ta/Si structures, Ta films were deposited at various bias voltages. When the substrate bias voltage was not applied, the Ta film showed a columnar structure and had a high resistivity of 2600 nΩm. On the other hand, when the substrate bias voltage of −50–−200 V was applied, the cross-sectional observation did not show columnar structure at all. In this case, film deposition was considered to be sufficient migration energy by the accelerated Ta+ ions. In particular, Ta films deposited at a bias voltage of −125 V had a very small resistivity of 360 nΩm. Thermal stability of Cu(100 nm)/Ta(50 nm)/Si films, where Ta plays a role of diffusion barrier, was evaluated after annealing in H2 atmosphere for 60 min at various temperatures. Non-columnar structure Ta films deposited at substrate bias voltages of −50 V and −125 V were found to be stable up to 600°C, while columnar structure Ta films deposited at zero bias voltage degraded at 300°C. This result indicates that the thermal stability of the Ta films is mainly governed by the film microstructure of the deposited layer.
  • All-Electron Mixed-Basis Calculation of Structurally Optimized Titanium Nitride Clusters

    pp. 482-484

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    DOI:10.2320/matertrans.43.482

    Ab initio total energy calculations based on the local density approximation (LDA) and the adiabatic approximation has attracted considerable attention as a conceptually new method. It is capable of describing dynamically the stability and reactivity of clusters, surfaces and bulk materials at finite temperatures, in principle, without using any adjustable parameters. Consequently, Ohno et al. have developed the all-electron mixed-basis approach which is applicable to the molecular dynamics of objects in any atomic environment. Titanium Nitride has unique features, such as self-lubricity, high wear resistance, high melting point, and high hardness, and the application to artificial bone and cutting tools, among others, is expected. We calculated optimized structures of titanium nitride micro clusters and compared these with silicon nitride which is tetravalent also. Both TiN2 and SiN2 clusters form isosceles triangles. The Ti–N bondlengths in TiN and TiN2 are much shorter than in the bulk.
  • Gold Cementation from Ammonium Thiosulfate Solution by Zinc, Copper and Aluminium Powders

    pp. 485-493

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    DOI:10.2320/matertrans.43.485

    Gold cementation test was conducted without de-aeration by using zinc, copper and aluminium powders from an ammonium thiosulfate solution contained 8 mg/l Au. The amount of metal powder was varied in the range of 30–450 Metal/Gold mass ratio. The solution composition was 1–5 mol/l NH4OH, 0.01–0.05 mol/l CuSO4∗5H2O, 0.2–0.4 mol/l (NH4)2S2O3 and pH 9.5–10.5. The results indicated that the gold was effectively recovered from a solution of lower ammonia and copper concentrations and higher thiosulfate concentration. The optimum reagent composition for the gold cementation from the ammonium thiosulfate solution was founded to be 1 mol/l NH4OH, 0.01 mol/l CuSO4∗5H2O and 0.4 mol/l (NH4)2S2O3 at pH 9.5. 100% of gold was recovered by zinc and aluminium powders at a Metal/Gold mass ratio of 30. Copper powder recovered 93% of gold at a Metal/Gold mass ratio of 50. Zinc might re-generate thiosulfate concentration and precipitate most of copper in the solution. Aluminium precipitation might recover gold with less amount of copper deposition and some thiosulfate reduction. Copper precipitation reduced a small amount of thiosulfate concentration and greatly increased copper concentration. Ammonia concentration stayed constant during cementation process.
  • Preferential Dynamic Nucleation at Triple Junction in Copper Tricrystal During High-Temperature Deformation

    pp. 494-500

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    DOI:10.2320/matertrans.43.494

    Preferential nucleation of dynamic grains at triple junction (TJ) was investigated in copper tricrystal during high-temperature deformation. The nucleation of the dynamic grains at the TJ was observed at much lower strain than the peak strain where dynamic recrystallization (DRX) extensively took place. Further straining caused the incremental nucleation of dynamic grains on sliding grain boundaries accompanied by grain-boundary migration and serration. This occurred also at relatively lower strain than the peak strain. The DRX grains evolved to the most area of the tricrystal when deformed to about the peak strain. The observed preferential nucleation of DRX grains at the TJ was considered with relation of stress and deformation concentration there induced by folding and grain-boundary sliding.
  • Flow Behaviour of Aluminium-Based Materials at Ultrahigh Temperatures in the Presence of a Liquid Phase

    pp. 501-509

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    DOI:10.2320/matertrans.43.501

    Experiments were conducted to determine the flow behavior of three materials at ultrahigh temperatures: an Al-6061 composite containing 20 vol% SiC whiskers and unreinforced Al-6061 and Al-1050 alloys prepared by casting. Tensile tests were performed at strain rates up to 5×10−1 s−1 and over a range of ultrahigh temperatures up to and above the temperatures where there is a small amount of liquid phase. High strain rate superplasticity was achieved in the composite material but not in the unreinforced alloys. For all three materials, it is shown that the true activation energy for flow changes from values of <200 kJ mol−1 at the lower temperatures where there is no liquid phase to exceptionally high values in the presence of a liquid phase: these values are up to >1000 kJ mol−1 for the composite and the Al-1050 alloy. It is concluded that exceptionally high activation energies are an inherent feature of flow in materials containing a small amount of discontinuous liquid at temperatures immediately above the onset of partial melting.
  • Nano-glass Mechanism of Bulk Metallic Glass Formation

    pp. 510-517

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    DOI:10.2320/matertrans.43.510

    A theory of local dynamics of liquid is developed in order to explain the glass transition and fragility of multi-component alloys as it relates to formation of bulk metallic glasses. Unlike the extended hydrodynamic theories in which liquid is regarded as a continuum body, the present approach focuses on the discreteness of the atomic structure and considers the stability of local topology of the network structure. This approach has led to the prediction of the glass transition temperature, melting and glass formability. We extend this approach to describe the effects of local topology on the atomic transport and glass transition and fragility of multi-component glasses. This theory leads to a picture of a strong liquid as a nano-scale composite of glass and liquid, and suggests compositional requirements for forming bulk metallic glasses.
  • Effects of Titanium and Oxygen Content on Microstructure in Low Carbon Steels

    pp. 518-522

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    DOI:10.2320/matertrans.43.518

    The effects of the titanium and oxygen concentration on the characteristics of inclusions and microstructure in low carbon wrought steels were investigated. Increasing the titanium concentration from 48 to 120 ppm promoted the formation of TiN particles and decreased the prior austenite grain size. The fraction of intragranular ferrite in the microstructure was relatively unchanged. When the oxygen concentration was increased from 50 to 130 ppm, the volume fraction and the number of inclusion increased. However, the fraction of intragranular ferrite in microstructures decreased abruptly above 80 ppm because the allotriomorph ferrite phase at the prior austenite grain boundary began to form.
  • High Frequency Behavior of La0.7Sr0.3MnO3 with Giant Magnetoimpedance Effect

    pp. 523-525

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    DOI:10.2320/matertrans.43.523

    In the present work it has been found that the room temperature impedance of La0.7Sr0.3MnO3 increases with increasing ac frequency from 7.38 to 110 MHz. The room temperature magnetoresistance ratio (R(0)–R(H))⁄R(0) for La0.7Sr0.3MnO3 can reach 31.4% with H=4.92×105 A/m at a frequency of 68.27 MHz. The frequency dependence of magnetoimpedance, as well as magnetoreactance and magnetoresistance, were investigated in detail.
  • Fabrication of Porous Iron by Unidirectional Solidification in Nitrogen Atmosphere

    pp. 526-531

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    DOI:10.2320/matertrans.43.526

    Porous iron whose long cylindrical pores are aligned in one direction has been fabricated by unidirectional solidification of the melt in a pressurized mixture gas of nitrogen and argon. Nitrogen dissolved in the molten iron is rejected at the solid-liquid interface during the solidification due to the solubility difference of nitrogen between the liquid and solid. The gas pores are evolved from the nitrogen insoluble in the solid iron, which grow unidirectionally. The porosity is controlled by the partial pressures of nitrogen and argon during melting and solidification. The porosity decreases with increase of the partial pressure of argon at a given nitrogen pressure according to the Boyle’s law. At a constant total pressure of the mixture gas, the porosity increases with increasing partial pressure of nitrogen and no pores are formed during solidification below a critical partial pressure of nitrogen. The nitrogen concentration in the solid iron increases with increasing partial pressure of nitrogen. The solid-solution hardening has been observed in as-cast porous iron, while more significant hardening has also been found in the porous iron quenched from a high temperature 1273 K, which is due to the martensitic transformation.
  • Electrorefining Electrolyte from Copper Plant Dust

    pp. 532-536

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    DOI:10.2320/matertrans.43.532

    An attempt was made to develop a suitable process for the recovery of copper from the dust sample of copper plant by sulphuric acid leaching with the idea that the resulting leached copper sulphate solution could be used directly as electrolyte in the copper electrorefining plant. XRD analysis of dust sample showed that copper was mainly present as sulphide and sulphate forms. Sulphuric acid leaching of the sample was carried out varying different parameters. The maximum copper recovery of 75% was achieved with the leaching parameters 353 K temperature, 4 h duration, 1:10 solid:liquid ratio and 10% H2SO4 concentration. Roasting followed by leaching experiments were also carried out. It was found that leaching of the roasted (873 K) sample in sulphuric acid medium yielded maximum copper recovery of 95%. Leaching kinetics of roasted product indicated that mixed control i.e. ash diffusion and chemical control reaction was prevalent. XRD analysis of the roasted sample showed that copper sulphide was converted to oxide which probably increased the recovery of copper. It was also found that composition of the leach liquor obtained in optimised condition was comparable with the composition of electrolyte of operating electrorefining plant.
  • Microstructure and Mechanical Properties of Gas Atomized Aluminum Alloy Powder Compact Densified by Pulsed Current Pressure Sintering Process

    pp. 537-543

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    DOI:10.2320/matertrans.43.537

    A Pulsed current pressure sintering (PCPS) method was employed to sinter compacts of gas atomized Al–8%Ni–2%Mn–1%Cu–0.8%Zr–0.7%Ti–0.25%Mg alloy powder which consisted of Al–Al3Ni eutectic and α-Al supersaturated solid solution due to high quenching rates. Results are as follows: (1) The sintered compacts had Al3Ni precipitates on the boundaries of the initial Al particles. As those precipitates increased, the hardness of the compact decreased. Maximum value of hardness of the compact was HV200 and about 3 at% of Ni atom was excessively dissolved in this compact. (2) The hydrogen content was decreased from 60 to 20 ppm by employing the sintering schedule to remove the adsorbed gas on the particle effectively. The tensile strength of the sintered compact was increased to 500 MPa which was comparable with that of an extruded compact.
  • Relation between Widths of the Grain Boundary Energy Cusps at Special Misorientations and the Microstructural Characteristics in the Sintering of a Fe-Cu-C Alloy

    pp. 544-550

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    DOI:10.2320/matertrans.43.544

    A new Monte Carlo model, three-dimensional multi-particle model, was developed to simulate the three-dimensional microstructural characteristic in the sintering of a Fe–Cu–C alloy. The probability model incorporated the energy-misorientation relationship assigned to randomly generated neighboring grains. The effect on microstructural characteristics of adding doped materials was also quantified and related to the energy-misorientation relationship. The present Monte Carlo model accounts for the relationship between the grain boundary energy and the dihedral angle distribution and determines the effect of the width of the grain boundary energy cusp at the special misorientation on the contiguity and coordination number in the sintering of a Fe–Cu–C alloy. All specimens show a strong correlation between the contiguity \\hatC and coordination number \\hatN, irrespective of the width of the grain boundary energy cusp at the special misorientation. The correlation can be expressed as: \\hatN⁄\\hatNO=\\hatCN⁄\\hatCO, where \\hatNO is the mean coordination number, \\hatCO is the mean contiguity, and \\hatCN is the mean contiguity having the coordination number \\hatN.
  • Computation of Partial Equilibrium Solidification with Complete Interstitial and Negligible Substitutional Solute Back Diffusion

    pp. 551-559

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    DOI:10.2320/matertrans.43.551

    A simple numerical scheme is presented to simulate partial equilibrium solidification with complete interstitial and negligible substitutional solute back diffusion in multi-component and multi-phase systems. Based on this scheme, a computing tool capable of using Thermo-Calc databases directly has been developed for the estimation of solidification behavior of steels and other interstitial-containing alloys. Agreements between calculated and experimental as well as DICTRA results have been obtained on the microsegregation, fraction of eutectic, and freezing range of several steels. This suggests that the partial equilibrium assumption and proposed numerical scheme are reasonable and satisfactory, and confirms that the carbon back diffusion plays a very important role in the solidification of steels.
  • Change of Microhardness in Stoichiometric CuAu

    pp. 560-565

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    DOI:10.2320/matertrans.43.560

    Microhardness of stoichiometric CuAu was measured during isochronal heating starting from the disordered and the ordered state as well as for isochronal cooling from the disordered state. It is shown that a continuous increase of long-range order connected with similar hardness behaviour was observed in all cases of thermal treatment and pre-treatment. In correspondence with earlier resistometric experiments during isochronal temperature variation no hysteresis between heating and cooling was observed.
  • Residual Stress of TiNi Shape Memory Alloy Thin Films with (111) Single-crystal Silicon Wafer

    pp. 566-570

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    DOI:10.2320/matertrans.43.566

    As micro-actuator materials, TiNi shape memory alloy thin films with substrate are used more and more in MEMS field. The residual stress in Ti-rich TiNi thin films with silicon substrate prepared by the magnetron-sputtering technique is measured by both X-ray glancing and contour method. The influence of crystallization annealing temperature and film thickness on the residual stress is tested. It is shown that the tensile residual stress decreases from 106 to 37 MPa with increasing annealing temperature from 723 to 923 K. However, it increases again above 1023 K. While increasing the film thickness from 2.4 to 6.5 \\micron, the residual stress reduces from 323 to 80 MPa. A lot of beautiful sunflower-like structures in crystal grains are observed by OM and TEM. The origin of the residual stress and its affecting factors are discussed. The thermal stress during cooling after annealing is the main factor resulting in tensile stress and the formation of martensite phase will release a part of tensile stress.
  • Oxygen Embrittlement and Effect of the Addition of Ni Element in a Bulk Amorphous Zr-Cu-Al Alloy

    pp. 571-574

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    DOI:10.2320/matertrans.43.571

    Oxygen embrittlement in Zr-based bulk amorphous alloys is an important problem, which must be solved before the application of the bulk amorphous alloys to industrial materials. In the Zr–Cu–Al ternary system, the cast bulk amorphous Zr50Cu40Al10 alloy near the ternary eutectic composition shows good ductility, in the case of the restriction of crystalline inclusions. Furthermore, the addition of Ni element brings about much higher ductility because of the proof ability against oxygen embrittlement. As a result, the Zr50Cu30Ni10Al10 bulk amorphous alloy exhibits good ductility and proof ability against oxidization.
  • Relationship Between the Liquidus Surface and Structures of Zr-Cu-Al Bulk Amorphous Alloys

    pp. 575-579

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    DOI:10.2320/matertrans.43.575

    By using a Al2O3 cell coated with Si3N4, the melting point (Tm) of the cast bulk amorphous samples were measured on DTA curves cooled from the molten state. Based on the Tm data, the partial liquidus surface of Zr–Cu–Al ternary alloys was determined. A ternary eutectic point is located around Zr50Cu40Al10, and low melting temperatures of less than 1273 K were obtained in a wide compositional area of 40–70 at%Zr, 30–60 at% Cu and 0–10 at%Al. Bulk amorphous alloys in Zr–Cu–Al ternary system were produced by an arc-casting method and the highest tensile strength of 2000 MPa was observed in Zr50Cu40Al10.
  • Novel Hexagonal Structure of Ultra-High Strength Magnesium-Based Alloys

    pp. 580-584

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    DOI:10.2320/matertrans.43.580

    A magnesium (Mg) solid solution with a novel long periodic hexagonal structure was formed for a Mg97Zn1Y2 (at%) alloy in a rod form prepared by extrusion of atomized powders at 573 K as well as in a melt-spun ribbon form. The novel structure of the rod alloy had an ABACAB-type six layered packing with lattice parameters of a=0.322 nm and c=3×0.521 nm. The Mg phase in the extruded rod alloy had fine grain sizes of 100 to 150 nm and included cubic Mg24Y5 particles with a size of about 10 nm at volume fractions below 10%. The density (ρ) was 1.84Mg/m3. The tensile yield strength (σy) and elongation of the rod alloy were 610 MPa and 5%, respectively, and the specific strength defined by the ratio of σy to ρ was 330 MPa/(Mg/m3), being the highest among all metallic alloys. The σy is 2.7 to 8 times higher than those for conventional high-strength Mg-based alloys. The excellent mechanical properties are due to the combination of fine grain size, new long periodic hexagonal solid solution, homogeneous dispersion of fine Mg24Y5 particles inside the nano-grains and the absence of the second precipitates along the grain boundary. The new Mg-based alloy is promising for future uses in many fields.
  • Effect of Pre-Deformation of Austenite on Shape Memory Properties in Fe-Mn-Si-based Alloys Containing Nb and C

    pp. 585-588

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    DOI:10.2320/matertrans.43.585

    The shape memory properties of Fe–Mn–Si-based alloys containing Nb and C are further improved by pre-rolling of the solution-treated austenite and the subsequent ageing treatment. For an Fe–28Mn–6Si–5Cr–0.53Nb–0.06C (mass%) alloy, 90% of an initial 4% strain is recovered on heating without any previous training treatment, if the alloy in austenitic state is rolled by 6–14% at 870 K and aged at 1070 K for 10 min to produce NbC precipitates. In the same condition, the alloy develops shape recovery stresses of 255 MPa and 295 MPa for 6% and 14% pre-rolling, respectively, when initially deformed by 4.5%. TEM observations indicate that these improved shape memory characteristics are related to a fine distribution of NbC precipitates in the fcc matrix and their interaction with stacking faults.
  • Structure and Magnetic Properties of Fe42.5Co42.5Nb7B8 Nanocrystalline Alloy

    pp. 589-592

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    DOI:10.2320/matertrans.43.589

    The microstructure and magnetic properties of nanocrystalline Fe42.5Co42.5Nb7B8 alloy were investigated. The bcc nanocrystalline alloy obtained by annealing the amorphous precursor at 873 K for 3.6 ks exhibits a high saturation magnetization (Is) of 1.90 T and a lower coercivity (Hc) of 60 A/m. It also exhibits a very high Curie temperature (Tc) more than 1173 K. The structure of the nanocrystalline alloy was found by high-resolution transmission electron microscopy (HRTEM) to consist of a mixture of nearly spherical bcc grains with sizes of 5 to 10 nm. HRTEM combined with EDS and nano-beam electron diffraction with a diameter of 2 nm revealed that the amount of Nb in the intergranular amorphous phase was larger than that in the bcc grain. The segregation of Nb element in the intergranular amorphous phase increases the thermal stability of the amorphous phase and suppresses the grain growth of the bcc phase. The high thermal stability of the structure and the high Curie temperature are promising for soft magnetic material for high temperature application.
  • Evaluation of Corrosion Resistance of Coated and Uncoated Stainless-Steel Separators at Cathode Side for Molten Carbonate Fuel Cell

    pp. 593-600

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    DOI:10.2320/matertrans.43.593

    In order to evaluate the corrosion resistance of a cathode-side separator for a molten carbonate fuel cell (MCFC), SUS316 and SACC-SUS316 (chromium and aluminum were simultaneously deposited by diffusion into SUS316 austenitic stainless steel substrate using the pack-cementation process) were used as the separator materials. In the case of SUS316, corrosion proceeded via three steps: the formation of a corrosion product until the corrosion product becomes stable; the protection against corrosion until breakaway occurs; and the advancement of corrosion after breakaway. Since SUS316 showed a high corrosion rate in the cathode environment, it would be impossible to use it as a separator without suitable surface modification because of the occurrence of severe stability problems of the cell during long-term operation. In contrast, SACC-SUS316 showed higher corrosion resistance than the present separator material, SUS316. No corrosion was observed on SACC-SUS316 after 480 h at 923 K. Therefore, this material is thought to be very useful as an alternative separator at the cathode side for MCFC in the future.
  • Effect of Partial Substitution of 3d Transition Metals for Co on the Thermoelectric Properties of NaxCo2O4

    pp. 601-604

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    DOI:10.2320/matertrans.43.601

    Layered P2 type NaxCo2O4 thermoelectric oxides partially substituted by 3d transition metal (up to 15 at%: Cr, Mn, Fe, Ni, or Zn) for Co were synthesized through calcination and sintering in air. The Cr-substituted samples were mostly decomposed into the NaCrO2+Co2CrO4 phases. On the other hand, the X-ray diffraction patterns of the Mn-substituted samples showed a single P2 type γ-NaxCo2O4 phase. The Fe- and Ni-substituted samples were mostly composed of the NaxCo2O4 phase with small amounts of Co3O4 and CoNiO2 phases. In the case of the Zn-substituted samples, only the Nax(Co0.95Zn0.05)2O4 was mostly composed of the NaxCo2O4 phase with a small amount of the NaO phase. The effects of partial substitution of these 3d transition metals for Co except for Cr in the layered NaxCo2O4 on thermoelectric properties were investigated. The electrical resistivity of these partially substituted samples significantly increased over the entire temperature range, as compared to the non-substituted sample, indicating reduction in carrier concentration. Except for Nax(Co1−yFey)2O4, the Seebeck coefficient was enhanced by the partial substitution, and in the case of Nax(Co1−yFey)2O4, it is suggested that the decrease in the Seebeck coefficient is associated with reduction in the electron-electron correlation due to the substitution. For the Mn-substituted samples, a small grain size and many pores compared to the non-substituted sample were effective for reducing the thermal conductivity. The figure-of-merit Z was enhanced in the case of the Nax(Co0.95Zn0.05)2O4 above 550 K and the maximum dimensionless figure-of-merit ZT, 0.68, was obtained at 965 K.
  • Thermally Enhanced Glass Formation in Multilayered Cu33Zr67 Composite Particles

    pp. 608-610

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    DOI:10.2320/matertrans.43.608

    A single phase of glassy Cu33Zr67 powders has been synthesized by post-annealing the mechanically alloyed Cu33Zr67 composite powders at 685 K for 1.8 ks. The heat of glassy phase formation was measured directly and found to be −2.59 kJ/mol. The glassy powders transform to big-cube CuZr2 metastable phase (E9 structure) upon heating to 760 K. This metastable phase does not withstand against the temperature increasing during the DSC analysis and therefore transforms completely into the most stable phase of tetragonal CuZr2 (C16 structure) at 918 K.

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