Ternary Nb-Re-Si alloy samples were melted and pulled simultaneously in a tetra-arc furnace and rapidly water-quenched after heat treatment at 1150°C for 1200 h. The microstructures of the samples that had been water-quenched after heat treatment were observed and the Nb, Re and Si concentrations in the constituent phases were measured using an electron probe microanalyzer (EPMA). In the cross-sectional structure of the obtained alloy samples, the lower portion of the pulled part consists of Nb₅Si₃ and Nb-Re-Si ternary compound phases. By contrast, the upper portion consists of Nb₅Si₃ and Nb solid solution phases. The Nb solid-solution phase, Nb₅Si₃ and Nb-Re-Si ternary compound are in equilibrium. It was found that the solubility limit of Si in the Nb solid-solution phase ranges from 0.6 to 1.7 at%, while the solubility limit of Re in the Nb₅Si₃ phase is 1.3-2.0 at%. The maximum amount of Re in the Nb₅Si₃ phase in equilibrium with the Nb solid solution is about 0.9 at%.

The log angles of a rotation matrix are three independent elements of the logarithm of the rotation matrix. Nye’s lattice curvature tensor κ_ij is discussed by using the log angles. For the change in a crystal orientation ΔR with the change in a position Δx_i, it is shown that the elements of κ_ij are written as κ_ij=Δω_i/Δx_j using the log angles Δω_i of ΔR. The log angles for the crystal rotation given by the axis/angle pair are also discussed.

The thermal effusivities of the AlO_1.5-R₂O-SiO₂(R=Li, Na)melts were measured by the front-heating front-detection laser flash method. The thermal conductivities of the AlO_1.5-R₂O-SiO₂ melts were tentatively determined from the specific heat capacities and bulk densities. In these results, the thermal conductivities were almost constant over the temperature range investigated. It was found that the thermal conductivity of AlO_1.5-Li₂O-SiO₂ melt was larger than that of AlO_1.5-Na₂O-SiO₂ melt. It was also found that the thermal conductivities were increased with AlO_1.5 content in the content range from 0 to 16.8 mol% and that was decreased with increasing AlO_1.5 content in the content range from 16.8 to 22.4 mol%.

The effect of solidification conditions on the tensile deformation behavior of pure copper castings for electrical parts was investigated. Two main types of tensile deformation properties were distinguished on the basis of the difference in uniform elongation. For the castings fabricated under a superheat of 100°C or 150°C, larger and smaller uniform elongation types corresponded to the absence and presence, respectively, of the Cu–Cu₂O eutectic phase in the microstructure. Meanwhile, for the castings fabricated under a superheat of 50°C, greater uniform elongation was sometimes obtained when the eutectic phase was present. In addition, irrespective of the presence or absence of the eutectic phase, greater uniform elongation was always obtained when chills were used. Cross-sectional observations showed the existence of considerable nonspherical porosity when the eutectic phase was present; the porosity was reduced when the pouring was conducted under the superheat of 50°C and when the chills were used because of lower hydrogen content in the melt and supersaturation of the hydrogen by rapid cooling, respectively. These results suggest that not only the presence of the eutectic phase but also the inferior casting soundness due to the existence of the porosity is a dominant factor responsible for the decrease in the uniform elongation. The findings presented here indicate that a decrease in the hydrogen content in the melt and/or the rapid cooling during solidification are effective measures to stably achieve practically sufficient deformation properties along with superior casting soundness.

Mater. Trans. 60（2019）（doi: 10.2320/matertrans.MG201801）に掲載

Experimentally obtained polarization curve for the hydrogen evolution reaction on titanium in a 0.5 mol dm^-3 sulfuric acid solution was studied using curve techniques in the differential polarization method (DPM). The values of exchange current density (i₀) were estimated to i₀=10^-2.6~10^-3.1 mA cm^-2 by the Tafel extrapolation method (TEM) and to i₀=10^-3 mA cm^-2 by the DPM, respectively. In addition, the DPM showed that the cathodic transfer coefficient was ca. 0.3. From viewpoints of easy and more accurate estimation, it was shown that the DPM has two advantages: (1) proper readings of the Tafel slope and (2) accurate elimination of undesired physical factors such as oxide film and solution resistance.

The thermal diffusivity measurement of plastics by using the laser flash method can be considered difficult owing to sample damage caused by the pulse laser. In this study, the thermal diffusivity of plastics was measured by the laser flash method, in which the metal surface of a two-layer sample was irradiated with the laser. This study revealed that the areal heat diffusion time method is useful for measuring the thermal diffusivity of plastics and that the effect of interlayer thermal resistance on the thermal diffusivity measurement is negligibly small.

Ultra-fine grained pure copper fabricated by equal-channel angular pressing was used as a sample. We made tensile-shear tests using specimens with notches cut from the sample and large shear deformation occurred between the notches. Microstructural changes between the notches caused by the large shear deformation were observed. Using micro scale lattices scribed on the surface of the specimen, we found both refinement and coarsening of grains caused by the large shear deformation. Although severe plastic deformation causes ultra-fine grained structure, it is known there is a limit of the grain refinement. The grain coarsening observed in the present study is considered to be the reason of the limit of the grain refinement caused by severe plastic deformation.

Journal of the Japan Institute of Metals and Materials Vol. 81, No. 12 (2017) 527-535

p.528, Fig. 1