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.

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.

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 characteristics of high-temperature oxide fuel cells and high-temperature steam electrolysis cells under millimeter-wave irradiation were evaluated and compared with those evaluated under conventional electric furnace heating. A reversible high-temperature electrochemical cell was fabricated using alumina-dispersed zirconia as the electrolyte, lanthanum strontium manganate as the air electrode, and nickel-ziconia based cermet as the fuel one. The power generation characteristic of the fuel cell under millimeter wave irradiation was 32% higher than that of a conventional electric furnace temperature heating, and the steam electrolysis efficiency was also 120% higher under millimeter-wave irradiation than that under conventional one. Impedance measurements using an air electrode-electrolyte half-cell showed that the millimeter wave irradiation facilitated the dissociation of oxygen molecule and/or diffusion of oxygen atoms on the surface of the air electrode as well as the oxide ion conduction in the electrolyte.

It is known that the anisotropic magnetic fields are improved by La and Co substitutions for M-type ferrite sintered magnets, and the coercive forces are significantly improved. On the other hand, since W-type ferrites have a crystal structure similar to that of M-type ferrites, it is expected that La-Co substitution would improve magnetic properties in the same way. However, evaluations of the effects of La and Co substitution are difficult because sintered bodies with a single phase of W-type has not been obtained and sintering at high temperatures is required. Recently, a method to determine the anisotropic magnetic fields using the saturation asymptotic law was proposed by T. Kuno et al., J. Jpn. Soc. Powder Powder Metallurgy 63 (2016) 1053, which makes it possible to evaluate the anisotropic magnetic fields. In this study, La-Co substituted W-type ferrite powders in the Ba, Sr and (Ba-Sr) based systems were prepared, and the effects of La-Co substitution and the ratio of Ba and Sr on the anisotropic magnetic fields were investigated.

To obtain an optimal powder bed condition for laser powder bed fusion (L-PBF), it is essential to clarify powder flow behaviors during the recoating process. In this work, the flow behaviors of Ti-6Al-4V powders were experimentally analyzed using a simple slope model by Particle image velocimetry (PIV) and were subsequently compared with the behaviors simulated using the similar model by discrete element method (DEM). The velocity of particles and the distribution were able to be obtained experimentally using PIV. In the DEM simulation, when the coefficient of restitution was increased, the angle between restituted particles and the slope and the average particle velocity were increased. Comparing those obtained by the DEM simulation, it was found that the velocity and distribution obtained by PIV analyses were close to those obtained by the DEM simulation at the coefficient of restitution of 0.3. These results suggest that the powder flow velocity analysis on the slope using PIV analyses is an effective method to validate the parameter of powder properties in DEM simulations.

The La-Co cosubstituted M-type strontium ferrite attracts attention as a base material for high-performance ferrite magnets. It is known that the uniaxial magnetic anisotropy of the material is enhanced by increasing the amount of Co by heat treatment under high oxygen pressure, but there is a problem in obtaining a pure sample. The present study investigated the conditions to obtain a single phase with increased La-Co substitution by heat treatments under several oxygen pressures. A single phase of M-type ferrite was obtained up to x = 0.35 at p_O2 = 1 atm, and up to x = 0.65 at p_O2 = 10 atm with the composition formula of Sr_1-xLa_xFe_12-xCo_xO₁₉. The magnetic anisotropy is enhanced according to the Co concentration in these samples.

The fracture of WC-Co cemented carbides with different WC particle sizes was investigated experimentally, and then a discrete element method (DEM) simulation was performed considering such experiments. The bending strength of ultra-fine grained cemented carbide with a WC particle size of 0.4 μm was extremely high. The ultra-fine grained cemented carbide sample after bending test had numerous fracture pieces and the short length of the specimens without fracture. Initial structures consisting of matrix and defect (d) particles were used in the DEM simulations. The DEM simulation results for a sample of 2% d particle, which was considered ultra-fine grained cemented carbide by comparison with experimental results, were as follows: The sample with the highest load at fracture, the most d particle bond-breaking, and the shortest length of remaining specimen without particle bond breaking was the 2% d sample. The DEM simulation was considered to be very useful in understanding the ultra-fine grained cemented carbide’s strength and fracture behavior.

Joined plates of WC-Co cemented carbides with different Co content, WC grain size and carbon content were fabricated by sintering, grinding into rectangular plates, and then reheating (joining) the two plates together. Distribution of Co, microstructure and shape of such joined plates were investigated in detail. It was confirmed that Co migrated from higher Co content to lower one, from coarser WC grains to finer ones and from higher carbon content to lower one as shown in previous studies by Lisovsky and Fang. Shapes of the joined plates were distorted caused by volume change of each plate resulting from migration of liquid Co and solute WC through the interface of the joined plates. In the joined plates with different Co content, Co distributed discontinuously at the interface. This result can be explained by the fact that Co content at the both sides of the interface had been almost fixed just after two faces were joined. This study was done under the special condition using joined plates, but the results obtained suggest that the shape of industrial-made WC-Co cemented carbides should be distorted when distribution of Co becomes non uniform.

The uniformity of shrinkages and the distribution of grain sizes were investigated for flash-sintered 3 mol%Y₂O₃-ZrO₂ compacts in direct current and alternating current (AC) electric fields using rectangular-shaped and circular truncated cone-shaped green compacts. The use of a high-frequency AC electric field enough to suppress electrode overvoltage was confirmed to be advantageous for uniform shrinkages, regardless of the shapes of the green compacts. However, the grain size distribution became larger in cone-shaped green compacts, the cross-sectional areas of which varied along the compact. The grain sizes in flashed cone-shaped green compacts were found to exhibit a near linear relation to current density, which provides a means for determining the grain size distribution upon the flash sintering of green compacts with different cross-sectional areas along an electric field.

The magnetic properties and microstructures of the HDDR powders fabricated from the NdFeB sintered magnets were investigated in order to improve their orientation. In case of fabricating from the strip cast alloys, the hydrogen-pulverized powders showed the dependence of the orientation on their powder sizes. On the other hand, the pulverized powders from the sintered magnets showed high orientation regardless of their powder sizes. This is due to inheritance of the high crystal orientations of the sintered magnets as starting materials. And the formation of the fine Nd₂Fe₁₄B crystals just at the surface area of the pulverized powders could be processed by the additional annealing under Ar atmosphere in advance of the HDDR treatment. As a result, the residual magnetization of the “capsule-structured” HDDR powders was improved from 100 to 125 emu/g due to remaining the unreacted Nd₂Fe₁₄B phases with high orientation at the inner core of the HDDR powders. This technique would provide the anisotropic NdFeB bonded magnets with high (BH)_max, and the new environment-friendly recycling process of the NdFeB magnets with low cost.

Uniaxial pressing is a utilized technique to prepare powder compacts in regions of ceramics, metal, drug, and functional food. On the other hand, it is known that the inhomogeneous structures are induced by stress distribution resulting from applying the anisotropic stress field to the powder bed and they become the origin which forms defect degrading the performance of products. However, the generation process of inhomogeneous structures has not been clarified experimentally. Directly understanding the formation mechanism of the internal structure during uniaxial pressing is very important to control the particle-assembled structure in the powder bed and the quality of products. In this work, the change process in void morphology under uniaxial pressing was observed dynamic-two-dimensionally and intermittent-three-dimensionally by the novel observation system composed of swept-source optical coherence tomography (SS-OCT) and material testing machine. Moreover, the detected voids were evaluated quantitively to directly clarify particle-packing behavior on the initial stage of pressing.

TiC-47 mass% Ti-20 mass% Mo (Mo added alloy) and TiC-52 mass% Ti-21 mass% Mo₂C (Mo₂C added alloy) were prepared through powder metallurgy. The TiC grain size of Mo₂C added alloy sintered at 1673 K was about 3 μm, which was smaller than that of the Mo added alloy. The mechanism was considered as follows. First, when C diffuses from Mo₂C to α-Ti, the Mo phase containing defects such as vacancies precipitates. Second, the solid solution of Mo and Ti is promoted by the mutual diffusion between the precipitated Mo phase and α-Ti, and the transformation from α-Ti to β-Ti occurs. Third, the solute diffusion coefficient of β-Ti is much larger than that of α-Ti, so C diffuses from TiC to β-Ti, producing TiC_0.6. Meanwhile, Mo has a smaller free energy for carbide formation than Ti has and then TiC_0.6 cannot contain Mo, so Mo is concentrated in β-Ti adjacent to precipitated TiC_0.6. This suppresses the growth of TiC_0.6, and then the grain size of TiC_0.6 becomes smaller. The transverse-rupture strength of the Mo₂C added alloy was 20% higher than that of the Mo added alloy, reaching 0.95 GPa. At that time, both alloys have almost the same hardness.

In the present study, we have examined the wear properties of the sintered pure iron subjected to two distinct heat treatments such as nitriding-quenching (NQ) and carburizing-quenching (CQ). Based on our current observations, the martensite layer was formed on the surface layer following each treatment, whereas the hardness of the NQ martensite was much higher than that of the CQ one. The wear of the CQ specimen was slightly smaller than that of the NQ martensite, despite the lower value of the initial hardness. Meanwhile, the hardness of the CQ surface after the sliding tests significantly elevated relative to the NQ surface resulting in the better wear resistance. EBSD analysis demonstrated that the plastic deformation on the CQ surface along the sliding direction. Furthermore, the micro area X-ray diffraction along the surface layer of the CQ surface showed that a small amount of the retained austeite which reduced locally during the test. Therefore, the CQ-treated surface showed the excellent wear resistivity due to the surface hardening by the stress-induced transformation of the retained austenite dispersed in the martensite, in addition to the strain hardening of the martensite itself. In contrast, the worn surface of the NQ specimen showed slight plastic deformations of the ferrite grains beneath the martensite layer, but not in the surface martensite layer. This deformation under the martensite layer was due to the hardness gap between inward and the heat-treated surface, and might contribute to form the concave profile on the sliding surface. Consequently, this study could demonstrate such the difference in the wear mechanisms between the CQ and the NQ specimens.

We report synthesis and characterization of structural and physical properties in YbInCu₄ and Yb-rich Yb_1+xIn_1-xCu₄. We have measured the powder X-ray diffraction, the temperature dependence of the magnetic susceptibility between 2 and 300 K in the magnetic field of 1 T, the high-field magnetization up to 72 T and the temperature dependence of the electrical resistivity in the magnetic field of 0 and 14 T to study the change of physical properties by substitution and to understand the origin of the valence transition.

The powder X-ray diffraction patterns suggest that Yb_1+xIn_1-xCu₄ crystallized in the cubic C15b-type Laves structure. We newly discovered a two-step magnetic anomaly in the high-field magnetization process interpreted by crystal field splitting effects. We finally made a magnetic phase diagram in H-x, which is consisting of 4 phases. Three phase boundaries are defined by valence transition from Yb valence fluctuation to Yb trivalent localized magnetism, change of the ground state due to crystal field splitting effects and disturbance of Kondo lattice.

Well-defined SiO₂-coated Fe nanoparticles with various SiO₂ thickness from 1.2 to 27.8 nm have been successfully prepared by controlling the amount of tetraethyl orthosilicate and by the subsequent reduction of SiO₂-coated Fe₃O₄ nanoparticles with CaH₂. The saturated magnetization of the SiO₂-coated Fe nanoparticles increased with decreasing SiO₂ thickness. The saturated magnetization of the SiO₂-coated Fe nanoparticles with SiO₂ thickness of 2.7 nm or more have slightly decreased by 192 hr and did not change above 192 hr throughout atmospheric exposure, whereas that with SiO₂ thickness of 1.2 nm steeply decreased in 24 hr and continued to decrease above 24 hr.

Molecular dynamics simulations were performed to study six grain boundaries of α-alumina (Al₂O₃) with a glassy phase of anorthite (CaAl₂Si₂O₈) composition. We calculated excess energy, diffusion constant and ratio of excess volume with different thickness of the glassy film. It was found that excess energy for some grain boundaries exhibited a minimum. When the thickness of the glassy film was thick adequately, excess energy corresponded to the energy of alumina-glass interface and they were different for each interface. Diffusion constants depended on the thickness of the glassy film. The diffusion constant of thin film was smaller than that of thick film. Excess volume was the maximum when the thickness of the glassy film was 0.2~0.3 nm. When the atomic arrangement of the crystals didn’t fit each either, the excess volume of the grain boundary with the glassy film was smaller than that of the pure grain boundary. When the glassy film width was nm order, the atomic arrangement of the glassy phase was regular and the atomic diffusion behavior was approached that of a solid (crystalline) phase. We need to consider not only solid-liquid interface but also solid-solid (crystalline) interface for the structure of ceramics made by liquid phase sintering.