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

MATERIALS TRANSACTIONS Vol. 59 (2018), No. 8

  • PREFACE

    Osamu Umezawa, Yoshikazu Shinohara, Wataru Nakao

    pp. 1215-1215

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    DOI:10.2320/matertrans.MPR2018903

    Recommended Articles: Simultaneous Prediction of Bendability and Deep Drawability Using Orientation Distribution Function for Aluminum Alloy Sheets [ View more ]

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  • Mechanical Properties of Lightweight Concrete Containing Melamine Formaldehyde Waste Using Full Factorial Design

    Sasiprapa Srichaiyo, Somsak Siwadamrongpong, Chalermchai Chaitongrat

    pp. 1216-1219

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    DOI:10.2320/matertrans.MF201712

    Abstract

    In this research, the utilization of melamine formaldehyde waste (MFW) as a fine aggregate in lightweight concrete was investigated. The MFW was used for replacing river sand 25% by weight with constant water-to-cement and cement-to-fine aggregate ratio of 0.5 and 1.0, respectively. Mechanical property tests were conducted on compressive strength and water absorption. The analysis of mechanical properties of lightweight concrete containing MFW was done by using 2k factorial design. Three factors of interest are MFW ratio, density and foaming agent. The results revealed that MFW could be potentially used in lightweight concrete with determined percentages. We ensured that the compressive strength and water absorption results are within the Thai Industrial Standards.

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    1. A Decision Making to Price Demand Resources for Voltage Management in Distribution Network with Photovoltaic Generations Transactions of the Institute of Systems, Control and Information Engineers Vol.31(2018), No.4
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  • Factors Affecting the Particle Size of Bio-Calcium Carbonate Synthesized from Industrial Eggshell Waste

    Ajchara I. Putkham, Somchai Ladhan, Apipong Putkham

    pp. 1220-1224

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    DOI:10.2320/matertrans.MF201708

    Abstract

    Calcium carbonate is broadly used as a catalyst support, filler, additive, and reinforcement in several types of industry e.g. chemical, food, and biomedical industry. Recently, eggshell waste has attracted much attention for the purpose of calcium carbonate production due to its compost about 96% calcium carbonate. However, direct use of egg shells as filler material can probably cause product defects. In this research, calcium chloride was extracted from chicken-eggshell waste followed by precipitation of micron size calcium carbonate. The effect of agitation time, the initial concentration of calcium chloride and synthesis temperature on particle size, and selected physicochemical properties of this precipitated calcium carbonate (PCC) were investigated. Scanning electron micrographs of the prepared materials illustrated that all of the PCCs obtained from these experiments exhibit uniform-round shape. The laser diffraction results show that the median size of the PCC particles increased significantly from about 6 µm to 19 µm with increasing agitation time and with decreasing initial concentration of calcium chloride. However, increasing the synthesis temperature from 30°C to 160°C only slightly increased the median size of the PCC particles. The results of X-ray diffraction indicated that both agitation time and initial concentration also have an effect on the crystalline morphology of the PCCs. In addition, calcite crystalline phase became dominant over the other crystalline phases when agitation time and initial concentration were increased. In comparison, PCCs synthesized from this eggshell waste have much smaller median particle size than commercial calcium carbonate. Furthermore, the purity of the PCC derived from shell waste was comparable to commercial calcium carbonate. This facile synthesis is environmentally friendly and cost effective.

  • Relationships between Thermoelectric Properties and Milling Rotational Speed on Bi0.3Sb1.7Te3.0 Thermoelectric Materials

    Masato Kitamura, Kenji Hirota, Kazuhiro Hasezaki

    pp. 1225-1232

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    DOI:10.2320/matertrans.MF201703

    Abstract

    A p-type Bi0.3Sb1.7Te3.0 thermoelectric semiconductor, which has a high dimensionless figure of merit (ZT), was prepared by milling at various milling rotational speeds. The milled Bi0.3Sb1.7Te3.0 powder changed from a partially alloyed state to a completely alloyed one with increasing rotational speed.The thermoelectric properties of Bi0.3Sb1.7Te3.0 sintered disks differed depending on the milling rotational speed. The minimum electrical conductivity σ, thermal conductivity κ, and maximum Seebeck coefficient α at the rotational speed at which the transition from PIES (pulverized intermixed elements sintering) process to MA (mechanical alloying) followed by HP (hot pressing) occurred.The ZT varied with changes in rotational speed, with a maximum value were obtained. This study have shown that the thermoelectric properties of materials prepared by powder metallurgy used milling were significantly affected by the milling energy, i.e., the rotational speed.

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  • Thermoelectric Behaviors of Bi0.3Sb1.7Te3.0 with Excess or Deficiency of Tellurium Prepared by Mechanical Alloying Followed by Hot Pressing

    Kenji Hirota, Masato Kitamura, Katsuhiro Takagi, Kazuhiro Hasezaki

    pp. 1233-1238

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    DOI:10.2320/matertrans.MF201704

    Abstract

    Bi0.3Sb1.7Te3.0+x thermoelectric materials with a deficiency or excess of doped tellurium (x from −0.025 to +0.2) were prepared by mechanical alloying followed by hot pressing (MA-HP). The MA-HP sintered disks were dense and finely grained. X-ray diffraction (XRD) patterns showed that materials with x < 0.2 consisted of a single-phase Bi2Te3–Sb2Te3 solid solution. XRD and scanning electron microscopy showed that tellurium precipitation only occurred in the MA-HP sintered disk with x = 0.2. The thermoelectric properties of MA-HP sintered disks of Bi0.3Sb1.7Te3.0+x with a tellurium-deficient region differed from those of disks with an excess-tellurium region. Tellurium deficiency, i.e., x < 0.05, was caused by dopant evaporation. Excess tellurium acted as a dopant for x > 0.075. The MA-HP sintered disk of Bi0.3Sb1.7Te3.1, i.e., x = 0.1, had the maximum dimensionless figure of merit, ZT = 1.11, at room temperature. These results indicate that the thermoelectric properties of Bi0.3Sb1.7Te3.0 thermoelectric materials with excess tellurium were better than those of tellurium-deficient ones.

  • Detection of Surface Roughness Evolution of Carbon Steel Subjected to Outdoor Exposure and Constant Humidity Corrosion Tests

    Dara To, Osamu Umezawa, Tadashi Shinohara

    pp. 1239-1243

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    DOI:10.2320/matertrans.MF201702

    Abstract

    The surface roughness evolution of carbon steel under corrosion was studied through outdoor exposure and constant humidity corrosion tests. The statistical analysis of the roughness parameters, such as the degree of skewness and kurtosis, are the good indicators to anticipate the corrosion stages. The results indicated that the corroded surface evolution could be classified into three stages of corrosion. The first stage showed shallow and sparsely distributed pits on the surface of the steel with a probability density function of negative skewness and a high degree of kurtosis (Ku > 3). The second stage exhibited pits distributed densely and partial overlapping of pits. In the third stage, the overlapping pits entirely covered the metal surface, thereby exhibiting uniform corrosion. Statistical analysis of the corroded surface indicated that the random depth variable of the uniform corrosion follows the normal distribution. The samples exposed to outdoor for one year exhibited the corrosion in the first stage only, while the samples exposed to constant humidity chamber for ten months showed all the three stages of corrosion.

  • Influence of Microstructure on Coercive Force of Pure Iron Powder Cores

    Takuya Takashita, Naomichi Nakamura

    pp. 1244-1250

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    DOI:10.2320/matertrans.Y-M2018821

    Abstract

    The recrystallization behavior of pure iron powder cores during the annealing process is visualized as Grain Orientation Spread (GOS) maps with an SEM/EBSD analysis. It is found to be significantly heterogeneous, leading to a heterogeneous dislocation density distribution. Nevertheless, a conventional dislocation pinning model well describes the coercive force behavior if the average dislocation density is applied. The pinning model is modified to separate the influence of the grain boundary pinning, and the relationship between the coercive force and the microstructure is discussed comprehensively. This Paper was Originally Published in Japanese in J. Jpn Soc. Powder Powder Metallurgy 64 (2017) 428–435. In order to more precisely explain the relationship between annealing temperature and area fraction of recrystallized grain, Fig. 11 was changed.

  • Metal Injected Copper Carbon Nanotube Composite Material with High Thermal Conductivity and Low CTE for IGBT Power Modules

    Farhad Mohammadi, Najmeddin Arab, Sheng-Shian Li

    pp. 1251-1258

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    DOI:10.2320/matertrans.M2018006

    Abstract

    Power modules, particularly in hybrid and electric vehicles, have become an essential part of their thermal management system design. In power cooling modules, the temperature variations are important issues, leading to thermal stresses caused by different coefficients of thermal expansion (CTE) in the composite materials. Thus, one should consider suitable materials and manufacturing processes to achieve the best performance and reliability during the device’s life cycle. The Cu/CNT-Cu material is assumed to have a unique combination of a high thermal conductivity and low coefficient of thermal expansion, which results in a new composite material that goes beyond the ability of regular materials. To address this, we have developed the Cu/CNT-Cu composite with a significant improvement in thermal conductivity (∼327 W/mK) which is within the industrial scale range of copper metal injection molding (320–340 W/mK) and low coefficient of thermal expansion (∼6 ppm/K), both of which make it an excellent choice for power modules in next generation automobiles. This was achieved by reducing the voids and increasing the interface bonding while adding the copper coated CNTs, which were made by an electroplating process. This mixed Cu/CNT-Cu property makes it the top material design selection in the Ashby map and has a better temperature stability due to its lower thermal distortion parameter (TDP). As a result, this material will represent a significant scientific and technological development in the advancement cooling of IGBT power module devices.

  • HAADF-STEM Study of Long-Period Stacking-Ordered Phases Formed in the Quaternary Mg–Li–Y–Zn Alloys

    Kaichi Saito, Shingo Kuzuya, Masahiko Nishijima, Katsuhiko Sato, Kenji Hiraga

    pp. 1259-1266

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    DOI:10.2320/matertrans.M2018123

    Abstract

    The crystal structures of Long-Period Stacking-Ordered (LPS) Phases formed in Mg97−xLixY2Zn1 (x = 3, 6, 10, 17 at%) alloys have been thoroughly investigated by means of High-Angle Annular Dark-Field Scanning Transmission Electron Microscopy. All the quaternary alloys with different Li contents, especially when subjected to annealing at 500°C for 50 hrs (hereafter called ‘as-annealed alloy’), allow certain polytypes of LPS-phases to form with α-Mg solid solutions. The as-annealed alloy with x = 3 at%Li has 14H-type LPS-phase with disordered arrangements of Y and Zn in the solute-enriched layers, as in the case of the ternary counterparts without Li. It is evidenced that an increase of Li additions has substantial effects of changing the LPS structure, progressively inducing both the phase transformation from 14H- to 24R-type and the in-plane ordering of Y/Zn atoms in their enriched layers. The as-annealed alloys with x = 6 at%Li, in fact, contain LPS-crystal grains made up of the two polytypes of 14H and 24R, both of which have the long-range in-plane ordered structures. Among all, the as-annealed alloy with x = 10 at%Li has the 24R-type LPS-phase dominant over the LPS-grains combined with the in-plane ordering. The crystal structures of such highly-ordered LPS-polytypes are found to be well characterized by the concept of order-disorder (OD) intermetallic phases.

  • Stress Corrosion Cracking Behavior of Type 316L and Type 310S Stainless Steels in Fusion Relevant Environments

    Yen-Jui Huang, Akihiko Kimura

    pp. 1267-1274

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    DOI:10.2320/matertrans.M2018064

    Abstract

    Stress corrosion cracking (SCC) susceptibility of type 316L and type 310S SS in pressurized water (561/613 K) and supercritical water (773 K) at deaerated condition and with dissolved-hydrogen (DH) ranging from 0.014 to 1.4 ppm were examined by means of slow strain rate test (SSRT) method at a strain rate of 5 × 10−7 s−1. SCC susceptibility of type 316L SS depends on test temperature and DH content. The SCC susceptibility, which was evaluated as a brittle fracture ratio, increased with increasing test temperature from 561 to 613 K, while it became much smaller in supercritical water at 773 K. At 613 K, the fracture ratio of intergranular (IG) SCC increased with increasing DH content in the pressurized water, although almost no IGSCC was observed at 561 K at any DH conditions. However, the IGSCC initiated at near specimen surface and transferred to transgranular (TG) SCC inside the specimen. The SCC susceptibility of type 310S SS is significantly lower than that of type 316L SS in the hydrogenated water at 561 and 613 K, while the trend appears to be reverse at 773 K. It is suggested that higher DH content in water is necessary to trigger IGSCC than TGSCC at 613 K.

  • Dependence of Load Angle on Static Strength of Resistance Spot Welded Lap Joint under Combined Load Test

    Tetsuya Akiyama, Takanori Kitamura, Tetsushi Ono

    pp. 1275-1279

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    DOI:10.2320/matertrans.M2018028

    Abstract

    The strength of resistance spot welded lap joints is very important. JIS prescribes tensile shear testing and cross-tension testing as a realistic environment under combined load. Thus, numerous strength prediction equations have been proposed. These equations use a threshold value based on the base material strength as a fracture condition. The relationship between the cross-tension strength and the opening angle only reflects the influence of the opening angle on the axial force acting geometrically on the base metal. However, it shows good agreement with the experimental results. The strength of resistance spot welded lap joints under combined load is known to be dependent on the load angle. However, it is not clear whether the only cause for this is the geometric influence as indicated by previously established equations or whether the fracture mechanism changes depending on the load angle. In this study, we examined the extent to which the dependence on load angle can be explained by macro geometric factors using a material dynamics model, before studying the micro fracture mechanism, which depends on the load angle in the vicinity of the crack initiation site in the nugget. Thus, we were able to explain the load angle dependence with a macro model. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 82 (2018) 59–63.

  • A New Glass Fibered Reinforced Composite with Improved Charpy Impact Properties at Low and High Temperatures beyond the Extremes of Aircraft Flight

    Michael C. Faudree, Yoshitake Nishi, Michael Gruskiewicz, Michelle Salvia

    pp. 1280-1287

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    DOI:10.2320/matertrans.M2018068

    Abstract

    In a highly CaCO3 filled compression molded short glass fiber polyester GFRP-BMC composite with high solidification texture angle of 71 ± ∼7 deg with respect to specimen length, Charpy impact strength, auc at both low −79°C (194 K) and high 70°C (343 K) temperatures were apparently increased 69 and 32%, respectively over that at RT (293 K). This result was highly unexpected. Test temperatures were beyond presently accepted extreme operating temperature range of commercial air flight of −62°C (211 K) to 53°C (326 K). As expected, optical observation of specimens showed number and size of surface cracks on tensile side increased, i.e. brittleness increased with decreasing temperature. In the 194 K samples, number of parallel cracks spanning most or all of specimen thickness increased exponentially with increasing auc with asymptote maxing out at about auc = 16 to 18 kJ m−2 absorbing increased fracture energy. SEM observation of fracture surfaces showed increased bare fiber exposed length from the 194 K sample indicating brittleness. There was smoother fracture surface in the 343 K sample indicating ductility compared to that of 293 K sample. The high 55 mass% of CaCO3 powder filler appears to play a role of increasing the auc of the composite at both low and high temperatures. Two strengthening mechanisms proposed are: 1) difference in coefficient of thermal expansion (CTE) between polymer matrix and CaCO3 nanoparticles creating residual compressive stresses with temperature change during either cooling or heating; and 2) crossing thermal transitions in the polymers during cooling and heating to enhance these residual stresses.

  • Primary Al Grain Size Measurement of Al–Si Hypo-Eutectic Alloy Using Mathematical Morphology Algorithms

    Yan Xu, Naoya Hirata, Koichi Anzai

    pp. 1288-1295

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    DOI:10.2320/matertrans.M2018076

    Abstract

    Homogeneous distribution of primary Al phase grain (hereafter, primary Al grain) size in an Al–Si alloy casting is desirable. Traditional image processing techniques found difficulties in making proper image segmentation for the individual primary Al grains. Recently, a new image processing technique, mathematical morphology, is paid attention to because of its capability for a flexible image processing. In this paper, an image processing method based on mathematical morphology algorithms was proposed for the appropriate image segmentation and measurement of primary Al grain size in aluminum alloys. Opening algorithm was applied to identify primary Al grains and Watershed transformation (WST) using Euclidean distance map (EDM) as marker-image was used to separate individual primary Al grains. Finally, a second implementation of WST was used to classify the isolated small primary Al grains that had not been individually identified in the first time WST. The results showed that the proposed method appropriately identified primary Al grains with enough quality to evaluate the size distribution. The quality of primary Al grain size measurement result was as high as human operations. Meanwhile, the proposed method also was more efficient than the subjective measurement by hands.

  • Fatigue Behavior of Multi-Directionally Forged Commercial Purity Grade 2 Ti Plate in Laboratory Air and Ringer’s Solution

    Ilhamdi, Toshifumi Kakiuchi, Hiromi Miura, Tomohiko Fukihara, Yoshihiko Uematsu

    pp. 1296-1303

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    DOI:10.2320/matertrans.M2018075

    Abstract

    Ultrafine-grained pure titanium (Ti) plates with the thickness of 1 mm were fabricated by a combined process of multi-directional forging (MDFing) and cold rolling (here after referred as MDFed pure Ti for simplicity) aiming at the dental implant application. The plates exhibited higher tensile strength than the conventional cold-rolled pure Ti plates due to the ultrafine-grained structure with an average size of 200 nm. The axial fatigue tests were conducted in laboratory air and in Ringer’s solution to investigate long-term durability as dental implants. The fatigue strengths of the MDFed pure Ti plates in laboratory air were higher than those of the cold-rolled pure Ti plates as well as the tensile properties. In the high cycle fatigue (HCF) regime, sub-surface crack initiation with fish-eye fracture surface was observed in the MDFed pure Ti plates, while surface crack initiation was dominant in the cold-rolled pure Ti plates. Sub-surface crack generally initiated at the mid-thickness of the thin plates. Inclusions were not recognized at the crack initiation sites, while microstructural analyses revealed that some coarse grains with the size of a few µm distributed around the crack initiation sites. Consequently, the sub-surface crack initiation mechanism was attributed to the inhomogeneity of the microstructure near the mid-thickness of the plates. The corrosion fatigue strengths in Ringer’s solution were comparable to those in laboratory air, where sub-surface crack initiation occurred in the HCF regime even in corrosive environment. That indicates the high corrosion resistance of the MDFed pure Ti plates.

  • Increasing Charpy Impact Value of Polycarbonate (PC) Sheets Irradiated by Electron Beam

    Yoshitake Nishi, Michael C. Faudree, Junhua Quan, Yoshiaki Yamazaki, Anna Takahashi, Syohei Ogawa, Keisuke Iwata, Akira Tonegawa, Michelle Salvia

    pp. 1304-1309

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    DOI:10.2320/matertrans.M2018095

    Abstract

    Applying low-potential electron beam irradiation (EBI) dose of 0.13 MGy to polycarbonate (PC) sheet on both side surfaces apparently improved the impact value (auc) over the untreated samples at all accumulative probabilities of fracture (Pf). Based on 3-parameter Weibull equation, the 0.13 MGy-EBI also raised the lowest limit of auc (25.5 kJ m−2) estimated at Pf = 0 (as) 14% over the untreated samples (22.0 kJ m−2), indicating improved reliability and safety. EBI generates dangling bonds where repulsive forces are generated between the outer shell electrons at terminated atoms in the PC polymer irradiated near the sample surface, probably inducing relaxation of heterogeneous stress concentration, as well as compressive stress (high molecular density) by micro-expansion around terminated atoms increasing the auc. Increasing EBI dose increased ductility by decreasing the fractured split ratio, Rs a characterization of separated portion of total cross-section of fractured PC. The 0.13 MGy dose (Rs = 0.30) appears to be at or near the optimal EBI dose obtaining the highest auc. Above 0.22 MGy the auc reduces with increasing dose. Excessive dangling bonds generation appeared to increase ductility in the form of lowering the Rs but weakens the molecular structure allowing chains to slide past each other easier decreasing impact values with less crack propagation. Therefore, when applying EBI to polycarbonate parts in industrial applications carefulness is highly recommended to adjust dose to optimal level for maximum strength and safety.

  • Chemical Vapor Infiltration of the Hexagonal Boron Nitride Interphase for SiC Fiber-Reinforced HP-Si3N4 Matrix Composite

    A. López Marure, H. Vincent, A.M. Vázquez Almaguer, M. García Hernández

    pp. 1310-1316

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    DOI:10.2320/matertrans.M2017368

    Abstract

    This work describes the processing of SiC fiber-reinforced Si3N4 matrix composites with boron nitride (BN) interphase. The BN interphase was processed by chemical vapor infiltration (CVI) with BF3/NH3 gaseous precursors. The BN interphase modification involved the continuous treatment of Hi-Nicalon SiC fibers. The relations between (i) the processing parameters, (ii) the mechanisms controlling the kinetics of the CVI of the BN, and (iii) the structure of the deposited BN are presented. A single- or multi-layer BN interphase can be produced depending on the CVI conditions imposed on the fibers during the continuous process. A surface reaction mechanism controlling the CVI promotes a smooth, isotropic BN coating. An anisotropic BN coating can be produced when the CVI kinetics are controlled by a mass transport mechanism. With a controlled temperature gradient, the BN interphase is then made by stacking successive isotropic and anisotropic layers.

  • Quantitative Evaluation of Eutectic Si Phase Distributions and Effect on Mechanical Properties in JIS AC4CH Aluminum Casting Alloy

    Naohiro Saruwatari, Yoshihiro Nakayama

    pp. 1317-1325

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    DOI:10.2320/matertrans.F-M2018823

    Abstract

    The effect of eutectic Si particles distributions on ductility in JIS AC4CH aluminum casting alloy (referred to as AC4CH alloy) was investigated through experimental approaches. AC4CH alloys were subjected to ECAP processing at the 2nd, 4th, 6th, and 8th-pass to prepare samples with various distributions of eutectic Si particles. First, a method for the quantitative evaluation of the distribution of the eutectic Si particles using an area grid was examined. The eutectic Si particle distributions were quantified for each plane in the test pieces for unprocessed and ECAP processed samples. These quantitative values corresponded with the eutectic Si particle distributions visually observed on the microstructural images. The relationship between the quantified values of eutectic Si particle distributions and the elongations obtained by the tensile test was investigated. The uniform, local, and fracture elongations determined by the tensile test were found to increase as the number of ECAP passes increased. After 8th-pass ECAP processing, each of these types elongation increased by 49%, 64%, and 54%, respectively, compared to the unprocessed sample. The correlation was found between the mean quantified values of eutectic Si particle distribution and elongations. The experiments confirmed that the homogenization of the three-dimensional distribution of eutectic Si particles leads to the elongation increasing.

  • Columnar Ferrite Structure in Cast Iron Formed by Decarburization of White Cast Iron

    Fumitaka Otsubo, Kousuke Matsuki, Hidenori Era, Hidenori Kuroki

    pp. 1326-1332

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    DOI:10.2320/matertrans.F-M2018822

    Abstract

    Cast iron objects such as axes and other artifacts excavated from ancient sites generally have a layered structure with columnar ferrite on the outside, changing to pearlite and ledeburite with increasing depth, together with a minor fraction of dispersed graphite; this structure is the result of the heat treatment used in the decarburization process. The formation of the columnar ferrite structure has previously been explained by assuming that cast iron was produced using a metal mold and then decarburized.In this study, in order to clarify this issue, decarburization experiments were performed on white cast iron. Part of a white cast iron block, containing the surface that had been in contact with the mold during casting, in addition to a cut surface, was heated to 1273 K, held at that temperature for 96 h, and then slowly cooled to 873 K at 67 K/h (for 6 h). It was found that columnar ferrite crystals grew in the direction perpendicular to the surface regardless of the solidification direction. The ferrite structure did not have a uniform crystal orientation, similar to the case for partially decarburized ancient cast iron. Therefore, this clarified that the issue was a misunderstanding without materials scientific grounds. In addition, when white cast iron was decarburized at 1123 K for 48 h and cooled to 873 K at 42 K/h, the overall thickness of the decarburized layers was close to that for ancient artifacts. Therefore, it is likely that in ancient times, the same type of cast iron and heat treatment conditions were used. This Paper was Originally Published in Japanese in J. JFS 90 (2018) 61–67.

  • Effect of Temperature Field and Mechanical Properties of Casting on Prediction of Hot Tearing Tendency Using FEM Thermal Stress Analysis

    Ryosuke Takai, Tatsuya Tsunoda, Yasutaka Kawada, Rei Hirohara, Toshimitsu Okane, Makoto Yoshida

    pp. 1333-1340

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    DOI:10.2320/matertrans.F-M2018824

    Abstract

    It is known that hot tearing tendency increases with the increase in the cooling rate of casting during the solidification. As the direct control factors of the hot tearing, the cooling rate dependences of the temperature field of the casting and the mechanical property of alloys in the semi-solid state have been implied. However, quantitative evaluation is not clarified yet to show which parameters is more important to predict hot tearing tendency.In this study, through the thermal stress analysis using cooling rate-dependent temperature fields of casting and cooling rate-dependent creep parameters in the semi-solid state, hot tearing tendency was predicted for an Al–Mg alloy during the solidification. For the prediction, the maximum principal creep strain accumulated during the solidification was used as the indicator of hot tearing tendencies. Then, the hot tearing tendencies were compared with experimental results. As a result, in the cooling rate range of this study which was corresponding to gravity die casting, it was found that the temperature fields are relatively more critical to predict hot tearing tendency than the creep parameters. This Paper was Originally Published in Japanese in J. JFS 89 (2017) 623–630.

  • Low-Temperature and High-Strain-Rate Superplasticity of Ultrafine-Grained A7075 Processed by High-Pressure Torsion

    Seungwon Lee, Katsumi Watanabe, Kenji Matsuda, Zenji Horita

    pp. 1341-1347

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    DOI:10.2320/matertrans.L-M2018825

    Abstract

    An A7075 alloy was processed by high-pressure torsion (HPT) under an applied pressure of 6 GPa for 1, 3 and 5 revolutions with a rotation speed of 1 rpm at room temperature. Vickers microhardness saturated to a level of 220 Hv after the HPT processing and the grain size was refined to ∼120 nm at the state of the hardness saturation. Tensile tests were conducted with initial strain rates from 2.0 × 10−2 to 2.0 × 10−4 s−1 at a temperature in the range of 200–400°C. It was shown that high-strain rate superplasticity (>1.0 × 10−2 s−1) and/or low-temperature superplasticity (0.5–0.6Tm) occurred in the HPT-processed A7075 alloy, where the superplasticity deformation is controlled by grain boundary sliding through grain boundary diffusion.

  • Low Frequency Electromagnetic Testing for Evaluating Wall Thinning in Carbon Steel Pipe

    Haicheng Song, Noritaka Yusa, Hidetoshi Hashizume

    pp. 1348-1353

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    DOI:10.2320/matertrans.M2018057

    Abstract

    This study proposes an inverse algorithm to evaluate the depth of full circumferential wall thinning from low-frequency electromagnetic field signals. Finite element simulations were performed and revealed that normalizing the magnetic fields enabled the elimination of the effects of the length and the position of wall thinning and the dimensions of the pipe under test. Subsequently, this study attempted to evaluate the residual wall thickness on the basis of the maximum normalized magnetic field using Gaussian process regression. Forty-eight signals obtained by numerical simulations were used to develop a regression model. Eighteen further signals obtained by numerical simulations and nine signals obtained by experiments using a carbon steel pipe (diameter 101.6 mm and thickness 5.7 mm) were used for validation. The root mean squared error of the validation was 0.07 mm for the simulated signals and 0.23 mm for the signals obtained by the experiment. The 95% confidence intervals of the predictions, which would contribute to probabilistic risk analysis, were approximately 0.5 mm.

  • An Electrodeposition Process for Producing Ductile Bulk Nanocrystalline Ni–Fe Alloys in a Wide Current Density Range

    Isao Matsui, Mizuki Kanetake, Hiroyuki Hosokawa, Naoki Omura, Yorinobu Takigawa, Kenji Higashi

    pp. 1354-1358

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    DOI:10.2320/matertrans.M2018115

    Abstract

    Current distribution become nonuniform as the shape becomes more complicated, following the edge effect. In creating complex shapes with near net shapes by an electrodeposition, it is required to obtain the same characteristics from a wide current density range. In this study, we prepared bulk samples of Ni–Fe alloys by an electrodeposition with different current densities of 10–150 mA/cm2, and their microstructure, mechanical properties, and magnetic properties were examined. In the current density range of 25–150 mA/cm2, a relatively constant Fe content of 17–20 at% was observed. X-ray diffraction analysis showed that these alloys had a similar microstructure, which was a strong (200) texture and an average grain size of 17 nm. Tensile tests of these alloys also showed a constant tensile strength of 1.8–1.9 GPa and elongation of 10%. Furthermore, the constant saturation magnetic flux density of 1.2–1.3 T and coercivity of 67–74 A/m were observed. The results of this study indicated the high compatibility of the developed electrodeposition process for Ni–Fe alloys with complicated shape forming.

  • Solderability Using Thermoset Resin-Based Solder Pastes Covered with Thermoplastic Resin Film

    Shinji Fukumoto, Ryoichi Wakimoto, Kohei Yamauchi, Michiya Matsushima, Kozo Fujimoto

    pp. 1359-1366

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    DOI:10.2320/matertrans.M2018088

    Abstract

    We developed novel bonding materials composed of thermoset epoxy resin, solder particles, and thermoplastic polyester resin film. The resistor chip component was bonded to the substrate using the thermoset resin-based solder pastes covered with the thermoplastic polyester resin film. The thermoplastic resin film can hold the thermoset resins having high fluidity on the substrate. The molten solder particles became coalesced and wetted on the electrodes during the heating process, resulting in the formation of a conductive path covered with the cured resin. The polyester resin film softened with increasing temperature, and the softening is assisted by the epoxy resin acting as a plasticizer for the thermoplastic resin. It was suggested that the epoxy resin mixed spontaneously with the polyester resin at elevated temperatures and did not prevent the molten solder particles from wetting on the electrode of the chip component. The viscosity of the thermoset resins increased during storage even at 298 K owing to the curing reaction and/or moisture absorption, which affected the solderability.

  • Optimizing Calcium Addition for Fabricating Aluminum Foams with Different Pore Sizes

    Ying Cheng, Yanxiang Li, Xiang Chen, Zhiyong Liu, Xu Zhou, Ningzhen Wang

    pp. 1367-1374

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    DOI:10.2320/matertrans.M2018131

    Abstract

    This study mainly investigated the influence of Calcium (Ca) addition on the pore size of aluminum foams made by using Cu–TiH2 composite powder as foaming agent. The Ca addition required for fabricating aluminum foams with different pore sizes was experimentally investigated. Two possible foam stabilization mechanisms were discussed and compared. For foams with pore size about 3 mm, the optimized Ca addition is 1 mass%. For foams with pore size about 2 mm, the optimized Ca addition is 3 mass%∼5 mass%. The main role of increasing melt viscosity in stabilizing foams is to prevent liquid films from thinning and rupture, rather than to prevent bubbles floating and escaping from the melt surface.

    Recommended Articles: Texture and Mechanical Properties of Al–Mg Alloy with Unimodal and Bimodal Grain-Structures Formed by Accumulative Roll Bonding and Annealing [ View more ]

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  • Effect of Cr Addition on Glass-Forming Ability and Corrosion Properties of FeCoSiBPC Bulk Glassy Alloys

    Xue Li, Yu Liu, Dechuan Yu, Xining Li, Dongying Ju, Akihiro Makino

    pp. 1375-1379

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    DOI:10.2320/matertrans.M2018062

    Abstract

    The FeCoSiBPCCr bulk glassy alloys (BGAs) were prepared by micro-alloying technique. The glass forming ability (GFA) and soft-magnetic properties of the BGAs were examined by X-ray diffraction, TEM, DSC and VSM. The corrosion resistance of the alloys was evaluated by electrochemical measurements and the mechanical properties were tested by macro-compression experiments. The results show that the GFA and corrosion resistance of the FeCoSiBPCCr BGAs are significantly improved with increasing Cr content while the mechanical and magnetic properties exhibit no obvious change. The Fe64.4Co7.6Si7B10P5C2Cr2 BGA rods with diameters up to 5 mm were produced by copper mold casting. These BGAs exhibit excellent corrosion resistance as well as high saturation magnetization of 1.3 T, low coercive force of 3.1 A/m and high fracture strength of more than 3700 MPa.

  • Effects of Crack Size Distribution and Voltage Probe Spacing on Variation of Critical Current and n-Value along the Longitudinal Direction in Superconducting Tape with Cracks

    Shojiro Ochiai, Hiroshi Okuda, Noriyuki Fujii

    pp. 1380-1388

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    DOI:10.2320/matertrans.MBW201701

    Abstract

    The effects of crack size distribution and voltage probe spacing on the variation of critical current and n-value along the longitudinal direction in heterogeneously cracked superconducting tape were studied using a Monte Carlo simulation combined with a model of crack-induced current shunting. The simulation results were as follows. The variation of the critical current along the longitudinal direction of the tape increases with increasing crack size distribution width, whereas it decreases when the voltage probe spacing is larger. The variation of n-value along the longitudinal direction is larger than that of critical current. The largest crack contributes most to the synthesis of the voltage-current curve, and this contribution increases with the crack size distribution width. Next, a model to predict the upper and lower bounds of distributed critical current and n-values was applied to the simulation results. It was confirmed that the critical current and n-values are within the upper and lower bounds in any crack size distribution width. In addition, it was revealed that the critical current value shifts from the lower to upper bound and the n-value shifts from the upper to lower bound with the increase in the crack size distribution width. Furthermore, an equivalent crack-current shunting model was applied to the simulation results. The multiple n-values for a critical current value and the correlation diagram between the n-value and critical current could be described with this model.

  • Precipitation Behavior and Its Effects on Mechanical Properties in a Pre-Twinned Mg–6Al–1Zn Alloy

    Jiejun He, Lushu Wu, Qihui Sun, Liping Zhai

    pp. 1389-1395

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    DOI:10.2320/matertrans.M2017406

    Abstract

    In the present study, an extruded Mg–6Al–1Zn alloy was pre-compressed along extrusion direction to generate sufficient tensile twins. Afterward, the pre-twinned samples were annealed at 170°C for aging. Precipitation of the second-phase particles was found to preferentially occur in twins and twin boundaries. The precipitation phase is proved to be Al12Mg17. Moreover, precipitation behaviors in the two twin boundaries on both sides of every twin were very different: a considerable number of second-phase particles precipitated in one twin boundary but only a few second-phase particles were present in the other twin boundary. The atomic structures or internal stresses of the two twin boundaries are assumed to be different. A theoretical model of atomic structure was constructed to analyze the difference between the two twin boundaries. This model shows that atomic densities of the two twin boundaries are different, thereby resulting in varying precipitation behaviors. Owing to precipitation in twins and twin boundaries, an obvious increase in yield stress was observed when the material was reloaded along the same direction.

  • Volatilization of Arsenic and Antimony from Tennantite/Tetrahedrite Ore by a Roasting Process

    Kazutoshi Haga, Batnasan Altansukh, Atsushi Shibayama

    pp. 1396-1403

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    DOI:10.2320/matertrans.M2017400

    Abstract

    The volatilization of arsenic (As) and antimony (Sb) impurities in a copper ore consisting of tennantite (Cu12As4S13)/tetrahedrite (Cu12Sb4S13) by roasting in both nitrogen and air atmospheres was investigated in this study. The roasting experiments were performed at different temperatures ranging from 500 to 1200°C and different retention times from 15 to 60 minutes while the nitrogen and air flow to a furnace chamber was same as 300 ml/min.The results showed that at 700°C, the maximum As volatilization in nitrogen and air atmospheres was reached over 90% and about 70%, respectively. Whereas the maximum Sb volatilization was about 90% at 1200°C in a nitrogen atmosphere and over 95% at 600°C in an air atmosphere. Meanwhile, copper and iron in the ore sample were not volatilized under the conditions. The contents of As, Sb and Cu in the residue obtained from roasting at 1200°C in a nitrogen atmosphere were 0.004 mass%, 0.75 mass% and 34.2 mass%, while their contents were 0.45 mass% As, 4.19 mass% Sb and 34.5 mass% Cu in the residue from roasting at 1000°C in an air atmosphere. Volatilization of arsenic from enargite, arsenic and antimony from tennantite/tetrahedrite sample containing chalcopyrite in a nitrogen atmosphere under the determined roasting condition were also discussed.It suggests that As and Sb can be selectively separated from each other/other metals by volatilization. On the other hands, high grade copper concentrate with lower As and Sb contents can be made by volatilization in a nitrogen atmosphere.
  • © 2018 The Japan Institute of Metals and Materials

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