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.

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.

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%).

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.

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.

Recently, Additive Manufacturing (AM) has been attracting attention as the breakthrough manufacturing technology and is being aggressively researched and developed around the world. Metal AM enables the integration of parts with complex 3D internal structures, such as topology optimization and lattice structures, which are difficult to achieve with conventional casting or machining processes and reduces costs by reducing the number of parts and weight. Therefore, it is applied in various industrial fields such as aircraft, medical, automotive, and die & mold. There are various processes for metal AM, of which powder bed fusion (PBF) and direct energy deposition (DED), which use metal powders, are technologically mature and industrially widespread. In metal AM using metal powder, the quality of the AM product is influenced by the interaction of complex factors such as AM build recipe, powder properties and powder feeding process. In case the raw powder with inappropriate powder properties is selected for the AM machine, defects may occur in the AM product and quality, such as mechanical property, may be deteriorated. This review is introduced on typical types of AM processes using metal powder, factors affecting powder properties of AM products, metal powder manufacturing methods, and evaluation methods.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.