Using ultrafine WC powders with different impurities contents, WC-10%Co ultrafine-grained cemented carbides with 5-9 mass% VC addition to the Co content were sintered and then HIPed or HIP-RQ (re-sintered with quenching after HIP). Their transverse-rupture strengths were measured, and the relationship between the stress σ_d acting on the fracture source and its source size 2a was evaluated using σ_d^-1 - a^1/2 and σ_d - A^-1/4 (= σ_d - (2a)^-1/2) correlation diagrams. Each cemented carbide had limiting strength which was constant σ_d when 2a ≦ 10 μm, regardless of 2a, in both diagrams. The limiting strength of σ_d was varied from 3.20 to 4.04 GPa, depending on the WC powder, VC addition amount, and HIP and HIP-RQ treatment. While the grinding residual stress proposal was unlikely to be the main cause for ultrafine-grained cemented carbide, the defect expansion proposal due to plastic deformation around the defect was able to explain a part of the phenomenon. It was revealed that if the stress applied to the defect varies due to interactions between defects, this could be the cause of the limiting strength phenomenon. By considering this interaction, it is possible to explain phenomena that could not be explained by the previous proposals.

A nanosecond pulse electric field is defined as the application of an electric field with a width of approximately 10 nanoseconds to 1 microsecond. Recent developments in power semiconductors such as SiC and GaN have made it possible to design power supplies with higher voltage and single pulse width. In such nanosecond pulsed electric fields, there are four major characteristics. The most important of these features is that dielectric breakdown does not occur even when an electric field higher than the breakdown voltage is applied because the pulse application time is shorter than the time during which breakdown occurs. In other words, the nanosecond pulsed electric field can be used to realize a material creation process with a higher electric field than before. In addition, when used in conjunction with optical switches, an electric field can be applied at a targeted timing. Short-time electrochemical reactions can be generated. Since the repetition frequency can be varied, the resonance phenomenon by frequency matching can be utilized as in the case of a high-frequency power supply. In this paper, we will explain the material process that makes use of these features.

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.

The microstructural and mechanical properties investigation on powder metallurgy (PM) Ti-Zr composite alloys dispersed with TiC particles via sintering and hot rolling process was carried out in this study. PM Ti-Zr-TiC composites were fabricated from the pre-mixed pure Ti, metal Zr and TiC powders, and heat treatment was applied to the sintered materials to homogenize Zr solid-solution in α-Ti matrix. XRD analysis results of these rolled composite materials indicated complete solid-solution of Zr elements. Microstructures observation clarified the binary Ti-(10-20%)Zr alloys had a mean grain size of around 4 µm, which was much smaller compered to pure Ti material with 10 µm grain diameter. According to the tensile test results, Ti-Zr alloys showed a remarkable increment of tensile strength due to Zr solid-solution and α-Ti grain refinement, and also had a large elongation. On the other hand, since Young’s modulus gradually decreased with increased in Zr content, TiC particles were added into Ti-10%Zr alloy to improve the modulus. The uniform dispersion of (2.5-5 wt%)TiC particles in the matrix resulted in the increase of both Young’s modulus and tensile strength. The experimental values of Young’s modulus showed a good agreement with the calculated ones by using the law of mixture.

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.

Monte Carlo simulation was performed to investigate the effect of sintering on the changes in microstructure, porosity, and pore distribution of thermal barrier coating layers synthesized by electron beam physical vapor deposition. First, the simulation well expressed the characteristic porous structures such as columnar and feather-like structures, which were fabricated under the condition of substrate rotation. Secondly, the sintering of such a porous structure by high-temperature annealing could be demonstrated using the simulation. The microstructure of the layer close to the substrate surface shows fine grains and pores, suggesting ease of sintering and grain growth, which is clearly demonstrated from the experimental results of the yttria-stabilized zirconia layer deposited by electron beam physical vapor deposition. The simulation also reveals the sintering behavior of the porous including heterogeneous structure and pore distribution. By introducing a small sintering step to the deposition process during the simulation, the experimental values of the porosity observed in the layers could be successfully explained. The doubled effects of sintering on porosity during both deposition and exposure to high temperature environment enhanced the heterogeneity of the microstructures of the layers.

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.

Powder metallurgy is a process for compacting and sintering powders such as metals and ceramics, and has been attracting new attention in recent years. This paper presents research examples in which simulation methods such as molecular dynamics (MD) method, Monte Carlo (MC) method, finite element method (FEM), and discrete element method (DEM) are applied to powder metallurgy. The MD method is used to calculate physical property values such as interfacial energy and diffusion coefficient that change depending on the type of grain boundaries. The MC method is used to calculate the microstructural development due to the sintering and grain growth. The microstructure can be predicted when the sintering process is changed. The FEM is used to calculate deformation and strain. The sintering simulation combined with the MC method can calculate the microstructural changes and deformation simultaneously. In the compaction simulation, density distribution due to the friction with the mold can be analyzed. The DEM is used to calculate the compaction structure. The interaction of the friction and stiffness between particles and particle/mold can be analyzed. As powder metallurgy technology develops, process design that considers the whole process will be important. Supporting technology based on simulation will become increasingly important.

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.

α+β dual phase Ti-(0~6 wt.%) Fe alloys were prepared via sintering and hot rolling process to clarify the effects of Fe contents and the rolling temperature on their microstructures and crystalline orientation. With an increase in the Fe content, the volumetric fraction of the β-Ti phase, contains high Fe solutes, drastically increased. When hot rolled at 750°C (α+β dual-phase temperature), each phase grew immediately after rolling and suppressed each other’s grain growth, resulting in fine microstructure formation and uniform residual strain. In Ti-Fe alloys rolled at 1000°C (single β-phase temperature), a very small amount of residual strain was observed, and acicular α-Ti grains with random crystalline orientations were formed due to the phase transformation from β-Ti grains after rolling.

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.

A non-firing solidification method using surface-activated ceramic powders with mechanochemical treatment and solidified without a high-temperature sintering process has been studied in our group. In this method, the surfaces of ceramic particles are activated by grinding, and this activated state is used as a driving force to bond the particles together. It is essential to computationally understand the mechanical activation and solidification processes in the non-firing process at various molecular and bulk scales. This paper first outlines the differences between the non-firing solidification process and the conventional sintering process. Next, we introduce our simulation results of the non-firing solidification process and discuss future prospects.

Inhibition mechanism of grain growth by metal carbide addition for WC-Co based ultrafine-grained cemented carbide was studied to develop 100 nm-grained cemented carbide. Two hypotheses of inhibition mechanism, a) inhibition by adsorption atoms at steps/kinks on WC crystal surface and b) inhibition by segregation layers on WC basal plane, were proposed. To judge which hypothesis is based on the inhibition mechanism, observation of TEM microstructure and analysis of segregation amount on WC/Co and WC/WC interfaces in WC-Co based cemented carbides including metal carbide additives were performed.

Determining the presence or absence of segregation layer on WC crystal surface during liquid phase sintering was the judgement point of inhibition mechanism. The judgement was considered comparison between predictive phenomena on each hypothesis and experiment results. The experimental results supported that grain growth inhibited by adsorption atoms at steps/kinks on WC crystal surface during liquid phase sintering and segregation layer formed by precipitation during cooling after liquid phase sintering. Segregation mechanism of grain growth inhibitor was proposed based on the composition, solubility limit in liquid Co and that in solid Co of the inhibitor.

Developments of 100 nm-grained WC-Co based cemented carbides with cobalt content of 4 and 10% were succeeded based on the resolution of inhibition mechanism. The hardness and transvers rupture strength of developed cemented carbides were 2300 HV and 4.7 GPa for 10%Co, 2600 HV and 3.0 GPa for 4%Co, respectively. Using the technique, 0.2 µm-grained cemented carbides were commercialized.

In order to investigate the cause of the liquid phase migration (LPM) and the shape distortion when WC-Co cemented carbides (alloys) undergo a temperature gradient during cooling, round bars of WC-10 mass%Co alloys are inserted halfway under the coil of the induction heating furnace and partially heated at 1673 K. The results showed that Co migrated from the higher temperature side to the lower one and increase of Co content and bar diameter occurred in a zone at the outside of the coil. The alloy containing free carbon had a significantly narrow Co-increased zone and the zone located at a lower temperature. The volume transfer (V) of Co during heating changed in proportional to the square root of the heating time (t). It was considered that the phenomenon was the same as the LPM between a couple of alloys having different Co content in our previous report. We have concluded that the Co-increased zone in this study corresponds to the Co solid-liquid coexistence zone during partial heating and the Co increase is caused by the migration pressure occurred in the zone, which we named Π_SL. Π_SL should be generated because F_WC/Co(S) derived from γ_WC/Co(S) and γ_Co(L)/Co(S) is higher than F_WC/Co(L) derived from γ_WC/Co(L).

The effects of the addition of platinum group metals Ru, Rh and Ir on the microstructure and mechanical properties of cemented carbide at room and high temperatures were investigated. It was found that the increase in hardness by the addition of platinum group elements was due to the grain growth inhibition of WC and solid solution hardening of the binder phase. Furthermore, when creep deformation resistance was investigated as a mechanical property at high temperature, it was found that the strain rate of the WC-Co with Ru, Rh and Ir were lower than that of the WC-Co alloy. As a practical test, cutting test was conducted using martensitic stainless steel, which is used as a material for turbine blades. It was found that cemented carbides containing Ru had superior plastic deformation resistance compared to alloy without Ru.

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.

Ultrafine-grained binderless cemented carbides using 0.4 µm WC particles were prepared by adding Cr₃C₂, VC, TaC, βt and various sizes of Ti(C,N) particles. SEM observations of the polished and fractured surfaces revealed that the WC grains became finer after the addition of the carbides or carbonitrides. In the Ti(C,N)-added binderless cemented carbides, the WC grains became finer with decreasing Ti(C,N) particle size and increasing Ti(C,N) content. The grain size of WC in the binderless cemented carbide containing 0.1 μm Ti(C,N) was comparable to that of the Cr₃C₂-containing binderless cemented carbide, although not as fine as that of the VC-containing binderless cemented carbide. The binderless cemented carbides containing fine Ti(C,N) grains were harder and had higher strengths than the other carbides. The combined addition of fine Ti(C,N) and Cr₃C₂ resulted in more homogeneous WC grains. These results indicate that the grain growth inhibition of binderless cemented carbides varies depending on the type and grain size of the added carbonitrides. These findings will contribute to the future development of binderless cemented carbides.

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 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.

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 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.

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.

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.