Microscopic hydrogen visualization has long been required to clarify the hydrogen embrittlement mechanism of metallic materials. In this study, hydrogen diffusion depending on microstructure in polycrystalline pure nickel film was successfully visualized using an Ir complex, whose color changes with hydrogen. The hydrogen flux in nickel was found to be large at random grain boundaries and small inside grains and at coincidence site lattice grain boundaries.

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Aging behavior, cluster formation including near grain boundaries, and mechanical properties of Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) alloy were investigated. The effect of Ag as a microalloying element was also clarified. The Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) alloy showed higher aging hardening ability and shorter time to peak aging than the Al-5%Zn-2%Mg(-0.3%Ag) alloy from the early aging stage. The effect was greater with the addition of Ag, showing that the effects of solute content and micro-alloying elements on age hardening were recognized. 3DAP analysis revealed that Ag contributed significantly to the initial stage of cluster formation even when the solute elements were high. It was also found that clustering occurred in the vicinity of the grain boundary at a high density and fineness from the early stage of aging. By increasing the solute content of Zn and Mg to 11% and 3% respectively, the tensile strength of the alloy was over 800 MPa, and the addition of Ag further increased the strength.

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In recent years, significant attention has been given to the physical properties of low-dimensional materials. Carbon nanotubes (CNTs), a prime example of such materials, are emerging as a promising next-generation candidate material for sensor components, including yoctogram (10⁻²⁴g) measurement devices and antennas capable of handling large-scale digital data. CNTs exhibit a variety of atomic arrangements due to their chirality. However, even 30 years after their discovery, controlling the chirality of CNTs remains challenging, and the specifics of their physical properties still require clarification. Understanding the vibration characteristics of carbon nanotubes (CNTs) is crucial for designing nanoscale structures and devices. In this study, we analyzed the effects of tube diameter, push ratio, and length of CNTs on vibration using molecular dynamics simulation. This method allows for the modeling of ideal geometric structures at the atomic level and the tracking of their behavior. The findings are as follows: For armchair carbon nanotubes, the resonance frequency decreased with an increase in the length of the CNTs. It was observed that the thermal energy generated during vibration tends to decrease with an increase in tube diameter. The full width at half maximum increases with an increase in the push ratio.

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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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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 (d_max), whereas the medium size hardly affected the maximum compressive residual stress (σ_max). The measured d_max was significantly smaller than the d_max 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 σ_max 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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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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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.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Light Metals 74 (2024) 180–187.

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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 (σ_UTS) and fracture strain (ε_f), 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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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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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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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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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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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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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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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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Announcement Concerning Article Retraction
The following paper has been withdrawn from the database of Mater. Trans., because a description based on a misinterpretation of the experimental results was found by the authors in advance of publication after acceptance.
Mater.Trans. 52(2011) Advance view.
Improvement in Fatigue Strength of Biomedical β-Type Ti-Nb-Ta-Zr Alloy while Maintaining Low Young’s Modulus through Optimizing ω-Phase Precipitation

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