Cu fine-particle paste is a promising material to form a low-cost interconnect for flexible electronics devices. It has been reported that Cu particles can be sintered at low temperature (well below the half of the melting point) through two-step heat treatment processes of oxidation and reduction. However, the mechanism of the low temperature sintering is not clear yet. In this study, we investigated the oxidation sintering process of Cu fine particles by thermal gravimetric analysis (TGA) in the temperature range of 200-300℃, X-ray diffraction (XRD), and microstructural observation. It was found from TGA that the oxidation process was initially rate-controlled by surface reaction and then by Cu diffusion at grain boundaries of Cu₂O. Transmission electron microscopy observation revealed the formation of a core (Cu)-shell (Cu₂O) structure during the oxidation process. The adjacent Cu₂O shells were bonded to each other resulting in a cross-linked structure. The subsequent reduction process led to the formation of a porous structure by oxygen removal, but the cross-linked structure was maintained, which would make the low-temperature sintered Cu body as robust as solidified solder and sintered Ag paste.

Friction stir welding (FSW) was performed under the two welding conditions (rotation speed-traveling speed) of 150 rpm-100 mm/min and 200 rpm-400 mm/min using 6 mass％Ni-0.63 mass％C steels. The slightly lower peak welding temperature and significantly higher cooling rate was obtained under the condition of 200 rpm-400 mm/min. Texture analysis for retained austenite and martensite revealed that the parent austenite had simple shear texture, which lead to the formation of {110}<111> texture in transformed martensite. Moreover, material flow behavior as a function of distance from the top surface in the stir zone was analyzed based on textures obtained by EBSD measurement. A concentric material flow, which has smaller radius as the far from the tool shoulder, was formed under the condition of 150 rpm-100 mm/min. On the other hand, a heterogeneous material flow with the center shifted to the retreating side was formed under the condition of 200 rpm-400 mm/min. In addition, a different vertical component of material flow was predicted to occur under each welding conditions.

A large step on the initial magnetization curve has been widely observed in Nd-Fe-B hot-deformed magnets. This behavior has been considered as that the first- and latter-half parts of the initial magnetization curve correspond to the magnetization reversals of multi- and single-domain grains, respectively. In this study, the detailed magnetic domain structure of a Nd-Fe-B hot-deformed magnet has been studied for the initial magnetization and demagnetization processes by using a soft X-ray magnetic circular dichroism (XMCD) microscopy. The observed magnetization reversal behavior for the initial magnetization process is quite different from that previously considered. The multi-domain states move from grains to grains through the gradual displacement of domain wall passing through many grains, and then the massive domain wall displacement takes place. The latter part of domain wall displacement is similar with that found in the demagnetization process near the coercivity. Moreover, we found that there are several strong pinning sites which are identical for both the initial magnetization and the demagnetization processes.

The effect of one-pass strain, |±Δε|, on grain refinement was systematically investigated by cyclic - HPT straining with a repetitive deformation process in which positive and negative shear strain are introduced. The steady-state grain size, d_ss, depended on |±Δε| rather than the given total strain, Σ |±Δε|. The unstable dislocation cell walls formed by positive strain, +Δε, was discomposed by negative strain, −Δε. The stability of dislocation cell wall increased as the number of dislocations introduced by applying |±Δε| in a grain, n, increased. The decrease in n was caused by decreasing +Δε and grain size. It was found that n affected the stability of dislocation cell walls and was an important factor in determining d_ss.

In tensile tests, α-Mg/C14-Mg₂Ca eutectic alloy with a lamellar structure is plastically deformed above 473 K but ruptures before yielding at temperatures below 423 K. This study investigates the effect of the α/C14 interface on the creep strength of α-Mg/C14-Mg₂Ca eutectic alloy at 473 K under 40 MPa stress. The creep curves of the alloy exhibited three stages: a normal transient creep stage, minimum creep-rate stage, and accelerating stage. The minimum creep rate was proportional to the lamellar spacing, indicating that the α/C14 lamellar interface plays a creep-strengthening role. In high-resolution transmission electron microscope observations of the specimens after the creep test, a dislocations appeared within the α-Mg lamellae and were randomly distributed on the α/C14 interface. It was deduced that the α/C14 interface presents a barrier to dislocation glide and does not annihilate and/or rearrange its dislocation caused by the creep test.