Papers by Author: Masahiko Morinaga

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Authors: Hiroshi Yukawa, Masahiko Morinaga, T. Nambu, Yoshihisa Matsumoto
Abstract: A concept for alloy design of Nb-based hydrogen permeable alloys has been proposed based on the mechanical properties of niobium in hydrogen atmosphere and also on the hydrogen chemical potential in metal membrane. Following this concept, Nb-based alloys are designed and developed that possess excellent hydrogen permeability without showing any hydrogen embrittlement.
Authors: Masahiko Morinaga, Yoshinori Murata, Hiroshi Yukawa
Abstract: A molecular orbital approach to alloy design has recently made great progress. Single crystal Ni-based superalloys and high Cr ferritic steels have been developed following this approach. Some perspectives will also be described on the design of heat resistant alloys.
Authors: Kenji Komiya, Y. Shinzato, Hiroshi Yukawa, Masahiko Morinaga, Isamu Yasuda
Abstract: Niobium metal is one of the promising material for hydrogen purification because of its high hydrogen permeability. In order to design and develop a new palladium-free hydrogen permeable membrane, it is important to understand the effects of alloying elements on the hydrogen permeability through metals. However, to the niobium metal, the alloying effects still remain unclear. In the present study, using a DC-polarization technique under the diffusion limiting condition, the hydrogen permeability of Nb-5mol%M alloys were investigated in high precision at 573K. Here, M’s were 4d transition metals, Zr, Mo, Ru and Pd. The permeability of niobium is found to be varied with the addition of a small amount of alloying element. For example, the hydrogen permeability of niobium increases by the addition of Zr but decreases by the addition of Ru.
Authors: Hiroshi Yukawa, G.X. Zhang, Masahiko Morinaga, T. Nambu, Yoshihisa Matsumoto
Abstract: The hydrogen solubility and the hydrogen permeability have been measured for Nb-based alloys in order to investigate the alloying effects on the hydrogen diffusivity during hydrogen permeation. The hydrogen diffusion coefficient during hydrogen permeation is estimated from a linear relationship between the normalized hydrogen flux, , and the difference of hydrogen concentration, C, between the inlet and the outlet sides of the membrane. It is found that the hydrogen diffusion coefficient during the hydrogen permeation is increased by alloying ruthenium or tungsten into niobium. On the other hand, the activation energy for hydrogen diffusion in pure niobium under the practical permeation condition is much higher than the reported values measured for dilute hydrogen solid solutions. It is interesting that the activation energy for hydrogen diffusion decreases by the addition of ruthenium or tungsten into niobium.
Authors: Yoshinori Murata, Masaaki Nakai, K. Nagai, Masahiko Morinaga, Y. Sasaki, Ryokichi Hashizume
Abstract: The effect of S in steels on high-temperature steam oxidation resistance was investigated with respect to the content and the state in high Cr ferritic steels. The beneficial sulfur effect on high-temperature steam oxidation resistance was verified in high Cr ferritic steels. It was considered that Cr was enriched in the vicinity of the segregated S on the specimen surface because of a strong affinity between Cr and S atoms, resulting in the easy formation of the passive Cr2O3 oxide layer on the surface even after the steam oxidation test for a short time. It was found that the precipitated S operated more effectively to the improvement of the steam oxidation resistance compared to the solid-solution state of S in the steels. Furthermore, the sulfur effect on the high temperature steam oxidation resistance was related strongly to the amount of dissolution hydrogen in the high Cr ferritic steels.
Authors: Masahiko Morinaga, M. Yoshino, A. Shimode, K. Okabayashi, H. Nakamatsu, R. Sekine
Abstract: The electron density distributions in a series of metal oxides are calculated using the DV-Xα molecular orbital method. It is found that the logarithm of the electron density, logρ(r), decreases with the distance, r, from the oxygen nucleus, while keeping a constant slope relevant to oxygen atom. The magnitude of the slope is about 15.75 for O-1s electrons, and about 6.61 for O-2s, 2p electrons, being nearly close to the respective values of 16 and 8, expected from the radial distribution functions of hydrogen-like atom containing only one electron. The extent of the region for the O-2s, 2p electrons changes with metal species in the oxides, but the slope remains unchanged. Furthermore, it is shown that the nature of the chemical bonding is well represented in log (ρ minZ-3) vs. 2(Z/n) rminb plots, where ρmin is the minimum electron density, rmin is the distance r at ρmin, Z is the atomic number, and n is the principal quantum number.
Authors: Yoshinori Murata, Shingo Sakurai, Efendi Mabruri, Toshiyuki Koyama, Masahiko Morinaga
Abstract: It is known that two main interdiffusion coefficients, ık Dii and ık Djj , as well as two cross interdiffusion coefficients, ık Dij and ık Dji , are necessary for understanding the atomic diffusion for ternary system. Here, k is the host element of ternary system, and i and j are solute elements. These four interdiffusion coefficients are obtained from a series of experiments using two kinds of ternary diffusion couples. In general, it is believed that ık Dij and ık Dji indicate the same sign to each other, but there are a lot of experimental data showing that ık Dij and ık Dji indicate opposite sign [1]. In such a case, the physical meaning of the cross interdiffusion coefficient has not always been understood thoroughly. The purposes of this study are to measure the interdiffusion coefficients by a series of experiments and to elucidate the physical meaning of the two cross interdiffusion coefficients on the basis of the consideration about the relationship between the thermodynamic functions and the cross interdiffusion coefficients. It is concluded that ık Dij exhibits the opposite sign to ık Dji without contradicting the Onsarger’s reciprocity theorem when the ( 2 2 ) c j ∂ G ∂c shows the opposite sign to ( 2 2 ) c i ∂ G ∂c . Here, c G is Gibbs free energy of the ternary system.
Authors: Yoshinori Murata, Tomonori Kunieda, Kouji Yamashita, Toshiyuki Koyama, Effendi, Masahiko Morinaga
Abstract: The diffusivity of refractory elements in heat resistant steels is crucial for the basic understanding of the microstructural stability during creep. The purposes of this study are to estimate the diffusivity in Fe-Cr alloys as a base alloy for the bcc matrix phase in high Cr ferritic steels and also to investigate the alloying effect of Re on the W diffusivity in them. Fe-15Cr and Fe-20Cr binary alloys, Fe-15Cr-5Re, Fe-15Cr-5W, Fe-20Cr-5Re ternary alloys [mol%] were used in this study. On the basis of the modified ternary Boltzmann-Matano method, the interdiffusion coefficients were obtained in Fe-Cr-Re ternary system. The apparent interdiffusion coefficient for the Re-doped Fe-Cr-W alloy was about one fifth of that for the Re-free alloy. It is concluded that the existence of Re retarded significantly the W diffusion in Fe-15mol%Cr based alloy. This is probably the main reason why a small amount of Re addition suppress the microstructural evolution of W containing high Cr ferritic steels.
Authors: Shingo Sakurai, Efendi Mabruri, Yoshinori Murata, Toshiyuki Koyama, Masahiko Morinaga
Abstract: Ni-based superalloys are strengthed by refractory elements such as Re, Ru and W [1]. Thus, the information on the interdiffusion coefficient as well as the thermodynamic interaction between the refractory elements is important for the future alloy design. In this study, interdiffusion coefficients of the refractory elements in Ni-X-Y (X, Y=Co, Re, Ru, W) ternary systems were estimated by a series of experiments. In the all systems studied in the present works, the main interdiffusion coefficients were much larger than the cross interdiffusion coefficients. In some systems, two cross interdiffuion coefficients had opposite signs each other. For example, in Ni-Co-Ru system, the main interdiffusion coefficients are 2.7 10 14 ~ Ru = × − CoCo D and 15 6.8 10 ~ Ru = × − RuRu D , while the cross interdiffusion coefficients are 16 6.6 10 ~ Ru = − × − CoRu D and 16 8.9 10 ~ Ru = × − RuCo D at 1523K. In Ni-Co-Ru and Ni-Re-Co systems, the activation energies and frequency factors for two main interdiffusion coefficients. For example, Q (kJ ) Co = 268 , 5 ( 2 1 ) 0( ) 4.4 10 D = × − m s − Co , 3 ( 2 1 ) 0( ) 2.9 10 D = × − m s − Ru in Ni-Co-Ru system.
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