Papers by Author: L.N. Pal-Val

Abstract: A detailed study of anelastic effects in submicrocrystalline copper using resonance (~70 kHz, 2 K to 320 K) and sub-resonance (0.05-100 Hz, 300 K to 675 K) techniques was carried out. Several relaxation processes were found in the temperature range of 2 K - 675 K: the relaxation loss peaks (Q^-1) near 35 (P1) and 90K (P2) with the activation energy and the pre-exponential factor (H₁ ≈ 0.02 eV, τ_ο1 ≈ 10^-9 s and H₂ ≈ 0.09 eV, τ_ο2 ≈ 10^-11 s) similar to those of the Bordoni and the Niblett-Wilks peaks in coarse-grained Cu. This suggests that the peaks are due to the thermally activated motion of dislocation kinks in the primary and secondary Peierls relief. The mean values of activation parameters (H₃ ≈1.4-1.6 eV, τ_ο3 ≈10^-17 s) of a third thermally activated peak (P3), which was significantly broadened, can be interpreted as a grain boundary peak with uncoupled activation parameters H₃^*≈0.45 eV and τ_ο3^* ≈10^-14 s. A pseudo peak P_R is associated with irreversible recrystallization processes. The influence of annealing on the observed effects is also discussed.

Abstract: Acoustic properties of polycrystalline Cr samples of 99.99 % purity are investigated at frequencies of longitudinal vibrations f ~ 75 kHz and of bending vibrations at 0.6 < f < 1.5 kHz when thermocycling within the temperature interval 5 − 330 K. Special attention is paid to the acoustic anomalies in the vicinity of the magnetic phase transitions: the Néel point and the spin-flip transition. In the as-received samples, a significant hysteresis of the acoustic properties has been found for the first time. The effect of heat treatments on internal friction and elastic properties of chromium polycrystals is also investigated. The data obtained are compared with the effect of small preliminary deformation and а long-time ageing at room temperature on the ultrasound anomalies in Cr single crystal. The observed behavior of the acoustic properties may be caused by changes in the antiferromagnetic domain structure in Cr polycrystals under the action of thermoelastic stresses arising from quenching, preliminary plastic deformation or thermocycling.

Abstract: An influence of Cd content on the kinetics of a spontaneous low-temperature structure transformation in In-rich In - Cd alloys has been investigated using acoustic, resistivity and DSCtechniques. It is established that increase of the concentration of Cd leads to an essential increase of a driving force of the transition that results in an increase of the transition rate and in decrease of the relaxation time. The low-temperature instability of acoustic, resistivity and thermal properties is caused presumably by a decomposition of the solid solution that has features of a phase transition of the 1st order. The main empirical activation parameters of the transformation are derived. The activation energy amounts to U0 = 0.43 eV, the attempt period is τ 0 =5 × 10-9 s. The probable border of the decomposition in the phase diagram of the In-Cd system is established.