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MATERIALS TRANSACTIONS Vol. 61 (2020), No. 3

ISIJ International
belloff
ONLINE ISSN: 1347-5320
PRINT ISSN: 1345-9678
Publisher: The Japan Institute of Metals and Materials

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MATERIALS TRANSACTIONS Vol. 61 (2020), No. 3

AC Impedance Measurement and Electron Holography of Ionic Liquid in a Transmission Electron Microscope

Yoh Iwasaki, Ken Harada, Keiko Shimada, Manabu Shirai, Daisuke Shindo

pp. 423-429

DOI:

10.2320/matertrans.MI201903

Abstract

Alternating current (AC) impedance measurements were performed with ionic liquid (IL) specimens to study feasibility of in-situ characterization method for conductive and dielectric properties of materials in a transmission electron microscope (TEM). A bridge-shaped IL specimen was prepared between two molybdenum (Mo) probe tips in a TEM, and was exposed to electron beam. The repeated AC impedance measurements during the irradiation revealed that the conductance of the IL bridge decreased faster at higher frequencies. Electron holography around the IL before and after the electron irradiation revealed enhanced charging after the irradiation, which is consistent with the loss of conductance by the irradiation. AC impedance measurement and electron holography are compatible with TEM to complementarily provide dynamic transport properties and potential distribution of a specimen.

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AC Impedance Measurement and Electron Holography of Ionic Liquid in a Transmission Electron Microscope

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Ductility Improvement Mechanism of Ti–6Al–4V+O Sintered Material

Kento Kamiyama, Shota Kariya, Mizuki Fukuo, Junko Umeda, Katsuyoshi Kondoh

pp. 430-437

DOI:

10.2320/matertrans.Y-M2019869

Abstract

The previous study indicated powder metallurgy (PM) Ti-64 alloys with oxygen showed the increment of not only their tensile strength but elongation. This study investigated the elongation improvement mechanism of Ti-64 alloys with oxygen atoms. The mix of Ti-64 alloy powder and TiO2 particles (0∼0.4 mass%) was used as starting materials and consolidated by spark plasma sintering (SPS). The following heat treatment in vacuum was applied to sintered materials. β transus temperature increased by oxygen addition because it was one of α-phase stabilizer elements. Prior-β grains size and aspect ratio of α-Ti grains were changed by heat treatment conditions. For example, Ti-64+O alloys after heat-treated at β-phase temperature range showed acicular α-Ti grains with a large aspect ratio (6.1∼7.0) although those with heat treatment at α+β-phase temperature had α-grains with a small aspect ratio of 3.3∼4.0. These grain morphology changes strongly depended on the temperature of heat treatment, not oxygen contents. In addition, the latter materials indicated high elongation (16∼17%) compared to the former with 9∼10%. When Ti-64+O alloy specimens after tensile test were analyzed by SEM-EBSD, Kernel average misorientation (KAM) maps showed many plastic strains induced in small aspect ratio α-Ti grains. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 65 (2018) 699–706.

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Elemental Distribution near the Grain Boundary in a Nd–Fe–B Sintered Magnet Subjected to Grain-Boundary Diffusion with Dy2O3

M. Itakura, M. Namura, M. Nishida, H. Nakamura

pp. 438-443

DOI:

10.2320/matertrans.MT-M2019265

Abstract

We have investigated the microstructure in a Nd–Fe–B sintered magnet subjected to the grain-boundary diffusion (GBD) process with Dy2O3. It was found that thin (Nd,Dy)2Fe14B shells with a thickness of at least 10 nm and an average Dy concentration of approximately 0.7 at% were formed even at the center of the specimen, at a depth of approximately 1 mm from the specimen surface. However, the area fraction of the fcc NdO phase remained almost constant at approximately 3% throughout the magnet irrespective of depth, and the grain-boundary wetting phase hardly changed except in the vicinity of the surface. Furthermore, the thickness (ca. 3 nm) and structure (amorphous) of the thin grain boundary phase existing between Nd2Fe14B grains remained almost unchanged by the Dy-GBD process, despite the formation of the core–shell structure. Therefore, the Dy concentration in the thin Dy-substituted shell is important for improving the coercivity via the GBD process.

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Elemental Distribution near the Grain Boundary in a Nd–Fe–B Sintered Magnet Subjected to Grain-Boundary Diffusion with Dy2O3

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Effect of Ultrasonic Radiation on the Grain Refinement of High Purity Aluminum

Ruiquan Wang, Haijun Huang

pp. 444-448

DOI:

10.2320/matertrans.MT-M2019296

Abstract

Effect of high-intensity ultrasonic irradiation on solidified structure of high purity aluminum was studied. The results reveal that the solidified structure was obviously divided into two regions: an effectively refined region I and a poorly refined region II. Cavitation induced nucleation was considered acting as a leading role in causing the final refinement. Re-distribution of cavitation induced nuclei by acoustic flow resulted in the cone-shape of the region I filled with remarkable columnar crystals.

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Effect of Ultrasonic Radiation on the Grain Refinement of High Purity Aluminum

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Deposition-Temperature Dependence of Vortex Pinning Property in YBa2Cu3O7+BaHfO3 Films

Tomoya Horide, Kenta Torigoe, Ryusuke Kita, Ryota Nakamura, Manabu Ishimaru, Satoshi Awaji, Kaname Matsumoto

pp. 449-454

DOI:

10.2320/matertrans.MT-M2019303

Abstract

Improvement of critical current density (Jc) in magnetic fields is required in YBa2Cu3O7 films, and process parameters should be optimized for controlling pinning centers. In the present study, a deposition temperature was varied in pulsed laser deposition of YBa2Cu3O7+BaHfO3 films to control the nanorod structure, and its influence on Jc was analyzed. The YBa2Cu3O7+BaHfO3 film deposited at 850°C exhibited pinning force maximum (Fp,max) as high as 413 GN/m3 at 40 K, while the Fp,max for the deposition temperature of 850°C at 77 K was smaller than that in the YBa2Cu3O7+BaHfO3 film deposited at 900°C. A critical temperature decreased and matching field increased with decreasing the deposition temperature. Increase in deposition temperature is effective in improving the Fp,max in high temperatures, since the critical temperature and matching field dependences of Jc value dominate the Fp,max. On the other hand, low deposition temperature improves the Fp,max in low temperatures since the Fp shift in accordance with matching field is dominant to the Fp,max. Thus, the deposition temperature should be set in pulsed laser deposition of YBa2Cu3O7 films containing nanorods considering the Jc variation with critical temperature and matching field. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 320–326.

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Deposition-Temperature Dependence of Vortex Pinning Property in YBa2Cu3O7+BaHfO3 Films

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Effect of Homogenization and Extrusion on Microstructure and Mechanical Properties of Cladding Billet by Cladding Casting

Pin-Feng Jia, Xing Han, Wenbin Li, Hai-tao Zhang, Jian-Zhong Cui

pp. 455-461

DOI:

10.2320/matertrans.MT-M2019234

Abstract

An AA4032/AA6069 cladding billet, fabricated by cladding casting process, was homogenized at 520°C for 12 h and then indirectly extruded into cladding pipe. The evolution in interfacial region was investigated in detail by the methods of optical microscope (OM), field emission electron scanning microscope (FESM), Vickers hardness, tensile and shear test. The interface region maintained original layered structure during the homogenization and extrusion process. During the process of homogenization, the eutectic silicon phases in AA4032 and Mg2Si in AA6069 became rounded markedly but still distributed dendritically. The homogenization improved the Vickers hardness and tensile strength of the interface region due to the precipitation strengthening and solution strengthening benefiting by element diffusion, and rarely affected the interfacial shear strength. The eutectic silicon and Mg2Si were spherized further and transformed into dispersive particles after extrusion process. Compared with that before deformation, the hardness of interface region got an obvious increase. The process of cladding casting and indirect extrusion is an idea method to fabricate cladding pipe.

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Effect of Homogenization and Extrusion on Microstructure and Mechanical Properties of Cladding Billet by Cladding Casting

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Formation of Spherical, Rod- and Branch-Shaped Colloidal In2O3 Nanocrystals through Simple Thermolysis of an Oleate Precursor

Satoshi Tsukuda, Hideo Uesugi, Masao Kita, Takahisa Omata

pp. 462-468

DOI:

10.2320/matertrans.MT-M2019245

Abstract

Synthesis of colloidal indium(III) oxide (In2O3) nanocrystals (NCs) by a simple non-injection method, using indium(III) oleate as an indium and oxygen source, was studied under conditions of various precursor concentrations, reaction temperatures and times. In the case of using a solution with a low precursor concentration, spherical In2O3 NCs that exhibited high crystallinity were successfully obtained. Their size was easily controllable in the range of 4 to 6 nm in diameter by changing the reaction temperature and time. Because the growth of the spherical NCs was developed by the precipitation of new In2O3 components from solution and not by Ostwald ripening, the obtained NCs exhibited a narrow size distribution and were almost monodispersed. In contrast to the case of using a solution with a low precursor concentration, rod- and triple-fork-shaped NCs were obtained in the case of using a solution with a high precursor concentration. Formation of the rod- and triple-fork-shaped NCs was attributed to the high growth rate after the nucleation because of the high initial precursor concentration.

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Formation of Spherical, Rod- and Branch-Shaped Colloidal In2O3 Nanocrystals through Simple Thermolysis of an Oleate Precursor

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Effect of Laser Patterning Preprocessing on Fatigue Strength of Adhesive Bonded Joints Using Thin Steel Plate

Katsuki Shikimoto, Shogo Ishida, Wataru Jinnouchi, Yuki Ogawa, Hiroyuki Akebono, Atsushi Sugeta

pp. 469-474

DOI:

10.2320/matertrans.Z-M2019870

Abstract

Reducing the weight of automobile bodies would help counteract environmental problems caused by greenhouse gas emissions by improving fuel efficiency. Multi-material structures have been investigated to construct an automobile body structure composed of steel in combination with lightweight metal materials and carbon-fiber-reinforced plastic. Thus, it is necessary to develop high-quality bonding techniques that can join dissimilar materials as quickly as possible. To this end, adhesive bonding has attracted attention from the viewpoint of building multi-material structures. However, from the viewpoint of durability and reliability, it is regarded as a complementary technique used to support other industrial welding methods. Moreover, to further improve the strength of adhesive bonding, the surface conditions of the adherend must be considered. In this study, to improve the interfacial strength of adhesively bonded joints, laser patterning pre-processing was applied as a surface treatment. The fatigue properties of adhesively bonded joints were evaluated and compared with those of untreated joints. It was found that the static and fatigue strengths of the joints were improved by the laser patterning pre-processing. In particular, the joint strength was improved by removing the weak boundary layer from the entire adhesion surface with laser irradiation. Therefore, the laser patterning pre-processing method proposed in this study is a very promising process for achieving adhesively bonded joints with excellent fatigue properties. This Paper was Originally Published in Japanese in J. Soc. Mater. Sci. Japan 68 (2019) 890–896.

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Effect of Laser Patterning Preprocessing on Fatigue Strength of Adhesive Bonded Joints Using Thin Steel Plate

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Tribological Behaviors of B6O/Si3N4 and B6O/Al2O3 Sliding Pairs in Water

Takashi Murakami, Atsushi Korenaga, Tsuguyori Ohana

pp. 475-481

DOI:

10.2320/matertrans.MT-M2019253

Abstract

In this study, B6O powder compacts were fabricated by spark plasma sintering B6O powder at 1800°C for 600 seconds. We then investigated the microstructures and mechanical properties of the powder compacts and assessed the tribological behaviors of the powder compacts by sliding them against commercially available Si3N4 and Al2O3 bearing balls in water at room temperature. The average friction coefficients of the B6O/Si3N4 sliding pairs were as low as 0.17, while the average friction coefficients of the B6O/Al2O3 sliding pairs gradually increased from 0.10 to 0.18. Also, the B6O/Si3N4 sliding pairs showed slightly more stable friction coefficients with smaller error bars than the B6O/Al2O3 sliding pairs 1200 seconds after starting the friction tests. The specific wear rates of the B6O powder compacts ranged from approximately 2 × 10−6 to 5 × 10−6 mm3/Nm when the Si3N4 and Al2O3 balls were used as the paired materials. We conjectured that the low friction coefficients and low specific wear rates stemmed from the formation of extremely thin H3BO3 films on the wear tracks of the powder compacts.

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Tribological Behaviors of B6O/Si3N4 and B6O/Al2O3 Sliding Pairs in Water

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Crystallographic Orientation and Microstructure Dependences of Surface Potential for Annealed S45C Steel Using Combined Scanning Kelvin Force Probe Microscopy and Electron Backscatter Diffraction Analyses

Yoshiharu Murase, Hiroyuki Masuda, Hideki Katayama

pp. 482-489

DOI:

10.2320/matertrans.MT-M2019338

Abstract

Scanning Kelvin force probe microscopy (SKPFM) and subsequent electron backscatter diffraction (EBSD) measurements were performed across the same area of a ferrite/pearlite microstructure for annealed S45C steel. Larger potential differences were observed at the heterogeneous phase boundaries between cementite and ferrite. The EBSD measurements confirmed the dependence of potential on the crystallographic orientation of the ferrite phases. Specific orientation relationships between ferrite and cementite phases were observed when both phases nucleated in the same pearlite colony, however, such relationships were not valid when nucleation occurred in separate colonies. The heterogeneous phase boundaries exhibiting larger potential differences, in addition to having no specific orientation relationship, could be considered as a highly plausible candidate location for corrosion initiation. Thus, combined SKPFM and EBSD analyses are a powerful technique to improve the evaluation of the corrosion initiation process in ferrite/pearlite microstructures with respect to potential difference and crystallographic orientation relationships.

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Crystallographic Orientation and Microstructure Dependences of Surface Potential for Annealed S45C Steel Using Combined Scanning Kelvin Force Probe Microscopy and Electron Backscatter Diffraction Analyses

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Effect of W Content on the Oxidation and Electrical Behaviors of Co–W Coatings for SOFC Interconnects Fabricated by Electrodeposition

Lu Gan, Hideyuki Murakami, Isao Saeki

pp. 490-496

DOI:

10.2320/matertrans.MT-M2019319

Abstract

Vaporization of Cr species from solid oxide fuel cell (SOFC) interconnectors must be avoided to prevent the degradation of the electrocatalytic activity of cathodes. A diffusion barrier against Cr ions in the thermally grown oxide is required for the prevention of vaporization because the origin of Cr is an interconnector substrate made of ferritic stainless steel. Additionally, the diffusion barrier should not decrease the electron conductivity of the interconnector. We found that a CoWO4 layer formed on type 430 stainless steel (18 mass% Cr) that was covered with a Co–2.4 at% W alloy via the electroplating process. The layer effectively blocked the outward diffusion of Cr because the trivalent Cr ion, Cr3+, cannot penetrate this layer. In this report, further understanding of Co–W electroplated ferritic stainless steels is described. First, a Co–W co-electroplating method with a high W content was developed. The W content increased with increasing W concentration in the bath and with the bath pH, and Co–30 at% W plating was obtained. Then, electroplating was conducted on types 430 and 445 (23 mass% Cr) for the comparative study of oxidation properties. A thick and compact CoWO4 layer was formed on the Co–5 at% W electroplated steel. Excess W in the plating with more than 10 at% W resulted in the formation of a Fe–Co–Cr intermetallic layer, which may cause a decrease in substrate toughness. The structures of the multi-layered oxides that formed on both alloy substrates were similar to each other. The low specific resistance of CoWO4 and the thin Cr2O3 that formed on the coated specimens resulted in the low area-specific resistance of the Co–W-coated specimen at 800°C, and the value was lower than for the uncoated steels. We concluded that Co–5 at% W electroplating on 23 mass% Cr stainless steels is optimal for SOFC interconnectors.

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Effect of W Content on the Oxidation and Electrical Behaviors of Co–W Coatings for SOFC Interconnects Fabricated by Electrodeposition

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Effect of Organic Additives on the Electrodeposition Behavior of Zn from an Alkaline Zincate Solution and Its Microstructure

Kenta Fukumoto, Satoshi Oue, Yoshiharu Kikuchi, Shinya Akamatsu, Tomio Takasu, Hiroaki Nakano

pp. 497-505

DOI:

10.2320/matertrans.MT-M2019316

Abstract

Electrodeposition of Zn was performed on an Fe electrode at a current density of 20–5000 A·m−2 and a charge of 4 × 104 C·m−2 in an unagitated zincate solution at 313 K containing 0.62 mol·dm−3 of ZnO, 4.0 mol·dm−3 of NaOH, and organic additives. The effects of organic additives on the deposition behavior of Zn and the microstructure of the deposits were investigated. Glossy films were obtained by depositing at current densities higher than 1000 A·m−2 from the solution containing additives of a straight-chain polymer composed of a quaternary ammonium cation (PQ) and a quaternary ammonium salt with a benzene ring (QA). The polarization curve was separated into partial polarization curves of Zn deposition and hydrogen evolution by using the galvanostatic data of Zn deposition. The overpotentials of the charge transfer of Zn deposition and that of ZnO22− ion diffusion increased with the addition of PQ and QA. The increase in overpotential was considerable at potentials less noble than −1.5 V. Zn deposition reached the diffusion limit of ZnO22− ions at potentials less noble than −1.5 V, indicating that the diffusion of ZnO22− ions was suppressed considerably by PQ and QA. With the addition of PQ and QA, C, N, and H were codeposited with Zn, which demonstrated that the additives of PQ and QA were incorporated into the deposited films. Zn crystallite size decreased with increasing current density. At a high current density of 5000 A·m−2, the crystallite size decreased with the addition of PQ and QA, and the surface of the film was smooth. The orientation index of the {1010} plane of Zn deposited from the solution containing PQ and QA increased with increasing current density. The changes in the crystallite size and crystal orientation of deposited Zn were explained by the deposition overpotential. This Paper was Originally Published in Japanese in J. Japan Inst. Metals 83 (2019) 399–406.

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Effect of Organic Additives on the Electrodeposition Behavior of Zn from an Alkaline Zincate Solution and Its Microstructure

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Effect of Cations on Protective Properties of Rust Layer Formed on Carbon Steel during Wet/Dry Cyclic Corrosion

Kyung-Tae Kim, Hiroaki Tsuchiya, Koushu Hanaki, Masato Yamashita, Shinji Fujimoto

pp. 506-514

DOI:

10.2320/matertrans.MT-M2019270

Abstract

The present work proposed a simple approach to modify the morphology and composition of rust layers formed on carbon steel during wet/dry cyclic atmospheric corrosion, and thereby improve the protective properties of the rust layers. Rust layers were grown on carbon steel by a laboratory cyclic corrosion test. Additional immersion in sulfate solutions containing Mg2+, Al3+, Cu2+, or Ni2+ was carried out during the cyclic corrosion test to modify the rust layers. The morphology of the rust layers on carbon steel in the reference specimen that was not subjected to additional immersion showed a plate-like structure. The rust layers on the Mg2+ specimen consisted of plate-like and needle structures. On the other hand, the other specimens subjected to additional immersion exhibited particulate structures, although the rust layers on the Cu2+ specimen consisted of finer secondary particles. Rust layers on the Al3+ specimen and the Ni2+ specimen were denser compared to the other specimens. XRD revealed that the composition of the rust layer was changed by additional immersion, that is, on all the specimens subjected to the additional immersion, the growth of α-FeOOH was enhanced whereas that of Fe3O4 was hindered. Variations in the corrosion potential and corrosion current density obtained from potentiodynamic polarization measurements were strongly related to the morphology and composition of the rust layers.

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Effect of Cations on Protective Properties of Rust Layer Formed on Carbon Steel during Wet/Dry Cyclic Corrosion

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Effect of Bending Method on Tube Hydroforming

Masaaki Mizumura, Yukihisa Kuriyama

pp. 515-521

DOI:

10.2320/matertrans.P-M2019866

Abstract

We studied the effect of the bending method on the hydroforming of a tube in a subsequent process, using experiments and the finite element method. Two bending methods, rotary draw bending and intrusion bending, were investigated. A tube was bent into an S-shape by each bending method, and a hydroforming test was carried out with the same hydroforming die. The wall thickness distribution was measured after the hydroforming. The wall thickness of the tube is smallest on the compression side when it is bent by the rotary draw bending method and on the tension side or the intermediate side when it is bent by the intrusion bending method. In both bending cases, burst occurs on the intermediate side during axial feeding. In rotary draw bending, a burst occurs on the compression side or at the R stop nearby, however, in intrusion bending, burst does not occur on the compression side but occurs on the R stop nearby during the final increase of internal pressure. Intrusion bending leaves a larger hydroforming allowance than rotary draw bending. This is because the wall thickness after intrusion bending is greater than that after rotary draw bending. This Paper was Originally Published in Japanese in J. JSTP 60 (2019) 175–181.

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Effect of Bending Method on Tube Hydroforming

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Effects of Interactions between Nodule Count of Spheroidal Graphite and Retained Austenite on Tensile Properties of Austempered Ductile Cast Iron Heat Treated from (α + γ) Range

Tatsuo Inoue, Atsushi Ito, Shiro Torizuka

pp. 522-527

DOI:

10.2320/matertrans.F-M2019867

Abstract

ADI (austempered ductile cast iron) has outstanding balance in strength and ductility, as the retained austenite improves ductility through the strain-induced transformation. In our previous report, the formation and mechanical properties of fine ferrite, bainitic ferrite, and retained austenite on the preheat-treated fine pearlite structure were investigated. However, the investigation into the effect of spheroidal graphite was insufficient. Therefore, the purpose of this study is to clear on the effect that the interaction between the nodule count of spheroidal graphite and retained austenite has on mechanical properties. Two methods were used for changing the nodule count of spheroidal graphite. The first method is that the nodule count is adjusted by changing the solidification speed in which crystallization of the spheroidal graphite occurs during casting. The second method is that the amount of added carbon is reduced to decrease the amount of spheroidal graphite being crystallized, which reduces the nodule count.Based on these conditions, the test results indicate that the condition in which more spheroidal graphite that it could be considered as a defect demonstrated better mechanical properties due to the strain-induced transformation of the retained austenite.However, the material that more nodule counts of spheroidal graphite decrease ductility due to work-hardening ability become too high.

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Effects of Interactions between Nodule Count of Spheroidal Graphite and Retained Austenite on Tensile Properties of Austempered Ductile Cast Iron Heat Treated from (α + γ) Range

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Effects of Reduced Pressure, Casting Design and Heat Transfer Resistance of Liquid Resin on Mold Filling in Expendable Pattern Casting Process of Aluminum Alloy

Sadatoshi Koroyasu

pp. 528-533

DOI:

10.2320/matertrans.F-M2019868

Abstract

Effects of reduced pressure and casting design on changes in mold filling due to coat permeability in the expendable pattern casting process of aluminum alloy were investigated experimentally. The effect of coat permeability on the melt velocity of molten aluminum alloy in the expendable pattern casting process was investigated experimentally under the conditions of reduced pressure and top pouring. Aluminum alloy plates were cast under conditions of the reduced pressure and top pouring, using eight kinds of coats with different permeabilities. The melt velocity was measured and the results showed that the difference in the melt velocity was not large depending on the casting design. The application of the reduced pressure condition and use of high permeability coats led to higher melt velocities. However in the high coat permeability region, the melt velocity did not increase much, even when the coat permeability increased. The experimental values of the melt velocity were compared with the calculated values based on the mold filling model used in the previous study. When the coat permeability was low, the experimental values were in relatively good agreement with the calculated values. However in the high coat permeability region, the experimental values of the melt velocity were lower than the calculated values. By considering the heat transfer resistance of the liquid resin at the EPS surface to the mold filling model, even in the high coat permeability region, the experimental values of melt velocity showed more or less good correlation with the calculated values. This Paper was Originally Published in Japanese in J. JFS 91 (2019) 737–742.

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Effects of Reduced Pressure, Casting Design and Heat Transfer Resistance of Liquid Resin on Mold Filling in Expendable Pattern Casting Process of Aluminum Alloy

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Improved Absorption and Desorption Kinetics of Mg–Ni–Ce Alloy Activated under Elevated Hydrogen Pressure

Lishuai Xie, Man Xu

pp. 534-539

DOI:

10.2320/matertrans.MT-M2019304

Abstract

The large-scale application of Mg as a hydrogen storage material has been limited by its slow absorption and desorption kinetics at moderate temperatures. Refining the microstructures is an effective way to improve the hydrogen storage performance. Aiming at improving the de-/absorption kinetics of Mg-based alloys by in situ formed superfine catalysts, Mg–7Ni4Ce (mass%) alloy has been prepared and activated by controlling the activation hydrogen pressure. The phase components, microstructure and hydrogen storage properties have been systematically investigated. It is found that an 18R-type long-period stacking ordered (LPSO) phase is formed in the eutectic region of as-cast Mg–Ce–Ni ternary alloy. The observed LPSO structure is a variant of Mg12Ce rather than Mg. Abundant secondary phase particles are obtained in the as-activated alloy. For the sample which is activated at 300°C under 7.5 MPa hydrogen pressure, the particle size of secondary phase is much finer than that of the sample activated under 3 MPa hydrogen pressure. The sample activated under higher hydrogen pressure shows superior absorption and desorption kinetics.

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Improved Absorption and Desorption Kinetics of Mg–Ni–Ce Alloy Activated under Elevated Hydrogen Pressure

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Formation of Mullite Coating by Aerosol Deposition and Microstructural Change after Heat Exposure

Toshiki Shibuya, Taisuke Mizuno, Atsuhisa Iuchi, Makoto Hasegawa

pp. 540-547

DOI:

10.2320/matertrans.MT-M2019354

Abstract

Optimal parameters for the aerosol deposition (AD) of a mullite coating and the microstructural change of the coating after heat exposure in air were investigated. Mullite, which is a component of environmental barrier coatings, was deposited on glass, Al2O3 and Si by the AD method. The angle of the gas flow direction from the nozzle to the substrate plane should be 60° to produce a homogeneous mullite coating. The deposition rate increased with the gas flow rate when the gas flow rate was in the range from 18 to 36 L/min. Further increase of the gas flow rate resulted in the formation of a heterogeneous coating. The mullite coating formed with the optimized parameters was almost fully dense and crystalline. The chemical composition of the mullite coating was almost the same as that of the raw mullite powder used for deposition. The coating was composed of a single mullite phase. No delamination was observed at the interface between the Si substrate and the mullite coating. The interface did have undulations; therefore, it was considered that the substrate and the coating were bonded due to the anchor effect. Heat treatment was performed at 1573 K for a mullite coating deposited on a Si substrate. When the specimen was exposed to heat for 10 h, the coating at the surface side and the coatings at the central part and near the interface between the substrate and the coating were composed of two phases, (Al2O3+mullite) and (SiO2+mullite), respectively. Further heat exposure results in the formation of a reacted layer of two phases (SiO2+mullite) containing more than 80 mol% of SiO2 near the interface. The thickness of the layer increased with increasing heat exposure time. The formation of the reacted layer was due to the diffusion of Al present in the mullite coating to the coating surface and the diffusion of Si into the coating from the Si substrate. This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 83 (2019) 186–192.

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Formation of Mullite Coating by Aerosol Deposition and Microstructural Change after Heat Exposure

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Spark Sintering of TiB2 Reinforced Fe Matrix Composites with Both High Thermal Conductivity and Hardness, and Their Microstructural Characterizations

Yujiao Ke, Kazuhiro Matsugi, Zhefeng Xu, Yongbum Choi, Mingzhi Wang, Jinku Yu

pp. 548-556

DOI:

10.2320/matertrans.MT-M2019286

Abstract

TiB2 reinforced Fe matrix composites were investigated for their potential as a new generation of hot work tools which are mainly characterized by high thermal conductivity and high hardness in comparison with conventional materials. In this work, Fe–30 vol%TiB2 composites were sintered at 1373 K for different holding times (0, 0.3, 0.6, 1.8 and 3.6 ks). Apart from Fe and TiB2, newly formed phases of Fe2B and TiC were found in all sintered compacts. A good Fe/TiB2 interfacial cohesion was confirmed at atomic level at 0 ks, which was due to the occurrence of the special orientation relationship between {110} planes of Fe and {1010} planes of TiB2. The observation of dislocations in TiB2 particles, attributed to the activation of slip systems, showed the plastic deformation ability of TiB2 at high temperature. The reaction between Fe and TiB2 was due to TiB2 dissolution in Fe at 1373 K and different diffusion depth of B and Ti atoms in Fe. Consequently, B directly reacted with Fe, since the solubility of B atoms was low in both α-Fe and γ-Fe. TiC probably precipitated from Fe–Ti–C solid solution along Fe grain boundaries in the cooling stage after sparking sintering, leading to a layer of Fe wrapping around TiB2. Among all the compacts, the one sintered at 1373 K for 0.6 ks displayed the excellent properties which were comparable in Vickers hardness and 133% higher in thermal conductivity, compared with that of SKD61 as the commonly used practical material. This work provides a new perspective to fabricate a future generation of hot work tools.

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Spark Sintering of TiB2 Reinforced Fe Matrix Composites with Both High Thermal Conductivity and Hardness, and Their Microstructural Characterizations

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Conduction Path Formation Mechanism of Solderable Polymer Composites with Low-Melting-Point Alloy/High-Melting-Point Alloy Mixed Filler

Byung-Seung Yim, Jae Woo Lee, Jong-Min Kim

pp. 557-560

DOI:

10.2320/matertrans.MT-M2019285

Abstract

A novel interconnection mechanism using a solderable polymer composite (SPC) with a low-melting-point alloy (LMPA)/high-melting-point alloy (HMPA) mixed filler was proposed to enhance the properties of the LMPA filler and establish a conduction path containing the HMPA filler. To investigate the feasibility of the proposed interconnection mechanism, three types of SPC with a different mixing ratios of LMPA/HMPA filler (100:0, 50:50, and 0:100) were formulated. The SPC with only an HMPA filler showed weak conduction path formation due to excessive curing of the polymer composite before melting of the HMPA filler. In contrast, the SPC with an LMPA/HMPA mixed filler formed a stable and wide conductive path due to the suitable flow-coalescence-wetting behaviors of the molten LMPA filler containing solid-state HMPA filler, which came into effect before excessive curing of the polymer composite.

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Conduction Path Formation Mechanism of Solderable Polymer Composites with Low-Melting-Point Alloy/High-Melting-Point Alloy Mixed Filler

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