Papers by Author: Vladimir V. Stolyarov

Abstract: It is shown that deformability of Ti50.0Ni50,0 alloy at the rolling with current is considerably above than at the cold rolling. The influence of deformation with a current and without a current on feature of martensitic transformations was investigated. Recovery strain and recovery stress were studied on heating the sample subjected to preliminary strain by a three-point bending and optimal regimes of electroplastic rolling were defined.

Abstract: Influence of the combined action severe deformation and a pulse current on a microstructure and mechanical behavior of long-size rods and strips with thin section out of Ti50Ni50 and Ti49.3Ni50.7 alloys is presented. Dependence of electroplastic effect on phase composition of the initial alloys is demonstrated. It is established, that electropulse postdeformation processing promotes acceleration of a stress relaxation at stages of recovery, polygonization and recrystallization in alloys.

Abstract: Systematized literature data related to the study of mechanical and functional properties of ultrafine-grained and nanostructured metallic materials processed by deformation methods are presented. Special attention is given to the mechanical behavior of titanium materials under tension, as well as under impact and cyclic loads. The advantage of the materials under investigation over their coarse-grained analogues is shown.

Abstract: Ultrafine-grained (UFG) CP titanium (Grade-4) sample was processed by electroplastic rolling (EPR) at room temperature which was compared to a specimen processed by conventional cold rolling (CR). EPR was performed using pulsed unidirectional current with a current density of 95 A/mm2, pulse duration of 10-4 s and frequency of 1000 Hz. It was found that the sample processed by EPR has slightly higher dislocation density and smaller crystallite size than for the CR specimen resulting in a higher tensile strength for the former specimen. In the case of EPR sample, the relative fraction of dislocations is lower than for CR specimen. During annealing the relative fraction of dislocations decreased for both samples which can be explained by the fact that the dislocations have larger Burgers-vector and consequently higher formation energy than the other two types.

Abstract: The paper presents data on structure refinement and electropulse current effects on deformability, strength and ductility of shape memory TiNi alloy, processed different severe plastic deformation techniques including equal channel angular pressing and electroplastic rolling. It was found that deformability and elongation to failure decreases with grain refinement but they can be enhanced by electropulse current.

Abstract: Application of electroplastic deformation (EPD) by rolling to bulk long-sized samples of Ti-50.7 at.%Ni alloy allows increasing of the deformation strain without macrofailure by 1.5 to 3 times in comparison to cold rolling without electrical current application. Structure formation and functional properties were studied after various EPD regimes: current density (84 to 168 А/mm2) and impulse duration (80 and 160 ms). When the stage of mixed nanocrystalline and amorphous structure formation is reached as a result of EPD, a post-deformation annealing at 400 °С leads to a nanocrystalline structure formation in austenite and highest recovery stress values generation by the martensite.

Abstract: Electropulse current effect during cold rolling on deformability, nanostructure formation and mechanical behavior in coarse-grained (CG) and ultrafine-grained (UFG) TiNi alloys enriched by nickel is investigated. The UFG sample subjected to cold rolling with current has a fracture strain (е = 1.91) which is higher than that without a current (е = 0.59). As a result of cold rolling with a current and a subsequent annealing at 400-450 °C, nanostructure is formed in both alloys, which leads to a significant enhancement of yield and ultimate stresses. It has been shown that the efficiency of electroplastic rolling depends on the purity of the alloys.

Abstract: The aim of this paper is the investigation of electroplastic deformation (EPD) and subsequent annealing influence on martensitic transformation in the shape memory Ni50.7Ti49.3 alloy. Using differential scanning calorimetry method it was shown that EPD at the low strain stimulates structure relaxation and recovers martensitic transformation in cooling, which is usually suppressed by cold rolling.