Shiomi Kikuchi

Tensile properties of a few Mg-Li-Zn alloy thin sheets

The tensile properties of experimentally produced Mg-6Li-1Zn, Mg-9.5Li-1Zn and Mg-12Li-1Zn alloy thin sheets at room temperature are investigated in this study. Uniaxial tension tests are carried out for various strain rates between 1.4 × 10−5 and 8.3 × 10−2 s−1, and the microstructural and textural changes during the tests are examined. The Mg-6Li-1Zn sheet is composed mainly of the α (hcp) phase and inferior to the other sheets in ductility. The β (bcc) phase is dominant in the Mg-9.5Li-1Zn and Mg-12Li-1Zn sheets, and they have a considerable sensitivity to strain rate. It is observed that the grains are elongated with textural change mainly in the β phase at low strain rates, and the Mg-9.5Li-1Zn and Mg-12Li-1Zn sheets have sufficiently high ductility at low strain rates. The Mg-9.5Li-1Zn sheet composed of (α + β) two phase is superior to the Mg-12Li-1Zn sheet of β single phase in the tensile strength.

Effect of strain rate on deformation behaviour of a Mg–8.5Li–1Zn alloy sheet at room temperature

Abstract The formability of a two-phase Mg–8.5Li–1Zn alloy thin sheet at room temperature is investigated in this study. Uniaxial tension tests are carried out for various strain rates between 1.4×10−5 and 8.3×10−2 s−1, and the microstructural and textural changes during the tests are observed. The sheet has high formability at comparatively low strain rates. Maximum elongation amounts to 100%. However, ductility decreases with the increase in strain rate. Even at room temperature, the stress is also sensitive to the strain rate. It is clarified that the grains are divided into fine sub-grains without any obvious textural change at high strain rates, and that the grains are elongated with textural change mainly in the β phase at low strain rates.

Effect of Aging on Yttria‐Stabilized Zirconia III. A Study of the Effect of Local Structures on Conductivity

Changes in local structures with aging in yttria-stabilized zirconia were examined by extended x-ray absorption fine structure (EXAFS) and internal friction measurement. An analysis of EXAFS shows that a decrease in the first nearest neighbor coordination number of Zr ions, which means short range ordering of oxygen ion vacancies, a decrease in distance between a Zr ion and its first nearest atoms, and an increase in distance between a Zr ion and its second nearest atoms occurred in aged 8YSZ. Aging caused a noticeable decrease in the relaxation peak of internal friction in 8YSZ. These phenomena are attributed to the short range ordering of oxygen ion vacancies around a Zr ion that results from relaxation in the anisotropy of periodical lattice distortion. Therefore, it is concluded that the trapping of oxygen ion vacancies at Zr ions in order to relax such distortion is responsible for a decrease in conductivity with aging. The relaxation peak of internal friction before aging changed with increasing dopant concentrations, and the behavior of this change from 8YSZ to 10YSZ was very similar to that when 8YSZ was aged, and that from 10YSZ to 15YSZ was similar to that when a single crystal of 10YSZ was aged. This marked similarity indicates that the changes in crystal structure which cause the decrease in conductivity with increasing dopant concentration are caused by the short range ordering of oxygen ion vacancies brought about by relaxation of the distortion, similar to those when conductivity decreases with aging.

Determination of diffusion coefficient of oxygen in γ-iron from measurements of internal oxidation in Fe-Al alloys

AbstractThe internal oxidation of iron alloys containing between 0.069 and 0.274 wt pct aluminum was investigated in the temperature range from 1223 to 1373 K for the purpose of determining the diffusion coefficients in γ-iron as well as in the internal oxidation layer. A parabolic rate law is obeyed in the internal oxidation of the present alloys. The rate constant for penetration of the oxidation front, the oxide formed, and the concentration of aluminum in the oxidation layer were determined. Pronounced enrichment of aluminum in the oxidation layer was observed, resulting from the counterdiffusion of aluminum. The oxygen concentration at the specimen surface was determined by combining the thermodynamic data on the dissociation of FeO and the solution of oxygen in y-iron. The diffusion coefficient of oxygen in the internal oxidation layer,Do10, was evaluated on the basis of the rate equation for internal oxidation.Do10 increases at a given temperature as the volume fraction of oxide,f10, in the oxidation layer increases. The diffusion coefficient of oxygen in γ-iron,Do, was determined by extrapolation ofDo10 = 0.Do may be expressed as

Effect of Aging on Yttria‐Stabilized Zirconia II. A Study of the Effect of the Microstructure on Conductivity

D_o = \left( {1.30\begin{array}{*{20}c} { + 0.80} \\ { - 0.50} \\ \end{array} } \right) \times 10^{ - 4} \exp \left[ { - \frac{{166 \pm 5(kJ \cdot mol^{ - 1} )}}{{RT}}} \right]m^2 \cdot s^{ - 1} .

Ion-nitriding of an Fe-19 wt % Cr alloy

Do is close to the diffusion coefficients of carbon and nitrogen in γ-iron.

Possibility of grain refinement for superplasticity of a Mg-AI-Zn alloy by pre-deformation

Abstract The effect of applying ultrasonic wave to soldering on the strength of the bonding interface in lead-free Sn–3.5%Ag, Sn–57%Bi and Sn–57%Bi–1%Ag solder joints has been investigated at various test temperatures and strain rates. The bonding strength of the solder joints depends on the test temperature and the strain rate. The bonding strength of the Sn–Bi solder joints near room temperature is much higher than that of the Sn–3.5Ag solder, but the ductility is lower. The relation between the maximum stress in the stress–strain curve and the strain rate is indicated by the same power law type equation as high temperature creep. Applying ultrasonic wave to soldering influences the microstructure near the bonding interface. As a result, the fine microstructure layer is formed near the interface between the solder and the copper and it increases the strength of the bonding interface in the solder joints.

Aging and composition dependence of electron diffraction patterns in Y2O3-stabilized ZrO2: Relationship between crystal structure and conductivity

Microstructural changes in yttria-stabilized zirconia with aging were investigated by X-ray diffraction, high resolution transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy under TEM, and electron diffraction. First, various microstructural changes reported in the literature as the causes of the decrease in conductivity were carefully examined. As a result, almost all of them proved not to be the direct cause. Therefore, the changes with aging were analyzed mainly by calling attention to a characteristically broad area that appears on the left shoulder of the X-ray diffraction peaks as well as the superlattice reflections and diffuse scattering seen on electron diffraction patterns, and the relationship between microstructural changes and conductivity was clarified. It is conducted that various phenomena due to aging at relatively lower temperatures are caused by short range ordering of oxygen ion vacancies, which occurs in order to relax the anisotropy of periodical lattice distortion. The authors also studied changes in microstructures occurring with changing dopant concentrations and concluded that the changes in microstructures responsible for the decrease in conductivity associated with increasing dopant concentration are caused by short range ordering of oxygen ion vacancies in order to relax the anisotropy in strain fields, similarly to those with aging.