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
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