Quantum creep of β–Sn in the normal and superconducting states. Influence of the NS transition on work hardening

Abstract

Previously we investigated the kinetics of transient logarithmic creep of ␤-tin single crystals at very low temperatures 0.5 K Ͻ T Ͻ 4.2 K with the sample under deformation in the normal ͑N͒ electronic state. In a continuation of that research, here we determine the boundary temperature T g Ϸ 1.3 K separating the regions of thermally activated ͑T Ͼ T g ͒ and quantum ͑T Ͻ T g ͒ plasticity governed by the motion of dislocations through Peierls barriers. Experiments are done on samples in the superconducting ͑S͒ state ͑0.5 K Ͻ T Ͻ T c = 3.7 K͒. It is shown that the NS transition preserves the logarithmic type of creep, its quantum character in the region T Ͻ T g , and the value of the boundary temperature ͑T gS Ϸ T gN Ϸ 1.3 K͒. Analysis of the curves of the logarithmic creep in the quantum region can yield empirical estimates for the work hardening coefficient of the samples. It is found to increase significantly at the NS transition: along the whole deformation curve the work hardening in the S state occurs more intensely, and, on the average, S Ϸ 1.5 N . Such an effect has been observed previously in a study of the plasticity of a series of fcc metals by the method of active deformation at a constant rate ͑V. V. Pustovalov, I. N. Kuz'menko, N. V. Isaev, V. S. Fomenko, S. É. Shumlin, Fiz. Nizk. Temp. 30, 109 ͑2004͒ ͓Low Temp. Phys. 30, 82 ͑2004͔͒͒. A comparison of the results of this study with previous results suggests that the increase in intensity of the work hardening at the superconducting transition is of a general nature for metallic superconductors and is manifested for other deformation regimes as well. The possible causes of the effect are discussed in the general conceptual framework of dislocation physics.

Effect of dynamic plastic deformation on the fluctuation stage of creep in single-crystal β-tin at 1.6 K

“…[6][7][8][9] The behavior of the following parameters was studied: the total increment in the creep deformation De, its fluctuating rate _ e m in the dynamic stage; and, the coefficient of logarithmic creep a.…”

“…Creep in single-crystal b-tin owing to the transition of this metal from the normal into the superconducting state (the NS transition) has been studied experimentally and theoretically in a series of papers. [6][7][8][9] These studies showed that the creep curves stimulated by the NS transition have a complicated stage structure including short-term dynamic sections with an exponential time dependence of the creep deformation and prolonged sections corresponding to fluctuation movement of dislocations in the crystal where the creep has a logarithmic time dependence. When the temperature is lowered the deformation in the logarithmic stage forms a small part of the overall increment and most of it occurs in the dynamic stage.…”