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

MATERIALS TRANSACTIONS Vol. 61 (2020), No. 9

  • Dispersing InP Nanocrystals in Nano-polycrystalline Diamond during the Direct Conversion from Graphite

    pp. 1707-1710

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    DOI:10.2320/matertrans.MT-M2020124

    We disperse InP nanocrystals into nano-polycrystalline diamond during the direct conversion from graphite as a possible technique to control its solid-state properties. We synthesize diamond, using the high-pressure, high-temperature technique, which encapsulates an InP alloy in close contact with the graphite starting material. X-ray diffraction of the synthesized sample suggests the formation of polycrystalline diamond where the mixed crystals contain InP. Cross-sectional transmission electron microscopy shows the existence of InP nanocrystals with sizes up to approximately 100 nm. The existence of the InP elements can promote the formation of larger crystalline diamond grains arising from liquid sintering, which show a larger grain size over 400 nm compared with the regions without InP, where a grain size of approximately 50 nm is observed.
  • Effect of Nb on Thermal-Shock Resistance of Austenitic Heat Resistant Cast Steel

    pp. 1711-1716

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    DOI:10.2320/matertrans.MT-M2020121

    The effect of Nb on microstructure and thermal-shock resistance was investigated for as cast and annealed JIS SCH21 steels. Primary NbC carbide were crystallized together with M23C6 at grain boundary in as cast steel. Decomposition of primary M23C6 was detected, while NbC was also hardly decomposed when annealed at elevated temperature. It was found that chromium carbides had low thermal stability but primary NbC carbides played a role in preventing propagation of micro-cracks and restraining shape deformation under condition both heating and quenching. As a result, thermal-shock resistance was improved in the Nb-added steel. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 474–478.
  • Mixing Entropy of Exact Equiatomic High-Entropy Alloys Formed into a Single Phase

    pp. 1717-1726

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    DOI:10.2320/matertrans.MT-M2020141

    Exact equiatomic high-entropy alloys (EE-HEAs) comprising N elements (N ≥ 5) formed into a single phase with either bcc, fcc or hcp structure were investigated based on sub-regular solution model. The analysis was performed by utilizing relationships among Gibbs energy (G), enthalpy (H), entropy (S), absolute temperature (T) and pressure (P), G = HTS and S = −(∂G/∂T)P, for representative EE-HEAs, such as bcc-MoNbTaVW, fcc-CoCrFeMnNi and hcp-EE-HEAs comprising heavy lanthanides with and without Y. Mixing entropy (Smix) was evaluated as the sum of excess entropy (Sexcess) and ideal entropy (Sideal), the latter of which is equivalent to configuration entropy (Sconfig). Calculation tools contained commercial software (Thermo-Calc 2020a) using a database for HEAs (TCHEA4) mainly for the bcc- and fcc-EE-HEAs and that for solid solutions (SSOL5) for the hcp-EE-HEAs. The analysis revealed that the bcc-MoNbTaVW and NbTaTiVW HEAs exhibited the greatest decrease in Smix normalized with gas constant (R) down to approximately 87% of Sideal/R = ln N due to a positive T dependence of interaction parameter, Ωi−j(T), of i-j atomic pairs in mixing enthalpy (Hmix). In contrast, Smix/R of the fcc-CoCrFeMnNi HEA was approximately 9% greater than ln N. The hcp-EE-HEAs from a class of athermal solutions behaved as ideal solutions in practice. The results revealed that a relationship of Smix/R = ln N does not always hold in EE-HEAs.
  • Nanocrystalline TiO2 Powders Prepared by Xerogel Hydrothermal in Water: Characterization Photocatalytic Oxidation of Acetone

    pp. 1727-1730

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    DOI:10.2320/matertrans.MT-M2020142

    Cu/N-codoped TiO2 was able to degrade solution under light irradiation with significantly. However, the photocatalytic activity of acetone gas-phase seldomly reported. In this research, we have developed novel method to photooxidation of acetone. The photocatalytic efficiency of different Cu/N-codoped TiO2 powders, prepared by a novel modified hydrothermal method at different temperatures, has been evaluated through the Cu/N-codoped TiO2 photo sensitized degradation of acetone. The as prepared samples were studied for their physicochemical property using XRD, SEM, UV-vis and N2 sorption analysis. Results indicated that when the temperature below 220°C, Cu/N-codoped TiO2 facilitated formation and stability of anatase and brookite phase. The sample prepared in 150°C (Ti–H2O-150) exhibited highest surface area and photo-absorption in the visible light region. The sample prepared in 150°C (Ti–H2O-150) shows highest photocatalytic activity (80.4%) with a rate constant k = 1.62 × 10−2. Cu/N-codoped TiO2 can be considered as a promising visible light-sensitized photocatalysts for removing acetone.
  • Effects of Process Parameters on the Microstructure and Hardness of Semi-Solid AlSi9Mg Aluminum Alloy Prepared by RAP Process

    pp. 1731-1739

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    DOI:10.2320/matertrans.MT-M2020088

    This paper investigated the microstructure and hardness of the cold rolled AlSi9Mg aluminum alloy after the heating at different maintained (semi-solid) temperatures with different duration times. The effects of process parameters on the microstructural evolution and hardness of semi-solid alloy were investigated. Results showed that the increase in the maintained temperature enlarged both the average grain size and the shape factor. The average grain size also increased when the duration time increased. The shape factor increased first and then decreased with the increase in the duration time at the maintained temperature of 560 and 565°C. However, the shape factor kept improved with increasing the duration time at the maintained temperature of 570°C. The coarsening of solid grains in the microstructure resulted from the coalescence and Ostwald ripening mechanisms. The latter one played a more significant role when the maintained temperature or the duration time increased. The hardness of semi-solid AlSi9Mg alloy decreased with the increase in the duration time or the temperature. The parameters in the Hall-Petch and the Lifshitz-Slyozov-Wagner relationships for the semi-solid alloy were identified. The coarsening rate of solid grain at 560, 565 and 570°C were 85.47, 1177.93 and 1357.2 µm3/s, respectively.
  • Influence of Morphology of Cementite on Kinetics of Austenitization in the Binary Fe–C System

    pp. 1740-1749

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    DOI:10.2320/matertrans.MT-M2019342

    When a binary Fe–C alloy with the ferrite (α) and cementite (θ) two-phase microstructure is isothermally annealed at a certain high temperature for the single-phase region of the austenite (γ) phase, the γ phase is produced at the α/θ interface by the reactive diffusion between the α and θ phases. Usually, this phenomenon is called austenitization. Owing to austenitization, the θ phase will completely dissolve into the γ phase at sufficiently long annealing times. For the flat plate of the γ phase produced between the α and θ lamellae, the one-dimensional diffusion of C occurs along the direction normal to the α/γ and γ/θ interfaces. In contrast, for the spherical particle of the θ phase distributed in the matrix of the α phase, the θ phase particle is covered with a spherical shell of the γ phase. In such a case, the three-dimensional diffusion of C in the spherical coordinate system occurs along the radial direction. The kinetics of the C diffusion is different from each other between the one-dimensional and three-dimensional coordinate systems. Consequently, the morphology of the θ phase will influence the growth behavior of the γ phase. To examine such influence, the dissolution of the θ phase was theoretically analyzed using kinetic models under various assumptions. On the basis of the analysis, the time-temperature-dissolution (TTD) diagram was constructed for each shape of the θ phase. This diagram provides quantitative information on the relationship between the dissolution time and the annealing temperature. According to the TTD diagram, the dissolution of the θ phase into the γ phase takes place much faster for the spherical morphology than for the flat one.
  • Mechanism of White Band (WB) Formation due to Rolling Contact Fatigue in Carburized SAE4320 Steel

    pp. 1750-1759

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    DOI:10.2320/matertrans.MT-M2020133

    We investigated the microstructural changes in carburized steel due to high stress rolling contact fatigue (RCF) in this study. The changes consisted of the formation of white bands (WBs), including the low angle bands (LABs) and high angle bands (HABs), following the formation of a dark etching area (DEA) in the bearing steels below the contact surface. Although several studies have analyzed the characteristics of WBs, their formation mechanism has not been sufficiently elucidated. We analyzed the orientation of the crystal constituting the WBs and investigated their relationship with the direction of the shear stress generated by the rolling contact. The morphology of the WBs as a function of depth from the surface was studied using an optical microscope, and the crystal orientation was analyzed using scanning electron microscopy–electron backscattering diffraction. It was found that the LABs and HABs respectively formed at a depth where the principal and orthogonal shear stresses were at their maximum. The results of the crystal orientation analysis revealed that the crystal were rotated under the principal shear stress at a specific depth, resulting in the formation of textures such as {111}〈211〉 and {122}〈411〉 in LABs and HABs, respectively. Thus, the WBs were revealed to be a type of shear band. The WB formation behaviors of the specimens with varying amounts of initially retained austenite (γR) were compared to elucidate the sub-surface initiated spalling life improvement mechanism of the γR. However, the WB formation behavior showed no difference regardless of the amount of initial γR. This suggested that the WB formation was not directly related to the sub-surface initiated spalling life. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 388–397. The captions of Fig. 1–10, 12–16 are slightly changed.
  • Effect of Weld Line Direction on Tensile Deformation Behavior —Development of Forming Technology for Tailor-Welded Blank Application 2nd Report—

    pp. 1760-1766

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    DOI:10.2320/matertrans.P-M2020835

    The stretch flangeability of tailor-welded blank depends on the angle between weld line and the tangential line of blank edge, which is generally the tensile direction in stretch flanging. This effect was studied by uniaxial tensile testing of tailor-welded high-strength-steel specimens with a weld line at 45, 60, or 90 degrees from the tensile direction. The 60-degree-weld-line specimen provides the highest elongation at the maximum load. This is the angle at which the strain component in the weld-line direction is close to zero. At the other angles, the weld lines, of which hardness sufficiently increases by welding, play a role as a constraint for vicinal base metal. This leads to early strain localization and low elongation. Furthermore, the elongation at the maximum load can, in some cases, exceed the uniform elongation of base metal. This is pronounced by a base metal with a low n-value. This Paper was Originally Published in Japanese in J. JSTP 59 (2018) 209–214.
  • Development of a Numerical Simulator for 3-D Dynamic Fracture Process Analysis of Rocks Based on Hybrid FEM-DEM Using Extrinsic Cohesive Zone Model

    pp. 1767-1774

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    DOI:10.2320/matertrans.Z-M2020833

    The combined finite-discrete element method (FDEM) is one of the promising hybrid methods that has attracted much interest for the numerical simulations of complex fracture processes of rocks. The mainstream FDEM simulators developed to date are based on the intrinsic cohesive zone model (ICZM) in which cohesive elements are inserted into all the boundaries of continuum solid elements at the onset of simulations, and a penalty elastic behavior must be incorporated to model the intact deformation of rocks. However, previous studies have not systematically discussed the effect of the introduction of the penalty elastic behavior on the precision of intact stress wave propagation, and this paper discusses this concern. This paper applies an FDEM based on the extrinsic cohesive zone model (ECZM) as an alternative to the FDEM(ICZM). An advantage of the FDEM(ECZM) is first presented through a three-dimensional (3D) numerical modeling of a dynamic tension test. In addition, the effect of considering the anisotropy of wave propagation in granite, which has been neglected in all the previous works using the FDEM, is investigated through the 3D FDEM(ECZM) simulation of a dynamic Brazilian test using a split-Hopkinson pressure bar apparatus. Through the presented numerical simulations, we can conclude that the FDEM(ECZM) is a useful alternative to FDEM(ICZM) for numerical simulations of complex dynamic fracture processes of rocks. This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Japan 69 (2020) 228–235.
  • Effect of Formic Acid on Corrosion Behavior of STBA24 Low-Alloyed Steel and Its Weldment in Simulated Boiler Water Containing Chloride Ions

    pp. 1775-1781

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    DOI:10.2320/matertrans.MT-M2020129

    The effect of formic acid (HCOOH) in simulated boiler water containing chloride ions (Cl) on the corrosion behavior of STBA24 low-alloyed steel and its weldment was investigated using electrochemical corrosion tests, immersion corrosion tests and surface analyses. The addition of 100 ppm HCOOH into water containing 100 ppm Cl resulted in thicker films with poor corrosion resistance that were formed easily on both the base metal and the weldment of STBA24, even though pit initiation was inhibited within a short time. The results suggest that the presence of 100 ppm formic acid in the simulated boiler water containing 100 ppm chloride ions promotes corrosion of the materials tested.
  • Characterization of the Compressive Stress Drop in the Plateau Region in Porous Metals with Unidirectional Pores

    pp. 1782-1789

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    DOI:10.2320/matertrans.MT-M2020138

    A drop in compressive stress in the plateau region is one of the issues in compressive behavior of porous metals since it has a negative effect on energy absorption efficiency. The compressive deformation behavior of porous aluminum with irregular unidirectional pores was investigated to clarify the mechanism of the drop. Compression tests of cubic specimens with various irregular circular pore geometries were performed. Digital image correlation and finite element analysis were also conducted to obtain strain and stress distribution of the surface perpendicular to the pores. Fracture of the cell walls was observed when the drop occurred. The results show that pore geometry has an effect on the number and the amount of drop in compressive stress. Measurement of an area of two nearest pores of the fractured cell walls suggests that the amount of drop in compressive stress increases as the area increases. Also, a calculation of normalized critical stress for the plastic collapse of the cell walls shows that the fractured cell walls tend to be geometrically weak. Furthermore, stress concentration occurred around the fractured cell walls, which resulted in a secondary fracture of the cell walls.
  • Investigations on Manufacturing of Magnesium Alloy Powder by Air Atomization

    pp. 1790-1797

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    DOI:10.2320/matertrans.Y-M2020834

    We investigated the possibility of atomizing a molten magnesium (Mg) alloy by air instead of argon gas in order to manufacture the powder at a low cost. As a result, we obtained a powder from a molten Mg alloy containing yttrium (Y), calcium (Ca) or aluminum (Al) by air atomization without combustion. Each powder had an approximately 100-nm thick oxide film with condensed Y, Ca or Al, which can make the oxide film dense enough to isolate the molten Mg alloy droplet surface from air. In the case of Al, 6 mass%Al or more was required to prevent combustion. Al was also condensed in the matrix near the interface with the oxide film, which can reduce the Mg vapor pressure on the matrix surface under the oxide film. A high cooling rate of the droplet is also effective to prevent combustion. As air-atomized AZX912 powder has the same matrix structures as the argon-gas-atomized one, we expect that the sintered parts of the air-atomized Mg alloy powder can be obtained by breaking the oxide film during the forming and sintering process. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 66 (2019) 485–492.
  • Influence of Al Concentration and Zn Addition on the Corrosion Resistance of Rolled Mg–Al–(Zn)–Ca Magnesium Alloys

    pp. 1798-1804

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    DOI:10.2320/matertrans.L-M2020839

    The effects of Al concentration and Zn addition on the corrosion resistance of Mg–Al–(Zn)–Ca-based magnesium alloy rolled sheets were investigated. AXM (Mg–Al–Ca) alloys containing 1 mass% Ca and AZX (Mg–Al–Zn–Ca) alloys containing 1 mass% Ca plus 1 mass% Zn with the Al concentration adjusted to 6, 7, 8, 9, and 11 mass% were prepared. The corrosion behaviors of the alloys in a 5 mass% NaCl solution were evaluated by weight loss and the penetration depth. Electrochemical methods based on corrosion potential measurements and impedance spectroscopy was applied to monitor the corrosion behavior. The hydroxide film formed on the alloy surface was characterized by GDOES and SEM/EDS. The AXM alloy with an Al content of approximately 8 mass% exhibited minimum corrosion rate, whereas the AZX alloy showed the opposite result in the same concentration range of Al. This phenomenon was analyzed in terms of the Al concentration in the matrix (α-phase), which was reduced by the precipitation of Mg17Al12 (β-phase) and the presence of Zn. The tendency of localized corrosion in high Al-containing AZX alloys was pointed out. This Paper was Originally Published in Japanese in J. JILM 70 (2020) 56–62. The caption of Fig. 3 is slightly modified.
  • Reduction Characteristics of Pure Gale Limonite Pellets in Gaseous Environments

    pp. 1805-1812

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    DOI:10.2320/matertrans.MT-M2019311

    In this study, the isothermal reduction mechanism of limonite, an important iron ore resource, in H2, CO, and a mixed atmosphere of both gases was studied as a function of reduction temperature and gas composition. The kinetics of the reduction process were studied using a shrinking kernel model. The experimental results show that the degree of reduction of the oxidized pellet particles increases with increases in both reduction time and temperature. Also, it has been found that an increase in the ratio of H2/(H2 + CO) and an increase in temperature result in shortened reduction times. During the reduction process, the kinetic studies show that the early stage of the gas reduction process is controlled by the interfacial chemical reaction and later stages are controlled by diffusion. SEM results show that the particles reduced in the H2 atmosphere have many micropores. Providing a gas passage during the reduction process reduces the gas diffusion resistance and promotes the diffusion reaction.
  • Effects of Heat Treatment on the Structures and Wear Behaviors of HVOF-Sprayed Ni–MoS2 Coatings

    pp. 1813-1819

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    DOI:10.2320/matertrans.MT-M2020108

    Numerous studies have addressed the augmentation of the hardness and tribological properties of material surfaces with the aim of diminishing the wear. However, there is significant scope for further enhancing the performance of self-fluxing nickel alloys utilized as abrasion-resistant coatings. In this work, Ni–MoS2 powders were prepared by electroless plating, and high-velocity oxy-fuel (HVOF) spraying was used to prepare low-coefficient-of-friction coatings with these powders. The coatings were then subjected to heat treatment. Various surface analysis techniques including hardness testing, scanning electron microscopy, and X-ray fluorescence were subsequently used to characterize the compositions and mechanical properties of the composite HVOF coatings. In addition, ball-on-disc tests were performed under dry abrasive conditions on specimens that were heat treated at different temperatures according to the ASTM G99 standard. The wear of each specimen was evaluated, and the measurements were used to provide a comprehensive assessment of the coating’s wear resistance. When the Ni–MoS2 composite coating was heat treated at 500°C, the growth of MoO2 crystals evaporates from the surface, and condenses on the protruding oxide crystals, which led to an increase in porosity and structural looseness. Consequently, the hardness and structural strength of the coating decreased significantly, dramatically increasing its wear loss. The HVOF Ni–MoS2 composite coatings are suitable for high-temperature abrasion environments with temperatures below 500°C, and an operating temperature of 500°C or higher should be avoided to maintain its hardness, structural strength, and wear resistance.
  • Investigation of Refractory Corrosion by Na2O–B2O3 Flux and Its Ability of Dissolving of Mn Oxides during a Melting Process for a Copper Alloy in the Atmosphere, Including Mn as Easily Oxidized Element

    pp. 1820-1828

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    DOI:10.2320/matertrans.MT-M2020084

    In order to clarify a guideline for designing of composition of a flux which can achieve both minimizing a refractory corrosion by the flux and maximizing of solubility of Mn oxides into the flux, corrosion tests for refractory was conducted in the air atmosphere. The basic composition of flux is Na2O–B2O3 and the refractory is Mullite (3Al2O3·2SiO2), assuming a process of melting of a copper alloy containing Mn as easily oxidized elements. Although the corrosion ratio of refractory became larger with increasing of mole fraction of Na2O in flux, the concentration of refractory’s constituents in the flux have different tendency predicted by the results of corrosion ratio. Through the corrosion test, the Na2O–B2O3 based flux has penetrated inside the refractory with Mn, and a part of that Mn has reacted with Al2O3 to form MnAl2O4. However, in the refractory/flux interface no clear formation of the compound layer could be confirmed due to the reaction between the refractory’s constituents and the flux. In addition, the relationship between the corrosion ratio and the equilibrium solubility of 3Al2O3·2SiO2 for Na2O–B2O3 flux calculated by thermodynamic database was investigated. The result shows that there are not clear relationships between them. The cause of this can be explained by the affection of corrosion inside the refractory by the penetration of the flux through the pores in the refractory. Furthermore, it was shown that the amount of Mn oxide dissolved in the flux was strongly affected by the viscosity of the flux by calculation.Consequently, in order to design a proper composition of flux in this study, it became clear that the thermodynamic approach alone was not enough and a more detailed examinations such as the wettability between the flux and refractory, properties of flux, especially penetration phenomena was also important. This Paper was Originally Published in Japanese in J. Japan. Inst. Met. Mater. 84 (2020) 1–10. Figures 1, 2, 4 and 7 were slightly changed. The references were also changed.
  • Microstructure and Micro-Hardness of Al2O3–TiO2 Coating by Plasma Spraying on SKD61 Steel

    pp. 1829-1832

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    DOI:10.2320/matertrans.MT-MN2019024

    In this research, the modified surface is created by cladding Al2O3 particles with 40% TiO2 particles on an SKD61 steel surface by plasma spraying method. The results indicated that the macrograph of the coating has no cracks, and the coating has an undulating flatness with relatively dark color and distribute uniformly. The coating surface can be divided into three distinct regions: the coating zone, the heat-affected zone, and the SKD61 steel substrate. The coating zone presents a smooth surface and does not have any porous inside it, indicating a good coating film. The microstructure of Al2O3–40%TiO2 coating mainly consists of plasma-spray stacked layers, includes two regions, in which Al2TiO5 phase appeared as gray regions while γ-Al2O3 and α-Al2O3 particles appeared as white regions. The micro-hardness distribution of the coating showed that the average hardness of the Al2O3–40% TiO2 coating reaches the highest number with 816.3 HV0.1, while the heat-affected zone gains a hardness number of 595 HV0.1. Both of these zones’ hardnesses are greatly higher than the hardness of the SKD61 steel substrate with 252.5 HV0.1.
  • Effect of Iron Addition on Corrosion Behavior of Ni20Cr–xFe Alloys in Air Containing NaCl–KCl–CaCl2 Vapor at 570°C

    pp. 1833-1841

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    DOI:10.2320/matertrans.MT-M2020156

    The effect of Fe on the corrosion behavior of Ni20Cr–xFe alloys in an oxidizing chlorine-containing atmosphere using air mixed with the salt vapor mixture of NaCl–KCl–CaCl2 at 570°C was investigated. The results revealed that the corrosion performance of the Ni–20Cr alloys in the oxidizing-chlorine atmosphere was improved by Fe addition. The oxide scale structure formed on all of the alloys containing Fe was similar with that formed on the Fe-free alloy. The potassium chromate and the internal precipitate zone were observed on all of the alloys. However, the internal Cr-chloride penetration and the Cr-depletion zone became thinner on the alloys with Fe addition. The Fe-oxide formed above Cr2O3 scale on the alloys with Fe addition helped Fe inhibit the chromate formation and maintained low chlorine potential at the alloy surface. Thus, a protective Cr2O3 scale can be maintained for a longer corrosion period.
  • Formation of Reaction Layer and Dissolution Behavior of Alkali and Alkaline-Earth Iron Phosphate Glasses in Water

    pp. 1842-1847

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    DOI:10.2320/matertrans.MT-M2020135

    The durability of iron phosphate glasses containing alkali and alkaline-earth oxides in water was investigated using two methods: materials characterization center (MCC)-2 static, leach test at 120°C for plate samples and product consistency test (PCT) at 90°C for granulated samples. The glass samples were classified into two types depending on the macroscopic appearance of the reaction layers, giving rise to interference colors formed on the glass surface after the MCC-2 test. The type I glasses had reaction layers with macroscopic cracks for the Li2O- or Na2O-containing iron phosphate (IP) glasses. Their weight loss per specific area showed a linear relation with immersion time due to the degradation of the protective layer. The type II glasses, on the other hand, exhibited superior water durability as a result of formation of the homogenous reaction layers for the K2O-, CaO-, and BaO-containing IP glasses. The main cations released into the water in the PCT method included alkali, alkaline-earth, and phosphorous elements for both type I and II glasses. The Raman spectroscopy results suggested that the macroscopic cracks formed in the reaction layers for type I glasses are attributed to the microscopic selective dissolution of Q2 phosphate tetrahedra in the glass matrix.
  • Pd-Dispersed CeO2 Catalyst Prepared from Dealloying the Pd–Ce–Al Ternary Amorphous Alloy Used for Oxidation Reaction

    pp. 1848-1852

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    DOI:10.2320/matertrans.MT-M2020139

    The relationship between preparation method and the catalytic activity as well as reusability for Pd–CeO2 catalyst was investigated. Pd-dispersed CeO2 prepared from dealloying in NaOH aqueous solution of a Pd–Ce–Al ternary amorphous alloy as a precursor. The dealloying proceeded by active dissolution of Al and Ce to form sodium aluminate ion, Na[Al(OH4)](aq), and CeO2 particles, respectively. At the same time, Pd acting as cathode resulted in directly to be metallic nailed-particles exposing partly from the matrices of the CeO2 particles. Its catalytic activity and reusability as a function of its surface area of exposed-Pd as well as sample surface area were investigated, compared with those of Pd-supported CeO2 which was prepared by conventional liquid phase reduction. Pd-dispersed CeO2 was higher in exposed Pd surface area than Pd-supported CeO2 despite its lower sample surface area. It is likely that the nailed Pd on the CeO2 prevents themselves from aggregation during sample preparation and reusability study. As a result, in the oxidation reaction of methyl benzyl alcohol, Pd-dispersed CeO2 showed higher catalytic activity and reusability than Pd-supported CeO2. The oxidation reaction of methyl benzyl alcohol is a measure of the oxidative decomposition reaction of harmful substances. Pd-dispersed CeO2 is expected to be widely used for the oxidative decomposition reaction of harmful substances.
  • Electron Microscopy on Cu Element Distribution in Spheroidal Graphite Cast Iron

    pp. 1853-1861

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    DOI:10.2320/matertrans.F-M2020836

    The solidification microstructure of spheroidal graphite cast iron was analyzed by electron probe micro analysis (EPMA) and scanning transmission electron microscopy (STEM), focusing on the distribution of Cu. EPMA and STEM results clarified the following tendency in the distribution of Cu in spheroidal graphite cast iron containing Cu within the pearlite matrix: (1) Cu–Sn–Mg enriched regions were distributed in the pearlite matrix, and (2) the distribution of metallic elements of Cu, Sn, and Mg in Cu–Sn–Mg enriched regions was not homogeneous, and a composite of the metallic and oxide phases was formed. EPMA with a field-emission electron gun (FE-EPMA) and FE-STEM apparatus with a silicon drift detector were highly effective in clarifying the distribution of Cu, compared with conventional EPMA employing a thermionic-emission electron gun (TE). The high-resolution observation using FE-STEM, and the combination with TE-EPMA, FE-EPMA and FE-STEM, are powerful tools for clarifying the distribution of Cu element in spheroidal graphite cast iron. This Paper was Originally Published in Japanese in J. JFS 91 (2019) 512–520. Minor corrections in abstract, main text, figure and table captions, and references were performed with translation from Japanese to English and proofreading by native speakers. Reference 18) was replaced from “H. Ito, I. Narita, H. Miyahara: Reports of JFS meeting, 170 (2018) 4.” to “H. Miyahara, G. Ito, I. Narita: J. JFS 91 (2019) 703–709.”
  • Reduction of Elongation Anisotropy in Cold-Rolled and Annealed Al–7% Si Alloy Strips Fabricated by Vertical-Type High-Speed Twin-Roll Casting

    pp. 1862-1867

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    DOI:10.2320/matertrans.F-M2020837

    Vertical-type high-speed twin-roll casting is a candidate method to realize up-grade recycling of aluminum, in which cast alloy is used to produce wrought alloy products due to its rapid solidification. Using A356 aluminum alloy (Al–Si–Mg) strips to produce wrought alloy sheets requires isotropy and high ductility for good formability. However, the elongation of the cold-rolled and annealed A356 strips after vertical-type high-speed twin-roll casting is different in the rolling direction (RD) and the transverse direction (TD) of the strips. In this study, strips of pure Al, Al–2% Si, and Al–7% Si alloys were fabricated by vertical-type high-speed twin-roll casting to investigate the effect of eutectic Si particles on the elongation anisotropy of the cold-rolled and annealed strips. The effect of increasing the rolling reduction rate of the strips on the reduction of the elongation anisotropy was examined. Elongation anisotropy was not observed in pure Al, whereas it was observed in Al–2% Si and Al–7% Si, and it was more pronounced in Al–7% Si. Although the eutectic Si particles were randomly distributed in the RD cross section, they were oriented in the RD in the TD cross section. When the strip was loaded in the TD, the voids that formed around the eutectic Si particles were often connected perpendicular to the load direction during the tensile test, and the elongation decreased. To reduce the elongation anisotropy, it is necessary to create a uniform distribution of eutectic Si particles in both the RD and TD cross sections. Tandem vertical-type high-speed twin-roll casting was used to fabricate a thick strip while maintaining the rapid cooling rate. In the clad strips, elongation increased in the TD, and the elongation anisotropy was reduced. Anisotropy was not observed in the five-layer clad strip because the eutectic Si particles were uniformly distributed by the increase in the rolling reduction rate due to the increase of the initial strip thickness.
  • Cu2O Nanoparticles: A Simple Synthesis, Characterization and Its Photocatalytic Performance toward Methylene Blue

    pp. 1868-1873

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    DOI:10.2320/matertrans.MT-MN2019039

    Cuprous oxide nanoparticles (Cu2O-NPs) were fabricated by a simple solution-phase reduction route with a one-step reduction method. The used original chemicals were the copper sulfate and the sodium sulfite. The physicochemical properties of Cu2O-NPs were investigated by different methods such as XRD, Raman, SEM, and UV-Vis spectra. The results show that the molar ratio of precursors ([CuSO4]/[Na2SO3]) not only affects crystal structure and morphology but also affects the crystallinity of crystals and optical characteristics of Cu2O-NPs samples. The photocatalytic activity of Cu2O-NPs was evaluated by the removal of methylene blue (MB) aqueous solution under visible light irradiation. The result shows that good photocatalytic activity with the MB degradation is higher than 98% under visible light irradiation for 40 minutes and the rate constant of 0.11281 min−1.
  • Prediction of Face-Centered Cubic Single-Phase Formation for Non-Equiatomic Cr–Mn–Fe–Co–Ni High-Entropy Alloys Using Valence Electron Concentration and Mean-Square Atomic Displacement

    pp. 1874-1880

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    DOI:10.2320/matertrans.MT-M2020144

    We have investigated the face-centered cubic (FCC) single-phase formability of non-equiatomic Cr–Mn–Fe–Co–Ni HEAs as well as equiatomic derivative medium/high-entropy alloys (M/HEAs) considering their valence electron concentration (VEC) and mean-square atomic displacement (MSAD). While VEC remains the most decisive parameter to predict phase formation, MSAD can be a complementary parameter that modifies the VEC boundary. Multiplicity of constituent elements was beneficial to accommodate a larger MSAD, which resulted in a downward shift of the VEC boundary for the FCC single phase. This offers information about the correlations between the phase formation preference, VEC, and MSAD of M/HEAs with various compositions.
  • Corrosion Behavior of Diecast Mg–Al–Mn–Ca–Si Magnesium Alloy

    pp. 1881-1888

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    DOI:10.2320/matertrans.MT-M2020059

    The corrosion behavior of diecast Mg–Al–Mn–Ca–Si (AMXS6020) magnesium alloy with superior flame-retardance and heat-resistance was systematically investigated and compared to diecast AZ91D magnesium alloy and ADC12 aluminum alloy by salt spray test, cyclic corrosion test, electrochemical experiment, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results showed that AMXS6020 alloy had a higher corrosion resistance than AZ91D and ADC12 alloys. The superior corrosion resistance of AMXS6020 alloy was attributed to netlike eutectic structure consisting of (Al, Mg)2Ca and α-Mg, which could hinder the corrosion growth. The barrier effect of netlike (Al, Mg)2Ca phase structure on corrosion growth was also confirmed by potentiodynamic polarization.
  • Evaluation of Deterioration Damage for Liquid Oxygen/Hydrogen Combustion Chamber of Copper Alloy by Replica Method for Oxide Film

    pp. 1889-1893

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    DOI:10.2320/matertrans.MT-M2019386

    Non-destructive damage evaluation of rocket engine combustion chambers was carried out using a replica method that employs a rapid-setting silicone rubber molding agent. Scratch marks, grinding marks and the oxide film on the combustion side surface that developed after repeated burning tests were successfully transferred to a silicone rubber sheet, eliminating any need for complex surface treatment before examination. The sampled replicas showed traces of oxide film formation and the disappearance of the grinding marks and crack formations on the oxide films caused by to redox reactions during repeated use. The surface roughness of the light and dark lines parallel to the cooling channels and cracked oxide film was evaluated by laser scanning microscopy. We found the surface roughness parameter to be potentially useful for evaluating the level of damage sustained by reusable sounding rocket engines. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 176–180. Equation (2) and the captions of Figs. 1, 3, 4, 6, 7 were slightly changed.

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