This paper reviewed development of Zn-bonded Sm-Fe-N magnets in our group, and reported interfacial diffusion and phase changes at the Sm₂Fe₁₇–Zn interface during annealing. For increasing magnetic properties of Zn-bonded Sm-Fe-N magnets, decreasing oxygen content, improving dispersibility of Zn, and increasing relative density are necessary, therefore we prepared low oxygen content Sm-Fe-N and fine Zn powders. The powders were sintered by spark plasma sintering process for increasing density under low oxygen atmosphere resulting in obtaining high (BH)_max of 200 kJm^-3 with relatively high coercivity of 1.28 MAm^-1 and β(H_cJ) of –0.34%C^-1. In order to further improve the (BH)_max, it is necessary to control interfacial diffusion and reaction between Sm₂Fe₁₇N₃ and Zn phases. Thus, as a first step, microstructural changes and interdiffusion coefficient at the Sm₂Fe₁₇–Zn interface were investigated using Sm₂Fe₁₇–Zn diffusion couples, in this study. It was clear that interdiffusion of Zn, Fe and Sm occurred during annealing below melting temperature of Zn, and the diffusion rate of Zn was faster than those of Fe and Sm. Furthermore, with Zn diffusing into Sm₂Fe₁₇ phase, the Sm₂Fe₁₇ decompose to ThMn₁₂-Sm(Zn,Fe)₁₂ and α-FeZn phases with specific crystal orientation relationship.

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.

This study aims to obtain the superior mechanical properties of Mo diffusion-bonded alloyed steel by the optimum combination of processes: primary-sintering (PS), cold-forging (CF), heat treatment (HT) and shotblast. In our previous research, it was found that the fracture of sintering connections, namely, micro-cracks occurred on the surface layer of high-density specimens in addition to the work hardening on materials, which decreased both the impact energy and the bending strength. Also, since the optimum heat treatment leads the diffusion bonding of the pressurized cracks in the surface layer, the microstructure could be reformed. In this study, it was found that the 0.4 mass%Mo-steel powder had both the highest densification and deformability among the powders of 0.4, 1, 2 and 4 mass%Mo without precipitation of the unneeded ternary molybdenum carbide Fe₃Mo₃C. Also, when sintered specimens were cold-forged, the impact waveform of those showed clearly effects of both the work hardening and the damage of the microstructure. Finally, both the superior fatigue strength and the wear resistance were implemented with the proper processes to 0.4 mass%Mo sintered steel such as a second sintering, vacuum carbonitriding heat treatment and shotblast. Obtained properties were equal to or more than those of wrought steel SCr420H.

The establishment of a carbon-neutral society has reached a stage when it is economically and industrially realistic. Based on this background, research on "non-firing ceramics" has attracted attention from the perspective of environmentally friendly manufacturing, such as energy conservation, low cost, and reduction of greenhouse gas emissions, because high temperatures and high pressures are not required. This technology involves a method to grind the surface of a ceramic raw material powder to obtain a chemical activity and solidify it. This paper provides an overview of non-firing ceramics, the mechanism of the surface activation of ceramic raw materials, and its application to porous materials. Although this method is not a substitute for all sintered ceramics, I hope that it will contribute to providing a new direction of manufacturing.

A high-energy ball mill, such as a planetary ball mill, is widely used for preparing a homogeneously mixed powder and reducing particle size. Because of the high impact energy generated by the collision of ball media, the planetary ball milling is expected to produce local high-temperature and high-pressure zones. In wet milling, the solubility of the material varies owing to the local and instantaneous changes caused by the collision. Consequently, mechanochemical reactions through a dissolution–precipitation mechanism can be attained without external heating. In this paper, we show the wet mechanochemical process in water to synthesize functional hydrous or hydrate materials with various shapes, including nanosheets, nanotubes, plates, flakes, rods, and nanoparticles. Morphology-controlled particles can be obtained by only adjusting the milling conditions, such as milling time, ball size, and centrifugal acceleration. Further, the products can be converted into electrode materials for Li-ion batteries, retaining the precursor morphologies. This wet mechanochemical synthesis can be also applied in a bead mill, where mass production and continuous processing are possible. The wet mechanochemical process is a new particle synthesis method that can achieve both grinding and crystal growth.

Nanocomposites with nanoparticles dispersed as the second phase have been reported to have improved mechanical properties. In spite of this potential processing methods to produce these nanocomposites are not well established. In this study, Al₂O₃/mullite/SiC nanocomposites were prepared by the reaction sintering of green compacts prepared by slip casting of a mixture of SiC and Al₂O₃ powders. Here, the surface of the SiC particles was first oxidized to produce SiO₂ and to reduce the core of the SiC particles, and then the surface SiO₂ was reacted with Al₂O₃ to produce mullite. By applying a strong magnetic field during slip casting, the Al₂O₃/mullite/SiC nanocomposites were fabricated with Al₂O₃ oriented, but not with mullite, Al₂O₃ was oriented so that the c-axis of the crystal was parallel to the direction of the strong magnetic field. The density was low due to the agglomeration of SiC raw powder. The bead mill using fine zirconia beads of 50 μm was effective to disperse the agglomerated particles and succeeded in obtaining high-density Al₂O₃/mullite/SiC with no agglomeration of SiC nanoparticles. The bending strength was greatly improved by dispersing the particles, but such improvement was not observed by texturing.

Application of new microbial dispersant to colloidal processing of fine powders of zirconia and alumina was conducted for obtaining fine-grained microstructures. Well-dispersed aqueous suspensions of the fine powders were prepared by adding appropriate amount of new microbial dispersant. The suspensions were characterized by measuring particle size, zeta-potential and rheological properties. Dense green bodies of zirconia and alumina were obtained by slip casting of the suspensions and further CIP treatment. Low-temperature densification was observed, and dense and fine-grained sintered bodies were obtained.