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

MATERIALS TRANSACTIONS Vol. 61 (2020), No. 11

  • SIP-Materials Integration Projects

    pp. 2041-2046

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    DOI:10.2320/matertrans.MT-MA2020003

    Materials play key roles to solve social problems. In order to accelerate materials research and development, it is crucial to use the power of cyberspace. This article overviews the concept and current status of Materials Integration (MI), a new concept that was proposed in the first-term Cross-ministerial Strategic Innovation Promotion Program (SIP) “Structural Materials for Innovation” and that has been centered in the second-term SIP “Materials Integration for Revolutionary Design System of Structural Materials.” The concept of MI is to computationally link the material four elements of process, structure, property, and performance for replacing experimental trials and errors in physical space by computational ones in cyberspace. The MI can be characterized by systems approaches and the deep use of data science. The first-term SIP demonstrated the proof of concept for some example problems by developing a computer system containing of computational modules and workflows connecting them. In the second-term SIP, the MI system has been further developed to solve inverse problems, i.e. to design materials and process from a target performance. Moreover, the target materials and processes are expanding to advanced ones used in aerospace and power generation industries as well. The article discusses the outlook of the MI-system based platform for accelerating materials innovation by academia-industry collaboration. This Paper was Originally Published in Japanese in Materia Japan 58 (2019) 489–493.
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  • Development of Microstructure Simulation System in SIP-Materials Integration Projects

    pp. 2047-2051

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    DOI:10.2320/matertrans.MT-MA2020001

    A simulation system for the phase transformations and microstructure changes in welded area of steels was built with Materials Integration (MI) concepts. We aimed to build an simulation environment suitable not only for conducting research on microstructure developments and performing high-quality simulations but also for integrating practical and academic viewpoints and insights from materials science and engineering. In particular, the methods discussed in this article, such as the coordination of CCT diagrams and phase field (PF) simulations, and combination between PF methods and cellular automaton method, are typical examples of the MI concept. The detail of framework on the simulation system is explained, comprehensively. This Paper was Originally Published in Japanese in Materia Japan 58 (2019) 494–497.
  • Development of Performance Prediction System on SIP-MI Project

    pp. 2052-2057

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    DOI:10.2320/matertrans.MT-MA2020007

    In our recent projects the development of performance prediction system for welded structures was planned to contribute the research and development of materials, where forward calculation modules for prediction of macroscopic performances such as fatigue strength, creep strength, hydrogen embrittlement, brittle fracture and so on have been developed using theoretical considerations and empirical rules. This Paper was Originally Published in Japanese in Materia Japan 58 (2019) 498–502.
  • Development of Data-Driven System in Materials Integration

    pp. 2058-2066

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    DOI:10.2320/matertrans.MT-MA2020006

    A Data-driven analysis system developed in the first-term SIP “Structural Material for Innovation” is briefly explained using several practical applications. The developed system is composed of two major systems: the data-driven prediction system and the 3D/4D analysis system. In the data-driven prediction system, the two methods in data science, that is, data assimilation and sparse modeling, are applied to optimize model parameters for the physical and phenomenological models developed in other MI systems, such as the structure and performance prediction and microstructure prediction modules, using experimental and numerical databases. Whereas, in the 3D/4D analysis system, it is demonstrated that the microstructural database can be efficiently utilized to predict mechanical properties, as well as to extract detailed geometrical information concerning the constituent microstructures. This Paper was Originally Published in Japanese in Materia Japan 58 (2019) 503–510.
  • Development of the Materials Integration System for Materials Design and Manufacturing

    pp. 2067-2071

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    DOI:10.2320/matertrans.MT-MA2020002

    The concept of the Materials Integration (MI) has been proposed as a framework to evaluate the performance of structural materials based on the PSPP (Process, Structure, Property, Performance) linkage. In order to solve direct problems for structural materials with complex input and output, this system designs and executes a workflow that enables continuous computation while focusing on data coordination and aggregation, and aggregates data.In the second phase of our project, we will develop an Application Programming Interface (API) to drive the MI-System from external programs so that the MI-System can be used in combination with various algorithms used to solve inverse problems, such as optimization and Bayesian statistical algorithms. In addition, we aim to solve the inverse problem systematically and efficiently by developing a mechanism to effectively utilize the computational resources distributed in various places and to handle large scale computations. This Paper was Originally Published in Japanese in Materia Japan 58 (2019) 511–514.
  • Simulations of Non-Equilibrium and Equilibrium Segregation in Nickel-Based Superalloy Using Modified Scheil-Gulliver and Phase-Field Methods

    pp. 2072-2078

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    DOI:10.2320/matertrans.MT-MA2020005

    Solute segregation significantly affects material properties and is an essential issue in the additive manufacturing (AM) process. In the present study, we have investigated (i) non-equilibrium segregation in solidification, and (ii) equilibrium segregation at grain boundary in Ni-based Hastelloy-X (HX) superalloy using the modified Scheil-Gulliver model (i.e., Scheil-Gulliver model with back diffusion) and a phase-field model. We have found that the concentrations of all solute elements on grain boundary differ from those in face-centered cubic (FCC) phase matrix even in equilibrium state. In the non-equilibrium segregation, the segregations of Mo, Cr, and Mn and the depletion of Fe become more remarkable than the equilibrium segregation. Moreover, we have investigated the segregation in HX-based alloys with different Fe concentrations to propose a guide for tailoring the chemical composition of HX via the control of the segregation behaviors. The equilibrium-segregation simulation revealed that the Cr segregation in the grain boundary phase increased with the increase of Fe concentration. This result suggests that by controlling the Fe concentration, the Cr concentrations on grain boundaries can be controlled without changing directly the Cr concentrations. This finding opens new way of controlling materials properties which are dominated by the nature of grain boundaries such as corrosion resistance, crack sensitivity, high temperature strength.
  • Vacancy Control and Enhancement of Thermoelectric Properties of Al–Ir Cubic Quasicrystalline Approximant via High-Pressure Synthesis

    pp. 2079-2082

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    DOI:10.2320/matertrans.E-M2020845

    Although the binary Al–Ir cubic quasicrystalline approximant has been expected to be a narrow-gap semiconductor, it has not yet been produced because the presence of Al site vacancies causes excess hole doping. We suggest that high-pressure synthesis (HPS) can effectively reduce these vacancies. In this work, we investigated how HPS affected the structural and thermoelectric properties of an Al–Ir quasicrystalline approximant, finding that the sample made by HPS had a larger Seebeck coefficient than a sample made by conventional spark plasma sintering (SPS). Further, applying high pressure increased the lattice constant and measured Al composition by increasing the number of Al atoms in the Ir12 icosahedral cluster. These results show that HPS suppressed vacancies in the cluster, which doubled the dimensionless figure of merit zT. This Paper was Originally Published in Japanese in J. Thermoelec. Soc. Jpn. 16 (2020) 139–143.
  • Prediction System for Solid Solubility Limits of Ag-, Cu-, Al-, and Mg-Based Alloys Using Artificial Neural Networks and First-Principles Calculations

    pp. 2083-2090

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    DOI:10.2320/matertrans.MT-MBW2019010

    A solid solubility prediction system using Hume-Rothery parameters and first-principles calculation to obtain explanatory variables was devised, and the resulting coefficients of determination, R2, were compared. When we used the Hume-Rothery parameter, R2 was 0.715, and when we used the first-principles calculation results, R2 was 0.900, indicating the improved accuracy of prediction. We tested 10-fold cross validation to evaluate the generalization performance of the network. The number of explanatory variables was optimized using the stepwise method. R2 was maximized when eight explanatory variables were used. As a result of 10-fold cross-validation, R2 of the constructed solid solubility prediction system which uses eight explanatory variables was 0.6993. The mean absolute error for this network was 0.45. The common logarithm value was used as the explained variable. Thus, the solid solubility limit predicted from this network was on an average 0.35 to 2.85 times the true value.
  • Influence of Thermal Annealing Media on Optical and Electrical Properties of FTO, ITO and TiO2 Films

    pp. 2091-2094

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    DOI:10.2320/matertrans.MT-MN2019002

    Metal oxides, in many cases, exhibit n-type semiconductors due to the existence of oxygen vacancies in the lattice. Therefore, the interactions of oxygen being in medium with oxygen vacancies during the annealing process can change concentrations of defects that will cause variations in optical and electric properties of such materials. However, research on such interactions for commercial FTO, ITO, and TiO2 products has been limited. This paper summarizes the results of some experiments conducted to determine the influence of thermal annealing media on the optical, electrical properties of thin films of these products. The thermal media considered are air medium, 10−1 torr low vacuum condition, and Argon gas environments, and the annealing condition is set at 450°C for 20 minutes. It is found that while FTO films change for the better after annealing, ITO films trend towards worse, and TiO2 films have the most photoconversion efficiency (Isc = 0.27 mA, η = 0.37%) under the moderate oxygen concentration environment.
  • Effect of Cr Addition on Microstructure and Mechanical Properties at Elevated Temperature of Al–Mn–Mg–Si Alloys

    pp. 2095-2100

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    DOI:10.2320/matertrans.MT-M2020178

    Recently, the remarkable strengthening effect of α-Al(Mn, Fe) Si dispersoids at both ambient temperature and elevated temperature were found by several researches. In AA3xxx alloys, a large amount of dispersoids can form by applying suitable heat-treatment. In the present work, the influences of Cr addition on mechanical properties and microstructures of the Al–Mn–Mg–Si alloys were investigated. The mechanical properties at ambient temperature were evaluated by micro-hardness and yield strength. Yield strength at 300°C and creep resistance at 300°C were used to evaluate materials’ mechanical properties at elevated temperature. Moreover, the microstructures in as-cast and heat-treated conditions were quantitatively analyzed by optical and transmission electron microscopes. Results revealed that the addition of Cr increased area percentage of Mn-containing intermetallic particles. It also indicated that solubility of Mn element decreased due to Cr addition. Very little amount of Cr were detected in Mn-containing intermetallic particles and dispersoids. The distribution of dispersoids was not influenced by Cr addition. Number density and volume fraction of dispersoids decreased because of Cr. Electrical conductivity decreased significantly because of 0.30% Cr addition which indicated that a large amount of Cr were still in solid solution condition. Micro-hardness and yield strength at ambient temperature increased with the increasing content of Cr, and the Cr addition increased yield strength at elevated temperature as well. Moreover, creep resistance at 300°C improved dramatically with the increasing content of Cr.
  • Hot Compression Behavior of Mg–14Li–6Al–1Ca Alloy

    pp. 2101-2106

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    DOI:10.2320/matertrans.MT-M2020157

    The hot deformation behavior of a Mg–14Li–6Al–1Ca alloy was studied using the hot compression true stress–strain curves corresponding to the temperature range of 473–673 K at strain rates of 1 × 10−1–1 × 10−3 s−1. The true stress–strain curves indicated dynamic softening under the test conditions. The peak stress during deformation could be correlated with the temperature and strain rate using a hyperbolic-sine equation. The activation energy of the Mg–14Li–6Al–1Ca alloy was determined to be 193 kJ mol−1. The Zener-Hollomon parameter (Z) for the Mg–14Li–6Al–1Ca alloy was determined. The tendency for dynamic recrystallization increases at low strain rates and high temperatures, corresponding to low Z values. The hot deformation behavior of the Mg–14Li–6Al–1Ca alloy was modelled by a suitable constitutive equation. Furthermore, the size of the equiaxed grains in the hot-deformed and quenched specimens was estimated from the Z value.
  • Comparison of In Situ SEM and TEM Observations of Thermoelastic Martensitic Transformation in Ti–Ni Shape Memory Alloy

    pp. 2107-2114

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    DOI:10.2320/matertrans.MT-M2020219

    To quantitatively understand the thin foil effect in in situ observations of the B2 to B19′ transformation in Ti–Ni alloy, the microstructure of the B19′ martensite in thin foil and bulk specimens was compared. The transformation temperatures decreased with decreasing specimen thickness. There were large habit plane variants more than several tens of micrometers in size in the area of the specimen less than 10 µm thick. The critical thicknesses for reproducing the transformation behavior in the bulk material was about 20 µm based on the self-accommodation morphology and 4 µm based on the twin width ratio of the 〈011〉 type II twin.
  • Effect of Cooling Rate on Precipitation during Homogenization Cooling in Balanced Al–Mg2Si Alloy

    pp. 2115-2120

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    DOI:10.2320/matertrans.MT-M2020189

    The effect of the cooling rate on the precipitation process during homogenization cooling in a balanced Al–0.64Mg–0.32Si mass% alloy was investigated. Different cooling rates (Furnace-cooling/Air-cooling) were used. During homogenization air-cooling (∼830 K/h), optical microscopy (OM) revealed that few precipitates could be observed in the matrix; however, there were many “boundaries” formed in the grains. Transmission electron microscopy (TEM) observations confirmed that these “boundaries” were caused by heterogeneous nucleation of precipitates along the dislocations during cooling, and many precipitates only grew along the [100]Al and [010]Al directions. Among the precipitates, over-aged β′/Type-B, together with string-like precipitates, were found on the dislocations. For the furnace-cooled samples (20 K/h), rod/lath-like precipitates of β′ and β′/Type-B were also found along the dislocations.
  • Mechanism for Excellent Shape Fixability in Hot Stamping Process

    pp. 2121-2127

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    DOI:10.2320/matertrans.P-M2020838

    Automobile body parts produced by the hot stamping process exhibit excellent shape fixability with an ultra-high tensile strength of 1.5 GPa. We investigated the effect of flow stress during forming and phase transformation in the hot stamping process. Referring to both experimental and FEM coupled simulation results, we discussed the mechanism behind the excellent shape fixability in the hot stamping process. Steel of 0.2% C was used for hot stamping in this study. IF steel and SUS 304, which have different transformation behaviors, were used for comparison. The forming start temperature varied from 400°C to 800°C. After hot stamping, the springback of the parts was evaluated. The results showed that shape fixability in hot stamping is caused by low flow stress during stamping and martensitic transformation. When martensitic transformation occurs after stamping, excellent shape fixability is obtained regardless of the flow stress during forming. Accordingly, it was concluded that the stress introduced by hot stamping is relaxed and becomes uniform during martensitic transformation. The application of tensile stress due to thermal contraction also contributes to the decrease in springback. This Paper was Originally Published in Japanese in J. JSTP 60 (2019) 45–50.
  • Effect of Punch Shape on Multiprocess Tube Flaring for Eccentric Parts

    pp. 2128-2133

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    DOI:10.2320/matertrans.P-M2020848

    In this work, by focusing on multiprocess tube flaring for eccentric parts, we studied the effect of punch shape on deformation behavior by finite element analysis. In the case of using only the eccentric punch, thickness deviation occurs in the circumferential direction and thickness reduction is suppressed because the tube is greatly expanded at the 180° circumferential position. However, it is found that the thickness deviation and thickness reduction are suppressed by evenly expanding both sides using a concentric punch. Furthermore, although the punch shoulder radius has a negligible effect on formability, it is confirmed that the deformation near the tube edge transitions from uniaxial tension to pure shear as the punch semiangle is increased. The above result clarify that by using concentric punches with punch semiangle larger than the taper angle of the part shape from the initial process, the thickness reduction is drastically minimized compared with other forming methods. This Paper was Originally Published in Japanese in J. JSTP 60 (2019) 182–186.
  • Precise Permeability Measurement for High Strength and Ultra Low Permeability Concrete under Controlled Temperature

    pp. 2134-2138

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    DOI:10.2320/matertrans.Z-M2020846

    High strength and ultra low permeability concrete (HSULPC) is being considered as a material used to package transuranic (TRU) waste for disposal in geological repositories. Therefore, information on the permeability of HSULPC is essential. Permeability tests need to be highly accurate to determine the hydraulic conductivity of HSULPC because of its ultralow permeability. In our study, we measured the permeability of HSULPC samples using the transient pulse method. The temperature of the concrete was finely controlled and held constant. The hydraulic conductivities were determined from the measurements to be around 10−13 to 10−12 m/s for confining pressures between 2 and 10 MPa. The pore pressure was a constant 1 MPa. The results further showed that the permeability of HSULPC had a hysteretic dependence on the effective confining pressure. We found that the hydraulic conductivity of HSULPC is comparable to or less than that of intact Toki granite obtained from Gifu Prefecture in central Japan. It was also considered that the hydraulic conductivity of HSULPC stabilized at around 10−13 m/s after being buried and stressed. The high density and impermeability of HSULPC would enable it to effectively confine 14C radionuclides found in TRU waste. This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 69 (2020) 263–268. Acknowledgement is added.
  • A Mechanism of Carbon-Cluster Strengthening through Atomic Simulations

    pp. 2139-2148

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    DOI:10.2320/matertrans.MT-M2020136

    To investigate the reason why low-carbon steels with carbon-clusters shows the maximum strength during low-temperature aging, interactions between an edge dislocation and carbon clusters are performed through molecular dynamics (MD) simulations. Carbon clusters are modeled based on atom probe tomography (APT) observations. To express a transition process of carbon configurations from solid solution state to carbon cluster state to precipitation state during aging process, we reduce a carbon presence area with a fixed number of carbon atoms, i.e., the carbon concentration can be continuously increased. The MD simulations can represent the age hardening/softening tendency observed in the experiment and the carbon cluster state shows the maximum strength where the dislocation passes through the carbon cluster not by the Orowan but by the cutting mechanism. The MD analysis found that partial clusters in the carbon cluster act as the main resistance to dislocation passage; the biased distribution of carbon atoms is also confirmed in the actual observed carbon clusters by APT. A new interaction mechanism between dislocation and carbon clusters is developed based on the phenomena in the MD simulations and the availability is discussed. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 84 (2020) 19–27. The title is partly corrected.
  • Reaction Process and Influence of WC Content on Microstructure and Mechanical Properties of Ti(C, N)-Based Cermets

    pp. 2149-2155

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    DOI:10.2320/matertrans.MT-M2020186

    The incorporation of WC promotes the sintering and grain refinement of Ti(C, N)-based cermets, leading to superior mechanical and functional properties. Herein, we present the reaction process of Co–Ti–C–BN–WC system and influence of WC content on microstructure and mechanical properties of Ti(C, N)-based cermets. The results reveal that Ti(C, N) is produced due to the combination of C/TiN or TiN/TiC, whereas TiB2 is formed due to the reaction between B/TiB or Ti/B. Moreover, (W, Ti)(C, N) solid-solution is synthesized due to the reaction of W and C with TiN in the liquid state. In addition, XRD analysis indicates the presence of a small amount of CoW2B2 and Co3C phases with WC content of 15 and 20 mass%. Furthermore, the content of core-ring structure gradually increases with the increase of WC content from 5 to 20 mass%. Also, the grain size increases from 0.364 µm to 0.484 µm with increasing WC content from 5 to 20 mass%. On the other hand, the porosity initially decreases with increasing WC content, followed by a gradual increase. Consequently, the microhardness, fracture toughness and bending strength initially increase with increasing WC content, followed by a decrease. The maximum microhardness, fracture toughness and bending strength are found to be 2010 HV10, 7.21 MPa·m1/2, and 725 MPa, respectively.
  • Influences of Carbon Addition on Mechanical Properties and Hydrogen Evolution of Thixomolded AM60B and AZ91D Magnesium Alloys

    pp. 2156-2161

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    DOI:10.2320/matertrans.MT-M2020236

    In this study, the effects of carbon nanoparticles fixed to the surfaces of AM60B and AZ91D magnesium alloy chips on the mechanical properties were examined. The manufacture of magnesium–carbon alloy is not easy because carbon does not possess the property of wettability for magnesium. However, magnesium alloy chips fixed to carbon nanoparticles enable magnesium–carbon alloys to be produced by the thixomolding process. Mechanical properties such as the tensile and fatigue strengths were improved by only 0.1 mass% of the carbon addition because of the decrease in the void and the refinement of crystal grains. In addition, the AZ91D magnesium alloy was proven to be more effective than the AM60B magnesium alloy for the decrease in the void and the refinement of crystal grains by the carbon addition. The aluminum content of the AZ91D magnesium alloy is higher than that of the AM60B alloy. It seems that the void formation is based on the hydrogen by the reaction between aluminum in the magnesium alloy and water. Therefore, the effect of carbon addition on the mechanical properties was dependent on the aluminum content in the magnesium alloys. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 84 (2020) 109–114.
  • Erosion-Corrosion Behavior and Mechanism of Heated Electroless Ni–P Coating under Flow

    pp. 2162-2169

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    DOI:10.2320/matertrans.MT-M2020113

    To study on erosion-corrosion behavior and mechanism of Ni–P coating (Ni–P) and Ni–P coating after heat treatment at 400°C (h-Ni–P) in liquid flow and solid-liquid flow, the numerical simulation, microstructure, and electrochemical methods were applied. It could be seen that the spherical structure of the coating surface was no longer dense, and the coating changed from amorphous to crystalline after heat treatment at 400°C. Numerical simulation showed that the coating possessed a higher velocity and a small static pressure at the edge in the straight pipe. The electrochemical analysis showed that the icorr of Ni–P and h-Ni–P became larger and the Rp became smaller as the solution speed increased, the icorr of h-Ni–P was larger than that of Ni–P, the Rp of Ni–P was larger than that of h-Ni–P. In addition, the both coating had a higher icorr in the solid-liquid flow than that of the liquid flow at the same speed. The results indicated that the corrosion resistance of Ni–P coating was reduced because it had become the crystal after heat treatment at 400°C. The numerical simulation was helpful to reveal the local stress information of Ni–P coating under flow.
  • Effect of Polyethylene Glycol on Electrodeposition of Zn Active Metal Oxide Composites from a Particle-Free Solution

    pp. 2170-2177

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    DOI:10.2320/matertrans.MT-M2020164

    Electrodeposition of Zn–Zr and Zn–V oxide composites was performed under galvanostatic conditions at 313 K on unagitated pH 2 sulfate solutions containing Zn2+ and Zr4+ or VO2+ ions and an additive such as polyethylene glycol (PEG). The effects of PEG addition on the co-deposition of Zr and V oxides and their polarization behavior, and on the microstructure of the deposits, were investigated. Although the Zr content in the deposits obtained from the Zn–Zr solution in the absence of PEG was approximately zero, it increased significantly at a current density of above 1000 A·m−2 following the addition of PEG. In the Zn–V solution, the V content in the deposits obtained from 100 to 2000 A·m−2 was higher with PEG than without it. In the presence of PEG, the cathode potential polarized, the rate of hydrogen evolution increased, and the hydrolysis reaction of Zr4+ and VO2+ ions proceeded smoothly, resulting in an increase in the Zr and V content in the deposits. Additionally, the crystal platelets of Zn in the Zn–Zr and the Zn–V oxide films became fine, and the surface coverage of the spongiform Zr and film-like V oxides increased. Furthermore, the corrosion current densities of the Zn–Zr and Zn–V oxide films obtained from the solution with PEG were lower than those from the solution without it. The reduction rate of dissolved oxygen decreased in the films in the presence of PEG, thereby leading to a decrease in the corrosion current density. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 84 (2020) 50–57.
  • Development of VGCF/MP Reinforced Al Matrix Composite by Low Pressure Infiltration Method and Their Thermal Property

    pp. 2178-2184

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    DOI:10.2320/matertrans.MT-M2020158

    To fabricate vapor grown carbon fibers and mesophase pitch reinforced Al matrix (VGCF/MP/Al) composites, porous VGCF/MP with high porosity was fabricated using the spacer method. Carbonization and electroless Ni plating were carried out on porous VGCF/MP to improve its thermal conductivity (TC) and wettability with Al matrix, respectively. In addition, VGCF/MP/Al composites were manufactured using a low pressure infiltration method at 0.1 MPa. The effect of volume fraction of VGCFs on the interface between VGCF/MP and Al matrix, and the reactivity of the Al matrix to the Ni plating were investigated. The composites with 0.5 vol% of VGCFs showed a bonded interface between VGCF/MP and Al matrix. The bonded interface can be attributed to the improved wettability between VGCF/MP and Al matrix from Ni plating, resulting in the good bonding seen between VGCF/MP and Al matrix. At the interface of this sample, an intermetallic compound, Al3Ni, formed from the reaction between Ni and Al. Furthermore, the thermal conductivities of the fabricated porous VGCF/MP and VGCF/MP/Al composites were determined.
  • Morphology Evolution of γ′ Precipitates for Wrought Ni-Based Superalloys

    pp. 2185-2194

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    DOI:10.2320/matertrans.MT-M2020183

    The morphology evolution of γ′ precipitates during isothermal aging at 1173 K is investigated for wrought Ni-based superalloys with various combinations of lattice misfit (δ) and γ′ volume fraction (fv) (i.e., Inconel X-750, Alloy 80A, Udimet 520, and Udimet 720Li). The resulting morphology evolution strongly depends on |δ|, which was classified into three types. The spherical morphology for |δ| < 0.10% remains unchanged with the increasing diameter of the γ′ precipitates (d) (Type A). In the case of 0.10 ≦ |δ| < 0.30%, the γ′ morphology evolves from spherical to cuboidal with a maintained coherency at the γ/γ′ interface with an increasing d, accompanied by the alignment of the cuboidal γ′ precipitates (Type B). The morphology evolution of the γ′ precipitates when |δ| ≧ 0.30% is from spherical to cuboidal and finally to globular. The coherent γ/γ′ interface turns to a semi-coherent one with the coalescence of the γ′ precipitates (Type C). The alignment of the cuboidal γ′ precipitates is promoted for superalloys with a larger fv value, whereas the effect of fv on the morphology evolution of the γ′ precipitates during aging treatment is quite limited. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 84 (2020) 151–160.
  • Effect of Microstructure on the Coercivity of SmCo5 Intermetallic Compound

    pp. 2195-2200

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    DOI:10.2320/matertrans.MT-M2019350

    SmCo5 is well known for its high coercive properties. This property helped the compound to become stable even at high temperatures. A lot of efforts had been made to improve this important property but so far only a few percentages of the theoretical coercivity values were achieved. Improving processing parameters or doping by other alloying elements are two popular ways to manipulate the properties of SmCo5. In this research work, the cooling temperature of the indigenously developed water-cooled copper mold was manipulated to control the solidifying peritectic structure. The obtained casting was milled to powder and the final sintered product was produced. It was noted that high coercive values i.e. 32.9 kOe was achieved at low water inlet temperature. The results were interpreted by using a scanning electron microscope (SEM), Differential thermal analysis and X-Ray diffraction analysis. SEM results revealed peritectic nano-structure in SmCo5 compounds. These nano-structures seem helped to improve the coercivity of SmCo5.
  • Preparation of Highly Heat–Resistant Sm–Fe–N Magnetic Powder by Reduction–Diffusion Process

    pp. 2201-2207

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    DOI:10.2320/matertrans.MT-M2020185

    We previously described the preparation of Mn- or Cr-containing core–shell Sm–Fe–N powders exhibiting high thermal stability by a reduction–diffusion process, in which powder mixtures of Sm2Fe17, Sm2O3, Mn3O4 or Cr2O3, and Ca were annealed and nitrided followed by the removal of residual CaO by washing with ethylene glycol in a glove box. We also found that Sm–Fe–N powder prepared by this process showed high heat resistance even without Mn or Cr addition. In the present work, we investigated the effects of the washing solvent and atmosphere on the coercivity, heat resistance, and microstructure of Sm–Fe–N powders. The heat resistance of the Sm–Fe–N powders was strongly dependent on their O content. Washing with ethylene glycol rather than water effectively suppressed oxidation during washing. Furthermore, the washing atmosphere also affected the increase in O content of the powders. The Sm–Fe–N powder washed with ethylene glycol in a glove box showed high heat resistance and the same microstructure before and after the heat resistance test. In contrast, the powder washed with water in air exhibited low heat resistance owing to the occurrence of α-Fe precipitation during the heat resistance test.
  • A Novel Process for Recycling of Aluminum Dross Using Alkali Fusion

    pp. 2208-2215

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    DOI:10.2320/matertrans.M-M2020849

    Aluminum dross discharged from an aluminum production factory can react with water and emit hazardous gases such as hydrogen and ammonia causing serious environmental pollution. Thus, it becomes necessary to recycle the by-products to avoid such problems. In this study, the feasibility of the alkali fusion process to convert the dross into benign and functional material was investigated. The effects of fusion temperature, dross/NaOH ratio, and the heating time on the amount of gas removed from the dross and the soluble contents of Si and Al in the fused dross were examined. Synthesis of zeolite–A from the fused dross was performed by reacting with sodium silicate. The optimum condition to dissolve the minerals Al and Si and maximize the generation of gases was a fusion temperature of 400°C, the ratio of the raw dross to NaOH of 1.0, and the heating time of 3 h. The fused dross can be converted into zeolite-A product with a high cation exchange capacity (3.22 mmol·g−1) by reacting with sodium silicate solution while generating as much gas as that generated in distilled water. These results demonstrate the applicability of the alkali fusion process to recycle the aluminum dross waste generated from an aluminum industry into value-added material, thus contributing to the circular economy while reducing the environmental impact.
  • Preparation of Eco-Friendly Fe2VAl-Based Thermoelectric Materials Using Cast Iron Scrap Chips as a Source Material

    pp. 2216-2221

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    DOI:10.2320/matertrans.MT-M2020197

    This study investigates the upgraded recycling of cast-iron scrap chips in synthesising Heusler alloys Fe2VAl for thermoelectric materials. It mainly examines the microstructure and the thermoelectric performance of the products. The thermoelectric performance showed positive results, as the maximum power factor, the PF value, of p-type 2C.I.–V–Al prepared using cast-iron scrap chips (the prefix ‘C.I.’ presumably stands for ‘cast-iron scrap chips’) was 1604 µWm−1K−2 at 200°C, the highest PF value. Meanwhile, the undoped 2C.I.–V–Al prepared using cast-iron scrap chips showed an approximate two-fold improvement in the power factor value, with 967 µWm−1K−2 at 200°C, a higher PF value than those previously reported. Unfortunately, in this study, the n-type 2C.I.–V–Al specimen made from cast-iron scrap chips could not be fabricated due to the effect of unavoidable impurities in the cast-iron scrap chips. The use of cast-iron scrap chips to produce undoped and p-type 2C.I.–V–Al alloys can contribute towards eco-friendly and cost-effective production processes.
  • Comprehensive Nondestructive Evaluation Technology for Safety and Reliability of Engine Crankshaft

    pp. 2222-2227

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    DOI:10.2320/matertrans.MT-M2020073

    Ultrasonic testing and metal magnetic memory testing were comprehensively applied to detect the internal defects and superficial defects of engine crankshaft. A special detection method and device were designed for the testing. The results indicated that the internal defects of crankshaft could be detected quantitatively by using the special detection device and ultrasonic testing, whereas, the superficial defects of crankshaft could be detected by metal magnetic memory testing. The magnetic stress concentration coefficient KM was used to characterize the fatigue damage degree. By the comprehensive nondestructive method, the internal and superficial damage of engine crankshaft can be evaluated to effectively guarantee the safety and reliability of engine crankshaft.
  • Interface Characteristics of GCr15/45 Carbon Steel Composite Billet Produced by Electroslag Remelting Cladding

    pp. 2228-2235

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    DOI:10.2320/matertrans.MT-M2020143

    In the present study, a GCr15/45 carbon steel composite billet is manufactured by the new electroslag remelting cladding (ESRC) method and a systematic analysis of the interface characteristics including the bonding state, element transition, microstructure evolution and tensile strength is carried out. It illustrates that an appropriate smelting power is beneficial to obtain a metallurgical bonding interface. Based on the temperature variation characteristics of the composite system, the bonding state of the bimetals (interface) changes gradually from entrapped slag defect to metallurgical bonding at the early stage of ESRC process, and the widths of elements transition and heat-affected zone (HAZ) become proportional to the composite height. It has an obvious influence on the grain size and precipitated phase at bimetallic interface. Tensile test results on both as-cast and annealed samples prove that the bimetallic interface is not the weakest zone as the fracture occurred at the roll core (45 carbon steel) side. In addition, an appropriate isothermal spheroidization annealing treatment is beneficial to refine the austenite grains and optimize the microstructure of the composite billet.
  • Extrusion Freeforming-Based 3D Printing of Ceramic Materials

    pp. 2236-2240

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    DOI:10.2320/matertrans.MT-M2020167

    Extrusion freeforming (EFF)-based 3D printing of ceramic materials is an additive manufacturing technology that builds 3D objects through layer-wise slurry deposition (LSP) of ceramics. This process offers advantages such as a high efficiency of formation, wide applicability, and low cost. The effect of solids content on the rheological behavior of Al2O3 ceramic slurry, and the effect of sintering temperature on microscopic morphologies and the precision of the parts fabricated by 3D printing, were investigated. Results show that the slurry viscosity gradually increases while the slurry flowability is reduced with an increasing solids content. Solids content should be high enough to prepare highly compact ceramic parts, however, an over-high solids content is likely to decrease the flowability of ceramic slurry. The optimal solids content was determined to be 50 vol%. As the sintering temperature increases, the green bodies become more compact and develop fewer cracks. However, the ceramic particles will be transformed to liquid phase at a high sintering temperature, which affects the shapes of sintered samples. The optimal sintering temperature was determined to be 1700°C. After being sintered at high temperature, the samples are found to be free from obvious surface defects or deformations and show slight uniform shrinkage, with a shrinkage rate of 20%. Surface roughness also decreases indicating that surface quality has improved. Finally, a set of sample ceramic structures were printed using optimized process parameters.
  • Severe Plastic Deformation for Nanostructure Controls

    pp. 2241-2247

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    DOI:10.2320/matertrans.MT-M2020134

    This paper presents a current research trend for micro- and nano-structure controls using severe plastic deformation (SPD). The survey is carried out based on the special issue published in July and August, 2019, in Materials Transactions (Vol. 60, Nos. 7 and 8). The SPD-related research is rapidly growing particularly after the year 2000. The research ranges over processing, modeling, simulation, synthesis, characterization and evaluation. Among the various topics, a brief introduction is given for innovative approaches which will further promote the development of the SPD-related research.
  • A Corrosion Resistant Sintered Stainless Steel: Type 304L Containing Mo-Rich Phases

    pp. 2248-2251

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    DOI:10.2320/matertrans.MT-M2020228

    Pure Mo and type 304L stainless steel powders were mixed to form type 304L with 2.5 mass% Mo and were subsequently sintered to fabricate a stainless steel containing Mo-rich phases. After sintering, heat treatments were performed at 1573 K (5 h) and 1373 K (0.5 h). It was confirmed that Mo- and Cr-enriched secondary phases were generated. Potentiodynamic polarization was conducted in 0.1 M NaCl. The pitting potential of the stainless steel containing Mo-rich phases was higher than that of the commercial type 316L sheet (non-sintered steel). The results of this study clearly indicate that the existence of Mo-rich phases in sintered stainless steels improves their pitting corrosion resistance, making them highly suitable for use in chloride environments.

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