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ated to the memory of V.L. Indenbom

The Plastic Deformation of Ultrafine Grained Aluminum at 0.52 K Yu. Z. Estrina, N. V. Isaevb, T. V. Grigorovab, V. V. Pustovalovb, V. S. Fomenkob, and S. É. Shumilinb a Monash

University, Clayton, Victoria, Australia Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, Kharkov, 61103 Ukraine b

Received March 5, 2009

Abstract—The plastic deformation of ultrafinegrained aluminum subjected to equalchannel angular pressing has been studied at a temperature below the superconducting transition point. The stress–strain curves σ(ε) for polycrystals and the effect of the superconducting transition on the jump of flow stress ΔσNS have been investigated. It is shown that the grain refinement, along with the increase in the flow stress, leads to a correlated change in the shapes of the dependences σ(ε) and ΔσNS(σ). The results obtained are explained by the features of dislocation accumulation in ultrafinegrained polycrystals and by the manifestation of the inertial properties of dislocations under lowtemperature plastic deformation. PACS numbers: 62.20.F, 62.20.x DOI: 10.1134/S1063774509060194

INTRODUCTION

selves at small values of the dimensionless damping parameter

The change in the macroscopic characteristics of the plastic deformation of metals at superconducting transition that was revealed in 1968 showed for the first time the efficiency of electronic dislocation drag at low temperatures. The results of further experimental and theoretical studies analyzed in review [1] made it possible to formulate the general regularities of this phenomenon, which is observed in the modes of active deformation, creep, and stress relaxation. Under deformation at a constant rate, this effect manifests itself in the form of a jump of flow stress ΔσSN (or ΔσNS) at the moment of destruction or recovery of the superconducting state, respectively, due to the switch ing on and off of the supercritical magnetic field. The modern theoretical models, which describe the effect of SN transition from the superconducting (S) state to the normal (N) state and vice versa [1, 2], take into account the effect of electronic friction on the fluctu ation overcoming local obstacles by moving disloca tions with allowance for their inertial properties. The studies by V.L. Indenbom and colleagues [3–7] made a significant contribution to the development of the concepts about the role of the inertial dislocation motion at superconducting transition. The inertial mechanism assumes that a moving dislocation, due to its intrinsic effective mass, overcomes a point obstacle via the inertial jump through the static equilibrium position [8]. The inertial properties manifest them

(1) BLυ / πμb 2 < 1, where B ≈ Bph(T) + Be is the dynamic friction coeffi cient, including phonon and electronic components; υ is the speed of sound in the crystal; L is the average length of the dislocation segment between the pinning points (stoppers); μ is the shear modulus; and b is the B