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. O²⁻ 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.

Polycrystalline Eu_2−xCe_xCuO_4+α−δ has been successfully synthesized with x = 0.09 and 0.10. The samples were prepared through a standard solid-state reaction method with annealing treatment to reduce the oxygen content. The investigation of the crystallographic parameters of Eu_2−xCe_xCuO_4+α−δ material was conducted by using XRD measurements. The crystallite size of the samples was determined and analyzed using the Debye-Scherrer and the Williamson-Hall Plot Method (W-H plot). It was found that the purity for all samples is 100% with tetragonal structure T′ type and CuO₂ conduction layer with a planar configuration. The value of the lattice parameter a-axis increases, while the lattice parameter c-axis decreases with the doping concentration of Ce (x). From the lattice parameter analysis, it was found that the Cu-O bond length increased by doping concentration x due to the strain factor and the volume expansion of the unit cell in the ab plane. The crystallite size of the sample increased by doping concentrations both using Debye-Scherrer equation and W-H plot. The crystallite size of samples determined by W-H plot is bigger than that of Debye-Scherrer method. It is because the W-H plot includes the micro-strain effect in the calculation which is coming from lattice imperfection. This result indicated that lattice imperfection such as atom dislocation and defect might occur in Eu_2−xCe_xCuO_4+α−δ. Therefore, utilizing the W-H plot is preferred because it provides more detailed data.

The microstructure changes in the precipitation hardening copper alloys during the thermal process after deformation are known to exhibit complex behavior due to the simultaneous progress of various phenomena such as precipitation, recovery, recrystallization, and grain growth. Understanding the mechanism is an important issue for designing the heat treatment processes.

In this study, the microstructure changes in the Cu-Co-P alloy during thermal process after a deformation was numerically simulated based on the N model coupled with the dislocation recovery model, where the interaction between dislocations and precipitation behavior was focused. As a result, the following peculiar phenomena were calculated:

The fcc-Co formation and the Co₂P precipitation on dislocations take place simultaneously in the Cu-0.32 at%Co-0.21 at%P-0.11 at%Sn alloy. The Co particles are left inside the bulk Cu matrix in the recovery process of dislocations, and then the Co particles are re-dissolved into matrix phase. The following mechanism was proposed to explain this peculiar behavior. Since the Co particles inside a bulk matrix left by the dislocation recovery have high interfacial energy, they re-dissolve into the matrix phase to release this energy. Furthermore, the decrease in Co concentration in the matrix phase due to the Co₂P precipitation on the dislocation accelerates the Co particle re-dissolution.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 258–266.

The classification of complex microstructures in low-carbon steels is sensitive to imaging conditions, often causing domain shifts that degrade the accuracy of deep learning classifiers and confuse visual identification by experts. In this study, we constructed two SEM image datasets of low-carbon steels with eight heat treatments using field emission (FE) and tungsten (W) SEM sources. The accuracy of classifiers trained on images from one source and tested on images from another source showed a significant drop, from over 90% to around 40%. This finding underscores the significant impact of domain shift on both automated and visual classification. To address this problem, we used cycle-consistent generative adversarial networks (cycleGAN) to translate images between domains. This approach restored classifier accuracy to more than 90% and successfully reproduced the distinct visual characteristics of each SEM source, thereby confirming the effectiveness of cycleGAN in standardizing imaging conditions for reliable microstructural analysis.

Ti-Si alloys with fin α-Ti grains and Si solutes were fabricated by laser powder bed fusion (LPBF) process and subjected to hot rolling to form ultrafine grains at the submicron level from fine acicular grain structures. The relationship between the microstructures and mechanical properties of each Ti-Si alloy sample was investigated, and the quantitative strengthening analysis was carried out to find the main strengthening factor by using the theoretical models of grain boundary strengthening, solid solution strengthening and precipitation hardening mechanism. Grain refinement was observed with increasing Si content, which was due to the solute drag effect of Si solute atoms as well as Zener pinning by the precipitation of ultrafine Ti₃Si particles of about 50 nm in the Ti-0.7%Si material. The 0.2% YS values were 1.5 to 2.2 times higher than those of Ti-0%Si specimens under sufficient ductility of 17–20% elongation. A quantitative analysis using each strengthening model revealed that grain boundary strengthening by grains refinement was the main strengthening factor for all specimens of LPBF Ti-Si alloys.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 499–509.

The effect of carbon elements on the microstructures and mechanical properties of pure Ti alloys fabricated through extruded powder metallurgy route was investigated. Furthermore, the strengthening mechanism of the extruded materials was investigated quantitatively. In Ti-C materials, the lattice parameter in c-axis of α-Ti increased due to solid solution of carbon atoms in the most stable octahedral interstitial sites. As the carbon contents increased, tensile strength was increased while maintaining a high elongation at break. The 0.2% yield stress of Ti-2.0 mass% TiC increased by 242 MPa compared with that of pure Ti. The elongation at break exceeded 35.0% for all specimens. According to this analysis, it was clarified that F_m value of Ti-C materials was 2.90 × 10⁻¹⁰ by using Labusch model. The estimated strengthening improvement using these values was significantly agreed with the experimental results of PM Ti alloys with carbon solution atoms. Furthermore, the strengthening mechanism of the alloys was quantitatively clarified that carbon solution strengthening was the dominant factor in this study.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 474–481.

The microstructure and fatigue crack initiation process of Ti-6Al-4V alloys were measured using a multimodal technique combining synchrotron X-ray microtomography and electron backscatter diffraction (EBSD) serial sectioning techniques. Various microstructural design variables were generated to describe the shape, size and crystallographic information of the polycrystalline microstructure that is the fatigue crack initiation point. The microstructural information was coarsened based on the similarity between the design variables and their correlation with fatigue crack initiation. An objective function describing the resistance to fatigue crack initiation was also established. By combining these variables, the relationship between the microstructural information and fatigue crack initiation resistance was described by a metamodel in the form of a multidimensional response surface using a support vector machine. A limited number of design variables with a high correlation with transgranular and intergranular fatigue cracking were identified, and the optimum or weakest microstructural patterns for fatigue crack initiation were quantitatively represented. This approach is expected to allow much more efficient microstructure control to enhance the fatigue crack initiation resistance than has previously been possible with the conventional surface-based approach.

The effect of carbon on the heterogeneous deformation behavior of a martensite was investigated by multiscale strain distribution analysis using the digital image correlation method. Specially, 18%Ni martensitic steels with and without carbon (0.15C steel and C-free steel, respectively) were studied. Low-magnification observation showed that in both steels, a macroscopic strain distribution was caused by the shape of the specimen. However, high-magnification observation revealed that the strain was concentrated in specific blocks in 0.15C steel, suggesting that its heterogeneous deformation behavior depends on the martensitic structure. Thus, addition of carbon in 18%Ni steel was concluded to cause preferential plastic deformation of the blocks owing to an in-lath plane slip system, which tends to promote heterogeneous deformation.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Heat Treatment 63 (2023) 192–198.

The stress-strain curves, glass-forming ability, and fracture properties of bulk metallic glasses with the composition Cu_47.5Zr_(45.5−x)Al₇Y_x, where yttrium content (x) is 1, 3, and 5 atomic percent (at%) are examined subjected to compressive strain rates between 10⁻³ and 4 × 10³ s⁻¹. The findings indicate that adding yttrium increases the reduced glass transition temperature T_rg. Moreover, the γ parameter, which indicates the ability to form glass, rises as the yttrium concentration goes from 0 to 3 at%, but experiences a slight decrease when the yttrium content is increased to 5 at%. In all the alloys that were tested, the fracture stress rises with increasing strain rates, whereas the fracture strain diminishes. The addition of 3 at% yttrium results in the highest fracture strain under tested conditions. The fracture surface observations reveal molten droplet structures, vein patterns, and dimples. The results demonstrate that strain rate and yttrium content are the primary factors influencing the fracture behavior of Cu_47.5Zr_(45.5−x)Al₇Y_x bulk metallic glasses.

The effects of extrusion and dispersed particles (SiC or SiO₂) on the mechanical properties are examined on aluminum (Al) based composites prepared from powder metallurgy. Extrusion is effective for i) grain refinement of the α-Al matrix and ii) producing high quality bulk specimens on a large scale. This is because of a high applied stress during hot-extrusion contributes to the degradation of oxide films covering the powder particles, leading to the creation of new real surfaces. Microstructural observations show that powder-based extruded Al and its composites have fine-grained structures, i.e., an average grain size of less than 5 µm in the α-Al matrix. Accordingly, associated to these microstructures, they show higher strength (∼30 MPa) and hardness (∼10 Hv) than those of cast Al and its composite. In addition to beneficial mechanical properties, the extrusion process does not give a negative impression as for wear property, i.e., the wear rate. Plasticity-controlled void growth mechanism is focused to consider the impact of extrusion on bonding quality. The time required to shrink voids is estimated, and this value is consistent with the actual processing duration.

To clarify the effect of pores on high temperature compressive behavior due to kink deformation, textured Ti₃SiC₂ pressureless sintered bodies were fabricated and examined by high temperature compression tests with different porosities.

The textured Ti₃SiC₂ pressureless sintered bodies were prepared by slip casting in a strong magnetic field and spark plasma sintering at 1400°C for 1 h. Samples were cut into rectangular shape with 45° between the casting direction and the compression axis, and compression tests were conducted at 1200°C at a strain rate of 3 × 10⁻⁴ s⁻¹. Porosity was evaluated by Archimedes method and binarization. Crystal orientation analysis using EBSD method was performed to observe the microstructure evolution before and after the compression test.

The sintered bodies had a strongly textured microstructure with homogeneous dispersed pores. The results of high temperature compression tests showed that the 0.2% proof stress depended on the porosity before compression tests. On the other hand, the work hardening coefficient was larger for plessureless sintered sample with high porosity, which attributed to the densification associated with the compression. Microstructural observations indicated that fine kink bands formed in the middle stage of the compression and then disappeared, suggesting that this is important for clarifying kink-band strengthening in the MAX phase.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 88 (2024) 297–305.

In order to fabricate multi-materials such as joining between aluminum alloy and engineering plastics for the purpose of lightening the weight of automobiles, this study investigated surface treatments to improve the adhesion and corrosion resistance of A5052 aluminum alloy. The two-step anodizing process of phosphoric acid anodizing + sulfuric acid formed a two-layer film with a phosphoric acid treated film on the upper layer and a sulfuric acid treated film on the lower layer. In this two-layer coating, the sulfuric acid-treated film on the lower layer improves the corrosion resistance, and the phosphoric acid-treated film on the upper layer improves adhesion, showing excellent adhesion and corrosion resistance.

This Paper was Originally Published in Japanese in J. JILM 74 (2024) 346–351.

In this study, a Ni-selective reduction process utilizing Ni laterites was developed to enhance the production efficiency of Fe-Ni metal. The reduction behavior of two distinct types of Ni laterites (limonite and saprolite) was investigated using high-temperature reduction experiments at 1380°C for no more than 30 min, using coal as the reductant. The results revealed that Ni was preferentially reduced relative to Fe, achieving a maximal reduction fraction of 91% and a Ni-grade of 11–13% in the metal. A comprehensive mineralogical analysis indicated that goethite, serpentine, and silicate (Ni-, Fe-, and Mg-free) were the predominant minerals in the Ni laterites, collectively constituting over 85 mass%. The contents of these three minerals significantly influence the reduction reaction from both thermodynamic and dynamic perspectives, i.e., reduction activity of Ni and Fe in silicates and the meltability of the sample, respectively. These findings strongly suggest mixing of limonite and saprolite for Ni-selective reduction.

We investigate the synthesis of nickel and cobalt nanoparticles at low temperatures (40°C) via a sonochemical process with nickelocene and cobaltocene as starting materials. The reduction and decomposition behaviors of nickelocene and cobaltocene are studied using ultrasound irradiation for different concentrations of hydrazine. At 5 and 10 vol% of hydrazine, nickel nanoparticles are synthesized from nickelocene by direct hydrazine reduction without intermediate formation. However, at a hydrazine concentration of 50 vol%, nickel nanoparticles are formed from Ni-hydrazine complexes. In contrast, from cobaltocene, microsized cobalt particles are formed by multistep reduction at 50 vol% hydrazine. Because nickelocene is more unstable than cobaltocene, it is assumed that nickel is formed by direct reduction under ultrasound irradiation at low concentrations of hydrazine. This sonochemical process using metallocene is expected to be an eco-friendly synthetic process as it does not require pH control, as in the conventional processes, and can be conducted at 40°C using a simple apparatus.

In order to develop a new oxide-dispersion strengthened Cu alloy for heat sinks of fusion helical reactors, Cu alloy powders containing Ti, Fe and Y were prepared by atmosphere controlled gas atomization, and the effect of oxygen was investigated. The microstructure of the Cu alloy powder had a typical solidification structure regardless of the alloying element and gas species. The Fe atom was uniformly solid-soluted in the matrix, while the Ti and Y atoms were swept out from the matrix to the grain boundaries and particle surfaces during solidification. The average particle size and aspect ratio of the obtained powders decreased with the use of the N₂ + O₂ gas mixture. This is due to the lower surface tension of Cu in the oxygen atmosphere, suggesting that the frequency of the strip breakage stage in the gas atomization process was suppressed due to the formation of oxide film on the particle surface.

This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 71 (2024) 467–473.

The applicability of lead-free bronze to permanent mold casting has been reported only in fundamental studies. This study experimentally and analytically studied the applicability of bismuth bronze alloy to permanent mold castings with casting shapes similar to actual pipe fittings. The Vickers hardness of a permanent mold-cast bismuth bronze pipe fitting was 22 HV higher than that of the sand mold-cast bismuth bronze pipe fitting, and the increase in tensile strength of 75 MPa can be expected from the conversion formula between hardness and tensile strength. However, the permanent mold-cast bismuth bronze pipe fitting had defects such as shrinkage porosity, solidification cracking, and surface porosity. As a result, all permanent mold-cast pipe fittings leaked in the pressure leak test. From the results of the retained melt modulus analysis using casting simulation software, it was found that a relatively small amount of molten metal compensated for solidification shrinkage in the permanent mold casting. This caused the shrinkage porosity, hot tearing, and surface porosity in the permanent mold-cast pipe fittings. Therefore, the gating and risering system must be carefully considered for permanent mold casting of bismuth bronze products. This study showed that the retained melt modulus analysis is effective for considering gating and risering systems and predicting defects caused by insufficient feeding. In addition, surface porosity requires measures such as increasing machining allowance.

This Paper was Originally Published in Japanese in J. JFS 96 (2024) 608–615.

Surface hardening treatment is used to have strength to mechanical parts, and carburizing and quenching are the most widely used. There are reports on various carburizing efforts to deal with recent environmental issues. The authors have proposed an ultra rapid carburizing above the eutectic temperature, due to realize in–line carburizing. Since this is an unprecedented carburizing treatment method, setting the carburizing conditions that are suitable for efficiency has been the future challenge.

In this paper, we investigated a method for predicting the carbon concentration profile in the steel based on the known carburizing reaction mechanism of ultra rapid carburization. In order to predict the carbon concentration profile in the steel, it was calculated by the finite difference method using the carbon penetration rate F, the use of F=4.04×10⁻¹¹e^{(1.20×10-2・T)}, which penetrates from the surface, and the carbon diffusion in the steel based on Fick’s law. In addition, among various carbon diffusion coefficients D_c, the use of D_c(T, C)=4.53×10⁻⁷{1+y_c(1-y_c)8339.9/T}・e^{{-(1/T-2.221・10-4)(17767-y_c・26436)}}, which takes into consideration the dependence of carbon concentration, gave a good agreement with the actual measurement results by EPMA. Furthermore, as a result of investigating efficient carburizing conditions using a prediction method, we could minimize the time required to obtain an effective case depth of 0.8 mm. In addition, the amount of carburizing gas used was also reduced. In other words, it suggests that the accumulation of a huge amount of condition data and the condition setting skills are no longer necessary.

This Paper was Originally Published in Japanese in J. Japan Inst. Met. Mater. 87 (2023) 179–185. Reference [3] was added as the English translation edition of Ref. [2]. In Ref. [14], book title was corrected.

Drawing a high-carbon steel wire increases the strength of the wire but significantly reduces its ductility. In addition, leading to the delamination, which is characteristic of a high-carbon steel wire and occurs in wires with reduced ductility, appears, and this is the biggest factor in the inhibition of high-strength wire. We investigated the possibility of suppressing delamination by using the alternating wire drawing process, which suppresses additional shear strain during drawing and increases ductility. First, we conducted tension tests on alternately and conventionally drawn wire to investigate changes in mechanical properties, with alternately drawn wire at a breaking strain of 1.9% and conventionally drawn wire at a breaking strain of 1.5%. Next, we conducted a torsion test, as stipulated in the Japanese Industrial Standards, and confirmed that the alternate wire drawing process suppressed the delamination. We also examined whether the alternate wire drawing process suppressed axial tensile residual stress on the wire surface by using the slit method and Finite element method analysis.

This Paper was Originally Published in Japanese in J. JSTP 65 (2024) 153–158.

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. Figure 6 was slightly modified.

Regarding the permanent mold casting (PM) method for spheroidal graphite irons castings, the attractive method has been developed to obtain a full graphite structure without forming Fe₃C in the as-cast condition by controlling the free-nitrogen. When using this method, additional processes, such as heat treatment, are not necessary. However, heat treatment must be applied when using conventional methods owing to the formation of ledeburite (chills). In this study, sample castings were cast using conventional and developed PM casting methods, and the relationship between graphite distribution and impact properties investigated. Consequently, the graphite distribution of conventional samples was determined that order tendency was higher than developed samples. Forthermore, the impact absorbed energy of the samples with high ordinal tendency was lower than that of the samples with high random tendency graphite distribution. The total absorbed energy, crack initiation or propagation energy were strongly correlated with randomization or not in characteristic graphite distribution by both developed and conventional manufacturing methods. Therefore, the developed methods confer the benefits of not only less processing for casting but also better impact properties that enhance design safety.