Papers by Author: Sergey V. Dobatkin

Abstract: A comparative study of the structure and properties of two biodegradable Fe – 27Mn and Fe – 27Mn – C alloys for biomedical use after equal channel angular pressing (ECAP) has been carried out. It is noted that addition of carbon in the alloy leads to a change in the mechanism of plastic deformation from the formation of martensite to deformation twinning in austenite. ECAP improves the strength characteristics of the alloys under study and the corrosion rate by refining the structure and increasing the dislocation density. The presence of a partially twinned structure in the Fe – 27Mn – C alloy results in a lower corrosion rate despite a stronger refinement of the alloy structure after ECAP.

Abstract: The article presents the results of the study of microstructure, mechanical properties, corrosion resistance and fatigue strength of the Zn-1%Mg and Zn-1%Mg-0.1%Ca alloys, processed by rotary swaging (RS). It is shown that the grain refinement leads to an increase in the strength of the alloys up to 196 ± 4 and 218 ± 6 MPa for the Zn-1%Mg and Zn-1%Mg-0.1%Ca alloys, respectively. The ductility of the Zn-1%Mg and Zn-1%Mg-0.1%Ca alloys also increases up to 5.7 ± 2.2 and 7.0 ± 0.7%, respectively. The structure caused by RS does not affect the corrosion potential of both investigated alloys, but changes the corrosion current density, decreasing it for the Zn-1%Mg alloy and increasing it for Zn-1%Mg-0.1%Ca. The fatigue limit of the Zn-1%Mg and Zn-1%Mg-0.1%Ca alloys after RS is equal to 115 MPa and 130 MPa, respectively.

Abstract: Magnetic force microscopy (MFM) and magnetometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to study the magnetic and structural properties of the (Nd,Pr)-Fe–B and (Nd,Ho)-(Fe,Co)-B alloys. The alloys are synthesized using an arc or induction furnaces. The nanocrystalline state of the (Nd,Ho)-(Fe,Co)-B alloys is reached by two techniques, namely, melt spinning (MS) and severe plastic deformation (SPD). Hydrogenation and multistage treatment of (Nd,Ho)-(Fe,Co)-B alloys, which includes severe plastic deformation of melt-quenched ribbons and subsequent heat treatment, is also used. The surface morphology and domain structure of samples are studied. These pictures are used to interpret the observed magnetic hysteresis loops of the samples. It was found that multistage treatment allows one to obtain samples with higher values of coercivity due to the formation of a special microstructure with oval grain (the aspect ratio equal to ∼ 3).

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: Equal channel angular pressing (ECAP) in magnesium alloys due to the severe plastic shear deformations provides both grain refinement and the slope of the initial basal texture at 40-50 ° to the pressing direction. Such changes in microstructure and texture contribute to the improvement of low-temperature ductility and deformability of the alloys. On the basis of analysis of data from various researchers, the main structure and texture factors affecting on the ductility increase of the Mg-Al-Zn-Mn alloys were defined.

Abstract: The effect of severe plastic deformation in Bridgman’s chamber on magnetic properties of the amorphous alloys of metal-metalloid type Ni44Fe29Co15Si2B10, Fe50Ni33B17, Fe70Cr15B15 obtained by the melt quenching was studied. The substantial alteration of saturation magnetization depending on the number of ferromagnetic and antiferromagnetic components in the alloy was revealed. It was supposed that the internal separation into nanoscaled areas enriched and depleted by ferromagnetic components took place in the amorphous matrix under the action of severe plastic deformation.

Abstract: In the present work a study of the influence of structural state on magnetic hysteresis properties of (Nd,Ho)2(Fe0.8Co0.2)14B compound was carried out. Starting alloy was prepared by induction melting in an Ar atmosphere. Nd-Ho-Fe-Co-B alloys with a nanograin structure were obtained by severe plastic deformation (SPD). Electron microscopy and X-ray analysis were used for the structural investigation. The magnetization measurements were performed using a SQUID magnetometer. It is shown that the relatively high values of coercive force are observed in case of achieved nanograin structure in (Nd,Ho)2(Fe0.8Co0.2)14B. The effect of structural state on hysteresis properties of Y2(Fe0.8Co0.2)14B is also investigated.

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 effect of chromium content (0.75, 9.85, 27%) and initial state on the thermal stability of copper-chromium alloys after severe plastic deformation has been studied by microhardness and electrical resistivity measurements. The stability of the structures is established to depend on the initial state of the alloys and on the content of chromium phase. In the low-alloy bronze, quenching before HPT substantially increases the thermal stability of the alloy relative to that observed after annealing. The softening temperature increases with increasing chromium phase content and reaches 450°C for the alloy with 27% Cr.

Abstract: Various equal channel angular pressing (ECAP) regimes by routes A and Bc were applied to a commercial MA2-1 (Mg-5wt.%Al-1wt.%Zn-0.4wt.%Mn) alloy for the development of texture which is different from the one of conventionally extruded and annealed alloy. In order to avoid the grain-size effect, the ECAP-processed alloy was annealed to coarsen the grains. The alloy texture before and after the ECAP was determined by the approximation of the X-ray measured pole figures with the canonical normal distributions of central type. The ECAP implementation results in the formation of ultra-fine grained structure of the alloy with an average grain size of 2.0-2.4 µm. The ECAP also drastically changes the initial axial texture characterized by a sharp basal component by splitting it into several more scattered orientations. The degree of the orientation scattering depends on the ECAP regime and route. The annealing of alloy after ECAP results in the grain size growth to the initial state of the extruded and annealed alloy. In addition to that the texture changes of the ECAP-processed alloy after annealing, unlike the structure changes, don’t result in texture of the initial state. The mechanical tensile properties of the annealed alloy substantially depend on the preceding ECAP routes. The yield strength of the annealed alloy decreases after all routes of ECAP. On the contrary, the uniform elongation compared with the one of the initial state of the alloy decreases after 4A route and increases after 4Bc route of ECAP. The effect of the texture and structure on the yield strength and tensile elongation of the alloy after ECAP and annealing was estimated using calculation of the generalized Schmid factors for specific preferred orientations of the active deformation systems and Hall-Petch relationship.