A Cu/carbon steel multilayered sheet was quenched, and its tensile properties and electrical conductivity were evaluated. A full martensite structure was developed in the carbon steel layers in the multilayered sheet after quenching at 1063 K. The obtained Cu/martensite steel multilayered sheet exhibited a much higher ultimate tensile stress and approximately identical electrical conductivity compared to those in the Cu/carbon steel multilayered sheet without a quenching process. The decrease in the electrical conductivity during the quenching process in the multilayered sheet can be predicted from the decrease in the conductivity of the Cu layers owing to the diffusion of Fe atoms into the Cu layer. The ultimate tensile stress-electrical conductivity balance in the Cu/martensite steel multilayered sheet was 5.0×10⁴ MPa%IACS, which is higher than that in conventional commercial Cu alloys. The ultimate tensile stress-total strain balance in the Cu/martensite steel multilayered sheet was significantly lower than that in each phase in the sheet. The measured ultimate tensile stress and electrical conductivity in the Cu/martensite steel multilayered sheet were approximately identical to the values estimated from the rule of mixture, using the tensile stress, electrical conductivity, and volume fraction of each component phase. This result indicates that the ultimate tensile stress and electrical conductivity of multilayered sheets can be easily controlled based on the rule of mixture.

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Severe plastic deformation (SPD) has emerged as a transformative tool in materials science, enabling the development of ultrafine-grained, nanostructured and heterostructured materials with exceptional mechanical and functional properties. Initially gaining prominence in the early 2000s for microstructure control and mechanical property enhancement, SPD is now increasingly applied to improve functional properties, particularly in biomedical, energy, and hydrogen-related applications. The scope of SPD has expanded from metallic materials to encompass a wide range of non-metallic materials, including ceramics and polymers. Additionally, SPD methods have provided insights into natural phenomena involving high strain and pressure, such as phase transformations and certain geological and astronomical processes. This article reviews recent research trends, as highlighted in the 2023 special issue of Materials Transactions entitled “Superfunctional Nanomaterials by Severe Plastic Deformation”, focusing on recent advancements and interdisciplinary applications of SPD.

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Additive manufacturing of workhorse Ti6Al4V aerospace alloy components by direct metal laser sintering (DMLS) offers cost-efficiency in producing complex designs. However, the rapid and complex heating and cooling cycles during manufacturing can lead to undesirable microstructures and mechanical properties that are inferior to the wrought product. The present investigation aims to study the microstructure-fracture toughness paradigm for the heat treated DMLS Ti6Al4V sample with conventional thermos-mechanically processed microstructures. To this end, DMLS Ti6Al4V samples were subjected to isothermal heat treatment at 800 °C for 1 h to obtain a basketweave α+β dual phase microstructure, while hot rolled samples with equiaxed α+β microstructure were subjected to heat treatment at 1000 °C for 1 h to obtain a lamellar α+β microstructure. Fracture toughness tests were performed in three-point bend geometry on fatigue pre-cracked specimens for the three distinct microstructures. The fracture toughness of the heat treated DMLS parts is comparable to the thermo-mechanically treated lamellar α+β microstructure and superior to the equiaxed microstructure. Full-field strain measurement was performed during fracture toughness testing using digital image correlation and detailed microstructural characterisation was performed using electron backscatter diffraction and synchrotron diffraction. It was revealed that the deformation within the lamellar α+β phase delays the crack nucleation, while further crack propagation through thicker α laths and prior β grain boundaries contribute to pronounced crack tortuosity or crack path deflection resulting in a more corrugated fracture surface and enhanced fracture toughness.

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In TiC-Ti₃SiC₂ composites, the introduction of the TiC hard phase could improve the hardness of the Ti₃SiC₂ phase and prepare high hardness, high toughness and self-lubricating materials. In this study, elementary Ti, Si and graphite powders in the molar ratio of 3:1+x:2 were used as starting powders, a small amount of Al powder was added as a sintering aid, and spark sintering technology was used to sinter in the temperature range of 1373 to 1673 K at 50 MPa in vacuum. The reacted phases were identified by X-ray diffraction, and microstructure characteristics were observed. The formation mechanism of TiC-Ti₃SiC₂ composites was investigated based on the sintering behavior of the elemental powders during spark sintering. Pure TiC-Ti₃SiC₂ composites could be prepared from Ti, Si, graphite powders and Al at a molar ratio of 3:1.1:2:0.3 at 1573 K with a holding time of 0.9 ks. In conclusion, dual phase consist of TiC and Ti₃SiC₂ composite could be synthesized through in-situ reaction by adjusting process parameters such as sintering temperature, holding time and the content of Si and Al in element blending method.

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Ni-TiB₂ composites can also maintain high hardness at high temperatures, which has a wide range of application prospects, but due to the low self-diffusion coefficient of TiB₂, dense sintering is more difficult. Adding Ni as the binder phase and using the SPS sintering process can significantly reduce the sintering temperature of the composites and obtain the composites denser and improve the toughness. In this research, we investigated the sintering process of Ni-TiB₂ composites at 5%–15% Ni content, sintering temperatures between 1273 K–1473 K, holding times between 300 s–1200 s, in vacuum environments with 50 MPa of pressure. Using Box-Benhnken (BBD) design and Response Surface Methodology (RSM) were applied to optimize the process parameter variables including sintering temperature, nickel content and holding time, and hardness as a response variable. Based on the statistical model, the predicted optimal sintering process is Ni-10%, sintering temperature is 1433 K and holding time is 930 s. At the optimum process, the hardness and relative density of the composites were 2036 HV and 96.8%. The experimental predictions yielded an optimal average hardness of 2065 HV, an optimal density of 4.56 g/cm³, and an optimal relative density of 96.5%. The experimental results are highly consistent with the model prediction.

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In the present work, the microstructure and texture evolution in commercially pure titanium subjected to blast assisted deformation has been investigated by means of electron backscattered diffraction and transmission electron microscopy. The evolved texture in the deformed material is primarily attributed to the dominant ⟨1010⟩ 64.4° contraction twinning. Other deformation twins were also observed in a low fraction. A uniform dislocation background with other microstructural features observed suggested the formation of a superimposed microstructure in the material. {1121} extension twins (ET2) with a thick uniform pile-up of dislocation along its boundary have formed in the material. Parts of ET2 have detwinned leaving gaps along the twin length, revealing the unstable nature of ET2 twins. The in-depth microstructural analysis reveals the ET2 twin formation mechanism, where the instability developed in the material due to progressive lattice rotation via accumulative slip is relieved by ET2 twin formation by atomic shuffling. The gaps (local detwinning) observed in the present case is attributed to the transient oscillatory response of the material under impulsive loading, which has been previously reported in the literature.

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Titanium has the highest strength-to-weight ratio of any metal. Titanium and its alloys are strong and lightweight, and are therefore used in many industrial applications. The ω-phase is known to form metastably during quenching and aging processes of titanium alloys, and the presence of this phase causes increases in strength and decreases in ductility. However, the mechanical properties of the ω-phase are poorly measured because this phase precipitates as nanograins in titanium alloys. Here we report the fabrication of bulk polycrystalline ω-phase samples in pure titanium under high pressure and temperature conditions of 12 GPa and 400°C. They are single-phase and randomly oriented polycrystalline materials with an average grain size of 21 ± 8 μm. The 0.2% offset yield strength was determined from compressive stress-strain curves to be 913 ± 3 MPa. The ω-phase is more than twice as strong as the α-phase in pure titanium and could be used as a non-toxic structural material for biomedical applications.

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In this current study, polycrystal modelling has been utilized to understand the anisotropic dwell fatigue behavior of Cp titanium along rolling and transverse directions. A 2D microstructure of polycrystalline Cp titanium obtained through Electron Back Scattered Diffraction (EBSD) microstructure which is used to study the heterogeneous stress distribution, slip activity, and evolution of texture during tensile and dwell fatigue deformation through experiments and crystal plasticity fast Fourier transform (CPFFT) simulations. A significant anisotropy in the strain hardening is observed when deformed along the rolling direction when compared to the transverse direction which was attributed to the difference in texture which eventually leads to high dwell fatigue life along RD when compared to TD. The grains which developed a higher amount of stress post-deformation are labelled as stress hotspots which interestingly were observed to be higher during tensile deformation when deformed along RD when compared to TD and during dwell fatigue deformation the number fraction of stress hotspots are high along TD when compared to RD. The tensile deformation stress hotspots along RD have initial orientations // <1010> and <2110> direction whereas in case of TD grains the stress hotspots have initial orientations which are closer to <0001> and <2110>. The stress hotspots grains tend to reorient towards the <1010> direction along RD and towards <0001> and <1010> along TD during tensile deformation. The present study shows that crystallographic texture is a great tool to understand the anisotropy of dwell fatigue life of Cp titanium.

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The onset of plasticity in engineering titanium alloys with bimodal microstructures depends on the activation of slip in the equiaxed equiaxed α grains. We use protocols based on slip trace offset analysis to measure the ratios of critical resolved shear strengths (CRSS) in the equiaxed α grains in bimodal microstructures of Ti 6242 and Ti 6246 alloys. The resulting CRSS ratios for prismatic<a>/basal<a> and pyramidal<a>/basal<a> for Ti 6242 vary depending on whether the probability of slip is estimated at high Schmid factors for these slip systems or average Schmid factors over the range of orientations of equiaxed α used in the dataset. We compare these ratios to the existing data on these and other titanium alloys. We then examine slip in transformed β in these bimodal structures and conclude that deformation in transformed β is influenced strongly by slip transfer from equiaxed α arising from orientation relationships between equiaxed α and β rather than global Schmid factors associated with the load axis.

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This study investigates the spark plasma sintering behavior of TiB₂-10vol.%Ni powder composites, focusing on the effects of TiB₂ particle size variation on microstructure and toughness. The experimental results confirm that utilizing TiB₂ powders with mixed particle sizes enhances sintering performance and improves fracture toughness. Two types of TiB₂ powders were used: fine TiB₂ powder (STiB₂, ~3 μm) and a mixed powder containing larger TiB₂ particles (LTiB₂, average size ~15 μm). These powders were mixture with Ni powder and using spark plasma sintering preparation of composite material. The sintering behaviors corresponded to the obtained characteristic microstructures, as follows: (1) For 100STiB₂-10Ni, the relative density increased from the lowest temperature compared with others, which corresponds to random distribution of STiB2 and Ni. (2) For 100LTiB₂-10Ni, heterogeneous area consisting of fractured particles by initial loading corresponded to high level in initial relative density. (3) For 50STiB₂+50LTiB₂-10Ni, there were both similar areas to in 100STiB₂-10Ni and 100LTiB₂-10Ni, which correspond to density increase at initial stage and sintering promotion after medium temperature. The highest final density level was obtained by deformation of continuous Ni layer in heterogeneous region, such as100LTiB₂-10Ni. The sintering curve of 50STiB₂+50LTiB₂-10Ni could be explained by the behavior of both 100STiB₂-10Ni and 100LTiB₂-10Ni. Its relative density showed the highest value, and its sintering rate was close to that of pure Ni, which showed a high value. Furthermore, it was found that 50STiB₂+50LTiB₂-10Ni exhibited high fracture toughness values.

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Composites of DNA and gold nanoparticles are expected to be stimuli-responsive and photo-functional materials that can synergistically utilize both the stimuli-responsiveness derived from DNA and the optical properties derived from gold nanoparticles. However, conventional methods require the bottom-up synthesis of artificial DNA modified with functional groups such as thiols that can form chemical bonds with gold nanoparticles, which limits the flexible design of the resulting composite. Therefore, we conceived the idea of introducing a “linker” that can interact with both gold nanoparticles and the bases naturally exist in DNA. The introduction of such a linker allows naturally occurring DNA, which is abundant in nature and has long strand lengths, to utilize as the multi-functional material platform. In this work, we designed and synthesized a linker complex with disulfide group and platinum(II) ion to interact with gold nanoparticles and the bases of DNA, respectively. Furthermore, the interaction between gold nanoparticles and naturally occurring DNA via the platinum linker complex was confirmed using UV–visible absorption spectroscopy.

 

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 123–127.

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The present work proposes a low-cost and scalable methodology to produce electrocatalytic layers based on nickel phosphide deposition for oxygen evolution reaction. Through controlled heat treatment, the composition of the Ni-P layer can be tailored to achieve a Ni-Fe-P composite layer, which is expected to enhance the electrochemical catalytic effect. The electrochemical performance of heat-treated electrodes is evaluated by examining the effects of heat treatment temperature and electroless deposition thickness. This study not only demonstrates an innovative approach for constructing heterogeneous interfaces for high-performance electrocatalysts but also hints at the potential extension of this strategy to modulate interfaces between other binary and ternary electrocatalysts, thus propelling the frontier of water splitting technologies.

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This study investigates the mechanical properties of fully-lamellar Ti-6Al-4V, focusing on thermally activated processes behind yielding. Temperature dependences of yield stress, effective stress, activation volume, and activation enthalpy were examined within the temperature range of 77 K to 650 K. The change in the activation volume indicates a change in the deformation mechanism as a thermally activated process. The activation enthalpy in the fully-lamellar Ti-6Al-4V was closer to that of the basal slip in single-crystalline commercially pure Ti, indicating the dominance of basal slip in the fully-lamellar Ti-6Al-4V. Additionally, this study compares the difference in activated slip systems of this alloy with bimodal Ti-6Al-4V and Ti-0.45O, and suggesting changes in deformation mechanisms.

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The bending strength of ultrafine-grained cemented carbides exceeds that of medium-grained cemented carbides. This was thought to be due to the smaller size of defects within the ultrafine-grained cemented carbides. However, this attribution had not been verified because the specimens broke into numerous small pieces during bending tests. In addition, previous studies on the bending strength of medium-grained cemented carbides reported that there is limiting strength which is a region of not increasing bending strength by reducing the defect size. Therefore, in this study, we conducted the tensile test, which is unlikely to produce many small pieces, and the bending test to determine the cause of the high strength in ultrafine-grained cemented carbides. The ratio of bending strength to tensile strength was comparable between the medium- and ultrafine-grained cemented carbides. The number of fragments produced by fractures were almost same between the medium- and ultrafine-grained cemented carbides in case of the almost same strength. It was clear that the tensile strength of both medium- and ultrafine-grained cemented carbides increased as the defect size decreased with no sign of limiting strength. These results suggest that further strength improvements can be achieved by controlling defect size in ultrafine-grained cemented carbides.

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The deformation behavior, processing maps and microstructure evolution of AA7050 aluminum alloy were investigated using plane strain compression at temperatures of 300~450 °C and various strain rates ranging from 0.01 to 10 s^-1. Based on the flow stress and processing maps, the optimum hot working domains were established in the temperatures range of 420~450 °C and strain rates from 0.01 to 0.06 s^-1. The microstructure characterization of the deformed sample with the maximal power dissipation efficiency indicated that the deformation mechanism is the combined effect of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). At low strain, dynamic recrystallization (DRX) nucleation start preferentially at triple junctions. With increasing strain, continuous dynamic recrystallization grains are developed by the progressive rotation of sub-grains and the transformation from low angle boundaries to high angle boundaries within deformed grains. At the same time, discontinuous dynamic recrystallization grains spread along grain boundaries, which is related to the local grain boundary bulging. [doi: 10.2320/matertrans.MT-M2024173]

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This study investigates the impact of nozzle cavity structure on the flow and thermal field of aluminum melt to enhance casting nozzle design. FLUENT was used to perform numerical simulations on an ultra-wide 8021 aluminum alloy Hunter-type nozzle. The findings reveal that the tertiary flow distribution method exhibits a more dispersed flow, larger vortices, and greater temperature changes, particularly from the center to the edge of the nozzle, compared with the secondary flow distribution method. Consequently, optimizing the two-stage flow distribution significantly reduces velocity and temperature fluctuations in the aluminum melt at the nozzle cavity exit. This optimization enhances both the thermal field and uniformity of the melt flow, confirming the feasibility of the improved nozzle structure design.

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This study presents measurements of electrical conductivity and Vickers microhardness of ω phase in pure Ti. Samples containing 100% ω phase is produced by a high-pressure synthesis under an elevated temperature. The results are compared with those of 100% α phase in an as-received state and of the samples processed by high-pressure torsion (HPT) where severe plastic strain is imposed under a high pressure. For the electrical conductivity measurement, a contactless method using a superconducting quantum interference device magnetometer is employed, which allows the measurement over a wide range of temperature down to the liquid helium temperature. Vickers microhardness measurement is conducted for the ω phase under different applied loads to minimize the effect of reveres transformation from the ω phase to the α phase during the measurement. Microstructures are observed by electron back scatter diffraction analysis, showing that the grain size is of ~12 µm containing less dislocations, and this structure is in contrast with the HPT-processed sample having high densities of dislocations and grain boundaries. This difference in the microstructure results in appreciably lower electrical conductivity in a temperature range below ~100 K for the HPT-processed sample. No anomaly of a superconductive signal is detected in the ω phase down to the temperature of 1.8 K, suggesting that a superconductive state does not exist at ambient pressure in the corresponding temperature range.

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This study investigates the effects of severe plastic deformation (SPD) techniques, particularly high-pressure torsion (HPT) and high-pressure sliding (HPS), on the microstructural evolution and mechanical properties of commercially pure (Grade 2) Ti. The experiments were conducted under pressures of 2, 5, and 6 GPa. For the crystallographic analyses, X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used. Nanostructured Ti was obtained after processing by HPT and HPS, and the phase transformation from alpha (α) to omega (ω) phase was confirmed under pressures of 5 and 6 GPa. Vickers microhardness and tensile tests confirmed that HPT-processed samples exhibited increased strength under higher pressures, while the HPS process produced more homogenous material properties, along with a promising strength-to-ductility ratio. These findings indicate that the HPS process may offer better control over microstructure and mechanical performance, making it a promising technique to enhance the mechanical properties of pure Ti for biomedical applications.

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This study examines the effect of shock loading on allotropic transformation of pure Ti. The samples are initially processed by high-pressure torsion under 2 and 6 GPa to impart intense shear strain and they are subjected to shock loading at an impact speed of 702 m/s. X-ray diffraction analysis as well as hardness measurement is carried out to check the formation of ω phase. It is shown that intense shear strain before shock loading does not promote the ω phase formation but concurrent shear straining under high pressure is effective for the ω phase formation.

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Copper tubes used in heat exchangers were joined by brazing using copper phosphorus brazing filler metals. Leakage due to the progression of groove–like corrosion near the joints of copper tubes using copper phosphorus brazing filler metals became a problem. In addition to copper, copper phosphorus brazing filler metals also contained phosphorous and silver. In this study, we investigated the effects of silver on the corrosion resistance of copper phosphorus brazing filler metals. Observation and analysis of the metallographic structure of the copper phosphorus brazing filler metals revealed uneven distributions of phosphorus and silver components. Electrochemical measurements of anodic polarization curves showed that the current density of the copper phosphorus brazing filler metals with silver at high potentials was higher than that without silver. Furthermore, on the surface of the brazing material after the test, part of the structure of the silver-containing brazing material was observed to be corroded in the form of black dots. Therefore, the silver contained in the brazing material was considered to have effect on corrosion resistance of copper phosphorus brazing filler metals.

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In previous pilot plant studies, the authors developed a method for producing permanent mold (PM) spheroidal graphite iron (SGI) castings that prevents chill formation under as-cast conditions. Despite the advancement, chill structures ( ledeburitic cementite, Fe₃C) are still commonly from PM-SGI castings produced through current methods. Although heat treatment can decompose Fe₃C and induce graphitization, concerns remain that the distribution of tempered graphite may adversely impact mechanical properties.

This study examines the graphite distribution in both the developed and conventional PM-SGI castings. Additionally, it identifies factors contributing to undesirable graphite distribution following heat treatment. Results demonstrate that the newly developed PM casting method offers advantages not only in eliminating the need for heat treatment but also in enhancing mechanical design safety.

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The impact properties at a low temperature of 213K were improved by statically heat treatment using the cast steel containing 0.13C (corresponding to JIS standard SCPL11) at low material and manufacturing costs. The objective of this study was to satisfy the mean value of 18 J on the absorbed energy for low-temperature cast steels showing the JIS standard for SCPL11, by employing conventional static heat treatment equipment for low manufacturing costs. Heat treatments consisting of quenching at 1203 K for 14.4 ks followed by tempering at 953 K and 983 K for 14.4 ks followed by air cooling, LQ-LTA, and LQ-HTA, were selected as candidates at the points of the primary α phase size and absorbed energy at 213 K. For both the LQ-LTA and LQ-HTA specimens, the mean values of the absorbed energy at 213 K were 18.5 and 29.3 J, respectively, indicating that the objective was 18 J. The DBTTs of LQ-LTA and -HTA were observed at approximately 255 K and 235 K, indicating a promising heat treatment condition, HTA, because of further equilibrium and morphological changes in tempered microstructures, including the primary α phase. According to the nanoindentation results, the purpose of tempering, which is to adjust the hardness and toughness, was fulfilled in both treatments according to the conversion Hv and Young’s modulus. For the tensile properties at 288 K, both the specimens satisfied the objectives of the JIS standard for SCPL11. For the absorbed energy and tensile behaviors, both candidate treatments are useful for satisfaction of the JIS standard for SCPL11. LQ-HTA with higher upper shelf energy and lower DBTT can be suggested as a promising treatment in terms of microstructural stability.

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This study presents an innovative approach to the fabrication of Barium stannate (BaSnO₃) nanofibers for carbon dioxide (CO₂) gas sensing applications. The nanofibers were synthesized using the electrospinning method, enabling the formation of one-dimensional structures with high surface area and enhanced electron mobility. These structural properties significantly improve gas sensing performance, allowing for rapid resistance changes when exposed to CO₂ concentrations ranging from 2,000 ppm to 10,000 ppm. Additionally, the sensor exhibits excellent response and recovery times of 5–7 seconds, confirming its applicability for real-time environmental monitoring. BaSnO₃ nanofibers also offer substantial advantages over conventional detection methods, including superior cost-effectiveness, scalability, and high sensitivity. The study further suggests that dopant incorporation could enhance performance, demonstrating the feasibility of BaSnO₃ nanofibers as a scalable and efficient material for advanced environmental monitoring systems.

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Titanium and Ti-based materials are advanced materials that have found applications across various fields of science and engineering. Over the past three decades, significant efforts have been made to employ severe plastic deformation (SPD) via the high-pressure torsion (HPT) method on Ti-based materials. These efforts aim to achieve ultrafine grains with a high density of lattice defects, control phase transformations, and synthesize new compounds. Pure titanium, and Ti-containing alloys, intermetallics, ceramics and composites have been processed by HPT to enhance mechanical and functional properties. These properties include high hardness, high strength combined with plasticity, biocompatibility, superconductivity, dielectric performance, photocatalysis, electrocatalysis and photovoltaic capabilities. Additionally, the synthesis of new high-entropy alloys and ceramics via HPT has emerged as a promising direction, contributing to various disciplines such as photocatalysis, biomedical devices and hydrogen storage. This article provides a brief overview of the SPD concept and the HPT method, followed by a summary of recent advances in the HPT processing of Ti-based materials.

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In this study, we explored a method for preparing evaluation samples for hydrogen analysis, aiming to advance hydrogen analysis technology in metallic materials. Titanium-titanium hydride sintered specimens with varying hydrogen concentrations were prepared via spark plasma sintering (SPS) using titanium powder and titanium hydride powder, and the hydrogen concentration and distribution in the sintered specimens were evaluated. The obtained results are summarized below. SPS proved to be an effective technique for producing dense sintered compacts in a short time, allowing for easy control of the hydrogen concentration. Furthermore, most hydrogen existed as titanium hydride in the titanium-titanium hydride sintered compact, and high densification with a relative density of 98% or higher was confirmed. In addition, the hydrogen distribution in the upper, inner, and lower parts of the sample was measured using glow discharge optical emission spectrometry (GD-OES). The relative standard deviation of the hydrogen emission intensity in the titanium-titanium hydride sintered body was less than 5%, indicating that the hydrogen was uniformly distributed throughout the sintered body. These results suggest that titanium-titanium hydride sintered by SPS is useful as an evaluation sample for hydrogen analysis and is expected to be particularly effective for hydrogen analysis in GD-OES.

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Solder alloys are susceptible to creep deformation when subjected to prolonged stress during practical applications, with the creep resistance playing a crucial role in determining the life of alloy. In this study, In was introduced as a modification element in Bi-based solder alloys to enhance creep resistance. The addition of In resulted in a noticeable reduction in grain size and the formation of the strengthening phase Ag₂In within the microstructure. Nanoindentation analysis revealed that while the elastic modulus exhibited no sensitivity to strain rate, the hardness showed a positive correlation with strain rate. The load-depth curves displayed displacement bursts, indicating the formation of dislocations at the initial stages of deformation. The stress exponents for pure Bi and the modified Bi-2Ag-0.5Cu-0.5In alloy were measured at 10.12 and 10.75, respectively, suggesting a dislocation slip mechanism. Furthermore, as the strain rate increased, the stress exponent of the Bi-2Ag-0.5Cu-1.5In alloy ranged from 2.5 to 13.78, leading to a transition in the creep mechanism from grain boundary slipping (GBS) to dislocation slipping. The enhanced elastic modulus, hardness, and resistance to creep in the alloy can be ascribed to the precipitation strengthening of Ag₂In and the refined microstructure.

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Commercially pure titanium rolled sheets with different grain sizes of 20, 50, and 80 µm were applied to tensile tests to investigate the effects of grain size on the relationship between mechanical properties and activities of slip systems. While the ductility was independent of grain size, the activity of first order pyramidal slips and second order pyramidal slips decreased with decreasing grain size. In addition, grain boundary sliding was found to contribute to ductility when the grain size was small. Prismatic slips were activated in all of the specimens when yielded. Activity of pyramidal slips increased with increasing strain and decreased with decreasing grain size. Tensile tests were interrupted and slip lines were observed after the unloading in this study. Yield stress increment was observed when reloaded in interrupted tensile tests, but not in immediate reloading tensile tests. We found room temperature strain aging in pure titanium sheets. Yield stress increment increased with increasing strain.

 

This Paper was Originally Published in Japanese in J. JILM 74 (2024) 421–426.

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Cryogenic applications require careful material selection due to severe property degradation at low temperatures. Face-centered cubic (FCC) alloys like high-manganese steel offer good low-temperature toughness but become brittle at cryogenic temperatures. This brittleness increases safety risks due to sudden, unpredictable fractures. Therefore, novel technologies are urgently needed to improve the mechanical properties of FCC alloys for cryogenic applications. This research presents a new surface-cracking process for high-manganese steels to address the degradation of mechanical properties at cryogenic temperatures. This technique involves the intentional introduction of surface micro-cracks, which significantly enhances the Charpy impact toughness of the steel at low temperatures. To observe the effect of surface cracks, specimens with varying crack densities were fabricated: 5 lines (5L) and 10 lines (10L). These were compared with a standard specimen without surface cracks (0L). Microstructural observations reveal that the dispersion of crack propagation energy by the surface micro-cracks improves Charpy impact toughness, promoting a ductile fracture mode even under cryogenic conditions.

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In this study, CNN models were developed to predict the changes in creep properties of long-term aged CMSX-4 alloy based on heat treatment time by training deep neural networks with microstructure images of the material. To predict the creep rupture time and fracture strain of specimens heat-treated for 0 to 10,000 hours, the CNN models were trained using BSE images of the specimens and their two-point spatial correlation images. As the heat treatment time of CMSX-4 alloy increases, topological inversion occurs, where the arrangement of the γ phase and γ' phase changes, leading to significant microstructural changes. When the CNN models, built to predict the creep properties based on microstructural evolution, were trained with 8-bit grayscale BSE raw images, γ-γ correlations, or γ-γ' correlations, the model trained on γ-γ' correlations exhibited the best performance in predicting creep rupture time and strain. With the development of CNN models and computational resources, it has become possible to directly learn from raw microstructure images. However, it remains essential to capture microstructures from areas large enough to adequately represent the characteristics of the specimen. In microstructures composed of γ and γ' phases, two-point spatial correlation analysis serves as a microstructure descriptor, providing sufficient information for artificial neural networks to predict material properties. This study demonstrates such findings and is expected to contribute to various artificial neural network research utilizing microstructure images.

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The authors proposed direct reduction from metallic oxides to their metals in 2000–2003. This concept was firstly applied for direct reduction of TiO₂, and called the OS process in comparison with FFC Cambridge process. Both processes commonly used the CaO-CaCl₂ melt, the electrolysis with the carbon anode, and TiO₂ as the starting oxide. OS process is designed as a 1-pot operation, the combination of thermal reduction by Ca in CaCl₂-CaO melt and the simultaneous electrolysis of the byproduct CaO to form metallic Ca. O^2- is extracted as CO/CO₂ gas from the carbon anode, and Ca²⁺ forms Ca (dissolved as the metallic state in the molten salt). This reducing environment near the cathode is suitable for metal formation from various oxides. This overview (part I) summarizes the basic concept of OS process, and the subsequent overview (part II, III) will report its experimental confirmation and its applications, respectively.

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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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