Papers by Author: Sergey Synkov

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: 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: 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: Twist Extrusion (TE) is a process of severe plastic deformation (SPD) being developed by us during recent 5 years. Upon this time we published few papers on mechanics of the process and influence of the TE processing on materials structure and properties. Here we reported some results on application of the twist extrusion processing and made few general conclusions.