Papers by Author: Viktor Varyukhin

Abstract: A new approach is proposed to control the processes of billets plastic deformation during metal treatment by the methods of severe plastic deformation (SPD). High strength and plasticity have been attained for the processed copper billets after multiple repetitions of equal channel angular hydroextrusion (ECAH) and direct hydroextrusion (HE) techniques and with ECAH and HE implementation in the fractional mode. The combined SPD treatment including ECAH, HE and drawing (D) provided for fire refined tough pitch copper (Cu-FRTP) the ultimate tensile strength =686 MPa, the elongation to failure =2% and the electrical conductivity (EC) at a level of 86.4% IACS and for oxidant free copper (Cu-OF) =576 MPa, =1.9%, EC=96.7% IACS in the 0.5 mm diameter wire. Such treatment is efficient due to the alternative schemes of deformation, the fractional mode and the optimum degrees of plastic deformation and periodic creation of favorable conditions for relaxation and dynamic recrystallization processes in the material.

Abstract: The influence of multipass processing by Twist Extrusion (TE) on distribution of mechanical properties by volume in commercially pure (CP) titanium billets is investigated. Experiments show that the mechanical properties are almost homogeneous in the billet cross-section already after the second pass of TE. This can be explained by mixing effect and saturation of properties as well. Warm TE leads to the formation of high strength properties in combination with high plasticity. Ultimate and yield stresses of the billet processed by two cycles of TE increased, in comparison with initial state, by 30% and 60% respectively. The value of the reduction in area remained at the initial value. This fact is indicating a high technological plasticity of the material, i.e. its ability for further shaping by metal forming methods.

Abstract: A hypothesis for two-stage character of deformation under load via the simple shear scheme is suggested. At the first stage in the shear strain range , where - the strain parameter, the metal microstructure changes in the way similar to that during elongation. At the second stage at accidental multi-scale rotative motions, similar to turbulent motions in liquids, take place in the metal. This stage of deformation is the proper simple shear. The results of experiments are presented, which testify in favor of the suggested hypothesis.

Abstract: We present a study of the kinematics of Twist Extrusion (TE) and show that the mode of deformation in ТЕ is a simple shear. Unlike in Equal-Channel Angular Pressing (ECAP), there are two main shear layers perpendicular to the specimen axis. TE has a significant commercial potential due to the following physical effects: intensive grain refinement; homogenization and mixing; intensive powder consolidation. Donetsk Institute for Physics and Engineering created a TE Center to showcase the process and educate investors. Our experience with the center has shown that the most prospective directions are producing ultrafine-grained (UFG) alloys for medical and aircraft applications.

Abstract: It is shown that for ultrafine grained materials obtained with severe plastic deformation methods, the value of elongation up to fracture does not determine ductility, while the reduction of area up to fracture does determine it. The latter characteristic gives information about how an alloy structure resists the formation of discontinuity flaws under deformation in a hard stress state. We show that for a commercial grade titanium that underwent Twist Extrusion (TE), the value of , and thus ductility, is higher in the UFG state than in the coarse-grained state.

Abstract: Microstructures of Fe-Cr-Ni and Fe-Mn alloys subjected to severe plastic deformation under pressure have been studied by high pressure torsion and twist extrusion. This processes have similar deformation schemes, but very different pressure levels. The paper shows that this has a dramatic effect on the value of the residual high pressure e-phase in Fe-Mn alloys that underwent severe plastic deformation using these methods. Under roughly the same equivalent deformation of 5-6 units, the value of the residual e-phase in HPT with 20 GPa pressure reaches 100%. In TE with 1.5 GPa, it does not exceed 50%.

Abstract: During the last decade it has been shown that severe plastic deformation (SPD) is a very effective for obtaining ultra-fine grained (UFG) and nanostructured materials. The basic SPD methods are High Pressure Torsion (HPT) and Equal Channel Angular Extrusion (ECAE). Recently several new methods have been developed: 3D deformation, Accumulative Roll Bonding, Constrained Groove Pressing, Repetitive Corrugation and Straightening, Twist Extrusion (TE), etc. In this paper the twist extrusion method is analyzed in terms of SPD processing and the essential features from the “scientific” and “technological” viewpoint are compared with other SPD techniques. Results for commercial, 99.9 wt.% purity, copper processed by TE are reported to show the effectiveness of the method. UFG structure with an average grain size of ~0.3 μm was produced in Cu billets by TE processing. The mechanical properties in copper billets are near their saturation after two TE passes through a 60º die. Subsequent processing improves homogeneity and eliminates anisotropy. The homogeneity of strength for Cu after TE is lower than after ECAE by route BC, but higher than after ECAE by route C. The homogeneity in ductility characteristics was of almost of inverse character. The comparison of mechanical properties inhomogeneity in Cu after TE and ECAE suggests that alternate processing by ECAE and TE should give the most uniform properties.

Abstract: It has been revealed that in Iridium influenced be severe plastic deformation (SPD) a ultrafine grained (UFG) structure is formed (the grain size of 20-30 nm), but in the bodies of grains there are practically no defects of structure, however, after irradiation a subgrain structure, (subgrain size of 3-5 nm) is formed, and in the bodies of subgrains there are defects. The subgrain structure was also revealed in UFG Nickel and Copper after SPD (subgrain size of 3-15 nm), but in the latter case the observed boundary region is broader and subgrain are highly disoriented.

Abstract: Amorphous Al86Ni6Co2Gd6 ribbons produced by melt-spinning processing were consolidated using twist extrusion (TE). Electrical resistance measurements showed that under continuous heating at 5 K/min crystallization begins at 473 K by formation of Al-nanocrystals and ends at 673 K by formation of equilibrium intermetallics. From one to five TE extrusion passes were conducted in several experiments at temperatures 458-573 K and applied pressures ranged between 1150-1700 MPa. The fully dense billets with dimensions 14×23×40 mm3 were produced at extrusion temperatures ≥ 523 K. The maximum microhardness (550 kgf/mm2) was reached for the bulk materials consolidated at 523 K with a nanocomposite structure consisted of Al-nanocrystals with size about 13 nm embedded in amorphous matrix. The billet compacted at 573 K has a fully crystallized structure and lower microhardness (380 kgf/mm2).

Abstract: It is shown that the twist hydroextrusion results in the formation of fine crystalline structure with grains of elliptical shape oriented at an angle of ≈450 to the axis of deformation. Mechanical properties of the processed copper are characterized by a high level of strength and plasticity characteristics. Peculiarities of the formed structure are inherited under the subsequent rolling, they are in untypical location of grains relative to the axis of deformation.