V. V. Pustovalov

Serrated deformation of metals and alloys at low temperatures (Review)

Plastic deformation at constant rate and low temperatures starting with 20–30K, as a rule, occurs in the form of oscillations of the deforming stress (serrated deformation). Low-temperature serrated deformation (LTSD) appears under special conditions where deformation occurs as a result of the specific conditions of dislocation dynamics and, possibly, as result of special physical conditions of deformation (low thermal conductivity and specific heat of the sample, heat exchange with the cooling medium). A large number of experimental and theoretical works have been performed since the discovery of LTSD in the 1950s but not even one review has appeared. Further advances in understanding the mechanism of LTSD and the development of a theory of this phenomenon require that the experimental data be systematized. As a rule, individual experimental facts have been used when theories of LTSD have been compared with experiment. The present review attempts to collect as much accessible experimental data as possibl...

Effect of superconducting transition on the low-temperature jumplike deformation of metals and alloys (Review)

The available experimental data on the effect of the superconducting transition on the low-temperature jumplike deformation of metals and alloys are examined. Different hypotheses as to the mechanism for this effect are stated and compared with experiment. The experimental and theoretical papers on the low-temperature jumplike deformation are discussed, and conjectures as to the mechanism for the effect are set forth.

Low-temperature plastic strain of ultrafine-grain aluminum

The microstructure and mechanical properties of ultrafine-grain (UFG) commercial-grade Al obtained by equichannel angular pressing (ECAP) are study in the temperature range 4.2–295K. Transmission electron microscopy and x-ray diffraction methods are used to show that as the number of passes increases, the grain size decreases, the grain shape becomes increasingly equiaxial, and the dislocation density inside a grain and the character of the intergrain boundaries change. An increase of the coherent scattering region and a decrease of the level of microdeformations indicate that pressing decreases the total density of imperfections of the crystal structure inside grains. As temperature decreases, the yield stress, plasticity, and strain hardening rate of UFG and coarse-grain polycrystals increase substantially. The deformation of UFG polycrystals at 4.2K becomes unstable (abrupt). The temperature dependences of the yield stress σy(T) of UFG and coarse-grain polycrystals, where the form of these dependences ...

Low-temperature plastic deformation of AZ31 magnesium alloy with different microstructures

Yu. Z. Estrin, P. A. Zabrodin, I. S. Braude, T. V. Grigorova, N. V. Isaev et al. Citation: Low Temp. Phys. 36, 1100 (2010); doi: 10.1063/1.3539781 View online: http://dx.doi.org/10.1063/1.3539781 View Table of Contents: http://ltp.aip.org/resource/1/LTPHEG/v36/i12 Published by the American Institute of Physics.

Influence of a superconducting transition on the macroscopic characteristics of the plasticity of metals and alloys: Fundamental and applied aspects (Review)

The results of observations and investigations of a new phenomenon—changes in the macroscopic characteristics of plastic the deformation of metals and alloys at a superconducting transition—are systematized. In these works it is shown for the first time that the electronic drag of dislocations accompanying low-temperature deformation is effective. The main experimental features of the phenomenon—the dependences of the characteristics of the change in plasticity at a superconducting transition on the stress, deformation, temperature, deformation rate, and concentration of the alloying element in the superconductor—and results indicating a correlation between the characteristics of the effect and the superconducting properties are presented. Experiments clarifying the mechanisms of the phenomenon are analyzed. A brief exposition of the theoretical investigations of the electronic drag of dislocations in metals in the normal and superconducting states and the influence of a superconducting transition on the ...

Strain hardening of metals and alloys in the superconducting state

The strain hardening of single crystals of pure Al and a Pb–In alloy in the normal (N) and superconducting (S) states is investigated. It is found that the strain hardening coefficients satisfy the inequality θS>θN irrespective of whether the SN transition is brought about by an external magnetic field or temperature.

Microstructure and low-temperature plastic deformation of Al–Li alloy

Features of the plastic deformation of solid Al–Li solutions with microstructures formed by direct and angular hydroextrusion are studied under tension at temperatures of 4.2–350 K. It is found that the grain size reductions, increases in the average density of defects, and changes in the orientational textures during combined hydroextrusion lead to increased strength and reduced plasticity of the microcrystalline alloy relative to initially large-grained samples. The high yield stress of the microcrystalline alloy is explained by a higher grain density and the evolution of an orientational texture. The strong temperature dependence of the yield stress is typical of thermally activated interactions between dislocations and local obstacles in the form of deformation defects produced during hydroextrusion. The low plasticity of the microcrystalline alloy, which already shows up as a localization of plastic deformation with small deformations, is caused by a low rate of work hardening owing to enhanced dynam...

Study of the structural nonuniformity and low-temperature micromechanical properties of ultrafine-grain aluminum

The optimal conditions for measuring the microhardness of aluminum, concerning the surface preparation of the samples (electropolishing) and the load on an indenter (at least 0.5N), are determined. The degree of structural uniformity of aluminum after deformation by equal-channel angular pressing (ECAP) is studied by the microindentation method. It is found that the microhardness of an extruded blank varies over the cross-section, and it reaches its maximum value in the central part. The nonuniformity decreases as the number of passes increases. The main structural changes giving rise to hardening occur during the first pass. The temperature dependence of the microhardness in the interval 77–295K intensifies as the number of ECAP passes increases. The Hall-Petch law describes the hardening of aluminum as result of grain-size reduction during ECAP well, and the Hall-Petch coefficient increases as temperature decreases. For ultrafine-grain aluminum the microhardness and yield stress with strain e=0.076 are ...

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

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 interpret...

Features of the low-temperature plasticity of Pb–In single crystals

The temperature dependence of the plasticity parameters of Pb–In single crystals with indium concentrations of 1–20 at. % are investigated under tensile deformation at a constant strain rate in the temperature interval 4.2–295 K. From an analysis of the experimental data, empirical estimates are obtained for the main parameters of the dislocation–impurity interaction and the dynamic drag coefficient of the dislocations. The calculated values of these parameters are consistent with the idea of a gradual transition on cooling, from a thermally activated motion of dislocations through local impurity barriers to a thermal–inertial motion. With increasing indium concentration (to 20 at. %) the low-temperature mechanisms of dislocation motion begin to be affected substantially by regions of short-range order (clusters), the presence of which is detected by the diffuse x-ray scattering method.