The simulation for sintering of co-firing double layer compacts and substrate-constrained compacts were obtained by coupled Monte Carlo method and finite element method. In the coupled simulation of a co-firing compacts with different sintering shrinkage curves, the amount of warpage during and after sintering changed significantly. As a result of detailed confirmation of the results, it was found that there was a difference between the porosity obtained by the Monte Carlo method and by finite element method, so the coupled simulation was modified to minimize the porosity difference. As a result of the coupled simulation of constraint sintering, it was not contracted in the surface direction, but only in the thickness direction, and the results were represented in the previous experimental results. We found that coupled simulation can be applied as a tool to design and analyze the sintering behavior of products obtained by co-firing and constrained sintering.

Cemented carbide is a composite material of hard WC and soft Co, and has been widely used as a tool material because of its excellent balance of hardness and toughness. Among them, superfine cemented carbide with WC grain size of less than 1 μm is widely used as a base material for cutting tools and wear-resistant tools because it can achieve both high hardness and high strength. When using superfine cemented carbide as a cutting tool, it is essential to adopt the finer WC particles with higher Co dispersibility, in addition to the appropriate addition of grain growth inhibitors. If the WC particles can be finer, the hardness and transverse rupture strength of the alloy can be expected to improve. In addition, if Co particles, which are softer than WC particles, can be distributed more finely and homogeneously in the mixed powder, the mechanical properties of the alloy may be further improved. In this paper, we report on the improvement of Co dispersibility and the development of new ultra-fine WC, and introduce the cutting performance of the developed practical tools using above the WC powder.

The gas atomized powder is generally spherical and shows the good flowability, low oxygen content and high tapping density. In addition, because of its good productivity, it has been used as a structural material for a long time by taking advantage of these characteristics. Subsequently, it has been applied as a high-performance material in electronic devices, such as sputtering target discs for perpendicular magnetic recording, shot peening with high hardness media and AM etc. In this paper, the author describes some examples of the practical applications of high-performance materials using gas atomized powders.

Anisotropic shrinkage of powder compacts is often observed in sintering process. Although controlling the shape and size of the sintered body is important to reduce manufacturing cost, it is difficult to understand the factors affecting anisotropic behavior only by experimental observation. In the present study, two-dimensional numerical simulation for sintering process of elliptical particles is performed with changing particle alignment and orientation by using a combined phase-field method (PFM) and discrete element method (DEM). The effects of the size of inter-particle contact plane, the sintering force, and the pore configuration on sintering anisotropy are examined. According to the calculated results, anisotropic shrinkage appears depending on the particle arrangement. The elliptical particles oriented horizontally enhance the horizontal shrinkage. The inter-particle contact in vertical direction reduces the vertical shrinkage. The shrinkage behavior of compacts of elliptical particles can be basically explained by considering the combination of the sintering stress and the size of inter-particle contact plane, except the case of arrangement with largely elongated pore structure.

Rapid industrialization and increasing electricity demand have highlighted the urgency to reduce energy losses in power generation, accounting for over 60% of global inefficiency. Thermoelectric materials are pivotal for improving energy conversion in high-performance systems. We synthesized La₅SrCu_6−xFe_xO_15−δ samples via solid-phase reaction to study elemental substitution effects on thermoelectric properties. The performance was evaluated by the dimensionless figure of merit ZT = TS²σ/κ, integrating the Seebeck coefficient (S), electrical conductivity (σ), and thermal conductivity (κ). Our results show Fe substitution significantly changes structural, electronic, magnetic, and thermoelectric properties of La₅SrCu₆O_15−δ compound. Fe dopants improve ZT, particularly at higher temperatures, highlighting the potential application on material properties.

The properties of MAX phase ceramics that possess metallic and ceramic nature are anisotropic because of their hexagonal and layered crystal structure. Slip casting under a strong magnetic field followed by spark plasm sintering is one of the methods to control the orientation of the MAX phase ceramics. In this study, first, the textured Ti₂AlC-MAX phase was fabricated by slip cast under 12 T, where the direction of magnetic field was fixed to the slip cast direction after clarifying the easily magnetizable axis of Ti₂AlC. Second, the crystal orientation dependence of the room temperature deformation behavior was investigated by the Vickers hardness test from various orientations. It was found that the easily magnetizable axis of Ti₂AlC was the c-axis and the textured body could be obtained by applying the magnetic field from one direction. In the room temperature deformation, Vickers indents show an anisotropic shape and the hardness changed depending on the loading direction against the c-axis due to different deformation modes such as kink deformation and slip deformation. For 0°, since the slip deformation was unlikely to occur, linear crack growth was observed to form from the indent. For 45°, on the other hand, since the slip deformation occurred relatively easily, the crack growth was suppressed through the stress relaxation due to the slip deformation. For 90°, although the slip deformation is unlikely to occur similar to 0°, the crack propagation was suppressed through pile-up due to kink deformations along the c-axis. It can be concluded that kink deformation prevents crack propagation and increases the fracture toughness of the textured Ti₂AlC-MAX phase.

A magnetic core of a reactor applied to the boost converter of hybrid vehicle was developed. The core is made of High-Density Magnetic Composite, which is a kind of the powder magnetic core. A great cost reduction was achieved while keeping the magnetic properties equal to conventional magnetic steel. In order to achieve both high magnetic flux density and mechanical properties of the core, high compaction density and high bending strength were coped with by developed warm compaction technique using die wall lubrication. The great decrease of a core loss was achieved by adopting the Fe-Si alloy, developing the particle shape of the raw material powder made by the new controlled atomization method and enabling the annealing at the high temperature.

The relationship between the flammability and ignition of magnesium alloy powder for additive manufacturing prepared by the gas atomization method was investigated. It was found that the AZX912 magnesium alloy powder does not burn. Therefore, the powders with the average particle size of about 100 μm, which were sieved to 75-150 μm, were additively manufactured by the PBF method. The microstructure of the additively manufactured body consisted of finer dendrites than the atomized powder, and the calculated cooling rate was on the order of 10⁴ to 10⁷ °C/s. Next, the influence of the laser conditions on the microstructural changes of the additively manufactured body was investigated. It was found that the hot crack area percentage decreased when the laser energy density was in the range of 110-170 J/mm³. Furthermore, a fine microstructure without defects was obtained even after HIP treatment at 450°C and 98 MPa for 6 hours. This is due to the cooling rate after laser melting during the additive manufacturing.

In this study, Ti-Zr-Sc sintered alloys with excellent biocompatibility were fabricated from the elemental mixture of pure Ti, ZrH₂ and ScH₂ powders, and their microstructures and mechanical properties were investigated to clarify the strengthening mechanism. In particular, the effect of scandium (Sc) used as the third alloying element on the strengthening behavior by grain refinement, oxygen (O) and Sc solid solution, and Sc₂O₃ particle dispersion was quantitatively evaluated by using the theoretical strengthening models. 0.2% YS of Ti-Zr-Sc alloys decreased with Sc content in the range of 0~1.0 at.% Sc, and increased in the range of 1.0~2.5 at.% Sc. In the former, the added Sc elements reacted with O solutes to form Sc₂O₃ particles and resulted in a significant decrease of O solid solution strengthening effect. On the other hand, when Sc content was over 1.0 at.%, the strengthening effects by both Sc solid solution and Sc₂O₃ dispersion were effective, and cause a remarkable increment of 0.2% YS of Ti-Zr-Sc sintered alloys.

WC-Ti(C,N)-Cr₃C₂-Co ultrafine-grained cemented carbides with different contents of C, N and Co binder phases were fabricated. Their microstructures and mechanical properties were examined, and the relationship between the existing form of Ti(C,N) and various conditions was mainly discussed. The hardness of the samples increased and their fracture toughness decreased with decreasing C content. The average T.R.S. peaked at 4.8 GPa on the low-C side. Their microstructures significantly changed when the N₂ partial pressure changed. At a N₂ partial pressure of 2.6 kPa, the microstructure became finer and the average T.R.S. was the highest. Meanwhile, at N₂ partial pressures of 0 and 11.7 kPa, the microstructure became coarser and the average T.R.S. decreased. As the content of Co binder phase decreased, the number of WC/WC interfaces increased. The average T.R.S. was maximum at 16.4 vol% Co, and decreases with the Co content, but was higher than those of conventional cemented carbides. The existing form of Ti(C,N) changed depending on the N content. Herein, a N₂ partial pressure of 2.6 kPa and low C contents were deemed optimal.

In this study, titanium (Ti) alloy with carbon (C) solid solution was fabricated by laser powder bed fusion (LPBF) from Ti-TiC mixture powder to investigate the effect of C solid solution on microstructure and tensile properties of LPBF Ti alloy. XRD and TEM analysis showed that part of TiC particles was decomposed from the surface during melting process of LPBF and C was solid soluted in α-Ti for Ti-(0.09~0.4 wt%) C. The solid solution of carbon changed the microstructure of the LPBF Ti alloy to fine acicular microstructure due to the martensitic phase transformation. This was also observed in Ti-0.4 wt% C, where solid solution of carbon was not confirmed, suggesting that in Ti-0.4 wt% C, C was once solid solution and precipitated as TiC after phase transformation. LPBF Ti-C alloys showed good strength-ductility, UTS and elongation at break for Ti-0.2 wt% C were 746 MPa and 26.3%, respectively.

We analyzed the distribution of Co and Mn in the microstructure of ZnO varistor and discussed the effects of Co and Mn addition on electrical properties from the viewpoint that the influences of Co and Mn on the grain boundary layer, not on ZnO grains, are important. ZnO varistor showed excellent non-ohmic properties even when Mn was not incorporated into the ZnO grains. It was also found that the grain boundary layers consisted of thin intergranular layers between ZnO grains and grain boundary multiple points. The spinel particles remain at the grain boundary multiple points, and then react with the liquid phase, which is mainly composed of Bi₂O₃, to form ZnO with conductive properties during the cooling process. In ZnO varistor, the grain boundary multiple points are connected in a mesh-like structure, and if leakage currents occur at these points, the non-ohmic characteristics are degraded. Co and Mn are soluble in the spinel phase and act to increase chemical stability, and they suppress the reaction with the liquid phase, thereby maintaining the insulating properties of the grain boundary multiple points and contributing to the improvement of non-ohmic properties.

We prepared a catalyst-coated wire-mesh filter by thermal plasma spray method in order to develop a new type of carbon soot particulate matter (PM) removal component. The halftone plate of a SUS316 mesh was newly used as a substrate for a PM oxidation catalyst. A thermal plasma-spray method was applied to form a Ni-Pd alloy catalytic layer on the filter. As for the performace of Ni-Pd supported filter, the PM oxidation started from approximately 420°C, and the combustion at the catalytic surface took place at around 500-540°C, and finally a noncatalytic oxidation proceeded at around 650°C. The catalyst lowered a peak temperature around 110-220°C than that of only PM. Furthermore, the catalytic performance was maintained after a 5 times-repeated PM oxidation test. By the characterization of the catalyst layer, it was found that Pd particles were dispersed in a matrix of Ni and segregated on the surface and upper part of the plasma-sprayed film on the wire. The surface morphology did not change after the repeated cycle test. In this study, we found the availability of the plasma-spray catalyzed mesh filter was fabricated and as an environmental material with PM removal catalytic function.

This study investigated the viability of Hf and/or W doping in Li₇La₃Zr₂O₁₂ (LLZO) through an alkoxide derived sol-gel process aimed at stabilizing the ion-conductive cubic garnet phase. Results revealed that Hf doping tends to favor the tetragonal garnet phase, while co-doping with Hf and W effectively stabilizes the cubic garnet structure. This stabilization is attributed to the similar ionic radii of Hf⁴⁺ (0.71 Å) and the slightly smaller W⁶⁺ (0.62 Å) compared to Zr⁴⁺ (0.72 Å), considering charge neutrality. In both doping scenarios, a coexisting Li-deficient pyrochlore phase is observed, likely due to the use of HfCl₄ and WCl₆ as starting reagents in the alkoxide process, which results in reduced Li-coordinated carboxyl sites attached to chelated Zr alkoxide. However, increasing the Li excess content above 30% effectively eliminates the pyrochlore phase, thus stabilizing the cubic garnet phase. Impedance measurements conducted on Hf-doped LLZO and Hf,W co-doped LLZO (with 40% excess Li) sintered ceramics reveal a significant enhancement in bulk ion conductivity, with the Hf,W co-doped LLZO pellet exhibiting two orders of magnitude higher conductivity (1.09 × 10⁻⁴ S cm⁻¹). This finding confirms the stability of the cubic phase even with partial substitution of W and with 40% excess Li.

This study was intended to investigate the mechanical property at high temperature and cutting performance of cemented carbide for machining of exotic materials, such as nickel alloys, cobalt alloys, and titanium alloys. Exotic materials are widely used for equipment and parts in the aerospace and automotive industries due to their superior heat and corrosion resistance. When machining exotic materials, its low thermal conductivity causes the cutting edge temperature to be higher than when cutting steel, and the hardness of the tool material decreases, resulting in extremely low tool life. However, because cemented carbide in particular contains metals in its composition, plastic deformation of the cemented carbide cannot be prevented even when the coating has sufficient heat resistance. The WC-Co-NiCr alloy, in which NiCr partially replaces Co as the binder phase of cemented carbide, has improved high-temperature properties while maintaining room temperature properties compared with conventional WC-Co alloys, and tool life has been improved in machining exotic alloys.

In this study, α-Ti alloys with supersaturated iron (Fe) elements were fabricated by laser powder bed fusion, and their microstructures and mechanical properties were investigated to clarify the strengthening mechanism. The formation of β-Ti was not confirmed in the LPBF prepared Ti-Fe alloy, and Fe was solid soluted in the α-Ti grain. With solid solution of Fe, the α-Ti grain became fine, and the width of α-Ti lath was 530 nm with solid solution of 2 wt% Fe. 0.2% YS of LPBF Ti-Fe alloys increased with solid solution of Fe while maintaining a high elongation at break. The tensile strength of the Ti-2 wt% Fe alloy increased by 600 MPa compared to Ti-0 wt% Fe. The strengthening mechanism of LPBF Ti-Fe alloys was quantitatively clarified as Fe solid solution strengthening and grain refinement strengthening.

Metal additive manufacturing has been applied to produce products in various industrial fields such as aerospace, medical and so on because it enables the integrated manufacturing of complex-shaped products with the addition of new functions. However, because generation of defects is possible owing to the intrinsic properties of metal laser powder bed fusion (PBF-LB/M), the development of an in-process monitoring and feedback control technology is demanded to assure the final product quality and process repeatability. In this study, an in-situ monitoring system capable of simultaneously measuring the surface textures of the powder bed and built part and investigating the melting phenomena was developed. The surface textures of the powder bed and built part were able to be quantified by introducing a parameter of 2σ which is nearly equal to the areal surface texture parameter of Sq. It was elucidated that the shape of the melt pool during multi-track scanning was asymmetric in the scanning direction, and spattering occurs excessively toward the built part side because the vapor plume direction turns to the built part side due to the asymmetric melt pool. Moreover, it was revealed that there is a strong correlation between the areal surface-texture parameters and density or internal defects. Consequently, the systematic understanding of the PBF process through the quantification of the surface texture of the built part and the consideration of melt pool behavior leaded to the development of the in-process monitoring and feedback control system for PBF machines.

In the machine parts industry, manufacturing with 3D printers that use resin materials is attracting attention because of the demand for complex-shaped products and small-lot production. Although this method does not require a mold, many of the resin materials are petroleum-based resins, and environmental problems are a concern. Therefore, in this study, PLA, which has carbon-neutral properties, was used as the main material. In order to suppress heat generation when used as a mechanical part, a compound containing MoS₂, known as a solid lubricant, is used. PLA pellets and MoS₂ powder were kneaded in a desktop kneader, formed into wire-like filaments, and shaped into tensile test pieces with a 3D printer using a Fused Deposition Modeling (FDM). In the tensile test, as the amount of MoS₂ added increases, the contact area of PLA, which is thought to be due to strength, decreases. Therefore, the tensile strength decreased. On the other hand, the shorter the heat-kneading time of the composite material, the more suppressed the thermal deterioration of PLA and the higher the tensile strength. It is presumed that PLA composite materials with high thermal conductivity combined with MoS₂ are greatly affected by thermal deterioration due to heating during kneading.

The authors have fabricated spark plasma sintering (SPS) compacts with hardness (>200 HV) exceeding those of practical Mg alloys from 20 vol% Al₂O₃/Mg (20 vol%) powder with uniform dispersion of Al₂O₃ particles in Mg using a mechanical milling (MM) method. In this study, for the purpose of surface modification of practical Mg alloy M1A, the properties of M1A laminated compacts with thin 20 vol% layers on the surface of M1A discs fabricated by MM/SPS method were investigated. The surface hardness, lubricity, and wear resistance of the M1A disc were improved by coating the surface of the M1A disc with a highly adherent 20 vol% layer. Based on the results of X-ray diffraction and elemental analysis by SEM-EDS, it is considered that Al diffuses to the M1A disc and Mn diffuses to the 20 vol% layer, resulting in the precipitation of MnAl, an Mn-Al intermetallic compound at the 20 vol% layer/M1A interface. The relationship between the sintering time and the adhesion of the interface was investigated. The results suggest that the amount of Al diffusion from the 20 vol% layer to the M1A disc affects the adhesion of the interface rather than the precipitation of the Mn-Al intermetallic compounds at the interface.

In shis study, 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 uni-axis compression test, yield stress equation of BaTiO₃ is expressed by Shima’s equation and flow rule is written by plastic equiation. The coefficient of flow stress of BaTiO₃ is significantly smaller than literature 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 exprerimentally introduced. In addition, the coefficient of flow stress could be determined by simulation sensitivily analysis. Through this study, experimentally obtained yield stress equation, flow rules and coefficient of flow stress are numerically validated.

Metal oxides have been prepared with high temperature annealing for a long time. However, metal oxides are synthesized in nature at ordinary temperature and atmospheric pressure. In this study, learning from nature, metal oxides were synthesized at room temperature. This study focuses on “Formation and two-dimensional patterning of particle self-assembled structure”, “Synthesis of ceramics in aqueous solution and their two-dimensional patterning”, “Microstructure control and crystal face control of ceramics”, “Gas and odor sensors with highly active crystal faces”, and “Molecular sensors for detection of environmental toxin or cancer marker”. In particular, concept of crystal growth control and nanostructure control of metal oxides was proposed. The two-dimensional patterning of ceramic nanostructured films and particle self-assembled structure was achieved. In addition, a dendritic structure of tin oxide with metastable {101} crystal facets was developed in aqueous solution. They were applied to chemical sensors and gas sensors.

Ti-Si alloys with fine 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 samples under sufficient ductility of 17-20% elongation. Quantitative analysis using each strengthening model revealed that grain boundary strengthening by grain refinement was the main strengthening factor for all specimens of LPBF Ti-Si alloys.

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 extruded materials was also 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 pure Ti. The elongation at break value 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.

Composite of Ca-α-SiAlON and β-SiAlON was obtained by hot pressing of mixture of commercially available Ca-α-SiAlON and SiO₂ powders under 40 MPa at 1800°C for 2hours. The Ca-α-SiAlON powder used in this study was manufactured with combustion synthesis technique. Effect of SiO₂ additive on the mechanical properties of the SiAlON composite was investigated by changing the amount of the additives; 1, 3, 5 and 7 wt%. The highest strength, 736 MPa for the 4 points bending strength, was obtained in the SiAlON composite sintered with the addition of 5 wt% SiO₂ powder. From the results of XRD, SEM, and EPMA analysis, we found the formation of columnar β-SiAlON grains facilitated by the addition of SiO₂ powder led to the high strength.

Fabrication of ceramic materials has been developed through building up block particles. One of the commonest process of building blocks is a sintering process, in which dense sintered bodies are fabricated via building up particles. This work shows a different type of building blocks. Oriented ZnO seed layers composed of hexagonal plate-like ZnO particles were prepared by dip-coating convective self-assembly method through adjusting the particle volume fraction in suspension and the substrate withdrawal rate. Oriented ZnO rod films were fabricated by growing seed layers using a hydrothermal method. Concentration of the precursor, and hydrothermal treatment time was optimized to synthesize homogeneous ZnO rod arrays. The uniformity of the rod arrays was improved by applying a strong magnetic field (12 T) during hydrothermal treatment.

Titanates are one of promising sorbents for toxic heavy metal ions and radionuclides due to various chemical formulas and crystal structures, and their functional properties. Herein, we present a unique seaweed-like sodium titanate mat (SST) with randomly distributed layered sodium dititanate nanofibers synthesized by a simple hydrothermal process. We focused on the effect of NaOH concentration during the hydrothermal process on crystallographic properties and investigated the synthesis conditions for SST. Furthermore, Sr²⁺ sorption properties of SST and related titanates, which were synthesized by hydrothermal process, was studied by batch tests. SST, which consist of a dititanate phase, was synthesized at 10 mol/L NaOH concentration and trititanate phase was formed when the NaOH concentration was increased to 15 mol/L. The SST showed a high ion-exchange selectivity of Sr²⁺ against H⁺ and a high maximum sorption capacity (2 mmol/g), compared with the case of trititanate phase (0.49 mmol/g), which shows the precipitation of SrCO₃. This was presumably due to the difference of crystal structure of two titanates. This study demonstrates that the design of the crystal structure is important for controlling the sorption mechanism of sorbents for water treatment.

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

Two-dimensional nanomaterials have been studied as materials that may exhibit properties and functions different from those of bulk materials. In this review, graphene oxide with controlled surface oxygen functional groups, transition meta dichalcogenide (hereafter referred to as TMDC), MXene nanosheets and oxynitride nanosheets using soft chemical exfoliation synthesis, and their typical functions are described.

Synchrotron X-ray nano computed tomography was employed to study how the microstructure changes during the co-sintering process of multi-layer ceramic capacitors (MLCC). MLCCs are composed of alternating Ni electrodes and BaTiO3 dielectric layers. When the thickness of the electrodes was reduced to submicron levels, on the order of a few particle diameters, it led to the development of defects in the inner electrodes, resulting in a loss of capacitance. The discontinuous electrode region contained circular holes and irregularly shaped channels. The creation of these gaps was linked to an increase in the characteristic length of the non-uniform electrode structure, which can be described as a coarsening process. The transformation of the electrode's shape through surface/interface diffusion triggered the separation of the material connecting two holes. This separation was driven by instability induced by surface tension and stress, causing the material to form sharp points as it broke apart. These sharp points could potentially enhance the local electric field and lead to dielectric breakdown. An explanation was provided for the generation of defects arising from the arrangement of heterogeneous particles in the electrode layer.

This study was intended to investigate the mechanical property and cutting performance of AlTiBN coating for machining of exotic materials such as heat-resistant alloys and Titanium alloys, which has been increasing for aerospace, energy and medical industries. In conventional PVD coatings for cutting tools, Cr and Si has often been added to AlTiN in order to increase hardness and heat resistance, achieving high wear resistance. However, these methods increase hardness as well as Young’s modulus, which reduces toughness of coating. In exotic materials milling, coatings with a high Young’s modulus tends to develop internal cracks, leading to early destruction of the coatings. In this research, optimizing B content of AlTiBN coating, we realized low Young’s modulus while maintaining high hardness. This is probably because the pure AlTiN changed to a mixed crystal structure of cubic and hexagonal by the addition of B. When the cutting performance of this AlTiBN coating was evaluated in milling for Inconel 718, it was found that internal cracks were suppressed at the initial stage of processing. As a result, cemented carbide tool with the AlTiBN coating achieved approximately 1.6 times longer tool life than that with B-free AlTiN coating.

In this research, the microstructure and tensile properties of Cu-7 mass%Al alloy in the α single-phase region and Cu-10 mass%Al alloy in the (α + γ₂) two-phase region on the phase diagram fabricated by laser powder bed fusion (PBF-LB) process and casting were systematically examined, and investigated their microstructure formation mechanism and strengthening mechanism. As a result, in the case of Cu-7 mass%Al alloy, the micro-fine cellular structures formed by segregation of Al due to the constitutional supercooling by rapid solidification phenomenon in PBF-LB process leaded to high tensile strength and 0.2% proof stress, which were much higher than those of the castings. On the other hand, in the case of Cu-10 mass%Al alloy, the fine β´ martensitic structure with stacking faults formed by rapid solidification phenomena results in lower proof stress and higher tensile strength than the castings. Consequently, it was revealed that the high performance of the Cu-Al alloys is attributed to unique microstructure of the alloys formed by rapid solidification phenomenon in PBF-LB process.

The reduction strengthening of various rare earth-added ceria-based electrolytes was investigated. Sm³⁺, Gd³⁺ and Y³⁺ were selected as the dopants, and the dependence of the lattice constant and conductivity on the doping amount was investigated. The lattice constant changed linearly with the amount added. Only the addition of Y³⁺ decreased the lattice constant with the addition amount. This is probably because Y³⁺ has a slightly larger ionic radius than Ce⁴⁺, but is affected by the formation of oxygen vacancies. The ionic conductivity increased with the addition of rare earth elements, and showed the maximum value at 20 mol% addition due to the relationship between the increase in carrier concentration and the association of defects. It was found that the conductivity of the sample with Y³⁺ addition was lower than that of the others when the addition amount was the same. A 10-20% improvement in strength was observed when contact reduction was carried out at the composition showing the maximum conductivity. Formation of a surface compression layer due to contact reduction was confirmed by a hardness test with different indentation depths. In addition, XPS confirmed that there is a concentration gradient of Ce³⁺ from the inside to the surface in the reinforced sample, suggesting that the formation of the compressive layer is due to the reduction expansion only on the surface. Depth profile of XPS and TG-MS showed that only Gd added ceria is difficult to be reduced, which is considered to be related to strength optimization temperature.

Ground round bars made of WC-20 mass%Co cemented carbides were used to accurately determine the changes in shape. The bars were heated at 1673 K and cooled under different conditions to investigate the changes in Co content and diameter (d) in the longitudinal direction. When the bars were heated in a conventional sintering furnace, rapid cooling increased the Co content and d at both ends, while slow cooling increased those at the center. In the latter case, the amount of change was smaller. When the bar was heated using a tubular furnace and then cooled under 30 K of temperature gradient in the longitudinal direction, the Co content and d on the higher temperature side decreased and those on lower temperature side increased. The relationship between the change in Co content and the change in d could be explained quantitatively by considering the migration of the liquid phase in the temperature range of solid-liquid Co coexistence region. This study revealed that when WC-Co cemented carbides were fabricated using the conventional sintering furnace, an inevitable temperature gradient in the specimen during cooing caused the liquid phase migration and the shape distortion, regardless of the cooling rate.

A new synthetic strategy to produce porous ceramic particles with well-defined polyhedral particle morphology and three-dimensionally interconnected mesoporous structure has been developed by means of the combination of topotactic conversion of polyhedral crystal precursors and pyrolysis-induced phase separation. The crystal morphology of precursors is controlled by the liquid-phase synthesis, while the mesoporous structure in each polyhedral particle is tailored by the selective removal of a phase-separated phase preserving the other phase. In this review, two examples of porous polyhedral metal oxides prepared from hydrogarnet precursors: mesoporous and mesocrystalline 12CaO • 7Al₂O₃ mayenite microcubes and porous SrFeO_3-δ perovskite polyhedral particles. The synthesis and characterization of these porous materials as well as their applications in catalysis are overviewed.

Laser powder bed fusion (LPBF) process, which is one of the additive manufacturing technologies, is useful for fine and unique microstructures formation of metal materials due to ultra-rapid solidification and cooling behavior. Titanium (Ti) alloys show a high specific strength by adding rare metals such as vanadium, zirconium, molybdenum and niobium. In this study, from a viewpoint of sustainable development goals (SDGs), we clarify a role of the ubiquitous light elements, in particular nitrogen (N) solute atoms on the fine microstructures formation and improved mechanical properties of LPBF Ti materials, and finally establish a new alloying design of Ti materials with no rare metals. Core-Shell structured Ti-N composite powders coated with Ti₂N/TiN thin layers were developed as starting materials. LPBF Ti with a very few N contents (0.01 wt.%) shows continuous epitaxial growth of α-Ti grains with a strong crystallographic texture, which causes an anisotropic tensile properties. On the other hand, Ti-0.31 wt.% N alloy formed different microstructures and textures from LPBF pure Ti by introduction of refined martensite grains with random crystallographic orientations. As a result, its anisotropic tensile properties were remarkably reduced, resulting an improved tensile strength (1065.7 MPa) and high ductility (24.5%).

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.