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 strain 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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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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Single crystal elastic constants are vital parameters associated with the mechanical properties of polycrystals. To accurately invert these constants, precise experimental techniques must be employed. However, traditional ultrasonic measurement methods can introduce errors when dealing with complex microstructures. To address this issue, we propose an approach that combines metallographic measurements, homogenization techniques, and intelligent algorithms to invert the single crystal elastic constants of polycrystals. First, we developed a modified single scattering response (SSR) model based on metallographic measurements and the best-fitted spatial correlation function (SCF). In addition, different homogenization techniques were compared to enhance the accuracy of the model. We then propose an Adaptive Probability Differential Evolution Quantum Particle Swarm Optimization (AP-DE-QPSO) algorithm to enhance the accuracy of optimization results with an adaptive probability (AP) operator in the optimization process. After verification with three standard test functions, we demonstrated that the algorithm achieved higher accuracy. Finally, by utilizing the AP-DE-QPSO algorithm and fitting the spatial variance of the modified SSR model to the ultrasonic backscattering experimental data, we successfully inverted the global optimal solution of the single crystal elastic constants. The Self-Consistent averaging technique yielded the best results, with relative errors of approximately 3% for C₁₁ and C₄₄, and a relative error of approximately 10% for C₁₂. Our study confirms the accuracy and reliability of the modified SSR model and AP-DE-QPSO algorithm in inverting the elastic constants of single crystals.

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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 534.3K, meeting the specified requirements for a high-temperature solder.

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The effect of structure of organic additives on the electrodeposition behavior of Zn from alkaline zincate solution and its crystal morphology was investigated. Zn was electrodeposited on an Fe electrode at 20–1000 A·m⁻², 2.4 × 10⁴ C·m⁻², 300 K from unagitated zincate solutions containing the various organic additives as a leveling agent. The suppression effect of additives on the charge transfer and diffusion of ZnO₂²⁻ ions in Zn electrodeposition corresponded to the number of adsorption site per a straight chain molecule of polymer. The effect of polymer alone on the decrease in size of Zn platelets crystals was small, but the crystal size significantly decreased with coexistence of low molecular additive. The crystal size of deposited Zn decreased in spite of small suppression effect on Zn deposition, showing that the crystal size of deposited Zn doesn’t depend on the overpotential for deposition. With coexistence of low molecular additive with polymer, the crystal of deposited Zn was fine regardless of kind of polymer even though Zn deposited at the diffusion control of ZnO₂²⁻ ions.

 

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 88 (2024) 58–67.

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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 adsorption structure of atomic oxygen on the PdZn(111) surface is studied using the first-principles calculation. At lower coverages up to 0.5 ML, oxygen atoms prefer to adsorb at threefold hollow sites surrounded by two Zn atoms and a Pd atom. Surface Zn atoms bonded with adsorbed oxygen atoms move toward the vacuum region, and the maximum displacement has reached 0.1 nm at 0.375 ML. At higher coverages from 0.625 ML to 1.0 ML, some oxygen atoms intruded into the surface layer and formed bonds with the Zn atoms in the second layer. At 0.75 ML, we observed the formation of the Zn-O hexagonal rings on the surface layer. It seems that the formation of the hexagonal rings largely contributes to the stability of the surface layer. However, the surface DOS and H₂O adsorption indicate no essential difference owing to the hexagonal Zn-O rings, and the hexagonal Zn-O rings disappeared at higher coverages. We discussed the relation of the adsorption energy, coverage, and the number of atoms located in the vicinity of the adsorbed oxygen atoms.

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The current trend in research on the physical properties of high-entropy alloys has been progressively increasing as there are many unknown possibilities for developing high-entropy alloys for advanced applications. This study investigated the effect of microstructures of rolled high-entropy alloy from the viewpoint of crystal orientation and dislocation density distribution to reproduce mechanical anisotropy using crystal plasticity finite element simulation. The crystal orientation and the geometrically necessary dislocation density of the rolled material were quantitatively estimated from experimental data of electron backscatter diffraction. Microstructural observation showed that particular textures were preferably oriented like in typical FCC metals. Even though the simulation results where only the preferred crystal orientation was considered did not show the expected mechanical anisotropy as in the experiment, the computational model with the dislocation density distribution and the preferred orientation showed the same tendency as the experiment.

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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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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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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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The 18th International Conference on Aluminium Alloys (ICAA18) was held in Toyama, Japan from September 4 to 8, 2022, and the special issue entitled “Aluminium and Its Alloys for Zero Carbon Society” was published on Materials Transactions in February 2023 (Vol. 64, No. 2). The biennial conference covered a wide range of current trends in aluminium research; e.g. “modeling and simulation”, “casting, solidification, recycling and refining”, “additive manufacturing”, “foams and composite materials”, “mechanical properties and advanced processing”, “thermomechanical processing, texture and recrystallization”, “heat treatment, phase transformation and precipitation”, “corrosion and surface treatments”, “joining, emerging processes and multi material” and “advanced characterization”. This article briefly reviews selected papers from the conference with significant experimental outcome and discussion on aluminium alloys. The author hopes that these papers are useful for all the researchers who develop next-generation technologies and materials concerning aluminium alloys.

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Chemically ordered face-centered cubic (fcc) phases consisting mainly of Cr, Co, and Ni were synthesized by annealing a Cr_26.7Co_26.7Ni_26.7Si₁₀B₅P₅ amorphous alloy. The annealed Cr_26.7Co_26.7Ni_26.7Si₁₀B₅P₅ sample was composed of Cr_4.5BP₂, Cr₃Co₅Si₂, and fcc phases. Synchrotron radiation anomalous X-ray scattering (AXS) measurements confirmed that the annealed Cr_26.7Co_26.7Ni_26.7Si₁₀B₅P₅ sample had superlattice reflections from an L1₀-, and/or L1₂-, and D0₂₂-type ordered structure. The diffraction intensities of the superlattice reflections observed in the AXS measurements indicated strong dependence on the incident X-ray energy. The diffraction intensity of the superlattice reflection increased at the X-ray energy near the K-edge of Cr, suggesting that Cr is mainly ordered in the L1₀- and D0₂₂-type structures. Microstructural analysis using scanning transmission electron microscopy (STEM) revealed crystal grains with diameters of approximately 20 nm, showing diffraction spots corresponding to superlattice reflections of 001 and 110, in addition to a two-dimensional diffraction pattern corresponding to the fcc structure. Simultaneous STEM–energy dispersive X-ray spectroscopy analysis indicated that the grains had a higher Cr concentration than the mother alloy composition of Cr_26.7Co_26.7Ni_26.7Si₁₀B₅P₅.

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This study explores the conduction mechanism of NbTe₄, a novel phase-change material (PCM) for phase-change random access memory (PCRAM), and addresses the limitations of the widely used Ge₂Sb₂Te₅ (GST). Unlike traditional PCMs, NbTe₄ in its amorphous state demonstrates low resistance, which indicates semiconductor behavior. However, the Hall and Seebeck coefficient measurements reveal an intriguing anomaly—amorphous NbTe₄ displays N-type conduction with Hall voltage and P-type conduction in the positive Seebeck coefficient. This Hall effect anomaly, which is typically associated with highly resistive chalcogenide materials, raises questions about the conduction mechanism in amorphous NbTe₄. This study delves into the electrical transport properties of NbTe₄ and provides insights into the unique characteristics of this PCM.

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Formation of stacking fault tetrahedra and diffuse streaks along <111> in the equiatomic Cr-Co-Ni medium-entropy alloy subjected to different heat-treatments and different specimen preparation methods are examined by transmission electron microscopy. Neither stacking faults nor stacking fault tetrahedra are formed simply by quenching from a high temperature due to the high energy barrier for the formation and migration of vacancies. These defects, however are found to form by Ar⁺-ion irradiation, as abundant vacancies are continuously introduced during ion-irradiation so as to bypass the high energy barrier for the formation. Diffuse streaks along <111> are usually observed in the SAED pattern with the <110> incidence regardless of heat-treatments and specimen preparation methods, indicating the occurrence of diffuse streaks is nothing to do with the formation of stacking faults and stacking fault tetrahedra.

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Neutron total-scattering experiments were conducted to search for signatures of the short-range ordering in medium-entropy alloys Tr-Co-Ni (Tr = Cr, Mn, and Fe). The reduced pair distribution function of the Mn-Co-Ni sample clearly deviates from that of the fully random face-centered cubic structure, whereas those of the as-quenched Cr-Co-Ni and Fe-Co-Ni samples can be explained with an almost random face-centered cubic structure model. The results of neutron thermal analyses and reverse Monte Carlo structure modeling indicate a possible compositional and/or magnetic short-range ordering in the Mn-Co-Ni system.

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The influence of sample geometry on various measured physical properties (including the magneto-Seebeck effect, Nernst effect, magnetoresistance effect, Hall effect, and thermal conductivity) in the presence of a magnetic field was examined using a polycrystalline Bi-Sb sample. The sample, consisting of polycrystalline Bi₈₈Sb₁₂, was prepared through spark plasma sintering and subsequent annealing. Measurements of the physical properties were conducted under a magnetic field of 5 T, and the obtained values were compared with simulated results derived using the finite element method for different sample geometries. Distinct shapes were found to be necessary for accurate measurements, with each physical property requiring a specific aspect ratio of sample length (l) to width (w). These ratios were determined to be l/w > 0.57, 2.9, 4.2, 1.2, and 3.1 for the magnetoresistance, Hall, two-wire magneto-Seebeck, four-wire magneto-Seebeck, and Nernst effects, respectively. Additionally, to achieve a minimal error of less than 2% in thermal conductivity measurement, a thermal conductance ratio of K_s/K_w > 27 was necessary, where K_s and K_w denote the thermal conductance of the sample and lead wire, respectively.

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In this study, we focused on the effects of various deformation amounts and subsequent heat treatment on σ-phase precipitation in CoCrFeMnNi high entropy alloy, known as Cantor alloy. Homogenized specimens with an initial FCC single-phase structure were deformed to various shear strains (1.1–25.8) using high-pressure torsion (HPT). This process resulted in a variety of deformation microstructures, with low to medium shear strains leading to the formation of twin-matrix lamellae intersected by shear bands, while high shear strains resulted in nanocrystalline structures. After deformation, the specimens were heat-treated at 700 °C for up to 5 h, which led to recrystallization of the FCC matrix accompanied by precipitation of σ phase. The kinetics of recrystallization and precipitation and their interactions during the heat treatment were greatly different among the specimens with different degrees of pre-deformation. Notably, the precipitation of σ phase was accelerated in the specimens subjected to higher shear strains, particularly in those with nanocrystalline structures. The increased rate of precipitation was beneficial for grain refinement since the presence of numerous precipitates within the recrystallized microstructures inhibited their grain growth. Tensile testing of the heat-treated specimens displayed various combinations of strength and ductility, with specimens subjected to higher pre-deformation exhibiting enhanced strength due to finer recrystallized grain sizes and larger fractions of precipitates. Our findings offer valuable insights into fabrication processing of HEAs, aiming to optimize microstructure and mechanical properties for potential engineering applications.

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The effective atomic radii of the constituent elements and their temperature dependence in quaternary and ternary subset alloys derived from the CrMnFeCoNi high-entropy alloy have been experimentally determined by a combination of lattice parameter measurements at room temperature and thermal expansion measurements down to the liquid helium temperature. The determined relative order of the effective atomic radii at 0 K is Co << Cr < Ni < Fe << Mn. The temperature dependence of the effective atomic radii differs from each other, but the difference is not large enough to change the relative order of the effective atomic radii at 0 K and room temperature. Absolute values and relative order among the elements do not agree with those calculated using the ab-initio calculations.

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Perovskite solar cells (PSCs) can produce solar energy that is both affordable and highly effective. Still, they currently face challenges in achieving peak performance in important areas, including sustainability, stability, and efficiency. Recent studies examine tandem perovskite solar cells based on CsPbI₃ in great detail, analyzing their photovoltaic characteristics with SCAPS 1D software. This work examines the effects of multiple parameters on performance metrics, including power conversion efficiency (PCE), fill factor (FF), open-circuit voltage (Voc), and short-circuit current (Jsc), with a focus on a multi-layered design. The photoactive layer thickness, defect densities, electrode contact quality, and operation temperatures are the factors. Compared to conventional lead-based perovskites, CsPbI₃ offers advantages in terms of long-term stability, reduced moisture susceptibility, and reduced lead toxicity. However, there is an issue with achieving efficiency levels comparable to MAPbI₃ and FAPbI₃. The research reveals correlations between material properties and device performance by applying advanced diagnostic techniques like quantum efficiency (QE), carrier concentration, and recombination rate analysis. This information has the potential to result in material enhancements and device optimization. With a particular focus on CsPbI₃, the work offers crucial insights into tandem perovskite solar cells that will advance the creation of more reliable, effective, and sustainable solar energy systems.

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In this study, FDEM (ECZM), which is the combined finite-discrete element method (FDEM) based on an extrinsic cohesive zone model (ECZM), was improved by incorporating a novel algorithm that makes it easier to insert the cohesive elements than the conventional adaptive remeshing and a scheme to avoid the generation of dormant cohesive element, which is generated as a result of inserting a single cohesive element within the FDEM mesh. The improved FDEM (ECZM) was implemented in a self-developed 2-dimentional code, and it was first validated against a numerical experiment assuming a virtual rock. Subsequently, the proposed FDEM was applied to model the uniaxial compression and the Brazilian tests of siliceous mudstones under quasi-static loading. The results of the proposed FDEM simulations reasonably captured the trends of fracturing and stress-strain curves observed in the experiments well. The proposed scheme can also be extended to parallel computation based on general-purpose-graphic-processing-unit (GPGPU) and 3-dimentional FDEM (ECZM) with minimal efforts.

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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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