Papers by Author: Kyosuke Kishida

Abstract: The activated slip systems were analyzed in the cold rolling of a Ni₃Al single crystal with an initial orientation of ~[-112](512), which showed an irregular rolling deformation, i.e. widening, bending, and shear deformation. A phenomenological crystal plasticity model was applied using a spectral method. The boundary condition was optimized to reproduce the actual rolling deformation, as follows. That is, the orthogonal components of the deformation gradient were given from the measured widening and reduction, and the shear components were iteratively optimized as to that the final orientation was as close to the experimental one as possible. The calculated result showed that three slip systems, a3, b1, and d1 in the Bishop-Hill notation, were mainly activated in the irregular rolling deformation, which result was consistent to the previous observation of the slip traces [Kishida et al., Philos. Mag. 83 (2003) 3029]. The three activated systems were identical to those activated in the plane-strain condition. However, the quantitative comparison revealed that the activity of b1 was significantly reduced in the irregular rolling deformation, while the activity of d1 was enhanced instead. The less activity of b1 and the enhancement of d1 can be understood assuming a strong interaction between a3 and b1. The reaction of this pair has been reported to form the superlattice intrinsic stacking fault (SISF) in Ni₃Al [Chiba and Hanada, Philos. Mag. A. 69 (1994) 751]. It is likely that the formation of the SISF, which are considered immobile in Ni₃Al, restrained the activation of b1, leading to the irregular rolling deformation.

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: 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: Primary recrystallization textures were examined in the 84% and 95% cold-rolled boron-free Ni3Al single crystals with a Goss texture using the electron backscatter diffraction method. It was found that the main components of the textures in the specimens heat-treated at 873K/0.5h had a 40° rotation relationship about <111> to the original, Goss texture. All the eight variants of 40°<111> rotated grains existed. However, the number density is not even but dependent on whether the rotation axis is identical to the normal of slip planes activated during the prior cold rolling. The ratio of the number density among the variants was same in both the 84% and 95% cold-rolled foils. Based on these results, the formation of these 40°<111> rotated grains was explained assuming the modified multiple twinning mechanism where the annealing twinning occurred at the activated slip planes, followed by the subsequent twinning.

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.

Abstract: The crystallographic orientation distribution, and its change as a function of creep deformation in Ni-based single crystal superalloys have been investigated by X-ray diffractometry. The distribution of the crystallographic orientation has significantly broadened by creep deformations. Directional broadening of the distribution agrees with creep dislocations having the burgers vector of 1/2<101>. High temperature creep strain of superalloys can be estimated by a non-destractive test where the width of rocking curve of a diffraction peak is measured.