Papers by Keyword: Twist Extrusion

Abstract: Severe Plastic Deformation (SPD) is well known process for producing nanostructured material from coarse material. Present paper is an effort to integrate the two well known SPD techniques Equal Channel Angular Pressing (ECAP) and Twist Extrusion (TE) to develop a new Hybrid ECAP (HECAP) technique that can produce nanostructured material more economically. In this technique, the specimen is subjected to both ECAP and TE in the same die setup. Finite Element (FE) modeling of metal forming processes has become an important tool for designing feasible production processes, because of its unique capability to describe the complex geometry and boundary conditions. FE Modeling of the above hybrid process is attempted in FORGE. The simulation results clearly depict the change in equivalent strain in the entire specimen on account of this process upto four passes. A comparison is made between FE results of simple ECAP and HECAP upto four passes. The study indicated that equivalent strain is much higher in case of HECAP in comparison to ECAP for same friction conditions. Also, the study is extended to analyse the effect of friction, channel angle and forging force on equivalent strain using current FE model. HECAP opens new possibilities for improving equivalent strain in same number of passes as compared to ECAP. This study is expected to contribute in forming UFG materials that are useful for automobile and aerospace industries.

Abstract: Severe plastic deformation is one of the emerging and promising techniques applied to bulk materials to produce fine grain structure with attractive properties. This study aims to investigate the effect of extrusion parameters like extrusion temperature, number of passes on the equal channel angular pressing and twist extrusion forming behavior of AA7075-T6 Aluminum alloy by hot extrusion process. AA7075-T6 samples of 70x28x18 mm cross sections extruded by equal channel angular pressing and twist extrusion process was subjected to microstructure analysis, hardness and tensile tests in order to determine their mechanical properties. As a result of the experiments, it was determined that twist extrusion leads to more grain refinement at high temperatures with more number of passes compared to equal channel angular pressing. SEM micrographs show that there is severe orientation of the grains facilitated by the extrusion process which enhances the strength. The dense banding of the grains had effected in marginal hardness enhancement in the matrix of the specimens processed by twist extrusion and equal channel angular extrusion process.

Abstract: Interest in processing of bulk ultrafine-grained materials has grown significantly over the last years. Severe plastic deformation processes such as twist extrusion have been the essence of these researches and used to decrease the bulk grain size. The bulk gain size can reduce if twist extrusion process combines with a conventional forming technique. In this study, the effects of reduction by employing the rolling process after the twist extrusion method were considered. The twist extrusion process of the commercially pure aluminum sample was carried out using a twisted die with 60º die angle, and the samples were processed through rolling subsequently. As a result of rolling, average microstructure grain size decreased significantly and the hardness amount increased accordingly

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: 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: 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.