Yohichi Kohzuki

By Yohichi Kohzuki

Strain-rate cycling tests associated with the ultrasonic oscillation were conducted for the purpose of investigation on the interaction between dislocation and dopant ions during plastic deformation of seven kinds of single crystals: NaCl doped with Li+, K+, Rb+, Cs+, F−, Br− or I− ions separately. Relative curves between the stress decrement (Δτ) due to ultrasonic oscillatory stress and strain-rate sensitivity (λ) of flow stress under superposition of the oscillation are obtained by the original method (combination method of strain-rate cycling tests and application of ultrasonic oscillations) at 77 K to room temperature and have stair-like shapes for the specimens at low temperatures. The Gibbs free energy for overcoming of the dopant ion by dislocation at absolute zero is calculated from the data analyzed in terms of Δτ vs. λ. As a result, the obtained energies are found to be varied linearly with the isotropic defect around it in the each specimen.

Part of the book: Electron Crystallography

By Yohichi Kohzuki

Combination method of strain-rate cycling tests and application of ultrasonic oscillations was conducted for KCl:Sr2+ (0.035, 0.050, 0.065 mol.% in the melt) single crystals at low temperatures. The measurement of strain-rate sensitivity (λ) of flow stress under the application of ultrasonic oscillatory stress provides useful information on the interaction between a mobile dislocation and impurities (Sr2+ ions) during plastic deformation and the variation of λ with stress decrement (Δτ) due to oscillation has stair-like shape: The first plateau place ranges below the first bending point (τp1) at low stress decrement and the second one extends from the second bending point (τp2) at high stress decrement. The value of λ decreases with the Δτ between the two bending points. The τp1 is considered to represent the effective stress due to impurities when a dislocation begins to break-away from the impurities with the help of thermal activation during plastic deformation. Annealing the impure crystal by heat treatment, τp1 decreases obviously at low temperature and the critical temperature Tc, at which τp1 is zero, also becomes slightly smaller. Furthermore, it was investigated whether a change in the state of a small amount of impurities has an influential factor of the flow parameters (e.g., the activation energy, the density of forest dislocations) from the data analyzed in terms of Δτ vs. λ curve.

Part of the book: Alkaline Chemistry and Applications

By Yohichi Kohzuki

The influence of the state of additive cations on the various deformation characteristics was studied for KCl:Sr2+ single crystal at room temperature. This result gives the heat treatment suitable for the crystal immediately before deformation tests, such as compression and tension. Four kinds of single crystals (KCl: Mg2+, Ca2+, Sr2+ or Ba2+) were plastically deformed by compression at 77 to room temperature. The plasticity of the crystal depends on dislocation motion from a microscopic viewpoint. When a dislocation breaks away from the defect around the additive cation with the help of thermal activation on the slip plane in the crystal, the variation of effective stress with the temperature was investigated by the combination method of strain-rate cycling tests and ultrasonic oscillations. Furthermore, the critical temperature Tc at which the effective stress due to the additives is zero was estimated for each of the crystals. As a result, Tc value tends to be larger with the divalent cationic size.

Part of the book: Elasticity of Materials

By Yohichi Kohzuki

Strain-rate cycling tests under superposition of ultrasonic oscillation were carried out at 77–293 K for two kinds of samples: non-irradiated and X-ray-irradiated KBr single crystals. Point defects induced by X-ray irradiation have weak interaction with dislocation and act as obstacles to dislocation motion. Assuming that the defect is tetragonal, the interaction energy for the break-away of a dislocation from the defect has been obtained by fitting the Barnett model to experimental results. Then, the value of interaction energy was determined to be 0.81 eV for the crystal. This result is compared with it in other crystals (NaCl, NaBr, and KCl) by the X-irradiation.

Part of the book: Recent Advances in Mineralogy