Due to the increasing demand for high-precision products in metal additive manufacturing, such as powder bed fusion, there is growing expectation for high-quality fine powders produced by the Plasma Rotating Electrode Process (PREP) method. However, the PREP method currently faces a bottleneck due to its low acquisition rate of fine powders below 50 μm. In this study, we analyzed the generation and control of molten layers in PREP and their relationship with centrifugal force, aiming for size reduction. Through experiments using SUS316L and Ti6Al4V alloys, we demonstrated that process parameters such as material diameter, melting current, and cooling gas could control powder size. A significant increase in the acquisition rate of fine powders with an average particle size below 40 μm was observed using a production-scale PREP apparatus with specific parameters. Furthermore, we found that the gas cooling mechanism plays a crucial role in controlling parameters like the melting temperature of the molten layer.

Recently, the material extrusion (MEX) method, known for its straightforward and economical setup, has become a focal point in metal additive manufacturing. MEX enables the fabrication of precise 3D models by molding metal powders with resin, followed by debinding and sintering processes. Through material development, this method is expected to become more extensively applied for the development of various functional parts by materials and shape designated using topology optimization and lattice structures. This review covers the MEX process, including feedstock, equipment, materials, printing, debinding, sintering, and the physical properties of sintered parts.

In this paper, we present the characteristics of our Directed Energy Deposition 3D printing machine LAMDA, focusing on the local shield nozzle and monitoring feedback. We explain the effects of the local shield nozzle, which ensures a wide shielding area, and the monitoring feedback, which stabilizes the melt pool and improves the stability of the metal material and shape, with examples of the resulting structures.

The effect of W addition on microstructure and creep properties of sintered 25Cr-20Ni-1.3Nb austenitic heat resistant steel is investigated. The 25Cr-20Ni-1.3Nb sintered compact had a structure in which fine spherical NbC was uniformly dispersed in the γ-Fe matrix grains and Cr₂₃C₆ was discontinuously precipitated in a thin film at the γ grain boundaries. In addition, the creep life of those compacts was lower than that of the cast material of the same composition. The addition of W resulted in higher creep properties than the cast material. The improvement in creep properties is due to the reduction in void ratio and grain growth. Fine W powders fill the pore between coarse powders of 25Cr-20Ni-1.3Nb and this leads to an increase in packing density. The increase in W addition caused a change in NbC precipitation from fine particles at intragranular to a film-like shape at grain boundaries. Therefore, the disappearance of fine NbC in the matrix grains, which had suppressed grain growth due to the pinning effect, leads to grain growth and improves the creep property.

A single-phase RuB₂ (orthorhombic, space group Pmmn) polycrystalline material was successfully synthesized by the arc melting method. The condition for obtaining a single-phase RuB₂ material is dependent on the composition and form of the raw materials, namely using the composition of atomic ratio Ru:B = 1:2.1 and using granules Ru and B as the raw materials. The lattice constants of a single-phase RuB₂ obtained by the arc melt method are a = 4.645(1), b = 2.865(1), c = 4.046(1) Å, V = 53.8(1) ų. A thermogravimetric-differential thermal analysis (TG-DTA) for RuB₂ was carried out from room temperature to 1473 K. The oxidation reaction of RuB₂ begins at about 570 K, and the weight gain rate of final oxidation is 29%. Interestingly, the RuB₂ material was found to have a significantly lower oxidation resistance than Ru metal. The product after heating up to 1473 K in air atmosphere is a mixture of RuB_1.1 (RuB) and Ru phases, and B₂O₃ which is probably produced in an amorphous state. The values for electrical resistivity of RuB₂ are in the ranges from 23.3 × 10⁻³ to 102.2 × 10⁻³ Ω ‧ cm.

This study focuses on technologies for manufacturing aluminum components and provides a framework for selecting appropriate manufacturing methods from a life cycle economics perspective. Conventional manufacturing and additive manufacturing were examined. Additive manufacturing can manufacture intricate geometries that are difficult to achieve using conventional methods. However, its low productivity and high cost have limited its implementation into the industry. In addition, there is no consensus on the environmental impact of additive manufacturing. To address these issues, we examined the hypothesis that a life cycle cost analysis, which considers environmental impact when selecting a manufacturing method, would enable users to make more reasonable decisions. The study compared the life cycle costs of manufacturing methods for power semiconductors cooling components in electric vehicles and bracket components in aircraft. The results show that greenhouse gas emissions are higher during the use phase than the manufacturing phase for both applications. Replacing conventional manufacturing with additive manufacturing can reduce overall greenhouse gas emissions. Although additive manufacturing has a higher manufacturing cost compared to conventional manufacturing, the life cycle cost analysis reveals an economic advantage in replacing conventional manufacturing with additive manufacturing in aircraft engine brackets when running costs and carbon pricing are taken into consideration.

This paper investigates the relationship between the flowability and electrical properties of metal powders in powder bed fusion – electron/laser beam melting (PBF-E/LBM) technology, with a focus on the impact of naturally formed oxide films on powder surfaces. Additive manufacturing (AM) technology is crucial in industries like aerospace, automotive, and medical, where forming a high-density, uniform powder bed is essential for product quality. Flowability is influenced by factors such as powder shape, particle size distribution, and surface characteristics, including the oxide film.

The study compares powders produced by gas atomization (GA), plasma atomization (PA), and the plasma rotating electrode process (PREP), specifically examining Inconel 718 alloy powder and SUS304 steel powder. It analyzes their electrical properties and flowability to understand the impact on powder recoating performance. The research utilizes particle image velocimetry (PIV) to visualize powder flow during recoating and discusses the electrical properties and thermal stability of the surface oxide film, especially under mechanical strain.

The goal is to enhance understanding of powder flowability in the PBF-AM process and contribute to better manufacturing techniques for high-quality metal components.

Additive manufacturing has been attracting attention in recent years. In this field, powder bed fusion which uses lasers and electron beams as energy sources is the mainstream for metallic materials.

However, due to low productivity and high equipment and running costs, its implementation has been limited to specific applications such as aerospace and medical applications.

Therefore, binder jetting, another additive manufacturing method that solidifies powder by applying a binder, is expected to be applied to mass production because of its high productivity and lower manufacturing costs. This article discusses the historical overview of binder jetting, the latest trends of companies applying it to metallic materials, and the challenges associated with the social implementation of binder jetting and the companies’ efforts to overcome them.

Laser powder bed fusion (L-PBF) is an effective fabrication method for creating complex shapes directly. In order to apply L-PBF for building metallic products in harsh corrosive environments, we have focused on a strategy involving the in-situ formation of a protective oxide layer on L-PBF builds. In this work, SiO₂ nanoparticles were uniformly decorated onto the surface of 316L stainless steel powders using a hetero-agglomeration method. The amount of attached SiO₂ was increased by utilizing surface-oxidized 316L powders and adjusting the pH values of the liquid solution. Microstructure observations revealed the formation of a (Si, Cr, and Mn)-containing oxide layer on the entire build surface. This surface layer consisted of discontinuous micrometer- and continuous nanometer-order oxide layers in thickness. This study suggests the possibility of in-situ formation of an oxide layer on complex L-PBF shapes, which holds promise for applying L-PBF builds in corrosive environments.

Mo₂NiB₂-Ni cermets, a type of boride-based cermet, exhibit attractive mechanical properties such as high hardness and good wear resistance. However, the mechanical properties of these cermets have predominantly been evaluated at room temperature. In this study, three-point bending tests were conducted at high temperatures to investigate the mechanical properties and fractography of Mo₂NiB₂-Ni cermets. A ternary Mo₂NiB₂-Ni cermet was prepared using a calcination process to synthesize Mo₂NiB₂ before sintering. The calcination process resulted in finer and more uniform Mo₂NiB₂ particles, enhancing the microstructure. Consequently, hardness and transverse rupture strength (TRS) were improved. Three-point bending strengths were measured for samples measuring 4.0 × 3.0 × 24 mm at temperatures up to 800°C in an argon environment, using silicon carbide jigs with a 16 mm span. The results indicated that TRS remained approximately constant at about 1.6 GPa up to 500°C but decreased sharply above 600°C, reaching about 0.12 GPa at 800°C. This decrease was attributed to the softening of the nickel binder phase, which adversely affected the TRS.

This article addresses the application of data science in additive manufacturing. Additive manufacturing, or 3D printer, has attracted much attention and has been utilized for not only prototyping, but also manufacturing real parts. In many cases to manufacture real metal parts by additive manufacturing, additive manufacturing technologies have a lot of problems to be solved. The problems include process optimization, defects detection during process, non-destructive inspection, etc. In the case of manufacturing structural metal parts, for example, defect free parts should be manufactured, but it needs a lot of cost and time to optimize process conditions for defect free parts. In order to solve the problems in the additive manufacturing field, data science approach has been investigated and applied. This article emphasizes recent achievements of the application of data science approach for process optimization in powder bed fusion type additive manufacturing technologies. In addition, this article introduces the problems of additive manufacturing technologies to be solved for expanding the application of them, and also introduces the recent achievement in an automation of the process design.

Recently, metal additive manufacturing (AM) has enabled a wide range of control over metallurgical structures. Originally, the unique manufacturing method of stacking tiny melted sections to fabricate products with complex shapes with high precision provided geometrically defined solidification units with specific solidification directions and steep cooling, which in turn enabled the control of the metallurgical microstructure. This article describes the work of the author’s research group on crystallographic texture control via laser powder bed fusion (LPBF), including (1) the influence of powder properties on the formation of dense products, which is essential for crystallographic texture formation; (2) the influence of melt pool shape and crystallographic characteristics of the materials on single crystal formation and determination of crystal orientation; and (3) the success of “Alloy Design” for a highly functional single crystalline bio-high-entropy alloy (BioHEA) considering specific solidification fields under LPBF.

To clarify the anomalous behavior of magnetization of Zr₂Co₁₂P₇, we synthesized solid solution systems Zr_2−xNb_xCo₁₂P₇ and Zr_2−yY_yCo₁₂P₇ and studied their magnetism. In addition to x = 2 and y = 2, we successfully obtained polycrystalline samples in a single phase in 0 < x < 1 and 0 < y < 1. The Y-substitution did not affect the Curie temperature (T_C), while the Nb-substitution decreased T_C from 150 K to 30 K. The electron doping from Nb or local deformation may cause the decrease of T_C. The low-temperature plateau in the temperature dependence of the magnetization expands to a higher-temperature region by the Nb-substitution. A comparison of the simulation in the two-magnetic-sublattice model and experimental results showed that the magnetic moment of Nb coupled to the ferromagnetic internal field stronger than that of Zr. Qualitative agreement between the simulation and the experiment indicated that d electrons of X are localized, and their magnetic moment couples to the ferromagnetic internal field as the case of 4f electrons of lanthanoids.

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 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, 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.

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.

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.

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%).