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

MATERIALS TRANSACTIONS Vol. 62 (2021), No. 11

  • Soft Magnetic and Mechanical Properties of FeNiCoSi0.25Alx (x = 0–1) High Entropy Alloys Prepared by Arc Melting

    pp. 1597-1603

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    DOI:10.2320/matertrans.MT-M2021111

    In this work, the effect of Al addition on the FeNiCoSi0.25Alx (x = 0, 0.25, 0.5, 0.75 and 1.0 mole) high entropy alloys prepared by arc melting route was investigated. The results show that the increase of Al content led to the change in phase structure of the high entropy alloys, from mainly FCC + minor Ni3Si to FCC+BCC and BCC phases, and resulted in various mechanical- and magnetic-properties of as-received alloys. The element mapping and SEM-EDS analysis results showed that the BCC phases contain two types of structure, BCC and B2 phase in which the B2 phase is rich in Ni and Al whilst BCC is enriched with Fe and Si. The Vickers hardness was enhanced with the increase of Al content. Maximum Vickers hardness was reached at 621.9 HV10 for FeNiCoSi0.25Al alloy containing the BCC and B2 phases. The obtained FeNiCoSi0.25Al0.5 high entropy alloys exhibit highest magnetic saturation of 114.1 Am2/kg and a low coercivity of 697 A/m, which, obviously indicate that these high entropy alloys need further investigations towards various applications, such as the soft magnetic materials.
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  • Superior Strength and Ultrahigh Ductility in Hierarchical Structured 2205 Duplex Stainless Steel from Nanoscale to Microscale

    pp. 1604-1608

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    DOI:10.2320/matertrans.MT-M2021085

    A laminated structured 2205 duplex stainless steel (DSS) with graded grain size was prepared via aluminothermic reaction and subsequent hot rolling with deformation of 80% at 1000°C, and its mechanical properties, strengthening and toughening mechanism were studied. Our materials have extraordinary elongation of 54% and high tensile strength of 990 MPa. The lamellar structure is characterized with heterogeneous lamella austenite (with nano-grain, ultrafine grain, micro-grain and nano-twin) and ferrite (with ultrafine grain and a proper amount of micro grain) coalesced alternately. The high strength is attributed to strengthening of complex grain (distribution from nanoscale to microscale) and interfaces arising from hierarchical and laminated dual-phase heterogeneous structure and distribution. The unusual high ductility is thought to be mainly attributed to the lamellar structure and dislocation hardening.
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    Readers Who Read This Article Also Read

    1. Direct Concentration of Iron, Slag and Britholite-(Ce,La,Pr,Nd) at 1473 K in a Super Gravitational Field ISIJ International Vol.57(2017), No.1
    2. Effect of Intercritical Deformation on Bainite Formation in Al-containing TRIP Steel ISIJ International Vol.43(2003), No.8
    3. A New Diamond Chemical Vapor Deposition Method on Steel Surface Journal of the Japan Institute of Energy Vol.101(2022), No.8
  • Influence of Annealing on Microstructure and Mechanical Properties of Equiatomic CoCrNiTiV 3d Transition Metal High Entropy Alloy Ingots

    pp. 1609-1613

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    DOI:10.2320/matertrans.MT-M2021078

    A novel equiatomic CoCrNiTiV high entropy alloy was fabricated by a vacuum arc-melting, and investigated from the view of phase component, microstructure, mechanical properties. The results experimentally displayed that a typical single phase BCC solid solution was acquired in the as-cast CoCrNiTiV alloy, while another BCC phase together with an FCC phase and a (Ni, Co)3Ti phase emerged through annealing. In mechanics performance, the ultimate strength significantly increases from 1729 ± 15 MPa of the as-cast alloy to 2820 ± 15 MPa of the annealed alloy, while a relatively high hardness of 825.8 ± 16.3 HV and 680 ± 23.9 HV was obtained. It was suggested that the majority BCC phase and other precipitation both take the responsibility for the good synergy in strength and hardness.
  • Incubation Time of Occurrence of Magnetic Field-Induced Martensitic Transformation in an Fe–24.8Ni–3.7Mn (at%) Alloy

    pp. 1614-1618

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    DOI:10.2320/matertrans.MT-M2021088

    Incubation time of occurrence of magnetic field-induced martensitic transformation has been investigated in an Fe–24.8Ni–3.7Mn (at%) alloy. Under a static magnetic field of 9 T, the alloy shows an isothermal martensitic transformation with a nose at 140 K in the time-temperature-transformation phase diagram. Under a pulsed magnetic field at 77 K, however, it exhibits an athermal martensitic transformation (a burst-type one). When the maximum field of 26.8 T is applied, the martensitic transformation starts in the field applying process at 16.54 T, but when the maximum field of 14.10 T is applied, the martensitic transformation starts in the field removing process. The time delay from the maximum field is in the order of several tens of microsecond and is probably related to the requirement of time to prepare for the nucleation of martensitic transformation.
  • Microstructure, Phase Relations, and Precipitation Hardening Studies in Mg Containing CoCrCuFeNi High-Entropy Alloys

    pp. 1619-1624

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    DOI:10.2320/matertrans.MT-M2021116

    CoCrCuFeNi high-entropy alloys (HEAs) have high ductility owing to their unique two-phase microstructure. Phase relations and microstructure evolution were investigated by scanning electron microscopy coupled with energy dispersive spectrometry and differential thermal analysis. These results contributed to clarifying the formation mechanism of the HEA microstructures. The effects of Mg addition as an alloying element in HEAs were also studied, with respect to precipitation hardening, thereby aiming to obtain strength-ductility balanced HEAs.
  • Evaluation of Effective Thermal Conductivity of Graphite Flake/Aluminum Composites by Two-Dimensional Image Simulation under a Correction Function

    pp. 1625-1631

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    DOI:10.2320/matertrans.MT-M2020341

    This study aims to evaluate the effective thermal conductivity of graphite flake/aluminum composites using two-dimensional (2D) image simulations. However, the effective thermal conductivity calculated from the two-dimensional microstructure images may not be equivalent to that measured using the experimental methods. The reason is that the two-dimensional microstructure image cannot reveal depth information based on the observation surface, which leads to the orientation difference between the graphite flakes in the 2D microstructure image and the experimental sample. Here, the orientation of the graphite flakes relative to heat flow direction was characterized by the angle between the graphite flake basal plane and the heat flow direction. The relationship between the angles in the 2D cross-sections extracted from three-dimensional (3D) models, angles in the 3D models, and aspect ratios of graphite flakes displayed in the 2D cross-sections were studied by computer simulation. We found that the angle in the 2D cross-section was larger than that in the corresponding 3D model, and the difference between the angles can result in a thermal conductivity error of up to 840 W m−1 K−1. In addition, all the angles and aspect ratios were distributed on a curved surface, and the curved surface function could convert the angle in the cross-section into the corresponding angle in the 3D model. Finally, the effective thermal conductivity of the graphite flake/aluminum composite with 10 vol% graphite flakes was determined using a 2D image simulation, and the interfacial thermal conductance was calculated by the reversed method.
  • Simple Liquid-Phase Synthesis of Cobalt Carbide (Co2C) Nanoparticles and Their Use as Durable Electrocatalysts

    pp. 1632-1638

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    DOI:10.2320/matertrans.MT-M2021147

    Cobalt carbide (Co2C) nanoparticles were synthesized simply in liquid phase using Co(II) acetylacetonate and oleylamine under reflux conditions. Even in the presence of carbon black XC-72, Co2C nanoparticles were formed and simultaneously deposited on the carbon surface. The thin layer consisting of cobalt (oxy)hydroxide was present on the outermost surface of the thus-prepared Co2C nanoparticles, which was confirmed by X-ray photoelectron spectroscopy, but the redox treatment using a cyclic voltammetry technique gradually removed such by-product phase. The resulting Co2C nanoparticles supported on XC-72 exhibited high durability for the oxygen reduction reaction.
  • Effect of Water Vapor on High-Temperature Oxidation Behavior of Fe–10 mass% Ni Alloy

    pp. 1639-1646

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    DOI:10.2320/matertrans.MT-M2021129

    In Fe–Ni alloys, protective oxide scales are not formed in a dry atmosphere as in an atmosphere containing water vapor; however, oxide scales consisting of duplexes with outer and inner layers are formed. This oxide scale structure is similar to that formed in an atmosphere containing water vapor. This enables accurate evaluation of the effect of water vapor on the oxidation behavior of alloys. In this study, we focused on the effect of water vapor on the growth kinetics and microstructure of the inner layer, and tried to verify a model according to which the growth of the inner oxide scale is caused by the dissociative mechanism of the outer oxide layer.Fe–10 mass%Ni alloys were oxidized at 1200°C in N2–10 O2 or N2–10 O2–20 H2O (vol%, unless state otherwise) at 1200°C for 5, 15, 30, 60, and 180 min, and the effect of water vapor on the microstructure of the oxide scale was investigated. The thickness of the outer layer was not considerably different in the N2–10 O2 atmosphere compared to that in the N2–10 O2–20 H2O atmosphere. The thickness of the inner layer was significantly greater in the N2–10 O2–20 H2O atmosphere than that in the N2–10 O2 atmosphere. The inner layer was of dense FeO in N2–10 O2–20 H2O, but contained many voids in N2–10 O2. The oxidation rate was higher in N2–10 O2–20 H2O than in N2–10 O2. This could be caused by the dissociation of FeO in the atmosphere containing water vapor, which additionally supplies Fe to the surface.
  • Effect of Halide Ions on Electrodeposition Behavior and Morphology of Electrolytic Copper Powder

    pp. 1647-1652

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    DOI:10.2320/matertrans.MT-M2021126

    To investigate the effect of halide ions on the electrodeposition behavior and morphology of copper powder, polarization curves were measured and constant current electrolysis of 300 and 500 A·m−2 was conducted in an electrolytic solution containing 0.079 mol·dm−3 Cu2+ and 0.5 mol·dm−3 free H2SO4 at 293 and 303 K without stirring. Cl promoted the deposition of copper powder, while Br and I suppressed deposition. The current efficiency for copper deposition increased with the addition of Cl and decreased with the addition of Br. The addition of Cl reduced the average particle size of the copper powder and caused the dendrite-shaped branches and trunks to grow thinner and longer, resulting in a lower tap density. In contrast, the addition of Br caused the average particle size, average crystallite size, and tap density of the copper powder to decrease. With increasing Cl concentration, the current efficiency for copper deposition increased, that is, copper deposition was promoted. This even occurred in the region in which Cu2+ ion diffusion was the rate-determining process, indicating that the deposition of copper powder was affected by the charge-transfer process. The change in the morphology of the copper powder with the addition of halide ions is attributed to the change in the charge-transfer process. The deposition of copper powder appears to proceed under a mixed rate-determining process involving the diffusion of Cu2+ ions and charge transfer. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 207–212. Captions of all figures and tables are slightly modified.
  • Computer Simulation for Sintering under the Presence of Liquid Phase by Monte Carlo Method

    pp. 1653-1659

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    DOI:10.2320/matertrans.MT-Y2021003

    The simulation for liquid phase sintering has been newly developed by Monte Carlo method. The basic three mechanisms in liquid phase sintering, namely (1) liquid wetting on solid surface, (2) rearrangement of solid particle by capillary force of liquid, (3) growth of solid particles by solution-reprecipitation through liquid phase (Ostwald ripening), have been introduced in the simulation. The liquid wetting on a solid plane or solid particle surface progressed more easily as decreasing the energy between solid and liquid (γSL). The introduction of rearrangement into the simulation brought the result that relative density increased with decreasing γSL and pores remained. The introduction of Ostwald ripening in addition to liquid wetting and rearrangement produced the result that relative density increased on the whole and the effect of γSL became clear. The simulation including Ostwald ripening was able to demonstrate clearly and continuously the influence of γSL on growth and contiguity of solid particles. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 66 (2019) 259–265.
  • Damage Evaluation of Carburizing Gear for Remanufacturing

    pp. 1660-1668

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    DOI:10.2320/matertrans.MT-M2021132

    To investigate the microstructure and damage of friction-fatigued carburized martensitic steels for the reliability of remanufacturing parts, the retained austenite (γ) phase and residual stress were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). We evaluated their changes before and after roller pitching tests, and before and after the operation of the gear parts.In the roller pitching tests, the retained γ phase decreased with increasing load and number of cycles, presumably due to martensitic transformation caused by the cyclic load. The residual stress ratio (after/before the test) was significantly lower at high loads than that before testing, which was ascribed to the appearance of surface microcracks and the resultant release of internal stress. From SEM observations of the cross-section of the friction surface, we confirmed that the changes in the retained γ phase and residual stress ratio reflect the process of formation of multiple microcracks in the 10 µm surface layer. The decreases in both the retained γ phase ratio and the residual stress ratio would therefore appear to rule out reuse. A decision on the potential for gear reuse can be made by means of non-destructive testing, i.e., investigating the relationship between the retained γ phase ratio and the residual stress ratio. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 85 (2021) 198–206.
  • Materials Integration for Accelerating Research and Development of Structural Materials

    pp. 1669-1672

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    DOI:10.2320/matertrans.MT-M2021135

    This paper provides a current research trend for “Materials Integration”, which is a concept to accelerate research and development of structural materials by computationally linking among process, structure, property, and performance. The survey is carried out based on the special issue published in February, 2019 in Materials Transactions (Vol. 60, No. 2) and the overviews published in November, 2020 in Materials Transactions (Vol. 61, No. 11). The concept has been embodied in a computer system named MInt (Materials Integration by Network Technology), on which computational modules and workflows are implemented to predict performance from process through microstructure and property. The research works on the system development and the computational materials analyses are briefly introduced, highlighting the rising trend of data-driven research in structural materials.
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  • Nondestructive Nanostructure Analysis of Al/Al–Zn Interdiffusion Layer by Quantitative SAXS Tomography

    pp. 1673-1676

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    DOI:10.2320/matertrans.MT-L2021012

    Tomographic images with absolute units have been reconstructed successfully from Small Angle X-ray Scattering (SAXS) intensities of an interdiffusion layer of a precipitation strengthened model alloy cut from a multilayered Al/Al–Zn/Al sample after heat treatment. Cross sectional images of specimen with Zn concentration distribution was obtained from the absolute X-ray mass attenuation coefficient; the volume fraction of precipitates from the absolute SAXS integrated intensity in each voxel. Mechanical property of the same cross-section was estimated from the nanostructure and composition obtained for each voxel determined by the reconstructed images.
  • Roles of Alloying Elements in the Corrosion Resistance of Equiatomic CoCrFeMnNi High-Entropy Alloy and Application to Corrosion-Resistant Alloy Design

    pp. 1677-1680

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    DOI:10.2320/matertrans.MT-M2021136

    The equiatomic CoCrFeMnNi alloy and the equiatomic quaternary alloys with no addition of one element of the CoCrFeMnNi alloy were fabricated, and the roles of the alloying elements in corrosion resistance were clarified. In 1 M H2SO4, the passivity of the CoCrFeMnNi alloy was mainly due to Cr. The Co and Fe additions also contributed the decrease in the passivity current density. While Ni addition was found to suppress active dissolution, Mn addition increased the active dissolution rate. The quaternary alloy without Mn indicated superior pitting corrosion resistance in 0.1 M NaCl. To improve the corrosion resistance of the CoCrFeMnNi alloy, Mn was replaced with Mo, and the effect of the Mo content on the pitting corrosion resistance and the role of Co addition were assessed in 1 M HCl.

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