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

MATERIALS TRANSACTIONS Vol. 55 (2014), No. 3

  • PREFACE

    pp. 395-395

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    DOI:10.2320/matertrans.MPR2013908

  • In-Situ Observation of Radiation Damage Using a Combined Facility of Electron Microscope and Heavy-Ion Accelerator(s) —History and Future Prospectives—

    pp. 396-402

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    DOI:10.2320/matertrans.MD201304

    Radiation effects in materials for fission and fusion reactors are caused by fast neutrons which produce cascade damage, which has been known to be considerably different from simple Frenkel pairs produced by relativistic electrons. In-situ observation of radiation damage using a combined facility of electron microscope and heavy-ion accelerators has been a powerful tool to investigate the nature of the cascade damage. In this overview, brief historical survey of this experimental technique will be given, followed by the results and discussions on cascade damage mainly in gold will be reviewed. Careful considerations will be required to generalize the results to other metals as well as to other experimental conditions. Finally, there are a number of points to be developed for better understanding of cascade damage and for extending the “in-situ” techniques to other materials as non-metallic solids and to other intriguing phenomena.
  • Development of TEM Holder Generating In-Plane Magnetic Field Used for In-Situ TEM Observation

    pp. 403-409

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    DOI:10.2320/matertrans.MD201310

    For easy performance of Lorentz microscopy with simultaneous electric measurements, a special specimen holder for transmission electron microscopy (TEM) has been developed that has electromagnets to generate magnetic field and four leads for electric measurements. This TEM holder was evaluated by checking experimental results of permalloy (Ni0.8Fe0.2) patterns. Clear observations of domain wall injection into a nanowire and movement of magnetic vortices as well as magnetoresitance during the development of magnetic domains were performed. It appeared possible to apply in-plane magnetic fields along any direction with intensities of less than about 15.9 kA/m (200 Oe).
  • A Triple Beam In-Situ Facility at Xiamen University

    pp. 410-412

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    DOI:10.2320/matertrans.MD201301

    The ion implantation is a powerful scientific and technological tool in material research. Multiple ion beam facilities have been used to simulate the irradiation effects of neutrons on relevant nuclear materials over 30 years. By the use of transmission electron microscope (TEM) link facility, the microstructure evolvement in material can be in-situ studied during the irradiation and following annealing processes. In this paper, a triple beam in-situ facility, composed of a 400 kV heavy ion implanter, a 50 kV hydrogen–helium coaxial ion implanter and a 300 kV electron microscope, will be presented. This facility will also be the first in-situ facility with the capacity of delivering the triple ion beam including hydrogen, helium and heavy ion beam to the specimen in TEM simultaneously. The angle between the two beam lines and microscope axis is 30°, respectively.
  • Simulation of Transmission Electron Microscope Images of Dislocations Pinned by Obstacles

    pp. 413-417

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    DOI:10.2320/matertrans.MD201312

    From a direct observation of dislocation-obstacle interaction utilizing in situ straining experiments in transmission electron microscope (TEM), the obstacle strength factor could be evaluated from pinning angles of dislocation cusps. We simulated this process: we produced a dislocation cusp by molecular dynamics simulation of interaction between an edge dislocation and a void or a hard precipitate in copper, and calculated the TEM image by multislice method. In two-beam conditions, cusp images showed inside-outside contrast depending on the sign of the diffracting vector and other variations with the specimen geometry. The pinning angles measured on TEM images ranged up to a few tens of degrees and were between the true angles for the two partial dislocations. Characteristics and contrast mechanisms of cusp images were discussed based on those of dislocation dipoles.
  • In Situ TEM Concurrent and Successive Au Self-Ion Irradiation and He Implantation

    pp. 418-422

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    DOI:10.2320/matertrans.MD201316

    The development of advanced computational methods used for predicting performance lifetimes of materials exposed to harsh radiation environments are highly dependent on fundamental understanding of solid-radiation interactions that occur within metal components. In this work, we present successive and concurrent in situ TEM dual-beam self-ion irradiation of 2.8 MeV Au4+ and implantation of 10 keV He1+, utilizing a new facility at Sandia National Laboratories. These experiments, using a model material system, provide direct real-time insight into initial interactions of displacement damage and fission products that simulate damage from neutron exposure. In successive irradiation, extensive dislocation loop and stacking fault tetrahedra damage was formed and could be associated with individual ion strikes, but no evidence of cavity formation was observed. In contrast, concurrent irradiation to the same dose resulted in the onset of cavity formation at the site of a heavy-ion strike. This direct real-time observation provides insight into the complex interplay between the helium and vacancy dynamics.
  • New Approach to In Situ Observation Experiments under Irradiation in High Voltage Electron Microscopes

    pp. 423-427

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    DOI:10.2320/matertrans.MD201315

    A new method for conducting in situ observations of experiments undergoing irradiation in a high voltage electron microscope (HVEM) is proposed. Intensity profile of a focused electron beam in HVEM introduces an atomic displacement gradient in the vicinity of the beam, which generates distribution of point defect concentration and enhances defect diffusion in matrix. In our experiments, tantalum carbide or yttrium titanate nanometer-scale particles embedded in iron matrices were irradiated at 673 K with a focused electron beam at energy ranges from 0.75 to 2.5 MeV. The results show that the instabilities of particles undergoing irradiation could be observed as diminishing either in size or contrast. The rate of shrinkage per fluence unit was successfully measured to derive the vacancy diffusion effect, with particles located in the vicinity of the electron beam showing higher rates of shrinkage. This indicates that the diffusion of vacancies enhanced both by irradiation and the concentration gradient is attributable to dissolution of the particle constituents into the matrix.
  • Microstructural Evolution of an Ion Irradiated Ni–Mo–Cr–Fe Alloy at Elevated Temperatures

    pp. 428-433

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    DOI:10.2320/matertrans.MD201311

    The irradiation behavior of a Ni–Mo–Cr–Fe alloy, of the type currently being considered for use in future molten salt cooled reactors, has been investigated in situ using 1 MeV Kr ions at temperatures of 723 and 973 K. When irradiated to 5 dpa, experimental observations reveal the instantaneous formation and annihilation of point defect clusters, with such processes attributed to the long range elastic interactions that occur between defects through multiple intra-cascade overlap. Corresponding differences in the defect cluster density and size distribution suggest that changes to the microstructure were dependent upon temperature and dose, affecting the growth, accumulation and mobility of irradiation-induced defect clusters under these conditions.
  • Comparison between In-Situ and Post-Irradiation Cyclic Deformation Structures in Ni by 150 MeV Proton Irradiation

    pp. 434-437

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    DOI:10.2320/matertrans.MD201305

    Stress-controlled cyclic deformation experiments under 150 MeV proton irradiation (5.2 × 10−11 dpa/s) were performed on Ni at room temperature, where a single deformation period was approximately 30 s. After deformation, defect structures were studied using positron annihilation lifetime spectroscopy and transmission electron microscopy. In deformations of 300 cycles and 900 cycles, residual vacancies were high in in-situ cyclic deformed Ni and low in nonirradiated Ni. Although dislocation cell structures were observed in all specimens, the development process and the cell size were different in each deformation condition. Well-developed large cells in nonirradiated Ni and small cells in deformed Ni after irradiation were observed. The cell structure was not well developed in the in-situ deformed Ni under irradiation. The relationship between these defect evolutions and fatigue life is discussed.
  • Effect of Additional Minor Elements on Accumulation Behavior of Point Defects under Electron Irradiation in Austenitic Stainless Steels

    pp. 438-442

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    DOI:10.2320/matertrans.MD201309

    Addition of minor elements to a base alloy is often applied with the aim of mitigating void swelling by decreasing the vacancy diffusivity and flux which influence vacancy accumulation behavior. However, the comparative evaluations of parameters, such as the diffusivity and flux, between a base alloy and modified alloys with specific additives have not been studied in detail. In this study, type 316 austenitic stainless steel as a base alloy and type 316 austenitic stainless steels modified with vanadium (V) or zirconium (Zr) additions were used to perform evaluations from the changes of widths of the void denuded zone (VDZ) formed near a random grain boundary during electron irradiation because these widths depend on vacancy diffusivity and flux. The formations of VDZs were observed in in-situ observations during electron irradiation at 723 K and the formed VDZ widths were measured from the transmission electron microscopic images after electron irradiation. As a result, the VDZs were formed in both steels without and with V, and respective widths were ∼119 and ∼100 nm. On the other hand, the VDZ formation was not observed clearly in the steel with Zr. From the measured VDZ widths in the steels without and with V addition, the estimated ratio of the vacancy diffusivity in the steel with V to that in the steel without V was about 0.50 and the estimated ratio of the vacancy flux in the steel with V to that in the steel without V was about 0.71. This result suggests that the effect of additional minor elements on vacancy accumulation behaviors under electron irradiation could be estimated from evaluations of the VDZ width changes among steels with and without minor elements. Especially, because void swelling is closely related with the vacancy diffusion process, the VDZ width changes would also be reflected on void swelling behavior.
  • Effect of Oxide Particles and Pre-Implanted Helium on Defect Evolution during Electron Irradiation

    pp. 443-446

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    DOI:10.2320/matertrans.MD201318

    In-situ observations of ferritic/martensitic steels by electron irradiation with a 1.25 MeV high voltage microscope at 573 K were carried out to study damage evolution in the steels. The development of interstitial type loops and cavities in both of the two steels, F82H-IEA and F82H-ODS, showed smaller and more numerous defects in the ODS steel. The cavities were formed preferentially at the interface between oxide particles and matrix. The results suggest that ODS particles may function to suppress the nucleation and growth of loops and cavities arising from irradiation. The effect of pre-implanted helium was also studied. The pre-implanted helium led to a homogenous distribution of black dots and cavities in the steels, and these may act as sinks for point defects arising from irradiation, causing a suppression of the subsequent growth of loops and cavities. The hardening corresponding to the microstructural evolution was estimated by assuming parameters extracted from the ion irradiation.
  • Kink Band Formation in Graphite under Ion Irradiation at 100 and 298 K

    pp. 447-450

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    DOI:10.2320/matertrans.MD201317

    The effects of displacing radiation in graphitic materials are important for technologies including nuclear power, graphitic-based nanocomposites and hybrid graphene–silicon high-speed integrated electronics. These applications expose graphitic materials to displacing irradiation either during manufacture and/or involve the deployment of these materials into irradiating environments. One of the most interesting phenomena in the response of graphite to irradiation is the formation of kink bands on the surface of the material. Here we apply the technique of transmission electron microscopy with in situ ion irradiation to observe the dynamic formation of these features. Kink bands were created at both 100 and 298 K with doming of the samples also observed due to radiation induced dimensional change leading to mechanical deformation. Probably at 298 K, but certainly at 100 K, there should be no point defect mobility in graphite according to the latest theoretical calculations. However, some of the theories of dimensional change in graphite require point defect motion and agglomeration in order to operate. The implications of the experimental results for existing theories and the possibility of thermal effects due to the ion irradiation are discussed.
  • In Situ TEM Observation of Structural Changes in Rapidly Solidified bcc Solid-Solution Phase in Ti–Cr Alloy Focusing on Spontaneous Vitrification (SV)

    pp. 451-457

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    DOI:10.2320/matertrans.MD201306

    Changes in the structure of the rapidly solidified body-centered-cubic (bcc) solid-solution phase in Ti–Cr alloy were investigated in order to determine whether or not the unique heat-induced amorphization (i.e., SV) actually occurs. Annealing-induced amorphization of the single solid-solution phase was not observed during either ex situ isothermal annealing at 873 K or in situ annealing experiments in HVEM. The previously reported SV may not correspond to the formation of an amorphous phase but could actually be due to the formation of a finely grained polycrystalline structure during the decomposition of the bcc solid-solution phase.
  • In-Situ Observations of Microstructure Evolution in Electron-Irradiated Multi-Wall Carbon Nanotubes

    pp. 458-460

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    DOI:10.2320/matertrans.MD201307

    In-situ observations of microstructure evolution of the electron-irradiated multi-wall carbon nanotubes (MWCNT) were carried out by using a high voltage electron microscope (HVEM). Electron irradiation at relatively low temperatures exhibited changes in the structure of the MWCNT, such as in the distance and ruggedness of walls. The MWCNT appeared to be stable during electron irradiation at relatively high temperatures probably due to a higher probability of recombination between knock-on atoms and vacancies in walls, meaning that composites developed with CNT could be stable and maintain high thermal conductivity during irradiation at high temperatures.
  • In Situ Observation of Gold Chloride Decomposition in a Confined Nanospace by Transmission Electron Microscopy

    pp. 461-465

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    DOI:10.2320/matertrans.MD201308

    The behavior of gold chloride (AuClx) encapsulated within the inner space of a single-wall carbon nanotube (SWCNT) was investigated under electron beam (e-beam) irradiation and high temperatures. Analysis of the pristine specimen by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and Raman spectroscopy show that AuClx is encapsulated within the SWCNTs as a dilute disordered structure. In situ TEM observation of the specimen under e-beam irradiation shows that, within the SWCNTs, AuClx is reduced to a crystalline Au nanowire (AuNW). The AuNW drifts significantly within the SWCNT during the reduction. At high temperatures (>673 K), in situ TEM shows that the AuNW oscillates intermittently at a frequency of ∼1.1 s−1 and amplitude of ∼60 nm. Raman spectroscopy and EDX suggest that these phenomena are caused by an increase in the internal gas pressure in the SWCNTs because the decomposition of AuClx by e-beam irradiation or heat treatment produced chlorine (Cl2) gas.
  • Volume and Enthalpy Relaxation in Pd42.5Cu30Ni7.5P20 Bulk Metallic Glass

    pp. 466-472

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    DOI:10.2320/matertrans.MBW201320

    The kinetics of structural relaxation in Pd42.5Cu30Ni7.5P20 bulk metallic glass (BMG) was investigated by means of volume relaxation and enthalpy relaxation in the temperature range below Tg (≈ 573 K). The measured relaxation time was significantly longer than the α-relaxation time reported by dynamical mechanical analysis (DMA), indicating that these two relaxation processes are fundamentally different from each other. The temperature dependence of electrical resistivity suggests that the origin of the β-relaxation process that occurs between room temperature and Tg may be the compositional short range ordering. Anomalous volume expansion was observed in the initial stage of relaxation, which was attributed to annihilation of the p-type defects with very short relaxation time.
  • Magnetic Behavior of FePt/AlN Layered Structure

    pp. 473-476

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    DOI:10.2320/matertrans.MBW201304

    FePt(x)/AlN(20 nm) layered structures (x = 1.5–9 nm) were fabricated on fused quartz substrate by magnetron sputtering method. The magnetic behaviors of as-deposited and annealed films have both been studied. It has been found that annealing of the films leads to a transition of magnetic anisotropy from in-plane to perpendicular direction for layered structures with thinner FePt layer thickness. The interface evaluation performed by X-ray reflectivity (XRR) measurement and transmission electron microscopy (TEM) observation indicates that perpendicular magnetic anisotropy of the annealed layered structure can be attributed to the improved interface anisotropy, which is due to the flattening of interfaces. However, for films with thicker FePt layer thickness (above 5 nm), the in-plane anisotropy was enhanced after annealing. The results of stress analysis reveal that the residual stress change inside FePt layers upon annealing can override the interface contribution through magneto-elastic effect in such layer thickness range.
  • Structural and Magnetic Properties of Magnetic Shape Memory Alloy Ni46Mn41In13 under Magnetic Fields

    pp. 477-481

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    DOI:10.2320/matertrans.M2013372

    The structural and magnetic properties of Heusler alloy Ni46Mn41In13 were studied by magnetization and X-ray powder diffraction measurements in the 4.5–350 K temperature range and in magnetic fields up to 5 T. The alloy undergoes martensitic transformation from a L21-type cubic structure with ac = 0.600 nm at 293 K to a six-layered monoclinic (6M) structure in the transition temperature of 160–230 K. The lattice parameters for the 6M structure were estimated to be am = 0.441 nm, bm = 0.557 nm, cm = 1.30 nm, αm = 90.0°, βm = 94.0°, and γm = 90.0° at 75 K. In this transformation from the L21 to 6M structures, the cell volume contracts by 0.34% at 8 K. In addition, we observed the magnetic field-induced reverse transformation of this alloy.
  • Effect of Pre-Aging Treatment on the Microstructure and Magnetic Properties of Sm(Co,Fe,Cu,Zr)7.8 Sintered Magnets

    pp. 482-488

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    DOI:10.2320/matertrans.MBW201325

    The effects of pre-aging treatment on the microstructure and magnetic properties of Sm(Cobal.Fe0.35Cu0.06Zr0.02)7.8 were investigated. The main phase of both solution-treated magnet and pre-aged magnet was the 1 : 7 phase, and there were no distinct differences between the X-ray diffraction profiles of these magnets. Fine Cu-rich precipitates a few tens of nanometers in size were observed in pre-aged magnet by scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy mapping, but such precipitates were not observed in solution-treated magnet. As for fully aged magnets, the cell size was smaller in pre-aged magnet than in non-pre-aged magnet. Thus, the pre-aging treatment gave a fine cellular structure. Mr and HcJ of pre-aged magnet were almost same as those of non-pre-aged magnet. Squareness of the demagnetization curve for fully aged magnet was increased by pre-aging treatment. As a result, (BH)max of magnet subjected to pre-aging treatment was greater than that of magnet not subjected to pre-aging treatment. The fine cellular structure seemed to result in higher squareness. The following magnetic properties were obtained for Sm(Cobal.Fe0.35Cu0.06Zr0.02)7.8 by pre-aging treatment: Mr = 1.24 T, HcJ = 1490 kA/m, and (BH)max = 266 kJ/m3.
  • Quantitative Evaluation of Phase Field Microstructure Based on the Variational Principle

    pp. 489-492

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    DOI:10.2320/matertrans.M2013362

    In order to investigate the quantitative feature of calculated microstructure which has undergone averaging processes, the change of microstructural image is evaluated by a single parameter which was derived based on the variational principle for the image restoration process. It is shown that the employed parameter well describes the sharpness of the calculated microstructure, and by tracing the evolution of the parameter with the averaging size, one can determine the threshold of averaging scale, which may be utilized to evaluate the validity of microstructural image obtained by calculations.
  • Formation Mechanisms of Beachrocks in Okinawa and Ishikawa, Japan, with a Focus on Cements

    pp. 493-500

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    DOI:10.2320/matertrans.M-M2013844

    Beachrock is a type of sedimentary deposit held together mainly by calcium carbonate cement in the tidal zone of sandy beaches in tropical and subtropical regions. Man-made beachrock has the potential to inhibit coastal erosion; considering this important application, we performed field investigations and laboratory tests to understand the formation mechanisms of beachrocks in Okinawa and Ishikawa, Japan. We performed a needle penetration test, microbial population count and urease activity test, and conducted elemental and mineral analyses. Our investigation showed that in Okinawa the evaporation of seawater and/or urease activity of the microorganisms may have resulted in precipitation of high Mg calcite, leading to the formation of beachrock. In Ishikawa, beachrock and sand were present near a spring with a relatively high concentration of Al3+. The mixing of spring water (pH 4.7) with seawater could have led to the precipitation of the Al- and Si-bearing cement that is consolidating the sand particles, leading to development of beachrock.
  • Twinning Induced Plasticity and Work Hardening Behavior of Aged Cu–Ni–Si Alloy

    pp. 501-505

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    DOI:10.2320/matertrans.MBW201326

    The work hardening behavior and deformed microstructure of the Cu–Ni–Si alloy aged at 723 K for various times and then deformed at 293 and 77 K were extensively investigated. The precipitate microstructure was also observed using transmission electron microscopy after aging treatment at 723 K for 0.30, 3.6, 64.8 and 345.6 ks. Deformation twins were clearly observed by transmission electron microscopy in the under-aged specimen deformed by 10% in tension at 293 K, in accordance with the enhanced work hardening rate observed during tensile deformation. The thickness of the deformation twins observed was approximately 1–40 nm. In addition, a significant fraction of larger deformation twins were observed by EBSD on the surface of the under-aged and peak-aged specimens tested at 77 K, for which the stress–strain behavior exhibited a nearly constant work hardening rate, i.e., high tensile strength and high elongation. These results show that the deformation twins formed during tensile deformation at 293 K contribute to strengthening of the specimen as new obstacles to the dislocation slip. Moreover, the enhanced twinning deformation at 77 K achieves high strength and elongation in the under-aged and peak-aged conditions. On the other hand, only a few deformation twins were observed in the supersaturated solid solution and over-aged specimens.
  • Effects of Hydrogen Water Chemistry on Stress Corrosion Cracking Behavior of Cold-Worked 304L Stainless Steel in High-Temperature Water Environments

    pp. 506-510

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    DOI:10.2320/matertrans.M2013325

    This study measured the stress corrosion cracking (SCC) growth rates of cold-worked 304L stainless steel in oxygenated and hydrogenated coolant environments. The effects of cold work at the levels of 5, 20, and 30% on SCC were also investigated. The SCC crack growth rate increased substantially with increases in the degree of cold work in oxygenated water environment. However, after hydrogen injection, SCC propagation in all cold worked specimens was gradually inhibited. The time to crack arrest decreased with increases in the degree of cold work. The slip bands caused by cold work facilitated the initiation and growth of transgranular (TG) cracks in specimens exposed to an oxygenated coolant environment. TG cracks were easier to arrest compared with intergranular cracks after the injection of hydrogen into the coolant system.
  • Effects of Cryo-Treatment on Corrosion Behavior and Mechanical Properties of Laser-Welded Commercial Pure Titanium

    pp. 511-516

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    DOI:10.2320/matertrans.M2013373

    The objective of this study was to investigate the effects of cryo-treatment on the microstructure, corrosion behavior, and mechanical properties of Ti before and after laser welding. The microstructure was studied by optical microscopy. It was found that the grain size for Ti became smaller after cryo-treatment. Cryo-treatment could also refine and stabilize the crystal lattice structure and distribute precipitate particles throughout the material in the welded metal. Potentiodynamic polarization measurements were employed to investigate the corrosion behavior in an artificial saliva solution. Electrochemical results showed that the laser-welded Ti after cryo-treatment exhibited the most obvious passivation behavior of all the specimens. The mechanical properties of Ti, cryo-treated Ti (C-Ti), laser-welded Ti (W-Ti), and cryo-treated, laser-welded Ti (CW-Ti) were characterized by tensile tests. It was found that the tensile strength and elongation could be improved for Ti and laser-welded Ti by cryo-treatment without impairing its corrosion resistance.
  • Synthesis of Fine Iron–Cobalt Alloy Particles by the Co-Reduction of Precursors with Solvated Electrons in Sodium–Ammonia Solution

    pp. 517-521

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    DOI:10.2320/matertrans.M2013375

    Fine iron–cobalt alloy particles were synthesized by the co-reduction of their precursors with sodium in liquid ammonia. The reaction took place instantaneously because of the highly reductive solvated electrons. Very reactive, fine particles of the order of ∼10 nm size were obtained. Annealing process is crucial for the magnetic properties of the products, the saturation magnetization being ranging from 29 to 238 A·m2·kg−1. One spot reduction with solvated electrons and the consequent annealing treatment in the synthesis vessel has potential ability for the synthesis of a variety of metal and alloy particles.
  • Microstructural and Electrical Properties of Copper–Titanium Alloy Dispersed with Carbon Nanotubes via Powder Metallurgy Process

    pp. 522-527

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    DOI:10.2320/matertrans.Y-M2013846

    Microstructural and electrical properties of powder metallurgy (P/M) copper alloy with carbon nanotubes (CNTs) were investigated. The Cu–0.5 mass% Ti pre-alloyed powder (Cu–0.5Ti) was made by water atomization process. The powders coated with un-bundled CNTs by using the zwitterionic surfactant water solution containing CNTs were consolidated at 1223 K in vacuum by spark plasma sintering, and then extruded at 1073 K. The P/M Cu–0.5Ti alloy without CNTs (monolithic alloy) had 202 MPa yield stress (YS) and 42.5 International-Annealed-Copper-Standard % (IACS%) conductivity. The extruded Cu–0.5Ti composite alloy containing CNTs revealed small decrease of YS compared to the monolithic Cu–0.5Ti alloy. On the other hand, the composites indicated a higher electrical conductivity than that of the monolithic alloy. For example, Cu–0.5Ti with 0.19 mass% CNTs showed 175.8 MPa YS and 83.5 IACS% conductivity. In the case of the Cu–0.5Ti composite with CNTs, the intermetallic compounds such as Cu4Ti and TiC were observed around CNTs by TEM-EDS analysis. The amount of the solid solute Ti in the above Cu–0.5Ti composite alloy matrix was 10% of the monolithic Cu–0.5Ti alloy, and resulted in the remarkable increment of its electrical conductivity due to the decrease of solid solute Ti content.
  • Microstructure and Mechanical Properties of Cu–40%Zn–0.5%Cr Alloy by Powder Metallurgy

    pp. 528-533

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    DOI:10.2320/matertrans.Y-M2013847

    In this study, the microstructure and mechanical properties of Cu–40Zn brass alloy with 0.5 mass% Cr additives produced by powder metallurgy (P/M) process were investigated. Cu–40Zn–0.5Cr and Cu–40Zn brass powders were made by water-atomization process, and used as raw materials. These powders were consolidated by hot extrusion at various temperatures by considering the precipitation behavior of β phase and Cr. Yield stress of Cu–40Zn–0.5Cr extruded at 773 K was 514.6 MPa, while that of the monolithic Cu–40Zn extruded at the same temperature was 332.6 MPa. Solid solution of chromium in the Cu–40Zn–0.5Cr brass alloy extruded at 773 K was about twice as that of the same brass alloy extruded at 873 K. The strength impact of Cr solid solution was much effective compared to Cr precipitation strengthening. The ratio of solid solution strengthening by chromium additive was 130 MPa/mass%[Cr]. The grain size of extruded materials increased with increasing the extrusion temperature.
  • Fabrication and Catalytic Decoloration Capacity of Nanodendritic Metals

    pp. 534-538

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    DOI:10.2320/matertrans.MBW201310

    Nanodendritic Pd was fabricated by square-wave potential pulse (SWPP) electrolysis on Pd surface. Dendrite cell sizes and dendrite arm spacings were well below 100 nm and decreased with the increase in the frequency of SWPP. Cyclic voltammetry revealed that true surface area of Pd increased by up to 57 times by the nanodendritic structure. Nanodendritic Au was also fabricated by SWPP and its catalytic decoloration capacity was compared with that of nanoporous Au. Nanodendritic Au decomposed methyl orange more efficiently than nanoporous Au. This may be attributed to high-index facets and edges commonly found in nanodendritic structures synthesized by SWPP electrolysis.
  • Surficial Chemical States of Li3N Synthesized on Lithium Target for Boron Neutron Capture Therapy

    pp. 539-542

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    DOI:10.2320/matertrans.M2013257

    To remove high level of contaminants by O and C from Li3N surface for Boron Neutron Capture Therapy target, high temperature thermal desorption was conducted up to 1123 K in ultra high vacuum and the following results were derived; During thermal desorption up to 1023 K, typical three peaks of vacuum pressure disturbance due to vaporization of contaminants were observed in vacuum pressure-temperature curve. Over-layered contaminants with high melting temperature below 1023 K on Li3N surface is completely removed by high temperature thermal desorption up to 1123 K in ultra high vacuum. From these desorption results, it is suggested that these contaminants corresponding to these vaporization peaks are H2O and Li compounds with high melting temperature below 1023 K, of which LiOH and Li2CO3 were synthesized by decomposition process of Li3N with residual H2O and CO2 in low temperature.
  • Effect of Microstructure on the Mechanical Properties of Magnesium Composites Containing Dispersed Alumina Particles Prepared Using an MM/SPS Process

    pp. 543-548

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    DOI:10.2320/matertrans.Y-M2013845

    Magnesium composites containing 0–20 vol% Al2O3 particles were produced via mechanical milling (MM) followed by spark plasma sintering (SPS), and the effect of the microstructure on their mechanical properties was investigated. Microstructural observation of the MM powders and SPS compacts was achieved using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM)/energy dispersive X-ray spectroscopy (EDS). The mechanical properties of the MM powders and SPS compacts were evaluated on the basis of the results of the Vickers hardness test. SEM micrographs indicated that Al2O3 fine particles were dispersed in the Mg composites with 10 and 20 vol% Al2O3. The hardness values for the MM powder and the SPS compact containing 10 vol% Al2O3 were nearly the same owing to their similar microstructures. However, the hardness of the SPS compact was higher than that of the MM powder for the Mg composite with 20 vol% Al2O3. TEM/EDS and XRD analyses revealed that the needle-like Mg17Al12 and equiaxed nano MgO particles formed in the Mg matrix with 20 vol% Al2O3 during the SPS process. The increase in hardness of the SPS compact compared to that of the MM powder is attributed to strengthening resulting from the formation of the Mg17Al12 and MgO phases.
  • Relation of n-Value to Critical Current for Local Sections and Overall Sample in a SmBCO Coated Conductor Pulled in Tension

    pp. 549-555

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    DOI:10.2320/matertrans.MBW201301

    Under application of tensile stress to a SmBCO (SmBa2Cu3O7−δ) coated conductor sample consisting of series electric circuit of local sections, the relation of voltage–current curve, critical current and n-value of the sections to those of overall sample was studied. The change in critical current and n-value with increasing applied stress was different from section to section due to the difference in damage behavior of the SmBCO layer among the sections. When the difference in extent of damage among the sections was small, the voltages developed in all sections contributed to the voltage of overall sample. In this case, the critical current and n-value of overall sample were within the range of the highest and lowest values among the sections. On the other hand, when the damage in one section was far severer than that of other sections, the voltage developed in the most severely damaged section largely contributed to the overall voltage, and hence the voltage–current curves of the most severely damaged section were almost the same as those of overall sample. In this case, critical current of the overall sample was slightly higher and n-value of the overall sample was lower than the critical current and n-value of the most severely damaged section. Accordingly, the decrease in n-value with decreasing critical current in overall sample was sharper than that in sections. This phenomenon was accounted for by the increase in shunting current at cracked part at higher voltage in the most severely damaged section.
  • Effect of Annealing on Magnetostrictive Properties of Fe–Co Alloy Thin Films

    pp. 556-560

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    DOI:10.2320/matertrans.MBW201315

    The effect of the annealing temperature on the magnetostrictive properties of Fe–Co alloy thin films on quartz glass was systematically investigated. The saturation magnetostriction was 56 ppm for the Fe32Co68-sputtered thin film quenched from 673 K, and it increased to 159 ppm with increasing annealing temperature up to 1073 K. The magnetostriction above 1093 K significantly decreased with the emerging fcc phase in the Fe–Co alloy. SEM images showed that the crystal grains present in the fcc phase aggregated to form a discontinuous surface, which resulted in a decrease in the effective magnetostriction. Measurements of the magnetic properties by vibrating sample magnetometer and magnetic force microscopy revealed the enhancement of the magnetization at the crystal grain boundaries of Fe–Co alloy thin films with large magnetostriction. Thus, the heterogeneity of the magnetization can play a key role in inducing the large magnetostrictive effect.
  • High Adhesive Force between Laminated Sheets of Copper and Polyurethane Improved by Homogeneous Low Energy Electron Beam Irradiation (HLEBI) Prior to Hot-Press

    pp. 561-565

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    DOI:10.2320/matertrans.MBW201312

    2-layer copper/polyurethane (Cu/PU) laminated sheets were prepared by a new adhesion method, a double-step treatment consisting of applying low dose (≦0.43 MGy) homogeneous low energy electron beam irradiation (HLEBI) prior to hot-press under 5 MPa and 413 K. Although the weak hot-press adhesion of the Cu/PU was observed without HLEBI, the new adhesion raised the bonding forces as evidenced by the mean adhesive forces of peeling resistance (oFp). Based on the 3-parameter Weibull equation, the lowest oFp value at peeling probability (Pp) of zero (Fs) could be estimated. An increasing trend in Fs occurred by the double-step treatment applying HLEBI up to 0.13 MGy reaching a maximum at 27.1 Nm−1, improving the safety level without radiation damage. When HLEBI cut the chemical bonds in PU polymer and generated terminated atoms with dangling bonds, they probably induced the chemical bonding and intermolecular coulomb attractive forces. Therefore, increasing adhesion force between the laminated sheets could be explained.
  • Creation of Adhesive Force between Laminated Sheets of Polytetrafluoroethylene (PTFE) and Polyethylene (PE) by Homogeneous Low Energy Electron Beam Irradiation Prior to Hot-Press for Bio-Adaptable Application

    pp. 566-571

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    DOI:10.2320/matertrans.M2013247

    Bio-adaptable 2-layer polytetrafluoroethylene/polyethylene (PTFE/PE) laminated sheets were prepared by a new adhesion method, a double-step treatment consisting of applying low dose (≦0.43 MGy) homogeneous low energy electron beam irradiation (HLEBI) to the 2-layer assembly where the HLEBI penetrates through the PTFE and PE layers, respectively, prior to hot-press under 5 MPa and 433 K. Although the adhesion of the PTFE/PE sheets cannot be observed without the new double-step treatment, bonding forces were created as evidenced by the mean adhesive forces of peeling resistance (oFp). The adhesion cannot be observed without HLEBI. On the other hand, application of a small dose of HLEBI (less than 0.43 MGy) prior to hot-press lamination enhances the oFp at each Pp. The maximum oFp values at each Pp (0.06, 0.50 and 0.94) of the laminated sheet irradiated at 0.13, 0.13, and 0.22 MGy are 5.44, 10.7, and 19.7 Nm−1, respectively. Based on the 3-parameter Weibull equation, the lowest oFp value at Pp of zero (Fs) could be estimated. An increasing trend in Fs occurs by the double-step treatment applying HLEBI up to 0.43 MGy reaching a maximum at 2.66 Nm−1, improving the safety level without radiation damage of PTFE/PE. It was more than 6 times higher than that of PTFE/Polyurethane (PU) (0.4 Nm−1). When HLEBI cuts the chemical bonds and generates dangling bonds with nonbonding electrons in PTFE and PE, the created adhesion between the laminated sheets can be explained. Based on X-ray photoelectron spectrometer (XPS) surface analysis of the PTFE/PE laminated sheets after the peeling tests, fluorine (F) was detected on the PE peeled surface, indicating both strong chemical and intermolecular bonds generated by the double-step treatment. For these reasons, double-step treatment is a useful method for quick lamination of PTFE and PE with sterilization without the use of glue.
  • Preparation and Properties of Ball-Milled MgH2/Al Nanocomposites for Hydrogen Storage

    pp. 572-576

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    DOI:10.2320/matertrans.M2013368

    For reversible hydrogen storage properties of 17MgH2 + 12Al ↔ Mg17Al12 + 17H2, MgH2/Al nanocomposites (I)–(IV) synthesized by ball milling of MgH2 and Al (or AlH3) were studied in connection with milling conditions. The milling processes consisting of two steps were effective to improve the hydrogen storage behavior; MgH2 was first milled with solutions of triethylaluminium (TEA) in hexane, followed by addition of Al and TEA solutions. The mixtures were further milled to yield the nanocomposite (III). In preparing the nanocomposite (IV), AlH3 was used instead of Al. For the nanocomposites (III) and (IV), it was proved by XRD, TDS, DSC and PCI that such ball-milling led to high dispersion of nanocrystalline MgH2 in Al and/or AlH3 matrix in the resulting nanocomposites. In DSC measured under a 0.1 MPa hydrogen atmosphere, the nanocomposites (III) and (IV) exhibited reversible H2 absorption and desorption at 493–503 and 573–593 K, respectively.
  • Control of Electrical and Thermal Properties by 8 vol% Al2O3 Distribution States in Zn–50Sn for AC-Low Voltage Fuses

    pp. 577-585

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    DOI:10.2320/matertrans.MBW201303

    The addition of 8 vol% Al2O3 in Zn–50 mass%Sn, was carried out for the control of electrical and thermal properties, for Pb-free fuse elements used in electric power line. The distribution-control of Al2O3 particles in Zn–50Sn was carried out by the varying process parameters such as the temperature and period for Al2O3-addition and -stir in its melt or semi-solid. Homogeneous and heterogeneous Al2O3-distributions were achieved in microstructure consisting of primary Zn and eutectic, which meant the location of Al2O3 in both regions and only eutectic in constituent phases, respectively. The temperature dependence of specific resistivity, thermal conductivity, specific heat and density was measured for electrical and thermal calculations to obtain the temperature distribution in fuses. The values on their properties were determined depending on Al2O3 distributed states in alloys. Both the melt and un-melt down performance for AC-low voltage fuse elements could be satisfied on both Zn–50Sn alloys with different distribution of Al2O3, and the superior performance was shown in the homogeneously Al2O3 distributed alloy.
  • Lead Trace Removal from Waste Electronic Scraps by Organic Acids

    pp. 586-590

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    DOI:10.2320/matertrans.M2013330

    The removal of Pb traces from Pb-free solder is an important process in the recycling of solder. Pb must be removed before the more valuable metals are extracted, otherwise the recycling becomes less efficient and the end product impure. Pb removal by three organic acids is investigated here. Acetic acid was shown to dissolve Pb selectively from waste solder better than citric acid or oxalic acid could. Leaching for 72 h in 0.01 M acetic acid removed approximately 137 mg/L Pb from the solder at 30°C, 220 rpm; in addition, no Sn was leached. Higher concentrations of acetic acid (0.05 and 0.1 M) led to increased Sn leaching and decreased Pb leaching, similar to the results observed in citric acid. A total of 0.01 M citric acid leached 7 mg/L Pb and 1831 mg/L Sn; 0.01 M oxalic acid leached 8 mg/L Pb and 1318 mg/L Sn. A comparison using pure Pb and Sn powders showed that the leaching of both metals increased with increasing concentrations of acetic acid and citric acid, contrary to the results observed using solder.
  • Production of Titanium Dioxide Directly from Titanium Ore through Selective Chlorination Using Titanium Tetrachloride

    pp. 591-598

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    DOI:10.2320/matertrans.M-M2013843

    For the production of high-grade titanium dioxide (TiO2) directly from titanium ore (Ti ore), a fundamental study on the development of a novel carbo-selective-chlorination method using titanium tetrachloride (TiCl4) as a chlorinating agent was carried out. In order to selectively remove iron directly from low-grade Ti ore (mainly FeTiO3), Ti ore and carbon powder were set in a gas-tight quartz tube that was then placed in a horizontal furnace to react with TiCl4 at 1100 K. In the experiments, various types of Ti ores produced in different countries were reacted with TiCl4 for durations from 4 to 6 h. Under certain conditions, the iron in the titanium ore was removed as iron chloride (FeCl2), and 98% TiO2 was obtained after the experiments. The effectiveness of TiCl4 as a chlorinating agent for the carbo-selective-chlorination of iron oxide was verified in this study. Thus, it was demonstrated that the carbo-selective-chlorination is feasible for the selective removal of iron directly from low-grade titanium ore containing 51% TiO2 to produce high-grade TiO2 feed in a single step.
  • Effect of Sintering Profile and Composition of Ni/Al2O3 Functional Gradient Materials Coating Layers via Pulsed DC Electrophoretic Deposition

    pp. 599-604

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    DOI:10.2320/matertrans.M2013347

    Ni/Al2O3 functional gradient material (FGM) coating layers with its thickness of 20–25 µm were fabricated by pulsed direct current (DC) electrophoretic deposition (EPD). The coarsening effect of Ni was studied to control sintering profile with an intermediate step of 1000°C for 3 h. Controlling the sintering conditions through an intermediate step and varying the number of layers played important roles in reducing cracks on the coating surface. The samples were characterized using X-ray diffraction (XRD), back scattered electron microscopy (BSE) and electron probe micro analyzer (EPMA). From these analyses, the effects of sintering step on microstructures of FGM coating layers were studied systematically to minimize crack problems within Ni-rich region by controlling its composition and form gradient through coarsening of Ni particles caused by intermediate step during sintering process. The high hardness was found for two- and three-layered samples by introducing intermediate step during sintering. Hence, pulsed DC EPD method was successfully employed to fabricate crack-free FGM with desirable microstructures.
  • Indium Tin Oxide Films with Low Resistivity at Room Temperature Using DC Magnetron Sputtering with Grid Electrode

    pp. 605-609

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    DOI:10.2320/matertrans.M2013316

    Indium tin oxide films were deposited at room temperature using a direct current magnetron sputtering system with a grid electrode. The glow discharge was confined between the target and the grid by inserting a grid electrode between the target and substrate of a conventional sputtering system. Next, various characterizations of indium tin oxide films were conducted including crystallinity, electrical properties, surface concentration, optical transmittance, and surface roughness. A negative grid voltage changed or decreased the crystallinity of the films. Moreover, suppressing the diffusion of the glow discharge by applying a negative grid voltage was highly effective in decreasing the resistivity of the indium tin oxide film by increasing the carrier concentration and mobility at room temperature.
  • Carbon Solubility in Liquid Iron Containing V, Mo and Ni

    pp. 610-615

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    DOI:10.2320/matertrans.M2013392

    Liquid iron alloys containing V, Mo, and Ni can be produced by the carbothermic reduction of spent catalysts used in petrochemical industry. Thermodynamics of carbon in these alloy melts is important for refining these alloys. In the present study, the carbon solubility in Fe–V, Fe–Mo, Fe–Ni, Fe–V–Mo, Fe–V–Ni, Fe–Mo–Ni and Fe–V–Mo–Ni alloy melts of various compositions was measured at 1873 K. The additions of vanadium and molybdenum significantly increased the carbon solubility in liquid iron alloys while nickel decreased the carbon solubility. The temperature dependency of carbon solubility in Fe–V melt was also measured in the temperature range from 1823 to 1923 K. The present and previous experimental results were thermodynamically analyzed using Lupis’ relation at constant activity to determine the first- and the second-order interaction parameters of vanadium, molybdenum and nickel on carbon at carbon saturated condition in liquid iron alloys. Using thermodynamic parameters determined in the present study, the carbon solubility in Fe–V–Mo–Ni alloy melts of various composition were accurately predicted and verified experimentally at 1873 K.
  • Reclaim of Rare Earth Metals from Bond Magnets by Means of Thermally Activated Semiconductors (TASC)

    pp. 616-621

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    DOI:10.2320/matertrans.M2013418

    Recovery of rare earth metals from bond magnets has been investigated by means of thermally activated semiconductors (abbreviated to TASC). TASC is a novel technology developed recently by us, allowing to decompose any organic materials including polymers in an instant into H2O and CO2. This technology has been utilized in the present investigation to reclaim rare earth metals from bond magnets by removing only polymer binders while retaining mostly the original composition of magnets. The TASC technology is based on our accidental finding that the semiconductor exhibits significant oxidative catalytic effects when heated at about 350–500°C. The initial process of the polymer decomposition is the capture of bonded electrons to create cation radicles in polymers. Then, the unstable radicles propagate throughout the polymer chains to make the whole polymer unstable, resulting in the fragmentation of the polymer into tiny molecules such as ethylene, propane etc. These fragmented molecules end up with reaction with oxygen in air to give rise to H2O and CO2. In this way, rare earth metals are successfully reclaimed from bond magnets in about one–two hours in the form of powders.
  • Effect of Powder Preheating Temperature on the Properties of Titanium Coating Layers Manufactured by Kinetic Spraying

    pp. 622-628

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    DOI:10.2320/matertrans.M2013367

    This study investigated the effect of powder preheating temperature on the properties of titanium coating layers made through the kinetic spray process. Specifically, kinetic sprayed coating layers were made under three different conditions with regard to powder preheating temperatures: no preheating, 500°C, and 800°C in manufacturing processes. Titanium coating layers using pure powder feedstock were made regardless of the powder preheating temperature without any change in phase. The porosity and hardness values of the coating layers were as follows: 3.3%, 281 Hv under the no preheating condition; 2.6%, 232 Hv under 500°C preheating, and; 0.4%, 224 Hv under 800°C preheating. As the powder preheating temperature increased, porosity decreased remarkably, and hardness increased; thus enabling the formation of denser coating layer. Note, however, that the thin oxide on the interface of the deposited particles increased as the powder preheating temperatures increased. The optimum process condition for manufacturing pure titanium coating layer was also discussed.
  • Impact Damping in NiMnGa/Polymer Composites

    pp. 629-632

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    DOI:10.2320/matertrans.M2013407

    Impact damping of Ni–Mn–Ga ferromagnetic shape memory alloy/polyurethane composites was studied by instrumented impact tests. By polymerizing the composite under a magnetic field, the martensitic Ni–Mn–Ga particles were spatially aligned in chains parallel to the field direction with the preferable crystallographic orientation of the martensitic twin variants. The rectangular prismatic samples with faces cut parallel and perpendicular to the particles chains in these composites appeared to be highly mechanically and magnetically anisotropic. The samples impacted parallel to the particles chains, have shown a considerably bigger damping capacity than the matrix material. The tests have also shown that the impact behavior is different for the first impact than for the consecutive ones. This is attributed to the stress-induced movement of the twin boundaries resulting in twin variant conversion. A corresponding rotation of the magnetic anisotropy of the samples is confirmed by measuring the magnetization curves.
  • Influence of Cold Rolling on Diffusion Bondability of SUS316L Stainless Steel Sheets

    pp. 633-636

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    DOI:10.2320/matertrans.M2013405

    The influence of cold rolling on diffusion bondability has been systematically investigated using SUS316L stainless steel sheets with different reduction ratios (0, 35, 50 and 70%) as specimens. According to the results of tensile testing of diffusion bonds, highly rolled sheets exhibit enhanced diffusion bondability. This phenomenon is discussed from the viewpoint of the microstructure.

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