Papers by Author: Evgeny V. Naydenkin

Abstract: The structure and misorientations of grain boundaries of ultrafine-grained nickel subjected to rolling and forging at liquid nitrogen temperature are studied. It is shown that as a result of rolling in UFG nickel obtained by the ECAP the forming of a band fragmented structure with the formation of special twin boundaries Σ3 is observed. An increase in the strain rate (forging) leads to the appearance of localized deformation bands in which the formation of new small grains is observed through dynamic recrystallization. The development of recrystallization results in increase up to 7% in UFG nickel the fraction of special twin boundaries Σ3 which are similar in nature to annealing twins.

Abstract: The studies showed that as a result of radial-shear rolling (RSR) in the temperature range of 850-650°C the formation of a quasi-globular ultrafine grain-subgrain structure with a size of structural elements of about 0.5-0.7 μm is observed in near β titanium alloy Ti-5Al-5V-5Mo-1Cr-1Fe. Subsequent annealing (aging) in the temperature range of 450°C for 5 hours leads to the decomposition of the β-phase matrix deformed during the rolling process with the formation of nanosized acicular precipitates of the martensitic α" phase along with finely dispersed inclusions of α phase particles preserved after rolling. The formation of such ultrafine-grained (UFG) structure leads to a significant (more than 25%) increase in the strength properties of the alloy compared to the initial state while maintaining sufficient ductility (~5%). Also obtained by the method UFG titanium alloy exhibits a high fatigue strength under very high cycle loading (fatigue strength based on 10⁸ cycles exceeds 700 MPa).

Abstract: The influence of the structural-phase state on the development of low-temperature superplasticity of titanium alloys with an ultrafine-grained structure and different volume fraction of the β phase was studied. It was shown that the formation of the structure by multi-directional pressing leads to a decrease in the temperature of the beginning of the superplastic flow realization up to 823K regardless of phase composition of the titanium alloys. It is assumed that the non-monotonic character of the temperature dependence of relative elongation to failure of the Ti-4Al-2V and Ti-6Al-4V alloys is related to their transition to a fine-grained state with an increase in the deformation temperature. It was established that the character and volume fraction of the β-phase precipitations have a significant effect on the grain growth and the temperature dependence of the relative elongation of the alloys to failure under conditions of superplasticity.

Abstract: Experimental studies on the grain boundary diffusion and processes controlled by it in the ultrafine-grained metallic materials produced by various methods of severe plastic deformation are reviewed. Correlation between the increased diffusion permeability of grain boundaries and features of recrystallization and deformation development in these materials possessing the non-equilibrium state of grain boundaries formed during severe plastic deformation in the temperature range of T < 0.35T_m is demonstrated and analyzed.

Abstract: The present work deals with the evolution of mechanical properties and structure of low-carbon Fe-1,12Mn-0,08V-0,07Ti-0,1C (wt.%) steel after severe plastic deformation (SPD) and high-temperature annealing. Steel in initial ferritic-pearlitic state was deformed by equal channel angular pressing (ECAP) at T=200°C and high pressure torsion (HPT) at room temperature. The evolution of ultrafine grained structure and its thermal stability were investigated after annealing at 400-700°C for 1 hour. The results shown that SPD leads to formation of structure with an average size of (sub-) grain of 260 nm after ECAP and 90 nm after HPT. Ultrafine grained structures produced by SPD reveal a high thermal stability up to 500°C after ECAP and 400°C after HPT. At higher annealing temperatures a growth of structural elements and a decrease in microhardness were observed.

Abstract: In this review the investigations of deformation process development are discussed which were carried out by tension and creep in the temperature range Т<0.4Tm (here Тm is the absolute melting point of material) for nanostructured metals produced by the methods of severe plastic deformation. The contribution of grain boundary sliding to the total deformation in the above temperature interval is also considered. An analysis is made of the effect of grain size and grain boundary state on the evolution of grain boundary sliding and cooperative grain boundary sliding in nanostructured metals.

Abstract: The mechanical and physical properties of ultrafine-grained titanium alloys produced by severe plastic deformation are considered. It is found that the formation of ultrafine-grained structure in these materials causes a significant enhancement in their mechanical properties at room temperature and in their resistance to hydrogen embrittlement as well as a change in their acoustic properties. Moreover, superplasticity is realized in these materials at less elevated temperatures relative to the respective coarse grained counterparts. It is shown that the above changes in material properties permit optimization of conditions by the production of items from the titanium alloys, e.g. medical implants having the requisite strength and stepped waveguides having long life even in the high power density conditions of an ultrasound system.

Abstract: Deformation mechanisms occurring by tension of ultrafine-grained aluminum processed by equal-channel angular pressing at room temperature are investigated using comparative study of the microstructure before and after tensile testing as well as deformation relief on the pre-polished surface of the sample tested. Deformation behavior and structure evolution during tension suggest development of grain boundary sliding in addition to intragrain dislocation slip. Contribution grain boundary sliding to the overall deformation calculated using the magnitude of shift of grains relative to each other is found to be ~40%.

Abstract: The present work deals with the evolution of mechanical properties and structure of low-carbon Fe-1,12Mn-0,08V-0,07Ti-0,1C (wt.%) steel after severe plastic deformation (SPD) and high-temperature annealing. Steel in initial ferritic-pearlitic state was deformed by equal channel angular pressing (ECAP) at T=200°C and high pressure torsion (HPT) at room temperature. The evolution of ultrafine grained structure and its thermal stability were investigated after annealing at 400-700°C for 1 hour. The results shown that SPD leads to formation of structure with an average size of (sub-) grain of 260 nm after ECAP and 90 nm after HPT. Ultrafine grained structures produced by SPD reveal a high thermal stability up to 500°C after ECAP and 400°C after HPT. At higher annealing temperatures a growth of structural elements and a decrease in microhardness were observed.

Abstract: The literature on the deformation behavior and plastic strain localization inherent to nanostructured metallic polycrystals produced by severe plastic deformation techniques is reviewed. The effects of the texture, structure heterogeneity and state of grain boundaries on the special features and evolution of mesoscopic and macroscopic localized deformation bands are investigated. The role of grain-boundary sliding in the development of mesoscopic plastic deformation bands is discussed.