Structure Transformation of Dispersionstrengthened Vanadium Alloys under Conditions of High-Pressure Torsion and Room-Te
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STRUCTURE TRANSFORMATION OF DISPERSIONSTRENGTHENED VANADIUM ALLOYS UNDER CONDITIONS OF HIGH-PRESSURE TORSION AND ROOM-TEMPERATURE TENSILE DEFORMATION I. V. Smirnov, K. V. Grinyaev, and I. A. Ditenberg
UDC 538.911; 548.4; 669.17; 620.186.8
A comparative study of the features of microstructure transformation in dispersion strengthened vanadium alloys of the V–Me(Cr, W)–Zr system under conditions of deformation by torsion under pressure and tension at room temperature is carried out. It is found out that suppression of dislocation plasticity in the high-strength state favors the formation of an anisotropic submicrocrystalline structure both during torsion deformation and in the region of strain localization in the case of tension at room temperature. It is shown that one of the main mechanisms of crystal fragmentation under these conditions is a dislocation-disclination mechanism, whose realization requires structural states with nonzero values of the curvature rotor or a high continual density of disclinations. Keywords: vanadium alloys, microstructure, structural transformation mechanisms.
INTRODUCTION It is common knowledge [1, 2] that the concept of a high-strength state implies a special material state with characteristic features of the motion of individual dislocations and the mechanisms of plastic deformation, strain hardening and fracture. In accordance with this concept, in high-strength materials under the conditions of severe deformations and other scenarios of low-efficiency dislocation deformation mechanisms, plastic deformation occurs by the mechanisms other than those induced by dislocations. High local stresses under the above-mentioned conditions favor the development of plastic flow by a cooperative motion of dislocation-disclination ensembles and other highenergy carriers of crystal deformation and crystal reorientation carriers. Among the most important features of plastic flow typical for high-strength states, irrespective of the method of their formation (solid solution and dispersion strengthening, decreasing of elatic modulus values in alloys with structural instabilities, formation of submicrocrystalline (SMC) and nanocrystalline (NC) structural states, changing of the test temperature, high-rate plastic deformation) it is worth mentioning the following: – defining role of cooperative deformation mechanisms since the very onset of plastic flow [1, 2]; – formation of high-energy structural states with high crystal-lattice curvature values, local internal stresses and their gradients (moments) – sources of rotational plasticity of crystals [1, 2]; – activation of new non-dislocational modes of plastic flow of the quasi-viscous mass transfer [3] or local structural transformations of a martensitic type [4]. A study of highly defective structural states and an identification of the mechanisms of their formation under the conditions of suppressed dislocation plasticity in metals and alloys of different classes is still one of the most important issues of the strength and plasticity physics.
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