In recent years, titanium aluminide (TiAl) alloys have replaced nickel-based superalloys in low-pressure turbine (LPT) blades of aircraft jet engines to improve the efficiency of the engines by reducing their weight. In addition, new β containing TiAl alloys that have an ordered β phase at service temperatures with mechanical properties superior to those of conventional alloys have been proposed. The next-generation TiAl alloys are likely to contribute to the advancement of more efficient aircraft jet engines. LPT blades of TiAl alloys are predominantly fabricated by precision investment casting. However, the surface oxidization and contamination from the crucible are significant concerns in the casting process. The surface layer containing oxide and contamination must be removed after the process. Thus, it is necessary to establish a new manufacturing process for TiAl LPT blades. The additive manufacturing process of electron beam powder fusion (EB-PBF) has attracted much attention for new fabrication process of TiAl LPT blades. In this article, we describe our research results on fabrication and microstructure control of β containing TiAl alloys by the EB-PBF process, as well as microstructure control techniques by heat treatment.

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 Focusing on the LPBF process, the application of AM technology to hot parts of industrial gas turbines and material issues in applying Nickel-based alloys as AM materials were introduced. The applications were started with components that have a relatively low operating temperature and do not be required high material properties, and development of advanced cooled structural components unique to AM has been carried out. On the other hand, with respect to high strength Nickel-based alloys, many material problems have arisen that were not found in conventional materials, such as the generation of cracks in building due to the influence of strengthening elements that are essential for ensuring strength, anisotropy of material properties due to fine columnar crystal grains, and degradation of creep properties. It is important to customize material properties considering operating conditions when applying them to actual parts.

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  This paper reviews the formation of microstructure and the mechanical properties of Ti-48Al-2Cr-2Nb alloys produced by Electron Beam Powder Bed Fusion (PBF-EB/M). In this paper, we first explain a unique layered microstructure that is caused by the layer-by-layer process in PBF-EB/M. The mechanical properties of the alloy fabricated by PBF-EB/M can be controlled by varying an angle θ between building directions and stress loading direction. At room temperature, the tensile elongation at θ = 45° is surprisingly larger than 2%, owing to the development of unique layered microstructure. These results suggested that the PBFEB/ M process enables not only the fabrication of complex shape TiAl products but also the further improvement of the mechanical properties associated with the formation of peculiar microstructure during this process.

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  Metallic materials are fundamental to a vast majority of industries. Although the understanding of the strengthening and microstructure relation of metals and alloys has matured, additive manufacturing of metallic materials is expanding the possibilities of obtaining unique microstructural characteristics and enhanced mechanical properties. In this review, the microstructure control of the crystallographic texture and grain morphology and its effect on the strengthening of Inconel 718, a major Ni-based superalloy fabricated by laser powder bed fusion (LPBF), is discussed in terms of characteristics that are unique to the manufacturing method. In particular, this review focuses on the unique crystallographic lamellar microstructure, which can only be formed by the LPBF method, and its enhancement by the effect of the lamellar microstructure interfaces.

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  Microstructure formation and evolution by various processing and heat treatment conditions were investigated for near-α Ti-6Al 4Nb-4Zr (wt%) prepared by Laser Beam Powder bed fusion (LPBF). High-temperature compression strength and creep behavior of samples with different microstructure were investigated. The martensitic transformation from bcc-β to hcp-α phase occurred for fast cooling rate during LPBF. The α/β lamellar structure formed for slow cooling rate. Heat treatment changed the martensite structure to Widmanstätten structure. The equiaxed α phase also formed during heat treatment along the melting-pool boundaries. The strength of the as-build samples was higher than those of the forged samples due to fine grain size and fine microstructure. The strength lowered by heat treatment due to coarsening of microstructure. Creep deformation dominantly occurred by grain sliding at 600℃ and 137 MPa. Then, creep life depends on grain size or melting pool size. The small equiaxed α phase accelerated grain boundary sliding.

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  Selective laser melting (SLM) was applied to TiAl4822. Electron beam melting (EBM) has been a major additive manufacturing process for TiAl4822, but low ductility is a technical challenge with EBM. This research investigates the microstructure and the tensile properties of TiAl4822 fabricated by a new SLM machine equipped with a heating unit. The elongation of the SLM specimen was 8.3 times larger than that of the EBM specimen; this was attributable to the γ-phase based homogeneous fine grains in the SLM. Furthermore, since SLM-HIP material has excellent creep properties, the development of SLM-HIP material is expected in the future.

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  Solidification microstructure formation in stai nless steels additively manufactured by powder bed fusion (PBF) has been reviewed, focusing on the characteristics owing to the unique solidification condition of the PBF process. The crystallographic orientation textures are controlled by using specially designed laser beam scanning strategies combined with appropriate beam power and beam scanning speed. Also, the rapid solidification with large temperature gradients has been found to give rise to extremely fine cellular structures associated with the microsegregation of solute atoms such as Cr and Mo. The hierarchical structures from nanometer to sub-millimeter scale are the key to the maximized potential of performance of stainless steels by the PBF. Studies on grain refinement and single crystal growth are also underway, focusing on the unique solidification condition.

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  Structural materials that are used in environmental and energy applications are expected to have various properties, such as strength at both room and elevated temperatures, corrosion and wear resistance, and fatigue strength, simultaneously. Additive manufacturing (AM), an emerging material processing technology, is highly promising for the development of novel materials by utilizing the unique thermal history that cannot be achieved in conventional manufacturing. In this review, we focus on high entropy alloys (HEAs), which generally consist of multiple principal elements in (near) equimolar ratios, and their intersection with AM technologies. The microstructural evolution during electron beam powder bed fusion and its effects on the mechanical and corrosion properties are summarized based on the results for an equimolar AlCoCrFeNi HEA. It was demonstrated that in addition to nonequilibrium solidification in a highly confined melt pool, the subsequent solid-state phase transformation and associated solute partitioning between the constituent phases during the in-process high-temperature exposure play an important role in the significant improvement of the alloy performance. Consequently, an excellent combination of mechanical properties and corrosion resistance, which surpasses that obtained in the conventional casting, was achieved. This obtained knowledge indicates the importance of optimizing not only the solidification behavior but also the entire thermal history (including post-processing), broadening the alloy design space, and providing opportunities for developing high-performance alloys for harsh environments.

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 This review focuses on the compressive mechanical properties of aluminum alloy lattice structures fabricated by laser powder bed fusion and discusses the deformation behavior of the lattice structures with various unit cell geometries. Three types of AlSi10Mg lattice structures consisting of body-centered cubic (BCC), truncated octahedral (TO), and hexagonal (Hexa) unit cells were fabricated and compression tests were conducted. The BCC and TO unit cell lattice exhibits shear bands during compression deformation. Therefore, the plateau region of the stress-strain curve is unstable and large stress fluctuations are observed. The relative modulus of elasticity（E^*/E_s）, relative yield strength（σ^*_y/σ_s） and plateau stress（σ_pl） of the lattice structures have a positive power-law relationship with the relative density（ρ^*/ρ_s）. The Hexa structural lattice showed no stress fluctuations in the plateau region. This is because the formation of shear bands, which cause stress fluctuations, was suppressed. However, contacts between neighboring struts were more likely to occur and the densification initiation strain became low. The BCC structure lattices had low plateau stresses. This is because the distribution of stress is not uniform within the lattice, with high stresses occurring in certain areas, causing large deformations in these areas.

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 The effects of oxidat ion on the properties of Zr-added 316L stainless steel powders was thoroughly investigated for the application of laser powder bed fusion (L-PBF) in this study. Three kinds of 316L powders with different Zr content were prepared by gas atomization. When the powders were oxidized at 823 K for 3.6 ks, the oxygen content increased by approximately 4-6 times. However, the oxygen content after the oxidization was independent on the Zr addition. The flowability and laser absorptivity of 316L powders were enhanced after the oxidation, attributing to the formation of oxide layer of several nanometers in thickness on the powder surface. Furthermore, the wetting angle of 316L droplets decreased with the addition of Zr and oxidation, which may benefit to the L-PBF processability. This work indicates the feasibility of fabricating high-performance metallic L-PBF builds by the positive use of oxidized powders.

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 High entropy alloys (HEAs), which consist of multicomponent elements, have been developed as a new class of structural materials. In 2017, Prof. Nakano’s group has proposed bio-high entropy alloys (BioHEAs) as a specially designed HEAs composed of non-bio-toxic elements and revealed its excellent mechanical properties and biocompatibility. However, owing to elemental segregation and phase separation occurred in several BioHEAs, BioHEAs does not fully exhibit the functions that should be exhibited as a complete solid solution. In this article, we reviewed the strategy for achieving high functionality of BioHEAs without elemental segregation and phase separation from the viewpoints of alloy design and creation method of BioHEAs with BCC (body centered cubic) type structures.

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 Due to the increasingly aging population, the number of spinal fixation surgeries is on the rise. A spinal fixation device is intended to bring the upper and lower vertebral bodies of an affected part of the spine into contact with each other and ultimately integrate them by bony fusion. In order to control the migration and extension of osteoblasts in the inner space of the spinal fixation device, we designed and fabricated a new spinal spacer with grooves in the craniocaudal direction. The efficacy was verified through implantation tests in a large animal model (sheep). We have successfully developed and put into practical use a spinal fixation device (UNIOS^® PL Spacer) that enables the orientation of newly formed bone tissue. UNIOS^® PL Spacer is increasingly used in clinical applications.

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 Exploitation of the geometric freedom of Additive Manufacturing technologies enables creative redesign of engineering components to improve performance and sustainability. Micro-lattices of Yttria Stabilized Zirconia (YSZ) have been designed to improve the performance of YSZ solid electrolytes for aluminium smelting. Computer Fluid Dynamics was used to predict the optimal part geometry for YSZ electrodes, enabling efficient ion conductivity. 12-coordinate YSZ lattices were predicted to allow aluminium smelting without releasing harmful CO₂ gas and were fabricated by stereolithography. To reduce the time and energy of post-process sintering, the Discrete Element Method was used to predict optimal YSZ particle size and paste composition. Particle dispersion models were created and used to estimate the number of particle contacts between YSZ particles of varying particle size and distribution. Stereolithography green parts were fabricated using the optimal YSZ paste and were heat treated in 20 hours, much shorter than conventional YSZ sintering. This research demonstrates the advantage of using computational methods when applied to ceramic stereolithography for environmental goals, and the benefit of additive manufacturing for designing complex components.

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The biological environment maintains vital functions by responding to the surrounding changes inside and outside the body in association with various kinds of substances including nucleic acids and proteins. In addition, dynamic environmental changes, such as pH fluctuations and changes in oxygen concentration due to cellular activities, are regulated by molecular mediators, leading to hierarchical tissue and organ function. In recent years, bio-3D （three-dimensional） printing technology for assembling organs from cells has evolved dramatically. In particular, bone tissue regulates its function by constructing a highly oriented micro-organization of the bone matrix through the action of multicellular systems. The creation of mini bone organs that enable the expression of highly regulated bone functions is expected by building up a three-dimensional structure with the interconnection of heterologous types of cells. Indeed, bone function is regulated by interactions with cells based on the responses of osteocytes （stress-sensitive cells in the bone matrix） to in vivo environmental stimuli. The aim of this study is to control cellular functions in the biological environment by controlling the osteocyte arrangement using the bioprinting technique. Drawing living cells at the single-cell level and constructing cell-cell interactions are expected to lead to the elucidation of mechanisms for highly regulated bone functions and also functional artificial organ development.

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Ceramic and glass materials exhibit desirable properties for various applications. A glass-ceramic composite material could be utilized as an alternative to pure ceramic materials, with a reduced energy requirement for processing and recycling. In this work, customized photosensitive pastes containing zirconia and glass particles were created and processed by stereolithography. Complex 2- dimensional and 3-dimensional Hilbert curve structures were designed and analysed by computational fluid dynamics to visualize heat transfer and fluid streamline distributions. Paste composition, stereolithography process parameters, and post-processing heat treatments were investigated, and complex components of the custom glass-ceramic composite material were successfully fabricated.

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