A low-temperature plasticity anomaly of concentrated fcc solid solutions: the Pb–In system

Abstract

This paper discusses the regularities of the plastic strain of single crystals of solid solutions of the Pb–In system at low and very low temperatures, 0.5 K<T<30 K. For Pb alloys with 5, 10, and 20 at. % In, the temperature dependences of the yield strength, τ0(T), and of the increment of the deforming stress, Δτ(T), are measured after a tenfold increase of the strain rate. Specific features (anomalies) of these dependences are detected that do not correspond to concepts of thermally activated motion of dislocations through impurity barriers. It is established that the character of the anomalies substantially changes as the indium concentration varies from moderate values (5 and 10 at. %) to high values (20 at. %). The low-temperature plasticity anomaly of moderately concentrated alloys is interpreted on the basis of the concepts of thermal-inertial and quantum-inertial motion of dislocations through a system of single impurity atoms. In the case of the highly concentrated alloy, the anomaly is interpreted in terms of a model of an inhomogeneous impurity distribution—the presence in the alloy of small clusters that create stronger barriers for the motion of dislocations than do single impurity atoms. The high level of efficient deforming stresses under conditions of deep cooling results in a dynamic regime of dislocation motion through the system of clusters and single impurities, with the yield strength τ0 of the alloy being determined by impurity inhibition of dry-friction type, while the rate sensitivity Δτ of the deforming stress is determined by viscous inhibition by electrons and phonons. The athermal character of impurity dry friction and the sharp decrease of viscous friction upon cooling determine the character of the anomaly in this case.