Papers by Author: Haruyuki Inui

Abstract: MoSi₂–based alloys are attracting attention as ultra-high temperature structural material for super-high efficiency gas turbine power generation systems. In this study, the effects of Cr-and Zr-addition on interface migration in MoSi₂/NbSi₂ lamellar silicide were examined by phase field simulations employing the segregation energies evaluated by the first principles calculation in addition to thermodynamic free energy in order to take into account the chemically-driven interfacial segregation. The simulation results indicate that both Cr and Zr can segregate at the lamellar interface to suppress its migration, and the Zr-addition is more effective to lower the interface migration rate than the Cr-addition owing to its higher segregation energy.

Abstract: The evolution of the raft structure in the Ni-based single-crystal superalloy TMS-138 crept at 1100 °C and 137 MPa has been investigated quantitatively by the Fourier analysis of scanning electron microscope (SEM) images. This method of analysis quantifies the extent of tilting of the γ/γ′ interface during creep deformation. The analysis is carried out on two different crystallographic planes, (100) and (110), on which SEM observations of deformation microstructures are made, to see if there is any difference in the results of analysis depending on observation planes. The tilt angle of the γ/γ′ interface, which is deduced by the Fourier analysis, increases with the accumulation of creep strain. The rate of the increase in the tilt angle is significantly large in the tertiary creep stage. The result of analysis does not depend significantly on crystallographic planes on which SEM observations of microstructures are made.

Abstract: The mechanical properties of Co3(Al,W) with the L12 structure have been investigated both in single and polycrystalline forms. The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co3(Al,W) experimentally determined by resonance ultrasound spectroscopy at liquid helium temperature are 15~25% larger than those of Ni3(Al,Ta) but are considerably smaller than those previously calculated. When judged from the values of Poisson’s ratio, Cauchy pressure and ratio of shear modulus to bulk modulus (Gh/Bh), the ductility of Co3(Al,W) is expected to be sufficiently high. In the yield stress-temperature curve, a rapid decrease and an anomalous increase in yield stress is observed in the low and intermediate (1000-1100 K) temperature ranges, respectively. The former is concluded to be due to the solid-solution hardening effect while the latter is attributed to thermally activated cross-slip of APB-coupled a/2<110> superpartial dislocations from octahedral to cube slip planes.

Abstract: The physical and mechanical properties of Co3(Al,W) with the L12 structure have been investigated both in single and polycrystalline forms. The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co3(Al,W) experimentally determined by resonance ultrasound spectroscopy at liquid helium temperature are 15~25% larger than those of Ni3(Al,Ta) but are considerably smaller than those previously calculated. When judged from the values of Poisson’s ratio, Cauchy pressure and Gh (shear modulus)/Bh (bulk modulus), the ductility of Co3(Al,W) is expected to be sufficiently high. Indeed, the value of tensile elongation obtained in air is as large as 28 %, which is far larger than that obtained in Ni3Al polycrystals under similar conditions.

Abstract: Interdiffusion coefficients of Al replacing elements in Ni-Al-X (X=Ti, V and Nb) were estimated by a series of experiments using diffusion couples of Al rich pseudo-binary systems at three different temperatures of 1423, 1473 and 1523K. In order to obtain interdiffusion coefficients of the pseudo-binary systems, the experimental data was analyzed by the Sauer and Freise method, and also impurity diffusion coefficients of Ti, V and Nb in Ni3Al were estimated by applying the Darken-Manning equation. The magnitude of interdiffusion coefficient decreased in order of V, Ti and Nb at all three temperatures. Impurity diffusion coefficients were described by the expressions: , , . The activation enthalpies obtained from the experimental data confirmed the retardation of Ti, V and Nb diffusion in Ni3Al by the anti-site diffusion mechanism. These results are consistent with our previous work on diffusion of Re and Ru in Ni3Al .

Abstract: The values of all the three independent single-crystal elastic constants and polycrystalline elastic constants of Co3(Al,W) experimentally determined by resonance ultrasound spectroscopy at liquid helium temperature are 15~25% larger than those of Ni3(Al,Ta) but are considerably smaller than those previously calculated. Because of the large value of E111/E100 and cij of Co3(Al,W), two-phase microstructures with cuboidal L12 precipitates well aligned parallel to <100> and well faceted parallel to {100} are expected to form very easily in Co-base alloys, as confirmed indeed by experiment. Values of yield stress obtained for [001]-oriented L12/fcc two-phase single crystals moderately decrease with the increase in temperature up to 800°C and then decrease rapidly with temperature above 800°C without any anomaly in yield stress.

Abstract: Manganese-alloyed Ru2Si3-based alloys with various alloy compositions have been prepared and the phase relationships of these alloys have been investigated as a function of the Mn concentration using X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. A series of Ru1-xMnxSiy chimney-ladder phases is confirmed to be formed over a wide compositional range (x ≥0.12). These chimney-ladder phases are considered to be formed to stabilize the HT-Ru2Si3 chimney-ladder phase through the substitution of Ru with Mn. The compositions of the chimney-ladder phases are, however, significantly deviated from the idealized composition satisfying the valence electron concentration rule: VEC=14.

Abstract: Electrochemical properties and microstructure evolution during lithiation and delithiation of Ni3Sn2 single crystals with the hexagonal B82-type related ordered structure have been studied as a function of the crystal orientation by charge/discharge tests, powder X-ray diffraction and transmission electron microscopy. Charge and discharge capacities are strongly dependent on the crystal orientation. When the surface of the thin plate anode is perpendicular to the basal plane of the parent B82 unit cell, the capacities are approximately twice as high as those for the sample whose surface is parallel to the basal plane, which is considered to be related to the difference in the diffusion behavior of lithium with respect to the crystal orientation.

Abstract: The temperature dependence of single-crystal elastic constants of L10-ordered single-crystals of FePd . A complete set of elastic constants has been determined with the resonance ultrasound spectroscopy technique. The compounds clearly show a tetragonal elastic anisotropy, c11 < c33 and c44 < c66. The temperature dependencies of the anisotropies are not simply explained by the variation of axial ratio (c/a) of the crystal.

Abstract: The effect of hydrostatic pressure mechanically applied to hydride on the equilibrium hydrogen gas pressure and temperature have been examined theoretically. From free energy calculations where elastic energy is taken into account, equilibrium gas pressure and temperature increases and decreases with increasing applied compressive stress, respectively. In the case of magnesium hydride, equilibrium temperature decreases to 63 °C at the hydrogen gas pressure being 1 atom when volume expansion at hydriding is perfectly suppressed by an external compressive stress. The temperature is remarkably lower than that obtained by alloying various elements.