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MATERIALS TRANSACTIONS Vol. 65 (2024), No. 10

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

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  1. Vol. 65 (2024)

    1. No.12
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    3. No.10
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  2. Vol. 64 (2023)

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  3. Vol. 63 (2022)

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  6. Vol. 60 (2019)

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  7. Vol. 59 (2018)

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  9. Vol. 57 (2016)

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  10. Vol. 56 (2015)

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  12. Vol. 54 (2013)

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  24. Vol. 42 (2001)

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MATERIALS TRANSACTIONS Vol. 65 (2024), No. 10

Deformation Behavior of Aluminum Alloys under Various Stress States: Material Modeling and Testing

Toshihiko Kuwabara, Frédéric Barlat

pp. 1193-1217

DOI:

10.2320/matertrans.MT-L2024010

Abstract

Forming simulation is an indispensable analysis tool in industry, the most important objective of which being the reproduction of the material deformation behavior during the process as accurately as possible to predict forming defects and determine optimum forming conditions precisely. This paper reviews the material models suitable for metal forming simulations and the material test methods that can reproduce the various types of stress states occurring in real forming operations. These test methods are essential to verify the validity of material models. Examples of forming simulation results for aluminum alloys are presented, illustrating the significant influence of the material models on the accuracy of the process predictions. Finally, the emerging research trends in the field of material modeling and testing are discussed.

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Deformation Behavior of Aluminum Alloys under Various Stress States: Material Modeling and Testing

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Recent Trends in Synthesis and Applications of Zeolite Membranes

Motomu Sakai

pp. 1218-1223

DOI:

10.2320/matertrans.MT-Y2024004

Abstract

Zeolites have been used as a separation membrane material by taking advantages of their unique adsorption properties and molecular sieving properties based on the micropores. Zeolite membranes are widely used in practical applications, mainly for dehydration of organic solvents. Furthermore, the research and development continue toward large-scale implementation in the energy and carbon neutral field. The high heat and chemical resistance of zeolite membranes are also expected to be utilized as membrane reactors. Zeolite membrane and membrane separation will contribute to the fulfillment of a carbon-neutral society through energy saving in separation, reaction, and CO2 recovery. In this review, the basic structure, the synthesis methods and the applications of zeolite membranes are introduced. The recent research trends of zeolite membrane in the research and applications are also explained.

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Recent Trends in Synthesis and Applications of Zeolite Membranes

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Analysis of Liquid Phase Sintering of Metal-Glass Mixed Powder by Experiment and Computer Simulation

Hiroyuki Tanaka, Hideaki Matsubara, Hideaki Yokota, Toshihiro Iguchi, Hiroshi Nomura

pp. 1224-1233

DOI:

10.2320/matertrans.MT-Y2024002

Abstract

Liquid phase sintering behavior of metal-glass system is experimentally and numerically analyzed. From the experimental observation, glass wets metal surfaces and assists the metal particles rearrangement, which is very important for annihilating pores. From the experiment, the amount of glass influences not only on the porosity but also on the grain growth behavior significantly. The sintering behavior is well reproduced by computational study by using Monte Carlo method with experimentally obtained surface energies of metal-glass system. The numerical study suggests that the frequency factor of Ostwald should be smaller than that of solid grain growth in this metal-glass powder system. Finally, this study suggests that spatial distribution is very important for grain growth. Although glass prevents the metal particle contact, the glass assists the metal particles rearrangement that contributes to metal grain growth.

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Analysis of Liquid Phase Sintering of Metal-Glass Mixed Powder by Experiment and Computer Simulation

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Phase Transformation and Mechanical Properties of G Phase (Mn6Ni16Si7) in Mn–Ni–Si Model Alloys after 1,000°C Annealing

Xinrun Chen, Tatsuya Suzuki, Huilong Yang, Ba Vu Chinh Nguyen, Zhehuan Zhang, Kenta Murakami

pp. 1234-1238

DOI:

10.2320/matertrans.MT-M2024052

Abstract

Mn6Ni16Si7 intermetallic compounds, referred to as the G phase, and their precursors are recognized as potential secondary phases precipitated in neutron-irradiated steels and are the main cause of embrittlement in low-alloyed reactor pressure vessel steels under long-term operation. To obtain the mechanical properties and thermal stability of the G phase, two Mn–Ni–Si model alloys (composed of 21 mol%Mn-58 mol%Ni-21 mol%Si and 30 mol%Mn-58 mol%Ni-12 mol%Si) were annealed at 1,000°C. The existence of the G phase in both annealed ternary model alloys was confirmed by XRD and SEM/EDS. Meanwhile, the process of different Mn–Ni–Si ternary regions to the G phase transformation under 1,000°C annealing has also been discussed. Young’s modulus and nano-hardness of the G phase were measured using the nanoindentation technique. The results showed similar values for the G phase in two alloys with Young’s modulus of approximately 220 GPa, which is similar to Young’s modulus of iron. This fact suggests the necessity of reconsideration of the hardening model contributed by G phase precipitates in reactor pressure vessels in the future.

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Phase Transformation and Mechanical Properties of G Phase (Mn6Ni16Si7) in Mn–Ni–Si Model Alloys after 1,000°C Annealing

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Effect of Indium on Microstructures and Mechanical Properties of Bismuth-Based High Temperature Solders

Bin Liu, Kazuhiro Matsugi, Zhefeng Xu, Yongbum Choi, Ken-ichiro Suetsugu, Jinku Yu

pp. 1239-1243

DOI:

10.2320/matertrans.MT-M2024067

Abstract

With the rapid development of the electronic information industry, the reliability of electronic interconnection materials is crucial for the longevity of electronic components. Bi-based alloys have garnered significant attention as potential candidates for high-temperature solders. However, the inherent brittleness of Bi-based alloys has been a limiting factor in their application. In order to develop high-temperature Bi-based solders with superior performance, In element was chosen to modify the Bi-2Ag-0.5Cu alloy. Through the introduction of Ag2In and BiIn phases, much finer microstructure of Bi-based alloy can be achieved (grain size decreases from 80 µm to 30 µm). Adding 2% Indium has led to notable improvements in ultimate tensile strength (σUTS) and fracture strain (εf), by 76.9% and 55.1% compared to Bi-2Ag-0.5Cu, respectively. Additionally, the melting point of the Bi-2Ag-0.5Cu-2In alloy is 534.3 K, meeting the specified requirements for a high-temperature solder.

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Effect of Indium on Microstructures and Mechanical Properties of Bismuth-Based High Temperature Solders

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Grain Refinement of Pure Zinc Single Crystals with Different Crystal Orientations during a Single Pass of ECAP

Hiromoto Kitahara, Yuta Matsuo, Yuki Oda, Masayuki Tsushida, Shinji Ando

pp. 1244-1250

DOI:

10.2320/matertrans.MT-M2024101

Abstract

Six types of pure zinc single crystals with different crystal orientations were applied to a single pass of equal channel angular pressing (ECAP) at 223 K so as to investigate the effects of {1012} twins and slips on grain refinement and texture development. Six ECAP deformation behaviors were categorized into three types: Type A, Type B, and Type C. Type A finally fractured during ECAP, and the grain refinement area was quite limited. Many {1012} twins and {1012}-{1012} double twins were observed above the theoretical shear plane (SP) in ECAP, and recrystallized grains with crystallographic texture were observed beneath the SP in Type B. In Type C, both twinning and double twinning above the SP, and then dynamic recrystallization occurred above the SP. The microstructure showed texture below the SP, and basal slips were mainly activated for texture development in both Types B and C. A single crystal with several hundred cubic millimeters was found to be subdivided into a large number of recrystallized grains solely by a single ECAP pass. Dynamic recrystallization caused by the pile-up of basal dislocations at twin and double twin boundaries above the SP is essential for efficient grain refinement below the SP.

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Grain Refinement of Pure Zinc Single Crystals with Different Crystal Orientations during a Single Pass of ECAP

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Mechanical Response and Microstructure Characteristics of Powder Metallurgical High-Speed Steel (ASP 60) Impacted at −195°C and 800°C

Woei-Shyan Lee, Ting-Ju Chen

pp. 1251-1259

DOI:

10.2320/matertrans.MT-M2024003

Abstract

The dynamic mechanical behaviour of high-alloyed powder metallurgical high-speed steel ASP 60 is investigated using a compressive split-Hopkinson pressure bar at strain rates of 2.5 × 103 and 4.0 × 103 s−1 and temperatures of −195°C and 800°C, respectively. The effects of the strain rate and temperature on the microstructure evolution of the impacted specimens are examined using scanning electron microscopy and transmission electron microscopy. A negative strain rate sensitivity is observed at both temperatures. The flow stress, strain rate sensitivity, temperature sensitivity, fracture mechanism, and dislocation substructures are all significantly affected by the strain rate and temperature. The SEM fractographs reveal a brittle fracture mode at −195°C and localized melting at 800°C. The specimens impacted at −195°C exhibit a dislocation multiplication microstructure entangled with fine precipitates, which collectively increase the flow resistance of the sample. However, the microstructures of the specimens impacted at 800°C show a lower density of dislocations and coarse precipitates, resulting in a loss of flow resistance. The flow stress of the ASP 60 specimens shows a linear decrease with the square root of the dislocation density at both temperatures. The rate of decrease in the flow stress is higher under a cryogenic temperature. Hence, the relationship between the dislocation density and the mechanical response is inferred to be temperature-dependent.

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Mechanical Response and Microstructure Characteristics of Powder Metallurgical High-Speed Steel (ASP 60) Impacted at −195°C and 800°C

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Temperature Dependence of Deformation and Fracture in a Beta Titanium Alloy of Ti-22V-4Al

Rei Yano, Masaki Tanaka, Shigeto Yamasaki, Tatsuya Morikawa, Tomohito Tsuru

pp. 1260-1267

DOI:

10.2320/matertrans.MT-L2024012

Abstract

Impact tests and tensile tests were conducted between 77 K and 450 K in order to elucidate the temperature dependence of absorbed-impact energy, yield stress, effective shear stress, activation volume, and activation enthalpy. The impact-absorbed energy decreased with decreasing test temperature, however, this alloy did not undergo low-temperature embrittlement although it has a bcc structure. Tensile tests showed changes in both the work-hardening rate and the temperature dependence of yield stress at approximately 120 K. This suggests a change in the mechanism behind the plastic deformation at the temperature. The temperature dependence of the activation enthalpy for dislocation glide suggests that double-kink nucleation of a screw dislocation is the dominant mechanism for the dislocation glide from 150 K to 200 K, while the interaction between a dislocation and solute atoms dominantly controls the dislocation glide above 200 K. Superelasticity appears in stress-strain curves tested below 120 K, suggesting that the yielding is governed by transformation-induced plasticity below 120 K. The enhanced toughness at low temperatures in these alloys is discussed from the viewpoint of dislocation shielding theory.

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Temperature Dependence of Deformation and Fracture in a Beta Titanium Alloy of Ti-22V-4Al

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Residual Stress, Surface Roughness and Microstructure on Specimen Surface Subjected to Gyrofinishing Process with Various Abrasive Media

Norimitsu Koga, Atsushi Yamashita, Reiya Yamazaki, Ryusei Kato, Kouhei Yamaya, Kenta Miyake, Yohei Hashimoto

pp. 1268-1276

DOI:

10.2320/matertrans.MT-H2024001

Abstract

Gyrofinishing is a mass-finishing process used for large and/or complex workpieces. In this process, abrasive media filled in a container are accelerated by rotating the container, impacting the workpiece fixed in it and smoothing the workpiece surface. In this study, the effects of the materials and sizes of the abrasive media on the surface roughness, microstructure, and residual stress on the specimen surface developed by gyrofinishing were revealed. The surface of the gyrofinished specimen was smooth. However, the specimen surface when using the HS medium, consisting of a mixture of ceramic and small abrasive grains, was slightly rougher compared to that finished using the PS medium, consisting of ceramic. An ultra-fine grained structure was formed at the surface after gyrofinishing, regardless of medium. A flow of the microstructure was observed in the specimens gyrofinished with the HS media, indicating that shear stress occurred during gyrofinishing. All the gyrofinished specimens exhibited a significant compressive residual stress near the surface. The residual-stress profile along the depth direction differed depending on the material and size of the media. The small media shallowed the depth of the maximum compressive residual stress (dmax), whereas the medium size hardly affected the maximum compressive residual stress (σmax). The measured dmax was significantly smaller than the dmax value estimated based on the Hertz contact theory, which is likely due to the shear stress generated by the rotation or sliding of the media on the specimen surface during gyrofinishing. The specimens gyrofinished using the HS series had a higher σmax than those gyrofinised using the PS series. The rough surface of the HS medium is expected to introduce a high compressive residual stress through the burnishing effect. It can be concluded that gyrofinishing provides the specimen surface with a smooth, ultra-fine grained structure and significant compressive residual stress.

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Residual Stress, Surface Roughness and Microstructure on Specimen Surface Subjected to Gyrofinishing Process with Various Abrasive Media

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Strain Evolution during Stretch Forming with a Hemispherical Punch in 5052 Aluminum Alloy Sheets

Sho Sato, Maya Tsukamoto, Naoki Miyazawa, Yasuhiro Maeda, Yasushi Maeda, Takayuki Hama

pp. 1277-1286

DOI:

10.2320/matertrans.MT-M2024069

Abstract

During plastic deformation, 5000 series aluminum alloys often exhibit serration and the Portevin-Le Chatelier (PLC) bands. The occurrence of the PLC bands is affected by strain paths, but the details are not understood. In this study, the effects of strain ratios on the PLC bands during hemispherical-punch stretch forming were investigated in 5052 aluminum alloy sheets. Strain evolution was measured using a digital image correlation method. When the strain ratio was close to uniaxial tension, the strain evolution was not uniform and apparent PLC bands were observed. By contrast, PLC bands were less pronounced under pseudo-plane-strain tension and were not visible under pseudo equibiaxial tension, showing that PLC bands became more difficult to appear as the strain ratio approached equibiaxial tension. The difference in the appearance of PLC bands occurred presumably because of the difference in the strain rate depending on the strain ratio. However, PLC bands were observed clearly at a strain rate similar to that under equibiaxial tension, suggesting that the strain rate at which PLC bands appear could differ depending on the strain ratio.

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Strain Evolution during Stretch Forming with a Hemispherical Punch in 5052 Aluminum Alloy Sheets

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Changes in Admittance and Internal Structure of Coating Films by Environmental Testing

Toshio Horie, Gaku Kitahara, Hirochika Tani, Mikio Asai

pp. 1287-1292

DOI:

10.2320/matertrans.MT-C2024006

Abstract

The impedance of the paint film varied depending on the environmental test. It is considered that the impedance spectrum of the coating films changed by the effects of water content in the paint film, polymer structure, and elements that penetrated the paint film. However, no clear relationship could be found between the impedance spectrum of the coating film and its internal structure. To understand the change in the impedance spectrum, we performed D-SIMS and AFM-IR analyses on the paint films after the environmental test. The results suggest that the admittance spectra may reflect the state of infiltrated moisture and elements into the coating films.

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Changes in Admittance and Internal Structure of Coating Films by Environmental Testing

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Direct-to-Blister Smelting of Copper-Rich Concentrates Using SiO2-FeO-CaO Slag System

Yingbao Yang, Yuxuan Liu, Shiwei Zhou, Yonggang Wei, Bo Li

pp. 1293-1300

DOI:

10.2320/matertrans.MT-D2023014

Abstract

The direct-to-blister process is considered as a short process, low energy consumption and environmentally friendly pyrometallurgical copper smelting process. In this study, direct-to-blister smelting experiments were conducted on a laboratory scale using high-grade chalcocite as the raw material and employing the SiO2-FeO-CaO slag system. The effects of smelting parameters including Fe/SiO2 ratio, oxygen blowing volume, and smelting temperature on copper recovery were investigated, and the optimal experimental scenario under the SiO2-FeO-CaO slag was ultimately obtained. The results showed that the maximum copper recovery of 96.23 wt.% was realized at the Fe/SiO2 ratio of 1.2 and with CaO addition of 2.8 wt.%. Moreover, the copper losses in the slag and the phases in the slag were analyzed in detail. The results of this paper may provide theoretical guidance for direct-to-blister of high-grade copper concentrates under SiO2-FeO-CaO slag system.

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Direct-to-Blister Smelting of Copper-Rich Concentrates Using SiO2-FeO-CaO Slag System

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Monitoring and Management Techniques for Persistent Organic Pollutants in Groundwater Environment of Subway Stations

Aihui Zhao, Peng Jiang

pp. 1301-1309

DOI:

10.2320/matertrans.MT-N2024004

Abstract

A photocatalyst based on Ti3C2/ZnCo2O4/ZnIn2S4 composite material is prepared for the detection and treatment of persistent organic pollutants in groundwater environment of subway stations. And it is characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. Then, a monitoring and governance system for persistent organic pollutants in the water environment is established, including sensor networks, data collection and processing, pollutant monitoring, and governance control. Finally, the degradation efficiency of the photocatalytic coupled ozone flow reactor for three types of chlorophenol organic compounds is experimentally verified to reach 93%, 86%, and 83%, respectively. The monitoring and treatment system for persistent organic pollutants in the water environment has achieved a removal rate of 90% for chemical oxygen demand (COD) and 80% for suspended solids. This study shows that the photocatalytic coupled ozone flow reactor has a high degradation effect on chlorophenol organic compounds. The monitoring and treatment system for persistent organic pollutants in the water environment has significantly reduced the concentration of heavy metal ions and achieved good removal effects on COD and suspended solids. This study provides effective technologies and methods for the monitoring and management of persistent organic pollutants in the water environment, which helps to solve water pollution problems, improve water environment quality, and protect water resources and ecological environment.

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Monitoring and Management Techniques for Persistent Organic Pollutants in Groundwater Environment of Subway Stations

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Gasification Behavior of Plant-Based Biomass and Its Application to the Manufacturing Process of Titanium Sulfides under Sulfur Partial Pressure

Ichiro Seki, Yuki Matsuoka, Chinami Matsuda, Noa Watanabe, Chiyu Nakano, Yuta Nishina

pp. 1310-1319

DOI:

10.2320/matertrans.MT-M2023220

Abstract

Metallic titanium ingots can be manufactured via thermal decomposition of titanium sulfides. In our previous study, we thermodynamically and experimentally investigated the phase relationship of titanium oxides and sulfides under carbothermic and hydrogen gas flow atmospheres, that is, non-carbothermic atmospheres. Recently, carbon neutral processes for metallurgical processes that use plant-based biomass, which plays essential roles in environmental protection, have been focused. In this study, the gasification behavior of biomass was investigated by thermal gravimetry-differential thermal analysis, and the deoxidization and sulfurization behaviors that generate titanium sulfides were also experimentally investigated. The gasification behavior differs according to the type of biomass, including the amounts of H2O in the biomass. The reaction temperature for CO2 generation decreased with increasing biomass H2O content. However, the total amounts of generated gas ratios of H2O/CO2 were hardly different, and the partial pressures of oxygen during gasification were also fixed as a function of temperature. The products were analyzed using X-ray diffractometry and identified as titanium disulfide (TiS2), similar to a carbothermic process.

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Gasification Behavior of Plant-Based Biomass and Its Application to the Manufacturing Process of Titanium Sulfides under Sulfur Partial Pressure

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Microstructure and Various High Temperature Properties in a Small Amounts of Aluminum Added High Silicon Spheroidal Graphite Cast Iron

Akito Okame, Chisato Yoshida, Jin Takeda, Naoyuki Kato

pp. 1320-1326

DOI:

10.2320/matertrans.F-M2024809

Abstract

The objective of this experiment is to increase the heat resistance of high Si spheroidal graphite cast iron (3.3%C-4%Si-0.6%Mo) which is used as turbine housing. It is known that when Al was added to the spheroidal graphite cast iron melt, nodularity and fluidity decreases, but heat resistance increases. This experiment thus aimed to demonstrate the effective utilization of Al. In samples added with a small amount of Al, microstructure was observed and mechanical properties and fluidity were measured. High temperature oxidation tests and high temperature tensile tests were also carried out. The high temperature oxidation results were used as measures of heat resistance.

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Microstructure and Various High Temperature Properties in a Small Amounts of Aluminum Added High Silicon Spheroidal Graphite Cast Iron

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Analysis of Compression Deformation at High-Temperatures and FEM Simulation for BaTiO3 Sintered Compacts

Hiroyuki Tanaka, Hideaki Matsubara, Hideaki Yokota, Toshihiro Iguchi, Yuko Takagi, Hiroshi Nomura, Sota Terasaka, Daisuke Igimi

pp. 1327-1340

DOI:

10.2320/matertrans.MT-Y2024003

Abstract

In this study, the yield stress equation, flow rules and physical properties of barium titanate (BaTiO3) are experimentally obtained. These basic equations and coefficient of flow stress are introduced to finite element method, and sintering behavior of barium titanate bulk is simulated. From the uniaxial compression test, the yield stress equation of BaTiO3 is expressed by Shima’s equation, and flow rule is written by plastic equation. The coefficient of flow stress of BaTiO3 is significantly smaller than that of alumina, and the value is different when the grain size is different. The experimental sintering deformation is quantitatively reproduced by numerical simulation, where basic equation and physical properties are experimentally introduced. In addition, the coefficient of flow stress could be determined by simulation sensitivity analysis. Through this study, experimentally obtained yield stress equation, flow rules, and coefficient of flow stress are numerically validated.

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Analysis of Compression Deformation at High-Temperatures and FEM Simulation for BaTiO3 Sintered Compacts

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Development of Partial Non-Magnetization Improvement for Silicon Steel and Rotor Evaluation

Norihiko Hamada, Aki Watarai, Katsunari Oikawa, Satoshi Sugimoto

pp. 1341-1348

DOI:

10.2320/matertrans.MT-MAW2024001

Abstract

Magnetic flux leakage from the rotor core bridge must be improved in interior permanent magnet motors to improve their performance. The partial non-magnetization of bridges is effective in reducing magnetic flux leakage. In our previous studies, we proposed a new partial non-magnetization process for silicon steel, which was used for the rotor core. The portion of the silicon steel sheets that becomes a bridge after pressing can be non-magnetized by melting and mixing Ni–Cr–B alloy powder with the silicon steel sheets using a laser beam and then laminated to produce the rotor core. In this study, the effect of B addition to Ni–Cr alloy powder was widely investigated to optimize the B addition amount. Based on the appearance, solidification defect, and magnetic and mechanical strength properties of the improved portion, the optimal content of B was within the range of 0.5–1.0 mass%. Furthermore, core sheet samples with an improved portion, which had the improved length of 1.0 mm and has the composition of Fe–13.9 mass%Cr–15.1 mass%Ni–2.3 mass%Si–0.5 mass%B, were prepared by laser and press processing. A rotor core was fabricated using core sheets and evaluated for its magnetic flux and high-speed rotation for practical use. The prototype rotor core exhibited a 32% higher magnetic force and could rotate at speeds of up to 43,000 rotations. It is expected that the size of interior permanent magnet motors will be reduced due to the increased magnetic force.

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Development of Partial Non-Magnetization Improvement for Silicon Steel and Rotor Evaluation

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Effects of Temperature Cycling on the Mechanical Properties of GFRP at Elevated Temperatures

Kunitaro Hashimoto, Gen Hayashi

pp. 1349-1357

DOI:

10.2320/matertrans.MT-Z2024012

Abstract

Previous studies have reported that the mechanical properties of GFRP, composed of E-glass and unsaturated polyester resin, decrease when subjected to 70 or more thermal cycles ranging from −5 to 40°C (14 hours per cycle). However, there are reports suggesting that the surface temperature of in-service GFRP bridges can exceed 70°C during summer. This indicates that current data on temperature ranges during thermal cycling tests might be insufficient. This study, therefore, investigates the effects of temperature cycling at elevated temperatures on the mechanical properties of GFRP by conducting cycles from −5 to 75°C. Results from the high-temperature range revealed that the strength of unidirectional materials increased in both tensile and bending tests. Conversely, the mechanical properties of bi-directional materials remained relatively unchanged in both tests. Additionally, a slight mass loss in the specimens was noted due to temperature cycling. This suggests that a reduction in water content within the specimens might be a major factor contributing to the observed strength increase.

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Effects of Temperature Cycling on the Mechanical Properties of GFRP at Elevated Temperatures

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Mg-1.88Zn-0.75Y Cast Alloys with High Thermal Conductivity of 141 Wm−1K−1

Yunsheng Wang, Shin-ichi Inoue, Yoshihito Kawamura

pp. 1358-1366

DOI:

10.2320/matertrans.MT-L2024015

Abstract

High thermal conductivity ternary Mg alloys composed of Zn and Y pair with a negatively large mixing enthalpy was developed by optimization of alloy composition and heat-treatment conditions. Optimal alloy composition was Mg-1.88Zn-0.75Y (at%) alloy, in which the ratio of Zn content to Y content was 2.5 and the Y content was 0.75 at%. The alloy was composed of α-Mg+W phase (Mg3Zn3Y2)+I phase (icosahedral Mg3Zn6Y). Heat treatment under the optimal heat treatment conditions, where temperature, time and cooling rate were 633 K, 15 h and air cooling, respectively, improved the thermal conductivity from 114 to 141 Wm−1K−1 that corresponds to 90% of the pure Mg thermal conductivity. Fine W phase precipitation in α-Mg matrix by the heat-treatment caused a reduction of solute Y element in α-Mg matrix, resulting in improvement of the thermal conductivity.

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Mg-1.88Zn-0.75Y Cast Alloys with High Thermal Conductivity of 141 Wm−1K−1

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Effect of Molten Al/Si Impregnation on the Oxidation Resistance of TiB2 at 1300°C

Koki Wakatabi, Yuki Jimba, Yasuki Okuno, Sosuke Kondo, Hao Yu, Yasuyuki Ogino, Ryuta Kasada

pp. 1367-1372

DOI:

10.2320/matertrans.MT-M2024012

Abstract

Despite their superior material properties at high temperatures, the poor oxidation resistance of borides such as TiB2 above 1000°C limits their applications. Herein, we demonstrate the liquid-phase impregnation of Al or Si into the sintered compact of TiB2 and study their effect on the oxidation behavior at 1300°C. The thermogravimetric curves obtained under oxidation and subsequent crystal phase identification suggest that Al impregnation can prevent the evaporation of boron oxide by forming aluminum borate, which is an unstable protective layer, resulting in a slight increase in the oxidation resistance. By contrast, the Si-impregnated specimens showed lesser mass change due to oxidation than that in the unimpregnated specimens, owing to the formation of a stable protective SiO2 phase on the sample surface. Hence, molten Si impregnation of sintered borides is a promising new approach for improving high-temperature oxidation resistance.

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Effect of Molten Al/Si Impregnation on the Oxidation Resistance of TiB2 at 1300°C

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Influence of Bend Holding on Springback and Time-Dependent Springback in Sheet Metal Bending

Kouki Matsugi, Ryutaro Hino

pp. 1373-1376

DOI:

10.2320/matertrans.MT-P2024003

Abstract

Springback of sheet metals consists of two components: springback caused by elastic recovery during unloading and time-dependent springback caused by viscoplastic phenomena over time after unloading. While springback can be reduced by punch holding (or bend holding), the influences of bend holding on each of these two springback components are unclear. This study aims to elucidate the effects of bend holding on these two springback components and total springback by conducting L-bending tests on an advanced high-strength steel (SPCN118Y) sheet and an aluminum (A1050-O) sheet. The total springback two days after unloading decreased when bending was held because the springback during unloading decreased due to stress relaxation while holding. The time-dependent springback also tended to decrease with bend holding in most cases, but its amount and reduction were considerably smaller than those in the springback during unloading. The percentage of time-dependent springback to total springback was larger for A1050-O than for SPCN118Y. The percentage of SPCN118Y was not much affected by bend holding, while that of A1050-O became larger when bending was held.

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Influence of Bend Holding on Springback and Time-Dependent Springback in Sheet Metal Bending

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